Design of Instrument Control Software for Solar Vector Magnetograph at Udaipur Solar Observatory

A magnetograph is an instrument which makes measurement of solar magnetic field by measuring Zeeman induced polarization in solar spectral lines. In a typical filter based magnetograph there are three main modules namely, polarimeter, narrow-band spectrometer (filter), and imager(CCD camera). For a successful operation of magnetograph it is essential that these modules work in synchronization with each other. Here, we describe the design of instrument control system implemented for the Solar Vector Magnetograph under development at Udaipur Solar Observatory. The control software is written in Visual Basic and exploits the Component Object Model (COM) components for a fast and flexible application development. The user can interact with the instrument modules through a Graphical User Interface (GUI) and can program the sequence of magnetograph operations. The integration of Interactive Data Language (IDL) ActiveX components in the interface provides a powerful tool for online visualization, analysis and processing of images.     

Imaging Spectropolarimeter for the Multi-Application Solar Telescope at Udaipur Solar Observatory: Characterization of Polarimeter and Preliminary Observations

The Multi-Application Solar Telescope (MAST) is a 50 cm off-axis Gregorian telescope that has recently become operational at the Udaipur Solar Observatory (USO). An imaging spectropolarimeter is being developed as one of the back-end instruments of MAST to gain a better understanding of the evolution and dynamics of solar magnetic and velocity fields. This system consists of a narrow-band filter and a polarimeter. The polarimeter includes a linear polarizer and two sets of liquid crystal variable retarders (LCVRs). The instrument is intended for simultaneous observations in the spectral lines 6173 Å and 8542 Å, which are formed in the photosphere and chromosphere, respectively. In this article, we present results from the characterization of the LCVRs for the spectral lines of interest and the response matrix of the polarimeter. We also present preliminary observations of an active region obtained using the spectropolarimeter. For verification purposes, we compare the Stokes observations of the active region obtained from the Helioseismic Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) with that of MAST observations in the spectral line 6173 Å. We find good agreement between the two observations, considering the fact that MAST observations are limited by seeing.     

Initial CHIP He I Observations of Solar Limb Activity

A new instrument capable of 3-min time resolution full-disk and limb observations in the Hei 1083 nm spectral line has been in operation at the High Altitude Observatory's Mauna Loa Solar Observatory (MLSO) since April 1996. We discuss instrument capabilities and performance and present some initial observations of limb activity from the first year of instrument operation. We compare limb Hei and Hα observations of quiescent and active prominences, comment on the role of Doppler shifts in interpreting the Hei observations, and illustrate the use of disk/limb Hei observations of a CME-associated eruptive filament in mass-ejection studies.     

Future instrumentation for solar physics: a double channel MOF imager on board ASI Space Mission ADAHELI

A Magneto-Optical Filter-based system has been proposed as an optional payload for ASI’s low-budget Solar Mission ADAHELI, which has completed its Phase A feasibility study. The instrument is capable of providing simultaneous Dopplergrams, intensity and magnetic solar full-disk maps using the potassium 770 nm and sodium 589 nm solar Fraunhofer lines. The instrument is a version, re-designed for a space environment, of the one which has run an observing campaign at the South Pole in 2008 with unprecedented performance. The MOF-based system we present here is a low-cost, low-weight instrument, thus particularly fit to space applications, capable of providing stability and sensitivity of signals on long-term observations. The instrument will explore regions of the oscillation spectrum not available to other missions’ instruments.     

