- 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.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/660/1556
- Title:
- Characterization of dusty debris disks
- Short Name:
- J/ApJ/660/1556
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Dusty debris disks around main-sequence stars are signposts for the existence of planetesimals and exoplanets. From cross-correlating Hipparcos stars with the IRAS catalogs, we identify 146 stars within 120pc of Earth that show excess emission at 60um. This search took special precautions to avoid false positives. Our sample is reasonably well distributed from late B to early K-type stars, but it contains very few later type stars. Even though IRAS flew more than 20 years ago and many astronomers have cross-correlated its catalogs with stellar catalogs, we were still able to newly identify debris disks at as many as 33 main-sequence stars; of these, 32 are within 100pc of Earth. The power of an all-sky survey satellite like IRAS is evident when comparing our 33 new debris disks with the total of only 22 dusty debris disk stars first detected with the more sensitive, but pointed, satellite ISO. Our investigation focuses on the mass, dimensions, and evolution of dusty debris disks.
- ID:
- ivo://CDS.VizieR/J/A+A/449/127
- Title:
- Chemical abundances of 32 mildly metal-poor stars
- Short Name:
- J/A+A/449/127
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present photospheric abundances of the O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Ni, and Ba elements for 32 mildly metal-poor stars with [Fe/H]~-0.7. High resolution and high signal-to-noise ratio spectra were obtained with the Coude Echelle Spectrograph mounted on the 2.16m telescope at the National Astronomical Observatories (Xinglong, China) on 10 nights during 1999. Effective temperatures were estimated from colour indices, and surface gravities from Hipparcos parallaxes. Stellar abundances were determined from a differential LTE analysis. Our element abundance results extend and confirm previous works. The oxygen and other alpha-elements (Mg, Si, Ca, and Ti) abundances of thin and thick disk stars show distinct trends at [Fe/H]<-0.60. The [Al/Fe] behaviour is exactly as an alpha-element, although the separation for [Na/Fe] of thin and thick disk stars is not clear. The elements V, Cr, and Ni follow Fe very closely, and there is no offset between thin and thick disk stars, but the Sc and Mn abundance trends of the thin and thick disk stars are different, and [Ba/Fe] of thin disk and thick disk stars shows different behaviour.
- ID:
- ivo://CDS.VizieR/J/A+A/562/A71
- Title:
- Chemical abundances of solar neighbourhood dwarfs
- Short Name:
- J/A+A/562/A71
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed elemental abundance study of 714 F and G dwarf and subgiant stars in the Solar neighbourhood. The analysis is based on high-resolution spectra obtained with MIKE on the Magellan telescope, FEROS on the ESO 1.5m and 2.2m telescopes, HARPS on the ESO 3.6m telescope, UVES on the ESO Very Large Telescope, SOFIN and FIES on the Nordic Optical Telescope. Our data show that there is an old and alpha-enhanced disk population, and a younger and less alpha-enhanced disk population. While they overlap greatly in metallicity between -0.7<[Fe/H]<+0.1, they show a bimodal distribution in [alpha/Fe]. This bimodality becomes even clearer if stars where stellar parameters and abundances show larger uncertainties (Teff<5400K) are discarded, showing that it is important to constrain the data set to a narrow range in the stellar parameters if small differences between stellar populations are to be revealed. In addition, we find that the alpha-enhanced population has orbital parameters placing the stellar birthplaces in the inner Galactic disk while the low-alpha stars mainly come from the outer Galactic disk, fully consistent with the recent claims of a short scale-length for the alpha-enhanced Galactic thick disk. We have also investigated the properties of the Hercules stream and the Arcturus moving group.
- ID:
- ivo://CDS.VizieR/J/A+AS/141/491
- Title:
- Chemical composition of halo and disk stars
- Short Name:
- J/A+AS/141/491
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Table 3. Atmospheric parameters, space velocities, distances, masses and ages of the program stars. Table 4. Atomic line data including wavelength, excitation energy of the lower level, the logarithm of the oscillator strength (the experimental or theoretical value, the corrected value and the differential value from standard stars) and the adopted enhancement factor of the Unsold approximation to the van der Waals damping constant. The last column gives the equivalent width in the spectrum of HD 142373 representing a typical metallicity of the sample of stars. Uncertain EWs marked by (:) and strong lines with EW>100m{AA} are not used in the abundance determination for this star. Table 5. Abundance ratios for the program stars. The oxygen abundance is derived from the 7774{AA} triplet but scaled to results from the forbidden [OI] line at 6300{AA}.
