Water in low-mass star-forming regions with Herschel . HIFI spectroscopy of NGC 1333
de Graauw, Th.; Liseau, R.; Braine, J.; Codella, C.; Dominik, C.; Ossenkopf, V.; Bontemps, S.; Benedettini, M.; van Dishoeck, E. F.; Bachiller, R.; Larsson, B.; Bergin, E. A.; Blake, G. A.; Cernicharo, J.; Daniel, F.; Encrenaz, P.; Goicoechea, J. R.; Johnstone, D.; Pearson, J. C.; Plume, R.; Stutzki, J.; Olberg, M.; Melnick, G.; Tielens, A. G. G. M.; Risacher, C.; Fuente, A.; Benz, A. O.; Bruderer, S.; van der Tak, F.; Wyrowski, F.; Shipman, R.; Beintema, D.; Dieleman, P.; Fich, M.; Herpin, F.; de Jonge, A.; McCoey, C.; Whyborn, N.; Bjerkeli, P.; Marseille, M.; Nisini, B.; Caselli, P.; Lis, D.; Kristensen, L. E.; Hogerheijde, M. R.; Tafalla, M.; Giannini, T.; Neufeld, D.; Saraceno, P.; Herczeg, G. J.; Wampfler, S. F.; Doty, S. D.; Baudry, A.; di Giorgio, A. M.; Helmich, F.; Jacq, T.; Jørgensen, J. K.; Parise, B.; Santiago-García, J.; van Kempen, T. A.; Visser, R.; Yıldız, U. A.; Roelfsema, P.; Brinch, C.; Deul, E.; Kaufman, M. J.; Liu, F. -C.
Netherlands, Germany, United States, Denmark, Switzerland, Spain, France, Italy, Sweden, United Kingdom, Canada, Chile
Abstract
“Water In Star-forming regions with Herschel” (WISH) is a key programme dedicated to studying the role of water and related species during the star-formation process and constraining the physical and chemical properties of young stellar objects. The Heterodyne Instrument for the Far-Infrared (HIFI) on the Herschel Space Observatory observed three deeply embedded protostars in the low-mass star-forming region NGC 1333 in several H_216O, H_218O, and CO transitions. Line profiles are resolved for five H_216O transitions in each source, revealing them to be surprisingly complex. The line profiles are decomposed into broad (>20 km s-1), medium-broad (~5-10 km s-1), and narrow (<5 km s-1) components. The H_218O emission is only detected in broad 110-101 lines (>20 km s-1), indicating that its physical origin is the same as for the broad H_216O component. In one of the sources, IRAS4A, an inverse P Cygni profile is observed, a clear sign of infall in the envelope. From the line profiles alone, it is clear that the bulk of emission arises from shocks, both on small (⪉1000 AU) and large scales along the outflow cavity walls (~10 000 AU). The H2O line profiles are compared to CO line profiles to constrain the H2O abundance as a function of velocity within these shocked regions. The H2O/CO abundance ratios are measured to be in the range of ~0.1-1, corresponding to H2O abundances of ~10-5-10-4 with respect to H2. Approximately 5-10% of the gas is hot enough for all oxygen to be driven into water in warm post-shock gas, mostly at high velocities.
Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Tables 2 and 3 (page 6) are only available in electronic form at http://www.aanda.org