P8	June 1997

¹ Institut d'Astrophysique et de Géophysique - Université de Liège, Avenue de Cointe 5, 4000 Liège, Belgium
² URA 173 CNRS-DAEC, Observatoire de Paris, F-92195 Meudon Principal Cédex, France
³ Harvard-Smithsonian Center for Astrophysics, MS-51, 60 Garden Street, Cambridge, MA 02138, USA
⁴ Institute of Theoretical Astrophysics, University of Oslo, Pb. 1029, Blindern, 0315 Oslo, Norway
⁵ NORDITA, Blegdamsvey 17, DK-2100 Copenhagen Ø, Denmark

^* Maître de Recherches FNRS, Belgium

⁺ Based on observations taken at the Nordic Optical Telescope and the Canada France Hamaii Telescope

Abstract

     Time delay measurements have recently been reported for the lensed quasar PG 1115+080. These measurements can be used to derive H₀, but only if we can constrain the lensing potential. We have applied a recently developed deconvolution technique to analyse sub-arcsecond I band images of PG 1115+080, obtained at the Nordic Optical Telescope (NOT) and the Canada France Hawaii Telescope (CFHT). The high performance of the deconvolution code allows us to derive precise positions and magnitudes for the four lensed images of the quasar, as well as for the lensing galaxy. The new measurement of the galaxy position improves its precision by a factor of 3 and thus strengthens the constraints on the lensing potential. With the new data, a range of models incorporating some of the plausible systematic uncertainties yields  km s^-1 Mpc^-1.