Line profile analysis of an astronomical spectrograph with a laser frequency comb

We present a study of the spectral line shape associated with a High Resolution Spectrograph on the 2.16 m telescope at the Xinglong Observing Station of National Astronomical Observatories,Chinese Academy of Sciences. This measurement is based on modeling the instrumental line shape obtained by unresolved modes from a Yb-fiber mode-locked laser frequency comb. With the current repetition rate of 250 MHz and 26 GHz mode spacing on the spectrograph,we find the absolute variation of the line center,0.0597 pixel in the direction of the CCDs,and 0.00275pixel(～3 m s-1) for relative variation in successive exposures on a short timescale. A novel double-Gaussian model is presented to improve the quality of the fit by a factor of 2.47 in a typical single exposure. We also use analysis with raw moments and central moments to characterize the change in line shape across the detector. A trend in charge transfer efficiency can be found on the E2 V 4096 × 4096 CCD that provides a correction for wavelength calibration aiming to reach a level of precision for radial velocity below 1 m s-1.     

An EUV imaging spectrograph for high-resolution observations of the solar corona

An extreme ultraviolet (EUV) imaging spectrograph for the wavelength range from 235 to 450 Å has been developed and used for high resolution observations of the Sun. The instrument incorporates a glancing incidence Wolter Type II Telescope and a near-normal incidence toroidal grating spectrograph to achieve near-stigmatic performance over this spectral range. The design of the spectrograph entrance aperture enables both stigmatic spectra with spectral resolution adequate to observe emission line profiles and spectroheliograms of restricted portions of the Sun to be obtained concurrently. In this paper we describe the design and performance of the instrument and provide an overview of results obtained during a sounding rocket flight on May 5, 1989.     

The improved ARTEMIS IV multichannel solar radio spectrograph of the University of Athens

We present the improved solar radio spectrograph of the University of Athens operating at the Thermopylae Satellite Telecommunication Station. Observations now cover the frequency range from 20 to 650 MHz. The spectrograph has a 7-meter moving parabola fed by a log-periodic antenna for 100–650 MHz and a stationary inverted V fat dipole antenna for the 20–100 MHz range. Two receivers are operating in parallel, one swept frequency for the whole range (10 spectrums/sec, 630 channels/spectrum) and one acousto-optical receiver for the range 270 to 450 MHz (100 spectrums/sec, 128 channels/spectrum). The data acquisition system consists of two PCs (equipped with 12 bit, 225 ksamples/sec ADC, one for each receiver). Sensitivity is about 3 SFU and 30 SFU in the 20–100 MHz and 100–650 MHz range respectively. The daily operation is fully automated: receiving universal time from a GPS, pointing the antenna to the sun, system calibration, starting and stopping the observations at preset times, data acquisition, and archiving on DVD. We can also control the whole system through modem or Internet. The instrument can be used either by itself or in conjunction with other instruments to study the onset and evolution of solar radio bursts and associated interplanetary phenomena.     

Gregor@night: The future high‐resolution stellar spectrograph for the GREGOR solar telescope

We describe the future night‐time spectrograph for the GREGOR solar telescope and present its science core projects. The spectrograph provides a 3‐pixel resolution of up to R = 87 000 in 45 échelle orders covering the wavelength range 390‐900 nm with three grating settings. An iodine cell can be used for high‐precision radial velocity work in the 500‐630 nm range. The operation of the spectrograph and the telescope will be fully automated without the presence of humans during night‐time and will be based on the successful STELLA control system. Future upgrades include a second optical camera for even higher spectral resolution, a Stokes‐V polarimeter and a link to the laser‐frequency comb at the Vacuum Tower Telescope. The night‐time core projects are a study of the angular‐momentum evolution of “The Sun in Time” and a continuation of our long‐term Doppler imaging of active stars (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the instrumental and atmospheric stray-light for solar observations

From aureole measurements made with a 40 cm-Vacuum-Telescope at Izaña (Tenerife) in the wavelength region 417 nm < λ < 785 nm and from a comparison with other aureole measurements we conclude the following: (a) Within one solar radius from the limb, the aureole is mostly of instrumental origin, (b) Beyond that distance, the contribution of atmospheric stray-light becomes noticeable, (c) The atmospheric contribution to the aureole intensity is, under good conditions at mountain stations, a very slowly decreasing function, and amounts to some 10^?5 of the solar disk intensity. A procedure is given to separate the variable atmospheric component of the stray-light from the constant instrumental one.     

