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18051. YSOs in the Serpens Molecular Cloud
ID:
ivo://CDS.VizieR/J/ApJ/714/778
Title:
YSOs in the Serpens Molecular Cloud
Short Name:
J/ApJ/714/778
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present Spitzer InfraRed Spectrograph (IRS) mid-infrared (5-35um) spectra of a complete flux-limited sample (>=3mJy at 8um) of young stellar object (YSO) candidates selected on the basis of their infrared colors in the Serpens Molecular Cloud. Spectra of 147 sources are presented and classified. Background stars (with slope consistent with a reddened stellar spectrum and silicate features in absorption), galaxies (with redshifted polycyclic aromatic hydrocarbon (PAH) features), and a planetary nebula (with high ionization lines) amount to 22% of contamination in this sample, leaving 115 true YSOs. Sources with rising spectra and ice absorption features, classified as embedded Stage I protostars, amount to 18% of the sample. The remaining 82% (94) of the disk sources are analyzed in terms of spectral energy distribution shapes, PAHs, and silicate features. The presence, strength, and shape of these silicate features are used to infer disk properties for these systems. About 8% of the disks have 30/13um flux ratios consistent with cold disks with inner holes or gaps, and 3% of the disks show PAH emission.
18052. YSOs in the star-forming regions W51 & W43
ID:
ivo://CDS.VizieR/J/ApJ/839/108
Title:
YSOs in the star-forming regions W51 & W43
Short Name:
J/ApJ/839/108
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of our investigation of the star-forming complexes W51 and W43, two of the brightest in the first Galactic quadrant. In order to determine the young stellar object (YSO) populations in W51 and W43 we used color-magnitude relations based on Spitzer mid-infrared and 2MASS/UKIDSS near- infrared data. We identified 302 Class I YSOs and 1178 Class II/transition disk candidates in W51, and 917 Class I YSOs and 5187 Class II/transition disk candidates in W43. We also identified tens of groups of YSOs in both regions using the Minimal Spanning Tree (MST) method. We found similar cluster densities in both regions, even though Spitzer was not able to probe the densest part of W43. By using the Class II/I ratios, we traced the relative ages within the regions and, based on the morphology of the clusters, we argue that several sites of star formation are independent of one another in terms of their ages and physical conditions. We used spectral energy distribution- fitting to identify the massive YSO (MYSO) candidates since they play a vital role in the star formation process, and then examined them to see if they are related to any massive star formation tracers such as UCH II regions, masers, or dense fragments. We identified 17 MYSO candidates in W51, and 14 in W43, respectively, and found that groups of YSOs hosting MYSO candidates are positionally associated with H II regions in W51, though we do not see any MYSO candidates associated with previously identified massive dense fragments in W43.
18053. YSOs in Vul OB1 association
ID:
ivo://CDS.VizieR/J/ApJ/712/797
Title:
YSOs in Vul OB1 association
Short Name:
J/ApJ/712/797
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Vulpecula OB association, Vul OB1, is a region of active star formation located in the Galactic plane at 2.3kpc from the Sun. Previous studies suggest that sequential star formation is propagating along this 100pc long molecular complex. In this paper, we use Spitzer MIPSGAL and GLIMPSE data to reconstruct the star formation history of Vul OB1, and search for signatures of past triggering events. We make a census of young stellar objects (YSOs) in Vul OB1 based on IR color and magnitude criteria, and we rely on the properties and nature of these YSOs to trace recent episodes of massive star formation. We find 856 YSO candidates, and show that the evolutionary stage of the YSO population in Vul OB1 is rather homogeneous -ruling out the scenario of propagating star formation. We estimate the current star formation efficiency to be ~8%. We also report the discovery of a dozen pillar-like structures, which are confirmed to be sites of small scale triggered star formation.
18054. YSOs on HII complex Sh2-252
ID:
ivo://CDS.VizieR/J/MNRAS/432/3445
Title:
YSOs on HII complex Sh2-252
Short Name:
J/MNRAS/432/3445
Date:
21 Oct 2021
Publisher:
CDS
Description:
The optically bright, extended HII region Sh2-252 is a part of the Gemini OB1 association. This region is mainly composed of two small clusters NGC 2175s and Teu 136 and four CHII regions namely A, B, C and E. In this paper, an extensive survey of the star-forming complex Sh2-252 has been undertaken with an aim to explore its hidden young stellar population, its characteristics, spatial distribution, morphology of the region and finally to understand the star formation scenario of the complex for the first time. Spitzer-IRAC, MIPS photometry (3.6-24um) are combined with 2MASS-NIR and optical data sets to identify and classify the YSOs by their IR excess emission from their circumstellar material. From the well-fit models for each source derived from the SED fitting tool, we calculated the {chi}^2^ weighted model parameters such as the stellar mass (M*), temperature (T*), stellar age (t*), mass of the disc (Mdisc), disc accretion rate (dMdisc/dt), envelope accretion rate (dMenv/dt) presented in table1.dat.
