Automatic Echelle Spectrograph Wavelength Calibration
arXiv:1910.08079 · doi:10.3847/1538-3881/ab929c
Abstract
Time domain astronomy and the increasing number of exoplanet candidates call for reliable, robust, and automatic wavelength calibration. We present an algorithm for wavelength calibrating échelle spectrographs that uses order-by-order extracted spectra and a list of laboratory wavelengths. Our approach is fully automatic and does not need the pixel locations of certain spectral features with which to anchor the wavelength solution, nor the true order number of each diffraction order. We use spectral features that are duplicated in adjacent orders to establish the scale-invariant component of the wavelength solution. We then match the central wavelengths of spectral features to laboratory wavelengths to establish the scale and higher order components of the wavelength solution. We demonstrate our method on the four spectrographs of Las Cumbres Observatory's Network of Robotic Échelle Spectrographs (NRES), on the High Accuracy Radial Velocity Planet Searcher (HARPS) spectrograph, and on synthetic data. We obtain a velocity-equivalent precision of 10 m/s on NRES. We achieve 1 m/s on HARPS, which agrees with the precision reported by the HARPS team. On synthetic data, we achieve the velocity precision set by Gaussian centroiding errors. Our algorithm likely holds for a wide range of spectrographs beyond the five presented here. We provide an open-source Python package, xwavecal (https://github.com/gmbrandt/xwavecal/), which outputs wavelength calibrated spectra as well as the wavelengths of spectral features.
arXiv comment13 pages, 9 figures
References in corpus (14)
- SciPy 1.0--Fundamental Algorithms for Scientific Computing in Python
- Astropy: A Community Python Package for Astronomy
- The NumPy array: a structure for efficient numerical computation
- Binary companions of evolved stars in APOGEE DR14: Search method and catalog of ~5,000 companions
- Real-time processing of the imaging data from the network of Las Cumbres Observatory Telescopes using BANZAI
- CERES: A Set of Automated Routines for Echelle Spectra
- Selection of ThAr lines for wavelength calibration of echelle spectra and implications for variations in the fine-structure constant
- An Extreme Precision Radial Velocity Pipeline: First Radial Velocities from EXPRES
- A new wavelength calibration for echelle spectrographs using Fabry-Perot etalons
- Decoding the radial velocity variations of HD41248 with ESPRESSO
- CAFE2: an upgrade to the CAFE high-resolution spectrograph. Commissioning results and new public pipeline
- Modelling high resolution Echelle spectrographs for calibrations: Hanle Echelle spectrograph, a case study
- WES - Weihai Echelle Spectrograph
- The list of tantalum lines for wavelengths calibration of the Hamilton echelle-spectrograph