FLASH: FLITECAM Limits on the Abundance of Silicate Hydrates in the ISM

Principal Investigator

Jean Chiar

Proposal ID

01_0096

Category

ISM AND CIRCUMSTELLAR MATTER

Keywords

• DUST

Abstract

The Science Vision for SOFIA identifies the Interstellar Medium (ISM) as a key area where SOFIA is well poised to make substantial contributions. As the SOFIA Vision points out, dust undergoes constant recycling in the ISM, from its creation in stellar outflows to its incorporation into protoplanetary disks. The observations we propose here will enable us to better understand the evolution of the silicate dust component, specifically the processing it undergoes in the ISM. The structure of the silicate, i.e., whether it is crystalline or amorphous, is a clue to its past evolution. In order to explain the extremely low abundance of crystalline silicates in the diffuse ISM, the process that amorphizes the stardust silicates must be efficient. Experiments show that one of the most efficient processes likely to occur in the diffuse ISM is irradiation by low-energy ions. This process will not only amorphize the grains, but also lead to formation of OH bonds within the grains. Just how much the grains are hydrated can be carefully measured by the SOFIA FLITECAM observations we propose here. To this end, we propose to use FLITECAM Grisms A and C to observe the OH stretching mode in hydrated silicates in the 2.216 to 3.467 micron region. Our targets are three bright highly reddened field stars that probe diffuse ISM dust. These observations are impossible from ground-based facilities due to telluric CO2 absorption, and existing spectra are only moderately reddened and/or of poor quality. The high S/N FLITECAM spectra will enable us to make a careful measurement of the actual hydration level of silicates, thus leading to a better understanding of the processes that affect silicates in the ISM.