_Hildrun.png) Modelled shape ofHildrun from itslightcurve | |
| Discovery[1] | |
|---|---|
| Discovered by | K. Reinmuth |
| Discovery site | Heidelberg Obs. |
| Discovery date | 23 February 1920 |
| Designations | |
| (928) Hildrun | |
Named after | Name picked from the almanac Lahrer Hinkender Bote[2] |
| A920 DC · 1920 GP 1959 EE1 | |
| main-belt[1][3] · (outer) background[4][5] | |
| Orbital characteristics[3] | |
| Epoch 31 May 2020 (JD 2459000.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 99.79yr (36,447 d) |
| Aphelion | 3.5999AU |
| Perihelion | 2.6698 AU |
| 3.1349 AU | |
| Eccentricity | 0.1484 |
| 5.55 yr (2,027 d) | |
| 9.2453° | |
| 0° 10m 39.36s / day | |
| Inclination | 17.653° |
| 129.83° | |
| 21.894° | |
| Physical characteristics | |
| 14.13±0.03 h[9][a] | |
| X(S3OS2)[10] | |
| 10.0[1][3] | |
928 Hildrun (prov. designation:A920 DCor1920 GP), is a darkbackground asteroid, approximately 64 kilometers (40 miles) in diameter, located in the outer region of theasteroid belt. It was discovered on 23 February 1920, by astronomerKarl Reinmuth at theHeidelberg-Königstuhl State Observatory in southwest Germany.[1] TheX-type asteroid has arotation period of 14.1 hours.[a] It was named "Hildrun", a common German female name unrelated to the discoverer's contemporaries, that was taken from the almanacLahrer Hinkender Bote.[2]
Hildrun is a non-family asteroid of the main belt'sbackground population when applying thehierarchical clustering method to itsproper orbital elements.[4][5] It orbits the Sun in theouter asteroid belt (IIIb) at a distance of 2.7–3.6 AU once every 5 years and 7 months (2,027 days;semi-major axis of 3.13 AU). Its orbit has aneccentricity of 0.15 and aninclination of 18° with respect to theecliptic.[3] The body'sobservation arc begins atHeidelberg Observatory on 24 February 1920, the night after its official discovery observation.[1]
Thisminor planet was named "Hildrun", after a female name picked from theLahrer Hinkender Bote, published inLahr, southern Germany.[2] AHinkender Bote (lit. "limping messenger") was a very popularalmanac,[11] especially in thealemannic-speaking region from the late 17th throughout the early 20th century. Thecalendar section containsfeast days, the dates of important fairs andastronomical ephemerides. For 19 May, the calendar gives "Hildrun" as the Germanname day analogue next toPotentia andPeter Cöl., the protestant and catholic entries in thecalendar of saints, likely referring toPudentiana andPope Celestine V.[12]
As with 22 other asteroids – starting with913 Otila, and ending with1144 Oda – Reinmuth selected names from this calendar due to his many asteroid discoveries that he had trouble thinking of proper names. These names are not related to the discoverer's contemporaries.Lutz Schmadel, the author of theDictionary of Minor Planet Names learned about Reinmuth's source of inspiration from private communications with Dutch astronomerIngrid van Houten-Groeneveld, who worked as a young astronomer at Heidelberg.[2]
In both the Tholen- and SMASS-like taxonomy of theSmall Solar System Objects Spectroscopic Survey (S3OS2),Hildrun is anX-type asteroid.[5][10]
In May 2004, a rotationallightcurve ofHildrun was obtained fromphotometric observations byBrian Warner at thePalmer Divide Observatory (716) in Colorado. Lightcurve analysis gave arotation period of14.13±0.03 hours with a brightness variation of0.34±0.02magnitude (U=3).[9][a]
Two tentative lightcurves were obtained byPierre Antonini in June 2010, and by Robin Esseiva, Nicolas Esseiva andRaoul Behrend in April 2015; both with a period of14.4±0.5 hours and an amplitude of0.27±0.05 and0.25±0.10 magnitude, respectively (U=2-/2-).[13][14] In 2016, a modeled lightcurves using photometric data from various sources, rendered a concurring sidereal period of14.1163±0.0005 hours and twospin axes of (247.0°, −29.0°) and (86.0°, −63.0°) inecliptic coordinates.[15]
According to the survey carried out by theNEOWISE mission of NASA'sWide-field Infrared Survey Explorer, the JapaneseAkari satellite, and the Infrared Astronomical SatelliteIRAS,Hildrun measures (62.817±0.293), (64.04±1.09) and (66.49±1.7) kilometers in diameter and its surface has analbedo of (0.043±0.007), (0.040±0.001) and (0.0365±0.002), respectively.[6][7][8] TheCollaborative Asteroid Lightcurve Link derives an albedo of 0.0437 and a diameter of 66.59 km based on anabsolute magnitude of 9.9.[14] Further published mean-diameters and albedos by the WISE team include (56.81±13.02 km), (60.559±0.798 km) and (64.517±1.054 km) with corresponding albedos of (0.06±0.06), (0.053±0.007) and (0.0387±0.0054).[5][14]