A View to the Future: Ultraviolet Studies of the Solar System

We discuss the status of ultraviolet knowledge of Solar System objects. We begin with a short historical survey, followed by a review of knowledge gathered so far and of existing observational assets. The survey indicates that UV observations, along with data collected in other spectral bands, are necessary and in some cases essential to understand the nature of our neighbors in the Solar System. By extension, similar observations are needed to explore the nature of extrasolar planets, to support or reject astro-biology arguments, and to compose and test scenarios for the formation and evolution of planetary systems.We propose a set of observations, describing first the necessary instrumental capabilitites to collect these and outlining what would be the expected scientific return. We identify two immediate programmatic requirements: the establishment of a mineralogic database in the ultraviolet for the characterization of planetary, ring, satellite, and minor planet surfaces, and the development and deployment of small orbital solar radiation monitors. The first would extend the methods of characterizing surfaces of atmosphere-less bodies by adding the UV segment. The latter are needed to establish a baseline against which contemporaneous UV observations of Solar System objects must be compared.We identify two types of UV missions, one appropriate for a two-meter-class telescope using almost off-the-shelf technology that could be launched in the next few years, and another for a much larger (5–20 meter class) instrument that would provide the logical follow-up after a decade of utilizing the smaller facility.Michel Festou, our co-author and a very important contributor to this paper, passed away while this paper was being completed. We dedicate it to his memory.Deceased 11 May 2005     

The Siberian Solar Radio Telescope: the current state of the instrument,observations, and data

The Siberian Solar Radio Telescope (SSRT) is one of the world's largest solar radio heliographs. It commenced operation in 1983, and since then has undergone several upgrades. The operating frequency of the SSRT is 5.7 GHz. Since 1992 the instrument has had the capability to make one-dimensional scans with a high time resolution of 56 ms and an angular resolution of 15 arc sec. Making one of these scans now takes 14 ms. In 1996 the capability was added to make full, two-dimensional images of the solar disk. The SSRT is now capable of obtaining images with an angular resolution of 21 arc sec every 2 min. In this paper we describe the main features and operation of the instrument, particularly emphasizing issues pertaining to the imaging process and factors limiting data quality. Some of the data processing and analysis techniques are discussed. We present examples of full-disk solar images of the quiet Sun, recorded near solar activity minimum, and images of specific structures: plages, coronal bright points, filaments and prominences, and coronal holes. We also present some observations of dynamic phenomena, such as eruptive prominences and solar flares, which illustrate the high-time-resolution observations that can be done with this instrument. We compare SSRT observations at 5.7 GHz, including computed `light curves', both morphologically and quantatively, with observations made in other spectral domains, such as 17 GHz radio images, Hα filtergrams and magnetograms, extreme-ultraviolet and X-ray observations, and dynamic radio spectra.     

Line-of-Sight Observables Algorithms for the <Emphasis Type="Italic">Helioseismic and Magnetic Imager</Emphasis> (HMI) Instrument Tested with <Emphasis Type="Italic">Interferometric Bidimensional Spectrometer</Emphasis> (IBIS) Observations

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.     

A Digital Imaging Multi-Slit Spectrograph for Measurement of Line-of-Sight Velocities on the sun

A multi-slit digital imaging spectrograph has been installed at Udaipur Solar Observatory, Udaipur (India) to measure the line-of-sight velocities in H associated with the mass motions of the dynamic phenomena on the solar surface viz. solar flares, eruptive prominences and surges. This spectrograph is being used in conjunction with a 15 cm aperture Coudé telescope to obtain the H spectra at a high rate of a specific region of interest on the Sun. In this paper, we describe the principal features of this instrument and the data acquisition method. We also present spectral observations of a surge and a quiescent prominence recorded using this instrument.     

Imaging X-ray Polarimeter for Solar Flares (IXPS)

We describe the design of a balloon-borne Imaging X-ray Polarimeter for Solar flares (IXPS). This novel instrument, a Time Projection Chamber (TPC) for photoelectric polarimetry, will be capable of measuring polarization at the few percent level in the 20?C50 keV energy range during an M- or X-class flare, and will provide imaging information at the ??10 arcsec level. The primary objective of such observations is to determine the directivity of nonthermal high-energy electrons producing solar hard X-rays, and hence to learn about the particle acceleration and energy release processes in solar flares. Secondary objectives include the separation of the thermal and nonthermal components of the flare X-ray emissions and the separation of photospheric albedo fluxes from direct emissions.     

