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dust grains in the interstellar medium (ism) can align with the magnetic fields, which in turn can cause the light from background stars to become polarized. by understanding the physics behind how grains align with magnetic fields, we can better understand many astrophysical processes. it is believed that the mineralogy of dust grains influences how they are aligned. however, grain types such as carbon and silicate are thoroughly mixed in the ism, making it near impossible to understand how specific pure grain compositions affect alignment. asymptotic giant branch (agb) stars have circumstellar envelopes (cse) which contain a purer dust composition, making them the perfect site to study dust induced polarization. ik tau, an oxygen rich agb star, has a cse that is composed of paramagnetic silicate oxides. irc+10216 is a carbon rich agb star with a cse dominated by diamagnetic carbonaceous solids. here, we contrast the behavior of the silicate dust in ik tau with the carbonaceous dust of irc+10216. we produced a temperature model of the cse of ik tau using observational data from the herschel satellite and the hawc+ instrument on sofia. this model indicates that the cse of ik tau is hotter than the cse of irc+10216. previous research shows that polarization data from irc+10216 is centro-symmetric, which could be due to a secondary radiative effect or a result of outflowing gas causing grains to tumble in a radial pattern. polarization data from ik tau does not follow this radial pattern. being paramagnetic in nature, silicate grains can be aligned by magnetic fields. preliminary analysis shows a possible dipole nature of the hawc+ polarimetry in ik tau. current work includes utilizing a numerical minimization of parameters to find a best fit model for a dipole magnetic field. | grain alignment and polarization in the envelope of ik tau |
polycyclic aromatic hydrocarbons (pah) are ubiquitous organic molecules populating the interstellar medium of galaxies and they are the major responsible of interstellar infrared spectral features (e.g., allamandola et al. 1989, tielens 2008). pah are also found as constituents in carbonaceous chondrites (e.g., kalpana et al. 2021). similarly to silicate dust, carbon-rich micrometric and submicrometric aggregates occur in different astrophysical environments where they are subjected to several weathering processes such as impact shock events and grain-grain collisions. these processes change the chemistry and structure of the original materials giving rise to new chemical species which contribute to the chemical richness of the cosmic environment (e.g., murri et al. 2022; mimura et al. 1995). the study of the chemical and structural evolution of aggregates of pah subjected to extreme conditions is relevant for examine in depth the origin of the densest phases of carbon (e.g., pre-solar grains) as that of prebiotic building blocks of life (giese et al. 2022). for this purpose, a lot of effort has been made by the whole scientific community for reproducing in laboratory the planetary conditions which trigger the processing of cosmic dust. in this framework, high-energy pulsed lasers represent consolidated tools for reproducing the high energy-density conditions similar to those occurring in shock events in the interstellar medium as a consequence of supernova explosions. liquid-phase pulsed laser ablation (lp-pla) is a technique in which high-energy laser pulses are focused on the surface of a solid target immersed in a liquid to induce ablation of material as a result of the ignition of a plasma plume, and recondensation of the ablated material in the surrounding liquid in the form of suspended nanoparticles. the presence of the liquid augments to a great extent the pressure achieved at the solid/liquid interface and allows the onset of cooling rates of the order of 105 k s-1, likewise to what occurs in circumstellar environments. using this technique, nanodiamonds are commonly produced from graphite targets in water or organic liquids (e.g., amans et al., 2017).in this paper we report the results of the high-energy laser processing of a pure nano-phase of rubrene (5,6,11,12-tetraphenyltetracene), a pah constituted by a backbone of four fused benzene rings (tetracene) bonded to four phenyl rings (figure 1). the choice of rubrene is motivated by the possibility to obtain commercially available batches of purity higher than 99.9%, its ability to organize in a high-symmetry molecular crystalline phase, and the in-depth knowledge of the photophysical and photochemical properties of both the isolated molecule and molecular aggregates. all these characteristics make rubrene an ideal model system to study the evolution of pah in response to high-energy processing. we performed lp-pla of rubrene nano-phases dispersed in water (i) to simulate space weathering in a water environment (e.g., hydrous or volatile-rich bodies) and (ii) to study its chemical and structural evolution. the laser processing of the water suspension was monitored by optical spectroscopy (absorption and luminescence) and high-resolution transmission electron microscopy and diffraction analyses. figure 1. molecular structure of rubrene (c42h28) and optical micrograph collected with cross polarizers on a thin orthorhombic single crystal or rubrene.we observed that laser processing brings about a progressive suppression of the absorption band in the visible range of the pristine rubrene nanocrystals, with increment of the signal in the uv range, indicating their transformation into a different phases. the structural and chemical features of these new phases are inferred by high-resolution transmission electron microscopy and analysis and compared with known carbon-rich phases populating the interstellar medium. acknowledgmentsfunding of the university of milano - bicocca through grant 2021-ateqc-0054 is acknowledged. we are grateful for the support of giancarlo capitani for electron microscopy analyses. referencesallamandola et al. (1989), the astrophysical journal supplement series 71, 733-775.amans et al. (2017), journal of colloid and interface science 489, 114-125.giese et al. (2022), acs earth space chemistry 6, 468-481.kalpana et al. (2021), planetary and space science 198, 105177.mimura et al. (1995), geochimica et cosmochimica acta 59, 579-591.murri et al. (2022), acs earth and space chemistry 6, 197-206.tielens (2008), annu. rev. astron. astrophys. 46, 289-337. | laboratory simulation of space weathering of nano-aggregates of polycyclic aromatic hydrocarbons dispersed in the water environment |
although it is known that the dust grains in the ism align with magnetic fields, the alignment physics of these particles is still somewhat unclear. utilizing direct observational data and radiative alignment torque (rat) theory, further constraints can be put onto this alignment. due to the physics of this alignment, there is a linear relationship between the extinction of the light seen through a dust cloud (av) and the wavelength of maximum polarization. a previous study, focusing on the taurus cloud, found that there is a second, steeper relationship seen beyond an extinction of about four magnitudes, likely due to grain growth, in addition to the original linear relationship. we present early results from observations of low-to-medium extinction lines of sight in the starless cloud l183 (aka l134n), aimed at testing the taurus results. we are currently extending the survey of stars behind l183 to higher extinctions to better probe the origins of the bifurcation seen in the taurus results. | understating polarization in the interstellar medium through the theory of radiative torque alignment |
interstellar dust grain alignment gives rise to polarization from uv to mm wavelengths, allowing the study of the geometry and strength of the magnetic field. over the last couple of decades observations and theory have led to the establishment of the radiative alignment torque (rat) mechanism as the leading candidate to explain the effect. with a quantitatively well constrained theory, polarization can be used not only to study the interstellar magnetic field, but also the dust and other environmental parameters. photo-dissociation regions (pdrs), with their intense, anisotropic radiation fields, consequent rapid h2 formation, and high spatial density-contrast provide a rich environment for such studies. here we discuss an expanded optical, nir and mm-wave study (cf. andersson et al. 2013) of the ic 63 reflection nebula, showing strong h2 formation-enhanced alignment and the first direct, empirical, evidence for disalignment due to gas-grain collisions. | dust grain alignment in ic 63 - h2 formation enhancement and collisional disalignment |
interstellar dust is an important foreground for observations across a wide range of wavelengths. dust grains scatter and absorb uv, optical and near-infrared light. these processes heat dust grains, causing them to radiate in the far-infrared. as a tracer of mass in the interstellar medium, dust correlates strongly with diffuse gamma-ray emission generated by cosmic-ray pion production. thus, while dust makes up just 1% of the mass of the interstellar medium, it plays an outsize role in our efforts to address questions as diverse as the chemical evolution of the milky way galaxy and the existence of primordial b-mode polarizations in the cmb.we present a new 3d map of milky way dust, covering three-quarters of the sky (δ > -30°). the map is based on high-quality photometry of more than 800 million stars observed by pan-starrs 1, with matched photometry from 2mass for approximately 200 million stars. we infer the distribution of dust vs. distance along sightlines with a typical angular scale of 6'. out of the midplane of the galaxy, our map agrees well with 2d maps based on far-infrared dust emission. after accounting for a 15% difference in scale, we find a mean scatter of approximately 10% between our map and the planck 2d dust map, out to a depth of 0.8 mag in e(r-z). our map can be downloaded at http://argonaut.skymaps.info.in order to extend our map, we have surveyed the southern galactic plane with decam, which is mounted on the 4m blanco telescope on cerro tololo. the resulting survey, the dark energy camera plane survey (decaps), is now publicly available. see edward schlafly's poster for more information on decaps. | a new 3d map of milky way dust |
when a star with stellar wind moves through the interstellar medium (ism) at a relative supersonic velocity, an arch like structure known as a stellar wind bow shock is formed. studying the characteristics of these structures can further our understanding of evolved stellar winds and the composition of the ism. observations of these structures have been performed for some time, but the recent discovery of many bow shock structures have opened more ways to study them. these stellar wind bow shocks display aspherical shapes, which cause light scattering through the dense shock material to become polarized. we selected a target star for observation using a catalog compiled from previous studies and observed it in polarized light with the university of denver’s dustpol instrument. our group has also simulated the polarization of stellar wind bow shocks using a monte carlo radiative transfer code. we present the data from our observations and compare them with the simulations. we also discuss the contribution of interstellar polarization to the data. | astronomy in denver: polarization of stellar wind bow shocks |
we present bvri polarimetric measurements of nine bright stars in a 15'-square region centered on stock 19. seven of them satisfy the serkowski equation for star light polarization due to interstellar dust. this allowed us to estimate the degree of maximum polarization (pmax) and the wavelength of maximum polarization (λmax). along this line of sight, pmax ranges from 0.332% to 0.948%, and the average λmax of 0.542 ± 0.018 μm yields a total-to-selective extinction ratio rv = 3.04 ± 0.11. four of the observed stars were previously listed as high-probability members of stock 19. however, based on their gaia distances, they are spread out along the line of sight and show a correlation between polarization and distance that is typical for the diffuse interstellar medium. the extinction, as obtained from dust maps, and the planck 353 ghz polarization are low for this line of sight, additionally suggesting that these stars might not represent an actual cluster. the polarization parameters of three of the observed stars indicate the possible presence of an intrinsic polarization component, likely due to circumstellar material. | bvri polarization of stars in the direction of stock 19 |
faraday effect - a common and useful probe of cosmic magnetic fields - is the result of magnetically-induced birefringence in plasmas causing rotation of the polarization plane of a linearly polarized electromagnetic wave. classically, the rotation angle scales with the wavelength as δϕ =rmλ2 , where rm is the rotation measure. although a typical rm in the milky way is of the order of a few hundred to a few thousand, a famous cygnus region shows anomalously small, even negative rotation measures. moreover, faraday rotation measurements seem to be inconsistent with the standard λ2-law. we argue that fast micro-turbulence can cause this anomaly. we demonstrate that electromagnetic high-frequency and/or small-scale fluctuations can lead to effective plasma collisionality by scattering electrons over pitch-angle. we show that such quasi-collisionality radically alters faraday rotation and other radiative transport properties, e.g., absorption, transmission and reflection. thus, we explain the cygnus puzzle by anomalous faraday rotation in a thin ``blanket'' of highly turbulent plasma at the front of an interstellar bubble/shock. supported by doe grant de-sc0016368. | evidence of high-frequency/small-scale turbulence in the cygnus region and anomalous faraday rotation |
in this paper, using the hydrodynamic model, the jeans gravitational instability in a dusty plasma with q-nonextensive velocity distributions is investigated. the change in the jeans instability criterion and growth rate due to the effects of the dust-ion collision, polarization force, and nonextensivity parameters are analyzed in the dust acoustic frequency range. it is shown that by increasing the nonextensivity and polarization parameters, the threshold condition and growth rate of the instability enhance. furthermore, it is represented that the dust-ion collisions have a stabilizing influence on the growth rate of the instability and drive the system toward thermal equilibrium. these results can be applied to astrophysical phenomena such as the collapse of interstellar gas clouds and subsequent star formation, and also, in the laboratory dusty plasmas. | jeans gravitational instability in a collisional nonextensive dusty plasma with polarization force |
a ftir study on the radiation chemistry of isolated ethanol molecules in noble gas matrices at 4.4 k revealed the formation of a variety of products due to dehydrogenation as well as c–c and c–o bond cleavage, remarkably dependent on the matrix.ethanol (c2h5oh) is one of the most common alcohol molecules observed in various space media (molecular clouds, star formation regions, and, highly likely, interstellar ices), where it is exposed to light and ionizing radiation, leading to more complex organic molecules and eventually to the biologically important species. to better understand the radiation-induced evolution of ethanol molecules in icy media, we have examined the transformations of isolated c2h5oh and c2d5oh under the action of x-rays and vacuum ultraviolet (vuv) radiation in solid inert matrices (ne, ar, kr, and xe) at 4.4 k using fourier transform infrared (ftir) spectroscopy. the results obtained with x-ray irradiation demonstrate the formation of a variety of radiolysis products corresponding to dehydrogenation (ch3choh˙, ch3cho, ch2choh, ch3co˙, h2cco–h2, h2cco, hcco˙, cco) and c–c bond rupture (h2co, hco˙, co, ch4, and ch3˙). the absorptions of the ch3choh˙ radical related to the cco stretching (the bands at 1249.1, 1247.0, 1246.2, and 1245.1 cm−1, in ne, ar, kr, and xe, respectively) were first tentatively characterized on the basis of comparison with available computational data. in addition, the c2h2⋯h2o complex, which corresponds to dehydrogenation, was found followed by c–o bond cleavage. the results were confirmed by experiments with isotopic substitution. it was found that dehydrogenation strongly predominated in a xenon matrix, while skeleton bond rupture is more feasible in neon and argon. the matrix effect was attributed to a significant role of "hot" reaction channels in neon and argon, which are efficiently quenched due to relaxation in more polarizable xenon. the vuv photolysis (185 nm) in ar and xe matrices yields a similar set of products, except for ch3choh˙ and ch2choh, which were not found (the nonobservation of the former species may be explained by its efficient secondary photolysis). the plausible mechanisms of product formation and astrochemical implications of the results are discussed. | radiation-induced transformations of matrix-isolated ethanol molecules at cryogenic temperatures: an ftir study |
the globular cluster terzan 5 contains 38 pulsars, each of which has the potential to generate new knowledge about pulsar emission mechanisms, the interstellar medium, nuclear physics, gravitational waves, and many other fields of physics and astronomy. timing these pulsars is one of the first and most important steps in studying them which requires accurate flux density measurements of the pulsar throughout many different epochs of observation. additionally, to better understand pulsar emission mechanisms, polarization data must also be recorded from each pulsar on every observation. in 2014, a hardware malfunction on the guppi instrument at the green bank observatory caused subsequent polarization measurements of the pulsars in terzan 5 to be uncalibrated and incorrect. i will be presenting a method of creating per-epoch receiver solutions for all of the observed pulsars to extract polarization measurements for multiple years worth of corrupted data. | polarization calibration of millisecond pulsars in terzan5 |
