Time, spatial, and spectral resolution of the Hα line-formation region of Deneb and Rigel with the VEGA/CHARA interferometer *
O. Chesneau1, L. Dessart2, D. Mourard1, Ph. Bério1, Ch. Buil3, D. Bonneau1, M. Borges Fernandes1,4, J. M. Clausse1, O. Delaa1, A. Marcotto1, A. Meilland5, F. Millour5, N. Nardetto1, K. Perraut6, A. Roussel1, A. Spang1, P. Stee1, I. Tallon-Bosc7, H. McAlister8,9, T. ten Brummelaar9, J. Sturmann9, L. Sturmann9, N. Turner9, C. Farrington9 and P. J. Goldfinger9
UMR 6525 H. Fizeau, Univ. Nice Sophia Antipolis, CNRS, Observatoire de la
Côte d'Azur, Av. Copernic, 06130 Grasse, France e-mail: Olivier.Chesneau@oca.eu
2 Laboratoire d'Astrophysique de Marseille, Université de Provence, CNRS, 38 rue Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France
3 Castanet Tolosan Observatory, 6 place Clemence Isaure, 31320 Castanet Tolosan, France
4 Observatório Nacional, Rua General José Cristino 77, 20921-400 São Cristovão, Rio de Janeiro, Brazil
5 Max-Planck Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
6 Laboratoire d'Astrophysique de Grenoble (LAOG), Université Joseph-Fourier, UMR 5571 CNRS, BP 53, 38041 Grenoble Cedex 09, France
7 Univ. Lyon 1, Observatoire de Lyon, 9 avenue Charles André, 69230 Saint-Genis Laval, France
8 Georgia State University, PO Box 3969, Atlanta GA 30302-3969, USA
9 CHARA Array, Mount Wilson Observatory, 91023 Mount Wilson CA, USA
Accepted: 10 June 2010
Context. BA-type supergiants are amongst the most optically-bright stars. They are observable in extragalactic environments, hence potential accurate distance indicators.
Aims. An extensive record of emission activity in the Hα line of the BA supergiants β Orionis (Rigel, B8Ia) and α Cygni (Deneb, A2Ia) is indicative of localized time-dependent mass ejections. However, little is known about the spatial distribution of these apparent structures. Here, we employ optical interferometry to study the Hα line-formation region in these stellar environments.
Methods. High spatial- (~0.001) and spectral- (R = 30 000) resolution observations of Hα were obtained with the visible recombiner VEGA installed on the CHARA interferometer, using the S1S2 array-baseline (34 m). Six independent observations were done on Deneb during the years 2008 and 2009, and two of Rigel in 2009. We analyze this dataset with the 1D non-LTE radiative-transfer code cmfgen, and assess the impact of the wind on the visible and near-IR interferometric signatures, using both Balmer-line and continuum photons.
Results. We observe a visibility decrease in Hα for both Rigel and Deneb, suggesting that the line-formation region is extended (~1.5–1.75 ). We observe a significant visibility decrease for Deneb in the Siii 6371 Å line. We witness time variations in the differential phase for Deneb, implying an inhomogeneous and unsteady circumstellar environment, while no such variability is seen in differential visibilities. Radiative-transfer modeling of Deneb, with allowance for stellar-wind mass loss, accounts fairly well for the observed decrease in the Hα visibility. Based on the observed differential visibilities, we estimate that the mass-loss rate of Deneb has changed by less than 5%.
Key words: techniques: interferometric / stars: early-type / stars: mass-loss / stars: individual: HD 34085 / stars: individual: HD 197345 / circumstellar matter
© ESO, 2010