The Composite Nature of the Peculiar Star HR 6560 (HD 159870)

Abstract

Ground based high dispersion photographic spectra and ultraviolet spectra obtained with the International Ultraviolet Explorer (IUE) satellite are described and employed to determine the nature of the peculiar star HR 6560 (HD 159870). Previously this object had been described as both a composite system and a strong Fm star. We inter-compare the UBVRI, Stromgren, and ultraviolet colors of HR 6560 with objects classified composite from the Bright Star Catalogue and normal dwarfs and giants. The colors of HR 6560 are not unusual for a composite and are consistent with a late A dwarf, combined with a late G or early K giant. The satellite ultraviolet clearly shows the presence of an A-component but its precise spectral type is difficult to assign. The IU and TD1 data suggest that the ultraviolet is dominated by light from an A5 V secondary and the visual from a G0 II primary. This does not agree well with the most plausible model that fits the visual photometry. We conclude that the peculiar nature of HR 6560's spectrum is most likely due to its composite nature. We cannot exclude that one or both components are chemically peculiar. (SECTION: Stars)