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context. life is distinctly homochiral. the origins of this homochirality are under active debate. recently, propylene oxide has been detected in the gas-phase interstellar medium (ism). the enantiomeric composition of ism propylene oxide may be probed through circular polarization measurements, but accurate estimates of the circular dichroism properties of the microwave transitions of propylene oxide are not available.aims: our aim is to develop a model of the circular dichroic activity in torsion-rotation transitions of closed-shell chiral molecules such as propylene oxide. with this model we can estimate the viability, and optimize the observation strategies, of enantiomeric excess detection in ism propylene oxide.methods: circular dichroism in spectral lines manifests through the simultaneous interaction of an electromagnetic radiation field with the molecular electric dipole moment and magnetic dipole moment. we developed techniques to quantify electric dipole and magnetic dipole moments of torsion-rotation transitions by expanding on earlier modeling of the electric and magnetic dipole properties of single torsion-rotation levels. to model the circular dichroism properties of propylene oxide, we used these techniques in combination with ab initio quantum chemical calculations.results: the expressions for the dichroic activity of the microwave transitions of torsionally active molecules are derived. we find that the torsional motion of molecules exhibiting internal rotation contributes significantly to the total magnetic moment. we present estimates for the dichroic activity of the torsion-rotation transitions of propylene oxide. we predict that the circular polarization fractions of emission lines of enantiopure propylene oxide relevant to astronomical detections are on the order of 10−6.conclusions: due to the low predicted circular polarization fractions, we conclude that enantiomeric characterization of propylene oxide in the gas phase of the ism is impossible with the current astronomical observation techniques. we suggest that only chiral radical species may be viably employed for purposes of enantiomeric excess detection. we estimate that laboratory experiments may be successful in detecting the enantiomeric composition of a mixture of propylene oxide through microwave dichroism spectroscopy. | detecting chiral asymmetry in the interstellar medium using propylene oxide |
we used high-resolution [c ii] 158 μm mapping of two nebulae ic 59 and ic 63 from sofia/upgreat in conjunction with ancillary data of the gas, dust, and polarization to probe the kinematics, structure, and magnetic properties of their photodissociation regions (pdrs). the nebulae are part of the sh 2-185 h ii region that is illuminated by the b0 ive star γ cas. the velocity structure of each pdr changes with distance from γ cas, which is consistent with driving by the radiation. based on previous far-ultraviolet (fuv) flux measurements of, and the known distance to, γ cas, along with the predictions of 3d distances to the clouds, we estimated the fuv radiation field strength (g 0) at the clouds. assuming negligible extinction between the star and clouds, we find their 3d distances from γ cas. for ic 63, our results are consistent with earlier estimates of distance from andersson et al., locating the cloud at ~2 pc from γ cas at an angle of 58° to the plane of the sky behind the star. for ic 59, we derive a distance of 4.5 pc at an angle of 70° in front of the star. we do not detect any significant correlation between the orientation of the magnetic field and the velocity gradients of [c ii] gas, which indicates a moderate magnetic field strength. the kinetic energy in ic 63 is estimated to be an order of 10 higher than the magnetic energies. this suggests that kinetic pressure in this nebula is dominant. | physics and chemistry of radiation driven cloud evolution. [c ii] kinematics of ic 59, and ic 63 |
the next generation balloon-borne large aperture submillimeter telescope (blast-tng) is a submillimeter polarimeter designed to map interstellar dust and galactic foregrounds at 250, 350, and 500 microns during a 24-day antarctic flight. the blast-tng detector arrays are comprised of 918, 469, and 272 mkid pixels, respectively. the pixels are formed from two orthogonally oriented, crossed, linear-polarization sensitive mkid antennae. the arrays are cooled to sub 300 mk temperatures and stabilized via a closed cycle 3he sorption fridge in combination with a 4he vacuum pot. the detectors are read out through a combination of the second-generation reconfigurable open architecture computing hardware (roach2) and custom rf electronics designed for blast-tng. the firmware and software designed to readout and characterize these detectors was built from scratch by the blast team around these detectors, and has been adapted for use by other mkid instruments such as toltec and olimpo.1 we present an overview of these systems as well as in-depth methodology of the ground-based characterization and the measured in-flight performance. | characterization, deployment, and in-flight performance of the blast-tng cryogenic receiver |
sulphur bearing nitrogenous compounds have been observed in space over this last decade. modelling their abundances has been done using rate coefficients of isoelectronic molecules. in order to satisfy the astrophysical precision required, we report the actual rate coefficients of ns+ induced by collision with the most abundant interstellar species (para-h2). considering the 23 low-lying rotational levels of ns+, we were able to compute the (hyperfine) rate coefficients up to 100 k. these latter were carried out by averaging cross-sections over the maxwell-boltzmann velocity distribution. the state-to-state inelastic cross-sections were determined in the quantum mechanical close coupling approach for total energies ranging up to 1400 cm-1. these dynamic data result from a four dimensional potential energy surface (4d-pes) which was spherically averaged over the h2 orientations. the 4d-pes was calculated using the explicitly correlated coupled cluster method with simple, double, and non-iterative triple excitation (ccsd(t)-f12) connected to the augmented-correlation consistent-polarized valence triple zeta gaussian basis set (aug-cc-pvtz). the so-averaged pes presents a very deep well of 596.72 cm-1 at r = 5.94 a0 and θ1 = 123.20°. discussions on the propensity rules for the (hyperfine) rate coefficients were made and they are in favour of (δj = δf) δj = 1 transitions. the results presented here may be crucially needed in order to accurately model the ns+ abundance in space. in addition, we expect that this paper will encourage investigations on the sulphur bearing nitrogenous compounds. | hyperfine excitation of ns+ due to para-h2(j = 0) impact |
modern radio spectrometers make measurement of polarized intensity as a function of faraday depth possible. i investigate the effect of depolarization along a model line of sight. i model sightlines with two components informed by observations: a warm ionized medium with a lognormal electron density distribution and a narrow, denser component simulating a spiral arm or hii region, all with synchrotron-emitting gas mixed in. i then calculate the polarized intensity from 300–1800 mhz and calculate the resulting faraday depth spectrum. the idealized synthetic observations show far more faraday complexity than is observed in global magneto-ionic medium survey observations. in a model with a very nearby hii region observed at low frequencies, most of the effects of a "depolarization wall" are evident: the hii region depolarizes background emission, and less (but not zero) information from beyond the hii region reaches the observer. in other cases, the effects are not so clear, as significant amounts of information reach the observer even through significant depolarization, and it is not clear that low-frequency observations sample largely different volumes of the interstellar medium than high-frequency observations. the observed faraday depth can be randomized such that it does not always have any correlation with the true faraday depth. | is there a polarization horizon? |
we present the first ab initio potential energy surfaces (pess) for the po(x2π)-he van der waals system. the pess were obtained using the open-shell partially spin-restricted coupled cluster approach with single, double and perturbative triple excitations [uccsd(t)]. the augmented correlation-consistent polarized valence triple-zeta (aug-cc-pvtz) basis set was employed supplemented by mid-bond functions. integral and differential cross sections for the rotational excitation in po-he collisions were calculated using the new pes and compared with results in similar systems. finally, our work presents the first hyperfine-resolved cross sections for this system that are needed for accurate modelling in astrophysical environments. | collisional excitation of interstellar po(x2π) by he: new ab initio potential energy surfaces and scattering calculations |
context. be/x-ray binaries represent the main group of high-mass x-ray binaries. the determination of the astrophysical parameters of the counterparts of these high-energy sources is important for the study of x-ray binary populations in our galaxy. x-ray observations suggest that sax j2239.3+6116 is a be/x-ray binary. however, little is known about the astrophysical parameters of its massive companion.aims: the main goal of this work is to perform a detailed study of the optical variability of the be/x-ray binary sax j2239.3+6116.methods: we obtained multi-colour bvri photometry and polarimetry and 4000-7000 å spectroscopy. the 4000-5000 å spectra allowed us to determine the spectral type and projected rotational velocity of the optical companion; the 6000-7000 å spectra, together with the photometric magnitudes, were used to derive the colour excess e(b-v), estimate the distance, and to study the variability of the hα line.results: the optical counterpart to sax j2239.3+6116 is a v = 14.8 b0ve star located at a distance of 4.9 kpc. the interstellar reddening in the direction of the source is e(b-v) = 1.70 ± 0.03 mag. the monitoring of the hα line reveals a slow long-term decline of its equivalent width since 2001. the line profile is characterized by a stable double-peak profile with no indication of large-scale distortions. we measured intrinsic optical polarization for the first time. although somewhat higher than predicted by the models, the optical polarization is consistent with electron scattering in the circumstellar disk.conclusions: we attribute the long-term decrease in the intensity of the hα line to the dissipation of the circumstellar disk of the be star. the longer variability timescales observed in sax j2239.3+6116 compared to other be/x-ray binaries may be explained by the wide orbit of the system. | the optical counterpart to the be/x-ray binary sax j2239.3+6116 |
tracing magnetic field is crucial as magnetic field plays an important role in many astrophysical processes. earlier studies have demonstrated that ground state alignment (gsa) is an effective way to detect a weak magnetic field (1g≳ b≳ {{10}-15} g) in a diffuse medium. we explore the atomic alignment in the presence of an extended radiation field for both absorption lines and emission lines. the alignment in the circumstellar medium, binary systems, disks, and the local interstellar medium are considered in order to study the alignment in the radiation field where the pumping source has a clear geometric structure. furthermore, the multipole expansion method is adopted to study gsa induced in the radiation field with unidentified pumping sources. we study the alignment in the dominant radiation components of the general radiation field: the dipole and quadrupole radiation field. we discuss the approximation of gsa in a general radiation field by summing the contribution from the dipole and quadrupole radiation field. we conclude that gsa is a powerful tool for detecting weak magnetic fields in the diffuse medium in general radiation fields. | tracing magnetic fields by atomic alignment in extended radiation fields |
polarization of interstellar dust emission is a powerful probe of dust properties and magnetic field structure. yet studies of external galaxies are hampered by foreground dust contribution. the study aims at separating the polarized signal from the large magellanic cloud (lmc) from that of the milky way (mw) to construct a wide-field, spatially complete map of dust polarization using the planck 353 ghz data. to estimate the foreground polarization direction, we used velocity gradients in h i spectral line data and assessed the performance of the output by comparing to starlight extinction polarization. we estimate the foreground intensity using the dust-to-gas correlation and the average intensity around the lmc and we assume the foreground polarization to be uniform and equal to the average of the mw around the galaxy to derive foreground i, q, and u parameters. after foreground removal, the geometry of the plane-of-the-sky magnetic field tends to follow the structure of the atomic gas. this is notably the case along the molecular ridges extending south and south-east of the 30 doradus star-forming complex and along the more diffuse southern arm extending towards the small magellanic cloud. there is also an alignment between the magnetic field and the outer arm in the western part. the median polarization fraction in the lmc is slightly lower than that observed for the mw as well as the anticorrelation between the polarization angle dispersion function and the polarization fraction. overall, polarization fraction distribution is similar to that observed in the mw. | unveiling polarized emission from interstellar dust of the large magellanic cloud with planck |
we discuss gamma-ray signatures associated with an asymmetric explosion and transport of positrons in sn ia ejecta. in particular, compton scattering of gamma-ray line photons can induce polarization in the continuum, which would be a direct probe of the asymmetries in the distribution of radioactive isotopes and/or of the scattering medium. even more interesting would be a comparison of the shapes of γ-ray lines and that of the electron-positron annihilation line at 511kev. the shapes of γ-ray lines associated with the decay of 56co (e.g. lines at 847 and 1238kev) directly reflect the velocity distribution of 56co. on the other hand, the 511 kev line arises from the annihilation of positions, which are also produced by the 56co decay but can propagate through the ejecta before they slow down and annihilate. therefore, the shape of the annihilation line might differ from other gamma-ray lines, providing constraints on the efficiency of positrons propagation through the ejecta and, as consequence, on the topology of magnetic fields in the ejecta and on the fraction of positrons that escape to the interstellar medium. we illustrate the above effects with two models aimed at capturing the main predicted signatures. | polarization of mev gamma-rays and 511 kev line shape as probesof snia asymmetry and magnetic field |
aims: ngc 1502 is located at the periphery of the cam ob1 association and probably within the orion spur, with published distance estimates varying between 0.7 and 1.5 kpc. we combine new polarimetric observations and existing uvbyβ and ubv photometries to provide new estimates of the cluster's parameters.methods: we present new multi-wavelength polarization observations of 22 stars in the direction of the cluster and, using the wavelength of maximum polarization, calculate the total-to-selective extinction ratio for each of these stars. these are combined with homogenized uvbyβ and ubv photometries to obtain the individual stellar distances and study the structure of the field.results: we found no evidence of significant extinction variation across the cluster and obtained an average color excess e(b - y) = 0.56 ± 0.02 mag, corresponding to e(b - v) = 0.76 mag. given the uniformity of both pmax and λmax toward the cluster and the distribution of the color excess with distance, it seems likely that the polarization in this region arises from aligned dust grains in the foreground of the cluster, not farther than 500-600 pc. based on 20 stars located beyond 500 pc within the studied field of view, we obtained an average polarization-based total-to-selective extinction ratio r = 2.83 ± 0.14 yielding visual absorption av = 2.14 ± 0.16 mag. using 11 stars with uvbyβ data that represent the main sequence of the cluster, we calculated a photometric distance of 1117-89+96 pc. this estimate is fully supported by the ubv -based analysis and the new individual membership probabilities that we derive. assuming a solar metallicity yields an age of 5 myr. our analysis yields controversial results regarding the membership of the stars associated with the sz cam system (hd 25638 and hd 25639) to the cluster. | interstellar polarization and extinction towards the young open cluster ngc 1502 |
