Astronomy and Astrophysics – Astronomy
Scientific paper
Jun 1987
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987mnras.226..813e&link_type=abstract
Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711), vol. 226, June 15, 1987, p. 813-827. NASA-supported research
Astronomy and Astrophysics
Astronomy
8
Binary Stars, Calcium, Emission Spectra, Giant Stars, Stellar Spectrophotometry, Ubv Spectra, F Stars, Iue, Late Stars, Radial Velocity, Stellar Cores, Stellar Luminosity, Stellar Orbits
Scientific paper
HD 158393 is a giant star of spectral type late G or early K which has moderately strong Ca II H and K emission cores. UBVRIJHK photometry and IUE spectra reveal a companion of type F0-F2, luminosity class IV or V. Radial velocity data yield an orbit with a period of 31 day. The K and F stars have nearly equal mass, with a minimum value of 1.7 solar masses if i of less than 72 deg is adopted, as required by the absence of eclipses. The strong Ca II emission indicates the enhanced chromospheric activity which is typical of giant stars in a binary system of this period, and the light is variable in a 31-day period, indicative of synchronous rotation as well as on a long time-scale. Analysis of the 31-day light period by fitting a spot model indicates the presence of two spots in 1975 and 1976; the major spot appears to have been present throughout the observing period (1973-1981). The potential confusion caused by the presence of the second spot for part of the observing period emphasizes the importance of fitting a model if the photometric period is to be understood in terms of the synchronous rotation. The two spots showed different periods and were at different latitudes, suggesting differential rotation of the giant star.
Balona Luis A.
Evans Tom Lloyd
Fekel Francis C.
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