Related papers: Automated photometry of $\gamma$ Cassiopeiae:the l…
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…
We report results of a nine-year monitoring effort on the unusual classical Be with a robotic ground-based (APT) B,V-filtered telescope as well as simultaneous observations in 2004 November with this instrument and the RXTE (X-ray)…
Context. Be stars are physically complex systems that continue to challenge theory to understand their rapid rotation, complex variability and decretion disks. $\gamma$ Cassiopeiae ($\gamma$ Cas) is one such star but is even more curious…
A detailed analysis of more than 800 electronic high-resolution spectra of gamma Cas, which were obtained during a time interval of over 6000 days (16.84 yrs) at several observatories, documents the smooth variations in the density and/or…
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…
gamma Cas has long been famous for its unique hard X-ray characteristics. We report herein on a 53 ks Chandra HETGS observation of this target. An inspection of our spectrum shows that it is quite atypical for a massive star, with…
gamma Cassiopeiae (gCas) is a B0.5e star with peculiar X-ray emission properties and yet the prototype of its own small class. In this paper we examine the X-ray spectra for a 2004 XMM-Newton observation and a previously published 2001…
Gamma Cassiopeiae is an enigmatic Be star with unusually strong hard X-ray emission. The Suzaku observatory detected six rapid X-ray spectral hardening events called "softness dips" in a ~100 ksec duration observation in 2011. All the…
The recorded activity of gamma Cas (B0.5 IVe) in the ultraviolet is important to an understanding of the mechanism behind this prototypical Be star's high energy activity, especially its hard X-ray emissions. Our analysis focuses first on…
In photometry of $\gamma$ Cas (B0.5 IVe) from the SMEI and BRITE-Constellation satellites, indications of low-order non-radial pulsation have recently been found, which would establish an important commonality with the class of classical Be…
\gamma Cas is the prototypical classical Be star and is 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 4 XMM observations. The…
We report broad-band X-ray measurements of the Be star Gamma Cassiopeiae by the BeppoSAX X-ray astronomy satellite. The observations took place on 1998 July, 18-23. The 0.1-200 keV X-ray spectrum is reasonably well fit by an optically thin…
The enigmatic X-ray emission from the bright optical star, $\gamma$ Cassiopeia, is a long-standing problem. $\gamma$ Cas is known to be a binary system consisting of a Be-type star and a low-mass ($M\sim 1\,M_\odot$) companion of unknown…
Massive B and Be stars produce X-rays from shocks in high velocity winds with temperatures of a few million degrees and maximum X-ray luminosities of $\approx$ 10$^{31}$ erg/s. Surprisingly, a sub-group of early Be stars exhibits > 20 times…
The core-collapse supernova remnant (SNR) Cassiopeia A (Cas A) is one of the brightest galactic radio sources with an angular radius of $\sim$ 2.5 $\arcmin$. Although no extension of this source has been detected in the $\gamma$-ray band,…
Long considered as the "odd man out" among X-ray emitting Be stars, \gamma Cas (B0.5e IV) is now recognized as the prototype of a class of stars that emit hard thermal X-rays. Our classification differs from the historical use of the term…
For the B-type supergiant $\kappa$ Cassiopeiae (HD 2905) variabilities with periods between several hours and a few days have been observed both photometrically and spectroscopically. A recent study of this star by Sim\'on-D\'{\i}az et al.…
Cassiopeia A (Cas A) as the nearby young remnant of a core-collapse supernova is the best candidate for astrophysical studies in supernova explosion and its environment. We studied hard X-ray emissions from Cas A using the ten-year data of…
gamma Cas (B0.5e) is known to be a unique X-ray source because ot its moderate L_x, hard X-ray spectrum, and light curve punctuated by ubiquitous flares and slow undulations. Its X-ray peculiarities have led to a controversy concerning…
We present the revised and high quality CCD time series observations in 2017 and 2018 of the W UMa-type contact binary BH~Cas. The combination of our new determinations of minimum times and those collected from the literatures reveal a…