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.
© 2020. The American Astronomical Society.
Chen, Christine; Mazoyer, Johan; Poteet, Charles A.; Ren, Bin; Duch ne, Gaspard; Hom, Justin; Arriaga, Pauline; Millar-Blanchaer, Maxwell A.; Arnold, Jessica; Bailey, Vanessa P.; Bruzzone, Juan Sebastián; Chilcote, Jeffrey; Choquet, lodie; De Rosa, Robert J.; Draper, Zachary H.; Esposito, Thomas M.; Fitzgerald, Michael P.; Follette, Katherine B.; Hibon, Pascale; Hines, Dean C.; Kalas, Paul; Marchis, Franck; Matthews, Brenda; Milli, Julien; Patience, Jennifer; Perrin, Marshall D.; Pueyo, Laurent; Rajan, Abhijith; Rantakyrö, Fredrik T.; Rodigas, Timothy J.; Roudier, Gael M.; Schneider, Glenn; Ward-Duong, Kimberly; and al, et, "Multiband GPI Imaging of the HR 4796A Debris Disk" (2020). Astronomy: Faculty Publications, Smith College, Northampton, MA.