Astronomy & Astrophysics

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Issue		A&A Volume 426, Number 1, October IV 2004
Page(s)		297 - 307
Section		Stellar atmospheres
DOI		10.1051/0004-6361:20035930

A&A 426, 297-307 (2004)
DOI: 10.1051/0004-6361:20035930

The angular sizes of dwarf stars and subgiants

Surface brightness relations calibrated by interferometry

P. Kervella^{1, 2}, F. Thévenin³, E. Di Folco⁴ and D. Ségransan⁵

¹ LESIA, UMR 8109, Observatoire de Paris-Meudon, 5 place Jules Janssen, 92195 Meudon Cedex, France
e-mail: Pierre.Kervella@obspm.fr
² European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Vitacura, Santiago 19, Chile
³ Observatoire de la Côte d'Azur, BP 4229, 06304 Nice Cedex 4, France
⁴ European Southern Observatory, Karl-Schwarzschild-str. 2, 85748 Garching, Germany
⁵ Observatoire de Genève, 1290 Sauverny, Switzerland

(Received 22 December 2003 / Accepted 17 June 2004 )

Abstract
The availability of a number of new interferometric measurements of Main Sequence and subgiant stars makes it possible to calibrate the surface brightness relations of these stars using exclusively direct angular diameter measurements. These empirical laws make it possible to predict the limb darkened angular diameters $\theta_{\rm LD}$ of dwarfs and subgiants using their dereddened Johnson magnitudes, or their effective temperature. The smallest intrinsic dispersions of $\sigma \le 1\%$ in $\theta_{\rm LD}$ are obtained for the relations based on the K and L magnitudes, for instance $\log \theta_{\rm LD} = 0.0502\,(B-L) + 0.5133 - 0.2\,L$ or $\log \theta_{\rm LD} = 0.0755\,(V-K) + 0.5170 - 0.2\rm\,K$ . Our calibrations are valid between the spectral types A0 and M2 for dwarf stars (with a possible extension to later types when using the effective temperature), and between A0 and K0 for subgiants. Such relations are particularly useful for estimating the angular sizes of calibrators for long-baseline interferometry from readily available broadband photometry.

Key words: stars: fundamental parameters -- techniques: interferometric

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