Letter to the Editor

First radius measurements of very low mass stars with the VLTI^*

¹ Observatoire de Genève, 51 chemin des maillettes, 1290 Sauverny, Switzerland
² European Southern Observatory, Casilla 19001, Vitacura, Santiago 19, Chile
³ Observatoire de Grenoble, BP 53X, 38041 Grenoble Cedex, France
⁴ Canada-France-Hawaii Telescope Corporation, PO Box 1597, Kamuela, HI 96743, USA

Corresponding author: D. Ségransan, Damien.Segransan@obs.unige.ch

Received: 15 October 2002
Accepted: 21 November 2002

Abstract

We present 4 very low mass stars radii measured with the VLTI using the 2.2 μm VINCI test instrument. The observations were carried out during the commissioning of the 104-meter-baseline with two 8-meter-telescopes. We measure angular diameters of 0.7–1.5 mas with accuracies of 0.04–0.11 mas, and for spectral type ranging from M0V to M5.5V. We determine an empirical mass-radius relation for M dwarfs based on all available radius measurements. The observed relation agrees well with theoretical models at the present accuracy level, with possible discrepancy around 0.5–0.8  that needs to be confirmed. In the near future, dozens of M dwarfs radii will be measured with 0.1–1% accuracy, with the VLTI, thanks to the improvements expected from the near infrared instrument AMBER. This will bring strong observational constraints on both atmosphere and interior physics.