Extragalactic stellar astronomy with the brightest stars in the universe Rolf Kudritzki, Fabio Bresolin, Miguel Urbaneja

Extragalactic stellar astronomy Properties of stellar populations Evolution of galaxies Chemical abundance and abundance pattern gradients Interstellar extinction Distances Quantitative stellar spectroscopy of individual stars in galaxies beyond the Local Group

TMT 2007 A supergiants – objects in transition B8–A4 Brightest normal stars at visual light: -7 ≥ M V ≥ -10 mag t ev ~ 10 3 yrs L, M ~ const. ideal to determine chemical compos. abundance grad. SF history extinction extinction laws distances of galaxies

TMT 2007 Spectroscopic studies beyond LG – present work selection of targets from wide field CMDs HST ACS imaging multi-object spectroscopy Δλ ~ 4-5 A with VLT Keck  T eff ~ 4%, Δ log g ~ 0.05, metallicity ~ 0.1 dex use Balmer jump for T eff galaxies out to 7 Mpc

TMT 2007 pilot study W. Gieren, G. Pietrzynski, Araucaria Project: F. Bresolin, M. Urbaneja, RPK NGC 300 NGC 300 – Sculptor Group (2 Mpc) 117 cepheids 70 blue supergiant spectra Kudritzki, Urbaneja, Bresolin, 2007, ApJ, in prep.

TMT 2007 Example: early A supergiant A2 Ia T eff = 9500 K log g = 1.45 HST/ACS + ground Kudritzki, Bresolin & Urbaneja et al SED fit E(B-V) A V extinction law T eff NGC 1.8 Mpc

TMT 2007 Balmer series fitting: log g

TMT 2007 Metallicity & chemical composition  2 i = S N 2 1 n p i x P n p i x j = 1 ( O j ¡ C j ) 2

TMT 2007 χ i spectral window Å

TMT 2007 Stellar metallicity gradient in NGC300 ■ B0 – B3 supergiants ● B8 – A4 supergiants --- [Z] = – 0.44ρ/ρ 0 = – 0.07d/kpc ρ 0 = 9.75 arcmin ≈ 5.7kpc [Z] = log(Z/Z_sun) Kudritzki, Urbaneja, Bresolin, Przybilla, Gieren, Pietrzynski, 2007, in prep.

AAS 2007 Bresolin, Kudritzki, Mendez, Przybilla 2001, ApJ Letters 548, L & 0.5 solar metallicity models A0 Ia star V = 20.5 M V = -9 NGC 3621 NGC 3621 : 7 Mpc HST/ACS Bresolin, Kudritzki, Mendez & Przybilla 2001 ~19 blue supergiant candidates (VLT/FORS) 4 analyzed

TMT 2007 Blue supergiants as distance indicators

AAS 2007 Flux weighted Gravity – Luminosity Relationship (FGLR) Kudritzki, Bresolin, Przybilla, ApJ Letters, 582, L83 (2003) M ~ g×R 2 ~ L×(g/T 4 ) = const. const. with L ~ M x ~ L x (g/T 4 ) x, x ~ 3  L 1-x ~ (g/T 4 ) x or with M bol ~ -2.5log L M bol = a log(g/T 4 ) + b FGLR a =2.5 x/(1-x) ~ 3.75 B1-A4 L,M ~ const.

TMT 2007 FGLR Local Group, NGC300 & NGC3621 Kudritzki, Bresolin & Przybilla, 2003,ApJL, 582, L83 Kudritzki, Urbaneja, Bresolin et al., ApJ, 2007, in prep. M bol = 3.75 log(g/T 4 eff,4 ) –  = 0.24

TMT 2007 WFOS  quantitative spectroscopy possible down to m V ~ 24.5 mag  with objects M V ≤ - 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