A purely reflective large wide-field telescope

Two versions of a fast, purely reflective Paul-Baker-type telescope are discussed, each with an 8.4-m aperture, 3° diameter flat field and f/1.25 focal ratio. The first version is based on a common, even asphere type of surface with zero conic constant. The primary and tertiary mirrors are 6th order aspheres, while the secondary mirror is an 8th order asphere (referred to here for brevity, as the 6/8/6 configuration). The D ₈₀ diameter of a star image varies from 0″.18 on the optical axis up to 0″.27 at the edge of the field (9.3–13.5 μm). The second version of the telescope is based on a polysag surface type, which uses a polynomial expansion in the sag z, 1 $$ r^2 = 2R_0 z - \left( {1 + b} \right)z^2 + a_3 z^3 + a_4 z^3 + a_4 z^4 + \ldots + a_N z^N $$ instead of the common form of aspheric surface. This approach results in somewhat better images, with D ₈₀ ranging from 0″.16 to 0″.23, using a lower-order 3/4/3 combination of powers for the mirror surfaces. An additional example with 3.5-m aperture, 3°.5 diameter flat field, and f/1.25 focal ratio featuring near-diffraction-limited image quality is also presented.     

Concerning five-minute variations of the global magnetic field of the Sun

For the purpose of identifying five-min oscillations we analyze long-term continuous observations of the solar magnetic field (with a duration from 3 to 11 hours) with 0.5 D spatial resolution obtained with the STOP telescope (Solar Telescope for Operative Predictions) at the Sayan observatory in 1987 and 1989. It is shown that global magnetic field fluctuations with such periods seem to be real, but the character of corresponding power spectra is strongly dependent on the mean field strength in the magnetograph aperture.     

A study of the degradation of daytime astronomical images due to turbulence in the lower atmosphere by measurement of the standard deviation of the angle of arrival

Fluctuations in the angle-of-arrival of a luminous wavefront are investigated by placing a narrow slit over the image of the solar limb, and observing the entrance pupil through this diaphragm. Measurement of the standard deviation _AA of these fluctuations, in a direction perpendicular to the solar limb, provides sufficient information to estimate an absolute parameter characterizing the seeing, i.e. Fried's parameter r ₀ or the equivalent parameter _L C _N ²(h) dh which gives the integral, over an atmosphere thickness L which depends on the spatial and angular filterings performed by the slit, of the structure constant C _N ² characterizing fluctuations in the air's refractive index. Simultaneous estimations of _AA ² and _L C _N ² (h) dh permit a linear relationship to be established between these two quantities. The result is interpreted theoretically by integration of the two-dimensional power spectrum for the angle-of-arrival fluctuations. The influence of filtering effects is discussed.Such a calibration can be performed for a given telescope and slit, enabling the system to be used as a seeing monitor.     

SARG: The High Resolution Spectrograph of TNG

SARG is a cross dispersed echelle spectrograph in operation since late spring 2000 at the Italian Telescopio Nazionale Galileo (TNG) 3.5 m telescope, La Palma. SARG offers both single object and long slit (up to 26 arcsec) observing modes covering a spectral range from λ = 0.37 up to1 μm, with resolution ranging from R = 29,000 up to R = 164,000. Cross dispersion is provided by means of a selection of four grisms; interference filters may be used for the long slit mode (up to 26 arcsec). A dioptric camera images the cross dispersed spectra onto a mosaic of two 2048 × 4096 EEV CCDs (pixel size: 13.5 μm) allowing complete spectral coverage at all resolving power for λ < 0.8 μm. In order to reach a high wavelength calibration precision an iodine-absorbing cell is provided. A Distributed Active Temperature Control System (DATCS) maintains constant the temperature of all spectrograph components at a preset value. Early results show that SARG works according to original specifications in terms of wavelength coverage, efficiency (measured peak efficiency is about 13%),resolution (maximum resolution R = 164,000 using a 0.3 arcsec slit, R ∼144,000 using an image slicer), and stability (preliminary estimates of radial velocity accuracy is ∼3 m/s using the iodine cell and ±150 m/s without the iodine cell). This revised version was published online in July 2006 with corrections to the Cover Date.     

On polarimetry in solar active regions

Phase retardation originating in a telescope is measured by means of polarizer and analyzer. The amount of this retardation depends only on the declination of the telescope. The retardation axes rotate with the Coudé image.The influence of this retardation on a Zeeman triplet, is measured photoelectrically. Consequences for solar polarimetry are discussed: Strong effects originate from the miscentering of the asymmetric Zeeman triplet introduced by the Doppler compensator. This yields a non-vanishing V-Stokes parameter in the central exit slit and thus the often observed crosstalk between the U and V-Stokes parameters.     

