_Hirayama.png) Modelled shape ofHirayama from itslightcurve | |
| Discovery[1] | |
|---|---|
| Discovered by | L. Kohoutek |
| Discovery site | Bergedorf Obs. |
| Discovery date | 27 February 1973 |
| Designations | |
| (1999) Hirayama | |
Named after | Kiyotsugu Hirayama (Japanese astronomer)[2] |
| 1973 DR · 1935 GF 1940 EH · 1951 EY1 1951 FA · 1965 UF 1969 NB · 1975 NE | |
| main-belt · (outer)[3] | |
| Orbital characteristics[1] | |
| Epoch 4 September 2017 (JD 2458000.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 77.24 yr (28,212 days) |
| Aphelion | 3.4757AU |
| Perihelion | 2.7575 AU |
| 3.1166 AU | |
| Eccentricity | 0.1152 |
| 5.50yr (2,010 days) | |
| 39.370° | |
| 0° 10m 44.76s / day | |
| Inclination | 12.529° |
| 148.03° | |
| 357.05° | |
| Physical characteristics | |
| 33.77 km(derived)[3] 33.95±2.1 km[4] 35.68±0.55 km[5] 38.28±0.40 km[6] | |
| 13.5921±0.0003 h[a] 15.63±0.01 h[7] 22.37±0.03 h[8] | |
| 0.053±0.005[6] 0.0617(derived)[3] 0.082±0.003[5] 0.0882±0.012[4] | |
| C[3][9] | |
| 10.6[4][5] · 10.78±0.31[9] · 10.90[6] · 11.0[1][3] | |
1999 Hirayama (prov. designation:1973 DR) is a darkbackground asteroid from the outer region of theasteroid belt, approximately 34 kilometers (21 miles) in diameter. It was discovered on 27 February 1973, by Czech astronomerLuboš Kohoutek at the HamburgerBergedorf Observatory in Germany, and later named after Japanese astronomerKiyotsugu Hirayama.[2][10]
Hirayama orbits the Sun in theouter main-belt at a distance of 2.8–3.5 AU once every 5 years and 6 months (2,010 days). Its orbit has aneccentricity of 0.12 and aninclination of 13° with respect to theecliptic.[1] The spectrum ofHirayama matches aC-type classification on theTholen taxonomic scheme, but with a "broadabsorption band that can be associated to a process ofaqueous alteration".[11] That is, the surface appears to show some form of water modification.
Thisminor planet is named in honour of Japanese astronomerKiyotsugu 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 calledHirayama families. The lunar craterHirayama is also named in his honour.[2] The officialnaming citation was published by theMinor Planet Center on 15 October 1977 (M.P.C. 4237).[12]
A rotationallightcurve ofHirayama was obtained at the Menke Observatory in February 2002. It showed a periodicity of15.63±0.01 hours, during which time the brightness ofHirayama varies by0.45±0.04 inmagnitude (U=3-).[7] 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).[8] 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.).[a]
According to the surveys carried out by the Infrared Astronomical SatelliteIRAS, the JapaneseAkari satellite, and NASA'sWide-field Infrared Survey Explorer with its subsequentNEOWISE mission, the asteroid measures between 34.0 and 38.3 kilometers in diameter and its surface has analbedo between 0.053 and 0.088.[4][5][6] TheCollaborative Asteroid Lightcurve Link derives an albedo of 0.062 and a diameter of 33.8 kilometers with anabsolute magnitude of 11.0.[3]
