Discovery of a second pulsating intermediate helium-enriched sdOB star

Latour, M.; Green, E. M.; Fontaine, G.

doi:10.1051/0004-6361/201935307

Cited by 18 publications

(38 citation statements)

References 48 publications

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“…Due to this blend, the frequencies of these two components are less accurately measured in the TESS data (see Table 1). Overall, we detect five of the six periods found by Latour et al (2019a). Their peak with the lowest amplitude, at 2586 s, is not visible in the TESS run.…”

Section: The Tess Light Curve Of Feige 46mentioning

confidence: 63%

“…Significant periodic signal is clearly detected in the 250−500 µHz range. Latour et al (2019a). Due to this blend, the frequencies of these two components are less accurately measured in the TESS data (see Table 1).…”

Section: The Tess Light Curve Of Feige 46mentioning

confidence: 98%

“…Since the TESS light curve and that of Latour et al (2019a) were obtained, on average, 698 days apart, it is possible to constrain a potential period decay, as predicted by Battich et al (2018). These authors propose that pulsators like Feige 46 are fast evolving stars experiencing helium sub-flashes before reaching the extreme horizontal branch.…”

Section: The Tess Light Curve Of Feige 46mentioning

confidence: 99%

“…They share many physical properties, which make them a unique pair not only among the iHe-sdOBs. A&A 643, A22 (2020) Kinematic analyses of LS IV-14 • 116 (Randall et al 2015) and Feige 46 (Latour et al 2019a) have shown that both stars are likely to be members of the Galactic halo unlike most of the helium-rich hot subdwarfs . Both stars show light variations attributed to pulsations.…”

Section: Introductionmentioning

confidence: 99%

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Heavy-metal enrichment of intermediate He-sdOB stars: the pulsators Feige 46 and LS IV–14°116 revisited

Dorsch

Latour

Heber

et al. 2020

A&A

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Hot subdwarf stars of spectral types O and B represent a poorly understood phase in the evolution of low-mass stars, in particular of close compact binaries. A variety of phenomena are observed, which make them important tools for several astronomical disciplines. For instance, the richness of oscillations of many subdwarfs are important for asteroseismology. Furthermore, hot subdwarfs are among the most chemically peculiar stars known. Two intermediate He-rich hot subdwarf stars, LS IV–14°116 and Feige 46, are particularly interesting, because they show extreme enrichments of heavy elements such as Ge, Sr, Y, and Zr, which are strikingly similar in both stars. In addition, both stars show light oscillations at periods incompatible with standard pulsation theory and form the class of V366 Aqr variables. We investigated whether the similar chemical compositions extend to more complete abundance patterns in both stars and validate the pulsations in Feige 46 using its recent TESS light curve. High-resolution optical and near-ultraviolet spectroscopy are combined with non-local thermodynamical-equilibrium model atmospheres and synthetic spectra calculated with TLUSTY and SYNSPEC to consistently determine detailed metal abundance patterns in both stars. Many previously unidentified lines were identified for the first time with transitions originating from Ga III, Ge III-IV, Se III, Kr III, Sr II-III, Y III, Zr III-IV, and Sn IV, most of which have not yet been observed in any star. The abundance patterns of 19 metals in both stars are almost identical, light metals being only slightly more abundant in Feige 46, while Zr, Sn, and Pb are slightly less enhanced compared to LS IV–14°116. Both abundance patterns are distinctively different from those of normal He-poor hot subdwarfs of a similar temperature. The extreme enrichment in heavy metals of more than 4 dex compared to the Sun is likely the result of strong atmospheric diffusion processes that operate similarly in both stars while their similar patterns of C, N, O, and Ne abundances might provide clues to their as yet unclear evolutionary history. Finally, we find that the periods of the pulsation modes in Feige 46 are stable to better than Ṗ ≲ 10−8 s s−1. This is not compatible with Ṗ predicted for pulsations driven by the ɛ-mechanism and excited by helium-shell flashes in a star that is evolving, for example, onto the extended horizontal branch.

