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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 galactic magnetic field. within this data lie clues to the statistical properties of its turbulent component, in particular its spectral index across spatial scales. to extract these properties, a thorough understanding of how they translate into those of the polarized emission maps is necessary. we address this problem using a model of the turbulent and magnetized interstellar medium based on fractional brownian motion fields. i will present simulated maps of polarized dust emission (stokes q and u) and show how various statistical observables depend on the model parameters. within the framework of this model, i will show that the polarization angle dispersion function $\delta \psi$ is unambiguously linked to the magnetic field spectral index, independently of the dust statistical distribution. | statistical properties of polarized dust emission : lessons from a model of the turbulent and magnetized interstellar medium |
we performed polarimetric observations of our sample during 2016, 2017, and 2018 with the robopol polarimeter, which is mounted on the 1.3m ritchey-chretien telescope at the skinakas observatory in crete, greece. the instrument is an imaging polarimeter, which uses two half-wave plates and two wollaston prisms to simultaneously measure the relative stokes parameters q=q/i and u=u/i (i is the total intensity and q, u are the absolute stokes parameters). observations were conducted during 13 nights from 2016 may to july, during five nights in 2017 july, and during six nights in 2018 august. the observing time for science targets was about 66hr in total. (1 data file). | vizier online data catalog: r-band linear polarization of gaia stars (panopoulou+, 2019) |
polarisation properties of radio signals provide valuable information about the source, its surrounding region, and the interstellar medium. radio sources are often polarised, but the measurement is not a straightforward as it may seem. instrumental effects distort the observed signal – the feed, telescope structure, dish surface, coaxial cables, optical fibers, and electronics can introduce gain and phase differences between the two orthogonal feed probes in the receiver waveguide. for altazimuth mounted radio telescopes, the dish and receiver instruments rotate with respect to the source as the telescope tracks the sky position, thus modifying the polarisation of the received signal. the stokes vector, comprising four parameters describes the polarised radio signal, and the muller matrix represent the instrument adjustment to the source stokes parameters. we will describe the measurement, analysis processes and outcome of determining c-band mueller matrices for the green bank telescope (gbt). mueller matrices have been calculated previously for the gbt but, each time changes are made to the equipment, new calibrations are required. gbt were eager to recreate the processes and analysis code required to determine the mueller matrices and make the matrix values available to enable further polarisation measurements. | point source c-band mueller matrices for the green bank telescope |
the study of polarization from the interstellar medium can provide insights into the properties of magnetic fields and other environmental characteristics of observed regions. we have used optical polarization of the dust in starless cloud l 183, and in the circumstellar envelope (cse) of the asymptotic giant branch (abg) star irc+10 216, to probe their magnetic fields and dust characteristics. our spectropolarimetric results for l 183 allow us to leverage existing optical, near- and far-infrared photo-polarimetric data to produce a more complete picture of the relationship between polarization fraction and visual extinction. these results allow us to accurately locate the break point in the fractional polarization versus extinction in the dense cores of dust clouds, likely indicating the loss of grain alignment (in so called "polarization holes"). our optical polarization in sightlines through the cse of irc+10 216 demonstrates the presence of polarizing dust to large distances in the cse and supports a purely radiatively driven grain alignment mechanism. in agreement with far infrared polarimetry from sofia/hawc+ and theoretical expectations, the grains are aligned with their long axis along the radial direction from the central star and show an alignment efficiency a factor of ~4-5 less than in the interstellar medium. | spectro-polarimetry of grain alignment |
measuring precisely the faint polarization of the far-infrared and sub-millimetre sky is one of the next observational challenges of modern astronomy and cmb cosmology. i will describe the concept and science goals of the pilot balloon-borne instrument, dedicated to measuring the linear polarization of the faint interstellar diffuse dust emission in the far-infrared in our galaxy and nearby galaxies. i will present the in-flight performance of the experiment, as measured during the two successful flights of pilot from timmins, canada in september 2015 and from alice springs, australia in april 2017. finally, i will show the first polarization maps obtained and discuss preliminary results and future objectives. | in-flight performance of the pilot balloon-borne experiment |
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.i will review our most recent searches for snrs in the magellanic clouds, m33, m31, ngc 300, ngc 45, ngc 6744 and ngc 7793. new high resolution (~1``) and sensitive (< 0.3 mjy beam-1) radio (askap, atca & mwa), x-ray (xmm & chandra), ir (herschel and spitzer) and optical (wifes) images of these galaxies have preliminarily revealed thousands of sources from which we found a total of over 300 extended sources that are snrs or candidates. we investigate their intrinsic and overall properties and found some remarkable and unexpected differences. i will also present our breakthrough studies of first extragalactic snrs expansion as well as our first detection of circular polarisation in extragalactic snr. you will have a chance to see the most complete sigma-d study of all known snrs and how they interact with nearby molecular clouds. i will present the case for dd vs. sd in type ia for some 15 lmc snrs based on our x-ray and radio observations. finally, i will present our strategies for the next 10 years on how to observe snrs with the next generation of instruments -- from askap/mwa2 to cta via erosita and whoever else. | observational facts of extragalactic snrs |
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. | why are carbonaceous grains unaligned in the ism? - hawc+ polarimetry of irc+10216 |
the current paper makes use of data taken using sirpol, mounted on the infrared survey facility 1.4m telescope at the south african astronomical observatory, during the nights of 2013 july 7-9. the instrument performance, observational information, weather conditions, and data reduction process were previously described in paper i (chen+, 2016apj...822..114c). the average full width at half maximum (fwhm) of point sources in the j-, h-, and ks-bands is 2.0", 1.9", and 1.8", respectively. (1 data file). | vizier online data catalog: jhk polarimetry of stars behind bubble n4 (chen+, 2017) |
interstellar polarization is caused by elongated grains, aligned with the magnetic field, and can provide invaluable tools for probing magnetic fields, dust grains, and their environment, if the alignment physics can be fully understood. radiative alignment torque (rat) theory has now been refined to a predictive theory, and tested in several experiments. rat predicts that the alignment should cease in star-less clouds when the light has been reddened to wavelengths longer than the grain diameters. combining optical/nir (av < 15 mag.) and sub-mm wave data (av > 20 mag.) appears to support this theory. however, these techniques do not probe the same material, leading to uncertainty in the results. we present our work on rectifying this inconsistency by mapping the star-less cloud l183 over an area where densely sampled h-band polarimetry exists. | grain alignment and polarization hole in a starless core l183 |
the data cube of hi emission (spectral resolution of 0.2km/s) is retrieved from koch+ (2018mnras.479.2505k). this data cube is a combination of new interferometric observations from the karl g. jansky very large array (project id 14b-088) and archival single dish observations from the robert c. byrd green bank telescope (2002 october). as part of the m33 co large program (gratier+ 2010, j/a+a/522/a3; druard+ 2014a&a...567a.118d), the co(2-1) line has been observed over the whole disk of m33 down to a noise level of 20mk per channel. the on-the-fly mapping technique was done with the heterodyne receiver array (hera) multibeam dual-polarization receiver on the institut radioastronomie millimetrique (iram) 30m telescope on pico veleta, spain. we adopt a line ratio co(2-1)/co(1-0) of 0.7. the data have a spatial resolution of 12" and a spectral resolution of 2.6km/s. (3 data files). | vizier online data catalog: hi and co observations of m33 interstellar medium (utomo+, 2019) |
the tables 1, 2, 3, 6 are described in the source paper. the master table table1.dat contains the polarization and reddening data for 5910 stars, i.e. not only for 3871 stars used in the study but also for some stars with lower precision of the polarization data. the table1.dat can be used in further investigations. all the e(b-v) estimates are interpolated from the 3d reddening maps and models by use of the distances from bailer-jones+, 2018 (2018aj....156...58b, cat. i/347). (4 data files). | vizier online data catalog: local bubble & gould belt polarization (gontcharov+, 2019) |
the faraday depth cube of the ic342 field in polarized intensity, produced from lofar hba observations as part of lofar proposal lc0_043. the cube is approximately 5x5 degrees in size, with 4-arcmin resolution, and covers faraday depths from -25 to +25rad/m2. the detailed specifications are given in the table and in the fits header. selected frames from this cubes are shown in the paper in figures 2 through 5. an extended description of the data processing leading to this cube is included in the paper. (2 data files). | vizier online data catalog: faraday tomography of foreground towards ic342 (van eck+, 2017) |
we selected 27 radio continuum sources from the nvss survey (condon et al. 1998aj....115.1693c, cat. viii/65), located over an area of roughly 500 deg2 centered on perseus with flux densities at 1.4 ghz greater than 0.8 jy. the observations were conducted with the arecibo telescope. using the l-wide receiver, we simultaneously recorded spectra centered at 1420 mhz and the two oh main lines (1665 and 1667 mhz), achieving a velocity resolution of 0.16 km/s. we sampled simultaneously two linearly polarized channels performing both auto- and cross-correlations with the arecibo's three-level "interim" digital correlator. the arecibo telescope has an angular resolution of 3.5' at these frequencies. as shown by heiles & troland (2003, j/apjs/145/329) in their millennium h i survey, arecibo can accurately measure h i absorption lines for strong sources (flux density larger than ~1 jy). (2 data files). | vizier online data catalog: perseus cloud sources gaussian parameters (stanimirovic+, 2014) |
we have observed the cluster ngc1817 by using the aries imaging polarimeter (aimpol) on 2018 january 18, 19, and 22 in four passbands b, v, r, and i. the aimpol is mounted as a backend of the 104cm cassegrain telescope of aryabhatta research institute of observational sciences (aries). the exposure times were in the range of 60-250s in different bands. (2 data files). | vizier online data catalog: polarization of 125 stars in ngc 1817 open cluster (singh+, 2020) |
we present multiple-epoch measurements of the size and surface brightness of the light echoes from supernova (sn) 2014j in the nearby starburst galaxy m82. hubble space telescope (hst) acs/wfc images were taken ∼277 and ∼416 days after b-band maximum in the filters f475w, f606w, and f775w. linear polarimetry of the sn 2014j has also been acquired. the images reveal the temporal evolution of at least two major light-echo components. the first one exhibits a filled ring structure with position-angle-dependent intensity. this radially extended, diffuse echo indicates the presence of an inhomogeneous interstellar dust cloud ranging from ∼100 pc to ∼500 pc in the foreground of the sn. the second echo component appears as an unresolved luminous quarter-circle arc centered on the sn. the wavelength dependence of scattering measured in different dust components suggests that the dust producing the luminous arc favors smaller grain sizes, while that causing the diffuse light echo may have sizes similar to those of the milky way dust. smaller grains can produce an optical depth consistent with that along the supernova-earth line of sight measured by previous studies around maximum light. therefore, it is possible that the dust slab, from which the luminous arc arises, is also responsible for most of the extinction towards sn 2014j. the optical depths produced by the diffuse milky way-like dust in the scattering matters are lower than that produced by the dust slab. apart from the resolved light echoes, the polarization of the sn 2014j point source measured at day 277 shows conspicuous deviations from other epochs and this can be identified as due to at least 10-6 msun of dust located at a distance of ~5×1017 cm away from the sn. the presence of this cs dust may set strong constraints on the progenitor system that led to the explosion of sn 2014j. | interstellar-medium mapping in m82 and circumstellar environment constraints through light echoes around supernova 2014j |
submillimeter polarimetry associated with grain alignment is accepted as one of the major avenues for detection of interstellar magnetic fields. the submm spectropolarimetry, on the other hand, is still unexplored beyond the molecular clouds. fine structure lines are polarized due to ground state alignment (gsa) by optical pumping. the polarization of the submillimeter fine-structure lines induced could be substantial. this method is applicable to all radiative-excitation dominant region, e.g., h ii regions, pdrs. the potential of the new magnetic tracer has been clearly revealed by the first detection of gsa effect on a binary system where 3d magnetic fields are precisely mapped (see my poster). our results demonstrate submillimeter polarimetry as a powerful magnetic tracer and is readily applicable for alma today if polarisation at band 8 is commissioned | tracing magnetic field with polarimetry of submillimeter lines |
