845 Naëma

845 Naëma (prov. designation: or ) is a large asteroid and the parent body of the Naëma family located in the outer regions of the asteroid belt. It was discovered on 16 November 1916, by astronomer Max Wolf at the Heidelberg-Königstuhl State Observatory in southwest Germany. The carbonaceous C-type asteroid has a rotation period of 20.9 hours and measures approximately 54 km in diameter on average, as it is likely elongated in shape. Any reference of the asteroid's name to a person is unknown.

Orbit and classification
Naëma is the parent body of the Naëma family (611), a smaller family of little more than 300 carbonaceous asteroids, when applying the hierarchical clustering method. This asteroid family is widely recognized by a number of Solar System dynamicists including Zappalà, Nesvorný, as well as Milani and Knežević (AstDyS) The family was first detected by Vincenzo Zappalà in 1994/95.

Naëma orbits the Sun in the outer asteroid belt at a distance of 2.7–3.1 AU once every 5.04 years (1,840 days; semi-major axis of 2.94 AU). Its orbit has an eccentricity of 0.07 and an inclination of 13° with respect to the ecliptic. The body's observation arc begins as  with its official discovery observation at Heidelberg Observatory on 16 November 1916.

Naming
Naëma is a German variant of the biblical name Naomi. However, any reference of this minor planet name to a person or occurrence is unknown.

Unknown meaning
Among the many thousands of named minor planets, Naëma is one of 120 asteroids for which no official naming citation has been published. All of these asteroids have low numbers, the first being. The last asteroid with a name of unknown meaning is. They were discovered between 1876 and the 1930s, predominantly by astronomers Auguste Charlois, Johann Palisa, Max Wolf and Karl Reinmuth.

Physical characteristics
In the Bus–Binzel SMASS classification, Naëma is a common, carbonaceous C-type asteroid, which is the overall spectral type of the Naëma family.

Rotation period
In September 2006, a rotational lightcurve of Naëma was obtained from photometric observations by Collin Bembrick at the Mount Tarana Observatory, Australia, in collaboration with Bill Allen and Greg Bolt. Lightcurve analysis gave a relatively long rotation period of $63.1 km$ hours with a brightness variation of $52.677 km$ magnitude (U=2). In December 2017, French amateur astronomer René Roy determined a lower-rated, tentative period of $54.36 km$ hours with an amplitude of $60.52 km$ magnitude (U=1).

Diameter and albedo
According to the surveys carried out by the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer (WISE), the Infrared Astronomical Satellite IRAS, and the Japanese Akari satellite, Naëma measures ($20.892 h$), ($0.065$) and ($0.079$) kilometers in diameter and its surface has an albedo of ($0.08$), ($20.892$) and ($0.16$), respectively. The Collaborative Asteroid Lightcurve Link derives an albedo of 0.0503 and a diameter of 54.05 kilometers based on an absolute magnitude of 10.2. Alternative mean diameter measurements published by the WISE team include ($12.1$), ($0.05$), ($52.677$), ($54.36$) and ($60.52$) with corresponding albedos of ($0.08$), ($0.079$), ($0.065$), ($47.19 km$) and ($52.419 km$).

Several asteroid occultations of Naëma have been observed between 2002 and 2010. The best-rated one from 10 April 2010, gave a best-fit ellipse dimension of ($52.91 km$). These timed observations are taken when the asteroid passes in front of a distant star.