- ID:
- ivo://CDS.VizieR/J/ApJ/743/39
- Title:
- Spitzer observations of W3 molecular cloud
- Short Name:
- J/ApJ/743/39
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work, we have carried out an in-depth analysis of the young stellar content in the W3 giant molecular cloud (GMC). The young stellar object (YSO) population was identified and classified in the Infrared Array Camera/Multiband Imaging Photometer color-magnitude space according to the "Class" scheme and compared to other classifications based on intrinsic properties. Class 0/I and II candidates were also compared to low-/intermediate-mass pre-main-sequence (PMS) stars selected through their colors and magnitudes in the Two Micron All Sky Survey. We find that a reliable color/magnitude selection of low-mass PMS stars in the infrared requires prior knowledge of the protostar population, while intermediate-mass objects can be more reliably identified. By means of the minimum spanning tree algorithm and our YSO spatial distribution and age maps, we investigated the YSO groups and the star formation history in W3.
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- ID:
- ivo://CDS.VizieR/J/ApJ/654/338
- Title:
- Spitzer photometry in W3 molecular cloud
- Short Name:
- J/ApJ/654/338
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new images of the giant molecular cloud W3 obtained with the Infrared Array Camera (IRAC) and the Multiband Imaging Photometer for Spitzer (MIPS) on board the Spitzer Space Telescope. The images encompass the star forming regions W3 Main, W3(OH), and a region that we refer to as the Central Cluster, which encloses the emission nebula IC 1795. We present a star count analysis of the point sources detected in W3. The star count analysis shows that the stellar population of the Central Cluster, when compared to that in the background, contains an over density of sources. The Central Cluster also contains an excess of sources with colors consistent with Class II young stellar objects (YSOs). An analysis of the color-color diagrams also reveals a large number of Class II YSOs in the Central Cluster. Our results suggest that an earlier epoch of star formation created the Central Cluster, created a cavity, and triggered the active star formation in the W3 Main and W3(OH) regions. We also detect a new outflow and its candidate exciting star.
- ID:
- ivo://CDS.VizieR/J/AJ/144/192
- Title:
- Spitzer survey of Orion A and B. I. YSO catalog
- Short Name:
- J/AJ/144/192
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a survey of the Orion A and B molecular clouds undertaken with the IRAC and MIPS instruments on board Spitzer. In total, five distinct fields were mapped, covering 9deg^2^ in five mid-IR bands spanning 3-24{mu}m. The survey includes the Orion Nebula Cluster, the Lynds 1641, 1630, and 1622 dark clouds, and the NGC 2023, 2024, 2068, and 2071 nebulae. These data are merged with the Two Micron All Sky Survey point source catalog to generate a catalog of eight-band photometry. We identify 3479 dusty young stellar objects (YSOs) in the Orion molecular clouds by searching for point sources with mid-IR colors indicative of reprocessed light from dusty disks or infalling envelopes. The YSOs are subsequently classified on the basis of their mid-IR colors and their spatial distributions are presented. We classify 2991 of the YSOs as pre-main-sequence stars with disks and 488 as likely protostars. Most of the sources were observed with IRAC in two to three epochs over six months; we search for variability between the epochs by looking for correlated variability in the 3.6 and 4.5{mu}m bands. We find that 50% of the dusty YSOs show variability. The variations are typically small (~0.2mag) with the protostars showing a higher incidence of variability and larger variations. The observed correlations between the 3.6, 4.5, 5.8, and 8{mu}m variability suggests that we are observing variations in the heating of the inner disk due to changes in the accretion luminosity or rotating accretion hot spots.
- ID:
- ivo://CDS.VizieR/J/ApJ/683/822
- Title:
- Star formation in Ophiuchus and Perseus II.
- Short Name:
- J/ApJ/683/822
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a census of the population of deeply embedded young stellar objects (YSOs) in the Ophiuchus molecular cloud complex based on a combination of Spitzer Space Telescope mid-infrared data from the "Cores to Disks" (c2d) legacy team and JCMT/SCUBA submillimeter maps from the COMPLETE team. We have applied a method developed for identifying embedded protostars in Perseus to these data sets and in this way construct a relatively unbiased sample of 27 candidate embedded protostars with envelopes more massive than our sensitivity limit (about 0.1M_{sun}_).
