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Dello Russo N.,Johns Hopkins University | Vervack R.J.,Johns Hopkins University | Weaver H.A.,Johns Hopkins University | Lisse C.M.,Johns Hopkins University | And 8 more authors.
Icarus | Year: 2013

We obtained high-resolution (λ/Δλ∼28,000) infrared spectra of Comet 103P/Hartley 2 on UT 2010 November 4.6 using the NIRSPEC spectrometer at the W.M. Keck Observatory. Here we present spectra of Hartley 2 between 2.832 and 3.639μm (3531-2748cm-1), representing the most complete high-resolution infrared survey of a Jupiter-family comet to date in this wavelength region. We have tabulated rest frequencies, line fluxes, line signal-to-noise ratios and line widths for all detected emissions. Fluorescence models, published line lists and laboratory spectra were used to obtain molecular assignments for detected emissions. Multiple lines of the following species were detected in Hartley 2: H2O, OH, CH3OH, C2H6, HCN, C2H2, H2CO, NH3 and NH2. All identified species seen in this survey have been previously detected in comets. There were 364 distinct emission features present in these spectra, of which 36 were unidentified. We compare the spectrum of Hartley 2 to chemically different Jupiter-family Comets 73P/Schwassmann-Wachmann 3-B and 17P/Holmes in order to obtain additional information on the characteristics of unknown lines through the comparison of relative line fluxes for corresponding emissions in these comets. For the strongest unidentified emissions, additional information was also obtained through a comparison of their spatial distributions in the coma to that of known emission features in Hartley 2. This spectral survey of Hartley 2 provides detailed information about its overall volatile chemistry, provides a comparison to past and future high-resolution infrared datasets, and further characterizes the most promising spectral regions for future molecular searches in comets. © 2012 Elsevier Inc. Source


Kawakita H.,Kyoto Sangyo University | Kobayashi H.,Kyoto Sangyo University | Dello Russo N.,Johns Hopkins University | Vervack R.J.,Johns Hopkins University | And 9 more authors.
Icarus | Year: 2013

We conducted high-dispersion spectroscopic observations of Comet 103P/Hartley 2 in the near-infrared wavelength region using the Keck II telescope with NIRSPEC. We obtained observations on four dates, with the last observations performed during the EPOXI closest approach. For this work we focus on the observations performed on UT 2010 October 17 and 21, while observations carried out on UT 2010 September 16 and November 4 have been reported elsewhere. On all dates the spatial distributions in the coma of C2H6, HCN and C2H2 were similar to each other and consistent with the CN-jet morphology observed from optical observations. The spatial distributions in the coma of H2O and CH3OH were also similar to each other, but were generally different from C2H6, HCN and C2H2. There might be two distinct phases of ice in Comet Hartley 2; one is enriched in H2O and CH3OH, and another is enriched in more volatile species (C2H6, C2H2, and HCN). It is possible that highly volatile species like C2H6 were segregated from the H2O matrix when warmer conditions were prevalent. We summarize our spectroscopic observations and report absolute production rates and mixing ratios of parent volatiles. There was no evidence of any significant diversity in the mixing ratios of parent volatiles on different dates. Comet Hartley 2 was normal in CH3OH/H2O, C2H6/H2O, C2H2/H2O, NH3/H2O but depleted in H2CO/H2O and CH4/H2O. OPRs of H2O in Comet Hartley 2 measured in its 2010 apparition were consistent with those observed by the Infrared Satellite Observatory in 1997. © 2012 Elsevier Inc. Source


Kawakita H.,Kyoto Sangyo University | Russo N.D.,Johns Hopkins University | Vervack Jr. R.,Johns Hopkins University | Kobayashi H.,Kyoto Sangyo University | And 12 more authors.
Astrophysical Journal | Year: 2014

