Physics
Scientific paper
Dec 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997hst..prop.7509b&link_type=abstract
HST Proposal ID #7509
Physics
Hst Proposal Id #7509 Interstellar Matter
Scientific paper
GHRS absorption spectra obtained for a nearby star located behind the complex of molecular clouds in Chamaeleon show that 10 cm^-2} is at large velocities {up to -50 km/s} compared to the main absorption component near v_lsr = 0 km/s. From the excitation of SiII and CII, we infer physical conditions { n_e 10 cm^-3 , T 1000K} which are unusual in a region where there is no ionizing star. The cooling rate in the 35Mum fine structure line of Si^+ alone is a factor 20 larger than the average cooling rate of the gas in the Solar Neighborhood. A large amount of kinetic energy is thus being deposited in this gas, possibly by a shock driven by infalling gas impacting onto the gas at 0 km/s. The line of sight was selected on the basis of IRAS data showing that the absorbing cloud has an exceptionally large abundance of small grains. The HST data shows that in the high velocity gas all of the Silicon is in the gas phase which suggests significant dust destruction. We propose to get high resolution absorption spectra for this unique sight-line to measure the abundance and excitation of Si, Fe, O, C and Mg. These measurements will be used to study physical conditions, gas energetics and dust destruction as a function of velocity. They should provide keys to the processes that heat the gas and disrupt dust grains and to the possible links between these processes.
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