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Measurement of magnetic field in this layer is challenging both from point of view of observations and interpretation of the data. We present in this work about spectropolarimetric observations of a pore, simultaneously in Ca ii (CaIR) at 854.2 nm (CaIR) and H α (656.28 nm). The observed region includes a small scale energetic event (SSEE) taking place in the region between the pore and the region which show opposite polarity to that of pore at the photosphere. The energetic event appears to be a progressive reconnection event as shown by the time evolution of the intensity profiles. Closer examination of the intensity profiles from the downflow regions suggest that the height of formation of CaIR is higher than that of Hi α, contrary to the current understanding about their height of formation. Preliminary results on the inversion of Stokes-I and V profiles of CaIR are also presented. [ABSTRACT FROM AUTHOR]

Analysis of spectropolarimetric observations of two circular sunspots located close to disk centre in H α (6562.8 Å) and Fe i (6569.22 Å) is presented in this paper. The corresponding active region numbers are NOAA 10940 and NOAA 10941 referred to as AR1 and AR2, respectively. The vector magnetic field at the photosphere is derived through inversion of Stokes profiles of Fe i under Milne–Eddington atmospheric model. The chromospheric vector magnetic field is derived from H α Stokes profiles under weak-field approximation. Azimuthally averaged magnetic field as a function of radial distance from the centre of sunspot at the photosphere and chromosphere are studied. At the photosphere, the radial variation shows a well known behaviour that the total field and the line-of-sight (LOS) component monotonically decrease from centre to the edge of the sunspot and the transverse component initially increases, reaches a maximum close to half the sunspot radius and then decreases. LOS and the transverse components become equal close to half the sunspot radius consistent with the earlier findings. At the chromosphere, all the components of the magnetic field decrease with the sunspot radius. However, the LOS component decreases monotonically whereas the transverse component decreases monotonically up to about 0.6 times the sunspot radius after which it reaches a constant value. Azimuthally averaged magnetic field gradient from photosphere to chromosphere is also presented here. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Ti doped CdO is firstly reported for electrochemical non-enzymatic H 2 O 2 sensor applications. • Fabricated nanostructured thin films were directly exploited as working electrodes toward the detection of harmful H 2 O 2 gas. • Ti: CdO film exhibits pronounced electrocatalytic activity for the reduction of H 2 O 2 when compared to pure CdO. Abstract A new material, Ti doped CdO (Ti: CdO) semiconductor, is firstly reported by this work for electrochemical non-enzymatic hydrogen peroxide (H 2 O 2) sensor applications which was deposited by a simple, versatile and cost-effective chemical spray pyrolysis method on indium doped tin oxide (ITO) substrate. In the basic studies, first, the withstanding of cubic crystal phase along with worthy crystalline nature is discerned on CdO film after Ti doping, here only the preferentially orientated (200) diffraction plane shifted to (111). Subsequently, the irregular spherically shaped CdO nanoparticles (NPs) morphology changed as nearly uniform size with Ti doping is noticed under thermal pyrolytic decomposition process. The existence of Ti atoms in Ti: CdO film is authentically identified and confirmed using EDX and XPS studies respectively. The absorption and emission properties of CdO and Ti: CdO films are studied and confirmed their narrow band gap nature. Importantly, the Ti: CdO film shows pronounced electrocatalytic activity for the reduction of hydrogen peroxide (H 2 O 2) than pure CdO. Hence, the non-enzymatic electrochemical sensing of Ti: CdO electrode shows a lower detection limit, broad linear range, rapid response time and high sensitivity toward H 2 O 2 detection. This result will boost exploring a new opportunity for the deposition of other metal oxides and semiconductors by using a simple chemical spray pyrolysis method for detection of non-enzymatic H 2 O 2 sensor applications. [ABSTRACT FROM AUTHOR]

Abstract The growth of one-dimensional (1D) zinc oxide (ZnO) nano/micro rod arrays (N/MRAs) thin films by using a facile, reproducible and cost effective method could be triggering nano/micro morphological structure based devices in the semiconductor technology. Therefore, in this work, the chemical bath deposition (CBD) and hydrothermal (HTM) methods have been used for growing 1D ZnO N/MRAs thin films on ZnO seeded glass substrates. Subsequently, we have studied their fundamental physicochemical properties for determining and distinguishing the growth characteristic of deposition methods. The formation of hexagonal wurtzite crystal structure in the CBD and HTM grown 1D ZnO N/MRAs films has been confirmed by XRD and μ-Raman studies. The intensity of the preferentially oriented diffraction peaks and electron microscopic images depict that the crystallinity, number density and aspect ratio of the 1D ZnO N/MRAs are strongly dependent on level of degree of supersaturation and its changes under deposition method is highlighted here. Further, the size, shape and single crystalline nature of the N/MRAs are strongly confirmed by TEM images and SAED patterns respectively. The photons absorption in the UV region ratify the wide bandgap characteristic of ZnO. Eventually, the presence of localized electron trapping and/or relaxing states in ZnO nuclei layer and in 1D ZnO N/MRAs films are determined from photoluminescence spectra. Graphical abstract Image 1 Highlights • ZnO nano/micro rod arrays thin films were grown by chemical bath deposition and hydrothermal on spray deposited ZnO seeded substrates. • The number density, aspect ratio of the NRs and MRs are strongly depends on the synthetic methods with respect to changing level of degree of supersaturation. • The optical band gap value is found to be 3.18 and 3.15 eV for CBD and hydrothermal grown film respectively. [ABSTRACT FROM AUTHOR]

