Deciphering the Mystery of Variable Stars

Emily Fryer

Advisor: Dr. Thomas Balonek

There are various times throughout the lifecycle of a star in which it may become variable. Towards the end of its life, instabilities of gravity and pressure in the core of a star (due to changes in internal nuclear processes) can cause a star’s outer layers to pulsate, and thereby change the star’s luminosity. A star may also change its luminosity through an outflow of material, or some other, more exotic process. The different classes of variable stars are characterized by their light-curves, the range of variability, the periodicity (or lack thereof) of the variability, along with the physical make-up of the star. The goal of this project is to look at some of the stars in the field of the quasar BL Lacertae and explore the characteristics of their variability in order to determine to which class of variable stars they belong. There are several different analyses we used to help in this process. We created light-curves (graphs of the star’s brightness as a function of time), did color analysis (to determine the spectral classification), and calculated the power spectrum (periodogram) to determine the most probable variability period. Our project focused on five of the brighter stars near BL Lacertae. Four of these stars are the comparison stars for the quasar so it is important to determine whether or not these stars are constant or variable in brightness. We concentrate our study on “Star 5,” which was previously known to be variable but of unknown type. This star appears to be a periodic variable of approximate period 2.79 days and amplitude 0.1 magnitudes. Star 5 also shows evidence of multiple or changing periods.