- ID:
- ivo://CDS.VizieR/J/ApJ/604/717
- Title:
- Polarization in OMC 1/4
- Short Name:
- J/ApJ/604/717
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use extensive 350{mu}m polarimetry and continuum maps obtained with the Hertz polarimeter and SHARC II (Submillimeter High Angular Resolution Camera II) along with HCN and HCO+ spectroscopic data to trace the orientation of the magnetic field in the Orion A star-forming region. Using the polarimetry data, we find that the direction of the projection of the magnetic field in the plane of the sky relative to the orientation of the integral-shaped filament varies considerably as one moves from north to south. By combining the polarimetry and spectroscopic data, we were able to measure a set of average values for the inclination angle of the magnetic field relative to the line of sight. We also present polarimetry data for the OMC-4 region located some 13' south of OMC-1.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/476/4442
- Title:
- Polarization of seven MBM clouds stars
- Short Name:
- J/MNRAS/476/4442
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We made R-band polarization measurements of 234 stars towards the direction of the MBM 33-39 cloud complex. The distance of the MBM 33-39 complex was determined as 120+/-10pc using polarization results and near-infrared photometry from the 2MASS survey. The magnetic field geometry of the individual clouds inferred from our polarimetric results reveals that the field lines are in general consistent with the global magnetic field geometry of the region obtained from previous studies. This implies that the clouds in the complex are permeated by the interstellar magnetic field. Multi-wavelength polarization measurements of a few stars projected on to the complex suggest that the size of the dust grains in these clouds is similar to those found in the normal interstellar medium of the Milky Way. We studied a possible formation scenario of the MBM 33-39 complex by combining the polarization results from our study with those from the literature and by identifying the distribution of ionized, atomic and molecular (dust) components of material in the region.
- ID:
- ivo://CDS.VizieR/J/ApJ/741/21
- Title:
- Polarization of stars in Taurus
- Short Name:
- J/ApJ/741/21
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present maps of the plane-of-sky magnetic field within two regions of the Taurus molecular cloud: one in the dense core L1495/B213 filament and the other in a diffuse region to the west. The field is measured from the polarization of background starlight seen through the cloud. In total, we measured 287 high-quality near-infrared polarization vectors in these regions. In L1495/B213, the percent polarization increases with column density up to A_V_~9mag, the limits of our data. The radiative torques model for grain alignment can explain this behavior, but models that invoke turbulence are inconsistent with the data. We also combine our data with published optical and near-infrared polarization measurements in Taurus. Using this large sample, we estimate the strength of the plane-of-sky component of the magnetic field in nine subregions. This estimation is done with two different techniques that use the observed dispersion in polarization angles. Our values range from 5 to 82uG and tend to be higher in denser regions. In all subregions, the critical index of the mass-to-magnetic flux ratio is sub-unity, implying that Taurus is magnetically supported on large scales (~2pc). Within the region observed, the B213 filament takes a sharp turn to the north and the direction of the magnetic field also takes a sharp turn, switching from being perpendicular to the filament to becoming parallel. This behavior can be understood if we are observing the rim of a bubble. We argue that it has resulted from a supernova remnant associated with a recently discovered nearby gamma-ray pulsar.
- ID:
- ivo://CDS.VizieR/J/ApJ/875/64
- Title:
- Polarization & photom. of stars toward LDN1225
- Short Name:
- J/ApJ/875/64
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results based on the optical R-band observations of the polarization of 280 stars distributed toward the dark globule LDN1225. Parallaxes from Gaia data release 2 along with the polarization data of ~200 stars have been used to (a) constrain the distance of LDN 1225 as 830+/-83pc, (b) determine the contribution of interstellar polarization, and (c) characterize the dust properties and delineate the magnetic field (B-field) morphology of LDN 1225. We find that B-fields are more organized and exhibit a small dispersion of 12{deg}. Using the ^12^CO molecular line data from the Purple Mountain Observatory, along with the column density and dispersion in B-fields, we estimate the B-field strength to be ~56+/-10{mu}G, the ratio of magnetic to turbulent pressure to be ~3+/-2, and the ratio of mass to magnetic flux (in units of the critical value) to be <1. These results indicate the dominant role of B-fields in comparison to turbulence and gravity in rendering the cloud support. B-fields are aligned parallel to the low-density parts (traced by a ^12^CO map) of the cloud; in contrast, they are neither parallel nor perpendicular to the high-density core structures (traced by ^13^CO and C^18^O maps). LDN1225 hosts two 70{mu}m sources, which seem to be low-mass Class 0 sources. The ratio of total to selective extinction derived using optical and near-infrared photometric data is found to be anomalous (RV=3.4), suggesting the growth of dust grains in LDN 1225. The polarization efficiency of dust grains follows a power law with an index of -0.7, implying that optical polarimetry traces B-fields in the outer parts of the cloud.
