Comprehensive analysis of a symbiotic candidate V503 Her

TL;DR

This study thoroughly examines V503 Her over a century, concluding it is not an eclipsing symbiotic binary but possibly a hidden accreting system with a K-type giant, based on photometric and spectroscopic data.

Contribution

It provides a comprehensive long-term analysis of V503 Her, clarifying its nature and challenging previous classifications as an eclipsing symbiotic star.

Findings

V503 Her is not an eclipsing binary.

The star is a K-type giant on the asymptotic giant branch.

Evidence suggests it may be a hidden accreting symbiotic system.

Abstract

V503 Her was previously proposed as an eclipsing symbiotic candidate based on photometric behavior and spectroscopic appearance indicating the composite optical spectrum. To investigate its nature, we analyzed long-term photometric observations covering one hundred years of its photometric history and new low-resolution optical spectroscopic data, supplemented with the multifrequency measurements collected from several surveys and satellites. Based on the analysis presented in this paper, we claim that V503 Her is not an eclipsing binary star. The optical and infrared wavelengths are dominated by a K-type bright giant with an effective temperature of 4 500 K, luminosity of 1 900 L$_\odot$, and sub-solar metallicity on the asymptotic giant branch showing semiregular complex multi-periodic pulsation behavior. V503 Her does not show the characteristics of strongly interacting symbiotic variables, but some pieces of evidence suggest that it could still be one of the 'hidden' accreting-only symbiotic systems. However, the currently available data do not allow us to fully confirm or constrain the parameters of a possible companion.