- Supergiant stars as tracers of young stellar populations in galaxies
- Planetary Nebulae as tracers of intermediate/old populations
- Extragalactic distances
- Science with the next generation of 30m-class ground-based optical/IR
telescopes
Wide field image of the Sculptor galaxy NGC 300 at 2 Mpc distance. We have
studied the stellar content in much detail and have spectroscopically
determined metallicity, metallicity gradient, extinction and distance from
the blue supergiants marked by blue squares or circles.
NLTE model atmosphere spectra for one of the A supergiants in NGC 300.
Different metallicities ranging from 1/20 solar to twice solar are
assumed.
NLTE model atmosphere spectrum with a metallicity a factor of three
smaller than solar compared with the observed spectrum of one of the A supergiant
in NGC 300.
Stellar metallicity gradient in NGC 300. Note that this is the first
determination of such a gradient based on the abundances of iron group
elements. See Kudritzki, Urbaneja, Bresolin et al., 2008, ApJ, in press
(astro-ph/0803.3654).
Flux-weighted gravity - luminosity relationship of blue supergiants in
galaxies in the Local Group and beyond. With gravities g and effectiv
temperatures T determined from the spectrum this relationship can be used
to determine precise extragalactic distances.
Note that spectroscopy of the supergiant stars provides an
independent determination of interstellar reddening and extinction. The method
is, thus, free from uncertainties introduced by inadequate estimates of
reddening.
Details in Kudritzki, Urbaneja, Bresolin et al., 2008, ApJ, in press,
(astro-ph/0803.3654).
The Local Group dwarf galaxy WLM at 1 Mpc distance.
Spectral analysis of an A supergiant in WLM. The metallicities found
for most blue supergiants are a factor of six below solar.
The FGLR of the blue supergiants in WLM. A distance modulus of 25.05 mag
is determined from the FGLR. (Urbaneja, Kudritzki, Bresolin et al., 2008).
The spiral galaxy NGC 3621 at a distance of 6.7 MPC. Blue supergiants
are indicated by circles. The object within the blue square is a Luminous
Blue Variable (LBV) with emission lines.
Quantitative spectral analysis of the LBV in NGC 3621. The NLTE model
atmosphere fit of the spectra allows to determine stellar effective
temperatures, gravities, chemical composition and stellar wind mass-loss
rates.
