Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009dps....41.1514v&link_type=abstract
American Astronomical Society, DPS meeting #41, #15.14
Astronomy and Astrophysics
Astronomy
Scientific paper
Before the advent of high-resolution IR instruments in the 1990s, low to moderate-resolution spectra were the only means of studying comet emissions at IR wavelengths but have been somewhat overlooked since then. Nevertheless, moderate-resolution IR spectroscopy remains a valuable technique for probing comet composition, and we have conducted a series of observations using the SpeX instrument (λ/Δλ 2500) at NASA's IRTF. We present SpeX observations of several comets that are chemically distinct and/or from different dynamical classes to demonstrate the benefits of moderate-resolution IR spectra in understanding comet composition.
Infrared spectra of comets generally contain a veritable forest of spectral lines in the so-called "organics” region between 3.2-3.6 microns, resulting in strong, broad organic emission features from many species at the resolving power provided by SpeX. In particular, there are three emission features that are often present in these spectra: 1) the X-CH stretch feature spanning roughly 3.3-3.45 microns due primarily to gas-phase organics emission from many species, 2) the emission near 3.52 microns due to the CH3OH ν3 band, and 3) the 3.28-micron feature potentially attributed to polycyclic aromatic hydrocarbons (PAHs). Additional features between 2.8-3.0 microns have been detected in dry atmospheric conditions and are attributable to H2O hot-band emissions. Whereas high-resolution spectroscopy can isolate emissions from individual molecules, allowing better chemical interpretation of broad organic features seen with SpeX, the generally limited spectral grasp of high-resolution measurements allows only a small part of this important region to be sampled at any given time. Observing time with SpeX is also generally more accessible than observations with high-resolution IR spectrometers on large telescopes. Therefore, SpeX observations complement high-resolution observations by providing a general overview of the carbon-chain chemistry of comets, enabling the overall organic emission from comets to be monitored as a function of heliocentric distance.
Biver Nicolas
Bockelée-Morvan Dominique
Crovisier Jacques
Dello Russo Neil
Vervack Ronald J. Jr.
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