4797 Ako

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]

4797 Ako
Discovery [1]
Discovered byT. Nomura
K. Kawanishi
Discovery siteMinami-Oda Obs. (374)
Discovery date30 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 arc38.49 yr (14,057 days)
Aphelion2.8553 AU
Perihelion1.9714 AU
2.4133 AU
Eccentricity0.1831
3.75 yr (1,369 days)
146.42°
0° 15m 46.44s / day
Inclination1.8108°
320.82°
78.111°
Physical characteristics
Dimensions4.00 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]

    References
    1. "JPL Small-Body Database Browser: 4797 Ako (1989 SJ)" (2017-05-01 last obs.). Jet Propulsion Laboratory. Retrieved 20 June 2017.
    2. Schmadel, Lutz D. (2007). "(4797) Ako". Dictionary of Minor Planet Names – (4797) Ako. Springer Berlin Heidelberg. p. 414. doi:10.1007/978-3-540-29925-7_4700. ISBN 978-3-540-00238-3.
    3. "LCDB Data for (4797) Ako". Asteroid Lightcurve Database (LCDB). Retrieved 4 May 2016.
    4. 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:1109.6407. Bibcode:2011ApJ...741...90M. doi:10.1088/0004-637X/741/2/90. Retrieved 4 May 2016.
    5. 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:1109.4096. Bibcode:2011ApJ...741...68M. doi:10.1088/0004-637X/741/2/68. Retrieved 5 December 2016.
    6. 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:1506.00762. Bibcode:2015Icar..261...34V. doi:10.1016/j.icarus.2015.08.007. Retrieved 4 May 2016.
    8. "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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