Antonio Pereyra

Concept of SPARC4:a simultaneous polarimeter and rapid camera in 4 bands

We present a summary of the concept design report of a new astronomical instrument: SPARC4, Simultaneous Polarimeter and Rapid Camera in 4 bands. SPARC4 will provide photometry and polarimetry in four optical broad bands (griz SDSS) simultaneously. This is achieved by the use of dichroic beam splitters. The square eld of view is around 5.6 arcmin on a side. SPARC4 time resolution is sub-second for photometry and somewhat longer for polarimetry. This is provided by the use of fast EMCCDs. The main motivation for building SPARC4 is to explore astrophysical objects which exhibit fast temporal variability in ux and polarization. The instrument will be installed at the 1.6-m telescope of the Observatorio do Pico dos Dias (Brazil).

SPARC4 A simultaneous polarimeter and rapid camera in 4 bands

We present the basic concept of a new astronomical instrument: SPARC4 - Simultaneous Polarimeter and Rapid Camera in 4 bands. SPARC4 combines in one instrument: (i) photometric and polarimetric modes; (ii) sub-second time-resolution in photometric mode and excellent timeresolution in polarimetric mode; (iii) simultaneous imaging in four broad-bands for both modes. This combination will make SPARC4 a unique facility for ground-based optical observatories. Presently, the project is in its conceptual design phase.

Hα spectropolarimetry of GG Car

We present spectropolarimetric observations of the B[e] supergiant star GG Car at two epochs. Polarization line effects along Hα are analysed using the Q–U diagram. In particular, the polarization position angle (PA) obtained using the line effect allows to constrain the symmetry axis of the disk/envelope. The depolarization line effect around Hα is evident in the Q–U diagram for both epochs, confirming that light from the system is intrinsically polarized. A rotation of the PA along Hα is also observed, indicating a counter-clockwise rotating disk. The intrinsic PA calculated using the line effect (∼85◦) is consistent between our two epochs, suggesting a clearly defined symmetry axis of the disk.