- 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.
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Search Results
- 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.
- ID:
- ivo://CDS.VizieR/J/A+A/643/A61
- Title:
- Prestellar cores H2D+ and N2H+ maps
- Short Name:
- J/A+A/643/A61
- Date:
- 07 Mar 2022 07:18:04
- Publisher:
- CDS
- Description:
- The study of prestellar cores is critical as they set the initial conditions in star formation and determine the final mass of the stellar object. To date, several hypotheses are describing their gravitational collapse. Deriving the dynamical model that fits both the observed dust and the gas emission from such cores is therefore of great importance. We perform detailed line analysis and modelling of H_2_D^+^ 1_10_-1_11_ and N_2_H^+^ 4-3 emission at 372GHz, using 2'x2' maps (JCMT).Our goal is to test the most prominent dynamical models by comparing the modelled gas kinematics and spatial distribution (H_2_D^+^ and N_2_H^+^) with observations towards four prestellar (L1544, L183, L694-2, L1517B) and one protostellar core (L1521f). We fit the line profiles at all offsets showing emission using single Gaussian distributions. We investigate how the line parameters (V_LSR_, FWHM and T_A_*) change with offset, to examine the velocity field, the degree of non-thermal contributions to the line broadening, and the distribution of the material in these cores. To assess the thermal broadening, we derive the average gas kinetic temperature towards all cores using the non-LTE radiative transfer code RADEX. We perform a more detailed non-LTEradiative transfer modelling using RATRAN, where we compare the predicted spatial distribution and line profiles of H_2_D^+^ and N_2_H^+^ with observations towards all cores. To do so, we adopt the physical structure for each core predicted by three different dynamical models taken from literature: Quasi-Equilibrium Bonnor-Ebert Sphere (QE-BES), Singular Isothermal Sphere (SIS), and Larson-Penston (LP) flow. In addition, we compare these results to those of a static sphere, whose density and temperature profiles are based on the observed dust continuum. Lastly, we constrain the abundance profiles of H_2_D^+^ and N_2_H^+^ towards each core. We find that variable non-thermal contributions (variations by a factor of 2.5) are required to explain the observed line width of both H_2_D^+^ and N_2_H^+^, while the non-thermal contributions are found to be 50% higher for N_2_H^+^. The RADEX modelling results in average core column densities of ~9x10^12^cm^-2^ for H_2_D+and N_2_H^+^. The LP flow seems to be the dynamical model that can reproduce the observed spatial distribution and line profiles of H_2_D^+^ on a global scale of prestellar cores, while the SIS model systematically and significantly overestimates the width of the line profiles and underestimates the line peak intensity. We find similar abundance profiles for the prestellar cores and the protostellar core. The typical abundances of H_2_D^+^ vary between 10^-9^-10^-10^ for the inner 5000au, and drop by about an order of magnitude for the outer regions of the core (2x10^-10^-6x10^-11^). In addition, a higher N_2_H^+^ abundance by about a factor of 4 compared to H_2_D^+^ is found towards the two cores with detected emission. The presence ofN_2_H^+^ 4-3 towards the protostellar core and towards one of the prestellar cores reflects the increasing densities as the core evolves. Our analysis provides an updated picture of the physical structure of prestellar cores. Although the dynamical models account for mass differences by up to a factor of 7, the velocity structure drives the shape of the line profiles, allowing for a robust comparison between the models. We find that the SIS model can be cleary excluded in explaining the gas emission towards the cores,but a larger sample is required to differentiate clearly between the LP flow, the QE-BES and the static models. All models of collapse underestimate the intensity of the gas emission by up to several factors towards the only protostellar core in our sample, indicating that different dynamics take place in different evolutionary core stages. If the LP model is confirmed towards a larger sample of prestellarcores, it would indicate that they may form by compression or accretion of gas from larger scales. If the QE-BES model is confirmed, it means that quasi hydrostatic cores can exist within turbulent ISM.
- ID:
- ivo://CDS.VizieR/J/ApJ/684/1240
- Title:
- Prestellar cores in Perseus, Serpens and Ophiuchus
- Short Name:
- J/ApJ/684/1240
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an unbiased census of starless cores in Perseus, Serpens, and Ophiuchus, assembled by comparing large-scale Bolocam 1.1mm continuum emission maps with Spitzer c2d surveys. We use the c2d catalogs to separate 108 starless from 92 protostellar cores in the 1.1mm core samples from Enoch and Young and their coworkers. A comparison of these populations reveals the initial conditions of the starless cores.
