849 Ara

849 Ara (prov. designation: A912 CD or 1912 NY) is a large, metallic background asteroid, approximately 80 kilometers (50 miles) in diameter, that is located in the outer region of the asteroid belt. It was discovered on 9 February 1912, by Russian astronomer Sergey Belyavsky at the Simeiz Observatory on the Crimean peninsula.[1] The M-type asteroid has a short rotation period of 4.1 hours and is likely elongated in shape. It was named after the American Relief Administration (ARA) for the help given during the Russian famine of 1921–22.[3]

849 Ara
Modelled shape of Ara from its lightcurve
Discovery [1]
Discovered byS. Belyavskyj
Discovery siteSimeiz Obs.
Discovery date9 February 1912
Designations
(849) Ara
Pronunciation/ˈɛərə/[2]
Named after
American Relief Administration [3]
A912 CD · 1935 FU
1960 WN · A915 UB
1912 NY · 1915 Σai
Orbital characteristics [4]
Epoch 31 May 2020 (JD 2459000.5)
Uncertainty parameter 0
Observation arc100.58 yr (36,737 d)
Aphelion3.7783 AU
Perihelion2.5141 AU
3.1462 AU
Eccentricity0.2009
5.58 yr (2,038 d)
323.29°
0° 10m 35.76s / day
Inclination19.530°
228.37°
63.293°
TJupiter3.0900
Physical characteristics
Dimensions97.5 km × 70.7 km[6]
Mean diameter
80.756±1.127 km[7]
4.116 h[8][9]
(223.0°, −41.0°) (λ1/β1)[10]
0.126±0.040[7]
8.2[1][4]

    Orbit and classification

    Ara is a non-family asteroid of the main belt's background population when applying the hierarchical clustering method to its proper orbital elements.[5][6] It orbits the Sun in the outer asteroid belt at a distance of 2.5–3.8 AU once every 5 years and 7 months (2,038 days; semi-major axis of 3.15 AU). Its orbit has an eccentricity of 0.20 and an inclination of 20° with respect to the ecliptic.[4] In addition, Ara has a low Jupiter tisserand of 3.09, just above the defined threshold of 3.0 which is used to distinguish asteroids from the Jupiter-family comets.[4] The body's observation arc begins at the Collegio Romano Observatory (531) in Italy on 3 July 1919, more than 6 years after its official discovery observation at Simeiz.[1]

    Naming

    This minor planet was named after American Relief Administration (ARA), in appreciation of the help it gave during the Russian famine of 1921–22. Headed by Herbert Hoover, ARA was a relief mission after World War I to Europe which also included post-revolutionary Russia later on. The naming was mentioned in The Names of the Minor Planets by Paul Herget in 1955 (H 83).[3]

    Physical characteristics

    In the Tholen classification as well as in the lesser known taxonomic method by Howell, Ara is a metallic M-type asteroid.[4][6][11] This spectral type translates into the X-type in more modern asteroid taxonomic systems. In 2018 and 2019, a study using photometry from the Korea Microlensing Telescope Network and the South African Astronomical Observatory, grouped Ara into the X-type category based on the Bus–DeMeo classification.[12][14][15]

    Rotation period and pole
    Lightcurve-based 3D-model of Ara

    In June 1981, a rotational lightcurve of Ara was obtained from photometric observations by Alan Harris. Lightcurve analysis gave a rotation period of 4.116 hours with a brightness variation of 0.34 magnitude, indicative of an elongated shape (U=3).[8] Numerous observations have since confirmed this period.[15] This includes Laurent Bernasconi 4.1165±0.0007 h (2004) and 4.123±0.007 h (2006),[9] Davide Gandolfi 4.117±0.001 h (2006),[13] Adam Marciniak 4.116±0.001 h (2009),[16] Maurice Audejean 4.1176±0.0007 h (2010),[9] and Richard E. Schmidt 4.1168±0.0025 h (2017).[17] In 2017, a modeled lightcurve gave a concurring sidereal period of 4.116391±0.000002 hours as well as a spin axis of (223.0°, −41.0°) in ecliptic coordinates (λ, β).[10]

    Diameter and albedo

    According to the surveys carried out by the Japanese Akari satellite, the Infrared Astronomical Satellite IRAS, and the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer (WISE), Ara measures (59.92±1.09), (61.82±3.3) and (80.756±1.127) kilometers in diameter and its surface has an albedo of (0.287±0.013), (0.2660±0.031) and (0.126±0.040), respectively.[7][18][19] Alternative mean-diameters published by the WISE team include (74.00±2.89 km) and (84.417±2.447 km) with corresponding albedos of (0.186±0.023) and (0.1155±0.0163).[6][15]

    In 2009 and 2015, several asteroid occultations of Ara were observed. The two best-rated observations from January 2009 and April 2015 and August 2008, gave a best-fit ellipse dimension of (97.5 km × 70.7 km) and (98.0 km × 98.0 km), respectively.[6] These timed observations are taken when the asteroid passes in front of a distant star. The Collaborative Asteroid Lightcurve Link adopts Petr Pravec's revised WISE albedo of 0.1149 and takes a diameter of 84.61 kilometers based on an absolute magnitude of 8.33,[15] while Josef Ďurech calculates a diameter of 76±14 km by combining lightcurve inversion models with asteroid occultation silhouettes.[20]

