B STAR 18 KPC ABOVE THE GALACTIC PLANE

In 1983 and 1984, the faint high galactic latitude star PG 0832+676 was observed at high spectral dispersion on the 5-m Hale telescope. From these observations PG 0832+676 appeared to be a normal early-type star rather than a hot subdwarf, which is how it had previously been classified.

Although astronomers were disappointed that their observations did not bear on the problem which they were investigating, they decided to take further spectra using the Isaac Newton Telescope. These data were analysed using model atmosphere techniques, and showed that PG 0832+676 is indeed a normal Population I OB-type star abundances for the heavier elements.

The galactic co-ordinates of PG 0832+676 and its apparent magnitude imply that the star lies at a distance of 18 kpc from the plane of the Galaxy. The questions that occurs is: what is a normal B-dwarf doing up in the halo? With their short lifetimes, B stars which form from gas in the galactic low velocity of the star coupled with its laerge z-distance effectively rules out the possibility that it formed in the disc and was then ejected into the halo. PG 0832+676 therefore becomes a member of a rare set of stars that appear to have been formed in the halo itself.

Where did the gas out of which it was formed come from? Was the star formed from the high velocity clouds which provoked the observations in the first place? The model atmospheres fitted to the observations indicate that the abundances in PG 0832+676 are "normal ", and typical of B stars formed from galactic plane material. So astronomers conjectures that the star is evidence for the transportation of gas from the galactic plane into the halo, in a process still occuring at the present time. This is reminiscent of the idea known as the "galactic fountain" in which supernovae energise interstellar material into the galactic halo.