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Starspot photometry with robotic telescopes. UBV(RI)_C and by light curves of 47 active stars in 1996/97
We present continuous multicolor photometry for 47 stars from October1996 through June 1997. Altogether, 7073 V(RI)_c, UBV, and by datapoints, each the average of three individual readings, were acquiredwith three automatic photoelectric telescopes (APTs) at FairbornObservatory in southern Arizona. Most of our targets arechromospherically active single and binary stars of spectral type G to Kbut there are also four pre-main-sequence objects and three pulsatingstars in our sample. The light variability is generally due torotational modulation of an asymmetrically spotted stellar surface andtherefore precise rotational periods and their seasonal variations aredetermined from Fourier analysis. We also report on photometricvariations of gamma CrB (A0V) with a period of 0.44534 days. All dataare available in numerical form. All data are available from CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Doppler imaging of stellar surface structure. VIII. The effectively single and rapidly-rotating G8-giant HD 51066 = CM Camelopardalis
We present first Doppler images of HD 51066 from observations in 1994,1995, 1996 and 1997, and find evidence for a vanishing polar spot inaccordance with the system's long-term brightness increase. Severalsmall spots with Delta T~500 K appear also at low latitudes. Ourcross-correlation maps indicate a latitude-dependent phase-shift patternbetween annual maps. New and continuous BVRI photometry from 1996 to1998 is presented and suggest a photometric period of 16.053+/-0.004days, that we interpret to be the stellar rotation period. Additionaloptical spectroscopy and the Hipparcos data are used to obtain absolutestellar parameters for HD 51066. A comparison with evolutionary tracksand the assumption of angular-momentum and magnetic-flux conservationsuggest that the main-sequence progenitor was a very rapidly-rotating Bpstar with a several kiloGauß\ magnetic field. We also examine theHα line profiles in this star and find some evidence that itsequivalent width is modulated with the stellar rotation period in phasewith the photospheric starspots. Our radial velocities indicate that HD51066 is likely a long-period (~10 yrs) spectroscopic binary and apreliminary orbit is presented. We emphasize that HD 51066 is aninteresting target for studies of evolutionary angular-momentum lossbecause it is effectively single, significantly evolved but stillrapidly rotating.
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