the first polarization data from alma have been delivered, and are both expanding and confounding our understanding of the role of magnetic fields in low-mass star formation. here i will show the highest resolution and highest sensitivity polarization images ever made of a class 0 protostellar source. these new alma observations of the source, known as ser-emb 8, achieve 140 au resolution, allowing us to probe polarization -- and thus magnetic field orientation -- in the innermost regions surrounding the protostar. the collapse of strongly magnetized dense gas is predicted to pinch the magnetic field into an hourglass shape that persists down to scales <100 au. however, in contrast with more than 50 years of theory, the alma data definitively rule out an hourglass morphology and instead reveal a chaotic magnetic field that has not been inherited from the field in the interstellar medium surrounding the source. we have simulated the star formation process with cutting-edge, moving-mesh arepo simulations on scales from a million au (5 pc) down to 60 au. we find that only in the case of a very strong magnetic field (~100 microgauss on 5 pc scales) is the field direction preserved from cloud to disk scales. when the field is weak, turbulence in the interstellar gas shapes the field on large scales, and the forming star system re-shapes the field again on small scales, divorcing the field from its history on larger scales. we conclude that this is what has happened in ser-emb 8. the main distinction from the strong-field star formation model is that in the weak-field case it is turbulence -- not the magnetic field -- that shapes the material that forms the protostar. | probing turbulent, magnetized star formation with alma observations and next-generation arepo simulations |
in this work, we have focused on microsolvation of isopropyl cyanide (i-prcn) as isopropyl cyanide has been recently detected in interstellar space and is of great importance from the astrochemical and bio-chemical point of view for its branching carbon chains. such branches are needed for many molecules crucial to life, such as the amino acids that build proteins. the phenomenon of the formation of hydrogen bond affects structure, energetic and electric properties of microhydrated isopropyl cyanide and this has been explored by using three different quantum chemical models. it is observed that the structural parameters calculated by the three models display similarities, however model dependence is evident from equilibrium electronic energies of the clusters. presence of water molecule has a significant effect on the values of dipole moments and polarizabilities. rayleigh intensities which are calculated using mean polarizibility and polarizibility anisotropy are increased much due to the formation of hydrogen bonding. for cn stretching vibration of isopropyl cyanide, intensification of raman scattering activities are observed upon complexation. | microhydration effect on structural, energetic and light scattering properties of first branched interstellar molecule ( i-prcn) |
light from nearby stars becomes linearly polarized while traversing a dichroic interstellar medium. polarization data which reveal heliosphere features are summarized. polarizing dust grains trace a magnetic field direction consistent with the field affecting the warm breeze of secondary interstellar helium found by ibex. polarization data also trace the field direction that dominates the configuration of the ibex ribbon of energetic neutral atoms (ena). the polarizations that echo heliospheric features appear to arise from magnetically-aligned submicron interstellar dust grains that are excluded from the inner heliosphere by large charge-to-mass ratios, but, due to long collision times, retain their alignment with respect to the interstellar magnetic field draping over the heliosphere. | magnetically-aligned interstellar dust grains at the heliosphere |
we present new multi-wavelength polarization measurements of 20 stars in the direction of the open cluster ngc 1502. polarimetric results are combined with uvbyβ photometric data to obtain precise estimates of the total-to-selective extinction and distance for each star. ngc 1502 is located at the periphery of the cam ob1 association and probably within the orion spur, with published distance estimates varying between 0.7 and 1.5 kpc. our analysis suggests that the stars studied here form two concentrations along the line of sight. if a value of 3.2 for the total-to-selective extinction is assumed, the stars group at 0.8 ± 0.02 kpc and 1.1 ± 0.05 kpc. however, using the wavelength of maximum polarization to calculate the total-to-selective extinction for each star yields 0.9 ± 0.03 kpc and 1.3 ± 0.04 kpc, respectively. this approach indicates that combining polarimetric and uvbyβ data provides a more detailed stellar distribution of this region. acknowledgments: part of this work was supported by nsf grant ast-1516932. | interstellar extinction toward the young open cluster ngc 1502 |
the interstellar medium (ism) mediates galactic evolution as the reservoir of material for future star formation and the repository of energy and matter output by stellar processes. it consists of matter (both gas and dust), magnetic fields, and relativistic particles in rough equipartition in energy density. understanding this equilibrium requires observing the discrete thermally-stable phases as well as tracing the phase transitions and turbulence that mix the phases and produce unstable gas. the heating, cooling, and ionization of the ism trace the flow of radiation through galaxies, so the impact of the ism must be understood to interpret observations of most astrophysical phenomena. canadians have played leading roles in ism science for decades. the canadian user community for the dominion radio astrophysical observatory (drao) synthesis telescope designed and completed the canadian galactic plane survey (cgps). the cgps identified a wealth of small-scale structure in h i emission as well as self-absorption and in the structure of polarized emission. these observations demonstrated that no phase of the ism, including the transition from atomic gas to star formation, can be understood in isolation. canadians have also played leading roles in the characterization of dust with planck and balloon-borne telescopes. canadians have also used pulsar scintillometry to measure structure in the ism at the smallest scales, below 1 au. the 2020s offer many opportunities for ism science in canada. a major but cost-effective upgrade to the synthesis telescope with broadband (400--1800 mhz) single-pixel feeds would enable broadband polarimetry as well as wide-area, arcminute surveys of radio recombination line emission tracing ionized gas that cannot be observed in any other way. the next generation of balloon-borne telescopes will investigate magnetic fields and dust properties in a wide range of regions. large single dishes remain essential for our understanding of the diffuse structure which characterizes the ism. the green bank telescope is the only facility available to canadians capable of observing the range of molecular transitions from 1--116 ghz. very long baseline interferometry (vlbi) capability enables parallax measurements of pulsars and masers, needed for measuring the structure of the galaxy and the ism within it, and for further progress in scintillometry. canadian ism astronomers will continue to participate in cosmological experiments including chime and chord. protecting quiet radio frequency interference environments at radio observatories will be ever more important as broadband observations are ever more central to ism spectral line and continuum science. computational capability is essential both for numerical work and for handling the observational data. | canadian investigations of the interstellar medium |
in this note, i report a r-band polarimetric study on a massive star-forming region gl 437 (a.k.a. afgl 437) to infer the magnetic field (b-field) geometry of this region. the mean b-field in the diffused region, is found to be parallel to the extended cloud structure and the galactic plane. i compared present optical polarization results with archival submm results adapted from curran & chrysostomou. a flipped field geometry is seen in denser parts of gl 437 which is an interesting finding. an infrared source wk 34 embedded in the cloud is associated with a poorly collimated outflow. these outflows are parallel to the inner field orientation but misaligned with outer b-fields. an investigation of gas kinematics of this region will be carried out to understand if the gas motion have some role in changing the field geometry. | magnetic fields in the massive star-forming region gl 437 |
we draw our targets from the mir objects in the wise catalog of anderson+, 2014, j/apjs/212/1. we also include in our sample sharpless h ii regions (sharpless 1959, vii/20). see section 2 for further details. our observations were made with the gbt 100m telescope from 2012 july through 2014 august. there are seven radio recombination lines (rrls) that can be cleanly observed simultaneously with the gbt in the x-band: h87α to h93α. we average these seven rrls (each at two orthogonal polarizations) to create a single average rrl spectrum. we followed the same gbt observational procedure as in the original hrds (green bank telescope h ii region discovery survey (gbt hrds; bania et al. 2010apj...718l.106b). (3 data files). | vizier online data catalog: radio observations of galactic wise hii regions (anderson+, 2015) |
the planck satellite has mapped the polarized microwave sky (from 30 ghz to 353 ghz) with unprecedented sensitivity and angular resolution. this wealth of data yields the first complete map of polarized thermal emission from dust in our own galaxy, shedding new light on the formation of dense cold structures within which new stars and planetary systems are born, under the combined effects of gravity, turbulence and magnetic fields. on behalf of the planck collaboration, i will present a statistical analysis of this polarized emission from nearby molecular clouds, focusing first on the evolution of the maximum polarization fraction observed as a function of column density, and on the anti-correlation between the polarization fraction and the local dispersion of polarization angles. to interpret this data, i will present numerical simulations of anisotropic mhd turbulence and show the essential role played by the topology of the interstellar magnetic field, in particular its large-scale component. to extend the analysis beyond the polarization fraction and angle, i will present the one-point and two-point statistics of stokes q and u, showing in particular how changes in magnetic field direction lead to multimodality in the (q,u) distributions. finally, using the results of a numerical experiment with fractional brownian motion (fbm) fields, i will exhibit the observables best suited to retrieve the spectral index of the turbulent component of the interstellar magnetic field. | polarized thermal dust emission from planck, a comparison with mhd simulations and lessons from a fbm model |
the canadian galactic plane survey (cgps) is the largest effort of its kind to study and understand the galactic magnetic field (gmf) and interstellar medium (ism) in our galaxy (see e.g. taylor et al. 2003). the cgps has mapped the galactic plane visible from drao on all spatial scales down to arcminute resolution in total intensity and polarized emission at νobs=1.4 ghz (see landecker et al. 2010). the latest results invoking faraday rotation and polarization gradient studies of the cgps are discussed. | cgps studies of the galactic magnetic field |
the relation between the interstellar magnetic field (ismf) controlling the configuration of the "ribbon" of energetic neutral atoms discovered by ibex, and the ismf in deep space, can be probed with polarized starlight. starlight is polarized in a dichroic interstellar medium formed by interstellar dust grains that are aligned with respect to the ismf. our ongoing survey of polarized starlight traces the ismf within 40 parsecs. the local ismf direction was evaluated using the weighted means of the linear polarization vectors. the dominant nearby magnetic field direction is within 7.6 (+14.9,-7.6) degrees of the ismf direction that is traced by the ibex ribbon. a low level of random magnetic turbulence is obtained from the polarization data that best trace the ibex ribbon field direction, 9 (+/-1) deg, which explains the continuity of the ibex ismf out into space where it can be traced by starlight polarization. the ismf direction is perpendicular to the velocity of the cloud around the heliosphere, and it orders the kinematics of the other local interstellar clouds. these results are obtained only after a well-defined subset of the polarization data is omitted from the sample. a separate analysis shows that these polarization vectors are oriented toward the upwind direction of the interstellar gas flowing into the heliosphere. this group of polarization data traces an elongated filamentary-type feature that is perpendicular to the hydrogen deflection plane. we suggest a heliosheath origin for the grains that create this polarized feature. one characteristic shown by the polarization and ibex field directions is that the ribbon ismf extends to the boundaries of the bicep2 region where the polarized cmb background has been studied. inside of the bicep2 region other nearby magnetic components are also present. the sightline toward the star capella suggests that the polarization mechanism is very efficient in this nearby cloud. | charting the interstellar magnetic field behind the interstellar boundary explorer (ibex) ribbon |
bok globules are small isolated dark cloud with a simple structure, when seen through optical wavelengths they looks like a dark patch surrounded by some bright foreground stars. because of their isolated location and simple structure, they are ideal laboratories, to study in detail the process of low-mass star formation. aligned dust grains in the interstellar medium (ism) and the bok globule polarize the radiation through dichroic extinction. magnetic fields plays a vital roles in interstellar processes and star formation, and the polarization that results from grain alignment provides the means to study magnetic fields. the relative role played by the magnetic field and the turbulence in cloud formation and evolution in different stages of star formation is quite interesting matter of study. in this paper we will present a combined study of polarization and extinction (av) of observed background field stars of cb56, cb60 and cb69. we have mapped the local magnetic fields of these globules in v-band by estimating the value of linear polarization of background stars and hence created respective polarization maps. background field stars are used to probe polarization efficiency (defined as pv/av) in the quiescent regions of these dark clouds as a function of visual extinction. our study indicates that the interstellar dust grains alignment decreases with the increase in extinction. this type of study help us in studying the direct interplay between protostellar collapse, fragmentation and magnetic fields. | photopolarimetric study of three selected bok globule (cb56, cb60 and cb69) |
the global sed of the milky way reaches a minimum at about 80 ghz. in the decade below this, three emission processes predominate: synchrotron, from cosmic ray leptons spiralling in the galactic magnetic field; free-free, from ionized gas in nebulae and the diffuse warm ionized medium; and anomalous microwaves (ame), believed to be dipole emission from spinning very small dust grains. each component provides unique diagnostics: synchroton traces the lepton energy spectrum near 20 gev and reveals the local and global structure of the galactic magnetic field, free-free probes ionized gas where the usual h-alpha tracer is obscured, and ame traces a new interstellar component, whose relation to the general dust population can now be explored. in total intensity, accurate separation of these components is a hard problem not yet completely solved, mainly due to the spatial variability of the ame spectrum, which in the planck 2015 analysis dominates the sed between 20 and 60 ghz. new large-area surveys in the frequency decade below the satellite microwave will, in combination with planck and wmap, will provide a far more robust determination of each component.in contrast to the confused situation in total intensity, only synchrotron contributes significant polarization in our band, and wmap and planck give a clear view of the polarized synchrotron sky, for the first time effectively free of faraday rotation and depolarization. new ground-based microwave polarization surveys such as gmims, s-pass, c-bass, and quijote, will add much higher sensitivity and also have the high frequency resolution needed to trace the line-of-sight component of the magnetic field via faraday synthesis. the polarization along the galactic plane constrains models of the global galactic magnetic field. away from the plane, polarization probes the tangling of the field in the galactic halo and clarifies the structure of the galactic loops and spurs, which impose a large-scale coherence on the synchrotron sky. these loops are the largest objects in the sky, but their nature and distance is still controversial, and will be clarified by on-going studies of the ism structure within 1-2 kpc of the sun. | "untangling the centimetre-wavelength sky" |