Abstract Quaternary Cu 2 ZnSnS 4 (CZTS) thin films with different S/(Cu+Zn+Sn) molar ratio have been deposited by homemade chemical spray pyrolysis unit. Secondary phase formation in CZTS thin films with respect to various S/(Cu+Zn+Sn) molar ratio was investigated. XRD and micro Raman results revealed that CZTS thin films belongs to kesterite crystal structure with a preferred orientation along (1 1 2) plane. Films deposited at x = 2, 1.72, 1.33 contain binary and ternary phases in addition to CZTS. High purity single phase CZTS was obtained at x = 0.80. The surface morphology of the films is found to be smooth. The optical absorption spectra showed that the absorption coefficient of the CZTS thin films is larger than 104 cm−1 in the visible region and the optical band gap varies from 2.05 eV to 1.45 eV. CZTS thin films were used as a photocatalyst to examine the effect of secondary phases in the decolorization of the Rhodamine B (RhB) dye under visible light. It was found that the presence of secondary phase significantly affects the photocatalytic performance of CZTS thin films. [ABSTRACT FROM AUTHOR]

The pure and Cu-doped CdO thin films with various doping concentrations (0.5 to 2 wt%) were deposited on amorphous glass substrates by a chemical spray pyrolysis technique for hydrogen gas sensor application. The crystallinity, morphology, optical and electrical properties of the CdO thin films were effectively modified by Cu doping. The CdO film exhibited a cubic crystal structure, which is retained after Cu doping with significant changes in the preferential orientation of the crystallographic plane. The SEM and AFM images clearly revealed that the grain size and roughness of the CdO film changed with the Cu doping level. The expected element compositions were initially identified by EDAX and then authentically confirmed by XPS to determine its binding energy states. The optical transmittance and near band edge emission (NBE) bands of the CdO film were significantly decreased by Cu doping level. The minimum resistivity (2.01 × 10−3Ω cm) as well as good mobility (19.5 cm2 V−1 s−1) and maximum carrier concentration (1.98 × 1020 cm−3) were obtained for the 1 and 0.5 wt% Cu-doped CdO thin films. The Cu-doped CdO thin films exhibit better hydrogen gas sensing behaviour than that of pure CdO film. Finally, it is concluded that the maximum sensitivity is vividly achieved for the Cu-doped CdO thin film at 1 wt%. [ABSTRACT FROM AUTHOR]

Pristine and vanadium (V) doped CuInS 2 (CIS) thin films were grown on glass substrate using home-built chemical spray pyrolysis unit. The structural, morphological, optical and electrical properties of pristine and V doped CIS thin films have been systematically inspected. The scanning electron and atomic force microscopic (SEM and AFM) images show the well-interconnected CIS nanoparticles changed to nanorods like morphology with respect to V doping level and also the number density of the nanorods increases with doping level. Furthermore, the formation of CIS nanoparticles and V doped CIS nanorods are authentically confirmed by the transmission electron microscopic (TEM) images. Both pristine and V doped CIS thin films exhibit the body centered tetragonal crystal structure along with polycrystalline nature which is characterized using X-ray diffraction (XRD) and selected area electron diffraction (SAED) patterns. The presence of dopant and host elements is confirmed by X-ray photoelectron and energy dispersive X-ray spectroscopic (XPS and EDX) analyses. The decreases of orbital energy gap values are observed using UV–Vis absorption spectra according to V doping level into the CIS lattice sites. A continuous suppression of defect related Cu-Au orderings are observed via Raman spectra as a function of V doping which also indicate the V doping significantly involved during deposition and improve the structural quality of the chalcopyrite CIS film. The electrical properties of CIS films transform enormously, switching from hole dominated (0.3782 S cm −1 ) p-type to electron dominated (27.16 S cm −1 ) n-type from 4 wt.% of V doping. It anticipates that this kind of self-assembled 1D CIS nanostructure will give huge interest to tune their physicochemical properties. [ABSTRACT FROM AUTHOR]

Transparent conducting cadmium oxide (CdO) and Fe (0.5, 1, 1.5 and 2 wt%) doped CdO thin films were deposited on glass substrate using facile chemical spray pyrolysis technique. The influence of Fe doping on the structural, morphological, optical and electrical properties of CdO thin films were systematically investigated using different characterization techniques such as X-ray diffraction (XRD), atomic force microscope (AFM), UV–vis transmittance and Hall measurement respectively. The XRD patterns clearly reveal the pure and Fe doped CdO films are polycrystalline nature along with cubic crystal structure. AFM images show the roughness of the CdO thin film decreases with respect to Fe doping concentration. The surface structure of the 1 wt% Fe doped CdO film was investigated by X-ray photoelectron spectroscopy (XPS). Optical transmittance of the CdO thin film decreases with increasing of Fe doping concentration. The optical band gap value of the CdO thin film gradually decreases from 2.61 to 2.18 eV with increasing Fe doping concentration. From Hall measurement, the minimum value of resistivity is obtained for (7.67×10 −4 Ω cm) 1 wt% of Fe doped CdO thin film. Finally, the ethanol sensor behaviour was observed using home-built sensor unit. The maximum ethanol gas response of 56.12% is observed for 1 wt% of Fe doped CdO thin films. This result suggests the Fe doped CdO is one of the promising material in sensor applications. [ABSTRACT FROM AUTHOR]

