Astrophysical calibration of the oscillator strengths of YJ-band absorption lines in classical Cepheids

TL;DR

This study empirically calibrates oscillator strengths of YJ-band absorption lines in classical Cepheids using high-resolution near-infrared spectra, enabling consistent stellar parameter and abundance determinations across optical and infrared data.

Contribution

It provides new astrophysically calibrated loggf values for YJ-band lines and demonstrates their use in accurate stellar parameter and abundance analysis of Cepheids.

Findings

Calibrated oscillator strengths for YJ-band lines.

Achieved optical-like precision in infrared stellar parameters.

Created a comprehensive absorption line atlas for Cepheids.

Abstract

Newly-developed spectrographs with increased resolving powers, particularly those covering the near-IR range, allow the characterization of more and more absorption lines in stellar spectra. This includes the identification and confirmation of absorption lines and the calibration of oscillator strengths. In this study, we provide empirical values of loggf based on abundances of classical Cepheids obtained with optical spectra in Luck (2018), in order to establish the consistency between optical and infrared abundance results. Using time-series spectra of classical Cepheids obtained with WINERED spectrograph (0.97-1.35 $\mu$ m, R ~28000, we demonstrate that we can determine the stellar parameters of the observed Cepheids, including effective temperature (Teff), surface gravity (logg), microturbulence, and metallicity. With the newly calibrated relations of line-depth ratios (LDRs), we can achieve accuracy and precision comparable to optical studies (Luck 2018), with uncertainties of 90K and 0.108 dex for Teff, and log g, respectively. Finally, we created a new atlas of absorption lines, featuring precise abundance measurements of various elements found in the atmosphere of Cepheids (including neutron-capture elements), with loggf values that have been astrophysically calibrated.