Welcome to the homepage of the IAU Working Group on Active B Stars and its Be Star Newsletter.

The Working Group on Active B Stars (WGABS) was formed to promote and stimulate research and international collaboration in the field of active B stars. The WGABS is open to all researchers interested in the field.

For an introduction to the features of this site and more details about the WGABS, please see "About this site", for further support or ideas how to improve the site please contact the online editors at This email address is being protected from spambots. You need JavaScript enabled to view it. or drop them in our suggestion box.

Please Note:  We will be gradually updating and refurbishing the web page, beginning with this home page. 

Upcoming: IAU Working Group on Active B Stars Talks

The WG has series of talks, normally held the third Wednesday of each month at 9:00 am Eastern Time (EST, 14:00 UT), by zoom.  The next talk is scheduled for Wednesday, Februrary 16, 2022.

Seminar organizing committee: Carol Jones, Alex Carciofi, Dietrich Baade, Gregg Wade and Atsuo Okazaki. If have questions or suggestions for the s3eries, please contact the any of the committee members.

Speaker: Shigeyuki Karino (Faculty of Science and Engineering, Kyushu Sangyo University, Japan)

Title: Be-type high-mass X-ray binaries as progenitors of ULXs

Link: https://westernuniversity.zoom.us/j/98111632482


Since the detection of X-ray pulses from ultraluminous X-ray sources (ULXs), neutron stars have been considered as their central objects. Recent observations suggest that at least some ULXs are special cases of Be-HMXBs.

To investigate the conditions under which neutron stars achieve mass-accretion rates beyond the Eddington limit, we use the framework of mass-accretion models for BeHMXBs. With simple accretion models, we show that a Be-HMXB may become a ULX if the magnetic field of the neutron star and the density of the Be disc meet certain conditions. Moreover, we adopt binary evolution models and investigate the duration for which BeHMXBs can be observed as transient ULXs.
The results indicate that BeHMXBs could be ULXs for a typical duration of 1 Myr.
Comparisons with nearby observed BeHMXBs indicate that many binary systems have the potential to become ULXs during their evolution. Particularly, a BeHMXB system tends to become a ULX when the Be donor has a dense disc.
Because BeHMXBs are common objects and a significant number of them can become ULXs, we expect that a reasonable fraction of the ULXs could consist of evolved BeHMXBs.





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