4713 Steel

For other uses, see Steel (disambiguation).

4713 Steel, provisional designation, 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. It was named after astronomer Duncan Steel.

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.

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.

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 $5.62$ hours with a brightness variation of 0.44 magnitude (U=3).

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).

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, 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. 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.

Naming
This minor planet was named for English-born New Zealander Duncan Steel (born 1955), astronomer and discoverer of minor planets, whose research focuses on small Solar System bodies, such as the dynamics of asteroids, comets and meteoroids, and on meteoric impact rates. He has also demonstrated that various asteroids of the Apollo group are the parents of meteor showers. The approved naming citation was published by the Minor Planet Center on 30 March 1991 (M.P.C. 17982).