Limiting magnitudes and night sky brightness at the Langkawi National Observatory based on observations of standard stars

We present the estimation of limiting magnitudes and night sky brightness at the Langkawi National Observatory with observations of selected standard stars. We first derived the transformation equations using the standard stars in our CCD images, followed by photometric calibration of the 2MASS point sources located in these images. Based on the calibrated magnitudes, we estimated a limiting magnitude of V=16.6±0.1 mag can be reached with a 60 second exposure time. For the night sky brightness, our measurements give V_sky=19.0±0.1 mag arc-second^-2 at the zenith direction. Our results can be used for planning the night time observations at the Langkawi National Observatory.