Blue Supergiants as a Tool for Extragalactic Distances

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Extragalactic stellar astronomy

• Rolf Kudritzki, Fabio Bresolin, Miguel Urbaneja

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Munich solar eclipse, 1999

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FORS transport to P.
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VLT 2
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FORS at 2 telescopes
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Extragalactic stellar astronomy
Quantitative stellar spectroscopy of
individual stars
in galaxies beyond the Local Group
Properties of stellar populations Evolution of
galaxies Chemical abundance and abundance pattern
gradients Interstellar extinction Distances Dark
matter content
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stellar spectroscopy of massive stars in the
Local Group and beyond more motivation

• stellar evolution with mass loss calibrate
  stellar parameters, SEDs (ionizing properties)
• stellar winds momentumenergy to the ISM
• core-collapse supernova progenitors
• stellar instabilities at high luminosity
• spectral synthesis of starbursts

Local Group ideal laboratory metallicity changes
by more than one order of magnitude WLM ? M31
extend beyond Local Group with 8-10m telescopes
NGC 3621 by HST/ACS
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Blue supergiants

• Brightest normal stars at visual light
• -7.0 Mv -9.0 mag (B4 Ia to A4 Ia)

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Milky Way LMC SMC
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Blue supergiants

• Brightest normal stars at visual light
• -7.0 Mv -9.0 mag (B4 Ia to A4 Ia)
• Evolution simple L const., M const.

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Evolution of blue supergiants
Tracks by Maeder Meynet (with and without
rotational mixing)
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Blue supergiants

• brightest normal stars at visual light
• -7 MV -10 mag (B4 Ia to A4 Ia)
• evolution simple L const., M const.
• evolution fast tev 103 yrs
• progenitors 15 Msun M 40 Msun ? O-stars
• age 0.5 to 1.3 107 yrs
• ? many outside OB-associations, HII-regions
• crowding/multiplicity less important

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diagnostics of blue supergiants
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Determination of Teff and log g

• ionization equilibria and/or Balmer jump ? Teff
• A supergiants Mg I/II, N I/II, O I/II, S
  II/III
• ?Teff/Teff 1
• Balmer lines ? log g
• ?log g 0.05
• fit-diagrams in (log g, Teff)-plane

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S II/III
O I/II
Balmer lines
N I/II
Przybilla, Butler, Kudritzki, Becker 2006, AA
445, 1099
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Hd
h Leo
Przybilla, Butler, Kudritzki, Becker 2006, AA
445, 1099
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? Leo, H?
Przybilla, Butler, Kudritzki, Becker 2006, AA
445, 1099
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Ionization Equilibrium
Mg I
Mg I
h Leo
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Stellar Parameter Determination Teff
h Leo
Mg I
Mg I
Ionization Equilibrium
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Mg I
Przybilla, Butler, Kudritzki, Becker 2006, AA
445, 1099
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Stellar Parameter Determination Teff
h Leo
Mg II
He I
Ionization Equilibrium
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He I
Mg II
Przybilla, Butler, Kudritzki, Becker 2006, AA
445, 1099
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S II/III
O I/II
Balmer lines
N I/II
Przybilla, Butler, Kudritzki, Becker 2006, AA
445, 1099
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• Problem with ionization equilibrium
  diagnostics for very distant objects
• Classic spectroscopic Teff-indicator ionization
  equilibrium
• Mg I/II, Fe I/II, N I/II, O I/II, S II/III
• Requires sufficient resolution high S/N for
  weak lines
• Not possible for objects beyond Local Group
• Balmer discontinuity (jump) as an alternative
• Requires near-UV photometry / spectroscopy ( ?
  3640Å )
• Some dependence on luminosity and on (very weak)
  metallicity

Balmer jump vs I.E.
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hydrogen bound-free absorption
late B
opacity ??
bound-free absorption cross-section
? in Å
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bound-free absorption edges in early type star
SEDs
Hydrogen dominant continuous absorber in B, A F
stars (later stars H-) Energy distribution
strongly modulated at the edges
Balmer
Paschen
Brackett
Vega
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Spectral types and Balmer Jump
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Isocontours of D_B and W?(H?) in
(Teff,log
g)-plane
DB log(F?gt3645/F?lt3645)
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• Classic spectroscopic Teff-indicator ionization
  equilibrium
• Mg I/II, Fe I/II, N I/II, O I/II, S II/III
• Requires high resolution high S/N for weak
  lines
• Balmer discontinuity (jump) as an alternative
• Requires near-UV photometry / spectroscopy ( ?
  3640 Å )
• Some dependence on luminosity and on (very weak)
  metallicity

