Journal Article

M dwarfs: effective temperatures, radii and metallicities

Luca Casagrande, Chris Flynn and Michael Bessell

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 389, issue 2, pages 585-607
Published in print September 2008 | ISSN: 0035-8711
Published online September 2008 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2008.13573.x
M dwarfs: effective temperatures, radii and metallicities

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We empirically determine effective temperatures and bolometric luminosities for a large sample of nearby M dwarfs, for which high accuracy optical and infrared photometry is available. We introduce a new technique which exploits the flux ratio in different bands as a proxy of both effective temperature and metallicity. Our temperature scale for late-type dwarfs extends well below 3000 K (almost to the brown dwarf limit) and is supported by interferometric angular diameter measurements above 3000 K. Our metallicities are in excellent agreement (usually within 0.2 dex) with recent determinations via independent techniques. A subsample of cool M dwarfs with metallicity estimates based on hotter Hipparcos common proper motion companions indicates our metallicities are also reliable below 3000 K, a temperature range unexplored until now. The high quality of our data allows us to identify a striking feature in the bolometric luminosity versus temperature plane, around the transition from K to M dwarfs. We have compared our sample of stars with theoretical models and conclude that this transition is due to an increase in the radii of the M dwarfs, a feature which is not reproduced by theoretical models.

Keywords: stars: abundances; stars: atmospheres; stars: fundamental parameters; Hertzsprung-Russell (HR) diagram; stars: low-mass, brown dwarf; infrared: stars

Journal Article.  17468 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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