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The rotation state of small asteroids is affected in the long term byperturbing torques of gravitational and radiative origin (the YORP effect).Direct observational evidence of the YORP effect is the primary goal of ourwork. We carried out photometric observations of five near-Earth asteroids:(1862) Apollo, (2100) Ra-Shalom, (85989) 1999 JD6, (138852) 2000 WN10, and(161989) Cacus. Then we applied the light-curve inversion method to allavailable data to determine the spin state and a convex shape model for each ofthe five studied asteroids. In the case of (2100) Ra-Shalom, the analysisrequired that the spin-axis precession due to the solar gravitational torquealso be included. We obtained two new detections of the YORP effect: (i) $(2.9\pm 2.0)\times 10^{-9}\,\mathrm{rad\,d}^{-2}$ for (2100) Ra-Shalom, and (ii)$(5.5\pm 0.7)\times 10^{-8}\,\mathrm{rad\,d}^{-2}$ for (138852) 2000 WN10. Theanalysis of Ra-Shalom also reveals a precession of the spin axis with aprecession constant $\sim 3000''\,\mathrm{yr}^{-1}$. This is the first suchdetection from Earth-bound photometric data. For the other two asteroids, weimproved the accuracy of the previously reported YORP detection: (i) $(4.94 \pm0.09)\times 10^{-8}\,\mathrm{rad\,d}^{-2}$ for (1862) Apollo, and (ii)$(1.86\pm 0.09)\times 10^{-8}\,\mathrm{rad\,d}^{-2}$ for (161989) Cacus.Despite the recent report of a detected YORP effect for (85989) 1999 JD6, weshow that the model without YORP cannot be rejected statistically. Therefore,the detection of the YORP effect for this asteroid requires futureobservations. The spin-axis precession constant of Ra-Shalom determined fromobservations matches the theoretically expected value. The total number ofasteroids with a YORP detection has increased to 12. In all cases, the rotationfrequency increases in time.

Secular change in the spin states of asteroids due to radiation and gravitation torques. New detections and updates of the YORP effect