4797 Ako

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4797 Ako
Discovery [1]
Discovered by T. Nomura
K. Kawanishi
Discovery site Minami-Oda Obs. (374)
Discovery date 30 September 1989
MPC designation (4797) Ako
Named after
Akō, Hyōgo
(Japanese city)[2]
1989 SJ · 1978 VY9
1985 QB4
main-belt · Nysa[3]
Orbital characteristics[1]
Epoch 16 February 2017 (JD 2457800.5)
Uncertainty parameter 0
Observation arc 38.00 yr (13,880 days)
Aphelion 2.8545 AU
Perihelion 1.9699 AU
2.4122 AU
Eccentricity 0.1834
3.75 yr (1,368 days)
0° 15m 47.16s / day
Inclination 1.8123°
Physical characteristics
Dimensions 4.00 km (calculated)[3]
6.000±0.496 km[4][5]
4.085±0.001 h[6]
0.21 (assumed)[3]
14.1[4] · 14.3[1][3] · 14.31±0.27[7]

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 by the Japanese astronomers Toshiro Nomura and Kōyō Kawanishi at the Minami-Oda Observatory, Japan, on 30 September 1989.[8]

The S-type asteroid is a member of the stony subgroup of the main-belt's Nysa family, which is named after its largest member 44 Nysa. It orbits the Sun at a distance of 2.0–2.9 AU once every 3 years and 9 months (1,368 days). Its orbit has an eccentricity of 0.18 and an inclination of 2° with respect to the ecliptic.[1] The first precovery was taken at Palomar Observatory in 1978, extending the asteroid's observation arc by 11 years prior to its discovery.[8]

A rotational light-curve of this asteroid 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]

According to NASA's space-based Wide-field Infrared Survey Explorer with its subsequent NEOWISE mission, the asteroid 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 the body's diameter, at a constant absolute magnitude (brightness).[3]

The minor planet was named for the city of Akō in the Hyōgo Prefecture, Japan, and for its ancient castle on the Seto Inland Sea. Known for its salt production, the city is the birthplace of the fictional account of Chūshingura, a tale about the forty-seven Ronin who committed seppuku after avenging their master. Ako is also the home of the second discoverer's private Minami-Oda observatory, where Kōyō Kawanishi observes small Solar System bodies.[2] Naming citation was published on 27 June 1991 (M.P.C. 18465).[9]


  1. ^ a b c d "JPL Small-Body Database Browser: 4797 Ako (1989 SJ)" (2016-11-05 last obs.). Jet Propulsion Laboratory. Retrieved 5 December 2016. 
  2. ^ a b Schmadel, Lutz D. (2007). Dictionary of Minor Planet Names – (4797) Ako. Springer Berlin Heidelberg. p. 414. ISBN 978-3-540-00238-3. Retrieved 4 May 2016. 
  3. ^ a b c d e f "LCDB Data for (4797) Ako". Asteroid Lightcurve Database (LCDB). Retrieved 4 May 2016. 
  4. ^ a b c d Mainzer, A.; Grav, T.; Masiero, J.; Hand, E.; Bauer, J.; Tholen, D.; et al. (November 2011). "NEOWISE Studies of Spectrophotometrically Classified Asteroids: Preliminary Results". The Astrophysical Journal. 741 (2): 25. arXiv:1109.6407Freely accessible. Bibcode:2011ApJ...741...90M. doi:10.1088/0004-637X/741/2/90. Retrieved 4 May 2016. 
  5. ^ a b c Masiero, Joseph R.; Mainzer, A. K.; Grav, T.; Bauer, J. M.; Cutri, R. M.; Dailey, J.; et al. (November 2011). "Main Belt Asteroids with WISE/NEOWISE. I. Preliminary Albedos and Diameters". The Astrophysical Journal. 741 (2): 20. arXiv:1109.4096Freely accessible. Bibcode:2011ApJ...741...68M. doi:10.1088/0004-637X/741/2/68. Retrieved 5 December 2016. 
  6. ^ a b Bennefeld, Craig; Bass, Stephen; Blair, Ricco; Cunningham, Kendrick; Hill, Da'quia; McHenry, Michael; et al. (October 2009). "Asteroid Lightcurve Analysis at Ricky Observatory". The Minor Planet Bulletin. 36 (4): 147–148. Bibcode:2009MPBu...36..147B. ISSN 1052-8091. Retrieved 4 May 2016. 
  7. ^ 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:1506.00762Freely accessible. Bibcode:2015Icar..261...34V. doi:10.1016/j.icarus.2015.08.007. Retrieved 4 May 2016. 
  8. ^ a b "4797 Ako (1989 SJ)". Minor Planet Center. Retrieved 4 May 2016. 
  9. ^ "MPC/MPO/MPS Archive". Minor Planet Center. Retrieved 4 May 2016. 

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