Pulsating extreme horizontal branch (EHB) stars offer the unique opportunity to use asteroseismology to probe their fundamental parameters and thus constrain one of the more poorly understood phases of stellar evolution. However, they have been observed only among the field population, which necessarily prevents asteroseismological tools from being applied to globular cluster EHB stars. We launched a search for rapid EHB pulsators in omega Cen on the basis of fast time-series photometry obtained with EFOSC2 at the New Technology Telescope. Fourier analysis uncovered four multi-mode oscillators with rather similar periods between 84 and 124 s and amplitudes up to 2.7% of the mean stellar brightness. Initially, it was assumed that these stars constitute the globular cluster counterparts to the EC 14026 stars, rapid subdwarf B pulsators with T-eff similar to 31,000 K that have been extensively studied among the field population, yet a subsequent atmospheric analysis of FORS MXU spectra reveals effective temperatures closely clustered around 50,000 K, implying that the four omega Cen variables are in fact helium-poor subdwarf O (sdO) stars rather than EC 14026 pulsators. It remains to be seen whether they are related to the one significantly hotter sdO oscillator known among the field star population, or belong to a hitherto unknown class of stellar pulsator that can now be subjected to asteroseismological scrutiny.

Randall, S., Calamida, A., Fontaine, G., Bono, G., Brassard, P. (2011). RAPIDLY PULSATING HOT SUBDWARFS IN omega CENTAURI: A NEW INSTABILITY STRIP ON THE EXTREME HORIZONTAL BRANCH?. THE ASTROPHYSICAL JOURNAL LETTERS, 737(2) [10.1088/2041-8205/737/2/L27].

RAPIDLY PULSATING HOT SUBDWARFS IN omega CENTAURI: A NEW INSTABILITY STRIP ON THE EXTREME HORIZONTAL BRANCH?

BONO, GIUSEPPE;
2011-01-01

Abstract

Pulsating extreme horizontal branch (EHB) stars offer the unique opportunity to use asteroseismology to probe their fundamental parameters and thus constrain one of the more poorly understood phases of stellar evolution. However, they have been observed only among the field population, which necessarily prevents asteroseismological tools from being applied to globular cluster EHB stars. We launched a search for rapid EHB pulsators in omega Cen on the basis of fast time-series photometry obtained with EFOSC2 at the New Technology Telescope. Fourier analysis uncovered four multi-mode oscillators with rather similar periods between 84 and 124 s and amplitudes up to 2.7% of the mean stellar brightness. Initially, it was assumed that these stars constitute the globular cluster counterparts to the EC 14026 stars, rapid subdwarf B pulsators with T-eff similar to 31,000 K that have been extensively studied among the field population, yet a subsequent atmospheric analysis of FORS MXU spectra reveals effective temperatures closely clustered around 50,000 K, implying that the four omega Cen variables are in fact helium-poor subdwarf O (sdO) stars rather than EC 14026 pulsators. It remains to be seen whether they are related to the one significantly hotter sdO oscillator known among the field star population, or belong to a hitherto unknown class of stellar pulsator that can now be subjected to asteroseismological scrutiny.
2011
Pubblicato
Rilevanza internazionale
Articolo
Esperti anonimi
Settore FIS/05 - ASTRONOMIA E ASTROFISICA
English
Con Impact Factor ISI
globular clusters: individual (omega Centauri); stars: oscillations; subdwarfs
Randall, S., Calamida, A., Fontaine, G., Bono, G., Brassard, P. (2011). RAPIDLY PULSATING HOT SUBDWARFS IN omega CENTAURI: A NEW INSTABILITY STRIP ON THE EXTREME HORIZONTAL BRANCH?. THE ASTROPHYSICAL JOURNAL LETTERS, 737(2) [10.1088/2041-8205/737/2/L27].
Randall, S; Calamida, A; Fontaine, G; Bono, G; Brassard, P
Articolo su rivista
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2108/103342
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