15 April 2004
15 April 2004
Speaker: Lucy Ziurys (Steward Observatory)
New Trends in Interstellar Chemistry: From Nucleosynthesis to Nucleic Acids
The field of molecular astrophysics has progressed remarkably over the past 30 years, primarily through millimeter and sub-millimeter observations. Despite this evolution, there are still many interesting questions in astrochemistry that have yet to be addressed. One of these is the fate of refractory elements, in particular the metals (in the chemists?s sense). Although many of these elements have high cosmic abundances, it is uncertain whether they are entirely contained in dust grains, or have a significant gas-phase component, particularly in molecular (i.e. dense) material. Another problem is concerns the ultimate complexity of gas-phase interstellar chemistry. While a variety of carbon-bearing species have been observed in molecular clouds that contain the basic organic functional groups, it is uncertain if this unusual synthesis can create biologically-relevant compounds. Furthermore, it is unclear if such species can be accurately identified in the interstellar mediu!
m, even if they do exist.
Using a combined approach of millimeter/sub-millimeter observations and high-resolution laboratory spectroscopy, we have begun to examine these questions. In conjunction with laboratory measurements, we have been systematically searching for new metal-bearing molecules in interstellar and circumstellar gas, primarily using the facilities of the Arizona Radio Observatory. Curiously, metal cyanides such as AlNC and KCN appear to be the preferred molecular carriers of the metallic elements in the late-type carbon star, IRC+10216. We have also been conducting a survey towards AGB envelopes for such molecules, and have found that they are not uncommon. In some cases, metal isotope ratios have been established, which can help constrain models of nucleosynthesis.
Studies have also begun examining the possible existence of simple sugars in the ISM, leading to ribose, combining new laboratory measurements and observations. This work is being done in conjunction with LAPLACE (Life And PLanets Astrobiology CEnter), the new Astrobiology initiative at the University of Arizona. Do the basic ingredients of life actually come from interstellar clouds ? This problem and ways to approach it quantitatively will be discussed.
References for students:
More Metal Cyanide Species: Detection of AlNC(X1?+) Towards IRC+10216, L.M.
Ziurys et al. Ap.J. 564, L45 (2002)
The Salty Scrambled Egg: Detection of NaCl Toward CRL2688, J. L. Highberger,
K.Thomsen, P.A. Young, D. Arnett, and L.M. Ziurys, Ap.J. 593, 393 (2003)
Detection of MgNC in CRL618: Tracing Metal Chemistry with AGB Evolution, J.L. Highberger and L.M. Ziurys, Ap.J. 597, 1065 (2003)
Further Studies of 3d Transition Metal Cyanides: The Pure Rotational Spectrum of NiCN(X2?i), P.M. Sheridan and L.M. Ziurys, J.Chem.Phys. 118, 6370 (2003)