Abundances of Post–Iron‐Peak Elements in HD 35155: A Symbiotic Star of Spectral Type S

Vanture, Andrew D.; Wallerstein, George; Gallino, R.; Masera, S.

doi:10.1086/368071

Cited by 8 publications

(9 citation statements)

References 27 publications

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“…It is also a binary with one of the longest orbital periods among the families of extrinsic stars (≥54 yr, could be up to 100 yr) (Jorissen et al 2016(Jorissen et al , 2019, but the orbital parameters still have to be confirmed. Our parameters and abundances are in good agreement with those from previous studies (Van Eck et al 2003;Vanture et al 2003;Goswami et al 2016). Here we add the abundances of Gd, Hf, and Os that were not reported earlier.…”

Section: Discussion On Individual Stars and Comparison With Previous supporting

confidence: 92%

Low-mass low-metallicity AGB stars as an efficient i-process site explaining CEMP-rs stars

Karinkuzhi

Eck

Goriely

et al. 2021

A&A

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Context. Among carbon-enhanced metal-poor (CEMP) stars, some are found to be enriched in slow-neutron capture (s-process) elements (and are then tagged CEMP-s), some have overabundances in rapid-neutron capture (r-process) elements (tagged CEMP-r), and some are characterized by both s- and r-process enrichments (tagged CEMP-rs). The current distinction between CEMP-s and CEMP-rs is based on their [Ba/Fe] and [Eu/Fe] ratios, since barium and europium are predominantly produced by the s- and the r-process, respectively. The origin of the abundance differences between CEMP-s and CEMP-rs stars is presently unknown. It has been claimed that the i-process, whose site still remains to be identified, could better reproduce CEMP-rs abundances than the s-process. Aims. We propose a more robust classification method for CEMP-s and CEMP-rs stars using additional heavy elements other than Ba and Eu. Once a secure classification is available, it should then be possible to assess whether the i-process or a variant of the s-process better fits the peculiar abundance patterns of CEMP-rs stars. Methods. We analyse high-resolution spectra of 24 CEMP stars and one r-process enriched star without carbon-enrichment, observed mainly with the high-resolution HERMES spectrograph mounted on the Mercator telescope (La Palma) and also with the UVES spectrograph on VLT (ESO Chile) and HIRES spectrograph on KECK (Hawaii). Stellar parameters and abundances are derived using MARCS model atmospheres. Elemental abundances are computed through spectral synthesis using the TURBOSPECTRUM radiative transfer code. Stars are re-classified as CEMP-s or -rs according to a new classification scheme using eight heavy element abundances. Results. Within our sample of 25 objects, the literature classification is globally confirmed, except for HE 1429−0551 and HE 2144−1832, previously classified as CEMP-rs and now as CEMP-s stars. The abundance profiles of CEMP-s and CEMP-rs stars are compared in detail, and no clear separation is found between the two groups; it seems instead that there is an abundance continuum between the two stellar classes. There is an even larger binarity rate among CEMP-rs stars than among CEMP-s stars, indicating that CEMP-rs stars are extrinsic stars as well. The second peak s-process elements (Ba, La, Ce) are slightly enhanced in CEMP-rs stars with respect to first-peak s-process elements (Sr, Y, Zr), when compared to CEMP-s stars. Models of radiative s-process nucleosynthesis during the interpulse phases reproduce well the abundance profiles of CEMP-s stars, whereas those of CEMP-rs stars are explained well by low-metallicity 1 M⊙ models experiencing proton ingestion. The global fitting of our i-process models to CEMP-rs stars is as good as the one of our s-process models to CEMP-s stars. Stellar evolutionary tracks of an enhanced carbon composition (consistent with our abundance determinations) are necessary to explain the position of CEMP-s and CEMP-rs stars in the Hertzsprung–Russell diagram using Gaia DR2 parallaxes; they are found to lie mostly on the red giant branch (RGB). Conclusions. CEMP-rs stars present most of the characteristics of extrinsic stars such as CEMP-s, CH, barium, and extrinsic S stars; they can be explained as being polluted by a low-mass, low-metallicity thermally-pulsing asymptotic giant branch (TP-AGB) companion experiencing i-process nucleosynthesis after proton ingestion during its first convective thermal pulses. As such, they could be renamed CEMP-sr stars, since they represent a particular manifestation of the s-process at low-metallicities. For these objects a call for an exotic i-process site may not necessarily be required anymore.

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Section: Discussion On Individual Stars and Comparison With Previous supporting

confidence: 92%

Low-mass low-metallicity AGB stars as an efficient i-process site explaining CEMP-rs stars

Karinkuzhi

Eck

Goriely

et al. 2021

A&A

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“…Only a small number of galactic red symbiotic stars have a cool carbon-rich star as a cool component. Recently, peculiar chemical composition was confirmed for the red symbiotic HD 35155; the star was found to be metal deficient, [Fe/H] = −0.8, and rich in neutron-capture elements, [n/Fe] = + 2 dex on average (Vanture et al 2003). It is not clear why among red symbiotic stars the percent of carbon and s-process rich stars is so low.…”

Section: Introductionmentioning

confidence: 99%

An abundance analysis of the symbiotic star CH Cygni

Schmidt¹,

Začs²,

Mikołajewska³

et al. 2006

A&A

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“…Abundances for the neutral species are consistently lower than those of the ionised species. This discrepancy is discussed by many authors for barium stars (Smith 1984;Allen & Barbuy 2006;Smiljanic et al 2007) and S stars (Vanture et al 2003). It is likely caused by NLTE effects affecting the minority species (here the neutral one when T eff ∼ 4500 K).…”

Section: S-processmentioning

confidence: 96%

When binaries keep track of recent nucleosynthesis

et al. 2018

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We determine Zr and Nb elemental abundances in barium stars to probe the operation temperature of the s-process that occurred in the companion asymptotic giant branch (AGB) stars. Along with Zr and Nb, we derive the abundances of a large number of heavy elements. They provide constraints on the s-process operation temperature and therefore on the s-process neutron source. The results are then compared with stellar evolution and nucleosynthesis models. We compare the nucleosynthetic profile of the present sample stars with those of CEMP-s, CEMP-rs and CEMP-r stars. One barium star of our sample is potentially identified as the highest-metallicity CEMP-rs star yet discovered.

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Abundances of Post–Iron‐Peak Elements in HD 35155: A Symbiotic Star of Spectral Type S

Cited by 8 publications

References 27 publications

Low-mass low-metallicity AGB stars as an efficient i-process site explaining CEMP-rs stars

Low-mass low-metallicity AGB stars as an efficient i-process site explaining CEMP-rs stars

An abundance analysis of the symbiotic star CH Cygni

When binaries keep track of recent nucleosynthesis

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