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

Raddi, R.; Drew, J. E.; Fabregat, J.; Steeghs, D.; Wright, N. J.; Sale, S. E.; Farnhill, H. J.; Barlow, M. J.; Greimel, R.; Sabin, L.; Corradi, R. M. L.; Drake, J. J.

Abstract

We investigate a region of the Galactic plane, between 120° ≤ ℓ ≤ 140° and −1° ≤ b ≤ +4°, and uncover a population of moderately reddened (E(B − V) ∼ 1) classical Be stars within and beyond the Perseus and Outer Arms. 370 candidate emission-line stars (13 ≲ r ≲ 16) selected from the Isaac Newton Telescope Photometric Hα 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 (Δλ ≈ 2–4 Å) 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 Hα 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 ∼12 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.

Citation

Raddi, R., Drew, J. E., Fabregat, J., Steeghs, D., Wright, N. J., Sale, S. E., …Drake, J. J. (2013). First results of an Hα based search of classical Be stars in the Perseus Arm and beyond. Monthly Notices of the Royal Astronomical Society, 430(3), 2169-2187. https://doi.org/10.1093/mnras/stt038

• Journal Article Type: Article
• Online Publication Date: Feb 9, 2013
• Publication Date: Apr 11, 2013
• Deposit Date: Jun 15, 2023
• Journal: Monthly Notices of the Royal Astronomical Society
• Print ISSN: 0035-8711
• Electronic ISSN: 0035-8711
• Publisher: Oxford University Press
• Peer Reviewed: Peer Reviewed
• Volume: 430
• Issue: 3
• Pages: 2169-2187
• DOI: https://doi.org/10.1093/mnras/stt038
• Keywords: Space and Planetary Science; Astronomy and Astrophysics; stars: early-type, stars: emission-line; Be; dust; extinction; ISM: structure; Galaxy: structure