WFC3/IR Starter Guide

TL;DR

This starter guide consolidates practical workflows for analyzing archival WFC3/IR data from HST, emphasizing data access via MAST, product types (IMA, FLT, HAP, DRZ), and the role of drizzle-based mosaics. It details data visualization, artifact identification (cosmic rays, persistence, dead pixels, TVB), and baseline analysis strategies for photometry and spectroscopy, including PSF modeling with model libraries and non-linearity corrections. An explicit error-budget framework based on four components (Poisson, background, read noise, and a systematic floor) is provided, with guidance on using the Exposure Time Calculator to forecast $SNR$ and $\sigma = 1/ ext{SNR}$; the guide also covers time-dependent sensitivity corrections and unit conversions for cross-epoch comparisons. The document catalogs instrument modes (imaging, slitless spectroscopy, spatial scanning), calibration steps, and the software ecosystem (DrizzlePac, HSTaXe/SlitlessUtils, PSF tools, and notebook/tutorial resources) to enable robust archival studies and long-term preservation of WFC3/IR data usability.

Abstract

In this starter guide, we provide a high-level overview of analysis of WFC3/IR data available from the Mikulski Archive for Space Telescopes (MAST). We intend this guide as a starting point for users examining WFC3/IR data for the first time, or for those refreshing their memory on WFC3/IR data analysis. Therefore, we focus on the analysis of archival data, not preparing new observations. Three appendices include A) a summary of the instrument and an optical schematic, B) examples from the Exposure Time Calculator, and C) a glossary of uncommon acronyms. This report addresses only data from WFC3's IR channel; not the UVIS channel.

Figures (8)

• Figure 1: Left: WFC3/UVIS mosaic of the "Pillars of Creation," part of the Eagle Nebula. Right: WFC3/IR mosaic of the same field of view. Credit: NASA/ESA/STScI.
• Figure 2: One example of Time-Variable Background (TVB) contamination before (left) and after manual correction (right). The top row illustrates the full field of view; scattered Earthshine is characteristically brighter (whiter) in the left ${\sim}200$ columns of WFC3/IR images than the rest of the image. The bottom row zooms in on a 200×200 pixel region, providing detail and illustrating the improvement achieved by digital removal of TVB (cf. § \ref{['sec:software']}) [DHB].
• Figure 3: Left: F110W internal flatfield image ("p-flat") 4ac1921ri_pfl.fits (from IHB). Right: clusters of dead or anomalous pixels (arrowed) and three named features.
• Figure 4: The predicted fractional photometric uncertainty, ${\rm \sigma = 1/SNR}$, in dimensionless units, of a WFC3/IR F110W 353s observation of a solar type star (G2 V) plotted with respect to the star's J-band magnitude in the Vega photometric system. The combined value (black) is the quadrature sum of four components: A) Poisson noise from the star itself (blue); B) background noise (red); C) read noise (yellow), and D) a noise floor (grey). Results (points) are from the Exposure Time Calculator; e.g. the fractional uncertainty is 10%, i.e. ${\sigma}=0.1$ or ${\rm SNR}=10$, at J=24.5 mag (see text for details).
• Figure 5: Filter throughputs (from the IHB).