B8Ia Rigel ( ? Ori )
12500K
11500 K
12000K
Balmer jump vs I.E.
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Przybilla, Butler, Kudritzki, Becker 2006, AA
445, 1099
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Przybilla, Butler, Kudritzki, Becker 2006, AA
445, 1099
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A0Ia HD20041
A2Iae Deneb ( ? Cyg )
Balmer jump vs I.E.
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Determination of Teff with the integrated flux
method a test
Ben Granett, Rolf Kudritzki Miguel Urbaneja
2007, ApJ, in prep.
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Motivation
Detailed NLTE model atmosphere codes
? Teff from ionization
equlibria or
Balmer Jump Are the models
correct? Systematic errors?
? need independent method to check!!!
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Integrated flux method
Uses original definition of Teff integral over
observed SED Advantages Insensitive to details
of model atmosphere codes. Do not require high
resolution spectroscopy. Challenge Strongly
affected by interstellar extinction. The
goal Achieve 5 systematic accuracy robust to
extinction and compare with
spectroscopic Teff.
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Method
Neglect extinction for a moment... f? observed
flux F? flux at stellar surface By
definition, the effective temperature,
following Stefan-Boltzmann, is,
Angular size
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Method
?N2 2 (f?/F?)
Use model flux for F? at V-band FV
but FV(Teff) ? Iteration required
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Iteration
start with guess for Teff
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Solution by iteration
Angular size
Temperature
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Application data ingredients
The photometric data available are IUE
spectrum (1150-3350A) Optical-mid IR broadband
photometry (Johnson BVRIJKL, Geneva B B1 V V1
G, 2MASS JHK, Cousins VRI.) We have a sample
of nine A - supergiant stars.
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Data ingredients
IUE
photometry
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SED reconstruction
We extrapolate the full SED from power law fits
of the data. The Balmer jump is approached from
both sides.
power-law
exponential
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Interstellar extinction and reddening
E(B-V) ? slope of A? A? small in IR ? with
O/IR photometry and model SED ? ? and E(B-V)
Note A? depends also on RV
AV/E(B-V) usually RV 3.1
is adopted
Extinction (magnitudes)
E(B-V)
Log wavelength (A)
Cardelli et al (1989)
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Iteration procedure
RVAV/E(B-V)3.1
Set Teff
Interpolate model atm
Fit angular size E(B-V) with photometry
Deredden
Integrate
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Rigel, for example
Rigel
IUE
Optical photometry
O/IR is in Rayleigh-Jeans tail of SED ?
independent of Teff ? E(B-V) ?
J
L
K
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Results
Rv3.1 assumed
Not a nice result, however
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Interstellar extinction and reddening
RV 3.1 commonly used for A? , but dust
properties vary dramatically with
environment. HII regions ? 2 lt RV lt 5 Note
this is ignored in almost all extragalactic and
cosmology work!!!!
Extinction (magnitudes)
E(B-V)
Log wavelength (A)
Cardelli et al (1989)
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Interstellar extinction
Extinction (magnitudes)
RV
E(B-V)
Log wavelength (A)
Rv describes the amplitude and shape.
Cardelli et al (1989)
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Fitting extinction law and E(B-V)
We can use the optical and IR photometry to fit
the interstellar extinction law.
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Fitting extinction
6000A
E(B-V)0.5
Extinction (magnitudes)
fit Rv here
fit E(B-V) here
0.2
0.05
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Iteration procedure
Vary Rv for minimum scatter
Set Teff
Interpolate model atm
Fit angular size E(B-V) with photometry
Deredden
Integrate
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Error analysis
We explore random errors with simulations on
synthetic data. At fixed Rv, uncertainty in the
final solution is 2. Uncertainty in Rv
dominates, But 5 accuracy possible.
Effective temp
Angular size
E(B-V)
Goodness of fit
Rv
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Rigel, for example
Rigel
IUE
Optical photometry
O/IR is in Rayleigh-Jeans tail of SED ?
independent of Teff ? E(B-V) RV ?
J
L
K
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Results
with best-fit Rv
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Integrated flux solutions
Results
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Summary
We have a robust method to determine effective
temperature to 5 accuracy allowing for
variations in interstellar extinction.
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Summary
We have a robust method to determine effective
temperature to 5 accuracy allowing for
variations in interstellar extinction. Plus, the
method is only weakly model dependent, and
complements spectroscopic techniques.
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Summary
We have a robust method to determine effective
temperature to 5 accuracy allowing for
variations in interstellar extinction. Plus, the
method is only weakly model dependent, and
complements spectroscopic techniques. Teff from
Integrated Flux Method agrees with spectroscopic
and Balmer Jump determinations within the error
limits. Note method does not work well for
early B-stars or O-stars, since
un-observable FUV and EUV contributes most to
flux integral. RV can be different from
3.1!!!
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Blue supergiants diagnostics

• Confidence in determination of Teff and log g
• ?Teff/Teff 4 and ?log g 0.05
• determination of chemical abundances

