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Spectropolarimetric Diagnostics at the Solar Photosphere near the Limb  [PDF]
L. Yelles Chaouche,S. K. Solanki,L. Rouppe van der Voort,M. van Noort
Physics , 2009,
Abstract: In the present work, we investigate the formation of Stokes profiles and spectro-polarimetric diagnostics in an active region plage near the limb. We use 3-D radiation-MHD simulations with unipolar fields of an average strength of 400 G, which is largely concentrated in flux tubes in which the field reaches typical kilo-Gauss values. We generate synthetic Stokes spectra by radiative transfer calculations, then we degrade the simulated Stokes signal to account for observational conditions. The synthetic data treated in this manner are compared with and found to roughly reproduce spectro-polarimetric high-resolution observations at Mu=0.39 obtained by the SOUP instrument with the Swedish 1-m Solar Telescope at the beginning of 2006.
The Chromospheric Telescope  [PDF]
C. Bethge,H. Peter,T. J. Kentischer,C. Halbgewachs,D. F. Elmore,C. Beck
Physics , 2011, DOI: 10.1051/0004-6361/201117456
Abstract: We introduce the Chromospheric Telescope (ChroTel) at the Observatorio del Teide in Izana on Tenerife as a new multi-wavelength imaging telescope for full-disk synoptic observations of the solar chromosphere. We describe the design of the instrument and summarize its performance during the first one and a half years of operation. We present a method to derive line-of-sight velocity maps of the full solar disk from filtergrams taken in and near the He I infrared line at 10830 \AA.
The Radiated Energy Budget of Chromospheric Plasma in a Major Solar Flare Deduced From Multi-Wavelength Observations  [PDF]
Ryan O. Milligan,Graham S. Kerr,Brian R. Dennis,Hugh S. Hudson,Lyndsay Fletcher,Joel C. Allred,Phillip C. Chamberlin,Jack Ireland,Mihalis Mathioudakis,Francis P. Keenan
Physics , 2014, DOI: 10.1088/0004-637X/793/2/70
Abstract: This paper presents measurements of the energy radiated by the lower solar atmosphere, at optical, UV, and EUV wavelengths, during an X-class solar flare (SOL2011-02-15T01:56) in response to an injection of energy assumed to be in the form of nonthermal electrons. Hard X-ray observations from RHESSI were used to track the evolution of the parameters of the nonthermal electron distribution to reveal the total power contained in flare accelerated electrons. By integrating over the duration of the impulsive phase, the total energy contained in the nonthermal electrons was found to be $>2\times10^{31}$ erg. The response of the lower solar atmosphere was measured in the free-bound EUV continua of H I (Lyman), He I, and He II, plus the emission lines of He II at 304\AA\ and H I (Ly$\alpha$) at 1216\AA\ by SDO/EVE, the UV continua at 1600\AA\ and 1700\AA\ by SDO/AIA, and the WL continuum at 4504\AA, 5550\AA, and 6684\AA, along with the Ca II H line at 3968\AA\ using Hinode/SOT. The summed energy detected by these instruments amounted to $\sim3\times10^{30}$ erg; about 15% of the total nonthermal energy. The Ly$\alpha$ line was found to dominate the measured radiative losses. Parameters of both the driving electron distribution and the resulting chromospheric response are presented in detail to encourage the numerical modelling of flare heating for this event, to determine the depth of the solar atmosphere at which these line and continuum processes originate, and the mechanism(s) responsible for their generation.
The Limb Brightening and its Relationship with the Millimeter-wave Cavity  [PDF]
Victor De la Luz,Miguel Chavez,Emanuele Bertone
Physics , 2014,
Abstract: Through a detailed theoretical analysis of the local emission at millimeter,sub-millimeter and infrared wavelength regimes (from \~ 10 GHz up to \~ 10 THz), we found that, associated with the temperature minimum, there is an optically thin cavity surrounded by two regions of high local emissivity. We call this structure the Chromospheric Solar Millimeter Cavity (CSMC). In order to search for traces of this cavity in the available radio observations on the solar limb, we have developed a robust method to associate the radiation at different heights with the observed brightness temperatures. We foresee that this approach will allow us to determine the relationship between the CSMC and the solar limb brightening.