- 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/ApJ/696/L84
- Title:
- Primordial circumstellar disks in binary systems
- Short Name:
- J/ApJ/696/L84
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We combine the results from several multiplicity surveys of pre-main-sequence stars located in four nearby star-forming regions with Spitzer data from three different Legacy Projects. This allows us to construct a sample of 349 targets, including 125 binaries, which we use to to investigate the effect of companions on the evolution of circumstellar disks. We find that the distribution of projected separations of systems with Spitzer excesses is significantly different (P~2.4e-5, according to the K-S test for binaries with separations less than 400AU) from that of systems lacking evidence for a disk. As expected, systems with projected separations less than 40AU are half as likely to retain at least one disk than are systems with projected separations in the 40-400AU range. These results represent the first statistically significant evidence for a correlation between binary separation and the presence of an inner disk (r~1AU). Several factors (e.g., the incompleteness of the census of close binaries, the use of unresolved disk indicators, and projection effects) have previously masked this correlation in smaller samples. We discuss the implications of our findings for circumstellar disk lifetimes and the formation of planets in multiple systems.
- 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/AJ/147/46
- Title:
- Properties of clumps in the NAN complex
- Short Name:
- J/AJ/147/46
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present observations of a 4.25deg^2^ area toward the North American and Pelican Nebulae in the J=1-0 transitions of ^12^CO, ^13^CO, and C^18^O. Three molecules show different emission areas with their own distinct structures. These different density tracers reveal several dense clouds with a surface density of over 500M_{sun}_pc^-2^ and a mean H_2_ column density of 5.8, 3.4, and 11.9x10^21^/cm2 for ^12^CO, ^13^CO, and C^18^O, respectively. We obtain a total mass of 5.4x10^4^M_{sun}_(^12^CO), 2.0x10^4^M_{sun}_(^13^CO), and 6.1x10^3^M_{sun}_(C^18^O) in the complex. The distribution of excitation temperature shows two phases of gas: cold gas (~10K) spreads across the whole cloud; warm gas (>20K) outlines the edge of the cloud heated by the W80 HII region. The kinetic structure of the cloud indicates an expanding shell surrounding the ionized gas produced by the HII region. There are six discernible regions in the cloud: the Gulf of Mexico, Caribbean Islands and Sea, and Pelican's Beak, Hat, and Neck. The areas of ^13^CO emission range within 2-10pc^2^ with mass of (1-5)x10^3^M_{sun}_ and line width of a few km/s. The different line properties and signs of star-forming activity indicate they are in different evolutionary stages. Four filamentary structures with complicated velocity features are detected along the dark lane in LDN 935. Furthermore, a total of 611 molecular clumps within the ^13^CO tracing cloud are identified using the ClumpFind algorithm. The properties of the clumps suggest that most of the clumps are gravitationally bound and at an early stage of evolution with cold and dense molecular gas.
- ID:
- ivo://CDS.VizieR/J/ApJ/699/742
- Title:
- Properties of cores in the Pipe Nebula
- Short Name:
- J/ApJ/699/742
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, we derive an improved core mass function (CMF) for the Pipe Nebula from a detailed comparison between measurements of visual extinction and molecular-line emission. We have compiled a refined sample of 201 dense cores toward the Pipe Nebula using a two-dimensional threshold identification algorithm informed by recent simulations of dense core populations. Measurements of radial velocities using complimentary C^18^O(1-0) observations enable us to cull out from this sample those 43 extinction peaks that are either not associated with dense gas or are not physically associated with the Pipe Nebula. Moreover, we use the derived C^18^O central velocities to differentiate between single cores with internal structure and blends of two or more physically distinct cores, superposed along the same line of sight. We then are able to produce a more robust dense core sample for future follow-up studies and a more reliable CMF than was possible previously.
