- Supergiant stars as tracers of chemical evolution and distances of galaxies
- Extragalactic distances
- Stellar spectroscopy
- Stellar atmospheres and radiative transfer
- Radiation driven winds of hot stars
Observed mass-metallicity relationship of galaxies from spectroscopic studies of blue supergiant stars.
The red square belongs to M81.
See Kudritzki, Urbaneja, Gazak et al., 2012, ApJ 747, 15.
The same relationship as above, but now overplotted with the average
relationships obtained by Kewley and Ellison (2008) obtained from strong
HII-region emssion lines. The 10 different overplotted relationships belong
to different strong-line calibrations. Obviously, the calibration uncertainty
of strong lines introduces enormous uncertainties for this method. These
uncertainties are poorly understood. Calibration (1) corresponds to
Tremonti et al. (2004) and (7), (8) represent two calibrations by
Pettini and Pagel (2004).
Our science goal is to use extensive blue supergiant spectroscopy to develop
an improved calibration of HII-region emission line strong line methods.
See Kudritzki, Urbaneja, Gazak et al., 2012, ApJ 747, 15.
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 681, 269.
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 681, 269.
Blue supergiant stars in the disk of the spiral galaxy M81 at 3.5 Mpc.
See Kudritzki, Urbaneja, Gazak et al., 2012, ApJ 747, 15.
M81 at 3.5 Mpc. Left: Selection of blue supergiant targets from the color-magnitude diagram.
Right: Location of selected targets within M81.
See Kudritzki, Urbaneja, Gazak et al., 2012, ApJ 747, 15.
Metallicity of blue supergiants in the disk of M81.
Metallicity determination of object C20 as an example.
See Kudritzki, Urbaneja, Gazak et al., 2012, ApJ 747, 15.
Metallicity of blue supergiants in the disk of M81 as a function of galactocentric distance.
We find slight super-solar metallicity in the center and a very shallow gradient.
See Kudritzki, Urbaneja, Gazak et al., 2012, ApJ 747, 15.
Metallicity of blue supergiants in the disk of M81 compared with
planetary nebulae (PNe data from Stanghellini et al. 2010.
The lower PN metallicity indicates strong chemical evolution of the disk over the last 5 Gyrs.
See Kudritzki, Urbaneja, Gazak et al., 2012, ApJ 747, 15.
The Hertzsprung-Russell diagram (top) and the (log g, log Teff)-diagram
of blue supergiant stars in M81.
See Kudritzki, Urbaneja, Gazak et al., 2012, ApJ 747, 15.
The distance to M81 from the observed FGLR compared to the
Kudritzki et al. (2008) calibration. A distance modulus of m-M = 27.7 pm 0.1 mag is obtained.
See Kudritzki, Urbaneja, Gazak et al., 2012, ApJ 747, 15.
