4,983 research outputs found
Magnetic field variations associated with umbral flashes and penumbral waves
Umbral flashes (UF) and running penumbral waves (RPWs) in sunspot
chromospheres leave a dramatic imprint in the intensity profile of the Ca II
854.2 nm line. Recent studies have focussed on also explaining the observed
polarization profiles, that show even more dramatic variations during the
passage of these shock fronts. While most of these variations can be explained
with an almost constant magnetic field as a function of time, several studies
have reported changes in the inferred magnetic field strength during UF phases.
In this study we investigate the origin of these periodic variations of the
magnetic field strength by analyzing a time-series of high temporal cadence
observations acquired in the Ca II line with the CRISP instrument at the
Swedish 1-m Solar Telescope. In particular, we analyze how the inferred
geometrical height scale changes between quiescent and UF phases, and whether
those changes are enough to explain the observed changes in . We have
performed non-LTE data inversions with the NICOLE code of a time-series of very
high spatio-temporal resolution observations in the Ca II and Fe I
630.15\630.25 nm lines. Our results indicate that the Ca II line in sunspots is
greatly sensitive to magnetic fields at during UFs and
quiescence. However, this optical depth value does not correspond to the same
geometrical height during the two phases. Our results indicate that during UFs
and RPWs the is located at a higher geometrical height than
during quiescence. Additionally, the inferred magnetic field values are higher
in UFs (~270 G) and in RPWs (~100 G). Our results suggest that opacity changes
caused by UFs and RPWs cannot explain the observed temporal variations in the
magnetic field, as the line seems to form at higher geometrical heights where
the field is expected to be lower.Comment: Accepted in A&
Spherical harmonic expansions of the Earth's gravitational potential to degree 360 using 30' mean anomalies
Two potential coefficient fields that are complete to degree and order 360 have been computed. One field (OSU86E) excludes geophysically predicted anomalies while the other (OSU86F) includes such anomalies. These fields were computed using a set of 30' mean gravity anomalies derived from satellite altimetry in the ocean areas and from land measurements in North America, Europe, Australia, Japan and a few other areas. Where no 30' data existed, 1 deg x 1 deg mean anomaly estimates were used if available. No rigorous combination of satellite and terrestrial data was carried out. Instead advantage was taken of the adjusted anomalies and potential coefficients from a rigorous combination of the GEML2' potential coefficient set and 1 deg x 1 deg mean gravity anomalies. The two new fields were computed using a quadrature procedure with de-smoothing factors. The spectra of the new fields agree well with the spectra of the fields with 1 deg x 1 deg data out to degree 180. Above degree 180 the new fields have more power. The fields have been tested through comparison of Doppler station geoid undulations with undulations from various geopotential models. The agreement between the two types of undulations is approximately + or - 1.6 m. The use of a 360 field over a 180 field does not significantly improve the comparison. Instead it allows the comparison to be done at some stations where high frequency effects are important. In addition maps made in areas of high frequency information (such as trench areas) clearly reveal the signal in the new fields from degree 181 to 360
The chromosphere above a -sunspot in the presence of fan-shaped jets
-sunspots are known to be favourable locations for fast and energetic
events like flares and CMEs. The photosphere of this type of sunspots has been
thoroughly investigated in the past three decades. The atmospheric conditions
in the chromosphere are not so well known, however. his study is focused on the
chromosphere of a -sunspot that harbours a series of fan-shaped jets in
its penumbra . The aim of this study is to establish the magnetic field
topology and the temperature distribution in the presence of jets in the
photosphere and the chromosphere. We use data from the Swedish 1-m Solar
Telescope (SST) and the Solar Dynamics Observatory. We invert the
spectropolarimetric FeI 6302~\AA\ and CaII ~8542~\AA\ data from the SST using
the the non-LTE inversion code NICOLE to estimate the magnetic field
configuration, temperature and velocity structure in the chromosphere. A
loop-like magnetic structure is observed to emerge in the penumbra of the
sunspot. The jets are launched from the loop-like structure. Magnetic
reconnection between this emerging field and the pre-existing vertical field is
suggested by hot plasma patches on the interface between the two fields. The
height at which the reconnection takes place is located between and . The magnetic field vector and the
atmospheric temperature maps show a stationary configuration during the whole
observation.Comment: 12 pages, 15 figures. Recommended for publication in A&
Short dynamic fibrils in sunspot chromospheres
Sunspot chromospheres display vigorous oscillatory signature when observed in
chromospheric diagnostics like the strong Ca II lines and H-alpha. New
high-resolution sunspot observations from the Swedish 1-m Solar Telescope show
the ubiquitous presence of small-scale periodic jet-like features that move up
and down. This phenomenon has not been described before. Their typical width is
about 0.3 arcsec and they display clear parabolic trajectories in space-time
diagrams. The maximum extension of the top of the jets is lowest in the umbra,
a few 100 km, and progressively longer further away from the umbra in the
penumbra, with the longest more than 1000 km. These jets resemble dynamic
fibrils found in plage regions but at smaller extensions. LTE inversion of
spectro-polarimetric Ca II 8542 observations enabled for a comparison of the
magnetic field inclination and the properties of these short jets. We find that
the most extended of these jets also have longer periods and tend to be located
in regions with more horizontal magnetic fields. This is a direct observational
confirmation of the mechanism of long-period waves propagating along inclined
magnetic fields into the solar chromosphere. This mechanism was identified
earlier as the driver of dynamic fibrils in plage, part of the mottles in quiet
Sun, and type I spicules at the limb. The sunspot dynamic fibrils that we
report here represent a new class of manifestation of this mechanism. They are
not the same as the transient penumbral and umbral micro-jets reported earlier.Comment: animations of figures can be found at
http://folk.uio.no/rouppe/dfsunspot
Is the sky the limit? Performance of the revamped Swedish 1-m Solar Telescope and its blue- and red-beam re-imaging systems
We demonstrate that for data recorded with a solar telescope that uses
adaptive optics and/or post-processing to compensate for many low- and
high-order aberrations, the RMS granulation contrast is directly proportional
to the Strehl ratio calculated from the residual (small-scale) wavefront error.
