My research has continued to focus on molecular astrophysics. My local collaborators are Nick Indriolo (assistant research scientist at JHU) and Paule Sonnentrucker (STScI). Our motivation is that—with careful interpretation—unique information, of general astrophysical interest, can be obtained from observations of astrophysical molecules.
My recent efforts have been focused in the following areas:
- Using the Spitzer Space Telescope to study warm, shocked-heated gas in the interstellar medium. Such gas is often present where supernova explosions or supersonic outflows from young stars impact the surrounding gas. Spectroscopic observations of supernova remnants and regions of active star formation—obtained with Spitzer—reveal mid-infrared line emissions from gaseous H2, H2O, HD, CO2, C2H2 and a large number of atomic ions; absorption by CO2 ice is also widely observed. These observations have allowed us to understand the physical and chemical effects of interstellar shock waves; the deuterium abundance in dense molecular clouds; and the thermal history of the interstellar gas.
- Studying interstellar and circumstellar molecules using the Herschel Space Observatory, an ESA cornerstone mission launched in 2009, and the Stratospheric Observatory for Infrared Astronomy (SOFIA), a NASA airborne observatory. I am involved with the HEXOS, PRISMAS, WADI, HIFISTARS, and WISH Guaranteed Key Time programs on Herschel, along with several Open Time programs on Herschel and SOFIA.
- Probing the chemistry of interstellar halogen elements. Fluorine is unique among the elements of the periodic table in undergoing an exothermic reaction with H2, the dominant constituent of interstellar molecular clouds. The product of that reaction, hydrogen fluoride, is widely observable with the Herschel Space Observatory, and an important probe of molecular clouds. Our theoretical model for the chemistry of fluorine-bearing molecules in the interstellar gas has motivated the first astronomical detection of the fluoromethylidynium (CF+) cation, which sounds exotic but is isoelectronic with CO. Herschel observations of chlorine-bearing molecules have led to the first detections of the HCl+ and H2Cl+, which show puzzling abundances that are unexpectedly large.
We are grateful for generous funding from the NASA Herschel Science Center (NHSC).