The InfraRed Imaging Spectrograph (IRIS) for TMT: photometric precision and ghost analysis

TL;DR

This paper evaluates the photometric precision of the IRIS instrument for TMT, analyzing ghosting effects and demonstrating that ghosts have minimal impact on flux measurements in typical scenarios.

Contribution

It provides a detailed simulation-based analysis of ghosting effects and photometric accuracy for the IRIS instrument, informing its science capabilities.

Findings

Ghost images generally have negligible impact on flux counts.

Ghosts only significantly affect measurements when co-aligned with a much brighter source.

Photometric precision and accuracy are validated through simulations.

Abstract

The InfraRed Imaging Spectrograph (IRIS) is a first-light instrument for the Thirty Meter Telescope (TMT) that will be used to sample the corrected adaptive optics field by NFIRAOS with a near-infrared (0.8 - 2.4 $\mu$m) imaging camera and Integral Field Spectrograph (IFS). In order to understand the science case specifications of the IRIS instrument, we use the IRIS data simulator to characterize photometric precision and accuracy of the IRIS imager. We present the results of investigation into the effects of potential ghosting in the IRIS optical design. Each source in the IRIS imager field of view results in ghost images on the detector from IRIS's wedge filters, entrance window, and Atmospheric Dispersion Corrector (ADC) prism. We incorporated each of these ghosts into the IRIS simulator by simulating an appropriate magnitude point source at a specified pixel distance, and for the case of the extended ghosts redistributing flux evenly over the area specified by IRIS's optical design. We simulate the ghosting impact on the photometric capabilities, and found that ghosts generally contribute negligible effects on the flux counts for point sources except for extreme cases where ghosts coalign with a star of $\Delta$m$>$2 fainter than the ghost source. Lastly, we explore the photometric precision and accuracy for single sources and crowded field photometry on the IRIS imager.