Limiting Magnitudes of the Wide Field Survey Telescope (WFST)

TL;DR

This paper estimates the limiting magnitudes of the WFST, a powerful survey telescope, under various observational conditions, providing essential data for its scientific planning and data analysis.

Contribution

It presents the first detailed estimation of WFST's limiting magnitudes across multiple bands under realistic observing conditions.

Findings

Limiting magnitudes range from 21.50 to 23.61 mag depending on the band.

Magnitudes vary with Moon phase and atmospheric conditions, affecting observational sensitivity.

Provides a baseline for future observational planning and data interpretation.

Abstract

Expected to be of the highest survey power telescope in the northern hemisphere, the Wide Field Survey Telescope (WFST) will begin its routine observations of the northern sky since 2023. WFST will produce a lot of scientific data to support the researches of time-domain astronomy, asteroids and the solar system, galaxy formation and cosmology and so on. We estimated that the 5 $\sigma$ limiting magnitudes of WFST with 30 second exposure are $u=22.31$ mag, $g=23.42$ mag, $r=22.95$ mag, $i=22.43$ mag, $z=21.50$ mag, $w=23.61$ mag. The above values are calculated for the conditions of $airmass=1.2$, seeing = 0.75 arcsec, precipitable water vapour (PWV) = 2.5 mm and Moon-object separation = $45^{\circ}$ at the darkest New Moon night of the Lenghu site (V=22.30 mag, Moon phase $\theta=0^{\circ}$). The limiting magnitudes in different Moon phase conditions are also calculated. The calculations are based on the empirical transmittance data of WFST optics, the vendor provided CCD quantum efficiency, the atmospherical model transmittance and spectrum of the site. In the absence of measurement data such as sky transmittance and spectrum, we use model data.