- 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.
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Search Results
- ID:
- ivo://CDS.VizieR/J/PASJ/68/92
- Title:
- Subaru NIR obs. of Pleiades stars in SEEDS survey
- Short Name:
- J/PASJ/68/92
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We find a new substellar companion to the Pleiades member star, Pleiades HII 3441, using the Subaru telescope with adaptive optics. The discovery is made as part of the high-contrast imaging survey to search for planetary-mass and substellar companions in the Pleiades and young moving groups. The companion has a projected separation of 0.49+/-0.02 (66+/-2au) and a mass of 68+/-5MJ based on three observations in the J-, H-, and Ks-bands. The spectral type is estimated to be M7 (~2700K), and thus no methane absorption is detected in the H band. Our Pleiades observations result in the detection of two substellar companions including one previously reported among 20 observed Pleiades stars, and indicate that the fraction of substellar companions in the Pleiades is about 10.0^+26.1^_-8.8_%. This is consistent with multiplicity studies of both the Pleiades stars and other open clusters.
- ID:
- ivo://CDS.VizieR/J/ApJ/680/495
- Title:
- Survey of Interstellar clouds in the Gould belt
- Short Name:
- J/ApJ/680/495
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present observations of two areas totalling 0.57deg^2^ in the IC 5146 star-forming region at 3.6, 4.5, 5.8, 8.0, 24, and 70um observed with the Spitzer Space Telescope. We reexamine the issue of the distance to this cloud and conclude a value of 950+/-80pc is most likely. We compare source counts, colors, and magnitudes in our observed region to a subset of the SWIRE data that was processed through our pipeline. We identify more than 200 young stellar object (YSO) candidates from color-magnitude and color-color diagrams, many of which were previously unknown. We compare the colors of these YSOs to the models of Robitaille et al. and perform simple fits to the SED's to estimate properties of the circumstellar disks likely to surround the Class II and III sources. We also compare the mid-IR disk excesses to H{alpha} emission-line data where available. We present a quantitative description of the degree of clustering, estimate the star formation efficiency, and discuss the fraction of YSOs in the region with disks relative to an estimate of the diskless YSO population. Finally, we compare the YSO distribution to the cold dust distribution mapped by SCUBA and briefly describe the diffuse emission likely due to PAHs associated with the HII region.
- ID:
- ivo://CDS.VizieR/J/MNRAS/424/1636
- Title:
- Swift/UVOT sources in NGC4321 (M100)
- Short Name:
- J/MNRAS/424/1636
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the star-forming regions in the spiral galaxy NGC 4321 (M100). We take advantage of the spatial resolution (2.5-arcsec full width at half-maximum) of the Swift/Ultraviolet/Optical Telescope camera and the availability of three ultraviolet (UV) passbands in the region 1600<{lambda}<3000{AA}, in combination with optical and infrared (IR) imaging from Sloan Digital Sky Survey, KPNO/H{alpha} and Spitzer/IRAC, to obtain a catalogue of 787 star-forming regions out to three disc scalelengths. We use a large volume of star formation histories, combined with stellar population synthesis, to determine the properties of the young stellar component and its relationship with the spiral arms.
375. System IMF of 25 Ori
- ID:
- ivo://CDS.VizieR/J/MNRAS/486/1718
- Title:
- System IMF of 25 Ori
- Short Name:
- J/MNRAS/486/1718
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The stellar initial mass function (IMF) is an essential input for many astrophysical studies but only in a few cases has it been determined over the whole cluster mass range, limiting the conclusions about its nature. The 25 Orionis group (25 Ori) is an excellent laboratory for investigating the IMF across the entire mass range of the population, from planetary-mass objects to intermediate/high-mass stars. We combine new deep optical photometry with optical and near-infrared data from the literature to select 1687 member candidates covering a 1.1{deg} radius area in 25 Ori. With this sample we derived the 25 Ori system IMF from 0.012 to 13.1M_{sun}_. This system IMF is well described by a two-segment power law with {GAMMA}=-0.74+/-0.04 for m<0.4M_{sun}_ and {GAMMA}=1.50+/-0.11 for m>=0.4M_{sun}_. It is also well described over the whole mass range by a tapered power-law function with {GAMMA}=1.10+/-0.09, mp=0.31+/-0.03 and {beta}=2.11+/-0.09. The best lognormal representation of the system IMF has mc=0.31+/-0.04 and {sigma}=0.46+/-0.05 for m<1M_{sun}_. This system IMF does not present significant variations with the radii. We compared the resultant system IMF as well as the brown dwarf/star ratio of 0.16+/-0.03 that we estimated for 25 Ori with that of other stellar regions with diverse conditions and found no significant discrepancies. These results support the idea that general star-formation mechanisms are probably not strongly dependent on environmental conditions. We found that the substellar and stellar objects in 25 Ori do not have any preferential spatial distributions and confirmed that 25 Ori is a gravitationally unbound stellar association.
- ID:
- ivo://CDS.VizieR/J/AJ/157/85
- Title:
- The CIDA Variability Survey of Orion OB1. II.
