918 Itha

918 Itha (prov. designation: A919 QD or 1919 FR) is a stony asteroid and the namesake as well as the principal body of the Itha family, located in the outer region of the asteroid belt. It was discovered by German astronomer Karl Reinmuth at the Heidelberg Observatory on 22 August 1919.[1] The S-type asteroid has a notably short rotation period of only 3.5 hours and measures approximately 21 kilometers (13 miles) in diameter. It was named "Itha", a female name taken from the almanac Lahrer Hinkender Bote, unrelated to the discoverer's contemporaries.[2][3]

918 Itha
Modelled shape of Itha from its lightcurve
Discovery [1]
Discovered byK. Reinmuth
Discovery siteHeidelberg Obs.
Discovery date22 August 1919
Designations
(918) Itha
Named after
Name picked from the almanac
Lahrer Hinkender Bote [2][3]
A919 QD · 1919 FR
A907 CA · 1907 CA
1943 PB
main-belt [1][4] · (outer)
Itha [5]
Orbital characteristics [4]
Epoch 31 May 2020 (JD 2459000.5)
Uncertainty parameter 0
Observation arc99.72 yr (36,421 d)
Aphelion3.4078 AU
Perihelion2.3197 AU
2.8637 AU
Eccentricity0.1900
4.85 yr (1,770 d)
273.51°
0° 12m 12.24s / day
Inclination12.070°
330.46°
15.565°
Physical characteristics
Mean diameter
  • 20.44±1.9 km[6]
  • 21.37±0.84 km[7]
  • 21.561±0.106 km[8]
3.47393±0.00006 h[9]
  • 0.203±0.018[7]
  • 0.2220±0.048[6]
  • 0.224±0.034[8]
S (SMASS-I; Xu)[10]
10.6[1][4]

    Orbit and classification

    When applying the synthetic hierarchical clustering method (HCM) by Nesvorný, Itha is the principal body and namesake of the Itha family (633),[5] a small family of stony asteroids with only a few dozen known members.[11]:23 Other larger and low-numbered members of this family include 968 Petunia, 1067 Lunaria, 3787 Aivazovskij, 4119 Miles and 5232 Jordaens. However, according to another HCM-analysis by Milani and Knežević (AstDys), Itha is a background asteroid as it is not a legitimate family in their analysis.[12] It orbits the Sun in the outer asteroid belt at a distance of 2.3–3.4 AU once every 4 years and 10 months (1,770 days; semi-major axis of 2.86 AU). Its orbit has an eccentricity of 0.19 and an inclination of 12° with respect to the ecliptic.[4] Itha was first observed as A907 CA (1907 CA) at the U.S. Taunton Observatory (803) in Massachusetts. The body's observation arc begins at Heidelberg Observatory on 23 August 1919, the night after its official discovery observation.[1]

    Naming

    This minor planet was named "Itha", picked from the Lahrer Hinkender Bote, an almanac which was published in Lahr, southern Germany.[2][3] Especially in the alemannic-speaking region, a Hinkender Bote (lit. "limping messenger") was very popular 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 January, the calendar gives "Itha" as the German name day analogue next to Maurus and Habakuk, the protestant and catholic entries in the calendar of saints, likely referring to Saint Maurus and prophet Habakkuk.[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

    Itha is an S-type asteroid in the SMASS-I classification by Xu (1995).[10] This agrees with the overall spectral type for members of the Itha family.[11]:23

    Rotation period

    In June 2011, a rotational lightcurve of Itha was obtained from photometric observations by Julian Oey at Kingsgrove Observatory (E19), Australia, in collaboration with three Argentinian astronomers. Lightcurve analysis gave a well-defined rotation period of 3.47393±0.00006 hours with a brightness variation of 0.30±0.03 magnitude (U=3).[9] Two modeled lightcurves using photometric data from the Lowell Photometric Database and from the BlueEye600 robotic telescope (L36) at Ondřejov Observatory gave a sidereal period of 3.473810±0.000001 and 3.473808±0.000002, respectively. The modelling of the former gave two poles at (59.0°, −59.0°) and (249.0°, −72.0°), while the one of the latter gave only one pole at (72.0°, −54.0°) in ecliptic coordinates (λ, β).[14][15]

