► We sampled in Comet C/2007 W1 (Boattini) 11 molecular abundances, and retrieved three cosmogonic indicators. ► The abundance ratios of almost all trace volatiles are among the highest ever observed ...in a comet. ► The comet revealed a complex outgassing, with the polar species presenting very asymmetric spatial profiles. ► We interpret the emission profiles in terms of release from two distinct moieties of ice.
We measured the chemical composition of Comet C/2007 W1 (Boattini) using the long-slit echelle grating spectrograph at Keck-2 (NIRSPEC) on 2008 July 9 and 10. We sampled 11 volatile species (H
2O, OH
∗, C
2H
6, CH
3OH, H
2CO, CH
4, HCN, C
2H
2, NH
3, NH
2, and CO), and retrieved three important cosmogonic indicators: the ortho-para ratios of H
2O and CH
4, and an upper-limit for the D/H ratio in water. The abundance ratios of almost all trace volatiles (relative to water) are among the highest ever observed in a comet. The comet also revealed a complex outgassing pattern, with some volatiles (the polar species H
2O and CH
3OH) presenting very asymmetric spatial profiles (extended in the anti-sunward hemisphere), while others (e.g., C
2H
6 and HCN) showed particularly symmetric profiles. We present emission profiles measured along the Sun–comet line for all observed volatiles, and discuss different production scenarios needed to explain them. We interpret the emission profiles in terms of release from two distinct moieties of ice, the first being clumps of mixed ice and dust released from the nucleus into the sunward hemisphere. The second moiety considered is very small grains of nearly pure polar ice (water and methanol, without dark material or apolar volatiles). Such grains would sublimate only very slowly, and could be swept into the anti-sunward hemisphere by radiation pressure and solar-actuated non-gravitational jet forces, thus providing an extended source in the anti-sunward hemisphere.
Gas-phase molecules in cometary atmospheres (comae) originate primarily from (1) outgassing by the nucleus, (2) sublimation of icy grains in the near-nucleus coma, and (3) coma (photo)chemical ...processes. However, the majority of cometary gases observed at radio wavelengths have yet to be mapped, so their production/release mechanisms remain uncertain. Here we present observations of six molecular species toward comet 46P/Wirtanen, obtained using the Atacama Large Millimeter/submillimeter Array during the comet's unusually close (∼0.1 au) approach to Earth in 2018 December. Interferometric maps of HCN, CH3OH, CH3CN, H2CO, CS, and HNC were obtained at an unprecedented sky-projected spatial resolution of up to 25 km, enabling the nucleus and coma sources of these molecules to be accurately quantified. The HCN, CH3OH, and CH3CN spatial distributions are consistent with production by direct outgassing from (or very close to) the nucleus, with a significant proportion of the observed CH3OH originating from sublimation of icy grains in the near-nucleus coma (at a scale length Lp = 36 ± 7 km). On the other hand, H2CO, CS, and HNC originate primarily from distributed coma sources (with Lp values in the range 550–16,000 km), the identities of which remain to be established. The HCN, CH3OH, and HNC abundances in 46P are consistent with the average values previously observed in comets, whereas the H2CO, CH3CN, and CS abundances are relatively low.
(ProQuest: Formulae and/or non-USASCII text omitted)We report production rates for H sub(2) O and eight trace molecules (CO, C sub(2) H sub(6), CH sub(4), CH sub(3) OH, NH sub(3), H sub(2) CO, HCN, C ...sub(2) H sub(2)) in the dynamically new, Sun-grazing Comet C/2012 S1 (ISON), using high-resolution spectroscopy at Keck II and the NASA IRTF on 10 pre-perihelion dates encompassing heliocentric distances R sub(h)= 1.21-0.34 AU. Measured water production rates spanned two orders of magnitude, consistent with a long-term heliocentric power law Q... .Abundance ratios for CO, C sub(2) H sub(6), and CH sub(4) with respect to H sub(2) O remained constant with R sub(h) and below their corresponding mean values measured among a dominant sample of Oort Cloud comets. CH sub(3) OH was also depleted for R sub(h)> 0.5 AU, but was closer to its mean value for R sub(h)< or = 0.5 AU. The remaining four molecules exhibited higher abundance ratios within 0.5 AU: for R sub(h)> 0.8 AU, NH sub(3) and C sub(2) H sub(2) were consistent with their mean values while H sub(2) CO and HCN were depleted. For R sub(h)< 0.5 AU, all four were enriched, with NH sub(3), H sub(2) CO, and HCN increasing most. Spatial profiles of gas emission in ISON consistently peaked sunward of the dust continuum, which was asymmetric antisunward and remained singly peaked for all observations. NH sub(3) within 0.5 AU showed a broad spatial distribution, possibly indicating its release in the coma provided that optical depth effects were unimportant. The column abundance ratio NH sub(2)/H sub(2) O at 0.83 AU was close to the "typical" NH/OH from optical wavelengths, but was higher within 0.5 AU. Establishing its production rate and testing its parentage (e.g., NH sub(3)) require modeling of coma outflow.
