Transformation Relations for UBV Photometric System of 1m Telescope at the TÜBİTAK National Observatory

Abstract

𝑈𝐵𝑉 CCDobservations of standard stars selected from Landolt (2009, 2013) were performed using the 1-meter telescope (T100) of the TÜBİTAK National Observatory equipped with a CCD camera and Bessell𝑈𝐵𝑉 filters. Observations were conducted over an extended period, spanning from 2012 to 2024, covering a total of 50 photometric nights. Photometric measurements were used to find the standard transformation relations of the T100 photometric system. The atmospheric extinction coefficients, zero points and transformation coefficients of each night were determined. It was observed that the primary extinction coefficients decreased until the year 2019 and increased after that year. Strong seasonal variations in the extinction coefficients were not evident. Small differences in seasonal median values of them were used to attempt to find the atmospheric extinction sources. We found calculated minus catalogue values for each standard star, Δ(U-B), Δ(B-V), and Δ𝑉. The means and standard deviations of these differences were estimated to be 1.4±76, 1.9±18, and 0.0±36 mmag, respectively. We found that our data well matched Landolt’s standards for 𝑉 andB-V, i.e. there are no systematic differences. However, there are systematic differences for U-B between the two photometric systems, which is probably originated from the quantum efficiency differences of the detectors used in the photometric systems, although the median differences are relatively small (|Δ(U-B)|<50 mmag) for stars with-0.5<(U-B)<1.6 and 0.2<(B-V)<1.8. We conclude that the transformation relations found in this study can be used for standardised photometry with the T100 photometric system.