111 research outputs found
Radiative emission of solar features in Ca II K
We investigated the radiative emission of different types of solar features
in the spectral range of the Ca II K line.
We analyzed full-disk 2k x 2k observations from the PSPT Precision Solar
Photometric Telescope. The data were obtained by using three narrow-band
interference filters that sample the Ca II K line with different pass bands.
Two filters are centered in the line core, the other in the red wing of the
line. We measured the intensity and contrast of various solar features,
specifically quiet Sun (inter-network), network, enhanced network, plage, and
bright plage (facula) regions. Moreover, we compared the results obtained with
those derived from the numerical synthesis performed for the three PSPT filters
with a widely used radiative code on a set of reference semi-empirical
atmosphere models.Comment: In Proceedings of the 25th NSO Workshop: Chromospheric Structure and
Dynamic
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On the reliability of the fractal dimension measure of solar magnetic features and on its variation with solar cycle
Several studies have investigated the fractal and multifractal nature of magnetic features in the solar photosphere and its variation with the solar magnetic activity cycle. Here we extend those studies by examining the fractal geometry of bright magnetic features at higher atmospheric levels, specifically in the solar chromosphere. We analyze structures identified in CaIIK images obtained with the Precision Solar Photometric Telescopes (PSPTs) at Osservatorio Astronomico di Roma (OAR) and Mauna Loa Solar Observatory (MLSO). Fractal dimension estimates depend on the estimator employed, the quality of the images, and the structure identification techniques used. We examine both real and simulated data and employ two different perimeter-area estimators in order to understand the sensitivity of the deduced fractal properties to pixelization and image quality. The fractal dimension of bright 'magnetic' features in CaIIK images ranges between values of 1.2 and 1.7 for small and large structures respectively. This size dependency largely reflects the importance of image pixelization in the measurement of small objects. The fractal dimension of chromospheric features does not show any clear systematic variation with time over the period examined, the descending phase of solar cycle 23. These conclusions, and the analysis of both real and synthetic images on which they are based, are important in the interpretation of previously reported results
Radiative emission of solar features in the Ca II K line: comparison of measurements and models
We study the radiative emission of various types of solar features, such as
quiet Sun, enhanced network, plage, and bright plage regions, identified on
filtergrams taken in the Ca II K line. We analysed fulldisk images obtained
with the PSPT, by using three interference filters that sample the Ca II K line
with different bandpasses. We studied the dependence of the radiative emission
of disk features on the filter bandpass. We also performed a NLTE spectral
synthesis of the Ca II K line integrated over the bandpass of PSPT filters. The
synthesis was carried out by utilizing both the PRD and CRD with the most
recent set of semi empirical atmosphere models in the literature and some
earlier atmosphere models. We measured the CLV of intensity values for various
solar features identified on PSPT images and compared the results obtained with
those derived from the synthesis. We find that CRD calculations derived using
the most recent quiet Sun model, on average, reproduce the measured values of
the quiet Sun regions slightly more accurately than PRD computations with the
same model. This may reflect that the utilized atmospheric model was computed
assuming CRD. Calculations with PRD on earlier quiet Sun model atmospheres
reproduce measured quantities with a similar accuracy as to that achieved here
by applying CRD to the recent model. We also find that the median contrast
values measured for most of the identified bright features, disk positions, and
filter widths are, on average, a factor 1.9 lower than those derived from PRD
simulations performed using the recent bright feature models. The discrepancy
between measured and modeled values decreases by 12% after taking into account
straylight effects on PSPT images. PRD computations on either the most recent
or the earlier atmosphere models of bright features reproduce measurements from
plage and bright plage regions with a similar accuracy.Comment: 14 pages, 18 figures, accepted by A&
Kinematics and Magnetic Properties of a Light Bridge in a Decaying Sunspot
We present the results obtained by analyzing high spatial and spectral
resolution data of the solar photosphere acquired by the CRisp Imaging
SpectroPolarimeter at the Swedish Solar Telescope on 6 August 2011, relevant to
a large sunspot with a light bridge (LB) observed in NOAA AR 11263. These data
are complemented by simultaneous Hinode Spectropolarimeter (SP) observation in
the Fe I 630.15 nm and 630.25 nm lines. The continuum intensity map shows a
discontinuity of the radial distribution of the penumbral filaments in
correspondence with the LB, which shows a dark lane (about 0.3" wide and about
8.0" long) along its main axis. The available data were inverted with the
Stokes Inversion based on Response functions (SIR) code and physical parameters
maps were obtained. The line-of-sight (LOS) velocity of the plasma along the LB
derived from the Doppler effect shows motions towards and away from the
observer up to 0.6 km/s, which are lower in value than the LOS velocities
observed in the neighbouring penumbral filaments. The noteworthy result is that
we find motions toward the observer up to 0.6 km/s in the dark lane where the
LB is located between two umbral cores, while the LOS velocity motion toward
the observer is strongly reduced where the LB is located between an umbral core
at one side and penumbral filaments on the other side. Statistically, the LOS
