EDP Sciences
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Volume 442, Number 2, November I 2005
Page(s) 567 - 578
Section Stellar structure and evolution
DOI http://dx.doi.org/10.1051/0004-6361:20042476

A&A 442, 567-578 (2005)
DOI: 10.1051/0004-6361:20042476

Gravitational-darkening of Altair from interferometry

A. Domiciano de Souza1, P. Kervella2, S. Jankov3, 4, F. Vakili3, N. Ohishi5, T. E. Nordgren6 and L. Abe5

1  Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
    e-mail: adomicia@mpifr-bonn.mpg.de
2  LESIA, UMR 8109, Observatoire de Paris-Meudon, 5 place Jules Janssen, 92195 Meudon Cedex, France
3  Lab. Univ. d'Astrophysique de Nice (LUAN), UMR 6525, UNSA, Parc Valrose, 06108 Nice Cedex 02, France
4  Astronomical Observatory Belgrade, MNTRS 1940, Volgina 7, 11050 Beograd, Serbia and Montenegro
5  National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
6  Department of Physics, University of Redlands, 1200 East Colton Avenue, Redlands, CA 92373, USA

(Received 3 December 2004 / Accepted 13 June 2005)

Interferometric observations have revealed that the rapid rotator Altair is a flattened star with a non-centrally symmetric intensity distribution. In this work we perform for the first time a physically consistent analysis of all interferometric data available so far, corresponding to three different interferometers operating in several spectral bands. These observations include new data (squared visibilities in the H and K bands from VLTI-VINCI) as well as previously published data (squared visibilities in the K band from PTI and squared visibilities, triple amplitudes, and closure phases in the visible between 520 nm and 850 nm from NPOI). To analyze these data we perform a $\chi^2$ minimization using an interferometry-oriented model for fast rotators, which includes Roche approximation, limb-darkening, and von Zeipel-like gravity-darkening. Thanks to the rich interferometric data set available and to this physical model, the main uniqueness problems were avoided. As a result, we show that the observations can only be explained if Altair has a gravity-darkening compatible with the expected value for hot stars, i.e., the von Zeipel effect ( $T_\mathrm{eff}\propto

Key words: techniques: high angular resolution -- techniques: interferometric -- methods: data analysis -- stars: rotation -- stars: individual: Altair

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