we present the optical linear polarization observation of stars toward the core of the czernik 3 cluster in the sloan i band. the data were obtained using the empol instrument on the 1.2 m telescope at mount abu observatory. we study the dust distribution toward this cluster by combining the results from our polarization observations with the data from gaia edr3, wise, and the h i, 12co surveys. in addition, we use the polarimetric data of previously studied clusters within 15° of czernik 3 to understand the large-scale dust distribution. the observational results of czernik 3 show a large range in the degree of polarization, indicating that the dust is not uniformly distributed over the plane of the sky, even on a small scale. the distance to czernik 3 is constrained to 3.6 ± 0.8 kpc using the member stars in the core region identified from gaia edr3 astrometry. this makes it one of the most distant clusters observed for optical polarization so far. the variation of observed degree of polarization and extinction toward this cluster direction suggests the presence of at least two dust layers along this line of sight at distances of ~1 and ~3.4 kpc. there is an indication of the presence of dust in the center of the cluster as seen from an increase in the degree of polarization and wise w4 flux. the large-scale distribution of dust reveals the presence of a region of low dust content between the local arm and the perseus arm. | optical linear polarization study toward czernik 3 open cluster at different spatial scales |
we present ubvri polarization observations of 12 b-type stars in the direction of the young open cluster ngc 6530, nine of them confirmed as probable members. the maximum degree of polarization for our target stars ranges from 0.16% to 2.84%, with an average value of 1.1%. we note variations of the polarization vector orientations across the cluster field. we use the polarization data to infer the wavelength of maximum polarization and obtain the total-to-selective extinction ratio for each star. based on all 12 observed stars, the weighted average wavelength of the maximum degree of polarization is 0.563 ± 0.001 μm. this yields an average value of r = 3.15 ± 0.06 for the total-to-selective extinction associated with this field. despite slight variations, rv is not abnormal. using ubv photometry combined with recent photometric calibrations yields average e(b - v) = 0.38 ± 0.07 (s.d.) mag and average av = 1.20 ± 0.24 (s.d.) mag. both rv and e(b - v) show star-to-star variations. our study yields a photometry-based distance of 1.6 kpc. for more precise distance estimates, especially when seeking agreement with the gaia parallaxes, better evaluation of peculiarity and duplicity of these stars is needed. we studied comparisons between the photometric ubv absolute magnitudes, gaia-based absolute magnitudes and magnitudes obtained from direct measurements of the balmer discontinuity and discuss the presently existing disagreements for the cluster field. | interstellar extinction in the direction of the young open cluster ngc 6530 |
context. computing polarised intensities from noisy data in stokes u and q suffers from a positive bias that should be suppressed.aims: we aim to develop a correction method that, when applied to maps, should provide a distribution of polarised intensity that closely follows the signal from the source.methods: we propose a new method to suppress the bias by estimating the polarisation angle of the source signal in a noisy environment with help of a modified median filter. we then determine the polarised intensity, including the noise, by projection of the observed values of stokes u and q onto the direction of this polarisation angle.results: we show that our new method represents the true signal very well. if the noise distribution in the maps of u and q is gaussian, then in the corrected map of polarised intensity it is also gaussian. smoothing to larger gaussian beamsizes, to improve the signal-to-noise ratio, can be done directly with our method in the map of the polarised intensity. our method also works in case of non-gaussian noise distributions.conclusions: the maps of the corrected polarised intensities and polarisation angles are reliable even in regions with weak signals and provide integrated flux densities and degrees of polarisation without the cumulative effect of the bias, which especially affects faint sources. features at low intensity levels like "depolarisation canals" are smoother than in the maps using the previous methods, which has broader implications, for example on the interpretation of interstellar turbulence. | a new method to suppress the bias in polarised intensity |
the polarized instrument for long-wavelength observation of the tenuous interstellar medium (pilot) is a balloon-borne experiment aiming at measuring the polarized emission of thermal dust at a wavelength of 240 mm (1.2 thz). a first pilot flight (flight#1) of the experiment took place from timmins, ontario, canada, in september 2015 and a second flight (flight#2) took place from alice springs, australia in april 2017. in this paper, we present the inflight performance of the instrument during these two flights. we concentrate on performances during flight#2, but allude to flight#1 performances if significantly different. we first present a short description of the instrument and the flights. we determine the time constants of our detectors combining inflight information from the signal decay following high energy particle impacts (glitches) and of our internal calibration source. we use these time constants to deconvolve the data timelines and analyse the optical quality of the instrument as measured on planets. we then analyse the structure and polarization of the instrumental background. we measure the detector response flat field and its time variations using the signal from the residual atmosphere and of our internal calibration source. finally, we analyze the detector noise spectral and temporal properties. the in-flight performances are found to be satisfactory and globally in line with expectations from ground calibrations. we conclude by assessing the expected in-flight sensitivity of the instrument in light of the above in-flight performances. | pilot balloon-borne experiment in-flight performance |
interstellar polarization in the optical/infrared has long been known to be due to asymmetrical dust grains aligned with the magnetic field and can potentially provide a resource effective way to probe both the topology and strength of the magnetic-field. however, to do so with confidence, the physics and variability of the alignment mechanisms must be quantitatively understood. the last 15 years has seen major advancements in both the theoretical and observational understanding of this problem. i here review the current state of the observational constraints on the grain alignment physics. while none of the three classes of proposed grain alignment theories: mechanical, paramagnetic relaxation and radiative alignment torque, can be viewed as having been empirically confirmed, the first two have failed some critical observational tests, whereas the latter has recently been given specific observational support and must now be viewed as the leading candidate. | interstellar grain alignment: observational status |
discoverable interstellar communication signals are expected to exhibit al least one signal characteristic clearly distinct from random noise. a hypothesis is proposed that radio telescope received signals may contain transmitted delta-t delta-f opposite circular polarized pulse pairs, conveying a combination of information content and discovery methods, including symbol repetition. hypothetical signals are experimentally measured using a 26 foot diameter radio telescope, a chosen matched filter receiver, and machine post processing system. measurements are expected to present likelihoods explained by an additive white gaussian noise model, augmented to reduce radio frequency interference. in addition, measurements are expected to present no significant differences across a population of right ascension ranges, during long duration experiments. the hypothesis and experimental methods described in this paper are based on multiple radio telescope delta-t delta-f polarized pulse pair experiments previously reported. (ref. arxiv:2105.03727, arxiv:2106.10168). in the current work, a right ascension filter spans twenty-one 0.3 hour right ascension bins over a 0 to 6.3 hr range, during a 143 day experiment. apparent symbol repetition is measured and analyzed. the 5.25 plus or minus 0.15 hr right ascension, -7.6 degree plus or minus 1 degree declination celestial direction has been associated with anomalous observations in previous work, and continues to present anomalies, having unknown cause. | symbol repetition in interstellar communications: methods and observations |
ngc 457 is a moderately reddened and relatively young open cluster very rich in variable stars, particularly be stars, but not associated with any prominent star-forming field. we combine new multi-wavelength polarization measurements with existing ubv and uvby photometries to obtain precise estimates of the total-to-selective extinction in the field of the cluster and re-evaluate its distance and age. the polarization measurements show a tight alignment of the polarization vectors with the galactic plane and yield an average value of the total-to-selective extinction of 3.05 ± 0.17 for the cluster’s field. using this value and the confirmed color excess e(b-v)=0.500+/- 0.030 mag, we obtain a distance modulus of 12.20 ± 0.39, corresponding to 2.75 ± 0.49 kpc and, assuming slightly sub-solar metallicity, an age of 15.8 myr. | interstellar polarization and extinction towards the open cluster ngc 457 |
linear polarization has been observed in both the prompt phase and afterglow of some bright gamma-ray bursts (grbs). polarization in the prompt phase spans a wide range, and may be as high as ≳ 50%. in the afterglow phase, however, it is usually below 10%. according to the standard fireball model, grbs are produced by synchrotron radiation and compton scattering process in a highly relativistic jet ejected from the central engine. it is widely accepted that prompt emissions occur in the internal shock when shells with different velocities collide with each other, and the magnetic field advected by the jet from the central engine can be ordered on a large scale. on the other hand, afterglows are often assumed to occur in the external shock when the jet collides with interstellar medium, and the magnetic field produced by the shock through, for example, weibel instability, is possibly random. in this paper, we calculate the polarization properties of the synchrotron self-compton process from a highly relativistic jet, in which the magnetic field is randomly distributed in the shock plane. we also consider the generalized situation where a uniform magnetic component perpendicular to the shock plane is superposed on the random magnetic component. we show that it is difficult for the polarization to be larger than 10% if the seed electrons are isotropic in the jet frame. this may account for the observed upper limit of polarization in the afterglow phase of grbs. in addition, if the random and uniform magnetic components decay with time at different speeds, then the polarization angle may change 90° during the temporal evolution. supported by fundamental research funds for the central universities (106112016cdjcr301206), national natural science fund of china (11375203, 11603005), and open project program of state key laboratory of theoretical physics, institute of theoretical physics, chinese academy of sciences, china (y5kf181cj1) | polarization of gamma-ray burst afterglows in the synchrotron self-compton process from a highly relativistic jet |
we study the polarized radio emission from young type ia supernova remnants by means of three-dimensional numerical mhd simulations and the assumption of relativistic electron distribution related to magnetic field energy density. in our simulations, the turbulent component of background plasma is taken into account by introducing a 3d kolmogorov-like power spectrum. the simulation results indicate (i) the different orientations of the interstellar magnetic field around snrs and lines of sight could produce different polarized radio emission shells, (ii) the fraction of polarization may be decreased through integrating the synchrotron emissivities along the line of sight, which is mainly due to the emission from the strong turbulent and disordered region of the magnetic field, and (iii) the total intensity is strong in some regions where the polarization degree is low. | 3d mhd numerical simulations of polarized emission in the turbulent background from young type ia supernova remnants |
polarized thermal emission from interstellar dust grains can be used to map magnetic fields in star forming molecular clouds and the diffuse interstellar medium (ism). the balloon-borne large aperture submillimeter telescope for polarimetry (blastpol) flew from antarctica in 2010 and 2012 and produced degree-scale polarization maps of several nearby molecular clouds with arcminute resolution. the success of blastpol has motivated a next-generation instrument, blast-tng, which will use more than 3000 linear polarization- sensitive microwave kinetic inductance detectors (mkids) combined with a 2.5 m diameter carbon fiber primary mirror to make diffraction-limited observations at 250, 350, and 500 µm. with 16 times the mapping speed of blastpol, sub-arcminute resolution, and a longer flight time, blast-tng will be able to examine nearby molecular clouds and the diffuse galactic dust polarization spectrum in unprecedented detail. the 250 μm detec- tor array has been integrated into the new cryogenic receiver, and is undergoing testing to establish the optical and polarization characteristics of the instrument. blast-tng will demonstrate the effectiveness of kilo-pixel mkid arrays for applications in submillimeter astronomy. blast-tng is scheduled to fly from antarctica in december 2017 for 28 days and will be the first balloon-borne telescope to offer a quarter of the flight for "shared risk" observing by the community. | instrumental performance and results from testing of the blast-tng receiver, submillimeter optics, and mkid detector arrays |
aims: the fact that the o-type close binary star system ao cassiopeiae exhibits variable phase-locked linear polarization has been known since the mid-1970s. in this work, we re-observe the polarization arising from this system more than 50 yr later to better estimate the interstellar polarization and to independently derive the orbital parameters, such as inclination, i, orientation, ω, and the direction of the rotation for the inner orbit from the phase-folded polarization curves of the stokes q and u parameters.methods: the dipol-2 polarimeter was used to obtain linear polarization measurements of ao cassiopeiae in the b, v, and r passbands with the t60 remotely controlled telescope at an unprecedented accuracy level of ~0.003%. we have obtained the first proper quantification of the interstellar polarization in the direction heading towards ao cas by observing the polarization of three neighboring field stars. we employed a lomb-scargle algorithm and detected a clear periodic signal for the orbital period of ao cas. the standard analytical method based on a two-harmonics fourier fit was used to obtain the inclination and orientation of the binary orbit.results: our polarimetric data exhibited an unambiguous periodic signal at 1.76 days, thus confirming the orbital period of the binary system of 3.52 days. most of the observed polarization is of interstellar origin. the de-biased values of the orbital inclination are i = 63° + 2°/−3° and orientation of ω = 29º(209º) ± 8°. the direction of the binary system rotation on the plane of the sky is clockwise. the polarization data for ao cas is only available at the cds via anonymous ftp to cdsarc.cds.unistra.fr (ftp://130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/j/a+a/670/a176 | high-precision broadband linear polarimetry of early-type binaries. iii. ao cassiopeiae revisited |
observational studies of magnetic fields are crucial. we introduce a process "ground state alignment" as a new way to determine the magnetic field direction in diffuse medium. the alignment is due to anisotropic radiation impinging on the atom/ion. the consequence of the process is the polarization of spectral lines resulting from scattering and absorption from aligned atomic/ionic species with fine or hyperfine structure. the magnetic field induces precession and realign the atom/ion and therefore the polarization of the emitted or absorbed radiation reflects the direction of the magnetic field. the atoms get aligned at their low levels and, as the life-time of the atoms/ions we deal with is long, the alignment induced by anisotropic radiation is susceptible to extremely weak magnetic fields ( 1 g gtrsim b gtrsim 10^{-15} g). in fact, the effects of atomic/ionic alignment were studied in the laboratory decades ago, mostly in relation to the maser research. recently, the atomic effect has been already detected in observations from circumstellar medium and this is a harbinger of future extensive magnetic field studies. a unique feature of the atomic realignment is that they can reveal the 3d orientation of magnetic field. in this chapter, we shall review the basic physical processes involved in atomic realignment. we shall also discuss its applications to interplanetary, circumstellar and interstellar magnetic fields. in addition, our research reveals that the polarization of the radiation arising from the transitions between fine and hyperfine states of the ground level can provide a unique diagnostics of magnetic fields in the epoch of reionization. | magnetic field measurement with ground state alignment |