Spectroscopy at the solar limb: I. Average off-limb profiles and Doppler shifts of Ca II H  [PDF]
C. Beck,R. Rezaei
Physics , 2011, DOI: 10.1051/0004-6361/201014976
Abstract: We present constraints on the structure of the chromosphere from observations of the Ca II H line profile near and off the solar limb. We obtained a data set of the Ca II H line in a field of view extending 20" across the limb. We analyzed the spectra for the properties of off-limb spectra. We used tracers of the Doppler shifts, such as the location of the absorption core, the ratio of the two emission peaks H2V and H2R, and intensity images at a fixed wavelength. The average off-limb profiles show a smooth variation with increasing limb distance. The line width increases up to a height of about 2 Mm above the limb. The profile shape is fairly symmetric with nearly identical H2V and H2R intensities; at a height of 5 Mm, it changes into a single Gaussian without emission peaks. We find that all off-limb spectra show large Doppler shifts that fluctuate on the smallest resolved spatial scales. The variation is more prominent in cuts parallel to the solar limb than on those perpendicular to it. As far as individual structures can be unequivocally identified at our spatial resolution, we find a specific relation between intensity enhancements and Doppler shifts: elongated brightenings are often flanked all along their extension by velocities in opposite directions. The average off-limb spectra of Ca II H present a good opportunity to test static chromospheric atmosphere models because they lack the photospheric contribution that is present in disk-center spectra. We suggest that the observed relation between intensity enhancements and Doppler shifts could be caused by waves propagating along the surfaces of flux tubes: an intrinsic twist of the flux tubes or a wave propagation inclined to the tube axis would cause a helical shape of the Doppler excursion, visible as opposite velocity at the sides of the flux tube.
A New Multi-wavelength Solar Telescope: Optical and Near-infrared Solar Eruption Tracer (ONSET)  [PDF]
C. Fang,P. F. Chen,Z. Li,M. D. Ding,Y. Dai,X. Y. Zhang,W. J. Mao,J. P. Zhang,T. Li,Y. J. Liang,H. T. Lu
Physics , 2013, DOI: 10.1088/1674-4527/13/12/011
Abstract: A new multi-wavelength solar telescope, Optical and Near-infrared Solar Eruption Tracer (ONSET) of Nanjing University, was constructed, being fabricated by Nanjing Institute of Astronomical Optics & Technology and run in cooperation with Yunnan Astronomical Observatory. ONSET is able to observe the Sun in three wavelength windows: He {\small I} 10830 \AA, H$\alpha$, and white-light at 3600 \AA and 4250 \AA, which are selected in order to obtain the dynamics in the corona, chromosphere, and the photosphere simultaneously. Full-disk or partial-disk solar images with a field of 10 arcmin at three wavelengths can be obtained nearly simultaneously. It is designed to trace solar eruptions with high spatial and temporal resolutions. This telescope was installed at a new solar observing site near Fuxian Lake in Yunnan Province, southwest China. The site is located at E102N24, with an altitude of 1722 m. The seeing is stable and of high quality. We give a brief description of the scientific objectives and the basic structure of the ONSET. Some preliminary results are also presented.
Solar Coronal Heating and Limb Effect  [PDF]
Yi-Jia Zheng
Physics , 2013,
Abstract: The quiet solar coronal heating problem and the observed center-to-limb wavelength variations of the solar lines (limb effect) can be explained. In this paper the quantitative calculations for these two phenomena are presented.
