Period Analysis, Photometry, and Astrophysical Models of the Eclipsing Binary TW Crucis

TW Crucis is a W-type W UMa contact eclipsing binary that has not been studied in detail since discovery in 1926. During 5 seasons from 2011 to 2015, photometric CCD observations were obtained mostly in the V passband, but also some in B and I passbands. The period was found to be 0.3881444 ± 0.0000006 day, which is not substantially different from the original period of 0.3881358 day. There were slight variations in the period from cycle to cycle and year to year, which are most likely due to asymmetry in the light curves caused by star spots. A preliminary model of the light curves indicates the mass ratio may be about 0.67, inclination 70.8°, and fillout factor 0.11. As no spectra are available, the range in B-V and V-I color indices of 0.8-0.87 and 0.87-0.92, respectively, were used to estimate the effective temperatures for the modelling, based on the spectral types of K0-K2. The spectral type may be earlier, if the color indices are affected by interstellar reddening. Star spots, which changed over short period cycles and were required to obtain good fits of the models to the light curves, indicate the stars are magnetically active.