MAGNITUDE TRANSFORMATION FROM RGB BAYER FILTER TO THE JOHNSON-COUSINS BVR FILTER BASED ON CAT-ITB TELESCOPE PHOTOMETRIC OBSERVATIONS OF M67, M11, IC 4665, AND RU 135 Raihan Amirul Husana (a*), Mahasena Putra (b), Anton Timur Jaelani (b), Chatief Kunjaya (b), Aliyya Nur Rahma (c), Firdaus Orvin Dwifauja Manalu (a)
a) Astronomy Study Program, FMIPA, Institut Teknologi Bandung, Jl. Ganesa 10, Bandung 40132, Indonesia
*hansamirul[at]gmail.com
b) Astronomy Research Group, FMIPA, Institut Teknologi Bandung, Jl. Ganesa 10, Bandung 40132, Indonesia
c) Astronomy Doctoral Program, FMIPA, Institut Teknologi Bandung, Jl. Ganesa 10, Bandung 40132, Indonesia
Abstract
Photometry is one of the astronomical measurement methods that provides astronomers with information about the brightness of astronomical objects at various wavelengths. Over time, various photometric systems have been developed. Therefore, transformations are necessary to convert results from one photometric system to another, with the aim of facilitating scientific communication among researchers working with various photometric systems. The CAT-ITB, or City Astronomical Telescope ITB, is an 11-inch optical telescope located at CAS ITB, equipped with detectors, one of which is the ZWO ASI 183MC that uses the RGB Bayer filter. Hence, transformation equations from the RGB Bayer filter system to the Johnson-Cousins BVR filter system must be established. By utilizing transformation equations that have historically been widely used by previous researchers, this study focuses on deriving the coefficients needed to solve those equations. Observational data of open clusters M67, RU 135, IC 4665, and M11 were obtained using CAT-ITB, which were used to optimize the transformation equations. The coefficients derived from M67 photometric data yielded the best results, with total RMS values for the magnitude transformations of clusters M67, RU 135, IC 4665, and M11 in each of the B_{Johnson}, V_{Johnson}, and R_{Cousins} conversions are 0.296, 0.152, and 0.161 respectively. All transformations produced small residuals and colour-magnitude diagrams that closely resemble those from catalog data.
