- ID:
- ivo://CDS.VizieR/J/ApJS/209/9
- Title:
- Unidentified gamma-ray sources. IV. X-ray
- Short Name:
- J/ApJS/209/9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A significant fraction (~30%) of the high-energy {gamma}-ray sources listed in the second Fermi Large Area Telescope (LAT) catalog are still of unknown origin, having not yet been associated with counterparts at lower energies. To investigate the nature of these enigmatic sources, we present an extensive search of X-ray sources lying in the positional uncertainty region of a selected sample of these unidentified gamma-ray sources (UGSs) that makes use of all available observations performed by the Swift X-ray Telescope before 2013 March 31, available for 205 UGSs. To detect the fainter sources, we merged all the observations covering the Fermi LAT positional uncertainty region at a 95% level of confidence of each UGS. This yields a catalog of 357 X-ray sources, finding candidate X-ray counterparts for ~70% of the selected sample. In particular, 25% of the UGSs feature a single X-ray source within their positional uncertainty region, while 45% have multiple X-ray sources. For each X-ray source, we also looked in the corresponding Swift UVOT merged images for optical and ultraviolet counterparts, also performing source photometry. We found ultraviolet-optical correspondences for ~70% of the X-ray sources. We searched several major radio, infrared, optical, and ultraviolet surveys for possible counterparts within the positional error of the sources in the X-ray catalog to obtain additional information on their nature. Applying the kernel density estimation technique to infrared colors of Wide-Field Infrared Survey Explorer counterparts of our X-ray sources we select six {gamma}-ray blazar candidates. In addition, comparing our results with previous analyses, we select 11 additional {gamma}-ray blazar candidates.
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- ID:
- ivo://CDS.VizieR/J/AJ/159/82
- Title:
- Updated cat. of extended objects in Magellanic clouds
- Short Name:
- J/AJ/159/82
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of star clusters, associations, and related extended objects in the Small Magellanic Cloud (SMC) and the Magellanic Bridge with 2741 entries, a factor 2 more than a previous version from a decade ago. Literature data up until 2018 December are included. The identification of star clusters was carried out with digital atlases in various bands currently available in the Digitized Sky Survey (DSS) and the Machine Automatique a Mesurer pour l'Astronomie (MAMA) imaging surveys. In particular, we cross-identified recent cluster samples from the Visible and Infrared Survey Telescope for Astronomy (VISTA) near-infrared YJKs survey of the Magellanic System (VMC; Rubele+, 2015, J/MNRAS/449/639), Optical Gravitational Lensing Experiment IV (OGLE IV; Sitek+ 2017, J/AcA/67/363), and Survey of the MAgellanic Stellar History (SMASH; Piatti 2017ApJ...834L..14P) surveys, confirming new clusters and pointing out equivalencies. A major contribution of the present catalog consists of the accurate central positions for clusters and small associations, including a new sample of 45 clusters or candidates in the SMC and 19 in the Magellanic Bridge, as well as a compilation of the most reliable age and metallicity values from the literature. A general catalog must also deal with the recent discoveries of 27 faint and ultra-faint star clusters and galaxies projected on the far surroundings of the Clouds, most of them from the Dark Energy Survey. The information on these objects has been complemented with photometric, spectroscopic, and kinematical follow-up data from the literature. The underluminous galaxies around the Magellanic System, still very few as compared to the predictions from {Lambda} Cold Dark Matter simulations, can bring constraints to galaxy formation and hierarchical evolution. Furthermore, we provide diagnostics, when possible, of the nature of the ultra-faint clusters, searching for borders of the Magellanic System extensions into the Milky Way gravitational potential.
