Photonic systems for high precision radial velocity measurements

Open Access
Halverson, Samuel Peter
Graduate Program:
Astronomy and Astrophysics
Doctor of Philosophy
Document Type:
Date of Defense:
May 27, 2016
Committee Members:
  • Suvrath Mahadevan, Dissertation Advisor
  • Suvrath Mahadevan, Committee Chair
  • Lawrence William Ramsey, Committee Member
  • Jason Thomas Wright, Committee Member
  • Kurt Gibble, Outside Member
  • exoplanets
  • spectroscopy
  • photonics
  • optical fibers
  • radial velocity
  • near-infrared
  • astronomy
The discovery of Earth-like exoplanets has profound implications for our understanding of the origins and diversity of life in our universe. As such, developing new and improved Doppler radial velocity (RV) spectrometers capable of discovering and characterizing these planets is a high priority in the astronomical community. However, detection of true Earth-analogs remains beyond the technical reach of current Doppler RV instruments. This thesis discusses a number of technological developments designed specifically to overcome classical instrumental limitations of high precision Doppler RV measurements. These technologies are essential components of next generation instruments that aim to achieve the RV precision necessary to detect low-mass planets. This instrumentation research is driven by the development of the Habitable-zone Planet Finder (HPF), a near-infrared (NIR) Doppler spectrograph currently under development at Penn State that will detect terrestrial-mass planets orbiting nearby M-dwarfs. Furthermore, many technologies discussed will also be applied to the NASA-NSF Extreme Precision Doppler Spectrometer concept NEID, a Doppler RV instrument for the 3.5 meter WIYN telescope, slated for delivery in 2019. NEID is an ultra-stable, high resolution optical spectrometer also under development at Penn State. This thesis describes new specialized optical fiber delivery systems, designed to significantly improve instrument illumination stability, modal noise suppression systems, which suppress mode interference in optical fibers and allow spectrometers to fully realize the exquisite precision of modern wavelength calibration sources, and new photonic calibration sources, which show significant promise as potential Doppler wavelength references. These technologies represent important steps in enabling next generation instruments to reach precisions sufficient to detect terrestrial-mass planets orbiting in the Habitable-zones of nearby stars. Improving measurement capabilities in both the optical and NIR is not only essential for enabling precision RV studies on a wide variety of stars, but can also aid in disentangling stellar activity signals from true reflex motion. Beyond independent planet discoveries, these instruments will be indispensable tools for measuring masses and densities of planets identified by future space observatories, and play key roles in directing future atmospheric characterization studies with the James Webb Space Telescope.