- ID:
- ivo://CDS.VizieR/J/ApJ/602/816
- Title:
- Chamaeleon I star-forming region census
- Short Name:
- J/ApJ/602/816
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- I present a new census of the members of the Chamaeleon I star-forming region. Optical spectroscopy has been obtained for 179 objects that have been previously identified as possible members of the cluster, that lack either accurate spectral types or clear evidence of membership, and that are optically visible (I<~18). I have used these spectroscopic data and all other available constraints to evaluate the spectral classifications and membership status of a total sample of 288 candidate members of Chamaeleon I that have appeared in published studies of the cluster. The latest census of Chamaeleon I now contains 158 members, eight of which are later than M6 and thus are likely to be brown dwarfs. I find that many of the objects identified as members of Chamaeleon I in recent surveys are actually field stars. Meanwhile, seven of nine candidates discovered by Carpenter and coworkers are confirmed as members, one of which is the coolest known member of Chamaeleon I at a spectral type of M8 (~0.03M_{sun}_). I have estimated extinctions, luminosities, and effective temperatures for the members and used these data to construct an H-R diagram for the cluster. Chamaeleon I has a median age of ~2Myr according to evolutionary models and hence is similar in age to IC 348 and is slightly older than Taurus (~1Myr). The measurement of an initial mass function for Chamaeleon I from this census is not possible because of the disparate methods with which the known members were originally selected and must await an unbiased, magnitude-limited survey of the cluster.
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- ID:
- ivo://CDS.VizieR/J/ApJS/178/339
- Title:
- ChaMP extended stellar survey (ChESS)
- Short Name:
- J/ApJS/178/339
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 348 X-ray-emitting stars identified from correlating the Extended Chandra Multiwavelength Project (ChaMP), a wide-area serendipitous survey based on archival X-ray images, with the Sloan Digital Sky Survey (SDSS-DR6). We use morphological star/galaxy separation, matching to an SDSS quasar catalog, an optical color-magnitude cut, and X-ray data-quality tests to create our catalog, the ChaMP Extended Stellar Survey (ChESS), from a sample of 2121 matched ChaMP/SDSS sources. Our cuts retain 92% of the spectroscopically confirmed stars in the original sample while excluding 99.6% of the 684 spectroscopically confirmed extragalactic sources. Fewer than 3% of the sources in our final catalog are previously identified stellar X-ray emitters. For 42 catalog members, spectroscopic classifications are available in the literature. We present new spectral classifications and H{alpha} measurements for an additional 79 stars. The catalog is dominated by main-sequence stars; we estimate the fraction of giants in ChESS is ~10%. We identify seven giant stars (including a possible Cepheid and an RR Lyrae star) as ChaMP sources, as well as three cataclysmic variables. Future papers will present analyses of source variability and comparisons of this catalog to models of stellar activity in the Galactic disk.
- ID:
- ivo://CDS.VizieR/J/ApJ/700/1702
- Title:
- ChaMPlane deep galactic bulge survey. I.
- Short Name:
- J/ApJ/700/1702
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have carried out a deep X-ray and optical survey with Chandra and HST of low-extinction regions in the Galactic bulge. Here we present the results of a search for low-luminosity (L_X_<~10^34^erg/s) accreting binaries among the Chandra sources in the region closest to the Galactic center, at an angular offset of 1.4{deg}, that we have named the Limiting Window (LW). Based on their blue optical colors, excess H{alpha} fluxes, and high X-ray-to-optical flux ratios, we identify three likely accreting binaries; these are probably white dwarfs accreting from low-mass companions (cataclysmic variables; CVs) although we cannot exclude that they are quiescent neutron-star or black-hole low-mass X-ray binaries. Distance estimates put these systems farther than >~2kpc. Based on their H{alpha}-excess fluxes and/or high X-ray-to-optical flux ratios, we find 22 candidate accreting binaries; however, the properties of some can also be explained if they are dMe stars or active galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/685/463
- Title:
- ChaMPlane X-ray sources in the Galactic bulge
- Short Name:
- J/ApJ/685/463
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have carried out optical and X-ray spectral analyses on a sample of 136 candidate optical counterparts of X-ray sources found in five Galactic bulge fields included in our Chandra Multiwavelength Plane Survey. We use a combination of optical spectral fitting and quantile X-ray analysis to obtain the hydrogen column density toward each object, and a three-dimensional dust model of the Galaxy to estimate the most probable distance in each case. We present the discovery of a population of stellar coronal emission sources, likely consisting of pre-main-sequence, young main-sequence, and main-sequence stars, as well as a component of active binaries of RS CVn or BY Dra type. We identify one candidate quiescent low-mass X-ray binary with a subgiant companion; we note that this object may also be an RS CVn system. We report the discovery of three new X-ray-detected cataclysmic variables (CVs) in the direction of the Galactic center (at distances <~2kpc). This number is in excess of predictions made with a simple CV model based on a local CV space density of <~10^-5^pc^-3^, and a scale height ~200pc. We discuss several possible reasons for this observed excess.
