6247 Amanogawa

6247 Amanogawa, provisional designation 1990 WY₃, is a background asteroid from the inner regions of the asteroid belt, approximately 7 kilometers (4 miles) in diameter. It was discovered on 21 November 1990, by Japanese amateur astronomers Kin Endate and Kazuro Watanabe at the Kitami Observatory.^[1] The X-type asteroid has a rotation period of 12.38 hours.^[6] It was named after the Amanogawa River on the island of Hokkaido, Japan.^[1]

6247 Amanogawa

Discovery[1]
Discovered by	K. Endate K. Watanabe
Discovery site	Kitami Obs.
Discovery date	21 November 1990
Designations
MPC designation	(6247) Amanogawa
Named after	Amanogawa River[1] (Japanese river)
Alternative designations	1990 WY3 · 1992 FR1
Minor planet category	main-belt[1][2] · (inner) background[3]
Orbital characteristics[2]
Epoch 23 March 2018 (JD 2458200.5)
Uncertainty parameter 0
Observation arc	27.45 yr (10,025 d)
Aphelion	2.5286 AU
Perihelion	2.2604 AU
Semi-major axis	2.3945 AU
Eccentricity	0.0560
Orbital period (sidereal)	3.71 yr (1,353 d)
Mean anomaly	168.98°
Mean motion	0° 15m 57.6s / day
Inclination	8.5728°
Longitude of ascending node	105.57°
Argument of perihelion	287.33°
Physical characteristics
Mean diameter	6.722±0.098 km[4][5] 11.63 km (calculated)[6]
Synodic rotation period	12.369±0.0107 h[7] 12.38±0.02 h[8]
Geometric albedo	0.057 (assumed)[6] 0.165±0.018[4][5]
Spectral type	C (assumed)[6] X (SDSS-MOC)[9]
Absolute magnitude (H)	13.2[5] 13.288±0.006 (R)[7] 13.3[2] 13.4[6]

Orbit and classification

Amanogawa is a non-family asteroid from the main belt's background population.^[3] It orbits the Sun in the inner asteroid belt at a distance of 2.3–2.5 AU once every 3 years and 9 months (1,353 days; semi-major axis of 2.39 AU). Its orbit has an eccentricity of 0.06 and an inclination of 9° with respect to the ecliptic.^[2] The body's observation arc begins with a precovery at Palomar Observatory on 14 November 1990, just one week prior to its official discovery observation at Kitami.^[1]

Physical characteristics

In the SDSS-based taxonomy, Amanogawa has been characterized as an X-type asteroid.^[9] It is also a generically assumed C-type asteroid.^[6]

Rotation period

In September 2008, a rotational lightcurve of Amanogawa was obtained from photometric observations at the Oakley Southern Sky Observatory and Oakley Observatory. Lightcurve analysis gave a well-defined rotation period of 12.38 hours with a brightness variation of 0.48 magnitude (U=3).^[8] In February 2014, astronomers at the Palomar Transient Factory measured a similar period of 12.369 hours and an amplitude of 0.38 magnitude in the R-band (U=2).^[7]

Diameter and albedo

According to the survey carried out by the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer, Amanogawa measures 6.722 kilometers in diameter and its surface has an albedo of 0.165.^[4][5] The Collaborative Asteroid Lightcurve Link assumes a standard albedo for a carbonaceous asteroid of 0.057 and calculates a diameter of 11.63 kilometers based on an absolute magnitude of 13.4.^[6]

Naming

This minor planet was named after the Japanese Amanogawa River that through the town of Kaminokuni on the island of Hokkaido. "Amanogawa" also means "Milky Way" in Japanese.^[1] The official naming citation was published by the Minor Planet Center on 22 February 1997 (M.P.C. 29146).^[10]