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Chemical composition

• Very detailed model atoms
• New atomic data (radiative/collisional)
• Opacity Project (Seaton et al. 94 and follow-up)
• IRON Project (Hummer et al. 93 and follow-up)
• ? ? log N(element) / N(H) 0.1

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Recent Improvements on Atomic Data

• requires solution of Schrödinger equation
• for N-electron system
• efficient technique
• R-matrix method in CC approximation
• Opacity Project Seaton et al. 1994, MNRAS, 266,
  805
• IRON Project Hummer et al. 1993, AA, 279,
  298
• accurate radiative/collisional
  data
• to 10 on the mean

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Confrontation with Reality
Photoionization
Electron Collision
Nahar 2003, ASP Conf. Proc.Ser. 288, in press
Williams 1999, Rep. Prog.
Phys., 62, 1431
ü high-precision atomic data ü
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Improved Modelling for Astrophysics
e.g. photoionization cross-sections for carbon
model atom
Przybilla, Butler Kudritzki 2001b, AA, 379, 936
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N I/II Model Atom N I 235 levels / 89 terms
757 radiative transitions 210
detailed collisions N II 151 levels / 77 terms
539 radiative transitions 242
detailed collisions Przybilla Butler
2001c, AA, 379, 955
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NLTE departure coefficients
biniNLTE/niLTE light a-process
elements overpopulation of metastable
levels Iron Group overionization
Przybilla Butler 2001c, AA, 379, 955
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log ni/niLTE
FeII
Przybilla, Butler, Kudritzki, Becker, AA, 2005
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Spectrum synthesis
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Abundance Determination CNO 1
? free from systematic effects
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Abundance Determination CNO 2
? small uncertainties
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C
? Leo (A0 Ib)
N
O
log x/H 12
S
Ti
Fe
log W? (mÅ)
Przybilla, Butler, Kudritzki, Becker 2006, AA
445, 1099
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Spectral diagnostics of A-supergiants
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M31 A-supergiant line info 1
Ba II
Ti II Fe II Ti II Cr
II Ti II Ti II Fe I Cr I Fe I Cr I
Cr II
Cr II Fe II Fe II Cr II
O I
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Id 2
Ba II
Ti II Fe I S II
Fe I
Sc II
Fe II Fe I S II Fe II Fe
I S II
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Id 3
Y II
S II Ti II
Cr I Fe II
Ti II Fe I Fe I Ti
II Fe II Mg I Mg I Mg I Ti II
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• Abundance Determination The Whole Picture
• redundancy from multiple parameter indicators in
  NLTE
• removed systematic errors
• reduced statistical uncertainties
• consistency in heavy element abundances in NLTE
• abundance pattern for He, C, N ? mixing signature
• stellar evolution models with rotation
• Meynet Maeder 2000, AA, 361, 101
• Heger Langer 2000, ApJ, 544, 1016

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Abundance Determination
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Abundance Determination
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Pitfalls _at_ high luminosity diagnosis from
inappropriate LTE analysis - metal poor
- a-enhancement NLTE mandatory for
highly luminous objects

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Spectroscopy of blue supergiants in the Local
Group
an incomplete list of recent studies beyond the
Magellanic Clouds
NGC 6822 Venn, Lennon, Kaufer, Kudritzki et al.,
2001, ApJ 547, 765 2 A supergiants (VLT/UVES
Keck/Hires) Muschielok, Kudritzki, Appenzeller
et al., 1999 AA Letters 352, 40 3 B supergiants
(VLT/FORS)
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Local Group Neighbourhood
Grebel 1999, Proc. IAUS 192, 17
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NGC 6822
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Spectroscopy of blue supergiants in the Local
Group
spectrum synthesis with 12log(O/H)8.5, 8.7 8.9
a-elements O, Mg, Si Fe-group elements Fe, Cr,
...
Venn, Lennon, Kaufer, Kudritzki et al. 2001
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Local Group Neighbourhood
Grebel 1999, Proc. IAUS 192, 17
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Other dwarf galaxies
Sextans A Kaufer, Venn, Tolstoy, Kudritzki et
al., 2004 AJ 127, 2723 3 A-type supergiants
(VLT/UVES)
WLM Venn, Tolstoy, Kaufer, Kudritzki et al.,
2003 AJ 126, 1326 2 A-type supergiants
(VLT/UVES)
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WLM

• infall of metal-poor gas?
• spatial variations?

