- ID:
- ivo://CDS.VizieR/J/ApJ/767/36
- Title:
- APEX observations of HOPS protostars
- Short Name:
- J/ApJ/767/36
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We perform a census of the reddest, and potentially youngest, protostars in the Orion molecular clouds using data obtained with the PACS instrument on board the Herschel Space Observatory and the LABOCA and SABOCA instruments on APEX as part of the Herschel Orion Protostar Survey (HOPS). A total of 55 new protostar candidates are detected at 70{mu}m and 160{mu}m that are either too faint (m_24_>7mag) to be reliably classified as protostars or undetected in the Spitzer/MIPS 24{mu}m band. We find that the 11 reddest protostar candidates with log{lambda}F_{lambda}_70/{lambda}F_{lambda}_24>1.65 are free of contamination and can thus be reliably explained as protostars. The remaining 44 sources have less extreme 70/24 colors, fainter 70{mu}m fluxes, and higher levels of contamination. Taking the previously known sample of Spitzer protostars and the new sample together, we find 18 sources that have log{lambda}F_{lambda}_70/{lambda}F_{lambda}_24>1.65; we name these sources "PACS Bright Red sources," or PBRs. Our analysis reveals that the PBR sample is composed of Class 0 like sources characterized by very red spectral energy distributions (SEDs; T_bol_<45K) and large values of sub-millimeter fluxes (L_smm_/L_bol_>0.6%). Modified blackbody fits to the SEDs provide lower limits to the envelope masses of 0.2-2M_{sun}_ and luminosities of 0.7-10L_{sun}_. Based on these properties, and a comparison of the SEDs with radiative transfer models of protostars, we conclude that the PBRs are most likely extreme Class 0 objects distinguished by higher than typical envelope densities and hence, high mass infall rates.
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- ID:
- ivo://CDS.VizieR/J/ApJS/236/27
- Title:
- APOGEE-2 survey of Orion Complex (OSFC). I.
- Short Name:
- J/ApJS/236/27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Orion Star-forming Complex (OSFC) is a central target for the APOGEE-2 Young Cluster Survey. Existing membership catalogs span limited portions of the OSFC, reflecting the difficulty of selecting targets homogeneously across this extended, highly structured region. We have used data from wide-field photometric surveys to produce a less biased parent sample of young stellar objects (YSOs) with infrared (IR) excesses indicative of warm circumstellar material or photometric variability at optical wavelengths across the full 420deg^2^ extent of the OSFC. When restricted to YSO candidates with H<12.4, to ensure S/N~100 for a six-visit source, this uniformly selected sample includes 1307 IR excess sources selected using criteria vetted by Koenig & Leisawitz (2014ApJ...791..131K) and 990 optical variables identified in the Pan-STARRS1 3{pi} survey: 319 sources exhibit both optical variability and evidence of circumstellar disks through IR excess. Objects from this uniformly selected sample received the highest priority for targeting, but required fewer than half of the fibers on each APOGEE-2 plate. We filled the remaining fibers with previously confirmed and new color-magnitude selected candidate OSFC members. Radial velocity measurements from APOGEE-1 and new APOGEE-2 observations taken in the survey's first year indicate that ~90% of the uniformly selected targets have radial velocities consistent with Orion membership. The APOGEE-2 Orion survey will include >1100 bona fide YSOs whose uniform selection function will provide a robust sample for comparative analyses of the stellar populations and properties across all sub-regions of Orion.
- ID:
- ivo://CDS.VizieR/J/ApJ/802/59
- Title:
- A search for YSO candidates in IRDC G53.2
- Short Name:
- J/ApJ/802/59
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present star formation activity in the infrared dark cloud (IRDC) G53.2, a remarkable IRDC located at Galactic coordinates (l,b)~(53.2{deg},0.0{deg}) based on the census of young stellar object (YSO) candidates. IRDC G53.2 was previously identified as several IRDCs in mid-IR images, but it is in fact a long (>~45pc) cloud, well consistent with a CO cloud at v~23km/s (or at d~1.7kpc). We present a point-source catalog of IRDC G53.2 that contains ~370 sources from our photometry of the Spitzer MIPS 24{mu}m data and Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) Catalog. The classification of the identified sources based on their spectral index and control field analysis to remove field star contamination reveals that IRDC G53.2 is an active star-forming region with ~300 YSO candidates. We compare the YSO classification based on spectral index, mid-IR colors, and the wavelength range used, which results in consistent classification, except for flat-spectrum objects, with some ambiguity between Class I and II. Comparison of the YSO population in IRDC G53.2 with those of other nearby star-forming clusters indicates that they are similar in age; on the other hand, stronger association with mid-IR stellar sources in IRDC G53.2 compared with other IRDCs indicates that IRDC G53.2 is at a later evolutionary stage among IRDCs. Spatial distribution of the YSO candidates in IRDC G53.2 shows a good correlation with ^13^CO column density and far-IR emission, and earlier-class objects tend to be more clustered in the regions with higher density.
