- ID:
- ivo://CDS.VizieR/J/AJ/138/1116
- Title:
- A Spitzer view of NGC 2264
- Short Name:
- J/AJ/138/1116
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have performed mid-IR photometry of the young open cluster NGC 2264 using the images obtained with the Spitzer Space Telescope Infrared Array Camera and Multiband Imaging Photometer for Spitzer instruments and presented a normalized classification scheme of young stellar objects in various color-color diagrams to make full use of the information from multicolor photometry. These results are compared with the classification scheme based on the slope of the spectral energy distribution (SED). From the spatial distributions of Class I and II stars, we have identified two subclusterings of Class I objects in the CONE region of Sung et al. (Cat. J/AJ/135/441). The disked stars in the other star-forming region S Mon are mostly Class II objects. In addition, we have derived a somewhat higher value of the primordial disk fraction for NGC 2264 members located below the main pre-main-sequence locus (so-called BMS stars). This result supports the idea that BMS stars are young stars with nearly edge-on disks.
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- ID:
- ivo://CDS.VizieR/J/ApJ/805/57
- Title:
- Atmosphere parameters model-derived for PMS & BDs
- Short Name:
- J/ApJ/805/57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We test state-of-the-art model atmospheres for young very-low-mass stars and brown dwarfs in the infrared, by comparing the predicted synthetic photometry over 1.2-24{mu}m to the observed photometry of M-type spectral templates in star-forming regions. We find that (1) in both early and late young M types, the model atmospheres imply effective temperatures (Teff) several hundred Kelvin lower than predicted by the standard pre-main sequence (PMS) spectral type-Teff conversion scale (based on theoretical evolutionary models). It is only in the mid-M types that the two temperature estimates agree. (2) The Teff discrepancy in the early M types (corresponding to stellar masses >~0.4M_{sun}_ at ages of a few Myr) probably arises from remaining uncertainties in the treatment of atmospheric convection within the atmospheric models, whereas in the late M types it is likely due to an underestimation of dust opacity. (3) The empirical and model-atmosphere J-band bolometric corrections are both roughly flat, and similar to each other, over the M-type Teff range. Thus the model atmospheres yield reasonably accurate bolometric luminosities (Lbol), but lead to underestimations of mass and age relative to evolutionary expectations (especially in the late M types) due to lower Teff. We demonstrate this for a large sample of young Cha I and Taurus sources. (4) The trends in the atmospheric model J-K_s_ colors, and their deviations from the data, are similar at PMS and main sequence ages, suggesting that the model dust opacity errors we postulate here for young ages also apply at field ages.
- 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/MNRAS/415/1202
- Title:
- BVI photometry in W5E HII region
- Short Name:
- J/MNRAS/415/1202
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The aim of this paper is to present the results of photometric investigations of the central cluster of the W5 E HII region as well as a follow-up study of the triggered star formation in and around bright-rimmed clouds (BRCs). We have carried out wide-field UBVIc and deep VIc photometry of the W5 E HII region. A distance of ~2.1kpc and a mean age of ~1.3Myr have been obtained for the central cluster. The young stellar objects (YSOs) associated with the region are identified on the basis of near-infrared and mid-infrared observations.
- ID:
- ivo://CDS.VizieR/J/ApJ/764/114
- Title:
- BVRI photometry of stars in Orion A
- Short Name:
- J/ApJ/764/114
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We extend our previous study of the stellar population of L1641, the lower-density star-forming region of the Orion A cloud south of the dense Orion Nebula Cluster (ONC), with the goal of testing whether there is a statistically significant deficiency of high-mass stars in low-density regions. Previously, we compared the observed ratio of low-mass stars to high-mass stars with theoretical models of the stellar initial mass function (IMF) to infer a deficiency of the highest-mass stars in L1641. We expand our population study to identify the intermediate-mass (late B to G) L1641 members in an attempt to make a more direct comparison with the mass function of the nearby ONC. The spectral-type distribution and the K-band luminosity function of L1641 are similar to those of the ONC, but problems of incompleteness and contamination prevent us from making a detailed test for differences. We limit our analysis to statistical tests of the ratio of high-mass to low-mass stars, which indicate a probability of only 3% that the ONC and the southern region of L1641 were drawn from the same population, supporting the hypothesis that the upper-mass end of the IMF is dependent on environmental density.
- ID:
- ivo://CDS.VizieR/J/ApJ/795/L26
- Title:
- Candidate eruptive young stars in Lynds 1340
- Short Name:
- J/ApJ/795/L26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on the discovery of three candidate eruptive young stars, found during our comprehensive multi-wavelength study of the young stellar population of the dark cloud L1340. These stars are as follows. (1) IRAS 02224+7227 (2MASS 02270555+7241167, HH 487S) exhibited FUor-like spectrum in our low-resolution optical spectra. The available photometric data restrict its luminosity to 23L_{sun}_<L_bol_<59L_{sun}_. (2) 2MASS 02263797+7304575, identified as a classical T Tauri star during our H{alpha} survey, exhibited an EXor-type brightening in 2005 November at the time of the Sloan Digital Sky Survey observations of the region. (3) 2MASSJ02325605+7246055, a low-mass embedded young star, associated with a fan-shaped infrared nebula, underwent an outburst between the DSS 1 and DSS 2 surveys, leading to the appearance of a faint optical nebula. Our [SII] and H{alpha} images, as well as the Spitzer Infrared Array Camera 4.5{mu}m images, revealed Herbig-Haro objects associated with this star. Our results suggest that amplitudes and timescales of outbursts do not necessarily correlate with the evolutionary stage of the stars.