Aditya-L1 mission will carry two high-spectral resolution X-ray spectrometers to study solar flares. The soft X-ray spectrometer will cover the energy range from 1 to 30 keV, while the hard X-ray spectrometer will cover from 10 to 150 keV. These two instruments together will provide opportunities to study the plasma parameters during solar flares as well as acceleration mechanisms of energetic particles during the flaring time. [ABSTRACT FROM AUTHOR]

Undoped and Cu doped ZnO nano/microrod arrays (N/MRAs) films were grown on seeded glass substrates by chemical bath deposition technique. The structural and morphological characterizations (X-ray diffraction and scanning electron microscopy) clearly illustrate that the pure ZnO N/MRAs has well-defined hexagonal prismatic cross-sectional crystallographic facets and its crystallographic plane is more vertically grown along (002) crystallographic direction. The horizontally aligned (100) crystallographic plane is induced at 20% Cu doping level. Morphological structure of ZnO N/MRAs changed into nanoplates/microballs with increasing of Cu doping level. Hexagonal crystal structure of undoped and Cu doped ZnO N/MRAs is then confirmed by µ-Raman scattering. Energy band gaps are found to be decreased with Cu doping and reached a minimum of 3.04 eV when doping level is 20%. The defect related peak intensity is suppressed in ZnO N/MRAs by Cu doping. [ABSTRACT FROM AUTHOR]

Sparse CuInS 2 (CIS) microspheres were grown on CIS seed layer by a wet-chemical approach in which the nuclei layer was prepared by the chemical spray pyrolysis technique. Both layers have been found to be polycrystalline in nature and possess body centered tetragonal crystal structure. SEM and AFM analyses reveal that the CIS seed layer consists of high dense nanoparticles with the thickness of 0.97 μm and the average diameter of the as-grown microspheres is ∼2.1 μm. CIS microspheres may degrade the Cu–Au phase and improve the chalcopyrite phase in CIS film. The electrical properties of prepared films change tremendously, switching from low conductive (0.378 S cm −1 ) hole dominated P-type (CIS seed layer) to high conductive (7.324 S cm −1 ) electron dominated N-type (CIS microspheres). The results demonstrated that CIS microspheres exhibited good morphological and electrical properties and might have potential applications in photovoltaic technology. [ABSTRACT FROM AUTHOR]

In this study, the modification induced by the variation of Cadmium (Cd) doping rate on the structural, optical, morphological and electrical properties of prepared CuInS 2 (CIS) thin films have been investigated. Pristine and Cd doped CIS films have found to be polycrystalline in nature and possess body centered tetragonal crystal structure. The decrease of band gap has been observed with Cd doping into the host films. The Raman spectra reveal a continuous suppression of defect related Cu–Au orderings by increasing the concentration of the dopant ion, which improves the structural quality of the chalcopyrite phase in CIS film. The electrical properties of as-grown CIS films change tremendously, switching from low conductive (0.3782 S cm −1 ) hole dominated p-type to high conductive (23.94 S cm −1 ) electron dominated n-type. By considering all the factors, we report that Cd is the judicious choice for use as donor dopant to fabricate CIS based solar cells. [ABSTRACT FROM AUTHOR]

A new approach has been employed to grow large size and high number density rutile TiO2 nanorods (NRs) by low cost chemical methods. Nuclei layers of low (~30 nm) and high (~150 nm) thickness have been optimized on glass substrates for growing NRs using spin coating and chemical spray pyrolysis methods respectively. The scanning electron and atomic force microscopic images clearly show that randomly aligned, large size, exotic NRs have grown on low thickness seed layers at a high temperature (180 °C), and that interconnected, NRs with good number density have grown on high thickness seed layers at a low temperature (120 °C) via hydrothermal synthesis. The structural studies clearly reveal that the as-grown NRs have tetragonal rutile structures with different anisotropic crystallographic plane growth along the c-axis. The preferentially oriented (110) Bragg reflection in the large size NRs and (101) Bragg reflection in the number dense NRs illustrate that the Ti atoms are positioned in the middle of the atomic layer and stimulate randomly standing NRs along the direction of stacking. The growth orientation and single crystalline nature of the NRs are confirmed by high resolution transmission electron microscopy and µ-Raman scattering. The absorbance value and the shift in the UV-vis energy region of the TiO2 NRs are strongly dependent on the number density and/or size of the NRs. The crystal defects of the prepared rutile TiO2 NRs are analyzed using photoluminescence spectra. Our results show that the thickness of the seed layer and the growth temperature play a pivotal role in determining the two anisotropic crystallographic plane growths of rutile TiO2 NRs. [ABSTRACT FROM AUTHOR]

Transparent and conducting cadmium oxide (CdO) and manganese doped CdO (Mn: CdO) thin films were deposited using a low cost spray pyrolysis method on the glass substrate at 300 °C. For Mn doping, various concentrations of manganese acetate (1–3 wt%) was used in the spraying precursor solution. The structural, electrical and optical properties of CdO and Mn: CdO films were investigated using X-ray diffraction (XRD), scanning electron microscope (SEM), atomic force microscope (AFM), UV–vis and Hall measurement. X-ray diffraction study reveals that the CdO and Mn: CdO films are possessing cubic crystal structures. SEM and AFM studies reveal that the grain size and roughness of the films are increased with increasing Mn doping concentration. Optical transmittance spectra of the CdO film decreases with increasing doping concentration of manganese. The optical band gap of the films decreases from 2.42 eV to 2.08 eV with increasing concentration of manganese. A minimum resistivity of 1.11×10 −3 Ω cm and maximum mobility of 20.77 cm 2 V −1 s −1 is achieved for 1 wt% of manganese doping. [ABSTRACT FROM AUTHOR]