the atmosphere of venus is known to contain trace amounts of so, so_{2}, ocs, h_{2}so_{4}, and possibly h_{2}s and elemental sulfur oligomers, s_{n}. modeling studies indicate that many more compounds containing sulfur and both sulfur and chlorine may also be present, given that the known compounds are photolyzed by solar radiation in the upper atmosphere of venus and yield reactive radical species. a large number of exotic compounds containing s, o, h, c, and/or cl of suspected or plausible significance for venus chemistry have been characterized at the rccsd(t)/aug-cc-pvtz level, yielding structures, dipole moments, and dipole polarizabilities. representative compounds and associated chemical reactions will be discussed. both abstraction and addition-elimination reactions have been characterized. | ab initio characterization of sulfur compounds and their chemistry for venus and the interstellar medium |
hildebrand carved out a distinguished career across two disciplines: first in particle physics, and then in astrophysics, where he revolutionized the field of far-infrared astronomy and took the first measurements of the polarized emissions from interstellar dust. | obituary: roger hildebrand (1922-2021) |
the magnetic (b) field is ubiquitous throughout the milky way. several fundamental questions about the b-field in the cool, star-forming interstellar medium (ism) remain unanswered. in this dissertation, near-infrared (nir) polarimetric observations are used to study the large-scale galactic b-field in the cool ism in a spiral arm and to determine the role of b-fields in the formation of infrared dark clouds (irdcs). nir polarimetry of 31 star clusters, located in and around the perseus spiral arm, were obtained to determine the orientation of the plane-of-sky b-field in the outer galaxy, and whether the presence of a spiral arm influenced b-field properties. cluster distances, which provide upper limits to the b-field probed by observations, were estimated by developing a maximum likelihood method to fit theoretical stellar isochrones to stars in cluster color-magnitude diagrams (cmds). using the distance estimates, the cluster locations relative to the perseus arm were found. the cluster polarization percentages and orientations were compared between clusters foreground to the arm and clusters inside or behind the arm. the cluster polarization orientations are predominantly parallel to the galactic plane. clusters inside and behind the arm have larger polarization percentages, likely a result of more polarizing material along the line of sight. the cluster polarization data were also compared to optical, inner galaxy nir, and planck submm polarimetry data, and showed agreement with all three data sets. the polarimetric properties of one irdc, g28.23, were determined using deep nir observations. the polarization orientations relative to the cloud major axis were found to change directions with distance from the cloud axis. the b-field strength was estimated to be 10 to 100microg. despite these large inferred b-field strengths, the b-field was found not to be the dominant force in the formation of the irdc, though the b-field morphology was influenced by the cloud. using nir observations, the b-field of 27 irdcs were studied. the relative polarization orientations with respect to the cloud major axes were found. no preferential relative orientation was found, implying that the b-field did not greatly influence the formation of this sample of irdcs. | magnetic fields in the perseus spiral arm and in infrared dark clouds |
diffuse interstellar bands (dibs) are the puzzling spectral features, originated in interstellar clouds, composed mostly of neutral hydrogen. the same clouds are the birthplaces of extinction and polarization. both these phenomena are believed to be caused by interstellar dust grains, oriented in the second case. despite of these one can observe atomic absorption lines as well as some bands, originating in simple radicals composed of the most abundant elements. dibs are now commonly believed to be carried by some complex molecules, remaining unidentified since nearly 100 years. the paper summarizes the most important observational facts concerning dibs and comments their relations to other interstellar features. | diffuse interstellar bands |
we used the turpol instrument on the 2.5m nordic optical telescope (not) at roque de los muchachos observatory on la palma, during the nights of 2007 november 3-6, to perform broadband multicolor polarimetry of stars background to the taurus molecular cloud. see section 2.2. we performed spectropolarimetric observations of high-extinction lines of sight using the red channel (0.4-1.1um) of the kast spectropolarimeter on the 3m shane telescope of lick observatory during the nights of 2009 november 15-17 (ut). see section 2.3. imaging polarimetric observations in the near-infrared h band (1.63um) took place on the nights of 2011 september 18 and 19 and again on 2012 january 11 using the mimir instrument on the 1.83m perkins telescope, located outside flagstaff, arizona. see section 2.4. (5 data files). | vizier online data catalog: optical and nir polarimetry in taurus (vaillancourt+, 2020) |
for the first time spectropolarimetric observations of wolf-rayet star wr156 (wn8h) were conducted. medium resolution spectropolarimetric data in the range of 3500-7200 åå were obtained at russian 6-m telescope of special astrophysical observatory (sao ras). these data show that the light from the star is significantly polarized, with the degree of polarization p=1.38+/-0.06%, and the position angle θ=77.4°+/-1.2°. this polarization, most probably, has an interstellar origin, as its magnitude and orientation are similar to the ones of field stars. also, we present results of numerical modeling of wr156 atmosphere performed using cmfgen code. according to it, wr156 is the richest hydrogen wolf-rayet star of wn8 type in the galaxy. | spectropolarimetry and modeling of wr156 |
rotation measure (rm) cubes of the 3c196 field in polarized intensity (pi), stokes q and stokes u, synthesized from the low frequency array (lofar) high band antennas (hba) observation taken on 16 dec 2012 (observational id: l80508). the rm cubes cover a faraday depth range from -3rad/m2 to +8rad/m2 in 0.25rad/m2 steps. a resolution in faraday depth is 0.9rad/m2, while the largest faraday structure that can be resolved is 1.1rad/m2. images are 8.3°x8.3° in size with a psf of 3.6-arcminx3.9-arcmin. selected frames of these cubes are presented in the paper in figure 4. a header of the fits files provides more details about the rm cubes using the standard fits header keywords. (2 data files). | vizier online data catalog: lofar-hba 3c196 field rm cubes (jelic+, 2015) |
we present a large-scale combination of near-infrared (near-ir) interstellar polarization data from background starlight, with polarized emission data at sub-millimetric (sub-mm) bands for the vela c molecular cloud. the sub-mm data were obtained by the balloon-borne large aperture submillimeter telescope for polarimetry (blastpol) during the 2012 flight in antartica. the near-ir data consist of more than 6700 detections in the i-band, covering a wide area around the cloud, mostly in the range of visual extinctions between 2 and 16 mag. the main goal was to determine the polarization efficiency ratio reff , defined as p500/(pi/τv), where p500 is the polarization fraction at 500 μm and optical depths τv are estimated from cataloged near-ir photometry. to ensure that the same column density of material is producing both polarization from emission and extinction, we introduce a new method to select stars that are located in the near-background, the gaussian-logistic (gl) technique. the polarization efficiency ratio is critically affected by stellar objects with background contamination from the diffuse galactic material, emphasizing the need for a careful selection. accounting for the statistical and systematic uncertainties from the gl method, we estimate an average reff value of 2.4 ± 0.8, which can be used to test dust grain models designed specifically for molecular clouds. reff appears to be relatively flat as a function of the cloud depth, suggesting that significant grain modification might occur only at higher densities. | comparing submillimeter polarized emission with near-infrared polarization of background stars for the vela c molecular cloud |
interstellar matter in star forming regions appears to form filamentary structures, which were suggested to line up either parallel or perpendicular to the magnetic field. our purpose is to investigate this possible alignment further, based on a combined analysis of herschel and planck data obtained towards a large variety of star forming regions. as a first step, we developed an optimized version of the original rolling hough transform code, particularly well suited to extract and analyse the orientation of filamentary structures over a broad range of densities, from striations to dense filaments. in this paper, we present an overview of our new method, called the rolling radon transform and we describe the preliminary results obtained for a star forming region at high galactic latitude. | methodology for a planck/herschel analysis of the interplay between filaments and magnetic fields in star forming regions |
observations of m101 and ngc 6946 were taken using the german receiver for astronomy at terahertz frequencies (great; and its improved successor upgreat) on board the stratospheric observatory for infrared astronomy (sofia) in cycles 2 and 4. the cycle 2 (pi: herrera-camus; project 02_0098) data used the original great instrument. observations were taken 2014 may 20 and 21, with receivers tuned to 1900.5ghz ([cii]158um) and 1461.1ghz ([nii]205um). we adopt a uniform beam size of 15" for [cii] and 18" for [nii]. the cycle 4 data (pi: bolatto; project 04_0151) comprised 11 total regions, five in m101 and six in ngc 6946, using the dual-polarization upgreat instrument on sofia. the observations of m101 were taken during the upgreat commissioning on 2015 december 9 and 10, and the ngc 6946 observations were taken on 2016 may 12, 18, 19, and 25. see section 2 for further details. (4 data files). | vizier online data catalog: sofia cii and nii obs. of m101 and ngc6946 (tarantino+, 2021) |
recent numerical models of the multiphase ism underline the importance of cosmic rays and magnetic fields for the physics of the ism in disc galaxies. observations of properties of the ism in galactic halos constrain models of the expected exchange of matter between the star-forming disc and the environment (circumgalactic medium, cgm). we present new observational evidence from radio-continuum polarization studies of edge-on galaxies on magnetic field strength and structure as well as cosmic ray electron transport in galactic halos. the findings are discussed in the context of the disk-halo interaction of the interstellar medium. in addition, it is also briefly demonstrated how recent lofar observations of edge-on galaxies further constrain the extent of magnetic fields in galactic halos. | a fresh view of magnetic fields and cosmic ray electrons in halos of spiral galaxies |
blastpol observes the linearly polarized emission from interstellar dust. dust polarization traces magnetic fields, and submillimetre wavelengths can see into the dense molecular clouds in which stars are born. with this measurement, blastpol can help resolve long-standing questions about the role of magnetic fields in the beginning of star formation. blastpol is a 1.8 m telescope with 288 herschel/spire-heritage bolometric detectors at 250 μm, 350 μm, and 500 μm. polarimetric capability was added with photolithographed grids and a stepped half-wave plate. this work outlines the instrument, with a focus on the blastbus electronics system for detector readout, telescope attitude control, and cryogenic housekeeping. in december 2010 and in december 2012, blastpol had two long duration balloon flights. an improved map making procedure has been used for reducing the 2012 dataset to maps of the polarized sky. the overall data analysis procedure is described, along with details of the map maker characterization. finally, maps are presented for the seven targets observed during the 2012 flight. the 14 square degree map of the vela c giant molecular cloud is of particularly high quality and will be used in several upcoming studies of dust physics and star formation. | mapping submillimetre polarization with blastpol |
star formation is a fundamental process in the evolution of the cosmos. yet given the abundance of stellar constituents, it remains prescient as to why the number of stars is not correspondingly large. if we cannot satisfactorily explain how stars are formed, then many further avenues of research are hindered. this thesis makes claims about one of the foremost theories as to the relative lack of stars, interstellar magnetic fields. these fields have been observationally verified on multiple scales. i will use the most direct method to probe magnetic fields in known star-forming regions, polarization, at millimetre/submillimetre wavelengths. in particular i will focus on the effect that magnetic fields have on the emission produced by rotational molecular transitions. much of the background behind the study of magnetic fields, and their deduction through submillimetre polarimetry, will be developed in chapter 1. here i provide an overview of not only the role that magnetic fields may play in star formation, but also the competing theories of turbulence and magnetohydrodynamic waves. the various manifestations of polarization will also be covered, including polarized molecular transitions. chapter 2 will look at one of the most well-studied star-forming regions, orion kl, through observations of a newly discovered water maser transition at 620.701 ghz. interstellar masers allow different environments to be probed , regions where more complex activity has created a population imbalance between rotational energy levels. the remaining two chapters will present methods and data from the four-stokes-parameter spectral-line polarimeter at the caltech submillimeter observatory. i will look at considerations that must be made when a small map is collected by way of quantifying the amount of instrumental polarization. spurious polarization signals may pervade the outer edges of the telescope beam, leading to a misrepresentation of the true amount of source polarization. chapter 3 details the methods involved in removing sidelobes plus the other sources of instrumental polarization, while chapter 4 goes on to present the actual data to which these techniques have been applied. the data itself is of the molecular transition $^{12}$co$(j=2\rightarrow1)$, prominent within the protostellar source omc-2 fir 4. | methods and results toward measuring magnetic fields in star-forming regions |