the magneto-optical polarization rotation effect has myriad applications in many research areas spanning the scientific spectrum, including space and interstellar research, nanotechnology, material science, biomedical imaging, and subatomic particle research. in the nonlinear magneto-optical rotation (nmor) effect, the angle of rotation of a linearly polarized optical field in a magnetized medium is dependent upon its intensity. however, typical nmor signals of conventional single-beam λ -scheme atomic magnetometers are peculiarly small, requiring sophisticated magnetic shielding and high-frequency phase-sensitive detection. here, we show the presence of an energy-symmetry-based propagation growth blockade that undermines the nmor effect in conventional single-beam λ -scheme atomic magnetometers. we further demonstrate, both experimentally and theoretically, an inelastic wave-mixing technique that breaks this nmor blockade, resulting in more-than-2-orders-of-magnitude enhancement of the nmor signal power amplitude that cannot be achieved with conventional single-beam λ -scheme atomic magnetometers. this technique, demonstrated here with substantially reduced light intensities at near-room temperatures, may lead to many applications, especially in the field of biomagnetism and high-resolution low-field magnetic imaging. | breaking the energy-symmetry-based propagation growth blockade in magneto-optical rotation |
based on the results from uv-irradiated interstellar ice analogues, we describe a two-step phenomenological theory for enantiomer-selective, asymmetric formation of molecules like amino acid precursors: (1) uv photolysis of interstellar ices to molecular fragments/radicals and formation of racemic population of chiral molecules and (2) asymmetric photolysis of precursors by uv-circularly polarized light (uv-cpl), resulting in preferred growth of one enantiomer. independent of specifics of step (1), when ice-analogue is irradiated with uv-cpl, enantiomeric excess of amino acids following hydrolysis is limited to |eeice(max)|=|(σ+ - σ-)/(σ+ + σ-)|, 0.5 times the anisotropy factor (g) for amino acid precursors (σ+/- is molecular cross-section for absorption of right/left uv-cpl light in cm2). for amino acids, the calculated eeice(max) ~ 1 per cent agrees with experiments. over small duration, ee is given by, |eeice(t)|=|(i+ - i-)(σ+ - σ-)|t/4, (i+/- is photon flux of right/left uv-cpl cm-2 s-1) which agrees with the observed dependence of ee on time-integrated flux of uv-cpl light. for ice irradiated with linearly polarized/unpolarized light followed by irradiation of residue with uv-cpl, |eeres(t)|=|tanh[(i+ - i-)(σ+ - σ-)t/2]| and can be much larger than eeice(max) for ice alone. when both ice and residue are irradiated with uv-cpl, ee = eeice + eeres and depends on the durations of irradiation for ice and residue. similar analysis by assuming asymmetric photosynthesis of precursors as the underlying mechanism does not agree with experimental observations. | enantiomeric excess of amino acids in interstellar ice analogues-asymmetric photolysis of precursors by circularly polarized uv light |
the fate of organometallic dust subjected to extreme conditions, especially the shock fronts, in the interstellar medium (ism) has not been explored to date. iron and cyclopentadiene, which have been found to be present in the ism, are known to react and produce the organometallic compound ferrocene under terrestrial conditions. in our experiment we subjected ferrocene, a possible proxy of such dust, to ~5.6 mach (m) shock commensurate with conditions encountered in the ism, leading to a temperature rise up to 7300 k within 2 ms. analysis of the post-shock residue showed the presence of a α-fe and fe3c composite that responded to an external magnetic field. these results show that a non-magnetic dust composed of molecules containing transition metals undergoing shock processing in the ism can dissociate and synthesize dust that is then magnetic. such drastic transformations from non-magnetic to magnetic dust induced by shocks might be of importance in interstellar polarization. | shock-induced transformation of non-magnetic to magnetic ism dust analogue |
a new method for measuring the global magnetic field structure of the galactic plane is presented. we have determined the near-infrared polarization of field stars around 52 cepheids found in recent surveys toward the galactic plane. the cepheids are located at the galactic longitudes $-10^{\circ} \le l \le +10.^{\!\!\!\circ }5$ and latitudes $-0.^{\!\!\!\circ }22\le b \le +0.^{\!\!\!\circ }45$ , and their distances are mainly in the range of 10 to 15 kpc from the sun. simple classification of the sightlines is made with the polarization behavior vs. $h-k_{\mathrm{s}}$ color of field stars, and typical examples of three types are presented. then, division of the field stars in each line of sight into (a) foreground, (b) bulge, and (c) background is made with the gaia dr2 catalog, the peak of the $h-k_{\mathrm{s}}$ color histogram, and $h-k_{\mathrm{s}}$ colors consistent with the distance of the cepheid in the center, respectively. differential analysis between them enables us to examine the magnetic field structure more definitely than just relying on the $h-k_{\mathrm{s}}$ color difference. in one line of sight, the magnetic field is nearly parallel to the galactic plane and well aligned all the way from the sun to the cepheid position on the other side of the galactic center. contrary to our preconceived ideas, however, sightlines having such well-aligned magnetic fields in the galactic plane are rather small in number. at least 36 cepheid fields indicate random magnetic field components are significant. two cepheid fields indicate that the magnetic field orientation changes more than $45^{\circ }$ in the line of sight. the polarization increase per color change $\delta p/\delta (h-k_{\mathrm{s}})$ varies from region to region, reflecting the change in the ratio of the magnetic field strength and the turbulence strength. | magnetic field structure of the galactic plane from differential analysis of interstellar polarization |
according to the theory of dilatons, one of the main sources of dilatonic radiation is the first invariant of the electromagnetic field tensor. since for a plane electromagnetic wave this invariant equals to zero, wave propagation does not cause dilaton radiation. the first invariant of the electromagnetic field tensor becomes nonzero when a wave propagates in an external electromagnetic field. in astrophysics conditions, the most interesting among such sources are plane electromagnetic waves that propagates around interstellar space through fields of positively and negatively charged particles, electrons and protons. in this paper, dilatonic radiation is calculated when its source is an elliptically polarized electromagnetic wave which propagates in a static coulomb field. it is shown that the solution for the dilatonic field is nonsingular. the angular distribution of dilatonic radiation that appeases under these conditions, is studied. the directions along which the dilatonic radiation is absent and those corresponding to local maxima of the dilatonic radiation pattern are found. | dilaton generation while a plane electromagnetic wave propagates in coulomb field |
the structure of carbodiimide has been studied by using quantum chemical methods. carbodiimide (hncnh) has been detected towards sagittarius b2 (n) in interstellar medium (ism). two reaction mechanisms have been proposed to study the formation of interstellar carbodiimide. the first reaction mechanism is based on molecule-radical and the second one is a radical-radical mechanism, through previously detected interstellar molecules or radicals. quantum chemical calculations have been performed by using density functional theory (dft) and moller-plesset second order perturbation (mp2) theory, in gas phase as well as in polarizable continuum model (pcm). the proposed reaction paths are exothermic and barrierless which indicates the possibility of carbodiimide formation in ism. several basis sets have been used to verify the validity and accuracy of the results. the isotropic and anisotropic polarizabilities of carbodiimide have been calculated from relevant tensor components for both reaction mechanisms with the help of data obtained by dft/b3lyp and mp2 methods using aug-cc-pvtz basis sets in gaseous phase as well as in pcm. | theoretical study of possible reaction mechanisms for the formation of carbodiimide in the interstellar medium (ism) and polarizabilities of carbodiimide |
we present polarimetric observations of stars in the field of the open cluster ngc 7160. the multi-wavelength ubvri polarization measurements of 21 stars that we performed indicate that some of the observed stars follow the typical wavelength dependence indicative of polarization by selective extinction in the interstellar medium, while others display multi-wavelength dependence strikingly different from nominal behavior. considering only the former stars, we obtained a value of rv = 3.01 ± 0.03 for the total-to-selective extinction ratio toward the cluster, almost identical to the nominal expected value. for the remaining stars we suggest that their wavelength dependence of polarization is most likely altered by the presence of circumstellar material. patterns in both the wavelength dependence of the degree of polarization and position angle show similarities found in the wavelength dependence of some carbon stars and pms stars. pms stars in ngc 7160 have been identified by gray & corbally and the multi-wavelength polarization obtained here suggests additional candidates. the rotation of the position vectors for a number of stars seems indicative for mixing of intrinsic and interstellar polarization components. it seems, however, that intra-cluster dust does not play a significant overall role in the polarization of these stars. the distribution of the interstellar extinction with distance as obtained from dust maps supports this finding. we also present v-band polarization measurements for 78 stars in and around the central region of cluster. the polarization ranges from 0.12% to 3.75% with a median value of 1.23%. while the polarization vectors display some scatter, an overall alignment exists, which would indicate polarization by foreground interstellar dust. using the planck 353 ghz channel we find agreement between polarization by emission and selective extinction and also that the optical polarization traces a magnetic field that is nearly parallel to the galactic plane in this region. | interstellar extinction and polarization of stars in the open cluster ngc 7160 |
starlight polarization serves one of the powerful tools to study magnetic fields in the galactic interstellar medium. heiles catalogue contains polarization information for 9286 stars, and is by far the biggest. this catalogue has been extensively used to study the magnetic fields. however, the distance parameters of the stars in this catalogue are from photometric observations, and very uncertain. we cross match heiles catalogue with gaia data release 2 (dr2), and identify 7613 stars using both angular separation and magnitude as constraints. we then obtain precise distances from gaia dr2 for these stars. for more than 90% of the stars, the relative errors of the new distances are within 20%. based on the new catalogue, we demonstrate how starlight polarization can probe galactic magnetic fields. | a revisit to the optical starlight polarization catalogue by heiles: distance update |
aluminium hydroxide (aloh) is ubiquitous in the interstellar medium. however, there are no reliable data available in the literature that can be used to interpret the observations. therefore, in this paper, we deal with the rotational rate coefficients of aloh induced by collision with helium. the potential energy surface of the aloh-he complex was computed within the coupled cluster ab initio method with single, double and perturbative triple excitation, in conjunction with the augmented-correlation consistent-polarized valence quadruple zeta gaussian basis set. using this potential energy surface, we computed rotational cross-sections for total energies ranging up to 1500 cm-1 with the close-coupling approach. by thermally averaging these cross-sections over the kinetic temperature range 5-300 k, we derived the aloh rate coefficients corresponding to the first 13 rotational levels. propensity rules have been found in favour of |δj| = 1. the data calculated in this paper have been compared with previous results and significant differences are observed. such a finding might greatly affect the calculation of the aloh abundance. in addition, this might encourage experimental work to settle the matter. | cross-sections and rate coefficients for rotational excitation of aluminium hydroxide by helium |
context. the planck catalogue of galactic cold clumps (pgcc) contains over 13 000 sources that are detected based on their cold dust signature. they are believed to consist of a mixture of quiescent, pre-stellar, and already star-forming objects within molecular clouds.aims: we extracted pgcc-type objects from cloud simulations and examined their physical and polarisation properties. the comparison with the pgcc catalogue helps to characterise the properties of this large sample of galactic objects and, conversely, provides valuable tests for numerical simulations of large volumes of the interstellar medium and the evolution towards pre-stellar cores.methods: we used several magnetohydrodynamical simulation snapshots to define the density field of our model clouds. sub-millimetre images of the surface brightness and polarised signal were obtained with radiative transfer calculations. we examined the statistics of synthetic cold clump catalogues extracted with methods similar to the pgcc. we also examined the variations of the polarisation fraction p in the clumps.results: the clump sizes, aspect ratios, and temperatures in the synthetic catalogue are similar to the pgcc. the fluxes and column densities of synthetic clumps are smaller by a factor of a few. rather than with an increased dust opacity, this could be explained by increasing the average column density of the model by a factor of two to three, close to n(h2) = 1022 cm-2. when the line of sight is parallel to the mean magnetic field, the polarisation fraction tends to increase towards the clump centres, which is contrary to observations. when the field is perpendicular, the polarisation fraction tends to decrease towards the clumps, but the drop in p is small (e.g. from p 8% to p 7%).conclusions: magnetic field geometry reduces the polarisation fraction in the simulated clumps by only δp 1% on average. the larger drop seen towards the actual pgcc clumps therefore suggests some loss of grain alignment in the dense medium, such as predicted by the radiative torque mechanism. the statistical study is not able to quantify dust opacity changes at the scale of the pgcc clumps. | synthetic observations of dust emission and polarisation of galactic cold clumps |
we present a near-infrared band-merged photometric and polarimetric catalog for the 39‧ × 69‧ fields in the northeastern part of the large magellanic cloud (lmc), which were observed using sirpol, an imaging polarimeter of the infrared survey facility. this catalog lists 1858 sources brighter than 14 mag in the h band with a polarization signal-to-noise ratio greater than three in the j, h, or ks bands. based on the relationship between the extinction and the polarization degree, we argue that the polarization mostly arises from dichroic extinctions caused by local interstellar dust in the lmc. this catalog allows us to map polarization structures to examine the global geometry of the local magnetic field, and to show a statistical analysis of the polarization of each field to understand its polarization properties. in the selected fields with coherent polarization position angles, we estimate magnetic field strengths in the range of 3-25 μg using the chandrasekhar-fermi method. this implies the presence of large-scale magnetic fields on a scale of around 100 parsecs. when comparing mid- and far-infrared dust emission maps, we confirmed that the polarization patterns are well aligned with molecular clouds around the star-forming regions. | near-infrared polarization source catalog of the northeastern regions of the large magellanic cloud |
the local interstellar magnetic field affects both the heliosphere and the surrounding cluster of interstellar clouds (clic). measurements of linearly polarized starlight provide the only test of the magnetic field threading the clic. polarization measurements of the clic magnetic field show multiple local magnetic structures, one of which is aligned with the magnetic field traced by the center of the "ribbon" of energetic neutral atoms discovered by the interstellar boundary explorer (ibex). comparisons between the bulk motion of the clic through the local standard of rest, the magnetic field direction, the geometric center of loop i, and the polarized dust bridge extending from the heliosphere toward the north polar spur direction all suggest that the clic is part of the rim region of the loop i superbubble. | connecting the interstellar magnetic field at the heliosphere to the loop i superbubble |
three-dimensional structure of the aquila rift of magnetized neutral gas is investigated by analysing h i and co line data. the projected distance on the galactic plane of the h i arch of the aquila rift is r⊥ ∼ 250 pc from the sun. the h i arch emerges at l ∼ 30°, reaches to altitudes as high as ∼500 pc above the plane at l ∼ 350°, and returns to the disc at l ∼ 270°. the extent of arch at positive latitudes is ∼1 kpc and the width is ∼100 pc. the eastern root is associated with the giant molecular cloud complex, which is the main body of the optically defined aquila rift. the h i and molecular masses of the rift are estimated to be m_{h i}∼ 1.4{×} 10^5 m_{⊙} and m_h_2∼ 3{×} 10^5 m_{⊙}. gravitational energies to lift the gases to their heights are e_{grav: h i}∼ 1.4{×} 10^{51} erg and e_{grav: h_2}∼ 0.3{×} 10^{51} erg, respectively. magnetic field is aligned along the h i arch of the rift, and the strength is measured to be b ∼ 10 μg using faraday rotation measures of extragalactic radio sources. the magnetic energy is estimated to be emag ∼ 1.2 × 1051 erg. a possible mechanism of formation of the aquila rift is proposed in terms of interstellar magnetic inflation by a sinusoidal parker instability of wavelength of ∼2.5 kpc and amplitude ∼500 pc. | three-dimensional aquila rift: magnetized h i arch anchored by molecular complex |
