Variable Stars

A number of naked eye stars vary perceptibly because of a variety of causes. The most spectacular variables, which may brighten to hundreds of thousands of times the Sun's luminosity (in the case of novae) to billions of times brighter (in the case of supernovae), but are rare, we save for later. Here, we describe stars that vary because of geometry (eclipsing double stars, or rotating spotted stars), pulsations (causing more or less periodic variations due to changing temperature and size), eruptions (where material is ejected causing dimming or brightening), or some combination of these events causing irregular light variation. Table 5.9 lists the brightest of these variables that vary more than 0.2 magnitude (roughly, 20% light variation; see (5.2) below). An exception is Polaris, included because of its prominent place in the sky even though its variation is only ~15%. For completeness, other bright or short-period variable stars, with amplitudes too low to be included in Table 5.9, are listed below in alphabetic order of constellation name; the amplitude in visual magnitude and period in days (if known) are given in parentheses:

b Aur (0m09, 4d); b CMa (0m07, 0?25); a CMa (0m06); p Car = PP Car (0m10); q Car = V337 Car (0m06); b Cas (0m05, P = 0d10); S Cas (0m08, 759d); b Cen (0m07); S Cen (0m14); b Cep (0m11, 0d2); a CrB (m11, 17?4); g Cru A (0m07); b Cru (0m08, 0?7:); S Cru (0m06, 015); a Lib (0m16); a Lup (0m03, 0d26); a Mus (0m07,0d1); 6 Oph (0m04, 0m14); g Peg (0m07, 0d15); g Phe (0m10); p Pup (0m10, 0?14); h Sgr A (0m04); l Sco (0m06, 0?21); k Sco (0m03, 0d2); a Sco A (0m12, 0?25); Z Tau (0m13); e UMa (0m03, 5d1); u UMa (0m18, 0d13); l Vel (0m08); a Vir (0m07, multiple: 3?1, 4?5, 7?5).

The name designations follow variable star usage when no naked-eye designation is used. Variable star names are determined by order of discovery within the constellation and, like the Bayer (Greek), Flamsteed (numbers), and Lacaille (Roman letters) designations, are followed by the Latin genitive name of the constellation. They start with the

Table 5.9. Bright, large-amplitude periodic variable stars.

Table 5.9. Bright, large-amplitude periodic variable stars.

Variable star



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