cooling and trapping of polar molecules have stimulated research in precise monitoring and controlling dynamics in ultracold regime. there has been considerable interest in the study of molecular inelastic collision processes at cold and ultracold temperatures. collisional study of polar interstellar species co, adds an additional astrophysical importance to model interstellar medium. present work focuses on rotational quenching of abundant interstellar species, co with h+ using quantum-mechanical scattering calculation. rate coefficients for molecular rotational transitions of co due to collision with h+ are obtained in the range of 10-5 k to 200 k from cross sections which are computed using close coupling calculations as implemented in molscat. the data generated from ultracold to higher temperatures assist in investigating the chemistry of interstellar clouds. calculations are performed on ground state ab initio potential energy surface using mrci/cc-pvtz method. rotational transitions are studied in the rigid-rotor approximation with co bond length fixed at an equilibrium value of 2.138 a.u. asymptotic potentials are computed using the dipole and quadrupole moments, and the dipole polarizability components. | ultracold rotational quenching study of co with h+ |
using a fourier transform infrared spectrophotometer and a low temperature cryostat, we have obtained the ir spectra of formaldehyde dissolved in liquid krypton between 125 k and 137 k. monomeric formaldehyde in gas phase was prepared by thermal decomposition of para-formaldehyde. peak positions ($\nu$), wavenumber shifts($\delta\nu$), and full widths at half maximum ($\delta\nu_{1/2}$) are reported. influence of the solvent on fundamental vibrational frequencies are studied using the polarizable continuum model (pcm). when used in combination with calculated anharmonic frequencies, the pcm model shows qualitative agreement with frequency shifts in liquid kr. the importance of formaldehyde ir characterization around 100 k will be discussed in reference to its detection in the interstellar medium, the ir detection of the $\nu_1$ vibration in the protostar w33a, and although the cassini infrared spectrometer (cirs) was not able to detect methanol, formaldehyde, and acetonitrile in titan's atmosphere, upper limits on their abundances and formation conditions have been proposed. b. zuckerman et al., observations of interstellar formalde hyde, astrophys. j., 1970, 160: 485-506. e. roueff et al., infrared detection of gas phase formaldehyde towards the high mass protostar w33a, a{\&}a, 2006, 447: 963 -969 c.a. nixon et al., upper limits for undetected trace species in the stratosphere of titan. faraday discuss. 2010, 147: 65-81. b.n. tran et al., titan's atmospheric chemistry: photolysis of gas mixtures containing hydrogen cyanide and carbon monoxide at 185 and 254 nm, icarus, 2008, 193: 224-232 | ir absorption and calculated frequencies of formaldehyde dissolved in liquid kr |
we have performed quantum mechanical calculations of cross-sections and rate coefficients for electron attachment to small, neutral, and positively charged grains. in addition to the polarization potential and - for charged grains - the coulomb potential, we considered the influence of the interaction between the charge of the electron and a possible permanent electric dipole on the grain. we found large discrepancies between the predictions of classical and quantal models of electron scattering on neutral grains at low energies (temperatures) in the absence of a permanent dipole moment, but much closer agreement when a dipole moment was present. the presence of the long-range coulomb potential also leads to better agreement between classical and quantal models. | electron attachment to interstellar grains |
multi-wavelength polarization measurements of stars in ngc 7380, centered on the emission nebula sh2-142 are presented. the polarization is found to be in the direction of the magnetic field of the galaxy for this region with the degree of polarization ranging from 1.8% to 3.3%. the wavelength of maximum polarization ranges from 0.413 μm to 0.661 μm. using the dependence of the ratio of total to selective extinction r = (5.6 ±0.3)λmax an average value of r = 3.05 ± 0.09 results. the wavelength of maximum polarization is also shown to be strongly correlated to e(b - v) color excess. | interstellar extinction in the direction of ngc 7380 (sh2-142) |
what roles do interstellar magnetic fields play in star formation processes? we have studied the b-field of l1544, a dark cloud with a starless dense core showing active gas infall, and located only 140 pc away in taurus, via deep near-infrared (nir) imaging polarimetry with the mimir instrument. we find the b-field orientations in the plane of the sky change significantly at l1544, mimicking its shape and extent. the elongated spine of l1544 is also where the dispersion of nir linear polarization position angles is smallest, suggesting strengthening of the b-field. archival wise, scupol, herschel, and planck data were analyzed to characterize dust extinction and emission across l1544 and the field around it. three-dimensional modeling, constrained through matching two-dimensional integrated model properties to observed dust distributions, led us to develop maps of effective gas mass densities and non-thermal gas velocity dispersions. these were combined with the nir polarimetry, under the chandrasekhar & fermi (1953) approach, to yield a map of b-field strength across the entire 400 sq-arcmin region surveyed. the trends of b-field strength with gas volume density, mass-to-flux ratio with radius, and plane-of-sky b-field strengths with zeeman-traced line-of-sight b-field strengths were found and compared to previous published work to establish the role of b-fields in l1544. we find field strengths in the 3 - 30 ug range, quite similar to the oh zeeman values found by crutcher et al. (2009) for l1544.this work was partially supported by grants to boston university from nsf (ast-0907790, 1412269) and nasa (nnx15ae51g). | the magnetic field of the l1544 starless dark cloud, traced using near-infrared background starlight |
the interstellar medium (ism) is a key part of our universe, affecting star formation, particle acceleration, and galaxy evolution. furthermore, magnetic fields play a critical role in the ism. it is therefore paramount to study magnetic fields and develop theoretical tools to characterize them. turbulence, like magnetic fields, is ubiquitous to the ism. in this thesis i will use our current understanding of turbulent magnetohydrodynamic theory, expand on it, and develop observational tools to measure magnetic fields. velocity centroids are the only observable that give information about the velocity field in the ism using spectroscopic information. in this thesis, i explore some of their properties and how they are affected by the magnetic fields in the ism. based on the properties of the velocity centroid, i introduce a new technique to map the plane of the sky (pos) magnetic field, the "velocity gradient technique" (vgt). i then expand the vgt to cover not only diffuse media but also molecular media. finally, i use the vgt to obtain the 3d structure in position-position-velocity (ppv) of the pos magnetic field in the galaxy and i corroborate the analysis with stellar polarization measurements.for the second part of the work i study the effects of magnetic fields on star formation. in star formation, the torques from the magnetic field can disrupt the proto-stellar disk formation. i find that solely the properties of turbulence can produce the observed proto-stellar disk. i also expand the use of the vgt in the early stages of star formation, providing a second tool in addition to dust polarization.finally i study the turbulent properties and magnetic fields in the small magellanic cloud (smc). i use our current understanding of turbulence and spectroscopy obsrevations to explore on the sources of turbulence. | magnetic fields as a source of anisotropy: mapping magnetic fields |
filamentary structures are ubiquitous in the interstellar medium (ism). this is particularly true in molecular clouds, with most clumps and cores forming inside the densest regions of filaments. both simulations and observations suggest that magnetic fields play a key role in the formation and evolution of filaments and in the process of star formation. in this context, the study of the relative orientations between filaments and magnetic fields has become a go-to method to obtain new insight. here, we use a dedicated method, fildreams, to detect and extract filaments at multiple scales in the 116 fields of the herschel 'galactic cold cores' (gcc) key-project (18 "-36 " resolution), which measures dust emission in star-forming regions located in various galactic environments. we then compare the filament orientations to the orientation of the plane-of-sky magnetic field (b\perp), inferred from planck observations of the dust polarized emission (7 ' resolution). we present the results of our statistical analysis of these relative orientations as functions of filament spatial scale, gas column density (n{h_{2}}) and galactic environment. in most herschel fields, we find that small, low-n{h_{2}} filaments tend to be roughly parallel to the magnetic field, while large, high-n{h_{2}} filaments tend to be roughly perpendicular. although this trend is not systematically observed, it is still prevalent, which confirms the existence of a coupling between magnetic fields at cloud scales and filaments at smaller scales. | statistical analysis of the relative orientations between filaments and magnetic fields in star forming regions |
the star-forming complexes in cygnus extend nearly 30 deg in galactic longitude and 20 deg in latitude, and most probably include star-formation sites located between 600 and 4000 pc. we combine the catalog by heiles (2000) with uvbyβ photometric data from the catalog of paunzen (2015) to collate a sample of o and b-type stars with precise homogeneous distances, color excess and available polarimetry. this allows us to identify star-forming sites at different distances along the line of sight and to investigate their spatial correlation to the interstellar matter. further, we use this sample to study the orientation of the polarization as revealed by the polarized light of the bright early-type stars and analyze the polarization-extinction correlation for this field. since dust grains align in the presence of a magnetic field cause the observed polarization at optical wavelengths, the data contain information about the large-scale component of the galactic magnetic field. in addition, wide-field astrophotography equipment was used to image the cygnus field in hydrogen-alpha, hydrogen-beta and the [oiii] line at 500.7 nm. this allows us to map the overall distribution of ionized material and the interstellar dust and trace large-scale regions where the physical conditions change rapidly due to supernova shock fronts and strong stellar winds. acknowledgments: this work was supported by nsf grant ast- 1516932 and the wisconsin space grant consortium, nasa space grant college and fellowship program, nasa training grant #nnx14ap22h. | study of the cygnus star-forming field |
magnetic regulation is an on-going research topic in star formation. on large scales the interstellar magnetic field can control the accumulation of gaseous material, affecting the rate at which new stars form. on small scales, the field can influence the formation of disks and control the flow of infalling material. dynamical processes, such as bipolar outflows or the presence of a companion, can rapidly change the field morphology close to the protostar, thus complicating observations aimed at constraining the magnetic field. to reduce the number of complicating factors, we observed the isolated bok globule, l483 using near-infrared and far-infrared polarization observations. in this talk, i will present these multi-wavelength magnetic field maps of l483 and discuss the implications of the observed morphology. i will show high-resolution alma observations, revealing that l483 is forming a close (~30 au) binary, and discuss how it may be possible to use the magnetic field morphology as a signpost for binary formation pathways. we will soon be able to test this conjecture with new observations of multiplicity and magnetic morphology for tens of targets. | the twisted magnetic field in the protobinary l483 |
recent observations using the wind and ulysses spacecrafts and the solar occultation for ice experiment (sofie) during the period between 2007 and 2020 indicate a total cosmic dust influx at earth ranging from 22 to 32 tonnes per day. much is still unclear about the formation, evolution, and propagation of this cosmic dust throughout our solar system, as well as the transport and chemical interaction of such particles within our own atmosphere. studying meteoroids, which are particles small and fast enough to ablate in the earth's upper atmosphere producing meteor plasma detectable by meteor radars, offers an opportunity to better understand these processes. while meteor radars provide a powerful tool to detect meteoroids, they are limited to detecting particles that produce a sufficient amount of plasma within the instrument's field-of-view, and thus most of their trajectory remains undetected. in this work, we report a novel methodology, using new polarization measurements as well as two state-of-the art models, to determine the pre-atmosphere dynamical characteristics of the detected particles, before they suffer any significant ablation or deceleration. we present the results for 20 meteor detection case studies, and find that for the majority of particles, at least 80% (typically 95%) of the particle mass has already been lost at the time of detection. in addition, while all particles experienced deceleration by the time of detection, this was typically small (≤4% of their initial velocity). future work will implement this new methodology to automatically determine the initial mass and velocities of individual meteors. this will help provide more precise meteor orbits and characterization of parent source populations, as well as the identification of potential interstellar particles. | a novel methodology to estimate pre-atmospheric dynamical conditions of small meteoroids |
