A → cross correlation technique for
computing average profiles from thousands of
→ spectral lines
simultaneously. The technique, first introduced by Donati et
al. (1997, MNRAS 291,658), is based on several assumptions:
additive → line profiles, wavelength independent
→ limb darkening,
self-similar local profile shape, and weak
→ magnetic fields. Thus, unpolarized/polarized
stellar spectra can indeed be seen
as a line pattern → convolved
with an average line profile. In this context, extracting this average
line profile amounts to a linear → deconvolution
problem. The method treats it as a matrix problem and
look for the → least squares
solution. In practice, LSD is very similar to
most other cross-correlation techniques, though slightly more
sophisticated in the sense that it cleans the cross-correlation
profile from the autocorrelation profile of the line pattern.
The technique is used to investigate the
physical processes that take place in stellar atmospheres and that
affect all spectral line profiles in a similar way. This includes
the study of line profile variations (LPV) caused by orbital motion
of the star and/or stellar surface inhomogeneities, for example.
However,
its widest application nowadays is the detection of weak magnetic
fields in stars over the entire → H-R diagram
based on → Stokes parameter V
(→ circular polarization) observations
(see also Tkachenko et al., 2013,
A&A 560, A37 and references therein).
See also: → least; → square;
→ deconvolution.