Highlights: [•] Contact angle were carried out for the first time for CdO thin film. [•] Effect of concentration influences the growth orientation of the CdO thin films. [•] Concentrations of Cd ions modify the physical properties of CdO thin films. [•] High Transmittance (more than 90%) was observed for CdO thin film. [Copyright &y& Elsevier]

Abstract: Dense rutile TiO2 nanorods were grown on an anatase TiO2 seed layer by a wet-chemical approach in which the nuclei layer was prepared by the chemical spray pyrolysis technique. Structural, morphological, and optical properties of prepared samples were investigated using X-ray diffraction (XRD), micro-Raman, scanning electron microscopy (SEM), atomic force microscopy (AFM), UV–vis spectroscopy, and fluorescence spectroscopy. From XRD, a clear authentication that, the preferentially oriented (101) crystallographic planes indicate that the rutile TiO2 nanorods are standing randomly along the normal to the substrate surface. Anatase TiO2 seed layer and rutile nanorods structural phases are clearly confirmed by micro-Raman measurement. SEM and AFM studies reveal that the TiO2 seed layer consists of high density nanoparticles with the thickness of 0.15μm and the height of the as-grown nanorods is ~0.6μm. The band gap energy of the anatase TiO2 seed layer and rutile as-grown nanorods is calculated using UV–vis absorption spectra and the band gap values of seed layer and nanorods are 3.21eV and 2.95eV respectively. The crystal defects of prepared films are measured using photoluminescence spectra. [Copyright &y& Elsevier]

Highlights: [•] Liquid Crystal Variable Retarders were characterized for operation. [•] Multi-slit spectrograph was calibrated for spectral resolution of 18mÅ. [•] Polarimeter package and CCD detector integrated using LabVIEW. [•] Linear polarization was successfully measured with multi slit spectropolarimeter. [ABSTRACT FROM AUTHOR]

Calibration and characterization of a dual-beam polarimeter installed at Kodaikanal Tower Telescope (KTT) for spectropolarimetric observations are presented in this paper. It was found that a slit width of 48 μ is optimum for the spectrograph setup at KTT and corresponding spectral resolution is 32.47 mÅ. It was demonstrated that the precision in polarization measurement can be achieved better than 0.1% by increasing the exposure time. However, the polarimetric calibration accuracy is limited to 0.35 % for Stokes Q and U parameters and 0.2 % for Stokes V parameter, mainly due to the uncertainty in the retardanee of the calibration retarder. A comparison of the magnetic field measurement between the Solar Optical Telescope (SOT) onboard Hinode and KTT for an active region was made and a good match was found after spatial smearing of Hinode/SOT measurements by 5.12″. [ABSTRACT FROM AUTHOR]

Over the last few years, several interesting observations were obtained with the help of solar Adaptive Optics (AO). In this paper, few observations made using the solar AO are enlightened and briefly discussed. A list of disadvantages with the current AO system are presented. With telescopes larger than 1.5m expected during the next decade, there is a need to develop the existing AO technologies for large aperture telescopes. Some aspects of this development are highlighted. Finally, the recent AO developments in India are also presented. [ABSTRACT FROM AUTHOR]

High spatial resolution spectro-polarimetric observation of a decaying spot was observed with the Diffraction Limited Spectro-Polarimeter. The spatial resolution achieved was close to the diffraction limit (0." 18) of the Dunn Solar Telescope. The fine scales present inside the decaying active region as well as surrounding areas were studied. Two interesting phenomenon observed are: (i) Canopy like structures are likely to be present in the umbral dots as well as in the light bridges providing evidence for field-free intrusion, (ii) There are opposite polarity loops present outside of the spot and some of them connects to the main spot and the surrounding magnetic features. [ABSTRACT FROM AUTHOR]

Snapshot spectroscopic imagers/instruments (SSI) are a class of spectroscopic instruments that are capable of acquiring spectral information of a given field of view in a single frame. Standard spectroscopic instruments like a grating-based spectrograph or a Fabry-Pérot-based spectrograph obtain two dimensional data of 2D space or 1D space and 1D wavelength. But SSIs have three dimensional data of 2D space and wavelength embedded in two dimensional detector/image plane. So standard data reduction techniques are not applicable. Lenslet array spectroscope is a novel SSI which images the object on to a hybrid spatio-spectral image plane. A procedure to extract the spatial and spectral information of the field of view from this hyperplane is presented. We demonstrate the snapshot capabilities of this instrument to study dynamic activities of the Sun as inferred from two measurements: (i) Evershed flow in a sunspot in NOAA 12526 at Fe I 6301.5 Å and (ii) oscillations in a quiescent prominence at Hα 6562.8 Å. This instrument can be used for large or small scale structures, making it efficient for studying a wide range of dynamic activities like helioseismology, Moreton waves, prominence oscillation etc. [ABSTRACT FROM AUTHOR]