- ID:
- ivo://CDS.VizieR/J/A+A/468/1009
- Title:
- Star formation in Perseus. II.
- Short Name:
- J/A+A/468/1009
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Hatchell et al. (2005, Cat. <J/A+A/440/151>, Paper I) published a submillimetre continuum map of the Perseus molecular cloud, detecting the starless and protostellar cores within it. The aim is to determine the evolutionary stage of each submm core in Perseus, and investigate the lifetimes of these phases.
- ID:
- ivo://CDS.VizieR/J/ApJ/833/229
- Title:
- Star forming cloud-giant molecular cloud complexes
- Short Name:
- J/ApJ/833/229
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Star formation on galactic scales is known to be a slow process, but whether it is slow on smaller scales is uncertain. We cross-correlate 5469 giant molecular clouds (GMCs) from a new all-sky catalog with 256 star-forming complexes (SFCs) to build a sample of 191 SFC-GMC complexes-collections of multiple clouds each matched to 191 SFCs. The total mass in stars harbored by these clouds is inferred from WMAP free-free fluxes. We measure the GMC mass, the virial parameter, the star formation efficiency {epsilon} and the star formation rate per freefall time {epsilon}_ff_. Both {epsilon} and {epsilon}_ff_ range over 3-4 orders of magnitude. We find that 68.3% of the clouds fall within {sigma}_log{epsilon}_=0.79+/-0.22dex and {sigma}_log{epsilon}_ff__=0.91+/-0.22dex about the median. Compared to these observed scatters, a simple model with a time-independent {epsilon}_ff_ that depends on the host GMC properties predicts {sigma}_log{epsilon}_ff__=0.12-0.24. Allowing for a time-variable {epsilon}_ff_, we can recover the large dispersion in the rate of star formation. This strongly suggests that star formation in the Milky Way is a dynamic process on GMC scales. We also show that the surface star formation rate profile of the Milky Way correlates well with the molecular gas surface density profile.
- ID:
- ivo://CDS.VizieR/J/AJ/153/214
- Title:
- Star-forming potential in the Perseus complex
- Short Name:
- J/AJ/153/214
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of our investigation of the star-forming potential in the Perseus star-forming complex. We build on previous starless core, protostellar core, and young stellar object (YSO) catalogs from Spitzer (3.6-70 {mu}m), Herschel (70-500 {mu}m), and SCUBA (850 {mu}m) observations in the literature. We place the cores and YSOs within seven star-forming clumps based on column densities greater than 5x10^21^/cm^2^. We calculate the mean density and free-fall time for 69 starless cores as ~5.55x10^-19^ g/cm^3^ and ~0.1 Myr, respectively, and we estimate the star formation rate for the near future as ~150 M_{sun}_/Myr. According to Bonnor-Ebert stability analysis, we find that majority of starless cores in Perseus are unstable. Broadly, these cores can collapse to form the next generation of stars. We found a relation between starless cores and YSOs, where the numbers of young protostars (Class 0 + Class I) are similar to the numbers of starless cores. This similarity, which shows a one-to-one relation, suggests that these starless cores may form the next generation of stars with approximately the same formation rate as the current generation, as identified by the Class 0 and Class I protostars. It follows that if such a relation between starless cores and any YSO stage exists, the SFR values of these two populations must be nearly constant. In brief, we propose that this one-to-one relation is an important factor in better understanding the star formation process within a cloud.