we present the measurement of the size and surface brightness of the expanding 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 the time of b-band maximum light) in the filters f475w, f606w, and f775w, each combined with the three polarizing filters: pol0v, pol60v, and pol120v. the two epochs' imaging reveals the time evolution of at least two major echoes. three concentric bright regions between position angles (pa, 0^{\circ} from north, counterclockwise). 80^{\circ} ~ 170^{\circ} have projected radius of 0.60" on the sky on ~277 days and expanding to 0.75" on ~416 days, corresponding to scattering materials at a foreground distance of 222\pm37 pc. another fainter but evident light echo extending over a wide range of pa has radii of 0.75" and 0.96" on ~277 and ~416 days. this corresponds to scattering material at a foreground distance of 367\pm61 pc. multiple light echoes with s/n > 2.5 reside at smaller radii on ~277 days but become less significant on ~416 days indicating a complex structure of foreground interstellar medium (ism). the light echo shows bluer color than predicted under a rayleigh scattering case. we also found the light echo brightened from v_{echo}=21.68\pm0.07 on 2014 september 5, to v_{echo}=21.05\pm0.08 on 2014 november 6, suggesting an enhancement of echoing materials at different distances projected on to the plane of the sky. | the expanding light echoes from supernova 2014j in m82 |
we study the observable properties of compressible magnetohydrodynamic (mhd) turbulence covering different turbulence regimes, based on synthetic synchrotron observations arising from 3d mhd numerical simulations. using the synchrotron emissivity and intensity, we first explore how the cosmic-ray spectral indices affect the measurements of the turbulence properties by employing normalized correlation functions. we then study how the anisotropy of the synchrotron total and polarization intensities arising from the three fundamental mhd modes varies with the viewing angle, i.e., the angle between the mean magnetic field and the line of sight. we employ the ratio of the quadrupole moment to the monopole moment (qm) for this purpose. our numerical results demonstrate that: (1) the two-point correlation function of synchrotron statistics for the arbitrary cosmic-ray spectral index is related to the special case of the magnetic field index γ = 2, in agreement with the analytical formulae provided by lazarian & pogosyan; (2) the anisotropy of the synchrotron total and polarization intensities arising from the alfvén and slow modes increases with the increase of the viewing angle, while that of fast mode remains almost unchanged with the viewing angle; and (3) the analytical formulae of the synchrotron intensities for studying turbulence can be applied to describe the statistics of the polarization intensities, and the qm can be successfully used to recover the turbulence anisotropy. this study validates the analytical approach of lazarian & pogosyan and opens up a way of studying turbulence from observations. | studying the properties of compressible magnetohydrodynamic turbulence using synchrotron fluctuation statistics |
we present the results of ubvri polarimetry of the tev γ-ray binary hess j0632+057 obtained on 2015 march 24 (jd 245 7106) and 2015 december 12 (jd 245 7369). the detected polarization values of hess j0632+057, just after periastron passage (march 24), are higher than all previously published values (pv ∼ 4.2 per cent), and the position angle (θobs ∼ 171°-172°) is also different by ∼6°-10° from previously published values. the data obtained just before the subsequent periastron passage (december 12) show a statistically lower polarization in all photometric bands (pv ∼3.9 per cent) and a different position angle θobs ∼ 167°-168°. from observations of a nearby field star, the interstellar component of the measured polarization was estimated as p_{is}v ∼ 0.65 per cent and θis ∼ 153°. this estimate was used with the previous `v'-band estimation by the `field-stars method' (p_{is}v ∼ 2 per cent and θis ∼ 165°) of yudin to identify the wavelength dependence of the intrinsic polarization in hess j0632+057. it was found that after subtraction of the interstellar component (for both pis estimates), the wavelength dependence of the intrinsic polarization in hess j0632+057 is essentially flat. we propose that the formation of an additional source of polarization or some perturbation of circumstellar material at this orbital phase can explain the changes in the level of polarization in hess j0632+057 close to periastron passage. | first multicolour polarimetry of tev γ-ray binary hess j0632+057 close to periastron passage |
polarized emission from polycyclic aromatic hydrocarbons (pahs) potentially provides a new way to test the basic physics of the alignment of ultrasmall grains. in this paper, we present a new model of polarized pah emission that takes into account the effect of pah alignment with the magnetic field. we first generate a large sample of the grain angular momentum {\boldsymbol{j}} by simulating the alignment of pahs due to resonance paramagnetic relaxation that accounts for various interaction processes. we then calculate the polarization level of the pah emission features for the different phases of the interstellar medium, including the cold neutral medium (cnm), reflection nebulae (rne), and photodissociation regions. we find that a moderate degree of pah alignment can significantly enhance the polarization degree of the pah emission compared to the previous results obtained with randomly oriented angular momentum. in particular, we find that the smallest negatively charged pahs in rne can be excited to slightly suprathermal rotation due to enhanced ion collisional excitation, resulting in an increase of the polarization with the ionization fraction. our results suggest that an rn is the most favorable environment in which to observe polarized pah emission and to test the alignment physics of nanoparticles. finally, we present an explicit relationship between the polarization level of pah emission and the degree of external alignment for the cnm and rne. the obtained relationship will be particularly useful for testing the alignment physics of pahs in future observations. | effect of alignment on polarized infrared emission from polycyclic aromatic hydrocarbons |
a photon can encode several bits of information based on an alphabet of its time of arrival, energy, and polarization. heisenberg's uncertainty principle places a limit on measuring pairs of physical properties of a particle, limiting the maximal information efficiency to <59 bits per photon in practice, and <171 bits per photon at planck energy, at a data rate of one photon per second. | interstellar communication. viii. hard limits on the number of bits per photon |
we report on over 13 yr of optical and near-ultraviolet spectropolarimetric observations of the famous luminous blue variable (lbv) p cygni. in the lives of the most massive stars, lbvs are a critical transitional phase and achieve the largest mass-loss rates of any group of stars. using spectropolarimetry, we are able to learn about the geometry of the near-circumstellar environment surrounding p cygni and gain insights into lbv mass loss. using data from the hpol and wuppe spectropolarimeters, we estimate the interstellar polarization contribution to p cygni's spectropolarimetric signal, analyze the variability of the polarization across the hα emission line, search for periodic signals in the data, and introduce a statistical method to search for preferred position angles in deviations from spherical symmetry that is novel to astronomy. our data are consistent with previous findings, showing free electron scattering off of clumps uniformly distributed around the star. this is complicated, however, by structure in the percent polarization of the hα line and a series of previously undetected periodicities. | 13 yr of p cygni spectropolarimetry: investigating mass loss through hα, periodicity, and ellipticity |
we have investigated the magneto-ionic turbulence in the interstellar medium through spatial gradients of the complex radio polarization vector in the canadian galactic plane survey (cgps). the cgps data cover 1300 square degrees, over the range 53^\circ ≤slant {\ell }≤slant 192^\circ , -3^\circ ≤slant b≤slant 5^\circ , with an extension to b=17\buildrel{\circ}\over{.} 5 in the range 101^\circ ≤slant {\ell }≤slant 116^\circ , and arcminute resolution at 1420 mhz. previous studies found a correlation between the skewness and kurtosis of the polarization gradient and the mach number of the turbulence, or assumed this correlation to deduce the mach number of an observed turbulent region. we present polarization gradient images of the entire cgps data set, and analyze the dependence of these images on angular resolution. the polarization gradients are filamentary, and the length of these filaments is largest toward the galactic anti-center, with the smallest toward the inner galaxy. this may imply that small-scale turbulence is stronger in the inner galaxy, or that we observe more distant features at low galactic longitudes. for every resolution studied, the skewness of the polarization gradient is influenced by the edges of bright polarization gradient regions, which are not related to the turbulence revealed by the polarization gradients. we also find that the skewness of the polarization gradient is sensitive to the size of the box used to calculate the skewness, but insensitive to galactic longitude, implying that the skewness only probes the number and magnitude of the inhomogeneities within the box. we conclude that the skewness and kurtosis of the polarization gradient are not ideal statistics for probing natural magneto-ionic turbulence. | polarization gradient study of interstellar medium turbulence using the canadian galactic plane survey |
using the first station of the long wavelength array (lwa1), we examine polarized pulsar emission between 25 and 88 mhz. polarized light from pulsars undergoes faraday rotation as it passes through the magnetized interstellar medium. observations from low-frequency telescopes are ideal for obtaining precise rotation measures (rms) because the effect of faraday rotation is proportional to the square of the observing wavelength. with these rms, we obtained polarized pulse profiles to see how polarization changes in the 25-88 mhz range. the rms were also used to derive values for the electron-density-weighted average galactic magnetic field along the line of sight. we present rms and polarization profiles of 15 pulsars acquired using data from lwa1. these results provide new insight into low-frequency polarization characteristics and pulsar emission heights, and complement measurements at higher frequencies. | detecting pulsar polarization below 100 mhz with the long wavelength array |
the canonical theory of star formation in a magnetized environment predicts the formation of hourglass-shaped magnetic fields during the prestellar collapse phase. in protostellar cores, recent observations reveal complex and strongly distorted magnetic fields in the inner regions that are sculpted by rotation and outflows. we conduct resistive, nonideal magnetohydrodynamic simulations of a protostellar core and employ the radiative transfer code polaris to produce synthetic polarization segment maps. a comparison of our mock-polarization maps based on the toroidal-dominated magnetic field in the outflow zone with the observed polarization vectors of sio lines in orion source i shows a reasonable agreement when the magnetic axis is tilted at an angle θ = 15° with respect to the plane of the sky and if the sio lines have a net polarization parallel to the local magnetic field. although the observed polarization is from sio lines and our synthetic maps are due to polarized dust emission, a comparison is useful and allows us to resolve the ambiguity of whether the line polarization is parallel or perpendicular to the local magnetic field direction. | synthetic polarization maps of an outflow zone from magnetohydrodynamic simulations |
a method for measuring the difference between centroids of polarized flux and total flux of an astronomical object - polaroastrometry - is proposed. the deviation of the centroid of flux corresponding to stokes parameter q or u from the centroid of total flux multiplied by dimensionless stokes parameter q or u, respectively, was used as a signal. the efficiency of the method is demonstrated on the basis of observations made in the v band by using an instrument combining features of a two-beam polarimeter with a rotating half-wave plate and a speckle interferometer. the polaroastrometric signal noise is 60-70 μas rms for a total number of accumulated photoelectrons ne of 109 from a 70-cm telescope; this corresponds to a total integration time of 500 s and an object magnitude v = 6 mag. at smaller ne, the noise increases as {≈} 1.7 arcsec/√{n_e}, while at larger ne, it remains the same owing to imperfection of the half-wave plate. for main-sequence stars that are unpolarized and polarized by interstellar dust and the mira-type variable r tri the signal was undetectable. for the mira-type variable χ cyg the polaroastrometric signal is found to be 310 ± 70 and 300 ± 70 μas for stokes q and u, respectively; for o cet these values are 490 ± 100 and 1160 ± 100 μas. the significant value of the polaroastrometric signal provides evidence of the asymmetry of the polarized flux distribution. | on-sky demonstration of optical polaroastrometry |
the next-generation balloon-borne large-aperture submillimeter telescope (blast-tng) is a submillimeter imaging polarimeter which will map the polarized thermal emission from interstellar dust, revealing magnetic field structures in nearby giant molecular clouds, external galaxies and the diffuse interstellar medium in three bands centered at 250, 350 and 500-μm (spatial resolution of 30″, 41″ and 59″). its camera contains over 2500 dual-polarization sensitive lumped element kinetic inductance detectors, which are read out using field-programmable gate array-based readout electronics. blast-tng was scheduled for a 28-day antarctic flight during the 2018/2019 summer season, but unfavorable weather conditions pushed the anticipated flight to 2019/2020. we present a summary of key results from the 2018/2019 preflight characterization of the detector and receiver. included in this summary are detector yields, estimates of in-flight sensitivity, a measurement of the optical passbands and estimates of polarization efficiency. | preflight detector characterization of blast-tng |
we report spectropolarimetric observations of the recurrent nova rs oph obtained during four nights between 2017 july and 2018 july. in the wavelength range from 5000 å to 8000 å, we find the maximum degree of linear polarization pl(obs)=2.9%±0.09 at λ≈5600 å and the position angle θ=47o.2±0o.9. we do not detect any variability of the degree of polarization and the position angle. at the time of our observations, there is no intrinsic polarization in rs oph and the observed values represent the interstellar polarization. | spectropolarimetric observations of the recurrent nova rs oph |
we present (bvri) multicolor linear polarimetric data of 73 of the brightest stars in the open cluster ngc 5662. our objective is to study the characteristics of the interstellar medium (ism) towards it and in its the environment. ngc 5662 is polarimetrically characterized by pv=2.27±0.13 and θv=89°.6±1.17. its polarization effciency is much higher than the normal effciency of ism. the observed visual polarization in ngc 5662 is caused at least by three components of dust at ≍200 pc, 500 pc and 900 pc from the sun. these have different polarimetric characteristics and the layer located at 500 pc has a variable density. the absorption presents a different behavior to polarization as the distance increases. a few of the observed stars present evidences of intrinsic polarization. | optical polarization study in the centaurus region: ngc 56621 |
we present the results of our ubvri polarimetric observations of a dozen stars located close to the well-studied bok globule barnard 5 (b5), with several of the stars being seen through its outer layers (with av up to ∼3 mag). using recent astrometric, spectroscopic and photometric surveys, we estimate the distance, spectral class and visual extinction for the observed stars and find that the results are in a good agreement with the available 3d extinction maps. we use a two-layer dust model of interstellar polarization towards b5, in which the layer closer to us is an extension of the taurus cloud complex, and the farther one (including b5 and its halo) is related to the perseus cloud complex (d ≈ 280-350 pc). using spectral, photometric and polarimetric data on about 30 additional stars, we estimate the parameters of the former layer as λmax ≈ 0.56 μm, pmax ≈ 0.7 per cent, θ ≈ 50°, av ≈ 0.7 mag, and show that the observed wavelength dependence of the position angle for the stars observed generally agrees with the two-layer model. we find that when the stars are seen through the globule layers with av = 2-3 mag, λmax ≈ 0.6-0.8 μm, which differs significantly from the λmax = 0.52-0.58 μm obtained by us for the diffuse interstellar medium in the direction of b5. we discuss the correlation of λmax with the optical thickness into the globule as well as other correlations of the extinction and polarization parameters. | dust in the outer layers of the barnard 5 globule |
