Establishing the nature of companion candidates to X-ray-emitting late B-type stars
Abstract
The most favoured interpretation for the detection of X-ray emission from late B-type stars is that these stars have a yet undiscovered late-type companion (or an unbound nearby late-type star) that produces the X-rays. Several faint infrared objects at (sub)arcsecond separation from B-type stars have been uncovered in our earlier adaptive optics imaging observations, and some of them have been followed up with the high spatial resolution of the Chandra X-ray observatory, pinpointing the X-ray emitter. However, firm conclusions on their nature require a search for spectroscopic signatures of youth. Here we report on our recent ISAAC observations carried out in low-resolution spectroscopic mode. Equivalent widths have been used to obtain information on spectral types of the companions. All eight X-ray-emitting systems with late B-type primaries studied contain dwarf-like companions with spectral types later than A7. The only system in the sample where the companion turns out to be of early spectral type is not an X-ray source. These results are consistent with the assumption that the observed X-ray emission from late B-type stars is produced by an active pre-main-sequence companion star.
Based on observations obtained at the European Southern Observatory, Paranal, Chile [ESO programmes 074.D-0374(A) and 075.C-0522(A)]. E-mail: shubrig@eso.org- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- November 2007
- DOI:
- 10.1111/j.1365-2966.2007.12325.x
- arXiv:
- arXiv:0708.0860
- Bibcode:
- 2007MNRAS.381.1569H
- Keywords:
-
- binaries: spectroscopic;
- binaries: visual;
- stars: pre-main-sequence;
- X-rays: stars;
- Astrophysics
- E-Print:
- 6 pages, 2 figures, 3 tables, accepted for publication in MNRAS