scholarly journals Systematic Errors in Double Star Observations

1992 ◽  
Vol 135 ◽  
pp. 311-313 ◽  
Author(s):  
Geoffrey G. Douglass ◽  
Charles E. Worley
Keyword(s):  
Root Mean Square ◽  
Proximity Effect ◽  
Position Angle ◽  
Systematic Errors ◽  
Double Star ◽  
Mean Square ◽  
Double Stars ◽  
Visual Double Stars ◽  
Systematic Effects

AbstractWe have examined the visual and speckle observations of visual double stars made by 31 experienced observers in order to evaluate possible systematic errors in these series. Using 57 “definitive” orbits, we find no appreciable errors in position angle. We do find systematic effects in separation for some observers, and, in particular, a “proximity” effect for measurements of pairs closer than 0″.5.Root-mean-square residuals are:

scholarly journals The Hertzsprung Multiple Exposure Technique and its Application to 61 Cygni

1983 ◽  
Vol 62 ◽  
pp. 16-27
Author(s):  
F. J. Josties
Keyword(s):  
Random Error ◽  
Systematic Errors ◽  
Double Star ◽  
Small Field ◽  
Multiple Exposure ◽  
Observational System ◽  
Double Stars ◽  
Observational Technique ◽  
Systematic Effects ◽  
Exposure Technique

E. Hertzsprung developed the multiple exposure technique for observing double stars photographically around 1914 at Potsdam (Hertzsprung, 1920). The technique consists in taking one or more rows of 17 to 35 exposures of a small field which normally includes only the double star itself. The total number of exposures on a plate can vary from 17 to 140, depending primarily on the separation of the double star and the anticipated systematic effects in the observational system. An important feature of the technique is the use of objective gratings to substantially reduce the problem of magnitude error. The large number of exposures serve to reduce the random error, while the objective gratings, together with other innovations introduced by Hertzsprung, help to minimize the systematic errors. In this way Hertzsprung provided us with an observational technique of considerably higher accuracy than the traditional visual micrometer work.

scholarly journals The New Index Catalog of Visual Double Stars-WDS

1986 ◽  
Vol 109 ◽  
pp. 649-651
Author(s):  
Charles E. Worley ◽  
Geoffrey G. Douglass
Keyword(s):  
Double Star ◽  
Star Catalog ◽  
Star Data ◽  
Double Stars ◽  
Visual Double Stars

A new index catalog of visual double stars, the Washington Double Star Catalog (WDS), 1984.0, is now available in tape form. All of the double star data has been updated, as well as the notes to the catalog. This report summarizes the contents of the WDS and describes its compilation.

Global Climate Model Performance over Alaska and Greenland

2008 ◽  
Vol 21 (23) ◽  
pp. 6156-6174 ◽  
Author(s):  
John E. Walsh ◽  
William L. Chapman ◽  
Vladimir Romanovsky ◽  
Jens H. Christensen ◽  
Martin Stendel
Keyword(s):  
Sea Level ◽  
Root Mean Square ◽  
Global Climate ◽  
Systematic Errors ◽  
The Arctic ◽  
Future Climate Change ◽  
Mean Square ◽  
Sea Level Pressure ◽  
Level Pressure ◽  
Mean Square Errors

Abstract The performance of a set of 15 global climate models used in the Coupled Model Intercomparison Project is evaluated for Alaska and Greenland, and compared with the performance over broader pan-Arctic and Northern Hemisphere extratropical domains. Root-mean-square errors relative to the 1958–2000 climatology of the 40-yr ECMWF Re-Analysis (ERA-40) are summed over the seasonal cycles of three variables: surface air temperature, precipitation, and sea level pressure. The specific models that perform best over the larger domains tend to be the ones that perform best over Alaska and Greenland. The rankings of the models are largely unchanged when the bias of each model’s climatological annual mean is removed prior to the error calculation for the individual models. The annual mean biases typically account for about half of the models’ root-mean-square errors. However, the root-mean-square errors of the models are generally much larger than the biases of the composite output, indicating that the systematic errors differ considerably among the models. There is a tendency for the models with smaller errors to simulate a larger greenhouse warming over the Arctic, as well as larger increases of Arctic precipitation and decreases of Arctic sea level pressure, when greenhouse gas concentrations are increased. Because several models have substantially smaller systematic errors than the other models, the differences in greenhouse projections imply that the choice of a subset of models may offer a viable approach to narrowing the uncertainty and obtaining more robust estimates of future climate change in regions such as Alaska, Greenland, and the broader Arctic.