Adjustment of a tower solar telescope and spectrograph: A method manual

Questions of the mounting and adjustment of a tower solar telescope are considered through the example of the TST-2 telescope of the Crimean Astrophysical Observatory Scientific Research Institute. The authors describe the optical circuits of the telescope and spectrograph and list the basic requirements for the mutual arrangement of individual components of the telescope. Simple methods for adjusting elements of the telescope and spectrograph are described.     

Multidirectional scanning of active regions with a slit-jaw spectrograph and a solar chromatograph

At the Swedish Solar Observatory in Anacapri we have simultaneously used the following combination of instruments in our investigation of active regions:

1. A spectrograph with an image rotator placed in front of the slit.
2. A subtractive double dispersive spectrograph (solar Chromatograph).
3. A Hα+0.5 Å patrol instrument. Scans over the 3b flare of August 4th 1972 are used to illustrate the method. The illustrations clearly show downflowing matter connected with bright knots and filaments in the emitting area, possibly in accordance with Hyder's infall-impact mechanism.

     

A CCD imaging spectrograph in the improved solar tower of Nanjing University

Since 1992 the solar tower telescope of Nanjing University (118°51 E, 32°03 N) as well as its multichannel solar spectrograph, originally established in 1982, have been reconstructed and a two-channel imaging spectrograph has been operated successfully. The apertures of the coelostat and the secondary mirror are both 60 cm. The spherical objective mirror, having an aperture of 43 cm and a focal length of 2170 cm, produces a solar image of 20 cm diameter. Two auxiliary telescopes using a small fraction of the coelostat's aperture were set up for guiding and H monochromatic monitoring. A multichannel spectrograph can be operated in six wavebands simultaneously. A CCD imaging spectrograph can be used for data acquisition at H and Caii K line wavebands automatically and simultaneously. The instrument consists of two CCD cameras, an image processor (SR-151), a personal computer, and a mechanical scanning device. The principal characteristics of the instruments are described. Some observational results are presented as examples.     

The thermoluminescence profile of a recent sea sediment core and the solar variability

The analysis of the thermoluminescence (TL) profile of the GT14 recent sea sedimentary core shows the existence of four main periodicities of 137.7, 59,12.06, and 10.8 years. Here we discuss the affinity of these waves to the known cycles of solar variability. The beats of the two high frequency components produce a modulated wavetrain with a carrier wave of 11.4 years and an amplitude modulation with period 206 years. The minima of this squared amplitude modulation fall in 1810 and 1913 A.D. and closely correspond to the periods of lowest solar activity as indicated by the sunspot series. The sum of the two low frequency waves can in turn be rewritten as a component with period 82.6 years which is amplitude modulated by a second component with period of 206 years. The 82.6-yr wave has the period commonly attributed to the Gleissberg cycle of solar activity. The maxima of the 82.6-yr wave occur in agreement with the dates of maximum solar radius as suggested by Gilliland (1981).     

Formation of the solar Hα profile

A series of non-LTE radiative transfer solutions for H was computed using the integrodifferential equation technique of Athay and Skumanich (1967). A model hydrogen atom consisting of three bound levels and a continuum was assumed. It was found that increasing the temperature of the chromosphere at the height of line formation decreases the central intensity of the line. The density structure of the atmosphere primarily affects the optical depth scale rather than the source function. The temperature minimum region of the atmosphere was found to be transparent to H radiation, so that the radiation in some part of the line will arise from two distinct layers of the atmosphere, one above the temperature minimum and one below it. The computed H profile was found to be highly sensitive to the assumed 2–3 collisional cross-section.     

A method for investigating the brightness distribution near the solar limb at millimeter wavelengths

The brightness distribution near the solar limb has been investigated by means of a technique in which derivatives of drift scans of the Sun were compared with derivatives of drift scans of the Moon. The results obtained at 88.3 GHz (3.4 mm) indicate that the Sun is limb neutral within the uncertainty of our measurement. If limb brightening or darkening is present, it represents less than 1.6 % or 1.2 %, respectively, of the total power received from the Sun at this wavelength.     

Polarization interferometer for 2800 MHz solar noise studies with a 0.5′ fan beam

The construction and operation of a high resolution interferometer for solar noise observations at 10.7 cm for the Algonquin Radio Observatory is described. One element is the existig 32 element array of 3 m reflectors while the second is a grating element of 4 reflectors symmetrically placed on the same E-W line. The aperture of 665 m produces a fan beam of 0.5 E.W. by 2° N.S. Four Faraday rotators in the antenna feeds of the newly commissioned grating enable three Stoke's parameters to be observed. The expected antenna pattern is confirmed by making observations on the brighter radio sources. Observations of the Sun on 1972, January 6 show the range of phenomena to be observed and a detailed study of the association of eight radio emissive regions with all centers of solar activity is presented.     