- Short Name:
- J/AJ/157/85
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results of our large-scale, optical, multi-epoch photometric survey across ~180 square degrees in the Orion OB1 association, complemented with extensive follow-up spectroscopy. Our focus is mapping and characterizing the off-cloud, low-mass, pre-main-sequence (PMS) populations. We report 2062 K- and M-type confirmed T Tauri members; 59% are located in the OB1a subassociation, 27% in the OB1b subassociation, and the remaining 14% in the A and B molecular clouds. We characterize two new clusterings of T Tauri stars, the HD 35762 and HR 1833 groups, both located in OB1a not far from the 25 Ori cluster. We also identify two stellar overdensities in OB1b, containing 231 PMS stars, and find that the OB1b region is composed of two populations at different distances, possibly due to the OB1a subassociation overlapping with the front of OB1b. A ~2 deg wide halo of young stars surrounds the Orion Nebula Cluster, corresponding in part to the low-mass populations of NGC 1977 and NGC 1980. We use the strength of H{alpha} in emission, combined with the IR excess and optical variability, to define a new type of T Tauri star, the C/W class, stars we propose may be nearing the end of their accretion phase, in an evolutionary state between classical and weak-lined T Tauri stars. The evolution of the ensemble-wide equivalent width of Li I{lambda}6707 indicates a Li depletion timescale of ~8.5 Myr. Disk accretion declines with an e-folding timescale of ~2 Myr, consistent with previous studies.
- ID:
- ivo://CDS.VizieR/VII/183
- Title:
- The Cluster System of the LMC
- Short Name:
- VII/183
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A new catalogue of clusters in the Large Magellanic Cloud has been constructed from searches of the IIIa-J component of the ESO/SERC Southern Sky Atlas. The catalogue contains coordinate and diameter measurements of 1762 clusters in a 25x25{deg} area of sky centred on the LMC, but excluding the very crowded 3.5 square deg. region around the Bar. The distribution of these clusters appears as two superimposed elliptical systems. The higher density inner system extends over about 8d; the lower density outer system can be represented by 13d X 10d disc inclined at 42d to the line of sight. There are suggestions of two weak "arms" in the latter.
- ID:
- ivo://CDS.VizieR/J/MNRAS/449/741
- Title:
- The massive star population of Cygnus OB2
- Short Name:
- J/MNRAS/449/741
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have compiled a significantly updated and comprehensive census of massive stars in the nearby Cygnus OB2 association by gathering and homogenising data from across the literature. The census contains 169 primary OB stars, including 52 O-type stars and 3 Wolf-Rayet stars. Spectral types and photometry are used to place the stars in a Hertzprung-Russell diagram, which is compared to both non-rotating and rotating stellar evolution models, from which stellar masses and ages are calculated. The star formation history and mass function of the association are assessed, and both are found to be heavily influenced by the evolution of the most massive stars to their end states. We find that the mass function of the most massive stars is consistent with a "universal" power-law slope of {Gamma}=1.3. The age distribution inferred from stellar evolutionary models with rotation and the mass function suggest the majority of star formation occurred more or less continuously between 1 and 7Myr ago, in agreement with studies of low- and intermediate mass stars in the association. We identify a nearby young pulsar and runaway O-type star that may have originated in Cyg OB2 and suggest that the association has already seen its first supernova. Finally we use the census and mass function to calculate the total mass of the association of 16500^+3800^_-2800_M_{sun}, at the low end, but consistent with, previous estimates of the total mass of Cyg OB2. Despite this Cyg OB2 is still one of the most massive groups of young stars known in our Galaxy making it a prime target for studies of star formation on the largest scales.
- ID:
- ivo://CDS.VizieR/J/AJ/114/198
- Title:
- The Monoceros R2 Cluster
- Short Name:
- J/AJ/114/198
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an extensive study of the stellar population of an embedded cluster in the MonR2 molecular cloud based upon a wide field (~15'x15') J, H, and K band mosaic, deep near-infrared imaging at J, H, K, and nbL' bands of the central cluster region, and spectroscopic observations of 34 stars. By comparing the properties of the MonR2 cluster with other star forming regions, we ultimately hope to learn how the properties and formation of stars of various masses are related to the local physical conditions. The K band star counts indicate that the MonR2 cluster extends over a ~1.1pcx2.1pc area with a FWHM cluster size of ~0.38pc. Within this region the cluster contains ~309 stars brighter than m_K=14.5m and >~475 stars over all magnitudes with a central stellar volume density of ~9000 stars pc^-3^. We have further explored the properties of the cluster by using the spectroscopic and photometric data to construct an extinction-limited sample of 115 stars in the central 0.77pcx0.77pc region of the cluster that is designed to contain all stars with A_V<=11.3m and stellar masses >=0.1M_{sun}_. As a lower limit, 62% of the stars in this sample contain a near-infrared excess at K and/or L band. The K band excess fraction may be as high as 72% if the accretion characteristics of the stars in the MonR2 cluster are similar to stars in Taurus-Auriga. An initial reconnaissance of the stellar mass function suggests that the ratio of high to low mass stars in the extinction-limited sample is consistent with the value expected for a Miller-Scalo IMF. We do not find compelling evidence for mass segregation in the extinction-limited sample for stellar masses <~2M_{sun}_, although the most massive star (~10M_{sun}_) in the cluster appears to be forming near the cluster center. The properties of the MonR2 cluster are similar to other rich young clusters in the solar neighborhood, such as NGC 2024 and the Trapezium. (c) 1997 American Astronomical Society.
- ID:
- ivo://CDS.VizieR/J/AJ/108/1256
- Title:
- The OB association LH 58
- Short Name:
- J/AJ/108/1256
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present CCD photometry and spectroscopy for stars in Lucke-Hodge 58, an isolated OB association in the Large Magellanic Cloud (LMC) northwest of 30 Doradus. The photometric catalog contains 839 stars with UBV magnitudes complete to V~19. We have obtained spectra and classified 35 stars; combined with previous published spectral types, we find 22 O-type stars. The earliest type is O3-4 V, and there are three WR stars in the association. The slope of the initial mass function, Gamma=-1.7+/-0.3, is in good agreement with other LMC associations. The presence of several evolved supergiants with masses about 15-25M_{sun}_ suggests that some star formation took place as early as 10 million years ago, but the majority of stars formed coevally within the past few million years.
