1995A&A...303L..33H

The discovery of an apparently normal B star far from the galactic plane by follow-up spectroscopy of faint blue star candidates from objective-prism plates of the Hamburg Schmidt survey is presented. The spectrum of HS 1914+7139 (B=14.5m) is classified as B2.5IV. the spectral lines are broadened by rotation (vsini=260km/s). From an LTE model atmosphere analysis an effective temperature of 18000K and a surface gravity of log g=3.75 are determined. A discussion of the effects of the large rotation allows the mass of HS 1914+7139 to be constrained with the aid of evolutionary tracks to the range 6-10M_sun. This analysis indicates that HS 1914+7139 lies at the outer edge of the Galaxy, i.e. more than 20kpc from the galactic center and 6.5-7.5kpc above the galactic plane. The main sequence lifetime of HS 1914+7139 lies in the range 20-60Myrs. If HS 1914+7139 was formed in the galactic disk and shortly thereafter ejected to reach its present position an exceedingly high ejection velocity would be required. Therefore, star formation in the halo appears to be more favourable to explain the properties and location of IIS 1914+7139.