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Hideyo Kawakita

Publications and source records attributed to Hideyo Kawakita.

18 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2026

Surprisingly Enriched CO and CH4 in Halley-type Comet 13P/Olbers: Clues to Its Interstellar Heritage

The native ice composition of Halley-type Comet 13P/Olbers (hereafter 13P) was measured post-perihelion, on UT 2024 August 16 using iSHELL, the 1–5 μm cross-dispersed, high-resolution facility spectrograph at the NASA InfraRed Telescope Facility. At that time, the heliocentric distance (Rh) of 13P was 1.37 au and the geocentric distance (Δ) was 1.99 au. Using a slit that delivered spectral resolving power RP λ/Δλ 4.5 × 104, two instrument settings targeted rovibrational emissions of seven parent molecules released into the coma through sublimation of ices in the nucleus. These settings provided broad and contiguous or nearly contiguous spectral coverage, one simultaneously measuring H2O, CO, and OCS, and the other simultaneously measuring CH4, C2H6, CH3OH, and H2CO. Meaningful abundances were obtained for all seven species. Our study revealed substantial enrichments of CO and CH4, the two most volatile species systematically targeted at IR wavelengths in comets. Relative to their respective mean abundance ratios among measured comets from the Oort cloud reservoir, CO in 13P was enriched by a factor of about six and CH4 was enriched by a factor of about three. Together with near-average abundances measured for CH3OH and C2H6, this suggests large endowments of CO and CH4 on interstellar grains, yet it could indicate inhibited surface chemistry on the pre-cometary grains subsequently contained in the nucleus or 13P. Assuming that this represents the primordial composition of 13P, it could reflect very low temperatures in its natal environment (∼10 K or lower).

Michael A Disanti↗
NASA NTRS2022

Volatile Abundances, Extended Coma Sources, and Nucleus Ice Associations in Comet C/2014 Q2 (Lovejoy)

High-resolution infrared spectra of comet C/2014 Q2 Lovejoy were acquired with NIRSPEC at the W. M. Keck Observatory on two post-perihelion dates(UT 2015 February 2 and 3).H2O was measured simultaneously with CO,CH3OH, H2CO, CH4, C2H6,C2H4, C2H2, HCN, and NH3 on both dates, and rotational temperatures, production rates, relative abundances, H2O ortho-to-para ratios, and spatial distributions in the coma were determined. The first detection of C2H4in a comet from ground-based observations is reported. Abundances relative to H2O for all species were found to be in the typical range compared with values for other comets in the overall population to date. There is evidence of variability in rotational temperatures and production rates on timescales that are small compared with the rotational period of the comet. Spatial distributions of volatiles in the coma suggest complex outgassing behavior.CH3OH, HCN, C2H6, and CH4 spatial distributions in the coma are consistent with direct release from associated ices in the nucleus and are peaked in a more sunward direction compared with co-measured dust. H2O spatial profiles are clearly distinct from these other four species, likely due to a sizable coma contribution from icy grain sublimation.Spatial distributions for C2H2,H2CO, and NH3suggest substantial contributions from extended coma sources, providing further evidence for distinct origins and associations for these species in comets. CO shows a different spatial distribution compared with other volatiles, consistent with jet activity from discrete nucleus ice sources.

Neil Dello Russo↗
NASA NTRS2021

Volatile Composition and Outgassing in C/2018 Y1 (Iwamoto): Extending Limits for High-Resolution Infrared Cometary Spectroscopy between 2.8 and 5.0 µm

We used the powerful high spectral resolution cross-dispersed facility spectrograph, iSHELL, at the NASAInfrared Telescope Facility(IRTF)to observe C/2018 Y1(Iwamoto), a long-period comet from the Oort cloud.We report production rates for water and eight other parent molecules(native ices),C2H6, CO, CH4,H2CO,CH3OH, HCN, NH3, and C2H2, on three preperihelion UT dates, 2019 January 13 and(near perihelion)February4–5. We present abundance ratios relative to both C2H6(a nonpolar molecule)and H2O(a polar molecule), thereby providing a more complete picture of the parent volatile composition of C/2018 Y1 and potential associations of ices in its nucleus. Overall, the measured spatial distributions for polar molecules(in particular, H2O and CH3OH)were broader, exhibiting more complex structure compared with nonpolar or weakly polar species(CH4,C2H6, andCO). Our January 13 results permitted quantitatively assessing the significant improvement in sensitivity delivered by iSHELL compared with previous capabilities at the IRTF. The efficient spectral coverage of iSHELL plus the favorable geocentric Doppler shift of C/2018 Y1 allowed for measuring>50% of CH4ν3-band emission intensity on both January 13 and February 5. Compositionally, compared to their respective mean abundances among comets from the Oort cloud, C2H6and CH3OH were enriched, CH4and HCN were near normal, and all other species were depleted. The abundance ratio CH3OH/C2H6was higher by 45%±8% on January 13 versusFebruary 5, whereas CH4/C2H6was unchanged within the uncertainty, suggesting nonhomogeneous composition among regions of the nucleus dominating activity on these dates