magnetism is one of the most important forces on interstellar gas dynamics, star formation, and galactic evolution. the next decade will transform our understanding of interstellar magnetism if we invest in polarimetry: surveys of polarized dust emission, starlight polarization, and single-dish measurements of zeeman splitting. | magnetic fields and polarization in the diffuse interstellar medium |
because of the extreme brightness of foreground emission relative to the desired signal, experiments seeking the 21 cm hi signal from the epoch of reionization must employ foreground removal or avoidance strategies with high dynamic range. almost all of these techniques rely on the spectral smoothness of the foreground emission, which is dominated by synchrotron emission. the polarized component of such emission can suffer faraday rotation through the interstellar medium of the milky way, thereby inducing frequency structure which can be mistaken for real reionization signal. therefore, it is of great importance for such experiments to eliminate leakage of faraday-rotated, polarized emission into the unpolarized (stokes i) component where the reionization signal lives. we discuss a number of approaches under investigation for mitigating this leakage in the paper and hera experiments, including calibration and careful instrument design. importantly, however, we show that the ionosphere may provide a very strong suppression of the polarized signal, when averaged over the integration times required for eor experiments, by scrambling the phase of polarized sources. moreover, this attenuation comes with very little suppression of the desired unpolarized signal. we consider the implications of this strategy for paper and hera. | eliminating polarized leakage as a systematic for 21 cm epoch of reionization experiments |
the observations of the 175 high-mass star-forming regions were performed in 2016 june, 2020 august and september, and 2021 april with the iram 30m telescope. the eight mixer receiver (emir) with dual polarization and the fourier transform spectrometer backend were used to cover the frequency ranges of 90.6-98.2ghz in the 3mm band, 108.0-115.4ghz and 138.4-146.0ghz in the 2mm band, and 215.6-224.2ghz in the 1.3mm band. (3 data files). | vizier online data catalog: iram 3mm, 2mm & 1.3mm obs. of star-forming regions (zhao+, 2023) |
we present commissioning results for the 0.7-4 ghz ultra-wideband receiver (uwbr) that has been built for the robert c. byrd green bank telescope (gbt). the primary science driver for the new receiver is improving sensitivity to nanohertz-frequency gravitational waves (as well as other areas of fundamental physics and astrophysics) via high-precision timing of millisecond pulsars. the uwbr frequency range is optimized for measuring and mitigating interstellar medium effects that act as a noise source in pulsar timing. uwbr will also enable wide-band studies of fast radio bursts, magnetars, and other fast radio transients, and will be useful for astrochemistry and observations of radio recombination lines, especially in the 3-4 ghz range (where the gbt does not currently operate). we will present measurements of the system noise and sensitivity, polarization characteristics, and continuum stability. we will also show results from early observations of key millisecond pulsars, star forming regions, and distant galaxies. finally, we will discuss plans for early science operations with uwbr. | the green bank telescope 0.7-4 ghz ultra-wideband receiver |
the wave modes and the stability of a magnetized viscous self-gravitating plasma system with maxwellian distribution of ions and radiative effect of electrons, charge gradient force and polarization force is theoretically analysed. the investigation is carried out with a theoretical model dealing with ions, electrons and dust grains to bring forth a dispersion relation defining the characteristics of the plasma by the normal mode analysis method. the dispersion relation is examined to understand the wave modes propagating longitudinally and transversely (along the direction of the magnetic field) with their significance. numerical calculations and graphical interpretations are also included to support the results. applications based on the interstellar clouds can utilize the result from the study. | low frequency waves and instability in magnetized radiative dusty plasma |
the 870um (band 7) alma dust polarization observations of ser-emb 8 were taken on 2015 june 3 and 7 and have ~0.3" angular resolution. (2 data files). | vizier online data catalog: alma obs. of polarized dust emission from ser-emb 8 (hull+, 2017) |
the astronomical searches for ph2cn and ch3ph<sub spectral-line survey of sgr b2(n), conducted from 2002 september to 2013 march at the facilities of the arizona radio observatory (aro), covering the 1, 2, and 3 mm atmospheric windows (68-116, 130-172, and 210-280 ghz: d. t. halfen et al. 2014, in preparation). only data from the 2 and 3 mm bands, obtained at the aro 12 m telescope at kitt peak, arizona, were examined in this study. the receivers used were dual-channel, cooled sis mixers, tuned single-sideband with image rejection typically >=18 db. data were also taken using a new dual-polarization receiver, utilizing alma band 3 (83-116 ghz) sideband-separating (sbs) mixers with typical image rejection >=16 db, achieved within the mixer assembly. (2 data files). | vizier online data catalog: ph2cn/ch3ph2 rotational transition f |
this dissertation details the development of state-of-the-art hybrid atom-ion trapping architecture and technique towards increasing the quantum control of matter and the detection of chemical processes at cold temperatures. experimental work discussed herein is performed primarily using the second-generation of the motion trap, a hybrid atom-ion trap consisting of a co-located magneto-optical trap (mot) and a linear quadrupole trap (lqt), with which 40ca and a variety of atomic and molecular ions (yb+, ba +, bacl+, and others) can be co-trapped and cooled. such a device enables the immersion of laser-cooled, ionic coulomb crystals in diffuse gases of laser-cooled, highly-polarizable neutral atoms, allowing for studies in sympathetic cooling, cold atom-ion chemistry, and nonequilbrium collisional dynamics. in the first of these studies, i discuss our method of sympathetic cooling in which we use a laser-cooled gas of ca atoms to sympathetically cool bacl + ions confined in the lqt. because of the large polarizability of ca, this method is found to be extremely efficient at cooling the notoriously difficult vibrational degree of freedom. this technique opens the door to research with general, ultracold, highly-localized molecular ions in the quantum ground-state which are not able to be produced using the more traditional methods of doppler-cooling or photoassociation. in the study of cold chemistry in the hybrid trap, i characterize a fundamental reaction, known as charge exchange, at the single-particle level in which an electron is transferred from a neutral atom to an atomic ion during an inelastic collision. this low-temperature process is thought to be foundational to the chemistry leading to the formation of stars, planets and interstellar clouds in our universe. herein i discuss how improved experimental architecture has enabled the determination of reaction rate constants for individual electronic states of the reactants. our theoretical study of the collisional processes in hybrid atom-ion traps has led to the discovery of surprising nonequilibrium physics which exists in the hybrid trap environment. herein i outline the collisional dynamics between neutral atoms and atomic ions in the presence of a time-dependent confining potential and describe how these dynamics manifest themselves in the emergence of nonequilbrium phenomena as indicated by bifurcations in steady-state energies of trapped ions. i show how the these dynamics can potentially limit the efficiency and overall viability of using neutral buffer gases to sympathetically cool the translational motion of trapped ions to ultracold temperatures. in addition to these experimental studies, the development of architecture is discussed with focus given to the implementation of a novel time-of-flight mass spectrometer (tof-ms) for use with hybrid atom-ion traps as well as standard lqts. this simple, modular device couples radially with the lqt and enables the straightforward mass analysis of trapped species without complications derived from typical experimental difficulties, engineering constraints, and financial concerns. with this robust device we precisely characterize chemical processes which can take place in these hybrid atom-ion traps. additionally, i describe how this new architecture is used to perform the action spectroscopy of several previously unstudied molecular ions in order to further establish the field of cold molecular ion research and the widespread use of hybrid atom-ion traps. | action spectroscopy of molecular ions and studies of cold collsions in a hybrid atom-ion trap |
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. 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 based on fractional brownian motion (fbm) fields. | polarized thermal dust emission as seen by planck : a comparison with mhd simulations and lessons from a toy model |
bow shocks around massive stars provide important information regarding the motion of the star, the stellar wind properties, and the density of the surrounding interstellar medium. we use a monte carlo radiative transfer code to investigate the polarization created when photons from a central star scatter from electrons or dust grains in a surrounding bow shock. we discuss the behavior of the polarization with respect to viewing angle as a function of parameters such as optical depth and scattering medium in both the resolved and unresolved cases. | polarization signatures of bow shocks in stellar winds |
magnetic fields, while ubiquitous in many astrophysical environments, are challenging to measure observationally. based on the properties of anisotropy of eddies in magnetized turbulence, the velocity gradient technique is a method synergistic to dust polarimetry that is capable of tracing plane-of-the-sky magnetic fields, measuring the magnetization of interstellar media and estimating the fraction of gravitational collapsing gas in molecular clouds using spectral line observations. here, we apply this technique to five low-mass star-forming molecular clouds in the gould belt and compare the results to the magnetic field orientation obtained from polarized dust emission. we find that the estimates of magnetic field orientations and magnetization for both methods are statistically similar. we estimate the fraction of collapsing gas in the selected clouds. by using the velocity gradient technique, we also present the plane-of-the-sky magnetic field orientation and magnetization of the smith cloud, for which dust polarimetry data are unavailable. | surveying magnetic field morphology with velocity gradient techniques in interstellar clouds |
the interstellar detection of the straight-chain (n-propyl cyanide) and branched chain (i propyl cyanide) molecules towards the star-forming region, sgr b2(n2) enables the search for other complex organic molecules (coms). these molecules are precursors of biologically relevant prebiotic molecules. in this light, we consider iso-propyl cyanide and other higher order branched chain molecules to form 3-pyrroline isomeric group. we predict new formation and destruction pathways which could lead to more insight into the formation and destruction schemes of complex organic aliphatic to aromatic molecules in space. quantum chemical calculations such as binding energy, enthalpy of formation, reaction enthalpy, activation barrier, dipole moments, polarizability and other spectroscopic information are presented, which assist to study the chemical evolution and examine the possibility of target molecule. | exploring the possibility of identifying 3-pyrroline in ism: a computational study |
the upcoming square kilometre array (ska) promises incredible advances across many areas of astrophysics: from the epoch of reionisation, galaxy evolution, and cosmology, to nearby galaxies, the milky way and the sun. in particular, the wide variety of observations (spectral, continuum, polarisation, multi-scale, wide-band) enabled by the ska, will allow us to perform new and exciting studies of the interstellar medium (ism) of our own galaxy. these cover the multiphase medium, mass flow in and out the galaxy, magnetic fields, the formation of molecular clouds, tomography, down to the evolution of dust grains and molecular complexity. such studies are well represented in the french ska white book, which demonstrates the broad expertise of the french ism community and therefore the important role that it has to play in the ska project. the aim of this article is to illustrate the prospects offered by the ska for ism studies by summarising the contributions in the galactic astronomy chapter of the french ska white book: http://adsabs.harvard.edu/abs/2017arxiv171206950a. | the galactic interstellar medium in the radio: prospects for the ska |
the far-uv wavelength range provides access to tracers of the interstellar medium (ism) in potentially all phases (neutral/ionized, atomic/molecular, dense/diffuse, hot/warm/cold). the combination of high spatial resolution and sensitivity enabled by the luvoir telescope, together with the high spectral resolution and polarization capabilities enabled by the pollux instrument will open a new era of exquisite details for milky way ism studies (e.g., molecular gas properties, molecule formation pathways, origin and distribution of phases...) and a dramatic improvement of the ism properties in nearby galaxies (e.g., interplay between galaxy evolution and ism properties, metallicity build-up, influence of the environment...). | ism science with pollux |
