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Extragalactic stellar astronomy with the brightest stars in the universe

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.

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Extragalactic stellar astronomy with the brightest stars in the universe

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  1. Extragalactic stellar astronomywiththe brightest stars in the universe Rolf Kudritzki, Fabio Bresolin, Miguel Urbaneja

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

  3. A supergiants – objects in transition Brightest normal starsat visual light:-7 ≥ MV ≥ -10 mag tev ~ 103 yrs L, M ~ const. ideal to determine B8–A4 • chemical compos. • abundance grad. • SF history • extinction • extinction laws • distances of galaxies

  4. 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

  5. 70 blue supergiant spectra 117 cepheids pilot study W. Gieren, G. Pietrzynski, Araucaria Project: F. Bresolin, M. Urbaneja, RPK NGC 300 – Sculptor Group (2 Mpc) Kudritzki, Urbaneja, Bresolin, 2007, ApJ, in prep.

  6. NGC 300 @ 1.8 Mpc Example: early A supergiant Kudritzki, Bresolin & Urbaneja et al. 2007 A2 Ia Teff = 9500 K log g = 1.45 SED fit E(B-V) AV extinction law Teff HST/ACS + ground

  7. Balmer series fitting: log g

  8. 2 S 1 n 2 2 i P ( ) O C p x ¡ Â = j j i j 1 N = n i p x Metallicity & chemical composition

  9. χispectral window 4497-4607Å

  10. 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.

  11. NGC 3621: 7 Mpc HST/ACS Bresolin, Kudritzki, Mendez & Przybilla 2001 ~19 blue supergiant candidates (VLT/FORS) 4 analyzed 0.2 & 0.5 solar metallicity models A0 Ia star V = 20.5 MV = -9 Bresolin, Kudritzki, Mendez, Przybilla 2001, ApJ Letters 548, L159

  12. Blue supergiants as distance indicators

  13. Flux weighted Gravity – Luminosity Relationship (FGLR) Kudritzki, Bresolin, Przybilla, ApJ Letters, 582, L83 (2003) L,M ~ const. B1-A4 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

  14. 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

  15. Conclusions and 30m perspectives • 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

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