A survey of hot subdwarf pulsators in<i>ω</i>Cen

Randal, S.K.; Calamida, A.; Fontaine, G.; Green, E.M.; Monelli, M.; Alonso, M. L.; Catelan, M.; Bono, G.; Dhillon, V. S.; Marsh, T. R.

doi:10.1051/epjconf/20134304006

EPJ Web of Conferences

2013

DOI: 10.1051/epjconf/20134304006

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A survey of hot subdwarf pulsators inωCen

S.K. Randal¹,

A. Calamida

G. Fontaine

et al.

Abstract: Abstract.We recently discovered an apparently new class of pulsating Extreme Horizontal Branch (EHB) star in Cen. Tightly clustered around ∼50,000 K, these H-rich sdO stars exhibit rapid, multi-periodic oscillations on a timescale of 100 s. While four such objects have been detected in Cen, no counterparts have yet been found among the field population. Conversely, the rapid sdB pulsators around 31,000 K that are well-studied in the Galactic field have yet to be found in a globular cluster. We discuss the impl… Show more

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Cited by 2 publications

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A Helium-Carbon Correlation on the Extreme Horizontal Branch in Ω Centauri

Latour

Randall²,

Fontaine

et al. 2014

ApJ

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Taking advantage of a recent FORS2/VLT spectroscopic sample of Extreme Horizontal Branch (EHB) stars in ω Cen, we isolate 38 spectra well suited for detailed atmospheric studies and determine their fundamental parameters (T eff , log g, and log N (He)/N (H)) using NLTE, metal line-blanketed models. We find that our targets can be divided into three groups: 6 stars are hot (T eff > ∼ 45,000 K) H-rich subdwarf O stars, 7 stars are typical H-rich sdB stars (T eff < ∼ 35,000 K), and the remaining 25 targets at intermediate effective temperatures are He-rich (log N (He)/N (H) > ∼ −1.0) subdwarfs. Surprisingly and quite interestingly, these He-rich hot subdwarfs in ω Cen cluster in a narrow temperature range (∼35,000 K to ∼40,000 K). We additionally measure the atmospheric carbon abundance and find a most interesting positive correlation between the carbon and helium atmospheric abundances. This correlation certainly bears the signature of diffusion processes -most likely gravitational settling impeded by stellar winds or internal turbulence -but also constrains possible formation scenarios proposed for EHB stars in ω Cen. For the He-rich objects in particular, the clear link between helium and carbon enhancement points towards a late hot flasher evolutionary history.

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A Helium-Carbon Correlation on the Extreme Horizontal Branch in Ω Centauri

Latour

Randall²,

Fontaine

et al. 2014

ApJ

Self Cite

View full text Add to dashboard Cite

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The Discovery of Pulsating Hot Subdwarfs in NGC 2808

Brown¹,

Landsman²,

Randall³

et al. 2013

ApJ

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We present the results of a Hubble Space Telescope program to search for pulsating hot subdwarfs in the core of NGC 2808. These observations were motivated by the recent discovery of such stars in the outskirts of ω Cen. Both NGC 2808 and ω Cen are massive globular clusters exhibiting complex stellar populations and large numbers of extreme horizontal branch stars. Our far-UV photometric monitoring of over 100 hot evolved stars has revealed six pulsating subdwarfs with periods ranging from 85 to 149 s and UV amplitudes of 2.0 to 6.8%. In the UV color-magnitude diagram of NGC 2808, all six of these stars lie immediately below the canonical horizontal branch, a region populated by the subluminous "blue-hook" stars. For three of these six pulsators, we also have low-resolution far-UV spectroscopy that is sufficient to broadly constrain their atmospheric abundances and effective temperatures. Curiously, and in contrast to the ω Cen pulsators, the NGC 2808 pulsators do not exhibit the spectroscopic or photometric uniformity one might expect from a well-defined instability strip, although they all fall within a narrow band (0.2 mag) of far-UV luminosity.

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A survey of hot subdwarf pulsators inωCen

Cited by 2 publications

References 18 publications

A Helium-Carbon Correlation on the Extreme Horizontal Branch in Ω Centauri

A Helium-Carbon Correlation on the Extreme Horizontal Branch in Ω Centauri

The Discovery of Pulsating Hot Subdwarfs in NGC 2808

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