- ID:
- ivo://CDS.VizieR/J/A+A/650/A146
- Title:
- Distant, pulsating red giants in southern halo
- Short Name:
- J/A+A/650/A146
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- To investigate the asymptotic giant branch (AGB) population in the Galactic halo, we search for pulsating AGB stars at a heliocentric distance over 50kpc. Our research is based on the Catalina Southern Survey (CSS) catalogue of variables, comprising 1286 long-period variables (LPVs) with declination less than -20{deg}. We first focus on the 77 stars in the cap abs(b)>30deg for which spectral M-type or C-type classification can be derived from Hamburg-ESO objective prism spectra. Most of these are oxygen-rich (M-type) and very few are carbon rich. The periods are in the range 100-500 days, and CSS amplitudes are up to 3mag. In this small sample, no halo AGB star is fainter than Ks0=12.5. This may be due to the scarcity of AGBs in the outer halo, or insufficient instrumental depth. Leaving aside spectral information, we then searched for even fainter pulsators (Ks>12.5) in the entire CSS catalogue. Gaia astrometry makes it possible to identify some contaminants. Our final result is the identification of ten candidate distant LPVs. If these ten stars obey the fundamental mode K-band period luminosity relation used for Miras and small-amplitude Miras, their distances are between 50 and 120kpc from the Sun. In a diagram showing distance versus Gaia tangential velocity, these ten stars have positions similar to those of other objects in the halo, such as globular clusters and dwarf galaxies. We also detect some underluminous AGBs that deserve further study. A detailed catalogue of the 77 high-latitude M or C stars will be made available at the CDS.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/506/306
- Title:
- EBLM project. VIII.43 M-dwarf light curve
- Short Name:
- J/MNRAS/506/306
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The accuracy of theoretical mass, radius and effective temperature values for M-dwarf stars is an active topic of debate. Differences between observed and theoretical values have raised the possibility that current theoretical stellar structure and evolution models are inaccurate towards the low-mass end of the main sequence. To explore this issue we use the CHEOPS satellite to obtain high-precision light curves of eclipsing binaries with low mass stellar companions. We use these light curves combined with the spectroscopic orbit for the solar-type companion to measure the mass, radius and effective temperature of the M-dwarf star. Here we present the analysis of three eclipsing binaries. We use the pycheops data analysis software to fit the observed transit and eclipse events of each system. Two of our systems were also observed by the TESS satellite - we similarly analyse these light curves for comparison. We find consistent results between CHEOPS and TESS, presenting three stellar radii and two stellar effective temperature values of low-mass stellar objects. These initial results from our on-going observing programme with CHEOPS show that we can expect to have ~24 new mass, radius and effective temperature measurements for very low mass stars within the next few years.
- ID:
- ivo://CDS.VizieR/J/A+A/556/A15
- Title:
- Effective temperature scale of M dwarfs
- Short Name:
- J/A+A/556/A15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Despite their large number in the Galaxy, M dwarfs remain elusive objects and the modeling of their photosphere has long remained a challenge (molecular opacities, dust cloud formation). Our objectives are to validate the BT-Settl model atmospheres, update the M dwarf T_eff_-spectral type relation, and find the atmospheric parameters of the stars in our sample. We compare two samples of optical spectra covering the whole M dwarf sequence with the most recent BT-Settl synthetic spectra and use a {chi}^2^ minimization technique to determine Teff. The first sample consists of 97 low-resolution spectra obtained with New Technology Telescope (NTT) at La Silla Observatory. The second sample contains 55 medium-resolution spectra obtained at the Siding Spring Observatory (SSO). The spectral typing is realized by comparison with already classified M dwarfs.
- ID:
- ivo://CDS.VizieR/J/A+A/560/A69
- Title:
- Emission lines in a flare of AB Dor A
- Short Name:
- J/A+A/560/A69
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a identification catalog of chromospheric emission lines in the optical range for two flares on AB Dor A, with event 1 being larger than event 3. An additional flare event 2 is not described here because of its overlap with event 1. All lines are identified in an flare- only spectrum, i.e. with a quiescent spectrum subtracted. The data were obtained with ESO's Kueyen telescope equipped with the UVES spectrograph on November 25/26 in 2009. The instrument was operated in dichroic mode (spectral coverage from 3720 to 4945 and from 5695 to 9465 AA). We tabulate measured wavelength, line flux and FWHM for every line and also provide the rest wavelength from the Moore catalog which was used for identification (Moore, 1972, Nat. Stand. Ref. Data. Ser., 40). Few lines were identified with the NIST database.
- ID:
- ivo://CDS.VizieR/J/A+A/487/293
- Title:
- Emission lines in a giant flare of CN Leo
- Short Name:
- J/A+A/487/293
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Flares on dM stars contain plasmas at very different temperatures and thus affect a wide wavelength range in the electromagnetic spectrum. While the coronal properties of flares are studied best in X-rays, the chromosphere of the star is observed best in the optical and ultraviolet ranges. Therefore, multiwavelength observations are essential to study flare properties throughout the atmosphere of a star.
