Solving wolf’s uvbyRI light curves for the star BM Ori

Abstract

We solve the uvbyRI light curves obtained by Wolf (1994) with a CCD photometer. Wolf did not solve the light curves, while particular interest in them stems from the fact that a secondary minimum, which other observers failed to detect, is clearly seen in the byRI light curves. This enables us to consider a new eclipse model in which we hypothesize that the secondary component at primary minimum completely obscures the primary, smaller B star, but, at the same time, the light from a third star is observed. Based on this hypothesis, we computed the brightness of each of the three stars for the six bands by analyzing the depths of the primary and secondary minima. Satisfactory agreement between theoretical and observed light curves was achieved by assuming the following parameters for the stars: effective temperature T1=17000 K, radius R1 = 2.5 R⊙, spectral type Sp1 = B3—B4 for the primary; T2=5700 K, R2 = 8.4 R⊙, Sp2 = G0—G2 for the secondary; and T3=29000 K, R3 = 1.0 R⊙, Sp3=B0 for the third star. In the Hertzsprung-Russell diagram, the first star lies on the zero-age main sequence, the second is on the way from the birthline to the main sequence in the region of giants, and the third falls within the region of hot subdwarfs.