* Astronomy

Members Login
Username 
 
Password 
    Remember Me  
Home -> Astronomy News -> Stars -> Gamma Cassiopeiae
Post Info TOPIC: Gamma Cassiopeiae
Blobrana


L

Posts: 131433
Date:
RE: Gamma Cassiopeiae
Permalink  
 

Title: High-Energy Properties of the Enigmatic Be Star gamma Cassiopeiae
Author: C. R. Shrader, K. Hamaguchi, S. J. Sturner, L.M. Oskinova, T. Almeyda, R.Petre

We present the results of a broad-band X-ray study of the enigmatic Be star Gamma Cassiopeiae (herein gamma Cas) based on observations made with both the Suzaku and INTEGRAL observatories. gamma Cas has long been recognized as the prototypical example of a small subclass of Be stars with moderately strong X-ray emission dominated by a hot thermal component in the 0.5-12 keV energy range Lx ~ 10^32 - 10^33 erg s^-1. This places them at the high end of the known luminosity distribution for stellar emission, but several orders of magnitude below typical accretion powered Be X-ray binaries. The INTEGRAL observations spanned an 8 year baseline and represent the deepest measurement to date at energies above ~50 keV. We find that the INTEGRAL data are consistent within statistics to a constant intensity source above 20 keV, with emission extending up to ~100 keV and that searches for all of the previously reported periodicities of the system at lower energies led to null results. We further find that our combined Suzaku and INTEGRAL spectrum, which we suggest is the most accurate broad-band X-ray measurement of gamma Cas to date, is fitted extremely well with a thermal plasma emission model with a single absorption component. We found no compelling need for an additional non-thermal high-energy component. We discuss these results in the context of a currently favoured models for gamma Cas and its analogs.

Read more (2756kb, PDF)



__________________
Blobrana


L

Posts: 131433
Date:
Permalink  
 

Title: Rotational and Cyclical Variability in gamma Cassiopeiae. II. Fifteen Seasons
Authors: Gregory W. Henry, Myron A. Smith

The B0.5IVe star gam Cas is of great interest because it is the prototype of a small group of classical Be stars having hard X-ray emission of unknown origin. We discuss results from ongoing B and V observations of the gam Cas star-disk system acquired with an APT during the observing seasons 1997-2011. In an earlier study, Smith, Henry, & Vishniac showed that light variations in gam Cas are dominated by a series of comparatively prominent cycles with amplitudes of 0.02-0.03 mag and lengths of 2-3 months, superimposed on a 1.21-day periodic signal some five times smaller, which they attributed to rotation. The cycle lengths clustered around 70 days. Changes in both cycle length and amplitude were observed from year to year. These authors also found the V-band cycles to be 30-40% larger than the B-band cycles. In the present study we find continued evidence for these variability patterns and for the bimodal distribution of the B/V amplitude ratios in the long cycles. During the 2010 observing season, gam Cas underwent a mass loss event (outburst), as evidenced by the brightening and reddening seen in our new photometry. This episode coincided with a waning of the amplitude in the ongoing cycle. The Be outburst ended the following year, and the light-curve amplitude returned to pre-outburst levels. This behaviour reinforces the interpretation that cycles arise from a global disk instability. Remarkably, we also find that both the amplitude and the asymmetry of the rotational waveform changed over the years. We review arguments for this modulation arising from transits of a surface magnetic disturbance. Finally, to a limit of 5 mmag, we find no evidence for any photometric variation corresponding to the gam Cas binary period, 203.55 days, or to the first few harmonics.

Read more (136kb, PDF)



__________________
Page 1 of 1  sorted by
 
Quick Reply

Please log in to post quick replies.
Home -> Astronomy News -> Stars -> Gamma Cassiopeiae


Create your own FREE Forum
Report Abuse 		Powered by ActiveBoard