A Next Generation RV Spectrograph in the Search for Earth-like Worlds. The new device has been built by Yale Scientist (ESPRESS): “To seek out new worlds and new civilizations…….”
The EXtreme PREcision Spectrograph (EXPRES) is an optical fiber fed echelle instrument being designed and built at the Yale Exoplanet Laboratory to be installed on the 4.3-meter Discovery Channel Telescope operated by Lowell Observatory. The primary science driver for EXPRES is to detect Earth-like worlds around Sun-like stars.
With this in mind, we are designing the spectrograph to have an instrumental precision of 15 cm/s so that the on-sky measurement precision (that includes modeling for RV noise from the star) can reach to better than 30 cm/s. This goal places challenging requirements on every aspect of the instrument development, including optomechanical design, environmental control, image stabilization, wavelength calibration, and data analysis.
In this paper we describe our error budget, and instrument optomechanical design. Keywords: precision radial velocity, white pupil spectrograph, double-scrambling, high resolution, laser frequency comb. The design and construction of EXPRES is funded by the National Science Foundation Major Research Instrumentation program.
The primary purpose will be to serve as the work-horse instrument for the 100 Earths Project. This project will search for planets that are similar in mass to our world, and that orbit their host stars at a similar distance where liquid water might flow in rivers and oceans. The NASA Kepler mission has been searching stars that are several hundred light years away and has demonstrated that Earth-sized planets are common. Armed with this important statistical information, we will take a census of the nearest neighboring stars to find terrestrial worlds.
These planets will be the targets of intense searches for life outside the solar system. The Path to Finding Earth Analogs A radial velocity (RV) measurement precision of 10 cm/s is required in order to detect Earth analogs. To reach this precision, the 100 Earths Project will build upon the state-of-the-art1 by advancing developments in six key areas: 1) instrument environmental stability, 2) stable light coupling, 3) high spectral resolution, line spread sampling, and signal to noise, 4) precision wavelength calibration, 5) removal of telluric contamination and stellar jitter, 6) near nightly observational cadence of target stars, and 7) new statistical treatment of stellar jitter.
The spectrograph optical bench will be under vacuum in a climate controlled room on a vibration isolated slab. EXPRES will have a resolving power of 150,000, and < 0.01 Å per pixel sampling to improve spectral line modeling and detecting and decorrelation stellar activity signals. The use of a Menlo Systems laser frequency comb (LFC) for wavelength calibration will enable access to the majority of the instrument free spectral range (380 to 680 nm), leading to higher Signal to Noise Ratio (SNR) and more information about stellar activity. Success is not only coupled to the instrument design, but the implementation of robust statistical and modeling techniques.
Source: Yale University
