MWC-297, B1.5VE - A ZERO-AGE MAIN-SEQUENCE STAR IN THE AQUILA-RIFT

Moderate-resolution optical spectra of the significantly reddened Herb ig Be star MWC 297 are presented. The data are of sufficient quality t hat it has been possible to obtain a spectral type for this star by co mparing heavy element absorption features with those present in early B held stars of known spectral type. The best fit is to B 1.5V, with a n uncertainty of half a sub-type. It is estimated that v sin i for MWC 297 is about 350 +/- 50 km s(-1), suggesting that the star's rotation is almost in the plane of the sky. The reddening towards this object is reviewed and is derived afresh from spectra at wavelengths spanning the B-R optical bands. Using A(v) similar or equal to 8 and the absol ute magnitude corresponding to B1.5V, it is argued that the distance t o MWC 297 is 250 +/- 50 pc rather than similar to 500 pc as has recent ly been quoted in the literature. At this distance the star can be loc ated very plausibly in the Aquila Rift. We go on to present a MERLIN 5 -GHz radio map of the source which shows it to be markedly elongated i n the north-south direction (to a dimension of 125 au at 250 pc). Exis ting data on the optical linear polarization of MWC 297 suggest a comp licated picture that leaves open the question of whether the radio axi s might trace an ionized electron-scattering equatorial disc. We also present and briefly discuss high-resolution Br alpha and He I 1.083-mu m line profiles obtained within a week of the optical spectra. The He I profile is very complex, but confirms that MWC 297 is an outflow so urce. It is noted that the H I emission lines are undoubtedly highly v ariable, although the time-scales for this are not yet clear.