A radial velocity error budget for single-mode Doppler spectrographs

Abstract

Single-mode fiber (SMF) spectrographs fed with adaptive optics (AO) offer a unique path for achieving extremely precise radial velocity (EPRV) measurements. We present a radial velocity (RV) error budget based on end-to-end numerical simulations of an instrument named iLocater that is being developed for the Large Binocular Telescope (LBT). Representing the first AO-fed, SMF spectrograph, iLocater's design is used to quantify and assess the relative advantages and drawbacks of precise Doppler time series measurements made at the diffraction limit. This framework can be applied for trade-study work to investigate the impact of instrument design decisions on systematic uncertainties encountered in the regime of sub-meter-per-second precision. We find that working at the diffraction-limit through the use of AO and SMF's allows for high spectral resolution and improved instrument stability at the expense of limiting magnitude and longer integration times. Large telescopes equipped with AO alleviates the primary challenges of SMF spectrographs.

Characterization of Single-mode Fiber Coupling at the Large Binocular Telescope

“…We investigate the impact of fiber injection losses on RV precision for iLocater at the LBT using the results from previous sections. RV uncertainties are calculated from end-to-end instrument simulations of the stellar spectrum across iLocater's 36 spectral orders (Bechter et al 2018(Bechter et al , 2019. The simulations utilize fiber coupling coefficients: ρ tel , ρ ncpa , ρ tip/tilt as well as the modeled Strehl ratio to determine a variable chromatic coupling efficiency for a given spectral type and apparent magnitude.…”

StarNAV: Autonomous Optical Navigation of a Spacecraft by the Relativistic Perturbation of Starlight

“…Recent studies have presented complete error models for spectrographs used to produce stellar radial velocity measurements [177,178]. These complement empirical models, such as that of [179], which suggests the standard deviation of the radial velocity error is given by σRV∝false(S/Nfalse)−1R−1B−1 where S/N is the SNR, B is the wavelength coverage, and R is the resolving power, scriptR=λΔλ…”

Instrument Simulator and Data Reduction Pipeline for the iLocater Spectrograph

“…precision (Halverson et al 2016). Using the simulation tools outlined in this paper, a comprehensive RV error budget that includes: photon noise, instrument systematic terms, software and barycentric removal residuals, and time-varying atmospheric contaminants has already been assembled for iLocater, the details of which can be found in Bechter et al (2018).…”

“…The small mode field of SMFs, typically only several microns in diameter in the near-infrared (by definition comparable to the wavelength of light), further allows for high spectral resolution observations while offering a compact opto-mechanical design (Schwab et al 2014;Crepp Corresponding author: Eric B. Bechter ebechter@nd.edu 2014; Jovanovic et al 2016). Realizing the advantages of improved wavelength sampling and instrument stability would allow diffraction-limited spectrographs to reach instrumental noise floors well below 1 m/s (Bechter et al 2018). Moreover, ultra-high resolution measurements (R ≥ 150, 000) present an opportunity to study asymmetries in the profiles of stellar absorption lines, a first step towards disentangling the effects of stellar variability (astrophysical "jitter") from the signal of orbiting planets (Davis et al 2017).…”