The subterahertz solar cycle: Polar and equatorial radii derived from SST and ALMA. (arXiv:2102.04570v2 [astro-ph.SR] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Menezes_F/0/1/0/all/0/1">Fabian Menezes</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Selhorst_C/0/1/0/all/0/1">Caius L. Selhorst</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Castro_C/0/1/0/all/0/1">Carlos Guillermo Giménez de Castro</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Valio_A/0/1/0/all/0/1">Adriana Valio</a>
At subterahertz frequencies — i.e., millimeter and submillimeter wavelengths
— there is a gap of measurements of the solar radius as well as other
parameters of the solar atmosphere. As the observational wavelength changes,
the radius varies because the altitude of the dominant electromagnetic
radiation is produced at different heights in the solar atmosphere. Moreover,
radius variations throughout long time series are indicative of changes in the
solar atmosphere that may be related to the solar cycle. Therefore, the solar
radius is an important parameter for the calibration of solar atmospheric
models enabling a better understanding of the atmospheric structure. In this
work we use data from the Solar Submillimeter-wave Telescope (SST) and from the
Atacama Large Millimeter/submillimeter Array (ALMA), at the frequencies of 100,
212, 230, and 405 GHz, to measure the equatorial and polar radii of the Sun.
The radii measured with extensive data from the SST agree with the
radius-vs-frequency trend present in the literature. The radii derived from
ALMA maps at 230 GHz also agree with the radius-vs-frequency trend, whereas the
100-GHz radii are slightly above the values reported by other authors. In
addition, we analyze the equatorial and polar radius behavior over the years,
by determining the correlation coefficient between solar activity and
subterahertz radii time series at 212 and 405 GHz (SST). The variation of the
SST-derived radii over 13 years are correlated to the solar activity when
considering equatorial regions of the solar atmosphere, and anticorrelated when
considering polar regions. The ALMA derived radii time series for 100 and 230
GHz show very similar behaviors with those of SST.
At subterahertz frequencies — i.e., millimeter and submillimeter wavelengths
— there is a gap of measurements of the solar radius as well as other
parameters of the solar atmosphere. As the observational wavelength changes,
the radius varies because the altitude of the dominant electromagnetic
radiation is produced at different heights in the solar atmosphere. Moreover,
radius variations throughout long time series are indicative of changes in the
solar atmosphere that may be related to the solar cycle. Therefore, the solar
radius is an important parameter for the calibration of solar atmospheric
models enabling a better understanding of the atmospheric structure. In this
work we use data from the Solar Submillimeter-wave Telescope (SST) and from the
Atacama Large Millimeter/submillimeter Array (ALMA), at the frequencies of 100,
212, 230, and 405 GHz, to measure the equatorial and polar radii of the Sun.
The radii measured with extensive data from the SST agree with the
radius-vs-frequency trend present in the literature. The radii derived from
ALMA maps at 230 GHz also agree with the radius-vs-frequency trend, whereas the
100-GHz radii are slightly above the values reported by other authors. In
addition, we analyze the equatorial and polar radius behavior over the years,
by determining the correlation coefficient between solar activity and
subterahertz radii time series at 212 and 405 GHz (SST). The variation of the
SST-derived radii over 13 years are correlated to the solar activity when
considering equatorial regions of the solar atmosphere, and anticorrelated when
considering polar regions. The ALMA derived radii time series for 100 and 230
GHz show very similar behaviors with those of SST.
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