Stellar Spots — Physical Implications

Abstract

Studies of certain late-type stars have revealed evidence for appreciable changes in their photospheric radiation. These stars are rotating much more rapidly than the Sun and/or are younger, and exhibit much enhanced examples of many kinds of solar activity, such as flares. The surface brightness distributions of these stzellar photospheres are nonuniform; dark areas are called “spots” in solar analogy. Areas of up to 30% may be covered by such spots, again indicating activity on a far greater scale than typical of the Sun.

Despite the lack of definitive bolometric observations, the detection of visual light variations on the order of 30% may be translated into total luminosity variations on the order of 10% with reasonable confidence. Spots may appear or decay over timescales of days, but longer-term trends exist, with timescales of decades. No direct evidence for spot cycles on the order of 10 years in length has been found, although some stars exhibit quasi-sinusoidal variations in mean light with time-scales ~ 50 years. Other cool stars of generally greater age and slower rotation exhibit evidence for decade periods in Ca II emission.