Lithium Enrichment Signatures of Planetary Engulfment Events in Evolved Stars

Abstract Planetary engulfment events have long been proposed as a lithium (Li) enrichment mechanism contributing to the population of Li-rich giants (A(Li) ≥ 1.5 dex). Using MESA stellar models and A(Li) abundance measurements obtained by the GALAH survey, we calculate the strength and observability of the surface Li enrichment signature produced by the engulfment of a hot Jupiter (HJ). We consider solar-metallicity stars in the mass range of 1–2 M ⊙ and the Li supplied by a HJ of 1.0 M J. We explore engulfment events that occur near the main-sequence turn-off (MSTO) and out to orbital separations of R ⋆ ∼ 0.1 au = 22 R ⊙. We map our results onto the Hertzsprung–Russell Diagram, revealing the statistical significance and survival time of Li enrichment. We identify the parameter space of masses and evolutionary phases where the engulfment of a HJ can lead to Li enrichment signatures at a 5σ confidence level and with meteoritic abundance strengths. The most compelling strengths and survival times of engulfment-derived Li enrichment are found among host stars of 1.4 M ⊙ near the MSTO. Our calculations indicate that planetary engulfment is not a viable enrichment pathway for stars that have evolved beyond the subgiant branch. For these sources, observed Li enhancements are likely to be produced by other mechanisms, such as the Cameron–Fowler process or the accretion of material from an asymptotic giant branch companion. Our results do not account for second-order effects, such as extra mixing processes, which can further dilute Li enrichment signatures.

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Monash Chemical Yields Project (Monχey) Element production in low- and intermediate-mass stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316004725 ◽

2015 ◽

Vol 11 (A29B) ◽

pp. 164-165

Author(s):

Carolyn Doherty ◽

John Lattanzio ◽

George Angelou ◽

Simon W. Campbell ◽

Ross Church ◽

...

Keyword(s):

Chemical Evolution ◽

Heavy Element ◽

Internal Surface ◽

Asymptotic Giant Branch ◽

Agb Stars ◽

Galactic Chemical Evolution ◽

Intermediate Mass ◽

Mixing Processes ◽

Intermediate Mass Stars ◽

Solar Metallicity

AbstractThe Monχey project will provide a large and homogeneous set of stellar yields for the low- and intermediate- mass stars and has applications particularly to galactic chemical evolution modelling. We describe our detailed grid of stellar evolutionary models and corresponding nucleosynthetic yields for stars of initial mass 0.8 M⊙ up to the limit for core collapse supernova (CC-SN) ≈ 10 M⊙. Our study covers a broad range of metallicities, ranging from the first, primordial stars (Z = 0) to those of super-solar metallicity (Z = 0.04). The models are evolved from the zero-age main-sequence until the end of the asymptotic giant branch (AGB) and the nucleosynthesis calculations include all elements from H to Bi. A major innovation of our work is the first complete grid of heavy element nucleosynthetic predictions for primordial AGB stars as well as the inclusion of extra-mixing processes (in this case thermohaline) during the red giant branch. We provide a broad overview of our results with implications for galactic chemical evolution as well as highlight interesting results such as heavy element production in dredge-out events of super-AGB stars. We briefly introduce our forthcoming web-based database which provides the evolutionary tracks, structural properties, internal/surface nucleosynthetic compositions and stellar yields. Our web interface includes user- driven plotting capabilities with output available in a range of formats. Our nucleosynthetic results will be available for further use in post processing calculations for dust production yields.

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Masses, oxygen, and carbon abundances in CHEPS dwarf stars

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834138 ◽

2019 ◽

Vol 621 ◽

pp. A112 ◽

Cited By ~ 7

Author(s):

Y. V. Pavlenko ◽

B. M. Kaminsky ◽

J. S. Jenkins ◽

O. M. Ivanyuk ◽

H. R. A. Jones ◽

...

Keyword(s):

