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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.

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).

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.

Table 1. Results of NEA photometry in 2006

Asteroid Orbit type H1
Rotation period
Observed amplitude
1036 Ganymed Amor 9.58 39 10.314±0.004 0.12 3
1293 Sonja Mars-cr. 13.57 6.6 2.878±0.001 0.23 3
1980 Tezcatlipoca Amor 13.78 6.1 7.246±0.009 0.58 3
3103 Eger Apollo (15.61) 2.5 5.7060.7 3
11405 1999 CV3 Apollo 15.73 2.45 6.507±0.006 1.1 3
23187 2000 PN9 Apollo (16.1) 2.1 2.5325±0.0004 0.13 3
2004 XP14 Apollo (19.8) 0.4 >24 ~0.05 1
2006 BQ6 B Apollo 19.45 0.44 4.414±0.01 1.65 3

1 H values in brackets were adopted from the Minor Planet Circulars.
2 Diameters were calculated assuming an albedo 0.15, if asteroid albedo and type is unknown.
3 Quality code of the rotational period.
B Supposed binary.

Conclusions and Perspectives

Receiving the larger and more sensitive camera FLI CCD 47-10 will noticeably improve our potential for future investigations the key properties of the NEA population in particular in order to make an optical support of their radar observation with RT-70 antenna in Evpatoria (Ukraine) at 6 cm wavelength (Konovalenko et al. 2005) and to make the photometric and astrometric observations of geostationary satellites and space debris in the frame of coordinated programs.


Fig. 1. Two individual lightcurves of NEA 1980 Tezcatlipoca observed on July 29 and 30, 2006 (top) and the composite lightcurve of the asteroid in July 2006 (bottom).

Fig. 2. The composite lightcurve of 11405 1999 CV3 in July 2006 showed considerable elongation of asteroid shape (a:b = 2.75).

Fig. 3. Two individual lightcurves of NEA 2004 XP14 observed on July 5 and 6, 2006.

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