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Time, spatial, and spectral resolution of the Halpha line-formation region of Deneb and Rigel with the VEGA/CHARA interferometer | | Olivier Chesneau
; Luc Dessart
; D. Mourard
; Ph. Berio
; Ch. Buil
; D. Bonneau
; M. Borges Fernandes
; J.M. Clausse
; O. Delaa
; A. Marcotto
; A. Meilland
; F. Millour
; N. Nardetto
; K. Perraut
; A. Roussel
; A. Spang
; Ph. Stee
; I. Tallon-Bosc
; Harold A. Mcalister
; T.A. Ten Brummelaar
; J. Sturmann
; L. Sturmann
; N. Turner
; C. Farrington
; P.J. Goldfinger
; | | Date: |
13 Jul 2010 | | Abstract: | 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%. | | Source: | arXiv, 1007.2095 | | Services: | Forum | Review | PDF | Favorites | |
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