- 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/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/747/51
- Title:
- Lagoon Nebula stars. I. Rotation periods
- Short Name:
- J/ApJ/747/51
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have conducted a long-term, wide-field, high-cadence photometric monitoring survey of ~50000 stars in the Lagoon Nebula H II region. This first paper presents rotation periods for 290 low-mass stars in NGC 6530, the young cluster illuminating the nebula, and for which we assemble a catalog of infrared and spectroscopic disk indicators, estimated masses and ages, and X-ray luminosities. The distribution of rotation periods we measure is broadly uniform for 0.5days<P<10days; the short-period cutoff corresponds to breakup. We observe no obvious bimodality in the period distribution, but we do find that stars with disk signatures rotate more slowly on average. The stars' X-ray luminosities are roughly flat with rotation period, at the saturation level (log L_X_/L_bol_{approx} -3.3). However, we find a significant positive correlation between L_X_/L_bol_ and corotation radius, suggesting that the observed X-ray luminosities are regulated by centrifugal stripping of the stellar coronae. The period-mass relationship in NGC 6530 is broadly similar to that of the Orion Nebula Cluster (ONC), but the slope of the relationship among the slowest rotators differs from that in the ONC and other young clusters. We show that the slope of the period-mass relationship for the slowest rotators can be used as a proxy for the age of a young cluster, and we argue that NGC 6530 may be slightly younger than the ONC, making it a particularly important touchstone for models of angular momentum evolution in young, low-mass stars.
- ID:
- ivo://CDS.VizieR/J/AJ/128/1684
- Title:
- NGC 2264: VRIH{alpha} photometry
- Short Name:
- J/AJ/128/1684
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The young open cluster NGC 2264 was observed on 2002 January 67 with the CFH12K mosaic CCD on the 3.6m Canada-France-Hawaii Telescope to investigate the shape of the initial mass function (IMF). In order to select the pre-main-sequence (PMS) members more completely, Chandra X-Ray Observatory archival data were retrieved and used for the identification of X-ray-emitting weak-line T Tauri stars. In addition, the (R-I, V-I) diagram was used to exclude background late-type giants, and a statistical approach was applied to estimate the number of contaminating foreground main-sequence stars.
- ID:
- ivo://CDS.VizieR/J/A+A/539/A119
- Title:
- Pismis 24 stars with X-ray emission
- Short Name:
- J/A+A/539/A119
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Circumstellar disks are expected to evolve quickly in massive young clusters harboring many OB-type stars. Two processes have been proposed to drive the disk evolution in such cruel environments: (1) gravitational interaction between circumstellar disks and nearby passing stars (stellar encounters), and (2) photoevaporation by UV photons from massive stars. The relative importance of both mechanisms is not well understood. Studies of massive young star clusters can provide observational constraints on the processes of driving disk evolution. We investigate the properties of young stars and their disks in the NGC 6357 complex, concentrating on the most massive star cluster within the complex: Pismis 24.
- ID:
- ivo://CDS.VizieR/J/A+A/430/941
- Title:
- Star formation region NGC 6530
- Short Name:
- J/A+A/430/941
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present astrometry and BVI photometry, down to V~22, of the very young open cluster NGC 6530, obtained from observations taken with the Wide Field Imager camera at the MPG/ESO 2.2m Telescope. We have positionally matched our optical catalog with the list of X-ray sources found in a Chandra-ACIS observation, finding a total of 828 common stars, 90% of which are pre-main sequence stars in NGC 6530.
- ID:
- ivo://CDS.VizieR/J/AJ/154/87
- Title:
- Stellar population of the young star cluster NGC 6231
- Short Name:
- J/AJ/154/87
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NGC 6231 is a young cluster (age ~2-7 Myr) dominating the Sco OB1 association (distance ~1.59 kpc) with ~100 O and B stars and a large pre-main-sequence stellar population. We combine a reanalysis of archival Chandra X-ray data with multiepoch near-infrared (NIR) photometry from the VISTA Variables in the Via Lactea (VVV) survey and published optical catalogs to obtain a catalog of 2148 probable cluster members. This catalog is 70% larger than previous censuses of probable cluster members in NGC 6231. It includes many low-mass stars detected in the NIR but not in the optical and some B stars without previously noted X-ray counterparts. In addition, we identify 295 NIR variables, about half of which are expected to be pre-main-sequence stars. With the more complete sample, we estimate a total population in the Chandra field of 5700-7500 cluster members down to 0.08 M_{sun}_ (assuming a universal initial mass function) with a completeness limit at 0.5 M_{sun}_. A decrease in stellar X-ray luminosities is noted relative to other younger clusters. However, within the cluster, there is little variation in the distribution of X-ray luminosities for ages less than 5 Myr. The X-ray spectral hardness for B stars may be useful for distinguishing between early-B stars with X-rays generated in stellar winds and B-star systems with X-rays from a pre-main-sequence companion (>35% of B stars). A small fraction of catalog members have unusually high X-ray median energies or reddened NIR colors, which might be explained by absorption from thick or edge-on disks or being background field stars.
- ID:
- ivo://CDS.VizieR/J/A+A/446/501
- Title:
- XMM observations of sigma Ori cluster
- Short Name:
- J/A+A/446/501
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of an XMM-Newton observation of the young (~2-4Myr) cluster around the hot star sigma Orionis. In a previous paper (Sanz-Forcada et al., 2004A&A...421..715S) we presented the analysis of the RGS spectrum of the central hot star; here we discuss the results of the analysis of the full EPIC field. We have detected 175 X-ray sources, 88 of which have been identified with cluster members, including very low-mass stars down to the substellar limit. We detected eleven new possible candidate members from the 2MASS (Cat. <II/246>) catalogue.
- ID:
- ivo://CDS.VizieR/J/MNRAS/372/661
- Title:
- XMM view of NGC 6231: OB stars
- Short Name:
- J/MNRAS/372/661
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this second paper of the series, we focus on the X-ray properties of the OB star population of NGC 6231. As a tool for our analysis, we performed a literature-based census of the OB stars in the field of view. More than one hundred objects are found, among which 30% can be associated with an X-ray source. All the O-type stars are detected in the X-ray domain as soft and reasonably strong emitters. [...] Among B-type stars, the detection rate is only about 25% in the sub-type range B0-B4 and remains mostly uniform throughout the different sub-populations while it drops significantly at later sub-types. The associated X-ray spectra are harder than those of O-type stars. Our analysis points towards the emission being rather associated with a physical (in a multiple system) PMS companion. However, we still observe a correlation between the bolometric luminosity of the B stars and the measured X-ray luminosity. [...]
