IRS-TR 12001: Spectral Pointing-Induced Throughput Error and Spectral Shape in Short-Low Order 1

TL;DR

This paper examines how spectral shape and throughput errors in the IRS Short-Low module are affected by source positioning, revealing asymmetries in the point spread function that influence calibration accuracy.

Contribution

It introduces a method to identify valid spectra for IRS calibration by analyzing flux ratios versus throughput to account for pointing-induced errors.

Findings

Spectral shape varies with throughput due to source positioning.

Asymmetries in the point spread function cause a double-valued relationship.

The method helps improve calibration accuracy by filtering out affected spectra.

Abstract

We investigate how the shape of a spectrum in the Short-Low module on the IRS varies with its overall throughput, which depends on how well centered a source is in the spectroscopic slit. Using flux ratios to quantify the overall slope or color of the spectrum and plotting them vs. the overall throughput reveals a double-valued function, which arises from asymmetries in the point spread function. We use this plot as a means of determining which individual spectra are valid for calibrating the IRS.