(9928) 1981 WE9

(9928) 1981 WE9, provisional designation 1981 WE9, is a stony Florian asteroid from the inner regions of the asteroid belt, approximately 3 kilometers in diameter. It was discovered on 16 November 1981, by astronomers at Perth Observatory in Bickley, Australia.[2]

(9928) 1981 WE9
Discovery [1]
Discovered byPerth Obs.
Discovery sitePerth Obs.
Discovery date16 November 1981
Designations
(9928) 1981 WE9
1981 WE9 · 1971 TJ1
1993 FC43
main-belt [1][2] · Flora [3]
Orbital characteristics [1]
Epoch 4 September 2017 (JD 2458000.5)
Uncertainty parameter 0
Observation arc65.74 yr (24,012 days)
Aphelion2.6101 AU
Perihelion1.8246 AU
2.2174 AU
Eccentricity0.1771
3.30 yr (1,206 days)
340.29°
0° 17m 54.6s / day
Inclination2.8472°
179.45°
176.04°
Physical characteristics
Dimensions2.441±0.327 km[4]
2.938±0.660 km[5]
3.00±0.42 km[6]
3.11 km (calculated)[3]
5.547±0.005 h[7]
18.310±0.0034 h[8]
18.3980±0.0034 h[3][8]
0.24 (assumed)[3]
0.283±0.152[6]
0.3557±0.2289[5]
0.428±0.109[4]
S [3]
14.4[5] · 14.60[4][6] · 14.7[1][3]

    Orbit and classification
    Orbit of 1981 WE9 (blue), with the inner planets and Jupiter

    The stony S-type asteroid is a member of the Flora family, one of the largest groups of asteroids in the main-belt. It orbits the Sun at a distance of 1.8–2.6 AU once every 3 years and 4 months (1,206 days).

    Its orbit has an eccentricity of 0.18 and an inclination of 3° with respect to the ecliptic.[1] A first precovery was taken at Palomar in 1951, extending the body's observation arc by 30 years prior to its official discovery observation at Bickley.[2]

    Physical characteristics

    In December 2014, astronomer Maurice Clark obtained a rotational lightcurve from photometric observations at Preston Gott Observatory. Lightcurve analysis gave an ambiguous rotation period of 18.3980 hours with a brightness variation of 0.41 magnitude, suggesting a non-spheroidal shape (U=2+). The alternative period solution is 9.14 hours with an amplitude of 0.32 magnitude.[8] The results supersede a previously obtained period of 5.547 hours (U=2).[7]

    Diameter and albedo

    According to the survey carried out by NASA's Wide-field Infrared Survey Explorer with its subsequent NEOWISE mission, the asteroid measures between 2.44 and 3.00 kilometers in diameter, and its surface has an albedo between 0.283 and 0.428.[4][5][6] The Collaborative Asteroid Lightcurve Link assumes an intermediate albedo of 0.24 – derived from 8 Flora, the largest member and namesake of this asteroid family – and calculates a diameter of 3.11 kilometers with an absolute magnitude of 14.7.[3]

    Numbering and naming

    This minor planet was numbered by the Minor Planet Center on 2 February 1999.[9] As of 2018, it has not been named.[2]

    References
    1. "JPL Small-Body Database Browser: 9928 (1981 WE9)" (2017-05-05 last obs.). Jet Propulsion Laboratory. Retrieved 26 May 2017.
    2. "9928 (1981 WE9)". Minor Planet Center. Retrieved 17 March 2017.
    3. "LCDB Data for (9928)". Asteroid Lightcurve Database (LCDB). Retrieved 17 March 2017.
    4. Nugent, C. R.; Mainzer, A.; Masiero, J.; Bauer, J.; Cutri, R. M.; Grav, T.; et al. (December 2015). "NEOWISE Reactivation Mission Year One: Preliminary Asteroid Diameters and Albedos". The Astrophysical Journal. 814 (2): 13. arXiv:1509.02522. Bibcode:2015ApJ...814..117N. doi:10.1088/0004-637X/814/2/117.
    5. Mainzer, A.; Grav, T.; Masiero, J.; Hand, E.; Bauer, J.; Tholen, D.; et al. (November 2011). "NEOWISE Studies of Spectrophotometrically Classified Asteroids: Preliminary Results". The Astrophysical Journal. 741 (2): 25. arXiv:1109.6407. Bibcode:2011ApJ...741...90M. doi:10.1088/0004-637X/741/2/90.
    6. Masiero, Joseph R.; Mainzer, A. K.; Grav, T.; Bauer, J. M.; Cutri, R. M.; Nugent, C.; et al. (November 2012). "Preliminary Analysis of WISE/NEOWISE 3-Band Cryogenic and Post-cryogenic Observations of Main Belt Asteroids". The Astrophysical Journal Letters. 759 (1): 5. arXiv:1209.5794. Bibcode:2012ApJ...759L...8M. doi:10.1088/2041-8205/759/1/L8.
    7. Clark, Maurice (June 2008). "Asteroid Lightcurves from the Chiro Observatory". The Minor Planet Bulletin. 35 (2): 42–43. Bibcode:2008MPBu...35...42C. ISSN 1052-8091.
    8. Clark, Maurice (July 2015). "Asteroid Photometry from the Preston Gott Observatory". The Minor Planet Bulletin. 42 (3): 163–166. Bibcode:2015MPBu...42..163C. ISSN 1052-8091.
    9. "MPC/MPO/MPS Archive". Minor Planet Center. Retrieved 24 February 2018.
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