Metallicity, temperature, and gravity scales of M subdwarfs

Lodieu, N.; Allard, F.; Rodrigo, C.; Pavlenko, Y.; Burgasser, A.; Lyubchik, Y.; Kaminsky, B.; Homeier, D.
Bibliographical reference

Astronomy and Astrophysics, Volume 628, id.A61, 31 pp.

Advertised on:
8
2019
Number of authors
8
IAC number of authors
4
Citations
10
Refereed citations
10
Description
Aims: The aim of the project is to define metallicity/gravity/temperature scales for different spectral types of metal-poor M dwarfs. Methods: We obtained intermediate-resolution ultraviolet (R ˜ 3300), optical (R ˜ 5400), and near-infrared (R ˜ 3900) spectra of 43 M subdwarfs (sdM), extreme subdwarfs (esdM), and ultra-subdwarfs (usdM) with the X-shooter spectrograph on the European Southern Observatory Very Large Telescope. We compared our atlas of spectra to the latest BT-Settl synthetic spectral energy distribution over a wide range of metallicities, gravities, and effective temperatures to infer the physical properties for the whole M dwarf sequence (M0-M9.5) at sub-solar metallicities and constrain the latest atmospheric models. Results: The BT-Settl models accurately reproduce the observed spectra across the 450-2500 nm wavelength range except for a few regions. We find that the best fits are obtained for gravities of log (g) = 5.0-5.5 for the three metal classes. We infer metallicities of [Fe/H] = -0.5, -1.5, and -2.0 ± 0.5 dex and effective temperatures of 3700-2600 K, 3800-2900 K, and 3700-2900 K for subdwarfs, extreme subdwarfs, and ultra-subdwarfs, respectively. Metal-poor M dwarfs tend to be warmer by about 200 ± 100 K and exhibit higher gravity than their solar-metallicity counterparts. We derive abundances of several elements (Fe, Na, K, Ca, Ti) for our sample but cannot describe their atmospheres with a single metallicity parameter. Our metallicity scale expands the current scales available for mildly metal-poor planet-host low-mass stars. Our compendium of moderate-resolution spectra covering the 0.45-2.5 micron range represents an important resource for large-scale surveys and space missions to come. All observed spectra are available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/628/A61Based on observations collected at the European Southern Observatory, Chile, under programmes 089.C-0140(A), 091.C-0264(A), 092.D-0600(A), and 093.C-0610(A).
Related projects
Discovery of a system of super-Earths orbiting the star HD 176986 with about 5.7 and 9.2 Earth masses.
Very Low Mass Stars, Brown Dwarfs and Planets
Our goal is to study the processes that lead to the formation of low mass stars, brown dwarfs and planets and to characterize the physical properties of these objects in various evolutionary stages. Low mass stars and brown dwarfs are likely the most numerous type of objects in our Galaxy but due to their low intrinsic luminosity they are not so
Rafael
Rebolo López