Radial velocity information content of M dwarf spectra in the near-infrared

Abstract

Aims. We evaluate the radial velocity (RV) information content and achievable precision on M0-M9 spectra covering the ZYJHK bands. We do so while considering both a perfect atmospheric transmission correction and discarding areas polluted by deep telluric features, as done in previous works. Methods. To simulate the M-dwarf spectra, PHOENIX-ACES model spectra were employed; they were convolved with rotational kernels and instrumental profiles to reproduce stars with a v sin i of 1.0, 5.0, and 10.0 km s −1 when observed at resolutions of 60 000, 80 000, and 100 000. We considered the RV precision as calculated on the whole spectra, after discarding strongly polluted areas, and after applying a perfect telluric correction. In the latter option, we took into account the reduction in the number of recorded photons due to a transmittance lower than unity and considered its effect on the noise of the recorded spectra. In our simulations we paid particular attention to the details of the convolution and sampling of the spectra, and we discuss their impact on the final spectra. Results. Our simulations show that the most important parameter ruling the difference in attainable precision between the considered bands is the spectral type. For M0-M3 stars, the bands that deliver the most precise RV measurements are the Z, Y, and H band, with relative merits depending on the parameters of the simulation. For M6-M9 stars, the bands show a difference in precision that is within a factor of ∼2 and does not clearly depend on the band; this difference is reduced to a factor smaller than ∼1.5 if we consider a non-rotating star seen at high resolution. We also show that an M6-M9 spectrum will deliver a precision about two times better as an M0-M3 spectra with the same signal-to-noise ratio. Finally, we note that the details of modeling the Earth atmosphere and interpreting the results have a significant impact on which wavelength regions are discarded when setting a limit threshold at 2−3%. The resolution element sampling on the observed spectra plays an important role in the atmospheric transmission characterization. As a result of the multiparameter nature of the problem, it is very difficult to precisely quantify the impact of absorption by the telluric lines on the RV precision, but it is an important limiting factor to the achievable RV precision.

Quantifying the Observational Effort Required for the Radial Velocity Characterization of TESS Planets

“…This empirical evidence somewhat contradicts theoretical calculations based on model spectra (e.g. Figueira et al 2016, this study), especially for late M dwarfs whose RV information content is theorized to peak in the HK bands from 1.4-2.4 µm. Convergence towards a more precise scaling of σ RV with wavelengthfor stars of various spectral types-will be achieved in the near future with the onset of multiple new spectrographs from the optical to the near-IR.…”

Optical and Near-infrared Radial Velocity Content of M Dwarfs: Testing Models with Barnard’s Star

“…Admittedly our measurement of the RV content of Barnard's star concerns an object ∼1000 K hotter, but if the missing opacities in H and K are also present in very-late-Ms and Ls, then these results will need to be revisited. Our results also underline the limitations of works such as Reiners et al (2010) and Figueira et al (2016) who, being based on stellar models very similar to the ones presented here, were affected by important systematic errors in the RV estimates.…”

Radial Velocity Photon Limits for the Dwarf Stars of Spectral Classes F–M

“…3, we create a grid of RV precision values for dwarf stars of spectral types F-M. We adopt empirical values where available from CARMENES and/or HARPS, and we rely on predictions from PHOENIX spectral models otherwise. We have no empirical information about the K-band from CARMENES and assume that in M dwarfs (T < 4000 K) the spectral information content of the K-band is similar to the H-band (see Rodler et al 2011;Figueira et al 2016;Artigau et al 2018). For hotter stars, we rely on our modelling results.…”