SMC
HII region
Venn, Tolstoy, Kaufer, Kudritzki et al. 2003
Lee, Skillman Venn 2005
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Local Group Neighbourhood
Grebel 1999, Proc. IAUS 192, 17
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The metallicity gradient of M33
from A B supergiants

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M33 B-supergiant
M33 UIT103 (B0.7Ia) ESI/Keck II R5000 S/N80
a/H-0.4 dex
Urbaneja, Herrero, Kudritzki et al., 2005, ApJ
635, 311
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M33 0755 A1-A2 I ISIS/WHT R5000
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M33 O/H gradient
Stars H II regions (from Vilchez et al. 1998)
Urbaneja, Herrero, Kudritzki et al., 2005, ApJ
635, 311
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N
B
E
N
B
E
Recent work with ESI/Keck in center of M33
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ESI/Keck Oct 2005
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Oxygen gradient in M33
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Spectral resolution for extragalactic
studies

• massive stars have angular momentum ? vrot?sin i
• even A supergiants still have v?sin i 30 to 50
  km/s
• ? FWHM (metal lines) 1 A
• ? with ?? 1 A and good S/N very accurate
  work
• possible
• ?? 2 A optimum for work beyond Local Group
• ? Teff 2, ? log g 0.05, abundances 0.1
  to
• 
  0.2 dex
• ?? 5 A with FORS _at_ VLT
• ? Teff 4, ? log g 0.05, metallicity
  0.2 dex
• use Balmer jump for Teff

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Spectrum synthesis from high resolution ...
... to ...
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... intermediate resolution
? ? log e 0.2 dex feasible
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The Araucaria Project some results
NGC 300 Sculptor Group (2 - 4 Mpc)
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The Araucaria Project recent results
NGC 300 cepheids optical (V,I) P-L relation
LMC slope
ESO 2.2m LCO 1.3m CTIO 4m
Gieren, Pietrzynski, Walker, Bresolin, Kudritzki
et al. 2004
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The Araucaria Project recent results
VLTISAAC

• NGC 300 cepheids
• near-IR (J,K) P-L relation
• small absorption corrections
• reduced width of instability strip
• reduced amplitudes

Gieren, Pietrzynski, Soszynski, Bresolin,
Kudritzki et al. 2005
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The Araucaria Project recent results
(m-M) 26.37 D 1.88 Mpc E(B-V) 0.10
Gieren, Pietrzynski, Soszynsk, Bresolin,
Kudritzkii et al. 2005
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Cycle 11 HST/ACS imaging
Effects of crowding Studied using HST/ACS
photometry
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Cycle 11 HST/ACS imaging
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Cycle 11 HST/ACS imaging
Distance from TRGBRizzi, Bresolin, Kudritzki et
al., 2005, ApJagrees with Cepheids
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Bresolin, Gieren, Kudritzki et al. 2002 ApJ 567,
277
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NGC 300 spectral classification
Galactic template
V 19.0
NGC 300 A2 supergiant
Galactic template
Bresolin, Gieren, Kudritzki et al. 2002, ApJ 567,
277
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NGC 300 2 Mpc
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Cycle 11 HST/ACS imagingblue supergiantsBresolin
et al. 2005
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• A grid of NLTE model calculations
• Late-B (B6) to mid-A (A3/A5)
• Luminosity class Ia to Ib/II
• 12 metallicities Z/Z_sun
• 2.0, 1.4, 1.0, 0.7, 0.5, 0.4, 0.3, 0.25, 0.2,
  0.14, 0.1, 0.05
• Chemical composition
• H,He,C,N,O,Mg,S,Ti,Fe
• Ne,Na,Al,Si,P,K,Ca,Sc,V,Cr,Mn,Co,Ni,Cr,Zn,Sr,Y,Zr,
  Ba
• 20000 models in total

The grid
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Determination of Teff
Low resolution spectra
? cannot use ionization equilibria Can we
just use relation between spectral
type and Teff ???
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Teff -scale of B8-A4 Ia
supergiants
Kudritzki, Bresolin, Przybilla, 2003,
ApJ Letters, 582, L83
A2
B8
A0
A4
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A problem ???

• spectral type - Teff relationship
• metallicity
  dependent???
• ? lower metallicity stars cooler
• _at_ same
  spectral type
• ? higher hotter
• spirals have abundance gradients !!!!

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Example two models
Teff 9500 K, log g 1.20, Z 0.0
8750 1.00 -0.3
Identical spectrum metal lines Balmer lines !!!
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definitely a problem !!!!

• spectral type - Teff relationship
• metallicity
  dependent !!!
• ? lower metallicity stars cooler
• _at_ same
  spectral type
• ? higher hotter
• spirals have abundance gradients !!!!
• could be devastating for low resolution
  diagnostics!!!

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A solution ???

• Balmer jump DB a Teff diagnostic ???

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Example two models
Teff 9500 K, log g 1.20, Z 0.0
8750 1.00 -0.3
Balmer jumps are different !!!
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Example two models
Teff 9500 K, log g 1.20, Z 0.0
8750 1.00 -0.3
Balmer jumps are different !!!
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Isocontours of D_B and W?(H?) in
(Teff,log
g)-plane
DB log(F?gt3645/F?lt3645)
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Przybilla, Butler, Kudritzki, Becker 2005, AA
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• Classic spectroscopic Teff-indicator ionization
  equilibrium
• Mg I/II, Fe I/II, N I/II, O I/II, S II/III
• Requires high resolution high S/N for weak
  lines
• Balmer discontinuity (jump) as an alternative
• Requires near-UV photometry / spectroscopy ( ?
  3640 Å )
• Some dependence on luminosity and on (very weak)
  metallicity

B8Ia Rigel ( ? Ori )
12500K
12000K
11500 K
Balmer jump vs I.E.
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Przybilla, Butler, Kudritzki, Becker 2005, AA
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A solution ???