- ID:
- ivo://CDS.VizieR/J/ApJ/888/118
- Title:
- Chandra and IR study toward IRAS 16562-3959
- Short Name:
- J/ApJ/888/118
- Date:
- 17 Jan 2022 11:46:14
- Publisher:
- CDS
- Description:
- We present the results from Chandra X-ray observations, and near- and mid-infrared analysis, using VISTA/VVV and Spitzer/GLIMPSE catalogs, of the high-mass star-forming region IRAS 16562-3959, which contains a candidate for a high-mass protostar. We detected 249 X-ray sources within the ACIS-I field of view. The majority of the X-ray sources have low count rates (<0.638cts/ks) and hard X-ray spectra. The search for YSOs in the region using VISTA/VVV and Spitzer/GLIMPSE catalogs resulted in a total of 636 YSOs, with 74 Class I and 562 Class II YSOs. The search for near- and mid-infrared counterparts of the X-ray sources led to a total of 165 VISTA/VVV counterparts, and a total of 151 Spitzer/GLIMPSE counterparts. The infrared analysis of the X-ray counterparts allowed us to identify an extra 91 Class III YSOs associated with the region. We conclude that a total of 727 YSOs are associated with the region, with 74 Class I, 562 Class II, and 91 Class III YSOs. We also found that the region is composed of 16 subclusters. In the vicinity of the high-mass protostar, the stellar distribution has a core-halo structure. The subcluster containing the high-mass protostar is the densest and the youngest in the region, and the high-mass protostar is located at its center. The YSOs in this cluster appear to be substantially older than the high-mass protostar.
- ID:
- ivo://CDS.VizieR/J/A+A/464/211
- Title:
- Chandra and near-IR obs. of Cyg OB2
- Short Name:
- J/A+A/464/211
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The aim of this work is to identify the so far unknown low mass stellar population of the ~2Myr old Cygnus OB2 star forming region, and to investigate the X-ray and near-IR stellar properties of its members. We analyzed a 97.7ks Chandra ACIS-I observation pointed at the core of the Cygnus OB2 region. Sources were detected using the PWDETECT code and were positionally correlated with optical and near- IR catalogs from the literature. Source events were extracted with the Acis E XTRACT package. X-ray variability was characterized through the Kolmogorov-Smirnov test and spectra were fitted using absorbed thermal plasma models. We detected 1003 X-ray sources. Of these, 775 have near-IR counterparts and are expected to be almost all associated with Cygnus OB2 members.
- ID:
- ivo://CDS.VizieR/II/253A
- Title:
- Chandra Deep Field South: multi-colour data
- Short Name:
- II/253A
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Table 3 contains the object catalogue of the COMBO-17 CDFS field. The observations were carried out with the Wide Field Imager (WFI) at the MPG/ESO 2.2-m telescope on La Silla, Chile, between October 1999 and January 2001 in four independent observing runs. The field measures 31.5'x30', is centered on RA=03:32:25, DE=-27:48:50 and contains the Chandra Deep Field South. The table contains 63501 objects found on the deep R-band image cdfs_r.fit by SExtractor with S/N>3. The 5-{sigma} magnitude limit for point sources is Rmag=26.0. Morphological information from the SExtractor measurement is included. Multiple observations in different observing runs of six different filters allow the identification of variable objects. The table contains positions, flags and flux measurements in UBVRI and 12 optical medium-band filters. In addition, we include multi-colour classification, photometric redshifts, luminosity distances and a number of absolute restframe magnitudes in different filters (Johnson, Sloan, Bessell). cdfs_u.fit, cdfs_b.fit, cdfs_v.fit, cdfs_r.fit and cdfs_i.fit are coadded sumframes in UBVRI of the CDFS field. These sumframes are stacked from flat-fielded and cosmic-corrected individual images by applying only full pixel shifts. Therefore, the coordinate frames differ slightly between the images. The coordinates in Table 3 refer to image cdfs_r.fit. The images in BVRI are obtained from observations carried out in observing run D (Oct 1999, see also Note (11) in the byte-by-byte description of table3.dat) while the U-band image is obtained from observing run G (Jan 2001). The exposure times are 14400s (U), 5000s (B), 8400s (V), 15000s (R) and 7550s (I). The intensity levels are given in units of photons hitting the detector (already corrected for the gain of the CCD). The data included here supersede the table2.dat of the COMBO-17 published in 2001 (J/A+A/377/442)
