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Project Progress

Molecules in Interstellar Cloud Cores:

Understanding the nature of the natal interstellar cloud is crucial to understanding the chemistry of the solar nebula, and hence the chemistry of the Sun and planets. Since that cloud no longer exists, it is necessary to study the cores of existing dense interstellar clouds where stars are forming. Moreover, since the physical conditions vary among and within such clouds, it is important to investigate the chemical and physical processes in a variety of such environments.

Irvine and colleagues in Korea have been studying molecular clouds in the vicinity of the center of our Milky Way Galaxy, where various energetic processes can influence the chemical composition of molecular clouds. As in some other regions of active star formation, overlapping clouds in the line of sight and the large optical depths of many spectral lines complicate the determination of chemical abundances and physical properties for individual clouds. One approach to this problem is to seek chemical tracers of particular properties. One such tracer is HNCO, which is not very abundant in typical molecular clouds. It presumably forms from the OCN^- ion, which can be liberated from icy grain mantles by shocks. Our observations of HNCO emission from the Sgr B2 cloud find evidence for an enhanced abundance of this species in an expanding ring of material, which seems to be colliding with the principal Sgr B2 cloud and triggering sequential star formation. It may be that HNCO will prove to be a useful tracer of such shock processes (Minh and Irvine, 2006).

Graduate student Jonathan Franklin and colleagues (Franklin et al., 2006) studied the distribution of H₂O in regions of massive star formation, using data from the Submillimeter Wave Astronomy Satellite (SWAS). The ground state transition of ortho-H₂O at 557 GHz was detected towards a number of molecular outflows. For 17 of these outflows an analysis of the H₂O emission was compared to the distribution of ¹²CO and ¹³CO as obtained with the University of Massachusetts’ 14-m diameter radio telescope at the Five College Radio Astronomy Observatory. Since the passage of a strong shock can greatly enhance the H₂O abundance, either through the evaporation of ice mantles or by permitting neutral-neutral gas-phase chemical reactions to proceed, it is expected that the gas-phase H₂O abundance can be used to probe how the molecular gas is accelerated in such regions. For a subset of the observed outflows, results from the Infrared Space Observatory (ISO) on the far-infrared lines of CO and H₂O are also available. We find that the warm gas probed by ISO has a greatly enhanced H₂O abundance; however, this warm gas represents less that 1% of the total mass of outflowing gas. Most of the latter gas mass has a significantly lower abundance of o-H₂O relative to H₂, only10-7 to 10-6, suggesting that the gas has not been subjected to strong shocks. Since an enhanced H₂O abundance should persist for longer than the age of the outflow, our results suggest that the bulk of the outflowing molecular gas is accelerated slowly and not subjected to strong shocks.

The chemistry of comets:

Irvine is part of a team that has a pending proposal for Target of Opportunity observations of molecular emission lines from bright comets at millimeter/sub-millimeter wavelengths, using the JCMT on Mauna Kea. Although no useful data were obtained during the period of this report, the proposal remains active (Matthews et al., 2005).

Reviews and Conferences Related to Astrobiology:

Irvine presented an invited review of organic chemistry in the interstellar medium and in comets for the Fourteenth International Congress on the Origin of Life, the triennial meeting of the International Society for the Study of the Origin of Life (ISSOL), in Beijing in June, 2005 (Irvine, 2006). In addition, he was a co-author on a review on future perspectives in astrobiology in the concluding session of the conference (Ehrenfreund et al., 2006).

Irvine attended the annual meeting of the Division for Planetary Sciences of the American Astronomical Society in Cambridge, UK, in September 2005, and presented a poster on applications of the Large Millimeter Telescope to astrobiology (Irvine and Schloerb, 2005).

Facilities:

The Large Millimeter Telescope (LMT) is a joint project of the University of Massachusetts Amherst and the Instituto Nacional de Astrofisica, Optica y Electronica (INAOE) in Tonantzintla, Puebla, Mexico. The LMT will be the largest single-dish telescope in the world operating at short millimeter wavelengths when it is completed in 2008-09. It will be a powerful instrument for various fields within astrobiology, including the study of the chemistry and physics of comets, other primitive bodies in the solar system, planetary and satellite atmospheres, and the interstellar medium. Irvine continued as Chair of the Management Working Group and as a member of the Science Working Group for the Large Millimeter Telescope Observatory (LMTO), the US-Mexican organization that will operate the LMT. Irvine and Mexican colleagues completed a short book about the LMT project (Irvine, Carrasco, and Aretxaga, 2005). A Spanish version is nearing completion (Carrasco, Aretxaga, and Irvine, 2006). Irvine is working to insure that the telescope will indeed be a powerful instrument for research in astrobiology.

Outreach:

Irvine continued to participate in the University of Massachusetts interdisciplinary course for non-science honors students entitled “Cosmos to Humanity: From the Big Bang to the Space Age”. The theme of the course is astrobiology/evolution, beginning with the evolution of the universe and continuing with the formation and evolution of the solar system, the origin and evolution of life, life in extreme environments, the evolution of complex life, the origin and evolution of humans, and the search for life elsewhere in the universe. Irvine continued development of several lectures with associated reading material and web-based units on the topics of cosmology, nucleosynthesis, organic matter in galaxies, the origin of the solar system, environments in the solar system for life, and extrasolar planets and the search for life in the universe.

The initial course for astronomy majors in the Five College Astronomy Department, which links Amherst, Smith, Mount Holyoke and Hampshire Colleges and the University of Massachusetts, is a course on the solar system (Astronomy 223, “Planetary Science”). Irvine has been adapting this course into one on astrobiology by linking the investigation of objects in the solar system to the search for extraterrestrial life. This is a particularly appropriate place for astrobiology in our curriculum, since the course attracts students from all five institutions and has a good gender balance.