UBV photometry of new flare stars in the Orion OB1 association

Abstract

As nonsteady stars have been detected in stellar aggregates, they have been investigated colorimetrically [1-8], which has not only conftrmed the conclusions of Haro and Herbig [9] that the ultraviolet excess of these stars is related to their H~ activity, but has also revealed new empirical relationships. The UBV photometry of different groups of nonsteady stars has shown an empirical relationship between the average distance of these stars from the main sequence on the two-color U-B, B-V diagram and the age of the stellar aggregate [10]. It turns out that the younger the system of investigated stars, the greater their average distance from the main sequence (along the U-B axis) on the U-B, B-V diagram and, vice versa, the older the system, the more its members are centrated toward the main sequence. The sensitivity of such a method of estimating the ages of young stellar systems is such that it may reveal an age difference between individual groups of stars that are even in the same aggregate. This is clearly confirmed by a comparison of the locations of stars with H~ emission and flare stars in Orion OB1 on the two-color U-B, B-V diagram (Figs. 2 from [6] and [7]). The age of stars with H~ emission in the Orion OB 1 association is estimated to be only about one third as much as the age of Orion flare stars, but the difference in their distributions on the U-B, B-V diagram is clearly seen: the concentration of flare stars toward the main sequence is considerably greater than that of stars with H~ emission. These and other conclusions were based on numerous and uniform data of UBV photometry of nonsteady stars, particularly of flare stars, discovered in various stellar aggregates. For flare stars in the Orion OB 1 association (in the vicinity of the Orion Nebula), discovered by Haro and Chavira [11] and by Rosino and Pigatto [12], the UBV photometry was carded out by Andrews [1, 2] and Gasparian [7]. But there have not yet been such uniform UBV data for the flare stars discovered by Chavira and Parsamian [13].