18055. YSOs population of Sh2-294 with Spitzer/IRAC
ID:
ivo://CDS.VizieR/J/ApJ/755/20
Title:
YSOs population of Sh2-294 with Spitzer/IRAC
Short Name:
J/ApJ/755/20
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Sh2-294 H II region ionized by a single B0V star features several infrared excess sources, a photodissociation region, and also a group of reddened stars at its border. The star formation scenario in this region seems to be quite complex. In this paper, we present follow-up results of Sh2-294 H II region at 3.6, 4.5, 5.8, and 8.0{mu}m observed with the Spitzer Space Telescope Infrared Array Camera (IRAC), coupled with H_2_(2.12{mu}m) observation, to characterize the young population of the region and to understand its star formation history. We identified 36 young stellar object (YSO, Class I, Class II, and Class I/II) candidates using IRAC color-color diagrams. It is found that Class I sources are preferentially located at the outskirts of the H II region and associated with enhanced H_2_emission; none of them are located near the central cluster. Combining the optical to mid-infrared (MIR) photometry of the YSO candidates and using the spectral energy distribution fitting models, we constrained stellar parameters and the evolutionary status of 33 YSO candidates. Most of them are interpreted by the model as low-mass (<4 M_{sun}_) YSOs; however, we also detected a massive YSO (~9 M_{sun}_) of Class I nature, embedded in a cloud of visual extinction of ~24 mag.
18056. YSOs search in LDN 1340 in optical
ID:
ivo://CDS.VizieR/J/ApJ/822/79
Title:
YSOs search in LDN 1340 in optical
Short Name:
J/ApJ/822/79
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have performed an optical spectroscopic and photometric search for young stellar objects associated with the molecular cloud Lynds 1340, and examined the structure of the cloud by constructing an extinction map, based on SDSS data. The new extinction map suggests a shallow, strongly fragmented cloud, having a mass of some 3700M_{sun}_. Longslit spectroscopic observations of the brightest stars over the area of L1340 revealed that the most massive star associated with L1340 is a B4-type, ~5M_{sun}_ star. The new spectroscopic and photometric data of the intermediate-mass members led to a revised distance of 825_-80_^+110^pc, and revealed seven members of the young stellar population with M>~2M_{sun}_. Our search for H{alpha} emission line stars, conducted with the Wide Field Grism Spectrograph 2 on the 2.2m telescope of the University of Hawaii and covering a 30'x40' area, resulted in the detection of 75 candidate low-mass pre-main sequence stars, 58 of which are new. We constructed spectral energy distributions (SEDs) of our target stars, based on SDSS, 2MASS, Spitzer, and WISE photometric data, derived their spectral types, extinctions, and luminosities from BVRIJ fluxes, estimated masses by means of pre-main sequence evolutionary models, and examined the disk properties utilizing the 2-24{mu}m interval of the SED. We measured the equivalent width of the H{alpha} lines and derived accretion rates. The optically selected sample of pre-main sequence stars has a median effective temperature of 3970K, a stellar mass of 0.7M_{sun}_, and an accretion rate of 7.6x10^-9^M_{sun}_/yr.
18057. YSOs search in Stock 8 with opt. to IR photom.
ID:
ivo://CDS.VizieR/J/ApJ/836/98
Title:
YSOs search in Stock 8 with opt. to IR photom.
Short Name:
J/ApJ/836/98
Date:
21 Oct 2021
Publisher:
CDS
Description:
The evolution of H II regions/supershells can trigger a new generation of stars/clusters at their peripheries, with environmental conditions that may affect the initial mass function, disk evolution, and star formation efficiency. In this paper we study the stellar content and star formation processes in the young cluster Stock 8, which itself is thought to be formed during the expansion of a supershell. We present deep optical photometry along with JHK and 3.6 and 4.5{mu}m photometry from UKIDSS and Spitzer-IRAC. We use multicolor criteria to identify the candidate young stellar objects in the region. Using evolutionary models, we obtain a median log(age) of ~6.5 (~3.0Myr) with an observed age spread of ~0.25dex for the cluster. Monte Carlo simulations of the population of Stock 8, based on estimates for the photometric uncertainty, differential reddening, binarity, and variability, indicate that these uncertainties introduce an age spread of ~0.15dex. The intrinsic age spread in the cluster is ~0.2dex. The fraction of young stellar objects surrounded by disks is ~35%. The K-band luminosity function of Stock 8 is similar to that of the Trapezium cluster. The initial mass function (IMF) of Stock 8 has a Salpeter-like slope at >0.5M_{Sun}_ and flattens and peaks at ~0.4M_{Sun}_, below which it declines into the substellar regime. Although Stock 8 is surrounded by several massive stars, there seems to be no severe environmental effect in the form of the IMF due to the proximity of massive stars around the cluster.
