Russian astronomers have managed to identify three new aspirants to bright blue variables (LBV) in the galaxy NGC 4736 with an active star birth process. One of the objects has already received confirmation as LBV, but the nature of the others remains doubtful.
LBV are rare and unstable evolved massive stars in one of the last evolutionary phases. They show strong photometric and spectroscopic variability associated with transient eruptions. The study of bright blue variables and eruptions make it possible to better understand the evolutionary processes of massive stars.
The image includes NGC 4736 1 (a), NGC 4736 2 (b) and NGC 4736 3 (s). Circles mark central objects.
Now scientists are aware of the existence of only 40 LBV in the Milky Way and in the galaxies of the Local Group. In order to find more similar objects, Russian scientists searched for the presence of alpha-radiation from hydrogen in the blue point-like stellar objects of the galaxy NGC 4736. Also referred to as Messier 94 and was discovered in 1781. This is a spiral galaxy with a star formation in the constellation Hounds Dogs. Located at a distance of 1.3 million light years from us. Researchers examined archived images from the Hubble Space Telescope and found three new candidates for LBV. Then they analyzed the spectral and photometric variability using a variety of ground-based telescopes. The stars exhibit broad and strong hydrogen signatures of the He I line, many of the Fe II and Fe III lines.
Candidate NGC 4736_1 reaches -10.2 mA in absolute value, bolometric - up to -11.5 mA, and in bolometric luminosity - about 6.5. Also, the source shows a significant change in brightness. The characteristic confirms that we really have the LBV star.
For NGC 4736_2, the lower limits for absolute and bolometric values are -8.6 and -10.0 mA. Bolometric luminosity remained at a level of at least 5.9. But because of the slight variability in brightness, scientists doubt 100% involvement in LBV.
In NGC 4736_3, the absolute and bolometric values are -8.2 and -8.4 mA, and the bolometric luminosity is about 5.3. But researchers do not have enough photometric data to assess the change in the brightness of the source.
