27 research outputs found
The statistical distribution of magnetic field strength in G-band bright points
G-band bright points are small-sized features characterized by high
photometric contrast. Theoretical investigations indicate that these features
have associated magnetic field strengths between 1-2 kG. Results from
observations instead lead to contradictory results, indicating magnetic fields
of only kG strength in some and including hG strengths in others. In order to
understand the differences between measurements reported in the literature, and
to reconcile them with results from theory, we analyze the distribution of
magnetic field strength of G-band bright features identified on synthetic
images of the solar photosphere, and its sensitivity to observational and
methodological effects. We investigate the dependence of magnetic field
strength distributions of G-band bright points identified in 3D
magnetohydrodynamic simulations on feature selection method, data sampling,
alignment and spatial resolution. The distribution of magnetic field strength
of G-band bright features shows two peaks, one at about 1.5 kG and one below 1
hG. The former corresponds to magnetic features,the second mostly to bright
granules. Peaks at several hG are obtained only on spatially degraded or
misalligned data. Simulations show that magnetic G-band bright points have
typically associated field strengths of few kG. Field strengths in the hG range
can result from observational effects, thus explaining the discrepancies
presented in the literature. Our results also indicate that outcomes from
spectro-polarimetric inversions with imposed unit filling-factor should be
employed with great caution
The correlation of synthetic UV color vs Mg II index along the solar cycle
Modeling of planets' climate and habitability requires as fundamental input
the UV emission of the hosting star. \citet{lovric2017} employed SORCE/SOLSTICE
solar observations to introduce a UV color index which is a descriptor of the
UV radiation that modulates the photochemistry of planets atmospheres. After
correcting the SOLSTICE data for residual instrumental effects that produced
asymmetric signals during different phases of the cycles analyzed, the authors
found that the UV color index is linearly correlated with the Mg II index.In
this paper we employ an irradiance reconstruction technique to synthetize the
UV color and Mg II index with the purpose of investigating whether the
correction applied by \citet{lovric2017} to SORCE/SOLSTICE data might have
compensated for solar variations, and to investigate the physical mechanisms
that produce such a strong correlation between the UV color index and the solar
activity. Reconstructed indices reproduce very well the observations and
present the same strong linear dependence. Moreover our reconstruction, which
extends back to 1989, shows that the UV color - Mg II index relation can be
described by the same linear relation for almost three cycles, thus ruling out
an overcompensation of SORCE/SOLTICE data in the analysis of
\citet{lovric2017}. We suggest that the strong correlation between the indices
results from the fact that most of the Far- and Middle- UV radiation originates
in the chromosphere, where atmosphere models of quiet and magnetic features
present similar temperature and density gradients.Comment: Accepted in Ap