J/ApJ/718/L97 Early asteroseismic results from Kepler (Van Grootel+, 2010) ================================================================================ Early asteroseismic results from Kepler: structural and core parameters of the hot b subdwarf KPD 1943+4058 as inferred from g-mode oscillations. Van Grootel V., Charpinet S., Fontaine G., Brassard P., Green E.M., Randall S.K., Silvotti R., Ostensen R.H., Kjeldsen H., Christensen-Dalsgaard J., Borucki W.J., Koch D. =2010ApJ...718L..97V ================================================================================ ADC_Keywords: Stars, B-type ; Stars, variable Keywords: stars: individual (KPD 1943+4058) - stars: interiors - stars: oscillations - subdwarfs Abstract: 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_=28050+/-470K, logg=5.52+/-0.03, M_*_=0.496+/-0.002M_{sun}_, log(M_env_/M*)=-2.55+/-0.07, log(1-M_core_/M_*_)=-0.3+/-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_{sun}_, the luminosity L=22.9+/-3.13L_{sun}_, the absolute magnitude M_V_=4.21+/-0.11, the reddening index E(B-V)=0.094+/-0.017, and the distance d=1180+/-95pc. Description: In this Letter, we exploit the exceptional data obtained on KPD 1943+4058 by Kepler. We also obtained a low-resolution (9{AA}), moderately high S/N (~112 in the blue) spectrum of KPD 1943+4058 with the Steward Observatory 2.3m Bok Telescope on 2008 12 June. Objects: ---------------------------------------------------------- RA (2000) DE Designation(s) ---------------------------------------------------------- 19 45 25.48 +41 05 33.8 KIC 005807616 = KPD 1943+4058 ---------------------------------------------------------- File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file table1.dat 50 35 List of frequencies f_n_ (n is by order of decreasing amplitude) detected in KPD 1943+4058 table2.dat 80 79 Mode identification and other properties -------------------------------------------------------------------------------- See also: J/A+A/525/A23 : Frequency analysis of HD 49434 (Mathias+, 2011) J/A+A/506/471 : Frequency analysis of CoRoT B stars (Degroote+, 2009) J/A+A/506/111 : Frequency analysis of HD 180642 (V1449 Aql) (Degroote+, 2009) J/A+A/506/79 : Asteroseismic analysis of HD 174936 (Garcia Hernandez+, 2009) Byte-by-byte Description of file: table1.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 5 A5 --- ID Mode identification (f_1_-f_27_, u_1_-u_14_) 7 A1 --- f_ID [*] *: pulsation period safely assumed to be independent (18 periods used in the analysis) 9- 15 F7.2 s Per Period 17- 23 F7.3 uHz Freq Frequency 25- 28 F4.1 --- S/N Signal to noise ratio 30- 50 A21 --- Comm Comments -------------------------------------------------------------------------------- Byte-by-byte Description of file: table2.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1 I1 --- l [1/4] Degree 3- 5 I3 --- k [-63/-3] Radial order 7- 13 F7.3 uHz nuObs ? Observed frequency 15- 22 F8.3 uHz nuTh Theoretical frequency 24- 30 F7.2 s PObs ? Observed period 32- 38 F7.2 s PTh Theoretical period 40- 45 F6.3 [10-7J] logE Log of the energy; in erg 47- 52 F6.4 --- Ckl Ledoux coefficient 54- 58 F5.2 % DelX/X ? Relative dispersion (on P or {nu}) 60- 65 F6.2 s DelP ? Period dispersion {Delta}P 67- 72 F6.3 uHz Delnu ? Frequency dispersion {Delta}{nu} 74- 78 A5 --- ID Mode identification (f_1_-f_27_, u_1_-u_14_) 80 A1 --- f_ID [1/2] Flag on ID (1) -------------------------------------------------------------------------------- Note (1): Flag as follows: 1 = Additional frequencies (see Table 1; u_n_). 2 = Left-aside frequencies (see section 3.2 and Table 1). -------------------------------------------------------------------------------- History: From electronic version of the journal ================================================================================ (End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 08-Jun-2012