Time, spatial, and spectral resolution of the Halpha line-formation region of Deneb and Rigel with the VEGA/CHARA interferometer

O. Chesneau$^1$,
L. Dessart$^2$
D. Mourard$^1$,
Ph. B'{e}rio$^1$,
Ch. Buil$^3$,
D. Bonneau$^1$,
M. Borges Fernandes$^1,9$,
J.M. Clausse$^1$,
O. Delaa$^1$,
A. Marcotto$^1$,
A. Meilland$^4$,
F. Millour$^4$,
N. Nardetto$^1$,
K. Perraut$^5$,
A. Roussel$^1$,
A. Spang$^1$,
P. Stee$^1$,
I. Tallon-Boscinst$^6$,
H. McAlisterinst$^7,8$, T. ten~Brummelaar$^8$, J. Sturmann$^8$, L. Sturmann$^8$, N. Turner$^8$, C. Farrington$^8$ and P.J. Goldfinger$^8$

UMR 6525 H. Fizeau, Univ. Nice Sophia Antipolis, CNRS, Observatoire de la C^{o}te d'Azur, Av. Copernic, F-06130 Grasse, France
Laboratoire d'Astrophysique de Marseille, Universit'e de Provence,
CNRS, 38 rue Fr'ed'eric Joliot-Curie, F-13388 Marseille Cedex 13,
Castanet Tolosan Observatory, 6 place Clemence Isaure, 31320 Castanet Tolosan, France
Max-Planck Institut f"ur Radioastronomie, Auf dem H¨ugel 69, 53121, Bonn, Germany
Laboratoire d'Astrophysique de Grenoble (LAOG), Universit'e Joseph-Fourier, UMR 5571 CNRS, BP 53, 38041 Grenoble Cedex 09, France
Univ. Lyon 1, Observatoire de Lyon, 9 avenue Charles Andr'e, Saint-Genis
Laval, F-69230, France
Georgia State University, P.O. Box 3969, Atlanta GA 30302-3969, USA
CHARA Array, Mount Wilson Observatory, 91023 Mount Wilson CA, USA
Observat'orio Nacional, Rua General Jos'e Cristino, 77, 20921-400, S~ao Cristov~ao, Rio de Janeiro, Brazil

BA-type supergiants are amongst the most optically-bright stars. They are observable in extragalactic environments, hence potential accurate distance indicators. Emission activity in the Halpha line of the BA supergiants Rigel (B8Ia) and Deneb (A2Ia) is indicative of presence of localized time-dependent mass ejections. Here, we employ optical interferometry to study the Halpha line-formation region in these stellar environments. High spatial- (0.001 arcsec) and spectral- (R=30 000) resolution observations of Halpha were obtained with the visible recombiner VEGA installed on the CHARA interferometer, using the S1S2 array-baseline (34m). Six independent observations were done on Deneb over the years 2008 and 2009, and two on 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. We observe a visibility decrease in Halpha for both Rigel and Deneb, suggesting that the line-formation region is extended (1.5-1.75 R*). We observe a significant visibility decrease for Deneb in the SiII6371 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 Halpha visibility. Based on the observed differential visibilities, we estimate that the mass-loss rate of Deneb has changed by less than 5%.

Reference: Astronomy and Astrophysics
Status: Manuscript has been accepted

Weblink: http://arxiv.org/abs/1007.2095


Email: Olivier.Chesneau@oca.eu