Aditya-L1 is India's first observatory-class solar space mission to study the Sun from the Lagrange L1 point. The Solar Ultra-Violet Imaging Telescope (SUIT) is one of the payloads onboard Aditya-L1. SUIT is an off-axis Ritchey–Chrétien (RC) telescope, which images the Sun onto a 4k×4k CCD covering a field-of-view of 1.5 R⊙ with a plate scale of 0.7 ″ pixel−1. One of the primary objectives of SUIT is to study the early evolution of solar flares with high temporal cadence in the near-UV wavelengths (200 – 400 nm). The SUIT onboard intelligence was developed to achieve this objective. The complete intelligence algorithm is divided into several sub-modules, each working on a specific aspect of intelligence. These are: the HEL1OS flare-trigger module: generates flare trigger using HEL1OS hard X-ray data, the flare-localization module: locates the flare on the SUIT full-disc images, the Region of Interest (RoI) tracking module: accounts for the shift in RoI coordinates caused by rotation of the Sun, auto-exposure control module: adjusts the exposure time depending upon the flare intensity for better contrast. In this article, these onboard-intelligence modules are explained in detail. The working principles of these modules are tested using available data from various existing missions and also using synthetic data, and the obtained results are presented. The modules are implemented in hardware using an Actel RTAX 2000S FPGA and are tested using a laboratory setup. From the testing, it is found that flares are successfully localized in a mean time of 40 seconds from the GOES soft X-ray catalog start time. Also, a temporal cadence of under three seconds for a single-filter flare RoI image is achieved. [ABSTRACT FROM AUTHOR]

This document is a correction notice for an article titled "The Solar Ultra-Violet Imaging Telescope (SUIT) Onboard Intelligence for Flare Observations" published in the journal Solar Physics. The correction addresses a spelling mistake in the name of one of the authors, Sreejith Padinhatteeri, and a typo in the affiliation of the Manipal Centre for Natural Sciences, Manipal Academy of Higher Education, India. The correction notice also includes a statement declaring no competing interests from the authors and a note from the publisher, Springer Nature, regarding jurisdictional claims and institutional affiliations. The authors of the original article are listed as Manoj Varma, Sreejith Padinhatteeri, Sakya Sinha, Anurag Tyagi, Mahesh Burse, Reena Yadav, Ghanshyam Kumar, Anamparambu Ramaprakash, Durgesh Tripathi, K. Sankarasubramanian, Krishnappa Nagaraju, Koushal Vadodariya, Srikar Tadepalli, Rushikesh Deogaonkar, Manjunath Olekar, Mohamed Azaruddin, and Amrita Unnikrishnan. [Extracted from the article]

This paper addresses some of the issues related to externally occulted solar coronagraph; vignetting and achievable resolution due to an external occulter. The analytical expression by Evans (J Opt Soc Am 38:1083-1085, ) is used to perform the initial calculations. An expression for the vignetting for a given external occulter and field angle is derived. The values obtained with the derived expression are verified with those obtained by ZEMAX an Optical design software. The degradation in angular resolution of the system due to vignetting is also presented and an empirical relation to calculate the normalized resolution for a given amount of vignetting is obtained. [ABSTRACT FROM AUTHOR]

Imaging systems based on a narrow-band tunable filter are used to obtain Doppler velocity maps of solar features. These velocity maps are created by taking the difference between the blue- and red-wing intensity images of a chosen spectral line. This method has the inherent assumption that these two images are obtained under identical conditions. With the dynamical nature of the solar features as well as the Earth’s atmosphere, systematic errors can be introduced in such measurements. In this paper, a quantitative estimate of the errors introduced due to variable seeing conditions for ground-based observations is simulated and compared with real observational data for identifying their reliability. It is shown, under such conditions, that there is a strong cross-talk from the total intensity to the velocity estimates. These spurious velocities are larger in magnitude for the umbral regions compared to the penumbra or quiet-Sun regions surrounding the sunspots. The variable seeing can induce spurious velocities up to about 1 km s. It is also shown that adaptive optics, in general, helps in minimising this effect. [ABSTRACT FROM AUTHOR]

An eight stage balanced modulation scheme for dual beam polarimetry is presented in this paper. The four Stokes parameters are weighted equally in all the eight stages of modulation resulting in total polarimetric efficiency of unity. The gain table error inherent in dual beam system is reduced by using the well known beam swapping technique. The wavelength defendant polarimetric efficiencies of Stokes parameters due to the chromatic nature of the waveplates are presented. The proposed modulation scheme produces better Stokes Q and V efficiencies for wavelengths larger than the design wavelength whereas Stokes U has better efficiency in the shorter wavelength region. Calibration of the polarimeter installed as a backend instrument of the Kodaikanal Tower Telescope is presented. It is found through computer simulation that a 14% sky transparency variation during calibration of the polarimeter can introduce &asymph; 1.8% uncertainty in the determination of its response matrix. [ABSTRACT FROM AUTHOR]

Elemental abundances in the solar corona are known to be different from those observed in the solar photosphere. The ratio of coronal to photospheric abundance shows a dependence on the first ionization potential (FIP) of the element. We estimate FIP bias from direct measurements of elemental abundances from soft X-ray spectra using data from multiple space missions covering a range of solar activity levels. This comprehensive analysis shows clear evidence for a decrease in FIP bias around the maximum intensity of the X-ray flare with coronal abundances briefly tending to photospheric values and a slow recovery as the flare decays. The departure from coronal abundances are larger for the low FIP elements Ca, Fe and Si than for S which have a mid FIP value. These changes in the degree of fractionation might provide inputs to model wave propagation through the chromosphere during flares. [ABSTRACT FROM AUTHOR]

