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We present H 2 O production rates for comet C/2012 S1 (ISON) derived from observations of [O I] and OH emission during its inbound leg, covering a heliocentric distance range of 1.8–0.44 AU. Our production rates are in agreement with previous measurements using a variety of instruments and techniques and with data from the various observatories greatly differing in their projected fields of view. The consistent results across all data suggest the absence of an extended source of H 2 O production, for example sublimation of icy grains in the coma, or a source with spatial extent confined to the dimensions of the smallest projected field of view (in this case  < 1000 km). We find that ISON had an active area of around 10 km 2 for heliocentric distances R h  >  1.2 AU, which then decreased to about half this value from R h = 1.2–0.9 AU. This was followed by a rapid increase in active area at about R h = 0.6 AU, corresponding to the first of three major outbursts ISON experienced inside of 1 AU. The combination of a detected outburst in the light curve and rapid increase in active area likely indicates a major nucleus fragmentation event. The 5–10 km 2 active area observed outside of R h = 0.6 AU is consistent with a 50–100% active fraction for the nucleus, larger than typically observed for cometary nuclei. Although the absolute value of the active area is somewhat dependent on the thermal model employed, the changes in active area observed are consistent among models. The conclusion of a 50–100+% active fraction is robust for realistic thermal models of the nucleus. However the possibility of a contribution of a spatially unresolved distribution of icy grains cannot be discounted. As our [OI]-derived H 2 O production rates are consistent with values derived using other methods, we conclude that the contribution of O 2 photodissociation to the observed [O I] emission is at most 5–10% that of the contribution of H 2 O for ISON. This is consistent with the expected contribution of O 2 photodissociation if O 2 /H 2 O  ∼  4%, meaning [O I] emission can still be utilized as a reliable proxy for H 2 O production in comets as long as O 2 /H 2 O  ≲  4%, similar to the abundance measured by the ROSINA instrument on Rosetta at comet 67P/Churyumov–Gerasimenko. [ABSTRACT FROM AUTHOR]

Recent observations have suggested that there is water ice present on the surfaces of 24 Themis and 1 Ceres. We present upper limits on the H 2 O production rate on these bodies derived using a search for [O I]6300 Å emission. For Themis, the water production is less than 4.5 × 10 27 mol s − 1 , while for Ceres our derived upper limit is 4.6 × 10 28 mol s − 1 . The derived limits imply a very low fraction of the surface area of each asteroid is active ( < 2 × 10 − 4 ), though this estimate varies by as much as an order of magnitude depending on thermal properties of the surface. This is much lower than seen for comets, which have active areas of 10 − 2 –10 − 1 . We discuss possible implications for our findings on the nature of water ice on Themis and Ceres. [ABSTRACT FROM AUTHOR]

Carbon dioxide is one of the most abundant ices present in comets and is therefore important for understanding cometary composition and activity. We present analysis of observations of CO 2 and [O I] emission in three comets to measure the CO 2 abundance and evaluate the possibility of employing observations of [O I] emission in comets as a proxy for CO 2 . We obtained NIR imaging sensitive to CO 2 of comets C/2012 K1 (PanSTARRS), C/2012 K5 (LINEAR), and 290P/Jäger with the IRAC instrument on Spitzer . We acquired observations of [O I] emission in these comets with the ARCES echelle spectrometer mounted on the 3.5-m telescope at Apache Point Observatory and observations of OH with the Swift observatory (PanSTARRS) and with Keck HIRES (Jäger). The CO 2 /H 2 O ratios derived from the Spitzer images are 12.6 ± 1.3% (PanSTARRS), 28.9 ± 3.6% (LINEAR), and 31.3 ± 4.2% (Jäger). These abundances are derived under the assumption that contamination from CO emission is negligible. The CO 2 abundance for PanSTARRS is close to the average abundance measured in comets at similar heliocentric distance to date, while the abundances measured for LINEAR and Jäger are significantly larger than the average abundance. From the coma morphology observed in PanSTARRS and the assumed gas expansion velocity, we derive a rotation period for the nucleus of about 9.2 h. Comparison of H 2 O production rates derived from ARCES and Swift data, as well as other observations, suggest the possibility of sublimation from icy grains in the inner coma. We evaluate the possibility that the [O I] emission can be employed as a proxy for CO 2 by comparing CO 2 /H 2 O ratios inferred from the [O I] lines to those measured directly by Spitzer . We find that for PanSTARRS we can reproduce the observed CO 2 abundance to an accuracy of ∼20%. For LINEAR and Jäger, we were only able to obtain upper limits on the CO 2 abundance inferred from the [O I] lines. These upper limits are consistent with the CO 2 abundances measured by Spitzer . [ABSTRACT FROM AUTHOR]

