1025 Riema
1025 Riema, provisional designation, is a bright Hungaria asteroid from the innermost regions of the asteroid belt, approximately 5 kilometers in diameter. It was discovered on 12 August 1923, by German astronomer Karl Reinmuth at the Heidelberg Observatory in southwest Germany. The asteroid was named after ARI astronomer Johannes Riem.
Orbit and classification
Riema is a member of the Hungaria family, which form the innermost dense concentration of asteroids in the Solar System. It orbits the Sun at a distance of 1.9–2.1 AU once every 2 years and 9 months. Its orbit has an eccentricity of 0.04 and an inclination of 27° with respect to the ecliptic. The asteroid's observation arc begins at Heidelberg, four nights after its official discovery observation.Physical characteristics
In the Tholen classification, Riema is a bright E-type asteroid. In the SMASS taxonomy, it has been classified as a Xe-type, which transitions from the E to the X-types. In addition, the asteroid has also been polarimetrically characterized as a metallic M-type asteroid.Lightcurves
In August 2001, a first rotational lightcurve of Riema was obtained from photometric observations by Ukrainian astronomers at Kharkiv and Simeiz. Lightcurve analysis gave a rotation period of 6.557 hours with a brightness variation of 0.25 magnitude.The Ukrainian team also determined the body's poles and axis-ratios. They found a spin axis of and in ecliptic coordinates, as well as a semi-axis ratio of 3.41 and 1.16 for the three-axial ellipsoid model.
Between 2003 and 2017, several additional lightcurves were obtained by American photometrists Robert Stephens and Brian Warner at the Santana Observatory, the Palmer Divide Observatory and the Palmer Divide Station, respectively. The constructed lightcurve gave a shorter period for Riema between 3.566 and 3.588 hours with a low amplitude of 0.06 to 0.19 magnitude.