- ID:
- ivo://CDS.VizieR/J/ApJ/716/893
- Title:
- Polarisation at 850mu{m} in OMC-2 and OMC-3
- Short Name:
- J/ApJ/716/893
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The SCUBA polarized 850um thermal emission data of the OMC-2 region in Orion A are added to and homogeneously reduced with data already available in the OMC-3 region. The data set shows that OMC-2 is a region generally less polarized than OMC-3. Where coincident, most of the 850um polarization pattern is similar to that measured in 350um polarization data. Only 850um polarimetry data have been obtained in and around MMS7, FIR1 and FIR2, and in the region south of FIR6. A realignment of the polarization vectors with the filament can be seen near FIR1 in the region south of OMC-3. An analysis shows that the energy injected by CO outflows and H2 jets associated with OMC-2 and OMC-3 does not appear to alter the polarization patterns at a scale of the 14" resolution beam. A second-order structure function analysis of the polarization position angles shows that OMC-2 is a more turbulent region than OMC-3. OMC-3 appears to be a clear case of a magnetically dominated region with respect to the turbulence. However, for OMC-2 it is not clear that this is the case. A more in-depth analysis of five regions displayed along OMC-2/3 indicates a decrease of the mean polarization degree and an increase of the turbulent angular dispersion from north to south. A statistical analysis suggests the presence of two depolarization regimes in our maps: one regime including the effects of the cores, the other one excluding it.
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- ID:
- ivo://CDS.VizieR/J/ApJ/847/92
- Title:
- Polarization data toward the protostar Serpens SMM1
- Short Name:
- J/ApJ/847/92
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present high angular resolution dust polarization and molecular line observations carried out with the Atacama Large Millimeter/submillimeter Array (ALMA) toward the Class 0 protostar Serpens SMM1. By complementing these observations with new polarization observations from the Submillimeter Array (SMA) and archival data from the Combined Array for Research in Millimeter- wave Astronomy (CARMA) and the James Clerk Maxwell Telescopes (JCMT), we can compare the magnetic field orientations at different spatial scales. We find major changes in the magnetic field orientation between large (~0.1pc) scales-where the magnetic field is oriented E-W, perpendicular to the major axis of the dusty filament where SMM1 is embedded-and the intermediate and small scales probed by CARMA (~1000au resolution), the SMA (~350au resolution), and ALMA (~140au resolution). The ALMA maps reveal that the redshifted lobe of the bipolar outflow is shaping the magnetic field in SMM1 on the southeast side of the source; however, on the northwestern side and elsewhere in the source, low-velocity shocks may be causing the observed chaotic magnetic field pattern. High-spatial-resolution continuum and spectral-line observations also reveal a tight (~130au) protobinary system in SMM1-b, the eastern component of which is launching an extremely high-velocity, one-sided jet visible in both CO(J=2->1) and SiO(J=5->4); however, that jet does not appear to be shaping the magnetic field. These observations show that with the sensitivity and resolution of ALMA, we can now begin to understand the role that feedback (e.g., from protostellar outflows) plays in shaping the magnetic field in very young, star-forming sources like SMM1.
- ID:
- ivo://CDS.VizieR/J/A+A/541/A52
- Title:
- Polarization efficiency and dust phase
- Short Name:
- J/A+A/541/A52
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We compiled the polarimetric data for a sample of lines of sight with known abundances of Mg, Si, and Fe. We correlated the degree of interstellar polarization P and polarization efficiency (the ratio of P to the colour excess E(B-V) or extinction AV) with dust phase abundances. We detect an anticorrelation between P and the dust phase abundance of iron in non silicate-containing grains [Fe(rest)/H]_d_, a correlation between P and the abundance of Si, and no correlation between P/E(B-V) or P/AV and dust phase abundances. These findings can be explained if mainly the silicate grains aligned by the radiative mechanism are responsible for the observed interstellar linear polarization.
