Evidence for enhanced mixing on the super-meteoritic Li-rich red giant HD 233517

Strassmeier, K. G.; Carroll, T. A.; Weber, M.; Granzer, T.

doi:10.1051/0004-6361/201424130

Cited by 18 publications

(19 citation statements)

References 69 publications

(86 reference statements)

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“…Then, either the fresh Li produced during the bump can survive the RGB tip or the CFM can operate at the He-flash. This last suggestion is supported by the asteroseismic analysis of a red giant burning He in its core (Silva Aguirre et al 2014) and by Li-rich red clump stars discovered by Monaco et al (2014) and Strassmeier et al (2015). Finally, other recent works report Li-rich stars all along the RGB challenging the idea that Li production is only possible at certain evolutionary phases (Gonzalez et al 2009;Monaco et al 2011;Lebzelter et al 2012).…”

Section: Introductionmentioning

confidence: 72%

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: Introductionmentioning

confidence: 72%

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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“…On the other hand, the stellar model constructed by Li et al (2014) shows that magnetic instabilities might produce additional mixing during the pre-main sequence, resulting in strong depletion. An anisotropic supergranulation pattern was found on the surface of the super Li-rich but magnetically non-active giant HD 233517 by means of Doppler imaging (Strassmeier et al 2015). It favors an additional mixing scenario as the cause for its extreme surface Li abundance opposite to an engulfing event.…”

Section: Introductionmentioning

confidence: 75%

Chromospheric activity and lithium line variations in the spectra of the spotted star LQ Hydrae

Soriano

Strassmeier

Weber

2015

A&A

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Context. Although the relationship between lithium abundance in stars and their magnetic activity is commonly accepted, it is still unclear how the different phenomena related to it can increase the amount of Li, reduce its depletion, or be a source of bias for the measurements. Aims. We study the rotational modulation of chromospheric and photospheric parameters of the young, active, single K2 dwarf LQ Hya and their connection with the variability of the Li i 6708 Å line. Methods.A total of 199 high-resolution STELLA spectra and quasi-simultaneous photometry were used to compute effective temperature, gravity, and chromospheric activity indicators such as Hα and Hβ emission, Balmer decrement, and chromospheric electron density, as a function of the rotational phase. The variation of the Li i 6708 Å line was characterized in terms of equivalent width, abundance, and of 6 Li/ 7 Li isotopic ratio in the form of line shifts. Results. Photospheric and chromospheric parameters show clear rotational modulation. Effective temperatures and continuum variations reveal a higher concentration of cool spots on the side of the star on which we also detect stronger chromospheric activity.Increased electron densities and the modulation of the He i D 3 line suggest that the source of this activity can be a combination of plages and repeated low-intensity flares. The Li line and other temperature-sensitive lines are clearly enhanced by the spots located on the most active side of the star. Li abundances calculated taking into account the temperature variations simultaneously show, although with high dispersion, a small overabundance of this element that correlates well with the surface magnetic activity. In addition, the Li line center is more intensely redshifted than in the other hemisphere, which might be interpreted as a weak enrichment of 6 Li.

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“…At this time extra Li is produced and very high Li abundances are reached (e.g. HD 233517; Strassmeier et al 2015). However, this phase is extremely short-lived because once the mixing extends deep enough the freshly synthesized Li is quickly destroyed.…”

Section: Summary and Discussionmentioning

confidence: 99%

“…A unique possibility for such long-term Doppler observations (see e.g. Kővári et al 2015;Strassmeier et al 2015;Künstler et al 2015) is provided by the STELLA robotic observatory of the AIP in Tenerife (Strassmeier et al 2010). In this paper we present and analyse such spectroscopic observations of the rapidly rotating (P rot ≈ 24 days) K-giant KU Peg (=HD 218153).…”

Section: Introductionmentioning

confidence: 99%

Time-series Doppler images and surface differential rotation of the effectively single, rapidly rotating K-giant KU Pegasi

Kővári

Künstler

Strassmeier

et al. 2016

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Context. According to most stellar dynamo theories, differential rotation (DR) plays a crucial role in the generation of toroidal magnetic fields. Numerical models predict surface differential rotation to be anti-solar for rapidly rotating giant stars, i.e. their surface angular velocity could increase with stellar latitude. However, surface differential rotation has been derived only for a handful of individual giant stars to date. Aims. The spotted surface of the K-giant KU Pegasi is investigated in order to detect its time evolution and to quantify the surface differential rotation. Methods. We present 11 Doppler images from spectroscopic data collected with the robotic telescope STELLA between 2006 and 2011. All maps are obtained with the surface reconstruction code iMap. Differential rotation is extracted from these images by detecting systematic (latitude-dependent) spot displacements. We apply a cross-correlation technique to find the best differential rotation law. Results. The surface of KU Peg shows cool spots at all latitudes and one persistent warm spot at high latitude. A small cool polar spot exists for most but not all of the epochs. Re-identification of spots in at least two consecutive maps is mostly possible only at middle and high latitudes and thus restricts the differential-rotation determination mainly to these latitudes. Our cross-correlation analysis reveals solar-like differential rotation with a surface shear of α = +0.040 ± 0.006, i.e., approximately five times weaker than on the Sun. We also derive a more accurate and consistent set of stellar parameters for KU Peg including a small Li abundance of ten times less than solar.

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Evidence for enhanced mixing on the super-meteoritic Li-rich red giant HD 233517

Cited by 18 publications

References 69 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

Chromospheric activity and lithium line variations in the spectra of the spotted star LQ Hydrae

Time-series Doppler images and surface differential rotation of the effectively single, rapidly rotating K-giant KU Pegasi

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