Cosmology
Research in cosmology at the Instituut voor Sterrenkunde focuses on
the study of gravitational lensed quasars. When a galaxy is very close
to the line-of-sight of a quasar, the light is deflected and many
images of the quasar appear. As quasars are intrinsically variable
objects, monitoring the luminosity variations of all images allows us
to measure time delays between images. These delays are due to the
different paths taken by light and also to the gravitational field of
the lensing galaxy. Time delays are a direct probe of the cosmology,
and measuring many time delays will allow us to determine the Hubble
constant very precisely and to constraint as well the other
cosmological parameters.
This monitoring is done with the new CCD camera available on the
Mercator telescope, in close collaboration with three other telescopes
(Euler, La Silla; Liverpool, La Palma; Maidanak, Uzbekistan), grouped
in the Cosmograil project.
Using many telescopes is important to obtain very well sampled quasar
image lightcurves, which is needed to get accurate time delays.
As angular separations between the quasar images are small, the
monitoring requires to perform accurate photometry of blended objects,
sometimes with several quasar images plus the lensing galaxy within
the seeing disk. Thus the data are processed using the MCS
deconvolution algorithm. The Cosmograil project involves people from
Belgium, Switzerland, United Kingdom, and Uzbekistan, spanning a broad
range of expertises.
Laurent Le Guillou
Hans Van Winckel
Gert Raskin
Christoffel Waelkens
The Cosmograil project
The Mercator Telescope at La Palma
The Euler Telescope at La Silla, Chile
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