A COLD MASSIVE INTERSTELLAR CLOUD WITHIN 120 PARSECS OF THE SUN - KI OPTICAL AND HI RADIO OBSERVATIONS

We first discovered the presence of a particularly massive cloud in th e neighborhood of the Sun, close to the Galactic plane in the directio n of Perseus, toward l= 150 degrees, b = -10 degrees, using interstell ar absorption by the 7699 Angstrom resonance line of K I (Trapero et a l. 1992). In the present investigation we show the results of mapping the cloud in the 21 cm line of H I, supplemented by further K I observ ations. This combination is particularly effective, since the K I obse rvations give us distances, within close limits, and accurate velociti es of the single strong interstellar component detected along each lin e of sight, which enables us to identify the cloud as seen in absorpti on in the H I spectra, from among many emission components due to more distant clouds in the plane. The absorption spectra in H I at 21 cm c an then be used to find temperatures and to carry out more comprehensi ve mapping than using K I. We find that the cloud has kinetic temperat ures going down to 30 K, densities in the range up to 70 cm(-3), a dia meter of similar to 15 pc, and a mass of some 1300 M(.). The cloud is a good candidate to contain a molecular core.