Revisiting the 16 Cygni planet host at unprecedented precision and exploring automated tools for precise abundances

Abstract

The binary system 16 Cygni is key in studies of the planet-star chemical composition connection, as only one of the stars is known to host a planet. This allows us to better assess the possible influence of planet interactions on the chemical composition of stars that are born from the same cloud and thus should have a similar abundance pattern. In our previous work, we found clear abundance differences for elements with Z ≤ 30 between both components of this system and a trend of these abundances as a function of the condensation temperature (Tc), which suggests a spectral chemical signature related to planet formation. In this work we show that our previous findings are still consistent even if we include more species, such as the volatile N and neutron capture elements (Z > 30). We report a slope with Tc of 1.56 ± 0.24 × 10−5 dex K−1, that is good agreement with our previous work. We also performed some tests using ARES and iSpec to measure automatically the equivalent width and found Tc slopes in reasonable agreement with our results as well. In addition, we determined abundances for Li and Be by spectral synthesis, finding that 16 Cyg A is richer not only in Li but also in Be, when compared to its companion. This may be evidence of planet engulfment, indicating that the Tc trend found in this binary system may be a chemical signature of planet accretion in the A component, rather than an imprint of the giant planet rocky core formation on 16 Cyg B.

Probing the interior physics of stars through asteroseismology

“…This, and more sophisticated diagnostics for additional modes, was used by Bellinger et al (2017) to find an asteroseismic estimate of τ ¼ 6.9 AE 0.4 Gyr. This is in excellent agreement with other methods for this well-characterized bright exoplanet host binary (Maia et al, 2019). The similarity of the nonradial oscillations of 16 Cyg A to those of the Sun as illustrated in Fig.…”

Lithium and beryllium in solar twins

“…Despite the difference in the mass of the binary components being only ∼0.05 M ⊙ , King et al (1997) found that 16 Cyg A has a much larger Li abundance (∼0.67 dex) than 16 Cyg B. This result has been recently confirmed using superb HDS/Subaru spectra with R = 160,000 and S / N = 1,000 by Maia et al (2019), who find that 16 Cyg A has an Li abundance 0.70 dex larger than 16 Cyg B (see also Gonzalez 1998; Ramírez et al 2011). This large difference could be due to the engulfment of planetary material by 16 Cyg A, which has an Li abundance larger than expected for its age (Carlos et al 2016).…”

“…Regarding Be, as discussed in the previous section, it is less affected by depletion than Li, and indeed, previous studies found comparable Be abundances between both components (Deliyannis et al 2000; Garcia Lopez & Perez de Taoro 1998; Takeda et al 2011). The most precise study by Maia et al (2019) found that Be is about 0.07 dex higher in 16 Cyg A than in 16 Cyg B. As Be is a refractory element (Lodders 2003), it is expected that the ingestion of planetary material will also increase Be, as observed.…”

“…Although there was some initial controversy regarding abundance differences between 16 Cyg A and B (Ramírez et al 2011; Schuler et al 2011), most studies of this binary pair show clear distinct composition between the components (e.g., Laws & Gonzalez 2001; Maia et al 2019; Mishenina et al 2016; Nissen et al 2017; Ramírez et al 2011; Tucci Maia et al 2014), and the most recent works based on high‐quality spectra ( R > 10 5 ) show a significant trend with dust condensation temperature (Maia et al 2019; Nissen et al 2017), strengthening the possible connection between abundance anomalies and planets.…”

Rocky planet engulfment in the binary system HIP 71726-37

“…The abundance patterns (versus condensation temperature) found by Meléndez et al (2009Meléndez et al ( , 2017; Oh et al (2018); Maia et al (2019); Ramírez et al (2019) and Saffe et al (2015) in solar twins and twin-star binary systems have been linked to the formation of planets (for an alternative explanation regarding dust cleansing, see Gustafsson 2018a,b). In particular, it is argued that the formation of rocky planets removes refractory elements from the hosted star.…”