Longitude Distribution of Bulge M Giants: The Mass and Large-Scale Structure of the Spheroid
Abstract
Star counts obtained from a survey of late-type giants along b = -6 deg confirm the extreme rarity of carbon stars relative to M giants in the bulge and the large excess of M stars near the galactic meridian over that expected from the disk. The results constrain the axial ratio of the bulge to between 0.6 and 0.8, and suggest that the usual representation of the spheroid using an R exp 1/4 law with an effective radius of 1/3 solar radius is inadequate to explain the large stellar density in the bulge. A simple mass model of the Galaxy and an observationally determined M/L ratio are used to determine the external appearance of the galactic spheroid. The absolute magnitude of the spheroid is found to be -20.3 + or - 0.3. The luminosity and size of the galactic bulge indicate that the Milky Way may be closer in morphology to NGC 4565 than to M31.
- Publication:
-
The Astronomical Journal
- Pub Date:
- September 1989
- DOI:
- 10.1086/115182
- Bibcode:
- 1989AJ.....98..843B
- Keywords:
-
- Galactic Bulge;
- Giant Stars;
- M Stars;
- Milky Way Galaxy;
- Star Distribution;
- Carbon Stars;
- Mass Distribution;
- Spheroids;
- Spiral Galaxies;
- Astrophysics;
- GALAXIES: THE GALAXY;
- STARS: CARBON;
- STARS: RED GIANTS