Imaging magnetographs for high‐resolution solar observations in the visible and near‐infrared wavelength region

The Coudé feed of the vacuum telescope (aperture D = 65 cm) at the Big Bear Solar Observatory (BBSO) is currently completely remodelled to accommodate a correlation tracker and a high‐order Adaptive Optics (AO) system. The AO system serves two imaging magnetograph systems located at a new optical laboratory on the observatory's 2^nd floor. The InfraRed Imaging Magnetograph (IRIM) is an innovative magnetograph system for near‐infrared (NIR) observations in the wavelength region from 1.0 μm to 1.6 μm. The Visible‐light Imaging Magnetograph (VIM) is basically a twin of IRIM for observations in the wavelength range from 550 nm to 700 nm. Both instruments were designed for high spatial and high temporal observations of the solar photosphere and chromosphere. Real‐time data processing is an integral part of the instruments and will enhance BBSO's capabilities in monitoring solar activity and predicting and forecasting space weather.     

The Master Mobile Astronomical System. Optical Observations of Gamma-Ray Bursts

The operating principles of the telescope-robot system MASTER (Mobile Astronomical System of Telescopes-Robots, http://observ.pereplet.ru), designed to search for fast transient phenomena in the optical range, are described. The robot-telescope includes the following: a Richter-Slefogt telescope with D=355 mm, F/D=2.4, a Richter-Slefogt telescope with D=200 mm, F/D=2.4, a Flugge telescope with D=280 mm, F/D=2.5, a TV camera with a field of 20x40 degrees, and three CCD cameras. A German mount with a slew rate of 8 deg/s is used. MASTER obtains images down to 19^m in a field of 6 square degrees in a 1.5 minute exposure. We present some observations of the optical afterglow of cosmic gamma-ray bursts. MASTER was the first system in Europe to record optical emission from GRB030329.__________Translated from Astrofizika, Vol. 48, No. 3, pp. 463–475 (August 2005).     

Scanned superresolution in theory and practice

We discuss some theoretical and practical considerations relating to achieving spatial resolution higher than /D, the nominal diffraction-limited resolution of a telescope of diameter D. Although the Nyquist criterion is often invoked as a justification for choosing pixel scales in array cameras, higher sampling densities are favored for imaging at and somewhat beyond the diffraction limit.     

Spectral classification of Be stars

In the course of observations of the LMC with the Glazar space telescope it was found that the star HD 269665 is unusually bright at 1640 A:m ₁₆₄₀ = 5 _. ^m ± 0 _. ^m 1,m ₁₆₄₀ –V = –6 _. ^m 2.     

GESE: a small UV space telescope to conduct a large spectroscopic survey of z∼1 Galaxies

One of the key goals of NASA’s astrophysics program is to answer the question: How did galaxies evolve into the spirals and elliptical galaxies that we see today? We describe a space mission concept called Galaxy Evolution Spectroscopic Explorer (GESE) to address this question by making a large spectroscopic survey of galaxies at a redshift, z～1 (look-back time of ～8 billion years). GESE is a 1.5-m space telescope with an ultraviolet (UV) multi-object slit spectrograph that can obtain spectra of hundreds of galaxies per exposure. The spectrograph covers the spectral range, 0.2–0.4 μm at a spectral resolving power, R～500. This observed spectral range corresponds to 0.1–0.2 μm as emitted by a galaxy at a redshift, z=1. The mission concept takes advantage of two new technological advances: (1) light-weighted, wide-field telescope mirrors, and (2) the Next-Generation MicroShutter Array (NG-MSA) to be used as a slit generator in the multi-object slit spectrograph.     

Forbidden sulphur I lines in the solar spectrum

The [SI] lines are due to transitions within the 3s²3p⁴ ground configuration of neutral sulphur. The results are presented from a search for the [Si] lines in the Fraunhofer spectrum. Two identifications are proposed with faint features in the Fraunhofer spectrum: ¹D₂-¹S₀ at = 7725.02 Å and ³P₂-¹D₂ at = 10821.23 Å. Their measured equivalent widths are shown to confirm the value for the solar abundance of sulphur, logN _S = 7.21 (in the scale logN _H = 12.00), which is derived from the permitted high-excitation lines. These lines give the first convincing identification of [Si] lines in an astrophysical source.     

