927 Ratisbona

927 Ratisbona is a large and dark background asteroid, approximately 76 kilometers (47 miles) in diameter, located in the outer region of the asteroid belt. It was discovered on 16 February 1920, by astronomer Max Wolf at the Heidelberg Observatory in southwest Germany.^[1] The carbonaceous C-type asteroid (CB) has a rotation period of 12.99 hours and is rather spherical in shape. It was named after the Bavarian city of Regensburg.^[2]

927 Ratisbona

Discovery[1]
Discovered by	M. F. Wolf
Discovery site	Heidelberg Obs.
Discovery date	16 February 1920
Designations
MPC designation	(927) Ratisbona
Pronunciation	/rætɪsˈboʊnə/
Named after	Regensburg (German city)[2]
Alternative designations	A920 DB · 1920 GO 1958 VD · 1958 XQ
Minor planet category	main-belt[1] · (outer)[3] background[4][5]
Orbital characteristics[3]
Epoch 31 May 2020 (JD 2459000.5)
Uncertainty parameter 0
Observation arc	99.57 yr (36,368 d)
Aphelion	3.5095 AU
Perihelion	2.9476 AU
Semi-major axis	3.2285 AU
Eccentricity	0.0870
Orbital period (sidereal)	5.80 yr (2,119 d)
Mean anomaly	88.007°
Mean motion	0° 10m 11.64s / day
Inclination	14.572°
Longitude of ascending node	7.6887°
Argument of perihelion	171.36°
Physical characteristics
Mean diameter	67.57±1.3 km[6] 75.892±0.187 km[7] 78.20±1.11 km[8]
Synodic rotation period	12.986±0.003 h[9]
Geometric albedo	0.044±0.002[8] 0.046±0.004[7] 0.0591±0.002[6]
Spectral type	Tholen = CB:[3] B–V = 0.722±0.034[3] U–B = 0.401±0.036[3] V–R = 0.407±0.016[10]
Absolute magnitude (H)	9.3[1][3]

Orbit and classification

Ratisbona is a non-family asteroid of the main belt's background population when applying the hierarchical clustering method to its proper orbital elements.^[4][5] It orbits the Sun in the outer asteroid belt at a distance of 2.9–3.5 AU once every 5 years and 10 months (2,119 days; semi-major axis of 3.23 AU). Its orbit has an eccentricity of 0.09 and an inclination of 15° with respect to the ecliptic.^[3] The body's observation arc begins at Heidelberg-Königstuhl State Observatory on 17 February 1920, the night after its official discovery observation.^[1]

Naming

This minor planet was named after the Latin name of the German city of Regensburg in Bavaria, where astronomer Johannes Kepler died in 1630. The naming was mentioned in the astronomical journal Astronomische Nachrichten in 1930 (AN 240, 135).^[2]

Physical characteristics

In the Tholen classification, Ratisbona is most similar to a common, carbonaceous C-type asteroid, and somewhat similar to a brighter B-type asteroid, based on a nosy spectrum (CB:).^[3][5]

Rotation period

Over the course of seven nights in January 2018, a rotational lightcurve of Ratisbona was obtained from photometric observations by Tom Polakis at the Command Module Observatory (V02) in Arizona. Lightcurve analysis gave a rotation period of 12.986±0.003 hours with a low brightness variation of 0.15±0.02 magnitude, indicative of a regular, spherical shape (U=3-).^[11] The result supersedes a period of 12.9938±0.0007 hours with an amplitude of 0.12±0.01 magnitude determined by René Roy, Raoul Behrend, Pierre Antonini and Donn Starkey in October 2004 (U=2).^[12]

Diameter and albedo

According to the survey carried out by the Infrared Astronomical Satellite IRAS, the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer (WISE), and the Japanese Akari satellite, Ratisbona measures (67.57±1.3), (75.892±0.187) and (78.20±1.11) kilometers in diameter and its surface has a very low albedo of (0.0591±0.002), (0.046±0.004) and (0.044±0.002), respectively.^[6][7][8]

The Collaborative Asteroid Lightcurve Link adopts the results from IRAS, that is, a albedo of 0.0591 and a diameter of 67.57 km based on an absolute magnitude of 9.54.^[9] Further published mean-diameters and albedos by the WISE team include (73.204±1.485 km) and (84.872±1.352 km) and albedos of (0.050±0.011) and (0.0375±0.0027).^[5][9] An asteroid occultation, observed on 13 September 2014, gave a best-fit ellipse dimension of 78.0 × 78.0 kilometers.^[5] These timed observations are taken when the asteroid passes in front of a distant star. However the quality of the measurement is rated poorly.^[5]