High-quality spectropolarimetry ( range 417-860 nm ; spectral resolution 1.27 nm and 0.265 nm/pixel ) of the SNÂ Ia 2001el were obtained with the ESO Very Large Telescope Melipal ( + FORS1 ) at 5 epochs .
The spectra a week before maximum and around maximum indicate photospheric expansion velocities of about 10,000 km s ^ { -1 } .
Prior to optical maximum , the linear polarization of the continuum was \approx 0.2 - 0.3 \% with a constant position angle , showing that SNÂ 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 SNÂ 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 s ^ { -1 } } ) involving \sim 0.004 M _ { \odot } Â of calcium and perhaps 0.1 M _ { \odot } Â 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 ( \approx 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 SNÂ Ia , perhaps associated with an accretion disk , or to the nature of the thermonuclear burning , perhaps representing a stream of material ballistically ejected from the site of the deflagration to detonation transition .

If modeled in terms of an oblate spheroid , the continuum polarization implies a minor to major axis ratio of around 0.9 if seen equator-on ; this level of asymmetry would produce an absolute luminosity dispersion of about 0.1 mag when viewed at different viewing angles .
If typical for SNe Ia , this would create an RMS scatter of several hundredths of a magnitude around the mean brightness-decline relation .
We discuss the possible implications of this scatter for the high precision measurements required to determine the cosmological equation of state .