in the last stages of their lives, sun-like stars evolve along the asymptotic giant branch (agb), and contribute a significant fraction of heavy elements to the interstellar medium, driving the chemical evolution of galaxies and providing the building material for new stars and planets. we observed the detached shells of dust around the evolved carbon agb star r scl in polarised, dust-scattered stellar light with the polcor instrument on the eso 3.6-metre telescope. the observations show the distribution of the dust in the shell with unprecedented detail. comparison with high angular resolution observations of the molecular gas with alma show that dust and co emission coincide almost exactly, implying a common evolution of the dust and gas since the creation of the shell. the results give unique insights into thermal pulses - the mechanism responsible for the chemical evolution of the star - and the way evolved stars lose their mass. | probing the effects of stellar evolution: the dust and gas in detached shells around agb stars |
table 1 lists the 9 emir multiline probe of the ism regulating galaxy evolution (empire; pi: f. bigiel) targets. all targets are nearby (d<=15mpc) face-on (i<=65°) spiral galaxies that are also large on the sky (>=2'). the observations for empire were carried out at the iram 30m telescope located at pico veleta, spain. most of the data were taken from 2014 december through 2016 december for ~440h over the course of 16 runs. we used the 3mm band (e090) of the dual-polarization emir receiver, which yields an instantaneous bandwidth of 15.6ghz per polarization. we tuned emir with a local oscillator frequency of ~98.6ghz. this allowed us to simultaneously observe the bright high critical density tracers hcn(1-0), hco+(1-0), and hnc(1-0) and the optically thin molecular column tracers 13co(1-0) and c18o(1-0). (4 data files). | vizier online data catalog: empire: iram 30m dense gas survey (jimenez-donaire+, 2019) |
protoplanetary disks are thought to be magnetically active and could transport angular momentum via magneto-rotational instabilities and disk winds. these hypothesis have been the theoretical background in order to understand magnetic fields in disks via high-angular resolution (<100 au scales) and great sensitivity (polarized fraction in these objects is typically ∼1%) polarimetric observations. due to the enormous capabilities of the atacama large millimeter/submillimeter array (alma) telescope, polarization studies at millimeter and submillimeter wavelengths toward protoplanetary disks have grown in the last six years. these observations were intended to map and measure the spatial distribution of the magnetic field in disks. surprisingly, the actual origin of the polarized emission in disks differs from the interstellar medium typical origin (dust grains aligned along magnetic field lines). in this contribution i will review the interferometric polarimetry research in protoplanetary disks both in the theoretical and the observational facets. i will present some paths currently proposed to obtain information of magnetic fields in disks. | emisión (sub)milimétrica polarizada de discos protoplanetarios |
recent studies, that determined the inflow longitude of the local interstellar medium from the anisotropy of interstellar pickup ion (pui) radial velocity, have once again raised the question, how transport effects and especially wave activity in the solar wind modifies the velocity distribution function of puis.this study investigates the modification of an oxygen pui torus distribution by alfvénic waves qualitatively with a numerical approach. the focus of this study is to understand this modification kinetically, which means, that instead of describing the pui transport through diffusion approaches, we trace the trajectories of test particles in pitch angle space with a time resolution of at least 100 time steps per gyro orbit in order to find first principles of wave particle interactions on the most basic scale.therefore we have implemented a leapfrog solver of the lorentz-newton equations of motion for a charged test particle in a electro-magnetic field. the alfvénic waves were represented through a continuous circularly polarized wave superimposed to a constant 5 nt background magnetic field. in addition an electric field arising from induction has been added to the simulation's boundary conditions. the simulation code computes the particles' trajectories in the solar wind bulk system.upon interaction with mono frequent single-frequency waves, the particles are found to perform stationary trajectories in pitch angle space, so that the pitch angle distribution of a conglomerate of test particles does not experience a systematic broadening over time. also the particles do not react most strongly with waves at resonant frequencies, since the pitch angle modification by the waves sweeps their parallel velocity out of resonance quickly. however, within frequencies close to first order resonance, strong interactions between waves and particles are observed.altogether the framework of our simulation is readily expandable to simulate additional effects, which may modify the test particles' pitch angle distribution strongly (e.g. collisions with solar wind particles or gradient drifts). so far we have expanded the simulation to support intermittent waves, where we have observed, that the pitch angle distribution of the test particles broadens systematically over time. | numerical study of alfvénic wave activity in the solar wind as a cause for pitch angle scattering with focus on kinetic processes |
the status of dib research has strongly advanced since 20 years [1], as well as the quest for fullerenes, pahs and large organics in space. in 1994 we reported the discovery of two near ir diffuse bands coincident with c60+, confirmed in subsequent years [2-6] and now by latest laboratory experiments. a number of dib observational studies have been published, dealing with: dib surveys [1,7-10]; measurements of dib families, correlations and environment dependences [11-14]; extragalactic dibs [15, 16]. resolved substructures were detected [17,18] and compared to predicted rotational contours by large molecules [19]. polarisation studies provided upper limits constraints [20, 21]. dibs carriers have been linked with organic molecules observed in the interstellar medium [22-25] such as ir bands (assigned to pahs), extended red emission or recently detected anomalous microwave emission (ame, assigned to spinning dust) and with spectroscopic ir emission bands measured with iso or spitzer. fullerenes and pahs have been proposed to explain some dibs and specific molecules were searched in dib spectra [eg 2-6, 26-31]. these could be present in various dehydrogenation and ionisation conditions [32,33]. experiments in the laboratory and in space [eg 34-36] allow to measure the survival and by-products of these molecules. we review dib observational results and their interpretation, and discuss the presence of large organics, fullerenes, pahs, graphenes in space. references [1] herbig, g. 1995 ara&a33, 19; [2] foing, b. & ehrenfreund, p. 1994 natur 369, 296; [3] foing, b. & ehrenfreund, p. 1997 a&a317, l59; [4] foing, b. & ehrenfreund, p. 1995 assl202, 65; [5] ehrenfreund, p., foing, b. h. 1997 adspr19, 1033; [6] galazutdinov, g. a. et al. 2000 mnras317, 750; [7] jenniskens, p., desert, f.-x. 1994 a&as106, 39; [8] ehrenfreund, p. et al. 1997 a&a318, l28; [9] tuairisg, s. ó. et al. 2000 a&as142, 225; [10] cox, n. et al. 2005 a&a438, 187; [11] cami, j. et al. 1997a&a.326, 822; [12] krelowski, j. et al. 1999a&a 347, 235; [13] sonnentrucker, p., cami, j., ehrenfreund, p., foing, b. h. 1997 a&a 327, 1215; [14] sonnentrucker, p., foing, b. h., breitfellner, m., ehrenfreund, p. 1999 a&a 346, 936; [15] cox, n. et al. 2007 a&a 470, 941; [16] ehrenfreund, p. et al. 2002 apj 576 l117; [17] ehrenfreund, p.; foing, b. h. 1996 a&a 307 l25; [18] sarre, p. j. et al. 1995 mnras.277 l41; [19] cossart-magos, c. & leach, s. 1990 a&a 233, 559; [20] cox, n. l., ehrenfreund, p., foing, b. h. et al. 2011 a&a 531, 25; [21] cox, n. l., boudin, n., foing, b. h. et al. 2007 a&a 465, 899; [22] ehrenfreund, p. & charnley, s. 2000 anraa 38, 427; [23] scarrott, s. m., watkin, s., miles, j. r., sarre, p. j. 1992 mnras 255, 11; [25] planck collaboration, 2011 a&a 536 20 (planck early results. xx.); [26] ehrenfreund, p. et al. 1995 a&a 299; 213; [27] ehrenfreund, p. & foing, b. h 1995 p&ss 43, 1183; [28] van der zwet, g. p., allamandola, l. j. 1985 a&a 146 76; [29] salama, f. et al. 1996 apj 458, 621; [30] ruiterkamp, r. et al. 2005 a&a 432, 515; [31] ruiterkamp, r. et al. 2002 a&a 390, 1153; [32] vuong, m. h. & foing, b. h 2000 a&a 363, l5; [33] le page, v. et al 2001 apjs 132, 233; [34] ehrenfreund, p et al. 2007 p&ss 55, 383; [35] bryson, k. l., peeters, z., salama, f., foing, b., ehrenfreund, p. et al. 2011 adspr 48, 1980; [36] mattioda, a., cook, a., ehrenfreund, p. et al. 2012 asbio 12, 841. | fullerenes, organics and the diffuse interstellar bands |
several black hole binaries (bhbs) present persistent soft gamma-ray emission (up to e ∼mev). although different models have been proposed to explain the origin of this component (non-thermal corona, relativistic jets), its nature still remains unknown. the detection of strong polarization at high-energies in the well-studied system cygnus x-1 provides new constraints on the emitting region of the radiation. in this work we study the case of the bhb xte j1118+480, a transient source that has been observed during two outbursts. in both cases multiwavelenght observations could be obtained because of the privileged location of the source, which implies low interstellar absorption. we apply a non-thermal lepto-hadronic coronal model to reproduce the x/γ-ray emission of this bhb during its outburts, and study the polarization of high-energy radiation expected for future episodes. | gamma-ray polarization in accreting black holes: the case of xte j1118+480 |
knowledge of temperature, densities, and chemical abundances of hot plasmas that exist in stars including the sun, in the interstellar and intergalactic medium, and in active galactic nuclei can be optimally determined through observations in key diagnostic spectral lines, many of which are in the far ultraviolet range (fuv, 100-200 nm), such as the lyman series of atomic hydrogen and deuterium, and the lyman bands of their molecules, along with lines of oi and ovi, civ, etc. for habitable exoplanet search, the fuv spectrum of m stars is a useful diagnostic tool of biologically generated gases in planet atmospheres. measuring the magnetic field in the different layers of the sun's atmosphere can be optimally performed by means of polarimetry in the fuv and in the uv. the development of more efficient fuv coatings is key to advance in many fields of astrophysics and solar physics. with this goal, gold (spanish acronym of thin film optics group) has been devoting a long effort to develop high-performance coatings to address specific targets.in this poster, gold's capacity to develop and measure fuv coatings will be summarized. a 75-cm diameter chamber in an iso-6 clean room is used to prepare fuv coatings satisfying space requirements. the main deposition technique is evaporation and ion-beam-sputtering is also available. coating performance is conveniently measured with an in-house reflectometer covering the 40-190 nm spectral range.the presentation will display the performance of fuv coatings that can be prepared at gold: 1) transmittance filters peaked at λ ≥ 120 nm with a strong peak-to-visible rejection 2) broadband mirrors with enhanced fuv reflectance 3) narrowband mirrors tuned at fuv wavelengths as short as h lyman β (102.6 nm) 4) polarizers at h lyman α (121.6 nm) and other fuv and uv spectral lines | coatings for improved far-uv astrophysics observations |
about 50 scientists belonging to the “friends of fors” family convened at the eso supernova planetarium & visitor centre to celebrate 20 years of successful science exploration with fors1 and fors2. scientific highlights from these instruments were discussed, covering various research areas rang-ing from interstellar bodies entering our solar system, to the detection of exo- planets and biomarkers, interstellar medium dust polarisation, binary star velocities, galaxy dynamics, high-redshift galaxies near the re-ionisation epoch, and transient astronomical events such as supernovae, gamma-ray bursts, and gravitational waves. in addition to reviewing the amazing scientific achievements from the fors instruments, a specific goal of the conference was to discuss ways in which to foster the high scientific impact of the instrument in the future. various suggestions from the eso community for upgrading the instrument were presented and discussed. | report on the eso event "20th anniversary of science exploration with fors" |
bvri polarization measurements of 14 selected young stars with circumstellar dust disks are presented. the interstellar polarization in the direction of these stars is not significant. the observed polarization data and its wavelength-dependence indicate that it is intrinsic, due to scattering by circumstellar, asymmetric dusty disks/envelopes. | polarization measurements of selected young stars with circumstellar dusty disks |
the importance of cosmic rays and magnetic fields for the physics of the interstellar medium and the evolution of galaxies is demonstrated by a number of recent numerical simulations. here we present new observations of the cosmic ray electron transport as well as the magnetic field strength and structure in galactic halos from radio-continuum polarization studies of edge-on disk galaxies obtained by the chang-es (continuum halos in nearby galaxies - an evla survey) project. the observations are discussed in the context of transport models for cosmic ray eelctrons (cres) from the star-forming disks into the halo. it is possible to distinguish between advection and diffusion as the dominant transport mechanism. the observations also allow to derive the magentic field structure in galactic halos. in addition, it is demonstrated how recent low frequency observations of edge-on galaxies with lofar help to further constrain the problem. | new constraints on cre transport into galactic halos from radio continuum observations |
extinction and polarization by interstellar dust taints astrophysical signals, frustrating precision measurement of cosmological standard candles, electromagnetic components of multimessenger transients, and cmb signals. understanding the origins of dust variations on small angular scales and along the line of sight in true three-dimensional detail, as informed by local physical influences, is now both possible and pressing. we propose stis 1600-3100 a spectroscopy of five background stars probing a diffuse cloud irradiated by the o9.2iv star zeta oph, the nearest (182 pc) high-uv environment. our optical polarization measurements along these mid-latitude low-confusion sightlines reveal a b field aligned with 8-micron bright filaments. the ratio of polarization to color excess, p/e(b-v), exceeds the empirical (serkowski) limit of 9, indicating very efficient polarization and a high degree of grain alignment, plausibly from spin-up by radiative torques. the optical/infrared data indicate a reddening curve characteristic of r_v=a_v/e(b-v)<2.4, a signature of extreme dust and a size distribution favoring small grains. with measurement of the near-uv reddening slope, the height and width of the 2175 a bump, and potentially the far-uv rise, we will be able to forge a compelling association between extinction curve morphology, polarization efficiency, grain magnetic field alignment, and the dominant radiative influence of a well-characterized hot star. characterizing the extinction of high-polarization low-rv pah-emitting grains in this local laboratory promotes understanding the conditions that produce anomalous dust in agn, sne, grbs, and starbursts further afield. | obtaining the uv reddening curve of extreme-rv highly polarizing dust irradiated by zeta ophiuchi |
we extracted faint radio emission from the optically identified snr g107.0+9.0 from published surveys at 22mhz and 408mhz and new observations at 1.4ghz and 4.8ghz. g107.0+9.0 is clearly visible on the effelsberg medium latitude survey (emls) 1.4-ghz maps (uyaniker et al., 1998a&as..132..401u, 1999a&as..138...31u; reich et al., 2004, in the magnetized interstellar medium, ed. b. uyaniker, w. reich, & r. wielebinski (copernicus gmbh, katlenburg-lindau), 45). this section of the emls is not yet published. the sino-german 4.8-ghz polarisation survey of the galactic plane within latitudes of +/-5° was carried out with the urumqi 25-m telescope between 2004 and 2009 and published in a series of papers (gao et al., 2010a&a...515a..64g; xiao et al., 2011a&a...529a..15x; sun et al., 2011a&a...527a..74s). a review and summary of the 4.8-ghz survey results was given by han et al. (2015, highlights of astronomy, 16, 394). (2 data files). | vizier online data catalog: supernova remnant g107.0+9.0 radio images (reich+, 2021) |
the multiphase nature of astrophysical environment and diversity of driving mechanisms give rise to spatial variation of turbulence properties. nevertheless, the employed model of magneto-hydrodynamic turbulence is often oversimplified being assumed to be only alfvenic due to a lack of observational evidence. here we report the employment of our novel method, the signature from polarization analysis (spa), on unveiling the plasma modes in interstellar turbulence. the method is based on the statistical properties of the stokes parameters (i,q,u) of the synchrotron radiation polarization. the application of spa on the synchrotron polarization data from the galactic medium has for the first time revealed that interstellar turbulence is magnetized with different plasma modes composition, pinpointing the necessity to account for plasma property of turbulence, which is neither hydrodynamic nor purely alfvenic, but depends on local physical conditions, particularly the driving process. a highly promising research field is foreseen to unroll with ample results anticipated from the advanced analysis of high resolution synchrotron polarization data and multiple wavelength comparison, that will shed light on the role of turbulence in various physical processes. | identification of magnetosonic modes in galactic turbulence |
