C/1990 K1 (Levy)

C/1990 K1 (Levy) is a non-periodic comet discovered by David H. Levy on 20 May 1990. The comet became bright enough to be visible by naked eye.

C/1990 K1 (Levy)
The comet on 14 September 1990
Discovery[1]
Discovered byDavid H. Levy
Discovery date20 May 1990
Designations
1990c, 1990 XX
Orbital characteristics[2]
Epoch1990-Oct-29.0
Observation arc920 days
Earliest precovery date24 September 1989
Perihelion0.939 AU
Eccentricity1.00058
Inclination131.58°
139.36°
Argument of
periapsis		242.67°
Last perihelion24 October 1990
Earth MOID0.209 AU
Comet total
magnitude (M1)		4.6

Observational history

Amateur astronomer David H. Levy discovered the comet on 20 May 1990, during his comet hunting routine, looking towards the star Alpheratz with a 40-cm reflector. He noted that the comet had a magnitude of 9.6 and a tail about 2 arcminutes long.[3][1] That was his sixth comet discovery.[4] The comet was then 2.59 AU from the Sun and 3.07 AU from Earth. The discovery was confirmed the next day, with reported magnitudes between 10 and 11.[3]

The comet brightened and the first naked eye observation of the comet was reported on 23 July, with a magnitude of 6.0. The comet the next week was reported to have tail a bit more than a degree long.[3] In August the comet continued to brighten, with John Bortle reporting magnitudes 5.7 and 4.1 on 3 and 28 August respectively. S. Garro, from France reported a magnitude of 3.6 on 23 August. The tail of the comet could be observed by naked eye, but most reports about its appearance were made with optical aid. The tail was reported to be about 3.5 degrees long at the end of the month. The closest approach to Earth was on 26 August 1990, at a distance of 0.43 AU (64 million km; 40 million mi).[3]

During September 1990, the comet faded slowly, as it was moving away from Earth, but towards perihelion. By 20 September its magnitude was reported to be around 5.[3] On 27 September the comet was observed by the Hubble Space Telescope,[5] the first one observed by it.[4] In October the comet was only visible from the Southern Hemisphere, with the comet fading to a magnitude of 6. Perihelion took place on 24 October.[3] Solar elongation decreased to 24 degrees in November and observations were few. The comet was recovered on 10 December by Alan Hale, at magnitude 7. Subsequently, the comet started moving northwards. The next two months tail lengths between 0.5 and 1.5 degrees were reported while the comet was fading slowly.[3]

The comet was last detected on 1 April 1992 in CCD images obtained by the Oak Ridge Observatory with 155-cm reflector.[3]

Scientific results
Comet Levy by the Hubble Space Telescope (core enlarged four-fold in smaller image)

Comet Levy was well positioned in the sky to be observed both before and after perihelion and quite bright. The production rates OH, NH, CN, C2, and C3 were measured in different distances from the Sun, with most species having a larger production rate before perihelion, with most pronounced asymmetry being that of hydroxyl, with its production peaking about a month before that of the other molecules.[6] In shorter timescales, the comet was found to variate both in optical and ultraviolet wavelengths.[7] The variation in optical wavelength was estimated to be 18.9 hours in late August,[6] while the International Ultraviolet Explorer (IUE) on 18 September detected a period of 17.0 ± 0.1 hours. That period also doesn't fit well with observations made by IUE on 11 and 13 September, indicating that the period decreased between the observations. By January 1991 the brightness variation was less than 1%.[7]

Comet Levy was observed by Hubble Space Telescope (HST) on 27 September 1990, about 5 months after its launch. As the tracking of Solar System objects had not yet been developed, HST obtained only short exposures of the comet with the Wide Field Camera.[8] Two 4 seconds exposures with a red broadband filter were obtained 6.5 hours apart. The coma was found to be brighter at the sunward side than the tailward, indicating that sublimation takes place primarily at the dayside of the nucleus. An arc of dust was found to expand in the coma, with the creation of such arcs probably resulting in the observed periodic brightness changes of the comet. No jets could be confidently observed.[8]

The velocity of H2O+ ions was measured using the Doppler shift of the emission lines from 16 to 25 August 1990. It was found that velocities near the nucleus were around 10 km/s while in the tail they accelerated to 50–70 km/s. The mean H2O+ production rate within these dates was 1.5×1027 per second.[9]

The comet was observed with the Hopkins Ultraviolet Telescope on 10 December 1990, during the Space Shuttle mission Astro-1. The ultraviolet spectrum obtained revealed the presence of carbon monoxide (CO), atomic hydrogen, carbon and sulfur. The OI and OII lines could be masked off due their presence in the airglow. CO production was estimated to be (1.4±0.3)×1028 molecules per second.[10] IUE detected emission lines of OH, CS, and CO2+, which exhibited flux variation within a period of hours. It also detected CO.[7]

