The GROUSE project - II. Detection of the Ks-band secondary eclipse of exoplanet HAT-P-1b E. J. W. de Mooij, R. J. de Kok, S. V. Nefs and I. A. G. Snellen A&A, 528 (2011) A49 Published online: 28 February 2011 DOI: 10.1051/0004-6361/201016142