18058. YSOVAR GGD 12-15 Light Curve Table
ID:
ivo://irsa.ipac/Spitzer/Catalog/YSOVAR/YSOVAR_GGD1215LC
Title:
YSOVAR GGD 12-15 Light Curve Table
Short Name:
YSOVAR_GGD1215LC
Date:
01 Oct 2018 20:27:19
Publisher:
NASA/IPAC Infrared Science Archive
Description:
The YSOVAR (Young Stellar Object VARiability) Spitzer Space Telescope observing program obtained the first extensive mid-infrared (IRAC 3.6 and 4.5 micron) time series photometry of the Orion Nebula Cluster plus smaller fields in 11 other star-forming cores (AFGL 490, NGC 1333, Mon R2, GGD 12-15, NGC 2264, L1688, Serpens Main, Serpens South, IRAS 20050+2720, IC 1396A, and Ceph C). There are ~29,000 unique objects with light curves in either or both IRAC channels in the YSOVAR data set. YSOVAR is a sister project to the Coordinated Synoptic Investigation of NGC 2264 (CSI 2264; Cody et al. 2014). Initial YSOVAR results were described in Morales-Calderon et al. (2011). Rebull et al. (2014) describes the details of target selection, data reduction, and other conventions established for this project.
18059. YSOVAR GGD 12-15 Object Table
ID:
ivo://irsa.ipac/Spitzer/Catalog/YSOVAR/YSOVARGGD1215Obj
Title:
YSOVAR GGD 12-15 Object Table
Short Name:
YSOVARGGD1215Obj
Date:
01 Oct 2018 20:27:19
Publisher:
NASA/IPAC Infrared Science Archive
Description:
The YSOVAR (Young Stellar Object VARiability) Spitzer Space Telescope observing program obtained the first extensive mid-infrared (IRAC 3.6 and 4.5 micron) time series photometry of the Orion Nebula Cluster plus smaller fields in 11 other star-forming cores (AFGL 490, NGC 1333, Mon R2, GGD 12-15, NGC 2264, L1688, Serpens Main, Serpens South, IRAS 20050+2720, IC 1396A, and Ceph C). There are ~29,000 unique objects with light curves in either or both IRAC channels in the YSOVAR data set. YSOVAR is a sister project to the Coordinated Synoptic Investigation of NGC 2264 (CSI 2264; Cody et al. 2014). Initial YSOVAR results were described in Morales-Calderon et al. (2011). Rebull et al. (2014) describes the details of target selection, data reduction, and other conventions established for this project.
18060. YSOVAR infrared photometry in GGD12-15
ID:
ivo://CDS.VizieR/J/AJ/150/145
Title:
YSOVAR infrared photometry in GGD12-15
Short Name:
J/AJ/150/145
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present an IR-monitoring survey with the Spitzer Space Telescope of the star-forming region GGD 12-15. More than 1000 objects were monitored, including about 350 objects within the central 5', which is found to be especially dense in cluster members. The monitoring took place over 38 days and is part of the Young Stellar Object VARiability project. The region was also the subject of a contemporaneous 67 ks Chandra observation. The field includes 119 previously identified pre-main sequence star candidates. X-rays are detected from 164 objects, 90 of which are identified with cluster members. Overall, we find that about half the objects in the central 5' are young stellar objects (YSOs) based on a combination of their spectral energy distribution, IR variability, and X-ray emission. Most of the stars with IR excess relative to a photosphere show large amplitude (>0.1 mag) mid-infrared (mid-IR) variability. There are 39 periodic sources, and all but one is found to be a cluster member. Almost half of the periodic sources do not show IR excesses. Overall, more than 85% of the Class I, flat spectrum, and Class II sources are found to vary. The amplitude of the variability is larger in more embedded YSOs. Most of the Class I/II objects exhibit redder colors in a fainter state, which is compatible with time-variable extinction. A few become bluer when fainter, which can be explained with significant changes in the structure of the inner disk. A search for changes in the IR due to X-ray events is carried out, but the low number of flares prevented an analysis of the direct impact of X-ray flares on the IR light curves. However, we find that X-ray detected Class II sources have longer timescales for change in the MIR than a similar set of non-X-ray detected Class IIs.

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