5751 Zao,

provisional designation Provisional designation in astronomy is the naming convention applied to astronomical objects immediately following their discovery. The provisional designation is usually superseded by a permanent designation once a reliable orbit has been calcu ...

, is an

Amor asteroid The Amor asteroids are a group of near-Earth asteroids named after the archetype object 1221 Amor . The orbital perihelion of these objects is close to, but greater than, the orbital aphelion of Earth (i.e., the objects do not cross Earth's orb ...

discovered by Japanese astronomer M. Koishikawa at the

Ayashi Station is a railway station on the Senzan Line in Aoba-ku, Sendai in Miyagi Prefecture, Japan, operated by East Japan Railway Company (JR East). The station also uses the moniker . The ''kanji'' characters for Ayashi are the same characters as in the ...

of the Sendai Astronomical Observatory on 5 January 1992

Physical properties

''Zao'' has been observed by several groups to determine its rotational period. Its

light curve In astronomy, a light curve is a graph of light intensity of a celestial object or region as a function of time, typically with the magnitude of light received on the y axis and with time on the x axis. The light is usually in a particular frequ ...

was observed by Pravec, et al. between 1992 and 1995 with the intention of determining its rotational period. From its nearly constant brightness it was determined that the asteroid is roughly spherical and has a rotational period of ≥ 21.7 hr. Another group led by Wisniewski conducted an approximately 5 hour observation and were unable to conclude a rotational period. ''Zao'' was again observed in 2001 by Delbó, et al. using the

Keck telescope The W. M. Keck Observatory is an astronomical observatory with two telescopes at an elevation of 4,145 meters (13,600 ft) near the summit of Mauna Kea in the U.S. state In the United States, a state is a constituent political entit ...

. They were able to determine the asteroid's

albedo Albedo (; ) is the measure of the diffuse reflection of sunlight, solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body ...

of 0.36 and re-classify the asteroid from X-type to E-type. Using the asteroid's albedo and the Near Earth Asteroid Thermal Model (NEATM) the asteroid's

diameter In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints lie on the circle. It can also be defined as the longest chord of the circle. Both definitions are also valid for ...

was estimated to be 2.3 km. Further study of the asteroid by the Ondrejov Asteroid Photometry Project concludes that a rotational period of 76 hours is consistent with earlier measurements.

References

External links

IAUC 5426 – Initial discovery

* * * {{DEFAULTSORT:Zao 005751 Discoveries by Masahiro Koishikawa Named minor planets 005751 19920105