Magnitude Transformation from RGB Bayer Filter to the Johnson-Cousins BVR Filter Based on CAT-ITB Telescope Photometric Observations of Selected Open Clusters

Authors

  • Raihan Amirul Husana Astronomy Study Program, FMIPA, Institut Teknologi Bandung, Jl. Ganesa 10, Bandung 40132, Indonesia
  • Mahasena Putra Astronomy Research Group, FMIPA, Institut Teknologi Bandung, Jl. Ganesa 10, Bandung 40132, Indonesia
  • Anton Timur Jaelani Astronomy Research Group, FMIPA, Institut Teknologi Bandung, Jl. Ganesa 10, Bandung 40132, Indonesia
  • Chatief Kunjaya Astronomy Research Group, FMIPA, Institut Teknologi Bandung, Jl. Ganesa 10, Bandung 40132, Indonesia
  • Aliyya Nur Rahma Astronomy Doctoral Program, FMIPA, Institut Teknologi Bandung, Jl. Ganesa 10, Bandung 40132, Indonesia
  • Firdaus Orvin Dwifauja Manalu Astronomy Study Program, FMIPA, Institut Teknologi Bandung, Jl. Ganesa 10, Bandung 40132, Indonesia

DOI:

https://doi.org/10.21009/SPEKTRA.112.05

Keywords:

Photometry, Transformation, RGB Bayer Filter, Johnson-Cousins BVR Filter, Open Cluster

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. The total RMS values for the magnitude transformations of clusters M67, RU 135, IC 4665, and M11 in each of the BJohnson, VJohnson, and RCousins 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. This study contributes a validated set of transformation coefficients and zero-point constants specific to the CAT-ITB RGB Bayer detector system, offering a practical reference for converting RGB-based photometric observations into the standard Johnson-Cousins system for future small-telescope and citizen-science photometric research.

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Published

2026-08-30

How to Cite

Husana, R. A., Putra, M., Jaelani, A. T., Kunjaya, C., Rahma, A. N., & Manalu, F. O. D. (2026). Magnitude Transformation from RGB Bayer Filter to the Johnson-Cousins BVR Filter Based on CAT-ITB Telescope Photometric Observations of Selected Open Clusters. Spektra: Jurnal Fisika Dan Aplikasinya, 11(2), 151–162. https://doi.org/10.21009/SPEKTRA.112.05

Issue

Vol. 11 No. 2 (2026): SPEKTRA: Jurnal Fisika dan Aplikasinya, Volume 11 Issue 2, August 2026

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Articles

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Copyright (c) 2026 Raihan Amirul Husana, Mahasena Putra, Anton Timur Jaelani, Chatief Kunjaya, Aliyya Nur Rahma, Firdaus Orvin Dwifauja Manalu

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