The following parameters are determined for 63 Galactic supergiants in the solar neighbourhood: effective temperature Teff; surface gravity logg iron abundance logɛ(Fe) microturbulent parameter Vt; mass M/Msolar age t and distance d. A significant improvement in the accuracy of the determination of logg, and all parameters dependent on it, is obtained through application of van Leeuwen rereduction of the Hipparcos parallaxes. The typical error in the logg values is now +/-0.06dex for supergiants with distances d < 300 pc and +/-0.12dex for supergiants with d between 300 and 700 pc; the mean error in Teff for these stars is +/-120K. For supergiants with d > 700 pc, parallaxes are uncertain or unmeasurable, so typical errors in their logg values are 0.2-0.3dex.A new Teff scale for A5-G5 stars of luminosity classes Ib-II is presented. Spectral subtypes and luminosity classes of several stars are corrected. Combining the Teff and logg with evolutionary tracks, stellar masses and ages are determined; a majority of the sample has masses between 4 and 15Msolar and, hence, their progenitors were early to middle B-type main-sequence stars. Using FeII lines, which are insensitive to departures from local thermodynamic equilibrium, the microturbulent parameter Vt and the iron abundance logɛ(Fe) are determined from high-resolution spectra. The parameter Vt is correlated with gravity: Vt increases with decreasing logg. The mean iron abundance for the 48 supergiants with distances d < 700 pc is logɛ(Fe) = 7.48 +/- 0.09, a value close to the solar value of 7.45 +/- 0.05, and thus the local supergiants and the Sun have the same metallicity.
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- February 2010
- stars: abundances;
- stars: fundamental parameters;
- Astrophysics - Solar and Stellar Astrophysics
- 12 pages, 9 figures. Will be published at MNRAS