identification of nucleobases in extraterrestrial carbonaceous chondrites implies their formation in an abiotic condition, and supports their prebiotic role in early earth. physicochemical processes by which these complex molecules are synthesized in icy grains are not well understood. the products of uv photo-irradiation of purine and pyrimidine in h2o, nh3 and ch4 ices have been explored using robust new density functional theory (dft) methods (wb97m–v) along with large correlation consistent basis sets and explicit solvent calculations using a polarized continuum model (pcm), and compared against laboratory experimental results. mechanisms studied include those starting with neutral pyrimidine and purine, and their cationic counterparts, and then reacting with neutrals and radicals generated by radiation. irradiation of astrophysical ice analogues containing h2o, ch3oh, co, and nh3 yields good quantities of hmt and hmt-methanol that are easily detectable in the resulting organic residues. these computational results support the scenario in which prebiotic molecules, such as the nucleobase uracil, and complex organic molecules such as hexamethylenetetramine can be formed under abiotic processes in astrophysically relevant interstellar environments, and on surfaces of icy grains before being delivered to telluric planets. the calculations also constrain the formation of thymine and its role in the origin of life. | biomolecule synthesis via uv-irradiation of their precursors in astrophysical ices: a quantum chemical perspective |
pilot is a balloon borne experiment, which will measure the polarized emission of dust grains, in the interstellar medium, in the sub millimeter range (with two photometric channels centered at 240 and 550 μm). the primary and secondary mirror must be positioned with accuracies better than 0.6 mm and 0.06°. these tolerances include environmental conditions (mainly gravity and thermo-elastic effects), uncertainties on alignments, and uncertainties on the dilatation coefficient. in order to respect these tolerances, we need precise characterization of each optical component. the characterization of the primary mirror and the integrated instrument is performed using a dedicated submillimeter test bench. a brief description of the scientific objectives and instrumental concept is given in the first part. we present, in the second and in the third part, the status of these ground tests, first results and planned tests. | pilot, a balloon borne experiment underground tests |
we measured the polarisation of the eclipsing binary ah cep in 29 nights from november 2019 until february 2020 with wollaston-polarimeters. after removing the interstellar component, we were able to analyse the intrinsic polarisation of the star system. it varies between 0.1 % and 0.9% (v) at angles between 80-100 degrees. we found higher intrinsic polarisation during eclipse phases. polarisation is increasing with smaller wavelenghts. rayleigh scattering of the starlight on an accretion disk would be a plausible explanation. | welchen zusammenhang gibt es bei dem bedeckungsveraenderlichen ah cep zwischen der lichtkurve und der variablen polarisation? |
nonspherical aligned dust grains produce strong linearly-polarized thermal emission at submm and microwave frequencies, with polarized fractions exceeding 20% in some parts of the high-latitude sky. observations of emission, absorption, and scattering by dust, together with our knowledge of the abundances of elements out of which dust grains can be formed, impose many constraints on dust modelers. the dust is in large part composed of amorphous silicates, but with a substantial component of carbonaceous materials, including nanoparticles of polycyclic aromatic hydrocarbons. the smallest particles radiate thermally in the mid-ir following single-photon heating, and also produce rotational emission at microwave frequencies. this rotational emission may account for the so-called anomalous microwave emission. iron contributes about 25% of the total mass of interstellar dust, but what form the fe is in is largely unknown; much of the fe could be in ferromagnetic or ferrimagnetic materials that could emit magnetic dipole radiation at microwave frequencies. i will review the observational constraints on dust models, the current state of our physical models, and prospects for further progress. | models of polarized emission from interstellar dust grains |
the disk of our galaxy is filled with clouds of diffuse matter, modifying spectra of distant stars. these clouds are sources of extinction, polarization and of spectral features such as atomic and molecular lines as well as the diffuse interstellar bands (dibs), still of unknown origin, though likely molecular. apparently physical parameters of individual translucent clouds are various. we try to provide some constraints on theoretical models of translucent interstellar clouds. it is demonstrated that intensities and profile details of dibs can be determined using the espresso spectrograph fed by vlt. this possibility follows its very high resolution and signal-to-noise ratio, necessary to analyze atomic and molecular features, detectable in spectra of ob-stars, and originated in single (thus - likely optically thin) interstellar clouds. our set of five high resolution (λ/δλ =140 000) espresso spectra of hot, reddened stars allows us to analyze profiles of some dibs. it is argued that more high quality spectra from espresso are necessary to identify the dib cariers. | profiles of interstellar spectral features caused by physical parameters of clouds |
simulated cometary ice experiments have indicated that circularly polarised light could be the initial source of life's handedness. we detected chiral sugars, amino acids and their molecular precursors within these interstellar achiral ice analogues. | chiral sugar and amino acid formation in simulated cometary matter inches closer to explaining the emergence of homochiral life |
elongated dust grains in the interstellar medium polarize background starlight, and they align perpendicularly to the ambient magnetic field. by examining the polarization percentage and position angle of background starlight, it is possible to determine characteristics of the intervening dust such as grain size, orientation, and alignment, as well as projected direction of the local magnetic field. the dust in the region surrounding the nearby (150 pc) o9.2iv star ζ ophiuchi is part of a highly irradiated diffuse cloud. previous optical polarimetry of background stars along this sight line has revealed dust grains with a high degree of alignment located coincident with prominent infrared 8 micron striations that are a component of this cloud. the high ratio of polarization to reddening in this cloud may reflect efficient radiative alignment of grains by ζ oph itself. in order to further characterize the dust and magnetic field in this high radiation environment, we present new v band polarimetry of 26 background stars along the sight lines surrounding ζ oph using data from the wyoming infrared observatory 2.3 m telescope. the stars are selected to probe this diffuse cloud, having gaia dr3 distances of 37 to 1200 pc with a median distance of approximately 200 pc. these data will allow us to measure the polarization efficiency as a function of radiation intensity, helping test models of radiative alignment for interstellar dust grains. | optical polarimetry of highly polarizing dust toward ζ ophiuchi |
polarization of dust thermal emissions shows that the dense filaments are extending perpendicular to the interstellar magnetic field. magnetohydrostatic structures of such filaments are studied. the magnetically-supported maximum line mass increases in proportion to the magnetic flux per unit length threading the filament. 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. | magnetohydrostatic structures of magnetically-supported filaments and their stability |
the spectropolarimetric data analyzed in this study were obtained by the university of wisconsin's hpol spectropolarimeter, mounted on the 0.9 m pine bluff observatory (pbo) telescope. data obtained before 1995 were recorded using a dual reticon array detector spanning the wavelength range of 3200-7600 å with a spectral resolution of 25 å (wolff et al. 1996aj....111..856w). beginning in 1995, hpol's detector was upgraded to a 400x1200 pixel ccd camera that provided coverage from 3200 to 6020 å at a resolution of 10 å and 5980-10500 å at a resolution of 7 å (nordsieck & harris 1996, polarimetry of the interstellar medium (asp conf. ser. 97), ed. w. g. roberge & d. c. b. whittet (san francisco, ca: asp), 1000). (3 data files). | vizier online data catalog: spectropolarimetric survey of classical be stars (draper+, 2014) |
interaction of electrons with cumulene carbenes (h2c2, h2c3, h2c4, h2c5, h2c6) and some of the possible outcomes are reported in this article. the prominent scattering channels like elastic, inelastic, ionization, and momentum transfer are examined through respective cross sections for these molecules and their polyacetylene isomers (c2h2, c4h2, c6h2). the quantum collision problem of the e-target system is solved through the optical potential approach. the optimized structures, ionization energies (ip), and polarizabilities of the target molecules are calculated using the density functional theory. these target parameters are found to be in good agreement with those available from the literature. the computations for cross sections were performed in the energy ranging from the ionization threshold of the targets to 5000 ev. to the best of the authors' knowledge, it is the first time that the cross section values of the above-mentioned molecules are reported. we have established a strong correlation between the maximum ionization cross section and ionization energy as well as polarizability, suggesting the consistency of the results reported here. an investigation into the isomeric effect reveals significant differences in the properties and magnitudes of cross sections of cumulene carbenes compared to polyacetylenes. the present findings would be helpful in astrophysical modelling, spectroscopy, and studying interstellar & circumstellar spaces. | electron scattering and ionization of astrophysical molecules |
the sensitivity upgrades of both the nrao very large array (vla) and the nrao very long baseline array (vlba) have begun to provide us with a much improved perspective on stellar centimeter radio emission, particularly concerning young stellar objects (ysos) and ultracool dwarfs. i will mainly present a deep vla and vlba radio survey of the orion nebula cluster (onc), where we have found 556 compact radio sources, a sevenfold increase over previous studies, and intricate detail on the radio emission of proplyds. we can now better disentangle thermal and nonthermal radio emission by assessing spectral indices, polarization, variability, and brightness temperatures (vlba). with simultaneous radio-x-ray time domain information (chandra), this project is providing unprecedented constraints on the magnetospheric activity of ysos across a wide mass range, including the massive trapezium stars and their impact on the interstellar medium. a particular focus of this talk will be the occurrence of radio flares in orion and their correlation with x-ray flares. starting with our ongoing orion observations, i will additionally discuss the use of the vlba for precision stellar astrometry in the gaia era, highlighting how vlbi astrometry is allowing us to extend the gaia sample of ysos and ultracool dwarfs by including embedded objects, distant obscured sources in the galactic plane, and faint ultracool dwarfs, while providing important opportunities for astrometric cross-calibration. | the orion radio all-stars: extreme yso radio and x-ray variability |
evolved cool stars exhibit a massive mass loss, which contributes to the enrichment of the interstellar medium and therefore to the recycling of matter in the universe. the mechanisms (e.g. the stellar magnetic field) behind this mass loss phenomena are not understood, but can be constrained thanks to observations of the star and its circumstellar envelope (cse). here, we focus on the sio maser line emission, which probes the inner region of the envelope (2-4 stellar radii from the photosphere) and can reveal the presence of a magnetic field. with radio-astronomical polarimetric observations, we derive the angle of polarization, the linear and circular polarization, which according to theories can lead to an estimate of the magnetic field strength along the line of sight. the magnetic field strength is hence estimated at between 0.1 and 10 g. a global poloidal field can be excluded. there are still questions about the origin of the magnetic field (solar-type dynamo, turbulent dynamo ...) and its evolution. | a magnetic field study in the envelope of cool evolved stars |
polarization of starlight can indirectly tell us many things about the universe around us. from identifying star nurseries to mapping galactic scale magnetic fields, the properties of polarized light allow astronomers to observe phenomena that would otherwise be very hard to observe. the wavelength dependence of visual-light polarization shows a characteristic dependence parametrized by the serkowski curve, which can be understood in terms of the size distribution of aligned dust grains. in the direction of per ob3, a loose association of super hot, massive stars, the polarization curves seem systematically shifted to short wavelengths than is typical of the interstellar medium. we have mapped the the origin of the polarization in 3d by observing stars at various positions in and around the per ob3. these observations allow us to probe the possible causes of this short wavelength excess, which will lead to a better understanding of how light becomes polarized in the interstellar medium. | probing the radiation field color towards (and beyond) per ob3 (richard spolizino, kristin kulas, b-g andersson, archana soam, ilija medan, andrew helton) |
