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&

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

Electron impact polarization expected in solar EUV lines from flaring chromospheres/transition regions

We have evaluated lower bounds on the degree of impact Extreme Ultraviolet/Ultraviolet (EUV/UV) line polarization expected during solar flares. This polarization arises from collisional excitation by energetic electrons with non-Maxwellian velocity distributions. Linear polarization was observed in the S I 1437 A line by the Ultraviolet Spectrometer and Polarimeter/Solar Maximum Mission (UVSP/SMM) during a flare on 15 July 1980. An early interpretation suggested that impact excitation by electrons propagating through the steep temperature gradient of the flaring transition region/high chromosphere produced this polarization. Our calculations show that the observed polarization in this UV line cannot be due to this effect. We find instead that, in some flare models, the energetic electrons can produce an impact polarization of a few percent in EUV neutral helium lines (i.e., lambda lambda 522, 537, and 584 A)

Effects of ion magnetization on the Farley-Buneman instability in the solar chromosphere

Intense heating in the quiet-Sun chromosphere raises the temperature from 4000 to 6500 K but, despite decades of study, the underlying mechanism remains a mystery. This study continues to explore the possibility that the Farley–Buneman instability contributes to chromospheric heating. This instability occurs in weakly ionized collisional plasmas in which electrons are magnetized, but ions are not. A mixture of metal ions generate the plasma density in the coolest parts of the chromosphere; while some ions are weakly magnetized, others are demagnetized by neutral collisions. This paper incorporates the effects of multiple, arbitrarily magnetized species of ions to the theory of the Farley–Buneman instability and examines the ramifications on instability in the chromosphere. The inclusion of magnetized ions introduces new restrictions on the regions in which the instability can occur in the chromosphere—in fact, it confines the instability to the regions in which heating is observed. For a magnetic field of 30 G, the minimum ambient electric field capable of driving the instability is 13.5 V/m at the temperature minimum.This work was supported by NSF-AGS Postdoctoral Research Fellowship Award No. 1433536 and NSF/DOE grant No. PHY-1500439. The authors also acknowledge a recent contribution from William Longley. (1433536 - NSF-AGS Postdoctoral Research Fellowship Award; PHY-1500439 - NSF/DOE grant)First author draftPublished versio

Expansion of magnetic flux concentrations: a comparison of Hinode SOT d ata and models

Context: The expansion of network magnetic fields with height is a fundamental property of flux tube models. A rapid expansion is required to form a magnetic canopy. Aims: We characterize the observed expansion properties of magnetic network elements and compare them with the thin flux tube and sheet approximations, as well as with magnetoconvection simulations. Methods: We used data from the Hinode SOT NFI NaD1 channel and spectropolarimeter to study the appearance of magnetic flux concentrations seen in circular polarization as a function of position on the solar disk. We compared the observations with synthetic observables from models based on the thin flux tube approximation and magnetoconvection simulations with two different upper boundary conditions for the magnetic field (potential and vertical). Results: The observed circular polarization signal of magnetic flux concentrations changes from unipolar at disk center to bipolar near the limb, which implies an expanding magnetic field. The observed expansion agrees with expansion properties derived from the thin flux sheet and tube approximations. Magnetoconvection simulations with a potential field as the upper boundary condition for the magnetic field also produce bipolar features near the limb while a simulation with a vertical field boundary condition does not. Conclusions: The near-limb apparent bipolar magnetic features seen in high-resolution Hinode observations can be interpreted using a simple flux sheet or tube model. This lends further support to the idea that magnetic features with vastly varying sizes have similar relative expansion rates. The numerical simulations presented here are less useful in interpreting the expansion since the diagnostics we are interested in are strongly influenced by the choice of the upper boundary condition for the magnetic field in the purely photospheric simulations.Comment: accepted for publication in A&

The Relation between the Radial Temperature Profile in the Chromosphere and the Solar Spectrum at Centimeter, Millimeter, Sub-millimeter, and Infrared Wavelengths

Solar observations from millimeter to ultraviolet wavelengths show that there is a temperature minimum between photosphere and chromosphere. Analysis based on semi-empirical models locate this point at about 500 km over the photosphere. The consistency of these models has been tested by means of millimeter to infrared observations. In the present work, we show that variations of the theoretical radial temperature profile near the temperature minimum impacts the brightness temperature at centimeter, submillimeter, and infrared wavelengths, but the millimeter wavelength emission remains unchanged. We found a region between 500 and 1000 km over the photosphere that remains hidden to observations at the frequencies under study in this work.Comment: Accepted in Solar Physic

