Cayman T. Unterborn^1,3 and Wendy R. Panero²
Astrophysical Journal 845, 61 Link to Article [https://doi.org/10.3847/1538-4357/aa7f79]
¹School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, USA
²School of Earth Sciences, The Ohio State University, Columbus, OH 43210, USA
³SESE Exploration Fellow.

Solar photospheric abundances of refractory elements mirror the Earth’s to within ~10 mol% when normalized to the dominant terrestrial-planet-forming elements Mg, Si, and Fe. This allows for the adoption of solar composition as an order-of-magnitude proxy for Earth’s. It is not known, however, the degree to which this mirroring of stellar and terrestrial planet abundances holds true for other star–planet systems without determination of the composition of initial planetesimals via condensation sequence calculations and post condensation processes. We present the open-source Arbitrary Composition Condensation Sequence calculator (ArCCoS) to assess how the elemental composition of a parent star affects that of the planet-building material, including the extent of oxidation within the planetesimals. We demonstrate the utility of ArCCoS by showing how variations in the abundance of the stellar refractory elements Mg and Si affect the condensation of oxygen, a controlling factor in the relative proportions of planetary core and silicate mantle material. This thereby removes significant degeneracy in the interpretation of the structures of exoplanets, as well as provides observational tests for the validity of this model.

Arumalla B. S. Reddy and David L. Lambert
Astrophysical Journal 845, 151 Link to Article [https://doi.org/10.3847/1538-4357/aa81d6]
W.J. McDonald Observatory and Department of Astronomy, The University of Texas at Austin, Austin, TX 78712-1205, USA

Several abundance analyses of Galactic open clusters (OCs) have shown a tendency for Ba but not for other heavy elements (La−Sm) to increase sharply with decreasing age such that Ba was claimed to reach [Ba/Fe]  +0.6 in the youngest clusters (ages < 100 Myr) rising from [Ba/Fe] = 0.00 dex in solar-age clusters. Within the formulation of the s-process, the difficulty to replicate higher Ba abundance and normal La−Sm abundances in young clusters is known as the barium puzzle. Here, we investigate the barium puzzle using extremely high-resolution and high signal-to-noise spectra of 24 solar twins and measured the heavy elements Ba, La, Ce, Nd, and Sm with a precision of 0.03 dex. We demonstrate that the enhanced Ba ii relative to La−Sm seen among solar twins, stellar associations, and OCs at young ages (<100 Myr) is unrelated to aspects of stellar nucleosynthesis but has resulted from overestimation of Ba by standard methods of LTE abundance analysis in which the microturbulence derived from the Fe lines formed deep in the photosphere is insufficient to represent the true line broadening imposed on Ba ii lines by the upper photospheric layers from where the Ba ii lines emerge. Because the young stars have relatively active photospheres, Ba overabundances most likely result from the adoption of a too low value of microturbulence in the spectrum synthesis of the strong Ba ii lines but the change of microturbulence in the upper photosphere has only a minor affect on La−Sm abundances measured from the weak lines.