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 100 yr 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 4500 K, luminosity of 1900 L (& ODOT;), and subsolar metallicity on the asymptotic giant branch showing semiregular complex multiperiodic 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.