- ID:
- ivo://CDS.VizieR/J/A+A/425/927
- Title:
- Stellar objects in the Serpens cloud field
- Short Name:
- J/A+A/425/927
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present near infrared (J, H and Ks) observations of a 5'x10' sample field in the Serpens Star Formation region obtained with SOFI at the NTT. These observations are sensitive enough to detect a 20M_Jup_ brown dwarf through an extinction of A_V_~16 and are used to build an infrared census of this field in the cluster. From photometry and mass-luminosity models, we have developed a detailed methodology to extract quantitative parameters (distance modulus, extinction, spectral type, masses) for objects observed towards and inside the Serpens molecular cloud. An extinction map of the region is derived allowing us to disentangle cloud members from background field objects. Luminosities and masses for 14 low-mass stars and substellar object candidate members of the cluster are derived.
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- ID:
- ivo://CDS.VizieR/J/A+A/618/A163
- Title:
- Stokes param. of Bok globules background stars
- Short Name:
- J/A+A/618/A163
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The role of magnetic fields in the process of star formation is a matter of continuous debate. Clear observational proof of the general influence of magnetic fields on the early phase of cloud collapse is still pending. In an earlier study on Bok globules with simple structures, we find strong indications of dominant magnetic fields across large spatial scales. The aim of this study is to test the magnetic field influence across Bok globules with more complex density structures. We apply near-infrared polarimetry to trace the magnetic field structure on scales of 10^4^-10^5^au in selected Bok globules. The combination of these measurements with archival data in the optical and sub-mm wavelength range allows us to characterize the magnetic field on scales of 10^3^-10^6^au. We present polarimetric data in the near-infrared wavelength range for the three Bok globules CB34, CB56, and [OMK2002] 18, combined with archival polarimetric data in the optical wavelength range for CB34 and CB56, and in the sub millimeter wavelength range for CB34 and [OMK2002] 18. We find a strong polarization signal (P>2%) in the near-infrared for all three globules. For CB34, we detect a connection between the structure on scales of 10^4^-10^5^au to 10^5^-10^6^au. For CB56, we trace aligned polarization segments in both the near-infrared and optical data, suggesting a connection of the magnetic field structure across the whole globule. In the case of [OMK2002]18, we find ordered polarization structures on scales of 10^4^-10^5^au. We find strongly aligned polarization segments on large scales which indicate dominant magnetic fields across Bok globules with complex density structures. To reconcile our findings in globules, the lowest mass clouds known, and the results on intermediate (e.g. Taurus) and more massive (e.g. Orion) clouds, we postulate a mass dependent role of magnetic fields, whereby magnetic fields appear to be dominant on low and high mass but rather sub dominant on intermediate mass clouds.
- ID:
- ivo://CDS.VizieR/J/ApJ/802/60
- Title:
- Structure of young stellar clusters. II.
- Short Name:
- J/ApJ/802/60
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the intrinsic stellar populations (estimated total numbers of OB and pre-main-sequence stars down to 0.1M_{sun}_) that are present in 17 massive star-forming regions (MSFRs) surveyed by the MYStIX project. The study is based on the catalog of >31000 MYStIX Probable Complex Members with both disk-bearing and disk-free populations, compensating for extinction, nebulosity, and crowding effects. Correction for observational sensitivities is made using the X-ray luminosity function and the near-infrared initial mass function --a correction that is often not made by infrared surveys of young stars. The resulting maps of the projected structure of the young stellar populations, in units of intrinsic stellar surface density, allow direct comparison between different regions. Several regions have multiple dense clumps, similar in size and density to the Orion Nebula Cluster. The highest projected density of ~34000 stars/pc2 is found in the core of the RCW 38 cluster. Histograms of surface density show different ranges of values in different regions, supporting the conclusion of Bressert et al. (B10; 2010MNRAS.409L..54B) that no universal surface-density threshold can distinguish between clustered and distributed star formation. However, a large component of the young stellar population of MSFRs resides in dense environments of 200-10000 stars/pc2 (including within the nearby Orion molecular clouds), and we find that there is no evidence for the B10 conclusion that such dense regions form an extreme "tail" of the distribution. Tables of intrinsic populations for these regions are used in our companion study of young cluster properties and evolution.
- ID:
- ivo://CDS.VizieR/J/ApJ/646/1009
- Title:
- Structures of dust in Perseus molecular cloud
- Short Name:
- J/ApJ/646/1009
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of 3.5deg^2^ of submillimeter continuum and extinction data of the Perseus molecular cloud. We identify 58 clumps in the submillimeter map, and we identify 39 structures (cores) and 11 associations of structures (super cores) in the extinction map. The cumulative mass distributions of the submillimeter clumps and extinction cores have steep slopes (alpha~2 and 1.5-2, respectively), steeper than the Salpeter initial mass function (IMF; alpha=1.35), while the distribution of extinction super cores has a shallow slope (alpha~1). Most of the submillimeter clumps are well fit by stable Bonnor-Ebert spheres with 10K<T<19K and 5.5<log_10_(Pext/k)<0.6. The clumps are found only in the highest column density regions (AV>5-7mag), although Bonnor-Ebert models suggest that we should have been able to detect them at lower column densities if they exist.
