Phosphorus-rich stars with unusual abundances are challenging theoretical predictions

Masseron, T.; García-Hernández, D. A.; Santoveña, R.; Manchado, A.; Zamora, Olga; Manteiga, M.; Dafonte, Carlos

doi:10.1038/s41467-020-17649-9

Cited by 32 publications

(30 citation statements)

References 73 publications

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“…Possible solutions of the Ba puzzle, both from the spectra and the nucleosynthesis prospective, are still under investigation. Masseron et al (2020b) reported anomalous Ba enhancements (ten times higher than the other s-process elements) in stars that are also anomalous in the lighter elements, specifically those rich in P (Masseron et al 2020a). As discussed above, this pattern cannot be reproduced by an s-process model because of the nuclear properties of the isotopes involved.…”

Section: Discussionmentioning

confidence: 97%

The Gaia-ESO Survey: a new approach to chemically characterising young open clusters

Baratella

D’Orazi

Sheminova

et al. 2021

A&A

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Context. Young open clusters (ages of less than 200 Myr) have been observed to exhibit several peculiarities in their chemical compositions. These anomalies include a slightly sub-solar iron content, super-solar abundances of some atomic species (e.g. ionised chromium), and atypical enhancements of [Ba/Fe], with values up to ~0.7 dex. Regarding the behaviour of the other s-process elements like yttrium, zirconium, lanthanum, and cerium, there is general disagreement in the literature: some authors claim that they follow the same trend as barium, while others find solar abundances at all ages. Aims. In this work we expand upon our previous analysis of a sample of five young open clusters (IC 2391, IC 2602, IC 4665, NGC 2516, and NGC 2547) and one star-forming region (NGC 2264), with the aim of determining abundances of different neutron-capture elements, mainly Cu I, Sr I, Sr II, Y II, Zr II, Ba II, La II, and Ce II. For NGC 2264 and NGC 2547 we present the measurements of these elements for the first time. Methods. We analysed high-resolution, high signal-to-noise spectra of 23 solar-type stars observed within the Gaia-ESO survey. After a careful selection, we derived abundances of isolated and clean lines via spectral synthesis computations and in a strictly differential way with respect to the Sun. Results. We find that our clusters have solar [Cu/Fe] within the uncertainties, while we confirm that [Ba/Fe] is super-solar, with values ranging from +0.22 to +0.64 dex. Our analysis also points to a mild enhancement of Y, with [Y/Fe] ratios covering values between 0 and +0.3 dex. For the other s-process elements we find that [X/Fe] ratios are solar at all ages. Conclusions. It is not possible to reconcile the anomalous behaviour of Ba and Y at young ages with standard stellar yields and Galactic chemical evolution model predictions. We explore different possible scenarios related to the behaviour of spectral lines, from the dependence on the different ionisation stages and the sensitivity to the presence of magnetic fields (through the Landé factor) to the first ionisation potential effect. We also investigate the possibility that they may arise from alterations of the structure of the stellar photosphere due to the increased levels of stellar activity that affect the spectral line formation, and consequently the derived abundances. These effects seem to be stronger in stars at ages of less than ~ 100 Myr. However, we are still unable to explain these enhancements, and the Ba puzzle remains unsolved. With the present study we suggest that other elements, for example Sr, Zr, La, and Ce, might be more reliable tracer of the s-process at young ages, and we strongly encourage further critical observations.

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Section: Discussionmentioning

confidence: 97%

The Gaia-ESO Survey: a new approach to chemically characterising young open clusters

Baratella

D’Orazi

Sheminova

et al. 2021

A&A

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“…However, this star does not show Na enhancement, and the Si enhancement seen here does not appear in our ω Cen stars (see Figure 22 below), though enhanced Si is found in a population of field stars in the inner halo (dubbed "Jurassic";Fernández-Trincado et al 2019b, which may arise from tidally disrupted globular clusters. Intriguingly, Masseron et al (2020a) identified 2M18120031-1350169 as one of 15 APOGEE stars with extreme P enhancement, finding [P/Fe]=1.65 using a custom analysis of the APOGEE spectrum (rather than the ASP-CAP abundance). The unusually high [X/Fe] values for Mg, O, Si, and Al are also found in the other members of this P-rich population (see Figure 9 of Masseron et al 2020a), and the high [Ce/Fe] accords with the enhanced s-process abundances found in follow-up optical spectroscopy by Masseron et al (2020b).…”

Section: High-χ 2 Starsmentioning

confidence: 99%

“…Intriguingly, Masseron et al (2020a) identified 2M18120031-1350169 as one of 15 APOGEE stars with extreme P enhancement, finding [P/Fe]=1.65 using a custom analysis of the APOGEE spectrum (rather than the ASP-CAP abundance). The unusually high [X/Fe] values for Mg, O, Si, and Al are also found in the other members of this P-rich population (see Figure 9 of Masseron et al 2020a), and the high [Ce/Fe] accords with the enhanced s-process abundances found in follow-up optical spectroscopy by Masseron et al (2020b). From the overall abundance patterns, Masseron et al (2020a,b) argue that the chemical peculiarities of these stars do not originate in globular clusters or binary mass transfer, and they are a challenge to explain with existing stellar nucleosynthesis models.…”

Section: High-χ 2 Starsmentioning

confidence: 99%

Chemical Cartography with APOGEE: Mapping Disk Populations with a Two-Process Model and Residual Abundances

