Starspot Activity Research Articles

An X-ray outburst from the RS CVn binary HR1099

RS CANUM VENATICORUM systems are the most plentiful binary stars known, having a space density of at least 10−6 systems pc−3 (ref. 1). They are detached subgiants of class KO+F to G with orbital periods between 1 day and 2 weeks (ref. 1). Many exhibit wave-like distortions in V which sometimes migrate to earlier binary phase with periods of 10–20 yr. This phenomenon has been interpreted by Hall2 as resulting from extensive star spot activity on the surface of the cooler companion. Steady radio emission has been detected from several RS CVn systems with occasional flares involving an order of magnitude change in flux3–5. More recently, HEAO-A has detected soft X-ray emission (0.2–2.8 keV) from three of these systems HR1099, UX Ari and RS CVn itself6,7, with source luminosities of ∼1030 erg s−1. We report here the detection by the Copernicus 2.5–7.5 keV detector of a 3-h outburst from HR1099, coincident with a radio flare.

Remarks on erratic period fluctuations of detached close binaries and the constancy of the orbital period of XY UMa

It is shown that the erratic changes of the orbital period, which are observed in some detached eclipsing binary systems, cannot be interpreted as real if their light curves show changing anomalies with asymmetric minimum profiles. In this case the photometrically determined times of the minima do not coincide with the ideal geometric ones, which are unobservable. This fact and the applied reduction methods for deriving the photometric times of minima cause systematic period errors of cumulative character. The discussion of six photoelectrically-determined minima obtained within the last 20 yr, and earlier photographic ones of the 0d.479 period eclipsing binary XY UMa yields a constant period. The long cyclic light curve variations due to starspot activity of the larger and hotter component of this system are reflected in corresponding period oscillations.

Is the Close Binary XY Ursae Majoris a Radio Star?

AbstractThe optical position of the short period eclipsing binary XY UMa, which shows large scale star spot activities, coincides within 2 minutes of arc with a radio source, listed in the 4C-, 4CP-, OK-catalogues, and the position obtained with the Effelsberg radio telescope. A fainter star, centered on the radio source position, is according its U-, B-, V-values a K main sequence star. The radio source is non-thermal, and has a spectral index α ~-0.85. If the radio source is identical with the binary, it would imply important consequences about the extragalactic nature of high latitude 4C-sources, the radio background and the high radio luminosity of the binary.

Starspot Activities as an Interpretation for the Light Curve Changes of the Close Binary Star XY UMa

The large light curve changes of XY UMa, observed in the last 20 yr, are interpreted as stellar starspot activity of the primary component of this binary.