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See detailThe 19 Feb. 2016 Outburst of Comet 67P/CG: An ESA Rosetta Multi-Instrument Study
Grün, E.; Agarwal, J.; Altobelli, N. et al

in Monthly Notices of the Royal Astronomical Society (2016)

On 19 Feb. 2016 nine Rosetta instruments serendipitously observed an outburst of gas and dust from the nucleus of comet 67P/Churyumov-Gerasimenko. Among these instruments were cameras and spectrometers ... [more ▼]

On 19 Feb. 2016 nine Rosetta instruments serendipitously observed an outburst of gas and dust from the nucleus of comet 67P/Churyumov-Gerasimenko. Among these instruments were cameras and spectrometers ranging from UV over visible to microwave wavelengths, in-situ gas, dust and plasma instruments, and one dust collector. At 9:40 a dust cloud developed at the edge of an image in the shadowed region of the nucleus. Over the next two hours the instruments recorded a signature of the outburst that significantly exceeded the background. The enhancement ranged from 50% of the neutral gas density at Rosetta to factors >100 of the brightness of the coma near the nucleus. Dust related phenomena (dust counts or brightness due to illuminated dust) showed the strongest enhancements (factors >10). However, even the electron density at Rosetta increased by a factor 3 and consequently the spacecraft potential changed from ˜-16 V to -20 V during the outburst. A clear sequence of events was observed at the distance of Rosetta (34 km from the nucleus): within 15 minutes the Star Tracker camera detected fast particles (˜25 m s[SUP]-1[/SUP]) while 100 μm radius particles were detected by the GIADA dust instrument ˜1 hour later at a speed of ~6 m s[SUP]-1[/SUP]. The slowest were individual mm to cm sized grains observed by the OSIRIS cameras. Although the outburst originated just outside the FOV of the instruments, the source region and the magnitude of the outburst could be determined. [less ▲]

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See detailThe compositional evolution of C/2012 S1 (ISON) from ground-based high-resolution infrared spectroscopy as part of a worldwide observing campaign
Dello Russo, N.; Vervack, R. J.; Kawakita, H. et al

in Icarus (2016), 266

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 × 10[SUP]4[/SUP ... [more ▼]

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 × 10[SUP]4[/SUP]) 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. H[SUB]2[/SUB]O was detected on all dates, with production rates increasing markedly from (8.7 ± 1.5) × 10[SUP]27[/SUP] molecules s[SUP]-1[/SUP] on October 26 (R[SUB]h[/SUB] = 1.12 AU) to (3.7 ± 0.4) × 10[SUP]29[/SUP] molecules s[SUP]-1[/SUP] on November 20 (R[SUB]h[/SUB] = 0.43 AU). Short-term variability of H[SUB]2[/SUB]O production is also seen as observations on November 19 show an increase in H[SUB]2[/SUB]O production rate of nearly a factor of two over a period of about 6 h. C[SUB]2[/SUB]H[SUB]6[/SUB], CH[SUB]3[/SUB]OH and CH[SUB]4[/SUB] abundances in ISON are slightly depleted relative to H[SUB]2[/SUB]O when compared to mean values for comets measured at infrared wavelengths. On the November dates, C[SUB]2[/SUB]H[SUB]2[/SUB], HCN and OCS abundances relative to H[SUB]2[/SUB]O appear to be within the range of mean values, whereas H[SUB]2[/SUB]CO and NH[SUB]3[/SUB] were significantly enhanced. There is evidence that the abundances with respect to H[SUB]2[/SUB]O increased for some species but not others between October 28 (R[SUB]h[/SUB] = 1.07 AU) and November 19 (R[SUB]h[/SUB] = 0.46 AU). The high mixing ratios of H[SUB]2[/SUB]CO/CH[SUB]3[/SUB]OH and C[SUB]2[/SUB]H[SUB]2[/SUB]/C[SUB]2[/SUB]H[SUB]6[/SUB] on November 19, and changes in the mixing ratios of some species with respect to H[SUB]2[/SUB]O 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 H[SUB]2[/SUB]O, HCN, C[SUB]2[/SUB]H[SUB]6[/SUB], C[SUB]2[/SUB]H[SUB]2[/SUB], and H[SUB]2[/SUB]CO on November 19 show no definitive evidence for significant contributions from extended sources; however, broader spatial distributions for NH[SUB]3[/SUB] and OCS may be consistent with extended sources for these species. Abundances of HCN and C[SUB]2[/SUB]H[SUB]2[/SUB] on November 19 and 20 are insufficient to account for reported abundances of CN and C[SUB]2[/SUB] 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 NH[SUB]3[/SUB] and NH[SUB]2[/SUB] are similar, suggesting that NH[SUB]3[/SUB] is the primary source of NH[SUB]2[/SUB] with no evidence of a significant dust source of NH[SUB]2[/SUB]; however, the higher production rates derived for NH[SUB]3[/SUB] compared to NH[SUB]2[/SUB] on November 19 and 20 remain unexplained. This suggests a more complete analysis that treats NH[SUB]2[/SUB] as a distributed source and accounts for its emission mechanism is needed for future work. [less ▲]

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See detailHyper-volatiles in Comet C/2010 G2 (Hill)
Kawakita, Hideyo; Dello Russo, N.; Vervack, R. J. J. et al

in Bulletin of the American Astronomical Society (2013, October 01), 45

We performed high-dispersion near-infrared spectroscopic observations of comet C/2010 G2 (Hill) at 2.5 AU from the Sun using NIRSPEC (R ~ 2.5x10^4) at the Keck II telescope on UT 2012 Jan 9 and 10. The ... [more ▼]