understanding the formation and evolution of galaxies across cosmic time is a major goal of modern astronomy. our current observations of the early universe come mainly from the optical and near-infrared rest-frame wavelengths, which are mostly biased towards dust-unobscured systems. the advent of millimetre and submillimetre (submm/mm) telescopes in the last two--three decades has greatly advanced the study of dusty star-forming galaxies (dsfgs), providing us with a more complete census of distant galaxies. meanwhile, it has posed new challenges: what are the internal and external properties of dsfgs? how do they connect to the galaxies in the local universe? what is their number density and contribution to the cosmic star-formation rate density? what do they tell us about the early universe? in this thesis, i will report two surveys: almacal and almared, which survey the populations of dsfgs at the faint and bright end of submm number counts, respectively. meanwhile, i will also report a new window through which to study galactic magnetic fields with dust polarisation in the early universe. in the almacal survey, i have exploited the 'free' calibration data from the atacama large millimetre/submillimetre array (alma) to conduct a sub-arcsec, multi-wavelength, and blind continuum survey of dsfgs. i used alma calibration scans to map the lines of sight towards and beyond the alma calibrators. almacal has now covered 1,001 calibrators, with a total sky coverage of around 0.3 deg2, distributed across the sky accessible from the atacama desert in chile, and has accumulated more than 1,000 h of integration. the depth reached by combining multiple visits to each field makes almacal capable of searching for faint dsfgs in different wavelength bands. based on the most up-to-date almacal database, i report the detection of 186 dsfgs with flux densities down to s870um~0.2mjy, comparable with existing alma large surveys but less susceptible to cosmic variance. i also report the number counts at five wavelengths between 870um and 3mm, in alma bands 3, 4, 5, 6 and 7, providing a benchmark for models of galaxy formation and evolution. by integrating the observed number counts and the best-fit functions, i present the resolved fraction of the cosmic infrared background (cib) and the cib spectral shape. combining existing surveys, i show that alma has currently resolved about half of the cib in the submm/mm regime. in the almared survey, i have combined an alma snapshot survey of the reddest ~3000 herschel-atlas sources with spectroscopic follow-up to search for galaxy proto-clusters. all the targets are selected to be 500um risers with s_500um > s_350um > s_250um. i found that about 1% of the 500um risers have been resolved into >=3 sources with alma. i then selected 12 over-dense fields with photometric redshifts, z>3. i conducted alma band 3 spectroscopic scans to search for emission lines in these 12 fields and confirmed four new proto-cluster cores. i will show that the detection fraction within almared, together with a serendipitous over-dense field in the almacal survey, has cautioned us that the projection effects of dsfgs can greatly contaminate the selection of proto-clusters based on photometric over-density. i derive their star-formation rate, total available molecular gas and halo mass based on the multi-wavelength photometry and spectral lines. i find that these proto-cluster cores are massive and sustain extreme star-forming activity. i show that their star-formation efficiency, the available molecular gas, and halo mass all support the idea that they could be the progenitors of today's 'brightest cluster galaxies' (bcgs). this discovery indicates that we are witnessing the formation of early-stage bcg in the mass centre of these proto-clusters. in addition to these two surveys, i am fortunate to be part of the group that has initiated the study of dust polarisation in distant dsfgs. i first investigated the feasibility of mapping the magnetic fields of the distant dsfgs with dust polarisation, based on the dust polarisation of nearby starburst galaxies. i then led one of the first full-polarisation dust observations towards two smgs: 9io9 and spt0326-52. based on these pioneering observations, i have confirmed the presence of polarised dust emission at $z=2.55$ and z=5.56, indicating that the development of galactic magnetic fields can be efficient in early galaxies. in 9io9, i also resolved the complex structure of the magnetic fields in the interstellar medium. i discuss several possible mechanisms to explain the formation of the observed early galactic magnetic fields. this pioneering survey has fully demonstrated the power of alma to observe the polarised dust emission in the early universe and opened a new window to explore the magnetised universe. finally, i look ahead to areas related to dsfgs and outline several intriguing projects to be pursued in the coming years. | distant, dusty star-forming galaxies |
though the source of fast radio bursts (frbs) is still unknown, magnetars are a compelling candidate for at least some of these bursts. since magnetars are generally very young neutron stars, they should be preferentially found in regions of recent or ongoing star formation. based on this, we have conducted a long high-frequency observing campaign targeting the star forming regions of the galaxies m77 and m82 using dss-13, one of the 34-m dishes in the deep space network. we observed each source for ~100 hours at 8.4 ghz using 360 mhz of bandwidth and a single polarization. by observing at high frequencies, we are largely unaffected by the dispersive smearing or scattering that might arise from the turbulent interstellar medium in star forming regions. here we will present preliminary results of this search and discuss the implications for future high frequency frb surveys. | high frequency frb search in star forming galaxies |
to explain the transfer of energy surrounding supermassive black holes (smbh), most of the theoretical models, if not all, must incorporate magnetic fields (b-fields). as matter rotates and gets closer to the black hole, the outgoing radiation results in an extraction of energy from the smbh— matter rotating around a smbh must have a b-field to account for the lost of angular momentum. this is the main physical mechanism for powering the core of galaxies that contain active nuclei. although this process can explain the dynamics of matter at sub-pc scales around the black hole, there is still no clear observations of how the matter from the host galaxy, which contains kpc-scale b-fields in close equipartition with the diffuse interstellar medium, feeds smbhs at scales of 10-100 pc. we have observed the signature of magnetically aligned dust grains at distances of a few tens-pc at infrared/sub-mm wavelengths in a sample of radio-loud (rl) and radio-quiet (rq) active galactic nuclei (agn). we found that rq agn are low polarized, while rl agn are highly polarized at 10-100 um. these results are particularly interesting because the dusty torus represents the agn accretion flow on pc-scales, and this result, besides the radio differences, may be the most telling and dramatic empirical difference between rl versus rq agn. for rl agn, the magnetic fields at pc-scales may be able to compress and sustain the dusty torus, which extends the inflow/outflow processes from sub-pc scales to pc-scales and links the inflow and outflow with the dynamics of the host galaxy. these findings have profound implications on how we classify and study the evolution of active galaxies. | on the origin of radio-loudness in active galactic nuclei using far-infrared polarimetric observations |
fits files of disk images in sphere/irdis (h-band) from the very large telescope. the stars are located at the mathematical centers of the arrays. the units are in counts per pixel for qphi data. (2 data files). | vizier online data catalog: fits images of v1247 ori (ren+, 2024) |
magnetic fields are ubiquitous in the universe and are one of the major components regulating the motion and evolution of interstellar medium. machine learning has gained increasing popularity among astronomers, allowing us to study magnetic fields in detail through gas morphology. we adopt the deep learning method casi-3d (convolutional approach to structure identification-3d) to infer the orientation of magnetic fields in sub-/trans- alfvenic turbulent clouds from molecular line emission. we carry out magnetohydrodynamic simulations with different magnetic field strength and use these to generate synthetic observations. we apply the 3d radiation transfer code radmc-3d to model 12co and 13co (j = 1-0) line emission from the simulated clouds. we train a casi-3d model to take in molecular line emission data cubes and predict magnetic fields on pixel level. the trained casi-3d model is able to infer the magnetic field direction with a low mean square error on test sets. we furthermore test the performance of casi-3d on a real sub-/trans- alfvenic region in taurus. the casi-3d prediction is consistent with the magnetic field direction traced by dust polarization from planck 353 ghz. | application of convolutional neural networks to predict magnetic fields directions in turbulent clouds |
the polarization data were obtained with the robopol polarimeter mounted at the 1.3m telescope at the skinakas observatory in crete, greece. all observations were carried out in the r band. all measurements are included; even those with low signal to noise ratio in the degree of polarization. we carried out co (1-0) observations toward the target cloud with the purple mountain observatory 13.7m telescope (pmo-13.7m) from june 3 to 15, 2019 (project code: 19c002). we used the heinrich hertz submillimeter telescope on mt. graham, arizona, to measure the j=2-1 transition of co toward the target cloud. the data were collected on march 1, 3, and 4, 2019. following bieging et al. (2014apjs..214....7b), we used the alma band 6 sideband separating mixers dual polarization receiver to observe the co (j=2-1) (230.5ghz) line. the spectrometers were filter banks with 0.25mhz bandwidth and 256 filters, providing a spectral resolution of 0.33km/s. (3 data files). | vizier online data catalog: hi-h2. exploring the role of magnetic field (skalidis+, 2022) |
an international group of scientists has tackled the task of mapping the interstellar magnetic field (ismf) surrounding the heliosphere [1]. starlight that is linearly polarized by foreground interstellar dust grains aligned with respect to the ismf provide the data for determining the ismf orientation. polarimeters mounted on telescopes at over eight observatories around the world have provideed the very high-sensitivity data needed to map the ismf in the tenuous partially ionized interstellar gas surrounding the heliosphere. these data, combined with data in the literature, yield a best-fitting ismf, b_{magpol}, that is aligned with galactic coordinates \gl=42°, \gb=49° (ecliptic coordinates λ,β=229°, 45°). fits to data for stars located more than 90° from b_{magpol} provide a higher confidence fit: \gl,\gb=40°, 56° (± 17°) (λ, β = 219° ± 15°, 43° ± 9°). the ismf orientation from the polarization data is in good agreement with the ismf obtained from ibex ribbon models [2]. the agreement with ibex results suggests that the ismf shaping the heliosphere has an orderly component. these polarization data trace a ∼ 300 ° long magnetic filament, ''filament a'', that (1) extends through the heliosphere nose region and overlaps positions of the voyager 3 khz emission detected in the earlier 1990s; (2) overlaps sightlines to three quasar intraday variables tracing local dense plasma scattering screens; (3) overlaps low order multipole moments describing wmap cmb data; (4) overlaps the ibex 1.7 kev ena ribbon configuration; (5) crosses through the nose of the heliosphere and the upwind direction of interstellar dust entering the heliosphere at a large angle to the ecliptic. a magnetic filament ∼ 55 ° long is aligned with a likely shock interface between local interstellar clouds and is adjacent to a dark spot that has been identified in the cmb. two large circular magnetic arcs are centered on the heliotail. spatial coincidences between locations of cmb multipole moments, filament a and the ibex ribbon are found. the spatial coincidences between the cmb and the magnetically organized heliosphere features suggest that interactions between interstellar dust and plasma entrained in the very local ismf contribute to the cmb foregrounds. refs: [1] frisch, piirola, berdyugin, heiles, cole, magalhaes, wiktorowicz, cotton, schwadron, bzowski, mccomas, zirnstein, funsten, et al. submitted to apjss. [2] zirnstein et al. apjl, 818:18, 2016. | interstellar magnetic field shaping the heliosphere |
pulsar astronomy arguably offers the most diverse range of scientific applications compared with any other sub-field of astronomy. despite pulsars being interesting in their own right, they serve as tools to study a rich breadth of astrophysical phenomena and fundamental physics ranging from the electron content and the magneto-ionic properties of the galactic interstellar medium, through studies of supernova kicks to probes of strong-field gravitational dynamics and the equation of state of ultra-dense matter. the research in this thesis focuses primarily on two key topics: firstly, on a comprehensive analysis of the gravitational dynamics of the binary pulsar system, psr j1141-6545 and secondly, on an attempt to increase the known population of sporadically emitting pulsars via rapid and repeated real-time pulsar surveys. psr j1141-6545 is a unique relativistic and asymmetric pulsar system consisting of a young pulsar and an older white dwarf companion. our analyses start with estimates of the geodetic precession and the geometry of the system derived from the secular evolution of pulse-widths over an ∼18 year dataset on the pulsar. this analysis assumes general relativity (gr) to be the correct description of gravity and that the pulsar beam is circularly symmetric. our study indicates that the pulsar is likely to be a near-orthogonal rotator and provides the first polarization-independent estimate of the scale factor (a) that relates the opening angle of the pulsar emission cone (ρ) to its rotational period (p) as ρ = ap^{-0.5}: we find the scale factor to be > 6 °s^{0.5} at 1.4 ghz with 99% confidence. furthermore, our investigation of the polarization evolution strongly argues that our line-of-sight crossed the magnetic axis of the pulsar in early 2007 and that the pulsar will precess away from our line-of-sight in the next 3-5 years. we also perform an analysis of the pulsar timing data from the pulsar under the assumption that gr is correct and report the first detections of a secular change of the projected semi-major axis of the pulsar (\dot{x}). our detailed investigation of the possible contributions to the observed \dot{x} revealed major contributions from the relativistic and classical spin-orbit coupling of the white dwarf (≥ 80%), while the remainder is predominantly contributed to by the rate of change of special-relativistic aberration of the pulse profile. the significant relativistic contributions from spin-orbit coupling are a consequence of the lense-thirring precession of the binary orbit and is seen convincingly for the first time outside the solar system. we used these detections to obtain the first-ever constraints on the rotation period of the spun-up white dwarf, finding it to be 900 seconds or less. we then take a theory-independent standpoint and measure the post-keplerian (pk) parameters of the system using the dd binary timing model, and perform strong-field tests of gr and scalar-tensor theories of gravity. we find that covariances between the theory-independent estimate of \dot{x} and the other pk parameters have worsened what would have otherwise been one of the most stringent tests of scalar-tensor theories of gravity. we then suggest improvements to the existing strong-field testing methodologies that might provide significant improvements on the constraints from this system. in the second topic of the thesis, we present the design, development and implementation of a new survey (smirf) the ``survey for magnetars, intermittent pulsars, rrats and frbs''. this real-time pulsar survey with the utmost telescope is aimed at performing regular, rapid sweeps of the southern galactic plane, searching in real-time for pulsars through single-pulse and periodicity searches, the first of its kind to be carried out with an interferometer. smirf is facilitated by a robotic scheduler which is capable of fully autonomous and commensal operations. we report on the smirf observational parameters, the data analysis methods, the survey's sensitivity to pulsars and provide early survey results including the detection of a new (possibly intermittent) pulsar psr j1705-54 found via its single pulses. finally, we summarise our major findings and suggest future work that may expand on the work in this thesis. | gravitational dynamics of a relativistic binary pulsar and a probe of radio pulsar intermittency |
polarization due to aligned dust grains is a well-known tool for probing interstellar magnetic fields. the detailed physics of the grain alignment mechanism has, however, been poorly understood and it's only in the last decade that the promise of a quantitative, observationally supported, theory has emerged. a well-tested alignment theory would allow dust polarimetry to more securely probe the magnetic fields, but also to address issues of grain size distributions, mineralogy, and environmental parameters. radiative alignment torque (rat) theory predicts that asymmetric dust grain are spun up and, if paramagnetic, aligned with the magnetic field, through interaction with the radiation field. the theory provides a number of quantitative predictions, many of which are supported by observations. one - as of yet untested - prediction would resolve the conundrum of why carbonaceous dust does not contribute to ism polarization. under rat alignment carbonaceous grains are spun-up by the radiation but, because such dust is diamagnetic, does not align with the magnetic field. the theory, however, also predicts that for an intense, highly anisotropic radiation field, the grains will align with the radiation. we will test this prediction by performing hawc+ polarimetry of the carbon rich circumstellar envelope of irc+10216. this is re-submission of an accepted ("must do") cy 4 program, which is unlikely to be scheduled due to delays in the hawc+ commissioning. the scientific background and justification has been updated. | why are carbonaceous grains unaligned in the ism? - hawc+ polarimetry of irc+10216 |
