This book contains the lectures delivered at the XII Canary Islands Winter School of Astrophysics on Astrophysical Spectropolarimetry. It highlights how recent developments in theoretical astrophysics and astronomical instrumentation are leading an ever-growing number of astrophysicists to appreciate the enormous diagnostic potential offered by

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The pulsating PG 1159 planetary nebula central star RXJ 2117+3412 has been observed over three successive seasons of a multisite photometric campaign. The asteroseismological analysis of the data, based on the 37 identified l=1 modes among the 48 independent pulsation frequencies detected in the power spectrum, leads to the derivation of the

An observing campaign with 10 participating observatories has undertaken to monitor the optical brightness of the Q0957 gravitationally lensed quasar for 10 consecutive nights in 2000 January. The resulting A image brightness curve has significant brightness fluctuations and makes a photometric prediction for the B image light curve for a second

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Substantial differences in the amplitudes of the fundamental frequency and its harmonics are observed in the temporal spectra of HP Lib in some specific nights. We interpret this photometric variations as a sign of the presence in the accretion disk of an active density wave which may develop changes in the energy production of the two spiral arms