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(Reference retrieved automatically from Web of Science through information on FAPESP grant and its corresponding number as mentioned in the publication by the authors.)

The relationship between gamma Cassiopeiae's X-ray emission and its circumstellar environment

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Smith, M. A. [1] ; Lopes de Oliveira, R. [2, 3] ; Motch, C. [4] ; Henry, G. W. [5] ; Richardson, N. D. [6] ; Bjorkman, K. S. [7] ; Stee, Ph. [8] ; Mourard, D. [8] ; Monnier, J. D. [9] ; Che, X. [9] ; Buecke, R. ; Pollmann, E. ; Gies, D. R. [6] ; Schaefer, G. H. [6] ; ten Brummelaar, T. [6] ; McAlister, H. A. [6] ; Turner, N. H. [6] ; Sturmann, J. [6] ; Sturmann, L. [6] ; Ridgway, S. T. [10]
Total Authors: 20
[1] Catholic Univ Amer, Baltimore, MD 21218 - USA
[2] Univ Fed Sergipe, Dept Fis, BR-49100000 Sao Cristovao, SE - Brazil
[3] Univ Sao Paulo, Inst Fis Sao Carlos, BR-13560970 Sao Carlos, SP - Brazil
[4] Univ Strasbourg, CNRS, Astron Observ, F-67000 Strasbourg - France
[5] Tennessee State Univ, Ctr Excellence Informat Syst, Nashville, TN 37203 - USA
[6] Georgia State Univ, Ctr High Angular Resolut Astron, Dept Phys & Astron, Atlanta, GA 30202 - USA
[7] Univ Toledo, Ritter Astrophys Res Ctr, Dept Phys & Astron, Toledo, OH 43606 - USA
[8] UMR 7293 UNS CNRS OCA, Lab Lagrange, F-06304 Nice 4 - France
[9] Univ Michigan, Dept Astron, Ann Arbor, MI 48109 - USA
[10] Natl Opt Astron Observ, Tucson, AZ 85719 - USA
Total Affiliations: 10
Document type: Journal article
Source: Astronomy & Astrophysics; v. 540, APR 2012.
Web of Science Citations: 26

gamma Cas is the prototypical classical Be star and is recently best known for its variable hard X-ray emission. To elucidate the reasons for this emission, we mounted a multiwavelength campaign in 2010 centered around four XMM-Newton observations. The observational techniques included long baseline optical interferometry (LBOI) from two instruments at CHARA, photometry carried out by an automated photometric telescope and H alpha observations. Because gamma Cas is also known to be in a binary, we measured radial velocities from the H alpha line and redetermined its period as 203.55 +/- 0.20 days and its eccentricity as near zero. The LBOI observations suggest that the star's decretion disk was axisymmetric in 2010, has an system inclination angle near 45 degrees, and a larger radius than previously reported. In addition, the Be star began an ``outburst{''} at the beginning of our campaign, made visible by a brightening and reddening of the disk during our campaign and beyond. Our analyses of the new high resolution spectra disclosed many attributes also found from spectra obtained in 2001 (Chandra) and 2004 (XMM-Newton). As well as a dominant hot (approximate to 14 keV) thermal component, the familiar attributes included: (i) a fluorescent feature of Fe K even stronger than observed at previous times; (ii) strong lines of N VII and Ne XI lines indicative of overabundances; and (iii) a subsolar Fe abundance from K-shell lines but a solar abundance from L-shell ions. We also found that two absorption columns are required to fit the continuum. While the first one maintained its historical average of 1 x 10(21) cm(-2), the second was very large and doubled to 7.4 x 10(23) cm(-2) during our X-ray observations. Although we found no clear relation between this column density and orbital phase, it correlates well with the disk brightening and reddening both in the 2010 and earlier observations. Thus, the inference from this study is that much (perhaps all?) of the X-ray emission from this source originates behind matter ejected by gamma Cas into our line of sight. (AU)

FAPESP's process: 09/06295-7 - High energy astrophysics
Grantee:Raimundo Lopes de Oliveira Filho
Support type: Research Grants - Young Investigators Grants
FAPESP's process: 10/08341-3 - High energy astrophysics
Grantee:Raimundo Lopes de Oliveira Filho
Support type: Scholarships in Brazil - Young Researchers