HIP 114328: a new refractory-poor and Li-poor solar twin

Abstract

Context. The standard solar model fails to predict the very low lithium abundance in the Sun, which is much lower than the proto-solar nebula (as measured in meteorites). This Li problem has been debated for decades, and it has been ascribed either to planet formation or to secular stellar depletion due to additional mixing below the convection zone, either during the pre-main sequence and thus possibly linked to planet formation, or additionally on secular time-scales during the main sequence. In order to test the evolution of Li, it is important to find solar twins in a range of ages, i.e., stars with about one solar mass and metallicity but in different evolutionary stages. Furthermore, the study of stars similar to the Sun is relevant in relation to the signature of terrestrial planet formation around the Sun, and for anchoring photometric and spectroscopic stellar parameter scales. Aims. We aim to identify and analyse solar twins using high quality spectra, in order to study Li depletion in the Sun and the possible relation between chemical abundance anomalies and planet formation. Methods. We acquired high-resolution (R ∼ 110 000), high S/N (∼300) ESO/VLT UVES spectra of several solar twin candidates and the Sun (as reflected from the asteroid Juno). Among the solar twin candidates we identify HIP 114328 as a solar twin and perform a differential line-by-line abundance analysis of this star relative to the Sun. Results. HIP 114328 has stellar parameters T eff = 5785 ± 10 K, log g = 4.38 ± 0.03, [Fe/H] = −0.022 ± 0.009, and a microturbulent velocity 0.05 ± 0.03 km s −1 higher than solar. The differential analysis shows that this star is chemically very similar to the Sun. The refractory elements seem slightly more depleted than in the Sun, meaning that HIP 114328 may be as likely to form terrestrial planets as the Sun. HIP 114328 is about 2 Gyr older than the Sun, and is thus the second oldest solar twin analysed at high precision. It has a Li abundance of A(Li) NLTE 0.46, which is about 4 times lower than in the Sun (A(Li) NLTE = 1.07 dex), but close to the oldest solar twin known, HIP 102152. Conclusions. Based on the lower abundances of refractory elements when compared to other solar twins, HIP 114328 seems an excellent candidate to host rocky planets. The low Li abundance of this star is consistent with its old age and fits very well the emerging Li-age relation among solar twins of different ages.

Shallow extra mixing in solar twins inferred from Be abundances

“…Our analysis revealed that the Be abundance is relatively constant with age, with a scatter of only 0.04 dex and a weak, if any, trend with age. This is in contrast to the large observed depletion of Li with age (Baumann et al 2010;Monroe et al 2013;Meléndez et al 2014b), showing that the transport mechanisms are deep enough to reach the region where Li is burned, but not deep enough to reach the higher temperatures needed to burn Be. Our Li and Be results provide stringent constraints on stellar models and nonstandard mixing processes beyond treating convection through the mixing length theory.…”

“…The importance of solar twins is that as they Article published by EDP Sciences L10, page 1 of 4 have nearly solar mass and composition (Meléndez et al 2014b), their evolution is similar to that of the Sun. Hence, solar twins at different evolutionary stages in the main sequence can be used as proxies of the Sun at different ages.…”

HIP 10725: The first solar twin/analogue field blue straggler

“…Severe Li depletion is also observed; this is a sign of old age (Monroe et al 2013;Meléndez et al 2014a) that also contradicts the young age scenario. When the phenomenon occurs through mass-transfer events (i.e., a mass exchange between a now "dead" star during its AGB phase, which pollutes its companion's photosphere, in the process also transferring angular momentum; McCrea 1964), enhancement of s-process elements is predicted for a sufficiently massive AGB donor, as well as abundance anomalies of light elements (Desidera et al 2007).…”

“…The observations for this sample are described in Meléndez et al (2014a). To summarise them briefly, we observed with UVES at the VLT in dichroic mode, with the 346 nm setting (306−387 nm) in the blue arm and the 580 nm setting (480−682 nm) in the red arm.…”

Evolution of lithium abundance in the Sun and solar twins

“…We estimate that the rate of lithium depletion is too small in the Sun and that this therefore favours the early depletion scenario. (Meléndez et al 2014). Grey and unfilled circles and triangles are twins from (Carlos et al 2016); triangles are the upper limits on lithium abundance; three unfilled circles are twins-exceptions which can be interpreted in the framework of the early depletion scenario.…”