5 research outputs found
Why do some spotted stars become bluer as they become fainter?
Chromospherically active, spotted stars generally become redder as well as
fainter when large starspots rotate into view on the stellar disc. However, the
RS CVn system UX Ari (a triple-lined system), becomes bluer as it gets fainter.
One possible explanation is that hot, bright facular regions accompany the
cool, dark photospheric spots of the active component. The bluer flux of the
hotter, inactive component does not appear to be sufficient to explain the
observed behaviour. We have begun a search for additional chromospherically
active stars with a similar relation between colour and brightness, to
investigate whether these relations can be explained in the same way. Our
results for V711 Tau are presented here, and we conclude that the faculae
explanation holds also in this case.Comment: 3 pages, 1 figure, proceedings from the 13th Cambridge Workshop on
cool stars, stellar systems, and the Sun, Hamburg, Germany, July 2004,
ESA-SP, in pres
Unravelling the nature of HD 81032 - a new RS CVn Binary
BVR photometric and quasi-simultaneous optical spectroscopic observations of
the star HD 81032 have been carried out during the years 2000 - 2004. A
photometric period of d has been detected for this star. A
large group of spots with a migration period of years is
inferred from the first three years of the data. H and Ca II H and K
emissions from the star indicate high chromospheric activity. The available
photometry in the BVRIJHK bands is consistent with spectral type of K0 IV
previously found for this star. We have also examined the spectral energy
distribution of HD 81032 for the presence of an infrared colour excess using
the 2MASS JHK and IRAS photometry, but found no significant excess in any band
abovethe normal values expected for a star with this spectral type. We have
also analyzed the X-ray emission properties of this star using data obtained by
the ROSAT X-ray observatory during its All-Sky Survey phase. An X-ray flare of
about 12 hours duration was detected during the two days of X-ray coverage
obtained for this star. Its X-ray spectrum, while only containing 345 counts,
is inconsistent with a single-temperature component solar-abundance coronal
plasma model, but implies either the presence of two or more plasma components,
non-solar abundances, or a combination of both of these properties. All of the
above properties of HD 81032 suggest that it is a newly identified, evolved RS
CVn binary.Comment: 18 pages, 10 figures, 3 tables, Accepted for the publication in JAp
Why does the spotted
We present simplified calculations of UX Ar
Separation of high resolution spectra of the multiple star system
This paper presents a technique for separation of individual
components in composite stellar spectra. The
technique is based on a comparison of residual depths of the
component spectral lines to residual depths of the corresponding
spectral lines of a single star of the same spectral class. We apply
the technique to high resolution spectra of the RS CV
Aa 402, 1033--1041 (2003)
We present 14.3 years of previously unpublished photometric observations of UX Ari. The observations were obtained between 1987.9 and 2002.2 using the T3 0.4-metre Automatic Photoelectric Telescope at Fairborn Observatory and consist of 1228 B band and 1213 V band measurements. The comparison star was 62 Ari. We have analyzed the new data together with previously published photometric observations. The V magnitude shows variations with dominant periods of about 12 and 25 years, where the longest period seems to correspond to an activity cycle. The previously reported anticorrelation between the B V colour and V magnitude variations is confirmed