873 Mechthild

873 Mechthild (prov. designation: or ) is a dark background asteroid from the central regions of the asteroid belt. It was discovered by German astronomer Max Wolf at the Heidelberg Observatory on 21 May 1917. The primitive P-type asteroid has a rotation period of 11.0 hours and measures approximately 34 km in diameter. The origin of the asteroid's name remains unknown.

Orbit and classification
Mechthild is a non-family asteroid of the main belt's background population when applying the hierarchical clustering method to its proper orbital elements. It orbits the Sun in the central asteroid belt at a distance of 2.2–3.0 AU once every 4 years and 3 months (1,555 days; semi-major axis of 2.63 AU). Its orbit has an eccentricity of 0.15 and an inclination of 5° with respect to the ecliptic. The body's observation arc begins with its first and official discovery observation at Heidelberg Observatory on 21 May 1917.

Naming
This minor planet is named "Mechthild", a German feminine given name. Any reference of this name to a specific person or occurrence is unknown.

Unknown meaning
Among the many thousands of named minor planets, Mechthild 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.

Physical characteristics
In the Tholen classification, Mechthild is closest to a very dark, primitive P-type, and somewhat similar to a common C-type asteroid. In the taxonomy by Barucci, it is a C0-type. P-type asteroids are more common in the outer asteroid belt and among the Jupiter trojan population.

Rotation period
In May 2015, a rotational lightcurve of Mechthild was obtained from photometric observations by Brian Warner at his Palmer Divide Observatory in Colorado. Lightcurve analysis gave a rotation period of $29.04 km$ hours with a brightness amplitude of $33.56 km$ magnitude (U=3).

Alternative period determinations were made by Claes-Ingvar Lagerkvist ($34.471 km$) in March 1976, by astronomers at the Palomar Transient Factory ($11.006 h$) in January 2014, and by the Spanish group of asteroid observers, OBAS ($0.04$) in May 2015 (U=2/2/3). In 2016, a modeled lightcurve gave a concurring sidereal period of $0.041$ hours using data from a large collaboration of individual observers (such as above). The study also determined two spin axes of (249.0°, −52.0°) and (51.0°, −61.0°) in ecliptic coordinates (λ,&thinsp;β).

Diameter and albedo
According to the surveys carried out by the Infrared Astronomical Satellite IRAS, and the Japanese Akari satellite, and the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer (WISE), Mechthild measures ($0.053$), ($0.684$) and ($0.319$) kilometers in diameter and its surface has an albedo of ($11.006$), ($0.27$) and ($10.6 h$), respectively. The Collaborative Asteroid Lightcurve Link adopts the results from IRAS, that is, an albedo of 0.0531 and a diameter of 29.04 kilometers based on an absolute magnitude of 11.49. Alternative mean-diameter measurements published by the WISE team include ($11.007 h$) and ($10.99 h$) with corresponding albedos of ($11.006$) and ($29.04$).