Characterizing the Atmospheres of the HR8799 ExoPlanets

Characterizing the Atmospheres of the HR8799 Planets with HST/WFC3

Authors:

Rajan et al

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

Gemini Planet Imager Spectroscopy of Exoplanets HR 8799c & d

Gemini Planet Imager Spectroscopy of the HR 8799 planets c and d

Authors:

Ingraham et al

Abstract:

During the first-light run of the Gemini Planet Imager (GPI) we obtained K-band spectra of exoplanets HR 8799 c and d. Analysis of the spectra indicates that planet d may be warmer than planet c. Comparisons to recent patchy cloud models and previously obtained observations over multiple wavelengths confirm that thick clouds combined with horizontal variation in the cloud cover generally reproduce the planets' spectral energy distributions. When combined with the 3 to 4 um photometric data points, the observations provide strong constraints on the atmospheric methane content for both planets. The data also provide further evidence that future modeling efforts must include cloud opacity, possibly including cloud holes, disequilibrium chemistry, and super-solar metallicity.