Temporal deconvolution of the hydrogen coma, II. Pre- and post-perihelion activity of Comet Hyakutake (1996 B2)

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Solar and Heliospheric Observatory/solar Wind Anisotropies Observations of five moderately bright comets: 1999-2002

Solar Wind Anisotropies (SWAN), the all-sky hydrogen Lyman-alpha camera, on the SOHO spacecraft makes routine all-sky images of the interplanetary neutral hydrogen around the Sun and thus monitors the effect of the variable solar wind on its distribution. SWAN has an ongoing campaign to make special observations of comets, both short- and long-period ones, in addition to making serendipitous observations of comets as part of the all-sky monitoring program. We report here on a study of the moderately active Oort cloud comets observed by SWAN during the period of 1999–2002: 1999 H1 Lee, 1999 T1 McNaught Hartley, 2000 WM1 LINEAR, 2001 A2 LINEAR, and 2002 C1 Ikeya Zhang (P153). SWAN is able to observe comets almost continuously over most of their visible apparitions and provide excellent temporal coverage of water production. In addition to calculating production rates from each single image, we also present results using our time-resolved model (TRM) that analyzes an entire sequence of images over many days to several weeks/months, and from which daily-averaged or two-day- averaged water production rates are extracted over continuous periods of several days to months. The short-term (outburst) behavior is correlated with other observations and is examined and associated with fragment release. The long-term heliocentric distance-dependent variations of water production rate are examined and compared and contrasted with the measured volatile compositions of the comets as well as their absolute production rate levels. The overall long-term variation is also distinguished from seasonal effects seen in the pre- to post-perihelion differences

SWAN observations of 9P/Tempel 1 around the Deep Impact event

International audienceThe SWAN instrument observed the coma of Comet 9P/Tempel 1 at Lyman alpha around the Deep Impact event. From these observations, a water production rate profile for 3 weeks after the impact was derived. The comet could not be identified in images taken before the impact because of the relatively low production rates. The most important feature of the profile is that the production rate increases by about a factor of two more than a week after the impact. This is too late to be directly caused by the impact plume itself. Although it is not impossible that the impact triggered a resurfacing event, the comet is known to show sudden outburts, and the elevated production rate is similar to what has been reported on previous apparitions

Water Production Rate of C/2020 F3 (NEOWISE) from SOHO/SWAN over Its Active Apparition

International audienceC/2020 F3 (NEOWISE) was discovered in images from the Near Earth Object program of the Wide-Field Infrared Survey Explorer (NEOWISE) taken on 2020 March 27 and has become the Great Comet of 2020. The Solar Wind ANisotropies (SWAN) camera on the Solar and Heliospheric Observatory (SOHO) spacecraft, located in a halo orbit around the Earth–Sun L1 Lagrange point, makes daily full-sky images of hydrogen Lyα. Water production rates were determined from the SWAN hydrogen Lyα brightness and spatial distribution of the comet measured over a 4 month period of time on either side of the comet's perihelion on 2020 July 3. The water production rate in s−1 was moderately asymmetric around perihelion and varied with the heliocentric distance, r, in au as (6.9 ± 0.5) × 1028 r −2.5±0.2 and (10.1 ± 0.5) × 1028 r −3.5±0.1 before and after perihelion, respectively. This is consistent with the comet having been through the planetary region of the solar system on one or more previous apparitions. Water production rates as large as 5.27 × 1030 s−1 were determined shortly after perihelion, once the comet was outside the solar avoidance area of SWAN, when the comet was 0.324 au from the Sun

Water production rates of recent comets (2014-2015) by SOHO/SWAN and the SOHO/SWAN survey

