The UKIRT Wide Field Camera ZYJHK Photometric System: Calibration from 2MASS

TL;DR

This paper details the calibration process of WFCAM data using 2MASS sources, addresses spatial systematics, and achieves high photometric accuracy suitable for survey needs.

Contribution

It introduces a calibration method from 2MASS data, analyzes spatial systematics, and provides throughput measurements for WFCAM.

Findings

Calibration accuracy of ~1.5% for JHK bands

Systematics present at up to 5%, corrected to improve accuracy

WFCAM transformations are affected by interstellar reddening in Z and Y bands

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 broadband ZYJHK data are directly calibrated from 2MASS point sources which are abundant in every WFCAM pointing. We perform an analysis of spatial systematics in the photometric calibration, both inter- and intra-detector and 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 application of the correction procedure the photometric calibration of WFCAM is found to be accurate to approximately 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 calibration is 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.