Gravitational-darkening of Altair from interferometry

• Published in: Astronomy and astrophysics (Berlin) Vol. 442; no. 2; pp. 567 - 578
• Main Authors: A. Domiciano de Souza, Kervella, P., Jankov, S., Vakili, F., Ohishi, N., Nordgren, T. E., Abe, L.
• Format: Journal Article
• Language: English
• Published: Les Ulis EDP Sciences 01.11.2005
• Subjects: Astrophysics; methods: data analysis; Physics; Sciences of the Universe; stars: individual: Altair; stars: rotation; techniques: high angular resolution; techniques: interferometric; Data analysis; methods: data analysis; stars: individual: Altair; Interferometric observation; Rotator; Limb darkening; Intensity distribution; Physical model; Hot star; techniques: high angular resolution; Stellar rotation; Visibility; stars: rotation; techniques: interferometric; Gravity; Interferometry
• ISSN: 0004-6361; 1432-0746; 1432-0756
• DOI: 10.1051/0004-6361:20042476

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 ($T_\mathrm{eff}\propto g^{0.25}$).