960 Birgit

960 Birgit (prov. designation: A921 TG or 1921 KH) is a background asteroid, approximately 8 kilometers (5 miles) in diameter, located in the Florian region of the inner asteroid belt. It was discovered on 1 October 1921, by astronomer Karl Reinmuth at the Heidelberg Observatory in southern Germany.[1] The possibly S-type asteroid has a rotation period of 8.9 hours. It was named after Birgit Asplind, daughter of Swedish astronomer Bror Asplind (1890–1954).[2]

960 Birgit
Discovery [1]
Discovered byK. Reinmuth
Discovery siteHeidelberg Obs.
Discovery date1 October 1921
Designations
(960) Birgit
Named after
Birgit Asplind
(daughter of Bror Asplind)[2]
A921 TG · 1921 KH
main-belt [1][3] · (inner)
background [4][5] (Florian)[6]
Orbital characteristics [3]
Epoch 31 May 2020 (JD 2459000.5)
Uncertainty parameter 0
Observation arc98.26 yr (35,889 d)
Aphelion2.6203 AU
Perihelion1.8770 AU
2.2486 AU
Eccentricity0.1653
3.37 yr (1,232 d)
123.62°
0° 17m 32.28s / day
Inclination3.0260°
249.16°
88.040°
Physical characteristics
Mean diameter
7.506±0.110 km[7]
8.85±0.05 h[8][9][lower-alpha 1]
0.217±0.027[7]
S (assumed)[8]
12.5[1][3]

    Orbit and classification

    Located in the Florian region,[6] Birgit 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 inner asteroid belt at a distance of 1.9–2.6 AU once every 3 years and 4 months (1,232 days; semi-major axis of 2.25 AU). Its orbit has an eccentricity of 0.17 and an inclination of 3° with respect to the ecliptic.[3] The body's observation arc begins at Heidelberg on 25 October 1925, three weeks after its official discovery observation.[1]

    Naming

    This minor planet was named after Birgit Asplind, daughter of Swedish astronomer Bror Ansgar Asplind (1890–1954). Asteroids 958 Asplinda, 959 Arne and 961 Gunnie are named after him and his other two children, respectively. The naming was mentioned in The Names of the Minor Planets by Paul Herget in 1955 (H 92).[2]

    Physical characteristics

    Based on its determined albedo, Birgit is an assumed S-type asteroid.[8] The albedo determined by the Wide-field Infrared Survey Explorer (WISE) for this asteroid agrees with that assumption (see below).

    Rotation period

    In February 2007, a rotational lightcurve of Birgit was obtained from photometric observations by Agnieszka Kryszczyńska at Poznań Observatory, Poland, and international collaborators. Lightcurve analysis gave a rotation period of 8.85±0.05 hours with a brightness variation of 0.28±0.02 magnitude (U=2+).[9][lower-alpha 1] The result supersedes observations by Federico Manzini, Roberto Crippa, and Pierre Antonini from August 2005, who determined a poorly rated period of 17.3558±0.0005 hours with an amplitude of 0.25±0.01 magnitude (U=1+).[10]

    Diameter and albedo

    According to the survey carried out by the NEOWISE mission of NASA's WISE telescope, Birgit measures 7.506±0.110 kilometers in diameter and its surface has an albedo of 0.217±0.027.[7] Another published measurement by the WISE team gives a mean-diameter of 8.154±0.566 km with an albedo of 0.291±0.044.[5] The Collaborative Asteroid Lightcurve Link assumes a standard albedo for a stony asteroid of 0.20 and calculates a diameter of 9.40 kilometers based on an absolute magnitude of 12.5.[8]

    Notes
    1. Lightcurve plot of (960) Birgit (1 of 3), Agnieszka Kryszczyńska et. al (2012). LCDB quality code of 2+. Summary figures at the LCDB and CDS-VizieR.

    References
    1. "960 Birgit (A921 TG)". Minor Planet Center. Retrieved 13 February 2020.
    2. Schmadel, Lutz D. (2007). "(960) Birgit". Dictionary of Minor Planet Names. Springer Berlin Heidelberg. p. 84. doi:10.1007/978-3-540-29925-7_961. ISBN 978-3-540-00238-3.
    3. "JPL Small-Body Database Browser: 960 Birgit (A921 TG)" (2020-01-04 last obs.). Jet Propulsion Laboratory. Retrieved 13 February 2020.
    4. "Asteroid 960 Birgit – Proper Elements". AstDyS-2, Asteroids – Dynamic Site. Retrieved 13 February 2020.
    5. "Asteroid 960 Birgit". Small Bodies Data Ferret. Retrieved 13 February 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 4 March 2020.} (PDS main page)
    7. 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.
    8. "LCDB Data for (960) Birgit". Asteroid Lightcurve Database (LCDB). Retrieved 13 February 2020.
    9. Kryszczynska, A.; Colas, F.; Polinska, M.; Hirsch, R.; Ivanova, V.; Apostolovska, G.; et al. (October 2012). "Do Slivan states exist in the Flora family?. I. Photometric survey of the Flora region" (PDF). Astronomy and Astrophysics. 546: 51. Bibcode:2012A&A...546A..72K. doi:10.1051/0004-6361/201219199. Retrieved 13 February 2020. (VizieR)
    10. Behrend, Raoul. "Asteroids and comets rotation curves – (960) Birgit". Geneva Observatory. Retrieved 13 February 2020.
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