BY Draconis variables are variable stars of late spectral types, usually K or M, and typically belong to the main sequence. The name comes from the archetype for this category of variable star system, BY Draconis. They exhibit variations in their luminosity due to rotation of the star coupled with starspots, and other chromospheric activity.[1] Resultant brightness fluctuations are generally less than 0.5 magnitudes. Light curves of BY Draconis variables are quasiperiodic. The period is close to the star's mean rotational rate. The light curve is irregular over the duration of the period and it changes slightly in shape from one period to the next. For the star BY Draconis the shape of the light curve over a period remained similar for a month.[1]
Some of these stars may exhibit flares, resulting in additional variations of the UV Ceti type.[3] Likewise, the spectra of BY Draconis variables (particularly in their H and K lines) are similar to RS CVn stars, which are another class of variable stars that have active chromospheres.[4]
References
^ abLopez-Morales, Mercedes; Morrell, N. I.; Butler, R. P.; Seager, S. (2006), "Limits to Transits of the Neptune-mass planet orbiting Gl 581", Publications of the Astronomical Society of the Pacific, 118 (849): 1506, arXiv:astro-ph/0609255, Bibcode:2006PASP..118.1506L, doi:10.1086/508904, BY Draconis variable. This type of variable is characterized by quasiperiodic photometric variations over time scales from less than a day to months, and amplitudes ranging from a few hundredths of a magnitude to 0.5 mags.
^Hoffmeister, Cuno; Richter, Gerold; Wenzel, Wolfgang (1984), Veränderliche Sterne, Springer