For a more precise modeling of polarized spectral lines formed in extended and expanding stellar atmospheres, the solution of the radiative transfer equation for the Stokes vectors must be obtained in a spherical geometry rather than in a planar geometry. In this paper, we present the modern iterative techniques based on operator perturbation to solve the spherically symmetric polarized radiative transfer equation with velocity fields. We consider scattering on a two-level atom and account for partial frequency redistribution. An accurate numerical solution to such problems requires the use of spatial grids with higher resolution. Consequently, Jacobi-based methods lead to slower convergence rate. The convergence rate can be improved by a factor of 2 or more when fast iterative schemes based on Gauss–Seidel (GS) and successive overrelaxation (SOR) methods are used over the Jacobi-based method. Here we present the Jacobi, GS, and SOR iterative techniques for solving the abovementioned problem, and discuss their convergence behavior. [ABSTRACT FROM AUTHOR]

Highlights • Highly transparent and conducting ZnO thin films have been optimized by Al doping. • Prepared films exhibit good optical transmittance ∼90–95% in the visible energies. • High conductivity (0.26 mho cm−1) and low resistivity (3.8 Ω cm) has been found in 2 wt% AZO film. • Solar cell configuration with SLG/Mo/CuInS 2 /CdS/iZnO/2 wt% AZO/Ag is delivered, 2.20% PCE. • This is superior to all other cells and especially 53% higher than that of the pristine ZnO. Abstract ZnO thin film with flake-like surface morphology has been optimized by Al doping via the home-built chemical spray pyrolysis technique at substrate temperature 250 °C. Then, its performance as an anti-reflecting as well as highly transparent and conducting window layer in CuInS 2 based solid-state solar cell is explored here. The solid-state properties of the pristine and Al-doped ZnO (AZO) thin films have been studied to determine its potential for use in photovoltaic applications. First, it substantiates that the Zn, O and Al atoms are mainly involved for the growth of hexagonal wurtzite crystal structure by EDAX, XPS and XRD studies. All the films exhibit good optical transmittance nearly ∼90–95% in the visible energy region. Further, the 2 wt% AZO film shows low reflection loss in the same region. The decreased electron forbidden gap size is noticed in Al doped ZnO as compared to pure ZnO film. The good electrical parameters i.e., high conductivity (0.26 mho cm−1) and low resistivity (3.8 Ω cm) are found in the 2 wt% AZO film. Wettability test confirms the 2 wt% AZO flake-like surface morphology exhibited hydrophobic nature. Eventually, the 2 wt% Al-doped ZnO flake-like morphology thin film utilized as a window layer in CuInS 2 based solid-state solar cell which exhibits a pronounced photocurrent density result in 2.20% power conversion efficiency (PCE) is achieved. This efficiency is superior to all others and 53% higher than that of pristine ZnO window layer based photovoltaic cell. [ABSTRACT FROM AUTHOR]

Context. Some post-merger galaxies are known to undergo a starburst phase that quickly depletes the gas reservoir and turns it into a red-sequence galaxy, though the details are still unclear. Aims. Here we explore the pattern of recent star formation in the central region of the post-merger galaxy NGC7252 using highresolution ultraviolet (UV) images from the UVIT on ASTROSAT. Methods. The UVIT images with 1.2 and 1.4 arcsec resolution in the FUV and NUV are used to construct a FUV-NUV colour map of the central region. Results. The FUV-NUV pixel colour map for this canonical post-merger galaxy reveals a blue circumnuclear ring of diameter ~1000 (3.2 kpc) with bluer patches located over the ring. Based on a comparison to single stellar population models, we show that the ring is comprised of stellar populations with ages ≲300 Myr, with embedded star-forming clumps of younger age (≲150Myr). Conclusions. The suppressed star formation in the central region, along with the recent finding of a large amount of ionised gas, leads us to speculate that this ring may be connected to past feedback from a central super-massive black hole that has ionised the hydrogen gas in the central ~400 ~1:3 kpc. [ABSTRACT FROM AUTHOR]

The National Large Solar Telescope (NLST) aims primarily to carry out observations of the solar atmosphere with high spatial, spectral and temporal resolution. A comprehensive site characterization programme, that commenced in 2007, has identified an excellent site in the Ladakh region at the Pangong lake, India. With an innovative optical design, NLST is an on-axis Gregorian telescope with a low number of optical elements to reduce the number of reflections and yield a high throughput with low polarization. In addition, it uses high-order adaptive optics to produce close to diffraction limited performance. To control atmospheric and thermal perturbations of the observations, the telescope will function with a fully open dome, to achieve its full potential atop a 25 m tower. The post-focus instruments include broadband and tuneable Fabry-Perot narrow band imaging instruments and a high-resolution spectropolarimeter. [ABSTRACT FROM AUTHOR]

The performance of the ultraviolet telescope (UVIT) on-board AstroSat is reported. The performance in orbit is also compared with estimates made from the calibrations done on the ground. The sensitivity is found to be within $$\sim $$ 15% of the estimates, and the spatial resolution in the NUV is found to exceed significantly the design value of $$1.8^{\prime \prime }$$ and it is marginally better in the FUV. Images obtained from UVIT are presented to illustrate the details revealed by the high spatial resolution. The potential of multi-band observations in the ultraviolet with high spatial resolution is illustrated by some results. [ABSTRACT FROM AUTHOR]