- ID:
- ivo://CDS.VizieR/J/ApJS/155/271
- Title:
- Chandra Deep Field-South: Optical spectroscopy
- Short Name:
- J/ApJS/155/271
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of our spectroscopic follow-up program of the X-ray sources detected in the 942ks exposure of the Chandra Deep Field-South (CDFS). A total of 288 possible counterparts were observed at the VLT with the FORS1/FORS2 spectrographs for 251 of the 349 Chandra sources (including three additional faint X-ray sources). Spectra and R-band images are shown for all the observed sources and R-K colors are given for most of them. Spectroscopic redshifts were obtained for 168 X-ray sources, of which 137 have both reliable optical identification and redshift estimate (including 16 external identifications). The R<24 observed sample comprises 161 X-ray objects (181 optical counterparts), and 126 of them have unambiguous spectroscopic identification.
- ID:
- ivo://CDS.VizieR/J/A+A/377/442
- Title:
- Chandra Deep Field South: R-band photometry
- Short Name:
- J/A+A/377/442
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Table2 is based on an object list that was created by applying SExtractor software to an R-band image coadded from 36 frames with 15070s total exposure time taken in October 1999 using the Wide Field Imager at the MPG/ESO 2.2-m telescope on La Silla, Chile. The field measures 31.5'x30', is centered on 03:32:25-27:48:50 and contains the Chandra Deep Field South. The average PSF is on the order of 0.75". The catalog contains 63501 objects found by SExtractor with S/N>3. It has not been cleaned for spurious detection of false objects arising from scattered light or diffraction spikes of extremely bright stars. Using this object list aperture magnitudes 'Bmag', 'Vmag' and 'Rmag' were measured on B-, V- and R-band images taken in October 1999. These are listed with its errors. Additionally an aperture magnitude 'R2mag' with its error is included that is taken from R-band imaging from February 2000 with an exposure time of 8440s taken in 21 frames, yielding a total exposure time in the R-band of 23510s=6.5h. The 10-sigma magnitude limits for point sources are Bmag=24.9, Vmag=24.6, Rmag=25.1 and R2mag=24.8. The aperture magnitudes were calculated by counting the flux in an aperture with a Gaussian weighting function of 1.3" width. The flux is scaled to the total flux expected for stars.
- ID:
- ivo://CDS.VizieR/J/ApJS/228/2
- Title:
- Chandra Deep Field-South survey: 7Ms sources
- Short Name:
- J/ApJS/228/2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present X-ray source catalogs for the ~7Ms exposure of the Chandra Deep Field-South (CDF-S), which covers a total area of 484.2arcmin^2^. Utilizing wavdetect for initial source detection and ACIS Extract for photometric extraction and significance assessment, we create a main source catalog containing 1008 sources that are detected in up to three X-ray bands: 0.5-7.0keV, 0.5-2.0keV, and 2-7keV. A supplementary source catalog is also provided, including 47 lower-significance sources that have bright (K_s_<=23) near-infrared counterparts. We identify multiwavelength counterparts for 992 (98.4%) of the main-catalog sources, and we collect redshifts for 986 of these sources, including 653 spectroscopic redshifts and 333 photometric redshifts. Based on the X-ray and multiwavelength properties, we identify 711 active galactic nuclei (AGNs) from the main-catalog sources. Compared to the previous ~4Ms CDF-S catalogs, 291 of the main-catalog sources are new detections. We have achieved unprecedented X-ray sensitivity with average flux limits over the central ~1arcmin^2^ region of ~1.9x10^-17^, 6.4x10^-18^, and 2.7x10^-17^erg/cm^2^/s in the three X-ray bands, respectively. We provide cumulative number-count measurements observing, for the first time, that normal galaxies start to dominate the X-ray source population at the faintest 0.5-2.0keV flux levels. The highest X-ray source density reaches ~50500deg^-2^, and 47%+/-4% of these sources are AGNs (~23900deg^-2^).
