925 Alphonsina

925 Alphonsina, provisional designation, is a stony Hansian asteroid from the central region of the asteroid belt, approximately 58 km in diameter. It was discovered on 13 January 1920, by Catalan astronomer Josep Comas i Solà at the Fabra Observatory in Barcelona, Spain. The S-type asteroid has a rotation period of 7.88 hours. It was named for the Spanish Kings Alfonso X and Alfonso XIII.

Orbit and classification
Together with asteroid 480 Hansa, Alphonsina is the largest member of the stony Hansa family (803), a high-inclination family with more than a thousand known members.

It orbits the Sun in the intermediate asteroid belt at a distance of 2.5–2.9 AU once every 4 years and 5 months (1,621 days; semi-major axis of 2.7 AU). Its orbit has an eccentricity of 0.08 and an inclination of 21° with respect to the ecliptic. The asteroid was first observed as at Heidelberg Observatory in March 1902. The body's observation arc begins ten days after its official discovery observation at Heidelberg.

Physical characteristics
Alphonsina is a common, stony S-type asteroid in both the Tholen and SMASS classification. Polarimetric observations in 2017 also characterized it as an S-type asteroid.

Rotation period and pole
Since 1980, several rotational lightcurves of Alphonsina have been obtained from photometric observations with rotation periods between 7.876 and 7.92 hours (U=3/3/3/2/2). The best-rated lightcurve by Alan Harris and James Whitney Young gave a period of 7.880 hours. The consolidated brightness amplitude is between 0.11 and 0.57 magnitude.

In 2011, two modeled lightcurves using data from the Uppsala Asteroid Photometric Catalogue (UAPC) and from asteroidal occultation silhouettes gave a concurring period 7.87754 hours. The studies also determined a spin axis at (296.0°, 41.0°) and (294.0°, 41.0°) in ecliptic coordinates (λ,&thinsp;β), respectively.

Diameter and albedo
According to the surveys carried out by the Infrared Astronomical Satellite IRAS, the Japanese Akari satellite and the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer, Alphonsina measures between 54.34 and 63.52 kilometers in diameter and its surface has an albedo between 0.204 and 0.2786.



In 2003, stellar occultation measured a diameter of 59.2 kilometres and deduced an albedo of 0.218, while the modelling of asteroid occultation silhouettes gave a diameter of 58 kilometres. The asteroid has been observed in stellar occultations 8 times since 2003.

The Collaborative Asteroid Lightcurve Link adopts Petr Pravec's revised WISE data, that is, an albedo of 0.2266 and a diameter of 58.06 kilometers based on an absolute magnitude of 8.41.

Naming
This minor planet was named in honor of the Iberian Kings, Alfonso X (1221–1284) and Alfonso XIII (1886–1941), King of Castile and Spain, respectively. The original citation from 1920, mentions, that the 13th century king inspired the field of astronomy in the Middle Ages, and, that the latter king was a great enthusiast of the scientific development in Spain. It also mentions that the King of Spain approved the naming of the asteroid (AN 211, 223).