Infrared Spectra of Low-Mass Stars: Toward a Temperature Scale for Red Dwarfs

We present new low-resolution (R ∼ 250)1.0-2.4 μm spectra for 13 red dwarf stars. The sample size is increased to 16 by including other published infrared spectra. New, as well as published, red spectra are presented for 10 of these 16 stars, and new and published VRIJHKLL' photometry is also presented. Both halo and disk stars are included in the sample, which covers a range of spectral type from dM0 to dM6.5. We derive bolometric luminosities and bolometric corrections from the observational data, finding good agreement with earlier results for the disk stars. We fit synthetic spectra generated by Allard & Hauschildt's state-of-the-art model atmospheres to the observed spectra. Although some discrepancies remain between the theoretical and observed spectra, we find that the molecular features give a consistent value for effective temperature across the entire observed wavelength range. The Teff values and radii derived, and their dependency on metallicity, are in agreement with the most recent structural models of low-mass stars, removing the long-standing discrepancy between the observed and calculated locations of such stars in the H-R diagram, at least for stars more massive than 0.1 Msun.