19741 Callahan

19741 Callahan (provisional designation ) is a stony background asteroid from the inner regions of the asteroid belt, approximately 3.5 kilometers in diameter.

It was discovered on 5 January 2000, by the Lincoln Near-Earth Asteroid Research, LINEAR, at the Lincoln Laboratory's Experimental Test Site, Socorro, New Mexico, and named after a mentor of the 2003 Discovery Channel Young Scientist Challenge.

Orbit and classification
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. Callahan was first identified as at ESO's La Silla Observatory in 1978, which extends the asteroid's observation arc by 22 years prior to its official discovery observation.

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 $3.876$ hours with a relatively high brightness variation of 0.81 in magnitude (U=2), indicative of a non-spherical shape.

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. 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.

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. The approved naming citation was published by the Minor Planet Center on 10 October 2003 (M.P.C. 49772).