Early asteroseismic results from kepler: Structural and core parameters of the hot b subdwarf kpd 1943+4058 as inferred from g-mode oscillations

We present a seismic analysis of the pulsating hot B subdwarf KPD 1943+4058 (KIC 005807616) on the basis of the long-period, gravity-mode pulsations recently uncovered by Kepler. This is the first time that g-mode seismology can be exploited quantitatively for stars on the extreme horizontal branch, all previous successful seismic analyses having been confined so far to short-period, p-mode pulsators. We demonstrate that current models of hot B subdwarfs can quite well explain the observed g-mode periods, while being consistent with independent constraints provided by spectroscopy. We identify the 18 pulsations retained in our analysis as lowdegree (ℓ = 1 and 2), intermediate-order (k=-9 through -58) g-modes. The periods (frequencies) are recovered, on average, at the 0.22% level, which is comparable to the best results obtained for p-mode pulsators. We infer the following structural and core parameters for KPD 1943+4058 (formal fitting uncertainties only): T _eff = 28,050 470 K, log g = 5.52 ± 0.03, M_* = 0.496 ±0.002 M⊙, log (M_env/M_*) = -2.55 ±0.07, log (1 - M_core/M_*) = -0.37±0.01, and X_core(C+O)=0.261±0.008.We additionally derive the age of the star since the zero-age extended horizontal branch 18.4±1.0Myr, the radius R=0.203±0.007R⊙, the luminosity L=22.9±3.13 L⊙, the absolute magnitude M_V = 4.21 ±0.11, the reddening index E(B -V ) = 0.094 ±0.017, and the distance d = 1180 ±95 pc.