1796 Riga

1796 Riga, provisional designation 1966 KB, is a dark asteroid from the outer region of the asteroid belt, approximately 70 kilometers in diameter. It was discovered on 16 May 1966, by Russian astronomer Nikolai Chernykh at the Crimean Astrophysical Observatory in Nauchnyj, on the Crimean peninsula.^[15] It is named after the Latvian capital Riga.^[2]

1796 Riga

Discovery[1]
Discovered by	N. Chernykh
Discovery site	Crimean Astrophysical Obs.
Discovery date	16 May 1966
Designations
MPC designation	(1796) Riga
Named after	Riga (capital city)[2]
Alternative designations	1966 KB · 1935 GE 1941 FC1 · 1947 GA 1950 TF2 · 1953 GW 1960 JA · A907 TG A907 UD
Minor planet category	main-belt · (outer)[1]
Orbital characteristics[1]
Epoch 4 September 2017 (JD 2458000.5)
Uncertainty parameter 0
Observation arc	66.06 yr (24,129 days)
Aphelion	3.5474 AU
Perihelion	3.1668 AU
Semi-major axis	3.3571 AU
Eccentricity	0.0567
Orbital period (sidereal)	6.15 yr (2,247 days)
Mean anomaly	142.11°
Mean motion	0° 9m 36.72s / day
Inclination	22.585°
Longitude of ascending node	186.73°
Argument of perihelion	25.620°
Physical characteristics
Dimensions	66.2±6.6 km[3] 68.089±1.037 km[4] 68.167±0.298 km[5] 71±7 km[6] 73.83±1.8 km[7] 85.79±1.57 km[8]
Synodic rotation period	10.608±0.002 h[9][a] 11.0±0.01 h[10] 16 h[11] 22.226±0.001 h[12]
Geometric albedo	0.028±0.001[8] 0.0376±0.002[7] 0.04±0.01[6] 0.044±0.005[5] 0.0442±0.0082[4] 0.05±0.01[3]
Spectral type	XFCU (Tholen)[1] Cb (SMASS)[1] P[4] · C[13][14] B–V = 0.676[1] U–B = 0.289[1]
Absolute magnitude (H)	9.59±0.40[14] · 9.84 (IRAS:12)[1][7] · 9.84[3][4][6][8][13]

Orbit and classification

The asteroid orbits the Sun in the outer main-belt at a distance of 3.2–3.5 AU once every 6 years and 2 months (2,247 days). Its orbit has an eccentricity of 0.06 and an inclination of 23° with respect to the ecliptic.^[1] The body was first identified as "1907 TG" at the U.S Taunton Observatory (803) in 1907, and its first used precovery was taken at the Goethe Link Observatory in 1953, extending the asteroid's observation arc by 13 years prior to its official discovery observation.^[15] It is a member of the Cybele group of asteroids.^[16]

Spectral type

The carbonaceous C-type asteroid is also classified as a very dark and featureless reddish P-type body by the NEOWISE survey of the Wide-field Infrared Survey Explorer (WISE).^[4][13][14] In the Tholen and SMASS taxonomy, it has a XFCU and Cb subtype, respectively.^[1]

Diameter and albedo

According to the surveys carried out by the Infrared Astronomical Satellite IRAS, the Japanese Akari satellite and NASA's WISE/NEOWISE mission, the asteroid measures between 66.2 and 85.7 kilometers in diameter and its surface has an albedo between 0.028 and 0.05.^{[3][4][5][6][7][8]} The Collaborative Asteroid Lightcurve Link (CALL) agrees with the results obtained by IRAS, adopting a diameter of 73.83 kilometers with an albedo of 0.0376, based on an absolute magnitude of 9.84.^[13]

Rotation period

Several rotational lightcurve for this asteroid were obtained from photometric observations since 1997. They gave a variety of rotation periods from 10.608 to 22.226 hours with inconsistent brightness variations in the range of 0.05 to 0.40 magnitude (U=2/2-/n.a./2).^{[9][10][11][12][a]} CALL adopts the results of the most observations made by astronomer Julian Oey at the Australian Blue Mountains Observatory (Q68) in March 2014, which gave a period of 22.226±0.001 hours and an amplitude of 0.40±0.05 magnitude (U=2).^[12][13]

Naming

The minor planet was named after Riga, the capital of Latvia and location of the Astronomical Observatory of the University of Latvia. The name was proposed by Matiss A. Dirikis, who was a member of the observatory at the Latvian State University, and after whom the asteroid 1805 Dirikis is named.^[2] The official naming citation was published by the Minor Planet Center on 25 September 1971 (M.P.C. 3185).^[17]

Notes

1. Lightcurve plot of 1796 Riga, Palmer Divide Observatory, by B. D. Warner (2003), with a rotation period 10.608±0.002 hours and a brightness amplitude of 0.14±0.02 mag. Summary figures at Collaborative Asteroid Lightcurve Link (CALL)