we present the results of a full-polarization, spatially-resolved study of the jetted active galactic nucleus (agn) hosted by the nearby galaxy ngc 3665. by analyzing archival data from the very large array, we have identified an intriguing region of rapidly varying polarization angle and low polarized flux in the nucleus compared to that of the jets. this region is spatially coincident with a central molecular disk, raising the possibility that the observed polarization properties in the center of ngc 3665 are a result of faraday depolarization caused by the production of thermal gas as the jet ionizes the interstellar medium (ism). ngc 3665 thus represents a rare example of depolarization potentially caused by a jet-ism interaction. while there is no evidence of a molecular outflow in ngc 3665, the jets may inject enough energy into the ism to contribute to the observed low star formation efficiency in the central molecular disk. we discuss prospects for future radio polarimetric and molecular gas observations as a means of improving our understanding of how jets influence galaxy evolution. | faraday depolarization as an indicator of a jet-ism interaction in ngc 3665 |
the canadian hydrogen intensity mapping experiment (chime) is a new radio transit interferometer located at the dominion radio astrophysical observatory (drao) near penticton, bc canada. chime is designed to measure 21 cm emission from neutral hydrogen at redshift 0.8 < z < 2.5 to map baryon acoustic oscillations to constrain the dark energy equation of state. the telescope consists of four 100 m x 20 m parabolic cylinders. the dominant foreground is synchrotron emission from the milky way. we are developing techniques for removing this foreground emission and will also use it to construct an all-northern sky survey of polarized emission from the magnetized interstellar medium at 400-800 mhz. we will present an update on the chime instrument and early scientific observations. | canadian hydrogen intensity mapping experiment (chime) update |
the recent planck results in polarization at sub-mm wavelengths allow us to gain insight into the galactic magnetic field topology, revealing its statistical correlation with matter, from the diffuse interstellar medium (ism), to molecular clouds (mcs) (planck intermediate results. xxxii, xxxiii, xxxv). this correlation has a lot to tell us about the dynamics of the turbulent ism, stressing the importance of considering magnetic fields in the formation of structures, some of which eventually undergo gravitational collapse producing new star-forming cores.investigating the early phases of star formation has been a fundamental scope of the herschel gould belt survey collaboration (http://gouldbelt-herschel.cea.fr), which, in the last years, has thoroughly characterized, at a resolution of few tens of arcseconds, the statistics of mcs, such as their filamentary structure, kinematics and column density.although at lower angular resolution, the planck maps of dust emission at 353ghz, in intensity and polarization, show that all mcs are complex environments, where we observe a non-trivial correlation between the magnetic field and their density structure. this result opens new perspectives on their formation and evolution, which we have started to explore.in this talk, i will present first results of a comparative analysis of the herschel-planck data, where we combine the high resolution herschel maps of some mcs of the gould belt with the planck polarization data, which sample the structure of the field weighted by the density.in particular, i will discuss the large-scale envelopes of the selected mcs, and, given the correlation between magnetic field and matter, i will show how to make use of the high resolution information of the density structure provided by herschel to investigate the statistics of interstellar magnetic fields in the planck data. | a challenge for probing the statistics of interstellar magnetic fields: beyond the planck resolution with herschel |
magnetic fields can have a significant effect on the formation and evolution of molecular clouds and the formation of stars. the presence of strong magnetic fields restricts the motion of gas along the magnetic field lines. therefore, it resists gravitational collapse, hinders mass accretion and suppresses fragmentation. while magnetic fields are an integral part of modern theory of interstellar medium and star formation, their direct measurements have been challenging. in this talk, i'll review recent progress on the observational front of magnetic fields. the emphasis will be on linear polarization of interstellar dust to probe the plane of sky component of magnetic fields. | magnetic fields and star formation |
we carried out co (1-0) observations toward the target cloud with the purple mountain observatory 13.7m telescope (pmo-13.7m). we used the heinrich hertz submillimeter telescope on mt. graham, arizona, to measure the j=2-1 transition of co toward the target cloud. we upload the position-position-velocity (ppv) data in a fits format. (2 data files). | vizier online data catalog: polaris flare co enhancement by mhd waves (skalidis+, 2023) |
molecular hydrogen is the most abundant element in the universe, particularly in interstellar plasmas such as atmospheres of gas giant planets and stars. electron collision data for hydrogen is critical to interpreting the spectroscopy of interstellar objects, as well as being of applied value for modelling technological plasmas. hydrogen is also fundamentally interesting, as while highly accurate wave functions for this simple molecule are available, providing an accurate, ab initio, treatment the collision dynamics has proven challenging, on account of the need to have a complete description of channel coupling and polarization effects. to date, no single theoretical approach has been able to replicate experimental results across all transitions and incident energies, while the experimental database that is available is far from complete and not all available measurements are in satisfactory agreement. in this talk, we present differential and integral cross section measurements for electronic excitation cross sections for molecular hydrogen by low-energy electron impact. the data were measured at incident energies below 20ev, using a well-tested crossed beam apparatus and employing a moveable gas source approach to ensure that background contributions to the scattering are accurately accounted for. these measurements are compared with new theoretical results employing the convergent close coupling approach. | electronic excitation of molecular hydrogen by low-energy electrons |
the planck satellite has mapped the polarized microwave sky (from 30 ghz to 353 ghz) with unprecedented sensitivity and angular resolution. this wealth of data yields the first complete map of polarized thermal emission from dust in our own galaxy, shedding new light on the formation of dense cold structures within which new stars and planetary systems are born, under the combined effects of gravity, turbulence and magnetic fields. we present a statistical analysis of this polarized emission from nearby molecular clouds, with an emphasis on the evolution of the maximum polarization fraction observed as a function of column density, and on the anti-correlation between the polarization fraction and the local dispersion of polarization angles. to interpret this data, numerical simulations of anisotropic mhd turbulence underline the essential role played by the topology of the interstellar magnetic field, in particular its large-scale component. indeed, the polarization of dust thermal emission at the scales observed by planck is essentially related to the geometry of the magnetic field. polarization fractions anti-correlate with column densities, which may be due to a succession of variously polarized structures on the line of sight. they also anti-correlate with the local dispersion of polarization angles. these features are well reproduced by mhd simulations of the diffuse ism, with comparable correlation coefficients. as an extension to this work published in planck intermediate results xx (a&a, 576, 105, 2015), the statistical properties of the random component of the interstellar magnetic field are explored using a toy model of the turbulent magnetized ism based on fractional brownian motion (fbm) fields. a least-squares analysis to retrieve the statistical properties of the interstellar magnetic field from planck observations is pursued. application of this method on the toy model shows good promise, and we are currently working towards its application on planck data. | polarized thermal dust emission as seen by planck : a comparison with mhd simulations and lessons from a toy model |
measurements of polarized thermal dust emission can be used to map magnetic fields in the interstellar medium. recently, blastpol, the balloon-borne large aperture submillimeter telescope for polarimetry, has published the most detailed map ever made of a giant molecular cloud forming high-mass stars. i will present an overview of the next generation blast polarimeter (blast-tng), the successor telescope to blastpol, which maps linearly polarized dust emission at 250, 350 and 500 μm. blast-tng utilizes a 2.5-meter carbon-fiber primary mirror that illuminates focal plane arrays containing over 3,000 microwave kinetic inductance detectors. this new polarimeter has an order of magnitude increase in mapping speed and resolution compared to blastpol and we expect to make over 500,000 measurements of magnetic field orientation per flight. blast-tng will have the sensitivity to map entire molecular cloud complexes as well as regions of diffuse high galactic latitude dust. it also has the resolution (fwhm = 25’’ at 250 μm) necessary to trace magnetic fields in prestellar cores and dense filaments. blast-tng will thus provide a crucial link between the low resolution planck all-sky maps and the detailed but narrow field of view polarimetry capabilities of alma. for our first antarctic flight in december 2017 we are putting out a call for shared-risk proposals to fill 25% of the available science time. in addition, blast-tng data will be publicly released within a year of the publication of our first look papers, leaving a large legacy data set for the study of the role played by magnetic fields in the star formation process and the properties of interstellar dust. | blast-tng: a next generation balloon-borne large aperture submillimeter polarimeter |
pilot is a balloon-borne astronomy experiment, designed to study the polarization of interstellar dust emission in our galaxy. the pilot instrument will allow simultaneous observations in two photometric channels at wavelengths 240 μm (1.2 thz) and 550 μm (545 ghz). the angular resolution is better than 3.5 arc minutes over an instantaneous field of view of 0.8°x1°, with diffraction limited image quality. | optical characteristics and performances of the pilot balloon-borne experiment |
alma polarization observations of g9.62+0.20, which is a massive star forming region presenting several cores at different evolutionary stages. i will show the relationship between the large-scale magnetic field probed by dust and the small- scale magnetic field already probed by masers, and the evolutionary differences between the magnetic field morphologies of the cores. i will also present our recent results from merlin observations of iras 18089-1732, a well studied massive protostar, where the small-scale magnetic field probed by methanol masers is consistent with the large-scale magnetic field probed by dust. leurini silvia large-scale flows in a cluster forming filament: the case of g351.77- 0.51 the initial steps of star formation are believed to be tightly linked to the evolution of interstellar filaments. in contrast to lower-mass filaments, mass accretion from large scales in the form of sub-filaments seems to play a key role for the formation of their high-mass counterparts. the build up of massive filaments is still poorly understood and only a few examples are known to date. g351.77-0.51 is the youngest and most massive filament in the atlasgal survey of the galactic plane within 1 kpc and it exhibits a remarkable large-scale network of filamentary structures seen in extinction at 8micron. in this talk, i will present a detailed study of the kinematics of g351.77 and of the network of sub-filaments converging based on c18o apex data. | the large-scale environment of the cluster forming filament g351.77-0.51 |
kepler orbits are usually associated with the motion of astronomical objects such as planets or comets. here we observe such orbits at the microscale in a system of charged, insulating grains. by letting the grains fall freely under vacuum, we eliminate the effects of air drag and gravity, and by imaging them with a co-falling high-speed camera we track the relative positions of individual particles with high spatial and temporal precision. this makes it possible to investigate the behaviors caused by the combination of long-range electrostatic interactions and short-range, dissipative, contact interactions in unprecedented detail. we make the first direct observations of microscopic elliptical and hyperbolic kepler orbits, collide-and-capture events between pairs of charged grains, and particle-by-particle aggregation into larger clusters. our findings provide experimental evidence for electrostatic mechanisms that have been suspected, but not previously observed at the single-event level, as driving the early stages of particle aggregation in systems ranging from fluidized particle bed reactors to interstellar protoplanetary disks. furthermore, since particles of different net charge and size are seen to aggregate into characteristic spatial configurations, our results suggest new possibilities for the formation of charge-stabilized ``granular molecules''. we can reproduce the observed molecule configurations by taking many-body, dielectric polarization effects into account. | complex kepler orbits and particle aggregation in charged microscopic grains |
pilot (polarized instrument for long wavelength observations of the tenuous interstellar medium) is a balloonborne astronomy experiment designed to study the polarization of dust emission in the diffuse interstellar medium in our galaxy. the pilot instrument allows observations at wavelengths 240 μm and 550 μm with an angular resolution of about two arcminutes. the observations performed during the two first flights performed from timmins, ontario canada, and from alice-springs, australia, respectively in september 2015 and in april 2017 have demonstrated the good performances of the instrument. pilot optics is composed of an off axis gregorian type telescope combined with a refractive re-imager system. all optical elements, except the primary mirror, which is at ambient temperature, are inside a cryostat and cooled down to 3k. the whole optical system is aligned on ground at room temperature using dedicated means and procedures in order to keep the tight requirements on the focus position and ensure the instrument optical performances during the various phases of a flight. we'll present the optical performances and the firsts results obtained during the two first flight campaigns. the talk describes the system analysis, the alignment methods, and finally the inflight performances. | pilot optical alignment |
we present linear polarization towards the direction of the star cluster alessi 1, which is located in the anti-galactic centre direction. we have observed the cluster using aries imaging polarimeter (aimpol) as a back-end instrument at 104-cm sampuranand telescope, aries, nainital. the average degree of polarization towards the cluster alessi 1 are found to be 0.80+/-0.38 %, 0.80+/-0.23 %, 0.81+/-0.26 %, 0.86+/-0.32 %, in b, v, r, and i photometric bands, respectively, whereas the position angles are found to be 86+/-11° , 81+/-10°, 78+/-8°, 85+/-8° in b, v, r, and i bands, respectively. polarization towards alessi 1 cluster is dominated by foreground dust grains and probably a single layer of the polarized source appears to exist at 0.7 kpc close to alessi 1 cluster. the minor axis of dust grains towards the cluster alessi 1 appears aligned along the galactic magnetic field. | linear polarization towards galactic anticenter direction: the case of alessi |
the observations in the direction of the cir-mms cluster region (see cir-mmss 1-4 in reipurth+ 1996a&a...314..258r) were carried out using the sirpol imaging polarimeter mounted on the 1.4m infrared survey facility (irsf) telescope at the south african astronomical observatory (saao). our irsf/sirpol observations were made on the night of 2011 march 19, during which we performed 10s exposures at 4 wave plate angles in the sequence of 0°, 45°, 22.5°, and 67.5° at 10 dithered positions for each set. the typical seeing size during the observations was approximately 3 pixels (corresponding to 1.4") in the jhks band. (4 data files). | vizier online data catalog: jhks polarimetry in circinus molecular cloud (kwon+, 2018) |
