3700 Geowilliams

3700 Geowilliams, provisional designation 1984 UL₂, is a stony background asteroid from the inner regions of the asteroid belt, approximately 8 kilometers (5 miles) in diameter. It was discovered on 23 October 1984, by American astronomer couple Carolyn and Eugene Shoemaker at the Palomar Observatory in California, United States.^[1] The S k-subtype has a rotation period of 14.38 hours. It was named for Australian geologist George E. Williams.^[1]

3700 Geowilliams

Discovery[1]
Discovered by	C. Shoemaker E. Shoemaker
Discovery site	Palomar Obs.
Discovery date	23 October 1984
Designations
MPC designation	(3700) Geowilliams
Named after	George E. Williams[1] (Australian geologist)
Alternative designations	1984 UL2 · 1973 YF2 1977 UJ
Minor planet category	main-belt[1][2] · (inner)[3] background[4]
Orbital characteristics[2]
Epoch 23 March 2018 (JD 2458200.5)
Uncertainty parameter 0
Observation arc	43.54 yr (15,902 d)
Aphelion	2.9602 AU
Perihelion	1.8695 AU
Semi-major axis	2.4148 AU
Eccentricity	0.2258
Orbital period (sidereal)	3.75 yr (1,371 d)
Mean anomaly	293.18°
Mean motion	0° 15m 45.36s / day
Inclination	12.121°
Longitude of ascending node	289.16°
Argument of perihelion	153.06°
Physical characteristics
Mean diameter	7.712±0.130 km[5] 7.74±1.83 km[6] 7.753±0.152 km[7] 8.70±0.30 km[8] 8.82±0.86 km[9] 8.97 km (calculated)[3]
Synodic rotation period	14.383±0.0183 h[10] 14.387±0.003 h[a]
Geometric albedo	0.20 (assumed)[3] 0.227±0.045[9] 0.23±0.13[6] 0.233±0.033[8] 0.2970±0.0516[5]
Spectral type	SMASS = S k[2]
Absolute magnitude (H)	12.443±0.002 (R)[10] 12.50[5][8][9] 12.6[2][3] 12.89[6] 12.94±0.46[11]

Orbit and classification

Geowilliams is a non-family asteroid from the main belt's background population.^[4] It orbits the Sun in the inner main-belt at a distance of 1.9–3.0 AU once every 3 years and 9 months (1,371 days; semi-major axis of 2.41 AU). Its orbit has an eccentricity of 0.23 and an inclination of 12° with respect to the ecliptic.^[2] The body's observation arc begins with its first observation as 1973 YF₂ at Crimea-Nauchnij in December 1973, almost 11 years prior to its official discovery observation at Palomar.^[1]

Physical characteristics

In the SMASS classification, Geowilliams is a Sk-subtype that transitions between the common S-type asteroid and the K-type asteroid. The latter spectral type is often found among members of the Eos family.^[2]

Rotation period

In January 2008, a rotational lightcurve of Geowilliams was obtained from photometric observations by Australian amateur astronomer David Higgins at the Hunters Hill Observatory (E14). Lightcurve analysis gave a well-defined rotation period of 14.387 hours with a brightness variation of 0.40 magnitude (U=3).^[a] In July 2010, a similar period of 14.383 hours and an amplitude of 0.42 was measured at the Palomar Transient Factory in California (U=2).^[10]

Diameter and albedo

According to the surveys carried out by the Japanese Akari satellite and the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer, Geowilliams measures between 7.712 and 8.82 kilometers in diameter and its surface has an albedo between 0.227 and 0.297.^{[5][6][7][8][9]}

The Collaborative Asteroid Lightcurve Link assumes a standard albedo for a stony asteroid of 0.20, and calculates a diameter of 8.97 kilometers based on an absolute magnitude of 12.6.^[3]

Naming

This minor planet was named after Australian geologist George E. Williams who discovered the Acraman crater when he worked for BHP in South Australia. The old 90-kilometer impact structure is one of the largest meteorite impact craters known on Earth and the largest one on the Australian continent.^[1] The official naming citation was published by the Minor Planet Center on 2 February 1988 (M.P.C. 12810).^[12]

Notes

1. David Higgins (2011): rotation period 14.387±0.003 hours with a brightness amplitude of 0.40±0.02 mag. Quality code is 3. Summary figures for (3700) Geowilliams at the LCDB and archived website of the Hunters Hill Observatory by David Higgins.