1446 Sillanpää

1446 Sillanpää, provisional designation 1938 BA, is a stony Florian asteroid from the inner regions of the asteroid belt, approximately 8.2 kilometers in diameter. It was discovered on 26 January 1938, by Finnish astronomer Yrjö Väisälä at Turku Observatory in Southwest Finland.[10] It was later named after writer Frans Eemil Sillanpää.[2]

1446 Sillanpää
Shape of Sillanpää modelled from its lightcurve
Discovery[1]
Discovered byY. Väisälä
Discovery siteTurku Obs.
Discovery date26 January 1938
Designations
(1446) Sillanpaa
Named after
Frans Sillanpää (writer)[2]
1938 BA · 1935 GB
1952 HQ3 · 1955 DQ
1965 EA
main-belt · Flora[3]
Orbital characteristics[1]
Epoch 16 February 2017 (JD 2457800.5)
Uncertainty parameter 0
Observation arc78.53 yr (28,683 days)
Aphelion2.4732 AU
Perihelion2.0179 AU
2.2455 AU
Eccentricity0.1014
3.37 yr (1,229 days)
98.112°
0° 17m 34.44s / day
Inclination5.2572°
17.549°
196.25°
Physical characteristics
Dimensions7.35±0.29 km[4]
8.167±0.154 km[5]
8.19 km (calculated)[3]
8.763±0.063 km[6]
9.65855±0.00005 h[7]
9.659±0.001 h[8]
9.6597±0.0172 h[9]
9.6602±0.0008 h[lower-alpha 1]
0.2109±0.0108[6]
0.24 (assumed)[3]
0.241±0.046[5]
0.327±0.080[4]
S[3]
12.394±0.002 (R)[9] · 12.50[4] · 12.6[1][3][6]

    Orbit and classification

    The S-type asteroid is a member of the Flora family, one of the largest populations of stony asteroids in the main-belt. It orbits the Sun at a distance of 2.0–2.5 AU once every 3 years and 4 months (1,229 days). Its orbit has an eccentricity of 0.10 and an inclination of 5° with respect to the ecliptic.[1] Sillanpää was first identified as 1935 GB at Simeiz Observatory in 1935, while its observation arc begins with its official discovery observation at Turku in 1938.[10]

    Lightcurves

    In March 2009, Czech astronomer Petr Pravec obtained a rotational light-curve from photometric observations at Ondřejov Observatory.[lower-alpha 2] It gave a well-defined rotation period of 9.6602 hours with a brightness variation of 0.55 magnitude (U=3).[lower-alpha 1] One month later, a concurring period of 9.659 hours with an amplitude of 0.71 magnitude was obtained by Adrián Galád at Modra Observatory (U=3).[8] Photometric observations at the Palomar Transient Factory in December 2011. gave a 9.6597 hours and Δ0.59 in magnitude (U=2).[9] A modeled light-curve using data from the Uppsala Asteroid Photometric Catalogue and other data sources, gave a period of 9.65855 hours, as well as a spin axis of (129.0°, 76.0°) in ecliptic coordinates (U=n.a.).[7]

    Diameter and albedo

    According to the survey carried out by NASA's Wide-field Infrared Survey Explorer with its subsequent NEOWISE mission, Sillanpää measures between 7.35 and 8.76 kilometers in diameter, and its surface has an albedo between 0.21 and 0.327.[5][6][4] The Collaborative Asteroid Lightcurve Link assumes an intermediate albedo of 0.24 – derived from 8 Flora, the largest member and namesake of this asteroid family – and calculates a larger diameter of 8.19 kilometers using an absolute magnitude of 12.6.[3]

    Naming

    This minor planet was named after one of the most famous Finnish writers, Frans Eemil Sillanpää (1888–1964), first Finnish writer to receive the Nobel Prize in Literature in 1939 (also see List of Laureates since 1901).[2] The official naming citation was published by the Minor Planet Center on 20 February 1976 (M.P.C. 3928).[11]