- ID:
- ivo://CDS.VizieR/J/A+A/579/A80
- Title:
- Star-forming regions deuteration
- Short Name:
- J/A+A/579/A80
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The chemical evolution in high-mass star-forming regions is still poorly constrained. Studying the evolution of deuterated molecules allows distinguishing between subsequent stages of high-mass star formation regions based on the strong temperature dependence of deuterium isotopic fractionation. We observed a sample of 59 sources including 19 infrared dark clouds, 20 high-mass protostellar objects, 11 hot molecular cores and 9 ultra-compact HII regions in the (3-2) transitions of the four deuterated molecules, DCN, DNC, DCO^+^, and N_2_D^+^ as well as their non-deuterated counterparts. The overall detection fraction of DCN, DNC, and DCO^+^ is high and exceeds 50% for most of the stages. N_2_D^+^ was only detected in a few infrared dark clouds and high-mass protostellar objects. This may be related to problems in the bandpass at the transition frequency and to low abundances in the more evolved, warmer stages. We find median D/H ratios of 0.02 for DCN, 0.005 for DNC, 0.0025 for DCO^+^, and 0.02 for N_2_D^+^. While the D/H ratios of DNC, DCO^+^, and N_2_D^+^ decrease with time, DCN/HCN peaks at the hot molecular core stage. We only found weak correlations of the D/H ratios for N_2_D^+^ with the luminosity of the central source and the FWHM of the line, and no correlation with the H_2_ column density. In combination with a previously observed set of 14 other molecules (Paper I), we fitted the calculated column densities with an elaborate 1D physico-chemical model with time-dependent D-chemistry including ortho- and para-H_2_ states. Good overall fits to the observed data were obtained with the model. This is one of the first times that observations and modeling were combined to derive chemically based best-fit models for the evolution of high-mass star formation including deuteration.
- ID:
- ivo://CDS.VizieR/J/A+A/540/A113
- Title:
- Starless clumps in ATLASGAL
- Short Name:
- J/A+A/540/A113
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Understanding massive star formation requires comprehensive knowledge about the initial conditions of this process. The cradles of massive stars are believed to be located in dense and massive molecular clumps. In this study, we present an unbiased sample of the earliest stages of massive star formation across 20deg^2^ of the sky. Within the region 10{deg}<l<20{deg} and |b|<1{deg}, we search the ATLASGAL survey at 870um for dense gas condensations. These clumps are carefully examined for indications of ongoing star formation using YSOs from the GLIMPSE source catalog as well as sources in the 24um MIPSGAL images, to search for starless clumps. We calculate the column densities as well as the kinematic distances and masses for sources where the v_lsr_ is known from spectroscopic observations. Within the given region, we identify 210 starless clumps with peak column densities >10^23^cm^-2^. In particular, we identify potential starless clumps on the other side of the Galaxy. The sizes of the clumps range between 0.1pc and 3pc with masses between a few tens of M_{sun}_ up to several ten thousands of M_{sun}_.
- ID:
- ivo://CDS.VizieR/J/A+A/630/A136
- Title:
- Starless core L1521E chemical structure
- Short Name:
- J/A+A/630/A136
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained ~2.5x2.5 arcminute maps toward L1521E using the IRAM-30m telescope in transitions of various species, including C^17^O, CH_3_OH c-C_3_H_2_, CN, SO, H_2_CS, and CH_3_CCH. We derived abundances for the observed species and compared them to those obtained toward L1544. We estimated CO depletion factors using the C^17^O IRAM-30m map, an N(H2) map derived from Herschel/ SPIRE data and a 1.2 mm dust continuum emission map obtained with the IRAM-30m telescope. Similarly to L1544, c-C_3_H_2_ and CH_3_OH peak at different positions. Most species peak toward the c-C_3_H_2_ peak: C_2_S, C_3_S, HCS^+^, HC_3_N, H_2_CS, CH_3_CCH, C^34^S. C^17^O and SO peak close to both the c-C_3_H_2_ and the CH_3_OH peaks. CN and N_2_H^+^ peak close to the Herschel dust peak. We found evidence of CO depletion toward L1521E. The lower limit of the CO depletion factor derived toward the Herschel dust peak is 4.3+/-1.6, which is about a factor of three lower than toward L1544. We derived abundances for several species toward the dust peaks of L1521E and L1544. The abundances of most sulfur-bearing molecules such as C_2_S, HCS^+^, C^34^S, C^33^S, and HCS^+^ are higher toward L1521E than toward L1544 by factors of ~2-20, compared to the abundance of A-CH_3_OH. The abundance of methanol is very similar toward the two cores.
