A SEARCH FOR CO(2-1) EMISSION FROM THE GLOBULAR-CLUSTER M15

A search for 230-GHz CO(2-1) emission in the direction of the globular cluster M15 has been made with the 15-m James Clerk Maxwell Telescope on Mauna Kea. A spectrum accumulated over a total integration time of 15 000 s shows no evidence of any CO(2-1) emission feature at the velocity of the cluster. The amount of gas that is expected to have been expelled by red giants into the intracluster environment since the most recent crossing of the Galactic plane by the cluster is in excess of 12 M(.). The upper limit placed on the mass of molecular gas in M15 by the JCMT observation is similar to 0.4 M(.). The upper limit to the combined mass of interstellar dust, and molecular H-2, neutral HI and ionized HII gas within M15 that has been placed by observations is similar to 3 M(.). Therefore some mechanism appears to have removed much of the expected interstellar medium from M15. In the particular case of this cluster, energy sources that might have promoted gas loss include ionizing radiation from X-ray binaries and UV-bright stars, and winds from millisecond pulsars and M dwarfs.