Structural and core parameters of the hot B subdwarf KPD 0629-0016 from CoRoT g-mode asteroseismology

Abstract

Context. The asteroseismic exploitation of long period, g-mode hot B subdwarf pulsators (sdBV s ), undermined so far by limitations associated with ground-based observations, has now become possible, thanks to high quality data obtained from space such as those recently gathered with the CoRoT (COnvection, ROtation, and planetary Transits) satellite. Aims. We propose a detailed seismic analysis of the sdBV s star KPD 0629-0016, the first compact pulsator monitored with CoRoT, using the g-mode pulsations recently uncovered by that space-borne observatory during short run SRa03. Methods. We use a forward modeling approach on the basis of our latest sdB models, which are now suitable for the accurate computation of the g-mode pulsation properties. The simultaneous match of the independent periods observed in KPD 0629-0016 with those of the models leads objectively to the identification of the pulsation modes and, more importantly, to the determination of the structural and core parameters of the star.Results. The optimal model we found closely reproduces the 18 observed periods retained in our analysis at a 0.23% level on average. These are identified as low-degree ( = 1 and 2), intermediate-order (k = −9 through −74) g-modes. The structural and core parameters for KPD 0629-0016 are the following (formal fitting errors only): T eff = 26 290 ± 530 K, log g = 5.450 ± 0.034, M * = 0.471 ± 0.002 M , log (M env /M * ) = −2.42 ± 0.07, log (1 − M core /M * ) = −0.27 ± 0.01, and X core (C+O) = 0.41 ± 0.01. We additionally derive an age of 42.6 ± 1.0 Myr after the zero-age extreme horizontal branch, the radius R = 0.214 ± 0.009 R , the luminosity L = 19.7 ± 3.2 L , the absolute magnitude M V = 4.23 ± 0.13, the reddening index E(B − V) = 0.128 ± 0.023, and the distance d = 1190 ± 115 pc. Conclusions. The advent of high-precision time-series photometry from space with instruments like CoRoT now allows as demonstrated with KPD 0629-0016 the full exploitation of g-modes as deep probes of the internal structure of these stars, in particular for determining the mass of the convective core and its chemical composition.

Stellar hydrodynamics caught in the act: Asteroseismology with CoRoT and Kepler

“…Also, an sdB star showing extensive g-mode pulsations has been observed by the CoRoT mission . Model fitting to the resulting periods by Van Grootel et al (2010b) yielded results rather similar to those discussed above.…”

Asteroseismic Signatures of Evolving Internal Stellar Magnetic Fields

“…Indeed, asteroseismic studies of clump stars (Montalbán et al 2013;Stello et al 2013;Mosser et al 2014;Bossini et al 2015;Constantino et al 2015) and subdwarf B stars (Van Grootel et al 2010a, 2010bCharpinet et al 2011;Schindler et al 2015) indicate that the convective core is somewhat larger than predicted by stellar evolution codes, even using optimistic overshooting prescriptions. MS convective cores may also be somewhat larger and show evidence for enhanced mixing (Moravveji et al 2015).…”

A preliminary look at the empirical mass distribution of hot B subdwarf stars

“…Thanks to the advent of space-borne photometers such as CoRoT and Kepler, however, suitable data have become available. We thus recently derived asteroseismological inferences (including measurements of the mass) for three sdB g-mode pulsators: KPD 0629−0016 (Van Grootel et al 2010c) from CoRoT photometry, KPD 1943+4058 (Van Grootel et al 2010b) and KIC02697388 (Charpinet et al 2011) from Kepler data.…”