extragalactic stellar astronomy with the brightest stars in the universe
DESCRIPTION
Extragalactic stellar astronomy with the brightest stars in the universe. Rolf Kudritzki, Fabio Bresolin, Miguel Urbaneja. Quantitative stellar spectroscopy of individual stars in galaxies beyond the Local Group. - PowerPoint PPT PresentationTRANSCRIPT
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Extragalactic stellar astronomy with
the brightest stars in the universe
Rolf Kudritzki, Fabio Bresolin, Miguel Urbaneja
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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
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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
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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
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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.
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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
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Balmer series fitting: log g
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Metallicity & chemical composition
Â2i = S
N2 1
npi x
P npi xj =1 (Oj ¡ Cj )2
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χi spectral window 4497-4607Å
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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.
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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
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Blue supergiants as distance indicators
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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.
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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
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• WFOS quantitative spectroscopy possible down to mV ~ 24.5 mag
with objects MV ≤ - 8 mag
m – M ~ 32.5 mag ~ 30 Mpc possible
chemical evolution studies SF ISM, extinction, extinction laws distances 10 objects per galaxy Δ(m-M) ~ 0.1 mag
Conclusions and 30m perspectives