731 Sorga

731 Sorga (prov. designation: A912 GH or 1912 OQ) is a highly elongated background asteroid from the outer regions of the asteroid belt, approximately 38 kilometers (24 miles) in diameter. It was discovered on 15 April 1912, by German astronomer Adam Massinger at the Heidelberg-Königstuhl State Observatory in soutwest Germany.[1] The C-type (CD) and X-type asteroid (Xe) has a rotation period of 8.2 hours. It was named Sorga, meaning "the heavens" in the Indonesian language.[2]

731 Sorga
Modelled shape of Sorga from its lightcurve
Discovery [1]
Discovered byA. Massinger
Discovery siteHeidelberg Obs.
Discovery date15 April 1912
Designations
(731) Sorga
Named after
"the heavens" [2]
(Indonesian language)
A912 GH · 1940 WP
1912 OQ
Orbital characteristics [3]
Epoch 31 May 2020 (JD 2459000.5)
Uncertainty parameter 0
Observation arc104.24 yr (38,075 d)
Aphelion3.4090 AU
Perihelion2.5656 AU
2.9873 AU
Eccentricity0.1412
5.16 yr (1,886 d)
201.03°
0° 11m 27.24s / day
Inclination10.689°
46.136°
288.62°
Physical characteristics
Mean diameter
8.184±0.005 h[11]
  • (83.0°, 40.0°) (λ1/β1)[5]
  • (275.0°, 21.0°) (λ2/β2)[5]
  • Tholen = CD [3]
  • SMASS = Xe [3]
  • B–V = 0.691±0.030[3]
  • U–B = 0.312±0.028[3]

    Orbit and classification

    Sorga 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][6] It orbits the Sun in the outer asteroid belt at a distance of 2.6–3.4 AU once every 5 years and 2 months (1,886 days; semi-major axis of 2.99 AU). Its orbit has an eccentricity of 0.14 and an inclination of 11° with respect to the ecliptic.[3] The body's observation arc begins at Heidelberg Observatory on 21 October 1919, more than seven years after its official discovery observation.[1]

    Naming

    This minor planet was named Sorga, the word for "the heavens" in the Indonesian language, also transliterated as "surga". The naming was not mentioned in The Names of the Minor Planets by Paul Herget.[2]

    Physical characteristics

    In the Tholen classification, Sorga is closest to a common, carbonaceous C-type asteroid and somewhat similar to a dark D-type asteroid (CD), while in the Bus–Binzel SMASS classification, it is an Xe-subtype which transitions from the X-type to the bright E-type.[3][5] Sorga has also been classified as a metallic M-type asteroid.[12]

    Rotation period and poles
    Lightcurve-based 3D shape model of Sorga

    In April 2005, a rotational lightcurve of Sorga was obtained from photometric observations by Brian Warner at his Palmer Divide Observatory (716) in Colorado. Analysis gave a classically shaped bimodal lightcurve with a well-defined rotation period of (8.184±0.005) hours and a high brightness variation of (0.52±0.02) magnitude, indicative of its elongated shape (U=3).[11] In February 2009, Warner revisited Sorga and determined a very similar period of (8.192±0.002) hours though with a much lower amplitude of (0.19±0.02) magnitude (U=3).[13][lower-alpha 1]

    In January 2010, astronomers at the Palomar Transient Factory measured a period of 8.188±0.0023 hours with an amplitude of 0.72 magnitude (U=2).[12][14] Additional observations by Christophe Demeautis in September 2017, and by Bruno Christmann in April 2020, gave a period of (8.186±0.003) and (8.1865±0.0003) hours with an amplitude of 0.54±0.02 and 0.57±0.02 magnitude, respectively (U=3–/3).[15]

    In 2016, a modeled lightcurve rendered a concurring sidereal period of 8.18633±0.00002 hours using data from the Uppsala Asteroid Photometric Catalogue, the Palomar Transient Factory survey, and individual observers, as well as sparse-in-time photometry from the NOFS, the Catalina Sky Survey, and the La Palma surveys (950). The study also determined two spin axes of (83.0°, 40.0°) and (275.0°, 21.0°) in ecliptic coordinates (λ, β).[16]