First Observations from the Multi-Application Solar Telescope (MAST) Narrow-Band Imager

The Multi-Application Solar Telescope is a 50 cm off-axis Gregorian telescope recently installed at the Udaipur Solar Observatory, India. In order to obtain near-simultaneous observations at photospheric and chromospheric heights, an imager optimized for two or more wavelengths is being integrated with the telescope. Two voltage-tuneable lithium-niobate Fabry–Perot etalons along with a set of interference blocking filters have been used for developing the imager. Both of the etalons are used in tandem for photospheric observations in Fe i 6173 Å and chromospheric observation in H\(\alpha\) 6563 Å spectral lines, whereas only one of the etalons is used for the chromospheric Ca II line at 8542 Å. The imager is also being used for spectropolarimetric observations. We discuss the characterization of the etalons at the above wavelengths, detail the integration of the imager with the telescope, and present a few sets of observations taken with the imager set-up.     

Initial Calibration of the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO)

The Atmospheric Imaging Assembly (AIA) instrument onboard the Solar Dynamics Observatory (SDO) is an array of four normal-incidence reflecting telescopes that image the Sun in ten EUV and UV wavelength channels. We present the initial photometric calibration of AIA, based on preflight measurements of the response of the telescope components. The estimated accuracy is of order 25%, which is consistent with the results of comparisons with full-disk irradiance measurements and spectral models. We also describe the characterization of the instrument performance, including image resolution, alignment, camera-system gain, flat-fielding, and data compression.     

Solar Cycle Variations of Large-Scale Flows in the sun

Using data from the Michelson Doppler Imager (MDI) instrument on board the Solar and Heliospheric Observatory (SOHO), we study the large-scale velocity fields in the outer part of the solar convection zone using the ring diagram technique. We use observations from four different times to study possible temporal variations in flow velocity. We find definite changes in both the zonal and meridional components of the flows. The amplitude of the zonal flow appears to increase with solar activity and the flow pattern also shifts towards lower latitude with time.     

Measurement of vector magnetic fields

The observations of Stokes line profiles require an accurate knowledge of the instrumental polarisation caused by optical components in the path of the light beam. In this context we present a theoretical approach to the instrumental polarisation caused by the 3-mirror coelostat system of the Kodaikanal Solar Tower.Collaborative Program in Astronomy and Astrophysics, Department of Physics, Indian Institute of Science, Bangalore 560 012 India.     

The NASA/NSO Spectromagnetograph

The NASA/NSO Spectromagnetograph is a new focal plane instrument for the National Solar Observatory/Kitt Peak Vacuum Telescope which features real-time digital analysis of long-slit spectra formed on a two-dimensional CCD detector. The instrument is placed at an exit port of a Littrow spectrograph and uses an existing modulator of circular polarization. The new instrument replaces the 512-channel Diode Array Magnetograph first used in 1973. Commercial video processing boards are used to digitize the spectral images at video rates and to separate, accumulate, and buffer the spectra in the two polarization states. An attached processor removes fixed-pattern bias and gain from the spectra in cadence with spatial scanning of the image across the entrance slit. The data control computer performs position and width analysis of the line profiles as they are acquired and records line-of-sight magnetic field, Doppler shift, and other computed parameters. The observer controls the instrument through windowed processes on a data control console using a keyboard and mouse. Early observations made with the spectromagnetograph are presented and plans for future development are discussed.The National Solar Observatory is a Division of the National Optical Astronomy Observatories which is operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation.     