interstellar dust grains are aligned with their physical and spin axes parallel to the ambient magnetic field. this fact is supported by polarization observations from ultraviolet to millimeter wavelengths. the radiative torque (rt) mechanism, by which the grains become aligned, has recently survived a number of specific observational tests. one such observation is the relation between the alignment efficiency and the angle between the magnetic field and the radiation responsible for the rts. the interaction of light with irregularly shaped grains results in a net torque and spin-up of the grain, while magnetization arising within a spinning grain results in precession of the spin axis about the magnetic field. the combination of these two effects leads to alignment of the grain with the field and predicts a correlation between alignment efficiency and the angle between the radiation- and magnetic- field directions. andersson et al. (2011, a&a, 534, a19) showed that the alignment efficiency, centered on the star hd 97300, varied with angle about the star with a 180-degree period, consistent with theory. while the geometry towards hd 97300 provides a strong test of the rt-vs.-angle prediction, finding such simple geometries for further tests is difficult. here we identify a similar geometry towards the becklin-neugebauer/kleinmann-low (bnkl) object in the orion molecular cloud. using polarized emission at 100, 350, and 850 micron we find a clear periodic signal in polarization vs. azimuth centered on bnkl, again, in agreement with rt theory predictions. additionally, the signal is stronger at shorter wavelengths, as would be expected if the same photons providing the rts are also heating the dust grains.the authors acknowledge support for this work from the national science foundation grant ast 11-09469. | a test of dust grain alignment via far-infrared polarization |
filaments are ubiquitous in the interstellar medium (ism), yet their formation and evolution remains the topic of intense debate. in order to obtain a more comprehensive view of the 3d morphology and evolution of the musca filament, we model the c18o(2-1) emission along the filament crest with several large-scale velocity field structures. this indicates that musca is well described by a 3d curved cylindrical filament with longitudinal mass inflow to the center of the filament unless the filament is a transient structure with a lifetime ≲~0.1 myr. gravitational longitudinal collapse models of filaments appear unable to explain the observed velocity field. to better understand these kinematics, we further analyze a map of the c18o(2-1) velocity field at the location of sofia hawc+ dust polarization observations that trace the magnetic field in the filament. this unveils an organized magnetic field that is oriented roughly perpendicular to the filament crest. although the velocity field is also organized, it progressively changes its orientation by more than 90o when laterally crossing the filament crest and thus appears disconnected from the magnetic field in the filament. this strong lateral change of the velocity field over the filament remains unexplained and might be associated with important longitudinal motion in the filament that can be associated to the large-scale kinematics along the filament. presentation of this work is supported by nsf grant ast 19-08653. | on the 3d curvature and dynamics of the musca filament |
the role of the magnetic field in the formation of the filamentary structures observed in the interstellar medium (ism) is a debated topic. the planck all-sky maps of linearly polarized emission from dust at 353ghz provide the required combination of imaging and statistics to study the correlation between the structures of the galactic magnetic field and of interstellar matter, both in the diffuse ism and in molecular clouds. the data reveal structures, or ridges, in the intensity map with counterparts in the stokes q and/or u maps. we focus on structures at intermediate and high galactic latitudes with column density from 10^20 to 10^22 cm^-2. we measure the magnetic field orientation on the plane of the sky from the polarization data, and present an algorithm to estimate the orientation of the ridges from the dust intensity map. we use analytical models to account for projection effects. comparing polarization angles on and off the structures, we estimate the mean ratio between the strengths of the turbulent and mean components of the magnetic field to be between 0.6 and 1.0, with a preferred value of 0.8. we find that the ridges are preferentially aligned with the magnetic field measured on the structures. this trend becomes more striking for increasing polarization fraction and decreasing column density. we interpret the increase of alignment with polarization fraction as a consequence of projections effects. the decrease of alignment for high column density is not due to a loss of correlation between the structures and the geometry of the magnetic field. in molecular complexes, we observe structures perpendicular to the magnetic field, which cannot be accounted for by projection effects. we discuss our results in the context of models and mhd simulations, which describe the formation of structures in the magnetized ism. | the relative orientation between the magnetic field and structures traced by interstellar dust |
magnetic fields are expected to be a crucial component of interstellar dynamics, but are difficult to measure with accuracy and precision, especially at low gas densities. recently, atomic ground state alignment (gsa) has been proposed as a new technique for probing diffuse gas magnetic fields, and has been reported in circumstellar gas (zhang et al., 2019). theory predicts that the [c ii] 158um line of ionized carbon should show strong gsa-induced interstellar polarization. because the upgreat instrument on sofia has two perpendicular linear feeds, we can use sofia/upgreat [c ii] observations to search for this predicted line polarization. we have used observations of the two reflection nebulae ic 59 and ic 63, illuminated by gamma cas, as our test case. we will describe the experimental set-up and report a preliminary detection of [c ii] gsa polarization in these regions. dedicated, optimized observations to confirm our detection are scheduled for the winter of 2019/2020. | a possible detection of [c ii] ground state alignment polarization |
the observations were carried out with the 22-m mopra radio telescope in november 2007. we used the dual 3-mm monolithic microwave integrated circuit (mmic) receiver connected to the 8-ghz spectrometer, which provided a velocity resolution of ~0.9 km/s at 90 ghz. spectra in two polarizations were observed simultaneously. two frequency ranges in the 3-mm window were covered, ~77-93 ghz and ~105-113 ghz. the beam size of the telescope was 38 arcsec at 90 ghz and 30 arcsec at 115 ghz. (3 data files). | vizier online data catalog: spectral line survey of two loss (armijos-abendano+, 2015) |
systematic enrichments of l-amino acids in meteorites is a strong indication that biological homochirality originated beyond earth. although still unresolved, stellar uv circularly polarized light (cpl) is the leading hypothesis to have caused the symmetry breaking in space. this involves the differential absorption of left- and right-cpl, a phenomenon called circular dichroism, which enables chiral discrimination. here we unveil coherent chiroptical spectra of thin films of isovaline enantiomers, the first step towards asymmetric photolysis experiments using a tunable laser set-up. as analogues to amino acids adsorbed on interstellar dust grains, cpl-helicity dependent enantiomeric excesses of up to 2% were generated in isotropic racemic films of isovaline. the low efficiency of chirality transfer from broadband cpl to isovaline could explain why its enantiomeric excess is not detected in the most pristine chondrites. notwithstanding, small, yet consistent l-biases induced by stellar cpl would have been crucial for its amplification during aqueous alteration of meteorite parent bodies. | uncovering the chiral bias of meteoritic isovaline through asymmetric photochemistry |
continuum observations of {rho} oph-a at 850um were made by inserting pol-2 into the optical path of scuba-2 on the james clerk maxwell telescope (jcmt) between 2016 april 15 and 2016 april 24. the region was observed in 20 sets of 41 minutes observations. continuum polarimetric observations were simultaneously taken at 450um with a resolution of 9.6". in this paper, we discuss the 850um data only. (1 data file). | vizier online data catalog: first-look analysis of {rho} oph-a at 850um (kwon+, 2018) |
through full-sky observations of the polarized intensity of galactic dust emission, the planck satellite has furnished important new constraints on the composition, size, and shape of interstellar grains. we present new models of interstellar dust consisting of silicate and carbonaceous components of spheroidal shape that are consistent with available data on interstellar abundances, polarized and total extinction, and polarized and total emission in the diffuse interstellar medium. possible contributions from ferromagnetic iron are also considered, including the polarization signatures of this component. we discuss updates to the draine and li 2007 optical properties of these components on the basis of new data, and present models that successfully reproduce the observed relatively flat nir extinction curve. finally, we discuss the prospects of extending our models to probe physical variations in the grain population in various galactic environments, such as regions of high extinction, and in extragalactic sources, such as the magellanic clouds. | a unified model of polarized extinction and emission from interstellar dust |
we live in a magnetic universe with magnetic fields spanning an enormous range of spatial and temporal scales. in particular, magnetic fields at the scale of a galaxy are known as galactic magnetic fields and are the focus of this phd thesis. these galactic magnetic fields are very important since they affect the dynamics of the interstellar gas as well as the gas distribution. the presence of these magnetic fields induces a certain type of radiation to occur at radio frequencies known as synchrotron radiation. the observed polarization properties of this synchrotron radiation then serves to record the imprint of these magnetic fields. the goal of this thesis has been to infer the structure of the magnetic field across various spatial scales in our own galaxy as well as the strength and structure of the magnetic field in other galaxies using radiopolarimetric observations. | reconstructing magnetic fields of spiral galaxies from radiopolarimetric observations |
the infrared spectra of formaldehyde (h2co) dissolved in liquid krypton between 125 k and 137 k have been obtained using a fourier transform infrared spectrophotometer and a low temperature cryostat. backing pressures higher than 1.5 atm were necessary to liquefy kr above 120 k. monomeric formaldehyde in gas phase was prepared by thermal decomposition of para-formaldehyde. peak positions (ν), wavenumber shifts between the gas and liquid solution spectra (δν), and full widths at half maximum (fwhm) are reported. the h2co vibrational frequencies in liquid kr are slightly lower than the gas phase frequencies at room temperature because of the inertness of the solvent. the gaussian 16 software package is used to determine the geometry and lowest energy of h2co at room temperature and at the temperature of the experiment. fundamental harmonic and anharmonic vibrational frequencies and relative intensities are calculated. the influence of the solvent on fundamental vibrational frequencies is studied using the polarizable continuum model (pcm). when used in conjunction with calculated anharmonic frequencies, the pcm model shows qualitative agreement with experimental frequency shifts and relative intensities in liquid kr. the presence of h2co in space is discussed in reference to the ν1 and ν5 absorption bands observed in comets, the ν1 and ν2 absorptions in interstellar clouds, and the lack of detection of the ν4 and ν6 bands of h2co in the atmosphere of titan. the carbonyl stretching mode ν2 is suggested as a possible candidate for confirmation and identification of h2co in space due to its larger strength in comparison to the other modes that have been studied at low temperatures and its characteristic frequency that is completely removed from co2, co, h2o and ch3oh vibrational modes. | infrared bands of formaldehyde dissolved in liquid krypton at cryogenic temperatures and the vibrational modes ν1, ν2, and ν5 of h2co in comets and interstellar clouds |
from the molecular point of view, life is asymmetric. proteins are made up of amino acids with l-configuration whereas dna and rna are composed of ribose and 2-deoxyribose with d-configuration. we believe that the origin of this symmetry breaking can be key to understanding the origin of life. based on in-situ observations and laboratory studies, this handedness is supposed to occur when chiral biomolecules are synthesized asymmetrically through interaction with circularly polarized light (cpl) in interstellar space. in this regard, the enantioselective analysis of chiral biomolecules and their precursors in authentic and simulated extraterrestrial matter is a crucial step to decipher the events that led to biological homochirality. in recent years, significant progress has been made to develop high-performance analytical protocols for the enantioseparation of chiral amino acids, monocarboxylic acids, amines, as well as aldehydes and ketones. the recent detection of sugar molecules in interstellar analogue ices suggests that the molecular building blocks of the genetic material are abundant in interstellar environments and potentially present in comets and small bodies, such as asteroids and interstellar dust particles. however, the chiral resolution of sugar compounds is very challenging and will be discussed here. | multidimensional gas chromatography applied to the enantioselective analysis of sugar compounds in extraterrestrial samples (screen 4) |
extinction. from 0.55 to 2.2μm, we employ the extinction curve of schlafly+, 2016apj...821...78s assuming ah/ak=1.55. from 2.2 to 37μm, we adopt the mir extinction curve derived by hensley & draine, 2020, j/apj/895/38 on the sight line toward cyg ob2-12. polarized extinction. between 0.12 and 4μm, we join a serkowski law with parameters k=0.87 and λmax=0.55μm smoothly to a power law with index β=1.6 in the ir. emission. in the mir, we adopt the akari and spitzer spectrum of a sample of pah-bright galaxies (lai+, 2020apj...905...55l) between 3 and 12μm and the spitzer irs observations of the translucent cloud dcld 300.2-16.9 between 6 and 38μm.in the fir, we adopt the hi-correlated dust emission measured in the dirbe and planck bands with ν>=353ghz, and the 353ghz-correlated emission measured in the lower frequency planck and wmap bands by planck collaboration int. xxii (2015a&a...576a.107p). polarized emission. we adopt the frequency dependence of the polarized infrared emission determined by planck collaboration xi (2020a&a...641a..11p) scaled to match the relation between polarized extinction and emission derived by planck collaboration xii (2020a&a...641a..12p). (4 data files). | vizier online data catalog: total/polarized extinction/emission postplanck era (hensley+, 2021) |
