_Ilsewa.png) Modelled shape ofIlsewa from itslightcurve | |
| Discovery[1] | |
|---|---|
| Discovered by | K. Reinmuth |
| Discovery site | Heidelberg Obs. |
| Discovery date | 29 June 1922 |
| Designations | |
| (979) Ilsewa | |
Named after | Ilse Walldorf (acquaintance of discoverer)[2] |
| A922 MA · 1932 EG1 1951 TW · 1966 HO A916 KD · A923 XB 1922 MC · 1916 KD | |
| main-belt[1][3] · (outer) background[4][5] | |
| Orbital characteristics[3] | |
| Epoch 31 May 2020 (JD 2459000.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 97.43yr (35,587 d) |
| Aphelion | 3.5941AU |
| Perihelion | 2.7230 AU |
| 3.1585 AU | |
| Eccentricity | 0.1379 |
| 5.61 yr (2,050 d) | |
| 123.47° | |
| 0° 10m 32.16s / day | |
| Inclination | 10.110° |
| 230.62° | |
| 115.40° | |
| Physical characteristics | |
| 42.61±0.01 h[5][9] | |
| (352.0°, −66.0°) (λ1/β1)[5][10] | |
| T(S3OS2)[11] | |
| 9.7[1][3] | |
979 Ilsewa (prov. designation:A922 MAor1922 MC) is abackground asteroid from the outer regions of theasteroid belt, approximately 36 kilometers (22 miles) in diameter. It was discovered by German astronomerKarl Reinmuth at theHeidelberg-Königstuhl State Observatory on 29 June 1922.[1] The uncommonT-type asteroid has a longer-than averagerotation period of 42.6 hours. It was named afterIlse Walldorf, an acquaintance of the discoverer.[2]
Ilsewa 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 at a distance of 2.7–3.6 AU once every 5 years and 7 months (2,050 days;semi-major axis of 3.16 AU). Its orbit has aneccentricity of 0.14 and aninclination of 10° with respect to theecliptic.[3]Ilsewa was first observed asA916 KD (1916 KD) at the CrimeanSimeiz Observatory on 27 May 1916. The body'sobservation arc begins at Heidelberg in September 1922, three months after its official discovery observation.[1]
Thisminor planet was named afterIlse Walldorf, an acquaintance of the discoverer. The naming was mentioned inThe Names of the Minor Planets byPaul Herget in 1955 (H 94).[2]
In both the Tholen- and SMASS-like taxonomy of theSmall Solar System Objects Spectroscopic Survey (S3OS2),Ilsewa is an uncommonT-type asteroid, part of the overall larger C-complex of carbonaceous asteroids.[5][11]
In August 2012, a rotationallightcurve ofIlsewa was obtained fromphotometric observations byRobert Stephens at the Santana Observatory (646). Additional observations were taken at theCenter for Solar System Studies (U81). Lightcurve analysis gave arotation period of42.61±0.01 hours with a brightness variation of0.30±0.03magnitude (U=3).[9] Andrea Ferrero at Bigmuskie Observatory (B88) determined a concurring period of42.97±0.01 hours and an amplitude of0.31±0.02 magnitude.[12]
A modeled lightcurve using photometric data from the Lowell Photometric Database was published in 2016. It gave a sidereal period of 42.8982 hours, as well as aspin axis at (352.0°, −66.0°) inecliptic coordinates (λ, β).[5][10]
According to the survey carried out by the Infrared Astronomical SatelliteIRAS, the JapaneseAkari satellite, and theNEOWISE mission of NASA'sWide-field Infrared Survey Explorer,Ilsewa measures between 35.7 and 38.8 kilometers in diameter and its surface has analbedo between 0.14 and 0.17.[6][7][8] TheCollaborative Asteroid Lightcurve Link derives an albedo of 0.1707 and calculates a diameter of 36.93 kilometers, based on anabsolute magnitude of 9.7.[12]