- ID:
- ivo://CDS.VizieR/J/ApJ/764/133
- Title:
- Auriga-California giant molecular cloud
- Short Name:
- J/ApJ/764/133
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have mapped the Auriga/California molecular cloud with the Herschel PACS and SPIRE cameras and the Bolocam 1.1mm camera on the Caltech Submillimeter Observatory with the eventual goal of quantifying the star formation and cloud structure in this giant molecular cloud (GMC) that is comparable in size and mass to the Orion GMC, but which appears to be forming far fewer stars. We have tabulated 60 compact 70/160 {mu}m sources that are likely pre-main-sequence objects and correlated those with Spitzer and WISE mid-IR sources. At 1.1 mm, we find 18 cold, compact sources and discuss their properties. The most important result from this part of our study is that we find a modest number of additional compact young objects beyond those identified at shorter wavelengths with Spitzer.
- ID:
- ivo://CDS.VizieR/J/ApJ/822/49
- Title:
- Candidate YSOs in AFGL 333 with NEWFIRM & Spitzer
- Short Name:
- J/ApJ/822/49
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- One of the key questions in the field of star formation is the role of stellar feedback on the subsequent star formation process. The W3 giant molecular cloud complex at the western border of the W4 super bubble is thought to be influenced by the massive stars in W4. This paper presents a study of the star formation activity within AFGL 333, a ~10^4^M_{sun}_ cloud within W3, using deep JHKs photometry obtained from the NOAO Extremely Wide Field Infrared Imager combined with Spitzer IRAC and MIPS photometry. Based on the infrared excess, we identify 812 candidate young stellar objects (YSOs) in the complex, of which 99 are Class I and 713 are Class II sources. The stellar density analysis of YSOs reveals three major stellar aggregates within AFGL333, namely AFGL 333 Main, AFGL 333 NW1 and AFGL 333 NW2. The disk fraction within AFGL 333 is estimated to be ~50%-60%. We use the extinction map made from the H-K_s_ colors of the background stars and CO data to understand the cloud structure and to estimate the cloud mass. From the stellar and cloud mass associated with AFGL 333, we infer that the region is currently forming stars with an efficiency of ~4.5% and at a rate of ~2-3M_{sun}_/Myr/pc^2^. In general, the star formation activity within AFGL 333 is comparable to that of nearby low mass star-forming regions. We do not find any strong evidence to suggest that the stellar feedback from the massive stars of nearby W4 super bubble has affected the global star formation properties of the AFGL 333 region.
- ID:
- ivo://CDS.VizieR/J/ApJ/696/47
- Title:
- Chandra study of Rosette star-forming complex. II.
- Short Name:
- J/ApJ/696/47
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We explore here the young stellar populations in the Rosette Molecular Cloud (RMC) region with high spatial resolution X-ray images from the Chandra X-ray Observatory, which are effective in locating weak-lined T Tauri stars as well as disk-bearing young stars. A total of 395 X-ray point sources are detected, 299 of which (76%) have an optical or near-infrared (NIR) counterpart identified from deep FLAMINGOS images. From X-ray and mass sensitivity limits, we infer a total population of ~1700 young stars in the survey region. Based on smoothed stellar surface density maps, we investigate the spatial distribution of the X-ray sources and define three distinctive structures and substructures within them. Structures B and C are associated with previously known embedded IR clusters, while structure A is a new X-ray-identified unobscured cluster. A high-mass protostar RMCX 89=IRAS 06306+0437 and its associated sparse cluster are studied.
