Observational Methods for the Study of Debris Disks: Gemini Planet Imager and Herschel Space Observatory




Draper, Zachary Harrison

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There are many observational methods for studying debris disks because of constraints imposed on observing their predominately infrared wavelength emission close to the host star. Two methods which are discussed here are ground-based high contrast imaging and space-based far-IR emission. The Gemini Planet Imager (GPI) is a high contrast near-IR instrument designed to directly image planets and debris disks around other stars by suppressing star light to bring out faint sources nearby. Because debris disks are intrinsically polarized, polarimetry offers a useful way to enhance the scattered light from them while suppressing the diffracted, unpolarized noise. I discuss the characterization of GPI's microlens point spread function (PSF) in polarization mode to try to improve the quality of the processed data cubes. I also develop an improved flux extraction method which takes advantage of an empirically derived high-resolution PSF for both spectral and polarization modes. To address the instrumental effects of flexure, which affect data quality, I develop methods to counteract the effect by using the science images themselves without having to take additional calibrations. By reducing the number of calibrations, the Gemini Planet Imager Exoplanet Survey (GPIES) can stand to gain ~66 hours of additional on-sky time, which can lead to the discovery of more exoplanetary systems. The Herschel Space Observatory offers another method for observing debris disks which is ideally suited to measure the peak dust emission in the far-IR. Through a careful analysis, we look at 100/160 μm excess emission around λ Boo stars, to differentiate whether the emission is from a debris disk or a bowshock with the interstellar medium. It has been proposed that the stars' unusual surface abundances are due to external accretion of gas from those sources. We find that the 3/8 stars observed are well resolved debris disks and the remaining 5/8 were inconsistent with bowshocks. To provide a causal explanation of the phenomenon based on what we now know of their debris disks, I explore Poynting-Robertson (PR) drag as a mechanism for secondary accretion via a debris disk. However, I find that the accretion rates are too low to cause the surface abundance anomaly. Further study into the debris disks in relation to stellar abundances and surfaces are required to rule out or explain the λ Boo phenomenon through external accretion.



astronomy, debris disks, exoplanets, Gemini Planet Imager, Herschel