Tuesday, August 14, 2012

1208.2431 (Tabetha S. Boyajian et al.)

Stellar Diameters and Temperatures II. Main Sequence K & M Stars    [PDF]

Tabetha S. Boyajian, Kaspar von Braun, Gerard van Belle, Harold A. McAlister, Theo A. ten Brummelaar, Stephen R. Kane, Phil Muirhead, Jeremy Jones, Russel White, Gail Schaefer, David Ciardi, Todd Henry, Mercedes López-Morales, Stephen Ridgway, Douglas Gies, Wei-Chun Jao, Bárbara Rojas-Ayala, J. Robert Parks, Laszlo Sturmann, Judit Sturmann, Nils H. Turner, Chris Farrington, P. J. Goldfinger, David H. Berger
We present interferometric diameter measurements of 21 K- and M- dwarfs made with the CHARA Array. This sample is enhanced by literature radii measurements to form a data set of 33 K-M dwarfs with diameters measured to better than 5%. For all 33 stars, we compute absolute luminosities, linear radii, and effective temperatures (Teff). We develop empirical relations for \simK0 to M4 main- sequence stars between the stellar Teff, radius, and luminosity to broad-band color indices and metallicity. These relations are valid for metallicities between [Fe/H] = -0.5 and +0.1 dex, and are accurate to \sim2%, \sim5%, and \sim4% for Teff, radius, and luminosity, respectively. Our results show that it is necessary to use metallicity dependent transformations to convert colors into stellar Teff's, radii, and luminosities. We find no sensitivity to metallicity on relations between global stellar properties, e.g., TEFF-radius and TEFF-luminosity. Robust examinations of single star TEFF's and radii compared to evolutionary model predictions on the luminosity-Teff and luminosity-radius planes reveals that models overestimate the Teff's of stars with Teff < 5000 K by \sim3%, and underestimate the radii of stars with radii < 0.7 R\odot by \sim5%. These conclusions additionally suggest that the models overestimate the effects that the stellar metallicity may have on the astrophysical properties of an object. By comparing the interferometrically measured radii for single stars to those of eclipsing binaries, we find that single and binary star radii are consistent. However, the literature Teff's for binary stars are systematically lower compared to Teff's of single stars by \sim 200 to 300 K. Lastly, we present a empirically determined HR diagram for a total of 74 nearby, main-sequence, A- to M-type stars, and define regions of habitability for the potential existence of sub-stellar mass companions in each system.
View original: http://arxiv.org/abs/1208.2431

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