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Time-series photometric spot modeling. IV. The multi-periodic K5Ve binary V833 Tauri
We analysed all the existing photometric observations of V833 Tau andfound long-term variability on time scales of ~70 years, 6.5 years and2.4 years. Using V and IC-band data from 1990-2000, weobtained starspot surface distributions from 20 suitable light curves.We found that the spot-area changes generally follow the long-term lightvariations. Spot temperatures are determined for each of the datasetsand an average value of 1230 K+/-270 K relative to the photosphere isfound. This value agrees with previous results from TiO modeling (1330K+/-110 K). Small scale spot temperature and area changes are recoveredduring 1997-1999, that we explain with a variable spot/faculae ratio. Apowerful flare in UBV(RI)C was observed in 1993 November. A10 000 K fit yielded a total emitted flare energy of more than1034 ergs from an area of about 1.3% of the stellar surface,60% of it in the V(RI)C bands. The flare characteristics arecompared to another, 100-times smaller flare observed earlier in 1983.
| The Henry Draper Extension Charts: A catalogue of accurate positions, proper motions, magnitudes and spectral types of 86933 stars
The Henry Draper Extension Charts (HDEC), published in the form offinding charts, provide spectral classification for some 87000 starsmostly between 10th and 11th magnitude. This data, being highlyvaluable, as yet was practically unusable for modern computer-basedastronomy. An earlier pilot project (Roeser et al. 1991) demonstrated apossibility to convert this into a star catalogue, using measurements ofcartesian coordinates of stars on the charts and positions of theAstrographic Catalogue (AC) for subsequent identification. We presenthere a final HDEC catalogue comprising accurate positions, propermotions, magnitudes and spectral classes for 86933 stars of the HenryDraper Extension Charts.
| Long-term behaviour of starspots. I - Polar starspots, rotational modulation and flare activity of V 833 Tauri
V 833 Tau is a late-type (dK5e) single lined spectroscopic binary wherethe primary is much brighter than the secondary. This paper presentsmulticolor photometry from 1983 and 1987-1990 to study the lightvariability of the star. In addition, the discovery of flare activity ofV 833 Tau is announced, and it is determined that 0.1 percent of theU-filter flux is due to flaring. Long-term changes on a time scale ofmonths with amplitudes of 0.1-0.2 mag in different filters were found.The system has a low inclination (about 20 deg), so this variability maybe interpreted as due to a changing polar spot area. Small amplitude(0.04 mag) periodic variations were discovered in 1983, presumablycaused by lower latitude spots rotating in and out of view. Superimposedon the longterm variability, such rotational modulation was alsodetected in 1989 and 1990, when the polar spot had a reduced size (i.e.during bright star intervals). The observed magnitude ranges fit thelong-term trend found by Hartmann et al. (1981). The rotational periodof the star is about 1.79 days.
| Observations of active chromosphere stars
It is pointed out that spectroscopic signatures of stellar chromosphericactivity are readily observable. The present study is concerned with newphotometric and spectroscopic observations of active-chromosphere RSCVn, BY Dra, and FK Com stars. Attention is given to the first resultsof a synoptic monitoring program of many active chromosphere stars.During the time from 1980 to 1982, photometric and spectroscopicobservations of 10 known or suspected active-chromosphere objects weremade. The results regarding the individual stars are discussed. Sevenstars observed with the International Ultraviolet Explorer (IUE) are allspectroscopic binaries.
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