For this weeks light curve of the week we return to the auxiliary data set and investigate the object ASASSN-V J210537.76+461530.1. Other than an entry in the ASAS-SN database, and listings in a number of large catalogues, not much is known about the nature of the object. The Gaia distance is about 730pc, and the light curve shows that it is clearly an eclipsing binary.

From the light curve we can infer that the system consists of two stars which are slightly different in size, since the minima have slightly different depth. The difference is about 0.05mag, or 5% in flux. The shape of the light curve also shows that the stars must be very close to each other or even touching. The maxima are completely rounded and there is no clear indication of the start or the end of the eclipse events. Such systems come in a variety of names and are usually referred to as EW type binaries, contact binaries or W-UMa type stars, after the prototype object in this class.

The ASAS-SN team has measured a period for the system of 0.4355d. This is 10hrs 27min 7s. Assuming the last digit is the accuracy, then this would be +-8s. With our data we find that this period is slightly wrong and we can improve the period accuracy. We find the period to be 0.435493d. This corresponds to 10hrs 27min 6.595s +-0.086s. So, within the errors the values are the same, but our data allows the period to be determined to within a tenth of a second. This is of course due to the long duration (6 years) of our light curves and the very short period of the object.