4713 Steel, provisional designation 1989 QL, is a rare-type Hungaria asteroid from the inner regions of the asteroid belt, approximately 6 kilometers in diameter. It was discovered on 26 August 1989, by Scottish–Australian astronomer Robert McNaught at the Siding Spring Observatory in New South Wales, Australia.[12] It was named after astronomer Duncan Steel.[2]
Classification and orbit
The rare and reddish A-type asteroid is a member of the Hungaria family, which form the innermost dense concentration of asteroids in the Solar System. It orbits the Sun in the inner main-belt at a distance of 1.8–2.1 AU once every 2 years and 8 months (977 days). Its orbit has an eccentricity of 0.07 and an inclination of 23° with respect to the ecliptic.[1]
A first precovery was taken at the discovering observatory in 1976, extending the asteroid's observation arc by 13 years prior to its official discovery observation in 1989.[12]
Lightcurves
In May 2005, the first rotational lightcurve was obtained for this asteroid from photometric observations made by French amateur astronomer Laurent Bernasconi. It gave a rotation period of 5.186±0.004 hours with a brightness variation of 0.44 magnitude (U=3).[7]
Between May 2010 and December 2014, American astronomer Brian D. Warner obtained another 3 well-defined lightcurves at the U.S. Palmer Divide Station, Colorado. They gave a slightly longer period of 5.193–5.203 hours with an amplitude of 0.28 to 0.42 magnitude (U=3/3/3).[8][9][10]
Diameter and albedo
According to the survey carried out by the Japanese Akari satellite, the asteroid measures 5.6 kilometers in diameter and its surface has a high albedo of 0.424,[4] while NASA's Wide-field Infrared Survey Explorer with its subsequent NEOWISE mission determined a diameter of 6.2 and 6.3 kilometers with an albedo of 0.347 and 0.381, respectively.[5][6] The Collaborative Asteroid Lightcurve Link assumes a much lower albedo of 0.18 and calculates a larger diameter of 7.5 kilometers with an absolute magnitude of 13.1.[3]
