The Astrophysics Division of INPE is developing an optical astronomical instrument as a demand of its scientific research. SPARC4 - Simultaneous Polarimeter and Rapid Camera in Four bands - combines in one instrument: (i) good time resolution; (ii) photometric and polarimetric modes; (iii) data simultaneously obtained in four broad-bands. See more details on this page.

Our activities focus on the measurement of the polarization of polars (and other classes of cataclysmic variables) as well as to model the accretion region responsible by the optical and X-ray emission.

Cataclysmic variables (CV) are short period binaries composed by a white dwarf (primary) and a late-type main-sequence star. The secondary star fills its Roche lobe, losing material to the primary by the inner Lagrangian point, L1. Due to its angular momentum, this material forms an accretion disk around the white dwarf. Polars (or AM Her systems) are CV in which the primary has a magnetic field in the range from 10 to 100 MG. Such a high magnetic field prevents disk formation. Therefore, the material from the secondary goes to the primary magnetic pole(s) via an accretion stream. Another consequence of the magnetic field is the synchronization of the white dwarf rotation with the orbital revolution.

In the accretion region, near the white dwarf surface, the material is fully ionized producing highly polarized cyclotron emission due to the presence of the strong magnetic field. As a large fraction of the optical flux in polars comes from such region, they have large values of polarization, mainly circular. Consequently, polarimetry is a fundamental tool to classify an object as an AM Her system.