Program: GN-2006B-Q-83
Title: | Towards a Nebular He II Diagnostic for Starbursts |
PI: | Sally Oey |
Co-I(s): | Daniel Schaerer, Paul Crowther |
Abstract
Nebular \heii\ \lam4686 emission is seen in 1/3 of all Wolf-Rayet
galaxies and offers a powerful diagnostic of the stellar population in
distant starburst regions. Both predictions and observations show that its
strength increases at low metallicity, and thus it promises to
be an especially useful probe for relatively unevolved systems.
WR stars are thought to be primarily responsible for the \heii\
emission, but stellar atmosphere model predictions vary greatly,
and SNR contributions could be important. Owing to its
high ionization potential at 54~eV, \heii\ is an especially sensitive
diagnostic of both ionizing stellar energy distributions and young
SNRs, as seen in starburst
conditions. Our discovery of a dozen \heii\ nebula candidates in
M33 at least doubles the number of known WR \heii\
nebulae, and offers a uniform sample of \heii-emitting SNRs. We
request spectroscopic follow-up data of both the objects and
associated stars. The data
will strongly constrain the locus of stellar parameters
that defines the boundary for He$^+$-ionizing conditions, and
thereby provide greatly-needed empirical constraints for WR and O star
model atmospheres. They will also quantify the SNR parameters that
produce \heii\ emission, which could be shocks or X-ray photoionization.
This will be the first systematic, empirical
test of \heii-emitting conditions, to develop its use as a
diagnostic for distant, low-metallicity and Pop III starbursts.
Publications using this program's data
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[data]
[ADS] Gemini GMOS spectroscopy of HeII nebulae in M 33