979 Ilsewa

979 Ilsewa (prov. designation: A922 MA or 1922 MC) is a background asteroid from the outer regions of the asteroid belt, approximately 36 kilometers (22 miles) in diameter. It was discovered by German astronomer Karl Reinmuth at the Heidelberg-Königstuhl State Observatory on 29 June 1922.[1] The uncommon T-type asteroid has a longer-than average rotation period of 42.6 hours. It was named after Ilse Walldorf, an acquaintance of the discoverer.[2]

979 Ilsewa
Modelled shape of Ilsewa from its lightcurve
Discovery [1]
Discovered byK. Reinmuth
Discovery siteHeidelberg Obs.
Discovery date29 June 1922
Designations
(979) Ilsewa
Named after
Ilse Walldorf
(acquaintance of discoverer)[2]
A922 MA · 1932 EG1
1951 TW · 1966 HO
A916 KD · A923 XB
1922 MC · 1916 KD
main-belt [1][3] · (outer)
background [4][5]
Orbital characteristics [3]
Epoch 31 May 2020 (JD 2459000.5)
Uncertainty parameter 0
Observation arc97.43 yr (35,587 d)
Aphelion3.5941 AU
Perihelion2.7230 AU
3.1585 AU
Eccentricity0.1379
5.61 yr (2,050 d)
123.47°
0° 10m 32.16s / day
Inclination10.110°
230.62°
115.40°
Physical characteristics
Mean diameter
  • 35.741±0.602 km[6]
  • 36.82±2.5 km[7]
  • 38.80±0.55 km[8]
42.61±0.01 h[5][9]
(352.0°, −66.0°) (λ1/β1)[5][10]
  • 0.142±0.005[8]
  • 0.1567±0.024[7]
  • 0.166±0.047[6]
T (S3OS2)[11]
9.7[1][3]

    Orbit and classification

    Ilsewa is a non-family asteroid of the main belt's background population when applying the hierarchical clustering method to its proper orbital elements.[4][5] It orbits the Sun in the outer asteroid belt at a distance of 2.7–3.6 AU once every 5 years and 7 months (2,050 days; semi-major axis of 3.16 AU). Its orbit has an eccentricity of 0.14 and an inclination of 10° with respect to the ecliptic.[3] Ilsewa was first observed as A916 KD (1916 KD) at the Crimean Simeiz Observatory on 27 May 1916. The body's observation arc begins at Heidelberg in September 1922, three months after its official discovery observation.[1]

    Naming

    This minor planet was named after Ilse Walldorf, an acquaintance of the discoverer. The naming was mentioned in The Names of the Minor Planets by Paul Herget in 1955 (H 94).[2]

    Physical characteristics

    In both the Tholen- and SMASS-like taxonomy of the Small Solar System Objects Spectroscopic Survey (S3OS2), Ilsewa is a uncommon T-type asteroid, part of the overall larger C-complex of carbonaceous asteroids.[5][11]

    Rotation period and poles

    In August 2012, a rotational lightcurve of Ilsewa was obtained from photometric observations by Robert Stephens at the Santana Observatory (646). Additional observations were taken at the Center for Solar System Studies (U81). Lightcurve analysis gave a rotation period of 42.61±0.01 hours with a brightness variation of 0.30±0.03 magnitude (U=3).[9] Andrea Ferrero at Bigmuskie Observatory (B88) determined a concurring period of 42.97±0.01 hours and an amplitude of 0.31±0.02 magnitude.[12]

    A modeled lightcurve using photometric data from the Lowell Photometric Database was published in 2016. It gave a sidereal period of 42.8982 hours, as well as a spin axis at (352.0°, −66.0°) in ecliptic coordinates (λ, β).[5][10]

    Diameter and albedo

    According to the survey carried out by the Infrared Astronomical Satellite IRAS, the Japanese Akari satellite, and the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer, Ilsewa measures between 35.7 and 38.8 kilometers in diameter and its surface has an albedo between 0.14 and 0.17.[6][7][8] The Collaborative Asteroid Lightcurve Link derives an albedo of 0.1707 and calculates a diameter of 36.93 kilometers, based on an absolute magnitude of 9.7.[12]

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    References
    1. "979 Ilsewa (A922 MA)". Minor Planet Center. Retrieved 9 February 2020.
    2. Schmadel, Lutz D. (2007). "(979) Ilsewa". Dictionary of Minor Planet Names. Springer Berlin Heidelberg. p. 85. doi:10.1007/978-3-540-29925-7_980. ISBN 978-3-540-00238-3.
    3. "JPL Small-Body Database Browser: 979 Ilsewa (A922 MA)" (2019-12-04 last obs.). Jet Propulsion Laboratory. Retrieved 9 February 2020.
    4. "Asteroid 979 Ilsewa – Proper Elements". AstDyS-2, Asteroids – Dynamic Site. Retrieved 9 February 2020.
    5. "Asteroid 979 Ilsewa". Small Bodies Data Ferret. Retrieved 9 February 2020.
    6. 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.
    7. 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 8 February 2020.
    8. 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 8 February 2020. (online, AcuA catalog p. 153)
    9. Stephens, Robert D. (January 2013). "Asteroids Observed from Santana and CS3 Observatories: 2012 July - September" (PDF). Minor Planet Bulletin. 40 (1): 34–35. Bibcode:2013MPBu...40...34S. ISSN 1052-8091.
    10. 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. doi:10.1051/0004-6361/201527573. ISSN 0004-6361.
    11. 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 8 February 2020.
    12. "LCDB Data for (979) Ilsewa". Asteroid Lightcurve Database (LCDB). Retrieved 9 February 2020.
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