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Starspot patterns on the M dwarfs HK Aqr and RE 1816 +541
We present the first Doppler images of two M dwarfs in the solarneighbourhood. Late-type dwarfs are generally too faint to enablespectra with sufficient signal-to-noise (S/N) ratios for Doppler imagingto be obtained in short enough exposure times. Using the large number ofphotospheric absorption lines in each spectrum, we apply least-squaresdeconvolution to derive composite line profiles with S/N ratios of100-500. The surface images of HK Aqr reveal a moderately spottedsurface, with the majority of starspots appearing at low latitudes,whereas RE 1816 +541 exhibits spots at all latitudes. Neither star showssignificant evidence for the oft-observed polar spot. Despite the boostin S/N ratio achieved with the least-squares deconvolution technique,the images are not consistent enough to determine reliably the magnitudeof differential rotation. Nevertheless, the images are consistent enoughto place upper limits on the rate of surface shear.
| Starspots
The study of starspots is discussed. The history of starspot observationis summarized, and observational methods are described. Thepossibilities for amateur observations are briefly addressed. Thechromospheres of active stars are examined. Whether 'superstarspots' arecoronal holes or active regions is discussed.
| Infrared and visible photometry of the RS CVn-star II Peg
Infrared photometry in J, H, K, L, M bands carried out in differentyears from 1983 to 1986, and U, B, V, R, I quasi-simultaneous to 1984are presented. Although the amplitude of the minima decrease as thewavelength increase, the infrared light curves show a similar behaviorto that observed in visible. Since no variations in the averagemagnitudes are noted from 1983 to 1986, it is assumed that the activityof II Peg is not increasing. Also from the light curves a concentrationprocess of the spots seems to have taken place from 1984 to 1986. In theanalysis of the infrared colors an excess attributable to circumstellardust emission is found.
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