4797 Ako
Stony Nysian asteroid from the inner regions of the asteroid belt
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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]
| Discovery[1] | |
|---|---|
| Discovered by | T. Nomura K. Kawanishi |
| Discovery site | Minami-Oda Obs. (374) |
| Discovery date | 30 September 1989 |
| Designations | |
| (4797) Ako | |
Named after | Akō, Hyōgo (Japanese city)[2] |
| 1989 SJ · 1978 VY9 1985 QB4 | |
| main-belt · Nysa[3] | |
| Orbital characteristics[1] | |
| Epoch 4 September 2017 (JD 2458000.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 38.49 yr (14,057 days) |
| Aphelion | 2.8553 AU |
| Perihelion | 1.9714 AU |
| 2.4133 AU | |
| Eccentricity | 0.1831 |
| 3.75 yr (1,369 days) | |
| 146.42° | |
| 0° 15m 46.44s / day | |
| Inclination | 1.8108° |
| 320.82° | |
| 78.111° | |
| Physical characteristics | |
| Dimensions | 4.00 km (calculated)[3] 6.000±0.496 km[4][5] |
| 4.085±0.001 h[6] | |
| 0.112±0.021[4][5] 0.21 (assumed)[3] | |
| S[3] | |
| 14.1[4] · 14.3[1][3] · 14.31±0.27[7] | |
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]
Naming
This minor planet was named for the city of Akō in the Hyōgo Prefecture, Japan, and for its ancient castle on the Seto Inland Sea.[2]
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]
