NOAO >   Observing Info >   Approved Programs >   2013A-0439

Small NOAO Logo

Proposal Information for 2013A-0439


PI: Diane Wooden, NASA Ames Research Center, dwooden@mac.com
Address: NASA Ames Research Center, Diane Wooden/Mail Stop 245-3, Bldg. 245, Rm. 224, P.O. Box 1, Moffett Field, CA, 94035-0001, United States

CoI: Mike Kelley, University of Maryland
CoI: Charles (Chick) Woodward, University of Minnesota
CoI: Jason Cook, SwRI
CoI: David Harker, UC San Diego
CoI: Neil Dello Russo, Johns Hopkins University APL
CoI: Ron Vervack, Johns Hopkins University APL
CoI: Aigel Li, University of Missouri

Title: Searching for organic nano-grains using GNIRS spectra of the naked eye comet C/2011 L4 (PanStarrs)

Abstract: Identifying organic species in comets is key to constraining the formation pathways for the robust and complex organics that pervade the interstellar media (ISM) of galaxies. Two mysteries that surround the study of organic grain materials in cometary comae: Where are the aromatic carbon macromolecules or PAHs that are so ubiquitous in the diffuse ISM and in meteoritic organics? Where are the aliphatic carbon materials that produce the 3.4 um absorption feature in the UV-protected dense ISM? With GNIRS, we measured the 3.3 um aromatic and 3.4 um aliphatic emission bands with unprecedented sensitivity and spectral resolution in comet 103P/Hartley 2 (i.e., EPOXI Mission target). The band shapes and ratios are consistent with these features arising from the same organic carrier. The QPAH/QH2O ratio is similar to 5 comets measured in the 1990’s and suggests the carrier is associated with the water ice and not the refractory grains. Lab measurements of comet samples, however, reveal that there are separate submicron regions of aromatic and aliphatic organics, that the aliphatics ubiquitously coat the submicron silicates in cometary aggregates, and that the PAHs and aliphatics formed or were inherited prior to refractory grain aggregation and incorporation into comet nuclei. We propose to obtain two epochs of GNIRS spectra of the relatively rare ‘naked eye’ comet C/2011 L4 (PanStarrs) to assess the variation of 3.3 to 3.4 um band ratios between comets, to use the long-slit to see if the 3.3/3.4 µm ratio changes with UV exposure in the coma on time-scales of 0.25–1.5 day, and observe at two different heliocentric distances to verify that the organic carrier’s temperature is constant and the band intensities decline proportional with declining solar flux as expected for fluorescing macro-molecules or thermally fluctuating organic nano-sized grains.


National Optical Astronomy Observatory, 950 North Cherry Avenue, P.O. Box 26732, Tucson, Arizona 85726, Phone: (520) 318-8000, Fax: (520) 318-8360



NOAO >   Observing Info >   Approved Programs >   2013A-0439

noaoprop-help@noao.edu

Small NOAO Logo