 Orbital diagram ofUlla | |
| Discovery[1] | |
|---|---|
| Discovered by | K. Reinmuth |
| Discovery site | Heidelberg Obs. |
| Discovery date | 7 February 1919 |
| Designations | |
| (909) Ulla | |
| Pronunciation | German:[ˈʊlaː][2] Classically:/ˈʌlə/[3] |
Named after | Ulla Ahrens[4] (observatory donor) |
| 1919 FA · 1936 SJ 1949 OF1 · 1949 PW 1966 BU · 1966 DM A912 CA · A919 CA | |
| main-belt · (outer)[5] Ulla · Cybele | |
| Orbital characteristics[6] | |
| Epoch 31 May 2020 (JD 2459000.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 100.99yr (36,886 d) |
| Aphelion | 3.8633AU |
| Perihelion | 3.2217 AU |
| 3.5425 AU | |
| Eccentricity | 0.0906 |
| 6.67 yr (2,435 d) | |
| 180.34° | |
| 0° 8m 52.08s / day | |
| Inclination | 18.797° |
| 146.35° | |
| 232.64° | |
| TJupiter | 3.0250 |
| Physical characteristics | |
| 8.73 h[9] | |
| 8.95[1][6][7][8] | |
909 Ulla is a large and darkasteroid from the outermost regions of theasteroid belt, that measures approximately 116 kilometers (72 miles) in diameter. It is the parent body and namesake of theUlla family, which belongs to the larger group ofCybele asteroids. It was discovered on 7 February 1919, by German astronomerKarl Reinmuth at theHeidelberg Observatory in southwest Germany.[1] TheX-type asteroid has arotation period of 8.7 hours and a notably low value for itsJupiter Tisserand's parameter. It was named after Ulla Ahrens, daughter of a friend of the discoverer.[4]
Ulla is theparent body of theUlla family (903),[11] a very smallasteroid family of less than 30 known bodies.[12] It orbits the Sun in theoutermost asteroid belt at a distance of 3.2–3.9 AU once every 6 years and 8 months (2,435 days;semi-major axis of 3.54 AU). Its orbit has aneccentricity of 0.09 and aninclination of 19° with respect to theecliptic.[6]
Thisminor planet was named after Ulla Ahrens, a daughter of a friend of the discoverer.[4]Karl Reinmuth also named the asteroid950 Ahrensa for the Ahrens family, who was a donor of theHeidelberg Observatory. The official naming citation was mentioned inThe Names of the Minor Planets byPaul Herget in 1955 (H 50).[4]
In theSMASS classification,Ulla is anX-type asteroid.[6][10]
A rotationallightcurve ofUlla was obtained fromphotometric observations in 2000. Lightcurve analysis gave arotation period of 8.73 hours with a brightness amplitude between 0.13 and 0.24magnitude (U=3).[9] Other photometric period determinations gave concurring results.[13][14]
According to the surveys carried out by the Infrared Astronomical SatelliteIRAS and the JapaneseAkari satellite,Ulla measures113.13±1.48 and116.44±2.4 kilometers in diameter and its surface has analbedo between0.0343±0.001 and0.037±0.001.[7][8] TheCollaborative Asteroid Lightcurve Link uses an albedo of 0.0450 and derives a diameter of 116.66 kilometers based on anabsolute magnitude of 8.65.[5]