- ID:
- ivo://CDS.VizieR/J/ApJ/775/84
- Title:
- Polarization from stars behind IC63 nebula
- Short Name:
- J/ApJ/775/84
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In the interstellar medium (ISM), molecular hydrogen is expected to form almost exclusively on the surfaces of dust grains. Due to that molecule's large formation energy (-4.5eV), several dynamical effects are likely associated with the process, including the alignment of asymmetric dust grains with the ambient magnetic field. Such aligned dust grains are, in turn, believed to cause the broadband optical/infrared polarization observed in the ISM. Here, we present the first observational evidence for grain alignment driven by H_2_ formation, by showing that the polarization of the light from stars behind the reflection nebula IC 63 appears to correlate with the intensity of H_2_ fluorescence. While our results strongly suggest a role for "Purcell rockets" in grain alignment, additional observations are needed to conclusively confirm their role. By showing a direct connection between H_2_ formation and a probe of the dust characteristics, these results also provide one of the first direct confirmations of the grain-surface formation of H_2_. We compare our observations to ab initio modeling based on Radiative Torque Alignment (RAT) theory.
- ID:
- ivo://CDS.VizieR/J/A+A/569/L1
- Title:
- Polarization hole in a starless core
- Short Name:
- J/A+A/569/L1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We aim to investigate the polarization properties of a starless core in a very early evolutionary stage. Linear polarization data reveal the properties of the dust grains in the distinct phases of the interstellar medium. Our goal is to investigate how the polarization degree and angle correlate with the cloud and core gas. We use optical, near infrared and submillimeter polarization observations toward the starless object Pipe-109 in the Pipe nebula. Our data cover a physical scale range of 0.08 to 0.4pc, comprising the dense gas, envelope and the surrounding cloud. The cloud polarization is well traced by the optical data. The near infrared polarization is produced by a mixed population of grains from the core border and the cloud gas. The optical and near infrared polarization toward the cloud reach the maximum possible value and saturate with respect to the visual extinction. The core polarization is predominantly traced by the submillimeter data and have a steep decrease with respect to the visual extinction. Modeling of the submillimeter polarization indicates a magnetic field main direction projected onto the plane-of-sky and loss of grain alignment for densities higher than 6x10^4^cm^-3^ (or A_V_>30mag). Pipe-109 is immersed in a magnetized medium, with a very ordered magnetic field. The absence of internal source of radiation significantly affects the polarization efficiencies in the core, creating a polarization hole at the center of the starless core. This result supports the theory of dust grain alignment via radiative torques.
- ID:
- ivo://CDS.VizieR/J/ApJ/897/90
- Title:
- Polarization measurements of S201 with JCMT
- Short Name:
- J/ApJ/897/90
- Date:
- 11 Mar 2022
- Publisher:
- CDS
- Description:
- We present the properties of magnetic fields (B fields) in two clumps (clump 1 and clump 2), located at the waist of the bipolar HII region Sh2-201, based on James Clerk Maxwell Telescope SCUBA-2/POL-2 observations of 850{mu}m polarized dust emission. We find that B fields in the direction of the clumps are bent and compressed, showing bow-like morphologies, which we attribute to the feedback effect of the HII region on the surface of the clumps. Using the modified Davis-Chandrasekhar-Fermi method, we estimate B-field strengths of 266 and 65{mu}G for clump 1 and clump 2, respectively. From virial analyses and critical mass ratio estimates, we argue that clump 1 is gravitationally bound and could be undergoing collapse, whereas clump 2 is unbound and stable. We hypothesize that the interplay of the thermal pressure imparted by the HII region, the B-field morphologies, and the various internal pressures of the clumps (such as magnetic, turbulent, and gas thermal pressures) has the following consequences: (a) formation of clumps at the waist of the HII region; (b) progressive compression and enhancement of the B fields in the clumps; (c) stronger B fields that will shield the clumps from erosion by the HII region and cause pressure equilibrium between the clumps and the HII region, thereby allowing expanding ionization fronts to blow away from the filament ridge, forming bipolar HII regions; and (d) stronger B fields and turbulence that will be able to stabilize the clumps. A study of a larger sample of bipolar HII regions would help to determine whether our hypotheses are widely applicable.