► A tool to interpret very high-resolution IR profiles is presented. ► Direct Simulation Monte Carlo model was applied to Comet 73P/Schwassmann–Wachmann 3. ► Icy grains are needed to reproduce H2O ...column densities and rotational temperatures. ► Pure and dirty icy grains are considered. ► Electron-H2O collision rotational heating is not negligible.
Direct sublimation of a comet nucleus surface is usually considered to be the main source of gas in the coma of a comet. However, evidence from a number of comets including the recent spectacular images of Comet 103P/Hartley 2 by the EPOXI mission indicates that the nucleus alone may not be responsible for all, or possibly at times even most, of the total amount of gas seen in the coma. Indeed, the sublimation of icy grains, which have been injected into the coma, appears to constitute an important source. We use the fully-kinetic Direct Simulation Monte Carlo model of Tenishev et al. (Tenishev, V.M., Combi, M.R., Davidsson, B. 2008. Astrophys. J., 685, 659−677; Tenishev, V.M., Combi, M.R., Rubin, M. 2011. Astrophys. J., 732) to reproduce the measurements of column density and rotational temperature of water in Comet 73P-B/Schwassmann–Wachmann 3 obtained with a very high spatial resolution of ∼30km using IRCS/Subaru in May 2006 (Bonev, B.P., Mumma, M.J., Kawakita, H., Kobayashi, H., Villanueva, G.L. 2008. Icarus, 196, 241−248). For gas released solely from the cometary nucleus at a heliocentric distance of 1AU, modeled rotational temperatures start at 110K close to the surface and decrease to only several tens of degrees by 10–20 nucleus radii. However, the measured decay of both rotational temperature and column density with distance from the nucleus is much slower than predicted by this simple model. The addition of a substantial (distributed) source of gas from icy grains in the model slows the decay in rotational temperature and provides a more gradual drop in column density profiles. Together with a contribution of rotational heating of water molecules by electrons, the combined effects allow a much better match to the IRCS/Subaru observations. From the spatial distributions of water abundance and temperature measured in 73P/SW3-B, we have identified and quantified multiple mechanisms of release. The application of this tool to other comets may permit such studies over a range of heliocentric and geocentric distances.
We report production rates, rotational temperatures, and related parameters for gases in C/2013 R1 (Lovejoy) using the Near InfraRed SPECtrometer at the Keck Observatory, on six UT dates spanning ...heliocentric distances (R sub(h)) that decreased from 1.35 AU to 1.16 AU (pre-perihelion). We quantified nine gaseous species (H sub(2)O, OH*, CO, CH sub(4), HCN, C sub(2)H sub(6), CH sub(3)OH, NH sub(3), and NH sub(2)) and obtained upper limits for two others (C sub(2)H sub(2) and H sub(2)CO). Compared with organics-normal comets, our results reveal highly enriched CO, (at most) slightly enriched CH sub(3)OH, C sub(2)H sub(6), and HCN, and CH sub(4) consistent with "normal", yet depleted, NH sub(3), C sub(2)H sub(2), and H sub(2)CO. Rotational temperatures increased from ~50 K to ~70 K with decreasing R sub(h), following a power law in R sub(h) of -2.0 + or - 0.2, while the water production rate increased from 1.0 to 3.9 x 10 super(28) molecules s super(-1), following a power law in R sub(h) of -4.7 + or - 0.9. The ortho-para ratio for H sub(2)O was 3.01 + or - 0.49, corresponding to spin temperatures (T sub(spin)) > or =, slanted 29 K (at the 1sigma level). The observed spatial profiles for these emissions showed complex structures, possibly tied to nucleus rotation, although the cadence of our observations limits any definitive conclusions. The retrieved CO abundance in Lovejoy is more than twice the median value for comets in our IR survey, suggesting this comet is enriched in CO. We discuss the enriched value for CO in comet C/2013 R1 in terms of the variability of CO among Oort Cloud comets.
