An international group of astronomers studied a population of subcarlic B-stars in the scattered cluster NGC 6791 and discovered an unusual type of pulsating space objects. The results of the study are published in the repository of preprints ARXIV.
Hot subcarlic stars B (SDB) are objects consisting of a helium nucleus and a very thin hydrogen shell. Their mass is about twice as smaller than the mass of the sun, the radius is 0.1-0.3 of the radius of the Sun, and the effective temperature reaches 20-40 thousand Kelvin. However, the so-called pulsising subcarlic stars B (SDBV) are the greatest interest for scientists, which change their brightness due to short-periodic changes in pressure (P-mods) and long-period gravitational modes (G-modams).
Researchers conducted a search for SDBV in scattered cluster NGC 6791 age eight billion years. It is about 13,300 light years from the ground in the constellation Lyra, and its mass is comparable to a mass of four thousand suns.
Three SDBVs were identified in NGC 6791: KIC 2569576 (B3), KIC 2438324 (B4) and KIC 2437937 (B5). The measured efficient temperatures B3, B4 and B5 amounted to 24,250, 24,786 and 23,844 Kelvin, respectively. Scientists also found that B4 is a double system containing the SDBV star and its main sequence companion, with an orbital period of about 9.5 hours. B3 and B5 can also be double because astronomers have found signs of changing their radial speeds.