Article (Scientific journals)
Observations and asteroseismological analysis of the rapid subdwarf B pulsator EC 09582-1137
Randall, Suzanna K.; Van Grootel, Valérie; Fontaine, Gilles et al.
2009In Astronomy and Astrophysics, 507, p. 911
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Keywords :
stars: fundamental parameters (masses); stars: individual: EC 09582-1137; stars: oscillations; subdwarfs; stars: variables: general; stars: interiors
Abstract :
[en] We made photometric and spectroscopic observations of the rapidly pulsating subdwarf B star EC 09582-1137 with the aim of determining the target's fundamental structural parameters from asteroseismology. This analysis forms part of a long-term programme geared towards distinguishing between different proposed formation scenarios for hot B subdwarfs on the basis of their internal characteristics. So far, secure asteroseismic solutions have been computed for 9 of these pulsators, and first comparisons with results from evolutionary calculations look promising. The new data comprise 30 h of fast time-series photometry obtained with SUSI2 at the NTT on La Silla, Chile, as well as 1 h of low-resolution spectroscopy gathered with EMMI, also mounted on the NTT. From the photometry we detected 5 independent harmonic oscillations in the 135-170 s period range with amplitudes up to 0.5% of the mean brightness of the star. In addition, we extracted two periodicities interpreted as components of a rotationally split multiplet that indicate a rotation period of the order of 2-5 days. We also recovered the first harmonic of the dominant pulsation, albeit at an amplitude below the imposed 4σ detection threshold. The spectroscopic observations led to the following estimates of the atmospheric parameters of EC 09582-1137: T_eff = 34 806±233 K, log{g} = 5.80±0.04, and log N(He)/N(H) = -1.68±0.06. Using the observed oscillations as input, we searched in model parameter space for unique solutions that present a good fit to the data. Under the assumption that the two dominant observed periodicities correspond to radial or dipole modes, we were able to isolate a well-constrained optimal model that agrees with the atmospheric parameters derived from spectroscopy. The observed oscillations are identified with low-order acoustic modes with degree indices ℓ = 0, 1, 2, and 4 and match the computed periods with a dispersion of 0.57%. Non-adiabatic calculations reveal all theoretical modes in the observed period range to be unstable, an important a posteriori consistency check for the validity of the optimal model. The inferred structural parameters of EC 09582-1137 are T_eff = 34 806 K (from spectroscopy), log{g} = 5.788±0.004, Mast = 0.485±0.011 Msun, log{(M_env/Mast)} = -4.39±0.10, R = 0.147±0.002 Rsun, and L = 28.6±1.7 Lsun. We additionally derive the absolute magnitude MV = 4.44±0.05 and the distance d = 1460±66 pc.
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Randall, Suzanna K.
Van Grootel, Valérie  ;  Laboratoire d'Astrophysique de Toulouse-Tarbes (LATT)
Fontaine, Gilles
Charpinet, Stéphane
Brassard, Pierre
Language :
English
Title :
Observations and asteroseismological analysis of the rapid subdwarf B pulsator EC 09582-1137
Publication date :
November 2009
Journal title :
Astronomy and Astrophysics
ISSN :
0004-6361
eISSN :
1432-0746
Publisher :
EDP Sciences, Les Ulis, France
Volume :
507
Pages :
911
Peer reviewed :
Peer Reviewed verified by ORBi
Available on ORBi :
since 22 January 2012

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