Determining the evolutionary stage of the delta Scuti star HIP 80088 with asteroseismology

Abstract

We have computed a grid of theoretical models to fit the twelve oscillation modes of HIP 80088 observed by K2. HIP 80088 is determined to be a pre-main sequence star, in which CN cycle has not arrived at the equilibrium state. Mass fractions of C12 and N14 in metal composition are 0.1277${}_{-0.0049}^{+0.0064}$ and 0.1092${}_{-0.0074}^{+0.0057}$ respectively, indicating that twenty-eight percent of C12 have turned into N14. Meanwhile, our fitting results show that physical parameters of HIP 80088 converge to a small range: $M$ = 1.68$-$1.78 $M_{\odot }$, $Z$ = 0.015$-$0.018, ${\upsilon }_{\mathrm{e}}$ = 120$-$136 km s${}^{-1}$, $\log g$ = 4.114$-$4.125, $R$ = 1.882$-$1.914 $R_{\odot }$, ${\tau }_0$ = 7636$-$7723 s, and age = 9.03$-$10.21 Myr. Based on our model fittings, $f_3$ is suggested to be one radial mode, $f_2$, $f_4$, $f_8$, and $f_{11}$ to be four $\ell$ = 1 modes, and $f_1$, $f_5$, $f_6$, $f_7$, $f_9$, $f_{10}$, and $f_{12}$ to be seven $\ell$ = 2 modes. In particularly, we find that ($f_2$, $f_4$, $f_8$) form one complete triplet with the averaged frequency spacing of 16.045 $\mu$Hz , and ($f_5$, $f_7$, $f_9$, $f_{10}$) form four components of one quintuplet with the averaged frequency spacing of 13.388 $\mu$Hz. The two averaged frequency spacings are not equal. Based on the best-fitting model, those $\ell$ = 2 modes of HIP 80088 are found to be mixed modes, which are p-dominated modes with pronounced g-mode features, while oscillation modes with $\ell$ = 1 are p modes.

arXiv comment11 pages,6 figures,6 Tables.accepted for publication in ApJ

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