Optical design and prototype of a high resolution near IR spectrograph for astronomy.
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2019
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Abstract
The search for extraterrestrial planets is an exciting current field of research. One of the
most efficient ways to detect exoplanets is through the measurement of the Radial Velocity
(RV) detection of Doppler shifts of the host star. Recently, the target of the exoplanet search
has moved to cooler and lower mass stars. Although these cool stars are abundant in our
galaxy, most of them are too faint to be detected by instruments operating in the visible.
Thus, it requires high resolution spectroscopy in the near infrared region. In this work, we
will contribute to the field by developing a cost-effective infrared spectrograph which will
empower the upcoming generation of telescopes.
The Tao Aiuc high Resolution (d) Y band Spectrograph (TARdYS) project is a collaboration
between the Center of Astro-Engineering UC-AIUC, Chile and the University of Tokyo,
Japan. The instrument is a high resolution near infrared spectrograph for astronomy being
developed at the AIUC for installation at the Tokyo Atacama Observatory TAO 6.5 m. telescope.
TARdYS is optimized for the precise measurement of radial velocities of cool stars.
For this science purpose, the instrument requires high resolution > 60,000 and RV precision of
5 m/s. Moreover, it will also be a powerful tool for the study of astroseismology, star-forming
regions, and exoplanet atmosphere.
The requirements of the instrument are derived from the science objectives and budget
constraint. We select a 1kx1k infrared detector and an R6 echelle disperser. This choice
enables high resolution with a small beam diameter. TARdYS can yield a spectral resolution
> 60,000 within the spectral coverage from 0.843-1.117 m. We plan to use a cryogenic
Dewar in the last part of the objectives to minimize the background radiation reaching the
detector. Thus, this will be operated in a semi-cryogenic system as a cost-effective solution.
In this work, I created and evaluated the optical design of the two different configurations
for a cost-effective high resolution near-infrared spectrograph. This work tests a cost-effective solution with less widely tested spectrograph choices, especially an R6 echelle, and only a
semi-cryogenic setup.
Optimization with computer-aided simulations yields excellent spectral resolution at the
diffraction limit even when taking realistic manufacturing and alignment tolerances into account.
I built a prototype of the spectrograph using commercially available components and
determined its performance. The measured spectral resolution agrees well with the simulation.
With a simple temperature control, I achieved a stability of ±0.1K over several hours.
The remaining spectral drift is predominately caused by environmental pressure.
Once TARdYS is installed at TAO, it will become available as a exoplanet hunter to the
Chilean science community.
Description
Tesis (Doctor en Ciencias de la Ingeniería)--Pontificia Universidad Católica de Chile, 2019