We demonstrate that the wings of the high-order compensated PSF for SST are
likely to extend to a radius of not more than about 2 arcsec, consistent with
earlier conclusions drawn from straylight compensation of sunspot images. We
report on simultaneous measurements of seeing and solar granulation contrast
averaged over 2 sec time intervals at several wavelengths from 525 nm to 853.6
nm on the red-beam (CRISP beam) and wavelengths from 395 nm to 484 nm on the
blue-beam (CHROMIS beam). These data were recorded with the Swedish 1-m Solar
Telescope (SST) that has been revamped with an 85-electrode adaptive mirror and
a new tip-tilt mirror, both of which were polished to exceptionally high
optical quality. The highest 2-sec average image contrast measured in April
2015 through 0.3-0.9 nm interference filters at 525 nm, 557 nm, 630 nm and
853.5 nm with compensation only for the diffraction limited point spread
function of SST is 11.8%, 11.8%, 10.2% and 7.2% respectively. Similarly, the
highest 2-sec contrast measured at 395 nm, 400 nm and 484 nm in May 2016
through 0.37-1.3 nm filters is 16%, 16% and 12.5% respectively. The granulation
contrast observed with SST compares favorably with that of other telescopes.
Simultaneously with the above wideband red-beam data, we also recorded
narrow-band continuum images with the CRISP imaging spectropolarimeter. We find
that contrasts measured with CRISP are entirely consistent with the
corresponding wide-band contrasts, demonstrating that any additional image
degradation by the CRISP etalons and telecentric optical system is marginal or
even insignificant.Comment: In press in Astronomy & Astrophysic
Dark Left-Right Gauge Model: SU(2)_R Phenomenology
In the recently proposed dark left-right gauge model of particle
interactions, the left-handed fermion doublet is connected to its
right-handed counterpart through a scalar bidoublet, but
couples to only through which has no vacuum expectation value.
The usual R parity, i.e. , can be defined for this
nonsupersymmetric model so that both and are odd together with
. The lightest is thus a viable dark-matter candidate (scotino).
Here we explore the phenomenology associated with the gauge group of
this model, which allows it to appear at the TeV energy scale. The exciting
possibility of charged leptons is discussed.Comment: 12 pages, 2 figure
The effect of isotopic splitting on the bisector and inversions of the solar Ca II 854.2 nm line
The Ca II 854.2 nm spectral line is a common diagnostic of the solar
chromosphere. The average line profile shows an asymmetric core, and its
bisector shows a characteristic inverse-C shape. The line actually consists of
six components with slightly different wavelengths depending on the isotope of
calcium. This isotopic splitting of the line has been taken into account in
studies of non-solar stars, but never for the Sun. We performed non-LTE
radiative transfer computations from three models of the solar atmosphere and
show that the asymmetric line-core and inverse C-shape of the bisector of the
854.2 nm line can be explained by isotopic splitting. We confirm this finding
by analysing observations and showing that the line asymmetry is present
irrespective of conditions in the solar atmosphere. Finally, we show that
inversions based on the Ca II 854.2 nm line should take the isotopic splitting
into account, otherwise the inferred atmospheres will contain erroneous
velocity gradients and temperatures.Comment: Accepted for ApJ
First order transitions by conduction calorimetry: Application to deuterated potassium dihydrogen phosphate ferroelastic crystal under uniaxial pressure
The specific heat c and the heat power W exchanged by a Deuterated Potassium Dihydrogen Phosphate ferroelectric-ferroelastic crystal have been measured simultaneously for both decreasing and increasing temperature at a low constant rate (0.06 K/h) between 175 and 240 K. The measurements were carried out under controlled uniaxial stresses of 0.3 and 4.5±0.1 bar applied to face (110). At Tt=207.9 K, a first order transition is produced with anomalous specific heat behavior in the interval where the transition heat appears. This anomalous behavior is explained in terms of the temperature variation of the heat power during the transition. During cooling, the transition occurs with coexistence of phases, while during heating it seems that metastable states are reached. Excluding data affected by the transition heat, the specific heat behavior agrees with the predictions of a 2-4-6 Landau potential in the range of 4–15 K below Tt while logarithmic behavior is obtained in the range from Tt to 1 K below Tt. Data obtained under 0.3 and 4.5 bar uniaxial stresses exhibit the same behavior.Dirección General de Investigación Científica y Técnica. Gobierno de España-PB91-60
A waypoint-based mission planner for a farmland coverage with an aerial robot - a precision farming tool
Remote sensing (RS) with aerial robots is becoming more usual in every day time in Precision Agriculture (PA) practices, do to their advantages over conventional methods. Usually, available commercial platforms providing off-the-shelf waypoint navigation are adopted to perform visual surveys over crop fields, with the purpose to acquire specific image samples. The way in which a waypoint list is computed and dispatched to the aerial robot when mapping non empty agricultural workspaces has not been yet discussed. In this paper we propose an offline mission planner approach that computes an efficient coverage path subject to some constraints by decomposing the environment approximately into cells. Therefore, the aim of this work is contributing with a feasible waypoints-based tool to support PA practice
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