context. the h2s molecule has been detected in several regions of the interstellar medium (ism). the use of non-lte models requires knowledge of accurate collisional rate coefficients of the molecules detected with the most common collider in the ism.aims: the main goal of this work is to study the collision of h2s with he.methods: a grid of ab initio energies was computed at the coupled cluster level of theory including single, double, and perturbative triple excitations (ccsd(t)) and using the augmented correlation consistent polarized quadruple zeta (aug-cc-pvqz) basis set supplemented by a set of mid-bond functions. these energies were fitted to an analytical function, which was employed to study the dynamics of the system. close coupling calculations were performed to study the collision of h2s with he.results: the rate coefficients determined from the close coupling calculation were compared with those of the collision with h2o+he, and large differences were found. finally, the rate coefficients for the lower rotational de-excitation of h2s by collision with he are reported. | rotational relaxation of h2s by collision with he |
the characteristics of radiative gravitational modes in non-thermal magnetized dusty plasma with charge fluctuation and the polarization force of dust particles are investigated. the electron species are assumed to be radiative and the ions are assumed to be non-thermal. a normal mode analysis is applied to derive the general dispersion relation for radiative magnetized self-gravitating dusty plasma. modified radiative condensation and self-gravitational instability criteria for both perpendicular and parallel modes of propagation are obtained. analytically, it is found that the presence of a non-thermal ion population significantly modified the usual radiative condensation instability criterion, and damped the growth rate of the radiative mode. the obtained analytical results are further discussed in the numerical result section. we investigate the fact that the non-thermal ion population acts as a stabilizing source for radiative condensation instability in magnetized self-gravitating dusty plasma fluid, including the dust polarization force and charge fluctuation. the thermal conductivity with non-thermal ion distribution quickly moves the system towards stability. the implications of the results in the region of the interstellar medium (ism) are discussed. | analysis of radiative gravitational modes in magnetized dusty plasma with non-thermal ion distribution |
the polarized instrument for long-wavelength observation of the tenuous interstellar medium (pilot) is a balloon-borne experiment that aims to measure the polarized emission of thermal dust at a wavelength of 240 µm (1.2 thz). a first pilot flight of the experiment took place from timmins, ontario, canada, in september 2015 and a second flight took place from alice springs, australia in april 2017. in this paper, we present the inflight performance of the instrument. here we concentrate on the instrument performance as measured during the second flight, but refer to the performance observed during the first flight, if it was significantly different. we present a short description of the instrument and the flights. we measure the time constants of the detectors using the decay of the observed signal during flight following high energy particle impacts (glitches) and switching off the instrument's internal calibration source. we use these time constants to deconvolve the timelines and analyze the optical quality of the instrument as measured on planets. we then analyze the structure and polarization of the instrumental background. we measure the detector response flat field and its time variations using the signal from the residual atmosphere and from the internal calibration source. finally, we analyze the spectral and temporal properties of the detector noise. the inflight performance is found to be satisfactory and globally in line with expectations from ground calibrations. we conclude by assessing the expected inflight sensitivity of the instrument in light of the measured inflight performance. | inflight performance of the pilot balloon-borne experiment |
the next generation balloon-borne large aperture submillimeter telescope (blast-tng) is a submillimeter mapping experiment planned for a 28 day long-duration balloon (ldb) flight from mcmurdo station, antarctica during the 2018-2019 season. blast-tng will detect submillimeter polarized interstellar dust emission, tracing magnetic fields in galactic molecular clouds. blast-tng will be the first polarimeter with the sensitivity and resolution to probe the ∼0.1 parsec-scale features that are critical to understanding the origin of structures in the interstellar medium. with three detector arrays operating at 250, 350, and 500 μm (1200, 857, and 600 ghz), blast-tng will obtain diffraction-limited resolution at each waveband of 30, 41, and 59 arcseconds respectively. to achieve the submillimeter resolution necessary for its science goals, the blast-tng telescope features a 2.5 m aperture carbon fiber composite primary mirror, one of the largest mirrors flown on a balloon platform. successful performance of such a large telescope on a balloon-borne platform requires stiff, lightweight optical components and mounting structures. through a combination of optical metrology and finite element modeling of thermal and mechanical stresses on both the telescope optics and mounting structures, we expect diffractionlimited resolution at all our wavebands. we expect pointing errors due to deformation of the telescope mount to be negligible. we have developed a detailed thermal model of the sun shielding, gondola, and optical components to optimize our observing strategy and increase the stability of the telescope over the flight. we present preflight characterization of the telescope and its platform. | design and characterization of a balloon-borne diffraction-limited submillimeter telescope platform for blast-tng |
we report the detection of a circular polarization signature in the stokes v profile of a 25 ghz class i ch3oh maser toward the high-mass star-forming region omc-1. such a feature usually constitutes a detection of the zeeman effect. if due to a magnetic field in omc-1, this would represent the first detection and discovery of the zeeman effect in the 25 ghz class i ch3oh maser. the feature in stokes v is detected in two observations with different angular resolutions taken eight years apart with the very large array; for our 2009 d-configuration observations, the fitted value for z ${b}_{\mathrm{los}}$ is 152 ± 12 hz, where z is the zeeman splitting factor and ${b}_{\mathrm{los}}$ is the line-of-sight magnetic field. for our 2017 c-configuration observations, the fitted value for z ${b}_{\mathrm{los}}$ = 149 ± 19 hz, likely for the same maser spot. these correspond to ${b}_{\mathrm{los}}$ in the range 171-214 mg, depending on which hyperfine transition is responsible for the maser line. while these ${b}_{\mathrm{los}}$ values are high, they are not implausible. if the magnetic field increases in proportion to the molecular hydrogen density in shocked regions, then our detected fields predict values for the pre-shock magnetic field that are in agreement with observations. with ${b}_{\mathrm{los}}$ = 171-214 mg, the magnetic energy in the post-shocked regions where these 25 ghz class i ch3oh masers occur would dominate over the kinetic energy density and be at least of the order of the pressure in the shock, implying that the magnetic field would exert significant influence over the dynamics of these regions. | a curious case of circular polarization in the 25 ghz methanol maser line toward omc-1 |
polarimetry provides an avenue for probing the geometry and physical mechanisms producing optical radiation in many astrophysical objects, including stellar binary systems. we present the results of multiwavelength (bvr) polarimetric studies of a sample of historical black hole x-ray binaries, observed during their outbursts or in the quiescent (or near-quiescent) state. we surveyed both long- and short-period systems, located at different galactic latitudes. we performed careful analysis of the interstellar polarization in the direction on the sources to reliably estimate the intrinsic source polarization. intrinsic polarization was found to be small (<0.2 per cent) in sources observed in bright soft states (maxi j0637-430 and 4u 1957+115). it was found to be significant in the rising hard state of maxi j1820+070 at the level of ~0.5 per cent and negligible in the decaying hard state and during its failed outbursts, while swift j1357.2-0933 showed its absence in the rising hard state. three (xte j1118+480 , v4641 sgr , v404 cyg) sources observed during quiescence show no evidence of significant intrinsic polarization, while maxi j1820+070 is the only black hole x-ray binary which showed substantial (>5 per cent) intrinsic quiescent-state polarization with a blue spectrum. the absence of intrinsic polarization at the optical wavelengths puts constraints on the potential contribution of non-stellar (jet, hot flow, accretion disc) components to the total spectra of black hole x-ray binaries. | optical polarization signatures of black hole x-ray binaries |
the polarized instrument for long-wavelength observation of the tenuous interstellar medium ( pilot) is a balloon-borne astronomy experiment designed to study the linear polarization of thermal dust emission in two photometric bands centred at wavelengths 240 μm (1.2 thz) and 550 μm (545 ghz), with an angular resolution of a few arcminutes. several end-to-end tests of the instrument were performed on the ground between 2012 and 2014, in order to prepare for the first scientific flight of the experiment that took place in september 2015 from timmins, ontario, canada. this paper presents the results of those tests, focussing on an evaluation of the instrument's optical performance. we quantify image quality across the extent of the focal plane, and describe the tests that we conducted to determine the focal plane geometry, the optimal focus position, and sources of internal straylight. we present estimates of the detector response, obtained using an internal calibration source, and estimates of the background intensity and background polarization. | the optical performance of the pilot instrument from ground end-to-end tests |
we investigate the magnetic field in an intermediate-velocity filament for which the hα intensity in the wham survey correlates with excess faraday rotation of extragalactic radio sources over the length of the filament from b ≈ 20° to b ≈ 55°. the density-weighted mean magnetic field is 2.8 +/- 0.8 μ {{g}}, derived from rotation measures and an empirical relation between hα emission measure and dispersion measure from berkhuijsen et al. in view of the uncertainties in the derived magnetic field strength, we propose an alternative use of the available data, rotation measure, and emission measure, to derive a lower limit to the alfvén speed, weighted by electron density {n}e3/2. we find lower limits to the alfvén speed that are comparable to or larger than the sound speed in a {10}4 {{k}} plasma, and conclude that the magnetic field is dynamically important. we discuss the role of intermediate-velocity gas as a locus of faraday rotation in the interstellar medium, and propose that this lower limit to the alfvén speed may also be applicable to faraday rotation by galaxy clusters. | magnetic field strength in an intermediate-velocity ionized filament in the first galactic quadrant |
this paper outlines the life and scientific legacy of professor nikolai vasil'evich voshchinnikov (1951-2017) who had many coauthors and friends among the jqsrt community. | nikolai voshchinnikov: from light scattering by spheroids to large interstellar polarisation survey |
in this report accurate microwave (mw) stark effect measurements have been performed to obtain precise dipole moment and precise zero-field microwave frequencies of singly deuterated quasi symmetric ch3od methanol species. this species is of significance to radio astronomers to study the hydrogen-deuterium exchange in interstellar space in cold clouds to study basic chemical processes in other worlds. the telescope facilities at atacama large millimeter array (alma), the facilities at institute for radio astronomy in the millimeter range (iram), and the nasa's floating stratospheric observatory for infrared astronomy (sofia), etc. routinely gauge the sky in the millimeter-wave (mmw) to infrared spectral (ir) regions (drozdovskaya et al., 2019; faure et al., 2015; neill et al., 2013; peng et al., 2012; taquet et al., 2011; whittet et al., 2011; parise et al., 2004, 2002, 2002, 2002, 2003, 2003, 2003; johns et al., 1998; charnley et al., 1997). the laboratory back up of the millimeter region of ch3od is of importance to astronomers for such studies as the determination of column densities and the deuteration process. in the present study, the mmw spectra previously recorded with unprecedented accuracy (mukhopadhyay and bo duan, 2000; mukhopadhyay et al., 1997; wang et al., 2001; mukhopadhyay, 1999; mukhopadhyay and bo duan, 2000; walsh et al., 2000) are presented at atlas form with minute details to aid such detection. the dipole results also should aid to find the strength of individual lines. in the ir region, the off-axis deuteration pushes the of the absorption bands of the molecule to the lower region, particularly the increased asymmetry of the molecule spreads the cod- bending and csbnd o stretching bands in a wide frequency range making them more accessible to strong co2 lasers resulting in preferential population transfer to excited states of the molecule. thus making this species a prolific source of coherent laser emission radiation in the scarce fir region (landsberg, 1980; gastaud et al., 1980; kon et al., 1984; pereira et al., 1994; telles et al., 1999; lundsgaard et al., 1968; dijkerman and ruitenberg, 1969; amano, 1981; lees et al., 2013; petersen, 2020). in this work, a large number of co2 laser pump/fir laser systems have been identified with specific quantum numbers and predict many new lines. schematic diagrams have been presented for the emission and prediction process along with important experimental diagnostic information about relative polarization. the assignments will aid the optimization of laser output and the predictions will enable new coherent light sources in the fir region. | far infrared laser, millimeter-wave and microwave microwave stark, millimeter wave, far infrared, infrared and far infrared laser spectroscopy of methanol-od (ch3 od): precise dipole moment and millimeter-wave atlas of astrophysical significance |
gravitational waves (gws, from binary merger) interacting with super-strong magnetic fields of the neutron star (in the same binary system), would lead to perturbed electromagnetic waves [emws, in the same frequencies of these gws, partially in the ultra-low-frequency (ulf) band for the emws]. such perturbed ulf-emws are not only the signals, but also a new type of special em counterparts of the gws. here, generation of the perturbed ulf-emws is investigated for the first time, and the strengths of their magnetic components are estimated to be around 10^{-12}tesla to 10^{-17}tesla (in fisco) at the earth for various cases [not including the influence of interstellar medium (ism)].the components with higher frequencies of the ulf-emws (e.g., especially produced by the gws of the post-merger stage) above 1.8khz (typical plasma frequency around solar system in the milky way), could propagate through the ism from the source until the earth, and the perturbed ulf-emws will be reprocessed before they arrived at the earth due to the ism. also, the waveforms of the perturbed ulf-emws will be modified into shapes different but related to the waveforms of the gws, by the amplification process during the binary mergers which could amplify the magnetic fields into 10^{12}tesla or even higher. specific connection relationships between the polarizations of the perturbed ulf-emws and the polarizations (tensorial and possible nontensorial) of the gws of binary mergers, are also addressed here. characteristic properties of the perturbed ulf-emws (which would bring us some different new information of fundamental properties of the gravity and universe) will be very helpful for extracting the signals from background noise for possible observations in the future. | ultra-low-frequency electromagnetic waves as signals and special counterparts of gravitational waves (from binary mergers) having tensorial and possible nontensorial polarizations |
we examine the evolution and emission of the supernova remnant (snr) ctb 109 using 3d magnetohydrodynamics simulations. the snr evolves in a medium divided by a plane interface into two media with different densities and pressure equilibrium. our results reveal that a remnant with the characteristics of ctb 109 is formed provided the supernova (sn) explosion takes place in the less dense medium and also if the interstellar magnetic field (ismf) is almost uniform. finally, we conclude that the quasi-parallel mechanism can explain the brightness synchrotron emission and the position angle of the projected ismf reported in previous works. | 3d mhd simulations of the supernova remnant ctb 109 |