deep within giant molecular clouds, hidden by dense gas and dust, stars form. unprecedented data from the atacama large millimeter/submillimeter array (alma) reveal the intricate magnetic structureswoven throughout one of the most massive star-forming regions in the milky way.how stars are bornthe horsehead nebulasdense column of gas and dust is opaque to visible light, but this infrared image reveals the young stars hidden in the dust. [nasa/esa/hubble heritage team]simple theory dictates that when a dense clump of molecular gas becomes massive enough that its self-gravity overwhelms the thermal pressure of the cloud, the gas collapses and forms a star. in reality, however, star formation is more complicated than a simple give and take between gravity and pressure. thedusty molecular gas in stellar nurseries is permeated with magnetic fields, which are thought to impede the inward pull of gravity and slow the rate of star formation.how can we learn about the magnetic fields of distant objects? one way is by measuring dust polarization. an elongated dust grain will tend to align itself with its short axis parallel to the direction of the magnetic field. this systematic alignment of the dust grains along the magnetic field lines polarizes the dust grains emission perpendicular to the local magnetic field. this allows us to infer the direction of the magnetic field from the direction of polarization.magnetic field orientations for protostars e2 and e8 derived from submillimeter array observations (panels a through c) and alma observations (panels d and e). click to enlarge. [adapted from koch et al. 2018]tracing magnetic fieldspatrick koch (academia sinica, taiwan) and collaborators used high-sensitivity alma observations of dust polarization to learn more about the magnetic field morphology of milky way star-forming region w51. w51 is one of the largest star-forming regions in our galaxy, home to high-mass protostars e2, e8, and north.the alma observations reveal polarized emission toward all three sources. by extracting the magnetic field orientations from the polarization vectors, koch and collaborators found that the molecular cloud contains an ordered magnetic field with never-before-seen structures. several small clumps on the perimeter of the massive star-forming cores exhibit comet-shaped magnetic field structures, which could indicate that these smaller cores are being pulled toward the more massive cores.these findings hint that the magnetic field structure can tell us about the flow of material within star-forming regions key to understanding the nature of star formation itself.maps of sin for two of the protostars (e2 and e8) and their surroundings. [adapted from koch et al. 2018]guiding star formationdo the magnetic fields in w51 help or hinder star formation? to explore this question,koch and collaborators introduced the quantity sin , where is the angle between the local gravity and the local magnetic field.when the angle between gravity and the magnetic field is small (sin 0), the magnetic field has little effect on the collapse of the cloud. if gravity and the magnetic field are perpendicular (sin 1), the magnetic field can slow the infall of gas and inhibit star formation.based on this parameter, koch and collaborators identified narrow channels where gravity acts unimpeded by the magnetic field. these magnetic channels may funnel gas toward the dense cores and aid the star-formation process.the authors observations demonstrate just one example of the broad realm almas polarimetry capabilities have opened to discovery. these and future observations of dust polarization will continue to reveal more about the delicate magnetic structure within molecular clouds, furtherilluminating the role that magnetic fields play in star formation.citationpatrick m. koch et al 2018 apj 855 39. doi:10.3847/1538-4357/aaa4c1 | magnetic fields versus gravity |
observations of background stars of the book globules cb34, cb56 and [omk2002] 18 were performed in the near-ir with the instrument son of isaac (sofi) at the 3.58m new technology telescope (ntt) from november 11 to 15, 2015. stokes parameters q, u and i in the near-infrared wavelength range for background stars of the globules were derived using these observations. these parameters are later used to calculate the polarization angle and polarization degree of the background stars. (3 data files). | vizier online data catalog: stokes param. of bok globules background stars (jorquera+, 2018) |
i will review recent progress in our observational understanding of the link between the structure of molecular clouds and the formation of solar-type stars. in particular, i will describe the filamentary paradigm favored by herschel studies of the nearest molecular clouds of the galaxy which point to the key role of the quasi-universal filamentary structure pervading the cold ism. i will also discuss observational constraints on the formation and evolution of molecular filaments, coming from planck polarization data and ground-based mm line studies. overall, the available observations support a picture in which interstellar filaments and prestellar cores represent two fundamental steps in the star formation process: first, large-scale compression of interstellar material in supersonic mhd flows generates a cobweb of filaments in the ism; second, the densest filaments fragment into prestellar cores (and subsequently protostars) by gravitational instability, while simultaneously growing in mass and complexity through accretion of background cloud material.i will end by emphasizing the need for high-resolution polarimetric imaging at far-infrared wavelengths to clarify the role of magnetic fields in the formation and evolution of star-forming filaments. | interstellar filaments and star formation |
pulsar polarimetry is widely used to infer interstellar magnetic fields. these magnetic field estimates typically rely on the assumption that the observed polarisation rotation stems entirely from faraday rotation in the magneto-optic plasma found between the linearly polarized point source pulsar and our planet. yet, the magnetosphere that surrounds pulsar can in principle also affect polarization. while the classical faraday rotation in the pair plasma magnetosphere itself may be negligible, we show that a mechanical polarization rotation (or mechanical faraday) effect should arise from the pulsar magnetosphere rapid rotation. importantly, while this mechanical effect can be mistaken for faraday rotation in the interstellar medium (ism) due to its identical wavelength-square signature at typical ghz observation frequency, it can in principle be disambiguated in the sub-ghz thanks to a different wavelength scaling near a cut-off frequency. separating these two contributions through low-frequency pulsar polarisation observations could thus permit correcting for possible systematic errors in ism magnetic field estimates. it also offers a conceptual means to determine the rotation direction of pulsars, which remains otherwise inaccessible. this work was supported, in part, by nnsa grant no. de-na0002948, u.s. doe contract no. de-ac52-07na27344 and through llnl-ldrd program project no. 19-erd-038. | mechanical faraday effect to inform on pulsar rotation direction |
dust thermal emissions observed with herschel have revealed that interstellar molecular clouds consist of many filaments. polarization observation of interstellar extinctions in the optical and near ir wavelengths shows that the dense filaments are extending perpendicular to the interstellar magnetic field. magnetohydrostatic structures of such filaments are studied. it is well known that a hydrostatic filament without magnetic field has a maximum line mass of ¥lambda_max=2c_s^2/g (c_s:the isothermal sound speed and g: the gravitational constant). on the other hand, the magnetically-supported maximum line mass increases in proportion to the magnetic flux per unit length threading the filament (¥phi), as ¥lambda_max 2c_s^2/g + ¥phi/(2¥pi g^1/2). comparison is made with 3d clouds. stability of these magnetized filaments is studied using time-dependent 3d mhd simulations to discuss star formation in the filaments. polarization pattern expected for the magnetically subcritical filaments is calculated. the distribution function of the angle between b-field and the axis of the filament, which is obtained with planck satellite, is compared with this mock observation. | structures of magnetically-supported filaments and their appearance in the linear polarization |
pilot is a balloon borne experiment which aims at measuring precisely the polarized emission of the interstellar dust emission, in the submm range (240 and 550 μm). these measurements will be used to reach a better understanding of the galactic magnetic field role in the structure of the galaxy and the star formation process. they will be useful too for cmb experiments by providing a precise knowledge of galactic foreground emission. simulations including realistic instrument performances show that after three flights (around 24 hours each), it will be possible to cover the full galactic plane map (+/-30° in latitude). in addition, several deep surveys will be performed at high galactic latitude. as the level of polarized emission of interstellar dust is less than 5%, an accurate knowledge of the instrumental polarization is mandatory for the data processing and analysis. | instrumental polarization modelling for the pilot submm experiment |
we make available 127 linear polarisation spectra of 101 stars, obtained with the fors2 instrument of the eso very large telescope. these spectra cover the wavelength range 380-950nm at a spectral resolving power of about 880. we have produced a catalogue with synthetic broadband polarimetry in the bvri filters, and we also provide the serkowski-curve parameters, as well as the wavelength gradient of the polarisation position angle for the interstellar polarisation along 76 different lines of sight. (2 data files). | vizier online data catalog: southern hemisphere ism fors2 spectropolarimetry (bagnulo+, 2017) |
we present a new single-shot, full-stokes optical astro-polarimeter design using stress-engineered optics (seos). the seo is a cylindrical glass window under static stress by radially-inward forces in three symmetrically-space regions, producing spatially-varying birefringence throughout (spilman and brown, applied optics ip, 46, 2007), and can be produced by using o-the-shelf supplies and some machining. by collimating light collected by a telescope through the seo and then focusing it onto a detector, the system's point spread function (psf) acquires a shape uniquely dependent on the full polarization vector of the input light (beckley and brown, proc. spie, 757011, 2010). by measuring the imaged psfs, the full-stokes polarization states of all point sources (stars) in the field can ideally be determined from a single exposure and without division of amplitude techniques. prior to our instrument, these techniques and technology had not yet been applied to astronomy. aside from filter wheels and focusing elements, our instrument contains no moving parts. the instrument will operate by first taking a set of calibration exposures of 100% polarized light using swap-in polarizers in one of its filter wheels. once the calibration images are taken, the polarizers are removed form the light path, and the science target (star) is imaged. using techniques described in this paper, the calibration images allow one to determine the unknown polarization of the science target. this process is repeated in multiple photometric bands at visible wavelengths for color-dependent studies. the successful application of this polarimeter technology in astronomy would mark a step forward for increasing polarimetry efficiency (no temporal modulation required) and simplicity of instrumentation (no spatial modulation required). contained in this paper are the on-sky commissioning results of our polarimeter on an 0:2m (8in) telescope at the university of denver, and an in-depth look at the effect of earth's atmospheric turbulence on the polarization-dependent psf detection. we have also begun testing the instrument's capabilities in measuring both linear and circular interstellar polarization, and a look at the variability of historic polarized and unpolarized "standard" stars. better understanding of the interstellar component of the polarization of stars and the nature of calibration stars are required for all future polarimetric measurements. the authors are grateful to the estate of william herschel womble for the support of astronomy at the university of denver. | the first polarimeter in astronomy to use a stress-engineered optic (seo) |
magnetic fields play important roles in many astrophysical processes. however, there is no universal diagnostic for the magnetic fields in the interstellar medium (ism) and each magnetic tracer has its limitation. any new detection method is thus valuable. theoretical studies have shown that submillimeter fine-structure lines are polarized due to atomic alignment by ultraviolet (uv) photon-excitation, which opens up a new avenue to probe interstellar magnetic fields. the method is applicable to all radiative-excitation dominant region, e.g., h ii regions, pdrs. the polarization of the submillimeter fine-structure lines induced by atomic alignment could be substantial and the applicability of using the spectro-polarimetry of atomic lines to trace magnetic fields has been supported by synthetic observations of simulated ism in our recent paper. our results demonstrate that the polarization of submillimeter atomic lines is a powerful magnetic tracer and add great value to the observational studies of the submilimeter astronomy. | tracing magnetic fields with the polarization of submillimeter lines |
stellar wind bow shocks are structures created when stellar winds with supersonic relative velocities interact with the local interstellar medium (ism). they can be studied to understand the properties of stars as well as the ism. since bow shocks are asymmetric, light becomes polarized by scattering in the regions of enhanced density they create. we use a monte carlo radiative transfer code calle slip to simulate the polarization signatures produced by both resolved and unresolved bow shocks with analytically derived shapes and density structures. when electron scattering is the polarizing mechanism, we find that optical depth plays an important role in the polarization signatures. while results for low optical depths reproduce theoretical predictions, higher optical depths produce higher polarization and position angle rotations at specific viewing angles. this is due to the geometrical properties of the bow shock along with multiple scattering effects. for dust scattering, we find that the polarization signature is strongly affected by wavelength, dust size, dust composition, and viewing angle. depending on the viewing angle, the polarization magnitude may increase or decrease as a function of wavelength. we will present results from these simulations and preliminary comparisons with observational data. | astronomy in denver: polarization of bow shock nebulae around massive stars |
linear polarimetry measurements were obtained in the nir h band (1.6 um) using the mimir instrument (clemens et al. 2007pasp..119.1385c) on the 1.8 m perkins telescope outside of flagstaff, az. mimir used a 10242 aladdin iii insb detector array, operated at 33.5 k. the instrument had a field of view (fov) of 10'x10' and pixel scale of 0.58''. polarimetric analysis was performed with a cold, stepping, h-band, compound half-wave plate (hwp) plus a fixed, cold wire-grid analyzer. sky observations were planned for a grid of 54 abutting fields (a 6x9 field grid) covering a 1°x1.5° region of l204 centered on cloud 3. they were conducted over several nights between 2010 may and 2012 may. to obtain polarimetry measurements, exposures of five second durations were obtained for 16 unique hwp position angles at six sky-dither positions, yielding a total of 96 images per field. the total on-sky integration time of the entire map (eight minutes per fov) was 7.2 hr. polarization flat-fields for each hwp position were taken using a lights-on/lights-off method against a uniformly illuminated flat-field screen inside the closed telescope dome. (1 data file). | vizier online data catalog: l204 - cloud 3 polarimetry and photometry (cashman+, 2014) |
pilot (polarized instrument for long wavelength observations of the tenuous interstellar medium) is a balloonborne astronomy experiment designed to study the polarization of dust emission in the diffuse interstellar medium in our galaxy. the pilot instrument allows observations at wavelengths 240 μm (1.2thz) with an angular resolution about two arc-minutes. the observations performed during the first flight in september 2015 at timmins, ontario canada, have demonstrated the optical performances of the instrument. | pilot optical alignment |
geomagnetic storms of the highest intensity are general driven by coronal mass ejections (cmes) impacting the earth's space environment. their intensity is driven by the speed, density, and, most-importantly, their magnetic-field orientation and magnitude of the incoming solar plasma. the most-significant magnetic-field factor is the north-south component (bz in geocentric solar magnetic - gsm - coordinates). at present, there are no reliable prediction methods available for this magnetic-field component ahead of the in-situ monitors around the sun-earth l1 point. observations of faraday rotation (fr) can be used to attempt to determine average magnetic-field orientations in the inner heliosphere. such a technique has already been well demonstrated through the corona, ionosphere, and also the interstellar medium. measurements of the polarisation of astronomical (or spacecraft in superior conjunction) radio sources (beacons/radio frequency carriers) through the inner corona of the sun to obtain the fr have been demonstrated but mostly at relatively-high radio frequencies. here we show some initial results of true heliospheric fr using the low frequency array (lofar) below 200 mhz to investigate the passage of a coronal mass ejection (cme) across the line of sight. lofar is a next-generation low-frequency radio interferometer, and a pathfinder to the square kilometre array (ska) - low telescope. we demonstrate preliminary heliospheric fr results through the analysis of observations of pulsar j1022+1001, which commenced on 13 august 2014 at 13:00ut and spanned over 150 minutes in duration. we also show initial comparisons to the fr results via various modelling techniques and additional context information to understand the structure of the inner heliosphere being detected. this observation could indeed pave the way to an experiment which might be implemented for space-weather purposes that will eventually lead to a near-global method for determining the magnetic field throughout the inner heliosphere. | observations and analyses of heliospheric faraday rotation of a coronal mass ejection (cme) using the low frequency array (lofar) and space-based imaging techniques |