We present analysis of high spectral resolution NIR spectra of CO and H 2 O in Comet C/2009 P1 (Garradd) taken during its 2011–2012 apparition with the CSHELL instrument on NASA’s Infrared Telescope Facility (IRTF). We also present analysis of observations of atomic oxygen in Comet Garradd obtained with the ARCES echelle spectrometer mounted on the ARC 3.5-m telescope at Apache Point Observatory and the Tull Coude spectrograph on the Harlan J. Smith 2.7-m telescope at McDonald Observatory. The observations of atomic oxygen serve as a proxy for H 2 O and CO 2 . We confirm the high CO abundance in Comet Garradd and the asymmetry in the CO/H 2 O ratio with respect to perihelion reported by previous studies. From the oxygen observations, we infer that the CO 2 /H 2 O ratio decreased as the comet moved towards the Sun, which is expected based on current sublimation models. We also infer that the CO 2 /H 2 O ratio was higher pre-perihelion than post-perihelion. We observe evidence for the icy grain source of H 2 O reported by several studies pre-perihelion, and argue that this source is significantly less abundant post-perihelion. Since H 2 O, CO 2 , and CO are the primary ices in comets, they drive the activity. We use our measurements of these important volatiles in an attempt to explain the evolution of Garradd’s activity over the apparition. [ABSTRACT FROM AUTHOR]

Highlights: [•] We report analysis of high spectral resolution optical observations of comet 103P/Hartley during it’s Fall 2010 apparition. [•] We determine that the daughter species exhibit a high degree of variability in their production rates with rotational phase. [•] We also infer changes in the mixing ratios C2/CN and CN/H2O. [•] We interpret the variable mixing ratios as indicating whether a given species is released from a nucleus or extended source. [•] We find that an additional source of C2 besides C2H2 is needed to account for the observed C2 abundance in 103P. [Copyright &y& Elsevier]

Abstract: We present analysis of observations of the forbidden oxygen lines in Comet 103P/Hartley, the target of the Deep Impact Extended Investigation (DIXI), during its Fall 2010 apparition. We obtained the observations using the ARCES echelle spectrometer mounted on the Astrophysical Research Consortium (ARC) 3.5-m telescope at Apache Point Observatory. We detected the 5577, 6300, and 6364Å lines on all dates, and so were able to calculate the ratio of the 5577Å line intensity to the sum of the intensities of the 6300Å and 6364Å lines (the oxygen line ratio). A ratio of 0.05–0.1 would suggest that water is the dominant parent, while a higher ratio suggests that another volatile, such as CO2, is an important contributor to the O I population. We find a range of values for the oxygen line ratio varying from ∼0.05–0.13. This range includes values that are higher than those typically measured for comets observed at a similar heliocentric distance to 103P (∼1AU). The higher measured ratio is likely a result of a higher intrinsic CO2 abundance in the material released from 103P than typical comets, as found by direct measurements of CO2 and H2O made by the DIXI spacecraft. The CO2/H2O ratio in 103P was also observed by the DIXI spacecraft to vary significantly with rotational phase of the nucleus, which explains the large range of oxygen line ratios observed. These observations of the forbidden oxygen lines in 103P, a comet for which a directly observed CO2/H2O ratio is available, suggest that high quality observations of the forbidden oxygen lines in comets can serve as a proxy for CO2/H2O ratio measurements. [Copyright &y& Elsevier]