The solar chromosphere at high resolution with IBIS. IV. Dual-line evidence of heating in chromospheric network  [PDF]
G. Cauzzi,K. P. Reardon,R. J. Rutten,A. Tritschler,H. Uitenbroek
Physics , 2009, DOI: 10.1051/0004-6361/200811595
Abstract: The structure and energy balance of the solar chromosphere remain poorly known. We have used the imaging spectrometer IBIS at the Dunn Solar Telescope to obtain fast-cadence, multi-wavelength profile sampling of Halpha and Ca II 854.2 nm over a sizable two-dimensional field of view encompassing quiet-Sun network. We provide a first inventory of how the quiet chromosphere appears in these two lines by comparing basic profile measurements in the form of image displays, temporal-average displays, time slices, and pixel-by-pixel correlations. We find that the two lines can be markedly dissimilar in their rendering of the chromosphere, but that, nevertheless, both show evidence of chromospheric heating, particularly in and around network: Halpha in its core width, Ca II 854.2 in its brightness. We discuss venues for improved modeling.
Photometric properties of new solar H alpha commercial Fabry-Perot etalons. Application to the analysis of the chromospheric fringe  [PDF]
Cyril Bazin,Serge Koutchmy
Physics , 2012,
Abstract: We consider the use of the commercially available Fabry-Perot etalons (FP) for the imaging of the solar chromosphere in the H alpha line of HI. Three etalons of 40, 60 and 90 mm diameter were accurately analysed. At normal incidence the maximum transmission wavelength as well as the finesse were evaluated. Polynomial curves precisely fitting the transmitted central wavelength variations when using a quasi-parallel beam from a point-like source are presented. Further calibrations have been done with photometric accuracy using a laboratory set-up comprising i/ a 16 bits CCD camera; ii/ a Littrow spectrograph of a spectral power 110000 giving a linear dispersion of 0.0058 nm/pixel and iii/ an artificial Sun used as a light source and iv/ precisely adjustable in position optical components, including the F-P etalons. In addition, a precise laboratory wavelength calibration was performed using a low pressure deuterium 2D spectral lamp simultaneously illuminating the adjustable entrance slit using a splitter before. The variations of the FWHM of the spectral transmission variations as a function of the incidence angle of a parallel beam are also given for each etalon. Consequences resulting from the use of a low but significant aperture/ratio are tentatively discussed for the first time. An application to a precise photometric work of solar physics interest when using limb filtergrams is illustrated and discussed, with emphasis on the photometric accuracy resulting from the use of such etalons put before the entrance aperture of an imaging telescope. Monochromatic images of the solar chromosphere shell in the vicinity of the polar and equatorial limbs were made using a small telescope, in order to deduce the variation of the typical average thicknesses at poles and equator interpreted as a prolateness effect of the chromospheric shell observed during the last minimum of solar activity (2009).
Multi-wavelength spectroscopic observation of EUV jet in AR 10960  [PDF]
Y. Matsui,T. Yokoyama,N. Kitagawa,S. Imada
Physics , 2012, DOI: 10.1088/0004-637X/759/1/15
Abstract: We have studied the relationship between the velocity and temperature of a solar EUV jet. The highly accelerated jet occurred in the active region NOAA 10960 on 2007 June 5. Multi-wavelength spectral observations with EIS/Hinode allow us to investigate Doppler velocities at the wide temperature range. We analyzed the three-dimensional angle of the jet from the stereoscopic analysis with STEREO. Using this angle and Doppler velocity, we derived the true velocity of the jet. As a result, we found that the cool jet observed with \ion{He}{2} 256 \AA $\log_{10}T_e[\rm{K}] = 4.9$ is accelerated to around $220 \rm{km/s}$ which is over the upper limit of the chromospheric evaporation. The velocities observed with the other lines are under the upper limit of the chromospheric evaporation while most of the velocities of hot lines are higher than that of cool lines. We interpret that the chromospheric evaporation and magnetic acceleration occur simultaneously. A morphological interpretation of this event based on the reconnection model is given by utilizing the multi-instrumental observations.
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