the composition of the relativistic plasma produced in active galactic nuclei and ejected via powerful jets into the interstellar/intergalactic medium is still a major unsettled issue. it might be a positron-electron plasma in case the plasma was created by pair production in the intense photon fields near accreting super-massive black holes. alternatively, it might be an electron-proton plasma in case magnetic fields lift and accelerate the thermal gas of accretion discs into relativistic jets as the recent detection of γ-rays from blazars indicates. despite various attempts to unambiguously establish the composition of the relativistic jets, this remains a major unknown. here, we propose a possible way to settle the question via sensitive measurements of circular polarization (cp) in the radio emission of the hot spots of bright radio galaxies like cygnus a. the cp of synchrotron emission is determined by the circular motions of the radiating relativistic leptons. in case of charge symmetric energy spectra of an electron-positron plasma, it should be exactly zero. in case of an electron-proton plasma the electrons imprint their gyration onto the cp and we expect the hot spots of cygnus a to exhibit a fractional cp at a level of 10-4(ν/ghz)-1/2, which is challenging to measure, but not completely unfeasible. | determining the composition of radio plasma via circular polarization: the prospects of the cygnus a hot spots |
starlight polarization serves one of the powerful tools to study magnetic fields in the galactic interstellar medium. heiles catalogue contains polarization information for 9286 stars and is by far the biggest. this catalogue has been extensively used to study magnetic fields. however, the distance parameters of the stars in this catalogue are from photometric observations and very uncertain. we cross match heiles catalogue with gaia data release 2 (dr2), and identify 7613 stars using both angular separation and magnitude as constraints. we then obtain precise distances from gaia dr2 for these stars. for more than 90\% of the stars, the relative errors of the new distances are within 20\%. based on the new catalogue, we demonstrate how starlight polarization can probe galactic magnetic fields. | a revisit to the optical starlight polarization catalogue by heiles: distance update |
for more than 5000 stars with accurate parallaxes from the hipparcos and gaia dr1 tycho-gaia astrometric solution (tgas), tycho-2 photometry, interstellar polarization from eight catalogues and interstellar extinction from eight 3d maps the largest up to date comparison of the polarization and extinction is provided. the direct comparison of the data from these catalogues for common stars shows that the data are free from considerable systematic errors and can be used together. the extinction maps give different estimations of the extinction and of the polarization efficiency as the polarization divided into extinction p/av as well as of the percentage of the stars with the polarization efficiency higher than the limit of serkowski p/av>0.03. using the hipparcos parallaxes we found about 200 stars (4%, mainly ob stars) drop higher than the limit when we use any extinction map. however, the usage of more accurate tgas parallaxes decreases them to only 17 stars (0.3%). the polarization and extinction are negligible inside the local bubble within 80 pc from the sun. in the vast bubble's shell at the distances 80-118 pc from the sun the polarization and extinction rapidly grow with the distance whereas the position angle of the polarization is oriented predominantly along the shell of the bubble. outside the bubble the polarization and extinction grow with the distance slowly. in addition, within a radius of 80-300 pc of the sun a disc of some filamentary dust clouds (including well-known markkanen cloud) is observed as in the polarization map as in the reddening one by schlegel et al. in this disc the position angle of polarization is preferably oriented along the plane of the disk. for the regions further than 300 pc the position angle of polarization is preferably oriented along the local spiral arm, i.e. y coordinate axis. the polarization and its efficiency is lower in the dust layer in the gould belt than in the equatorial dust layer. it may means different properties of dust in these two layers. | spatial variations of the interstellar polarization and interstellar extinction |
polarimetry of starlight observed through dust and observations of polarized thermal emission from this dust are some of the few ways to observe the presence of magnetic fields in the interstellar medium. not only is the strength and overall geometry of the magnetic field important in physical processes in the ism, the turbulent component to the field also plays an important role. turbulence in the field is directly tied to turbulence in the gas and consequently to the dynamics of the gas, on both large and small scales. using interstellar polarization to measure parameters relating to turbulence in the magnetic field is necessarily an indirect process. in this chapter we explore several techniques and results for using polarimetry to explore the turbulent component of the magnetic field in the galaxy. | interstellar polarization and magnetic turbulence |
gigaparsec scale alignments of the quasar optical polarization vectors have been proven to be robust against a scenario of contamination by the galactic interstellar medium (ism). this claim has been established by means of optical polarization measurements of the starlight surrounding the lines of sight of the 355 quasars for which reliable optical polarization measurements are available. in this paper, we take advantage of the full-sky and high quality polarization data released by the \textit{planck} satellite to provide an independent, complementary, and up-to-date estimation of the contamination level of the quasar optical polarization data by the galactic dust. our analysis reveals signatures of galactic dust contamination at the two sigma level for about 30 per cent of the quasar optical polarization data sample. the remaining 70 per cent of the lines of sight do not show galactic dust contamination above the two sigma level, suggesting low to negligible contamination of the quasar optical polarization signal. we further found arguments suggesting that galactic thermal dust cannot fully account for the reported quasar optical polarization alignments. based on the measurements of the ratio of the polarized intensity of the dust in the submillimeter to the degree of linear polarization of the quasar in the optical, we provide a new and independent quality criteria to apply to the quasar optical polarization sample. we argue that, unless correction is applied, such a criterion should be imposed on the data for future investigations in the framework of the cosmological-scale correlations of quasar optical polarization vector orientations that still could compete with the isotropic principle of the cosmological paradigm. | cosmological-scale coherent orientations of quasar optical polarization vectors in the $planck$ era investigating the galactic dust contamination scenario |
the self-gravitational jeans instability has been studied in dusty plasma containing significant background of neutral pressure and recombination of ions and electrons on the dust surface. the full dynamics of charged dust grains, ions and neutral species are employed considering the electrons as maxwellian. we have derived the general dispersion relation for collisional dusty plasma with ionization, recombination and polarization force. the general dispersion relation describes the effects of considered parameters which are solved in different dusty plasma situations. further, the dispersion relation is solved numerically. the present work is applicable to understand the structure formation of interstellar molecular clouds in astrophysical plasma. | jeans instability of inhomogeneous dusty plasma with polarization force, ionization and recombination |
we present the results of near-infrared (nir) linear imaging polarimetry in the j, h, and ksbands of the low-mass star cluster-forming region in the circinus molecular cloud complex. using aperture polarimetry of point-like sources, positive detection of 314, 421, and 164 sources in the j, h, and ksbands, respectively, was determined from among 749 sources whose photometric magnitudes were measured. for the source classification of the 133 point-like sources whose polarization could be measured in all 3 bands, a color-color diagram was used. while most of the nir polarizations of point-like sources are well-aligned and can be explained by dichroic polarization produced by aligned interstellar dust grains in the cloud, 123 highly polarized sources have also been identified with some criteria. the projected direction on the sky of the magnetic field in the cir-mms region is indicated by the mean polarization position angles (70°) of the point-like sources in the observed region, corresponding to approximately 1.6× 1.6 pc2. in addition, the magnetic field direction is compared with the outflow orientations associated with infrared astronomy satellite sources, in which two sources were found to be aligned with each other and one source was not. we also show prominent polarization nebulosities over the cir-mms region for the first time. our polarization data have revealed one clear infrared reflection nebula (irn) and several candidate irne in the cir-mms field. in addition, the illuminating sources of the irne are identified with near- and mid-infrared sources. | first near-infrared imaging polarimetry of young stellar objects in the circinus molecular cloud |
starlight linearly polarized by aligned interstellar dust grains provides the necessary data for tracing the structure of the very local interstellar magnetic field (ismf). two methods have been developed to recover the ismf direction from polarized starlight, using data from an ongoing polarization survey. both methods rely on the probability distribution function for polarized light. method 1 calculates the ismf direction from polarization position angles regardless of the data accuracy, while method 2 relies on high-probability data points. the ismf direction bibex recovered by method 1 corresponds to the closest ismf to the heliosphere, traced by the center of the ibex ribbon arc. method 2 reveals a new direction for the more distant ismf, b new, toward l=41.1° ± 4.1° and b= 25.8° ± 3.0°, which differs by 30.4° ± 5.6° from the ibex ismf direction. polarizations of filament stars that are located within 25° of a pole of bnew, where background polarizations would be minimal, show the highest statistical probabilities of tracing the filament ismf. the ibex ismf direction orders the kinematics of interstellar clouds within 15 pc, and b new must therefore dominate beyond 15 pc. these new data are consistent with the location of the sun in the rim of an expanding superbubble shell associated with the evolved loop i superbubble. | following the interstellar magnetic field from the heliosphere into space with polarized starlight |
we present h-band (1.6 μm) scattered light observations of the transitional disk rx j1615.3-3255, located in the 1 myr old lupus association. from a polarized intensity image, taken with the hiciao instrument of the subaru telescope, we deduce the position angle and the inclination angle of the disk. the disk is found to extend out to 68 ± 12 au in scattered light and no clear structure is observed. our inner working angle of 24 au does not allow us to detect a central decrease in intensity similar to that seen at 30 au in the 880 μm continuum observations. we compare the observations with multiple disk models based on the spectral energy distribution (sed) and submm interferometry and find that an inner rim of the outer disk at 30 au containing small silicate grains produces a polarized intensity signal which is an order of magnitude larger than observed. we show that a model in which the small dust grains extend smoothly into the cavity found for large grains is closer to the actual h-band observations. a comparison of models with different dust size distributions suggests that the dust in the disk might have undergone significant processing compared to the interstellar medium. | radial decoupling of small and large dust grains in the transitional disk rx j1615.3-3255 |
we analyse 45 spectropolarimetric observations of the eclipsing, interacting binary star v356 sgr, obtained over a period of ∼21 yr, to characterize the geometry of the system's circumstellar material. after removing interstellar polarization from these data, we find that the system exhibits a large intrinsic polarization signature arising from electron scattering. in addition, the lack of repeatable eclipses in the polarization phase curves indicates the presence of a substantial pool of scatterers not occulted by either star. we suggest that these scatterers form either a circumbinary disc coplanar with the gainer's accretion disc or an elongated structure perpendicular to the orbital plane of v356 sgr, possibly formed by bipolar outflows. we also observe small-scale, cycle-to-cycle variations in the magnitude of intrinsic polarization at individual phases, which we interpret as evidence of variability in the amount of scattering material present within and around the system. this may indicate a mass-transfer or mass-loss rate that varies on the time-scale of the system's orbital period. finally, we compare the basic polarimetric properties of v356 sgr with those of the well-studied β lyr system; the significant differences observed between the two systems suggest diversity in the basic circumstellar geometry of roche lobe overflow systems. | the complex circumstellar and circumbinary environment of v356 sgr |
much of the information about the magnetic field in the milky way and other galaxies comes from measurements which are path integrals, such as faraday rotation and the polarization of synchrotron radiation of cosmic ray electrons. the measurement made at the radio telescope results from contributions of volume elements along a long line of sight (los). a magnetic field measurement at a given spatial location is of much more physical significance. in this paper, i point out that h ii regions fortuitously offer such a "point" measurement, albeit of one component of the magnetic field, and averaged over the sightline through the h ii region. however, the los through an h ii region is much smaller (e.g., 30-50 pc) than one through the entire galactic disk, and thus constitutes a "pseudo-local" measurement. i use published h ii region faraday rotation measurements to provide a new constraint on the magnitude of magnetohydrodynamic turbulence in the galaxy. | a method for a pseudo-local measurement of the galactic magnetic field |
massive young stars dynamically modify their surroundings, altering their stellar nurseries and the gas that exists between stars. with my research, i assess the modification of the galactic magnetic field within hii regions and stellar bubbles associated with ob stars. because hii regions are plasmas, magnetic fields should be important to the dynamics of the region. understanding how the magnetic field is modified in these structures is critical for inputs to simulations and for assessing stellar feedback. to obtain information on the properties of the magnetic field, i measure the faraday rotation of linearly polarized radio waves that pass through the plasma of the hii region. in this thesis, i present results of faraday rotation studies of two galactic hii regions. the first is the rosette nebula (l = 206 deg, b = -1.2 deg), and the second is ic 1805 (l = 135 deg, b = 0.9 deg), which is associated with the w4 superbubble. i measure positive rotation measure (rm) values in excess of +40 to +1200 rad m-2 due to the shell of the rosette nebula and a background rm of +147 rad m-2 due to the general interstellar medium in this area of the galactic plane. in the area of ic 1805, i measure negative rm values between +600 and -800 rad m-2 due to the hii region. the sign of the rm across each hii region is consistent with the expected polarity of the large-scale galactic magnetic field that follows the perseus spiral arm in the clockwise direction, as suggested by van eck et al. (2011, apj, 728, 14). i find that the rosette nebula and ic 1805 constitute a ``faraday rotation anomaly'', or a region of increased rm relative to the general galactic background value. although the rm observed on lines of sight through the region vary substantially, the |rm| due to the nebula is commonly 100-1000 rad m-2. in spite of this, the observed rms are not as large as simple, analytic models of magnetic field amplification in hii regions (such as by magnetic flux conservation in a swept-up shell) might indicate. this suggests that the galactic field is not increased by a substantial factor within the ionized gas in an hii region. finally, these results show intriguing indications that some of the largest values of |rm| occur for lines of sight that pass outside the fully ionized shell of the ic 1805 hii region, but pass through the photodissociation region (pdr) associated with ic 1805. | a study of magnetic fields in h ii regions using faraday rotation |
