Slow X-ray bursts and flares with filament disruption

The data from OGO-5 and OSO-7 X-ray experiments have been compared with optical data from six chromospheric flares with filament disruption associated with slow thermal X-ray bursts. Filament activation accompanied by a slight X-ray enhancement precedes the first evidence of Hα flare by a few minutes. Rapid increase of the soft X-ray flux accompanies the phase of fastest expansion of the filament. Plateau or slow decay phases in the X-ray flux are associated with slowing and termination of filament expansion. The soft X-ray flux increases as F～(A + Bh) h, where h is the height of the disrupted prominence at any given time and A and B are constants. We suggest that the soft X-ray emission originates from a growing shell of roughly constant thickness of high-temperature plasma due to the compression of the coronal gas by the expanding prominence.     

Modeling the uranian rings at 2.2 μm: Comparison with Keck AO data from July 2004

We present a Monte Carlo model of the uranian rings, and compare this model to images of the system obtained with the Keck adaptive optics system in July 2004, at a wavelength of 2.2 μm (from de Pater et al. (de Pater, I., Gibbard, S.G., Hammel, H.B. [2006a]. Icarus 180, 186-200)). We confirm the presence of the ζ ring, but show that this ring must extend inwards much further than previously thought, although with an optical depth much lower than that in the main ζ ring component. We further confirm dust rings between rings α-4 and β-α, as well as near the λ ring. In addition, we show that a broad sheet of faint material (τ₀ ∼ 10⁻³) must be present through most of the ring region, from the α ring through the λ ring.     

Properties of optical fibres at cryogenic temperatures

A perhaps surprising property of optical fibres is that they remain flexible at cryogenic temperatures. This implies that they may be used for multiple-object and integral field spectroscopy in the thermal infrared in cryogenic instrumentation. In this paper the results of performance tests of optical fibres (silica and zirconium fluoride) at cryogenic temperatures are presented. By mounting the fibres in glass tubes with the appropriate adhesive, it was found that only negligible focal ratio degradation occurs when the fibre is cooled to 77 K.     

Strategy for Realizing High-Precision VUV Spectro-Polarimeter

Spectro-polarimetric observations in the vacuum ultraviolet (VUV) range are currently the only means to measure magnetic fields in the upper chromosphere and transition region of the solar atmosphere. The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) aims to measure linear polarization at the hydrogen Lyman-α line (121.6 nm). This measurement requires a polarization sensitivity better than 0.1 %, which is unprecedented in the VUV range. We here present a strategy with which to realize such high-precision spectro-polarimetry. This involves the optimization of instrument design, testing of optical components, extensive analyses of polarization errors, polarization calibration of the instrument, and calibration with onboard data. We expect that this strategy will aid the development of other advanced high-precision polarimeters in the UV as well as in other wavelength ranges.     

The specific molecular identification of life experiment (SMILE)

We describe a compact, highly integrated instrument concept for the detection and identification of a wide range of molecules associated with extinct/extant life or potential life processes. The Specific Molecular Identification of Life Experiment (SMILE) will be sensitive to the presence of a range of target molecules using both electrical and optical transduction techniques, and incorporates molecular imprinted polymers in addition to traditional biological receptors such as antibodies. A number of versions of the concept are possible depending on available resources e.g. mass, volume, etc. The full concept utilises a novel imaging interferometer where a large number of molecular receptors are deposited on the measurement plane of an imaging interferometer and read out by an imaging detector, enabling multiple targets—biomarkers—within a sample to be measured simultaneously. The optics can also form the basis of an UV-NIR imaging Fourier spectrometer allowing basic mineralogy studies to be conducted using optical properties to assist in the determination of the geological context of the samples. By incorporating micro-fabricated transducer arrays, micro-fluidics and artificial molecular recognition systems, as well as recombinant antibody technology with appropriate integration methods, SMILE forms a compact and robust “Life Marker Chip” which has been proposed for future planetary missions including ESA's ExoMars mission, where the instrument offers the possibility of conducting a direct in situ search for signs of past or present biological activity on Mars. In addition to its role in planetary exploration, derivatives of SMILE have multiple terrestrial applications in fields such as forensic analysis and environmental monitoring.     

