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Session 43 - The Diffuse ISM: Milky Way and Beyond.
Display session, Tuesday, June 11
Great Hall,
We present initial results of KPNO 4-m spectroscopy of discrete emission line nebulae in M31. The spectra cover the wavelength range 3500 to 7000 ÅLong-slit spectra of 16 positions in M31 were obtained, over a range in radial distance from the center. Slit positions were chosen such that several emission-line nebulae fell in each slit. The overall goal of the project is to obtain spectra of supernova remnant candidates found by Braun amp; Walterbos and to improve the measurement of abundances of heavy elements in M31. The spectra generally confirm the shock-excited nature of the supernova remnant candidates. The M31 HII regions generally show low-excitation spectra, with weak [OIII], and strong [NII], [SII], and [OII] emission. There is an increase towards higher excitation in the bright cores of several HII regions. Inspection of the spectra has led to serendipitous detection of four Wolf-Rayet stars, three of which were not known before. One of the new candidates is part of a star cluster centered on a supernova remnant. Another is an isolated star located off-center inside an asymmetric flattened shell. This shell is possibly a windblown bubble created by the Wolf-Rayet star. It is about 100 pc in size, however, which is much larger than the typical size of such nebulae. It is possible that the shell is the result of a previous supernova explosion but in that case it is surprising why it does not show the characteristic [OI] emission or strong [SII] emission that is normally seen in supernova remnants.