sensitive, high resolution observations of galactic hi reveal an intricate network of slender linear features, much as sensitive surveys of dust in galactic molecular clouds reveal ubiquitous filamentary structure. across the high galactic latitude sky, diffuse hi structures are aligned with the interstellar magnetic field, as revealed by background starlight polarization (clark, peek, putman 2014). we present the discovery that the orientation of hi structures traces the planck 353 ghz polarization angle measurements with extraordinary accuracy. we explore the physical properties of the hi structures, and the physical mechanisms responsible for their alignment, by examining the hi structures across a range of densities and environments. we discuss the insights that may be gained from a deeper understanding of the interplay between gas, dust, and magnetic fields in the ism. | magnetically aligned hi and dust: new insights into the physical properties of the diffuse ism |
pulsar emission which we observe is fundamentally tied to the strong magnetic fields encasing the neutron star. charged particles follow these field lines before emitting curvature radiation. the projected polarization position angles of such radiation are a glimpse directly at the structure of these magnetic field lines. the rotating vector model is the typical formulation for relating polarization position angle sweep (versus pulsar phase) data to the geometry of the pulsar. this model assumed a simple dipole for the magnetic field lines and can be described analytically. the rotating vector model works well for a large number of pulsars but fails mostly for high-energy pulsars. in this talk, i explore data-driven, physically-motivated modifications to the rotating vector model. we begin by numerically calculating polarization with models that include relativistic effects, sweep-back effects, and finite altitude emission and compare model to model. further by including the effects of orthogonal mode jumps, multiple emission altitudes, open zone growth via y-point lowering, interstellar scattering, and inward-directed emission we show a wide range of departures from the rotating vector model (as seen in the polarization data) can be understood while retaining a geometrical picture. overall, we take the view of letting the data drive our models and our understanding of the emission mechanism in pulsar magnetospheres. | one does not simply model radio polarization of pulsars (and connect it to data) |
little is known about biological radiation action on the molecular level. the response of isolated biomolecules upon energetic photons is of great interest i.e. for astrobiology and radiobiology. key questions concern ion chemistry in the interstellar medium, possible transport of biomolecules from space to earth and molecular mechanisms underlying biological radiation damage. experiments with small biomolecules in the gas phase have the advantage of studying ionization and fragmentation dynamics in finite systems but are less realistic radiation damage models. to be able to investigate more complex biomolecular systems, such as peptides and proteins, we have developed a new apparatus in which a home-made electrospray source can be interfaced with a low energy (kev) ion beamline or different photon beamlines (e.g. of synchrotrons or free electron lasers). spectra of peptides obtained with this set-up will be presented. dependencies on energy and polarization of the radiation as well as peptide length and structure will be thereby discussed. | dissociation of peptides by ions and photons |
cooling and trapping of polar molecules has attracted attention at cold and ultracold temperatures. extended study of molecular inelastic collision processes of polar interstellar species with proton finds an important astrophysical application to model interstellar medium. present study includes computation of rate coefficient for molecular rotational quenching process in proton collision with isovalent co and cs molecules using quantum dynamical close-coupling calculations. full dimensional ab initio potential energy surfaces have been computed for the ground state for both the systems using internally contracted multireference configuration interaction method and basis sets. quantum scattering calculations for rotational quenching of isovalent species are studied in the rigid-rotor approximation with cx (x=o, s) bond length fixed at an experimental equilibrium value of 2.138 and 2.900 a.u., respectively. asymptotic potentials are computed using the dipole and quadrupole moments, and the dipole polarizability components. the resulting long-range potentials with the short-range ab initio interaction potentials have been fitted to study the anisotropy of the rigid-rotor surface using the multipolar expansion coefficients. rotational quenching cross-section and corresponding rates from j=4 level of cx to lower j' levels have been obtained and found to obey wigner's threshold law at ultra cold temperatures. | rotational quenching study in isovalent h+ + co and h+ + cs systems |
in our companion papers (hollick+ 2018apj...863...75h and 2018apj...863...76h) we analyze 637 intervals of magnetic wave activity observed by the voyager 1 and 2 spacecraft from its launch in 1977 through the end of 1990. we argue that these waves originate from cyclotron resonance with newborn interstellar pickup he+ and h+. as the list of wave events is long and potentially useful to other researchers, we take this opportunity to list the times of those wave events here, along with their heliocentric location, ellipticity (often referred to as polarization), and whether thermal ion data is available from the pls instrument. a brief overview of the analysis contained within the companion papers is also provided. (4 data files). | vizier online data catalog: magnetic wave activity observed by voyager 1 & 2 (hollick+, 2018) |
the planck satellite (planck 2015 results i) has mapped the polarized microwave sky (from 30 ghz to 353 ghz) with unprecedented sensitivity and angular resolution. this wealth of data yields the first complete map of polarized thermal emission from dust in our own galaxy (planck intermediate results xix),, shedding new light on the formation of dense cold structures within which new stars and planetary systems are born, under the combined effects of gravity, turbulence and magnetic fields. we present a statistical analysis of this polarized emission from nearby molecular clouds, with an emphasis on the evolution of the maximum polarization fraction observed as a function of column density, and on the anti-correlation between the polarization fraction and the local dispersion of polarization angles. to interpret this data, numerical simulations of anisotropic mhd turbulence (fromang, hennebelle, & teyssier 2006, hennebelle et al. 2008) underline the essential role played by the topology of the interstellar magnetic field, in particular its large-scale component (planck intermediate results xx). indeed, the polarization of dust thermal emission at the scales observed by planck is essentially related to the geometry of the magnetic field. polarization fractions anti-correlate with column densities, which may be due to a succession of variously polarized structures on the line of sight. they also anti-correlate with the local dispersion of polarization angles. these features are well reproduced by mhd simulations of the diffuse ism, with comparable correlation coefficients. as an extension to this work published in planck intermediate results xx, the statistical properties of the random component of the interstellar magnetic field are explored using a toy model of the turbulent magnetized ism based on fractional brownian motion (fbm) fields. a least-squares analysis to retrieve the statistical properties of the interstellar magnetic field from planck observations is pursued. application of this method on the toy model shows good promise, and we are currently working towards its application on planck data. | polarized thermal dust emission as seen by planck : a comparison with mhd simulations and lessons from a toy model |
observations of faraday rotation (fr) can be used as a remote-sensing method of determining magnetic fields which has been well demonstrated through the corona, ionosphere, and interstellar medium. fr values are obtained via observations of polarised radio sources with well-documented characteristics (astronomical radio sources observed are typically pulsars). measurements of the inner corona of the sun in fr have been shown from both spacecraft beacons and some natural radio sources but at relatively-high radio frequencies. here we show some initial results of true heliospheric fr using the low frequency array (lofar) below 200 mhz to investigate the passage of a coronal mass ejection (cme) across the line of sight. lofar is arguably the most-advanced interferometer radio telescope at present with wide-ranging radio-astronomy capabilities from imaging to beam forming multiple beams on the sky. we demonstrate preliminary heliospheric fr results through the analysis of observations of pulsar j1022+1001, which commenced on 13 august 2014 at 13:00ut and spanned over 150 minutes in duration. we also show initial comparisons to the fr results via modelling techniques and additional context information to understand the structure of the inner heliosphere being detected. this observation could pave the way to a set of observations and modelling techniques that might be implemented for space-weather purposes eventually leading to a near-global method for determining the magnetic field throughout the inner heliosphere. the most-intense space weather at earth is due to geomagnetic storms. they are driven by the speed, density, and magnetic-field of the incoming plasma. the most-important determining factor of the intensity of geomagnetic storms is that of the north-south component of magnetic field (bz in geocentric solar magnetic - gsm - coordinates). currently, there is no reliable prediction of this magnetic-field component until the incoming plasma from the sun has reached in-situ monitors around the l1 point and this provides only 15-60 minutes advanced warning. | preliminary analysis of observations of heliospheric faraday rotation of a cme using lofar |
pilot is a stratospheric experiment designed to measure the polarization of dust fir emission, towards the diffuse interstellar medium. the first pilot flight was carried out from timmins in ontario-canada on september 20th 2015. the flight has been part of a launch campaign operated by the cnes, which has allowed to launch 4 experiments, including pilot. the purpose of this paper is to describe the performance of the instrument in flight and to perform a first comparison with those achieved during ground tests. the analysis of the flight data is on-going, in particular the identification of instrumental systematic effects, the minimization of their impact and the quantification of their remaining effect on the polarization data. at the end of this paper, we shortly illustrate the quality of the scientific observations obtained during this first flight, at the current stage of systematic effect removal. | inflight performance of the pilot balloon-borne experiment |
the remnants of core-collapse supernovae often present significant asymmetries while those of thermonuclear supernovae are, more or less, spherically symmetric. as superluminous supernovae (slsn) do not occur in milky way-type galaxies (they prefer metal-poor starburst dwarfs), our chances of studying directly a slsn remnant are very limited, except perhaps in the magellanic clouds. therefore, the only way of probing the slsn geometry, and thus identifying potential slsn remnant candidates, is through polarimetry of the explosions themselves. i will present the first polarimetric observations of slsne obtained through a dedicated too program at the vlt. lsq14mo is a slsn-i that showed only a very limited degree of polarisation (p = 0.52%), which corresponds to an upper limit of 10% in the photosphere asphericity. in addition, this signal can be entirely due to interstellar polarisation in the host galaxy. this is perhaps surprising as the leading models for h-poor slsne involve a magnetar or csm interaction, i.e. configurations that are not expected to be spherically symmetric. observations of a slsn-ii yielded a more significant degree of polarisation, while preliminary analysis for a slsn-r reveals similarly low levels of asphericity as for lsq14mo. | what do the remnants of superluminous supernovae look like? |
the linear polarization data used in this work are a combination of observations conducted at the cerro tololo interamerican observatory (ctio, chile), using the 0.9m telescope, and also at the observatorio pico dos dias/laboratorio nacional de astrofisica (opd/lna, brazil), using both the 0.6m and the 1.6m telescopes. the optical data (v, r, and i johnson-cousins bands) were obtained with the ctio-0.9m and opd-0.6m telescopes, while the near-ir data (h band) were collected with the opd-1.6m telescope. the content and organization of the polarization values set is shown in table1. (1 data file). | vizier online data catalog: vri and h polarization toward sh 2-29 (santos+, 2014) |
measurements of optical circular polarization (stokes v) introduced by dust grains in the ism are important for two main reasons. first of all, the polarization itself contains information about the metallic versus dielectric composition of the dust grains themselves (h. c. van de hulst 1957, textbook). additionally, circular polarization can help constrain the interstellar component of the polarization of any source that may have intrinsic polarization, which needs to be calibrated for astrophysical study. though interstellar circular polarization has been observed (p. g. martin 1972, mnras 159), most broadband measurements of ism polarization include linear polarization only (stokes q and u), due to the relatively low circular polarization signal and the added instrumentation complexity of including v-measurement capability. prior circular polarization measurements have also received very little follow-up in the past several decades, even as polarimeters have become more accurate due to advances in technology. the university of denver is pursuing these studies with polvis, a prototype polarimeter that utilizes a stress-engineered optic ("seo", a. k. spilman and t. g. brown 2007, applied optics ip 46) to produce polarization-dependent psfs (a. m. beckley and t. g. brown 2010, proc spie 7570). these psfs are analyzed to provide simultaneous stokes i, q, u, and v measurements, in a single beam and single image, along the line-of-sight to point source-like objects. polvis is the first polarimeter to apply these optics and measurement techniques for astronomical observations. we present the first results of this instrument in b, v, and r wavebands, providing a fresh look at full stokes interstellar polarization. importantly, this set of efforts will constrain the ism contribution to the polarization with respect to intrinsic stellar components. the authors are grateful to the estate of william herschel womble for the support of astronomy at the university of denver, and for funding provided by the mt. cuba astronomical foundation. | astronomy in denver: probing interstellar circular polarization with polvis, a full stokes single shot polarimeter |
we seek to quantify the regions where dust grains are, and are not aligned by the local magnetic field in molecular cloud cores with embedded class 0 ysos . an understanding of where grains are aligned is crucial for any effort to compare models of magnetized core collapse with polarization vector maps. we propose to use hawc+ in polarimetry mode to investigate interstellar polarization associated with three very young ysos, heavily embedded in the infrared dark cloud g034.43+00.24. hawc+ observations at 53 and 154 microns will allow us to explore: 1) grain alignment in a class 0 yso envelope, 2) the wavelength dependence of the polarization from 53 microns to 3 mm, and 3) the magnetic field geometry outside the cloud core, left over from the collapse phase. | grain alignment in class 0 ysos |
the robopol optical polarization data of the polaris flare were obtained with the robopol polarimeter at the 1.3m telescope at the skinakas observatory in crete, greece. observations cover the area l=[122.6deg, 126.0deg], b=[+24.7deg, +27.9deg] (almost 10 square degrees). all observations were in the r band. measurements presented in the accompanying table have fractional linear polarization (p) to error (σ_p) greater or equal to 2.5. coordinates are those of the corresponding source in the usno-b1.0 star catalog. (1 data file). | vizier online data catalog: optical polarization of the polaris flare (panopoulou+, 2015) |
