791 Ani

791 Ani (prov. designation: A914 MB or 1914 UV) is a very large asteroid of the Meliboea family, located in the outer regions of the asteroid belt. It was discovered on 29 June 1914, by Russian astronomer Grigory Neujmin at the Simeiz Observatory on the Crimean peninsula.[1] The dark carbonaceous C-type asteroid has a rotation period of 11.2 hours and measures approximately 65.7 × 103.5 kilometers, with a mean-diameter of 100 km (62 mi). It was named after the historic Armenian city of Ani.[2]

791 Ani
Modelled shape of Ani from its lightcurve
Discovery [1]
Discovered byG. Neujmin
Discovery siteSimeiz Obs.
Discovery date29 June 1914
Designations
(791) Ani
Named after
Historic city of Ani [2]
A914 MB · 1949 WH
1964 PO · 1975 XM
1914 UV
main-belt [1][3] · (outer)
Meliboea [4][5] · Bg [6]
Orbital characteristics [3]
Epoch 31 May 2020 (JD 2459000.5)
Uncertainty parameter 0
Observation arc104.08 yr (38,017 d)
Aphelion3.7242 AU
Perihelion2.5197 AU
3.1219 AU
Eccentricity0.1929
5.52 yr (2,015 d)
33.057°
0° 10m 43.32s / day
Inclination16.381°
129.81°
201.49°
Physical characteristics
Dimensions65.7 km × 103.5 km
Mean diameter
  • 97.87±1.15 km[7]
  • 99.799±11.027 km[8]
  • 103.52±1.9 km[9]
11.174±0.004 h[10]
  • (94.0°, −25.0°) (λ1/β1)[11]
  • (269.0°, 4.0°) (λ2/β2)[11]
  • 0.0329±0.001[9]
  • 0.035±0.016[8]
  • 0.037±0.001[7]

    Orbit and classification

    When applying the hierarchical clustering method (HCM) to its proper orbital elements, Ani is a member of the Meliboea family (604),[4][5] a small family of carbonaceous asteroids in the outer main belt, named after its principal body, 137 Meliboea.[13]: 23  However, according to another HCM-analysis by Milani and Knežević (AstDyS), it is a background asteroid as this analysis does not recognize the Meliboea family.[6] Ani orbits the Sun in the outer asteroid belt at a distance of 2.5–3.7 AU once every 5 years and 6 months (2,015 days; semi-major axis of 3.12 AU). Its orbit has an eccentricity of 0.19 and an inclination of 16° with respect to the ecliptic.[3] The body's observation arc begins at Algiers Observatory in North Africa on 6 December 1915, some 17 months after its official discovery observation at Simeiz Observatory.[1]

    Naming

    This minor planet was named after the medieval city of Ani, which was destroyed by an earthquake in 1319. The ruins of the former capital of the Armenian kingdom are located near the border to Armenia, in what is now Turkey. Ani was known as "the city of 1001 churches". The naming was also mentioned in The Names of the Minor Planets by Paul Herget in 1955 (H 79).[2]

    Physical characteristics

    In the Tholen classification, Ani is a common, carbonaceous C-type asteroid.[3] It is also a common C-type in the Tholen-like taxonomy of the Small Solar System Objects Spectroscopic Survey (S3OS2), while in the survey's SMASS-like taxonomic variant, the asteroid is a hydrated carbonaceous subtype (Ch).[4][12]

    Rotation period and poles

    In May 2018, a rotational lightcurve of Ani was obtained from photometric observations by American amateur astronomer Tom Polakis at the Command Module Observatory (V02) in Arizona . Lightcurve analysis gave a well-defined rotation period of 11.174±0.004 hours with a brightness variation of 0.28±0.02 magnitude (U=3).[10]

    In June 2002, Brian Warner at his Palmer Divide Observatory first observed this asteroid and later derived a period of 16.8±0.1 hours and an amplitude of 0.35±0.05 magnitude, based on poor data (U=1).[lower-alpha 1] In December 2004, and in May 2007, two periods of 22.850±0.003 h and 22.85±0.05 h with a corresponding amplitude of 0.17±0.01 and 0.38±0.02 magnitude were determined by European astronomers Raymond Poncy (177) as well as Yves Revaz, Raoul Behrend, Alain Klotz, Michel Hernandez, Robert Soubie, Jean-François Gauthier, Bernard Tregon, Pierre Antonini, Laurent Bernasconi, Federico Manzini (A12), Yassine Damerdji and Horacio Correia. The two periods are slightly longer than twice Polakis' period solution (U=2/2−).[14] In April 2007, astronomers at the Oakley Observatory (916), Indiana, obtained a period of 16.72±0.03 hours and an amplitude of 0.32±0.05 magnitude (U=2).[15] In February 2011, French amateur astronomer René Roy determined a period of 12±0.5 hours and a brightness variation of 0.38±0.02 magnitude (U=2).[14]

