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Establishing the nature of companion candidates to X‐ray‐emitting late B‐type stars
Ist Teil von
Monthly notices of the Royal Astronomical Society, 2007-11, Vol.381 (4), p.1569-1574
Ort / Verlag
Oxford, UK: Blackwell Publishing Ltd
Erscheinungsjahr
2007
Link zum Volltext
Quelle
Wiley Online Library
Beschreibungen/Notizen
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.