Stellar Population ◽

Statistical Significance ◽

Dwarf Stars ◽

Angular Momentum Loss ◽

Solar Metallicity ◽

Tentative Evidence ◽

Using Data ◽

Stellar Masses ◽

Host Stars

Context. We report the results from the determination of stellar masses, carbon, and oxygen abundances in the atmospheres of 107 stars from the Calan-Hertfordshire Extrasolar Planet Search (CHEPS) programme. Our stars are drawn from a population with a significantly super-solar metallicity. At least 10 of these stars are known to host orbiting planets. Aims. In this work, we set out to understand the behaviour of carbon and oxygen abundance in stars with different spectral classes, metallicities, and V sin i within the metal-rich stellar population. Methods. Masses of these stars were determined using data from Gaia DR2. Oxygen and carbon abundances were determined by fitting the absorption lines. We determined oxygen abundances with fits to the 6300.304 Å O I line, and we used 3 lines of the C I atom and 12 lines of the C2 molecule for the determination of carbon abundances. Results. We determine masses and abundances of 107 CHEPS stars. There is no evidence that the [C/O] ratio depends on V sin i or the mass of the star within our constrained range of masses, i.e. 0.82 < M*∕M⊙ < 1.5 and metallicities − 0.27 < [Fe∕H] < +0.39. We also confirm that metal-rich dwarf stars with planets are more carbon rich in comparison with non-planet host stars with a statistical significance of 96%. Conclusions. We find tentative evidence that there is a slight offset to lower abundance and a greater dispersion in oxygen abundances relative to carbon. We interpret this as potentially arising because the production of oxygen is more effective at more metal-poor epochs. We also find evidence that for lower mass stars the angular momentum loss in stars with planets as measured by V sin i is steeper than stars without planets. In general, we find that the fast rotators (V sin i > 5 km s−1) are massive stars.

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The first water fountain in a planetary nebula

Proceedings of the International Astronomical Union ◽

10.1017/s1743921312007016 ◽

2012 ◽

Vol 8 (S287) ◽

pp. 230-234

Author(s):

Olga Suárez ◽

José Francisco Gómez ◽

Philippe Bendjoya ◽

Luis. F. Miranda ◽

Martín. A. Guerrero ◽

...

Keyword(s):

Mass Loss ◽

Planetary Nebula ◽

Asymptotic Giant Branch ◽

Survival Times ◽

Jet Formation ◽

Evolved Stars ◽

Water Masers ◽

First Time ◽

Water Maser

AbstractWater fountains are evolved stars showing water masers with velocity spanning more than ~100 km/s. They usually appear at the end of the Asymptotic Giant Branch (AGB) phase or at the beginning of the post-AGB phase, and their masers trace the first manifestation of axisymmetric collimated mass-loss. For the first time, masers with water fountain characteristics have been detected towards a PN (IRAS 15103–5754), which might require a revision of the current theories about jet formation and survival times. IRAS 15103-5754 was observed using the ATCA interferometer at 22 GHz (both continuum and water maser). The main results of these observations are summarized here. The evolutionary classification of this object is also discussed.

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Additional fluorine abundance determinations in evolved stars

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935286 ◽

2019 ◽

Vol 625 ◽

pp. A40 ◽

Cited By ~ 6

Author(s):

C. Abia ◽

S. Cristallo ◽

K. Cunha ◽

P. de Laverny ◽

V. V. Smith

Keyword(s):

High Resolution ◽

State Of The Art ◽

Carbon Star ◽

Asymptotic Giant Branch ◽

Agb Stars ◽

Evolved Stars ◽

Current State ◽

Model Predictions ◽

Solar Metallicity ◽

Low Mass

We present new fluorine abundance measurements for a sample of carbon-rich asymptotic giant branch (AGB) stars and two other metal-poor evolved stars of Ba/CH types. The abundances are derived from IR, K-band, high-resolution spectra obtained using GEMINI-S/Phoenix and TNG/Giano-b. Our sample includes an extragalactic AGB carbon star belonging to the Sagittarius dSph galaxy. The metallicity of our stars ranges from [Fe/H] = 0.0 down to − 1.4 dex. The new measurements, together with those previously derived in similar stars, show that normal (N-type) and SC-type AGB carbon stars of near solar metallicity present similar F enhancements, discarding previous hints that suggested that SC-type stars have larger enhancements. These mild F enhancements are compatible with current chemical-evolution models pointing out that AGB stars, although relevant, are not the main sources of this element in the solar neighbourhood. Larger [F/Fe] ratios are found for lower-metallicity stars. This is confirmed by theory. We highlight a tight relation between the [F/⟨s⟩] ratio and the average s-element enhancement [⟨s⟩/Fe] for stars with [Fe/H] > −0.5, which can be explained by the current state-of-the-art low-mass AGB models assuming an extended 13C pocket. For stars with [Fe/H] < −0.5, discrepancies between observations and model predictions still exist. We conclude that the mechanism of F production in AGB stars needs further scrutiny and that simultaneous F and s-element measurements in a larger number of metal-poor AGB stars are needed to better constrain the models.

