The S-type asteroid orbits the Sun in the inner main-belt at a distance of 2.0–2.5 AU once every 3 years and 4 months (1,231 days). Its orbit has an eccentricity of 0.13 and an inclination of 8° with respect to the ecliptic.[1] Callahan was first identified as 1978 RQ8 at ESO's La Silla Observatory in 1978, which extends the asteroid's observation arc by 22 years prior to its official discovery observation.[3]
Physical characteristics
In December 2009, a rotational lightcurve for this asteroid was obtained from photometric observations at the U.S. Palomar Transient Factory, California. It gave a rotation period of 7.2684±0.0015 hours with a relatively high brightness variation of 0.81 in magnitude (U=2), indicative of a non-spherical shape.[7]
According to the survey carried out by the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer, Callahan measures 3.9 kilometers in diameter and its surface has an albedo of 0.22.[5] The Collaborative Asteroid Lightcurve Link assumes a standard albedo for stony asteroids of 0.20 and calculates a diameter of 3.1 kilometers, with an absolute magnitude of 14.89.[4]
Naming
This minor planet was named after Diane Callahan, teacher at U.S. Fairfield Middle School, Ohio, who mentored a finalist in the 2003 Discovery Channel Youth Science Challenge (DCYSC), a middle school science competition.[2] The approved naming citation was published by the Minor Planet Center on 10 October 2003 (M.P.C. 49772).[8]
