extragalactic stellar astronomy with the brightest stars in the universe rolf kudritzki, fabio...
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Extragalactic stellar astronomy with
the brightest stars in the universe
Rolf Kudritzki, Fabio Bresolin, Miguel Urbaneja
Extragalactic stellar astronomy
Properties of stellar populationsEvolution of galaxiesChemical abundance and abundance pattern gradientsInterstellar extinctionDistances
Quantitative stellar spectroscopy of individual stars
in galaxies beyond the Local Group
TM
T
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A supergiants – objects in transition
B8–A4
Brightest normal stars at visual light: -7 ≥ MV ≥ -10 mag
tev ~ 103 yrs L, M ~ const.
ideal to determine• chemical compos.• abundance grad.• SF history• extinction• extinction laws• distances
of galaxies
TM
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Spectroscopic studies beyond LG – present work
• selection of targets from wide field CMDs
• HST ACS imaging
• multi-object spectroscopy Δλ ~ 4-5 A with FORS @ VLT LRIS @ Keck
Teff ~ 4%, Δ log g ~ 0.05, metallicity ~ 0.1 dex use Balmer jump for Teff
• galaxies out to 7 Mpc
TM
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pilot study W. Gieren, G. Pietrzynski, Araucaria Project: F. Bresolin, M. Urbaneja, RPK
NGC 300NGC 300 – Sculptor Group (2 Mpc)
117 cepheids
70 blue supergiant spectra
Kudritzki, Urbaneja, Bresolin, 2007, ApJ, in prep.
TM
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Example: early A supergiant
A2 Ia
Teff = 9500 K
log g = 1.45
HST/ACS + ground
Kudritzki, Bresolin & Urbaneja et al. 2007
SED fit E(B-V) AV
extinction law Teff
NGC 300 @ 1.8 Mpc
TM
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Stellar metallicity gradient in NGC300
■ B0 – B3 supergiants
● B8 – A4 supergiants
--- [Z] = -0.03 – 0.44•ρ/ρ0
= -0.03 – 0.07•d/kpc
ρ0 = 9.75 arcmin ≈ 5.7kpc
[Z] = log(Z/Z_sun)
Kudritzki, Urbaneja, Bresolin, Przybilla, Gieren, Pietrzynski, 2007, in prep.
AA
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Bresolin, Kudritzki, Mendez, Przybilla 2001, ApJ Letters 548, L159
0.2 & 0.5 solar metallicity models
A0 Ia star
V = 20.5 MV = -9
NGC 3621NGC 3621: 7 Mpc HST/ACS
Bresolin, Kudritzki, Mendez & Przybilla 2001
~19 blue supergiant candidates (VLT/FORS)
4 analyzed
AA
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Flux weighted Gravity – Luminosity Relationship (FGLR)
Kudritzki, Bresolin, Przybilla, ApJ Letters, 582, L83 (2003)
M ~ g×R2 ~ L×(g/T4) = const.
const.
with L ~ Mx ~ Lx(g/T4)x, x ~ 3 L1-x ~ (g/T4)x
or with Mbol ~ -2.5log L
Mbol = a log(g/T4) + b FGLR
a =2.5 x/(1-x) ~ 3.75
B1-A4
L,M ~ const.
TM
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FGLR Local Group, NGC300 & NGC3621 Kudritzki, Bresolin & Przybilla, 2003,ApJL, 582, L83
Kudritzki, Urbaneja, Bresolin et al., ApJ, 2007, in prep.
Mbol = 3.75 log(g/T4eff,4) – 13.73
= 0.24