We present a multi-wavelength study of comet C/2016 R2 (PanSTARRS). This comet was observed on 23 and 24 January 2018 with the IRAM 30 m telescope, and in January to March 2018 with the Nançay radio ...telescope. Visible spectroscopy was performed in December 2017 and February 2018 with small amateur telescopes. We report on measurements of CO, CH3OH, H2CO and HCN production rates, and on the determination of the N2/CO abundance ratio. Several other species, especially OH, were searched for but not detected. The inferred relative abundances, including upper limits for sulfur species, are compared to those measured in other comets at about the same heliocentric distance of ~2.8 AU. The coma composition of comet C/2016 R2 is very different from all other comets observed so far, being rich in N2 and CO and dust poor. This suggests that this comet might belong to a very rare group of comets formed beyond the N2 ice line. Alternatively, comet C/2016 R2 (PanSTARRS) could be the fragment of a large and differentiated transneptunian object, with properties characteristic of volatile-enriched layers.
(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.
► 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.
•The total productivity of ISON increased by about a factor of 40 between Rh=1.12AU and Rh=0.43AU.•The relative abundances of parent volatiles changed as ISON approached perihelion.•NH3/HCN, ...H2CO/CH3OH, and C2H2/C2H6 measured at Rh=0.46AU are among the highest ratios measured in comets.•Connections between related volatile species in ISON are derived from their spatial distributions in the coma.•C2H2 and HCN are not the primary parents of C2 and CN in ISON.
Volatile production rates, relative abundances, rotational temperatures, and spatial distributions in the coma were measured in C/2012 S1 (ISON) using long-slit high-dispersion (λ/Δλ∼2.5×104) infrared spectroscopy as part of a worldwide observing campaign. Spectra were obtained on UT 2013 October 26 and 28 with NIRSPEC at the W.M. Keck Observatory, and UT 2013 November 19 and 20 with CSHELL at the NASA IRTF. H2O was detected on all dates, with production rates increasing markedly from (8.7±1.5)×1027moleculess−1 on October 26 (Rh=1.12AU) to (3.7±0.4)×1029moleculess−1 on November 20 (Rh=0.43AU). Short-term variability of H2O production is also seen as observations on November 19 show an increase in H2O production rate of nearly a factor of two over a period of about 6h. C2H6, CH3OH and CH4 abundances in ISON are slightly depleted relative to H2O when compared to mean values for comets measured at infrared wavelengths. On the November dates, C2H2, HCN and OCS abundances relative to H2O appear to be within the range of mean values, whereas H2CO and NH3 were significantly enhanced. There is evidence that the abundances with respect to H2O increased for some species but not others between October 28 (Rh=1.07AU) and November 19 (Rh=0.46AU). The high mixing ratios of H2CO/CH3OH and C2H2/C2H6 on November 19, and changes in the mixing ratios of some species with respect to H2O between October 28 to November 19, indicates compositional changes that may be the result of a transition from sampling radiation-processed outer layers in this dynamically new comet to sampling more pristine natal material as the outer processed layer was increasingly eroded and the thermal wave propagated into the nucleus as the comet approached perihelion for the first time. On November 19 and 20, the spatial distribution for dust appears asymmetric and enhanced in the antisolar direction, whereas spatial distributions for volatiles (excepting CN) appear symmetric with their peaks slightly offset in the sunward direction compared to the dust. Spatial distributions for H2O, HCN, C2H6, C2H2, and H2CO on November 19 show no definitive evidence for significant contributions from extended sources; however, broader spatial distributions for NH3 and OCS may be consistent with extended sources for these species. Abundances of HCN and C2H2 on November 19 and 20 are insufficient to account for reported abundances of CN and C2 in ISON near this time. Differences in HCN and CN spatial distributions are also consistent with HCN as only a minor source of CN in ISON on November 19 as the spatial distribution of CN in the coma suggests a dominant distributed source that is correlated with dust and not volatile release. The spatial distributions for NH3 and NH2 are similar, suggesting that NH3 is the primary source of NH2 with no evidence of a significant dust source of NH2; however, the higher production rates derived for NH3 compared to NH2 on November 19 and 20 remain unexplained. This suggests a more complete analysis that treats NH2 as a distributed source and accounts for its emission mechanism is needed for future work.
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.
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.
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.
PDF