- 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/A+A/567/A109
- Title:
- Carina nebula optically identified YSOs
- Short Name:
- J/A+A/567/A109
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The low obscuration and proximity of the Carina nebula make it an ideal place to study the ongoing star formation process and impact of massive stars on low-mass stars in their surroundings. To investigate this process, we have generated a new catalogue of the pre-main-sequence (PMS) stars in the Carina west (CrW) region and studied their nature and spatial distribution. We have also determined various parameters (reddening, reddening law, age, mass) which are further used to estimate the initial mass function (IMF) and K-band luminosity function (KLF) for the region under study. We obtained deep UBVRI H{alpha} photometric data of the field situated to the west of the main Carina nebula and centered around WR22. Medium-resolution optical spectroscopy of a subsample of X-ray selected objects along with archival data sets from Chandra, XMM-Newton and 2MASS surveys are used for the present study. Our spectroscopic results indicate that the majority of the X-ray sources are late spectral type stars. The region shows a large amount of differential reddening with minimum and maximum values of E(B-V) as 0.25 and 1.1mag, respectively. Our analysis reveals that the total to selective absorption ratio R_V_ is ~3.7+/-0.1 suggesting an abnormal grain size in the observed region. We identify 467 young stellar objects (YSOs) and study their characteristics. The ages and masses of the 241 optically identified YSOs range from ~0.1 to 10Myr and ~0.3 to 4.8M_{sun}_, respectively. However, the majority of them are younger than 1Myr and have masses below 2M_{sun}_. The high mass star WR22 does not seem to have contributed to the formation of YSOs in the CrW region. The initial mass function slope, Gamma in this region is found to be -1.13+/-0.20 in the mass range of 0.5<M/M_{sun}_<4.8. The K-band luminosity function slope ({alpha}) is also estimated as 0.31+/-0.01. We also performed minimum spanning tree analysis of the YSOs in this region which reveals that there are at least ten YSO cores associated with the molecular cloud and that leads to an average core radius and median branch length 0.43pc and 0.28pc, respectively.
- ID:
- ivo://CDS.VizieR/J/AJ/153/95
- Title:
- Catalog of Suspected Nearby Young Stars
- Short Name:
- J/AJ/153/95
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new nearby young moving group (NYMG) kinematic membership analysis code, LocAting Constituent mEmbers In Nearby Groups (LACEwING), a new Catalog of Suspected Nearby Young Stars, a new list of bona fide members of moving groups, and a kinematic traceback code. LACEwING is a convergence-style algorithm with carefully vetted membership statistics based on a large numerical simulation of the Solar Neighborhood. Given spatial and kinematic information on stars, LACEwING calculates membership probabilities in 13 NYMGs and three open clusters within 100 pc. In addition to describing the inputs, methods, and products of the code, we provide comparisons of LACEwING to other popular kinematic moving group membership identification codes. As a proof of concept, we use LACEwING to reconsider the membership of 930 stellar systems in the Solar Neighborhood (within 100 pc) that have reported measurable lithium equivalent widths. We quantify the evidence in support of a population of young stars not attached to any NYMGs, which is a possible sign of new as-yet-undiscovered groups or of a field population of young stars.
- ID:
- ivo://CDS.VizieR/J/A+A/392/971
- Title:
- Catalogue of bright YSO candidates in ISOGAL
- Short Name:
- J/A+A/392/971
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The 7 and 15{mu}m observations of selected fields in the Galactic Plane obtained with ISOCAM during the ISOGAL program offer an unique possibility to search for previously unknown YSOs, undetected by IRAS because of lower sensitivity or confusion problems. In a previous paper (Felli et al., 2000, Cat. <J/A+A/362/199>) we established criteria of general validity to select YSOs from the much larger population of Post Main Sequence (Post-MS) stars present in the ISOGAL fields by comparing radio and IR observations of five fields located at l~45{deg}. The selection was based primarily on the position of the point sources in the [15]-([7]-[15]) diagram, which involves only ISOGAL data and allows to find possible YSOs using the survey data alone. In the present work we revise the adopted criteria by comparing radio-identified ultra-compact HII regions and ISOGAL observations over a much larger region. The main indications of the previous analysis are confirmed, but the criteria for selecting YSO candidates had to be revised to select only bright objects, in order to limit the contamination of the sample by Post-MS stars. The revised criteria ([15]<=4.5, [7]-[15]>=1.8) are then used to extract YSO candidates from the ISOGAL Point Source Catalogue in preparation. We select a total of 715 YSO candidates, corresponding to ~2 of the sources with good detections at 7 and 15{mu}m. The results are presented in a table form that provides an unique input list of small diameter, <=6", Galactic YSO candidates. The global properties of the sample of YSO candidates are briefly discussed.