1089 Tama, provisional designation 1927 WB, is an elongated Florian asteroid and synchronous binary system from the inner regions of the asteroid belt, approximately 12 kilometers in diameter.
It was discovered by Japanese astronomer Okuro Oikawa at the old Tokyo Astronomical Observatory (389) on 17 November 1927.[18] The asteroid was named after the Tama River in Japan.[2] Its minor-planet moon was discovered in December 2003 and measures approximately 9 kilometers.[6]
Orbit and classification
Tama is a member of the Flora family (402), a giant asteroid family and the largest family of stony asteroids in the main-belt.[3] It is, however, a non-family asteroid from the main belt's background population when applying the Hierarchical Clustering Method to its proper orbital elements.[4]
The asteroid orbits the Sun in the inner main-belt at a distance of 1.9–2.5 AU once every 3 years and 3 months (1,203 days). Its orbit has an eccentricity of 0.13 and an inclination of 4° with respect to the ecliptic.[1]Tama was first identified as A894 VA at Heidelberg Observatory in November 1894. The body's observation arc begins with its identification as A904 VD at Heidelberg in November 1904, or 23 years prior to its official discovery observation at Tokyo.[18]
A large number of rotational lightcurves of Tama were obtained from photometric observations since it has been identified as a binary asteroid(see below). Lightcurve analysis gave a rotation period between 16.4 and 16.464 hours with a brightness variation between 0.08 and 0.41 magnitude (U=2-/2-3-/3), superseding a period of 4 hours from a fragmentary lightcurve obtained in the 1990s (U=1).[6][8][12][13][15]
Tama appears to be somewhat elongated in shape.[6] LCDB's consolidated result gives a period of 16.44 hours and an amplitude of 0.41 magnitude (U=3).[3]
Tamas lightcurve has also been modeled. In 2013, modelling by an international study using photometric data from the US Naval Observatory, the Uppsala Asteroid Photometric Catalogue (UAPC) and the Palmer Divide Observatory, gave a concurring rotation period of 16.4655 hours.[16] Another modeled lightcurve using data from UAPC, the Palomar Transient Factory survey, and individual observers, gave a period of 16.4461 hours as well as two spin axes of (193.0°, 32.0°) and (9.0°, 28.0°) in ecliptic coordinates (λ, β).[19]
^Hanus, J.; Durech, J.; Broz, M.; Marciniak, A.; Warner, B. D.; Pilcher, F.; et al. (March 2013). "Asteroids' physical models from combined dense and sparse photometry and scaling of the YORP effect by the observed obliquity distribution". Astronomy and Astrophysics. 551: 16. arXiv:1301.6943. Bibcode:2013A&A...551A..67H. doi:10.1051/0004-6361/201220701.