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Description
The near-Earth asteroid (NEA) 2015 TB145 had a very close encounter with Earth at 1.3 lunar distances on October 31, 2015. We obtained 3-band mid-infrared observations of this asteroid with the ESO VLT-VISIR instrument covering about 4 hours in total. We also monitored the visual lightcurve during the close-encounter phase. The NEA has a (most likely) rotation period of 2.939+/-0.005-hours and the visual lightcurve shows a peak-to-peak amplitude of about 0.12+/-0.02mag. A second rotation period of 4.779+/-0.012h, with an amplitude of the Fourier fit of 0.10+/-0.02mag, also seems compatible with the available lightcurve measurements. We estimate a V-R colour of 0.56+/-0.05mag from different entries in the MPC database. A reliable determination of the object's absolute magnitude was not possible. Applying different phase relations to the available R-/V-band observations produced H_R_=18.6mag (standard H-G calculations) or H_R_=19.2mag and H_V_=19.8mag (via the H-G_12_ procedure for sparse and low-quality data), with large uncertainties of about 1mag. We performed a detailed thermophysical model analysis by using spherical and partially also ellipsoidal shape models. The thermal properties are best explained by an equator-on (+/-~30{deg}) viewing geometry during our measurements with a thermal inertia in the range 250-700J/m^2^/s^0.5^/K (retrograde rotation) or above 500J/m^2^/s^0.5^/K (prograde rotation). We find that the NEA has a minimum size of about 625m, a maximum size of just below 700m, and a slightly elongated shape with a/b~1.1.
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