Cassini thermal observations of Saturn's main rings: Implications for particle rotation and vertical mixing

In late 2004 and 2005 the Cassini composite infrared spectrometer (CIRS) obtained spatially resolved thermal infrared radial scans of Saturn's main rings (A, B and C, and Cassini Division) that show ring temperatures decreasing with increasing solar phase angle, α, on both the lit and unlit faces of the ring plane. These temperature differences suggest that Saturn's main rings include a population of ring particles that spin slowly, with a spin period greater than 3.6 h, given their low thermal inertia. The A ring shows the smallest temperature variation with α, and this variation decreases with distance from the planet. This suggests an increasing number of smaller, and/or more rapidly rotating ring particles with more uniform temperatures, resulting perhaps from stirring by the density waves in the outer A ring and/or self-gravity wakes.The temperatures of the A and B rings are correlated with their optical depth, τ, when viewed from the lit face, and anti-correlated when viewed from the unlit face. On the unlit face of the B ring, not only do the lowest temperatures correlate with the largest τ, these temperatures are also the same at both low and high α, suggesting that little sunlight is penetrating these regions.The temperature differential from the lit to the unlit side of the rings is a strong, nearly linear, function of optical depth. This is consistent with the expectation that little sunlight penetrates to the dark side of the densest rings, but also suggests that little vertical mixing of ring particles is taking place in the A and B rings.     

H α Observations of 8 June, 2004 Venus Transit

The cosmic event of Venus transit across the solar disk occurred on 8 June, 2004. The previous such event was witnessed about 122 years ago on 6 December, 1882. We observed this rare transit in H _α 6563 Å line-center from Udaipur Solar Observatory (USO) using both the full-disk and small field-of-view solar telescopes. In the earlier historical transits, a “black-drop” effect was observed in white light images, during the contact phases. The transit of 8 June, 2004 provided a unique opportunity to observe this effect, for the first time, in H _α. We report that the “black-drop” effect is present in H _α also, as in the white light observations made by the ground-based Global Oscillation Network Group (GONG) instrument and the space-borne Transition Region and Coronal Explorer (TRACE) satellite. We did not observe any noticeable “aureole” (atmospheric glow) around Venus during the ingress or egress phases. We have compared the H _α images with the multi-wavelength data obtained from the TRACE satellite.     

2-D spectroscopy of polar-ring galaxies candidates. II. The peculiar galaxies NGC 2748 and UGC 4385

This article is devoted to the analysis of new observational data obtained on the 6-m telescope using multimode instrument SCORPIO for two peculiar galaxies NGC 2748 and UGC 4385. Using scanning Fabry-Perot interferometer (FPI) large-scale velocity fields of ionized gas in lines Hα and [N II] λ6584 Å for NGC 2748 and in line Hα for UGC 4385 and the maps of brightness distribution in continuum and in corresponding lines for both galaxies were constructed. Observational data obtained in the long-slit mode of spectroscopy gave information about the kinematics of stellar component. The analysis of the received materials for NGC 2748 have shown that this object is a disky galaxy with stellar shell which rotates around the major axis of main body. The origin of such shell is most likely connected with the capture and disruption of dwarf companion. The structure of ionized gas velocity field of UGC 4385 appeared to be very complex. The most regular part of the field which concerns the supposed ring is best represented by the model of circular rotation with expansion. In addition long-slit observations showed that the optical spectra of two bright in the infrared region condensations resemble the spectra of galaxies’ nuclei. A supposition was made that UGC 4385 is two galaxies in the stage of head-on collision.     

The optical performance of the PILOT instrument from ground end-to-end tests

The Polarized Instrument for Long-wavelength Observation of the Tenuous interstellar medium (PILOT) is a balloon-borne astronomy experiment designed to study the linear polarization of thermal dust emission in two photometric bands centred at wavelengths 240 μm (1.2 THz) and 550 μm (545 GHz), with an angular resolution of a few arcminutes. Several end-to-end tests of the instrument were performed on the ground between 2012 and 2014, in order to prepare for the first scientific flight of the experiment that took place in September 2015 from Timmins, Ontario, Canada. This paper presents the results of those tests, focussing on an evaluation of the instrument’s optical performance. We quantify image quality across the extent of the focal plane, and describe the tests that we conducted to determine the focal plane geometry, the optimal focus position, and sources of internal straylight. We present estimates of the detector response, obtained using an internal calibration source, and estimates of the background intensity and background polarization.     

