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Imaging and spectroscopy of the LMC He II nebula N 44C and its ionizing star

  • Vanessa C. Galarza (a1), Donald R. Garnett (a2) and You-Hua Chu (a3)

Abstract

We present results from new HST imaging and spectroscopy of the peculiar Large Magellanic Cloud H II region N 44C and its ionizing star. While this nebula exhibits strong He II recombination emission, the source of the He+ ionizing photons has not been found. The UV spectrum of the ionizing star suggests an approximate spectral class of 07–08; the UV Si IV, He II, and N IV features do not show P-Cygni profiles, indicating that the ionizing star is not a supergiant. No companion star has yet been detected. Ground-based and HST optical spectroscopy of the ionized gas shows that the nebular abundances of C, N, O and He are not anomalous relative to other LMC H II regions, suggesting that no previous WR/SN companion has disappeared. Echelle spectroscopy has also ruled out the presence of high velocity shocked gas. Deep ROSAT imaging shows no X-ray point source in this location. The “fossil X-ray binary” hypothesis of Pakull & Motch (1989) remains the best explanation for the ionization of this nebula; however, convincing evidence for this hypothesis remains elusive.

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References

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Garnett, D.R., Kennicutt, R.C. Jr., Chu, Y.-H., Skillman, E.D. 1991, ApJ 373, 458
Magnier, E.A., Chu, Y.-H., Points, S.D., Hwang, U., Smith, R.C. 1996, ApJ 464, 829
Pakull, M.W., Motch, C. 1989, Nature 337, 337
Stasińska, G., Testor, J.G., Heydari-Malayeri, M. 1986, A&A 170, L4

Imaging and spectroscopy of the LMC He II nebula N 44C and its ionizing star

  • Vanessa C. Galarza (a1), Donald R. Garnett (a2) and You-Hua Chu (a3)

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