    A modeled lightcurve by Josef Ďurech and Josef Hanuš, using photometric data including from the Lowell Photometric Database and from the Wide-field Infrared Survey Explorer (WISE) was published in 2018. It gave a sidereal period of 11.16954±0.00002 and two spin axes at (94.0°, −25.0°) and (269.0°, 4.0°) in ecliptic coordinates (λ, β).[16][11]

    Diameter and albedo

    According to the surveys carried out by the Japanese Akari satellite, the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer (WISE), and the Infrared Astronomical Satellite IRAS, Ani measures (97.87±1.15), (99.799±11.027) and (103.52±1.9) kilometers in diameter and its surface has an albedo of (0.037±0.001), (0.035±0.016) and (0.0329±0.001), respectively.[7][8][9] The Collaborative Asteroid Lightcurve Link adopts the results obtained by IRAS, that is, an albedo of 0.0329 and a diameter of 103.52 kilometers based on an absolute magnitude of 9.25.[11] Alternative mean-diameter measurements published by the WISE team include (82.500±5.957 km), (83.31±21.31 km), (93.29±31.33 km) and (116.865±1.024 km) with corresponding albedos of (0.0518±0.0131), (0.04±0.02), (0.04±0.02) and (0.026±0.003).[4][11] On 7 April 2000, an asteroid occultation of Ani gave a best-fit ellipse dimension of (65.7 km × 103.5 km) with a good quality rating of 3. These timed observations are taken when the asteroid passes in front of a distant star.[4]

    Notes
    1. Lightcurve plot of (791) Ani, Palmer Divide Observatory, B. D. Warner (2002). Rotation period 16.8±0.1 hours with a brightness amplitude of >0.1 mag, based on a revision from 2011. Quality code is 1. Summary figures at the LCDB.

    References
    1. "791 Ani (A914 MB)". Minor Planet Center. Retrieved 28 March 2020.
    2. Schmadel, Lutz D. (2007). "(791) Ani". Dictionary of Minor Planet Names. Springer Berlin Heidelberg. p. 74. doi:10.1007/978-3-540-29925-7_792. ISBN 978-3-540-00238-3.
    3. "JPL Small-Body Database Browser: 791 Ani (A914 MB)" (2020-01-06 last obs.). Jet Propulsion Laboratory. Retrieved 28 March 2020.
    4. "Asteroid 791 Ani – Nesvorny HCM Asteroid Families V3.0". Small Bodies Data Ferret. Retrieved 28 March 2020.
    5. Zappalà, V.; Bendjoya, Ph.; Cellino, A.; Farinella, P.; Froeschle, C. (1997). "Asteroid Dynamical Families". NASA Planetary Data System: EAR-A-5-DDR-FAMILY-V4.1. Retrieved 28 March 2020.} (PDS main page)
    6. "Asteroid 791 Ani – Proper Elements". AstDyS-2, Asteroids – Dynamic Site. Retrieved 28 March 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. 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. Retrieved 28 March 2020.
    9. 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 28 March 2020.
    10. Polakis, Tom (October 2018). "Lightcurve Analysis for Fourteen Main-belt Minor Planets" (PDF). Minor Planet Bulletin. 45 (4): 347–352. Bibcode:2018MPBu...45..347P. ISSN 1052-8091. Retrieved 28 March 2020.
    11. "LCDB Data for (791) Ani". Asteroid Lightcurve Database (LCDB). Retrieved 28 March 2020.
    12. Lazzaro, D.; Angeli, C. A.; Carvano, J. M.; Mothé-Diniz, T.; Duffard, R.; Florczak, M. (November 2004). "S3OS2: the visible spectroscopic survey of 820 asteroids" (PDF). Icarus. 172 (1): 179–220. Bibcode:2004Icar..172..179L. doi:10.1016/j.icarus.2004.06.006. Retrieved 28 March 2020.
    13. Nesvorný, D.; Broz, M.; Carruba, V. (December 2014). "Identification and Dynamical Properties of Asteroid Families". Asteroids IV. pp. 297–321. arXiv:1502.01628. Bibcode:2015aste.book..297N. doi:10.2458/azu_uapress_9780816532131-ch016. ISBN 9780816532131.
    14. Behrend, Raoul. "Asteroids and comets rotation curves – (791) Ani". Geneva Observatory. Retrieved 28 March 2020.
    15. Sauppe, Jason; Torno, Steven; Lemke-Oliver, Robert; Ditteon, Richard (December 2007). "Asteroid Lightcurve Analysis at the Oakley Observatory - March/April 2007" (PDF). Minor Planet Bulletin. 34 (4): 119–122. Bibcode:2007MPBu...34..119S. ISSN 1052-8091. Archived from the original (PDF) on 20 February 2020. Retrieved 28 March 2020.
    16. Ďurech, J.; Hanuš, J.; Alí-Lagoa, V. (September 2018). "Asteroid models reconstructed from the Lowell Photometric Database and WISE data". Astronomy and Astrophysics. 617: A57. arXiv:1807.02083. Bibcode:2018A&A...617A..57D. doi:10.1051/0004-6361/201833437. ISSN 0004-6361.
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