Doppler imaging of stellar surface structure. III. The X-ray source HD 116544 = IN Virginis.

Abstract

We present the first Doppler image of the EXOSAT X-ray source EXO 1321.8-0203, recently identified to be a chromospherically active star exhibiting periodic light variations and consequently named INVirginis. Our high-resolution spectra show INVirginis to be a single-lined spectroscopic binary with an orbital period of 8.2 days, very strong CaII emission, and an inverse P-Cygni type Hα line profile. A detailed spectrum synthesis yields a photospheric temperature of 4600+/-70 K and logg=3.5-4.0 and slight overabundance of the heavy elements but otherwise solar abundances. We redetermine the photometric period from a new set of photometry obtained with a robotic photoelectric telescope in the years 1994 and 1995 and conclude that IN Virginis is more likely a K2-3 subgiant instead of a K5 dwarf or K4 subgiant as previously published. The Doppler images from March 1994 show a cool polar spot that is dominated by a large appendage reaching a latitude of +40°. Its average temperature difference, photosphere minus polar spot, is 1000K. Additionally, three equatorial spots are clearly recovered but have ΔT=~400K. Possibly, we also detected a warm equatorial feature with ΔT=~-150K. We emphasize that Doppler imaging of IN Virginis is very challenging because of both the small vsin i of the star (24.0km/s) and its relatively cool photosphere causing many weak absorption-line blends. Still, maps from the different lines appear encouragingly similar.