- ID:
- ivo://CDS.VizieR/J/ApJ/706/1095
- Title:
- Chemical compositions of 26 outer halo stars
- Short Name:
- J/ApJ/706/1095
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Chemical abundances of 26 metal-poor dwarfs and giants are determined from high-resolution and high signal-to-noise ratio spectra obtained with the Subaru/High Dispersion Spectrograph. The sample is selected so that most of the objects have outer-halo kinematics. Self-consistent atmospheric parameters were determined by an iterative procedure based on spectroscopic analysis. Abundances of 13 elements, including {alpha}-elements (Mg, Si, Ca, Ti), odd-Z light elements (Na, Sc), iron-peak elements (Cr, Mn, Fe, Ni, Zn), and neutron-capture elements (Y, Ba), are determined by two independent data reduction and local thermodynamic equillibrium analysis procedures, confirming the consistency of the stellar parameters and abundances results.
- ID:
- ivo://CDS.VizieR/J/A+A/551/L8
- Title:
- Chromospheric activity of field stars
- Short Name:
- J/A+A/551/L8
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Compilation of S-index measurements available in the literature cross-correlated with the CDS catalog. The S-index is a measure of the strength of the chromospheric emission in the core of the CaII H and K lines, and it is a proxy for chromospheric activity. Its conversion into logR'HK is also reported, along with temperature, age and metallicity from the CDS.
- ID:
- ivo://CDS.VizieR/J/ApJ/835/61
- Title:
- Chromospherically active stars in RAVE. II.
- Short Name:
- J/ApJ/835/61
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A large sample of over 38000 chromospherically active candidate solar-like stars and cooler dwarfs from the RAVE survey is addressed in this paper. An improved activity identification with respect to the previous study was introduced to build a catalog of field stars in the solar neighborhood with an excess emission flux in the calcium infrared triplet wavelength region. The central result of this work is the calibration of the age-activity relation for main-sequence dwarfs in a range from a few 10Myr up to a few Gyr. It enabled an order of magnitude age estimation of the entire active sample. Almost 15000 stars are shown to be younger than 1Gyr and ~2000 younger than 100Myr. The young age of the most active stars is confirmed by their position off the main sequence in the J-K versus N_UV_-V diagram showing strong ultraviolet excess, mid-infrared excess in the J-K versus W_1_-W_2_ diagram, and very cool temperatures (J-K>0.7). They overlap with the reference pre-main-sequence RAVE stars often displaying X-ray emission. The activity level increasing with the color reveals their different nature from the solar-like stars and probably represents an underlying dynamo-generating magnetic fields in cool stars. Of the RAVE objects from DR5, 50% are found in the TGAS catalog and supplemented with accurate parallaxes and proper motions by Gaia. This makes the database of a large number of young stars in a combination with RAVE's radial velocities directly useful as a tracer of the very recent large-scale star formation history in the solar neighborhood.
- ID:
- ivo://CDS.VizieR/J/ApJS/152/261
- Title:
- Chromospheric Ca II emission in nearby stars
- Short Name:
- J/ApJS/152/261
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present chromospheric CaII H and K activity measurements, rotation periods, and ages for ~1200 F, G, K, and M type main-sequence stars from ~18000 archival spectra taken at Keck and Lick Observatories as a part of the California and Carnegie Planet Search Project. We have calibrated our chromospheric S-values against the Mount Wilson chromospheric activity data. From these measurements we have calculated median activity levels and derived R'_HK_, stellar ages, and rotation periods from general parameterizations for 1228 stars, ~1000 of which have no previously published S-values. We also present precise time series of activity measurements for these stars.
- ID:
- ivo://CDS.VizieR/J/AJ/131/1674
- Title:
- Close binary systems from SDSS DR4
- Short Name:
- J/AJ/131/1674
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a spectroscopic sample of 746 detached close binary systems from the Sloan Digital Sky Survey (SDSS) Fourth Data Release (2006ApJS..162...38A). The majority of these binaries consist of a white dwarf primary and a low-mass secondary (typically M dwarf) companion. We have determined the temperature and gravity for 496 of the white dwarf primaries and the spectral type and magnetic activity properties for 661 of the low-mass secondaries. We have estimated the distances for each of the white dwarf-main-sequence star binaries and use white dwarf evolutionary grids to establish the age of each binary system from the white dwarf cooling times.