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Section: The Tess Light Curve Of Feige 46mentioning

confidence: 63%

Section: The Tess Light Curve Of Feige 46mentioning

confidence: 98%

Section: The Tess Light Curve Of Feige 46mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Heavy-metal enrichment of intermediate He-sdOB stars: the pulsators Feige 46 and LS IV–14°116 revisited

Dorsch

Latour

Heber

et al. 2020

A&A

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“…Lower panel: T eff -g diagram of our computed DM, SM and EHF sequences for an initially He-enhanced population (X ZAMS , Y ZAMS , Z ZAMS ) = (0.695, 0.285, 0.02)) as compared with the known pulsating He-sdOBs shown as yellow points with black error bars (from left to right UVO 0825+15, Feige 46, LS IV -14 • 116, and KIC 1718290). Errorbars correspond to the formal fitting errors provided by each author[41,42,43,44]. Colours indicate the He-burning luminosity in the parts of the evolution in which models harbour an internal convective zone.…”

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confidence: 99%

Asteroseismic signatures of the helium core flash

et al. 2019

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All evolved stars with masses M 2M undergo a helium(He)-core flash at the end of their first stage as a giant star. Although theoretically predicted more than 50 years ago [1,2], this core-flash phase has yet to be observationally probed. We show here that gravity modes (g modes) stochastically excited by He-flash driven convection are able to reach the stellar surface, and induce periodic photometric variabilities in hot-subdwarf stars with amplitudes of the order of a few mmag. As such they can now be detected by spacebased photometry with the Transiting Exoplanet Survey Satellite (TESS) in relatively bright stars (e.g. magnitudes I C 13) [3]. The range of predicted periods spans from a few thousand seconds to tens of thousand seconds, depending on the details of the excitation region. In addition, we find that stochastically excited pulsations reproduce the pulsations observed in a couple of He-rich hot subdwarf stars. These stars, and in particular the future TESS target Feige 46, are the most promising candidates to probe the He-core flash for the first time.After the end of their adult lives burning hydrogen (H) in the core, lowmass stars (up to about 2 M ) evolve into the Red Giant Branch (RGB), where they develop a He core surrounded by a H-burning shell. Due to the high densities, the structure of the He-core is supported by the pressure of degenerate electrons. As H burning proceeds, the mass of the He core 1 arXiv:2005.02070v1 [astro-ph.SR] 5 May 2020

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Heavy metals in intermediate He-rich hot subdwarfs: the chemical composition of HZ 44 and HD 127493

Dorsch¹,

Latour

Heber³

2019

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Context. Hot subluminous stars can be spectroscopically classified as subdwarf B (sdB) and O (sdO) stars. While the latter are predominantly hydrogen deficient, the former are mostly helium deficient. The atmospheres of most sdOs are almost devoid of hydrogen, whereas a small group of hot subdwarf stars of mixed H/He composition exists, showing extreme metal abundance anomalies. Whether such intermediate helium-rich (iHe) subdwarf stars provide an evolutionary link between the dominant classes is an open question.Aims. The presence of strong Ge, Sn, and Pb lines in the UV spectrum of HZ 44 suggests a strong enrichment of heavy elements in this iHe-sdO star and calls for a detailed quantitative spectral analysis focusing on trans-iron elements. Methods. Non-LTE model atmospheres and synthetic spectra calculated with TLUSTY/SYNSPEC are combined with high-quality optical, UV and FUV spectra of HZ 44 and its hotter sibling HD 127493 to determine their atmospheric parameters and metal abundance patterns.Results. By collecting atomic data from literature we succeeded to determine abundances of 29 metals in HZ 44, including the transiron elements Ga, Ge, As, Se, Zr, Sn, and Pb and provide upper limits for 10 other metals. This makes it the best described hot subdwarf in terms of chemical composition. For HD 127493 the abundance of 15 metals, including Ga, Ge, and Pb and upper limits for another 16 metals were derived. Heavy elements turn out to be overabundant by one to four orders of magnitude with respect to the Sun. Zr and Pb are among the most enriched elements.Conclusions. The C, N, and O abundance for both stars can be explained by nucleosynthesis of hydrogen burning in the CNO cycle along with their helium enrichment. On the other hand, the heavy-element anomalies are unlikely to be caused by nucleosynthesis. Instead diffusion processes are evoked with radiative levitation overcoming gravitational settlement of the heavy elements.

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Discovery of a second pulsating intermediate helium-enriched sdOB star

Cited by 18 publications

References 48 publications

Heavy-metal enrichment of intermediate He-sdOB stars: the pulsators Feige 46 and LS IV–14°116 revisited

Heavy-metal enrichment of intermediate He-sdOB stars: the pulsators Feige 46 and LS IV–14°116 revisited

Asteroseismic signatures of the helium core flash

Heavy metals in intermediate He-rich hot subdwarfs: the chemical composition of HZ 44 and HD 127493

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