M dwarfs: Effective temperatures, radii and metallicities

Luca Casagrande*, Chris Flynn, Michael Bessell

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    170 Citations (Scopus)


    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.

    Original languageEnglish
    Pages (from-to)585-607
    Number of pages23
    JournalMonthly Notices of the Royal Astronomical Society
    Issue number2
    Publication statusPublished - Sept 2008


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