A survey of blue – objects in the galaxy M 33

Special Astrophysical Observatory of the Russian AS, Nizhnij Arkhyz 357147, Russia

Received: 18 June 1999
Accepted: 19 July 1999

Abstract

For the purposes of a search for SS 433 type objects, LBV stars and hypergiants in M 33, we have carried out a photometry of blue stars in Hα images of this galaxy. From 2332 listed OB stars, we have isolated 549 objects, which have Hα excess over stars of the same V magnitude. Among them 81 emission stars (s) have been selected. About 60% of isolated objects found to be extended in , among them 154 diffuse (d) and 180 bubble–type (b) nebulae. 117 objects are compact (c) and faint sources. These groups are different in colour indices, fluxes, surface brightness and sizes. The most probable size of the nebulae is  pc. There is evidence that their properties and location in the galaxy are defined by interstellar gas pressure and related to spiral arms. The d objects are H II regions with an embedded star. The b objects are probably envelopes around WR stars or SN remnants. Among s–type objects we isolated a group of 20 brightest stars, which in their average properties fit well to the parameters of blue hypergiants or LBV–type stars. The stars of intermediate brightness follow very well to blue Ia supergiants. The interstellar absorption derived from brightest stars is . We classify the faintest stars as blue Ib supergiants, their average absorption is . They are restricted in number by the limiting stellar magnitude in the original sample.