6244 Okamoto

6244 Okamoto, provisional designation 1990 QF, is a background asteroid and binary system from the inner regions of the asteroid belt, approximately 5 kilometers (3 miles) in diameter. It was discovered on 20 August 1990, by Japanese astronomer Tsutomu Seki at the Geisei Observatory in Kōchi, Japan, and later named after Japanese school teacher Hiroshi Okamoto.[1] The presumed S-type asteroid has a short rotation period of 2.9 hours.[4] The discovery of its minor-planet moon was announced in October 2006.[6]

6244 Okamoto
Discovery [1]
Discovered byT. Seki
Discovery siteGeisei Obs.
Discovery date20 August 1990
Designations
(6244) Okamoto
Named after
Hiroshi Okamoto [1]
(Japanese school teacher)
1990 QF · 1952 SG1
1987 SL25
main-belt [1][2] · (inner)
background [3] · Flora [4]
Orbital characteristics [2]
Epoch 23 March 2018 (JD 2458200.5)
Uncertainty parameter 0
Observation arc84.58 yr (30,893 d)
Aphelion2.4888 AU
Perihelion1.8319 AU
2.1604 AU
Eccentricity0.1520
3.18 yr (1,160 d)
208.44°
0° 18m 37.44s / day
Inclination5.3954°
331.33°
51.576°
Known satellites1 (D: 1.67 km P: 20.32 h)[4][5][6]
Physical characteristics
Mean diameter
4.59 km (derived)[4]
6.69 km (estimated)[5]
2.8958±0.00009 h[7]
2.8958±0.0001 h[6]
2.89585±0.00009 h[8]
2.899±0.003 h[9]
0.14 (estimated)[5]
0.24 (assumed)[4]
S (assumed)[4]
13.41±0.04 (R)[7]
13.5[2]
13.66±0.26[10]
13.9[4][11]

    Orbit and classification

    Okamoto is a non-family asteroid of the main belt's background population when applying the hierarchical clustering method to its proper orbital elements.[3] Based on osculating Keplerian orbital elements, the asteroid has also been classified as a member of the Flora family (402), a giant asteroid family and the largest family of stony asteroids in the main-belt.[4]

    It orbits the Sun in the inner asteroid belt at a distance of 1.8–2.5 AU once every 3 years and 2 months (1,160 days; semi-major axis of 2.16 AU). Its orbit has an eccentricity of 0.15 and an inclination of 5° with respect to the ecliptic.[2] The body's observation arc begins with a precovery taken at the Uccle Observatory in September 1933, nearly 57 years prior to its official discovery observation at Geisei.[1]

    Physical characteristics

    Okamoto is an assumed S-type asteroid,[4] the most common spectral type in the inner asteroid belt.

    Rotation period

    Several rotational lightcurves of Okamoto have been obtained from photometric observations since 2006.[7][6][8][9] Analysis of the best-rated lightcurve gave a well-defined rotation period of 2.8958 hours with a consolidated brightness amplitude between 0.11 and 0.15 magnitude (U=3).[4][7]

    Diameter and albedo

    The Collaborative Asteroid Lightcurve Link assumes an albedo of 0.24 – taken from 8 Flora, the parent body of the Flora family – and derives a diameter of 4.59 kilometers based on an absolute magnitude of 13.9.[4] Based on an assumed albedo of 0.14, the Johnston's archive estimates a diameter of 6.69 and 6.89 kilometer for the primary and the combined system, respectively (see below).[5]

    Satellite

    In 2006, photometric observations obtained by David Higgins (E14) at Canberra, Australia, Donald Pray at Carbuncle Hill Observatory (912), as well as Peter Kušnirák and Petr Pravec at Ondřejov Observatory revealed that Okamoto is a synchronous binary asteroid with a minor-planet moon orbiting it every 20.32 hours at an estimated average distance of 13 km. The discovery was announced on 19 October 2006.[6] The mutual occultation events indicated the presence of a satellite 25% the size of its primary, which translates into an estimated diameter of 1.15–1.67 kilometers depending on the underlying size estimate of the primary.[4][5]

    Naming

    This minor planet was named after Japanese Entomologist and elementary-school teacher Hiroshi Okamoto (born 1915), who inspired the discoverer Tsutomu Seki with a love of the stars.[1] The official naming citation was published by the Minor Planet Center on 10 June 1998 (M.P.C. 32093).[12]

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    References
    1. "6244 Okamoto (1990 QF)". Minor Planet Center. Retrieved 22 May 2018.
    2. "JPL Small-Body Database Browser: 6244 Okamoto (1990 QF)" (2018-04-25 last obs.). Jet Propulsion Laboratory. Retrieved 22 May 2018.
    3. "Asteroid 6244 Okamoto". Small Bodies Data Ferret. Retrieved 22 May 2018.
    4. "LCDB Data for (6244) Okamoto". Asteroid Lightcurve Database (LCDB). Retrieved 22 May 2018.
    5. Johnston, Wm. Robert (21 September 2014). "Asteroids with Satellites Database – (450894) 2008 BT18". Johnston's Archive. Retrieved 22 May 2018.
    6. Higgins, D.; Pray, D.; Kusnirak, P.; Pravec, P. (October 2006). "(6244) Okamoto". Central Bureau Electronic Telegrams. 681 (681): 1. Bibcode:2006CBET..681....1H. Retrieved 22 May 2018.
    7. Pravec, P.; Scheirich, P.; Vokrouhlický, D.; Harris, A. W.; Kusnirák, P.; Hornoch, K.; et al. (March 2012). "Binary asteroid population. 2. Anisotropic distribution of orbit poles of small, inner main-belt binaries". Icarus. 218 (1): 125–143. Bibcode:2012Icar..218..125P. doi:10.1016/j.icarus.2011.11.026.
    8. Higgins, David; Oey, Julian; Pravec, Petr (January 2011). "Period Determination of Binary Asteroid Targets Observed at Hunters Hill Observatory: May–September 2009". The Minor Planet Bulletin. 38 (1): 46–49. Bibcode:2011MPBu...38...46H. ISSN 1052-8091.
    9. Aznar Macias, Amadeo (April 2017). "Lightcurve Analysis for Nine Main-belt Asteroids. Rotation Period and Physical Parameters from APT Observatory Group: 2016 October–December". The Minor Planet Bulletin. 44 (2): 139–141. Bibcode:2017MPBu...44..139A. ISSN 1052-8091.
    10. Veres, Peter; Jedicke, Robert; Fitzsimmons, Alan; Denneau, Larry; Granvik, Mikael; Bolin, Bryce; et al. (November 2015). "Absolute magnitudes and slope parameters for 250,000 asteroids observed by Pan-STARRS PS1 – Preliminary results". Icarus. 261: 34–47. arXiv:1506.00762. Bibcode:2015Icar..261...34V. doi:10.1016/j.icarus.2015.08.007.
    11. Pravec, Petr; Harris, Alan W.; Kusnirák, Peter; Galád, Adrián; Hornoch, Kamil (September 2012). "Absolute magnitudes of asteroids and a revision of asteroid albedo estimates from WISE thermal observations". Icarus. 221 (1): 365–387. Bibcode:2012Icar..221..365P. doi:10.1016/j.icarus.2012.07.026.
    12. "MPC/MPO/MPS Archive". Minor Planet Center. Retrieved 22 May 2018.

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