Nearinfrared spectral analysis of young OB stars

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Near-infrared spectral analysis of young OB stars

• Margaret M HansonDepartment of Physics,
  University of Cincinnati

Joachim Puls Tamara Repolust Institut fuer
Astronomie Astrophysik, der LMU Muenchen
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Important applications of an IR-based spectral
analysis for OB stars

• Study of galactic OB clusters.
  Massive IMF, high mass
  cutoff, galactic SFR and structure. Nearby
  analogues of extragalactic super star clusters.
  (see posters 19 113 on Westerlund 1)
• Early evolution of shrouded, young massive stars
  (YSO).
  Determine stellar
  characteristics at extremely early stages.

Our code, FASTWIND (Puls et al. 2005), allows for
the analysis of optically thin winds, down to the
base of the photosphere.
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Nearly half of all O9 V stars in the Galaxy can
be analyzed in the NIR
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Infrared methods will allow us to see most of
our Galaxy
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NIR spectral characteristics of OB stars
The O7 stars NIR lines of O stars are just a few
percent of the continuum. Temperature scale
1) HeI/HeII 2) Brackett lines Luminosity
scale 1) Deep, narrow lines of HeI, HeII. 2)
Hydrogen goes into emission.
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Data from Subaru/IRCS (Hanson et al. 2005)
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Questions uniquely answered with quantitative
spectral analysis (QSA)
Q Where on the HRD is the star? QSA tells us
Teff and log g. Q Is mass accretion still
occurring and what is the nature of the wind?
When fitting spectral lines we can identify in
fall or disk signatures and determine mass loss
rates of stellar wind. Q Is the star a binary?
QSA uses numerous spectral lines, thus can
readily identify spectroscopic binaries. Q What
affect has high accretion had on the rotation
rate of very young massive stars? QSA determines
vsini of the stars.
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Challenges in NIR spectral analysis
AT THE STAR Contamination from strong nebular
emission and thermal continuum. AT THE EARTH
Earth atmospheric absorption strong and messy.
AT THE COMPUTER NIR is extremely sensitive
(non-linear) to even small departures to LTE.
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Calibration of NIR Quantitative Analysis
See poster 132 Puls, Repolust, Hanson (Repolust
et al. 2005 AA, in press).

• Approximate values are first obtained with a
  model grid of line strengths. Profile fitting is
  used to further constrain the star and wind
  properties.
• This has been done for 25 optically visible stars
  to check consistency of NIR with results from
  Opt/UV.
• NIR characteristics are consistent with opt/UV
  when available.

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Non-LTE effects in the NIR
E.W -1.0
E.W -1.10
E.W -1.8
E.W -0.5
The NIR lines react differently to variations in
log g. Optical HeI becomes stronger with
increased log g (dwarfs). NIR HeI becomes
stronger with decreased log g (supergiants).
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The model profiles with the spectra
Poor BrG fit due to clumping in wind
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Comparison of NIR and optical for Teff and Log g
Error in optical
Teff
Log g
Results determined from NIR lines alone, are
typically within the error range for the same
values derived using optical lines.
(Repolust, Puls, Hanson et al. AA, in press)
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Where are the youngest massive stars?Powering
UCHII regions.

• G29.96 0.02
• Identified by Wood Churchwell (1989).
• HII 0.1 pc (4)
• Central Star O5-O6 V (Watson Hanson 1997)
• Extinction Av 25
• Age lt100,000 yrs?

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Subaru spectra of G29.96-0.02
S/N 200
S/N 60
H and K-band classification indicates early-O,
but precise luminosity, information about the
wind, etc. is not obtainable.
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First fit results of G29.96-0.02 spectra
Teff 41,000K (O4/O5) Log g 3.8 Vsini 80
km/s (Assume YHe 0.1) Log Q -12.5 to
12.8 (R 18, vinf 2200 km/s ? few x 10-6
Moyr-1)
Some lines are well fit, but others remain
problematic. The S/N ( 60) may not be high
enough for a rigorous analysis.
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Summary Conclusions

• NIR derived characteristics are consistent with
  opt/UV Analysis based on NIR alone can begin.
• H-band lines are as important as K-band lines.
  High extinction sightlines (Av gt
  30) will become difficult. Resolution gt
  5,000 and S/N gt 150, recommended.
• Contamination from thermal and nebular emission,
  particularly in strategic H and He lines, will be
  a challenge for YSO work. AO Spectrographs will
  help in this regard.

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