The Interpolation Constraint in the RV Analysis of M-Dwarfs Using Empirical Templates

Abstract

Precise radial velocity (pRV) measurements of M dwarfs in the near-infrared (NIR) rely on empirical templates due to the lack of accurate stellar spectral models in this regime. Templates are assumed to approximate the true spectrum when constructed from many observations or in the high signal-to-noise limit. We develop a numerical simulation that generates SPIRou-like pRV observations from PHOENIX spectra, constructs empirical templates, and estimates radial velocities. This simulation solely considers photon noise and evaluates when empirical templates remain reliable for pRV analysis. Our results reveal a previously unrecognized noise source in templates created from stacking registered observations, establishing a noise floor for such template-based pRV measurements. We find that these templates inherently include distortions in stellar line shapes due to imperfect interpolation at the detector's sampling resolution. The magnitude of this interpolation error depends on sampling resolution and RV content. Consequently, for stars with higher RV content, such as cooler M-dwarfs, interpolation noise has a larger relative impact, making their performance comparable to hotter M-dwarfs when using detectors with low sampling. For a typical M4V star, SPIRou's spectral and sampling resolution imposes an RV uncertainty floor of 0.5-0.8 m/s, independent of the star's magnitude or the telescope's aperture. These findings reveal a limitation of template-based pRV methods, underscoring the need for improved spectral modeling and better-than-Nyquist detector sampling to reach the next level of RV precision.

13 pages, 7 figures, published in AJ

References in corpus (8)

• Spectrum radial velocity analyser (SERVAL). High-precision radial velocities and two alternative spectral indicators
• SPIRou: nIR velocimetry & spectropolarimetry at the CFHT
• SPIRou: the near-infrared spectropolarimeter/high-precision velocimeter for the Canada-France-Hawaii telescope
• Measuring precise radial velocities on individual spectral lines : II. Dependance of stellar activity signal on line depth
• Line-by-line velocity measurements, an outlier-resistant method for precision velocimetry
• APERO: A PipelinE to Reduce Observations -- Demonstration with SPIRou
• Suppression of Fiber Modal Noise Induced Radial Velocity Errors for Bright Emission-Line Calibration Sources
• The CARMENES search for exoplanets around M dwarfs. Mapping stellar activity indicators across the M dwarf domain

Cited by in corpus (1)

• TILARA: Template-Independent Line-by-line Algorithm for Radial velocity Analysis. I. Description of the code and application on a Sun-like star