27 research outputs found
Spectrally resolved interferometric observations of α Cephei and physical modeling of fast rotating stars
This is the final version of the article. Available from the publisher via the DOI in this record.Context. When a given observational quantity depends on several stellar physical parameters, it is generally very difficult to obtain observational constraints for each of them individually. Therefore, we studied under which conditions constraints for some individual parameters can be achieved for fast rotators, knowing that their geometry is modified by the rapid rotation which causes a non-uniform surface brightness distribution.
Aims. We aim to study the sensitivity of interferometric observables on the position angle of the rotation axis (PA) of a rapidly rotating star, and whether other physical parameters can influence the determination of PA, and also the influence of the surface differential rotation on the determination of the β exponent in the gravity darkening law that enters the interpretation of interferometric observations, using α Cep as a test star.
Methods. We used differential phases obtained from observations carried out in the Hα absorption line of α Cep with the VEGA/CHARA interferometer at high spectral resolution, R = 30 000 to study the kinematics in the atmosphere of the star.
Results. We studied the influence of the gravity darkening effect (GDE) on the determination of the PA of the rotation axis of α Cep and determined its value, PA = −157-10°+17°. We conclude that the GDE has a weak influence on the dispersed phases. We showed that the surface differential rotation can have a rather strong influence on the determination of the gravity darkening exponent. A new method of determining the inclination angle of the stellar rotational axis is suggested. We conclude that differential phases obtained with spectro-interferometry carried out on the Hα line can in principle lead to an estimate of the stellar inclination angle i. However, to determine both i and the differential rotation parameter α, lines free from the Stark effect and that have collision-dominated source functions are to be preferred.VEGA is a collaboration between CHARA and
OCA/LAOG/CRAL/LESIA that has been supported by the French programs
PNPS and ASHRA, by INSU and by the Région PACA. The project has
obviously benefitted from the strong support of the OCA and CHARA technical
teams. The CHARA Array is operated with support from the National Science
Foundation through grant AST-0908253, the W. M. Keck Foundation, the
NASA Exoplanet Science Institute, and from Georgia State University. This
work has made use of the BeSS database, operated at GEPI, Observatoire de
Meudon, France: http://basebe.obspm.fr, use of the Jean-Marie Mariotti
Center SearchCal service1 co-developed by FIZEAU and LAOG, and of
CDS Astronomical Databases SIMBAD and VIZIER2. We are grateful to an
anonymous referee for her/his valuable suggestions that helped to improve the
presentation of our results
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Spectrally resolved interferometric observations of α Cephei and physical modeling of fast rotating stars
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