The use of a laser beam for investigating the instrumental profile of a double-pass solar spectrograph

Some peculiarities of the use of a laser for the determination of the instrumental profile of the high-resolution spectrograph have been described. The results of the investigation of the instrumental profile of the Kiev-Golosejevo double-pass solar spectrograph are presented in graphs.The influence of the width of the slits of the double-pass spectrograph upon the main features of its instrumental profile is discussed briefly.     

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.     

测定天文大气折射和建立电磁波折射延迟实测模型(Ⅲ)-专用测量仪器

针对用天文大气折射测定值,建立随观测站和随方位而异的电磁波折射延迟改正模型的高精度要求,提出了新的仪器误差理论,其主要内容是允许仪器误差存在,并看成是不断变化的,采用相应的测量方法作实时的测定和修正,同时消除仪器的各种变形和误差的影响,排除观测数据中的各种系统误差来源,并达到提高单次测定精度目的;文中还针对不同纬度的观测站、多方位、从天顶直到低空的观测需要,给出了仪器总体结构的安排,和采用视频CCD作为接收器的终端设计方案,也给出了各种仪器误差的测定方法和测量装置的设计要求。     

Stray-light measurements at the Observatorio del Teide

A new procedure to separate the instrumental and atmospheric components of stray light is presented. It is based on the dependence of the aureole's atmospheric component on the air mass and is applied to measurements taken with the Vacuum Newton Telescope (VNT) at the Observatorio del Teide (Tenerife). The resulting instrumental part is independent of the air mass.The variation of both components with wavelength is also studied. The instrumental component shows no dependence on wavelength, in contrast to the atmospheric one which is greater in the blue than in the red.It is concluded that observations with air masses larger than two will probably be strongly affected by stray light.     

低纬子午环仪器误差的测定及其处理方法

仪器误差的精确测定和消除对于提高子午环的观测精度有着至关重要的意义。本文简单介绍了低纬子午环的观测原理和仪器结构，系统地探讨了它的各种仪器误差的来源、测定和处理方法。为了进一步完善采用组合固定角距法测定对径改正的方法，在第三章，研究了提高对径改正测量精度的方法，重新推导了对径改正的计算公式，并就某些具体的条件，对其进行了模拟验证，得到了较为满意的结果     

Solar rotation measurements at Mount Wilson

We examine the background velocity fields of the Sun as observed at Mount Wilson. The method of velocity reduction of the full-disk Mount Wilson data is outlined. We describe a number of tests that have been carried out in order to find an instrumental origin for short-term rotation variations and a large-scale background line-shift - the ears. No instrumental cause can be found for this ear effect, although such a cause cannot yet be ruled out.Operated jointly by the Carnegie Institution of Washington and the California Institute of Technology.     

低纬子午环的研制过程

叙述了低纬子午环研制的全过程，从低纬度地区子午绝对测定方法的提出和验证，仪器几种主要误差测定方法的提出，到设计、加工和安装，最后叙述了在调试中遇到的几个主要问题和解决办法。文中还以与传统子午环比较的方式，论述了在对加工精度未提出苛刻要求的情况下如何能达到高精度测量的原因。     

A new iterative technique for the deconvolution of real data

A fast new deconvolution technique has been developed which employs a complex iterative scheme in order to deconvolve severely broadened noisy data. A great many computer-simulated experiments have been made using the iterative scheme in order to test its reliability and stability in many different situations. It is found to be extremely reliable in the reclaiming of partially resolved multi-featured spectra and can be used with any type of instrumental profile. Deconvolution of single Gaussian features are achieved in 5% noise conditions, where the instrumental profile is 5 times broader than the spectral features to be reclaimed.     

Instrumental lines of astrophysical relevance in TGRS and SPI

High resolution γ-ray spectroscopy at energies around 1 MeV, as with SPI on board INTEGRAL, is a powerful tool for astronomy with radioactivities. We do not expect the SPI signal-to-background ratio for any of the anticipated γ-ray sources to exceed a few percent; hence detailed modelling of the instrumental background will be crucial. We exploit the similarities between TGRS on board WIND and SPI with respect to orbit and radiation environment, as well as detector design and material composition, to anticipate the most important instrumental background lines and their production channels in SPI at the energies of selected γ-ray lines of astrophysical relevance.     

Modeling of EIS Spectrum Drift from Instrumental Temperatures

An empirical model has been developed to reproduce the drift of the spectrum recorded by the EIS on Hinode using instrumental temperatures and relative motion of the spacecraft. The EIS spectrum shows an artificial drift in wavelength dimension in sync with the revolution of the spacecraft, which is caused by temperature variations inside the spectrometer. The drift amounts to 70 km s⁻¹ in Doppler velocity and introduces difficulties in velocity measurements. An artificial neural network is incorporated to establish a relationship between the instrumental temperatures and the spectral drift. This empirical model reproduces observed spectrum shift with an rms error of 4.4 km s⁻¹. This procedure is robust and applicable to any spectrum obtained with EIS, regardless of the observing field. In addition, spectral curvatures and spatial offset in the north – south direction are determined to compensate for instrumental effects.     

