Physics
Scientific paper
Jun 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994soph..152..314s&link_type=abstract
Solar Physics (ISSN 0038-0938), vol. 152, no. 1, p. 314
Physics
Brightness, Chromosphere, Doppler Effect, Photosphere, Starspots, Stellar Luminosity, Stellar Radiation, Calcium, H Alpha Line, Imagery, K Lines, Magnetic Field Configurations, Photometry, Temperature
Scientific paper
Observations of rotational modulation of continuum brightness and photospheric and chromospheric spectral-line profiles of late-type stars indicate the presence of very inhomogeneous surface temperature distributuions. We present three stellar examples (VY Ari, HR 7275, HU Vir) where time-series photometry is used to trace the evolution of spotted regions. Simultaneous spectroscopy and Doppler imaging for one of the three stars (HU Virgo) makes it possible to compute the temperature distribution of the photosphere and the relative intensity distribution of parts of the chromosphere (from Ca II K and H alpha profiles). The combination of time-series spot modeling and Doppler imaging enabled us to determine the sign and amount of differential surface rotation on HU Vir. We found a big, cool polar spot and a differential (surface) rotation law where higher-latitude regions rotate faster than lower-latitude regions (opposite to what we see on the Sun). Currently, this ensemble of techniques -- is only applicable to stars overactive by approximately a factor of 100 as compared to the active Sun, e.g. the evolved components in RS CVn-type binaries and some rapidly-rotating, single, pre-main sequence stars or giant stars. Stellar rotation is a fundamental parameter for (magnetic) activity. Starspots, or any other surface inhomogeneities, allow one to derive very precise stellar rotation rates and, if coupled with seismological observations of solar-type stars, could provide information on the internal angular momentum distribution in overactive late-type stars.
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