We performed high-dispersion near-infrared spectroscopic observations of comet C/2010 G2 (Hill) at 2.5 AU from the Sun using NIRSPEC (R ~ 2.5x10^4) at the Keck II telescope on UT 2012 Jan 9 and 10. The comet had been in outburst. 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. The mixing ratios of CO, HCN, CH4, C2H6, and CH3OH with respect to H2O are higher than those for normal comets by a factor of five or more. Hyper-volatile species such as CO and CH4 were enriched in the coma of comet Hill suggesting that the sublimation of these hyper-volatiles could sustain the outburst of the comet. Based on a comparison with optical observations, some fraction of water in the inner coma existed as icy grains. Those icy ice grains were likely ejected from nucleus by the sublimation of hyper-volatiles. [less ▲]

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See detailEPOXI: Comet 103P/Hartley 2 Observations from a Worldwide Campaign
Meech, K. J.; A'Hearn, M. F.; Adams, J. A. et al

in Astrophysical Journal (2011), 734(Letters), 11-9

Earth- and space-based observations provide synergistic information for space mission encounters by providing data over longer timescales, at different wavelengths and using techniques that are impossible ... [more ▼]

Earth- and space-based observations provide synergistic information for space mission encounters by providing data over longer timescales, at different wavelengths and using techniques that are impossible with an in situ flyby. We report here such observations in support of the EPOXI spacecraft flyby of comet 103P/Hartley 2. The nucleus is small and dark, and exhibited a very rapidly changing rotation period. Prior to the onset of activity, the period was ~16.4 hr. Starting in 2010 August the period changed from 16.6 hr to near 19 hr in December. With respect to dust composition, most volatiles and carbon and nitrogen isotope ratios, the comet is similar to other Jupiter-family comets. What is unusual is the dominance of CO[SUB]2[/SUB]-driven activity near perihelion, which likely persists out to aphelion. Near perihelion the comet nucleus was surrounded by a large halo of water-ice grains that contributed significantly to the total water production. [less ▲]

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See detailDeep Impact: Observations from a Worldwide Earth-Based Campaign
Meech, K. J.; Ageorges, N.; A'Hearn, M. F. et al

in Science (2005), 310

On 4 July 2005, many observatories around the world and in space observed the collision of Deep Impact with comet 9P/Tempel 1 or its aftermath. This was an unprecedented coordinated observational campaign ... [more ▼]

On 4 July 2005, many observatories around the world and in space observed the collision of Deep Impact with comet 9P/Tempel 1 or its aftermath. This was an unprecedented coordinated observational campaign. These data show that (i) there was new material after impact that was compositionally different from that seen before impact; (ii) the ratio of dust mass to gas mass in the ejecta was much larger than before impact; (iii) the new activity did not last more than a few days, and by 9 July the comet's behavior was indistinguishable from its pre-impact behavior; and (iv) there were interesting transient phenomena that may be correlated with cratering physics. [less ▲]

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See detailH[SUB]2[/SUB] temperature and self-absorption: analysis of Jovian auroral spectra obtained with the FUSE satellite
Gustin, Jacques ULg; Feldman, P. D.; Gérard, Jean-Claude ULg et al

in Bulletin of the American Astronomical Society (2001, November 01)

High-resolution spectra of the Jovian aurora have been obtained with unprecedented spectral resolution in the 900-1190 Ì· window with the the Far Ultraviolet Spectroscopic Explorer (FUSE), using the 30 ... [more ▼]

High-resolution spectra of the Jovian aurora have been obtained with unprecedented spectral resolution in the 900-1190 Ì· window with the the Far Ultraviolet Spectroscopic Explorer (FUSE), using the 30"x30" LWRS aperture. All observed features belong to the H[SUB]2[/SUB] transitions from the B, C, B', D, B" and D' electronic states to the ground-state. These emissions are excited by inelastic collisions of the primary and secondary auroral electrons with H[SUB]2[/SUB] molecules. The relative intensity distribution of the observed lines depends on the rotational temperature of the emitting layer and self-absorption. Below 1100 Ì· , the transitions leading to the v" = 0, 1 and 2 levels of ground-state are partially or totally absorbed by H[SUB]2[/SUB], giving indications about the vibrational H[SUB]2[/SUB] distribution and overlying column. After a validation with an unabsorbed and a self-absorbed laboratory spectrum obtained in controlled conditions (100K, 300 eV), this study compares the observations and synthetic spectra, generated by a code including the B, C and B', D, B" and D' Rydberg states. The rotational and vibrational H[SUB]2[/SUB] temperatures are determined as well as the overlying H[SUB]2[/SUB] column. The combination of these parameters is used to determine the depth of the auroral energy deposition. This work is based on data obtained for the Guaranteed Time Team by the NASA-CNES-CSA FUSE mission operated by the Johns Hopkins University. French participants are supported by CNES. Financial support to U.S. participants has been provided by NASA contract NAS5-32985. [less ▲]

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See detailA Model to Explain the Activity of Comet Levy (1990c)
Samarasinha, N. H.; A'Hearn, M. F.; Weaver, H. A. et al

in Bulletin of the American Astronomical Society (1991, June 01)

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