• Balmer jump DB a Teff diagnostic ??? ? yes
• do models reproduce DB ??? ? yes
• DB by spectrophotometry from the ground???

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A Ia in WLM high res study ? Teff 8300K
compare with DB from low res FORS/VLT spectrum
yellow 8300K pink 8500K blue 8750K

• ?Very good
• temperature
• resolution

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A solution ???

• Balmer jump DB a Teff diagnostic ??? ? yes
• do models reproduce DB ??? ? yes
• DB by spectrophotometry from the ground??? ?
  yes
• well, then lets try beyond Local Group.

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Example early A supergiant
Kudritzki, Bresolin Urbaneja et al. 2007
A2 Ia Teff 9250 K log g 1.45
HST/ACS ground
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Balmer jump fitting
Teff 9000K
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Balmer jump fitting
Teff 9250K
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Balmer jump fitting
Teff 9750K
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Balmer jump fitting
Teff 9000K
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Balmer series fitting
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Balmer line fitting
H?
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Balmer line fitting
Hd
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Balmer line fitting
H8
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Balmer line fitting
H9
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Balmer line fitting
H10, 11
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Another example late B supergiants
B8 Ia Teff 11750 K log g 1.95 E(B-V) 0.06
HST/ACS ground
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Balmer jump fitting a late B Ia
Teff 12000K
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metallicity and chemical composition

• B supergiants ? a - elements
• A supergiants ? a elements, iron group

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NGC 300 metal abundances
B3 Ia Teff 17000 log g 2.0 0.6 X solar Z
Urbaneja, Herrero, Bresolin, Kudritzki et al. 2005
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Metallicity
Z -0.3,-0.5
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Metallicity spectral window
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Spectral window 4497-4607Å
B9 Ia Teff 10000K log g 1.75
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Spectral window 4497-4607Å
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Spectral window 4497-4607Å
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?i spectral window 4497-4607Å
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another spectral window
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Spectral window 4117-4197Å
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?i spectral window 4117-4197Å
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another spectral window
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Spectral window 4284-4322Å
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?i spectral window 4284-4322Å
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another spectral window
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Spectral window 4438-4497Å
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?i spectral window 4438-4497Å
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?i all windows ? Z -0.40.1
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Spectral window 4117-4195Å
A3 Ia Teff 8500K log g 1.65
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?i spectral window 4117-4195Å
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Spectral window 4360-4426Å
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?i spectral window 4360-4426Å
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?i all windows ? Z -0.50.15
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Spectral window 4495-4610Å
A1 Ia Teff 9250K log g 1.60
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?i spectral window 4495-4610Å
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?i all windows ? Z -0.650.15
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Spectral window 4497-4610Å
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?i spectral window 4497-4610Å
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Spectral window 3995-4085Å
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?i spectral window 3995-4085Å
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?i all windows ? Z -0.150.10
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Wolf-Rayet star in NGC 300
WN11 star
emission line diagnostics first detailed
abundance pattern outside Local Group
Bresolin, Kudritzki, Najarro et al. 2002, ApJ
Letters 577, L107
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NGC 300 WN11 star
non-LTE line-blanketed hydrodynamic model
atmospheres with stellar winds
stellar parameters wind parameters H, He, CNO,
Al, Si, Fe abundances
Bresolin, Kudritzki, Najarro et al. 2002, ApJ
Letters 577, L107
180
NGC 300 WN11 star
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NGC 300 nebular vs stellar abundances
stellar O abundance gradient
Urbaneja, Herrero, Bresolin, Kudritzki et al.
2005, ApJ 622, 862
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Stellar metallicity gradient in NGC300
B0 B3 supergiants ? B8 A4 supergiants
--- Z -0.03 0.45?/?0
-0.03 0.08d/kpc ?0 9.75 arcmin
5.7kpc Z log(Z/Z_sun)
Kudritzki, Urbaneja, Bresolin, Przybilla, Gieren,
Pietrzynski, 2007, in prep.
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Comparison with nebular abundances
Pagel, Edmunds, Blackwell et al. 1979
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Comparison with nebular abundances
Bresolin, Garnett Kennicutt 2004
see also Bresolin, Schaerer, Gonzalez Delgado
Stasinska 2005
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Comparison with nebular abundances
Bresolin, 2006
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NGC 300

• Different R23 and N2 calibrations
• HII em. line fluxes from Deharveng et al. (1988)

