The UKIRT wide field camera<i>ZYJHK</i>photometric system: calibration from 2MASS

TLDR

The photometric calibration of WFCAM data shows spatial systematics up to ~5 % whose causes are not fully understood. This paper describes the photometric calibration of WFCAM data taken with UKIRT. The calibration uses abundant 2MASS point sources, analyzes spatial systematics, applies a correction procedure, and examines transformations and Vega‑system corrections. After correction, WFCAM photometry is accurate to ~1.5 % for JHK and 2 % for ZY, with Z and Y bands sensitive to reddening, JHK largely unaffected, a small Y‑band Vega correction applied, and empirically determined throughput measurements presented.

Abstract

In this paper, we describe the photometric calibration of data taken with the near-infrared Wide Field Camera (WFCAM) on the United Kingdom Infrared Telescope (UKIRT). The broad-band ZYJHK data are directly calibrated from Two-Micron All-Sky Survey (2MASS) point sources which are abundant in every WFCAM pointing. We perform an analysis of spatial systematics in the photometric calibration, both inter- and intradetector show that these are present at up to the ∼5 per cent level in WFCAM. Although the causes of these systematics are not yet fully understood, a method for their removal is developed and tested. Following the application of the correction procedure, the photometric calibration of WFCAM is found to be accurate to ≃1.5 per cent for the JHK bands and 2 per cent for the ZY bands, meeting the survey requirements. We investigate the transformations between the 2MASS and WFCAM systems and find that the Z and Y calibrations are sensitive to the effects of interstellar reddening for large values of E(B−V)′, but that the JHK filters remain largely unaffected. We measure a small correction to the WFCAM Y-band photometry required to place WFCAM on a Vega system, and investigate WFCAM measurements of published standard stars from the list of UKIRT faint standards. Finally, we present empirically determined throughput measurements for WFCAM.