- ID:
- ivo://CDS.VizieR/J/A+A/651/A36
- Title:
- Probing the ISF in Orion A with ArTeMiS
- Short Name:
- J/A+A/651/A36
- Date:
- 17 Jan 2022 11:38:53
- Publisher:
- CDS
- Description:
- The Orion molecular cloud is the closest region of high-mass star formation. It is an ideal target for investigating the detailed structure of massive star-forming filaments at high resolution and the relevance of the filament paradigm for the earliest stages of intermediate- to high-mass star formation. Within the Orion A molecular cloud, the integral-shaped filament (ISF) is a prominent, degree-long structure of dense gas and dust with clear signs of recent and ongoing high-mass star formation. Our aim is to characterise the structure of this massive filament at moderately high angular resolution (8" or ~0.016pc) in order to measure the intrinsic width of the main filament, down to scales well below 0.1pc, which has been identified as the characteristic width of filaments. We used the ArTeMiS bolometer camera at APEX to map a ~0.6x0.2deg^2^ region covering OMC-1, OMC-2, and OMC-3 at 350 and 450um. We combined these data with Herschel- SPIRE maps to recover extended emission. The combined Herschel-ArTeMiS maps provide details on the distribution of dense cold material, with a high spatial dynamic range, from our 8" resolution up to the transverse angular size of the map, ~10-15'. By combining Herschel and ArTeMiS data at 160, 250, 350, and 450um, we constructed high-resolution temperature and H_2_ column density maps. We extracted radial intensity profiles from the column density map in several representative portions of the ISF, which we fitted with Gaussian and Plummer models to derive their intrinsic widths. We also compared the distribution of material traced by ArTeMiS with that seen in the higher-density tracer N_2_H^+^(1-0) that was recently observed with the ALMA interferometer. All the radial profiles that we extracted show a clear deviation from a Gaussian, with evidence for an inner plateau that had not previously been seen clearly using Herschel-only data. We measure intrinsic half-power widths in the range 0.06 to 0.11pc. This is significantly larger than the Gaussian widths measured for fibres seen in N_2_H^+^, which probably only traces the dense innermost regions of the large-scale filament. These half-power widths are within a factor of two of the value of ~0.1 pc found for a large sample of nearby filaments in various low-mass star-forming regions, which tends to indicate that the physical conditions governing the fragmentation of pre-stellar cores within transcritical or supercritical filaments are the same over a large range of masses per unit length.
- ID:
- ivo://CDS.VizieR/J/ApJS/216/33
- Title:
- Probing the Local Bubble with DIBs. III.
- Short Name:
- J/ApJS/216/33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new high signal-to-noise ratio (S/N) observations of the diffuse interstellar bands (DIBs) in the Local Bubble and its surroundings. We observed 432 sightlines and obtain the equivalent widths of the {lambda}5780 and {lambda}5797{AA} DIBs up to a distance of ~200pc. All of the observations were carried out using the Intermediate Dispersion Spectrograph on the 2.5m Isaac Newton Telescope, during three years, to reach a minimum S/N of ~2000. All of the {lambda}5780 and {lambda}5797 absorptions are presented in this paper and we tabulate the observed values of the interstellar parameters, {lambda}5780, {lambda}5797, Na ID_1_, and Na ID_2_, including the uncertainties.
- ID:
- ivo://CDS.VizieR/J/A+A/588/A30
- Title:
- Properties of cores in OMC 2/3
- Short Name:
- J/A+A/588/A30
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new measurements of the dust emissivity index, {beta}, for the high-mass, star-forming OMC 2/3 filament. We combined 160-500um data from Herschel with long-wavelength observations at 2mm and fit the spectral energy distributions across a=~2pc long, continuous section of OMC 2/3 at 15000AU (0.08pc) resolution. With these data, we measured {beta} and reconstructed simultaneously the filtered-out large-scale emission at 2mm. We implemented both variable and fixed values of {beta}, finding that {beta}=1.7-1.8 provides the best fit across most of OMC 2/3. These {beta} values are consistent with a similar analysis carried out with filtered Herschel data. Thus, we show that {beta} values derived from spatial filtered emission maps agree well with those values from unfiltered data at the same resolution. Our results contradict the very low {beta} values (~0.9) previously measured in OMC 2/3 between 1.2mm and 3.3mm data, which we attribute to elevated fluxes in the 3.3mm observations. Therefore, we find no evidence of rapid, extensive dust grain growth in OMC 2/3. Future studies with Herschel data and complementary ground-based long-wavelength data can apply our technique to obtain reliable determinations of {beta} in nearby cold molecular clouds.