Estimation Of Seeing Quality Using Low-Resolution Solar Image Data

Modulation transfer functions (MTFs), generated as a by-product of the analysis of low-resolution solar images taken for the Global Oscillation Network Group, were used to estimate the quality of seeing at its six sites. These MTFs, after approximate correction for the effects of the instrumental point spread function, were fitted with physically-motived functional forms representing the effects of seeing and scattering. It was found that the estimates of seeing quality were relatively robust to the effects of scattering, but were severely biased by effects caused by changes in instrumental focus. Relative trends in seeing quality are preserved on time scales shorter than a few months and it is found that local topography dominates the observed trends in daytime seeing quality.     

Spectroscopic investigation of a birefringent Lyot-filter for Hα

The instrumental profile of a Lyot-filter with 0.5 Å pass-band for H has been determined from photographic spectra obtained with a large grating spectrograph and a continuous light source.After fine adjustment of the filter, the transmission profile in parallel light agrees closely with the theoretical profile as given by crystal optics. The peak transmission has been found to be 12% of the incident unpolarized radiation.Convolving the measured instrumental profile with the average solar spectral distribution near H, it can be shown that the parasitic light (transmission outside the main pass-band) contributes 10% to the total light flux with the filter centered on the line. At wavelength shifts of 0.5 and 0.8Å, the parasitic light contribution is 25% and 40%, respectively.The deformation of the line-profile of various solar phenomena (faculae, filaments, flares) by the instrumental profile is discussed quantitatively.Mitteilungen aus dem Fraunhofer Institut Nr. 82.     

Circular scans for cosmic microwave background anisotropy observation and analysis

A number of experiments for measuring anisotropies of the cosmic microwave background (CMB) use scanning strategies in which temperature fluctuations are measured along circular scans on the sky. It is possible, from a large number of such intersecting circular scans, to build two-dimensional sky maps for subsequent analysis. However, since instrumental effects — especially the excess low-frequency 1/ f noise — project on to such two-dimensional maps in a non-trivial way, we discuss the analysis approach which focuses on information contained in the individual circular scans. This natural way of looking at CMB data from experiments scanning on the circles combines the advantages of elegant simplicity of Fourier series for the computation of statistics useful for constraining cosmological scenarios, and superior efficiency in analysing and quantifying most of the crucial instrumental effects.     

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.     

Sacramento Peak Observatory

This article provides a brief summary of instrumental developments at Sacramento Peak Observatory over the past decade, and describes highlights of past and present staff research programs.     

Instrumental polarization concerning magnetographic measurements,II

Solar Physics - To eliminate the influence of the instrumental polarization from magnetographic measurements an approximate method is presented, which enables to evaluate with a sufficient high...     

Will point sources spoil 21-cm tomography?

21-cm tomography is emerging as a promising probe of the cosmological dark ages and the epoch of reionization, as well as a tool for observational cosmology in general. However, serious sources of foreground contamination must be subtracted for experimental efforts to be viable. In this paper, we focus on the removal of unresolved extragalactic point sources with smooth spectra, and evaluate how the residual foreground contamination after cleaning depends on instrumental and algorithmic parameters. A crucial but often ignored complication is that the synthesized beam of an interferometer array shrinks towards higher frequency, causing complicated frequency structure in each sky pixel as 'frizz' far from the beam centre contracts across unresolved radio sources. We find that current-generation experiments should none the less be able to clean out this point source contamination adequately, and quantify the instrumental and algorithmic design specifications required to meet this foreground challenge.     

方位指向检测系统的参数测定

针对低纬子午环的观测方式和方位定向系统的精度，叙述了配备方位指向检测系统的必要性，介绍了方位指向检测的原理和系统参数的测定方法，分析了在仪器的三个支承螺杆有晃动的情况下，系统参数测定的不可靠性，提出了克服参数测定不可靠性影响的方法。     

Second‐order error propagation in the Mueller matrix of a spectropolarimeter

Accurate measurements of Stokes IQUV in spectral lines is required for precise reconstruction of stellar magnetic field geometries with Zeeman‐Dopper imaging. Spectral Zeeman features are intrinsically weak and subjected to a number of instrumental uncertainties. The aim of this work is to study the details of the instrumental uncertainties in the Stokes IQUV measurements in spectral lines and ways of their reduction. We make a practical comparison of the polarimetric performances of two high‐resolution échelle spectropolarimeters, namely SOFIN at the NOT, and HARPS at ESO. We show the residual spectra for both instruments to characterize the cross‐talk between the observed Stokes parameters. We employ a self‐calibrating least‐squares fit to eliminate some of the polarization uncertainties to derive the full Stokes vector from stellar spectra (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Non-Varying Granulation and Photospheric Network During the Extended 2007?�C?2009 Solar Minimum

We have analysed the wide band images taken by Hinode/SOT, in a blue continuum window and in the G-band, more or less on a daily basis in the frame of the synoptic program, to investigate the variation of the solar granulation and of the photospheric network with the activity cycle. A particular attention has been given to disentangle solar effects from instrumental ones. It appears that a substantial fraction of the images are more or less blurred and/or defocussed. During the analysed period November 2006??C?July 2010, the granulation contrast of the sharpest selected images decreased steadily, the granulation scale increased and the number of MBPs decreased (they are the Bright Points of Magnetic origin which form the photospheric network in G-band images). These trends are likely of instrumental origin. Consequently, the granulation and the photospheric network have most probably not changed during the extended solar minimum 2007??C?2009.