Herschel-PACS photometry of faint stars

TL;DR

This study assesses the photometric accuracy of Herschel-PACS for faint stars, establishing new FIR standard candidates with high precision and analyzing sensitivity dependence on flux and time.

Contribution

It provides a comprehensive sensitivity assessment of the PACS photometer and identifies five new faint FIR primary standard stars with high accuracy.

Findings

Established five new faint FIR standard stars with <6% accuracy.

Analyzed signal-to-noise dependence on flux and time.

Validated Herschel exposure-time predictions against observations.

Abstract

Our aims are to determine flux densities and their photometric accuracy for a set of seventeen stars that range in flux from intermediately bright (<2.5 Jy) to faint (>5 mJy) in the far-infrared (FIR). We also aim to derive signal-to-noise dependence with flux and time, and compare the results with predictions from the Herschel exposure-time calculation tool. The PACS faint star sample has allowed a comprehensive sensitivity assessment of the PACS photometer. Accurate photometry allows us to establish a set of five FIR primary standard candidates, namely alpha Ari, epsilon Lep, omega,Cap, HD41047 and 42Dra, which are 2 -- 20 times fainter than the faintest PACS fiducial standard (gamma Dra) with absolute accuracy of <6%. For three of these primary standard candidates, essential stellar parameters are known, meaning that a dedicated flux model code may be run.