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8306 Shoko
Discovery
Discovered by	A. Nakamura
Discovery site	Kuma Kogen Obs.
Discovery date	24 February 1995
Designations
MPC designation	(8306) Shoko
Named after	Shoko Sawada ; (Japanese singer)
Alternative designations	1995 DY1 · 1986 QA6
Minor planet category	main-belt · (inner); Flora
Orbital characteristics
	Epoch 23 March 2018 (JD 2458200.5)
	Uncertainty parameter 0
Observation arc	31.41 yr (11,474 d)
Aphelion	2.7366 AU
Perihelion	1.7455 AU
Semi-major axis	2.2411 AU
Eccentricity	0.2211
Orbital period (sidereal)	3.35 yr (1,225 d)
Mean anomaly	126.86°
Mean motion	0° 17m 37.68s / day
Inclination	4.7821°
Longitude of ascending node	208.66°
Argument of perihelion	143.48°
Known satellites	1 (D: 1.28 km P: 36.20 h)
Physical characteristics
Mean diameter	2.38 km (calculated); 3.21 km (estimate)
Synodic rotation period	3.3503±0.0002 h; 3.604±0.002 h
Geometric albedo	0.24 (assumed)
Spectral type	S (assumed)
Absolute magnitude (H)	14.83±0.07 (R); 14.9; 15.28

8306 Shoko, provisional designation 1995 DY₁, is a Florian asteroid and a synchronous binary system from the inner regions of the asteroid belt, approximately 3 kilometers (2 miles) in diameter. It was discovered on 24 February 1995, by Japanese astronomer Akimasa Nakamura at the Kuma Kogen Astronomical Observatory in southern Japan, who named it after Japanese singer-songwriter Shoko Sawada.^[1] The likely S-type asteroid has a rotation period of 3.35 hours.^[3] The discovery of its 1.3-kilometer minor-planet moon was announced in December 2013.^[6]

Orbit and classification

Shoko is a member of the Flora family (402),^[3]^[4] a giant asteroid family and the largest family of stony asteroids in the main-belt.^[9] It orbits the Sun in the inner asteroid belt at a distance of 1.7–2.7 AU once every 3 years and 4 months (1,225 days; semi-major axis of 2.24 AU). Its orbit has an eccentricity of 0.22 and an inclination of 5° with respect to the ecliptic.^[2] The body's observation arc begins with its first observation as 1986 QA₆ at the Siding Spring Observatory in August 1986, nearly 9 years prior to its official discovery observation at Kuma Kogen.^[1]

Physical characteristics

Shoko is an assumed, stony S-type asteroid,^[3] which is also the overall spectral type of the Florian asteroids.^[9]^: 23 It has an absolute magnitude between 14.83 and 15.28.^[2]^[3]

Rotation period

In September and October 2013, two rotational lightcurves of Shoko were obtained from photometric observations by astronomers Petr Pravec and David Polishook.^[6]^[7] Lightcurve analysis gave a well-defined rotation period of 3.3503 and 3.604 hours with a low brightness amplitude of 0.11 and 0.10 magnitude, respectively (U=3/3).^[3]

Diameter and albedo

The Collaborative Asteroid Lightcurve Link assumes an albedo of 0.24 – derived from 8 Flora, the parent body of the Flora family – and calculates a diameter of 2.38 kilometers based on an absolute magnitude of 15.28,^[3] while the Johnston's Archive estimates a diameter 3.21.^[5]

Satellite

In October 2013, photometric observations by Petr Pravec and a large international collaboration, revealed, that Shoko is an synchronous binary asteroid with a minor-planet moon orbiting it every 36.20 hours (1.508 days) at an estimated average distance of 9.4 km.^[5] The discovery was announced in December 2013.^[6] The mutual occultation events suggest the presence of a satellite with a diameter 1.28 km or more than 40% the size of its primary.^[5] The discoverers also suspect that there might be a possible third body,^[6] which would make it a rare trinary asteroid. As of 2018, no follow-up observations have been conducted.^[3]

Naming

This minor planet was named by the discoverer after Japanese singer-songwriter of ballads and pop songs, Shoko Sawada (born 1962), who has recorded a large number of studio albums since her debut in 1979.^[1] The official naming citation was published by the Minor Planet Center on 10 June 1998 (M.P.C. 32095).^[10]

References

^ ^a ^b ^c ^d ^e ^f "8306 Shoko (1995 DY1)". Minor Planet Center. Retrieved 2 May 2018.
^ ^a ^b ^c ^d ^e "JPL Small-Body Database Browser: 8306 Shoko (1995 DY1)" (2018-01-24 last obs.). Jet Propulsion Laboratory. Retrieved 2 May 2018.
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l "LCDB Data for (8306) Shoko". Asteroid Lightcurve Database (LCDB). Retrieved 2 May 2018.
^ ^a ^b "Asteroid 8306 Shoko – Nesvorny HCM Asteroid Families V3.0". Small Bodies Data Ferret. Retrieved 27 October 2019.
^ ^a ^b ^c ^d ^e Johnston, Wm. Robert (21 September 2014). "Asteroids with Satellites Database – (8306) Shoko". Johnston's Archive. Retrieved 2 May 2018.
^ ^a ^b ^c ^d ^e ^f ^g Pravec, P.; Kusnirak, P.; Hornoch, K.; Galad, A.; Krugly, Yu. N.; Chiorny, V.; et al. (December 2013). "(8306) Shoko". IAU Circ. 9268 (9268): 1. Bibcode:2013IAUC.9268....1P.
^ ^a ^b Polishook, David (January 2014). "Spins, Lightcurves, and Binarity of Eight Asteroid Pairs: 4905, 7745, 8306 16815, 17288, 26416, 42946, and 74096". The Minor Planet Bulletin. 41 (1): 49–53. Bibcode:2014MPBu...41...49P. ISSN 1052-8091.
^ 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. S2CID 53493339.
^ ^a ^b Nesvorný, D.; Broz, M.; Carruba, V. (December 2014). "Identification and Dynamical Properties of Asteroid Families". Asteroids IV. pp. 297–321. arXiv:1502.01628. Bibcode:2015aste.book..297N. doi:10.2458/azu_uapress_9780816532131-ch016. ISBN 9780816532131. S2CID 119280014.
^ "MPC/MPO/MPS Archive". Minor Planet Center. Retrieved 2 May 2018.