scholarly journals Observational Procedures for Visual Double-Star Work

1973 ◽  
Vol 18 ◽  
pp. 81-87
Author(s):  
Otto G. Franz
Keyword(s):  
United States ◽  
The United States ◽  
Double Star ◽  
Image Tube ◽  
International Conference ◽  
Double Stars ◽  
Visual Double Stars ◽  
Early Image ◽  
The Subject ◽  
Observational Techniques

When IAU Symposium No. 17, the most recent international conference on visual double stars to take place in the United States, was held in Berkeley in 1961, there was little discussion on observational techniques and no introductory remarks were presented on the subject. The reasons for this are obvious. The classical techniques of double-star observation, those that provided virtually all the data available on visual double stars, were too well known to require introduction or discussions; other methods, with the possible exception of early image tube and electronic camera experiments, did not exist.Today, more than ten years later, most double-star work continues to be carried out by the same classical techniques. However, several methods have come into use or have recently been developed that are capable of contributing importantly to visual double-star research.

scholarly journals The Discovery of Double Stars at Occultations

1983 ◽  
Vol 62 ◽  
pp. 63-72 ◽  
Author(s):  
David S. Evans
Keyword(s):  
Position Angle ◽  
Visual Observation ◽  
Double Star ◽  
Double Stars ◽  
Photoelectric Observations ◽  
Vector Separation ◽  
Successful Observation

When systematic photoelectric observations of occultations were started some dozen years ago it was realised that they yielded a significant crop of double star discoveries and observations. The limitations of the method were well recognised: only about ten percent of the area of the sky would ever be available and one could not choose which stars to be observed. Moreover the data obtained from a successful observation of a double star are less comprehensive than the normal visual observation. The result is the vector separation or the true separation projected along a line perpendicular to the actual lunar limb, that is the position angle of the point of occultation modified by the slope of the limb at that point.

Travel-time errors in the laterally inhomogeneous earth

1971 ◽  
Vol 61 (6) ◽  
pp. 1639-1654 ◽  
Author(s):  
Cinna Lomnitz
Keyword(s):  
Travel Time ◽  
Root Mean Square ◽  
Time Estimation ◽  
Systematic Errors ◽  
Least Square ◽  
Travel Time Estimation ◽  
Mean Square ◽  
Travel Times ◽  
The Earth ◽  
Lateral Inhomogeneity

abstract Travel times from earthquakes or explosions contain both positive and negative systematic errors. Positive skews in travel-time residuals due to epicenter mislocation, and negative skews due to lateral inhomogeneity in the Earth, are analyzed. Methods for travel-time estimation are critically reviewed. Recent travel-time tables, including the J-B tables, are within the range of root-mean-square travel-time fluctuations; the J-B tables are systematically late but cannot be reliably improved by least-square methods. Effects of lateral inhomogeneity at teleseismic distances can be estimated by chronoidal methods independently of standard tables, but the available explosion data are insufficiently well-distributed in azimuth and distance for this purpose.

scholarly journals CCD Astrometry and Photometry of Visual Double Stars: Northern Hipparcos Wide Pairs Measured in the Years 2003-2005

2006 ◽  
Vol 2 (S240) ◽  
pp. 613-618
Author(s):  
D. Sinachopoulos ◽  
P. Gavras ◽  
Th. Medupe ◽  
Ch. Ducourant ◽  
O. Dionatos
Keyword(s):  
Angular Separation ◽  
Double Star ◽  
Solar Neighborhood ◽  
Common Origin ◽  
Double Stars ◽  
The North ◽  
Visual Double Stars ◽  
Wide Pairs ◽  
Stellar Formation ◽  
Formation And Evolution

