Other
Scientific paper
Mar 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008sptz.prop50437l&link_type=abstract
Spitzer Proposal ID #50437
Other
Scientific paper
We have recently discovered extraordinarily high-J pure-rotational OH (v=0) emission in the young protostellar outflow HH211 as part of a Spitzer survey of protostars in the young cluster IC348. The high-res IRS spectrum shows an exceptionally rich sequence of high-J OH emission with a total number of 30 detected lines covering pure rotational transitions with upper levels J'=69/2 to 15/2. The highest excited transition has an upper state energy E/hc of almost 19,600cm^-1 (E/k about 28,000K) above the ground level. This is to our knowledge by far the highest rotational OH excitation observed to date. In addition, HH211 shows several pure rotational water transitions, H2 S(0) to S(7), HD R(3) to R(6), and atomic fine-structure lines from Fe+, Si+, Ne+, S, and Cl. This new discovery provides access to a new regime of density and temperature in a strong shock. For the first time, highly excited OH can be studied spatially resolved and in combination with H2, HD, H2O, and the complete range of atomic tracers in the Spitzer IRS range. Shock-driven chemistry models predict that OH primarily forms in a high temperature environment from endothermic reactions of atomic oxygen and H2, followed by further reaction with H2 to form water. This crucial reaction sequence forms two of the main coolants in molecular shocks, OH and H2O. The detection of highly excited OH provides a new probe to study the initiation of this sequence in the high excitation regions of interstellar shocks and a critical test for existing shock models. We therefore propose to survey a carefully selected sample of Herbig-Haro shocks and jets. Our primary aim is to find further examples of highly excited OH occurring together with H2O and H2 in protostellar outflows and to determine the physical conditions that lead to the formation of high-J OH. This will provide new insights into the high-temperature chemistry and the high observed OH/H2O abundances associated with interstellar shocks.
Black John Harry
lada Charles
Muench August A.
Tappe Achim
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