3309 Brorfelde, provisional designation 1982 BH, is a nearly spheroidal, binary[a] Hungaria asteroid from the inner regions of the asteroid belt, approximately 4 kilometers in diameter. It was discovered on 28 January 1982, by Danish astronomers Kaare Jensen and Karl Augustesen at the Brorfelde Observatory near Holbæk, Denmark.[3] It was named for the discovering observatory and the village where it is located.[2]
Orbit and classification
Brorfelde is a bright stony asteroid and member of the Hungaria family, which form the innermost dense concentration of asteroids in the Solar System. It orbits the Sun at a distance of 1.7–1.9 AU once every 2 years and 5 months (895 days). Its orbit has an eccentricity of 0.05 and an inclination of 21° with respect to the ecliptic.[1] The body's observation arc begins with its official discovery observation, as no precoveries were taken, and no prior identifications were made.[3]
Between 2005 and 2010, astronomers Brian Warner and Petr Pravec obtained a large number of rotational lightcurves of Brorfelde. Best rated lightcurve analysis gave a rotation period between 2.5041 and 2.5046 hours with a brightness amplitude between 0.09 and 0.13 in magnitude, indicating that the body has a nearly spheroidal shape (U=3/3/3).[9][10]
These results superseded photometric observations taken by Wiesław Z. Wiśniewski in the 1990s (U=2),[12] and by Federico Manzini and René Roy in 2005 and 2009, respectively (U=2-/n.a.),[13] as well as observations taken at the Palomar Transient Factory in 2010, which gave an incorrect period solution of more than 9 hours (U=1).[14]
Satellite
During the photometric observation in 2005, it was revealed that Brorfelde is a binary asteroid. Its asteroid moon has an orbital period of 18.48±0.01 hours, and measures approximately 1 kilometer in diameter, based on a mean-diameter ratio of 0.26±0.02 for the system's secondary and primary body.[a][5] In January 2014, repeated observations by Brian Warner confirmed a period of 2.503 and 18.51 hours for the primary and secondary, respectively (U=3),[8] with several online-published lightcurve plots.[b]
Diameter and albedo
According to the survey carried out by NASA's Wide-field Infrared Survey Explorer with its subsequent NEOWISE mission, Brorfelde measures 3.78 kilometers in diameter, and its surface has an albedo of 0.46 (most recent result only).[6] The Collaborative Asteroid Lightcurve Link derives an albedo of 0.2747 and a diameter of 3.91 kilometers with an absolute magnitude of 14.062.[4]
Naming
This minor planet was named on the occasion of the Brorfelde Observatory's 40th anniversary. Brorfelde was the observatory's first minor planet discovery.[2] The approved naming citation was published by the Minor Planet Center on 7 September 1987 (M.P.C. 12210).[16]
Notes
^ abcElectronic Telegram No. 279, (3309) Brorfelde, 7 November 2005[5] Photometric observations obtained from 25 October to 3 November 2005, revealed that 3309 Brorfelde is a binary system with an orbital period of 18.48±0.01 hours. The primary rotates with a period of 2.5041±0.0002 hours, and its light-curve has a brightness variation of 0.13 magnitude, indicating a nearly spheroidal shape. Mutual eclipse/occultation events with an amplitude of 0.07-0.15 magnitude suggest a ratio of 0.26±0.02 for its secondary-to-primary mean-diameter. Assuming G = 0.15, the calibrated data gives an absolute magnitude of 13.4±0.2. B. D. Warner, Palmer Divide Observatory, Colorado Springs; P. Pravec and P. Kusnirak, Ondrejov Observatory; W. Cooney, J. Gross, and D. Terrell, Sonoita Research Observatory, Sonoita, AZ; and S. Nudds, Elginfield Observatory, University of Western OntarioCentral Bureau for Astronomical Telegrams No.279
^Lightcure plots of (3309) Brorfelde at the Center for Solar System Studies (CS3) in 2014
