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