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.

2Research School of Astronomy & Astrophysics, Australian National University, Private Bag, Weston Creek PO, ACT 2611, Australia


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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