Photometric study of Centaur (60558) 2000 EC 98 and trans-neptunian object (55637) 2002 UX 25 at different phase angles

Abstract

We present photometric observations of Centaur (60558) 2000 EC 98 and trans-neptunian object (55637) 2002 UX 25 at different phase angles and with different filters (mainly R but also V and B for some data). Results for 2000 EC 98 are: (i) a rotation period of 26.802 ± 0.042 h if a double-peaked lightcurve is assumed, (ii) a lightcurve amplitude of 0.24 ± 0.06 for the R band, (iii) a phase curve with H = 9.03 ± 0.01 and G = − 0.39 ± 0.08 (R filter) and H = 9.55 ± 0.04 and G = − 0.50 ± 0.35 (V filter) or a slope of 0.17 ± 0.02 mag deg −1 (R filter) and 0.22 ± 0.06 (V filter), (iv) the color indices B – V = 0.76 ± 0.15 and V – R = 0.51 ± 0.09 (for α = 0.1 – 0.5 ° ) and 0.55 ± 0.08 (for α = 1.4 – 1.5 ° ). The rotation period is amongst the longest ever measured for Centaurs and TNOs. We also show that our photometry was not contaminated by any cometary activity down to magnitude ≃ 27 / arcsec 2 . For 2002 UX 25 the results are: (i) a rotation period of 14.382 ± 0.001 h or 16.782 ± 0.003 h (if a double-peaked lightcurve is assumed) (ii) a lightcurve amplitude of 0.21 ± 0.06 for the R band (and the 16.782 h period), (iii) a phase curve with H = 3.32 ± 0.01 and G = + 0.16 ± 0.18 or a slope of 0.13 ± 0.01 mag deg −1 (R filter), (iv) the color indices B – V = 1.12 ± 0.26 and V – R = 0.61 ± 0.12 . The phase curve reveals also a possible very narrow and bright opposition surge. Because such a narrow surge appears only for one point it needs to be confirmed.