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Published July 20, 2020 | Published + Accepted Version
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Multiband GPI Imaging of the HR 4796A Debris Disk


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.

Additional Information

© 2020. The American Astronomical Society. Received 2020 March 6; revised 2020 June 5; accepted 2020 June 8; published 2020 July 23. Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina), and Ministério da Ciência, Tecnologia e Inovação (Brazil). This material is based on work supported by the National Science Foundation under Astronomy and Astrophysics grant No. 1616097 (J.M., B.R.) and No. 1518332 (T.M.E., R.J.D.R., J.R.G., P.K., G.D.) and NASA grants NNX15AC89G and NNX15AD95G/NExSS (T.M.E., R.J.D.R., G.D., J.J.W., P.K.). J.M. acknowledges that support for part of this work was provided by NASA through the NASA Hubble Fellowship grant No. HST-HF2-51414 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. This work benefitted from NASA's Nexus for Exoplanet System Science (NExSS) research coordination network sponsored by NASA's Science Mission Directorate. This research has made use of the VizieR catalog access tool, CDS, Strasbourg, France (doi: 10.26093/cds/vizier)). The original description of the VizieR service was published in A&AS 143, 23 (Ochsenbein et al. 2000). This research project (or part of this research project) was conducted using computational resources (and/or scientific computing services) at the Maryland Advanced Research Computing Center (MARCC). This paper is dedicated to UCLA Professor Michael Jura, who not only discovered the very bright infrared excess associated with HR 4796A but also taught a generation of young astronomers how to think about debris disks. Software: Gemini Planet Imager Data Pipeline (Perrin et al. 2014, 2016, http://ascl.net/1411.018), pyKLIP (Wang et al. 2015, http://ascl.net/1506.001), numpy, scipy, Astropy (Astropy Collaboration et al. 2018), matplotlib (Hunter 2007), emcee (Foreman-Mackey et al. 2013, http://ascl.net/1303.002), corner (Foreman-Mackey 2016, http://ascl.net/1702.002), DebrisDiskFM (Ren et al. 2019).

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Published - Chen_2020_ApJ_898_55.pdf

Accepted Version - 2006.16131.pdf


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August 22, 2023
October 20, 2023