Water hot-band lines were detected in comets C/1999 H1 (Lee), C/1999 S4 (LINEAR), and C/2001 A2 (LINEAR) in the 2.9 mu m spectral region using high-dispersion ( lambda / Delta lambda similar to 2 x ...10 super(4)) infrared spectroscopy with NIRSPEC at the W. M. Keck Observatory. The density of H sub(2)O emissions in this spectral region, the spectral coverage and resolution of NIRSPEC, and fluorescence models developed for these hot bands enabled the determination of H sub(2)O production rates, rotational temperatures, and ortho-to-para ratios (OPRs) in these comets. Previous studies revealed clear diversity in the volatile organic chemistries of these comets, suggesting that they may have formed in different regions of the early solar nebula. The nuclear spin temperature of H sub(2)O as derived from its OPR is another possible indicator of cometary formation temperature and region. Nuclear spin temperatures for H sub(2)O were derived on one date in comet S4 and two dates in Lee and A2. Derived spin temperatures for H sub(2)O in these comets are greater than or equal to 30, 30 super(+) sub(-) super(1) sub(6) super(5), and 23 super(+) sub(-) super(4) sub(3) K for S4, Lee, and A2, respectively. Measurements are consistent with a possible link between nuclear spin temperatures and volatile abundances, but studies of more comets and continued improvements in water hot-band fluorescence models are needed to more stringently test this.
We report a sensitive search for deuterated water (HDO) in comet 8P/Tuttle using high-resolution spectroscopy at infrared (IR) wavelengths. The deuterium enrichment of cometary water is one of the ...most important cosmogonic indicators in comets. The ratio preserves information about the conditions under which comet material formed, and tests the possible contribution of comets in delivering water for Earth's oceans. Water (H2O) and HDO were sampled in comet 8P/Tuttle from 2008 January 27 to 2008 February 3 using the new IR spectrometer (Cryogenic Infrared Echelle Spectrograph) at the 8.2 m Antu telescope of the Very Large Telescope Observatory atop Cerro Paranal, Chile. Twenty-three lines of HDO were sampled near 3.7 is a subset of m, leading to a production rate of 4.73 ± 1.68 X 1025 s-1. Combining this value with the H2O production rate of 5790 ± 250 X 1025 s-1 provides a formal value of = 4.09 ± 1.45 X 10-4 in comet 8P/Tuttle. This value is larger by a factor of 2.62 ± 0.93 than Vienna Standard Mean Ocean Water, and is comparable to enrichment factors measured for three other Oort cloud comets. The technique described here provides unprecedented sensitivities, ultimately permitting us to routinely measure this prime cosmogonic indicator, even in comets having relatively modest gas production rate like 8P/Tuttle.
