Pulsating hydrogen-deficient white dwarfs and pre-white dwarfs observed with TESS -- IV. Discovery of two new GW Vir stars: TIC0403800675 and TIC1989122424

Abstract

We present two new GW Vir-type pulsating white dwarf stars, TIC\,0403800675 (WD\,J115727.68-280349.64) and TIC\,1989122424 (WD J211738.38-552801.18) discovered in the Transiting Exoplanet Survey Satellite (TESS) photometric data. For both stars, the TESS light curves reveal the presence of oscillations with periods in a narrow range between 400 and 410\,s, which are associated with typical gravity ($g$)-modes. Follow-up ground-based spectroscopy shows that both stars have similar effective temperature ($T_{\mathrm{eff}}=110,000\pm 10,000$\,K) and surface gravity ($\log g=7.5\pm 0.5$), but different He/C composition (mass fractions): He\,=\,0.75 and C\,=\,0.25 for TIC\,0403800675, and He\,=\,0.50 and C\,=\,0.50 for TIC\,1989122424. By performing a fit to their spectral energy distributions, we found for both stars radii and luminosities of $R=0.019\pm 0.002R_{\odot }$ and $\log (L/L_{\odot })=1.68_{-0.24}^{+0.15}$, respectively. By employing evolutionary tracks of PG~1159 stars, we find the masses of both stars to be $0.56\pm 0.18M_{\odot }$ from the $\log g$-$T_{\mathrm{eff}}$ diagram and $0.60_{-0.09}^{+0.11}{M}_{\odot }$ from the Hertzsprung Russell diagram.

arXiv comment8 Pages. arXiv admin note: text overlap with arXiv:2108.11093

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