4606 Saheki

4606 Saheki, provisional designation 1987 UM₁, is a stony Flora asteroid from the inner regions of the asteroid belt, approximately 7 kilometers in diameter.

4606 Saheki

Lightcurve-based 3D-model of Saheki
Discovery [1]
Discovered by	T. Seki
Discovery site	Geisei Obs.
Discovery date	27 October 1987
Designations
MPC designation	(4606) Saheki
Named after	Tsuneo Saheki (astronomer)[2]
Alternative designations	1987 UM1 · 1972 GA1 1977 TJ7 · 1977 VF2 1982 FH4
Minor planet category	main-belt · Flora [3]
Orbital characteristics [1]
Epoch 4 September 2017 (JD 2458000.5)
Uncertainty parameter 0
Observation arc	63.81 yr (23,305 days)
Aphelion	2.4805 AU
Perihelion	2.0231 AU
Semi-major axis	2.2518 AU
Eccentricity	0.1016
Orbital period (sidereal)	3.38 yr (1,234 days)
Mean anomaly	202.74°
Mean motion	0° 17m 30.12s / day
Inclination	2.6338°
Longitude of ascending node	241.26°
Argument of perihelion	251.92°
Physical characteristics
Dimensions	6.655±0.069[4] 6.712±0.041 km[5] 7.14 km (calculated)[3]
Synodic rotation period	4.969±0.003 h[a] 4.97347±0.00005 h[6] 5.032±0.001 h[7]
Geometric albedo	0.24 (assumed)[3] 0.3266±0.0245[5] 0.332±0.088[4]
Spectral type	S [3]
Absolute magnitude (H)	12.7[5] · 13.0[1][3] · 13.35±0.32[8]

The asteroid was discovered on 27 October 1987, by Japanese astronomer Tsutomu Seki at Geisei Observatory, Japan.^[9] It was later named after Japanese astronomer Tsuneo Saheki.^[2]

Classification and orbit

Saheki is a member of the Flora family, one of the largest families of stony asteroids. It orbits the Sun in the inner main-belt at a distance of 2.0–2.5 AU once every 3 years and 5 months (1,234 days). Its orbit has an eccentricity of 0.10 and an inclination of 3° with respect to the ecliptic.^[1] The first precovery was taken at Palomar Observatory in 1953, extending the asteroid's observation arc by 34 years prior to its discovery.^[9]

Physical characteristics

Rotation period

In January 2009, a rotational lightcurve of Saheki was obtained from photometric observations by David Higgins at Hunters Hill Observatory, Australia. Lightcurve analysis rendered a well-defined rotation period of 4.969 hours with a brightness variation of 0.56 in magnitude (U=3).^[a]

Two months later, in March 2009, a second lightcurve was obtained at the Via Capote Observatory (G69), California. It gave a period of 5.032 and an amplitude of 0.68 in magnitude (U=3-).^[7]

Spin axis

In 2013, an international study modeled a lightcurve with a concurring period of 4.97347 hours and found a spin axis of (44.0°, 59.0°) and (222.0°, 68.0°) in ecliptic coordinates (λ, β), respectively (Q=2).^[6]

Diameter and albedo

According to the survey carried out by the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer, Saheki has a high albedo of 0.33 and a diameter of 6.7 kilometers,^[4][5] while the Collaborative Asteroid Lightcurve Link calculates a diameter of 7.1 kilometers, based on an assumed albedo of 0.24, derived from 8 Flora, the Flora family's namesake and largest member.^[3]

Naming

This minor planet was named after Japanese astronomer and president of the Toa Astronomical Society, Tsuneo Saheki (1916–1996). Over half a century, Saheki as gathered large inventory of observational data of the planet Mars.^[2] The Martian crater Saheki is also named in his honour. The official naming citation was published by the Minor Planet Center on 28 May 1991 (M.P.C. 18308).^[10]

Notes

1. Higgins (2011) web: rotation period 4.969±0.003 hours with a brightness amplitude of 0.56 mag. The Collaborative Asteroid Lightcurve Link assigns a quality code of U=3 to the period solution, which denotes a secure result within the precision given and no ambiguity. Summary figures for (4606) Saheki at Collaborative Asteroid Lightcurve Link (CALL)