the massive and rich globular cluster terzan 5 contains at least 37 millisecond pulsars -- the most of any globular cluster. we have been timing these pulsars in the radio since 2004 using the green bank telescope, and the individual and combined properties have provided a wealth of science. we have measured long-term accelerations and "jerks" of almost all of the pulsars, allowing a unique probe of the physical parameters of the cluster, completely independent from optical/ir measurements. we have directly measured the absolute proper motion of cluster and see evidence for internal velocity dispersion. numerous post-keplerian (i.e. relativistic) orbital parameters are significant, allowing measurements or constraints on the neutron star masses for nine systems. ensemble flux density, dispersion measure, and polarization measurements constrain the pulsar luminosity function and the interstellar medium. finally, we observe many interesting properties of and long-term variabilty from several eclipsing systems. | three dozen pulsars over a dozen+ years in terzan 5 |
introductiononly two interstellar objects have been observed passing through our solar system to date. the first one, 1i/'oumuamua, discovered in 2017 in its post-perihelion phase, showed mostly asteroidal characteristics with some potential evidence of comet-like behaviour, but 2i/borisov has showed clear evidence of comet activity since its discovery in 2019, prior to its perihelion passage in december of that year. this made it the first confirmed interstellar comet, so naturally many different observations were conducted by astronomers around the world to learn more about the peculiar object.methodologyin this work we present the analysis of polarimetric observations of the interstellar comet 2i/borisov conducted with the fors2 instrument located on the european southern observatory's very large telescope unit 1 (antu). a series of polarimetric observations was performed between december 2019 and march 2020 using three different broadband filters in the visible regime in order to ascertain the physical characteristics of the coma dust particles.results & conclusionswe find that polarisation of 2i/borisov is higher than is usually measured for solar system comets. this distinguishes the interstellar comet from all dynamically evolved comets in our solar system. this evidence of 2i/borisov being more pristine than the observed solar system comets is corroborated by the fact that the comet with the closest polarimetric properties is c/1995 o1 (hale-bopp), which is believed to have approached the sun only once before its apparition in 1997. furthermore, and unlike both hale-bopp and many other comets, interstellar comet 2i/borisov shows a polarimetrically homogeneous coma, unchanging with cometocentric distance, again suggesting it is even more pristine than the observed comets from our own solar system. it is thus likely that it has never passed very close to its native star. | unusual polarimetric properties for interstellar comet 2i/borisov |
"bespoke" refers to something custom or self-made. this paper continues the journey of an amateur learning spectropolarimtetry using an 18inch f3.5 reflector with homebuilt spectrometer modified to perform polarimetry, thus yielding the wavelength dependence of stellar polarization. polarization of starlight occurs as the light passes through polarizing material in space near to the star or through a more distant, larger interstellar cloud. polarization may occur by several different mechanisms, and may give insight into the presence of stellar winds or magnetic fields and into the polarizing material itself. many stars show very substantial time variations in both polarization and direction. in the case of spectral class b (hot) stars that show emission (rather than absorption) at the ha line, the change of polarization with wavelength may give insight into where the emitting region is. i will show results from some 200 measurements on about 95 stars ranging down to mag 5. this is a new, challenging, and potentially fruitful endeavor for amateurs and for possible pro-am projects. | a bespoke spectropolarimetrist |
high resolution polarization observations of spiral galaxies in far-infrared are enabling for the first time to study galactic magnetic fields deep into the cold dark molecular disks, where the most complex gas kinematics and star formation take place. taking advantage of hawc+, the far-infrared polarization imaging instrument installed in the stratospheric observatory for infrared astronomy (sofia), we study the polarized thermal emission of magnetically aligned dust grains at 155um of the grand design spiral galaxy m51. we compare quantitatively the magnetic spiral structure obtained from the dust polarization maps of m51 with the archival radio observations of the 3 cm and 6 cm synchrotron emission of the diffuse interstellar medium of m51. we found that the spiral magnetic field is wrapped tighter at shorter wavelengths, showing significantly lower values for the magnetic pitch angle in far-infrared than in radio observations. in addition, the spiral arm closer to the the companion galaxy shows a significant distortion in the far-infrared magnetic pitch angle profile which is not observable in the radio polarization maps. moreover, we find a strong negative correlation of the far-infrared polarization fraction with the intensity, pointing to an effect of turbulence in the magnetic fields on higher-density environments. these two parameters clearly separate the galactic core, arms, and the interarm regions of the galactic disk. these regions show also different magnetic pitch angles, suggesting that small-scale turbulent fields are dynamically different in each region. our analysis of the m51 galactic system reveal a previously unknown and very complex scenario: radio observations do not trace the same magnetic field than far-infrared polarization observations, being related to different depths in the galactic disk. this lack of homogeneity with environment density is confirmed by the polarization fraction maps, revealing a limiting effect of magnetic turbulence on the densest regions. multi-wavelength polarization observations are the key to disentangle the interlocked relation between star formation, magnetic fields and gas kinematics in the different phases of the interstellar medium. | the multi-phase spiral magnetic field of m51 |
the laser communication system with polarized beam splitting is a useful method for interstellar networking. in longdistance communication terminals which adopts a system of common aperture same frequency transmitting-receiving, the stray light comes from the inside system is generated by retroreflectance and scattering, which will cause interference to the reception of signal light. the ability of internal stray light suppression is the main factor restricting the output power of the system signal and the distance of communication chain-establishment. the optical antenna as the key component of the common channel, coaxial optical antennas are replaced by off-axis optical antennas to reduce paraxial stray light. this work designed miniaturized off-axis optical antenna with a large field of view, and combined the yni factor to analyze the factors affecting the internal stray light. the proportion of stray light generated on each surface was determined through surface modeling and simulation in tracepro, and the optical antenna was actually tested by constructing optical path. the test result 71db is close to the simulation result73db. it indicates that the off-axis angle and yni factor can be used to characterize the isolation indicator of optical antenna. we believe this work is of great significance for guiding the rapid design and indicator analysis of the system, meanwhile provides reference for other systems of stray light suppression. | stray light suppression of common aperture optical antenna for laser communication system |
dust continuum polarization observations have been conducted using the pol-2 polarimeter installed on the scuba-2 camera (hereafter scubapol2) at the james clerk maxwell telescope (jcmt), a 15m single-dish submillimeter observatory located on the summit of maunakea in hawaii, usa. pol-2 observations of the s201 region (project code: m17bp041; pi: eswaraiah chakali) were carried out on 2017 november 18 using the pol-2 daisy mapping mode. three sets of observations were acquired under jcmt band 1 weather conditions, during which the atmospheric optical depth at 225ghz, {tau}225, was 0.03. each set was observed for 30 minutes, resulting in a total integration time of ~1.5hr. (1 data file). | vizier online data catalog: polarization measurements of s201 with jcmt (eswaraiah+, 2020) |
the spectral energy distribution of the coronal gas for two angularly large face-on spiral galaxies observed with xmm-newton observations, namely ngc 6946 and m83, are compared in detail with measurements of the regular and random magnetic field components as deduced from radio continuum data obtained with the vla in all stokes parameters. the large extent of these grand design-spiral galaxies allows us to separate the spiral arm and inter-arm regions and to compare the magnetic field strengths and energies derived from the total and polarized radio emission with the parameters of hot component of the interstellar medium in these areas. the available x-ray data are best described by two thermal components in the halo. we find slightly higher average temperatures of the hot gas above the interarm regions which are also characterized by "magnetic spiral arms". the observed differences in the energy budget between the spiral arms and the interarm regions are discussed in the context of gas heating by magnetic reconnection. | heating of coronal gas in galaxies by magnetic reconnection |
we review five recent publications that extend magnetic turbulence studies that were pioneered using data from 1 au to now include voyager observations from 1977 through 1990 and 1 to 45 au. we examine the spectral scale at which evidence of dissipation sets in and evaluate the spectral indices, anisotropies, polarizations, and spectral transfer of energy. we compare the latter to predictions from transport theory and the rate of energy injection through wave excitation by newborn interstellar pickup ions. while many of our results agree with conclusions from 1 au, we find that the magnetic spectral anisotropy that relates to the underlying anisotropy of the wave vectors exceeds theoretical predications for reasons we are unable to determine. we also establish that wave energy excitation by newborn interstellar pickup h+ forms the dominant energy source driving the turbulence beyond 10 au. | solar wind turbulence from 1 to 45 au |
we present 0.4 arcsec-resolution mid-ir imaging polarimetry, obtained with canaricam at gtc, of the central 0.11 pc x 0.28 pc (4.2 arcsec x 10.8 arcsec) region of w51 irs2. the observed mid-ir polarization across this region is typically several percent, with values as high as 12%. the polarization arises from ensembles of non-spherical silicate particles aligned by the interstellar magnetic field (b-field). applying aitken's method, we decompose the polarization of each sight line into emission and absorption components, from which we infer the morphologies of the corresponding projected b-fields that thread the emitting and foreground-absorbing regions. we conclude that the projected b-field in the foreground material is part of the larger-scale ambient field. the morphology of the projected b-field in the mid-ir emitting region spanning the cometary h ii region w51 irs2w is similar to that in the absorbing region. elsewhere, the two b-fields differ significantly with no clear relationship between them. the morphology of the b-field in w51 irs2w implies that it may be an integral part of a champagne outflow of gas originating in the cometary core and merging with one or more of the previously observed large-scale outflows, in qualitative agreement with mhd simulations by gendelev & krumholz (2012). in those models, outflowing gas powered by an ob star is funneled along a preexisting ambient b-field while also perturbing that b-field locally. this research is supported by nsf grant ast-1908625 to c. telesco. | gtc/canaricam mid-ir polarimetry of magnetic fields in star-forming region w51 irs2 |
the original appearance of chiral organic molecules in our universe is an essential component of the asymmetric evolution of life on earth. simulated interstellar ice experiments have indicated that circularly polarised light could be the initial source of life's handedness following prebiotic astrochemical condensation of primordial gases (meinert et al. 2011). with advanced analytical techniques, chiral sugar molecules (meinert et al. 2016, nuevo et al. 2018), amino acids (munoz caro et al. 2002, meinert et al. 2012) and/or their molecular precursors produced within these interstellar analogue ices have been detected and are likely to be abundant in interstellar media. these molecular species are considered key prebiotic intermediates in the first steps towards the formation of biomolecular homochirality. the study of interstellar ices (h2o, co, co2, ch3oh, nh3, ch4, etc.) – widely observed in the mid-infrared range around protostellar objects (öberg et al. (2011)), from which planets, but also debris such as comets and asteroids form – provides key information about the pristine materials present in the early solar system and clues for how solar system dynamics/processing could have redistributed and amplified any initial chiral bias among various solar system bodies. | photochemical synthesis, chirality and detection of the building blocks of life in 'simulated' cometary matter |
