Events in Physics
Roberto Raddi: Emission line stars in and beyond the Perseus Arm
The Isaac Newton Telescope (INT) Photometric H-halpha Survey of the Northern Galactic plane (IPHAS, Drew et al. 2005) is a powerful tool for selecting effectively emission line stars. More than 50% of the IPHAS emitters are suggested to be classical Be stars (Corradi et al., 2008). We proposed this class of stars, which are intrinsically bright and relatively young (< 100 Myr old), as novel structure tracers of the Milky Way disc. The focus of the talk is on a sub-sample of 67 classical Be stars that are drawn out of our larger sample of 248 newly uncovered classical Be stars, in a section of the Galactic disc towards the Perseus Arm. I will present the optical spectroscopic follow-up and the spectral classification of the
sample. I will discuss the determination of interstellar reddenings and the problems concerning it, along with the assessment of spectroscopic parallaxes.
The discussion will focus on the study of the spatial distribution of the sample. The stars are confirmed to be distant classical Be stars, found at heliocentric distances ranging between ~2 kpc and ~12 kpc. However, the errors on the distances are too large to allow statistical distinction between models
placing the stars in the spiral arms or in a smooth exponential declining distribution. The total sample of 248 objects doubles the number of known classical Be stars in this part of the Galactic plane and it is offered for more exploitation in future, when Gaia parallaxes will be available.