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Date and Time of the Query: 2019-03-18 T15:55:32 PDT
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For refcode 1990A&A...234...89F:
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Copyright by European Southern Observatory (ESO). Reproduced by permission
1990A&A...234...89F Research Note Systematic errors in the geometrical parameters of elliptical galaxies G. Fasano and C. Bonoli Osservatorio Astronomico, Vicolo dell'Osservatorio 5, I-35122 Padova, Italy Received October 25, 1989; accepted January 16, 1990 Abstract. We present a statistical comparison of the data available in the literature concerning the geometry of the isophotes in elliptical galaxies. We found that the discrepancies in position angles and ellipticities are much greater than the errors quoted by the various authors. Since they cannot be explained as due to the random errors arising from the ellipse fitting procedure, we suggest the influence of systematic errors to be largely underestimated. In particular we concentrate ourselves on the analysis of the outer isophotes where the mean disagreement is surprisingly high, probably due to the effect of bad flat fielding and/or sky removal. To interpret quantitatively this result, we have analyzed several synthetic galaxy images for which an incorrect flat fielding or sky subtraction has been simulated. Simple expressions for the expected errors, mainly depending on the estimated background uncertainty and on the ellipticity of the isophote, are given in some particular cases. Key words: galaxies: elliptical - photometry - image processing
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