We performed high-dispersion near-infrared spectroscopic observations of comet C/2010 G2 (Hill) at 2.5 AU from the Sun using NIRSPEC (R ≈ 25,000) at the Keck II Telescope on UT 2012 January 9 and 10, about a week after an outburst had occurred. Over the two nights of our observations, prominent emission lines of CH4 and C2H6, along with weaker emission lines of H2O, HCN, CH3OH, and CO were detected. The gas production rate of CO was comparable to that of H2O during the outburst. The mixing ratios of CO, HCN, CH4, C 2H6, and CH3OH with respect to H2O were higher than those for normal comets by a factor of five or more. The enrichment of CO and CH4 in comet Hill suggests that the sublimation of these hypervolatiles sustained the outburst of the comet. Some fraction of water in the inner coma might exist as icy grains that were likely ejected from nucleus by the sublimation of hypervolatiles. Mixing ratios of volatiles in comet Hill are indicative of the interstellar heritage without significant alteration in the solar nebula. © 2014. The American Astronomical Society. All rights reserved.. Source


Dello Russo N.,Johns Hopkins University | Vervack R.J.,Johns Hopkins University | Kawakita H.,Kyoto Sangyo University | Kobayashi H.,Kyoto Sangyo University | And 6 more authors.
Icarus | Year: 2014

Volatile abundances in Jupiter-family Comet 81P/Wild 2 were measured on four dates in February and March 2010 using high-dispersion (λδλ~2.5×104) infrared spectroscopy with NIRSPEC at the W.M. Keck Observatory. H2O was detected on all dates, including measurements on UT March 29 of lines from the ν2+ν3-ν2 hot-band not previously targeted in comets. C2H6 and HCN were detected on three dates, and CH3OH was detected on one date. Tentative detections or upper-limits are reported for CH3OH on other dates, as well as for C2H2, H2CO, and NH3. Abundances of all species relative to H2O are in the typical range with the exception of CH3OH, which is depleted compared to other comets. Gas production was significantly higher in late February than in late March. Rotational temperatures were determined for H2O on UT February 22 and 23 and found to be about 30-40K. The spatial distributions of H2O, C2H6, and CH3OH are all symmetric and similar to the spatial distribution of the dust continuum. H2O abundances from this work are compared to other measurements from both the 1997 and 2010 apparitions. There is no clear evidence of a change in overall gas productivity between the two apparitions within measurement accuracy. Abundances of C2H2, C2H6, HCN and NH3 are consistent with these species being the primary parents of C2, CN, NH and NH2 as measured at optical wavelengths. Although optically classified as carbon-chain depleted, Wild 2 appears more chemically similar in parent volatile chemistry to carbon-chain typical comets; however, we note that in the small sample of Jupiter-family comets measured to date, each comet is chemically distinct. © 2014 Elsevier Inc. Source


Dello Russo N.,Johns Hopkins University | Vervack R.J.,Johns Hopkins University | Lisse C.M.,Johns Hopkins University | Weaver H.A.,Johns Hopkins University | And 8 more authors.
Astrophysical Journal Letters | Year: 2011

We report time-resolved measurements of the absolute and relative abundances of eight parent volatiles (H2O, CH3OH, C 2H6, C2H2, NH3, HCN, H2CO, and HC3N) in the coma of 103P/Hartley 2 on UT 2010 November 4, the date the EPOXI spacecraft made its closest approach to the comet, using high-dispersion infrared spectroscopy with NIRSPEC at the W. M. Keck Observatory. Overall gas and dust production increased by roughly 60% between UT 10:49 and 15:54. Differences in the spatial distributions of species in the coma suggest icy sources of different composition in the nucleus of 103P/Hartley 2. However, differences in the relative abundances of species with time are minor, suggesting either internal compositional heterogeneity in 103P/Hartley 2 is small compared with the diversity of chemistry observed within the comet population, or more significant heterogeneity exists on scales smaller than our spatial resolution. Observations contemporaneous with the EPOXI encounter test how compositional heterogeneity over the surface and the inner coma of a comet manifests itself in remote-sensing observations of the bulk coma. © 2011. The American Astronomical Society. All rights reserved. Source

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