Spectral imaging of martian water ice clouds and their diurnal behavior during the 1999 aphelion season (Ls = 130°)

We report high-spectral-resolution (λ/δλ = 800-2300) near-infrared mapping observations of Mars at L_s = 130° (April 1999), which were obtained by drift-scanning the cryogenic long-slit spectrometer at the KPNO 2.2-m telescope across the disk. Data were reformatted into calibrated spectral image cubes (x,y,λ) spanning 2.19 to 4.12 μm, which distinguish atmospheric CO₂ features, solar lines, and surface and aerosol features. Maps of relative band depth between 3.0 and 3.5 μm trace water ice clouds and show the diurnal evolution of features in the persistent northern summer aphelion cloud belt, which was mapped contemporaneously but at fixed local time by the Mars Global Surveyor Thermal Emission Spectrometer (MGS/TES). Cloud optical depth, particle sizes, and ice aerosol content were estimated using a two-stream, single-layer scattering model, with Mie coefficients derived from recently published ice optical constants, followed by a linear spectral deconvolution process. A comparison of data and model spectra shows evaporating nighttime clouds in the morning followed by afternoon growth of a prominent orographic cloud feature on the west flank of Elysium Mons. Cloud optical depth at 3.2 μm evolved to 0.28 ± 0.13 and ice aerosol column abundance to 0.9 ± 0.3 pr μm in the afternoon. Column abundances as large as 0.17 pr μm were retrieved in nonorographic clouds within the aphelion cloud band around midday. These clouds exhibit a modest decline in optical depth during the afternoon. Results show that ice particle radii from <2 μm to >4 μm exist in both cloud types. However, large particles dominate the spectra, consistent with recent MGS/TES emission phase function measurements of aphelion cloud aerosol properties.     

Chromospheric telescope modification for digital imaging

The optical and technical characteristics of the tie-in between the chromospheric AFR-2 telescope and the digital camera Sony DSC-S85 are determined by computer simulation. The optimal layout of the camera, telescope optics, and collective lens is established. The modulation transfer function is used as an optimization parameter (quality criterion for the solar disk image in H_α).     

Optical identification of the hard X-ray source IGR J18257-0707

We present the results of our optical identification of the hard X-ray source IGR J18257-0707 through its spectrophotometric observations with the optical RTT-150 telescope. The accurate position of the X-ray source determined using Chandra observations has allowed this source to be confidently associatedwith a faint optical object (m _R ≈ 20.4) whose optical spectrumexhibits a broad H _α emission line at redshift z = 0.037. Thus, the source IGR J18257-0707 is a type-1 Seyfert galaxy at redshift z = 0.037.     

Optical observations of the galactic supernova remnants G59.5+0.1, G84.9+0.5 and G67.7+1.8

We present here the optical CCD observations and long slit spectra of the galactic supernova remnants G59.5+0.1, G84.9+0.5 and G67.7+1.8, the first two being observed for the first time. The observations were carried out with the 1.5 m Russian-Turkish joint Telescope (RTT150) at TÜB?TAK National Observatory (TUG). The images were taken with Hα, [SII] and their continuum filters. After subtracting the continuum from Hα and [SII], [SII]/Hα ratio is obtained. The average ratio is found to be 0.41 for G59.5+0.1 and 0.44 for G84.9+0.5, in a very good agreement with the ratios obtained from the optical spectra, namely 0.46 and 0.40, respectively, indicating that these remnants are close to, or interacting with, HII regions. G59.5+0.1 and G84.9+0.5 remnants show diffuse-shell morphology while G67.7+1.8 shows arc-shell morphology. From the emission lines of the spectra, the electron density N _e , pre-shock density n _c , explosion energy E, interstellar extinction E(B-V), and neutral hydrogen column density N(HI) are calculated and shock velocity V _s is estimated for these remnants.     

Mutual neutralization rates of ionospherically important ions

Following our recently published measurements of the rate coefficients for mutual neutralization, α, of the ionospherically important reactions NO⁺ + NO₂^?(α₁) and NO⁺ + NO₃^?(α₂) carried out in ion-ion flowing afterglow plasmas at 300 K, we have determined the mutual neutralization rates for the water cluster ion H₃O⁺ · (H₂O)₃ with a mixture of several negative ions which are known to exist in the D region. The α coefficients for these cluster ion reactions do not differ significantly from alpha;₁ and α₂, all of these reactions having α ?6 × 10^?8 cm³/sec which is significantly smaller than values usually adopted in ionospheric calculations. Current information on the ionic composition of the D region and the implications of the present results to de-ionization rate calculations are discussed.     

