High-quality spectropolarimetry (range 417-860 nm; spectral resolution 1.27
nm and 0.265 nm/pixel) of the SN 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 ≈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). This feature could be
an important clue to the binary nature of SN Ia, perhaps associated with an
accretion disk, or to the nature of the thermonuclear burning. 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.Comment: ApJ, in pres