Weinberg,

Holtzman,

Johnson

et al. 2021

Preprint

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We apply a novel statistical analysis to measurements of 16 elemental abundances in 34,410 Milky Way disk stars from the final data release (DR17) of APOGEE-2. Building on recent work, we fit median abundance ratio trends [X/Mg] vs. [Mg/H] with a 2-process model, which decomposes abundance patterns into a "prompt" component tracing core collapse supernovae and a "delayed" component tracing Type Ia supernovae. For each sample star, we fit the amplitudes of these two components, then compute the residuals ∆[X/H] from this two-parameter fit. The rms residuals range from ∼ 0.01 − 0.03 dex for the most precisely measured APOGEE abundances to ∼ 0.1 dex for Na, V, and Ce. The correlations of residuals reveal a complex underlying structure, including a correlated element group comprised of Ca, Na, Al, K, Cr, and Ce and a separate group comprised of Ni, V, Mn, and Co. Selecting stars poorly fit by the 2-process model reveals a rich variety of physical outliers and sometimes subtle measurement errors. Residual abundances allow comparison of populations controlled for differences in metallicity and [α/Fe]. Relative to the main disk (R = 3 − 13 kpc), we find nearly identical abundance patterns in the outer disk (R = 15 − 17 kpc), 0.05-0.2 dex depressions of multiple elements in LMC and Gaia Sausage/Enceladus stars, and wild deviations (0.4-1 dex) of multiple elements in ω Cen. Residual abundance analysis opens new opportunities for discovering chemically distinctive stars and stellar populations, for empirically constraining nucleosynthetic yields, and for testing chemical evolution models that include stochasticity in the production and redistribution of elements.

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“…(v) For our selection, we also disregarded stars in GCs from our sample, i.e., those sources analyzed in Masseron et al (2019) and Mészáros et al (2020b). (vi) Lastly, field stars identified previously as P-, N-and Si-rich stars from Martell et al (2016), Fernández-Trincado et al (2016a), Fernández-Trincado et al (2017, 2019d, and Masseron et al (2020) were excluded from our sample.…”

Section: Datamentioning

confidence: 99%

“…The search for field stars that were born in GCs (Lind et al 2015;Martell et al 2016;Fernández-Trincado et al 2015a, 2016b, 2019d,c,b,a, 2020cSimpson et al 2020) is one clear example of the power of chemical tagging. This is possible because GCs appear to be the only environment responsible for the presence of light-element anti-correlations at all stellar evolutionary phases (e.g., Martell et al 2016;Pancino et al 2017;Bastian & Lardo 2018;Masseron et al 2019;Mészáros et al 2020a), unless they are part of a binary system (Bastian & Lardo 2018;Fernández-Trincado et al 2019c), or part of the new kind of recently discovered anomalous Phosphorus-rich field stars (see, e.g., Masseron et al 2020). Thus, a complete census of all those chemically anomalous stars will help develop a better understanding for the assembly of the inner and outer halo, where substantial amount of stellar debris from GCs are thought to currently reside (see, e.g., Martell et al 2016;Fernández-Trincado et al 2019b,a, 2020c.…”

Section: Introductionmentioning

confidence: 99%

Jurassic: A Chemically Anomalous Structure in the Galactic Halo

Fernández-Trincado,

Beers,

Minniti

2020

Preprint

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Detailed elemental-abundance patterns of giant stars in the Galactic halo measured by APOGEE-2 have revealed the existence of a unique and significant stellar sub-population of silicon-enhanced ([Si/Fe] +0.5) metal-poor stars, spanning a wide range of metallicities (−1.5 [Fe/H] −0.8). Stars with over-abundances in [Si/Fe] are of great interest because these have very strong silicon ( 28 Si) spectral features for stars of their metallicity and evolutionary stage, offering clues about rare nucleosynthetic pathways in globular clusters (GCs). Si-rich field stars have been conjectured to have been evaporated from GCs, however, the origin of their abundances remains unclear, and several scenarios have been offered to explain the anomalous abundance ratios. These include the hypothesis that some of them were born from a cloud of gas previously polluted by a progenitor that underwent a specific and peculiar nucleosynthesis event, or due to mass transfer from a previous evolved companion. However, those scenarios do not simultaneously explain the wide gamut of chemical species that are found in Si-rich stars. Instead, we show that the present inventory of such unusual stars, as well as their relation to known halo substructures (including the in-situ halo, Gaia-Enceladus, the Helmi Stream(s), and Sequoia, among others) is still incomplete. We report the chemical abundances of the iron-peak (Fe), the light-(C and N), the α− (O and Mg), the odd-Z (Na and Al), and the s-process (Ce and Nd) elements of 55 newly identified Si-rich field stars (among more than ∼600,000 APOGEE-2 targets), that exhibit over-abundances of [Si/Fe] as extreme as those observed in some Galactic GCs, and are relatively cleanly from other stars in the [Si/Fe]-[Fe/H] plane. This new census confirms the presence of a statistically significant and chemically-anomalous structure in the inner halo: Jurassic. The chemo-dynamical properties of the Jurassic structure is consistent with it being the tidally disrupted remains of GCs, easily distinguished by an over-abundance of [Si/Fe] among Milky Way populations or satellites.

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Phosphorus-rich stars with unusual abundances are challenging theoretical predictions

Cited by 32 publications

References 73 publications

The Gaia-ESO Survey: a new approach to chemically characterising young open clusters

The Gaia-ESO Survey: a new approach to chemically characterising young open clusters

Chemical Cartography with APOGEE: Mapping Disk Populations with a Two-Process Model and Residual Abundances

Jurassic: A Chemically Anomalous Structure in the Galactic Halo

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