Characterizing Debris Disks With Multi-Wavelength High-Contrast Imaging
- Author(s): Hung, Li-Wei
- Advisor(s): Fitzgerald, Michael P
- et al.
Thousands of extrasolar planets (exoplanets) have been discovered so far, indicating the ubiquity of planetary systems in our galaxy. These exoplanets have an enormous range of characteristics. While the formation mechanism for small planets is well-accepted and mostly understood, how giant planets form and evolve is still under debate. One approach towards understanding giant planet formation and evolution process is to study the associated debris disks. Debris disks are composed of dust produced by planetesimals that are in orbit around main sequence stars. The grain composition, dust distribution, and disk morphology can be used to infer the system’s dynamical history and even predict the possible existence of unseen exoplanets.
My thesis focuses on studying the debris disk around HD 131835 with multi-wavelength high-contrast imaging. Multi-wavelength imaging allows us to characterize the distribution of grains of various sizes since an observation is most sensitive to grains with the size similar to the probing wavelength. The target, HD 131835, is a ∼15 Myr A2 star in the Scorpius-Centaurus OB association at a distance of ∼120 parsec. I first report the discovery of the resolved disk around HD 131835 in mid-infrared at 11.7 μm and 18.3 μm with T-ReCS on Gemini South. Next, I present the first scattered-light image of the debris disk around HD 131835 using the Gemini Planet Imager (GPI). The disk is detected in H-band polarized light. Compared to its mid-infrared thermal emission, the disk in scattered light shows similar orientation but different morphology. Unlike the continuous and extended feature in thermal emission, the disk in scattered light has a cleared region inward of ∼ 75 AU. In addition, I discover a weak brightness asymmetry along the major axis that is only present in the scattered-light image. The results of my thesis work imply that the system has multiple grain populations, and those grains could be composed of a mixture of silicates and amorphous carbon. The brightness asymmetry and the richness in the morphological features indicate that the system is dynamic, possibly with strong interactions between dust and gas and perturbations from unseen objects. In the final chapters, I present my instrumentation work including developing the photometric calibration method in the polarimetry mode for the GPI coronagraphic observations and creating a more automatic process for aligning the focal plane mask to the star while observing.