Project B

A cosmic dance: hunting the mysterious companion of a rapidly rotating classical Be star

Jens Kammerer & Julia Bodensteiner

(email advisors)

Massive stars are important cosmic engines, yet their evolution still remains poorly understood. One of the biggest gaps in our understanding concerns the Be phenomenon: about 20% of the galactic B-type stars are so-called classical Be stars, that is stars which exhibit strong emission in hydrogen spectral lines originating in a gaseous circumstellar disk. Be stars are generally observed to be rapidly rotating, potentially near to their critical break-up velocities. The origin of their rapid rotation, however, remains elusive. 

One possible origin for the rapid rotation of Be stars is angular momentum gain due to previous mass transfer in a binary system. If Be stars truly form through mass transfer, many of them should be in binary systems with an envelope-stripped companion or a compact object. Given the difficulties of detecting such systems directly in the stellar spectra, only a handful of Be binary systems are known. One potential additional candidate is omicron Puppis, a bright star in the Southern night sky. 

Omi Pup was proposed to have a stripped, low-mass companion based on indirect, multi-epoch spectroscopic observations. In this project, we will use a complementary data set, namely recently obtained interferometric observations from GRAVITY at the VLTI in Chile, combined with state-of-the-art modelling approaches. The superior resolution of the GRAVITY dataset will enable us to resolve and directly detect such a companion. We will confirm the presence of the putative stripped companion, investigate its properties, and constrain its nature. This will allow us to understand the evolutionary history of this particular system, and to shed light on the potential binary origin of Be stars in general. 

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