Speckle imaging observations of 2005 YU55 with the NACO-VLT no-AO mode

The asteroid 2005 YU55 swept past the Earth on November 8, 2011 at 23:28 UTC at 0.85 lunar distance. Such events provide an excellent opportunity to study the physical and chemical properties and the surface details of the asteroids through spectroscopic and imaging observations. 2005 YU55 was observed by several ground and space based observatories during its closest approach. Here, we report the details of the speckle imaging observations of 2005 YU55 carried out the La-Silla Paranal Observatory with the NACO-VLT (no-AO mode) in the Ks band. The angular speed of the asteroid decreased from 8.5 arcsec/sec to 7.6 arcsec/sec during our observations and the tangential speed decreased from 13.5 km/s to 12.7 km/s. We reconstructed the images of 2005 YU55 with our speckle masking code. The average reconstructed images show spheroidal shape with diameter of 270 m. These observations demonstrate the potential of speckle technique in imaging low contrast, near-earth objects and deducing their overall sizes and shapes even under moderate observing conditions.