Characterizing the Atmospheres of the HR8799 Planets with HST/WFC3

TL;DR

This study uses HST/WFC3 to analyze the atmospheres of HR8799 planets, detecting water absorption and refining atmospheric models with high-contrast imaging techniques.

Contribution

First HST/WFC3 observations of HR8799 planets using advanced image processing, including water-band detection and improved atmospheric characterization.

Findings

Detected HR8799 b and c in F127M; first detection of HR8799 b in water-band F139M.

Photometry of HR8799 c matches atmospheric models, resolving previous flux modeling issues.

Achieved high-contrast imaging at sub-arcsecond resolution with HST.

Abstract

We present results from a Hubble Space Telescope (HST) program characterizing the atmospheres of the outer two planets, in the HR8799 system. The images were taken over 15 orbits in three near-infrared medium-band filters - F098M, F127M and F139M - using the Wide Field Camera 3. One of the three filters is sensitive to water absorption band inaccessible from ground-based observations, providing a unique probe of the thermal emission from the atmospheres of these young giant planets. The observations were taken at 30 different spacecraft rolls to enable angular differential imaging, and the full data set was analyzed with the Karhunen-Loeve Image Projection (KLIP) routine, an advanced image processing algorithm adapted to work with HST data. To achieve the required high contrast at sub arcsecond resolution, we utilized the pointing accuracy of HST in combination with an improved pipeline designed to combine the dithered, angular differential imaging data with an algorithm designed to both improve the image resolution and accurately measure the photometry. The results include F127M ($J$) detections of the outer planets, HR8799 b and c and the first detection of HR8799 b in the water-band (F139M) filter. The F127M photometry for HR8799 c agrees well with fitted atmospheric models resolving a long standing difficulty to model the near-IR flux for the planet consistently