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Asteroseismic analysis of RY Leporis: an evolved blue straggler with δ Scuti pulsations Wojciech Niewiadomski1, Jadwiga Daszyńska-Daszkiewicz1, Przemysław Walczak1, Wojciech Szewczuk1, Eloy Rodriguez2, Aliz Derekas3 1Instytut Astronomiczny, Uniwersytet Wrocławski, Poland 2Instituto de Astrofísica de Andalucía, Granada, Spain 3ELTE Eötvös Lòrànd University, Gothard Astrophysical Observatory, Szombathely Szent Imre, Hungary SPECTROSCOPY OF RY LEP SEISMIC MODELLING OF RY LEP We used a Monte Carlo approach combined with Bayesian inference to determine the stellar parameters of RY Lep. Stellar structure and evolution models were computed using the Warsaw–New Jersey evolutionary code (Paczyński, 1969; Pamyatnykh, 1999). We adopted the OPAL opacity tables (Iglesias & Rogers, 1996), chemical mixture of AGSS09 (Asplund et al., 2009), and the OPAL 2005 equation of state (Rogers et al., 1996). Linear non-adiabatic pulsations were calculated using the Dziembowski’s code. We fitted: 1) the frequency 𝛎1=4.4416 d−1 as the first radial overtone, 2) 𝛎2=6.5991 d−1 as the third radial overtone or a dipole mode, 2) effective temperature 3) luminosity, as well as 4) the photometric amplitudes and phases in the Strömgren uvby system for 𝛎1. We adopted initial hydrogen abundance X0 = 0.7 and microturbulence velocity of ξ = 4 km s-1. We considered the whole range of effective temperature found in the literature and our estimate from spectroscopy (6150, 7540) K. The luminosity log L/L⊙ = 1.82(5) was derived using the StarHorse distance (based on the Gaia DR2 parallax) and the bolometric correction from Kurucz models. The median values of the parameters derived from our seismic modeling are given in the table. The histograms shown on the left show the results for the case where 𝛎2is assumed to be the third radial overtone. We present a comprehensive analysis of the star RY Lep, which was classified as a high-amplitude δ Scuti variable. The star is in a long-period binary system, and its companion is most likely a white dwarf. Based on TESS data from sectors S06, S32, and S33, we identified three independent frequencies in S06 and seven in S32+S33. Only two frequencies, 4.4416 d⁻¹ and 7.9945 d⁻¹, are common in both data sets, while the frequency 6.5991 d⁻¹, detected in the ground-based observations, appears only in S06. Using low-resolution spectroscopy obtained with the SSO telescope, we determined the metallicity [m/H] and discovered a significant barium overabundance, which is a further evidence for the presence of a white dwarf. The barium enrichment in the atmosphere of RY Lep, the white dwarf companion, and long orbital period suggest that RY Lep may be an evolved blue straggler star (BSS) formed in Case C mass-transfer scenario. Using amplitudes and phases in the Strömgren passbands, we have unambiguously identified that the dominant frequency of RY Lep is a radial mode, most probably the first overtone. Besides, it was possible to derive its empirical value of the non-adiabatic parameter f, which gives the relative amplitude of the bolometric flux variations. The frequency 6.5991 d⁻¹, with large amplitude changes, can be either a radial mode (third overtone) or a dipole mode. We made extensive seismic modelling with Bayesian analysis based on Monte Carlo simulations, aiming to reproduce the dominant frequency 4.4416 d⁻¹ as the radial mode, its empirical value of f, and the frequency 6.5991 d⁻¹ as a radial mode or a dipole mode, considering all azimuthal orders m. ACKNOWLEDGEMENTS: the work was financially supported by the Polish National Science Centre grant 2023/50/A/ST9/00144 RY Lep was observed in three TESS sectors. All frequencies with a signal-to-noise ratio (S/N) greater than 5.0 were considered as significant. The noise level was estimated as the mean amplitude within a 1 d⁻¹-wide window centred on each frequency. We used an algorithm based on the fast Fourier transforms for non-equally spaced data (e.g., Leroy 2012) and proceeded the standard pre-whitening procedure. The left table gives the whole set of the extracted frequencies from the S06 TESS data. The lower table contains the whole set of frequencies found in combined S32+S33 sectors. The panel on the right shows the periodograms for the original data of sector S06, after subtracting 4 frequencies, and after subtracting 12 frequencies. Two frequencies, 4.4416 d⁻¹ and 7.9945 d⁻¹, are present in all sectors. The frequency 6.5991 d−1 was observed only in sector S06, whereas 5.8212 d⁻¹ and 3.2616 d⁻¹ were observed in combined S32+S33 sectors. Three independent frequencies near 7.9972 d-1, detected in S32+S33, may be related to amplitude or frequency modulation of 7.9972 d-1 between two sectors. PULSATION FREQUENCIES OF RY LEP FROM TESS We re-analysed a set of 852 low-resolution spectra of RY Lep, obtained by Derekas et al. (2009) using the 2.3 m Australian National University telescope at the Siding Spring Observatory (SSO). The overall metallicity was estimated as [m/H] = -0.35. In all analysed spectra we found two strong lines of the barium ion Ba II with wavelengths 6141.7 Å and 6496.9 Å. The left panel presents two lines of Ba II in the median SSO spectrum of RY Lep. Strong Ba II lines were also observed in the high-resolution SALT spectrum (2023) of RY Lep. We also found significantly higher abundances of other heavy elements with Z>30, which are typically produced in neutron-capture processes, such as those occurring in AGB stars. The panel below shows the derived chemical abundances from the SALT spectrum, with the vertical red line indicating the iron abundance [Fe/H].
