Effects Of Atmospheric Dispersion Research Articles

The impact of atmospheric dispersion in the performance of high-resolution spectrographs

ABSTRACT Differential atmospheric dispersion is a wavelength-dependent effect introduced by the atmosphere. It is one of the instrumental errors that can affect the position of the target as perceived on the sky and its flux distribution. This effect will affect the results of astronomical observations if not corrected by an atmospheric dispersion corrector (ADC). In high-resolution spectrographs, in order to reach a radial velocity (RV) precision of 10 cm s−1, an ADC is expected to return residuals at only a few tens of milliarcseconds (mas). In fact, current state-of-the-art spectrograph conservatively require this level of residuals, although no work has been done to quantify the impact of atmospheric dispersion. In this work, we test the effect of atmospheric dispersion on astronomical observations in general, and in particular on RV precision degradation and flux losses. Our scientific objective was to quantify the amount of residuals needed to fulfil the requirements set on an ADC during the design phase. We found that up to a dispersion of 100 mas, the effect on the RV is negligible. However, on the flux losses, such a dispersion can create a loss of ∼2 per cent at 380 nm, a significant value when efficiency is critical. The requirements set on ADC residuals should take into consideration the atmospheric conditions where the ADC will function, and also all the aspects related with not only the RV precision requirements but also the guiding camera used, the tolerances on the flux loss, and the different melt data of the chosen glasses.

大气色散对4 m望远镜成像分辨力的影响与校正

This paper counts and analyzes the effect of atmospheric dispersion on image resolution of 4 m optical telescope system. It is introduced that atmospheric dispersion will influence image resolution when the zenith angle is larger than 15°. With the zenith angle increasing,especially up to 45°,the image quality would be degraded greatly,so it is quite necessary that the atmospheric dispersion corrector( ADC) is applied to compensate atmospheric dispersion. By comparing the advantages and drawbacks of three modes for ADC: tilt mode,move mode and rotate mode,the glue prism pairs is used to eliminate the influence of atmospheric dispersion for 4 m telescope system,which would rotate with each other when the zenith angle changes. In 4 mtelescope optical system,the ADC is positioned in front of imaging elements of collimated optical layout. Then we analyze the relation between zenith angle and rotating angle of ADC. The largest wedge angle of the ADC is9. 65°,and the rotating accuracy is ± 0. 1°,having an effect of 1 /1 000 on resolution. So it is obviously concluded that the results satisfied the request of image resolution,and it is an effective way for the analysis of atmospheric dispersion and the application of ADC.

自适应光学系统校正后实际分辨率评价指标

A new index,Resolved Cells Ratio( RCR),was proposed to evaluate the actual resolution of ground-based large-aperture telescope for spatial objective observation after adaptive optical system partial correcting. We discussed the physical meaning of the RCR combined with the observation instances of the 1. 23 adaptive optical telescope. The range of the application of the RCR,the error influence factors and the effect of the atmospheric dispersion on the RCR were also analyzed. The result shows that the RCR could completely reflect the correction effectiveness of the adaptive optical telescope and the physical meaning of the RCR wasintuitive. RCR can be applied to the estimation of the correction effectiveness of a telescope that can get the characterization of the wavefront. The error of the RCR mainly depend on the measurement error of the wavefront sensor. The effect of atmospheric dispersion on the RCR can be neglected.

