We present optical V and i -band light curves of the gravitationally lensed BAL quasar HE 2149 - 2745 .
The data , obtained with the 1.5m Danish Telescope ( ESO-La Silla ) between October 1998 and December 2000 , are the first from a long-term project aimed at monitoring selected lensed quasars in the Southern Hemisphere .
A time delay of 103 \pm 12 days is determined from the light curves .
In addition , VLT/FORS1 spectra of HE 2149 - 2745 are deconvolved in order to obtain the spectrum of the faint lensing galaxy , free of any contamination by the bright nearby two quasar images .
By cross-correlating the spectrum with galaxy-templates we obtain a tentative redshift estimate of z = 0.495 \pm 0.01 .
Adopting this redshift , a \Omega = 0.3 , \Lambda = 0.7 cosmology , and a chosen analytical lens model , our time-delay measurement yields a Hubble constant of H _ { 0 } = 66 \pm 8 { km } ~ { } { s ^ { -1 } } ~ { } { Mpc ^ { -1 } } ( 1 \sigma error ) with an estimated systematic error of \pm 3 { km } ~ { } { s ^ { -1 } } ~ { } { Mpc ^ { -1 } } .
Using non-parametric models yields H _ { 0 } = 65 \pm 8 { km } ~ { } { s ^ { -1 } } ~ { } { Mpc ^ { -1 } } ( 1 \sigma error ) and confirms that the lens exhibits a very dense/concentrated mass profile .
Finally , we note , as in other cases , that the flux ratio between the two quasar components is wavelength dependent .
While the flux ratio in the broad emission lines - equal to 3.7 - remains constant with wavelength , the continuum of the brighter component is bluer .
Although the data do not rule out extinction of one quasar image relative to the other as a possible explanation , the effect could also be produced by differential microlensing by stars in the lensing galaxy .