We report measurements of eight primary volatiles (H2O, HCN, CH4, C2H6, CH3OH, C2H2, H2CO, and NH3) and two product species (OH and NH2) in comet 103P/Hartley 2 using high-dispersion infrared ...spectroscopy. We quantified the long- and short-term behavior of volatile release over a three-month interval that encompassed the comet's close approach to Earth, its perihelion passage, and flyby of the comet by the Deep Impact spacecraft during the EPOXI mission. We present production rates for individual species, their mixing ratios relative to water, and their spatial distributions in the coma on multiple dates. The production rates for water, ethane, HCN, and methanol vary in a manner consistent with independent measures of nucleus rotation, but mixing ratios for HCN, C2H6, and CH3OH are independent of rotational phase. Our results demonstrate that the ensemble average composition of gas released from the nucleus is well defined and relatively constant over the three-month interval (September 18 through December 17). If individual vents vary in composition, enough diverse vents must be active simultaneously to approximate (in sum) the bulk composition of the nucleus. The released primary volatiles exhibit diverse spatial properties which favor the presence of separate polar and apolar ice phases in the nucleus, establish dust and gas release from icy clumps (and from the nucleus), and provide insights into the driver for the cyanogen (CN) polar jet. The spatial distributions of C2H6 and HCN along the near-polar jet (UT October 19.5) and nearly orthogonal to it (UT October 22.5) are discussed relative to the origin of CN. The ortho-para ratio (OPR) of water was 2.85 ? 0.20; the lower bound (2.65) defines T spin > 32 K. These values are consistent with results returned from the Infrared Space Observatory in 1997.
Formaldehyde (H sub(2)CO) was observed in comet C/2002 T7 (LINEAR) with spectral resolving power l/ lambda 62.5 x 10 super(4) using the Cryogenic Echelle Spectrometer (CSHELL) at the NASA Infrared ...Telescope Facility, on UT 2004 May 5, 7, and 9. The observations, which sampled emission in the u sub(1) and u sub(2) rovibrational bands between 3.53 and 3.62 km, represent the first spectrally resolved detection, at infrared wavelengths, of monomeric H sub(2)CO spanning a range of rotational energies. A comparison of measured line intensities with an existing fluorescence model permitted extraction of rotational temperatures and production rates. Two complementary approaches were used: (1) a correlation analysis that provided a direct global comparison of the observed cometary emissions with the model and (2) an excitation analysis that provided a robust line-by-line comparison. Our results validate the fluorescence model. The overall correlation coefficient was near or above 0.9 in our two principal grating settings. The excitation analysis provided accurate measures of rotational excitation (rotational temperature) on all three dates, with retrieved values of T sub(rot) clustering near 100 K. Through simultaneous measurement of OH prompt emission, which we use as a proxy for H sub(2)O, we obtained native production rates and mixing ratios for H sub(2)CO. The native production of H sub(2)CO varied from day to day, but its abundance relative to H sub(2)O, X sub(native), remained approximately constant within the errors, which may suggest an overall homogeneous composition of the nucleus. We measured a mean mixing ratio X sub(native) = (0.79 c 0.09) x 10 super(-2) for the three dates.
► We report chemical composition and spatial properties of parent volatiles in JFC 10P. ► We attempt to distinguish possible formation scenarios. ► We compare water production in its 2010 and 1988 ...apparitions. ► Our measurements were contemporaneous with a jet-like feature observed at optical wavelengths. ► There is some evidence of a distributed source in the coma (icy grains).
We present spectral and spatial information for major volatile species in Comet 10P/Tempel 2, based on high-dispersion infrared spectra acquired on UT 2010 July 26 (heliocentric distance Rh=1.44AU) and September 18 (Rh=1.62AU), following the comet’s perihelion passage on UT 2010 July 04. The total production rate for water on July 26 was (1.90±0.12)×1028moleculess−1, and abundances of six trace gases (relative to water) were: CH3OH (1.58%±0.23%), C2H6 (0.39%±0.04%), NH3 (0.83%±0.20%), and HCN (0.13%±0.02%). A detailed analysis of intensities for water emission lines provided a rotational temperature of 35±3K. The mean OPR is consistent with nuclear spin populations in statistical equilibrium (OPR=3.01±0.18), and the (1σ) lower bound corresponds to a spin temperature >38K. Our measurements were contemporaneous with a jet-like feature observed at optical wavelengths. The spatial profiles of four primary volatiles display strong enhancements in the jet direction, which favors release from a localized vent on the nucleus. The measured IR continuum is much more sharply peaked and is consistent with a dominant contribution from the nucleus itself. The peak intensities for H2O, CH3OH, and C2H6 are offset by ∼200km in the jet direction, suggesting the possible existence of a distributed source, such as the release of icy grains that subsequently sublimed in the coma. On UT September 18, no obvious emission lines were present in our spectra, nevertheless we obtained a 3σ upper limit Q(H2O)<2.86×1027moleculess−1.
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