    References
    1. Pravec (2009) web: rotation period 9.6602±0.0008 hours with a brightness amplitude of 0.55 mag. Summary figures at Collaborative Asteroid Lightcurve Link (CALL) for (1446) Sillanpaa and Pravec, P.; Wolf, M.; Sarounova, L. (2009)
    2. Light-curve analysis: screenshot
    1. "JPL Small-Body Database Browser: 1446 Sillanpaa (1938 BA)" (2016-08-07 last obs.). Jet Propulsion Laboratory. Retrieved 4 January 2017.
    2. Schmadel, Lutz D. (2007). "(1446) Sillanpää". Dictionary of Minor Planet Names – (1446) Sillanpää. Springer Berlin Heidelberg. p. 116. doi:10.1007/978-3-540-29925-7_1447. ISBN 978-3-540-00238-3.
    3. "LCDB Data for (1446) Sillanpää". Asteroid Lightcurve Database (LCDB). Retrieved 4 January 2017.
    4. Masiero, Joseph R.; Mainzer, A. K.; Grav, T.; Bauer, J. M.; Cutri, R. M.; Nugent, C.; et al. (November 2012). "Preliminary Analysis of WISE/NEOWISE 3-Band Cryogenic and Post-cryogenic Observations of Main Belt Asteroids". The Astrophysical Journal Letters. 759 (1): 5. arXiv:1209.5794. Bibcode:2012ApJ...759L...8M. doi:10.1088/2041-8205/759/1/L8. Retrieved 4 January 2017.
    5. Masiero, Joseph R.; Grav, T.; Mainzer, A. K.; Nugent, C. R.; Bauer, J. M.; Stevenson, R.; et al. (August 2014). "Main-belt Asteroids with WISE/NEOWISE: Near-infrared Albedos". The Astrophysical Journal. 791 (2): 11. arXiv:1406.6645. Bibcode:2014ApJ...791..121M. doi:10.1088/0004-637X/791/2/121. Retrieved 4 January 2017.
    6. Mainzer, A.; Grav, T.; Masiero, J.; Hand, E.; Bauer, J.; Tholen, D.; et al. (November 2011). "NEOWISE Studies of Spectrophotometrically Classified Asteroids: Preliminary Results". The Astrophysical Journal. 741 (2): 25. arXiv:1109.6407. Bibcode:2011ApJ...741...90M. doi:10.1088/0004-637X/741/2/90.
    7. Hanus, J.; Broz, M.; Durech, J.; Warner, B. D.; Brinsfield, J.; Durkee, R.; et al. (November 2013). "An anisotropic distribution of spin vectors in asteroid families". Astronomy and Astrophysics. 559: 19. arXiv:1309.4296. Bibcode:2013A&A...559A.134H. doi:10.1051/0004-6361/201321993. Retrieved 4 January 2017.
    8. Galad, Adrian (October 2009). "Byproduct Targets During Photometric Observations from Modra". The Minor Planet Bulletin. 36 (4): 183–186. Bibcode:2009MPBu...36..183G. ISSN 1052-8091. Retrieved 4 January 2017.
    9. Waszczak, Adam; Chang, Chan-Kao; Ofek, Eran O.; Laher, Russ; Masci, Frank; Levitan, David; et al. (September 2015). "Asteroid Light Curves from the Palomar Transient Factory Survey: Rotation Periods and Phase Functions from Sparse Photometry". The Astronomical Journal. 150 (3): 35. arXiv:1504.04041. Bibcode:2015AJ....150...75W. doi:10.1088/0004-6256/150/3/75. Retrieved 4 January 2017.
    10. "1446 Sillanpaa (1938 BA)". Minor Planet Center. Retrieved 4 January 2017.
    11. Schmadel, Lutz D. (2009). "Appendix – Publication Dates of the MPCs". Dictionary of Minor Planet Names – Addendum to Fifth Edition (2006–2008). Springer Berlin Heidelberg. p. 221. doi:10.1007/978-3-642-01965-4. ISBN 978-3-642-01964-7.

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