Michael A. Disanti↗
NASA NTRS2021

The Volatile Composition of the Inner Coma of Comet 46P/Wirtanen: Coordinated Observations Using iSHELL at the NASA-IRTF and Keck/NIRSPEC-2

The 2018 perihelion passage of comet 46P/Wirtanen afforded an opportunity to measure the abun-dances and spatial distributions of coma volatiles in a Jupiter-family comet with exceptional spatialresolution for several weeks surrounding its closest approach to Earth (∆min∼0.078 au on UT Decem-ber 16). We conducted near-infrared spectroscopic observations of 46P/Wirtanen using iSHELL at theNASA Infrared Telescope Facility on UT 2018 December 18 in direct coordination with observations using the newly upgraded NIRSPEC-2 instrument at the W. M. Keck Observatory, and securely de-tected fluorescent emission from CH3OH, C2H6, and H2O. This coordinated campaign utilizing the twopremier near-infrared facilities in the northern hemisphere enabled us to sample distinct projections ofthe coma into the plane of the sky simultaneously, and provided an unprecedented view into the innercoma of 46P/Wirtanen near closest approach. We report rotational temperatures, production rates,and abundance ratios (i.e., mixing ratios) for all sampled species and compare ouriSHELLresultsto simultaneous (or near-simultaneous) measurements taken with NIRSPEC-2. We demonstrate theextraordinary synergy of coordinated measurements using iSHELL and NIRSPEC-2, and advocate forfuture cometary studies that jointly leverage the capabilities of these two facilities.

Molecular spectroscopy;↗
NASA NTRS2021

The Volatile Composition of the Inner Coma of Comet 46P/Wirtanen: Coordinated Observations Using iSHELL at the NASA-IRTF and Keck/NIRSPEC-2

The 2018 perihelion passage of comet 46P/Wirtanen afforded an opportunity to measure the abundances andspatial distributions of coma volatiles in a Jupiter-family comet with exceptional spatial resolution for severalweeks surrounding its closest approach to Earth(Δmin∼0.078 au on UT December 16). We conducted near-infrared spectroscopic observations of 46P/Wirtanen using iSHELL at the NASA Infrared Telescope Facility onUT 2018 December 18 in direct coordination with observations using the newly upgraded NIRSPEC-2 instrumentat the W. M. Keck Observatory, and securely detectedfluorescent emission from CH3OH, C2H6, and H2O. Thiscoordinated campaign utilizing the two premier near-infrared facilities in the northern hemisphere enabled us tosample distinct projections of the coma into the plane of the sky simultaneously, and provided an unprecedentedview into the inner coma of 46P/Wirtanen near closest approach. We report rotational temperatures, productionrates, and abundance ratios(i.e., mixing ratios)for all sampled species and compare our iSHELL results tosimultaneous(or near-simultaneous)measurements taken with NIRSPEC-2. We demonstrate the extraordinarysynergy of coordinated measurements using iSHELL and NIRSPEC-2, and advocate for future cometary studiesthat jointly leverage the capabilities of these two facilities.

Nathaniel X Roth↗
NASA NTRS2021

The Volatile Composition of the Inner Coma of Comet 46P/Wirtanen: Coordinated Observations Using iSHELL at the NASA-IRTF and Keck/NIRSPEC-2

The 2018 perihelion passage of comet 46P/Wirtanen afforded an opportunity to measure the abundances and spatial distributions of coma volatiles in a Jupiter-family comet with exceptional spatial resolution for several weeks surrounding its closest approach to Earth (Δ(min) ~0.078 au on UT December 16). We conducted near-infrared spectroscopic observations of 46P/Wirtanen using iSHELL at the NASA Infrared Telescope Facility on UT 2018 December 18 in direct coordination with observations using the newly upgraded NIRSPEC-2 instrument at the W. M. Keck Observatory, and securely detected fluorescent emission from CH3OH, C2H6, and H2O. This coordinated campaign utilizing the two premier near-infrared facilities in the northern hemisphere enabled us to sample distinct projections of the coma into the plane of the sky simultaneously, and provided an unprecedented view into the inner coma of 46P/Wirtanen near closest approach. We report rotational temperatures, production rates, and abundance ratios (i.e., mixing ratios) for all sampled species and compare our iSHELL results to simultaneous (or near-simultaneous) measurements taken with NIRSPEC-2. We demonstrate the extraordinary synergy of coordinated measurements using iSHELL and NIRSPEC-2, and advocate for future cometary studies that jointly leverage the capabilities of these two facilities.

