SIMBAD references

2000ApJ...545..251G - Astrophys. J., 545, 251-265 (2000/December-2)

The He II emitting nebula N44C in the Large Magellanic Cloud: Optical/Ultraviolet spectroscopy of the nebula and its ionizing star.

GARNETT D.R., GALARZA V.C. and CHU Y.-H.

Abstract (from CDS):

We present HST spectroscopy and imaging, along with new ground-based spectroscopy and ROSAT HRI imaging, of the He II emitting nebula N44C and its ionizing star. A GHRS spectrogram of the ionizing star yields a spectral type of about O7 for the star. The lack of P Cygni profiles for Si IV and C IV indicates that the star is not a supergiant. The nebular abundances in the ionized gas are consistent with average abundances for LMC H II regions, with the possible exception that nitrogen may be enhanced. Enrichment by a former evolved companion star is not evident. A long-slit echelle spectrogram in Hα+[N II] shows no evidence for high-velocity gas in N44C. This rules out high-velocity shocks as the source of the nebular He II emission. A 108 ks ROSAT HRI image of N44C shows no X-ray point source to a 3 σ upper limit LX<1034 ergs.s–1 in the 0.1-2.0 keV band. Based on new measurements of the electron density in the He II emitting region, we derive recombination timescales of ~20 yr for He+2 and ~4 yr for Ne+4. If N44C is a fossil X-ray ionized nebula, this places severe constraints on when the putative X-ray source could have turned off. The presence of strong [Ne IV] emission in the nebula is puzzling if the ionizing source has turned off. It is possible the system is related to the Be X-ray binaries, although the O star in N44C does not show Be characteristics at the present time. Monitoring of X-rays and He II emission from the nebula, as well as a radial velocity study of the ionizing star, are needed to fully understand the emission line spectrum of N44C.

Abstract Copyright:

Journal keyword(s): galaxies: individual (Large Magellanic Cloud) - ISM: H II Regions - ISM: individual (LMC N44C) - Stars: Early-Type - Stars: Peculiar

Simbad objects: 17

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2023.02.05-17:40:19

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