polarization is an under-exploited technique in the investigation of exoplanet atmospheres. a polarization detection, particularly if extended over a broad spectral range, will set valuable constraints on the gas and clouds in an exoplanet atmosphere that are impossible through brightness-only observations. in this presentation, i will describe simulations that show that the polarization of a spatially unresolved exoplanet may be detected by cross-correlating high-dispersion linear polarization and brightness spectra of the planet-star system. in this approach, the doppler shift of the planet-reflected starlight facilitates the separation of the signal from other polarization sources, including the star, the interstellar medium and the terrestrial atmosphere. i will elaborate on the case of close-in giant exoplanets with non-uniform cloud coverage, in which cases the hemispheres east and west of the substellar point will produce different polarizations. the simulations show that high-dispersion spectropolarimetry can rule out some of the proposed cloud scenarios and, in particular, set additional constraints on the cloud particles' optical properties. | mapping exoplanet clouds with high-dispersion spectro-polarimetry |
we present results taken from a study aiming at detecting the emission from relativistic particles jets in neutron star-low mass x-ray binaries using optical polarimetric observations. first, we focus on a polarimetric study performed on the persistent lmxb 4u 0614+091. once corrected for interstellar effects, we measured an intrinsic linear polarization in the r-band of ∼ 3 % at a 3 σ confidence level. this is in-line with the observation of an infrared excess in the spectral energy distribution (sed) of the source, reported in a previous work, which the authors linked to the optically thin synchrotron emission of a jet. we then present a study performed on the transitional millisecond pulsar psr j1023+0038 during quiescence. we measured a linear polarization of 1.09 ± 0.27 % and 0.90 ± 0.17 % in the v and r bands, respectively. the phase-resolved polarimetric curve of the source in the r-band reveals a hint of a sinusoidal modulation at the source orbital period. the nir -optical sed of the system did not suggest the presence of a jet. we conclude that the optical linear polarization observed for psr j1023+0038 is possibly due to thomson scattering with electrons in the disc, as also suggested by the hint of the modulation of the r-band linear polarization at the system orbital period. | searching for jet emission in lmxbs: a polarimetric view |
starlight polarization provides insight into the physical mechanisms in and around the source as well as its geometry, whether or not the source is resolved. in this talk we will review mechanisms that polarize light in stellar envelopes. the observations and modeling can be used to probe the physics of the circumstellar environment as well as its relation to the ambient interstellar environment. | circumstellar polarimetry |
polarization is a potentially powerful, but underutilized, tool for understanding interstellar, circumstellar environments. to accurately interpret dust-induced polarization, in terms of magnetic fields and other environmental parameters, a quantitative understanding of the alignment of the dust grains is, however, required. significant progress has been made recently in clarifying the physics of grain alignment, such that we now know that radiative processes is the main driver. one remaining open issue is the role of grain mineralogy on the alignment, specifically whether carbonaceous grains can be aligned. we have acquired sofia/hawc+ polarimetry of the carbon rich envelope of the agb star irc+10216 to probe this issue. strong, systematic far-infrared polarization is seen in the envelope. we will discuss these data, their interpretation and their implication on the physics of grain alignment and interstellar, and circumstellar, polarimetry. | sofia/hawc+ polarization in the envelope of irc+10216 |
magnetic fields and turbulent flows pervade the interstellar medium on all scales. the magnetic turbulence that emerges on the large scales cascades towards the small scales where it influences molecular cloud structure, and star formation within the densest and coldest clumps of the clouds. active star formation results in supernovae, and the supernova-driven turbulence takes part in the galactic dynamo process leading to the inverse cascade of turbulent energy. such a process is one example of self-organisatory processes in the interstellar medium where order arises from chaos. supernovae also induce and influence other important processes in the galactic disks, and this thesis examines some of them. differentially rotating disk systems, such as galaxies, are prone to magnetorotational instability, where weak magnetic fields destabilise the otherwise hydrodynamically stable disk system, and lead to angular momentum transport outwards. however, magnetorotational instability can be quenched or even damped by another source of turbulence such as supernovae. as both magnetorotational instability and supernovae are capable of producing dynamo effects, the galactic large-scale magnetic fields are proposed to arise as an interplay of these two effects. in addition, supernovae are observed to be able to generate and sustain large-scale flows in galaxies through the anisotropic kinetic alpha effect. thermodynamical effects have a significant influence on the properties of turbulence. due to baroclinicity, the supernova-driven turbulence is highly vortical in nature. these types of flows produce a narrow, non-gaussian velocity distribution with extended wings and an exponential magnetic field distribution. such effects should be taken into account when interstellar turbulence is parametrized in the form of initial conditions and forcing functions for the purpose of making smaller scale models of molecular cloud formation. the gaussianity of the magnetic field fluctuations is a common assumption, for example, when fitting magnetic field models to explain large-scale polarization maps of the interstellar dust, and our results suggest that such assumptions should require more examination. to study these phenomena, a combination of numerical approaches and observational methods are needed. exploring physics of turbulence requires the tools of high-performance computing and precise, high-order numerical schemes. because of the rapidly increasing demands of computation, novel approaches have to be investigated. to improve computational efficiency this thesis shows how the sixth-order finite difference method can be accelerated with the help of graphics processing units. the properties of the interstellar medium can be examined best by the emission of atomic/molecular gas and by the emission, absorption and scattering of interstellar dust. looking at small-scale phenomena, molecular line emission from cold prestellar cores is explored. more large-scale effects are examined with the help of polarized dust emission, by combining radiative transfer calculations with the results of a supernova-driven model of the interstellar medium, including a realistic multiphase structure and dynamo-generated small- and large-scale magnetic fields. this thesis contains seven papers. of these, three papers examine the processes driving turbulence in differentially rotating disks via numerical modelling, while one paper looks into how graphics processing units can accelerate such calculations. observationally, two papers study cold cores and early stages of star formation with the help of radio telescopes, and one paper examines how supernova-driven turbulence is reflected in the large-scale emission of diffuse interstellar dust. | magnetic phenomena of the interstellar medium in theory and observation |
the motion of diamagnetic dust particles in interstellar magnetic fields is studied numerically with several different sets of parameters. two types of behaviour are observed, depending on the value of the critical number r, which is a function of the grain inertia, the magnetic susceptibility of the material and of the strength of rotation braking. if r ≤ 10, the grain ends up in a static state and perfectly aligned with the magnetic field, after a few braking times. if not, it goes on precessing and nutating about the field vector for a much longer time. usual parameters are such that the first situation can hardly be observed. fortunately, in the second and more likely situation, there remains a persistent partial alignment that is far from negligible, although it decreases as the field decreases and as r increases. the solution of the complete equations of motion of grains in a field helps understanding the details of this behaviour. one particular case of an ellipsoidal forsterite silicate grain is studied in detail and shown to polarize light in agreement with astronomical measurements of absolute polarization in the infrared. phonons are shown to contribute to the progressive flattening of extinction and polarization towards long wavelengths. the measured dielectric properties of forsterite qualitatively fit the serkowski peak in the visible. | on interstellar light polarization by diamagnetic silicate and carbon dust in the infrared |
hawc+, a second-generation sofia instrument designed to map far-infrared intensity and polarization, was commissioned in late 2016 and made first science observations in sofia cycles 4 and 5. we describe basic characteristics of the instrument, report on the commissioning flights and data analysis pipeline, and show some example science products resulting from guaranteed-time observations (gto). hawc+ and sofia provide unique access to the far-infrared (50 - 250 micron) spectral range for polarimetry. far-ir polarization arises from dust grains aligned with respect to the magnetic field, as well as synchrotron radiation, and the gto program focuses primarily on the magnetic field structure of nearby molecular clouds and the galactic center, and the physical characteristics of dust. | first results on interstellar magnetic fields from the hawc+ instrument for sofia |
the interstellar medium is suffused with magnetic fields, which inform the shape of structures in the diffuse gas. recent high-dynamic range observations of galactic neutral hydrogen, combined with novel data analysis techniques, have revealed a deep link between the morphology of neutral gas and the ambient magnetic field. at the same time, an observational revolution is underway in low-frequency radio polarimetry, driven in part by the need to characterize foregrounds to the cosmological 21-cm signal. a new generation of experiments, capable of high angular and faraday depth resolution, are revealing complex filamentary structures in diffuse polarization. the relationship between filamentary structures observed in radio-polarimetric data and those observed in atomic hydrogen is not yet well understood. multiwavelength observations will enable new insights into the magnetic interstellar medium across phases. | galactic neutral hydrogen and the magnetic ism foreground |
we have compiled the all-sky data on optical interstellar linear polarization from 13 data sources for 6420 stars without considerable intrinsic polarization from gaia dr2 within 500 pc from the sun. we display these data versus the stellar reddening estimates from five 3d maps and models. we have considered variations of the polarization degree p, its positional angle θ, reddening e(b-v), and polarization efficiency p/e(b-v) with the galactic coordinates l and b, distance r, and dereddened color. a border between the local bubble with lower polarization and the gould belt with higher polarization can be drawn at p=0.1%. p has a maximum at the mid-plane of the gould belt, but not at the galactic mid-plane. too high values of p/e(b-v) from the reddening maps/models of arenou et al., drimmel et al., and lallement et al. in some regions of space lead us to suggest that the reddening is systematically underestimated in these cases. the most reliable maps/models show nearly similar dust volume density e(b-v)/r everywhere in the space under consideration. the drop of p inside, compared to outside, the bubble together with constant e(b-v)/r, i.e. dust volume density everywhere within 500 pc can be explained by a much lower volume density of neutral gas, a much higher volume density of ionized gas, the same volume density of dust, and the same gas/dust ratio inside, compared to outside, the bubble. in the belt, all variations of p and e(b-v) dependent on dereddened color and coordinates compensate each other, resulting in a nearly constant p/e(b-v), including a variation for different stellar spectral classes. in the bubble, θ demonstrates a chaotic behaviour, while the belt is dominated by a giant envelope of aligned dust oriented nearly along the local interstellar tunnel. | interstellar polarization in the local bubble and the gould belt based on gaia dr2 data |
studying the interaction between the interstellar medium and the black hole environment on the parsec scale is of crucial importance in the full understanding of galaxy evolution. since the galactic centre is the closest galactic nucleus, it offers us the unique possibility to observationally study the dynamics of individual stars as well as the properties of the nuclear star cluster as a whole. this thesis deals with the transition region where the complex interstellar medium in the galactic centre meets a rather simple object at the very centre - most probably a black hole of 4 million solar masses characterized by only three classical parameters: mass, spin, and electric charge. recently, a nir-excess object named dso/g2 was detected that is moving on a highly eccentric orbit, with the pericentre reached in 2014 at 2000 schwarzschild radii. the monitoring, the analysis of nir data, and the comparison with models have provided an unprecedented opportunity to constrain the properties of previously unexplored region around sgr a* as well as to determine the nature of this enigmatic source. in a series of papers, we explored the dynamics of different scenarios for dso/g2, its interaction with the ambient medium close to the galactic centre, and the radiative properties of its nir continuum emission. the main findings include the asymmetry of the stellar bow-shock evolution along the orbit when the outflow from the galactic centre is present. subsequently, using polarimetry measurements and 3d monte carlo radiative transfer, we were able to set up a model of a young star with a non-spherical dusty envelope that can explain its compactness, nir-excess as well as its linearly polarized emission. finally, we explore a possibility that the dso and objects with similar characteristics could be candidates for young neutron stars that should be observable in nir bands with current and future facilities, which can help to resolve the ``missing pulsar paradox''. approaching the innermost region of the galactic centre, we explore the problem of an electric charge associated with sgr a*, which is assumed to be zero in most studies. we found that a stable charge can be maintained by several mechanisms. one of the most promising ones is the charging due to the rotating black hole that is immersed in a uniform magnetic field. realistic values of the charge that we calculated do not influence space-time metric, but can significantly influence the dynamics of plasma in the vicinity of the galactic centre. furthermore, we also propose a novel observational test for detecting the signature of the charge using a bremsstrahlung brightness distribution. | interaction between interstellar medium and black hole environment |
the galway astronomical stokes polarimeter (gasp) is a high time resolution, full-stokes imaging polarimeter which utilises a fresnel rhomb prism as a beam-splitter and quarter wave retarder. the ability to perform optical photometry and polarimetry at high frame rates enables more detailed studies of a multitude of compact objects including; optical pulsars, magnetars and active galactic nuclei (agn). we present a brief discussion of the instruments' current capabilities and hardware design. gasp is currently configured with two electron multiplying charge-coupled devices (emccds), which offer sub-millisecond frame readout speeds over a defined region of interest on the sensor. we will report results from an observational campaign at the william herschel telescope (wht) in december, 2015. during this campaign gasp was used to study the crab pulsar, v404 cygni and polarisation standards. as a subset of our analysis we have identified a significant contribution from the interstellar medium (ism) and the interaction of a varying polarised source with the ism, the subsequent conversion of linearly polarised light to circular, and its dependence on the angle of the source emission electric field orientation. further to the presentation of results we will discuss future observational work, which is planned for september 2017 and subsequent improvements to increase the temporal resolution of the detectors. | high time resolution astronomical polarimetry with gasp |
identification of methyl acetate in the interstellar medium (ism) and its spectroscopic studies have prompted us to investigate the structure of crystalline methyl acetate using numerical calculations. here, we present a theoretical study of the structure of crystalline methyl acetate and its isotopologues and compare the calculated infrared (ir) spectra with the available experimental data. the optimized structure and vibrational properties were calculated using siesta software at 0 k. in the optimization process, the perdew-burke-ernzerhof functional and conjugate gradient methods were used with double zeta polarization basis functions. after optimization of the periodic structure, the vibrational frequencies and normal modes were calculated within the harmonic approximation. using the calculated results, we refine the mode assignments of experimental work on crystalline methyl acetate and determine the low frequency modes (below 650 cm- 1). to investigate the accuracy of the pseudopotential and confirm the ir frequencies, we performed molecular calculations using a periodic model of methyl acetate and its isotopologues using siesta and compared them with results obtained from gaussian 09 (all electron method) calculations. finally, we assigned the vibrational modes of crystalline cd3-coo-ch3 and ch3-coo-cd3, for which experimental data are not available in the crystalline phase under ism conditions. for all of the calculation methods, the ir vibrational modes of molecular and crystalline methyl acetate and its isotopologues were in good agreement with the available experimental data and predict the unavailable values. | theoretical study of the infrared frequencies of crystalline methyl acetate under interstellar medium conditions |
