Effect of telescope vibrations upon high angular resolution imaging

ABSTRACT We have analysed short-exposure high-resolution images obtained on the William HerschelTelescope (WHT), Big Telescope Azimuthal (BTA) and Canada–France–Hawaii Telescope(CFHT) in order to investigate mechanical vibrations that are capable of reducing the highangular resolution allowed by speckle-interferometric methods. After filtering the photonnoise we have computed power spectra of the image centres of gravity. In these spectra wehave found vibration features that differ from one telescope to another and that vary inparticular with the zenith angle. In the case of the WHT we discuss these results in terms ofpossible causes and in terms of degradation of the transfer function. We present some meansto improve the data.Key words: atmospheric effects – instrumentation: high angular resolution – methods: dataanalysis – techniques: high angular resolution – techniques: image processing – telescopes. 1 INTRODUCTIONTelescope motions are negligible for long-time exposures incomparison with the scale of the seeing disc, i.e. l=r