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 will begin a series of monthly talks, normally held the third Wednesday of each month at 9:00 am Eastern Daylight Time (GMT-4), by zoom.  The next talk is scheduled for Wednesday, August 18, 2021.

Speaker: Dr. Robert Klement

Title: Interferometric View on Classical Be Stars - Revealing Close Binarity

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


Both optical/IR and radio interferometry have been instrumental in revealing the nature of classical Be stars. For example, the angular resolution of the edge-on disk of psi Per achieved by the Very Large Array at centimeter wavelengths was the first direct confirmation of a flattened envelope. With optical interferometry, Be stars and their disks are routinely resolved and those with larger angular extent can be studied in great detail or even imaged in a model-independent way. Today, the still enigmatic classical Be stars remain among favorite targets of state-of-the-art interferometric facilities like VLTI and CHARA.

Near-critical rotation, which is an essential property of Be stars, could have been acquired by means of mass and angular momentum transfer in a close binary. The originally more massive component in this case loses a large fraction of its mass and becomes an evolved remnant stripped of its outer envelope. The present-day Be star, on the other hand, is rejuvenated and spun up, which leads to a possible subsequent formation of the characteristic mass-loss disk. The observational test for this scenario is that Be stars should not have main-sequence dwarf companions, and if the binary system remained bound after a possible supernova explosion of the evolved component, we should be able to observe a population of Be binaries with evolved companions, or possibly Be stars that are merger products. Detecting faint evolved companions to Be stars poses many difficulties, but luckily the question can also be addressed with interferometry, which is currently capable of directly detecting companions down to an angular separation of ~0.5 milliarcsec and up to a contrast ratio of ~6 magnitudes in the near-IR. To address the question of whether we can detect faint evolved companions around nearby Be stars, I have recently started a CHARA/MIRC-X interferometric survey of Be stars, and I will present some promising initial results. Recently, we also looked into the possible importance of hierarchical triple systems with a Be star, of which only about a dozen examples are currently known. I will present our full orbital solution of the triple system nu Gem - with only the second dynamical mass measurement of a classical Be star - and its possible implications.




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