926 Imhilde

926 Imhilde (prov. designation: A920 CB or 1920 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]

926 Imhilde
Discovery [1]
Discovered byK. Reinmuth
Discovery siteHeidelberg Obs.
Discovery date15 February 1920
Designations
(926) Imhilde
Named after
Name picked from the almanac
Lahrer Hinkender Bote [2]
A920 CB · 1920 GN
1931 GB · 1964 WB
main-belt [1][3] · (outer)
Imhilde [4]
Orbital characteristics [3]
Epoch 31 May 2020 (JD 2459000.5)
Uncertainty parameter 0
Observation arc99.70 yr (36,416 d)
Aphelion3.5251 AU
Perihelion2.4365 AU
2.9808 AU
Eccentricity0.1826
5.15 yr (1,880 d)
97.231°
0° 11m 29.4s / day
Inclination16.325°
48.971°
173.79°
Physical characteristics
Mean diameter
  • 46.369±1.133 km[5]
  • 48.48±1.1 km[6]
  • 49.87±0.92 km[7]
26.8±0.5 h[8][lower-alpha 1]
  • 0.052±0.007[5]
  • 0.054±0.002[7]
  • 0.0570±0.003[6]
C (SDSS-MOC)[9]
10.5[1][3]

    Orbit and classification

    When applying the synthetic hierarchical clustering method (HCM) by Nesvorný, Imhilde is the principal body and namesake of the Imhilde family (639), a small asteroid cluster with only a few dozens members.[4][10]: 23  However, according to another HCM-analysis by Milani and Knežević (AstDys), it is a background asteroid as the analysis does not recognize this family.[11] Imhilde orbits the Sun in the outer asteroid belt at a distance of 2.4–3.5 AU once every 5 years and 2 months (1,880 days; semi-major axis of 2.98 AU). Its orbit has an eccentricity of 0.18 and an inclination of 16° with respect to the ecliptic.[3] The body's observation arc begins at Heidelberg Observatory on 17 February 1920, two nights after its official discovery observation.[1]

    Naming

    This minor planet was named "Imhilde", after a female name picked from the Lahrer Hinkender Bote, published in Lahr, southern Germany.[2] A Hinkender Bote (lit. "limping messenger") was a very popular almanac,[12] especially in the alemannic-speaking region from the late 17th throughout the early 20th century. The calendar section contains feast days, the dates of important fairs and astronomical ephemerides. For 15 May, the calendar gives "Imhilde" as the German name day analogue next to Sophie and Torquatus, the protestant and catholic entries in the calendar of saints, likely referring to Sophia of Rome and Torquatus of Acci.[13]

    Reinmuth's calendar names

    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]

    Physical characteristics

    In the SDSS-based taxonomy, Imhilde is a carbonaceous C-type asteroid.[9][14] The Imhilde family's overall spectral type is CX.[10]: 23 

    Rotation period

    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±0.02 magnitude (U=2).[8][lower-alpha 1] 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
    1. Lightcurve 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.

    References
    1. "926 Imhilde (A920 CB)". Minor Planet Center. Retrieved 20 February 2020.
    2. Schmadel, Lutz D. (2007). "(926) Imhilde". Dictionary of Minor Planet Names. Springer Berlin Heidelberg. p. 82. doi:10.1007/978-3-540-29925-7_927. ISBN 978-3-540-00238-3.
    3. "JPL Small-Body Database Browser: 926 Imhilde (A920 CB)" (2019-10-29 last obs.). Jet Propulsion Laboratory. Retrieved 20 February 2020.
    4. "Asteroid 926 Imhilde – Nesvorny HCM Asteroid Families V3.0". Small Bodies Data Ferret. Retrieved 20 February 2020.
    5. Mainzer, 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.
    6. Tedesco, E. F.; Noah, P. V.; Noah, M.; Price, S. D. (October 2004). "IRAS Minor Planet Survey V6.0". NASA Planetary Data System. 12: IRAS-A-FPA-3-RDR-IMPS-V6.0. Bibcode:2004PDSS...12.....T. Retrieved 20 February 2020.
    7. Usui, 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)
    8. Warner, Brian D. (April 2011). "Upon Further Review: VI. An Examination of Previous Lightcurve Analysis from the Palmer Divide Observatory" (PDF). Minor Planet Bulletin. 38 (2): 96–101. Bibcode:2011MPBu...38...96W. ISSN 1052-8091. Archived from the original (PDF) on 20 February 2020. Retrieved 20 February 2020.
    9. Carvano, J. M.; Hasselmann, P. H.; Lazzaro, D.; Mothé-Diniz, T. (February 2010). "SDSS-based taxonomic classification and orbital distribution of main belt asteroids". Astronomy and Astrophysics. 510: 12. Bibcode:2010A&A...510A..43C. doi:10.1051/0004-6361/200913322. Retrieved 20 February 2020. (PDS data set)
    10. Nesvorný, D.; Broz, M.; Carruba, V. (December 2014). "Identification and Dynamical Properties of Asteroid Families". Asteroids IV: 297–321. arXiv:1502.01628. Bibcode:2015aste.book..297N. doi:10.2458/azu_uapress_9780816532131-ch016.
    11. "Asteroid 926 Imhilde – Proper Elements". AstDyS-2, Asteroids – Dynamic Site. Retrieved 20 February 2020.
    12. "Lahrer hinkender Bote – Kalender 1925". Badischen Landesbibliothek. 1925. p. 1. Retrieved 20 February 2020. Lahrer Bote archive
    13. "Lahrer hinkender Bote – Kalender 1925". Badischen Landesbibliothek. 1925. p. 10. Retrieved 20 February 2020.
    14. "Asteroid 926 Imhilde". Small Bodies Data Ferret. Retrieved 20 February 2020.
    15. Warner, Brian D. (March 2004). "Rotation rates for asteroids 875, 926, 1679, 1796, 3915, 4209, and 34817" (PDF). Minor Planet Bulletin. 31 (1): 19–22. Bibcode:2004MPBu...31...19W. ISSN 1052-8091. Archived from the original (PDF) on 20 February 2020. Retrieved 20 February 2020.
    16. "LCDB Data for (926) Imhilde". Asteroid Lightcurve Database (LCDB). Retrieved 20 February 2020.
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