Origin of Lithium Enrichment in K Giants

Kumar, Yerra Bharat; Reddy, Bacham E.; Lambert, David L.

doi:10.1088/2041-8205/730/1/l12

Cited by 135 publications

(289 citation statements)

References 24 publications

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“…Four out of these five Li-enhanced stars seem to be very close to the luminosity bump experienced by low-mass red giants. This phase has already been proposed as a probable scenario for the appearance of Li-rich stars (CB00; Kumar et al 2011;Sackmann & Boothroyd 1999). However, NGC 4349 No.…”

Section: Discussionmentioning

confidence: 87%

“…We note here that the maximum allowed mass to experience the luminosity bump depends on the metallicity and the isochrone chosen here does not show this stage. Many of the discovered Li-rich stars are found to be close to the luminosity bump, as shown by CB00 and Kumar et al (2011). However, being in the luminosity bump does not guarantee the appearance of Li-rich stars.…”

Section: Li-enhanced Starsmentioning

confidence: 93%

“…The decrease in the 12 C/ 13 C that begins to take place at this phase is probably caused by some extra-mixing processes, which in turn support the CFM to enhance Li in these stars (CB00; Eggleton et al 2008). On the other hand, Kumar et al (2011) claim that the highest concentration of Li-rich stars happens at the red clump rather than the luminosity bump. Then, either the fresh Li produced during the bump can survive the RGB tip or the CFM can operate at the He-flash.…”

Section: Introductionmentioning

confidence: 88%

“…Thus, the stars in the red giant branch (RGB) are expected to show low Li abundances, though a number of Lirich giants have been observed in clusters and in the field (e.g. Kumar et al 2011;Carlberg et al 2012;Anthony-Twarog et al 2013;D'Orazi et al 2015), sometimes exceeding the meteoritic values.…”

Section: Introductionmentioning

confidence: 99%

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Searching for Li-rich giants in a sample of 12 open clusters

Delgado-Mena

Tsantaki

Sousa

et al. 2016

A&A

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Aims. The aim of this work is to search for Li-rich giants in a sample of clusters where planets have been searched, thus we can study the planet engulfment scenario to explain Li replenishment using a proper comparison sample of stars without detected giant planets. Methods. We derived Li abundances for a sample of 67 red giant stars in 12 different open clusters using standard spectral synthesis techniques and high-resolution spectra (from HARPS and UVES). We also determined masses, ages, and radius from PARSEC stellar isochrones to constrain the evolutionary stage of these stars. Results. We found three stars in different clusters with clearly enhanced Li abundances compared to other stars within the cluster. Interestingly, the only two stars with a detected substellar companion in our sample belong to that group. One of the planet hosts, NGC 2423 No. 3, might lie close to the luminosity bump on the HR diagram, a phase where Li production by the Cameron-Fowler process is supported by extra-mixing to bring fresh Li up to the surface. On the other hand, NGC 4349 No. 127 is a more massive and more evolved giant that does not seem to be in the evolutionary phase where other Li-rich stars are found. We discuss the possibility that the Li enhancement of this star is triggered by the engulfment of a planet, considering that close-in planets hardly survive the RGB tip and the early AGB phases.

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Section: Discussionmentioning

confidence: 87%

Section: Li-enhanced Starsmentioning

confidence: 93%

Section: Introductionmentioning

confidence: 88%

Section: Introductionmentioning

confidence: 99%

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Searching for Li-rich giants in a sample of 12 open clusters

Delgado-Mena

Tsantaki

Sousa

et al. 2016

A&A

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“…However, recently Kumar, Reddy & Lambert (2011) argued that the finite luminosity spread they found in their spectroscopy survey for Li-rich K giants, does not support the idea that Li enhancement is in general a consequence of swallowing a planet.…”

Section: Planets and Evolved Starsmentioning

confidence: 85%

Planets, evolved stars, and how they might influence each other.

Villaver

2011

Proc. IAU

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Abstract. Over the last 20 years planetary searches have revealed a wealth of systems orbiting stars on the main sequence. Most of these low-mass stars eventually will evolve into the Giant phases before entering the planetary nebulae (PNe) stage. In the last years, the presence of planets has also been discovered around more massive evolved stars, mostly, along the Red Giant but also along the Horizontal Branch. Moreover, disks have been found around White Dwarfs presumably formed by tidally disrupted asteroids. In all, there is evidence that an evolved (ing) star might influence the survival of planets. In this review I will try to summarize such evidence but furthermore I will present the other side of the story, that is, how the presence of a planet might alter the evolution of stars and with that the PN formation.

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Li‐enrichment in red giant rapid rotators: Planet engulfment versus extra mixing

Carlberg

Cunha

Smith³

et al. 2013

Astron Nachr

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Low mass stars undergo dramatic changes during the post main sequence evolution as the nuclear energy source shifts from the stellar core to a thin shell of active hydrogen burning. The outer convection zones of these stars deepen, dredging up nuclear-processed material and altering the stellar surface abundances. Some light elements, such as lithium, are easily destroyed in the stellar interior, and dredge-up depletes the surface abundances of these elements. The red giant stars' expanding radii also pose a threat to the stability of close orbiting planets, which can be tidally engulfed by the star. Planet engulfment may be able to account for two of the well known classes of atypical red giant stars: the rapid rotators and Lirich red giants. Alternatively, internal Li regeneration combined with "extra-mixing" in red giants may account for Li-rich giants, but this mechanism may not be able to explain rapid rotation. We have recently completed an observational study of field red giant stars, targeting both slow and rapid rotators, to compare the light element distribution between these two classes of rotators. We find that the rapid rotators have enriched Li abundances compared to the slow rotators; however, both classes of stars have similar distributions of 12 C/ 13 C -a proxy for mixing. Lower 12 C/ 13 C ratios are expected in stars that have regenerated Li internally. The peculiar red giant stars in our sample (both Li-rich and rapid rotators) are not easily explained with either planet engulfment or Li regeneration alone. Both processes are likely at work.

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Origin of Lithium Enrichment in K Giants

Cited by 135 publications

References 24 publications

Searching for Li-rich giants in a sample of 12 open clusters

Searching for Li-rich giants in a sample of 12 open clusters

Planets, evolved stars, and how they might influence each other.

Li‐enrichment in red giant rapid rotators: Planet engulfment versus extra mixing

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