2010/07/13 by Olivier Chesneau, O. Chesneau, Luc Dessart +31 · 26 citations
Physics and Astronomy · #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Star Formation Studies #Balmer series #Emission spectrum #Interferometry #Line (geometry) #Optics #Photosphere #Physics #Radiative transfer #Spectral line #Stars #Stellar, planetary, and galactic studies #astro-ph.SR
paper · pdf · doi:10.1051/0004-6361/201014509
published in Astronomy and Astrophysics 521, A5 (EDP Sciences)
arxiv created 2010/07/13 · openalex publication_date 2010/07/13 · arxiv updated 2015/05/19 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
<i>Context. <i/>BA-type supergiants are amongst the most optically-bright stars. They are observable in extragalactic environments, hence potential accurate distance indicators. <i>Aims. <i/>An extensive record of emission activity in the H<i>α<i/> line of the BA supergiants <i>β<i/> Orionis (Rigel, B8Ia) and <i>α<i/> 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 H<i>α<i/> line-formation region in these stellar environments. <i>Methods. <i/>High spatial- (~0.001) and spectral- (<i>R<i/> = 30 000) resolution observations of H<i>α<i/> 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. <i>Results. <i/>We observe a visibility decrease in H<i>α<i/> 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 H<i>α<i/> visibility. Based on the observed differential visibilities, we estimate that the mass-loss rate of Deneb has changed by less than 5%.