Reference : Mode identification from monochromatic amplitude and phase variations for the rapidly...
Scientific journals : Article
Physical, chemical, mathematical & earth Sciences : Space science, astronomy & astrophysics
http://hdl.handle.net/2268/109073
Mode identification from monochromatic amplitude and phase variations for the rapidly pulsating subdwarf B star EC 20338-1925
English
Randall, S. K. [ > > ]
Fontaine, G. [ > > ]
Brassard, P. [ > > ]
Van Grootel, Valérie mailto [Laboratoire d'Astrophysique de Toulouse-Tarbes (LATT) > > > >]
Nov-2010
Astronomy and Astrophysics
EDP Sciences
522
48
Yes (verified by ORBi)
International
0004-6361
1432-0746
Les Ulis
France
[en] asteroseismology ; techniques: imaging spectroscopy ; stars: oscillations ; stars: individual: EC 20338-1925 ; stars: variables: general ; stars: atmospheres
[en] We obtain time-series spectrophotometry observations at the VLT with the aim of partially identifying the dominant oscillation modes in the rapidly pulsating subdwarf B star EC 20338-1925 on the basis of monochromatic amplitude and phase variations. From the data gathered, we detect four previously known pulsations with periods near 147, 168, 126 and 140 s and amplitudes between 0.2 and 2.3 % of the star's mean brightness. We also determine the atmospheric parameters of EC 20338-1925 by fitting our non-LTE model atmospheres to an averaged combined spectrum. The inferred parameters are Teff = 34 153±94 K, log g = 5.966±0.017 and log N(He)/N(H) = -1.642±0.022, where the uncertainty estimates quoted refer to the formal fitting errors. Finally, we calculate the observed monochromatic amplitudes and phases for the periodicities extracted using least-squares fitting to the light curves obtained for each wavelength bin. These observed quantities are then compared to the corresponding theoretical values computed on the basis of dedicated model atmosphere codes and also taking into account non-adiabatic effects. We find that the quality of the data is sufficient to identify the dominant pulsation at 146.9 s as a radial mode, while two of the lower amplitude periodicities must be low-degree modes with ell = 0-2. This is the first time that monochromatic amplitudes and phases have been used for mode identification in a subdwarf B star, and the results are highly encouraging.
http://hdl.handle.net/2268/109073

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