The edison infrared space observatory and the study of extra-solar planetary material

Edison is a proposed large-aperture, radiatively-cooled space observatory planned to operate at wavelengths between 2 and 130m or longer. Current estimates for the telescope allow an aperture of 1.7 m which will achieve a final equilibrium temperature of about 30 K, although use of cryocoolers may permit temperatures below 20 K.Edison will be a powerful tool to investigate our Solar System, as well as planetary material around distant stars. At near- and mid-infrared wavelengths, where planetary material emits most of its radiation,Edison will be the most sensitive photometric and spectroscopic observatory under current consideration by the space agencies. With its large aperture,Edison will be able both to resolve the structure in nearby circumstellar Vega disks and to discriminate faint IR emission in the crowded environment of the galactic plane. With its long lifetime,Edison will allow extensive follow-up observations and increase the likelihood of catching transient events. We proposeEdison as a precursor to elements of a future space-based IR interferometer.Paper presented at the Conference onPlanetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A.     

The Hei D 3 5876 Å line as an activity and structural indicator in F-type Hyades stars

We give the first results of a study in F-type MS stars using the Hei D ₃ absorption feature at 5876 Å as an indicator of stellar activity and structure. The observations were obtained with the QUB echelle spectrograph at the Cassegrain focus of the 4.2 m William Herschel telescope, and have spectral resolution /6×10⁴, and signal-to-noise ratios 200. We chose as a first sample 17 F-stars of the Hyades Main Sequence. It was found that Hei D ₃ and X-ray emission appear aroundB-V 0.3, indicating the onset of sub-surface convection zones. Below this value, in stars withB-V0.42–0.44 the behaviour of the Hei D ₃ equivalent width against Rossby number is different from that observed in later type stars, indicating that the presence of nonradiative mechanisms other than dynamo must be important in heating the chromospheres of these hotter stars.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.Based on observations made with the William Herschel telescope, operated on the island of La Palma by the Royal Greenwich Observatory, in the Spanish Observatorio del Roque de Los Muchachos of the Instituto de Astrofisica de Canarias.     

A new concept and a preliminary design for a high resolution (HR) and very‐high resolution (VHR) spectrograph for the LBT

A way to fully exploit the large collecting area of modern 8–10m class telescopes is high resolution spectroscopy. Many astrophysical problems from planetary science to cosmology benefit from spectroscopic observations at the highest resolution currently achievable and would benefit from even higher resolutions. Indeed in the era of 8–10m class telescopes no longer the telescope collecting area but the size of the beam – which is related to the maximum size in which reflection gratings are manufactured – is what mainly limits the resolution. A resolution‐slit product R_φ ≃ 40,000 is the maximum currently provided by a beam of 20 cm illuminating the largest grating mosaics. We present a conceptual design for a spectrograph with R_φ ≃ 80,000, i.e. twice as large as that of existing instruments. Examples of the possible exploitation of such a high R_φ value, including spectropolarimetry and very high resolution (R ∼ 300,000), are discussed in detail. The new concept is illustrated through the specific case of a high resolution spectropolarimeter for the Large Binocular Telescope.     

A mathematical interpretation of diffusion processes with concentration-dependent diffusion coefficient

The integral balance method has been used to obtain an approximate analytical solution of a nonlinear boundary value problem which arises in the theory of diffusion with a concentration-dependent coefficient. It is the purpose of this paper to give an interpretation of the supposition of interface reactions which obey the law of kinetic mass action.Nomenclature C(Z,t) concentration - C ₀ concentration at initial time - D diffusivity - D ₀ diffusivity at initial time - F(t) a function of time - K ₀ half-order reaction rate constant - k ₁ first-order reaction rate constant - k ₂ second-order reaction rate constante - L characteristic length - n parameter - t time - Z space variable Dimensionless variables and similarity criteria nondimensional half-order reaction rate constant - nondimensional first-order reaction rate constant - nondimensional second-order reaction rate constant - x=Z/L dimensionless space variable - F ₀=D ₀ t/L ² Fourier number - g(F ₀)=[F(t)–C ₀]/C ₀ a function of generalized time - (x, F ₀)=[C(x,t)–C ₀]/C ₀ dimensionless concentration - <(F ₀)> dimensionless average concentration     

