Observations of X-ray emission from the RS CVn binary HD 155555 and the detection of a nearby serendipitous source.

Abstract

Results of the EXOSAT observation of the RS CVn binary HD 155555 are reported. A new source EXO 171224-6653.9 has been discovered, lying only 40 arcsec away from HD 155555. Broad band X-ray photometry allows constraints to be placed on the plasma temperature (5×10⁵ - 1.3×10⁶K) and emission measure (4.5×10⁵¹ - 8×10⁵¹cm^-3) of HD 155555. When compared with earlier X-ray observations, the combined luminosity of the two sources can be seen to have decreased by an order of magnitude. Several explanations of this are discussed. A likely optical counterpart (m_j = 12.6) to EXO 171224-6653.9 has been found. The X-ray to optical luminosity ratio indicates that it is an accretion driven source, probably a cataclysmic variable or high mass X-ray binary.