The development of a spectrometer is being carried out in the Near-Infrared (NIR) wavelength range of 1.0-1.7 μm using an Acousto-Optic Tunable Filter (AOTF). The AOTF is based on Tellurium-di-oxide (TeO) crystal that acts as a dispersing medium and is driven by an external Radio Frequency (RF) signal. The characterization of AOTF is based on the wavelength-tuning frequency relation, spectral bandwidth as a function of wavelength through AOTF Transfer Function (Sinc), their dependence on the angular aperture and the peak diffraction efficiency of the AOTF. To demonstrate the full scanning capability of the AOTF in the wavelength range of 1.0-1.7 μm, Argon (Ar) and Krypton (Kr) line sources are used. The overall functionality of the spectrometer using the wavelength selection capability of AOTF is demonstrated by scanning the RF in the NIR band to detect water vapour absorption signatures in the Earth's atmosphere. This spectrometer is being designed for future interplanetary missions of ISRO with an aim to study the atmospheres of planets such as Mars or Venus. [ABSTRACT FROM AUTHOR]

The X-ray Solar Monitor (XSM) on the Indian lunar mission Chandrayaan-1 was flown to complement lunar elemental abundance studies by the X-ray fluorescence experiment C1XS. XSM measured the ≈ 1.8 - 20 keV solar X-ray spectrum during its nine months of operation in lunar orbit. The soft X-ray spectra can be used to estimate absolute coronal abundances using intensities of emission-line complexes and the plasma temperature derived from the continuum. The best estimates are obtained from the brightest flare observed by XSM: a C2.8-class flare. The well-known first-ionization potential (FIP) effect is observed; abundances are enhanced for the low-FIP elements Fe, Ca, and Si, while the intermediate-FIP element S shows values close to the photospheric abundance. The derived coronal abundances show a quasi-mass-dependent pattern of fractionation. [ABSTRACT FROM AUTHOR]

Observations of the transit of Venus were made from the Kodaikanal Observatory on 2012 June 06 in Ca-K wavelengths. Only half of the event was visible from India. We utilized this unique opportunity to compute the contribution of the scattered light within the Twin Telescope optics at Kodaikanal. The instrumental and atmospheric scattered light are derived from the model point spread function which is a combination of four Gaussians with different widths and weights. The restoration procedure has significantly improved the rms contrast of the images. The rms contrast of the stray light corrected images are almost two fold larger than that those of the uncorrected images. The derived network element sizes matches well with previous observations. [ABSTRACT FROM AUTHOR]

The Helioseismic and Magnetic Imager (HMI) instrument onboard the Solar Dynamics Observatory produces line-of-sight (LOS) observables (Doppler velocity, magnetic-field strength, Fe i line width, line depth, and continuum intensity) as well as vector magnetic-field maps at the solar surface. The accuracy of LOS observables is dependent on the algorithm used to translate a sequence of HMI filtergrams into the corresponding observables. Using one hour of high-cadence imaging spectropolarimetric observations of a sunspot in the Fe i line at 6173 Å through the Interferometric Bidimensional Spectrometer installed at the Dunn Solar Telescope, and the Milne-Eddington inversion of the corresponding Stokes vectors, we test the accuracy of the observables algorithm currently implemented in the HMI data-analysis pipeline: the MDI-like algorithm. In an attempt to improve the accuracy of HMI observables, we also compare this algorithm to others that may be implemented in the future: a least-squares fit with a Gaussian profile, a least-squares fit with a Voigt profile, and the use of second Fourier coefficients in the MDI-like algorithm. [ABSTRACT FROM AUTHOR]

The outer atmosphere of the sun - called the corona - has been observed during total solar eclipse for short periods (typically < 6 min), from as early as the eighteenth century. In the recent past, space-based instruments have permitted us to study the corona uninterruptedly. In spite of these developments, the dynamic corona and its high temperature (1-2 million K) are yet to be fully understood. It is conjectured that their dynamic nature and associated energetic events are possible reasons behind the high temperature. In order to study these in detail, a visible emission line space solar coronagraph is being proposed as a payload under the small-satellite programme of the Indian Space Research Organisation. The satellite is named as Aditya-1 and the scientific objectives of this payload are to study: (i) the existence of intensity oscillations for the study of wavedriven coronal heating; (ii) the dynamics and formation of coronal loops and temperature structure of the coronal features; (iii) the origin, cause and acceleration of coronal mass ejections (CMEs) and other solar active features, and (iv) coronal magnetic field topology and three-dimensional structures of CMEs using polarization information. The uniqueness of this payload compared to previously flown space instruments is as follows: (a) observations in the visible wavelength closer to the disk (down to 1.05 solar radii); (b) high time cadence capability (better than two-images per second), and (c) simultaneous observations of at least two spectral windows all the time and three spectral windows for short durations. [ABSTRACT FROM AUTHOR]