The use of solar faculae in studies of the sunspot cycle

Comparison of the long-term variation of photospheric faculae areas with that of sunspots shows that studies of faculae provide both complementary and supplementary information on the behaviour of the solar cycle. Detailed studies of the development of sunspots with respect to faculae show that there is a high degree of order over much of a given cycle, but marked differences from cycle to cycle. Within a cycle the relationship between spot and faculae areas appears to be similar for the N and S solar hemispheres, and over the early stages of a cycle it is directly related to the magnitude of the maximum sunspot number subsequently attained in that cycle.This result may well have predictive applications, and formulae are given relating the peak sunspot number to simple parameters derived from this early developmental stage. Full application to the current cycle 21 is denied due to the cessation of the Greenwich daily photoheliographic measurements, but use of the cruder weekly data suggests a maximum smoothed sunspot number of 150 ± 22.The effects of the incompatibility of the spot and faculae data, in that faculae are unobservable over a large fraction of the solar disc and also do not always develop associated spots, have been examined in a detailed study of two cycles and shown not to vitiate the results.Now at NOAA, Environmental Data Service, NGSTDC, Boulder, Colo. 80302, U.S.A.     

The instrumental polarization of a Gregory-Coudé telescope

We calculate a theoretical model of the polarization properties of a Gregory-Coudé telescope to predict the behaviour of the German Gregory-Coudé Telescope installed at the Observatorio del Teide (Spain). Measurements of the real effects produced by this telescope acting upon light of known polarization are compared with the model. We estimate an uncertainty in its predictions of about 10%, which is produced by the uncertainties of the (complex) refractive index of the metallic layers covering the mirrors. The paper concludes by briefly considering the way in which the plain telescope changes the Stokes' profiles.     

Observations of the supernova 1985F with a new spectrograph

We present the spectrum of the supernova 1985F over the wavelength range 4600 to 10000 Å as recorded in one 200 s exposure on 16 May, 1985, when its age was estimated to bet240 days. This wideband measurement with a resolution of 20 Å was made with the new Faint Object Spectrograph on the Isaac Newton Telescope (INT) at the Observatorio del Roque de los Muchachos. Broad line features were observed for the ionsOi,Oii, andOiii, Caii, and Nai although broad H was noteably absent. This suggests type I rather than type II properties but Filippenko and Sargent (1985c) have concluded this object to be of neither type and of a new peculiar class. We have observed the Caii infra-red triplet at 8600 Å which has not been previously reported in the spectrum of SN1985F and alsoCi] at 9800 Å.     

A numerical model of a solar flare based on electron beam heating of the chromosphere

There are two parts to this paper. In the first we calculate the hydrodynamic response of the solar atmosphere to the injection of an intense beam of electrons in a numerical simulation of a solar flare. In the second we predict the spectroscopic consequences of the hydrodynamic behaviour calculated in the first part. The hydrodynamics is predicted by solving the equations of conservation of mass, momentum, and energy. The latter is expressed as two temperature equations; one for the electrons and the other for the neutral atoms and positive ions of hydrogen. The equations are solved in one dimension and the geometric form is of a semi-circular loop having its ends in the photosphere. The results show how the loop is filled at supersonic speed with plasma at temperatures characteristic of flares. At the same time a compression wave is predicted to propagate down towards the photosphere. After the heating pulse stops, the plasma that has risen into the loop, starts to decay and return to the condition it was in before the pulse started. In predicting the spectrum that would be emitted by such a plasma calcium was chosen for illustration. The first and main part of this calculation was setting up and solving the time-dependent equations of ionization/recombination. In order to provide a standard for comparison the same ionization and recombination rate coefficients are used to predict the steady-state distribution of populations of ionization stages. This is then compared with the distribution found from the time-dependent solution and shows that there is a negligibly small time lag predicted by the time-dependent result. However the more significant comparisons to make are between the temperatures of the peak abundances of the various ions under the assumptions of steady-state and time-dependent ionization. For the particular circumstances chosen here the temperature differences are predicted to be in the neighbourhood of 10% or less and in view of the overall accuracy of the atomic data are not significant. It would appear therefore that the much simpler assumption of steady-state ionization balance leads to results of acceptable accuracy for the particular case considered.