Volume 656, December 2021
|Number of page(s)||9|
|Section||Planets and planetary systems|
|Published online||10 December 2021|
Photometry and model of near-Earth asteroid 2021 DW1 from one apparition
Astronomical Observatory Institute, Faculty of Physics, A. Mickiewicz University,
2 Lowell Observatory, 14000 W Mars Hill Rd, 86001 Flagstaff, AZ, USA
3 Astronomical Observatory of Odessa I.I.Mechnikov National University, Odessa, Ukraine
4 Korea Astronomy & Space Science Institute, 776 Daedeok-daero, Yuseong-gu, Daejeon 34055, Republic of Korea
5 National Youth Space Center, Goheung, Jeollanam-do 59567, Korea
6 Deutsches Zentrum för Luft- und Raumfahrt (DLR), Institute of Planetary Research, Berlin, Germany
7 Departamento de Física, Ingeniería de Sistemas y Teoría de la Señal, Universidad de Alicante, Alicante, Spain
8 Institut de Ciencies del Cosmos (ICCUB), Universitat de Barcelona, Barcelona, Spain
9 Platanus Observatory (IAU code K80), Lusówko, Poland
10 “G.V. Schiaparelli” Astronomical Observatory, Varese, Italy
11 Osservatorio di San Marcello Pistoiese, GAMP Gruppo Astrofili Montagna Pistoiese, Italy
12 Great Shefford Observatory, Berkshire, UK
13 British Astronomical Association, Burlington House, Piccadilly, London, UK
14 Las Cumbres Observatory, Goleta, CA 93117, USA
Accepted: 22 September 2021
Aims. Very small asteroids (VSAs, objects with diameters smaller than about 150 m) can be spun up by the YORP effect to rotation periods as short as tens of seconds. This effect has been observed for many of them. It is also hypothesised, that in the same process their spin axes are asymptotically drawn to the position perpendicular to the orbital plane. So far this effect has been observed only for one VSA and needs further verification. For that, spin axes of several other VSAs should be determined by observing their brightness variations at many different positions on the sky.
Methods. On 4 March 2021 at 9 UTC a 30-m in diameter near-Earth asteroid 2021 DW1 passed the Earth at a distance of 570 000 km, reaching the maximum brightness of V = 14.6 mag. We observed it photometrically from 2 March, when it was visible at V = 16.5 mag, until 7 March (V = 18.2 mag). During that time 2021 DW1 swept a 170° long arc in the northern sky, spanning solar phase angles in the range from 36° to 86°. This made it an excellent target for physical characterisation, including spin axis and shape derivation.
Results. Convex inversion of the asteroid lightcurves gives a sidereal period of rotation Psid = 0.013760 ± 0.000001 h, and two solutions for the spin axis ecliptic coordinates: (A) λ1 = 57° ± 10°, β1 = 29° ± 10° and (B) λ2 = 67° ± 10°, β2 = −40° ± 10°. The magnitude-phase curve can be fitted with a standard H, G function with H = 24.8 ± 0.5 mag and an assumed G = 0.24. The asteroid colour indices are g − i = 0.79 ± 0.01 mag, and i − z = 0.01 ± 0.02 mag which indicates an S taxonomic class, with an average geometric albedo pV = 0.23 ± 0.02. The asteroid effective diameter, derived from H and pV, is Deff = 30 ± 10 m.
Conclusions. It was found that the inclination of the spin axis of 2021 DW1 is not perpendicular to the orbital plane (obliquity ϵ = 54° ± 10° or ϵ = 123° ± 10°). More spin axes of VSAs should be determined to check, if 2021 DW1 is an exception or a typical case.
Key words: methods: observational / techniques: photometric / minor planets, asteroids: individual: 2021 DW1
© ESO 2021
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