Atmospheric Dispersion Effects in Weak Lensing Measurements

ABSTRACTThe wavelength dependence of atmospheric refraction causes elongation of finite-bandwidth images along the elevation vector, which produces spurious signals in weak gravitational lensing shear measurements unless this atmospheric dispersion is calibrated and removed to high precision. Because astrometric solutions and point spread function (PSF) characteristics are typically calibrated from stellar images, differences between the reference stars’ spectra and the galaxies’ spectra will leave residual errors in both the astrometric positions () and in the second moment (width) of the wavelength-averaged PSF (ΔV) for galaxies. We estimate the level of ΔV that will induce spurious weak lensing signals in PSF-corrected galaxy shapes that exceed the statistical errors of the Dark Energy Survey (DES) and the Large Synoptic Survey Telescope (LSST) cosmic-shear experiments. We also estimate the signals that will produce unacceptable spurious distortions after stacking of exposures taken at different air masses and hour angles. Using standard galaxy and stellar spectral templates we calculate the resultant errors in the griz bands and find that atmospheric dispersion shear systematics, left uncorrected, are up to 6 and 2 times larger in g and r bands, respectively, than the thresholds at which they become significant contributors to the DES error budget, but can be safely ignored in i and z bands. For the stricter LSST requirements, the factors are about 30, 10, and 3 in g, r, and i bands, respectively. These shear systematic errors scale with observed zenith angle z as 〈 tan2 z〉, for which we take a nominal value of unity—simulations of DES and LSST suggest 0.6–1.0. We find that a simple correction linear in galaxy color is accurate enough to reduce dispersion shear systematics to insignificant levels in the r band for DES and i band for LSST, but still as much 5× above the threshold of significance for LSST r-band observations. More complex approaches to correction of the atmospheric dispersion signal will likely be able to reduce the systematic cosmic shear errors below statistical errors for LSST r band. But g-band dispersion effects remain large enough that it seems likely that induced systematics will dominate the statistical errors of both surveys, and cosmic-shear measurements should rely on the redder bands.

Correlation of stellar scintillation in different photometric bands

Theoretical relations were obtained to calculate the correlation of stellar scintillation, when a star is measured simultaneously in two different photometric bands (channels). Differential color scintillation and the respective indices are proposed for practical evaluation of the correlation. Asymptotic dependence for the case of an infinitely small receiving aperture is derived and analyzed. The effect of atmospheric dispersion, which transforms the color differences into spatial differences, is examined. Additionally, the effect of the deviation of real optical turbulence from Kolmogorov turbulence is estimated. The obtained relations were compared with simultaneous measurements in three photometric bands and different receiving apertures in the range of 1 to 15 cm. It is shown that the measurements and calculated estimations of the color scintillation agree well.

The Effects of Atmospheric Dispersion on High-Resolution Solar Spectroscopy

We investigate the effects of atmospheric dispersion on observations of the Sun at the ever-higher spatial resolutions afforded by increased apertures and improved techniques. The problems induced by atmospheric refraction are particularly significant for solar physics because the Sun is often best observed at low elevations, and the effect of the image displacement is not merely a loss of efficiency, but the mixing of information originating from different points on the solar surface. We calculate the magnitude of the atmospheric dispersion for the Sun during the year and examine the problems produced by this dispersion in both spectrographic and filter observations. We describe an observing technique for scanning spectrograph observations that minimizes the effects of the atmospheric dispersion while maintaining a regular scanning geometry. Such an approach could be useful for the new class of high-resolution solar spectrographs, such as SPINOR, POLIS, TRIPPEL, and ViSP.

Improvements for group delay fringe tracking

Group delay fringe tracking using spectrally-dispersed fringes is suitable for stabilising the optical path difference in ground-based astronomical optical interferometers in low light situations. We discuss the performance of group delay tracking algorithms when the effects of atmospheric dispersion, high-frequency atmospheric temporal phase variations, non-ideal path modulation, non-ideal spectral sampling, and the detection artifacts introduced by electron-multiplying CCDs (EMCCDs) are taken into account, and we present ways in which the tracking capability can be optimised in the presence of these effects.

THE IMPLICATIONS OF ATMOSPHERIC EFFECTS FOR FIBER-FED SPECTROSCOPY

ABSTRACT The effects of atmospheric dispersion in terms of S/N losses are calculated as a function of displacement of an optical fiber with respect to the source image. The results are presented as response curves for a wide variety of seeing conditions and source-to-sky brightness ratios. The limitations of fiber systems for precision spectrophotometry and ways in which these limitations may be overcome are discussed. The effects of differential refraction and field rotation are also calculated, showing that it can be a nonnegligible effect at large zenith angles for observations of more than 1-hour duration.

