The origins and evolutionary status of B stars found far from the galactic plane

Since the discovery of faint blue stars at high galactic latitudes, which spectroscopically appear to be similar to Population I B stars, a debate has raged about their origin and characteristics. Their faint apparent magnitudes have been interpreted to place many of them several kiloparsecs above the galactic plane in the halo. Some have been thought to be too far from the galactic plane and moving too slowly to be young B stars which were ejected from the star forming regions of the disk. A sample of these stars, taken from the Hipparcos catalog, was observed at high spectroscopic dispersion (R = 60000), analyzed for chemical composition, traced back in time along their trajectory in the galactic potential using their full computed space velocities (determined from radial velocity and proper motions), and investigated for other oddities including infrared flux excesses.; The analysis shows that all the stars in the sample are runaway Population I B stars or old evolved stars. None are Population I B stars that formed in situ in the galactic halo. The runaway Population I B stars have kinematics and chemical compositions which are consistent with their formation in, and ejection from the star forming regions of the galactic disk. The low mass old evolved stars show abundance patterns affected by stellar evolution and potential conflicts between their time of flight and main-sequence lifetime. This study shows that the population of high galactic latitude B stars is composed of roughly 70% runaway Population I stars and 30% old evolved stars. The data also show that there are fewer slow rotating runaway Population I B stars than expected from surveys of Population I B stars in the disk. Additionally, at least two nearby metal-rich BHB stars and several rapidly rotating PAGB stars have been identified.