Standard Stars - CCD Photometry, Transformations and Comparisons

Hwankyung Sung , Michael. S. Bessell, PASA, 17 (3), 244.
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Contents Page: Volume 17, Number 3

Standard Stars - CCD Photometry, Transformations and Comparisons

Hwankyung Sung 1
Michael. S. Bessell 2

1Bohyun-san Optical Astronomy Observatory, Yeongcheon 770-820, Korea.
sungh@boao.re.kr

2Research School of Astronomy & Astrophysics, Australian National University, Private Bag, Weston Creek PO, ACT 2611, Australia
bessell@mso.anu.edu.au

Abstract:

We discuss variations of the atmospheric extinction coefficients and transformation equations to the standard UBVRI system based on observations of standard stars during 1996-1997 at Siding Spring Observatory using a thinned SITe CCD and coloured glass filters. In the transformation from the initial natural system to the Landolt version of the standard system, a large non-linear term related to the Balmer discontinuity was required for the U transformation. We then modified the U filter and the subsequent transformation to the SAAO version of the standard UBVRI system had only small non-linear correction terms for U, B, and I. The correction terms relating to U and B are evidently due to the Balmer discontinuity, while that relating to I seems to be due to the Paschen discontinuity at

$\lambda \approx 8200\AA$. We also compared the results with Landolt's observations, and confirmed the difference between the two sets of standard stars (SAAO and Landolt)

Keywords: techniques: photometric -- stars: imaging -- standards





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