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 low-degree (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 circle dot, 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 +/- 1.0 Myr, the radius R = 0.203 +/- 0.007 R circle dot, the luminosity L = 22.9 +/- 3.13 L circle dot, 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.