International audienceThe all-sky hydrogen Lyman-alpha camera, SWAN (Solar Wind Anisotropies), on the SOlar and Heliospheric Observatory (SOHO) satellite makes observations of the hydrogen coma of comets. Most water vapor produced by comets is ultimately photodissociated into two H atoms and one O atom producing a huge atomic hydrogen coma that is routinely observed in the daily full-sky SWAN images in comets of sufficient brightness. Water production rates are calculated using our time-resolved model (Mäkinen & Combi, 2005, Icarus 177, 217), typically yielding about 1 observation every 2 days on the average. Here we describe the progress in analysis of observations of comets observed during 2014-2015 and those selected from the archive for analysis. These include comets C/2012 K1 (PanSTARRS), C/2013 V5, (Oukaimeden), C/2014 Q2 (Lovejoy) and 15P/Finlay. A status report on the entire SOHO/SWAN archive of water production rates in comets will also be given. SOHO is an international cooperative mission between ESA and NASA. Support from grants NNX11AH50G from the NASA Planetary Astronomy Program and NNX13AQ66G from the NASA Planetary Mission Data Analysis Program are gratefully acknowledged as is support from CNRS, CNES, and the Finnish Meteorological Institute (FMI)

Water production rates from SOHO/SWAN observations of six comets: 2017–2020

International audienceThe Solar Wind ANisotropies (SWAN) all-sky hydrogen Lyman-alpha camera on the SOlar and Heliosphere Observer (SOHO) satellite makes daily images of the entire sky to monitor the three-dimensional distribution of solar wind and solar radiation via its imprint on the stream of interstellar hydrogen that flows through the solar system. In the process it also records the distribution of the hydrogen comae of comets. We report here the analyses of six comets originally from the Oort Cloud observed during the 2017–2020 period by SWAN: C/2015 V2 (Johnson), C/2019 Y1 (ATLAS), C/2017 T2 (PanSTARRS), C/2020 F8 (SWAN), C/2019 Y4 (ATLAS), and C/2019 U6 (Lemmon). Of these the nuclei of C/2019 Y4 (ATLAS) and C/2020 F8 (SWAN) both broke up on their inbound orbit before perihelion. The water production rates over the detectable portion of each comet's orbit are determined and discussed in light of the comet's dynamical sub-class of Oort Cloud comets

Water production activity of nine long-period comets from SOHO/SWAN observations of hydrogen Lyman-alpha: 2013–2016

International audienceNine recently discovered long-period comets were observed by the Solar Wind Anisotropies (SWAN) Lyman-alpha all-sky camera on board the Solar and Heliosphere Observatory (SOHO) satellite during the period of 2013 to 2016. These were C/2012 K1 (PanSTARRS), C/2013 US10 (Catalina), C/2013 V5 (Oukaimeden), C/2013 R1 (Lovejoy), C/2014 E2 (Jacques), C/2014 Q2 (Lovejoy), C/2015 G2 (MASTER), C/2014 Q1 (PanSTARRS) and C/2013 XI (PanSTARRS). Of these 9 comets 6 were long-period comets and 3 were possibly dynamically new. Water production rates were calculated from each of the 885 images using our standard time-resolved model that accounts for the whole water photodissociation chain, exothermic velocities and collisional escape of H atoms. For most of these comets there were enough observations over a broad enough range of heliocentric distances to calculate power-law fits to the variation of production rate with heliocentric distances for pre- and post-perihelion portions of the orbits. Comet C/2014 Q1 (PanSTARRS), with a perihelion distance of only ∼0.3 AU, showed the most unusual variation of water production rate with heliocentric distance and the resulting active area variation, indicating that when the comet was within 0.7 AU its activity was dominated by the continuous release of icy grains and chunks, greatly increasing the active sublimation area by more than a factor of 10 beyond what it had at larger heliocentric distances. A possible interpretation suggests that a large fraction of the comet's mass was lost during the apparition

Discovery of a comet by its Lyman-α emission

International audienceSeveral searches for near-Earth objects have recently been initiated, as a result of increased awareness of the hazard of impacts on the Earth. These programs mainly search for asteroids, so amateur astronomers can still contribute to the discovery of comets, especially out of the orbital plane of the Solar System. An ideal way to search for comets would be to use a spaceborne instrument capable of imaging the whole sky on a daily basis in a systematic and repeatable way. Such an instrument already exists on the solar observatory SOHO; it operates at the Lyman-α wavelength of neutral hydrogen, which is the main component of the emission cloud of a comet. Here we report the discovery, using archival data from this satellite, of a hitherto unnoticed comet which reached a perihelion of 1.546 a.u. on 26 June 1997. We derive the water production rate of the comet as a function of time and find that it increases after perihelion, like that of comet Halley