TWO-DIMENSIONAL SPECTROPHOTOMETRY OF PLANETARY NEBULAE BY CCD IMAGING.

ABSTRACT The authors have derived the spatial distribution of the electron temperature and density and the ionic abundances of O+, O++, N+, and S+ from CCD images of the planetary nebulae NGC 40 and NGC 6826 taken in the important emission lines of [O II], [O III], Hβ, [N II], and [S II]. Advantages of the imaging technique include complete spatial coverage and excellent spatial resolution, good light throughput, reduced effects of spatial averaging over filamented and knotted regions, elimination of the effects of atmospheric dispersion, and absolute spectrophotometry for objects having angular sizes of several arcmin. The disadvantages include additional effort to analyze the data, limited spectral coverage, and added difficulties in deblending nearby lines, removing the nebular continuum contribution, and correcting for nonphotometric conditions.

A survey of trigonometric parallaxes and proper motions with the UK Schmidt Telescope: I. Methods and first results for stars brighter than B = 14 in a field near the South Galactic Pole

AbstractIn an attempt to investigate the statistics of stars in the solar neighbourhood, independent of the bias toward high velocity stars introduced by selection of stars with large proper motion, a major astrometric investigation is being carried out at RGO using U.K. Schmidt plates measured on the GALAXY machine.So far more than 15000 objects brighter than B = 18 in a field near the South Galactic Pole have been measured on more than 50 plates taken between 19 74 and 1977.This paper describes the methods of analysis and the results of a pilot investigation on nearly 900 stars with B < 14. The measurements show a very high degree of internal consistence, demonstrating the astrometric excellence of the U.K. Schmidt telescope and the GALAXY machine; random errors of measurement are found to be about ±0075 (=1.1.μm) per coordinate over the whole area (4° x 4°) measured, using a simple linear plate constant model for all plates. The external error of a single component of proper motion is estimated to be ± 0013 which is exactly consistent with the internal measurement error. The external error of a parallax in the present data is about ± 0018 whereas that predicted from the errors of measurement, and the self-consistency of two subsets of the data, is ± 0013; it is shown that the discrepancy can be largely accounted for by the random errors (± O11) in the B-V colours used in computing the effect of atmospheric dispersion, and should be reduced when better photometry becomes available.

Minimizing atmospheric dispersion effects in compensated imaging

A compensated imaging system that corrects optical path length distortions due to atmospheric turbulence by means of an achromatic corrector will have residual errors caused by the dispersion of the atmosphere. These errors become significant for astronomical objects at large zenith angles, but they may be minimized by special dispersion correctors.

Astronomical Objective Gratings

This article deals with the use of objective gratings in contemporary astronomy. It is shown that their use in photometry may help considerably toward reducing the photoelectric effort in calibrating the magnitudes of faint stars. Their usefulness in dense star fields is also explained. The article contains a discussion of the precautions that have to be taken to ensure first-class results. The use of objective gratings in astrometry for the elimination of magnitude equation is explained. The effects of atmospheric dispersion in work with objective gratings are discussed.

Effects of Atmospheric Dispersion upon Determinations of Stellar Parallax

Effects of Atmospheric Dispersion upon Determinations of Stellar Parallax

The Effect of Atmospheric Dispersion on the Greenwich Photographs of Eros

The Effect of Atmospheric Dispersion on the Greenwich Photographs of Eros

On the Effect of Atmospheric Dispersion on the position of a Star

On the Effect of Atmospheric Dispersion on the position of a Star

Note on the Effect of Atmospheric Dispersion on the Determination of the Solar Parallax by Meridian Observations of Mars

Note on the Effect of Atmospheric Dispersion on the Determination of the Solar Parallax by Meridian Observations of Mars