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Register a new userSpectropolarimetry with CRISP at the Swedish 1-m Solar Telescope
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CRISP (Crisp Imaging Spectro-polarimeter), the new spectropolarimeter at the Swedish 1-m Solar Telescope, opens a new perspective in solar polarimetry. With better spatial resolution (0.13) than Hinode in the Fe I 6302 A line and similar polarimetric sensitivity reached through postprocessing, CRISP complements the SP spectropolarimeter onboard Hinode. We present some of the data which we obtained in our June 2008 campaign and preliminary results from LTE
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We have developed a general framework for modeling gyrosynchrotron and free-free emission from solar flaring loops and used it to test the premise that 2D maps of source parameters, particularly magnetic field, can be deduced from spatially resolved microwave spectropolarimetry data. In this paper we show quantitative results for a flaring loop with a realistic magnetic geometry, derived from a magnetic field extrapolation, and containing an electron distribution with typical thermal and nonthermal parameters, after folding through the instrumental profile of a realistic interferometric array. We compare the parameters generated from forward fitting a homogeneous source model to each line of sight through the folded image data cube with both the original parameters used in the model and with parameters generated from forward fitting a homogeneous source model to the original (unfolded) image data cube. We find excellent agreement in general, but with systematic effects that can be understood as due to finite resolution in the folded images and the variation of parameters along the line of sight, which are ignored in the homogeneous source model. We discuss the use of such 2D parameter maps within a larger framework of 3D modeling, and the prospects for applying these methods to data from a new generation of multifrequency radio arrays now or soon to be available.
The brightness temperature of the radio free-free emission at millimeter range is an effective tool for characterizing the vertical structure of the solar chromosphere. In this paper, we report on the first single-dish observation of a sunspot at 85 and 115 GHz with sufficient spatial resolution for resolving the sunspot umbra using the Nobeyama 45 m telescope. We used radio attenuation material, i.e. a solar filter, to prevent the saturation of the receivers. Considering the contamination from the plage by the side-lobes, we found that the brightness temperature of the umbra should be lower than that of the quiet region. This result is inconsistent with the preexisting atmospheric models. We also found that the brightness temperature distribution at millimeter range strongly corresponds to the ultraviolet (UV) continuum emission at 1700 {AA}, especially at the quiet region.
The tropical wisdom that when it is hot and dense we can expect rain might also apply to the Sun. Indeed, observations and numerical simulations have shown that strong heating at footpoints of loops, as is the case for active regions, puts their coronae out of thermal equilibrium, which can lead to a phenomenon known as catastrophic cooling. Following local pressure loss in the corona, hot plasma locally condenses in these loops and dramatically cools down to chromospheric temperatures. These blobs become bright in H-alpha and Ca II H in time scales of minutes, and their dynamics seem to be subject more to internal pressure changes in the loop rather than to gravity. They thus become trackers of the magnetic field, which results in the spectacular coronal rain that is observed falling down coronal loops. In this work we report on high resolution observations of coronal rain with the Solar Optical Telescope (SOT) on Hinode and CRISP at the Swedish Solar Telescope (SST). A statistical study is performed in which properties such as velocities and accelerations of coronal rain are derived. We show how this phenomenon can constitute a diagnostic tool for the internal physical conditions inside loops. Furthermore, we analyze transverse oscillations of strand-like condensations composing coronal rain falling in a loop, and discuss the possible nature of the wave. This points to the important role that coronal rain can play in the fields of coronal heating and coronal seismology.
We present a precise and complete procedure for processing spectral data observed by the 1-meter New Vacuum Solar Telescope (NVST). The procedure is suitable for both the sit-and-stare and raster-scan spectra. In this work, the geometric distortions of the spectra are firstly corrected for subsequent processes. Then, considering the temporal changes and the remnants of spectral lines in the flat-field, the original flat-field matrix is split into four independent components for ensuring a high precision flat-fielding correction, consisting of the continuum gradient matrix, slit non-uniform matrix, CCD dust matrix, and interference fringe matrix. Subsequently, the spectral line drifts and intensity fluctuations of the science data are further corrected. After precise reduction with this procedure, the measuring accuracies of the Doppler velocities for different spectral lines and of the oscillation curves of the chromosphere and photosphere are measured. The results show that the highest measuring accuracy of the Doppler velocity is within 100 ms-1, which indicates that the characteristics of the photosphere and chromosphere can be studied co-spatially and co-temporally with the reduced spectra of NVST.
We present results from the commissioning and early science programs of FIDEOS, the new high-resolution echelle spectrograph developed at the Centre of Astro Engineering of Pontificia Universidad Catolica de Chile, and recently installed at the ESO 1m telescope of La Silla. The instrument provides spectral resolution R = 43,000 in the visible spectral range 420-800 nm, reaching a limiting magnitude of 11 in V band. Precision in the measurement of radial velocity is guaranteed by light feeding with an octagonal optical fibre, suitable mechanical isolation, thermal stabilisation, and simultaneous wavelength calibration. Currently the instrument reaches radial velocity stability of = 8 m/s over several consecutive nights of observation.
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