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Theoretical modeling of GHRS observations of the Of/WN-type star R136a5
de Koter, Alex; Hubeny, Ivan; Heap, Sara R.; Lanz, Thierry
AA(NASA. Goddard Space Flight Center, Greenbelt, MD, US), AB(NASA. Goddard Space Flight Center, Greenbelt, MD, US), AC(NASA. Goddard Space Flight Center, Greenbelt, MD, US), AD(NASA. Goddard Space Flight Center, Greenbelt, MD, US)
Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X), vol. 435, no. 1, p. L71-L74 (ApJL Homepage)
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NASA/STI Keywords:
Astronomical Models, Ionization, O Stars, Stellar Atmospheres, Stellar Luminosity, Ultraviolet Spectra, Helium, Hubble Space Telescope, Magellanic Clouds, Temperature Profiles
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We present a theoretical analysis of the Hubble Space Telescope (HST) Goddard High Resolution Spectrograph (GHRS) spectrum of R136a5, an O3fWN star in the R136a cluster in 30 Doradus. Using non-LTE extended and expanding model atmospheres, we find a surprisingly high mass-loss rate dot-M = 1.8 +/- 0.5 x 10-5 solar mass/yr and an effective temperature Teff = 42.5 +/- 2.5 kK. With the observed visual magnitude, this implies a radius R* = 17 +/- 2 solar radius and a solar luminosity L = 8.5 +/- 1 x 105 solar luminosity. We discuss possible sources of the uncertainties in the derived stellar parameters and conclude that the effective temperature may be underestimated; however, if so, the value of the mass-loss rate would not be affected.

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