AbstractThe relative positions of Hipparcos visual double star components are currently known with a precision around fifty mas. Modern CCD astrometric observations of these objects achieve an accuracy of their angular separation between ten and twenty mas per observation. New CCD measurements have been obtained at Kryonerion Observatory in the north hemisphere. They provide current relative positions of visual double stars which are at least twice as accurate as the ones provided by Hipparcos. The new measurements will permit us to extract the physical pairs from the sample, and the double stars, which have components of common origin. Final statistics of these systems will improve our understanding of stellar formation and evolution rates of wide binaries in the solar neighborhood.

scholarly journals Detection of Double Stars with the Two-Color Refractometer

1983 ◽  
Vol 62 ◽  
pp. 28-35 ◽  
Author(s):  
James W. Christy ◽  
Dennis D. Wellnitz ◽  
Douglas G. Currie
Keyword(s):  
Position Angle ◽  
Angular Distance ◽  
Double Star ◽  
Measured Quantity ◽  
University Of Maryland ◽  
Additional Information ◽  
Double Stars ◽  
Color Differences ◽  
Nearby Stars ◽  
The University

AbstractAttempts to detect double stars are being made with the Two-Color Refractometer (TCR). The refractometer is an instrument developed by the Quantum Electronics Group of the University of Maryland to measure atmospheric refraction.During check-out observations using the U.S. Naval Observatory’s (USNO’s) 24“ reflecting telescope, the refractometer is being used to detect the astrometric separation of the ultraviolet and red photocenters of the combined light from a double star, differentially referenced to nearby stars. The refractometer contains two dispersive wedges which null the incoming dispersion; the positions of the wedges then provide a measure of the dispersion of the incoming light. The angular part of this measure immediately gives the position angle of the double. The angular distance between the two components of the pair is a combined function of the measured quantity and of the magnitude and color differences of the components of the double star, and is therefore obtainable only with additional information.

scholarly journals Double Star Astrometry with the Hipparcos Data

1995 ◽  
Vol 166 ◽  
pp. 69-76
Author(s):  
F. Mignard
Keyword(s):  
Position Angle ◽  
Double Star ◽  
Recognition Procedure ◽  
Double Stars ◽  
Multiple Stars ◽  
Relative Coordinates ◽  
Double And Multiple Stars

As we approach the final processing of the observations carried out by HIPPARCOS, in particular for the double and multiple stars, it is possible to provide reliable statistics on the number of such objects detected and on the quality of the relative and absolute astrometry and photometry. About 24 000 stars have been recognized as non-single, including 11 000 already known as double and multiple before the mission and 13000 discovered by Hipparcos. Also, a subset of 16 000 stars among the 24 000 have been successfully solved for their relative coordinates (position angle and separation) with an accuracy in the range of 3 to 30 mas, including 7000 new double stars. I outline in this paper the principle of the internal recognition procedure and present some statistics on the solution.

scholarly journals HIPPARCOS First Results in the Double Star Processing by the FAST Consortium

1992 ◽  
Vol 135 ◽  
pp. 403-411
Author(s):  
F. Mignard ◽  
M. Badiali ◽  
P.L. Bernacca ◽  
H. Bernstein ◽  
D. Cardini ◽  
...  
Keyword(s):  
Position Angle ◽  
Double Star ◽  
Double Stars ◽  
Multiple Stars ◽  
Relative Coordinates ◽  
First Results ◽  
Double And Multiple Stars ◽  
Quantitative Results ◽  
One Year

AbstractAfter the processing of one year of observations carried out by HIPPARCOS it is possible to provide quantitative results as to the number of new double and multiple stars to be detected and the real capacity of this mission to perform relative astrometry on double stars. We present and discuss the methods developed to this end and include the first results concerning the detection statistics and the determination of separation and position angle for double stars. About 16,000 stars have been recognized as non-single, including 9,000 already known as double and mutliple before the mission. Also, a subset of 10,500 stars have been successfully solved for their relative coordinates with an accuracy in the range of 3 to 10 mas.

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