- ID:
- ivo://CDS.VizieR/J/A+A/640/A66
- Title:
- Updated X-ray view of the Hyades cluster
- Short Name:
- J/A+A/640/A66
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We revisit the X-ray properties of the main sequence Hyades members and the relation between X-ray emission and stellar rotation. As an input catalog for Hyades members, we combined three recent membership lists derived from Gaia DR2 data that include the Hyades core and its tidal tails. We searched for X-ray detections of the main sequence Hyades members in the ROSAT all-sky survey (RASS), and pointings from ROSAT, the Chandra X-Ray Observatory, and XMM-Newton. Furtmermore, we adopted rotation periods derived from Kepler's K2 mission and other resources. We find an X-ray detection for 281 of 1066 bona fide main sequence Hyades members and provide statistical upper limits for the undetected sources. The majority of the X-ray detected stars are located in the Hyades core because of its generally smaller distance to the sun. F- and G-type stars have the highest detection fraction (72%), while K- and M-type dwarfs have lower detection rates (22 %). The X-ray luminosities of the detected members range from about 2x10^27^ for late M-type dwarfs to approximately 2x10^30^erg/s for active binaries. The X-ray luminosity distribution functions formally differ for the members in the core and tidal tails, which is likely caused by a larger fraction of field stars in our Hyades tails sample. Compared to previous studies, our sample is slightly fainter in X-rays due to differences in the Hyades membership list used; furthermore, we extend the X-ray luminosity distribution to fainter luminosities. The X-ray activity of F- and G-type stars is well defined at F_X_/F_bol_=10^-5^. The fractional X-ray luminosity and its spread increases to later spectral types reaching the saturation limit (F_X_/F_bol_=10^-3^) for members later than spectral type M3. Confirming previous results, the X-ray flux varies by less than a factor of three between epochs for the 104 Hyades members with multiple epoch data, significantly less than expected from solar-like actvity cycles. Rotation periods are found for 204 Hyades members, with about half of them being detected in X-rays. The activity-rotation relation derived for the coeval Hyades members has properties very similar to those obtained by other authors investigating stars of different ages.
- ID:
- ivo://CDS.VizieR/V/135A
- Title:
- Uranometria Argentina catalog of bright southern stars
- Short Name:
- V/135A
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In 1879 Benjamin Apthorp Gould published in Buenos Aires, Argentina, the Uranometria Argentina catalog of 7756 stars south of declination +10 degrees. This included all those stars he considered magnitude 7 or brighter and some fainter stars which are close companions to brighter stars or to each other and have combined magnitude 7 or brighter. Star positions are in 1875 coordinates, and constellation boundaries also in 1875 coordinates were defined within the aforementioned declination range. With only a few small changes these were incorporated into the boundaries adopted by the IAU in 1930 and subsequently universally accepted. In terms of accurate photoelectric magnitude measurements the Uranometria Argentina is nearly complete to magnitude 6.5 in its declination range. In each constellation the individual stars considered to be magnitude 7 and brighter were numbered in sequence of increasing right ascension in 1875 coordinates, except that in a few cases this sequence was somewhat adjusted so that stars close together could be listed on adjacent lines of text. The numbering system is analogous to that in the Flamsteed Catalogus Brittanicus and now widely used. Star numbers from the Uranometria Argentina rarely appear in the 21st century despite the potential utility of their use. They were included in the American Ephemeris and Nautical Almanac until 1978, and in the FK5 catalog until 1999, always with the letter G following the number in the Uranometria Argentina catalog. This serves to distinguish Flamsteed numbers with no following letters from Gould numbers, and is utilized in this presentation and recommended for general use. The file catalog.dat includes every star in the original Uranometria Argentina. In the original the constellations were presented in sequence of increasing distance from the south pole and numbered accordingly. For the convenience of 21st century astronomers the constellations are presented here by alphabetical sequence in constellation name and the stars in each constellation in the same sequence as in the original. A separate file notes.txt includes a large number of notes for individual stars and for groups of stars recognized in the original catalog as belonging together. Each note is referenced by an asterisk * in the file catalog.dat. Columns 43-63 provide J2000 coordinates and cross identifications from the Flamsteed, HD, and SAO catalogs for the stars and have been added by the author of this data set. Columns 82-154 have been copied verbatim from the Uranometria Argentina catalogue, except that where asterisks are shown errors in the original printed catalogue have been corrected and the originally published values are stated in the notes. Two publications state corrections to the printed Uranometria Argentina. These are by B.A. Gould, Astronomische Nachrichten 116, 379-382 (1887AN....116..379G), and by T. W. Backhouse, Astronomical Journal 12, 112 (1892AJ.....12Q.112B). All of these, and a few others, mostly typographical misprints found by the present author, are presented in this digital version.
- ID:
- ivo://CDS.VizieR/J/ApJS/238/25
- Title:
- UV variability with GALEX gPhoton archive. I.
