Del Toro Iniesta, J. C.; Martínez-Pillet, V.
Referencia bibliográfica
The Astrophysical Journal Supplement, Volume 201, Issue 2, article id. 22 (2012).
Fecha de publicación:
8
2012
Número de citas
20
Número de citas referidas
20
Descripción
The design and later use of modern spectropolarimeters and magnetographs
require a number of tolerance specifications that allow the developers
to build the instrument and then the scientists to interpret the data
accuracy. Such specifications depend both on device-specific features
and on the physical assumptions underlying the particular measurement
technique. Here we discuss general properties of every magnetograph,
such as the detectability thresholds for the vector magnetic field and
the line-of-sight velocity, as well as specific properties of a given
type of instrument, namely, that based on a pair of nematic liquid
crystal variable retarders and a Fabry-Pérot etalon (or several)
for carrying out the light polarization modulation and spectral
analysis, respectively. We derive formulae that give the detection
thresholds in terms of the signal-to-noise ratio of the observations and
the polarimetric efficiencies of the instrument. Relationships are also
established between inaccuracies in the solar physical quantities and
instabilities in the instrument parameters. Such relationships allow,
for example, one to translate scientific requirements for the velocity
or the magnetic field into requirements for temperature or voltage
stability. We also demonstrate that this type of magnetograph can
theoretically reach the optimum polarimetric efficiencies of an ideal
polarimeter, regardless of the optics in between the modulator and the
analyzer. Such optics induce changes in the instrument parameters that
are calculated.
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