Strange Among the Strange: The B-emission Star <i>γ</i> Cassiopeiæ

Harmanec, P.

doi:10.1017/s0252921100001433

International Astronomical Union Colloquium

2002

DOI: 10.1017/s0252921100001433

|View full text |Cite

Strange Among the Strange: The B-emission Star γ Cassiopeiæ

P. Harmanec

Abstract: Abstractγ Cas (HD 5394) is an important representative of Be stars, hot B stars exhibiting Balmer and other emission lines in their spectra at certain epochs. Its emission spectrum was observed as early as in 1863 and has undergone spectacular changes since then. γ Cas is also extremely interesting because it qualifies for several phenomenologically defined groups: it is a light and colour variable, long-term radial-velocity variable, X-ray source, IRAS source, rapid line-profile variable, a single-line spectr… Show more

Help me understand this report

Search citation statements

Order By: Relevance

Paper Sections

Select...

Citation Types

Supporting

Mentioning

Contrasting

Year Published

2005

2022

Publication Types

Select...

Article5

Relationship

Self Cite2

Independent3

Authors

Journals

Cited by 5 publications

References 57 publications

(61 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

The X-ray emission of theγCassiopeiae stars

Smith

Oliveira

Motch

2016

Advances in Space Research

View full text Add to dashboard Cite

Long considered as the "odd man out" among X-ray emitting Be stars, γ 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 "γ Cas stars" defined from optical properties alone. The luminosity output of this class contributes significantly to the hard X-ray production in massive stars in the Galaxy. The γ Cas stars have light curves showing variability on a few broadly-defined timescales and spectra indicative of an optically thin plasma consisting of one or more hot thermal components. By now 9-13 Galactic ≈B0-1.5e main sequence stars are judged to be members or candidate members of the γ Cas class. Conservative criteria for this designation are for a ≈B0-1.5e III-V star to have an X-ray luminosity of 10 32 -10 33 ergs s −1 , a hot thermal spectrum containing the short wavelength Lyα Fe XXV and Fe XXVI lines and the fluorescence FeK feature all in emission. If thermality cannot be demonstrated, for example from either the presence of these Lyα lines or curvature of the hard continuum of the spectrum of an X-ray active Be star, we call them γ Cas candidates. We discuss the history Email addresses: masmith@noao.edu (Myron A. Smith), rlopes@ufs.br/ (R. Lopes de Oliveira), christian.motch@unistra.fr (C. Motch) Preprint submitted to Advances in Space ResearchJanuary 21, 2016 of the discovery of the complicated characteristics of the variability in the optical, UV, and X-ray domains, leading to suggestions for the physical cause of the production of hard X-rays. These include scenarios in which matter from the Be star accretes onto a degenerate secondary star and interactions between magnetic fields on the Be star and its decretion disk. The greatest aid to the choice of the causal mechanism is the temporal correlations of X-ray light curves and spectra with diagnostics in the optical and UV wavebands. We show why the magnetic star-disk interaction scenario is the most tenable explanation for the creation of hard X-rays on these stars.

show abstract

The X-ray emission of theγCassiopeiae stars

Smith

Oliveira

Motch

2016

Advances in Space Research

View full text Add to dashboard Cite

show abstract

HD 161306: a radiatively interacting Be binary?

Koubský

Kotková

Kraus

et al. 2014

A&A

Self Cite

View full text Add to dashboard Cite

The spectrum of the Be star HD 161306 is shown to vary periodically with a period of ∼100 days. The radial velocity of the He i 6678 Å emission peak varying in antiphase to the radial velocity of the Hα emission wings component suggests that the star is a binary similar to φ Per, 59 Cyg, or FY CMa, i.e. a radiatively interacting Be binary -a rare case among Be stars. This type of object is also called a φ Per-type binary or Be + sdO binaries. The range of radial-velocity variations of the strong emission peak in the helium line observed in HD 161306 is about 180 km s −1 , similar to what is observed for these systems. We therefore conclude that HD 161306 may represent another case of a Be star with a hot subdwarf companion.

show abstract

The X-ray Emission ofγCassiopeiae During the 2020–2021 disc eruption

Rauw

Nazé

Motch

et al. 2022

A&A

View full text Add to dashboard Cite

Context. γ Cas is known for its unusually hard and intense X-ray emission. This emission could trace accretion by a compact companion, wind interaction with a hot sub-dwarf companion, or magnetic interaction between the star and its Be decretion disc. Aims. These various scenarios should lead to diverse dependences of the hard X-ray emission on disc density. To test these scenarios, we collected X-ray observations of γ Cas during an episode of enhanced disc activity that took place around January 2021. Methods. We investigate the variations in the disc properties using time series of dedicated optical spectroscopy and existing broadband photometry. Equivalent widths and peak velocity separations are measured for a number of prominent emission lines. Epochdependent Doppler maps of the Hα, Hβ, and He  λ 5876 emission lines are built to characterise the emission regions in velocity space. We analyse four XMM-Newton observations obtained between January 2021 and January 2022 at key phases of the episode of enhanced disc activity. Archival XMM-Newton, Chandra, MAXI, and RXTE-ASM data are also used to study the long-term correlation between optical and X-ray emission. Results. Optical spectroscopy unveils a clear increase in the radial extent of the emission regions during the episode of enhanced disc activity, whilst no increase in the V-band flux is recorded. Our Doppler maps do not reveal any stable feature in the disc resulting from the putative action of the companion on the outer parts of the Be disc. Whilst the hard X-ray emission is found to display the usual level and type of variability, no specific increase in the hard emission is observed in relation to the enhanced disc activity. However, at two occasions, including at the maximum disc activity, the soft X-ray emission of γ Cas is strongly attenuated, suggesting more efficient obscuration by material from a large flaring Be disc. In addition, there is a strong correlation between the long-term variations in the X-ray flux and the optical variations in the V-band photometry. Conclusions. The observed behaviour of γ Cas suggests no direct link between the properties of the outer regions of the Be disc and the hard X-ray emission, but it favours a link between the level of X-ray emission and the properties of the inner part of the Be disc. These results thus disfavour an accretion or colliding wind scenario.

show abstract

scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.

Contact Info

customersupport@researchsolutions.com

10624 S. Eastern Ave., Ste. A-614

Henderson, NV 89052, USA

Blog Terms and Conditions API Terms Privacy Policy Contact Cookie Preferences Do Not Sell or Share My Personal Information

Made with 💙 for researchers

Part of the Research Solutions Family.

Strange Among the Strange: The B-emission Star γ Cassiopeiæ

Cited by 5 publications

References 57 publications

The X-ray emission of theγCassiopeiae stars

The X-ray emission of theγCassiopeiae stars

HD 161306: a radiatively interacting Be binary?

The X-ray Emission ofγCassiopeiae During the 2020–2021 disc eruption

Contact Info

Product

Resources

About