_Frieda.png) Modelled shape ofFrieda from itslightcurve | |
| Discovery[1] | |
|---|---|
| Discovered by | J. Palisa |
| Discovery site | Vienna Obs. |
| Discovery date | 18 October 1911 |
| Designations | |
| (722) Frieda | |
| Pronunciation | German:[ˈfʁiːdaː][2] |
Named after | Frieda Hillebrand,[3] daughter and grand-daughter of: Karl Hillebrand [de](1861–1939) Edmund Weiss(1837–1917) |
| A911 UN · 1926 GR 1946 SH · 1911 NA | |
| Orbital characteristics[4] | |
| Epoch 31 May 2020 (JD 2459000.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 109.52yr (40,002 d) |
| Aphelion | 2.4858AU |
| Perihelion | 1.8575 AU |
| 2.1717 AU | |
| Eccentricity | 0.1447 |
| 3.20 yr (1,169 d) | |
| 47.845° | |
| 0° 18m 28.8s / day | |
| Inclination | 5.6371° |
| 45.668° | |
| 257.23° | |
| Physical characteristics | |
| 131.1±0.2 h[11] | |
| S(SMASS-I)[6] | |
722 Frieda (prov. designation:A911 UNor1911 NA) is a brightbackground asteroid andslow rotator from the inner regions of theasteroid belt. It was discovered by Austrian astronomerJohann Palisa at theVienna Observatory on 18 October 1911.[1] The stonyS-type asteroid has a notably longrotation period of 131.1 hours and measures approximately 9 kilometers (6 miles) in diameter. It was named after Frieda Hillebrand, daughter of Austrian astronomerKarl Hillebrand [de] (1861–1939), and grand-daughter ofEdmund Weiss (1837–1917) who had been the director of the discovering observatory.[3]
Located in the region of theFlora family (402),[11][12] the largestfamily of stony asteroids,Frieda is a non-family asteroid of the main belt'sbackground population when applying thehierarchical clustering method to itsproper orbital elements.[5][6][7] It orbits the Sun in theinner asteroid belt at a distance of 1.9–2.5 AU once every 3 years and 2 months (1,169 days;semi-major axis of 2.17 AU). Its orbit has aneccentricity of 0.14 and aninclination of 6° with respect to theecliptic.[4] The body'sobservation arc begins atHeidelberg Observatory on 19 January 1912, or three months after its official discovery observation byJohann Palisa atVienna Observatory.[1]
According to Alexander Schnell, thisminor planet was named after Frieda Hillebrand, daughter of Austrian astronomer and professor atGraz University,Karl Hillebrand [de] (1861–1939). Frieda is also the grand-daughter of astronomerEdmund Weiss (1837–1917), who wasdirector of the Vienna Observatory (1877–1908) where this asteroid was discovered. Thenaming citation was not mentioned inThe Names of the Minor Planets byPaul Herget in 1955.[3] Palisa also named asteroid794 Irenaea after Frieda's mother, Irene Hillebrand (née Weiss).[13]
In the SMASS-I classification by Xu (1995),Frieda is a common, stonyS-type asteroid.[6]
In April 2019, a rotationallightcurve ofFrieda was obtained for the first time from 12 nights ofphotometric observations by American amateur astronomerTom Polakis at the Command Module Observatory (V02) in Arizona. Lightcurve analysis gave arotation period of131.1±0.2 hours with a high brightness variation of0.45±0.05magnitude (U=2).[11]
According to the surveys carried out by theNEOWISE mission of NASA'sWide-field Infrared Survey Explorer (WISE) and the JapaneseAkari satellite,Frieda measures (8.257±0.073) and (11.43±0.23) kilometers in diameter and its surface has analbedo of (0.435±0.069) and (0.201±0.009), respectively.[8][9][10]
TheCollaborative Asteroid Lightcurve Link adoptsPetr Pravec's revised WISE-data, with an albedo of 0.2721 and a diameter of 8.794 kilometers based on anabsolute magnitude of 12.31.[12] Alternative mean-diameters published by the WISE team include (8.835±0.044 km), (9.19±0.22 km) and (10.51±2.46 km) with a corresponding albedo of (0.3309±0.3309), (0.252±0.025) and (0.23±0.10).[6][12]