the synthesis telescope (st) at the dominion radio astrophysical observatory (drao) is the premier telescope in the world for imaging of large-scale neutral hydrogen and polarized radio continuum emission at arcmin resolution. a seven-element radio interferometer, its most prominent achievement to date is the completion of the canadian galactic plane survey (cgps), which exploited the st's excellent wide-field imaging capability in both the hi line and diffuse continuum imaging at 1420 mhz (stokes i, q, and u) and 408 mhz (stokes i). the wide field of view of its 8.6~m antennas, the complete coverage of the uv plane, and the excellent on- and off-axis polarization imaging capability provide a powerful and cost-effective niche for the instrument with capabilities that no other telescope can match. drao and university partners have developed a new vision for the telescope as a forefront scientific instrument, an engineering testbed for new technologies, and a training ground for future canadian and global radio engineers and astronomers. the renewed telescope will have nearly complete frequency coverage from 400-1800 mhz in stokes i, q, and u, with extensive and flexible spectral line zoom modes. this will enable a wide range of scientific applications to interstellar gas and magnetic fields in our own and nearby galaxies as well as precision characterization of cosmological foregrounds. the telescope will also demonstrate a two-octave single-pixel feed, a highly innovative correlator, and revolutionary digitization and clocking technology. the scientific and engineering development of the telescope will be a joint effort of drao, a national observatory, and university partners, with heavy student involvement. | drao synthesis telescope |
the origin of large-scale magnetic fields, detected in some low-mass (dwarf and irregular) galaxies via polarised synchrotron emission and faraday rotation, has remained unexplained for a long time. we suggest that mean-field dynamos can be active in galaxies of this class despite their slow rotation because their discs are relatively thick. earlier assessments of the possibility of the mean-field dynamo action in low-mass galaxies relied on estimates applicable to thin discs, such as those in massive spiral galaxies. using both order-of-magnitude estimates and numerical solutions, we show that the strength of differential rotation required to amplify magnetic field reduces as the aspect ratio of the galactic gas layer increases. as in a thin disc, quadrupolar magnetic fields dominate in thick discs. thus, the origin of large-scale magnetic fields in low-mass galaxies has been clarified. this class of galaxies provides a new ground for testing our understanding of galactic magnetism. | the origin of large-scale magnetic fields in low-mass galaxies |
the nika2 polarization channel at 260 ghz (1.15 mm) has been proposed primarily to observe galactic star-forming regions and probe the critical scales between 0.01-0.05 pc at which magnetic field lines may channel the matter of interstellar filaments into growing dense cores. the nika2 polarime-ter consists of a room temperature continuously rotating multi-mesh hwp and a cold polarizer that separates the two orthogonal polarizations onto two 260 ghz kids arrays. we describe in this paper the preliminary results obtained during the most recent commissioning campaign performed in december 2018. we concentrate here on the analysis of the extended sources, while the observation of compact sources is presented in a companion paper [12]. we present preliminary nika2 polarization maps of the crab nebula. we find that the integrated polarization intensity flux measured by nika2 is consistent with expectations. in terms of polarization angle, we are still limited by systematic uncertainties that will be further investigated in the forthcoming commissioning campaigns. | observing with nika2pol from the iram 30m telescope : early results on the commissioning phase |
the polarized instrument for long-wavelength observation of the tenuous interstellar medium (pilot) is a balloon-borne astronomy experiment designed to study the linear polarization of the far infra-red emission, 240 ~im (1.2 thz) and 550 ~tm (545 ghz) with an angular resolution of a few minutes of arc, from dust grains present in the diffuse interstellar medium, in our galaxy and nearby galaxies. the polarisation of light is measured using a half-wave plate (hwp). we performed the instrumental tests from 2012 to 2014 and are planning a first scientific flight in september 2015 from timmins, ontario, canada. this paper describes the measurement principles of pilot, the results of the laboratory tests and its sky coverage. these include defocus tests, transmission measurements using a fourier transform spectrometer at various positions of the hwp, and identification of internal straylight. | pilot end-to-end calibration results |
the highly filamentary structure of the interstellar medium (ism) is now impressively revealed by herschel and planck images. previous observations have shown that clouds are filamentary, however, only recently the mapping capabilities of herscheland planck have discovered their ubiquity in the ism. in particular, herschel images, with their high spatial and intensity dynamic ranges, show that dense filaments are associated with the main sites of star formation, demonstrating their key role in the star formation process.the analysis of the column density profiles of filaments indicates that they all share a common central width of 0.1pc, while they span a wide range in length, column density, mass per unit length. the results derived from observations tracing cold dust and gas emission, in total and polarised intensity, suggest that filaments can be divided into two families: on the one hand, low column density, unbound, and quiescent filaments mostly aligned with the magnetic field orientation, and on the other hand, dense, self-gravitating filaments, which fragment into star forming cores.i will present the properties of the filamentary structures derived from herschel, planck, and molecular line observations, and i will discuss the observational constraints on the formation and evolution of interstellar filaments. | properties of interstellar filaments derived from herschel, planck, and molecular line observations |
sensitive, high resolution observations of galactic neutral hydrogen (hi) reveal an intricate network of slender linear features, much as sensitive surveys of dust in galactic molecular clouds reveal ubiquitous filamentary structure. across the high galactic latitude sky, diffuse histructures are aligned with the interstellar magnetic field, as revealed by background starlight polarization (clark, peek, & putman 2014) and by planck 353 ghz polarized dust emission (clark et al. 2015). these discoveries were enabled by the rolling hough transform, a recently developed, open source machine vision algorithm. | quantifying the magnetic alignment of hi and dust in the diffuse ism |
we use radio-continuum all-sky surveys at 1420 and 408 mhz with the aim to investigate properties of the galactic radio source lupus loop. the survey data at 1435 mhz, with the linear polarization of the southern sky, are also used. we calculate properties of this supernova remnant: the brightness temperature, surface brightness and radio spectral index. to determine its borders and to calculate its properties, we use the method we have developed. the non-thermal nature of its radiation is confirmed. the distribution of spectral index over its area is also given. a significant correlation between the radio spectral index distribution and the corresponding polarized intensity distribution inside the loop borders is found, indicating that the polarization maps could provide us information about the distribution of the interstellar medium, and thus could represent one additional way to search for new galactic loops. | snr radio spectral index distribution and its correlation with polarization. a case study: the lupus loop |
this paper reports the results of new chemical modelling measurements of the faraday rotation braking mechanism operating on a diamagnetic molecule in a magnetic field. the time length of the experiment is extended, more relevant variables are measured (rotation, vibration, drift energies; molecule orientation), and more accurately, as a function of time. the polarization of light by the moving molecule is computed. the observed behaviour of the molecule may be understood, and the rotation damping time more accurately deduced by fitting a mathematical model built upon the classical equations of motion in a field. this model, meant to include the essential physics involved in the experiment, with the minimum number of parameters, also allows the chemical modelling experimental results to be extrapolated to other molecular structures, shapes and sizes, and other magnetic fields. for a given particle, the rotation damping time scales like 1/h and is independent of the rotation frequency. as an example, we follow the motion of a rod of homogeneous material, 10-5 cm in length, moving in a field 5 × 10-6 g in intensity. its angular rotation is found to decrease to 0, while its axis settles perpendicularly to the field within a few years. molecular vibrations appear as an illustration of the fluctuation-dissipation theorem: they absorb friction heat and, at the same time, are the very cause of this friction. | on the alignment of diamagnetic molecules in interstellar magnetic fields |
aims: the interstellar polarization in the northern high-latitude sky is low and rather smooth in the local spiral (ls) longitude range 60° < l < 240°, except for an extension of aligned higher polarization within 120° < l < 180° up to b ≈ 50°. we compare this view with results from other indicators of interstellar matter.methods: some indicators of dust are sensitive to diffuse matter on large scales, others provide information on clumpy structures. we describe results that are mainly from surveys of dark and molecular clouds in the ls longitude range at high latitudes.results: the structured feature in the polarization map for the ls region corresponds to known dark cloud complexes. these extensions to higher latitudes (and some other dust indicators) may signal the presence of more dust in some form (like compact cold clouds) than is suggested by regular low interstellar polarization. | on high-latitude interstellar polarization toward the local spiral |
recent herschel and planck observations of submillimeter dust emission revealed the omnipresence of filamentary structures in the interstellar medium (ism). the ubiquity of filaments in quiescent clouds as well as in star-forming regions indicates that the formation of filamentary structures is a natural product of the physics at play in the magnetized turbulent cold ism. an analysis of more than 270 filaments observed with herschel in 8 regions of the gould belt, shows that interstellar filaments are characterized by a narrow distribution of central width sharply peaked at ~0.1 pc, while they span a wide column density range. molecular line observations of a sample of these filaments show evidence of an increase in the velocity dispersion of dense filaments with column density, suggesting an evolution in mass per unit length due to accretion of surrounding material onto these star-forming filaments. the analyses of planck dust polarization observations show that both the mean magnetic field and its fluctuations along the filaments are different from those of their surrounding clouds. this points to a coupling between the matter and the -field in the filament formation process. these observational results, derived from dust and gas tracers in total and polarized intensity, set strong constraints on our understanding of the formation and evolution of filaments in the ism. they provide important clues on the initial conditions of the star formation process along interstellar filaments. | properties of interstellar filaments as derived from herschel, planck, and molecular line observations |
we present ubvri polarimetric observations of 66 stars in the direction of ngc 4755, including eleven β cephei stars. about half of these variables show indications of intrinsic polarization, but according to the theory neither radial nor non-radial pulsations could cause such polarizations. from the main characteristics of their p_{v} vs. λ_{v} curves we found as a possible origin, in some cases, scattering of light in extended atmospheres and suspected binarity, in some cases. the parameters of the interstellar medium towards the cluster are p_{v}=2.76± 0.13(%) and θ_{v}=76.6° ± 0.9°; the mean wavelength of maximum polarization amounts to 0.56± 0.04μ m. the value of polarization efficiency is higher than the mean, indicating a good alignment of the dust particles. a total of 25 stars were identified as members of ngc 4755; the identification task was improved through the use of polarimetric tools. | multicolor ubvri polarimetry of ngc 4755 and the β cephei population |
recent observations of synchrotron emission in protostellar jets are important because they allow us to determine the jet and/or the interstellar magnetic field structure, thus giving insights on the jet ejection and collimation mechanisms. in this proceeding, we show the results obtained from the analysis of polarized (synchrotron) synthetic emission maps from axisymmetrical simulations of magnetized protostellar jets. we consider models with different jet velocities and variability, as well as toroidal or helical magnetic field. our simulations show that variable, low-density jets with velocities 1000 km/s and 10 times less dense than the environment can produce internal knots with significant synchrotron emission. while models with a purely toroidal magnetic field show a very large degree of polarization, models with helical magnetic field show lower values and a decrease of the degree of polarization, in agreement with observations of protostellar jets. | simulación de jets protoestelares |
the rotation measure (rm) map we present here was calculated using stokes q and u data from the canadian galactic plane survey polarisation dataset. the data were observed using the dominion radio astrophysical observatory synthesis telescope as part of the cgps, in 4 frequency channels centred at 1407.2, 1414.1, 1427.7 and 1436.6mhz. we calculated rms for the extended emission assuming a linear fit to polarisation angle as a function of wavelength squared. we then applied a filtering process as described in the paper. the size of the pixels in the map is 0.005 degrees by 0.005 degrees, and the entire map is 1825 by 29025 pixels, covering the cgps longitude and latitude range. (2 data files). | vizier online data catalog: faraday rotation of extended emission (ordog+, 2019) |
this dissertation talk presents a new single-shot, full-stokes optical polarimeter using stress-engineered optics (seos), the first in the field of astronomy to do so (wolfe et al. 2018, proc. spie 107063b) . seos are cylindrical glass windows under static stress by radially inward forces in three symmetrically-spaced regions, producing spatially varying birefringence throughout. light from a telescope and collimated through the seo acquires a point spread function (psf) dependent on the source's full polarization vector (stokes parameters). the polarization of light from a point source is thus encoded within a single image, from an instrument with no temporal modulation or division of amplitude. our instrument, "polvis", obtained first light in may 2018. this presentation provides comparisons of lab data with on-sky results (both simulated and experimental) of our polarimeter on a 0.2m (8in) telescope at the university of denver. as earth's atmospheric turbulence interferes with the ideal polarization-dependent psfs, studying these effects and how to reproduce a polarization measurement through turbulence have been crucial to creating the instrument. lab experiments compare measurement efficiency as a function of spectral bandwidth. also presented is a look at the variability of polarized and unpolarized "standard" stars, plus an argument to further studies of interstellar circular broadband polarization, which has been historically under-measured but contains useful physical information about the ism. applications of this instrument also exist in improving exoplanet polarimetry and high time resolution astrophysics. next steps include proposing to observe with the instrument on larger telescopes, and modeling the performance of such an instrument in space-based applications. the original descriptions of seos from the institute of optics at the university of rochester can be found in spilman and brown, 2007 (applied optics ip, 46, 2007), and the description of polarimetry in beckley and brown 2010 (proc. spie, 757011). the presenter is grateful to the estate of william herschel womble for the support of astronomy at the university of denver. | simultaneous full-stokes polarimetry with stress-engineered optics |
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