F. F. Bauer

Calibrating echelle spectrographs with Fabry-Pérot etalons

Over the past decades hollow-cathode lamps have been calibration standards for spectroscopic measurements. Advancing to cm/s radial velocity precisions with the next generation of instruments requires more suitable calibration sources with more lines and less dynamic range problems. Fabry-Perot interferometers provide a regular and dense grid of lines and homogeneous amplitudes making them good candidates for next generation calibrators. We investigate the usefulness of Fabry-Perot etalons in wavelength calibration, present an algorithm to incorporate the etalon spectrum in the wavelength solution and examine potential problems. The quasi periodic pattern of Fabry-Perot lines is used along with a hollow-cathode lamp to anchor the numerous spectral features on an absolute scale. We test our method with the HARPS spectrograph and compare our wavelength solution to the one derived from a laser frequency comb. The combined hollow-cathode lamp/etalon calibration overcomes large distortion (50 m/s) in the wavelength solution of the HARPS data reduction software. Direct comparison to the laser frequency comb bears differences of only maximum 10 m/s. Combining hollow-cathode lamps with Fabry-Perot Interferometers can lead to substantial improvements in the wavelength calibration of echelle spectrographs. Etalons can provide economical alternatives to the laser frequency comb, especially for smaller projects.

Spectrum radial velocity analyser (SERVAL): High-precision radial velocities and two alternative spectral indicators

Context: The CARMENES survey is a high-precision radial velocity (RV) programme that aims to detect Earth-like planets orbiting low-mass stars. Aims: We develop least-squares fitting algorithms to derive the RVs and additional spectral diagnostics implemented in the SpEctrum Radial Velocity Analyser (SERVAL), a publicly available python code. Methods: We measured the RVs using high signal-to-noise templates created by coadding all available spectra of each star.We define the chromatic index as the RV gradient as a function of wavelength with the RVs measured in the echelle orders. Additionally, we computed the differential line width by correlating the fit residuals with the second derivative of the template to track variations in the stellar line width. Results: Using HARPS data, our SERVAL code achieves a RV precision at the level of 1m/s. Applying the chromatic index to CARMENES data of the active star YZ CMi, we identify apparent RV variations induced by stellar activity. The differential line width is found to be an alternative indicator to the commonly used full width half maximum. Conclusions: We find that at the red optical wavelengths (700--900 nm) obtained by the visual channel of CARMENES, the chromatic index is an excellent tool to investigate stellar active regions and to identify and perhaps even correct for activity-induced RV variations.

Radial velocity observations of the 2015 Mar. 20 eclipse - A benchmark Rossiter-McLaughlin curve with zero free parameters

On March 20, 2015, we obtained 159 spectra of the Sun as a star with the solar telescope and the FTS at the Institut fur Astrophysik Gottingen, 76 spectra were taken during partial solar eclipse. We obtained RVs using

CARMENES input catalogue of M dwarfs: III. Rotation and activity from high-resolution spectroscopic observations★★★

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Physical modeling of echelle spectrographs: the CARMENES case study

as wavelength reference and determined the RM curve with a peak-to-peak amplitude of almost 1.4 km s

Comparing the emission spectra of U and Th hollow cathode lamps and a new U line list

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The CARMENES search for exoplanets around M dwarfs: Radial-velocity variations of active stars in visual-channel spectra★

at typical RV precision better than 1 m s

Metal abundances in subdwarf O stars.

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The influence of convective blueshift on radial velocities of F, G, and K stars

. We modeled disk-integrated solar RVs using surface velocities, limb darkening, and information about convective blueshift from 3D magneto-hydrodynamic simulations. We confirm that convective blueshift is crucial to understand solar RVs during eclipse. Our best model reproduced the observations to within a relative precision of 10% with residuals less than 30 m s