THE UNITED KINGDOM INFRARED TELESCOPE
ANNUAL REPORT
1997

2.2. Star Formation, the Interstellar Medium, and Stellar Evolution

UKIRT continues to make significant contributions to the study of brown dwarfs. Based on JHK photometry Prof. Richard Jameson and co-workers identified approximately 20 new brown dwarfs in nearby open clusters, more than doubling the number of known brown dwarfs. Dr Keith Noll and collaborators detected carbon monoxide in the 5 m spectrum of the cool (T1200 K) brown dwarf Gl229B; Dr. Maria Teresa Ruiz and her team's IR spectrum of the T2000 K lithium-confirmed brown dwarf Kelu-1 demonstrated that dust grains must be present in the atmospheres of this, and probably other, brown dwarfs.

The molecular ion H, which in 1996 was detected for the first time in the dense interstellar medium, was found by Dr. Thomas Geballe and co-workers in the diffuse interstellar medium along the line-of-sight to the galactic centre and to Cygnus OB2 No. 12. The surprisingly large column densities of H imply that either it exists over unexpectedly long path lengths, the ionization rate of H by cosmic rays is considerably higher than expected, or the rate of destruction of H is considerably less than current predictions.