Statistical distribution of atmospheric dust devils

Theoretical predictions with regard to dust devil (apparent) angular size–frequency distribution are made and critically compared with Mars Exploration Rover (MER) Spirit optical observations. For an idealized horizontal viewing geometry one should expect that the number of dust devils having the apparent angular diameter greater than a given angle α is inversely proportional to α squared. The actual dependency for Spirit dust devils is in between the inverse-squared and simple inverse laws, and close to the latter one for small and moderate angles α. It is emphasized that such a comparison can be considered as a benchmark for completeness and adequateness of dust-devil optical observations and correctness of competing analytical formulations for dust devil size–frequency distribution.     

Optical spectra of supernova remnant candidates in the Sculptor Group galaxy NGC 300

We present moderate-resolution (<5 Å) long-slit optical spectra of 51 nebular objects in the nearby Sculptor Group galaxy NGC 300 obtained with the 2.3 meter Advanced Technology Telescope at Siding Spring Observatory, Australia. Adopting the criterion of [S?ii]_Total:Hα≥0.4 to confirm supernova remnants (SNRs) from optical spectra, we find that of 28 objects previously proposed as SNRs from optical observations, 22 meet this criterion with six showing [S?ii]_Total:Hα of less than 0.4. Of 27 objects suggested as SNRs from radio data, four are associated with the 28 previously proposed SNRs. Of these four, three (included in the 22 above) meet the criterion. In all, 22 of the 51 nebular objects meet the [S ii]_Total:Hα criterion as SNRs while the nature of the remaining 29 objects remains undetermined by these observations.     

Structure and kinematics of the interstellar medium in the star-forming region in the BCD galaxy VII Zw 403 (UGC 6456)

The structure and kinematics of ionized supershells in the star-forming region in the BCD galaxy VII Zw 403 (UGC 6456) are analyzed using observations with the SCORPIO focal reducer on the 6-m Special Astrophysical Observatory telescope in three modes: direct imaging (in the Hα, [O III], and [S II] lines), long-slit spectroscopy, and spectroscopy with a scanning Fabry-Perot interferometer. In addition to the previously known bright H II regions and the faint giant ring that surrounds the entire starforming region, many new faint diffuse and arc structures have been detected. A fine structure of the giant ring has been revealed. We do not confirm the previously detected expansion of the bright shells around young stellar associations with a velocity of 50–70 km s^?1. We have estimated their expansion velocities to be no higher than 15–20 km s^?1; the corresponding kinematic age, no younger than 3–4 Myr, agrees well with the age of the compact OB associations associated with them. We correlate the faint extended filamentary and diffuse regions of ionized gas identified almost in the entire central region of the galaxy and the giant H II ring with the older (10 Myr) stellar population of the most recent starburst. Weak high-velocity [O III] and Hα line wings (up to 300 km s^?1 from the line center) have been detected in the brightest H II region. Such velocities have been observed in the galaxy for the first time. The previously published Hα luminosity measurements for the galaxy are refined.     

Improvements on Fresnel arrays for high contrast imaging

The Fresnel Diffractive Array Imager (FDAI) is based on a new optical concept for space telescopes, developed at Institut de Recherche en Astrophysique et Planétologie (IRAP), Toulouse, France. For the visible and near-infrared it has already proven its performances in resolution and dynamic range. We propose it now for astrophysical applications in the ultraviolet with apertures from 6 to 30 meters, aimed at imaging in UV faint astrophysical sources close to bright ones, as well as other applications requiring high dynamic range. Of course the project needs first a probatory mission at small aperture to validate the concept in space. In collaboration with institutes in Spain and Russia, we will propose to board a small prototype of Fresnel imager on the International Space Station (ISS), with a program combining technical tests and astrophysical targets. The spectral domain should contain the Lyman-α line (λ =?121 nm). As part of its preparation, we improve the Fresnel array design for a better Point Spread Function in UV, presently on a small laboratory prototype working at 260 nm. Moreover, we plan to validate a new optical design and chromatic correction adapted to UV. In this article we present the results of numerical propagations showing the improvement in dynamic range obtained by combining and adapting three methods : central obturation, optimization of the bars mesh holding the Fresnel rings, and orthogonal apodization. We briefly present the proposed astrophysical program of a probatory mission with such UV optics.