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Nucleosynthesis of Light-Element Isotopes in Evolved Stars Experiencing Extended Mixing

Publications of the Astronomical Society of Australia ◽

10.1071/as08040 ◽

2009 ◽

Vol 26 (3) ◽

pp. 161-167 ◽

Cited By ~ 21

Author(s):

S. Palmerini ◽

M. Busso ◽

E. Maiorca ◽

R. Guandalini

Keyword(s):

Mass Transport ◽

Isotopic Composition ◽

Light Element ◽

Asymptotic Giant Branch ◽

Red Giants ◽

Agb Stars ◽

Intermediate Mass ◽

Evolved Stars ◽

Magnetic Buoyancy ◽

Slow Mixing

AbstractWe present computations of nucleosynthesis in red giants and Asymptotic Giant Branch (AGB) stars of Population I experiencing extended mixing. The assumed physical cause for mass transport is the buoyancy of magnetized structures, according to recent suggestions. The peculiar property of such a mechanism is to allow for both fast and slow mixing phenomena, as required for reproducing the spread in Li abundances displayed by red giants and as discussed in an accompanying paper. We explore here the effects of this kind of mass transport on CNO and intermediate-mass nuclei and compare the results with the available evidence from evolved red giants and from the isotopic composition of presolar grains of AGB origin. It is found that a good general accord exists between predictions and measurements; in this framework we also show which type of observational data best constrains the various parameters. We conclude that magnetic buoyancy, allowing for mixing at rather different speeds, can be an interesting scenario to explore for explaining together the abundances of CNO nuclei and of Li.

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Stellar models and isochrones from low-mass to massive stars including pre-main sequence phase with accretion

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935051 ◽

2019 ◽

Vol 624 ◽

pp. A137 ◽

Cited By ~ 8

Author(s):

L. Haemmerlé ◽

P. Eggenberger ◽

S. Ekström ◽

C. Georgy ◽

G. Meynet ◽

...

Keyword(s):

Star Formation ◽

Stellar Evolution ◽

Main Sequence ◽

Massive Stars ◽

Mass Range ◽

Stellar Clusters ◽

Solar Metallicity ◽

Low Mass ◽

Stellar Models ◽

Young Clusters

Grids of stellar models are useful tools to derive the properties of stellar clusters, in particular young clusters hosting massive stars, and to provide information on the star formation process in various mass ranges. Because of their short evolutionary timescale, massive stars end their life while their low-mass siblings are still on the pre-main sequence (pre-MS) phase. Thus the study of young clusters requires consistent consideration of all the phases of stellar evolution. But despite the large number of grids that are available in the literature, a grid accounting for the evolution from the pre-MS accretion phase to the post-MS phase in the whole stellar mass range is still lacking. We build a grid of stellar models at solar metallicity with masses from 0.8 M⊙ to 120 M⊙, including pre-MS phase with accretion. We use the GENEC code to run stellar models on this mass range. The accretion law is chosen to match the observations of pre-MS objects on the Hertzsprung-Russell diagram. We describe the evolutionary tracks and isochrones of our models. The grid is connected to previous MS and post-MS grids computed with the same numerical method and physical assumptions, which provides the widest grid in mass and age to date.

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Recovering the Star Formation History of IC1613 Dwarf Galaxy Using Evolved Stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921318006324 ◽

2018 ◽

Vol 14 (S344) ◽

pp. 77-80

Author(s):

Seyed Azim Hashemi ◽

Atefeh Javadi ◽

Jacco Th. van Loon

Keyword(s):

Star Formation ◽

Dwarf Galaxy ◽

Stellar Populations ◽

Asymptotic Giant Branch ◽

Star Formation History ◽

Evolved Stars ◽

Formation History ◽

The Galaxy ◽

Red Supergiants ◽

Period Variable

AbstractDetermining the star formation history (SFH) is key to understand the formation and evolution of dwarf galaxies. Recovering the SFH in resolved galaxies is mostly based on deep colour–magnitude diagrams (CMDs), which trace the signatures of multiple evolutionary stages of their stellar populations. In distant and unresolved galaxies, the integrated light of the galaxy can be decomposed, albeit made difficult by an age–metallicity degeneracy. Another solution to determine the SFH of resolved galaxies is based on evolved stars; these luminous stars are the most accessible tracers of the underlying stellar populations and can trace the entire SFH. Here we present a novel method based on long period variable (LPV) evolved asymptotic giant branch (AGB) stars and red supergiants (RSGs). We applied this method to reconstruct the SFH for IC1613, an irregular dwarf galaxy at a distance of 750 kpc. Our results provide an independent confirmation that no major episode of star formation occurred in IC1613 over the past 5 Gyr.

