Reference File Updates Following the Application of New Geometric Distortion and Walk Corrections I: Overview

TL;DR

This paper discusses the update of 56 reference files used in the CalCOS pipeline to incorporate new geometric distortion, delta-geometric, and walk corrections, leading to improved wavelength and flux calibration of COS FUV spectra.

Contribution

It presents the re-derivation of reference files to support new corrections, enhancing calibration accuracy for the Cosmic Origins Spectrograph data processing.

Findings

Improved wavelength calibration for COS FUV spectra.

Enhanced flux calibration accuracy.

Updated reference files for all relevant lifetime positions.

Abstract

The calibration of Cosmic Origins Spectrograph (COS) data is performed by the data processing pipeline known as CalCOS. CalCOS utilizes several reference files that store information required for data processing (e.g., dispersion solutions), and these reference files can be updated for the purpose of improving calibrated data products. In 2024 a major effort to improve the far-ultraviolet (FUV) geometric distortion, delta-geometric, and walk corrections was completed. Those three corrections occur early in the CalCOS workflow and shift photon events into the corrected reference frame ((XCORR, YCORR) coordinate system) in which subsequent calibration steps-and their reference files-are defined. This change necessitated the re-derivation of all "downstream" reference files in use at the time. Here we summarize the effort to create new versions of 56 reference files applicable to lifetime positions 1 through 6 and intended for use with the new geometric distortion, delta geometric, and walk corrections. The primary outcome of this work is improved wavelength and flux calibrations for COS FUV spectra.