- ID:
- ivo://CDS.VizieR/J/A+A/455/903
- Title:
- ACIS-I observations of NGC 2264
- Short Name:
- J/A+A/455/903
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper's goal is to improve the member census of the NGC 2264 star-forming region and study the origin of X-ray activity in young PMS stars. We analyze a deep, 100ks long, Chandra ACIS observation covering a 17'x17' field in NGC 2264. The preferential detection in X-rays of low-mass PMS stars gives strong indications of their membership. We study X-ray activity as a function of stellar and circumstellar characteristics by correlating the X-ray luminosities, temperatures, and absorptions with optical and near-infrared data from the literature.
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- ID:
- ivo://CDS.VizieR/J/ApJ/787/108
- Title:
- Age estimates for massive SFR stellar populations
- Short Name:
- J/ApJ/787/108
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A major impediment to understanding star formation in massive star-forming regions (MSFRs) is the absence of a reliable stellar chronometer to unravel their complex star formation histories. We present a new estimation of stellar ages using a new method that employs near-infrared (NIR) and X-ray photometry, Age_JX_. Stellar masses are derived from X-ray luminosities using the L_X_-M relation from the Taurus cloud. J-band luminosities are compared to mass-dependent pre-main-sequence (PMS) evolutionary models to estimate ages. Age_JX_ is sensitive to a wide range of evolutionary stages, from disk-bearing stars embedded in a cloud to widely dispersed older PMS stars. The Massive Young Star-Forming Complex Study in Infrared and X-ray (MYStIX) project characterizes 20 OB-dominated MSFRs using X-ray, mid-infrared, and NIR catalogs. The Age_JX_ method has been applied to 5525 out of 31784 MYStIX Probable Complex Members. We provide a homogeneous set of median ages for over 100 subclusters in 15 MSFRs; median subcluster ages range between 0.5 Myr and 5 Myr. The important science result is the discovery of age gradients across MYStIX regions. The wide MSFR age distribution appears as spatially segregated structures with different ages. The Age_JX_ ages are youngest in obscured locations in molecular clouds, intermediate in revealed stellar clusters, and oldest in distributed populations. The NIR color index J-H, a surrogate measure of extinction, can serve as an approximate age predictor for young embedded clusters.
- ID:
- ivo://CDS.VizieR/J/A+A/384/890
- Title:
- BVRIHalpha photometry of NGC 2244 X-ray stars
- Short Name:
- J/A+A/384/890
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present high spatial resolution optical photometry of NGC 2244 in the Rosette Nebula using the NOAO MOSAIC Imager at Kitt Peak. We obtained BVIR and H{alpha} images of the central cluster and surrounding nebulae, and present results for 138 sources selected from X-ray observations with the ROSAT PSPC and HRI. Color-magnitude diagrams of the cluster show a large number of the stars are still undergoing contraction onto the main sequence. The faintest X-ray selected cluster members have the highest X-ray-to-optical luminosities (L_x_~>7x10^30^erg/s; L_x_/L_bol_=~10^-2^ to 10^-3^) and indicate they are a population of young active late-type stars. H{alpha} emission from the X-ray emitters is also remarkable. We have extended the detections of PMS stars in NGC 2244 well into the ran ge of K spectral types. While most of the cluster stars are located in the color-magnitude diagrams in between the ZAMS and the 3Myrs isochrone, significantly younger low mass stars exist and confirm earlier reports that star formation is still going on in the Rosette Nebula/NGC 2244 region.
- ID:
- ivo://CDS.VizieR/J/ApJ/838/61
- Title:
- Candidate X-ray OB stars in MYStIX regions
- Short Name:
- J/ApJ/838/61
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Massive O-type and early B-type (OB) stars in the nearby Galaxy remain incompletely cataloged due to high extinction, bright visible and infrared nebular emission in H II regions, and high field star contamination. These difficulties are alleviated by restricting the search to stars with X-ray emission. Using the X-ray point sources from the Massive Young Star-forming Complex Study in Infrared and X-Rays (MYStIX) survey of OB-dominated regions, we identify 98 MYStIX candidate OB (MOBc) stars by fitting their 1-8{mu}m spectral energy distributions (SEDs) with reddened stellar atmosphere models. We identify 27 additional MOBc stars based on JHK_S_ photometry of X-ray stars lacking SED fitting. These candidate OB stars indicate that the current census of stars earlier than B1, taken across the 18 MYStIX regions studied, is less than 50% complete. We also fit the SEDs of 239 previously published OB stars to measure interstellar extinction and bolometric luminosities, revealing six candidate massive binary systems and five candidate O-type (super)giants. As expected, candidate OB stars have systematically higher extinction than previously published OB stars. Notable results for individual regions include identification of the OB population of a recently discovered massive cluster in NGC 6357, an older OB association in the M17 complex, and new massive luminous O stars near the Trifid Nebula. In several relatively poorly studied regions (RCW 38, NGC 6334, NGC 6357, Trifid, and NGC 3576), the OB populations may increase by factors of 2.
