CCD-photometry of near-Earth asteroids in 2006

An opportunity of ground-based photometric observations of NEAs during their close approaching the Earth occurs usually once per tens years, which makes difficulties for accumulation of information about these bodies. Therefore, observations of newly discovered NEAs were the most important part of the reported project. We use a possibility to observe NEAs in a wide range of phase angles and aspects to constrain their models.

Observations
The observations were carried out in the standard Johnson-Cousins UBVRI photometric system (mainly in the most effective R band), using the 0.7-m telescope at Chuguev Observation Station of Institute of Astronomy of Kharkiv National University (Ukraine). Two CCD-cameras ST-6 and new camera FLI CCD 47-10 (obtained thanks to this INTAS grant Ref. No 03-70-567), installed in Newtonian focus (f/4) and equipped with 3-lens focal corrector were used. The standard procedure of the image reduction included dark removing and flat-fielding. The image reduction and the aperture photometry have been done with AstPhot package (Mottola et al., 1995). The differential lightcurves were calculated with respect to the comparison star ensemble by method described in Erikson et al. (2000) and Krugly (2004). Typical errors of a single asteroid measurement at different nights were about 0.01-0.03 mag RMS depending on asteroid brightness. The absolute calibration of comparison stars was done using stars from LONEOS-list (ftp://ftp.lowell.edu/pub/bas/starcats/loneos.stds). The observations have been corrected for the light-time intervals and reduced to the unit heliocentric and geocentric distances. Details of the reduction are explained in Krugly et al. (2002).

Results
In Table 1 the results of NEA photometry are presented which include the estimated asteroid absolute magnitude H, its diameter D (km) and determined period of axis rotation and lightcurve amplitude. Observations of Apollo asteroid 2004 XP14 were carried out as an optical support of its radar observations on 3 July 2006 with Evpatoria radar RT-70. This asteroid showed very slow for NEOs rotation (see Tabl. 1) and very small amplitude of lightcurve (Fig. 3). Due to this reason its rotation period (P>24 hr) is not determined well. The small lightcurve amplitude (~0.05 mag) means that shape of the object is near spherical or not spherical but we observed it at near pole-on aspect (that is, along the rotation axis). In order to solve this ambiguity the observations at other aspects are needed.

Conclusions and Perspectives

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• Krugly, Yu.N., Belskaya, I.N., Shevchenko V.G. et al. 2002. The Near-Earth Objects Follow-Up Program. IV. CCD Photometry in 1996-1999. Icarus 158, 294-304.
• Krugly, Yu.N. 2004. Problems of CCD Photometry of Fast-Moving Asteroids. Solar System Research 38, No. 3, 241-248. Mottola, S., de Angelis, G., di Martino, M. et al. 1995. The near-earth objects follow-up program: First results. Icarus 117, 62-70.