FIESTA – disentangling stellar variability from exoplanets in the Fourier domain

Abstract

We propose a new analysis methodology – FourIEr phase SpecTrum Analysis (FIESTA, or $\mathit {\Phi }$ESTA) – for the study of spectral line profile variability in Fourier space. The philosophy of $\mathit {\Phi }$ESTA is highlighted in its interpretation of a line deformation as various shifts of the composing Fourier modes. With this ability, $\mathit {\Phi }$ESTA excels in distinguishing the effects of a bulk shift in a line profile, from changes in a line profile shape. In other words, it can distinguish a radial velocity shift due to orbiting companions like planets, from an apparent radial velocity shift due to stellar variability (often referred to as ‘jitter’). Most importantly, it can quantify the radial velocity impact of stellar jitter on each epoch. Our simulations show that (compared to a model that does not account for stellar activity), $\mathit {\Phi }$ESTA can almost triple the fraction of planets recovered with orbital parameters measured to within 10 per cent of their input parameters, when extracting a 2 m s−1 amplitude planetary signal in the midst of ∼2 m s−1 amplitude starspot jitter for high signal-to-noise ratio (>200 pixel−1) data. $\mathit {\Phi }$ESTA can also be used to identify stellar activity related periods in a periodogram analysis and classify relative amplitudes of stellar jitter and planetary signals, with examples for the analysis of HARPS data of the active star HD 224789 and the active planet-host star HD 103720. In the end, we demonstrate that $\mathit {\Phi }$ESTA’s framework is working as well as other activity indicators in correlating with stellar jitter.

The EXPRES Stellar Signals Project II. State of the Field in Disentangling Photospheric Velocities

“…FIESTA requires careful normalization of the CCFs for each observation, as vertical translational differences could be mistaken for a shape change. More information can be found in Zhao & Tinney (2020), Zhao & Ford (2022), and Appendix B.3.…”

“…The FIESTA method, submitted by the PennState team, decomposes the CCF of a spectrum into Fourier basis functions (Zhao & Tinney 2020;Zhao & Ford 2022). The shifts of each of these basis functions are then calculated for a range of Fourier frequencies.…”

Friends and Foes: Conditional Occurrence Rates of Exoplanet Companions and their Impact on Radial Velocity Follow-up Surveys

“…The current and next generation spectrographs are promising sub-m/s RV precisions; the NASA commissioned NEID spectrograph (Schwab et al 2016) on the WIYN Telescope, the EXtreme PREcision Spectrograph (EXPRES; Ju-rgenson et al 2016) on the Lowell Discovery Telescope, and the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO; Pepe et al 2021) on the Very Large Telescope are currently being tested and pushing 0.3 m/s or better precision. In addition to these technologies, there is active research in modeling stellar noise and applying novel statistical methods to extract the smallest signals from the data (Davis et al 2017;Jones et al 2017;Collier Cameron et al 2020;Cretignier et al 2020;de Beurs et al 2020;Gilbertson et al 2020;Rajpaul et al 2020;Zhao & Tinney 2020).…”

A HARPS-N mass for the elusive Kepler-37d: a case study in disentangling stellar activity and planetary signals

“…More recently, though, there has been a rapidly growing number of efforts to develop improved ways of extracting RVs from stellar spectra, particularly with a view to mitigating stellar activity and/or telluric contamination from the final RVs (e.g. Anglada-Escudé & Butler 2012;Zechmeister et al 2018;Dumusque 2018;Bedell et al 2019;Zhao & Tinney 2020;Rajpaul et al 2020;Collier Cameron et al 2020;de Beurs et al 2020). These techniques are often data-driven, exploiting the vast quantity of wavelengthand/or time-dependent information in stellar spectra -each typically containing hundreds of thousands of flux/wavelength pairs -to extract 'cleaner' RVs (i.e.…”