Discovered by L. Kohoutek Discovered 27 February 1973 Asteroid group Asteroid belt | Discovery date 27 February 1973 Minor planet category main-belt · (outer) Orbits Sun Discovery site Hamburg Observatory | |
Alternative names 1973 DR · 1935 GF1940 EH · 1951 EY11951 FA · 1965 UF1969 NB · 1975 NE Similar Asteroid belt, Sun, Comet Kohoutek, 1865 Cerberus | ||
1999 Hirayama, provisional designation 1973 DR, is a carbonaceous asteroid from the outer region of the asteroid belt, approximately 34 kilometers in diameter. It was discovered by Czech astronomer Luboš Kohoutek at the Hamburger Bergedorf Observatory, Germany, on 27 February 1973.
The asteroid orbits the Sun at a distance of 2.8–3.5 AU once every 5 years and 6 months (2,008 days). Its orbit has an eccentricity of 0.11 and an inclination of 13° with respect to the ecliptic. The spectrum of Hirayama matches a C-type classification on the Tholen taxonomic schem, but with a "broad absorption band that can be associated to a process of aqueous alteration". That is, the surface appears to show some form of water modification.
A rotational light curve obtained at the Menke Observatory in February 2002, showed a periodicity of 7001156300000000000♠15.63±0.01 hours, during which time the brightness of Hirayama varies by 6999450000000000000♠0.45±0.04 in magnitude (U=3-). At the same time, photometric observations by astronomers Roberto Crippa and Federico Manzini gave a rotation period of 22.37 hours and a brightness variation of 0.47 magnitude (U=2). These results supersede an observation from January 2005, by Hiromi and Hiroko Hamanowa at their Hamanowa Astronomical Observatory, Japan, that gave a shorter period of 13.59 hours with an amplitude of 0.57 magnitude.(U=n.a.).
According to the surveys carried out by the Infrared Astronomical Satellite IRAS, the Japanese Akari satellite, and NASA's Wide-field Infrared Survey Explorer with its subsequent NEOWISE mission, the asteroid measures between 34.0 and 38.3 kilometers in diameter and its surface has an albedo between 0.053 and 0.088. The Collaborative Asteroid Lightcurve Link derives an albedo of 0.062 and a diameter of 33.8 kilometers based on an absolute magnitude of 11.0.
The minor planet is named in honour of Japanese astronomer Kiyotsugu Hirayama (1874–1943), best known for his discovery that many asteroid orbits were more similar to one another than chance would allow, leading to the concept of asteroid families, now called Hirayama families. The lunar carter Hirayama is also named in his honour. Naming citation was published before November 1977 (M.P.C. 4237).