Doppler imaging of stellar surface structure

Abstract

Abstract. We present eight Doppler images of UZ Librae from the years 1994, 1996, 1997, 1998 and 2000. These maps indicate a preferred temperature distribution from one year to the other and suggest preferred spot locations for at least the seven years of our observations. Two equatorial active regions appear facing towards and opposite the (unseen) companion star. A large and cool polar spot, with two or maybe three appendages extending down to a latitude of 40• -50• , is present and causes the long-term light variability of UZ Lib. The appendages appear at longitudes very similar to the two equatorial active regions and sometimes are possibly even attached to them. No coherent sign of differential rotation is found for the equatorial regions up to a latitude of approximately +50• , but the polar appendages may indicate a general acceleration of the polar regions. If interpreted as being due to differential rotation, if real at all, then UZ Lib clearly exhibits a non-solar flow pattern.

X-ray spectroscopy of UZ Librae

“…The strongest emission occurs at photometric minimum, in accord with the presence of cool starspots on the rapidly rotating K giant (v sin i ≈ 90 km s −1 ; Bopp & Stencel 1981). Modelling photometric data, Olah et al (2002) found a surprisingly well-defined phase coherence of the light curve minima for eight consecutive years. If interpreted as being due to spots, two main spotted regions centered at approximately 90 • and 270 • longitude were present at all times between 1993 and 2001.…”

“…Doppler images presented by Olah et al (2002) suggest prefered spot locations for at least seven years between 1993 and 2001 onto the surface of UZ Librae primary star. According to these maps, two equatorial active regions are facing towards and opposite the unseen companion star.…”

“…The review of coronal activity by pointed out that the Sun, if completely covered with active regions, would have an X-ray luminosity of 2 × 10 29 ergs s −1 . When scaled to the surface of UZ Librae primary (R ≈ 8.2 R ; Olah et al 2002), an X-ray luminosity of 7 × 10 30 erg s −1 is obtained assuming no X-ray contribution from the secondary star. This value is lower than the observed luminosity of UZ Librae (13 to 22×10 30 erg s −1 ) derived using Hipparcos parallaxes but comparable with the X-ray Table 6.…”

“…Wisniewski (1973) reported an IR excess and Bopp et al (1984) tentatively suggested a dM companion. More recently, Olah et al (2002) also favour a binary scenario where UZ Lib, a K0 giant, has a low mass secondary. The ultraviolet excess observed with IUE (Grewing et al 1989) would then be explained by its very active chromosphere.…”

The chromospherically active binary star EI Eridani: II. Long‐term Doppler imaging

“…per observing season): Korhonen et al (2007, FK Com, 24 maps from 1993, Vogt et al (1999, HR 1099 Visiting Astronomer, Kitt Peak National Observatory and National Solar Observatories, National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation. from 1981 to 1992), , II Peg, 9 maps from 1992and 2001, LQ Hya, 9 maps from 1993 to 1999), Oláh et al (2002b, UZ Lib, 8 maps from 1994, Marsden et al (2007, IM Peg, 31 maps from 2003, Donati et al (2003, AB Dor, LQ Hya, HR 1099 and others. All of them are active stars and most of them are close binaries with their rotation period usually spun up by tidal forces.…”