Heavy metal enrichment in the intermediate He-sdOB pulsator Feige 46

Latour, M.; Dorsch, M.; Heber, U.

doi:10.1051/0004-6361/201936247

Cited by 13 publications

(24 citation statements)

References 46 publications

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“…The same is true for optical Xe IV lines as predicted by Rauch et al (2017). Our results for Feige 46 are in good agreement with the abundances derived by Latour et al (2019b). The excellent agreement for Ti, Ni, Zn, Ga, Sr, and Sn is remarkable because these abundances were previously solely based on UV data.…”

Section: Discussionsupporting

confidence: 88%

“…To model these lines, we used oscillator strengths provided by Kaur et al (2020), but the rest wavelengths had to be adjusted (see Table 7). The abundance of tin derived from the two newly identified lines turns out to be 22 000 times solar for LS IV-14 • 116 and 3700 times solar for Feige 46, which is consistent with the value derived from UV lines by Latour et al (2019b).…”

Section: Heavy Metalssupporting

confidence: 84%

“…To minimise systematic errors, we analysed the spectra of both Feige 46 and LS IV-14 • 116 using the same fitting method and the same type of model atmospheres, following the procedure described in Latour et al (2019b) and Dorsch et al (2019). This analysis is based on model atmospheres and synthetic spectra computed using the hydrostatic, homogeneous, plane-parallel, non-local thermodynamic equilibrium (NLTE) codes TLUSTY and SYNSPEC (Hubeny 1988;Lanz & Hubeny 2003;Hubeny & Lanz 2011).…”

Section: Methodsmentioning

confidence: 99%

“…Heavy elements (here Z > 30) in ionisation stages I-III are included in LTE using the treatment of Proffitt et al (2001), who added ionisation energies and partition functions from R. Kurucz's ATLAS9 code (Kurucz 1993) to SYNSPEC. Partition functions for higher ionisation stages are calculated as described in Latour et al (2019b).…”

Section: Methodsmentioning

confidence: 99%

“…No lines from the iron-peak elements chromium, manganese, iron, and cobalt are observed in UVES spectra of either star. For completeness, we list the abundances derived from UV lines for Feige 46 by Latour et al (2019b) in Table 5. The absence of high-resolution UV spectra of LS IV-14 • 116 means that no information on the abundance of these elements can be obtained for that star, except for iron.…”

Section: Light Elements and The Iron Group: Carbon To Zincmentioning

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

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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: Discussionsupporting

confidence: 88%

Section: Heavy Metalssupporting

confidence: 84%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Light Elements and The Iron Group: Carbon To Zincmentioning

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

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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

A&A

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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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Stellar laboratories

Rauch¹,

Gamrath

Quinet

et al. 2020

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IX. New Se v, Sr ivvii, Te vi, and I vi oscillator strengths and the Se, Sr, Te, and I abundances in the hot white dwarfs G191−B2B and RE 0503−289 ⋆,⋆⋆,⋆⋆⋆ ABSTRACT Context. To analyze spectra of hot stars, advanced non-local thermodynamic equilibrium (NLTE) model-atmosphere techniques are mandatory. Reliable atomic data is crucial for the calculation of such model atmospheres.Aims. We aim to calculate new Sr iv-vii oscillator strengths to identify for the first time Sr spectral lines in hot white dwarf (WD) stars and to determine the photospheric Sr abundances. To measure the abundances of Se, Te, and I in hot WDs, we aim to compute new Se v, Te vi, and I vi oscillator strengths. Methods. To consider radiative and collisional bound-bound transitions of Se v, Sr ivvii, Te vi, and I vi in our NLTE atmosphere models, we calculated oscillator strengths for these ions.Results. We newly identified four Se v, 23 Sr v, 1 Te vi, and three I vi lines in the ultraviolet (UV) spectrum of RE 0503−289. We measured a photospheric Sr abundance of 6.5 +3.8 −2.4 × 10 −4 (mass fraction, 9 500 -23 800 times solar). We determined the abundances of Se (1.6 +0.9 −0.6 × 10 −3 , 8 000 -20 000), Te (2.5 +1.5 −0.9 × 10 −4 , 11 000 -28 000), and I (1.4 +0.8 −0.5 × 10 −5 , 2 700 -6 700). No Se, Sr, Te, and I line was found in the UV spectra of G191−B2B and we could determine only upper abundance limits of approximately 100 times solar. Conclusions. All identified Se v, Sr v, Te vi, and I vi lines in the UV spectrum of RE 0503−289 were simultaneously well reproduced with our newly calculated oscillator strengths.

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Heavy metal enrichment in the intermediate He-sdOB pulsator Feige 46

Cited by 13 publications

References 46 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

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

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