High-resolution analysis of solar photospheric oscillations

The coherent 5-min photospheric pressure oscillations with spherical harmonic degrees in the range 100 <l< 1000 were directly imaged over the photosphere with the monochromatic solar telescope FPSS at Meudon Observatory. Movie films were obtained with images spatially filtered to select sizes of increasing wave numbers (or l). Areas with ephemeral concentrations of coherent waves evolve in shape and may move horizontally with velocities of several tenths of km s^–1. When a large number of waves are interacting, the maximum vertical velocity V _max of the pulsation reaches around 1000 m s^–1, irrespective of the size. Extrapolation to the ideal case of a single isolated wave gives V _max proportional to size. For the areas of the smallest scale measured (l = 1000), when about 100 waves are interacting, V _max is found to be 260 + 25 m s^–1 at an altitude of 210 km above the reference level ₅₀₀₀ = 1 and increases vertically with a scale height of 750 ± 400 km.     

Effect of fluctuations in Doppler width on the center of strong absorption lines

Stochastic temperatures and turbulence are characterized by average velocities u _th and < u _turb  > ≡ u ₀ and fluctuations u￠_th {u'_{th}} and u′ (<u′ > = 0). Thus, the Doppler width of a line also has a fluctuating component Dl￠_D \Delta {\lambda '_D} . Observed spectra correspond to the radiative flux averaged over time and over a star’s surface, <H_λ>. Usually, only the average velocities u _th and u ₀ are taken into account in photospheric models and these yield the Doppler width Dl_D⁽⁰⁾ \Delta \lambda_D^{(0)} of a line in the customary way. The fluctuations Dl￠_D \Delta {\lambda '_D} mean that near a line center the average absorption coefficient < α_λ > is larger than the usual α_λ, which depends only on the average velocities u _th and u ₀. This enhances the absorption line near the center and is not explained by the photospheric models. This new statistical effect depends on the wavelength of the line. A comparison of observed lines with model profiles yields an estimate for the average level of fluctuations in the Doppler width, h = á | Dl￠_D | ñ

A multiplex imaging spectrometer for low energyX-ray astronomy

A multiplexX-ray image analyser is described. It consists in a time-modulated coded aperture associated with a solid state detector. The system combines the high efficiency and good spectral resolution of solid state spectrometers with the spatial resolution of the coded aperture (200 ).The device can be installed at the focus of a grazing incidence telescope to make images and spectra of faint astronomicalX-ray sources.     

ASTRONIRCAM—the infrared camera-spectrograph for the 2.5-m telescope of SAI Caucasian observatory

ASTRONIRCAM is a cryogenic-cooled slit camera-spectrograph for the spectral range 1–2.5 μm installed at the Nasmyth focus of the 2.5-meter telescope of the Caucasian observatory of the Sternberg Astronomical Institute of Lomonosov Moscow State University. The instrument is equipped with a HAWAII-2RG 2048×2048 HgCdTe array. Grisms are used as dispersive elements. In the photometric mode ASTRONIRCAM allows for extended astronomical object imaging in a 4.′6 × 4.′6 field of view with a 0.269 arcsec/pixel scale in standard photometric bands J, H, K, and K _s as well as in the narrow-band filters centered on the lines CH₄, [Fe II], H₂ v=1-0 S(1), Br _γ , and CO. In the spectroscopic mode, ASTRONIRCAM takes spectra of extended or point-like sources with a spectral resolution of R = λ/Δλ ≤ 1200. The general design, optical system, detector electronics and readout, amplification and digitization schemes are considered. The GAIN conversion factor measurement results are described as well as its dependence on the accumulated signal (nonlinearity).The full transmission of the atmosphere-to-detector train ranges from 40 to 50% in the wide-band photometry mode. The ASTRONIRCAMsensitivity at the 2.5-m telescope is characterized by the limiting J = 20, K = 19 stellar magnitudes measured with a 10% precision and 15 minute integration for 1″ atmospheric seeing conditions. References to the first results based on ASTRONIRCAM observations are given.     

Der offene sternhaufen NGC 2362

The very young open star cluster NGC 2362 was investigated by the strip method on charts of two photographs taken with the 1-m Schmidt telescope of the European Southern Observatory. Up to the limiting magnitudeM _v ^* =5 _. ^m 8 the cluster contains 100 stars and can be described by the Gaussian density law (6). Further results are: Mass = 246 , central mass density ₀ = 43.1 = 246 pc^-3 , radiusR2.6 pc, mean velocity of the stars = 0.64 km s^–1.

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Mitteilungen Serie A.