High-precision K-band photometry of the secondary eclipse of HD 209458

Recently, mid-infrared Spitzer observations have been presented that show the light decrement due to the passage of a planet behind its host star. These measurements of HD 209458b and TrES-1 are the first detections of direct light from an extrasolar planet. Interpretation of these results in terms of planet equipartition temperature and bond albedo is however strongly model-dependent and requires additional observations at shorter wavelengths. Here we report on two attempts to detect the secondary eclipse of HD 209458b from the ground in the K band, using the United Kingdom Infrared Telescope. A photometry precision of 0.12 per cent relative to two nearby reference stars was reached during both occasions, but no firm detection of the eclipses was obtained. The first observation shows a flux decrement of −0.13 ± 0.18 per cent, and the second of −0.10 ± 0.10 per cent. A detailed description of the observing strategy, data reduction and analysis is given, and a discussion on how the precision in ground-based K-band photometry could be further improved. In addition, we show that the relative photometry between the target and the reference stars between the two epochs is consistent down to the <0.1 per cent level, which is interesting in the light of possible near-infrared surveys to search for transiting planets around M and L dwarfs.