- Short Name:
- J/ApJS/238/25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In order to develop and test a methodology to search for UV variability over the entire Galaxy Evolution Explorer (GALEX) database down to the shortest timescales, we analyzed time-domain photometry of ~5000 light curves of ~300 bright (mFUV, mNUV<=14) and blue (mFUV-mNUV<0) GALEX sources. Using the gPhoton database tool, we discovered and characterized instrumentally induced variabilities in time-resolved GALEX photometry that may severely impact automated searches for short-period variations. The most notable artifact is a quasi-sinusoidal variation mimicking light curves typical of pulsators, seen occasionally in either one or both detectors, with amplitudes of up to 0.3mag and periods corresponding to the periodicity of the spiral dithering pattern used during the observation (P~120s). Therefore, the artifact may arise from small-scale response variations. Other artifacts include visit-long "sagging" or "hump" in flux, occurring when the dithering pattern is not a spiral, or a one-time change in flux level during the exposure. These instrumentally caused variations were not reported before, and are not due to known (and flagged) artifacts such as hotspots, which can be easily eliminated. To characterize the frequency and causality of such artifacts, we apply Fourier transform analysis to both light curves and dithering patterns, and examine whether artificial brightness variations correlate with visit or instrumental parameters. Artifacts do not correlate with source position on the detector. We suggest methods to identify artifact variations and to correct them when possible.
- ID:
- ivo://CDS.VizieR/J/A+A/403/247
- Title:
- Variability in the ROSAT All-Sky Survey
- Short Name:
- J/A+A/403/247
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a systematic search for variability among the ROSAT All-Sky Survey (RASS) X-ray sources. We generated lightcurves for about 30000 X-ray point sources detected sufficiently high above background. For our variability study different search algorithms were developed in order to recognize flares, periods and trends, respectively. The variable X-ray sources were optically identified with counterparts in the SIMBAD, the USNO-A2.0 and NED data bases, but a significant part of the X-ray sources remains without cataloged optical counterparts. A complete list of the 1207 variable sources we found is presented here.
- ID:
- ivo://CDS.VizieR/J/AJ/135/907
- Title:
- Variables in Praesepe identified with KELT
- Short Name:
- J/AJ/135/907
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Kilodegree Extremely Little Telescope (KELT) project is a small aperture, wide-angle search for planetary transits of solar-type stars. In this paper, we present the results of a commissioning campaign with the KELT telescope to observe the open cluster Praesepe for 34 nights in early 2005. Light curves were obtained for 69337 stars, out of which we identify 58 long-period variables and 152 periodic variables. Sixteen of these are previously known as variable, yielding 194 newly discovered variable stars for which we provide properties and light curves. We also searched for planetary-like transits, finding four transit candidates. Follow-up observations indicate that two of the candidates are astrophysical false positives, with two candidates remaining as potential planetary transits.
- ID:
- ivo://CDS.VizieR/I/226
- Title:
- Vatican AC Zone Data Reduced to ACRS
- Short Name:
- I/226
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The U.S. Naval Observatory is in the process of making new reductions of the Astrographic Catalogue (AC) using a modern reference system, the ACRS, which represents the system of the FK5. The data from the Vatican Zone, whose plates are centered between declinations +55 and +64 degrees (eq. 1900), have been analyzed for scale, rotation, tilt, coma, magnitude equation, radial distortion and distortions introduced by the use of reseaux in the Carte du Ciel program. The result is a positional catalog of over 256,000 stars on eq. J2000.0, epoch of observation. Additionally, all stars have been matched with the Tycho Input Catalog (revised); those numbers have been added for additional identification purposes.
- ID:
- ivo://CDS.VizieR/J/A+AS/109/29
- Title:
- Very low mass stars in Praesepe
- Short Name:
- J/A+AS/109/29
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a deep proper motion survey of a 19 square degree area of the Galactic open cluster Praesepe. Details of the astrometric and photometric reductions are given, along with the selection process for members. A list of these probable members, along with cross identifications from previous less sensitive surveys, is presented and finder charts given in an Appendix.
- ID:
- ivo://CDS.VizieR/J/ApJS/219/41
- Title:
- VLA & Chandra obs. of IRAS20126+4104 region
- Short Name:
- J/ApJS/219/41
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from Chandra ACIS-I and Karl G. Jansky Very Large Array 6cm continuum observations of the IRAS 20126+4104 massive star-forming region. We detect 150 X-ray sources within the 17'x17' ACIS-I field, and a total of 13 radio sources within the 9.2' primary beam at 4.9GHz. Among these observations are the first 6cm detections of the central sources reported by Hofner et al. (2007A&A...465..197H), namely, I20N1, I20S, and I20var. A new variable radio source is also reported. Searching the 2MASS archive, we identified 88 near-infrared (NIR) counterparts to the X-ray sources. Only four of the X-ray sources had 6cm counterparts. Based on an NIR color-color analysis and on the Besancon simulation of Galactic stellar populations, we estimate that approximately 80 X-ray sources are associated with this massive star-forming region. We detect an increasing surface density of X-ray sources toward the massive protostar and infer the presence of a cluster of at least 43 young stellar objects within a distance of 1.2pc from the massive protostar.