The Solar Optical Telescope of Solar-B (Hinode): The Optical Telescope Assembly

The Solar Optical Telescope (SOT) aboard the Solar-B satellite (Hinode) is designed to perform high-precision photometric and polarimetric observations of the Sun in visible light spectra (388 – 668 nm) with a spatial resolution of 0.2 – 0.3 arcsec. The SOT consists of two optically separable components: the Optical Telescope Assembly (OTA), consisting of a 50-cm aperture Gregorian with a collimating lens unit and an active tip-tilt mirror, and an accompanying Focal Plane Package (FPP), housing two filtergraphs and a spectro-polarimeter. The optomechanical and optothermal performance of the OTA is crucial to attain unprecedented high-quality solar observations. We describe in detail the instrument design and expected stable diffraction-limited on-orbit performance of the OTA, the largest state-of-the-art solar telescope yet flown in space.     

Influence Of Stray Light in the Instrument on Measurements of Longitudinal Magnetic Signals and Magnetic Field Azimuths

Magnetic saturation is investigated by numerical simulations and observations. It is found that this effect is not a main disturbance factor in measurements of longitudinal field signals. To examine the stray light in the instrument in magnetograph observations, we determined the point spread function of the Video Vector Magnetograph mounted on the Solar Magnetic Field Telescope (SMFT) installed at the Huairou Solar Observing Station (HSOS). Then we obtained the distribution of large-spread-angle (LSA) stray light intensity as a function of distance from disk center. A new way to correct LSA stray light is proposed. Also, we investigate stray light influence on measuring magnetic field azimuths.     

Hard X-ray Imager (HXI) onboard the ASO-S mission

Hard X-ray Imager(HXI) is one of the three scientific instruments onboard the Advanced Spacebased Solar Observatory(ASO-S) mission, which is proposed for the 25th solar maximum by the Chinese solar community. HXI is designed to investigate the non-thermal high-energy electrons accelerated in solar flares by providing images of solar flaring regions in the energy range from 30 keV to 200 keV. The imaging principle of HXI is based on spatially modulated Fourier synthesis and utilizes about 91 sets of bi-grid sub-collimators and corresponding LaBr_3 detectors to obtain Fourier components with a spatial resolution of about 3 arcsec and a time resolution better than 0.5 s. An engineering prototype has been developed and tested to verify the feasibility of design. In this paper, we present background, instrument design and the development and test status of the prototype.     

A Heliospheric Imager for Deep Space: Lessons Learned from Helios, SMEI, and STEREO

The zodiacal-light photometers on the twin Helios spacecraft, the Solar Mass Ejection Imager (SMEI) on the Coriolis spacecraft, and the Heliospheric Imagers (HIs) on the Solar-TErrestrial RElations Observatory (STEREO) twin spacecraft all point the way to optimizing future remote-sensing Thomson-scattering observations from deep space. Such data could be provided by wide-angle viewing instruments on Solar Orbiter, Solar Probe, or other deep-space probes. Here, we present instrument specifications required for a successful heliospheric imager, and the measurements and data-processing steps that make the best use of this remote-sensing system. When this type of instrument is properly designed and calibrated, its data are capable of determining zodiacal-dust properties, and of three-dimensional reconstructions of heliospheric electron density over large volumes of the inner heliosphere. Such systems can measure fundamental properties of the inner heliospheric plasma, provide context for the in-situ monitors on board spacecraft, and enable physics-based analyses of this important segment of the Sun-spacecraft connection.     

A High-Resolution Solar Telescope Using Dark-Lens Diffractive Optics

A telescope based upon dark-lens diffractive optics would be a uniquely new instrument for solar astronomy. The image formation process in such a telescope gives an intrinsically higher resolving power and a greatly reduced image intensity compared to that of refracting or reflecting optical systems of similar lens dimension. This low image intensity would be an advantage for solar observations made using a very large imaging element. After a brief overview of the history of solar instrument development, a quantitative evaluation of the dark-lens diffracting solar telescope concept is presented, showing the potential of this imaging method to meet or even to exceed the most demanding resolution goals currently being considered for future space-borne solar telescopes.