| Abstract | New BV photometric data for about 170 blue and red stars in M 81 have been obtained from the plates of the 6 m and 2 m telescopes. The populated areas in the blue and red parts of the color-magnitude diagram begin at about 20.0 mag. A few bright blue stars appear at about 18.2 mag. Some of them are starlike objects which coincide with compact HII regions. If they belong to M 81 and using the distance modulus of M 81 m-M = 27.6 mag (Freedman & Madore 1988), their absolute magnitudes are estimated to be ~-9.6 mag. Five bright red stars occur at about 19.2 mag and two of them have (B-V) > 1.75 mag. The number of such stars in the narrow interval of 18.9-19.4 mag in M 81 and its periphery (studied in the previous papers of the authors) grows to 14. If some of them belong to M 81, their absolute magnitudes are estimated to be ~-8.6 mag. Such bright red supergiant candidates are not known in the Local Group of galaxies, but apparently they also exist in M 101. The estimated absolute magnitudes of the brightest blue and red supergiant candidates in M 81 support the recent relations between absolute magnitude of the parent galaxy and absolute magnitude of its brightest stars, as given by Sandage (1986) and Humphreys & Aaronson (1987). The magnitudes and colors of the selected blue and red stars do not give any evidence of significant foreground extinction toward M 81. The reddening effect in the comparison between the eastern and western parts of M 81 is visible, but poorly pronounced because of the mixing of the stars in front and behind the M 81 plane. However, the red stars, selected in the eastern part are about twice as abundant as in the western one. The colors of the blue stars in the eastern part are redder by about 0.5 mag as compared to the western part. |