velocities correspond to upflows/downflows andcomparing these results with
Hinode/SP data, we conclude that the surrounding magnetic field configuration
(whether more or less inclined) could have a role in maintaining the conditions
for the process of plasma piling up along the dark lane. The results obtained
from our study support and confirm outcomes of recent magnetohydro-dynamic
simulations showing upflows along the main axis of a LBs
Polarised kink waves in magnetic elements: evidence for chromospheric helical waves
In recent years, new high spatial resolution observations of the Sun's atmosphere have revealed the presence of a plethora of small-scale magnetic elements down to the resolution limit of the current cohort of solar telescopes (~100–120 km on the solar photosphere). These small magnetic field concentrations, due to the granular buffeting, can support and guide several magnetohydrodynamic wave modes that would eventually contribute to the energy budget of the upper layers of the atmosphere. In this work, exploiting the high spatial and temporal resolution chromospheric data acquired with the Swedish 1 m Solar Telescope, and applying the empirical mode decomposition technique to the tracking of the solar magnetic features, we analyze the perturbations of the horizontal velocity vector of a set of chromospheric magnetic elements. We find observational evidence that suggests a phase relation between the two components of the velocity vector itself, resulting in its helical motion
Experimental evaluation of the thermal polarization in direct contact membrane distillation using electrospun nanofiber membranes doped with molecular probes
Membrane distillation (MD) has recently gained considerable attention as a valid process for the production of fresh-water due to its ability to exploit low grade waste heat for operation and to ensure a nearly feed concentration-independent production of high-purity distillate. Limitations have been related to polarization phenomena negatively affecting the thermal efficiency of the process and, as a consequence, its productivity. Several theoretical models have been developed to predict the impact of the operating conditions of the process on the thermal polarization, but there is a lack of experimental validation. In this study, electrospun nanofiber membranes (ENMs) made of Poly(vinylidene fluoride) (PVDF) and doped with (1, 10-phenanthroline) ruthenium (II) Ru(phen) 3 were tested at different operating conditions (i.e., temperature and velocity of the feed) in direct contact membrane distillation (DCMD). The temperature sensitive luminophore, Ru(phen) 3 , allowed the on-line and non-invasive mapping of the temperature at the membrane surface during the process and the experimental evaluation of the effect of the temperature and velocity of the feed on the thermal polarization
Stray-light restoration of full-disk CaII K solar observations: a case study
AIMS: We investigate whether restoration techniques, such as those developed
for application to current observations, can be used to remove stray-light
degradation effects on archive CaII K full-disk observations. We analyze to
what extent these techniques can recover homogeneous time series of data.
METHODS:We develop a restoration algorithm based on a method presented by
Walton & Preminger (1999). We apply this algorithm to data for both present-day
and archive CaII K full-disk observations, which were acquired using the PSPT
mounted at the Rome Observatory, or obtained by digitization of Mt Wilson
photographic-archive spectroheliograms. RESULTS:We show that the restoring
algorithm improves both spatial resolution and photometric contrast of the
analyzed solar observations. We find that the improvement in spatial resolution
is similar for analyzed recent and archive data. On the other hand, the
improvement of photometric contrast is quite poor for the archive data, with
respect to the one obtained for the present-day images. We show that the
quality of restored archive data depends on the photographic calibration
applied to the original observations. In particular, photometry can be
recovered with a restoring algorithm if the photographic-calibration preserves
the intensity information stored in the original data, principally outside the
solar-disk observations.Comment: 10 pages; 9 figure
Dynamic properties along the neutral line of a delta spot inferred from high-resolution observations
Delta (δ) spots are complex magnetic configurations of sunspots characterized by umbrae of opposite polarity sharing a common penumbra. In order to investigate the fine structure of the region separating the two magnetic polarities of a δ spot, we studied the morphology, the magnetic configuration, and the velocity field in such a region using observations of active region (AR) NOAA 11267 obtained with the CRisp Imaging SpectroPolarimeter (CRISP) at the Swedish Solar Telescope on 2011 August 6. The analysis of CRISP data shows upflows and downflows of ~ ± 3 km s–1 in proximity of the δ spot polarity inversion line (PIL), and horizontal motions along the PIL of the order of ~1 km s–1. The results obtained from the SIR inversion of CRISP data also indicate that the transverse magnetic field in the brighter region separating the two opposite magnetic polarities of the δ spot is tilted about ~45° with respect to the PIL. Solar Dynamics Observatory/Helioseismic and Magnetic Imager observations confirm the presence of motions of ~ ± 3 km s–1 in proximity of the PIL, which were observed to last 15 hr. From the data analyzed, we conclude that the steady, persistent, and subsonic motions observed along the δ spot PIL can be interpreted as being due to Evershed flows occurring in the penumbral filaments that show a curved, wrapped configuration. The fluting of the penumbral filaments and their bending, continuously increased by the approaching motion of the negative umbra toward the positive one, give rise to the complex line-of-sight velocity maps that we observed.
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