| Discovery[1] | |
|---|---|
| Discovered by | M. F. Wolf |
| Discovery site | Heidelberg Obs. |
| Discovery date | 6 February 1916 |
| Designations | |
| (817) Annika | |
| Pronunciation | /ˈænɪkə/German:[ˈanikaː][2] |
Named after | a girl named "Anika"[3] |
| A916 · CD 1916 YW | |
| Orbital characteristics[4] | |
| Epoch 31 May 2020 (JD 2459000.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 103.99yr (37,982 d) |
| Aphelion | 3.0570AU |
| Perihelion | 2.1231 AU |
| 2.5900 AU | |
| Eccentricity | 0.1803 |
| 4.17 yr (1,523 d) | |
| 61.065° | |
| 0° 14m 11.4s / day | |
| Inclination | 11.336° |
| 125.47° | |
| 285.18° | |
| Physical characteristics | |
| Dimensions | 22.0 km × 22.0 km |
Meandensity | ~2.7 g/cm3(estimate)[13] |
817 Annika (prov. designation:A916 CDor1916 YW) is abackground asteroid in the region of theEunomia family, located in the central portion of theasteroid belt. It was discovered on 6 February 1916, by German astronomerMax Wolf at theHeidelberg-Königstuhl State Observatory in southwest Germany.[1] The stonyS-type asteroid (Sl) has arotation period of 10.56 hours and measures approximately 23 kilometers (14 miles) in diameter .[3]
Annika is a non-family asteroid of the main belt'sbackground population when applying thehierarchical clustering method (HCM) to itsproper orbital elements byNesvorný as well as byMilani andKnežević (AstDyS).[5][6] In the 1995 HCM-analysis byZappalà,[8] however,Annika is a member of theEunomia family (502), a prominent family of stony asteroids and the largest one in the intermediate main belt with more than 5,000 members.[7] It orbits the Sun in thecentral main-belt at a distance of 2.1–3.1 AU once every 4 years and 2 months (1,523 days;semi-major axis of 2.59 AU). Its orbit has aneccentricity of 0.18 and aninclination of 11° with respect to theecliptic.[4] The body'sobservation arc begins with its official discovery observation atHeidelberg Observatory on 6 February 1916.[1]
"Annika" is a common German feminine given name. Any reference to a person or occurrence for the naming of thisminor planet is unknown.[3]
Among the many thousands ofnamed minor planets,Annika is one of 120 asteroids for which no official naming citation has been published. All of these asteroids have low numbers, the first being164 Eva. The last asteroid with a name of unknown meaning is1514 Ricouxa. They were discovered between 1876 and the 1930s, predominantly by astronomersAuguste Charlois,Johann Palisa,Max Wolf andKarl Reinmuth.[17]
In the Tholen-like taxonomy of theSmall Solar System Objects Spectroscopic Survey (S3OS2),Annika is a common, stonyS-type asteroid, while in the SMASS-like taxonomic variant of the S3OS2 survey, it is an Sl-subtype which transitions from the S-type to the uncommonL-type asteroid.[6][16]
In October 2002, a rotationallightcurve ofAnnika was obtained fromphotometric observations by Colin Bembrick at Mount Tarana Observatory (431), Australia, in collaboration with Greg Bolt and Tom Richards near Perth and Melbourne, respectively. Lightcurve analysis gave a well-definedrotation period of10.560±0.004 hours with a brightness variation of0.27±0.02magnitude (U=3).[14] This period was confirmed by Gérald Rousseau in March 2012, who determined a very similar period of10.564±0.001 hours with an amplitude of0.16±0.02 magnitude (U=3).[15]
According to the surveys carried out by the Infrared Astronomical SatelliteIRAS, theNEOWISE mission of NASA'sWide-field Infrared Survey Explorer (WISE), and the JapaneseAkari satellite,Annika measures (22.05±1.7), (22.891±0.100) and (23.02±0.34) kilometers in diameter and its surface has analbedo of (0.1740±0.030), (0.191±0.027) and (0.163±0.006), respectively.[9][10][11][12] TheCollaborative Asteroid Lightcurve Link derives an albedo of 0.2062 and a diameter of 22.20 kilometers based on anabsolute magnitude of 10.6.[7] Alternative mean-diameter measurements published by the WISE team include (17.65±4.40 km), (22.59±5.70 km), (24.38±0.50 km) and (26.569±0.191 km) with corresponding albedos of (0.26±0.13), (0.22±0.17), (0.187±0.025) and (0.1199±0.0098).[6][7]
On 26 August 2010, anasteroid occultation ofAnnika gave a best-fit ellipse dimension of (22.0 km × 22.0 km). These timed observations are taken when the asteroid passes in front of a distant star. However, these two observations have received a poor quality rating.[6]
