Exploring the Helium Core of the δ Scuti Star CoRoT 102749568 with Asteroseismology

Abstract

Based on regularities in rotational splitting, we seek possible multiplets for the observed frequencies of CoRoT 102749568. There are 21 sets of multiplets identified, including four sets of multiplets with l = 1, nine sets of multiplets with l = 2, and eight sets of multiplets with l = 3. In particular, there are three complete triplets (f₁₀, f₁₂, f₁₄), (f₃₁, f₃₄, f₃₅), and (f₄₁, f₄₃, f₄₄). The rotational period of CoRoT 102749568 is estimated to be {1.34}_-0.05^+0.04 days. When doing model fittings, three l = 1 modes (f₁₂, f₃₄, and f₄₃) and the radial first overtone f₁₃ are used. Our results shows that the three nonradial modes (f₁₂, f₃₄, and f₄₃) are mixed modes, which mainly provide constraints on the helium core. The radial first overtone f₁₃ mainly provides constraint on the stellar envelope. Hence the size of the helium core of CoRoT 102749568 is determined to be {M}_{He} = 0.148 ± 0.003 M_⊙ and {R}_{He} = 0.0581 ± 0.0007 R_⊙. The fundamental parameters of CoRoT 102749568 are determined to be M = 1.54 ± 0.03 M_⊙, Z=0.006, {f}_{ov}=0.004+/- 0.002, {log} g=3.696+/- 0.003, {T}_{eff}=6886+/- 70 K, R = 2.916 ± 0.039 R_⊙, and L = 17.12 ± 1.13 L_⊙.