2 research outputs found
Heights of solar tracers observed at 8Â mm and an interpretation of their radiation
Context. At the wavelength of 8Â mm, emissive features (high brightness-temperatrue regions, HTRs)
and absorptive features (low brightness-temperature regions, LTRs) can be traced for
the determining the solar rotation. From earlier studies it is known that
about two thirds of LTRs are associated with Hα filaments.
Aims. Thermal bremsstrahlung and gyromagnetic (cyclotron) radiation mechanism can be
important for explaining the observed phenomena, so we
determine the heights of solar structures
and interpret their radiation mechanism(s).
Methods. We use the method of simultaneous determination of the solar synodic rotation
velocity and the height of tracers.
The rotation velocities were determined by the linear least-square fit of their
central meridian distance as a function of time.
We used a procedure for calculating the brightness temperature for a given wavelength
and
model atmosphere, which integrates the radiative transfer equation for the thermal
bremsstrahlung.
Results. The mean value of the low brightness-temperature regions' heights is about
45 600Â km. This height was used as input for constructing prominence and
coronal condensation models, which, when assuming thermal bremsstrahlung as the
radiation mechanism, yield a decrease in the brightness temperature
of 2–14%,
in agreement with observations. If the same radiation mechanism is considered, the
models of the solar corona above active regions give an increase in the
brightness temperature of 5–19%,
also in agreement with observations. In this case an indirect indication
(from the rotational analysis) that the HTRs are located higher in the solar
atmosphere than the LTRs was taken into account.
Conclusions. The method for simultaneously determining the solar synodic rotation
velocity and the height of tracers could have only been properly applied on
LTRs, since a homogeneous distribution over latitudes and central meridian
distances of a large enough data set is necessary. Thermal bremsstrahlung
can explain both the LTR (prominences and coronal condensations) and HTR (ordinary
active regions) phenomena observed at 8Â mm. At this wavelength, thermal gyromagnetic
emission is almost surely excluded as a possible radiation mechanism