stars form during gravitational collapse in molecular clouds. this process governs how galaxies evolve over cosmic time by creating their stellar components. it also affects properties of the planets formed along with the young stars. collapse in molecular clouds during star formation is controlled by self-gravity, random "turbulent" gas motions inside clouds, and interstellar magnetic fields. past studies have revealed a detailed picture of the role of self- gravity and gas kinematics during star formation — but observational assessments of magnetic fields remain challenging. a coordinated and ambitious project is needed to systematically fill the gaps in our current understanding of magnetic fields in star formation. simplifi ("study of interstellar magnetic polarization: a legacy investigation of filaments") is primarily a sofia legacy project designed to study a sample of molecular clouds at near (d < 500 pc) and intermediate (d <5 kpc) distances in polarized far-ir light. near-ir starlight polarization combined with gaia data provide information on the connection of dense clouds to its diffuse natal environment. simplifi also uses molecular line emission to study the relative alignment of gas flows and magnetic fields and tests key theoretical predictions of mhd turbulence. i will present highlights from the legacy survey program that start to clarify the role of magnetic fields in a diverse sample of star-forming filaments, and provide a framework to simplify the diversity of filament properties. | simplifi: a legacy investigation of interstellar magnetic polarization in star forming filaments |
the optical to submillimetre continuum radiation of the ism is polarised by aligned non-spherical dust particles. modelling of this polarisation spectrum in combination with abundance constraints and simultaneous fit to extinction and emission yields important information on dust grains, including chemistry, mineralogy, particle sizes, and shapes. the pristine nature of dust is better revealed by studying sight-lines that include a single-cloud in the observing beam as compared to attempts at analysing averages of the observing characteristics over multiple-clouds. the propagation of polarised light through dust enshrouded objects is solved by polarisation radiative transfer for which we outline the central methodology. | dust polarisation in the interstellar medium |
we present alma 343ghz (band 7; 870um) polarization observations toward the very embedded intermediate-mass protostar serpens smm1. we complement these observations with new submillimeter array (sma) 345ghz (880um) dust polarization observations as well as with archival polarization maps obtained with the james clerk maxwell telescope (jcmt; 850um) and the combined array for research in millimeter-wave astronomy (carma; 1.3mm). the 870um alma dust polarization observations that we present were taken on 2015 june 3 and 7, and have a synthesized beam (resolution element) of ~0.33", corresponding to a linear resolution of ~140au at a distance of 436pc. we also present 1.3mm (band 6) alma spectral-line data, which were taken in two different array configurations on 2014 august 18 (~0.3" angular resolution) and 2015 april 06 (~1" resolution). finally, we present 1.3mm alma continuum data with ~0.1" resolution (r. pokhrel et al. 2017, in preparation), observed on 2016 september 10, 13, and 2016 october 31. the sma polarization observations (figure 1(c)) were taken on 2012 may 25 (compact configuration) and 2012 september 2 and 3 (extended configuration), and have a synthesized beam of ~0.8". the archival jcmt scuba polarization data (figure 1(a)) were obtained from supplementary data provided by matthews+ (2009, j/apjs/182/143). the carma polarization data (figure 1(b)) were taken between 2011 and 2013 as part of the tadpol survey (hull+ 2014, j/apjs/213/13). the data were taken using the 1.3mm polarization receiver system in the c, d, and e arrays at carma, which correspond to angular resolutions at 1.3mm of approximately 1", 2", and 4", respectively. (2 data files). | vizier online data catalog: polarization data toward the protostar serpens smm1 (hull+, 2017) |
the next generation balloon-borne large aperture submillimeter telescope (blast-tng) is an experiment designed to map magnetic fields in molecular clouds in order to study their role in the star formation process. the telescope will be launched aboard a high-altitude balloon in december 2016 for a 4-week flight from mcmurdo station in antarctica. blast-tng will measure the polarization of submillimeter thermal emission from magnetically aligned interstellar dust grains, using large format arrays of kinetic inductance detectors operating in three bands centered at 250, 350, and 500 microns, with sub-arcminute angular resolution. the optical system includes an achromatic half wave plate (hwp), mounted in a half wave plate rotator (hwpr). the hwp and hwpr will operate at 4 k temperature to reduce thermal noise in our measurements, so it was crucial to account for the effects of thermal contraction at low temperature in the hwpr design. it was also equally important for the design to meet torque requirements while minimizing the power from friction and conduction dissipated at the 4 k stage. we also discuss our plan for cold testing the hwpr using a repurposed cryostat with a silicon diode thermometer read out by an edas-ce ethernet data acquisition system. | the half wave plate rotator for the blast-tng balloon-borne telescope |
astrophysical dust grains become partially aligned due to magnetic fields that permeate the interstellar medium. measurements of far-infrared polarized emission provide a tool to characterize magnetic fields and test their effect on star formation in molecular clouds. the hawc+ camera provides polarimetric imaging capability for sofia in four bands between 50 and 300 microns. as part of the science commissioning of the instrument, hawc+ has obtained more than 1000 independent measurements of polarization in the omc-1 star forming region. the observations were made at a wavelength of 89 microns with an angular resolution of 8 arcseconds. we present these preliminary data and initial analysis. | hawc+/sofia polarimetric observations of omc-1 |
the far-infrared imager and polarimeter (fip) for the origins space telescope (origins) is a basic far-infrared imager and polarimeter. the camera will deliver continuum images and polarization measurements at 50 and 250 μm. currently available detector technologies provide sufficient sensitivity for background limited observations from space, at least on a single pixel basis. fip incorporates large next-generation superconducting detector arrays and our technology development plan will push the pixel numbers for the arrays to the required size of 8000. two superconducting detector technologies are currently candidates for the instrument: transition edge sensors or microwave kinetic inductance devices. using these detectors and taking advantage of the cryogenic telescope that is provided by origins, fip will achieve mapping speeds of up to eight orders of magnitude faster than what has been achieved by existing observatories. the science drivers for fip include observations of solar system objects, dust properties, and magnetic field studies of the nearby interstellar medium, and large scale galaxy surveys to better constrain the star formation history of the universe to address one of the main themes of origins: "how does the universe work?" in addition to the science, the fip instrument plays a critical functional role in aligning the mirrors during on orbit observatory commissioning. | far-infrared imager and polarimeter for the origins space telescope |
the sun modulates with the solar wind flow the shape of the whole heliosphere interacting with the surrounding interstellar medium. recent results from ibex and inca experiments, as well as recent measurements from voyager 1 and 2, demonstrated that this interaction is much more complex and subject to temporal and heliolatitudinal variations than previously thought. these variations could be also related with the evolution of solar wind during its journey through the heliosphere. hence, understanding how the solar wind evolves from its acceleration region in the inner corona to the heliospheric boundaries is very important.in this work, swan lyman-α full-sky observations from soho are combined for the very first time with measurements acquired in the inner corona by soho uvcs and lasco instruments, to trace the solar wind expansion from the sun to 1 au. the solar wind mass flux in the inner corona was derived over one full solar rotation period in 1997, based on lasco polarized brightness measurements, and on the doppler dimming technique applied to uvcs lyman-α emission from neutral h coronal atoms due to resonant scattering of chromospheric radiation. on the other hand, the swan lyman-α emission (due to back-scattering from neutral h atoms in the interstellar medium) was analyzed based on numerical models of the interstellar hydrogen distribution in the heliosphere and the radiation transfer. the swan full-sky lyman-α intensity maps are used for solving of the inverse problem and deriving of the solar wind mass flux at 1 au from the sun as a function of heliolatitude. first results from this comparison for a chosen time period in 1997 are described here, and possible future applications for solar orbiter data are discussed. | evolution of solar wind flows from the inner corona to 1 au: constraints provided by soho uvcs and swan data |
pilot is a balloon-borne astronomy experiment designed to study the polarization of dust emission in the diffuse interstellar medium in our galaxy at wavelengths 240 μm with an angular resolution about two arcminutes. pilot optics is composed an off-axis gregorian type telescope and a refractive re-imager system. all optical elements, except the primary mirror, are in a cryostat cooled to 3k. we combined the optical, 3d dimensional measurement methods and thermo-elastic modeling to perform the optical alignment. the talk describes the system analysis, the alignment procedure, and finally the performances obtained during the first flight in september 2015. | pilot optical alignment |
probing magnetic fields in the diffuse interstellar medium (ism) is generally achieved by polarimetry, including stellar polarization and polarized dust thermal emission. here we present a novel approach, i.e., the velocity gradient technique (vgt), for tracing the magnetic fields. vgt is developed from the fact that magneto-hydrodynamic turbulence is anisotropic in a sub-alfvenic environment. in this work, we test vgt's accuracy by applying it to an h i cloud extracted from the hi4pi survey. we compare vgt with the planck 353ghz polarization and stellar polarization showing that vgt gives an accurate measurement. we also find alfven mach number of the hi cloud is around 0.3 from vgt's estimation. | probing magnetic field tomography with the velocity gradients technique |
scattering of pickup ion ring-beam distributions in the outer heliosheath is a fundamental element in the spatial retention scenario of the energetic neutral atom (ena) ribbon observed by the interstellar boundary explorer (ibex). according to our earlier linear instability analysis, pickup ion ring-beam distributions trigger magnetic field-aligned, right-hand polarized unstable waves in two separate frequency ranges which are near and far above the proton cyclotron frequency, respectively. we have performed hybrid simulations to study the unstable waves near the proton cyclotron frequency. however, the high-frequency waves well above the proton cyclotron frequency are beyond the reach of hybrid simulations. in the present study, particle-in-cell simulations are carried out to investigate the parallel- and anti-parallel-propagating high-frequency waves excited by the outer heliosheath pickup ions at different pickup angles as well as the scattering of the pickup ions by the waves excited. in the early stages of the simulations, the results confirm the excitation of the parallel-propagating, right-hand polarized high-frequency waves as predicted by the earlier linear analysis. later in the simulations, enhanced anti-parallel-propagating modes also emerge. furthermore, the evolution of the pickup ion ring-beam distributions of the selected pickup angles reveals that the high-frequency waves do not significantly contribute to the pickup ion scattering. these results are favorable regarding the plausibility of the spatial retention scenario of the ibex ena ribbon. | high-frequency waves driven by pickup ion ring-beam distributions in the outer heliosheath |
because venus does not have a dynamo, the interactions between the solar wind and the ionized upper atmosphere are more extreme at venus than at earth. wave propagation direction with respect to the background magnetic field is necessary for calculation of energy exchange and wave mode identification, but local wave-field variability hinders most software. in this study, we present a new plasma wave polarization software called minerva and provide extensive analyses in the venusian foreshock and explore foreshock regions at earth, jupiter, and saturn. the minerva code is applicable to interstellar, solar, and planetary plasmas. future work will include studies of diverse environments within and beyond our solar system. | analysis of foreshock plasma waves in the inner and outer heliosphere using minerva |
scattering properties of irregularly shaped interstellar composite dust analogues consisting of graphite and fayalite (fe2sio4) were studied using discrete dipole approximation (dda). two dust models were developed to calculate the scattering and extinction efficiencies, single scattering albedo, asymmetry parameter, phase functions and degree of linear polarizations. laboratory measurements were also performed at three incident wavelengths 543.5, 594.5 and 632.8 nm on chemically synthesized graphite and fayalite composite particles of sizes ranging from 0.3 to 5 μm. a comparative analysis of the theoretical and experimental results of shape- and size-averaged scattering parameters shows that changes in the percentage composition of a two-species mixture model has a pronounced effect on the light-scattering properties of dust particles. the developed computational models are successful in representing a two-species mixture of interstellar dust analogues considering diverse size, shapes and percentage composition. this technique can be applied to fit observed scattering and absorption peaks in the visible region produced by astrophysical dust, provided large number of particle species are included and the influence of more physical parameters (e.g., porosity, fluffiness, temperature, density, etc.) are considered. further, this study is also applicable to remote sensing, atmospheric and planetary sciences. all the physical parameters employed as variables in the models influence the oscillations observed in theoretical curves and change the values of scattering parameters. | scattering by interstellar graphite and fayalite composite dust analogues: computer simulation and laser-based laboratory measurements |
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