N2 calibration
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Stellar vs. HII metallicity gradient
---- Dopita Evans (1986)
---- Kobolnicky et al. (1999)
---- Denicolo et al. (2002)
---- Pilyugin (2001)
---- Pettini Pagel (2004)
---- Zaritsky et al. (1994)
Almost identical with stellar regression!!!!
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NGC 300
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Stellar vs. HII metallicity gradient
---- Dopita Evans (1986)
---- Kobolnicky et al. (1999)
---- Denicolo et al. (2002)
---- Pilyugin (2001)
---- Pettini Pagel (2004)
---- Zaritsky et al. (1994)
Almost identical with stellar regression!!!!
190
Future chemical abundances work

• low resolution diagnostics of individual
  elements
• gradients of abundance patterns (a/Fe, etc.)
• more galaxies
• interpretation ? galaxy evolution, SH history
  etc.

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4500Å
4660Å

• Teff, logg, metallicity
• Identify spectral features that provide
  information about individual elements
• Fe
• Ti
• Cr

full spectrum
Fe subtracted
Ti subtracted
Cr subtracted
Ba
Ba subtracted
Low Spectral Resolution
192
4500Å
4660Å

• S/NR limitations
• minimum metallicity
• spectral type metallicity
• hotter and/or more luminous objects have weaker
  lines

S/N200
S/N50
S/N30
S/N15
Z - 1.0
Z 0.0
Z - 0.3
8300 K, 1.20 dex
8300 K, 1.20 dex
9750K, 1.30 dex
Low Spectral Resolution SNR
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• low resolution spectra of A and B supergiants
  allow for diagnostics with reasonable accuracy
• ALL the fundamental stellar parameters (Teff, log
  g, chemical composition, distance, radius,
  luminosity, mass-loss rates) and interstellar
  reddening, extinction and reddening law can be
  derived from the spectra (and accurate
  photometry)
• What can be pursued (scientific goals) depends
  primarily on the signal-to-noise
• Teff and logg can be easily derived with S/N 15
  
• Distance determinations (FGLR)
• Abundance analysis is more demanding (telescope
  time)
• S/N 30 to 50 is required for metallicities of
  the order of SMC metallicity ( 0.3 solar)
• The lower the metallicity, the larger the S/N
  required
• M101, V 22.5 mag (Mv -7.5 mag) requires 16
  hours _at_ Keck (S/N50)
• 
  6
  30

Closing thoughts
194
Future chemical abundances work

• low resolution diagnostics of individual
  elements
• gradients of abundance patterns (a/Fe, etc.)
• more galaxies
• interpretation ? galaxy evolution, SH history
  etc.

195
NGC 3621 7 Mpc HST/ACS Bresolin, Kudritzki,
Mendez Przybilla 2001 19 blue supergiant
candidates (VLT/FORS) 4 analyzed
196
Galactic template
NGC 3621 A0 supergiant
NGC 3621 Bresolin, Kudritzki, Mendez
Przybilla 2001 19 blue supergiant candidates
(VLT/FORS) 4 analyzed
Galactic template
Bresolin, Kudritzki, Mendez, Przybilla 2001, ApJ
Letters 548, L159
197
Galactic template F0 Ia
NGC 3621 F1 Ia
NGC 3621 Bresolin, Kudritzki, Mendez
Przybilla 2001 19 blue supergiant candidates
(VLT/FORS) 4 analyzed
Galactic template F2 Ia
Bresolin, Kudritzki, Mendez, Przybilla 2001, ApJ
Letters 548, L159
198
Bresolin, Kudritzki, Mendez, Przybilla 2001, ApJ
Letters 548, L159
199
Teff 10000K, L 3.1 105 Lsun
mass fraction X/Xsun H
0.688 0.97 He 0.301
1.06 Mg 1.5 10-4
0.22 Fe 1.5 10-3 1.08
LBV
Najarro, Urbaneja, Kudritzki, Bresolin 2005
200
Blue supergiants as distance
indicators

• 2 major problems with Cepheids
• Interstellar extinction
• Metallicity dependence of PL-rel.
• Spectroscopic distance
• indicator needed !!!

201
Why more stellar distance indicators?

• 2 major problems with
• photometric methods
• Interstellar extinction
• Metallicity dependence
• Spectroscopic distance
• indicator needed !!!

