1990 Pilcher

1990 Pilcher, provisional designation 1956 EE, is a stony background asteroid from the Florian region of the inner asteroid belt, approximately 7 kilometers (4.3 miles) in diameter. It was discovered on 9 March 1956, by German astronomer Karl Reinmuth at the Heidelberg-Königstuhl State Observatory in Heidelberg, Germany. In 1982, it was named by the MPC for American physicist and photometrist Frederick Pilcher.^[1] The S-type asteroid has a short rotation period of 2.8 hours.^[5]

1990 Pilcher

Discovery[1]
Discovered by	K. Reinmuth
Discovery site	Heidelberg Obs.
Discovery date	9 March 1956
Designations
MPC designation	(1990) Pilcher
Named after	Frederick Pilcher[1] (American photometrist)
Alternative designations	1956 EE · 1937 JL 1940 FA · 1959 CE1 1964 VS2 · 1972 EC 1972 GO · 1973 QM
Minor planet category	main-belt[1][2] · (inner) background[3][4] · Flora[5][6]
Orbital characteristics[2]
Epoch 23 March 2018 (JD 2458200.5)
Uncertainty parameter 0
Observation arc	80.17 yr (29,283 d)
Aphelion	2.2851 AU
Perihelion	2.0625 AU
Semi-major axis	2.1738 AU
Eccentricity	0.0512
Orbital period (sidereal)	3.21 yr (1,171 d)
Mean anomaly	92.884°
Mean motion	0° 18m 27s / day
Inclination	3.1320°
Longitude of ascending node	193.63°
Argument of perihelion	11.957°
Physical characteristics
Mean diameter	6.39 km (calculated)[5] 6.754±0.167 km[7] 7.273±0.064 km[8]
Synodic rotation period	2.842±0.001 h[9]
Geometric albedo	0.1864±0.0254[8] 0.215±0.039[7] 0.24 (assumed)[5]
Spectral type	Tholen = S[2] S (assumed)[5] B–V = 0.850[2] U–B = 0.504[2]
Absolute magnitude (H)	13.14[2][5][8]

Orbit and classification

Pilcher is a non-family asteroid of the main belt's background population when applying the hierarchical clustering method (HCM) to its proper orbital elements (Nesvorný, Milani and Knežević).^[3][4] In a previous HCM-analysis (Zappalà) and based on osculating Keplerian orbital elements, the asteroid has also been classified as a member of the Flora family (402), a giant asteroid family and the largest family of stony asteroids in the main-belt.^[5][6]

It orbits the Sun in the Florian region of the inner asteroid belt at a distance of 2.1–2.3 AU once every 3 years and 3 months (1,171 days; semi-major axis of 2.17 AU). Its orbit has an eccentricity of 0.05 and an inclination of 3° with respect to the ecliptic.^[2]

The asteroid was first observed as 1937 JL at Nice Observatory in May 1937. The body's observation arc begins with a precovery taken at Palomar Observatory in June 1950, or six years prior to its official discovery observation at Heidelberg.^[1]

Physical characteristics

In the Tholen classification, Pilcher is a common, stony S-type asteroid.^[2]

Rotation period

In March 2017, a first rotational lightcurve of Pilcher was obtained from photometric observations at the Flarestar Observatory on the island of Malta. Lightcurve analysis gave a short rotation period of 2.842 hours with a brightness amplitude of 0.10 magnitude, indicative for a rather spherical shape (U=2+).^[9]

Diameter and albedo

According to the survey carried out by the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer, Pilcher measures between 6.754 and 7.273 kilometers in diameter and its surface has an albedo between 0.1864 and 0.215.^[7][8]

The Collaborative Asteroid Lightcurve Link assumes an albedo of 0.24 – derived from 8 Flora, the Flora family's parent body and namesake – and calculates a diameter of 6.39 kilometers based on an absolute magnitude of 13.14.^[5]

Naming

This minor planet was named after American astronomer Frederick Pilcher, a retired professor of Physics at Illinois College and prolific lightcurve photometrist at his Organ Mesa Observatory (G50) in New Mexico.^[1] The official naming citation was published by the Minor Planet Center on 8 April 1982 (M.P.C. 6833).^[10]