Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 1977
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1977aj.....82..916b&link_type=abstract
Astronomical Journal, vol. 82, Nov. 1977, p. 916-924.
Astronomy and Astrophysics
Astronomy
74
Dwarf Stars, Late Stars, Stellar Spectrophotometry, Variable Stars, Colorimetry, Light Curve, M Stars, Starspots, Stellar Magnetic Fields
Scientific paper
Results are reported for a BVr photometric survey of 22 dK, dKe, dM, and dMe stars conducted to search for slow quasi-sinusoidal fluctuations in V (the BY Draconis syndrome). The (B-V) and (V-r) color indices are determined in an attempt to detect wavelength-dependent color changes produced by starspots and to infer starspot temperatures. It is found that nine of the stars exhibit variations in V of the order of 0.05 to 0.10 magnitude on a time scale of days or weeks, that at least three more display changes in mean light level over a period of years, that the stars generally tend to become redder at minimum light, and that some of the stars show no detectable color changes over their photometric cycle. The color data are taken to suggest a probable temperature difference of about 200 to 500 K between the stellar photospheres and starspots if the V variations are attributed to dark spots. It is concluded that the BY Draconis syndrome is clearly a very common occurrence among dMe stars.
Bopp Bernard William
Espenak Fred
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