A high resolution spectroscopic atlas of M subdwarfs - Effective temperature and metallicity

Abstract

Context. M subdwarfs are metal poor and cool stars. They are important probes of the old galactic populations. However, they remain elusive due to their low luminosity. Observational and modeling efforts are required to fully understand their physics and to investigate the effects of metallicity in their cool atmospheres. Aims. We perform a detailed study of a sample of subdwarfs to determine their stellar parameters and constrain the stat-of-the art atmospheric models. Methods. We present UVES/VLT high resolution spectra of three late-K subdwarfs and 18 M subdwarfs. Our atlas covers the optical region from 6400 AA up to the near infrared at 8900 AA. We show spectral details of cool atmospheres at very high resolution (R= 40 000) and compare with synthetic spectra computed from the recent BT-Settl atmosphere models. Results. Our comparison shows that molecular features (TiO, VO, CaH), and atomic features (Fe I, Ti I, Na I, K I) are well fitted by current models. We produce an effective temperature versus spectral type relation all over the subdwarf spectral sequence. Thanks to the high resolution of our spectra, we perform a detailed comparison of line profiles of individual elements such as Fe I, Ca II, Ti I, and are able to determine accurate metallicities of these stars. These determinations contribute to calibrate the relation between metallicity and molecular band strength indices from low-resolution spectra. Conclusions. This work shows that the new generation of models are able to reproduce various spectral features of M subdwarfs. Working with these high resolution spectra allowed us to disentangle the atmospheric parameters (effective temperature, gravity, metallicity), which is not possible when using low resolution spectroscopy or photometry.

15 pages, 20 figures, 2 tables, accepted for publication in Astronomy and Astrophysics

References in corpus (10)

• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• Revised metallicity classes for low-mass stars: dwarfs (dM), subdwarfs (sdM), extreme subdwarfs (esdM), and ultra subdwarfs (usdM)
• M dwarfs: effective temperatures, radii and metallicities
• Chemical abundances of 451 stars from the HARPS GTO planet search program: Thin disc, thick disc, and planets
• Accurate M Dwarf Metallicities from Spectral Synthesis: A Critical Test of Model Atmospheres
• Cool Subdwarf Investigations (CSI) I: New Thoughts for the Spectral Types of K and M Subdwarfs
• Discovery of the Coolest Extreme Subdwarf
• Energy transport, overshoot, and mixing in the atmospheres of M-type main- and pre-main-sequence objects
• A high resolution spectral atlas of brown dwarfs
• Optical spectroscopy of high proper motion stars: new M dwarfs within 10 pc and the closest pair of subdwarfs

Cited by in corpus (37)

• ExoMol molecular line lists XXX: a complete high-accuracy line list for water
• ExoMol line lists XVIII. The high temperature spectrum of VO
• CARMENES input catalogue of M dwarfs. I. Low-resolution spectroscopy with CAFOS
• Ionized outflows in local luminous AGN: what are the real densities and outflow rates?
• Constructing A Flexible Likelihood Function For Spectroscopic Inference
• The CARMENES search for exoplanets around M dwarfs. Stellar atmospheric parameters of target stars with SteParSyn
• The Extended IRTF Spectral Library: Expanded coverage in metallicity, temperature, and surface gravity
• Stellar parameters of early M dwarfs from ratios of spectral features at optical wavelengths
• The AllWISE Motion Survey, Part 2
• Primeval very low-mass stars and brown dwarfs. I. Six new L subdwarfs, classification and atmospheric properties
• ExoMol molecular line lists XIX: high accuracy computed hot line lists for H${}_2$${}^{18}$O and H${}_2$${}^{17}$O
• The Gaia-ESO Survey: Empirical estimates of stellar ages from lithium equivalent widths (EAGLES)
• New ultra-cool and brown dwarf candidates in Gaia DR2
• What are little worlds made of? Stellar abundances and the building blocks of planets
• Radii of 88 M Subdwarfs and Updated Radius Relations for Low-Metallicity M Dwarf Stars
• Fundamental M-dwarf parameters from high-resolution spectra using PHOENIX ACES models: I. Parameter accuracy and benchmark stars
• The physical mechanism behind M dwarf metallicity indicators and the role of C and O abundances
• Stellar parametrization of LAMOST M dwarf stars
• Sporadic radio pulses from a white dwarf binary at the orbital period
• The Mass-Activity relationships in M and K dwarfs. I. Stellar parameters of our sample of M and K dwarfs
• Photospheric properties and fundamental parameters of M dwarfs
• The Gaia-ESO survey: A lithium depletion boundary age for NGC 2232
• Chemical Properties of the Local Galactic Disk and Halo. I. Fundamental Properties of 1,544 Nearby, High Proper-Motion M dwarfs and subdwarfs
• Physical properties and trigonometric distance of the peculiar dwarf WISE J181005.5$-$101002.3
• Characterisation of 92 Southern TESS Candidate Planet Hosts and a New Photometric [Fe/H] Relation for Cool Dwarfs
• Spectral energy distribution of M-subdwarfs: A study of their atmospheric properties
• Chemical Properties of the Local Disk and Halo. II. Abundances of 3745 M dwarfs and Subdwarfs from Improved Model Fitting of Low-Resolution Spectra
• Metallicity, temperature, and gravity scales of M subdwarfs
• A search for lithium in metal-poor L dwarfs
• Probing M subdwarf metallicity with an esdK5+esdM5.5 binary
• An ancient F-type subdwarf from the halo crossing the Galactic plane
• M Subdwarf Research. II. Atmospheric Parameters and Kinematics
• First Results from MFOSC-P : Low Resolution Optical Spectroscopy of a Sample of M dwarfs within 100 parsecs
• Cool and Data-Driven: An Exploration of Optical Cool Dwarf Chemistry with Both Data-Driven and Physical Models
• Planetary host stars: Evaluating uncertainties in ultra-cool model atmospheres
• M Subdwarf Research III. Spectroscopic Diagnostics for Breaking Parameter Degeneracy
• Estimating Stellar Atmospheric Parameters and [α/Fe] for LAMOST O-M type Stars Using a Spectral Emulator