When binaries keep track of recent nucleosynthesis

Karinkuzhi, D.; Eck, S. Van; Jorissen, A.; Goriely, Stéphane; Siess, Lionel; Merle, Thibault; Escorza, A.; Swaelmen, M. Van der; Boffin, M.; Masseron, T.; Shetye, S.; Plez, B.

doi:10.1051/0004-6361/201833084

Cited by 46 publications

(96 citation statements)

References 82 publications

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“…Extrinsic S-stars should show an enhancement of Nb, while intrinsic S-stars should be depleted. For five stars in our sample we found measurements of Nb abundance in the literature, namely, BD Cam, V613 Mon, DT Psc, HR Peg, and NQ Pup (Neyskens et al 2015;Karinkuzhi et al 2018). In all five cases, the classification derived from the presence or absence of Tc is confirmed.…”

Section: S-type Starssupporting

confidence: 64%

Carbon and Oxygen Isotopic Ratios. II. Semiregular Variable M Giants

Lebzelter

Hinkle

Straniero

et al. 2019

ApJ

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Carbon and oxygen isotopic ratios are reported for a sample of 51 SRb-and Lb-type variable asymptotic giant branch stars. Vibration-rotation first-and second-overtone CO lines in 1.5 to 2.5 µm spectra were measured to derive isotopic ratios for 12 C/ 13 C, 16 O/ 17 O, and 16 O/ 18 O. Comparisons with previous measurements for individual stars and with various samples of evolved stars, as available in the extant literature, are discussed. Using the oxygen isotopic ratios, the masses of the SRb stars can be derived. Combining the masses with Gaia luminosities, the SRb stars are shown to be antecedents of the Mira variables. The limiting parameters where plane-parallel, hydrostatic equilibrium model atmospheres can be used for abundance analysis of M giants are explored. Lebzelter et al.This is our second Paper In a series to study the isotopic ratios of C and O in AGB stars. In the first paper of this series (Hinkle et al. 2016, Paper I) we presented an extensive discussion on the influence of stellar parameters and evolution on the isotopic ratios of these two key elements measured at the stellar surface. Here we confine the discussion to a brief summary of the main effects and refer to Paper I (note in particular Figure 10), Lebzelter et al. (2015a), and references therein for a more extensive description.The CNO cycle depletes 12 C and enhances 13 C, a change that becomes visible as a steep drop in the 12 C/ 13 C ratio down to 10 to 25 after the first dredge up. A slight dependence of the resulting ratios on stellar mass is expected, with the more massive stars showing higher 12 C/ 13 C values (Paper I). Extensive observational evidence (e.g. Charbonnel et al. 1999) exists that extra-mixing along the red giant branch (RGB) can further reduce the ratio between the two carbon isotopes by a factor of two in low-mass stars. The interplay between production, mixing, and destruction of the various oxygen isotopes results in a dependence of 16 O/ 17 O on stellar mass (Boothroyd et al, 1994;El Eid 1994;Karakas & Lattanzio 2014), with the istopic ratio decreasing with increasing mass as different depths and thus different regions of 17 O enhancement are reached by the first dredge-up. 18 O, on the other hand, is depleted by H burning and therefore 16 O/ 18 O is increasing with the first dredge-up. This effect, however, is almost independent of mass.The second dredge-up has only a mild effect on the isotopic ratios on the surface. With the third dredge-up episodes, which are predicted to occur in stars with main-sequence masses between approximately 1.3 and 5 M at solar metallicity, 12 C/ 13 C is strongly enhanced, while there is little effect on the oxygen isotopic ratios. In the more massive AGB stars, Hot Bottom Burning (HBB) can effect the oxygen isotopes, in particular the abundance of 18 O which is significantly depleted (Lattanzio et al. 1996). As pointed out by Lebzelter et al. (2015a), the 16 O/ 18 O is good indicator of the primordial 18 O abundance in a star, so that star-to-star variations of this ratio also ...

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Section: S-type Starssupporting

confidence: 64%

Carbon and Oxygen Isotopic Ratios. II. Semiregular Variable M Giants

Lebzelter

Hinkle

Straniero

et al. 2019

ApJ

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“…This is why a spectral-synthesis approach is required, as opposed to relying solely on equivalent widths. As in Neyskens et al (2015), Karinkuzhi et al (2018) and S18, we only used the two Zr i lines at 7819.37 Å and 7849.37 Å with transition probabilities from laboratory measurements (Biémont et al 1981). The Y i and Y ii available lines lie in regions subject to blending by molecular lines of ZrO.…”

Section: Abundance Determination and Uncertaintiesmentioning

confidence: 99%

Observational evidence of third dredge-up occurrence in S-type stars with initial masses around 1 M_⊙

