AAS 198th Meeting, June 2001
Session 59. Galactic ISM
Display, Wednesday, June 6, 2001, 10:00am-7:00pm, Exhibit Hall

## [59.07] G28.17+0.05, A New Type of Cloud in the ISM?

A.H. Minter, F.J. Lockman (NRAO)

21 cm HI observations with the NRAO 140 Foot telescope have revealed a giant HI cloud (G28.17+0.05) in the Galactic plane that has unusual properties. The cloud is 150 pc in diameter, is at a distance of 5 kpc, and contains as much as 105 M\sun of atomic hydrogen. The cloud consists of a cold core, T ~40~K, and a hotter outer envelope, T \ge 200~K. There is no observable difference in the HI line widths, ~7 km~s-1, between the core and the envelope. Anomalously-excited 1720 MHz OH emission, with a similar line width, is associated with the core of the cloud. The cloud core also contains 12CO emission which indicates that most of the cloud mass is in molecules. The total mass of the cloud is > 2 \times 105 M\sun. The cloud has only a few sites of current star formation. If similar clouds are associated with other observed sites of anomalously-excited 1720 MHz OH emission, there may be as many as 100 more of these objects in the inner galaxy.