Tiit Nugis together with Henny Lamers (The Netherlands) derive a formula of the mass loss rate for the brightest and most massive stars, the so-called Wolf-Rayet stars.

The stars lose a part of their mass during their evolution. The mass loss as a continuous departure of particles from the surface of a star is called the stellar wind. It has been ascertained that the more massive and brighter is the star the bigger is the mass loss rate. The most massive stars have been discovered in 1867 by the astronomers of the Paris observatory - Wolf and Rayet. These stars are very hot - up to 50 000 K and the rate of their mass loss can be as high as 10-5 solar masses in a year. The Wolf-Rayet stars may also explode as supernovas.

Using the observational data of the 64 Wolf-Rayet stars in our Galaxy T. Nugis derived a formula of the mass loss rate for these stars. The mass loss rate depends on the luminosity of the star and on its chemical composition. According to Nugis' formula the mass loss rate was lower than obtained by other authors. This result, very important for describing the stellar evolution, shows that thanks to their lower mass loss rate the Wolf-Rayet stars are so massive at the end of their evolution that they can turn into black holes.

Wolf-Rayet stars (http://jumk.de/astronomie/about-stars/wolf-rayet-stars.shtml)