Chandra Spectroscopy of the Hot Star Beta Cru and the Discovery of a Pre-Main Sequence Companion
Abstract
Using a 75 ks Chandra grating observation, we have studied x-ray emission from the B0.5 III star beta Cru one of the four bright stars in the Southern Cross and a newly discovered companion. The companion is separated from beta Cru by 4" and it has about 3 times fewer x-ray counts. The flux contrast must be much greater in the optical, though, or the companion would have been discovered earlier. The system is a member of the Sco-Cen association, and is estimated to be 8 to 11 million years old; old enough for the B star primary to have evolved off the main sequence, but young enough that a coeval, late-type companion would still be descending to the main sequence. We marginally resolved individual line profiles of the primary in the grating spectra. The lines show slight broadening, suggesting an origin in a slow stellar wind rather than a corona. The secondary has a harder spectral energy distribution (temperatures > 20 million K) than the primary (< 4 million K), making it a probable pre-main-sequence star. The secondary is also more variable than the primary, consistent with the x-ray flaring seen in pre-main-sequence stars.
We acknowledge grants GO2-3030A and AR5-6003X to Swarthmore College from the Chandra X-ray Center at the Smithsonian Astrophysical Observatory, and also support from Swarthmore College via a Eugene M. Lang Summer Research Fellowship.- Publication:
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American Astronomical Society Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AAS...20915803K