    Diameter and albedo

    According to the surveys carried out by the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer (WISE), the Japanese Akari satellite, and the Infrared Astronomical Satellite IRAS, Sorga measures (34.597±0.409), (38.93±0.44) and (41.78±2.0) kilometers in diameter and its surface has an albedo of (0.209±0.042), (0.173±0.005) and (0.1436±0.015), respectively.[7][8][9][10] The Collaborative Asteroid Lightcurve Link derives an albedo of 0.1339 and a diameter of 41.70 kilometers based on an absolute magnitude of 9.7.[12] The WISE team also published an alternative mean-diameter of (31.955±0.293 km) with an albedo of (0.2605±0.0759).[12]

    Two asteroid occultations on 24 October 2007, and on 31 October 2012, gave a best-fit ellipse dimension of (45.7 km × 45.7 km) and (38.0 km × 38.0 km), with an intermediate and low quality rating of 2 and 1, respectively.[5] These timed observations are taken when the asteroid passes in front of a distant star.[5]

    Notes
    1. Lightcurve plot of (731) Sorga, Palmer Divide Observatory, B. D. Warner (2009). Rotation period of 8.192±0.002 hours with a brightness amplitude of 0.19±0.02 mag. Quality code is 3. Summary figures at the LCDB.
    gollark: I was just worried, since you haven't applied for planning permission, and I'd hate to have to activate the permission lasers.
    gollark: Oh, good.
    gollark: Wait, are these *Chorus City* streets?
    gollark: I was looking at just transcoding everything from m4a-whatever-codec to opus, but I can't figure out how to do that without quality loss.
    gollark: Anyway, I have *no* idea how to fix this.

    References
    1. "731 Sorga (A912 GH)". Minor Planet Center. Retrieved 10 June 2020.
    2. Schmadel, Lutz D. (2007). "(731) Sorga". Dictionary of Minor Planet Names. Springer Berlin Heidelberg. p. 70. doi:10.1007/978-3-540-29925-7_732. ISBN 978-3-540-00238-3.
    3. "JPL Small-Body Database Browser: 731 Sorga (A912 GH)" (2020-04-28 last obs.). Jet Propulsion Laboratory. Retrieved 10 June 2020.
    4. "Asteroid 731 Sorga – Proper Elements". AstDyS-2, Asteroids – Dynamic Site. Retrieved 10 June 2020.
    5. "Asteroid 731 Sorga". Small Bodies Data Ferret. Retrieved 10 June 2020.
    6. 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 10 June 2020.} (PDS main page)
    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 10 June 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. 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 10 June 2020. (online, AcuA catalog p. 153)
    10. 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 10 June 2020.
    11. Warner, Brian D. (December 2005). "Asteroid lightcurve analysis at the Palmer Divide Observatory - spring 2005" (PDF). Minor Planet Bulletin. 32 (4): 90–92. Bibcode:2005MPBu...32...90W. ISSN 1052-8091.
    12. "LCDB Data for (731) Sorga". Asteroid Lightcurve Database (LCDB). Retrieved 10 June 2020.
    13. Warner, Brian D. (July 2009). "Asteroid Lightcurve Analysis at the Palmer Divide Observatory: 2008 December - 2009 March" (PDF). Minor Planet Bulletin. 36 (3): 109–116. Bibcode:2009MPBu...36..109W. ISSN 1052-8091.
    14. Waszczak, Adam; Chang, Chan-Kao; Ofek, Eran O.; Laher, Russ; Masci, Frank; Levitan, David; et al. (September 2015). "Asteroid Light Curves from the Palomar Transient Factory Survey: Rotation Periods and Phase Functions from Sparse Photometry". The Astronomical Journal. 150 (3): 35. arXiv:1504.04041. Bibcode:2015AJ....150...75W. doi:10.1088/0004-6256/150/3/75.
    15. Behrend, Raoul. "Asteroids and comets rotation curves – (731) Sorga". Geneva Observatory. Retrieved 10 June 2020.
    16. Hanuš, J.; Ďurech, J.; Brož, M.; Marciniak, A.; Warner, B. D.; Pilcher, F.; et al. (March 2013). "Asteroids' physical models from combined dense and sparse photometry and scaling of the YORP effect by the observed obliquity distribution". Astronomy and Astrophysics. 551: A67. arXiv:1301.6943. Bibcode:2013A&A...551A..67H. doi:10.1051/0004-6361/201220701. ISSN 0004-6361.
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