- ID:
- ivo://CDS.VizieR/J/A+A/454/1047
- Title:
- XMM view of NGC 6231 open cluster
- Short Name:
- J/A+A/454/1047
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of an X-ray campaign towards the young open cluster NGC 6231. The XMM-Newton observations, of a total duration of about 180 ks, reveals that NGC 6231 is very rich in the X-ray domain too. Indeed, 610 X-ray sources are detected in the present field of view, centered on the cluster core. The limiting sensitivity of our survey is approximately 610^-15^erg/s/cm^2^ but clearly depends on the location in the field of view and on the source spectrum. Using different existing catalogues, over 85% of the X-ray sources could be associated with at least one optical and/or infrared counterpart within a limited cross-correlation radius of 2.5 or 3-arcsec according to the optical/IR catalogue used. The surface density distribution of the X-ray sources presents a slight N-S elongation. Once corrected for the spatial sensitivity variation of the EPIC instruments, the radial profile of the source surface density is well described by a King profile with a central density of about 8 sources per arcmin^2^ and a core radius close to 3.1-arcmin. The distribution of the X-ray sources seems closely related to the optical source distribution. The expected number of foreground and background sources should represent about 9% of the detected sources, thus strongly suggesting that most of the observed X-ray emitters are physically belonging to NGC 6231. Finally, beside a few bright but soft objects -- corresponding to the early-type stars of the cluster -- most of the sources are relatively faint (~5x10^-15^erg/s/cm^2^) with an energy distribution peaked around 1.0-2.0keV.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/743/166
- Title:
- X-ray and infra-red study of RCW 38
- Short Name:
- J/ApJ/743/166
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of the structure of the high-mass star-forming region RCW 38 and the spatial distribution of its young stellar population. Spitzer Infrared Array Camera (IRAC) photometry (3-8um) is combined with Two Micron All Sky Survey near-IR data to identify young stellar objects (YSOs) by IR-excess emission from their circumstellar material. Chandra X-ray data are used to identify class III pre-main-sequence stars lacking circumstellar material. We identify 624 YSOs: 23 class 0/I and 90 flat spectrum protostars, 437 class II stars, and 74 class III stars. We also identify 29 (27 new) O star candidates over the IRAC field. Seventy-two stars exhibit IR-variability, including 7 class 0/I and 12 flat spectrum YSOs. A further 177 tentative candidates are identified by their location in the IRAC [3.6] versus [3.6]-[5.8] color-magnitude diagram. We find strong evidence of subclustering in the region.
- ID:
- ivo://CDS.VizieR/J/ApJ/715/671
- Title:
- X-ray and IR emission from YSOs
- Short Name:
- J/ApJ/715/671
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on a multiwavelength study of a partially embedded region of star formation centered on the Herbig Be star LkH{alpha} 101. Using two 40ks Chandra observations, we detect 213 X-ray sources in the ~17'x17' ACIS-I field. We combine the X-ray data with Two Micron All Sky Survey near-IR observations and Spitzer IRAC and MIPS 24um observations to obtain a complete picture of the cluster. A total of 158 of the X-ray sources have infrared counterparts. Of these, we find nine protostars, 48 Class II objects, five transition objects, and 72 Class III objects. From the Spitzer data we identify an additional 10 protostars, 53 Class II objects, and four transition disk candidates which are not detected by Chandra. We obtained optical spectra of a sample of both X-ray-detected and non-X-ray-detected objects. Combining the X-ray, Spitzer, and spectral data, we obtain independent estimates of cluster distance and the total cluster size -excluding protostars. We obtain consistent distance estimates of 510^+100^_-40_pc and a total cluster size of 255^+50^_-25_ stars. We find the Class II:III ratio is about 5:7 with some evidence that the Class III sources are spatially more dispersed. The cluster appears very young with three sites of active star formation and a median age of about 1Myr.