Abstract: We present observations and analysis of the forbidden oxygen lines in Comets C/2006 W3 (Christensen) and C/2007 Q3 (Siding Spring) at heliocentric distances of 3.13 and 2.96AU, respectively. We obtained the observations using the ARCES echelle spectrometer, which is mounted on the Astrophysical Research Consortium 3.5-m telescope at Apache Point Observatory. We detected the 5577, 6300, and 6364Å atomic oxygen lines in Christensen and we calculated the ratio of the green (5577Å) line flux to that of the red doublet (6300 and 6364Å). We obtained a ratio of 0.24±0.08, a number higher than previous measurements for other comets at smaller heliocentric distance. This shows that CO and/or CO2 made detectable contributions to the O I population in the coma of Christensen. We only detected the 6300Å line in Siding Spring, resulting in an upper limit for the oxygen line ratio of 0.20. Based on the derived flux for the 6300Å line, we constrain the CO2 and H2O production rate in Siding Spring. A comparison of our results at ∼3AU to previous findings for comets at this approximate heliocentric distance suggests that a heliocentric distance of 3AU is a transition region between H2O and CO2 dominated activity in comets. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: The eukaryotic ribosomal stalk, composed of the P-proteins, is a part of the GTPase-associated-center which is directly responsible for stimulation of translation-factor-dependent GTP hydrolysis. Here we report that yeast mutant strains lacking P1/P2-proteins show high propagation of the yeast L-A virus. Affinity-capture-MS analysis of a protein complex isolated from a yeast mutant strain lacking the P1A/P2B proteins using anti-P0 antibodies showed that the Gag protein, the major coat protein of the L-A capsid, is associated with the ribosomal stalk. Proteomic analysis revealed that the elongation factor eEF1A was also present in the isolated complex. Additionally, yeast strains lacking the P1/P2-proteins are hypersensitive to paromomycin and hygromycin B, underscoring the fact that structural perturbations in the stalk strongly influence the ribosome function, especially at the level of elongation. [Copyright &y& Elsevier]

High-resolution infrared spectra of Jupiter-family comet 45P/Honda-Mrkos-Pajdušáková were obtained with NIRSPEC at the W. M. Keck Observatory on two post-perihelion dates (UT 2017 February 13 and 19), when the comet was at heliocentric distances of 1.01 and 1.10 AU, respectively. On UT February 13, H 2 O was measured simultaneously with six trace parent molecules: CH 3 OH, C 2 H 6 , HCN, NH 3 , C 2 H 2 , and H 2 CO. On UT February 19, CH 4 and CO were also targeted in addition to the species measured on UT February 13. Abundances of CO, CH 4 , and C 2 H 2 relative to H 2 O are consistent with values obtained from IRTF/iSHELL observations of 45P in early January 2017 just after perihelion when the heliocentric distance was 0.55–0.56 AU. Differences are seen in H 2 CO/H 2 O, C 2 H 6 /H 2 O, CH 3 OH/H 2 O, and HCN/H 2 O in February compared to January. Additionally, NH 3 abundances appear highly variable during the February measurements, suggesting possible fluctuations of a factor of ten; however, there is significant uncertainty in quantifying NH 3 owing to the marginal detections of only one or two lines on each of the two dates. Combining all infrared spectroscopic observations of 45P in January and February 2017, a post-perihelion relationship of Q(H 2 O) = (2.81 ± 0.25) × 1027 [R h (−3.83±0.18)] molecules s−1 is derived. However, all measurements suggest significant variability in H 2 O production on timescales of hours and days. Compared to other comets, volatile abundances relative to H 2 O in 45P are as follows: CO (depleted relative to all measured comets), CH 3 OH (enriched/all comets), CH 4 and C 2 H 6 (typical/all comets, enriched/Jupiter-family comets), C 2 H 2 (depleted/all comets, typical/Jupiter-family comets), H 2 CO (January: typical, February depleted/all comets), HCN (January: severely depleted, February: typical/Jupiter-family comets). The small geocentric distances of the comet in February 2017 provide high spatial resolution in the coma of 45P (~12 and 19 km/pixel on February 13 and 19, respectively). Overall, the spatial distributions of volatiles and dust suggest a relatively symmetric and uniform coma during the UT February 13 and 19 observations, with small spatial differences noted between some volatile species. Measured C 2 H 2 and HCN abundances are consistent with HCN as the primary parent of CN and C 2 H 2 as a significant but not primary parent for C 2 , based on C 2 and CN production rate measurements from the 2017 and previous apparitions. Extracted spectra show an increase in the dust-to-gas ratio in 45P from February 13 to 19 in agreement with contemporaneous narrowband optical measurements. • Reports production rates and relative abundances for parent volatiles in comet 45P. • Significant chemical differences measured in 45P near perihelion compared to six weeks later near closest Earth approach. • Dust-to-gas ratio in 45P increased significantly from February 13 to 19. • 45P chemistry is further evidence that comets retain a significant if not dominant natal signature. [ABSTRACT FROM AUTHOR]