- ID:
- ivo://CDS.VizieR/J/ApJ/804/64
- Title:
- Empirical and model parameters of 183 M dwarfs
- Short Name:
- J/ApJ/804/64
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Precise and accurate parameters for late-type (late K and M) dwarf stars are important for characterization of any orbiting planets, but such determinations have been hampered by these stars' complex spectra and dissimilarity to the Sun. We exploit an empirically calibrated method to estimate spectroscopic effective temperature (T_eff_) and the Stefan-Boltzmann law to determine radii of 183 nearby K7-M7 single stars with a precision of 2%-5%. Our improved stellar parameters enable us to develop model-independent relations between T_eff_ or absolute magnitude and radius, as well as between color and T_eff_. The derived T_eff_-radius relation depends strongly on [Fe/H], as predicted by theory. The relation between absolute K_S_magnitude and radius can predict radii accurate to ~=3%. We derive bolometric corrections to the VR_C_I_C_grizJHK_S_ and Gaia passbands as a function of color, accurate to 1%-3%. We confront the reliability of predictions from Dartmouth stellar evolution models using a Markov chain Monte Carlo to find the values of unobservable model parameters (mass, age) that best reproduce the observed effective temperature and bolometric flux while satisfying constraints on distance and metallicity as Bayesian priors. With the inferred masses we derive a semi-empirical mass-absolute magnitude relation with a scatter of 2% in mass. The best-agreement models overpredict stellar T_eff_ values by an average of 2.2% and underpredict stellar radii by 4.6%, similar to differences with values from low-mass eclipsing binaries. These differences are not correlated with metallicity, mass, or indicators of activity, suggesting issues with the underlying model assumptions, e.g., opacities or convective mixing length.
- ID:
- ivo://CDS.VizieR/J/MNRAS/475/1960
- Title:
- ESPaDOnS spectropolarimeter obs. of M dwarfs
- Short Name:
- J/MNRAS/475/1960
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Present and future high-precision radial-velocity spectrometers dedicated to the discovery of low-mass planets orbiting low-mass dwarfs need to focus on the best selected stars to make an efficient use of telescope time. In the framework of the preparation of the SPIRou Input Catalogue (SPIC), the CoolSnap program aims at screening M dwarfs in the solar neighbourhood against binarity, rapid rotation, activity, etc. To optimize the selection, this paper describes the methods used to compute effective temperature, metallicity, projected rotation velocity of a large sample of 440 M dwarfs observed in the visible with the high-resolution spectropolarimeter Echelle SpectroPolArimetric Device for the ObservatioN of Stars (ESPaDOnS) at Canada-France-Hawaii Telescope. It also summarizes known and newly discovered spectroscopic binaries, and stars known to belong to visual multiple systems. A calibration of the projected rotation velocity versus measured line widths for M dwarfs observed by the ESPaDOnS spectropolarimeter is derived, and the resulting values are compared to equatorial rotation velocities deduced from rotation periods and radii. A comparison of the derived effective temperatures and metallicities with literature values is also conducted. Finally, the radial-velocity uncertainty of each star in the sample is estimated, to narrow down the selection of stars to be included into the SPIC.
- ID:
- ivo://CDS.VizieR/J/MNRAS/407/465
- Title:
- Fast-rotating M dwarfs in NGC2516
- Short Name:
- J/MNRAS/407/465
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report radial velocities (RVs), projected equatorial velocities (vsini) and CaII triplet (CaT) chromospheric activity indices for 237 late-K to mid-M candidate members of the young open cluster NGC 2516. These stars have published rotation periods between 0.1 and 15d. Intermediate-resolution spectra were obtained using the Giraffe spectrograph at the Very Large Telescope. Membership was confirmed on the basis of their RVs for 210 targets.
- ID:
- ivo://CDS.VizieR/J/MNRAS/411/2099
- Title:
- Fast-rotating M-dwarf stars in NGC 2547
- Short Name:
- J/MNRAS/411/2099
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- At fast rotation rates, the coronal activity of G- and K-type stars has been observed to "saturate" and then decline again at even faster rotation rates - a phenomenon dubbed "supersaturation". In this paper, we investigate coronal activity in fast-rotating M-dwarfs using deep XMM-Newton observations of 97 low-mass stars of known rotation period in the young open cluster NGC 2547 and combine these with published X-ray surveys of low-mass field and cluster stars of known rotation period.
- ID:
- ivo://CDS.VizieR/J/PASP/121/117
- Title:
- Fe and Ti abundances of 12 low-metallicity M stars
- Short Name:
- J/PASP/121/117
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have calculated Fe and Ti abundances in 12 low-metallicity main sequence M stars using high-resolution spectra. These subdwarf and extreme-subdwarf stars allow us to extend our calibration of a method to determine cool-dwarf-star metallicities using molecular band strength indices from low-resolution spectra. Our calibration can now be used to determine metallicity to within +/-0.3dex for stars with [Fe/H] between -1.5 and +0.05 and temperatures between 3500 and 4000K. We also report a method to estimate temperatures for M dwarfs using equivalent width measurements of the infrared CaII triplet and the KI line at 7699{AA}. Our metallicity measurements show that the recently proposed classification system for low-mass stars (dwarfs, subdwarfs, extreme subdwarfs, and ultrasubdwarfs) does represent a metallicity sequence, with the ultrasubdwarfs the most metal-poor stars.