faraday effect is a common and useful way to deduce cosmic magnetic fields in the interstellar and intracluster media (ism and icm). faraday rotation is the result of magnetically-induced birefringence in a dielectric medium causing a linearly polarized wave to suffer a rotation of its polarization axis as it traverses such a medium. however, the standard λ2-law of the rotation angle may not hold in strongly turbulent plasmas. electromagnetic high-frequency and/or small-scale fluctuations may lead to effective collisionality with the pitch-angle diffusion coefficient being an effective ``quasi-collision'' frequency. recently, we showed that quasi-collisionality may radically alter radiative transport properties of plasmas, such as absorption, transmission and reflection and other effects, which can be very important in laboratory and astrophysical plasmas. here we briefly discuss the quasi-collisional generalization of the classical faraday effect, which is drastically modified and can even become negative. furthermore, we explore the origin of the long-known anomaly of faraday rotation in a famous cygnus regions. we argue that the anomaly can be due to the anomalous faraday rotation in a thin ``blanket'' of turbulent plasma at the front of an interstellar bubble/shock. supported by ku clas and doe grant id0000225143 (07/01/16). | anomalous faraday rotation in the ism/icm |
blue luminescence (bl) in the emission spectra of the red rectangle centered on the bright star hd44179 is recently reported by vijh et al [1]. this results is consistent with the broad band polarization measurements obtained in 1980 by schmidt et al. both experimental and theoretical studies support that bl emission could be attributed the luminescence of polycyclic aromatic hydrocarbon (pah) excited with ultraviolet light from the center of the star [4 and reference therein]. the abundance on n to c in the interstellar medium suggest also that nitrogen substituted pah (panh) are likely abundant in the interstellar medium [3]. they exhibit similar features as pahs and could contribute to the unidentified spectral bands. comparing the bl to laboratory spectra obtained on similar environment is crucial for the identification of interstellar molecules. we present in this works the absorption and the laser induced emission spectra of several isolated and cold pahs and panhs. laser induced emission was performed first to pahs and panhs isolated in argon matrix at 10 k. then, measurements are performed with the supersonic jet technique of the cosmic laboratory facility at nasa ames. we focus, here, on the emission spectra (fluorescence and (or) phosphorescence) of these molecules and we discuss their contributions to the blue luminescence emission in the red rectangle nebula.[1] vijh,u.p., witt. a.n. & gordon,k.d, apj, 606, l69 (2004)[2] schmidt, g. d., cohen, m. & margon, b., apj, 239l.133s (1980)[3] spitzer, l., physical processes in the interstellar medium (new york wiley-interscience) (1978)[4] salama, f., galazutdinov, g. a., kre lowski, j., allamandola, l. j., & musaev, f. a. apj, 526,(1999) | laser induced emission spectroscopy of cold and isolated neutral pahs and panh: implications for the red rectangle emission |
this is an exciting time for the discovery of supernova remnants (snrs) in galaxies other than our milky way. snrs reflect a major process in the elemental enrichment of the interstellar medium (ism). the study of this interaction in different domains including radio, optical, ir and x-ray, allow a better understanding of these remnants and their environments. nearby external galaxies offer an ideal laboratory, since they are near enough to be resolved, yet located at relatively known distances.we highlight our radio studies of snrs in both the small and large magellanic clouds (lmc), and share some of our multi-wavelength analytics for these objects. we also present new unpublished combined radio observations at 5.5 ghz of snr 1e 0102-7219 in the small magellanic cloud (smc). these observations used the australia telescope compact array (atca) with the compact array broadband backend (cabb). the 2 ghz bandwidth from cabb not only increases sensitivity but also allows the data to be split into channels that can be used to measure the object's faraday rotation. we show our new combined 5.5 ghz image, a full 2 ghz bandwidth polarization image having fractional polarization vectors up to 39% and a rotation measure image. | supernova remanents in the magellanic clouds: are there any surprises? |
massive stars strongly affect their surroundings through their energetic stellar winds and deaths as supernovae. the bow shock structures created by fast-moving massive stars contain important information about the winds and ultimate fates of these stars as well as their local interstellar medium (ism). since bow shocks are aspherical, the light scattered in the dense shock material becomes polarized. analyzing this polarization reveals details of the bow shock geometry as well as the composition, velocity, density, and albedo of the scattering material. with these quantities, we can constrain the properties of the stellar wind and thus the evolutionary state of the star, as well as the dust composition of the local ism.in my dissertation research, i use a monte carlo radiative transfer code that i optimized to simulate the polarization signatures produced by both resolved and unresolved stellar wind bow shocks (swbs) illuminated by a central star and by shock emission. i derive bow shock shapes and densities from published analytical calculations and smooth particle hydrodynamic (sph) models. in the case of the analytical swbs and electron scattering, i find that higher optical depths produce higher polarization and position angle rotations at specific viewing angles compared to theoretical predictions for low optical depths. this is due to the geometrical properties of the bow shock combined with multiple scattering effects. for dust scattering, the polarization signature is strongly affected by wavelength, dust grain properties, and viewing angle. the behavior of the polarization as a function of wavelength in these cases can distinguish among different dust models for the local ism. in the case of sph density structures, i investigate how the polarization changes as a function of the evolutionary phase of the swbs. my dissertation compares these simulations with polarization data from betelgeuse and other massive stars with bow shocks. i discuss the implications of these model for the stellar winds and interstellar environments of these influential objects. | polarized bow shocks reveal features of the winds and environments of massive stars |
we explore the use of the recently introduced velocity gradient technique (see yuen & lazarian 2017 (2017apj...837l..24y) and lazarian et al. 2017 (arxiv:1703.03119)) to neutral and ionic species in two fluid mhd simulations representing the partially ionized interstellar medium. we use the fact that below the decoupling scale, the turbulent eddies for ions remain anisotropic in length while the neutral eddies are isotropic. using this difference between the ion and neutral eddy shape and a new scale dependent velocity gradient, we are able to determine the length scale at which the ion and neutral turbulent cascades begin to deviate. in addition, the change in alignment between velocity gradients and the polarization direction indicate a possible way to measure the plane of sky magnetic field strength. | probing local decoupling scale using spectroscopic ion-neutral velocity gradients |
turbulence and magnetic fields are ubiquitous in the interstellar medium, shaping star formation and molecular cloud dynamics. as such, it is crucial to understand their effects. traditional techniques like dust polarization, however, are limited in their ability to probe high density or high opacity environments. to address this, we present the velocity gradient technique (vgt), a new way to measure the direction and strength of magnetic fields perpendicular to the line of sight. the technique uses only spectroscopic observations and an understanding of current magnetohydrodynamic theory in the presence of turbulence. we demonstrate two applications of the vgt in the form of a map of the plane of sky galactic magnetic field and a 3d map (in velocity) of the magnetic field in the region around a forming protostellar disk. | the velocity gradient technique: a new way to map magnetic fields |
we measured the polarization of background stars toward the ic5146 filamentary cloud system with several instruments: the aryabhatta research institute of observational sciences (aries) imaging polarimeter (aimpol) and triple-range (g', r', i') imager and polarimeter (tripol; at the lulin observatory) provided optical rc- and i'-band polarimetry data, respectively. mimir (at the lowell observatory perkins telescope) measured the h- and k-band polarizations at near-infrared wavelengths. (1 data file). | vizier online data catalog: polarimetry obs. toward ic5146 background stars (wang+, 2017) |
polarization is an under-exploited technique in the investigation of exoplanet atmospheres. a polarization detection, particularly if extended over a broad spectral range, can potentially set valuable constraints on the gas and clouds in an exoplanet atmosphere that is not possible through brightness-only observations. i will present simulations that show that the polarization of a spatially unresolved exoplanet may be detected by cross-correlating high-dispersion linear polarization and brightness spectra of the planet-star system. in this approach, the doppler shift of the planet-reflected starlight facilitates the separation of the signal from other polarization sources, including the star, the interstellar medium and the terrestrial atmosphere. i will elaborate on the case of close-in giant exoplanets with non-uniform cloud coverage, in which cases the hemispheres east and west of the sub-stellar point will produce different polarizations. the simulations show that high-dispersion polarimetry can separate some of the proposed cloud scenarios and, in particular, set additional constraints on the cloud particles optical properties. | mapping exoplanet clouds with high-dispersion spectro-polarimetry |
ccd observations in the vilnius seven-color photometric system of two 13'x13' areas, centered on the nebulae ic59 and ic63, were obtained with the 1.8m vatican advanced technology telescope (vatt) telescope on mt.graham, arizona, using the sta0500a camera and a 4x4k ccd chip. observations in table 1 and 2. to cover all the stars with the available polarization data, another set of ccd exposures with a 35'x35' field of view were obtained with the maksutov-type 35/50cm telescope of the moletai observatory in lithuania, using an apogee alta u-47 ccd camera. observations in table 3. optical imaging (r-band) polarization measurements of nebulae ic59 and ic63 were also extracted from soam+, 2017, j/mnras/465/559. these observations were acquired with the aries imaging polarimeter (aimpol) mounted in the cassegrain focus of the 104 cm optical telescope, india. observations in table 4. (4 data files). | vizier online data catalog: vilnius photometry in ic 59 and ic 63 (soam+, 2021) |
understanding the underlying mechanisms of collisional processes between atoms and molecules is of fundamental importance for a large number of areas of research, including chemical reactivity, ultracold atoms and molecules, and astrophysics of the interstellar medium. in general, molecules are not spherically symmetric objects and as a result most collisional processes involving them strongly depend on the relative alignment of the colliding partners. we have studied experimentally the changes in the alignment of the rotational angular momentum of diatomic molecules during elastic and inelastic collisions. in the experiment we use a system consisting of diatomic lithium molecules colliding with noble gas atoms (helium and argon) in a thermal gas phase sample. the collisions are studied in the first excited a1σu+ state using combination of polarized laser light and fluorescence to selectively excite and detect the molecules in specific rotational sublevels. this work was supported by the national science foundation grant nsf phy 1607432. | study of the effect of collisions on the rotational angular momentum of diatomic molecules with polarized light |
polarization dust emission, from non-spherical grains aligned with magnetic field lines, is a key tracer in the study of interstellar magnetic fields. however, interpreting polarization is a nontrivial task. polarization angles only provide a 2d picture of the 3d interstellar magnetic field structure, and the polarization fraction depends on several factors that are difficult to disentangle. one way of breaking these degeneracies is to study polarized emission at multiple wavelengths. i show the results of a pilot study of star-forming region n2071 that combines 850 $\mu$m polarimetry from the bistro jcmt large project with 154 $\mu$m and 214 $\mu$m polarimetry from the hawc+ instrument on sofia. we observe a variation of polarization angle with wavelength which is likely a result of a change in magnetic field orientation on the line of sight, although a change in the alignment regime could be an alternative explanation. furthermore, the ratio of polarizations at 154 $\mu$m and 214 $\mu$m could not be reproduced using single dust models, which suggests the need for heterogeneous cloud models. | studying dust properties, grain alignment and magnetic field structure with multi-wavelength submillimeter polarization |
we observed 29 disks between november 27 and july 7, 2020, using vlt/sphere in the star-hopping mode in ksband with the infra-red dual-band imager and spectrograph (irdis). the data were obtained through six programs: 0103.c-0470, 105.209e, 105.20hv, 106.21hj, and 108.22ee (pi: m. benisty), and 105.20jb (pi: m. keppler). fits files of disk images in sphere/irdis (ks-band) from the very large telescope. the stars are located at the mathematical centers of the arrays. the units are in counts per pixel for qphi and uphi data. the polarization fraction images are unitless. divide qphi by polarization fraction to obtain total intensity images. (6 data files). | vizier online data catalog: fits images of sphere protoplanetary disks (ren+, 2023) |
the observing strategy and data processing procedure for the full catalog are similar to that of paper i (wenger+ 2019apjs..240...24w). we used the atca c/x-band receiver and compact array broadband backend (cabb) to simultaneously observe 4-8ghz radio continuum emission and 20 hydrogen radio recombination line (rrl) transitions in two orthogonal linear polarizations (note that paper i incorrectly states that circular polarizations were observed). our observations took place between 2015 june and 2019 january with a total of 900hr of telescope time split equally between the h75 and h168 antenna configurations. we observed each field for a total of ~30 to ~90min in ~5 to ~10 minute snapshots spread over ~9 hours in hour angle. see section 3. (7 data files). | vizier online data catalog: southern hii region discovery survey. ii. full cat (wenger+, 2021) |
eta carinae, the brightest, massive binary in our galaxy, ejected prodigious amounts of material in two major eruptions in the 19th century. highly polarized starlight scatters off of the 10"x20" bipolar homunculus. extinction is very grey from the uv to deep red, indicating dust in the form of large grains. composition of the dust is likely very different from interstellar dust and dust formed in less massive stars. carbon and oxygen are greatly depleted relative to nitrogen, which is thought due to the ejecting star having an initial mass exceeding 60 solar masses. spectral emissions and absorptions of strontium, scandium, vanadium (never seen in the ism) and many other metals are seen in abundance with the ejecta. a census of identified molecules is very different from that of stars rich in carbon or oxygen. since the 1940s, eta carinae has been gradually brightening, but recent evidence suggests that the visible brightness of the homunculus is nearly constant. spectra of the scattered light show variations of balmer alpha relative to continuum across the nebula. very bright emission clumps (the weigelt blobs) located within 0.1 to 0.3" of eta carinae have far less extinction, but are fading relative to the star. an explanation is that the clumped gas and dust, located close to the luminous binary, obscures starlight in many directions, including our own, but is gradually dissipating. much can be learned about this complex system as eta carinae has a 5.52-year very eccentric orbit that leads to turning off the fuv radiation for several months across periastron, which next occurs in february, 2020. we encourage thoughts and comments on the character of the dust, how it formed in gas already depleted of oxygen and carbon. we solicit observations and modeling of this fascinating, evolving system. | what and where is the dust surrounding eta carinae? |
we present near-infrared polarimetric results for the n159/n160 star-forming complex in the large magellanic cloud with sirpol, the polarimeter of the infrared survey facility. we separated foreground sources using their visual extinction derived from near-infrared photometric data. the 45 young stellar candidates and 2 high-excitation blobs were matched with our sources, and 12 of them showed high polarization that did not originate from the interstellar dust. we made a polarimetric catalog of 252, 277, and 89 sources at the j, h, and ksbands, respectively. based on the ratios of the polarization degree between these bands, we verify that the origin of these polarized sources is the dichroic extinction from the interstellar dust aligned by the magnetic field and that the ratios follow a power-law dependence of {p}λ∼ {λ }-0.9. the linear polarization vectors projected onto the hα image of the complex turned out to follow the local magnetic field structure. the vector map overlaid on dust and gas emissions shows the close correlation between the magnetic field structure and surrounding interstellar medium. we suggest that the derived magnetic field structure supports the sequential formation scenario of the complex. | near-infrared polarimetric study of the n159/n160 star-forming complex in the large magellanic cloud |
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