IMAGING OBSERVATIONS OF THE HYDROGEN COMA OF COMET 67P/CHURYUMOV–GERASIMENKO IN 2015 SEPTEMBER BY THE PROCYON/LAICA
- National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan)
- Department of Climate and Space Sciences and Engineering, University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48109-2143 (United States)
- Laboratory of Infrared High-resolution spectroscopy (LiH), Koyama Astronomical Observatory, Kyoto Sangyo University, Motoyama, Kamigamo, Kita, Kyoto 603-8555 (Japan)
- Department of Physics, Rikkyo University, 3-34-1 Nishi-Ikebukuro, Toshima, Tokyo 171-8501 (Japan)
- Department of Complexity Science and Engineering, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561 (Japan)
The water production rate of a comet is one of the fundamental parameters necessary to understand cometary activity when a comet approaches the Sun within 2.5 au, because water is the most abundant icy material in the cometary nucleus. Wide-field imaging observations of the hydrogen Lyα emission in comet 67P/Churyumov–Gerasimenko were performed by the Lyman Alpha Imaging Camera (LAICA) on board the 50 kg class micro spacecraft, the Proximate Object Close Flyby with Optical Navigation (PROCYON), on UT 2015 September 7.40, 12.37, and 13.17 (corresponding to 25.31, 30.28, and 31.08 days after the perihelion passage of the comet, respectively). We derive the water production rates, Q{sub H{sub 2O}}, of the comet from Lyα images of the comet by using a 2D axi-symmetric Direct Simulation Monte-Carlo model of the atomic hydrogen coma; (1.46 ± 0.47) × 10{sup 28}, (1.24 ± 0.40) × 10{sup 28}, and (1.30 ± 0.42) × 10{sup 28} molecules s{sup −1} on 7.40, 12.37, and 13.17 September, respectively. These values are comparable to the values from in situ measurements by the Rosetta instruments in the 2015 apparition and the ground-based and space observations during the past apparitions. The comet did not show significant secular change in average water production rates just after the perihelion passage for the apparitions from 1982 to 2015. We emphasize that the measurements of absolute Q{sub H{sub 2O}} based on the wide field of view (e.g., by the LAICA/PROCYON) are so important to judge the soundness of the coma models used to infer Q{sub H{sub 2O}} based on in situ measurements by spacecraft, like the Rosetta.
- OSTI ID:
- 22863136
- Journal Information:
- The Astronomical Journal (Online), Vol. 153, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 1538-3881
- Country of Publication:
- United States
- Language:
- English
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