4797 Ako, provisional designation 1989 SJ, is a stony Nysian asteroid from the inner regions of the asteroid belt, approximately 5 kilometers in diameter. It was discovered on 30 September 1989, by the Japanese astronomers Toshiro Nomura and Kōyō Kawanishi at the Minami-Oda Observatory (374), Japan.[8] The asteroid was named for the Japanese city of Akō.[2]
Orbit and classification
Ako is a member of the stony subgroup of the Nysa family, which is named after its largest member 44 Nysa. It orbits the Sun in the inner main-belt at a distance of 2.0–2.9 AU once every 3 years and 9 months (1,369 days). Its orbit has an eccentricity of 0.18 and an inclination of 2° with respect to the ecliptic.[1]
In 1978, it was first identified as 1978 VY9 at Palomar Observatory, extending the body's observation arc by 11 years prior to its official discovery observation at Minami-Oda Observatory.[8]
Physical characteristics
Rotation period
A rotational lightcurve of Ako was obtained for the first time from photometric observations made at the U.S. Ricky Observatory, Missouri, in November 2008. It gave a well-defined rotation period of 4.085±0.001 hours with a relatively high brightness variation of 0.90 in magnitude (U=3), indicative of a non-spheroidal shape.[6]
Diameter and albedo
According to NASA's space-based Wide-field Infrared Survey Explorer with its subsequent NEOWISE mission, Ako measures 6.0 kilometers in diameter and its surface has an albedo of 0.11,[4][5] while the Collaborative Asteroid Lightcurve Link (CALL) assumes a standard albedo for stony asteroids of 0.21, and calculates a diameter of 4.0 kilometers, as the higher the albedo (reflectivity), the smaller a body's diameter for a certain absolute magnitude (brightness).[3]
Known for its salt production, Ako is the birthplace of the fictional account of Chūshingura, a tale about the forty-seven Ronin who committed seppuku after avenging their master. The city is also the home of the second discoverer's private Minami-Oda observatory, where Kōyō Kawanishi observes small Solar System bodies.[2] The official naming citation was published by the Minor Planet Center on 27 June 1991 (M.P.C. 18465).[9]