MODELO EXPERIMENTAL DE GLOMERULONEFRITIS MEMBRANOSA INDUCIDA CON ALBUMINA BOVINA

El objetivo del presente trabajo fue diseñar un modelo experimental de Glomerulonefritis Membranosa (GM) en ratas Wistar, inducida con Seroalbúmina Bovina (BSA), y validarlo mediante la determinación de parámetros bioquímicos, histológicos, ultraestructurales y detección de inmunocomplejos por inmunofluorescencia (IF). Los animales del grupo experimental fueron inmunizados por vía subcutánea, con dosis de 3 mg c/u de BSA/PBS con adyuvante de Freund. Se efectuaron diferentes esquemas de inmunización. Cuando el título de anticuerpos fue ≥1/2, comenzó la administración diaria de 2 mg, por vía endovenosa de BSA/PBS, durante 15 días. Se evaluó la funcionalidad renal por la proteinuria; después de la 5° semana, desde su aparición, se determinó: depuración (clearance) de creatinina, uremia, proteinemia y perfil lipídico. Los dos riñones se usaron para estudios histológicos, ultraestructurales y detección de inmunocomplejos por IF. Los resultados mostraron que la inmunización fue efectiva con 5 R E S U M E N inoculaciones c/15 días. En los animales nefróticos la proteinuria, depuración (clearance) de creatinina, proteinemia , uremia y el perfil lipídico presentaron alteraciones significativas (p<0.0001). Al microscopio óptico se observó hipercelularidad, engrosamiento difuso de las membranas basales de los capilares glomerulares y diferentes grados de atrofia, esclerosis e hialinización de los glomérulos. Por IF se detectó inmunocomplejos IgG en el 100 % de los glomérulos. Ultraestructuralmente, se observaron depósitos subepiteliales electrodensos en la membrana basal engrosada, compatibles con inmunocomplejos . Se encontraron alteraciones en la estructura de los podocitos. En conclusión, los estudios bioquímicos, estructurales y ultraestructurales permitieron inferir la inducción de un síndrome nefrótico experimental. Concluimos que el protocolo utilizado tiene validez para la inducción de una glomerulonefritis membranosa en ratas Wistar

Time-dependent hydrogen ionisation in the solar chromosphere. I: Methods and first results

An approximate method for solving the rate equations for the hydrogen populations was extended and implemented in the three-dimensional radiation (magneto-)hydrodynamics code CO5BOLD. The method is based on a model atom with six energy levels and fixed radiative rates. It has been tested extensively in one-dimensional simulations. The extended method has been used to create a three-dimensional model that extends from the upper convection zone to the chromosphere. The ionisation degree of hydrogen in our time-dependent simulation is comparable to the corresponding equilibrium value up to 500 km above optical depth unity. Above this height, the non-equilibrium ionisation degree is fairly constant over time and space, and tends to be at a value set by hot propagating shock waves. The hydrogen level populations and electron density are much more constant than the corresponding values for statistical equilibrium, too. In contrast, the equilibrium ionisation degree varies by more than 20 orders of magnitude between hot, shocked regions and cool, non-shocked regions. The simulation shows for the first time in 3D that the chromospheric hydrogen ionisation degree and electron density cannot be calculated in equilibrium. Our simulation can provide realistic values of those quantities for detailed radiative transfer computations.Comment: 8 pages, 7 figure

RF Characterisation of Laser Treated Copper Surfaces for the Mitigation of Electron Cloud in Accelerators

In accelerator beam chambers and RF waveguides, electron cloud and multipacting can be mitigated effectively by reducing the secondary electron yield (SEY). In recent years, it has been established that laser-engineered surface structuring is a very efficient method to create a copper surface with a SEY maximum close to or even below unity. Different laser pulse durations, from nanoseconds to picoseconds, can be used to change surface morphology. Conversely, the characteristics that minimise the SEY, such as the moderately deep grooves and the redeposited nanoparticles, might have unfavourable consequences, including increased RF surface resistance. In this study, we describe the techniques used to measure the surface resistance of laser-treated copper samples using an enhanced dielectric resonator with 12 cm diameter sample sizes operating in the GHz range. The quantification basis lies in a non-contact measurement of the high-frequency losses, focusing on understanding the variation of surface resistance levels depending on the specifics of the treatment and possible post-treatment cleaning procedures.</p