3309 Brorfelde, provisional designation1982 BH, is a nearly spheroidal,binary[a] Hungariaasteroid from the inner regions of theasteroid belt, approximately 4 kilometers in diameter. It was discovered on 28 January 1982, by Danish astronomersKaare Jensen andKarl Augustesen at theBrorfelde Observatory near Holbæk, Denmark.[3] It was named for the discovering observatory and the village where it is located.[2]
Brorfelde is a brightstony asteroid and member of theHungaria family, which form theinnermost dense concentration of asteroids in theSolar 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 aneccentricity of 0.05 and aninclination of 21° with respect to theecliptic.[1] The body'sobservation arc begins with its official discovery observation, as noprecoveries were taken, and no prior identifications were made.[3]
Between 2005 and 2010, astronomersBrian Warner andPetr Pravec obtained a large number of rotationallightcurves of Brorfelde. Best rated lightcurve analysis gave arotation period between 2.5041 and 2.5046 hours with a brightness amplitude between 0.09 and 0.13 inmagnitude, indicating that the body has a nearly spheroidal shape (U=3/3/3).[9][10]
These results superseded photometric observations taken byWiesław Z. Wiśniewski in the 1990s (U=2),[12] and by Federico Manzini andRené Roy in 2005 and 2009, respectively (U=2-/n.a.),[13] as well as observations taken at thePalomar Transient Factory in 2010, which gave an incorrect period solution of more than 9 hours (U=1).[14]
During the photometric observation in 2005, it was revealed that Brorfelde is abinary asteroid. Itsasteroid moon has an orbital period of18.48±0.01 hours, and measures approximately 1 kilometer in diameter, based on a mean-diameter ratio of0.26±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]
According to the survey carried out by NASA'sWide-field Infrared Survey Explorer with its subsequentNEOWISE mission, Brorfelde measures 3.78 kilometers in diameter, and its surface has analbedo of 0.46 (most recent result only).[6] TheCollaborative Asteroid Lightcurve Link derives an albedo of 0.2747 and a diameter of 3.91 kilometers with anabsolute magnitude of 14.062.[4]
Thisminor 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 theMinor Planet Center on 7 September 1987 (M.P.C. 12210).[16]
^abcElectronic Telegram No. 279, (3309) Brorfelde, 7 November 2005[5] Photometric observations obtained from 25 October to 3 November 2005, revealed that3309 Brorfelde is a binary system with an orbital period of18.48±0.01 hours. The primary rotates with a period of2.5041±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 of0.26±0.02 for its secondary-to-primary mean-diameter. Assuming G = 0.15, the calibrated data gives an absolute magnitude of13.4±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