Shetye

Goriely

Siess

et al. 2019

A&A

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Context. S stars are late-type giants with spectra showing characteristic molecular bands of ZrO in addition to the TiO bands typical of M stars. Their overabundance pattern shows the signature of s-process nucleosynthesis. Intrinsic, technetium (Tc)-rich S stars are the first objects, on the Asymptotic Giant Branch (AGB), to undergo third dredge-up (TDU) events. Gaia exquisite parallaxes now allow to precisely locate these stars in the Hertzsprung-Russell (HR) diagram. Here we report on a population of low-mass, Tc-rich S stars, previously unaccounted for by stellar evolution models. Aims. Our aim is to derive parameters of a sample of low-mass Tc-rich S stars and then, by comparing their location in the HR diagram with stellar evolution tracks, to derive their masses and to compare their measured s-process abundance profiles with recently derived STAREVOL nucleosynthetic predictions for low-mass AGB stars. Methods. The stellar parameters were obtained using a combination of HERMES high-resolution spectra, accurate Gaia Data Release 2 (Gaia-DR2) parallaxes, stellar-evolution models and newly-designed MARCS model atmospheres for S-type stars. Results. We report on 6 Tc-rich S stars lying close to the 1 M (initial mass) tracks of AGB stars of the corresponding metallicity and above the predicted onset of TDU, as expected. This provides direct evidence for TDUs occurring in AGB stars with initial masses as low as ∼1 M and at low luminosity, i.e. at the start of the thermally-pulsing AGB. We present AGB models producing TDU in those stars with [Fe/H] in the range −0.25 to −0.5 There is a reasonable agreement between the measured and predicted s-process abundance profiles. For 2 objects however (CD -29 • 5912 and BD +34 • 1698), the predicted C/O ratio and s-process enhancements do not match simultaneously the measured ones.

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“…8 and 9). As discussed by Neyskens et al (2015) and Karinkuzhi et al (2018), the above Zr I lines systematically lead to Zr I abundances 0.30 dex lower than abundances derived from lines with transition probabilities from Corliss & Bozman (1962). We favour the former lines as they rely on measured transition probabilities.…”

Section: S-process Elementsmentioning

confidence: 71%

“…Hence, extrinsic stars should be enhanced in niobium as compared to intrinsic stars. The Zr-Nb pair may therefore be used to confirm the Tc-rich/Tc-poor dichotomy (see the more extensive discussion by Neyskens et al 2015 andKarinkuzhi et al 2018). Figure 15 shows the trend of [Zr/Fe] vs. [Nb/Fe] for the intrinsic and extrinsic S stars of our sample.…”

Section: The Zr-nb Pairmentioning

confidence: 94%

S stars and s-process in the Gaia era

Shetye

Eck

Jorissen

et al. 2018

A&A

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Context. S stars are transition objects between M-type giants and carbon stars on the asymptotic giant branch (AGB). They are characterized by overabundances of s-process elements. Roughly half of them are enhanced in technetium (Tc), an s-process element with no stable isotope, while the other half lack technetium. This dichotomy arises from the fact that Tc-rich S stars are intrinsically producing s-process elements and have undergone third dredge-up (TDU) events, while Tc-poor S stars owe their s-process overabundances to a past pollution by a former AGB companion which is now an undetected white dwarf, and since the epoch of the mass transfer, technetium has totally decayed. Aims. Our aim is to analyse the abundances of S stars and gain insights into their evolutionary status and on the nucleosynthesis of heavy s-process elements taking place in their interior. In particular, the location of extrinsic and intrinsic S stars in the HR diagram will be compared with the theoretical onset of the TDU on the thermally pulsing AGB. Methods. A sample of 19 S-type stars was analysed by combining HERMES high-resolution spectra, accurate Gaia Data Release 2 (GDR2) parallaxes, stellar-evolution models, and newly designed MARCS model atmospheres for S-type stars. Various stellar parameters impact the atmospheric structure of S stars, not only effective temperature, gravity, metallicity and microturbulence but also C/O and [s/Fe]. We show that photometric data alone are not sufficient to disentangle these parameters. We present a new automatic spectral-fitting method that allows one to constrain the range of possible atmospheric parameters. Results. Combining the derived parameters with GDR2 parallaxes allows a joint analysis of the location of the stars in the Hertzsprung-Russell diagram and of their surface abundances. For all 19 stars, Zr and Nb abundances are derived, complemented by abundances of other s-process elements for the three Tc-rich S stars. These abundances agree within the uncertainties with nucleosynthesis predictions for stars of corresponding mass, metallicity and evolutionary stage. The Tc dichotomy between extrinsic and intrinsic S stars is seen as well in the Nb abundances: intrinsic, Tc-rich S stars are Nb-poor, whereas extrinsic, Tc-poor S stars are Nb-rich. Most extrinsic S stars lie close to the tip of the red giant branch (RGB), and a few are located along the early AGB. All appear to be the cooler analogues of barium stars. Barium stars with masses smaller than 2.5 M turn into extrinsic S stars on the RGB, because only for those masses does the RGB tip extend to temperatures lower than ∼4200 K, which allows the ZrO bands distinctive of S-type stars to develop. On the contrary, barium stars with masses in excess of ∼2.5 M can only turn into extrinsic S stars on the E-AGB, but those are short-lived, and thus rare. The location of intrinsic S stars in the HR diagram is compatible with them being thermally-pulsing AGB stars. Although nucleosynthetic model predictions give a satisfactory distribution...

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When binaries keep track of recent nucleosynthesis

Cited by 46 publications

References 82 publications

Carbon and Oxygen Isotopic Ratios. II. Semiregular Variable M Giants

Carbon and Oxygen Isotopic Ratios. II. Semiregular Variable M Giants

Observational evidence of third dredge-up occurrence in S-type stars with initial masses around 1 M_⊙

S stars and s-process in the Gaia era

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When binaries keep track of recent nucleosynthesis

Cited by 46 publications

References 82 publications

Carbon and Oxygen Isotopic Ratios. II. Semiregular Variable M Giants

Carbon and Oxygen Isotopic Ratios. II. Semiregular Variable M Giants

Observational evidence of third dredge-up occurrence in S-type stars with initial masses around 1 M⊙

S stars and s-process in the Gaia era

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Observational evidence of third dredge-up occurrence in S-type stars with initial masses around 1 M_⊙