202
Flux weighted Gravity Luminosity Relationship
(FGLR)
Kudritzki, Bresolin, Przybilla, ApJ Letters, 582,
L83 (2003)
L,M const.
B4-A4
M gR2 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
203
Theoretical Flux weighted Gravity
Luminosity Relationship (FGLR)
L,M const.
B4-A4
take evolutionary tracks and plot Mbol
f(g/T4) ?
204
Outline
a 3.75
FGLR from stellar evolution tracks by Maeder
Meynet, 2000 ? Z Zgal with rotation ?
ZSMC with Zgal no ? ZSMC no
205
Example early A supergiant
Kudritzki, Bresolin Urbaneja et al. 2007
A2 Ia Teff 9250 K log g 1.45
HST/ACS ground
206
Balmer series fitting
207
FGLR first test
Spectra in Milky Way, LMC, SMC NGC 6822, M31,
M33 NGC 300, NGC 3621
A0 Ia in NGC 300 Fit of Balmer lines 2 models
with ? log g 0.05
Kudritzki, Bresolin, Przybilla, ApJ Letters, 582,
L83 (2003)
208
Flux weighted gravityluminosity
relationship first
results
Mbol 3.85 log(g/T4eff,4) 13.73

• 0.26
• NGC 300
• NGC3621

Kudritzki, Bresolin Przybilla (2003)ApJ
Letters, 582, L83
209
Flux weighted gravityluminosity
relationship first
results
Mbol 3.71 log(g/T4eff,4) 13.49

• 0.26

Kudritzki, Bresolin Przybilla, 2003,ApJ
Letters, 582, L83
210
FGLR NGC300 B-type Sgs
Urbaneja, Bresolin, Kudritzki et al., 2005,ApJ
211
Flux weighted gravityluminosity
relationship new results
FGLR Local Group NGC 300, NGC 3621
Kudritzki, Bresolin Przybilla, 2003,ApJL, 582,
L83 Kudritzki, Urbaneja, Bresolin et al., ApJ,
2006
Mbol 3.27 log(g/T4eff,4) 13.02

• 0.22

212
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

213
FGLR Local Group, NGC300 NGC3621
214
FGLR including WLM
215
Supergiant photometric variability

• blue supergiants reported to be variable
• reviews by Sterken (1989), van Genderen
  (2001)
• non-radial oscillations
• Maeder (1986), Baade (1992)
• variable winds
• Kaufer et al.(1996, 1997), Rivinius et
  al. (1997)
• Stahl et al.(2003)

How does photometric variability
affect the FGLR??
216
A photometric study in NGC 300

• 6 months, 29 nights study with ESO 2.2m WFI
• original goal detect Cepheids in NGC 300
• by-product systematic study of
• photometric variability of
• blue
  supergiants
• 
  _at_ 2 Mpc

217
standard deviation from mean magnitude vs. mean
magnitude
M supergiant

• standard stars
• . . . 2s
• - - - 1s

Bresolin, Pietryzynski, Gieren,
Kudritzki, Przybilla, Fouque, 2004, ApJ 600,
182
218
light curves (V,B) 6 months, 29 nights
Bresolin, Pietryzynski, Gieren,
Kudritzki, Przybilla, Fouque, 2004, ApJ 600, 182
219
2 periodic objects spectral type A2 Ia
Bresolin, Pietryzynski, Gieren,
Kudritzki, Przybilla, Fouque, 2004, ApJ 600,
182
220
Effects of photometric variability

• ?m small, s 0.07 mag per object
• maximum zero point shift through all 29 epochs
• 0.05 mag
• FGLR robust against
• photometric
  variability!

221
Conclusions

• blue supergiants excellent distance indicators
• tight relationship FGLR
• methods based on spectroscopy
• ? precise intrinsic properties
• Teff, log g, chemical composition, SEDs,
  colors
• ? reddening, extinction

222
Conclusions

• multiplicity, crowding ? less important
• much
  brighter
• spectroscopy
  helps to identify
• contaminating
  sources
• potential ? quantitative spectroscopy
• possible down to mV 22.5
  mag
• ? with objects MV - 8 mag
• m M 30.5 mag possible, maybe
  beyond
• 10 objects per galaxy ? ?(m-M)
  0.1 mag

223
Future work

• careful calibration of FGLR and WLR
• using Local Group
  galaxies
• application of methods to determine
• distances to crucial galaxies between
• Local Group and Virgo/Fornax clusters

224
The Araucaria Project
improve the calibration of the environmental
dependences of several stellar distance indicators
Cepheids RR Lyrae Red
clump stars Blue supergiants
Wolfgang Gieren Concepción, Chile Grzegorz
Pietrzynski Igor Soszynski Rolf Kudritzki IfA,
Hawaii, USA Fabio Bresolin Miguel Urbaneja Dante
Minniti Universidad Católica, Chile Jesper
Storm Potsdam, Germany
225
The Araucaria Project
TARGETS IC 1613 NGC 6822 WLM NGC 3109
LOCAL GROUP
NGC 300 NGC 7793 NGC 247 NGC 55
SCULPTOR GROUP
226
Local Group Neighbourhood
Grebel 1999, Proc. IAUS 192, 17
227
WLM
WLM faintest dwarf irregular in LG few HII
regions O -0.8
228
WLM

• infall of metal-poor gas?
• spatial variations?

