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Detection and Characterization of Exoplanet and Binary Star Systems Through Direct Imaging and Spectroscopy

  • Author(s): Lipartito, Isabel Alexandra
  • Advisor(s): Mazin, Benjamin
  • et al.

High contrast imaging and high-resolution spectroscopy are powerful techniques to characterize multi-component astronomical systems, examples of which range from stars with planetary companions to similar-mass stellar binaries. The first part of this thesis concerns the instrumentation and science behind detecting substellar companions. We present the development of single photon-counting detectors known as Microwave Kinetic Inductance Detectors (MKIDs) for exoplanet direct imaging. Optical/Near-IR MKIDs are low noise detectors which can resolve both the energy and arrival time of individual photons, returning microsecond-accurate time-tagged photon lists. These lists allow for image processing techniques that take advantage of photon spectral and arrival time information to model and subtract the stellar background, leaving behind signal from the faint planetary companion.

We discuss the commissioning and characterization of the MKID Exoplanet Camera (MEC), a 20,440 pixel MKID infrared camera that interfaces with the The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) planet finding instrument on the Subaru Telescope at Mauna Kea. MEC is the first permanently deployed near-infrared MKID instrument and is designed to operate both as an IFU, and as a focal plane wavefront sensor in a multi-kHz feedback loop with SCExAO. We present the development and construction of a second generation digital readout system for MEC. Our readout system is capable of identifying, analyzing, and recording photon detection events in real time with a time resolution of order a few microseconds.

The second part of this thesis addresses the characterization of the orbital properties and stellar components of multiple star systems through high-resolution spectroscopy. We analyze stellar binaries observed with the Michigan/Magellan Fiber System (M2FS), a fiber-fed double spectrograph that was used to complete a several year-long survey of the core half-degree of open clusters NGC 2516 and NGC 2422. This survey targeted all stars identified as solar-analog photometric members. We present orbits for 24 binaries in the field of NGC 2516 (300 Myr) and 13 binaries in the field of NGC 2422 (130 Myr). Six of these systems are double-lined spectroscopic binaries (SB2s). We fit these RV variable systems with orvara, a MCMC-based fitting program that models Keplerian orbits. We use precise stellar parallaxes and proper motions from Gaia EDR3 to determine cluster membership. We impose a barycentric radial velocity prior on all cluster members; this significantly improves our orbital constraints.

Two of our systems have periods between 5 and 15 days, the critical window in which tides efficiently damp orbital eccentricity. These binaries should be included in future analyses of circularization across similarly-aged clusters. We also find a relatively flat distribution of binary mass ratios, consistent with previous work. We identify a field star whose secondary has a mass in the brown dwarf range, as well as two cluster members whose RVs suggest the presence of an additional companion. Our orbital fits will help constrain the binary fraction and binary properties across stellar age and across stellar environment

This thesis explores the detection and characterization of stellar companions at opposite ends of the companion mass range: planetary and stellar. We present technological advances ranging across the fields of instrumentation, image processing (both real-time and post-processing), and stellar system characterization.

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