Evidence of Rocky Planet Engulfment in the Wide Binary System HIP 71726/HIP 71737

Binary stars are supposed to be chemically homogeneous, as they are born from the same molecular cloud. However, high-precision chemical abundances show that some binary systems display chemical differences between the components, which could be due to planet engulfment. In this work, we determine precise fundamental parameters and chemical abundances for the binary system HIP 71726/HIP 71737. Our results show that the pair is truly conatal, coeval, and comoving. We also find that the component HIP 71726 is more metal-rich than HIP 71737 in the refractory elements such as iron, with Δ[Fe/H] = 0.11 ± 0.01 dex. Moreover, HIP 71726 has a lithium abundance 1.03 dex higher than HIP 71737, which is the largest difference in Li detected in twin-star binary systems with ΔT eff ≤ 50 K. The ingestion of 9.8 − 1.6 + 2.0 M ⊕ of rocky material fully explains both the enhancement in refractory elements and the high Li content observed in HIP 71726, thereby reinforcing the planet-engulfment scenario in some binary systems.

NGC 6124: a young open cluster with anomalous- and fast-rotating giant stars

We present the results of a chemical analysis of fast and anomalous rotator giants members of the young open cluster NGC 6124. For this purpose, we carried out abundances of the mixing sensitive species such as Li, C, N, Na and 12C/13C isotopic ratio, as well as other chemical species for a sample of four giants among the seven observed ones. This study is based on standard spectral analysis technique using high-resolution spectroscopic data. We also performed an investigation of the rotational velocity (v sin i) once this sample exhibit abnormal values – giant stars commonly present rotational velocities of few km s−1. In parallel, we have been performed a membership study, making use of the third data release from ESA Gaia mission. Based on these data, we estimated a distance of d = 630 pc and an age of 178 Myr through isochrone fitting. After that procedure, we matched all the information raised and investigated the evolutionary stages and thermohaline mixing model through of spectroscopic Teff and log g and mixing tracers, as 12C/13C and Na, of the studied stars. We derived a low mean metallicity of [Fe/H] = −0.13 ±0.05 and a modest enhancement of the elements created by the s-process such as Y, Zr, La, Ce, and Nd, which is in agreement of what has already been reported in the literature for young clusters. The giants analyzed have homogeneous abundances, except for lithium abundance [log ε(Li)NLTE = 1.08±0.42] and this may be associated to a combination of mechanisms that act increasing or decreasing lithium abundances in stellar atmospheres.

Chemical composition of stars with massive planets*

Stellar parameters of 25 planet-hosting stars and abundances of Li, C, O, Na, Mg, Al, S, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Ni, Zn, Y, Zr, Ba, Ce, Pr, Nd, Sm and Eu, were studied based on homogeneous high resolution spectra and uniform techniques. The iron abundance [Fe/H] and key elements (Li, C, O, Mg, Si) indicative of the planet formation, as well as the dependencies of [El/Fe] on Tcond, were analyzed. The iron abundances determined in our sample stars with detected massive planets range within –0.3 < [Fe/H] < 0.4. The behaviour of [C/Fe], [O/Fe], [Mg/Fe] and [Si/Fe] relative to [Fe/H] is consistent with the Galactic Chemical Evolution trends. The mean values of C/O and [C/O] are <C/O> = 0.48 ±0.07 and <[C/O]> = –0.07 ±0.07, which are slightly lower than solar ones. The Mg/Si ratios range from 0.83 to 0.95 for four stars in our sample and from 1.0 to 1.86 for the remaining 21 stars. Various slopes of [El/Fe] vs. Tcond were found. The dependencies of the planetary mass on metallicity, the lithium abundance, the C/O and Mg/Si ratios, and also on the [El/Fe]–Tcond slopes were considered.

Lithium pollution of a white dwarf records the accretion of an extrasolar planetesimal

Tidal disruption and subsequent accretion of planetesimals by white dwarfs can reveal the elemental abundances of rocky bodies in exoplanetary systems. Those abundances provide information on the composition of the nebula from which the systems formed, which is analogous to how meteorite abundances inform our understanding of the early Solar System. We report the detection of lithium, sodium, potassium, and calcium in the atmosphere of the white dwarf Gaia DR2 4353607450860305024, which we ascribe to the accretion of a planetesimal. Using model atmospheres, we determine abundance ratios of these elements, and, with the exception of lithium, they are consistent with meteoritic values in the Solar System. We compare the measured lithium abundance with measurements in old stars and with expectations from Big Bang nucleosynthesis.

Detailed abundances in a sample of very metal-poor stars

Context. Unevolved metal-poor stars bore witness to the early evolution of the Galaxy, and the determination of their detailed chemical composition is an important tool to understand its chemical history. The study of their chemical composition can also be used to constrain the nucleosynthesis of the first generation of supernovae that enriched the interstellar medium. Aims. We aim to observe a sample of extremely metal-poor star (EMP stars) candidates selected from the Sloan Digital Sky Survey data release 12 (SDSS DR12) and determine their chemical composition. Methods. We obtained high-resolution spectra of a sample of five stars using HDS on Subaru telescope and used standard 1D models to compute the abundances. The stars we analysed have a metallicity [Fe/H] of between −3.50 and −4.25 dex. Results. We confirm that the five metal-poor candidates selected from low-resolution spectra are very metal poor. We present the discovery of a new ultra metal-poor star (UMP star) with a metallicity of [Fe/H] = −4.25 dex (SDSS J1050032.34−241009.7). We measured in this star an upper limit of lithium (log(Li/H) ≤ 2.0. We found that the four most metal-poor stars of our sample have a lower lithium abundance than the Spite plateau lithium value. We obtain upper limits for carbon in the sample of stars. None of them belong to the high carbon band. We measured abundances of Mg and Ca in most of the stars and found three new α-poor stars.

TYC 8327-1678-1: a new super lithium-rich K giant

ABSTRACT In this work, we show that TYC 8327-1678-1 is a low-mass red giant star with a super lithium abundance in its atmosphere. For this, we used high-resolution spectroscopy to determine atmospheric parameters, the chemical abundances of the light elements and the isotopic ratio 12C/13C using the spectral synthesis techniques and the equivalent width measurements. Also, we used theoretical evolutionary tracks to find out the mass and the evolutionary stage of TYC 8327-1678-1. The lithium abundance was determined using the Li i resonance doublet at 6708 Å and the subordinate line at 6104 Å that yielding a mean value of $\log \, \epsilon {\rm (Li)_{NLTE}}\, =\, 3.48$. The projected rotational velocity ($v\, \sin \, i$) has been determined using spectral synthesis based on the isolated Fe i lines. Our results show that TYC 8327-1678-1 has a mass of $M\, =\, 1.60$ $\pm \, 0.20\, {\rm M}_{\odot }$, a low rotational velocity ($v\, \sin \, i$ = 2.35 ± 0.24 km s−1) and metallicity of [Fe/H] = +0.23 ± 0.09. Finally, we discuss the possibility that TYC 8327-1678-1 became a lithium-rich star after a merging event involving a red giant and a helium white dwarf.