Nathaniel X. Roth↗
NASA NTRS2021

First Comet Observations with NIRSPEC-2 at Keck: Outgassing Sources of Parent Volatiles and Abundances Based on Alternative Taxonomic Compositional Baselines in 46P/Wirtanen

A major upgrade to the NIRSPEC instrument at the Keck II telescope was successfully completed in time for near-infrared spectroscopic observations of comet 46P/Wirtanen during its exceptionally close flyby of Earth in 2018 December. These studies determined the abundances of several volatiles, including C2H2, C2H6, CH3OH, NH3, HCN, H2CO, and H2O. Long-slit spatial distributions of gas rotational temperature and column density are diagnostic for the presence of icy grains in the coma and understanding if different volatiles are associated with common or distinct outgassing sources. These spatial distributions suggest that C2H2, C2H6, and HCN have a common outgassing source, whereas H2O and CH3OH have additional, more extended sources. The synergy of these findings with observations by space missions (Rosetta and EPOXI) motivates continuing studies to address whether or not C2H6, C2H2, and HCN have a common source of release (plausibly associated with CO2) in a larger sample of comets and whether systematic differences exist in the release of these species compared to H2O and CH3OH. Abundances of volatiles are reported relative to H2O, as traditionally done, as well as C2H6. While not unique, the choice of C2H6 demonstrates the value of extending the chemical taxonomy of parent volatiles in comets toward additional compositional "baselines" and, importantly, closer integration between coma abundances and the underlying volatile associations as revealed by spatial distributions. Our findings on composition and sources of outgassing include information relevant to future evaluations of 46P/Wirtanen as a prospective spacecraft target.

Boncho P. Bonev↗
NASA NTRS2021

Quantifying the Hypervolatile Abundances in Jupiter-family Comet 46P/Wirtanen

We present analysis of IR and optical spectroscopy of Jupiter-family comet (JFC) 46P/Wirtanen obtained in 2019 January, when the comet had sufficient geocentric velocity to enable studies of the hypervolatiles CO and CH4, as well as [OI] emission. These species could not be studied near closest approach in mid-December because there was insufficient Doppler shift to separate the cometary emission from their corresponding telluric absorption lines. We employed the [OI] observations as a proxy for the CO2/H2O ratio, as CO2 cannot be observed directly from the ground, and space-based assets sensitive to CO2 were not able to observe 46P during this apparition. We focused our analysis on H2O, CO, CH4, C2H6, CH3OH, and CO2 (via [OI] emission). We detected strong emissions from H2O, C2H6, and CH3OH. Over the 3 nights, we found evidence for changing mixing ratios, mostly due to a variable H2O production rate. In 46P, C2H6 and CH3OH are enriched compared to cometary averages, with mixing ratios relative to H2O of ∼1% and ∼3%, respectively. Measurements of CH4 and CO have been especially rare in JFCs. We report significant 3σ upper limits on CH4/H2O<0.97% and CO/H2O<0.54%. They place CH4 being near-average or depleted, and CO being strongly depleted in 46P compared with Oort cloud comets. 46P has comparable CO/H2O to the few other measurements in JFCs, but enriched in C2H6 and CH3OH. Our inferred CO2/H2O mixing ratio is∼15%, though accounting for systematic uncertainties from the lack of knowledge of [OI] photochemistry means a value between 10% and 20% is likely. The compositional profile of46P is similar to another small, hyperactive comet: 103P/Hartley 2. The mechanism of CO2-driven water-rich ice grain production proposed for 103P/Hartley 2 may be operating on 46P as well.

