Calculation of the Non-Gravitational A2 Parameter Using Ground-Based Observations of the Apparent Close Approaches between Near-Earth Asteroids and Gaia Stars

The Yarkovsky effect is one of the noticeable factors in the orbital evolution of near-Earth asteroids (NEAs). The A₂ non-gravitational parameter describes the corresponding acceleration in the NEA motion model. This parameter can be derived from astrometric observations of the NEA. We present the results of astrometric observations of two NEAs (2010 XC15 and 2014 HK129). The measurements were performed with the MTM-500M telescope (Mountain Astronomical Station of the Pulkovo Observatory). The modified Gaia star apparent approach technique was applied. As a result, the astrometric accuracy of our observations reached the 0.05 arcsec level. It allowed us to estimate the A₂ values of the 2010 XC15 asteroid: –139.5 × 10^–15 ± 20.2 × 10^–15 au/d². It is in good agreement with the NASA JPL estimate for this asteroid. The 2014 HK129 A₂ parameter formal value extracted from our data is 61.3 × 10^–15 ± 1583.4 × 10^–15 au/d². Introduction of this A₂ value into the asteroid motion model provides a significant decrease (about 0.05–0.1 arcsec) of the (O–C) values for the first epoch of 2014 HK129 observations. It can be considered as faint evidence of the reality of Yarkovsky drift for the 2014 HK129 asteroid.