763 Cupido

763 Cupido (prov. designation: or ) is a Flora asteroid, tumbler and slow rotator from the inner regions of the asteroid belt, approximately 7 km in diameter. It was discovered on 25 September 1913, by German astronomer Franz Kaiser at the Heidelberg-Königstuhl State Observatory in southwest Germany. The S/L-type asteroid has an exceptionally long rotation period of 151 hours. It was named by its Latin name after Cupid, the Roman god of erotic love, attraction and affection.

Orbit and classification
When applying the synthetic hierarchical clustering method (HCM) by Nesvorný, or the 1995 HCM-analysis by Zappalà, Cupido is a member of the Flora family (402), a giant asteroid family and the largest family of stony asteroids in the main-belt. However, according to another HCM-analysis by Milani and Knežević (AstDys), it is a background asteroid as this analysis does not recognize the Flora asteroid clan. Cupido orbits the Sun in the inner asteroid belt at a distance of 1.9–2.6 AU once every 3 years and 4 months (1,226 days; semi-major axis of 2.24 AU). Its orbit has an eccentricity of 0.17 and an inclination of 4° with respect to the ecliptic. The body's observation arc begins at Yerkes Observatory in September 1933, or 20 years after to its official discovery observation by Franz Kaiser at Heidelberg Observatory in 1913.

Naming
This minor planet was named "Cupido", the Latin name of Cupid, god of erotic love, attraction and affection in Roman mythology whose Greek counterpart is Eros (also see asteroid 433 Eros). Cupido was named due to its relative proximity to the Sun probably by Swedish astronomer Bror Ansgar Asplind (1890–1954) who was honored by asteroid 958 Asplinda. The was mentioned in The Names of the Minor Planets by Paul Herget in 1955 (H 76).

Physical characteristics
In the SDSS-based taxonomy, Cupido is an SL-type that transitions from the common, stony S-type asteroids to the uncommon L-type asteroids.

Rotation period
In October 2017, a rotational lightcurve of Cupido was obtained from photometric observations by American astronomer Frederick Pilcher in collaboration with Vladimir Benishek at Belgrade Observatory and Daniel A. Klinglesmith at Etscorn Observatory. Lightcurve analysis gave a rotation period of $7.005 km$ hours with a brightness variation of $151.5 h$ magnitude (U=3-). The observations also showed that it is a tumbling asteroid, which wobbles on its non-principal axis rotation. During the same opposition, Tom Polakis at the Command Module Observatory also observed the asteroid and measured a period of $0.373$ hours and an amplitude of $151.5$ magnitude (U=2+). The results supersede a tentative period determination of $0.45$ hours by René Roy from 2005.

Diameter and albedo
According to the survey carried out by the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer (WISE), Cupido measures ($151.1$) kilometers in diameter and its surface has an albedo of ($0.24$). Other publications by the WISE team give a mean diameter of ($14.88$), ($7.005$) and ($0.373$) with a corresponding albedo of ($7.38 km$), ($7.644 km$) and ($7.76 km$), respectively. The Collaborative Asteroid Lightcurve Link assumes a standard albedo for a Flora asteroid of 0.20 and calculates a diameter of 8.97 kilometers based on an absolute magnitude of 12.6.