930 Westphalia

930 Westphalia (prov. designation: A920 EE or 1920 GS) is a very dark background asteroid and a slow rotator from the inner regions of the asteroid belt, that measures approximately 36 kilometers (22 miles) in diameter. It was discovered on 10 March 1920, by German astronomer Walter Baade at the Bergedorf Observatory in Hamburg.[1] The carbonaceous C-type asteroid (Ch) has an exceptionally long rotation period of 100.7 hours and is likely spherical in shape. It was named after Westphalia, a region in northwestern Germany.[3]

930 Westphalia
Discovery [1]
Discovered byW. Baade
Discovery siteBergedorf Obs.
Discovery date10 March 1920
Designations
(930) Westphalia
Pronunciation/wɛstˈfeɪliə/[2]
Named after
Westphalia
(German region)[3]
A920 EE · 1920 GS
A916 DD · 1916 DD
main-belt [1][4] · (inner)
background [5][6] · slow [6][7]
Orbital characteristics [4]
Epoch 31 May 2020 (JD 2459000.5)
Uncertainty parameter 0
Observation arc99.58 yr (36,370 d)
Aphelion2.7792 AU
Perihelion2.0828 AU
2.4310 AU
Eccentricity0.1432
3.79 yr (1,384 d)
32.395°
0° 15m 36s / day
Inclination15.336°
340.94°
329.98°
Physical characteristics
Mean diameter
100.66±0.12 h[7][11]
SMASS = Ch [4]

    Orbit and classification

    Westphalia 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 inner asteroid belt at a distance of 2.1–2.8 AU once every 3 years and 9 months (1,384 days; semi-major axis of 2.43 AU). Its orbit has an eccentricity of 0.14 and an inclination of 15° with respect to the ecliptic.[4] The asteroid was first observed as A916 DD (1916 DD) at the Simeiz Observatory on 24 February 1916. The body's observation arc begins with its official discovery observation at Bergedorf Observatory on 10 March 1920.[1]

    Naming

    This minor planet was named after the region of Westphalia in northwestern Germany, bordering the Netherlands and the Rhine river. It is the birthplace of the discoverer Walter Baade (1893–1960). The naming was mentioned in The Names of the Minor Planets by Paul Herget in 1955 (H 90).[3]

    Physical characteristics

    In the Bus–Binzel SMASS classification, Westphalia is a hydrated carbonaceous C-type asteroid (Ch).[4]

    Rotation period

    In April 2015, a rotational lightcurve of Westphalia was obtained from photometric observations by Eduardo Manuel Álvarez at the Los Algarrobos Observatory (I38) in Uruguay. Lightcurve analysis gave a rotation period of 100.66±0.12 hours with a brightness amplitude of 0.15±0.02 magnitude, indicative of a spherical, non-elongated shape (U=2). This was the first time a period could be determined for this asteroid, and, as the observer noted, there were only 18 tree-digit asteroids left for which no such measurement had yet been made.[11] With a period above 100 hours, Westphalia is a slow rotator. While the slowest rotators have periods above 1000 hours, the vast majority of asteroids have periods between 2.2 and 20 hours.

    Diameter and albedo

    According to the survey carried out by the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer (WISE), the Infrared Astronomical Satellite IRAS, and the Japanese Akari satellite, Westphalia measures (34.922±0.153), (36.48±1.4) and (39.51±1.47) kilometers in diameter and its surface has a very low albedo of (0.040±0.007), (0.0366±0.003) and (0.031±0.002), respectively.[8][9][10]

    The Collaborative Asteroid Lightcurve Link derives an albedo of 0.0438 and a diameter of 36.53 km based on an absolute magnitude of 11.2.[7] Further published mean-diameters and albedos by the WISE team in ascending order include (35.34±1.13 km), (35.602±0.157 km), (35.896±10.36 km), (38.107±12.56 km), (38.502±10.778 km) and (44.522±0.240 km) and albedos of (0.031±0.021), (0.0312±0.0240), (0.032±0.001), (0.0373±0.0253), (0.0384±0.0059) and (0.04±0.01).[6][7]

    References
    1. "930 Westphalia (A920 EE)". Minor Planet Center. Retrieved 18 February 2020.
    2. Noah Webster (1884) A Practical Dictionary of the English Language
    3. Schmadel, Lutz D. (2007). "(930) Westphalia". Dictionary of Minor Planet Names. Springer Berlin Heidelberg. pp. 82–83. doi:10.1007/978-3-540-29925-7_931. ISBN 978-3-540-00238-3.
    4. "JPL Small-Body Database Browser: 930 Westphalia (A920 EE)" (2019-10-16 last obs.). Jet Propulsion Laboratory. Archived from the original on 19 September 2020. Retrieved 18 February 2020.
    5. "Asteroid 930 Westphalia – Proper Elements". AstDyS-2, Asteroids – Dynamic Site. Retrieved 18 February 2020.
    6. "Asteroid 930 Westphalia". Small Bodies Data Ferret. Retrieved 18 February 2020.
    7. "LCDB Data for (930) Westphalia". Asteroid Lightcurve Database (LCDB). Retrieved 18 February 2020.
    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. 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 18 February 2020.
    10. 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)
    11. Álvarez, Eduardo Manuel (July 2015). "Period Determination for the Slow Rotator 930 Westphalia" (PDF). The Minor Planet Bulletin. 42 (3): 212. Bibcode:2015MPBu...42..212A. Archived from the original (PDF) on 18 February 2020. Retrieved 18 February 2020.
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