SMC
HII region
Venn, Tolstoy, Kaufer, Kudritzki et al. 2003
Lee, Skillman Venn 2005
229
WLM Araucaria VLT/FORS 35 targets
Additional Araucaria dwarf galaxies with FORS
spectra IC 1613 NGC 3109
230
Bresolin, Pietrzynski,Urbaneja,
Gieren, Kudritzki, Venn, 2006, ApJ 648, 1007
WLM new results
A-supergiant Fe -0.6
Kudritzki, Urbaneja, Bresolin et al. 2007
B-supergiant O -0.8
Mg -0.8 Si
-0.6 N -0.1
C -1.9
B-supergiant O -1.0
Mg -0.8 Si
-0.6 N -0.5
C -1.4
B-supergiant O -0.8
Mg -0.6 Si
-0.7 N -0.5
C -1.9
For all 3 B-supergiants O in
agreement with HII regions!!!
231
FGLR including WLM, m-M 24.84 (McConacchie et
al. 2005, TRGB)
232
FGLR including WLM, m-M 24.84 (McConacchie et
al. 2005, TRGB)
New Cepheid distance m-M 25.14 Pietrzynski
et al. 2007
233
Local Group Neighbourhood
NGC 3109 dark matter dominated dwarf stellar
photometry ? low Z?
Grebel 1999, Proc. IAUS 192, 17
234
Pietrzynsky, Gieren, Bresolin, Kudritzki et al.,
ApJ, 2006
NGC 3109 New Cepheid distance
235
Evans,Bresolin,Urbaneja,Pietrzynsky, Gieren,
Kudritzki et al., ApJ, 2006
X log(X/H)-log(X/H)sun O -0.9 N
-0.2 Mg -0.7 Si -0.7
B-supergiants model atmosphere fits
spectral analysis
X log(X/H)-log(X/H)sun O -1.1 N
-0.6 Mg -0.7 Si -0.7
NGC 3109 New results
? stellar vrad along major axis HI rotation
curve --- Ha rotation curve
O-stars
Late B- early A- supergiants
Early B-supergiants
Early B-supergiants
A-supergiants
236
The Araucaria Project
TARGETS IC 1613 NGC 6822 WLM NGC 3109
LOCAL GROUP
M81 NGC 2403
M81 GROUP
NGC 300 NGC 7793 NGC 247 NGC 55
SCULPTOR GROUP
237
N3621
238
Additional Araucaria galaxies Sculptor
Luca Rizzi, IfA, Hawaii
239
Additional Araucaria galaxies Sculptor
FORS spectra NGC 55 ( 200 spectra) NGC 247
(100 spectra) NGC 7793 ( 30 spectra)
95 stars
NGC 55
240
Mauna Kea
241
View MK ? Haleakala
242
Adaptive Optics
243
M81 CFHT 3.5 Mpc
244
M101 CFHT 6.7 Mpc
245
The Araucaria Project
improve the calibration of the environmental
dependences of several stellar distance indicators
Cepheids RR Lyrae Red
clump stars Blue supergiants
Wolfgang Gieren Concepción, Chile Grzegorz
Pietrzynski Igor Soszynski Rolf Kudritzki IfA,
Hawaii, USA Fabio Bresolin Miguel Urbaneja Dante
Minniti Universidad Católica, Chile Jesper
Storm Potsdam, Germany
246
The Araucaria Project
TARGETS IC 1613 NGC 6822 WLM NGC 3109
LOCAL GROUP
NGC 300 NGC 7793 NGC 247 NGC 55
SCULPTOR GROUP
247
WLM Araucaria VLT/FORS 35 targets
Additional Araucaria dwarf galaxies with FORS
spectra IC 1613 NGC 3109
248
The Araucaria Project
TARGETS IC 1613 NGC 6822 WLM NGC 3109
LOCAL GROUP
NGC 300 NGC 7793 NGC 247 NGC 55
SCULPTOR GROUP
249
Bresolin, Urbaneja, Kudritzki et al., ApJ, 2006
WLM new results
FGLR WLR NGC 300 other LG
B supergiant
A supergiant
250
Pietrzynsky, Gieren, Bresolin, Kudritzki et al.,
ApJ, 2006
NGC 3109 New Cepheid distance
251
N3621
252
Additional Araucaria galaxies Sculptor
Luca Rizzi, IfA, Hawaii
253
Additional Araucaria galaxies Sculptor
FORS spectra NGC 55 ( 200 spectra) NGC 247
(100 spectra) NGC 7793 ( 30 spectra)
95 stars
NGC 55
254
The next generation of 30m telescopes.
255
IAU Symposium 250 Massive Stars as Cosmic
Engines Kauai, December 10 14, 2007 SOC Paul
Crowther, Joachim Puls , RPK .. LOC Fabio
Bresolin, Miguel Urbaneja, RPK,
256
Star trails