Comets↗
NASA NTRS2021

Testing Short-term Variability and Sampling of Primary Volatiles in Comet 46P/Wirtanen

The exceptionally favorable close approach of Jupiter-family comet 46P/Wirtanen in 2018 December enabled characterization of its primary volatile composition with exceptionally high spatial resolution and sensitivities using the iSHELL spectrograph at the NASA Infrared Telescope Facility on Maunakea, HI. We sampled emissions from H2O, HCN, C2H2, NH3,C2H6, and CH3OH on UT 2018 December 21 using two instrumental settings that spanned the 2.9–3.6μm spectral region. We also obtained a sensitive 3σupper limit for H2CO and for the rarely studied molecule HC3N. We report rotational temperatures, production rates, and mixing ratios(relative to H2O as well as to C2H6). We place our results in context by comparing them with other comets observed at near-IR wavelengths. We also compare our results with those obtained using the NIRSPEC-2 spectrograph on Keck II on UT December 17 and 18 and with results obtained from iSHELL on other dates during the same apparition. Within1–2σ uncertainty, production rates obtained for all molecules in this work were consistent with those obtained using NIRSPEC-2 except H2O, indicating low-level variability on a timescale of days. Mixing ratios with respect to H2O in 46P/Wirtanen were consistent with corresponding values from NIRSPEC-2 within the uncertainty with the exception of CH3OH, which yielded a higher ratio on December 21. Our measurements afforded a high temporal resolution that spanned∼2/3 of the rotational period of 46P/Wirtanen, enabling us to test short-term variability in the production rates of H2O and HCN due to rotational effects. Both H2O and HCN production rates showed similar temporal variability, resulting in nearly constant HCN/H2O

Younas Khan↗
NASA NTRS2020

Carbonyl Sulfide (OCS): Detections in Comets C/2002 T7 (LINEAR), C/2015 ER61 (PanSTARRS), and 21P/Giacobini-Zinner and Stringent Upper Limits in 46P/Wirtanen

Carbonyl sulfide(OCS)is one of the sulfur-bearing molecules detected in different astronomical environments, including comets. The present-day sulfur chemistry in comets may reveal much about the origin of these ices and their subsequent processing history. Cometary sulfur molecules such as H2S, H2CS, SO2, SO, CS, CS2,S2, and NShave been detected in many comets. However, OCS, the only sulfur-bearing species with fluorescence emission lines at infrared wavelengths, is under-represented in comet volatile studies, having been reported in only six comets so far. We targeted OCS with the NASA Infrared Telescope Facility in comets 46P/Wirtanen, 21P/Giacobini–Zinner, and C/2015 ER61(Pan STARRS)in 2017–2018 using the high-resolution iSHELL spectrograph, and in C/2002 T7(LINEAR)in 2004 using the heritage CSHELL spectrograph. In comet C/2015 ER61, the OCS abundance was similar to those measured in bright comets such as comets C/2012 S1(ISON)and C/1996 B2(Hyakutake), whereas in C/2002 T7 it was relatively depleted. Our OCS measurement in21P/Giacobini–Zinner is the first definitive detection of this molecule in a Jupiter-family comet from a ground-based facility and is close to the average OCS abundance determined in comet 67P/ Churyumov–Gerasimenko by the Rosetta mission. Our 3σupper limit for comet 46P/Wirtanen is the lowest reported OCS abundance in any comet. We present production rates and mixing ratios(with respect to H2O)for these comets and place our results in the context of comets measured to date

Mohammad Saki↗
NASA NTRS2020

Carbonyl Sulfide (OCS): Detections in Comets C/2002 T7 (LINEAR), C/2015 ER61 (PanSTARRS), and 21P/Giacobini-Zinner and Stringent Upper Limits in 46P/Wirtanen

Carbonyl sulfide (OCS) is one of the sulfur-bearing molecules detected in different astronomical environments, including comets. The present-day sulfur chemistry in comets may reveal much about the origin of these ices and their subsequent processing history. Cometary sulfur molecules such as H2S, H2CS, SO2, SO, CS, CS2, S2, and NS have been detected in many comets. However, OCS, the only sulfur-bearing species with fluorescence emission lines at infrared wavelengths, is under-represented in comet volatile studies, having been reported in only six comets so far. We targeted OCS with the NASA Infrared Telescope Facility in comets 46P/Wirtanen, 21P/Giacobini–Zinner, and C/2015 ER61 (PanSTARRS) in 2017–2018 using the high-resolution iSHELL spectrograph, and in C/2002 T7 (LINEAR) in 2004 using the heritage CSHELL spectrograph. In comet C/2015 ER61, the OCS abundance was similar to those measured in bright comets such as comets C/2012 S1 (ISON) and C/1996 B2 (Hyakutake), whereas in C/2002 T7 it was relatively depleted. Our OCS measurement in 21P/Giacobini–Zinner is the first definitive detection of this molecule in a Jupiter-family comet from a ground-based facility and is close to the average OCS abundance determined in comet 67P/Churyumov–Gerasimenko by the Rosetta mission. Our 3σ upper limit for comet 46P/Wirtanen is the lowest reported OCS abundance in any comet. We present production rates and mixing ratios (with respect to H2O) for these comets and place our results in the context of comets measured to date.

Mohammad Saki↗