Planet-Finding Spectrometers Should Use Adaptive Optics
Justin Crepp (Notre Dame University)
The Doppler radial velocity method is an important and venerable technique for studying extrasolar planets. However, technology advances in this field have leveled off, Doppler precision has reached an impasse, and progress is impeded by fundamental limitations set forth by basic physics and the initial design of early spectrometers. Rather than recording measurements under seeing-limited conditions, I will argue that planet-finding spectrometers should instead operate at the diffraction limit using adaptive optics (AO) to correct for image distortions caused by Earth's turbulent atmosphere. AO-fed spectrometers achieve ultra-high spectral resolution, eliminate modal noise entirely, reduce the intensity of OH-emission lines by 2 orders of magnitude, allow for exquisite temperature and pressure control, and naturally operate in a wavelength range that is ideal for detecting extrasolar planets (the NIR). Given the cascade of practical advantages offered by an AO-fed spectrometer, Doppler instruments that operate at the diffraction-limit may represent the only viable solution for improving velocity precision to levels where the mass, density, and orbits of terrestrial exoplanets may be studied with confidence.