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Warm CO in evolved stars from the THROES catalogue

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834141 ◽

2019 ◽

Vol 622 ◽

pp. A123 ◽

Cited By ~ 2

Author(s):

J. M. da Silva Santos ◽

J. Ramos-Medina ◽

C. Sánchez Contreras ◽

P. García-Lario

Keyword(s):

Mass Loss ◽

Loss Rate ◽

Mass Loss Rate ◽

Asymptotic Giant Branch ◽

Strong Line ◽

Order Estimate ◽

Evolved Stars ◽

Flux Variability ◽

The Impact ◽

Loss Rates

Context. This is the second paper of a series making use of Herschel/PACS spectroscopy of evolved stars in the THROES catalogue to study the inner warm regions of their circumstellar envelopes (CSEs). Aims. We analyse the CO emission spectra, including a large number of high-J CO lines (from J = 14–13 to J = 45–44, ν = 0), as a proxy for the warm molecular gas in the CSEs of a sample of bright carbon-rich stars spanning different evolutionary stages from the asymptotic giant branch to the young planetary nebulae phase. Methods. We used the rotational diagram (RD) technique to derive rotational temperatures (Trot) and masses (MH2) of the envelope layers where the CO transitions observed with PACS arise. Additionally, we obtained a first order estimate of the mass-loss rates and assessed the impact of the opacity correction for a range of envelope characteristic radii. We used multi-epoch spectra for the well-studied C-rich envelope IRC+10216 to investigate the impact of CO flux variability on the values of Trot and MH2. Results. The sensitivity of PACS allowed for the study of higher rotational numbers than before indicating the presence of a significant amount of warmer gas (∼200 − 900 K) that is not traceable with lower J CO observations at submillimetre/millimetre wavelengths. The masses are in the range MH2 ∼ 10−2 − 10−5 M⊙, anticorrelated with temperature. For some strong CO emitters we infer a double temperature (warm T¯rot ∼ 400 K and hot T¯rot ∼ 820 K) component. From the analysis of IRC+10216, we corroborate that the effect of line variability is perceptible on the Trot of the hot component only, and certainly insignificant on MH2 and, hence, the mass-loss rate. The agreement between our mass-loss rates and the literature across the sample is good. Therefore, the parameters derived from the RD are robust even when strong line flux variability occurs, and the major source of uncertainty in the estimate of the mass-loss rate is the size of the CO-emitting volume.

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Theoretical predictions of mass, semimajor axis and eccentricity distributions of super-Earths

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311019958 ◽

2010 ◽

Vol 6 (S276) ◽

pp. 64-71

Author(s):

Shigeru Ida

Keyword(s):

Semimajor Axis ◽

Mass Range ◽

Model Parameters ◽

Type I ◽

Orbital Eccentricity ◽

Resonant Orbits ◽

Theoretical Predictions ◽

Giant Impacts ◽

Solar Type ◽

Host Stars

AbstractWe discuss the effects of close scattering and merging between planets on distributions of mass, semimajor axis and orbital eccentricity, using population synthesis model of planet formation, focusing on the distributions of close-in super-Earths, which are being observed recently. We found that a group of compact embryos emerge interior to the ice line, grow, migrate, and congregate into closely-packed convoys which stall in the proximity of their host stars. After the disk-gas depletion, they undergo orbit crossing, close scattering, and giant impacts to form multiple rocky Earths or super-Earths in non-resonant orbits around ~ 0.1AU with moderate eccentricities of ~ 0.01–0.1. The formation of these planets does not depend on model parameters such as type I migration speed. The fraction of solar-type stars with these super-Earths is anti-correlated with the fraction of stars with gas giants. The newly predicted family of close-in super-Earths makes less clear “planet desert” at intermediate mass range than our previous prediction.

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Water fountains: bipolar fast stellar jets traced by water vapor maser emission

Proceedings of the International Astronomical Union ◽

10.1017/s1743921312019746 ◽

2012 ◽

Vol 8 (S290) ◽

pp. 227-228

Author(s):

Hiroshi Imai

Keyword(s):

Active Galactic Nuclei ◽

Galactic Nuclei ◽

Asymptotic Giant Branch ◽

Young Stellar Objects ◽

Agb Stars ◽

Stellar Objects ◽

Stellar Jets ◽

The Masses ◽

Host Stars ◽

Maser Sources

AbstractHighly collimated, bipolar fast jets are found in asymptotic giant branch (AGB) and post-AGB stars as well as in active galactic nuclei and young stellar objects. It is still unclear how to launch such jets from dying stars that were originally spherically symmetric. Exploration of the stellar jet evolution is also expected to probe its role in shaping a planetary nebula. Interestingly, some of stellar H2O maser sources — water fountains — exhibit stellar jets with spatially and kinematically high collimation in the earliest phase (<1000 years) of the jet evolution. Such water fountains have been identified in 14 sources to date. We have recently conducted interferometric (VLBA, EVN, VERA, VLA) maser and the single-dish (ASTE) CO J = 3 → 2 line observations of the water fountains. They have revealed a typical dynamical age (< 100 yr) and the detailed kinematical structures of the water fountains, possibility of the coexistence of “equatorial flows”, and their locations and kinematics in the Milky Way. Based on these results, the masses and evolutionary statuses of the host stars are also estimated.

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