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909 Ulla
	Orbital diagram of Ulla
Discovery
Discovered by	K. Reinmuth
Discovery site	Heidelberg Obs.
Discovery date	7 February 1919
Designations
MPC designation	(909) Ulla
Pronunciation	German: [ˈʊlaː]; Classically: /ˈʌlə/
Named after	Ulla Ahrens ; (observatory donor)
Alternative designations	1919 FA · 1936 SJ; 1949 OF1 · 1949 PW; 1966 BU · 1966 DM; A912 CA · A919 CA
Minor planet category	main-belt · (outer) ; Ulla · Cybele
Orbital characteristics
	Epoch 31 May 2020 (JD 2459000.5)
	Uncertainty parameter 0
Observation arc	100.99 yr (36,886 d)
Aphelion	3.8633 AU
Perihelion	3.2217 AU
Semi-major axis	3.5425 AU
Eccentricity	0.0906
Orbital period (sidereal)	6.67 yr (2,435 d)
Mean anomaly	180.34°
Mean motion	0° 8m 52.08s / day
Inclination	18.797°
Longitude of ascending node	146.35°
Argument of perihelion	232.64°
TJupiter	3.0250
Physical characteristics
Mean diameter	113.13±1.48 km; 116.44±2.4 km;
Synodic rotation period	8.73 h
Geometric albedo	0.0343±0.001; 0.037±0.001;
Spectral type	Tholen = X ; B–V = 0.689; U–B = 0.279;
Absolute magnitude (H)	8.95

909 Ulla is a large and dark asteroid from the outermost regions of the asteroid belt, that measures approximately 116 kilometers (72 miles) in diameter. It is the parent body and namesake of the Ulla family, which belongs to the larger group of Cybele asteroids. It was discovered on 7 February 1919, by German astronomer Karl Reinmuth at the Heidelberg Observatory in southwest Germany.^[1] The X-type asteroid has a rotation period of 8.7 hours and a notably low value for its Jupiter Tisserand's parameter. It was named after Ulla Ahrens, daughter of a friend of the discoverer.^[4]

Orbit and classification

Ulla is the parent body of the Ulla family (903),^[11] a very small asteroid family of less than 30 known bodies.^[12] It orbits the Sun in the outermost asteroid belt at a distance of 3.2–3.9 AU once every 6 years and 8 months (2,435 days; semi-major axis of 3.54 AU). Its orbit has an eccentricity of 0.09 and an inclination of 19° with respect to the ecliptic.^[6]

Naming

This minor planet was named after Ulla Ahrens, a daughter of a friend of the discoverer.^[4] Karl Reinmuth also named the asteroid 950 Ahrensa for the Ahrens family, who was a donor of the Heidelberg Observatory. The official naming citation was mentioned in The Names of the Minor Planets by Paul Herget in 1955 (H 50).^[4]

Physical characteristics

In the SMASS classification, Ulla is an X-type asteroid.^[6]^[10]

Rotation period

A rotational lightcurve of Ulla was obtained from photometric observations in 2000. Lightcurve analysis gave a rotation period of 8.73 hours with a brightness amplitude between 0.13 and 0.24 magnitude (U=3).^[9] Other photometric period determinations gave concurring results.^[13]^[14]

Diameter and albedo

According to the surveys carried out by the Infrared Astronomical Satellite IRAS and the Japanese Akari satellite, Ulla measures 113.13±1.48 and 116.44±2.4 kilometers in diameter and its surface has an albedo between 0.0343±0.001 and 0.037±0.001.^[7]^[8] The Collaborative Asteroid Lightcurve Link uses an albedo of 0.0450 and derives a diameter of 116.66 kilometers based on an absolute magnitude of 8.65.^[5]

References

^ ^a ^b ^c "909 Ulla (1919 FA)". Minor Planet Center. Retrieved 7 July 2018.
^ (German Names)
^ Noah Webster (1884) A Practical Dictionary of the English Language
^ ^a ^b ^c ^d Schmadel, Lutz D. (2007). "(909) Ulla". Dictionary of Minor Planet Names. Springer Berlin Heidelberg. p. 81. doi:10.1007/978-3-540-29925-7_910. ISBN 978-3-540-00238-3.
^ ^a ^b ^c "LCDB Data for (909) Ulla". Asteroid Lightcurve Database (LCDB). Retrieved 7 July 2018.
^ ^a ^b ^c ^d ^e ^f ^g "JPL Small-Body Database Browser: 909 Ulla (A919 CA)" (2020-02-04 last obs.). Jet Propulsion Laboratory. Archived from the original on 19 September 2020. Retrieved 24 February 2020.
^ ^a ^b ^c ^d Usui, Fumihiko; Kuroda, Daisuke; Müller, Thomas G.; Hasegawa, Sunao; Ishiguro, Masateru; Ootsubo, Takafumi; et al. (October 2011). "Asteroid Catalog Using Akari: AKARI/IRC Mid-Infrared Asteroid Survey". Publications of the Astronomical Society of Japan. 63 (5): 1117–1138. Bibcode:2011PASJ...63.1117U. doi:10.1093/pasj/63.5.1117. (online, AcuA catalog p. 153)
^ ^a ^b ^c ^d Tedesco, E. F.; Noah, P. V.; Noah, M.; Price, S. D. (October 2004). "IRAS Minor Planet Survey V6.0". NASA Planetary Data System. 12: IRAS-A-FPA-3-RDR-IMPS-V6.0. Bibcode:2004PDSS...12.....T. Retrieved 23 February 2020.
^ ^a ^b Lagerkvist, Claes-Ingvar; Erikson, Anders; Lahulla, Felix; De Martino, Mario; Nathues, Andreas; Dahlgren, Mats (January 2001). "A Study of Cybele Asteroids. I. Spin Properties of Ten Asteroids". Icarus. 149 (1): 190–197. Bibcode:2001Icar..149..190L. doi:10.1006/icar.2000.6507.
^ ^a ^b De Prá, M. N.; Pinilla-Alonso, N.; Carvano, J. M.; Licandro, J.; Campins, H.; Mothé-Diniz, T.; et al. (September 2018). "PRIMASS visits Hilda and Cybele groups". Icarus. 311: 35–51. arXiv:1711.02071. Bibcode:2018Icar..311...35D. doi:10.1016/j.icarus.2017.11.012. S2CID 119383924.
^ "Asteroid 909 Ulla". Small Bodies Data Ferret. Retrieved 7 July 2018.
^ Nesvorný, D.; Broz, M.; Carruba, V. (December 2014). "Identification and Dynamical Properties of Asteroid Families". Asteroids IV. pp. 297–321. arXiv:1502.01628. Bibcode:2015aste.book..297N. doi:10.2458/azu_uapress_9780816532131-ch016. ISBN 9780816532131. S2CID 119280014.
^ Gonano, M.; di Martino, M.; Mottola, S.; Neukum, G. (December 1990). "Physical study of outer belt asteroids". Space Dust and Debris; Proceedings of the Topical Meeting of the Interdisciplinary Scientific Commission B /Meetings B2. 11 (12): 197–200. Bibcode:1991AdSpR..11l.197G. doi:10.1016/0273-1177(91)90563-Y. ISSN 0273-1177.
^ Behrend, Raoul. "Asteroids and comets rotation curves – (909) Ulla". Geneva Observatory. Retrieved 7 July 2018.