Relative and absolute calibration for multi-band data collected with the 2.2m ESO/MPI and 1.54m Danish Telescopes

TL;DR

This paper details calibration strategies for multi-band astronomical data from two telescopes, addressing filter differences and positional effects to improve photometric accuracy.

Contribution

It introduces specific calibration methods for different filter sets and corrects positional effects in multi-chip data, enhancing data consistency.

Findings

Calibration methods effectively correct filter and positional effects.

Positional trends identified and corrected in photometry.

Improved photometric accuracy across datasets.

Abstract

We present the strategies adopted in the relative and absolute calibration of two different data sets: U,B,V,I-band images collected with the Wide Field Imager (WFI) mosaic camera mounted on the 2.2m ESO/MPI Telescope and u,v,b,y Stroemgren images collected with the 1.54m Danish Telescope (ESO, La Silla). In the case of the WFI camera we adopted two methods for the calibration, one for images collected before 2002, with the ESO filters U/38_ESO841 and B/99_ESO842, and a different one for data secured after 2002, with the filters U/50_ESO877 and B/123_ESO878. The positional and color effects turned out to be stronger for images collected with the old filters. The eight WFI chips of these images were corrected one by one, while in the case of images secured with the new filters, we corrected the entire mosaic in a single step. In the case of the Danish data set, we compared point-spread function (PSF) and aperture photometry for each frame, finding a trend in both the X and Y directions of the chip. The corrections resulted in a set of first and second order polynomials to be applied to the instrumental magnitudes of each individual frame as a function of the star position.