The enigmatic He-sdB pulsator LS IV-14°116: new insights from the VLT

Randall, S. K.; Bagnulo, S.; Ziegerer, E.; Geier, S.; Fontaine, G.

doi:10.1051/0004-6361/201425251

Cited by 37 publications

(52 citation statements)

References 40 publications

(61 reference statements)

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“…Comparing our predictions with the pulsational properties of known pulsating subdwarfs with mixed H+He surface compositions, namely LS IV-14 ∘ 116 with observed periods P ≃ 1950 − 5080 s (T e = 35150 ± 111, log g = 5.88 ± 0.02, log n(He)/n(H) = −0.62 ± 0.01, Randall et al 2015;Ahmad et al 2005;Green et al 2011), KIC 1718290 with P ≃ 1 − 12h (T e = 22100, log g = 4.72, log n(He)/n(H) = −0.45, Østensen et al 2012) and UVO 0825+156 with P ≃ 10.8 − 13.3h (T e = 38900 ± 270, log g = 5.97 ± 0.11, log n(He)/n(H) = −0.57 ± 0.01, Jeffery et al 2017), we found that their values of T e , log g, and log n(He)/n(H) (Figure 2) are well reproduced by our theoretical predictions. Quantitatively, however, the observed periods in these stars are systematically longer than the predicted ones (200 − 2000 s).…”

Section: Discussionsupporting

confidence: 54%

“…Coloured points correspond to models with excited modes and the colour coding shows the minimum e-folding time for each model. Also shown for comparison is the location of the known He-rich hot subdwarf pulsators LS IV-14 ∘ 116 (Randall et al 2015), UVO 0825+15 (Jeffery et al 2017), and KIC 1718290 (Østensen et al 2012). This trend is more notorious for the long-period limit.…”

Section: Periods Of Excited Modesmentioning

confidence: 99%

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ε-mechanism driven pulsations in hot subdwarf stars with mixed H-He atmospheres

et al. 2017

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Abstract:The ϵ mechanism is a self-excitation mechanism of stellar pulsations which acts in regions where nuclear burning takes place. It has been shown that the ϵ mechanism can excite pulsations in hot pre-horizontal branch stars before they settle into the stable helium core-burning phase and that the shortest periods of LS IV-14 ∘ 116 could be explained that way. We aim to study the ϵ mechanism in stellar models appropriate for hot pre-horizontal branch stars to predict their pulsational properties. We perform detailed computations of non-adiabatic non-radial pulsations on such stellar models. We predict a new instability domain of long-period gravity modes in the log g − log T e plane at roughly 22000 K T e 50000 K and 4.67 log g 6.15, with a period range from ∼ 200 to ∼ 2000 s. Comparison with the three known pulsating He-rich subdwarfs shows that the ϵ mechanism can excite pulsations in models with similar surface properties except for modes with the shortest observed periods. Based on simple estimates we expect at least 3 stars in the current samples of hot-subdwarf stars to be pulsating by the ϵ mechanism. Our results could constitute a theoretical basis for future searches of pulsators in the Galactic field.

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Section: Discussionsupporting

confidence: 54%

Section: Periods Of Excited Modesmentioning

confidence: 99%

ε-mechanism driven pulsations in hot subdwarf stars with mixed H-He atmospheres

et al. 2017

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“…Its uncertainty is much lower than the symbol size. the equations of Randall et al (2014) by varying the position and velocity components within their respective errors by A96, page 7 of 9 applying a Monte Carlo procedure with a depth of 100 000. The distance of the sun from the Galactic centre was assumed to be 8.4 kpc.…”

