SPECTROPOLARIMETRY OF SN 2001el IN NGC 1448: ASPHERICITY OF A

High-quality spectropolarimetry (range 417–860 nm; spectral resolution 1.27 nm and 0.265 nm pixel1) of the Type Ia supernova (SN Ia) 2001el was obtained with the ESO Very Large Telescope Melipal (+FORS1) at five epochs. The spectra a week before maximum and around maximum indicate photospheric expansion velocities of about 10,000 km s1. Prior to optical maximum, the linear polarization of the continuum was 0.2%–0.3 % with a constant position angle, showing that SN 2001el has a well-defined axis of symmetry. The polarization was nearly undetectable a week after optical maximum. The spectra are similar to those of the normally bright SN 1994D, with the exception of a strong double-troughed absorption feature seen around 800 nm (FWHM about 22 nm). The 800 nm feature is probably due to the Ca ii IR triplet at very high velocities (20,000–26,000 km s1) involving 0.004 M of calcium and perhaps 0.1 M total mass. The 800 nm feature is distinct in velocity space from the photospheric Ca ii IR triplet and has a significantly higher degree of polarization (0.7%) and different polarization angle than the continuum. Taken together, these aspects suggest that this high-velocity calcium is a kinematically distinct feature with the matter distributed in a filament, torus, or array of ‘ ‘ blobs ’ ’ almost edge-on to the line of sight. This feature could thus be an important clue to the binary nature of SNe Ia, perhaps associated with an accretion disk, or to the nature o