New Generation Stellar Spectral Libraries in the Optical and Near-Infrared I: The Recalibrated UVES-POP Library for Stellar Population Synthesis

Abstract: We present re-processed flux calibrated spectra of 406 stars from the UVES-POP stellar library in the wavelength range 320-1025 nm, which can be used for stellar population synthesis. The spectra are provided in the two versions having spectral resolving power R=20,000 and R=80,000. Raw spectra from the ESO data archive were re-reduced using the latest version of the UVES data reduction pipeline with some additional algorithms that we developed. The most significant improvements in comparison with the original UVES-POP release are: (i) an updated Echelle order merging, which eliminates "ripples" present in the published spectra, (ii) a full telluric correction, (iii) merging of non-overlapping UVES spectral setups taking into account the global continuum shape, (iv) a spectrophotometric correction and absolute flux calibration, and (v) estimates of the interstellar extinction. For 364 stars from our sample, we computed atmospheric parameters $T_\mathrm{eff}$, surface gravity log $g$, metallicity [Fe/H], and $\alpha$-element enhancement [$\alpha$/Fe] by using a full spectrum fitting technique based on a grid of synthetic stellar atmospheres and a novel minimization algorithm. We also provide projected rotational velocity $v\sin i$ and radial velocity $v_{rad}$ estimates. The overall absolute flux uncertainty in the re-processed dataset is better than 2% with sub-% accuracy for about half of the stars. A comparison of the recalibrated UVES-POP spectra with other spectral libraries shows a very good agreement in flux; at the same time, $Gaia$ DR3 BP/RP spectra are often discrepant with our data, which we attribute to spectrophotometric calibration issues in $Gaia$ DR3.