S Coronae Borealis was discovered to vary in brightness by German amateur astronomer Karl Ludwig Hencke in 1860.[11] It was classified as a long period variable star as other similar objects were discovered,[12] and later as a Mira variable.[2] The maximum range of variation is from magnitude 5.3 to 13.6 although individual maxima and minima can vary in brightness. The period of 360 days is fairly predictable.[13]
Properties
S Coronae Borealis is a cool red giant on the asymptotic giant branch (AGB). It pulsates, which causes its radius and temperature to change. One calculation found a temperature range of 2,350 K to 2,600 K,[8] although a more modern calculation gives a temperature of 2,864 K.[7] Similarly a calculation of the varying radius gives 537 to 664 R☉[8] although a modern calculation of the radius gives 308 R☉.[7] The bolometric luminosity varies much less than the visual magnitude and is estimated to be 5,623 L☉.[7] Its parallax has been measured by very-long-baseline interferometry (VLBI), yielding a result of 2.39 ± 0.17 millarcseconds, which converts to a distance of 1300 ± 100 light-years.[5]
The masses of AGB stars are poorly known and cannot be calculated from their physical properties, but they can be estimated using asteroseismology. The pulsations of S Coronae Borealis lead to a mass estimate of 1.34 times that of the Sun.[7]
^ abcdWallerstein, G. (1977). "Are long-period variables really pulsating". Journal of the Royal Astronomical Society of Canada. 71: 298. Bibcode:1977JRASC..71..298W.
^Campbell, Leon (1926). "Maxima and minima of two hundred and seventy-two long period variable stars during the years 1900 – 1920". Annals of Harvard College Observatory. 79: 87. Bibcode:1926AnHar..79...87C.
