Pyodine: An open, flexible reduction software for iodine-calibrated precise radial velocities

• Main Authors: Heeren, Paul, Tronsgaard, René, Grundahl, Frank, Reffert, Sabine, Quirrenbach, Andreas, Pallé, Pere L
• Format: Journal Article
• Language: English
• Published: 23-06-2023
• Subjects: Physics - Earth and Planetary Astrophysics; Physics - Instrumentation and Methods for Astrophysics; Physics - Solar and Stellar Astrophysics
• DOI: 10.48550/arxiv.2306.13615

A&A 674, A164 (2023) For existing and future projects dedicated to measuring precise radial
velocities (RVs), we have created an open-source, flexible data reduction
software to extract RVs from \'echelle spectra via the iodine (I$_2$)
absorption cell method. The software, called $pyodine$, is completely written
in Python and has been built in a modular structure to allow for easy
adaptation to different instruments. We present the fundamental concepts
employed by $pyodine$, which build on existing I$_2$ reduction codes, and give
an overview of the software's structure. We adapted $pyodine$ to two
instruments, Hertzsprung SONG located at Teide Observatory (SONG hereafter) and
the Hamilton spectrograph at Lick Observatory (Lick hereafter), and demonstrate
the code's flexibility and its performance on spectra from these facilities.
Both for SONG and Lick data, the $pyodine$ results generally match the RV
precision achieved by the dedicated instrument pipelines. Notably, our code
reaches a precision of roughly $0.69 \,m\,s^{-1}$ on a short-term solar time
series of SONG spectra, and confirms the planet-induced RV variations of the
star HIP~36616 on spectra from SONG and Lick. Using the solar spectra, we also
demonstrate the capabilities of our software in extracting velocity time series
from single absorption lines. A probable instrumental effect of SONG is still
visible in the $pyodine$ RVs, despite being a bit damped as compared to the
original results. With $pyodine$ we prove the feasibility of a highly precise,
yet instrument-flexible I$_2$ reduction software, and in the future the code
will be part of the dedicated data reduction pipelines for the SONG network and
the Waltz telescope project in Heidelberg.