Digital Scholarship @ Tennessee State University

Title

The relationship between γ Cassiopeiae’s X-ray emission and its circumstellar environment II. Geometry and kinematics of the disk from MIRC and VEGA instruments on the CHARA Array

Authors

Philippe Stee, Laboratoire LagrangeFollow
O. Delaa, Laboratoire Lagrange
John D. Monnier, University of MichiganFollow
Anthony Meilland, Laboratoire Lagrange
Karine Perraut, Institut de Planétologie et d’Astrophysique de Grenoble
Denis Mourard, Laboratoire LagrangeFollow
Xiao Che, University of MichiganFollow
Gail H. Schaefer, Georgia State UniversityFollow
Ettore Pedretti, University of St. AndrewsFollow
Myron A. Smith, Catholic University of AmericaFollow
Raimundo Lopes de Oliveira, Universidade Federal de SergipeFollow
Christian Motch, Université de StrasbourgFollow
Gregory W. Henry, Tennessee State UniversityFollow
Noel D. Richardson, Georgia State UniversityFollow
Karen S. Bjorkman, University of ToledoFollow
R. BückeFollow
E. PollmannFollow
Juan Zorec, Institut d’Astrophysique de Paris
Douglas R. Gies, Georgia State UniversityFollow
Theo A. ten Brummelaar, Georgia State UniversityFollow
Harold A. McAlister, Georgia State UniversityFollow
Nils H. Turner, Georgia State UniversityFollow
Judit Sturmann, Georgia State UniversityFollow
Laszlo Sturmann, Georgia State UniversityFollow
Stephen T. Ridgway, National Optical Astronomy ObservatoryFollow

Document Type

Article

Publication Date

9-10-2012

Abstract

Context.γ Cas is thought to be the prototype of classical Be stars and is the most studied object among this group. However, as for all Be stars, the origin and the physics of its circumstellar disk responsible for the observed near IR-excess, emission lines, and peculiar X-ray emission is still being debated.

Aims. We constrain the geometry and kinematics of its circumstellar disk from the highest spatial resolution ever achieved on this star. This investigation is a part of a large multi-technique observing campaign to obtain the most complete picture of γ Cas which emphasizes the relation of the circumstellar environment to the star’s X-ray flux.

Methods. We present new observations in the near infrared (MIRC) and in the visible (VEGA) obtained with the CHARA interferometer. The VEGA instrument allows us to not only obtain a global disk geometry but also spectrally dispersed visibility modulus and phases within the Hα emission line, which enables us to study the kinematics within γ Cas’s disk.

Results. We obtain a disk extension in the nearby Hα continuum of 1.72 stellar diameter and 1.86 stellar diameter in the H band at 1.65 μm assuming a Gaussian disk model but also compatible with an elliptical ring model with a minor internal diameter of 1.38 stellar diameter in H. For the first time we demonstrate that the rotation mapped by the emission in the Hα line within the disk of γ Cas and up to 10 R_⋆ is Keplerian.

Conclusions. These observations have pushed the size of the disk to greater proportions. γ Cas was also confirmed to be a nearly critical rotator. The disk imaging gives neither indication of a 1-arm spiral feature nor evidence of a secondary star reinforcing the interpretation that the secondary is certainly a low-mass and low-luminosity star or a degenerate companion.

Recommended Citation

The relationship between γ Cassiopeiae’s X-ray emission and its circumstellar environment - II. Geometry and kinematics of the disk from MIRC and VEGA instruments on the CHARA Array Ph. Stee, O. Delaa, J. D. Monnier, A. Meilland, K. Perraut, D. Mourard, X. Che, G. H. Schaefer, E. Pedretti, M. A. Smith, R. Lopes de Oliveira, C. Motch, G. W. Henry, N. D. Richardson, K. S. Bjorkman, R. Bücke, E. Pollmann, J. Zorec, D. R. Gies, T. ten Brummelaar, H. A. McAlister, N. H. Turner, J. Sturmann, L. Sturmann and S. T. Ridgway A&A, 545 (2012) A59 DOI: https://doi.org/10.1051/0004-6361/201219234