Multiband GPI Imaging of the HR 4796A Debris Disk
Christine Chen, Johan Mazoyer, Charles A. Poteet, Bin Ren, Gaspard Duchêne, Justin Hom, Pauline Arriaga, Maxwell A. Millar-Blanchaer, Jessica Arnold, Vanessa P. Bailey, Juan Sebastián Bruzzone, Jeffrey Chilcote, Élodie Choquet, Robert J. De Rosa, Zachary H. Draper, Thomas M. Esposito, Michael P. Fitzgerald, Katherine B. Follette, Pascale Hibon, Dean C. Hines, Paul Kalas, Franck Marchis, Brenda Matthews, Julien Milli, Jennifer Patience, Marshall D. Perrin, Laurent Pueyo, Abhijith Rajan, Fredrik T. Rantakyrö, Timothy J. Rodigas, Gael M. Roudier, Glenn Schneider, Rémi Soummer, Christopher Stark, Jason J. Wang, Kimberly Ward-Duong, Alycia J. Weinberger, David J. Wilner, Schuyler Wolff
Abstract
Abstract We have obtained Gemini Planet Imager (GPI) J -, H -, K1 -, and K2 -Spec observations of the iconic debris ring around the young, main-sequence star HR 4796A. We applied several point-spread function (PSF) subtraction techniques to the observations (Mask-and-Interpolate, RDI-NMF, RDI-KLIP, and ADI-KLIP) to measure the geometric parameters and the scattering phase function for the disk. To understand the systematic errors associated with PSF subtraction, we also forward-modeled the observations using a Markov Chain Monte Carlo framework and a simple model for the disk. We found that measurements of the disk geometric parameters were robust, with all of our analyses yielding consistent results; however, measurements of the scattering phase function were challenging to reconstruct from PSF-subtracted images, despite extensive testing. As a result, we estimated the scattering phase function using disk modeling. We searched for a dependence of the scattering phase function with respect to the GPI filters but found none. We compared the H -band scattering phase function with that measured by Hubble Space Telescope STIS at visual wavelengths and discovered a blue color at small scattering angles and a red color at large scattering angles, consistent with predictions and laboratory measurements of large grains. Finally, we successfully modeled the SPHERE H2 HR 4796A scattered phase function using a distribution of hollow spheres composed of silicates, carbon, and metallic iron.