- ID:
- ivo://CDS.VizieR/J/ApJ/838/49
- Title:
- CO large-field observations around l=150{deg}
- Short Name:
- J/ApJ/838/49
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present large-field (4.25x3.75deg^2^) mapping observations toward the Galactic region centered at l=150{deg},b=3.5{deg} in the J=1-0 emission line of CO isotopologues (^12^CO, ^13^CO, and C^18^O), using the 13.7m millimeter-wavelength telescope of the Purple Mountain Observatory. Based on the ^13^CO observations, we reveal a filamentary cloud in the Local Arm at a velocity range of -0.5 to 6.5km/s. This molecular cloud contains 1 main filament and 11 sub-filaments, showing the so-called "ridge-nest" structure. The main filament and three sub-filaments are also detected in the C^18^O line. The velocity structures of most identified filaments display continuous distribution with slight velocity gradients. The measured median excitation temperature, line width, length, width, and linear mass of the filaments are ~9.28K, 0.85km/s, 7.30pc, 0.79pc, and 17.92M_{sun}_/pc, respectively, assuming a distance of 400pc. We find that the four filaments detected in the C^18^O line are thermally supercritical, and two of them are in the virialized state, and thus tend to be gravitationally bound. We identify in total 146 ^13^CO clumps in the cloud, about 77% of the clumps are distributed along the filaments. About 56% of the virialized clumps are found to be associated with the supercritical filaments. Three young stellar object candidates are also identified in the supercritical filaments, based on the complementary infrared data. These results indicate that the supercritical filaments, especially the virialized filaments, may contain star-forming activities.
- ID:
- ivo://CDS.VizieR/J/ApJ/897/74
- Title:
- Cold & molecular clumps and YSOs within G15.684-0.29
- Short Name:
- J/ApJ/897/74
- Date:
- 11 Mar 2022
- Publisher:
- CDS
- Description:
- The bubble G15.684-0.29 has a radius of 15.7pc. Its large size indicates that it may have enough time to trigger star formation. We identify 39 dense cold clumps around the bubble from the HI-GAL survey. All of them satisfy the criteria for forming massive stars, and most of them lie in the bubble shell. We identify 19 molecular clumps around the bubble from the 12CO(3-2) survey, all of which are gravitationally bound. We found 9 Class I YSOs, 28 Class II YSOs, and 12 transition disks (TDs) around the bubble. For those young stellar objects (YSOs) located within the bubble boundary, 6 of 7 Class I YSOs lie in the shell, 15 of 22 Class II YSOs lie inside the bubble, and 3 of 5 TDs lie inside the bubble. The dynamical age of G15.684-0.29 in a turbulent medium is ~4Myr, which is much greater than the shell fragmentation time, ~0.82-1.74Myr. We suggest that triggered star formation may be ongoing in the shell of the bubble, and the collect and collapse model may work here. However, we cannot rule out the possibility that the radiation-driven implosion model may work on the formation of some YSOs. As we expected, the larger bubble has a much longer dynamical age, but we failed to find a clear age gradient for YSOs around the bubble.
- ID:
- ivo://CDS.VizieR/J/ApJ/706/83
- Title:
- Embedded YSO candidates in W51
- Short Name:
- J/ApJ/706/83
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 737 candidate young stellar objects (YSOs) near the W51 giant molecular cloud over an area of 1.25x1.00{deg} selected from Spitzer Space Telescope data. We use spectral energy distribution fits to identify YSOs and distinguish them from main-sequence (MS) or red giant stars, asymptotic giant branch stars, and background galaxies. Based on extinction of each YSO, we separate a total of 437 YSOs associated with the W51 region from the possible foreground sources. We identify 69 highly embedded Stage 0/I candidate YSOs in our field with masses >5M_{sun}_ (corresponding to mid- to early-B MS spectral types), 46 of which are located in the central active star-forming regions of W51A and W51B. From the YSOs associated with W51, we find evidence for mass segregation showing that the most massive YSOs are concentrated on the W51 HII region complex.
- ID:
- ivo://CDS.VizieR/J/AJ/137/4072
- Title:
- Infrared photometry of G216-2.5 YSOs
- Short Name:
- J/AJ/137/4072
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The giant molecular cloud G216-2.5, also known as Maddalena's cloud or the Maddalena-Thaddeus cloud, is distinguished by an unusual combination of high gas mass (1-6x10^5^_M{sun}), low kinetic temperatures (10K), and the lack of bright far-IR emission. Although star formation has been detected in neighboring satellite clouds, little evidence for star formation has been found in the main body of this cloud. Using a combination of mid-IR observations with the IRAC and Multiband Imaging Photometer for Spitzer instruments onboard the Spitzer Space Telescope, and near-IR images taken with the Flamingos camera on the KPNO 2.1m telescope, we identify a population of 41 young stars with disks and 33 protostars in the center of the cloud. Most of the young stellar objects are coincident with a filamentary structure of dense gas detected in CS (2->1). These observations show that the main body of G216 is actively forming stars, although at a low stellar density comparable to that found in the Taurus cloud.
