Multiband GPI Imaging of the HR 4796A Debris Disk
Weinberger, Alycia J.; Schneider, Glenn; Duchêne, Gaspard; Esposito, Thomas M.; Hom, Justin; Kalas, Paul; Wilner, David J.; Arriaga, Pauline; De Rosa, Robert J.; Fitzgerald, Michael P.; Hines, Dean C.; Mazoyer, Johan; Millar-Blanchaer, Maxwell A.; Perrin, Marshall D.; Pueyo, Laurent; Rantakyrö, Fredrik T.; Matthews, Brenda; Marchis, Franck; Milli, Julien; Wolff, Schuyler; Draper, Zachary H.; Chilcote, Jeffrey; Ward-Duong, Kimberly; Wang, Jason J.; Bailey, Vanessa P.; Choquet, Élodie; Ren, Bin; Follette, Katherine B.; Hibon, Pascale; Patience, Jennifer; Rajan, Abhijith; Soummer, Rémi; Roudier, Gael M.; Rodigas, Timothy J.; Poteet, Charles A.; Chen, Christine; Stark, Christopher; Arnold, Jessica; Bruzzone, Juan Sebastián
United States, Poland, France, Canada, Chile, Greece, Netherlands
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.