| Discovery[1] | |
|---|---|
| Discovered by | K. Reinmuth |
| Discovery site | Heidelberg Obs. |
| Discovery date | 12 August 1923 |
| Designations | |
| (1025) Riema | |
Named after | Johannes Riem (German astronomer)[2] |
| 1923 NX · A923 QA | |
| main-belt · (inner)[1] · Hungaria[3][4] | |
| Orbital characteristics[1] | |
| Epoch 4 September 2017 (JD 2458000.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 93.81 yr (34,264 days) |
| Aphelion | 2.0572AU |
| Perihelion | 1.9009 AU |
| 1.9790 AU | |
| Eccentricity | 0.0395 |
| 2.78yr (1,017 days) | |
| 102.31° | |
| 0° 21m 14.4s / day | |
| Inclination | 26.863° |
| 163.39° | |
| 349.06° | |
| Physical characteristics | |
| Dimensions | 4.605±0.171 km[5] 5.48 km(derived)[3] |
| 3.566±0.005h[6] 3.578±0.002 h[a][b] 3.580±0.005 h[7] 3.581±0.002 h[8][c] 3.581±0.001 h[9][b] 3.588±0.002 h[10][b] 6.557±0.001 h[11] | |
| 1.000±0.000[5] 0.166±0.036[12] 0.40(assumed)[3] | |
| E(Tholen), Xe(SMASS) M[13] · Xe[3] B–V = 0.714[1] U–B = 0.294[1] V–R =0.440±0.010[11] | |
| 12.30[5] · 12.5[1] 12.57±0.28[14] · 12.92±0.04[3][15][16] | |
1025 Riema, provisional designation1923 NX, is a bright Hungariaasteroid from the innermost regions of theasteroid belt, approximately 5 kilometers in diameter. It was discovered on 12 August 1923, by German astronomerKarl Reinmuth at theHeidelberg Observatory in southwest Germany.[17] The asteroid was named afterARI astronomerJohannes Riem.[2]
Riema is a member of theHungaria family, which form theinnermost dense concentration of asteroids in theSolar System. It orbits the Sun at a distance of 1.9–2.1 AU once every 2 years and 9 months (1,017 days). Its orbit has aneccentricity of 0.04 and aninclination of 27° with respect to theecliptic.[1] The asteroid'sobservation arc begins at Heidelberg, four nights after its official discovery observation.[17]
In theTholen classification,Riema is a brightE-type asteroid. In theSMASS taxonomy, it has been classified as a Xe-type, which transitions from the E to theX-types.[1] In addition, the asteroid has also been polarimetrically characterized as a metallicM-type asteroid.[13]
In August 2001, a first rotationallightcurve ofRiema was obtained from photometric observations by Ukrainian astronomers at Kharkiv (101) and Simeiz (094). Lightcurve analysis gave arotation period of 6.557 hours with a brightness variation of 0.25magnitude (U=2).[11]
The Ukrainian team also determined the body's poles and axis-ratios. They found a spin axis of (141.0°, 11.0°) and (321.0.0°, −13.0°) inecliptic coordinates (λ, β), as well as a semi-axis ratio of 3.41 (a/b) and 1.16 (b/c) for the three-axialellipsoid model (Q=2).[11]
Between 2003 and 2017, several additional lightcurves were obtained by American photometristsRobert Stephens andBrian Warner at the Santana Observatory (646), the Palmer Divide Observatory (716) and the Palmer Divide Station (U82), respectively. The constructed lightcurve gave a shorter period forRiema between 3.566 and 3.588 hours with a low amplitude of 0.06 to 0.19 magnitude (U=2/2/2+/2+/3/3).[7][8][9][10][a][c][b]
According to the survey carried out by theNEOWISE mission of NASA'sWide-field Infrared Survey Explorer,Riema measures 4.605 kilometers in diameter and its surface has an outstandingly highalbedo of 1.000.[5] TheCollaborative Asteroid Lightcurve Link assumes an albedo for E-type Hungaria asteroids of 0.40 – taken from434 Hungaria, the family's largest member and namesake – and derives a diameter of 5.48 kilometers based on anabsolute magnitude of 12.92.[3]
Thisminor planet was named after Johannes Karl Richard Riem (1868–1945), a German astronomer at theAstronomisches Rechen-Institut (ARI) in Berlin. The name was suggested by ARI. The official naming citation was published byPaul Herget inThe Names of the Minor Planets in 1955 (H 98).[2]