    Diameter and albedo

    According to the surveys carried out by the Infrared Astronomical Satellite IRAS, the Japanese Akari satellite, and the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer (WISE), Itha measures (20.44±1.9), (21.37±0.84) and (21.561±0.106) kilometers in diameter, and its surface has an albedo of (0.2220±0.048), (0.203±0.018) and (0.224±0.034), respectively.[6][7][8] The Collaborative Asteroid Lightcurve Link derives an albedo of 0.2412 and a diameter of 20.53 km based on an absolute magnitude of 10.6.[16] Other published mean-diameters by the WISE team include (20.335±0.281 km) and (23.715±0.094 km) with corresponding albedos of (0.224±0.034) and (0.1672±0.0333).[16][10]

    References
    1. "918 Itha (A919 QD)". Minor Planet Center. Retrieved 22 February 2020.
    2. Schmadel, Lutz D. (2007). "(918) Itha". Dictionary of Minor Planet Names. Springer Berlin Heidelberg. p. 82. doi:10.1007/978-3-540-29925-7_919. ISBN 978-3-540-00238-3.
    3. "Lahrer hinkender Bote – Kalender 1925". Badischen Landesbibliothek. 1925. p. 1. Retrieved 21 February 2020. Lahrer Bote archive
    4. "JPL Small-Body Database Browser: 918 Itha (A919 QD)" (2019-05-11 last obs.). Jet Propulsion Laboratory. Retrieved 22 February 2020.
    5. "Asteroid 918 Itha – Nesvorny HCM Asteroid Families V3.0". Small Bodies Data Ferret. Retrieved 22 February 2020.
    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 22 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. Retrieved 22 February 2020. (online, AcuA catalog p. 153)
    8. Masiero, Joseph R.; Grav, T.; Mainzer, A. K.; Nugent, C. R.; Bauer, J. M.; Stevenson, R.; et al. (August 2014). "Main-belt Asteroids with WISE/NEOWISE: Near-infrared Albedos". The Astrophysical Journal. 791 (2): 11. arXiv:1406.6645. Bibcode:2014ApJ...791..121M. doi:10.1088/0004-637X/791/2/121.
    9. Oey, Julian; Colazo, Carlos; Mazzone, Fernando; Chapman, Andrés (January 2012). "The Lightcurve Analysis of 918 Itha and 2008 Konstitutsiya" (PDF). Minor Planet Bulletin. 39 (1): 1–2. Bibcode:2012MPBu...39....1O. ISSN 1052-8091.
    10. "Asteroid 918 Itha". Small Bodies Data Ferret. Retrieved 22 February 2020.
    11. 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.
    12. "Asteroid 918 Itha – Proper Elements". AstDyS-2, Asteroids – Dynamic Site. Retrieved 22 February 2020.
    13. "Lahrer hinkender Bote – Kalender 1925". Badischen Landesbibliothek. 1925. p. 2. Retrieved 20 February 2020.
    14. Ďurech, J.; Hanuš, J.; Oszkiewicz, D.; Vančo, R. (March 2016). "Asteroid models from the Lowell photometric database". Astronomy and Astrophysics. 587: A48. arXiv:1601.02909. Bibcode:2016A&A...587A..48D. ISSN 0004-6361.
    15. Ďurech, Josef; Hanuš, Josef; Brož, Miroslav; Lehký, Martin; Behrend, Raoul; Antonini, Pierre; et al. (April 2018). "Shape models of asteroids based on lightcurve observations with BlueEye600 robotic observatory". Icarus. 304: 101–109. arXiv:1707.03637. Bibcode:2018Icar..304..101D. ISSN 0019-1035.
    16. "LCDB Data for (918) Itha". Asteroid Lightcurve Database (LCDB). Retrieved 22 February 2020.
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