STEPARSYN: A Bayesian code to infer stellar atmospheric parameters using spectral synthesis^⋆,⋆⋆

¹ Centro de Astrobiología (CSIC-INTA), Crta. Ajalvir km 4, 28850 Torrejón de Ardoz, Madrid, Spain
e-mail: htabernero@cab.inta-csic.es
² Departamento de Física de la Tierra y Astrofísica and IPARCOS-UCM (Instituto de Física de Partículas y del Cosmos de la UCM), Facultad de Ciencias Físicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
³ Instituto de Astrofísica de Canarias (IAC), 38205 La Laguna, Tenerife, Spain
⁴ Universidad de La Laguna (ULL), Departamento de Astrofísica, 38206 La Laguna, Tenerife, Spain

Received: 10 July 2021
Accepted: 3 September 2021

Abstract

Context. STEPARSYN is an automatic code written in Python 3.X designed to infer the stellar atmospheric parameters T_eff, log g, and [Fe/H] of FGKM-type stars following the spectral synthesis method.

Aims. We present a description of the STEPARSYN code and test its performance against a sample of late-type stars that were observed with the HERMES spectrograph mounted at the 1.2-m Mercator Telescope. This sample contains 35 late-type targets with well-known stellar parameters determined independently from spectroscopy. The code is available to the astronomical community in a GitHub repository.

Methods. STEPARSYN uses a Markov chain Monte Carlo sampler to explore the parameter space by comparing synthetic model spectra generated on the fly to the observations. The synthetic spectra are generated with an spectral emulator.

Results. We computed T_eff, log g, and [Fe/H] for our sample stars and discussed the performance of the code. We calculated an internal scatter for these targets of −12 ± 117 K in T_eff, 0.04 ± 0.14 dex in log g, and 0.05 ± 0.09 dex in [Fe/H]. In addition, we find that the log g values obtained with STEPARSYN are consistent with the trigonometric surface gravities to the 0.1 dex level. Finally, STEPARSYN can compute stellar parameters that are accurate down to 50 K, 0.1 dex, and 0.05 dex for T_eff, log g, and [Fe/H] for stars with v sin i ≤ 30 km s⁻¹.