Life on the fast lane: The burst mode at the vlt at present and in the future

Abstract

The recent implementation of the high-speed burst mode at the ISAAC instrument on UT1, and its propagation to other ESO instruments, has opened the door to observational capabilities which hold the potential for a wealth of novel results. In the ELT era, when the accent will likely be on lengthy programs aimed at the best sensitivity and angular resolution, the VLT telescopes could continue to play a significant and largely unique role by performing routinely observations of transient events at high temporal resolution. In our contribution, we provide details on two such kinds of observations, namely lunar occultations of stars and of asteroids. For the first ones, we report on two passages of the Moon in regions with high stellar density as the Galactic Center. The VLT-UT1 telescope was used for the first time to record successfully 53 and 71 occultations on March 22 and August 6, 2006, with an angular resolution of 0.5–1 milliarcsecond and K ∼ 12.5 limiting magnitude. We note that the angular resolution is superior to that achieved at present by Adaptive Optics on any telescope, and also superior to that foreseen for the ELT at the same wavelength. LO are also very efficient in terms of telescope time. We present some of the results, including the discovery of close binaries, and the detection and study of compact circumstellar components of cool giants, AGB stars and embedded IR sources. Concerning asteroidal occultations, we aim at observations starting in P80 which would permit high-accuracy, direct determinations of asteroid sizes for bodies larger than ≈ 50 km. This is a critical information to improve our understanding of the physical properties of these bodies. It will allow us an independent, crucial calibration of the indirect techniques commonly used to derive estimates of asteroid sizes and albedo, namely radiometry (Harris and Lagerros [Asteroids III, ed. by W.F. Bottke, A. Cellino, P. Paolicchi, R.P. Binzel (Univ. of Arizona Press, Tucson, 2002), p. 205]) and polarimetry (Cellino et al. [Icarus 179, 304 (2005)], and references therein). Lunar occultations can be used also to detect asteroid binary systems, which have been found recently to be not very rare. Binary systems are invaluable to estimate asteroid masses and densities, parameters that are at present very poorly known.