641 Agnes

641 Agnes, provisional designation, is a stony Florian asteroid and slow rotator from the inner regions of the asteroid belt, approximately 9 km in diameter.

It was discovered on 8 September 1907, by German astronomer Max Wolf at Heidelberg Observatory in southern Germany. The meaning of the asteroids's name is unknown.

Classification and orbit
Agnes is a stony S-type asteroid and a member of the Flora family, one of the largest groups of stony asteroids in the asteroid belt. It orbits the Sun in the inner main-belt at a distance of 1.9–2.5 AU once every 3 years and 4 months (1,208 days). Its orbit has an eccentricity of 0.13 and an inclination of 2° with respect to the ecliptic. The body's observation arc begins with a recovered observation at Vienna Observatory, one month after its official discovery observation at Heidelberg.

Rotation period
In March 1975, photometric observations by Swedish astronomer Claes-Ingvar Lagerkvist measured a period of 8.9 hours for Agnes. The lightcurve, however, was fragmentary and the result uncertain (U=1).

In October 2013, the first reliable rotational lightcurve of Agnes was obtained by astronomers Frederick Pilcher, Lorenzo Franco and Luis Martinez at Organ Mesa and Balzaretto Observatory  respectively. Lightcurve analysis gave a well-defined rotation period of 178.0 hours with a brightness variation of 0.55 magnitude (U=3). The team also assumed a standard albedo for stony S-type asteroids of 0.20, calculated an absolute magnitude of 12.64, estimated a mean diameter of $8.26$ kilometers, and measured a V–R color index of 0.50.

With such a long rotation period, Agnes is a slow rotator, of which a few hundred minor planets are currently known.

Diameter and albedo
According to the surveys carried out by the Japanese Akari satellite and NASA's Wide-field Infrared Survey Explorer with its subsequent NEOWISE mission, Agnes measures between 8.26 and 9.74 km in diameter, and its surface has an albedo between 0.21 and 0.30. The Collaborative Asteroid Lightcurve Link adopts the results obtained by Pilcher, and calculates a diameter of 8.81 kilometers.

Naming
Any reference of this minor planet's name to a person or occurrence is unknown.

Unknown meaning
Among the many thousands of named minor planets, Agnes is one of 120 asteroids, for which no official naming citation has been published. All of these low-numbered asteroids have numbers between and  and were discovered between 1876 and the 1930s, predominantly by astronomers Auguste Charlois, Johann Palisa, Max Wolf and Karl Reinmuth.