First results of an H alpha based search of classical Be stars in the Perseus Arm and beyond

Author(s): Raddi, R.; Drew, J. E.; Fabregat, J.; et al.

Source: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY  Volume: 430   Issue: 3   Pages: 2169-2187   DOI: 10.1093/mnras/stt038   Published: APR 2013

We investigate a region of the Galactic plane, between 120 degrees <= l <= 140 degrees and -1 degrees <= b <= +4 degrees, and uncover a population of moderately reddened (E(B – V) similar to 1) classical Be stars within and beyond the Perseus and Outer Arms. 370 candidate emission-line stars (13 less than or similar to r less than or similar to 16) selected from the Isaac Newton Telescope Photometric H alpha Survey of the Northern Galactic plane have been followed up spectroscopically. A subset of these, 67 stars with properties consistent with those of classical Be stars, have been observed at sufficient spectral resolution (Delta lambda approximate to 2-4 angstrom) at blue wavelengths to narrow down their spectral types. We determine these to a precision estimated to be +/-1 subtype and then we measure reddenings via spectral energy distribution fitting with reference to appropriate model atmospheres. Corrections for contribution to colour excess from circumstellar discs are made using an established scaling to H alpha emission equivalent width. Spectroscopic parallaxes are obtained after luminosity class has been constrained via estimates of distances to neighbouring A/F stars with similar reddenings. Overwhelmingly, the stars in the sample are confirmed as luminous classical Be stars at heliocentric distances ranging from 2 kpc up to similar to 2 kpc. However, the errors are presently too large to enable the cumulative distribution function with respect to distance to distinguish between models placing the stars exclusively in spiral arms, or in a smooth exponentially declining distribution.