- ID:
- ivo://CDS.VizieR/J/AJ/135/693
- Title:
- X-ray and IR sources in RCW 108
- Short Name:
- J/AJ/135/693
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on the results of an approximately 90ks Chandra observation of a complex region that hosts multiple sites of recent and active star formation in ARA OB1a. The field is centered on the embedded cluster RCW 108-IR and includes a large portion of the open cluster NGC 6193. We detect over 420 X-ray sources in the field and combined these data with deep near-IR, Spitzer/IRAC and Midcourse Space Experiment (MSX) mid-IR data. We find about 360 of the X-ray sources have near-IR counterparts. We divide the region into five parts based on the X-ray point source characteristics and extended 8um emission. The most clearly defined regions are the central region, identified by embedded sources with high luminosities in both the near-IR and X-ray as well as high X-ray temperatures (~3keV), and the eastern region, identified by low extinction and ~1keV X-ray temperatures. The cluster members range in X-ray luminosity from 10^29^ to 10^33^erg/s. Over 18% of the cluster members with over 100 counts exhibit flares. All sources with over 350 counts are variable. Overall about 10% (16% in RCW 108-IR) appear to have optically thick disks as derived from their position in the (J-H), (H-K) diagram. The disk fraction becomes much higher when IRAC data are employed. We fit the bulk of the X-ray spectra as absorbed Raymond-Smith-type plasmas, and find that the column to the RCW 108-IR members varies from 10^21^ to 10^23^cm^-2^. We find that the field contains 41 candidate O or B stars, and estimate that the total number of pre-main-sequence stars in the field is about 1600+/-200.
- ID:
- ivo://CDS.VizieR/J/MNRAS/429/775
- Title:
- X-ray and mid-IR study of NGC 2023
- Short Name:
- J/MNRAS/429/775
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results obtained in the X-ray and infrared study in the star-forming region NGC2023. The X-ray observation (ID=0112640201) was performed as a single 30ks exposure on 2002. Afer our processing, the useful exposure time was reduced around to 15ks. Spitzer photometry (AORKEY 8773120 and 8773632) we used MOPEX to create the mosaic image and DAOPHOT package to derived the fluxes. Optical photometry (V and I magnitude) was obtained from DENIS and Mid-Infrared from 2MASS and WISE. We used Robitaille et al. (2007ApJS..169..328R) to SED fitting and derived stellar parameters.
- ID:
- ivo://CDS.VizieR/J/ApJ/688/418
- Title:
- X-ray flares in Orion young stars. I.
- Short Name:
- J/ApJ/688/418
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Pre-main-sequence (PMS) stars are known to produce powerful X-ray flares, which resemble magnetic reconnection solar flares scaled by factors up to 104. However, there are numerous puzzles, including the structure of X-ray-emitting coronae and magnetospheres, the effects of protoplanetary disks, and the effects of stellar rotation. To investigate these issues in detail, we examine 216 of the brightest flares from 161 PMS stars observed in the Chandra Orion Ultradeep Project (COUP, Getman et al. Cat. J/ApJS/160/319). The current study (Paper I) examines the flare morphologies, and provides a general comparison of COUP flare characteristics with those of other active X-ray stars and the Sun.
3617. X-ray imaging of RCW 49
- ID:
- ivo://CDS.VizieR/J/ApJ/665/719
- Title:
- X-ray imaging of RCW 49
- Short Name:
- J/ApJ/665/719
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a high-resolution X-ray imaging study of the stellar population in the Galactic massive star-forming region RCW 49 and its central OB association Westerlund 2. We obtained a ~40ks X-ray image of a ~17'x17' field using the Chandra X-Ray Observatory and deep NIR images using the Infrared Survey Facility in a concentric ~8.3'x8.3' region. We detected 468 X-ray sources and identified optical, NIR, and Spitzer MIR counterparts for 379 of them.
