SDSS-IV MaStar: Stellar parameter determination with continuum-supplemented full-spectrum fitting

¹ Department of Physics and Astronomy, University of Kentucky, 505 Rose St., Lexington, KY 40506-0057, USA
e-mail: dan.lazarz.mail@gmail.com
² Department of Physics, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong S.A.R., PR China
e-mail: rbyan@cuhk.edu.hk
³ New York University Abu Dhabi, Abu Dhabi PO Box 129188, United Arab Emirates
⁴ Institute of Cosmology and Gravitation, University of Portsmouth, Burnaby Road, Portsmouth PO1 3FX, UK
⁵ Department of Astronomy, New Mexico State University, Box 30001, MSC 4500, Las Cruces NM 88003, USA
⁶ Institute of Cosmology & Gravitation, University of Portsmouth, Dennis Sciama Building, Portsmouth PO1 3FX, UK
⁷ MTA-ELTE Exoplanet Research Group, ELTE Eötvös Loránd University, Gothard Astrophysical Observatory, 9700 Szombathely, Szent Imre H. st. 112, Hungary
⁸ MTA-ELTE Lendület “Momentum” Milky Way Research Group, ELTE Eötvös Loránd University, Gothard Astrophysical Observatory, 9700 Szombathely, Szent Imre H. st. 112, Hungary
⁹ Center for Astrophysics and Space Astronomy, Department of Astrophysical and Planetary Sciences, University of Colorado, 389 UCB, Boulder, CO 80309-0389, USA
¹⁰ Department of Physics and Astronomy and JINA Center for the Evolution of the Elements (JINA-CEE), University of Notre Dame, Notre Dame, IN 46556, USA
¹¹ Apache Point Observatory and New Mexico State University, PO Box 59, Sunspot, NM 88349, USA
¹² Sternberg Astronomical Institute, Moscow State University, Universitetskij pr. 13, Moscow, Russia
¹³ McDonald Observatory, The University of Texas at Austin, 1 University Station, Austin, TX 78712, USA
¹⁴ Centro de Investigación en Astronomía, Universidad Bernardo O’Higgins, Avenida Viel, 1497 Santiago, Chile
¹⁵ Centro de Astronomía (CITEVA), Universidad de Antofagasta, Avenida Angamos 601, Antofagasta 1270300, Chile

Received: 3 April 2022
Accepted: 25 July 2022

Abstract

Aims. We present a stellar parameter catalog built to accompany the MaStar Stellar Library, which is a comprehensive collection of empirical, medium-resolution stellar spectra.

Methods. We constructed this parameter catalog by using a multicomponent χ² fitting approach to match MaStar spectra to models generated by interpolating the ATLAS9-based BOSZ model spectra. The total χ² for a given model is defined as the sum of components constructed to characterize narrow-band features of observed spectra (e.g., absorption lines) and the broadband continuum shape separately. Extinction and systematics due to flux calibration were taken into account in the fitting. The χ² distribution for a given region of model space was sampled using a Markov chain Monte Carlo (MCMC) algorithm, the data from which were then used to extract atmospheric parameter estimates (T_eff, log g, [Fe/H], and [α/Fe]), their corresponding uncertainties, and direct extinction measurements.

Results. Two methods were used to extract parameters and uncertainties: one that accepts the MCMC’s prescribed minimum-χ² result, and one that uses Bayesian inference to compute a likelihood-weighted mean from the χ² distribution sampled by the MCMC. Results were evaluated for internal consistency using repeat observations where available and by comparing them with external data sets (e.g., APOGEE-2 and Gaia DR2). Our spectral-fitting exercise reveals possible deficiencies in current theoretical model spectra, illustrating the potential power of MaStar spectra for helping to improve the models. This paper represents an update to the parameters that were originally presented with SDSS-IV DR17. The MaStar parameter catalog containing our BestFit results is available on the SDSS-IV DR17 website as part of version 2 of the MaStar stellar parameter value-added catalog.