926 Imhilde (prov. designation: A920 CBor1920 GN) is a dark asteroid and the principal body and namesake of the Imhilde family, located in the outer regions of the asteroid belt. It was discovered by astronomer Karl Reinmuth at the Heidelberg Observatory in southwest Germany on 15 February 1920.[1] The carbonaceous C-type asteroid has a rotation period of 26.8 hours and measures approximately 48 kilometers (30 miles) in diameter. It was named "Imhilde", a common German female name unrelated to the discoverer's contemporaries, that was taken from the almanac Lahrer Hinkender Bote.[2]
As with 22 other asteroids – starting with 913 Otila, and ending with 1144 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 the Dictionary of Minor Planet Names learned about Reinmuth's source of inspiration from private communications with Dutch astronomer Ingrid van Houten-Groeneveld, who worked as a young astronomer at Heidelberg.[2]
In April 2003, a rotational lightcurve of Imhilde was obtained from photometric observations by Brian Warner at the Palmer Divide Observatory (716) in Colorado. In 2011, after more than a decade of additional experience in asteroid lightcurve photometry, Warner reexamined the data set using improved tools and techniques. Lightcurve analysis gave a rotation period of 26.8±0.5 hours with a brightness variation of 0.27±0.02magnitude (U=2).[8][a] Originally, the same data gave a period of 26.1±0.5 hours with an amplitude 0.2±0.02 magnitude (U=2).[15]
Diameter and albedo
According to the survey carried out by the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer (WISE), the Infrared Astronomical Satellite IRAS, and the Japanese Akari satellite, Imhilde measures (46.369±1.133), (48.48±1.1) and (49.87±0.92) kilometers in diameter and its surface has a low albedo of (0.052±0.007), (0.0570±0.003) and (0.054±0.002), respectively.[5][6][7]
The Collaborative Asteroid Lightcurve Link derives an albedo of 0.0476 and a diameter of 48.39 km based on an absolute magnitude of 10.5.[16] Further published mean-diameters and albedos by the WISE team include (44.148±10.193 km) and (46.37±1.13 km) and albedos of (0.055±0.020) and (0.052±0.007).[14][16] An asteroid occultation observed on 8 November 2011, gave a best-fit ellipse dimension of 49.0 × 49.0 kilometers.[14] These timed observations are taken when the asteroid passes in front of a distant star. However the quality of the measurement is rated poorly.[14]
Notes
^ abLightcurve plot of (926) Imhilde, Palmer Divide Observatory, Brian Warner (2003): rotation period 26.8±0.5 hours with a brightness amplitude of 0.27±0.02 mag. Quality code of 2. Summary figures for at the LCDB.
^ abcMainzer, A. K.; Bauer, J. M.; Cutri, R. M.; Grav, T.; Kramer, E. A.; Masiero, J. R.; et al. (June 2016). "NEOWISE Diameters and Albedos V1.0". NASA Planetary Data System: EAR-A-COMPIL-5-NEOWISEDIAM-V1.0. Bibcode:2016PDSS..247.....M.
^ abcUsui, Fumihiko; Kuroda, Daisuke; Müller, Thomas G.; Hasegawa, Sunao; Ishiguro, Masateru; Ootsubo, Takafumi; et al. (October 2011). "Asteroid Catalog Using Akari: AKARI/IRC Mid-Infrared Asteroid Survey". Publications of the Astronomical Society of Japan. 63 (5): 1117–1138. Bibcode:2011PASJ...63.1117U. doi:10.1093/pasj/63.5.1117. (online, AcuA catalog p. 153)