Publications of the MPIfR
Optical & Infrared
Interferometry Group
Domiciano de Souza, A., Kervella, P.,
Jankov, S., Vakili, F., Ohishi, N., Nordgren, T.E., Abe, L.
Gravitational-darkening of Altair from
interferometry
Astronomy & Astrophysics, Vol.442,
Issue
2, pg.567-578 (2005)
Abstract
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 χ2 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_eff∝ g0.25).
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