976 Benjamina

976 Benjamina (prov. designation: or ) is a dark background asteroid from the outer regions of the asteroid belt, approximately 81 km in diameter. It was discovered on 27 March 1922, by Russian-French astronomer Benjamin Jekhowsky at the Algiers Observatory in North Africa. The large X/D-type asteroid has a rotation period of 9.7 hours and is likely regular in shape. It was named after the discoverer's son.

Orbit and classification
Benjamina 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 outer main-belt at a distance of 2.9–3.5 AU once every 5 years and 9 months (2,092 days; semi-major axis of 3.2 AU). Its orbit has an eccentricity of 0.10 and an inclination of 8° with respect to the ecliptic.

The asteroid was first observed as  at Heidelberg Observatory on 8 January 1910. The body's observation arc begins at the Crimean Simeiz Observatory in September 1930, more than 7 years after its official discovery observation at Algiers Observatory in March 1922.

Naming
This minor planet was named after Benjamin Jekhowsky Jr., son of discoverer Benjamin Jekhowsky. The was mentioned in The Names of the Minor Planets by Paul Herget in 1955 (H 93).

Physical characteristics


In the Tholen classification, and based on a noisy spectra, Benjamina is an X-type asteroid, somewhat similar to that of a dark D-type (XD), which are common in the outer asteroid belt and among the Jupiter trojan population.

Rotation period and pole
In September 2004, a rotational lightcurve of Benjamina was obtained from photometric observations by French amateur astronomer Laurent Bernasconi. Lightcurve analysis gave a well-defined rotation period of $79.94 km$ hours with a brightness variation of $80.53 km$ magnitude (U=3). Follow-up observation by his college René Roy in March 2018, determined a concurring period of $83.195 km$ hours but with a much higher amplitude of $9.701 h$ magnitude (U=2). The objects first lightcurve was obtained by Colin Bembrick at Mount Tarana Observatory in Australia in March 2003. It showed a period of $0.052$ hours with an amplitude of $0.056$ magnitude (U=2). The overall amplitude suggest a rather regular shape with a ratio of 0.86 for the length of the a and b axes.

In 2018, Czech astronomers Josef Ďurech and Josef Hanuš published a modeled lightcurve using photometric data from the Gaia probe's second data release. It showed a sidereal period of $0.057$ hours, and gave a spin axis at (354.0°, 80.0°) in ecliptic coordinates (λ,&thinsp;β).

Diameter and albedo
According to the surveys carried out by the Japanese Akari satellite, the Infrared Astronomical Satellite IRAS, and the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer (WISE), Benjamina measures $0.74$, $0.25$ and $9.701$ kilometers in diameter with an albedo of its surface of $0.19$, $9.705$ and $0.6$, respectively. Additional measurements by the WISE telescope were published giving a mean-diameter as low as $9.746$, and as high as $0.18$.

The Collaborative Asteroid Lightcurve Link adopts the result from IRAS, that is, an albedo of 0.0559 and a diameter of 80.53 kilometers based on an absolute magnitude of 9.22.

The asteroid had been observed in 7 stellar occultation events since 2003. On 19 July 2003 the mag. 5.7 star HIP 88816 was occulted by the asteroid, and was observed at 11 stations; 1 in Argentina, 3 in New Zealand, and 7 in Australia. From these observations, the best-fit ellipse measures 85.2&thinsp;x&thinsp;56.2 +/-12.4 kilometres.