1521 Seinäjoki

1521 Seinäjoki, provisional designation 1938 UB₁, is a Brasilia asteroid from the outer region of the asteroid belt, approximately 14 kilometers in diameter. It was discovered on 22 October 1938, by Finnish astronomer Yrjö Väisälä at the southwestern Turku Observatory, Finland.^[12] The asteroid was later named after the Finnish city of Seinäjoki.^[2]

1521 Seinäjoki

Shape model of Seinäjoki from its lightcurve
Discovery[1]
Discovered by	Y. Väisälä
Discovery site	Turku Obs.
Discovery date	22 October 1938
Designations
MPC designation	(1521) Seinäjoki
Named after	Seinäjoki (Finnish city)[2]
Alternative designations	1938 UB1 · 1933 UR1 1967 UW
Minor planet category	main-belt · (outer)[3] Brasilia[4]
Orbital characteristics[1]
Epoch 4 September 2017 (JD 2458000.5)
Uncertainty parameter 0
Observation arc	78.62 yr (28,716 days)
Aphelion	3.2435 AU
Perihelion	2.4633 AU
Semi-major axis	2.8534 AU
Eccentricity	0.1367
Orbital period (sidereal)	4.82 yr (1,760 days)
Mean anomaly	123.44°
Mean motion	0° 12m 16.2s / day
Inclination	15.059°
Longitude of ascending node	12.593°
Argument of perihelion	48.805°
Physical characteristics
Mean diameter	13.66±3.61 km[5] 14.813±0.070 km[6] 16.095±0.070 km[7] 16.29±0.20 km[8] 24.30 km (calculated)[3]
Synodic rotation period	4.32±0.01 h[9] 4.328159±0.000001 h[10]
Geometric albedo	0.057 (assumed)[3] 0.116±0.018[8] 0.1733±0.0300[7] 0.205±0.015[6] 0.22±0.12[5]
Spectral type	C[3]
Absolute magnitude (H)	11.5[7] · 11.8[1][3] · 11.90[8] · 11.92[5] · 12.17±0.45[11]

Orbit and classification

Seinäjoki is a member of the Brasilia family, a smaller asteroid family of X-type asteroids in the outer main-belt. Since the family's namesake, 293 Brasilia, is a suspected interloper in its own family, it has also been named Seinäjoki family after Seinäjoki.^{[4][13]: 37}

It orbits the Sun in the outer main-belt at a distance of 2.5–3.2 AU once every 4 years and 10 months (1,760 days). Its orbit has an eccentricity of 0.14 and an inclination of 15° with respect to the ecliptic.^[1] In 1933, Seinäjoki was first identified as 1933 UR₁ at Simeiz Observatory. The body's observation arc, however, begins with its official discovery observation at Turku.^[12]

Physical characteristics

Rotation and pole

In October 2010, a rotational lightcurve of Seinäjoki was obtained by Russell Durkee at the U.S. Shed of Science Observatory (H39) in Minneapolis. It gave it a well-defined rotation period of 4.32 hours with a brightness variation of 0.15 magnitude (U=3).^[9] A modeled lightcurve form Lowell photometric database gave a concurring period of 4.328 hours and a spin axis of (-18.0°, 230.0°) in ecliptic coordinates.^[10]

Diameter and albedo

According to the survey carried out by NASA's Wide-field Infrared Survey Explorer (WISE) with its subsequent NEOWISE mission, Seinäjoki measures between 13.66 and 14.81 kilometers in diameter, and its surface has an albedo between 0.205 and 0.22 (more recent results only).^[5][6][7][8]

The Collaborative Asteroid Lightcurve Link assumes a standard albedo for carbonaceous C-type asteroids of 0.057 and calculates a much larger diameter of 24.30 kilometers as a body's and diameter and reflectivity (albeo) correlate indirectly.^[3] However, based on the much higher albedo given by WISE/NEOWISE, the body is rather of a stony composition, which is untypical for asteroids in the outer main-belt.

Naming

This minor planet was named for the city of Seinäjoki, located in Southern Ostrobothnia, western Finland.^[2] The official naming citation was published by the Minor Planet Center on 20 February 1976 (M.P.C. 3929).^[14]