    References
    1. "849 Ara (A912 CD)". Minor Planet Center. Retrieved 7 March 2020.
    2. Noah Webster (1884) A Practical Dictionary of the English Language
    3. Schmadel, Lutz D. (2007). "(849) Ara". Dictionary of Minor Planet Names. Springer Berlin Heidelberg. p. 78. doi:10.1007/978-3-540-29925-7_850. ISBN 978-3-540-00238-3.
    4. "JPL Small-Body Database Browser: 849 Ara (A912 CD)" (2020-01-31 last obs.). Jet Propulsion Laboratory. Retrieved 7 March 2020.
    5. "Asteroid 849 Ara – Proper Elements". AstDyS-2, Asteroids – Dynamic Site. Retrieved 7 March 2020.
    6. "Asteroid 849 Ara". Small Bodies Data Ferret. Retrieved 7 March 2020.
    7. 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. Bibcode:2016PDSS..247.....M. Retrieved 7 March 2020.
    8. Harris, A. W.; Young, J. W.; Dockweiler, Thor; Gibson, J.; Poutanen, M.; Bowell, E. (January 1992). "Asteroid lightcurve observations from 1981". Icarus. 95 (1): 115–147. Bibcode:1992Icar...95..115H. doi:10.1016/0019-1035(92)90195-D. ISSN 0019-1035.
    9. Behrend, Raoul. "Asteroids and comets rotation curves – (849) Ara". Geneva Observatory. Retrieved 7 March 2020.
    10. Hanuš, J.; Viikinkoski, M.; Marchis, F.; Ďurech, J.; Kaasalainen, M.; Delbo', M.; et al. (May 2017). "Volumes and bulk densities of forty asteroids from ADAM shape modeling". Astronomy and Astrophysics. 601: A114. arXiv:1702.01996. Bibcode:2017A&A...601A.114H. doi:10.1051/0004-6361/201629956. ISSN 0004-6361.
    11. Belskaya, I. N.; Fornasier, S.; Tozzi, G. P.; Gil-Hutton, R.; Cellino, A.; Antonyuk, K.; et al. (March 2017). "Refining the asteroid taxonomy by polarimetric observations". Icarus. 284: 30–42. Bibcode:2017Icar..284...30B. doi:10.1016/j.icarus.2016.11.003. ISSN 0019-1035.
    12. Erasmus, N.; McNeill, A.; Mommert, M.; Trilling, D. E.; Sickafoose, A. A.; Paterson, K. (June 2019). "A Taxonomic Study of Asteroid Families from KMTNET-SAAO Multiband Photometry". The Astrophysical Journal Supplement Series. 242 (2): 15. arXiv:1903.08019. Bibcode:2019ApJS..242...15E. doi:10.3847/1538-4365/ab1344. ISSN 0067-0049.
    13. Gandolfi, D.; Cigna, M.; Fulvio, D.; Blanco, C. (January 2009). "CCD and photon-counting photometric observations of asteroids carried out at Padova and Catania observatories". Planetary and Space Science. 57 (1): 1–9. arXiv:0810.1560. Bibcode:2009P&SS...57....1G. doi:10.1016/j.pss.2008.09.014. ISSN 0032-0633.
    14. Erasmus, N.; McNeill, A.; Mommert, M.; Trilling, D. E.; Sickafoose, A. A.; van Gend, C. (July 2018). "Taxonomy and Light-curve Data of 1000 Serendipitously Observed Main-belt Asteroids". The Astrophysical Journal Supplement Series. 237 (1): 19. arXiv:1805.04478. Bibcode:2018ApJS..237...19E. doi:10.3847/1538-4365/aac38f. ISSN 0067-0049.
    15. "LCDB Data for (849) Ara". Asteroid Lightcurve Database (LCDB). Retrieved 7 March 2020.
    16. Marciniak, A.; Michałowski, T.; Hirsch, R.; Polińska, M.; Kamiński, K.; Kwiatkowski, T.; et al. (April 2009). "Photometry and models of selected main belt asteroids. VI. 160 Una, 747 Winchester, and 849 Ara". Astronomy and Astrophysics. 498 (1): 313–320. Bibcode:2009A&A...498..313M. doi:10.1051/0004-6361/200811078. ISSN 0004-6361.
    17. Schmidt, Richard E. (July 2017). "Near-IR Minor Planet Photometry from Burleith Observatory" (PDF). Minor Planet Bulletin. 44 (3): 191–192. Bibcode:2017MPBu...44..191S. ISSN 1052-8091.
    18. 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 7 March 2020. (online, AcuA catalog p. 153)
    19. 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 7 March 2020.
    20. Ďurech, Josef; Kaasalainen, Mikko; Herald, David; Dunham, David; Timerson, Brad; Hanuš, Josef; et al. (August 2011). "Combining asteroid models derived by lightcurve inversion with asteroidal occultation silhouettes". Icarus. 214 (2): 652–670. arXiv:1104.4227. Bibcode:2011Icar..214..652D. doi:10.1016/j.icarus.2011.03.016. ISSN 0019-1035.
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