Observational detection of eight mutual eclipses and occultations between the satellites of Uranus

¹ Armagh Observatory, College Hill, Armagh BT61 9DG, Northern Ireland, UK e-mail: aac@star.arm.ac.uk
² Faulkes Telescope Project, School of Physics and Astronomy, Cardiff University, Queens Buildings, 5 The Parade, Cardiff CF24 3AA, UK
³ Las Cumbres Observatory Global Telescope, 6740 Cortona Dr. Ste. 102, Goleta, CA 93117, USA
⁴ Department of Physics and Astronomy, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
⁵ South African Astronomical Observatory, PO Box 9, Observatory, 7935, South Africa
⁶ Southern African Large Telescope Foundation, PO Box 9, Observatory, 7935, South Africa
⁷ Poznan (A. Mickiewicz Univ.), Astr. Obs. of A. Mickiewicz Univ., ul.Sloneczna, 60-286 Poznan, Poland
⁸ Hellenic-American Educational Foundation, Athens College, PO Box 65005, Psychico, 15410 Athens, Greece
⁹ Educational Research and Pedagogy Unit, School of Humanities, Hellenic Open University, 23 Sachtouri Str., 26222 Patras, Greece
¹⁰ Hellenic Astronomical Association, I. Metaxa & Vas. Pavlou Str., Palaia Penteli Attikis, 15236 Athens, Greece
¹¹ Ellinogermaniki Agogi School Observatory, Dimitriou Panagea Str., Pallini Attikis, 15351 Athens, Greece
¹² Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
¹³ Department of Astrophysics, Astronomy and Mechanics, University of Athens, 15784 Zografos, Athens, Greece
¹⁴ Department of Physics, University of California, Santa Barbara, CA 93106, USA

Received: 15 December 2008
Accepted: 9 February 2009

Abstract

Aims. We carried out observations, with five different instruments ranging in aperture from 0.4 m to 10 m, of the satellites of Uranus during that planet's 2007 Equinox. Our observations covered specific intervals of time when mutual eclipses and occultations were predicted.

Methods. The observations were carried out in the near-infrared part of the spectrum to mitigate the glare from the planet. Frames were acquired at rates . Following modelling and subtraction of the planetary source from these frames, differential aperture photometry was carried out on the satellite pairs involved in the predicted events. In all cases but one, nearby bright satellites were used as reference sources.

Results. We have obtained fifteen individual lightcurves, eight of which show a clear drop in the flux from the satellite pair, indicating that a mutual event took place. Three of these involve the faint satellite Miranda. All eight lightcurves were model-fitted to yield best estimates of the time of maximum flux drop and the impact parameter. In three cases best-fit albedo ratios were also derived. We used these estimates to generate intersatellite astrometric positions with typical formal uncertainties of , several times better than conventional astrometry of these satellites. The statistics of our estimated event midtimes show a systematic lag, with the observations later than predictions. In addition, lightcurves of two partial eclipses of Miranda show no statistically significant evidence of a light drop, at variance with the predictions. These indicate that new information about the Uranian satellite system is contained in observations of mutual events acquired here and by other groups.