- ID:
- ivo://CDS.VizieR/J/ApJ/818/73
- Title:
- Study of protostars in the Perseus molecular cloud
- Short Name:
- J/ApJ/818/73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a multiplicity study of all known protostars (94) in the Perseus molecular cloud from a Karl G. Jansky Very Large Array survey at Ka-band (8 mm and 1 cm) and C-band (4 and 6.6 cm). The observed sample has a bolometric luminosity range between 0.1 L_{sun}_ and ~33 L_{sun}_, with a median of 0.7 L_{sun}_. This multiplicity study is based on the Ka-band data, having a best resolution of ~0.065" (15 au) and separations out to ~43" (10000 au) can be probed. The overall multiplicity fraction (MF) is found to be 0.40+/-0.06 and the companion star fraction (CSF) is 0.71+/-0.06. The MF and CSF of the Class 0 protostars are 0.57+/-0.09 and 1.2+/-0.2, and the MF and CSF of Class I protostars are both 0.23+/-0.08. The distribution of companion separations appears bi-modal, with a peak at ~75 au and another peak at ~3000 au. Turbulent fragmentation is likely the dominant mechanism on >1000 au scales and disk fragmentation is likely to be the dominant mechanism on <200 au scales. Toward three Class 0 sources we find companions separated by <30 au. These systems have the smallest separations of currently known Class 0 protostellar binary systems. Moreover, these close systems are embedded within larger (50-400 au) structures and may be candidates for ongoing disk fragmentation.
- ID:
- ivo://CDS.VizieR/J/ApJ/639/259
- Title:
- Sub-mm clumps in Orion B South molecular cloud
- Short Name:
- J/ApJ/639/259
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from a survey of a 1300arcmin^2^ region of the Orion B South molecular cloud, including NGC 2024, NGC 2023, and the Horsehead Nebula (B33), obtained using the Submillimetre Common-User Bolometer Array (SCUBA) on the James Clerk Maxwell Telescope (JCMT). Submillimeter continuum observations at 450 and 850{mu}m are discussed. Using an automated algorithm, 57 discrete emission features ("clumps") are identified in the 850{mu}m map.
- ID:
- ivo://CDS.VizieR/J/ApJ/559/307
- Title:
- Sub-mm mapping in Orion B molecular cloud
- Short Name:
- J/ApJ/559/307
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from a survey of a 900 arcmin^2^ region of the Orion B molecular cloud, including NGC 2068, NGC 2071, and HH 24/25/26, at 850{mu}m using the Submillimeter Common-User Bolometer Array (SCUBA) on the James Clerk Maxwell Telescope. Following the techniques developed by Johnstone et al. (2000ApJ...545..327J), we identify 75 independent objects and compute size, flux, and degree of central concentration. Comparison with isothermal, pressure-confined, self-gravitating Bonnor-Ebert spheres implies that the clumps have internal temperatures of 20-40K and surface pressures 5.5<log(P/k)[CGS]<6.5. The clump masses span 0.2-12.3M_{sun}_ assuming typical dust temperatures and a dust emissivity {kappa}_850_=0.01cm^2^/g.
- ID:
- ivo://CDS.VizieR/J/ApJS/201/13
- Title:
- Submm polarization of Galactic clouds
- Short Name:
- J/ApJS/201/13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Hertz and SCUBA polarimeters, working at 350um and 850um, respectively, have measured the polarized emission in scores of Galactic clouds. Of the clouds in each data set, 17 were mapped by both instruments with good polarization signal-to-noise ratios. We present maps of each of these 17 clouds comparing the dual-wavelength polarization amplitudes and position angles at the same spatial locations.
- ID:
- ivo://CDS.VizieR/J/ApJ/599/1049
- Title:
- Supergiant molecular complexes in the Antennae
- Short Name:
- J/ApJ/599/1049
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used previously published observations of the CO emission from the Antennae (NGC 4038/4039) to study the detailed properties of the supergiant molecular complexes with the goal of understanding the formation of young massive star clusters.
- ID:
- ivo://CDS.VizieR/J/ApJ/526/788
- Title:
- Survey of infall motions toward starless cores
- Short Name:
- J/ApJ/526/788
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first results of a survey of 220 starless cores selected primarily by their optical obscuration and observed in CS (2-1), N_2_H^+^ (1-0), and C^18^O (1-0) using the Northeast Radio Observatory Corporation (NEROC) Haystack 37 m telescope. We have detected 163 out of 196 sources observed in CS, 72 out of 142 in N_2_H^+^, and 30 out of 30 in C18O. In total, 69 sources were detected in both CS and N_2_H^+^. The isolated component of the N_2_H^+^ (1-0) spectrum (F_1_F = 0,1-1,2) usually shows a weak symmetric profile that is optically thin. In contrast, a significant fraction of the CS spectra show non-Gaussian shapes, which we interpret as arising from a combination of self-absorption due to lower excitation gas in the core front and kinematics in the core. The distribution of the normalized velocity difference ({delta}V_CS_) between the CS and N_2_H^+^ peaks appears significantly skewed to the blue (V_CS_ < 0), as was found in a similar study of dense cores with embedded young stellar objects (YSOs). The incidence of sources with blue asymmetry tends to increase as the total optical depth or the integrated intensity of the N_2_H^+^ line increases.