Section: Photometric Distance and Space Velocitymentioning

confidence: 99%

An ancient F-type subdwarf from the halo crossing the Galactic plane

Scholz

Heber

Heuser

et al. 2015

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Aims. We selected the bluest object, WISE J0725−2351, from Luhman's new high proper motion (HPM) survey based on observations with the Wide-field Infrared Survey Explorer (WISE) for spectroscopic follow-up observations. Our aim was to unravel the nature of this relatively bright (V ∼ 12, J ∼ 11) HPM star (µ = 267 mas/yr). Methods. We obtained low-and medium-resolution spectra with the European Southern Observatory (ESO) New Technology Telescope (NTT)/EFOSC2 and Very Large Telescope (VLT)/X-Shooter instruments, investigated the radial velocity and performed a quantitative spectral analysis that allowed us to determine physical parameters. The fit of the spectral energy distribution based on the available photometry to low-metallicity model spectra and the similarity of our target to a metal-poor benchmark star (HD 84937) allowed us to estimate the distance and space velocity. Results. As in the case of HD 84937, we classified WISE J0725−2351 as sdF5: or a metal-poor turnoff star with [Fe/H] = −2.0 ± 0.2, T eff = 6250 ± 100 K, log g = 4.0 ± 0.2, and a possible age of about 12 Gyr. At an estimated distance of more than 400 pc, its proper motion translates to a tangential velocity of more than 500 km s −1 . Together with its constant (on timescales of hours, days, and months) and large radial velocity (about +240 km s −1 ), the resulting Galactic restframe velocity is about 460 km s −1 , implying a bound retrograde orbit for this extreme halo object that currently crosses the Galactic plane at high speed.

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“…So far, there has been no entirely satisfactory explanation for the pulsations observed. Quite intriguingly, it was recently shown to be a halo object (Randall et al 2015), which may indicate a distinct evolutionary history compared to the garden variety sdB stars. The second unique object is V499 Ser (often referred to as SDSS J160043.6+074802.9 in the literature), a hot (T eff ∼ 68 500 K according to Latour et al 2011) He-rich sdO star that exhibits very rapid multi-periodic oscillations with periods between 60 and 120 s (Woudt et al 2006).…”

Section: Introductionmentioning

confidence: 99%

Pulsating hot O subdwarfs inωCentauri: mapping a unique instability strip on the extreme horizontal branch

Randall¹,

Calamida

Fontaine

et al. 2016

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We present the results of an extensive survey for rapid pulsators among Extreme Horizontal Branch (EHB) stars in ω Cen. The observations performed consist of nearly 100 hours of time-series photometry for several off-centre fields of the cluster, as well as low-resolution spectroscopy for a partially overlapping sample. We obtained photometry for some 300 EHB stars, for around half of which we are able to recover light curves of sufficient quality to either detect or place meaningful non-detection limits for rapid pulsations. Based on the spectroscopy, we derive reliable values of log g, T eff and log N(He)/N(H) for 38 targets, as well as good estimates of the effective temperature for another nine targets, whose spectra are slightly polluted by a close neighbour in the image. The survey uncovered a total of five rapid variables with multi-periodic oscillations between 85 and 125 s. Spectroscopically, they form a homogeneous group of hydrogen-rich subdwarf O stars clustered between 48,000 and 54,000 K. For each of the variables we are able to measure between two and three significant pulsations believed to constitute independent harmonic oscillations. However, the interpretation of the Fourier spectra is not straightforward due to significant fine structure attributed to strong amplitude variations. In addition to the rapid variables, we found an EHB star with an apparently periodic luminosity variation of ∼2700 s, which we tentatively suggest may be caused by ellipsoidal variations in a close binary. Using the overlapping photometry and spectroscopy sample we are able to map an empirical ω Cen instability strip in log g − T eff space. This can be directly compared to the pulsation driving predicted from the Montréal "second-generation" models regularly used to interpret the pulsations in hot B subdwarfs. Extending the parameter range of these models to higher temperatures, we find that the region where p-mode excitation occurs is in fact bifurcated, and the well-known instability strip between 29,000-36,000 K where the rapid subdwarf B pulsators are found is complemented by a second one above 50,000 K in the models. While significant challenges remain at the quantitative level, we believe that the same κ-mechanism that drives the pulsations in hot B subdwarfs is also responsible for the excitation of the rapid oscillations observed in the ω Cen variables. Intriguingly, the ω Cen variables appear to form a unique class. No direct counterparts have so far been found either in the Galactic field, nor in other globular clusters, despite dedicated searches. Conversely, our survey revealed no ω Cen representatives of the rapidly pulsating hot B subdwarfs found among the field population, though their presence cannot be excluded from the limited sample.

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The enigmatic He-sdB pulsator LS IV-14°116: new insights from the VLT

Cited by 37 publications

References 40 publications

ε-mechanism driven pulsations in hot subdwarf stars with mixed H-He atmospheres

ε-mechanism driven pulsations in hot subdwarf stars with mixed H-He atmospheres

An ancient F-type subdwarf from the halo crossing the Galactic plane

Pulsating hot O subdwarfs inωCentauri: mapping a unique instability strip on the extreme horizontal branch

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