On the Causes of Brightness Variability of a Young Star BP Tau

Abstract

We have constructed and analyzed the secular light curve of BP Tau, a classical T Tau star. Wave-like variations in the average brightness level of the star with an amplitude of \(\Delta B\approx 0\overset{\textrm{m}}{.}2\) and a characteristic time of several decades were found. We present arguments in favor of the concept that three deep \((\Delta B\sim 1\overset{\textrm{m}}{.}5)\) dimming episodes lasting from one hour to several days are associated with the eclipse of a hot (accretion) spot by the dust infalling on the star along with gas. It is possible that such eclipses, albeit with a smaller amplitude, are the reason for the lack in BP Tau of a strictly expressed brightness variation periodicity related to axial rotation. We found that in the distance range of 0.1 to 200 AU, BP Tau has no companions with masses greater than \(0.2\;M_{\odot}\). Possible reasons of brightness and color index variability of the star on different time scales are discussed.