- ID:
- ivo://CDS.VizieR/J/AJ/150/42
- Title:
- Catalog of 2612 M dwarfs from LAMOST
- Short Name:
- J/AJ/150/42
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We develop a template-fit method to automatically identify and classify late-type K and M dwarfs in spectra from the Large Sky Area Multi-object Fiber Spectroscopic Telescope (LAMOST). A search of the commissioning data, acquired in 2009-2010, yields the identification of 2612 late-K and M dwarfs. The template fit method also provides spectral classification to half a subtype, classifies the stars along the dwarf-subdwarf (dM/sdM/esdM/usdM) metallicity sequence, and provides improved metallicity/gravity information on a finer scale. The automated search and classification is performed using a set of cool star templates assembled from the Sloan Digital Sky Survey spectroscopic database. We show that the stars can be efficiently classified despite shortcomings in the LAMOST commissioning data which include bright sky lines in the red. In particular we find that the absolute and relative strengths of the critical TiO and CaH molecular bands around 7000{AA} are cleanly measured, which provides accurate spectral typing from late-K to mid-M, and makes it possible to estimate metallicity classes in a way that is more efficient and reliable than with the use of spectral indices or spectral-index based parameters such as {zeta}_TiO/CaH_. Most of the cool dwarfs observed by LAMOST are found to be metal-rich dwarfs (dM). However, we identify 52 metal-poor M subdwarfs (sdM), 5 very metal-poor extreme subdwarfs (esdM) and 1 probable ultra metal-poor subdwarf (usdM). We use a calibration of spectral type to absolute magnitude and estimate spectroscopic distances for all the stars; we also recover proper motions from the SUPERBLINK and PPMXL catalogs. Our analysis of the estimated transverse motions suggests a mean velocity and standard deviation for the UVW components of velocity to be: <U>=-9.8km/s, {sigma}_U_=35.6km/s; <V> =-22.8km/s, {sigma}_V_=30.6km/s; <W> =-7.9km/s, {sigma}_W_=28.4km/s. The resulting values are in general agreement with previous reported results, which yields confidence in our spectral classification and spectroscopic distance estimates, and illustrates the potential for using LAMOST spectra of K and M dwarfs for investigating the chemo-kinematics of the local Galactic disk and halo.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/435/2161
- Title:
- Catalogue of bright (K<9) M dwarfs
- Short Name:
- J/MNRAS/435/2161
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the Position and Proper Motion Extended-L (PPMXL) catalogue, we have used optical and near-infrared colour cuts together with a reduced proper motion cut to find bright M dwarfs for future exoplanet transit studies. PPMXL's low proper motion uncertainties allow us to probe down to smaller proper motions than previous similar studies. We have combined unique objects found with this method to that of previous work to produce 8479 K<9 M dwarfs. Low-resolution spectroscopy was obtained of a sample of the objects found using this selection method to gain statistics on their spectral type and physical properties. Results show a spectral-type range of K7-M4V. This catalogue is the most complete collection of K<9 M dwarfs currently available and is made available here.
- ID:
- ivo://CDS.VizieR/J/MNRAS/443/2815
- Title:
- Cerro Armazones spectroscopy of F dwarfs
- Short Name:
- J/MNRAS/443/2815
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a spectroscopic survey of a sample of F stars that have not yet been searched for planets. The observations of 187 stars obtained with the Bochum Echelle Spectrographic Observer of the Cerro Armazones Observatory were aimed at nearby (closer than 70pc) main-sequence stars without sufficient archive ([fiber-fed extended range optical spectrograph (FEROS)/high accuracy radial velocity planet search (HARPS)]) spectroscopy. The primary goal of the survey was to select the best candidates for radial-velocity searches of extrasolar planets. The spectra were analysed using the broadening-function technique, the method of choice for rapid rotators later than about A5. The analysis was focused not only at the determination of projected rotational velocity (defining precision of radial-velocity determination), but also at the detection of previously unknown spectroscopic binaries/multiples or stars showing strong line asymmetries. 12 previously unknown spectroscopic binaries/triples were detected. For all observed targets the spectral type was determined. About 140 stars are rotating faster than the resolution limit of 10km/s sampling the onset of convection and slow rotation at mid-F spectral types in great detail. Radial-velocity precision of the data (about 100m/s) is insufficient to detect planets but could indicate most SB1 systems with stellar companions. As there are already 2-3 observations per object for these newly detected binary stars, only a few additional follow-up observations will be needed to obtain constraints on orbital parameters. We identified a sample of 68 bright F-type dwarf stars which are perfect targets for future planet searches. They rotate moderately or slowly and do not show any sign of binarity, pulsations, or surface activity.
- 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/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.
