In September 2017, a rotational lightcurve of Altona was obtained from photometric observations by Brian Warner at his Palmer Divide Station (U82) of the Center for Solar System Studies in California. Lightcurve analysis gave a well-defined rotation period of 11.1913±0.0009 hours with a brightness variation of 0.17±0.01magnitude (U=3).[10][a]
The result supersedes previous period determinations of:[12]11.131±0.0066 and 11.16±0.380 hours by astronomers at the Palomar Transient Factory, California, in January 2014 (U=2/2),[13][14]11.195±0.001 hours by Michael Alkema at the Elephant Head Observatory (G35) in Arizona in December 2012 (U=2+),[15]11.197±0.002 hours by Frederick Pilcher at the Organ Mesa Observatory (G50) in June 2010 (U=2),[16] and 11.9±0.5 hours by Robin Esseiva, Nicolas Esseiva and Raoul Behrend in April 2015 (U=2).[17]
Diameter and albedo
According to the surveys carried out by the Japanese Akari satellite, the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer (WISE), and the Infrared Astronomical Satellite IRAS, Altona measures (73.16±0.88), (77.097±2.263) and (80.90±1.8) kilometers in diameter and its surface has an albedo of (0.048±0.001), (0.043±0.009) and (0.0390±0.002), respectively.[7][8][9]
The Collaborative Asteroid Lightcurve Link derives an albedo of 0.0356 and a diameter of 80.85 kilometers based on an absolute magnitude of 9.7.[12] Alternative mean-diameter measurements published by the WISE team include (59.945±0.585 km), (63.25±16.39 km), (69.47±2.17 km) and (81.518±19.16 km) with corresponding albedos of (0.0710±0.0051), (0.06±0.04), (0.053±0.018), and (0.0403±0.0278).[6][12] An asteroid occultation observed on 3 April 2008, gave a best-fit ellipse dimension of (80.0 km × 80.0 km). These timed observations are taken when the asteroid passes in front of a distant star.[6]
Notes
^ abLightcurve plot of (850) Altona by Brian Warner, Palmer Divide Station (U82) at Center for Solar System Studies (2017). Rotation period 11.1913±0.0009 hours with a brightness amplitude of 0.17±0.01 mag. Quality code is 3. Summary figures at the LCDB and CS3.
^ abcUsui, Fumihiko; Kuroda, Daisuke; Müller, Thomas G.; Hasegawa, Sunao; Ishiguro, Masateru; Ootsubo, Takafumi; et al. (October 2011). "Asteroid Catalog Using Akari: AKARI/IRC Mid-Infrared Asteroid Survey". Publications of the Astronomical Society of Japan. 63 (5): 1117–1138. Bibcode:2011PASJ...63.1117U. doi:10.1093/pasj/63.5.1117. (online, AcuA catalog p. 153)