- ID:
- ivo://CDS.VizieR/J/ApJ/724/L113
- Title:
- Polarization of IRAS 18089-1732
- Short Name:
- J/ApJ/724/L113
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To characterize the magnetic field structure of the outflow and core region within a prototypical high-mass star-forming region, we analyzed polarized CO(3-2) -for the first time observed with the Submillimeter Array- as well as 880um submillimeter continuum emission from the high-mass outflow/disk system IRAS 18089-1732. Both emission features with polarization degrees at a few percent level indicate that the magnetic field structure is largely aligned with the outflow/jet orientation from small core scales to larger outflow scales. Although quantitative estimates are crude, the analysis indicates that turbulent energy dominates over magnetic energy. The data also suggest a magnetic field strength increase from the lower-density envelope to the higher-density core.
- ID:
- ivo://CDS.VizieR/J/AJ/160/256
- Title:
- Polarization of 125 stars in NGC 1817 open cluster
- Short Name:
- J/AJ/160/256
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Multiband linear polarimetric observations of 125 stars in the region of the cluster NGC1817 have been carried out intending to study properties of interstellar dust and grains in that direction. The polarization is found to be wavelength-dependent, being maximum in the V-band with an average value of 0.95%. The foreground interstellar dust grains appear to be the main source of linear polarization of starlight toward the direction of NGC1817. The average value of the position angle in the V-band of 119.2{deg} is found to be less than the direction of the Galactic parallel in the region, indicating that the dust grains in the direction are probably not yet relaxed. Spatial distribution of dust appears to be more diverse in the coronal region than the core region of the cluster. The maximum value of the degree of polarization is estimated to be 0.93% for members of the cluster using the Serkowski relation. The average value of wavelength corresponding to the maximum polarization of 0.54{+/-}0.02{mu}m indicates that the size distribution of dust grains in the line of sight is similar to that of the general interstellar medium. Several variable stars in the cluster were also observed polarimetrically and pulsating variables appear to have a slightly lower value of polarization from other nonvariable member stars of the cluster. There are indications of the existence of dust layers in front of those clusters which are located close to galactic plane while for clusters located away from galactic plane no major dust layers are observed.
- ID:
- ivo://CDS.VizieR/J/ApJ/633/871
- Title:
- Positions and photometry of HII knots in M51
- Short Name:
- J/ApJ/633/871
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Far-ultraviolet to far-infrared images of the nearby galaxy NGC 5194 (M51a), from a combination of space-based (Spitzer, GALEX, and Hubble Space Telescope) and ground-based data, are used to investigate local and global star formation and the impact of dust extinction. The Spitzer data provide unprecedented spatial detail in the infrared, down to sizes 500 pc at the distance of NGC 5194. The multiwavelength set is used to trace the relatively young stellar populations, the ionized gas, and the dust absorption and emission in HII-emitting knots, over 3 orders of magnitude in wavelength range.
- ID:
- ivo://CDS.VizieR/J/A+A/534/A118
- Title:
- Predicted dust emissivity in 100-10000um bands
- Short Name:
- J/A+A/534/A118
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In a previous paper we proposed a new model for the emission by amorphous astronomical dust grains, based on solid-state physics. The model uses a description of the disordered charge distribution (DCD) combined with the presence of two-level systems (TLS) defects in the amorphous solid composing the grains. The goal of this paper is to compare this new model to astronomical observations of different Galactic environments in the far-infrared/ submillimeter, in order to derive a set of canonical model parameters to be used as a Galactic reference to be compared to in future Galactic and extragalactic studies. We compare the TLSmodel with existing astronomical data. We consider the average emission spectrum at high latitudes in our Galaxy as measured with FIRAS and WMAP, as well as the emission from Galactic compact sources observed with the Archeops balloon experiment, for which an inverse relationship between the dust temperature and the emissivity spectral index has been proven.