Methanol fluorescence was detected in infrared images of the comet. These images also constitute the first two-dimensional images of methanol distribution in a comet's coma.[11] The methanol production rate was estimated to be (3±1)×1026 molecules per second on 10 August 1990.[12] The rotational lines of methanol as observed by IRAM indicate a production of 2.2×1027 per second on 26–31 August. It indicates that methanol is an important volatile in comets.[13] IRAM also detected rotational lines of hydrogen sulfide. Its presence indicates that the comet was formed in a location with very low temperatures.[14]

Caltech submillimeter observatory detected emission lines of hydrogen cyanide (J=4-3 transion line), formaldehyde (J=5(1,5)-4(1,4) lines) and methanol (J=5-4 band). The rotational temperature of HCN was estimated to be 33 ± 1 K, which was higher than predicted, indicating that collisions of HCN take place. Formaldehyde rotational temperature was close to the expected.[15]

References
  1. Levy, D. H.; Hale, A.; Morris, C. S. (1 May 1990). "Comet Levy (1990c)". International Astronomical Union Circular (5017): 1. ISSN 0081-0304.
  2. "Small-Body Database Lookup: C/1990 K1 (Levy)". ssd.jpl.nasa.gov. Retrieved 21 August 2023.
  3. Kronk, Gary W.; Meyer, Maik; Seargent, David A. J. (2017). Cometography: a catalog of comets. Cambridge: Cambridge university press. pp. 501–509. ISBN 9780521872164.
  4. Hale, Alan (15 August 2020). "Comet of the Week: Levy 1990c". RocketSTEM. Retrieved 21 August 2023.
  5. "Comet Levy". hubblesite.org. 4 October 1990. Retrieved 21 August 2023.
  6. Schleicher, David G.; Millis, Robert L.; Osip, David J.; Birch, Peter V. (December 1991). "Comet Levy (1990c): Groundbased photometric results". Icarus. 94 (2): 511–523. Bibcode:1991Icar...94..511S. doi:10.1016/0019-1035(91)90244-N.
  7. Feldman, P.D.; Budzien, S.A.; Festou, M.C.; A'Hearn, M.F.; Tozzi, G.P. (January 1992). "Ultraviolet and visible variability of the coma of Comet Levy (1990c)". Icarus. 95 (1): 65–72. Bibcode:1992Icar...95...65F. doi:10.1016/0019-1035(92)90191-9.
  8. Weaver, H.A.; A'Hearn, M.F.; Feldman, P.D.; Arpigny, C.; Baum, W.A.; Brandt, J.C.; Light, R.M.; Westphal, J.A. (May 1992). "Inner coma imaging of Comet Levy (1990c) with the Hubble space telescope". Icarus. 97 (1): 85–98. Bibcode:1992Icar...97...85W. doi:10.1016/0019-1035(92)90058-F.
  9. Rauer, H.; Jockers, K. (March 1993). "Doppler Measurements of the H2O+ Ion Velocity in the Plasma Tail of Comet Levy 1990c". Icarus. 102 (1): 117–133. Bibcode:1993Icar..102..117R. doi:10.1006/icar.1993.1037.
  10. Feldman, P. D.; Davidsen, A. F.; Blair, W. P.; Bowers, C. W.; Dixon, W. V.; Durrance, S. T.; Ferguson, H. C.; Henry, R. C.; Kimble, R. A.; Kriss, G. A.; Kruk, J. W.; Long, K. S.; Moos, H. W.; Vancura, O.; Gull, T. R. (September 1991). "Observations of Comet Levy (1990c) with the Hopkins Ultraviolet Telescope". The Astrophysical Journal. 379: L37. Bibcode:1991ApJ...379L..37F. doi:10.1086/186148.
  11. Klavetter, James Jay; Hoban, Susan (January 1992). "Imaging the 3.4-μm feature in Comet Levy (1990c)". Icarus. 95 (1): 60–64. Bibcode:1992Icar...95...60K. doi:10.1016/0019-1035(92)90190-I.
  12. Hoban, Susan (July 1993). "Serendipitous Images of Methanol in Comet Levy (1990 XX)". Icarus. 104 (1): 149–151. Bibcode:1993Icar..104..149H. doi:10.1006/icar.1993.1089.
  13. Bockelee-Morvan, D.; Crovisier, J.; Colom, P.; Despois, D. (1 July 1994). "The rotational lines of methanol in comets Austin 1990 V and Levy 1990 XX". Astronomy and Astrophysics. 287: 647–665. Bibcode:1994A&A...287..647B. ISSN 0004-6361.
  14. Crovisier, J.; Despois, D.; Bockelée-Morvan, D.; Colom, P.; Paubert, G. (October 1991). "Microwave observations of hydrogen sulfide and searches for other sulfur compounds in comets Austin (1989c1) and Levy (1990c)". Icarus. 93 (2): 246–258. Bibcode:1991Icar...93..246C. doi:10.1016/0019-1035(91)90210-K.
  15. Schloerb, P.; Ge, W. (1 September 1990). "Comet Levy (1990c)". International Astronomical Union Circular (5086): 1. ISSN 0081-0304.
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