This is a nice example of a single-night's work on a very busy star, the SX Phoenicis variable BL Cam. BL Cam is a pulsating variable, and the light changes are caused by radial pulsations -- the surface of the star is expanding and contracting as well as changing in temperature, and both cause the brightness variations. The pulsations in SX Phe stars are almost identical to those in their cousins, the high amplitude delta Scuti stars, or HADS. The only real difference between the SX Phe stars and the HADS is that the former typically have low metal abundances typical of Population II stars, while the latter are Pop I.
Although these data were obtained in the past several months, BL Cam was the subject of a global campaign several years ago that included several amateur observers. Favaud et al detected variations in the time of maximum of BL Cam suggestive of binarity, or perhaps even multiple stars in the system. The authors of that paper recommended continued observations, and a number of AAVSO observers continue to obtain occasional times of maximum for this (and many other) short period pulsators.
Prepared By: Matthew Templeton