The Chandrayaan-2 Large Area Soft X-ray Spectrometer (CLASS) onboard the Chandraayaan-2 spacecraft around the Moon, has been remotely measuring the lunar X-ray fluorescence spectra since September, 2019. The primary objective of the experiment is to provide global maps of O, Mg, Al, Si at a resolution of 12.5 km/pix and of Ca, Ti and Fe at localized regions during enhanced solar activity, using the lunar X-ray fluorescence measurements in the 0.5 to 10 KeV range. CLASS is an array of swept charge devices (SCDs), a variant of X ray Charge Coupled Devices (CCDs) that provide good spectral resolution and large area. The quality of X-ray measurements strongly depends on accuracy of its calibration techniques. In this work, the results from the pre-launch calibration of the instrument that combines experimental measurements and simulations are described. The spectral redistribution function of the swept charge device is simulated using an augmented version of a previously developed charge transport model (Athiray et al., 2015). Response matrices built from these models are verified with in-flight data. We study the background in SCDs arising from particles in the lunar orbit over many months and identify the sources. We demonstrate the in-flight performance of the instrument that enables generation of direct elemental maps. Elemental abundances for a region in the farside highland and in the nearside western mare are derived demonstrating the method and the instrument capability of deriving the elemental abundances at different spatial scales and at different solar activity levels. • An end-to-end science data calibration is developed for the X-ray fluorescence spectrometer, CLASS onboard Chandrayaan-2. • In-flight performance of the X ray spectrometer and capabilities are evaluated. • Calibrated elemental abundances from a far side highland and mare regions are presented. [ABSTRACT FROM AUTHOR]

The study of polarized sunlight scattered from planetary atmospheres provides diagnostic tools that can help explore the possible composition and size distribution of clouds and aerosol particles. Previous studies have shown the potential of this technique in studying Water clouds on Earth and in the discovery of Sulphuric Acid clouds on Venus. The atmosphere of Mars is unique as it hosts three different types of aerosols: water (H 2 O) ice, carbon dioxide (CO 2) ice and dust. We considered scenarios analogous to Martian conditions and calculated the single and multiple scattering polarization for Martian dust, water ice and carbon dioxide ice with the help of a Radiative Transfer algorithm for Nadir and Limb spacecraft observation positions. The polarization features (-Q/I) of Mars atmosphere have low amplitude and have been found to be within the range of ±0.1 in the Nadir/Limb geometry for the spherical, spheroidal and cylindrical shapes considered here. We study its dependence upon the observation geometry, shape, size and composition of the scatterer. Future spacecraft studies of microphysical properties of dust and clouds through polarization will reveal the nature of condensation processes active in the Martian atmosphere. • A detailed theoretical study of polarization signatures of Mars atmosphere. • Consideration of various size distributions, shapes and atmospheric configurations (like dust or clouds). • Mars atmospheric polarization (-Q/I) is found to be constrained within +0.1 to −0.1 in near infrared for various observation geometries and shapes of the dust and clouds. • Non-spherical particle shapes (more likely for solid aerosols of Mars) offering large polarization features at around 90° scattering angles, which is missed by Earth based observations, can be effectively probed by spacecraft observation. • These predictions will help future exploration of Mars atmosphere for better understanding of dust and clouds. [ABSTRACT FROM AUTHOR]

Cadmium oxide (CdO) thin film was optimized on glass substrate at 250 °C using a chemical spray pyrolysis (CSP) technique followed by Al atoms doped into it with various wt% in order to study its influence on structural, electrical, optical, morphological and gas adsorption properties of the CdO thin films. All the films are deposited in polycrystalline cubic crystal phase is confirmed by XRD. The 90% of the visible as well as near infrared (650–850 nm) region energies is transmitted in pure and Al doped CdO films. Smooth surfaces and spherical shaped nanoparticles morphologies are conspicuous in CdO films after Al doping. The prepared CdO film is of n-type conductivity with having mobility of 64.4 cm2 V-1s-1 and carrier concentrations of 2.2 ×1020 cm-3. Importantly, the mobility increases and resistivity decreases is observed on CdO film as for Al doping level. After procuring some interesting physicochemical properties in CdO films by Al doping, trimethylamine (TMA) gas sensing analysis has been scrutinized using a simple and cost effective route. Finally, it is found that low resistive and high mobility of 1.5% Al doped CdO film exhibited pronounced sensitivity, 32.12%, is due to its higher specific surface area and as well as existence of more defective sites. [ABSTRACT FROM AUTHOR]

Solar flares and coronal mass ejections (CMEs) are two very important active events from Sun. Inspite of several theoretical and statistical analyses, the relation between solar flares and CMEs is so far not well established, and strong opinions and arguments still continue. Statistical approaches use a lot of data available from many measurements by space and ground instruments. They try to map the measured parameters of one event to that of another event and try to establish the relation between them. Halo CMEs are a kind of special CMEs in the sense that they are directed towards Earth and hence can influence Earth's atmosphere. For a scientist interested in Sun-Earth interactions and the effect on Earth's atmosphere, study of Halo CMEs is extremely important. In this paper the relation between solar flares and Halo CMEs is studied. The data sets used are for the period from October 2006 to March 2017. For the first time, the Halo CMEs are categorized into four different groups based on the relative time of occurrence with respect to the flares and the relation between the flare and Halo CME parameters is studied. It is shown that: (a) there is a good correlation between certain flare parameters (like flare flux and peak intensity) and CME parameters (like kinetic energy, linear speed, and mass) especially when the Halo CME occurs during the flare; (b) For the same set of CMEs, the correlation is poor with flare duration; and (c) For CMEs before or after the flare, the correlation is lesser than the CMEs occurring during the flare. [ABSTRACT FROM AUTHOR]