- ID:
- ivo://CDS.VizieR/J/ApJ/876/50
- Title:
- X-ray & MIR AGNs in Stripe 82 with eBOSS spectra
- Short Name:
- J/ApJ/876/50
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the results of a Sloan Digital Sky Survey IV eBOSS program to target X-ray sources and mid-infrared-selected Wide-field Infrared Survey Explorer (WISE) active galactic nucleus (AGN) candidates in a 36.8deg^2^ region of Stripe 82. About half this survey (15.6deg^2^) covers the largest contiguous portion of the Stripe 82 X-ray survey. This program represents the largest spectroscopic survey of AGN candidates selected solely by their WISE colors. We combine this sample with X-ray and WISE AGNs in the field identified via other sources of spectroscopy, producing a catalog of 4847 sources that is 82% complete to r~22. Based on X-ray luminosities or WISE colors, 4730 of these sources are AGNs, with a median sample redshift of z~1. About 30% of the AGNs are optically obscured (i.e., lack broad lines in their optical spectra). BPT analysis, however, indicates that 50% of the WISE AGNs at z<0.5 have emission line ratios consistent with star-forming galaxies, so whether they are buried AGNs or star-forming galaxy contaminants is currently unclear. We find that 61% of X-ray AGNs are not selected as mid-infrared AGNs, with 22% of X-ray AGNs undetected by WISE. Most of these latter AGNs have high X-ray luminosities (Lx>10^44^erg/s), indicating that mid-infrared selection misses a sizable fraction of the highest luminosity AGNs, as well as lower luminosity sources where AGN-heated dust is not dominating the mid-infrared emission. Conversely, ~58% of WISE AGNs are undetected by X-rays, though we do not find that they are preferentially redder than the X-ray-detected WISE AGNs.
- ID:
- ivo://CDS.VizieR/J/ApJ/809/161
- Title:
- X-ray obs. and membership probabilities of M37
- Short Name:
- J/ApJ/809/161
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Empirical calibrations of the stellar age-rotation-activity relation (ARAR) rely on observations of the co-eval populations of stars in open clusters. We used the Chandra X-ray Observatory to study M37, a 500-Myr-old open cluster that has been extensively surveyed for rotation periods (P_rot_). M37 was observed almost continuously for five days, for a total of 440.5ks, to measure stellar X-ray luminosities (L_X_), a proxy for coronal activity, across a wide range of masses. The cluster's membership catalog was revisited to calculate updated membership probabilities from photometric data and each star's distance to the cluster center. The result is a comprehensive sample of 1699 M37 members: 426 with P_rot_, 278 with X-ray detections, and 76 with both. We calculate Rossby numbers, R_0_=P_rot_/{tau}, where {tau} is the convective turnover time, and ratios of the X-ray-to-bolometric luminosity, L_X_/L_bol_, to minimize mass dependencies in our characterization of the rotation-coronal activity relation at 500Myr. We find that fast rotators, for which R_0_<0.09+/-0.01, show saturated levels of activity, with log(L_X_/L_bol_)=-3.06+/-0.04. For R_0_>=0.09+/-0.01, activity is unsaturated and follows a power law of the form R_0_^{beta}^, where {beta}=-2.03^+0.17^_-1.14_. This is the largest sample available for analyzing the dependence of coronal emission on rotation for a single-aged population, covering stellar masses in the range 0.4-1.3M_{sun}_, P_rot_ in the range 0.4-12.8 days, and L_X_ in the range 10^28.4-30.5^erg/s. Our results make M37 a new benchmark open cluster for calibrating the ARAR at ages of ~500Myr.
- ID:
- ivo://CDS.VizieR/J/AJ/134/999
- Title:
- X-ray observations of NGC 2264
- Short Name:
- J/AJ/134/999
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from an X-ray imaging survey of the young cluster NGC 2264, carried out with the European Photon Imaging Cameras (EPIC) on board the XMM-Newton spacecraft. The X-ray data are merged with extant optical and near-infrared photometry, spectral classifications, Halpha emission strengths, and rotation periods to examine the interrelationships between coronal and chromospheric activity, rotation, stellar mass, and internal structure for a statistically significant sample of pre-main-sequence stars. A total of 300 distinct X-ray sources can be identified with optical or near-infrared counterparts. The sources are concentrated within three regions of the cluster: in the vicinity of S Mon, within the large emission/reflection nebulosity southwest of S Mon, and along the broad ridge of molecular gas that extends from the Cone Nebula to the NGC 2264 IRS 2 field.