- ID:
- ivo://CDS.VizieR/J/AJ/127/1014
- Title:
- CCD UBVRIHa photometry in NGC 3603
- Short Name:
- J/AJ/127/1014
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present UBVRI and H{alpha} photometry of the extremely compact, starburst cluster NGC 3603. Ground-based images, Hubble Space Telescope (HST) archival data, as well as Chandra X-ray data have been used for this study. We present, for the first time, optical color-magnitude diagrams (CMDs) for the stars in the cluster core down to V=22mag. A well-defined main sequence (MS) as well as low-mass pre-main-sequence (PMS) stars can clearly be seen in the CMDs. This result confirms the finding by Eisenhauer et al. (1998ApJ...498..278E) that low-mass stars are forming in the starburst cluster. We also derive an age (1+/-1Myr) and distance of the cluster (V_0_-M_V_=14.2+/-0.2mag, i.e., d=6.9+/-0.6kpc).
- ID:
- ivo://CDS.VizieR/J/AJ/137/3210
- Title:
- Chandra observations of h Persei
- Short Name:
- J/AJ/137/3210
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We describe Chandra/ACIS-I observations of the massive ~13-14Myr-old cluster, h Persei, part of the famous Double Cluster (h and {chi} Per) in Perseus. Combining the list of Chandra-detected sources with new optical/IR photometry and optical spectroscopy reveals ~165 X-ray bright stars with V<~23. Roughly 142 have optical magnitudes and colors consistent with cluster membership.
- ID:
- ivo://CDS.VizieR/J/AJ/127/2659
- Title:
- CHANDRA observations of NGC 2264
- Short Name:
- J/AJ/127/2659
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results of a Chandra observation of a field in NGC 2264. The observations were taken with the ACIS-I camera with an exposure time of 48.1ks. We present a catalog of 263 sources, which includes X-ray luminosity, optical and infrared photometry, and X-ray variability information. We found 41 variable sources, 14 of which have a flarelike light curve, and two of which have a pattern of a steady increase or decrease over a 10-hr period. The optical and infrared photometry for the stars identified as X-ray sources are consistent with most of these objects being premain-sequence stars with ages younger than 3Myr.
- ID:
- ivo://CDS.VizieR/J/ApJ/614/267
- Title:
- Chandra sources in Cha I North
- Short Name:
- J/ApJ/614/267
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Sensitive X-ray imaging surveys provide a new and effective tool to establish the census of pre-main-sequence (PMS) stars in nearby young stellar clusters. We report here a deep Chandra X-Ray Observatory observation of PMS stars in the Chamaeleon I North cloud, achieving a limiting luminosity of log L_t_~27ergs/s (0.5-8keV band) in a 0.8x0.8pc^2^ region. Of the 107 X-ray sources, 37 are associated with Galactic stars of which 27 are previously recognized cloud members.
- ID:
- ivo://CDS.VizieR/J/ApJ/588/1009
- Title:
- Chandra X-ray observations of NGC 2516
- Short Name:
- J/ApJ/588/1009
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a comprehensive study of the Chandra X-ray observations of the young open cluster NGC 2516. We have analyzed eight individual Chandra observations. We have combined the data to achieve the greatest sensitivity, reaching down to log f_X_=-14.56(erg/s/cm^2^), or logLX=28.69(erg/s) at the distance of NGC 2516. Out of 284 X-ray sources detected, 155 are identified with photometric cluster members, with very little ambiguity.
- ID:
- ivo://CDS.VizieR/J/A+A/650/A156
- Title:
- Cluster formation toward Be87/ON2. I.
- Short Name:
- J/A+A/650/A156
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Disentangling line-of-sight alignments of young stellar populations is crucial for observational studies of star-forming complexes. This task is particularly problematic in a Cygnus-X subregion where several components, located at different distances, overlap: the Berkeley 87 young massive cluster, the poorly known [DB2001] Cl05 embedded cluster, and the ON2 star-forming complex, which in turn is composed of several HII regions. We provide a methodology for building an exhaustive census of young objects that can consistently treat large differences in extinction and distance. OMEGA2000 near-infrared observations of the Berkeley 87 / ON2 field were merged with archival data from Gaia, Chandra, Spitzer, and Herschel, and with cross-identifications from the literature. To address the incompleteness effects and selection biases that arise from the line-of-sight overlap, we adapted existing methods for extinction estimation and young object classification. We also defined the intrinsic reddening index, R_int_, a new tool for separating intrinsically red sources from those whose infrared color excess is caused by extinction. Finally, we introduce a new method for finding young stellar objects based on R_int_. We find 571 objects whose classification is related to recent or ongoing star formation. Together with other point sources with individual estimates of distance or extinction, we compile a catalog of 3005 objects to be used for further membership work. A new distance for Berkeley 87, (1673+/-17)pc, is estimated as a median of 13 spectroscopic members with accurate Gaia EDR3 parallaxes. The flexibility of our approach, especially regarding the R_int_ definition, allows overcoming photometric biases caused by large variations in extinction and distance, in order to obtain homogeneous catalogs of young sources. The multiwavelength census that results from applying our methods to the Berkeley 87 / ON2 field will serve as a basis for disentangling the overlapped populations.
