Nine Nearby K-Giants with Planets: A Detailed Analysis of their Chemical Composition

• Published in: Astrophysics Vol. 65; no. 4; pp. 494 - 511
• Main Authors: Lyubimkov, L. S., Poklad, D. B., Korotin, S. A.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.12.2022; Springer; Springer Nature B.V
• Subjects: Abundance; Analysis; Astrochemistry; Astronomy; Astrophysics; Astrophysics and Astroparticles; Astrophysics and Cosmology; Carbon 12; Carbon 13; Carbon isotopes; Chemical composition; Chemical elements; Convective mixing; Correlation; Extrasolar planets; Hafnium; Hypotheses; Infrared analysis; Isotope ratios; Jupiter; Lithium; Local thermodynamic equilibrium; Magnetic fields; Metallicity; Nitrogen; Observations and Techniques; Parameters; Physics; Physics and Astronomy; Planets; Space Exploration and Astronautics; Space Sciences (including Extraterrestrial Physics; Stars; Stellar atmospheres; Stellar magnetic fields; Red giants; Chemical composition; Exoplanets
• ISSN: 0571-7256; 1573-8191
• DOI: 10.1007/s10511-023-09755-5

The chemical composition of 9 K-giants with planets located within 100 pc of the sun is studied. Here fundamental parameters of the stars which we have found previously are used; for the giant μ Leo the metallicity index [Fe/H] = +0.26 is redetermined along with the microturbulence parameter V t =1.3 km/s from the lines of FeI. The abundances of 17 chemical elements from lithium (Z = 3) to hafnium (Z = 72) are found. Some elements are analyzed without assuming LTE (local thermodynamic equilibrium). Infrared CN molecular lines are used to determine the nitrogen abundance and the carbon isotope ratio 12 C/ 13 C. Low values of 12 C/ 13 C=8-18 show that the program giants have passed through deep convective mixing in the FDU (First Dredge-Up) phase. When analyzing the abundances obtained we added our recent data for the magnetic giants EK Eri and OU And found by the same technique. Lithium was not found for 7 of the 11 giants in question. An absence of lithium in atmospheres of stars that have passed through deep mixing in the FDU phase agrees with theoretical predictions. However for 4 of the giants, we found lithium; earlier for 3 of these 4 stars a magnetic field has been detected. These two phenomena, i.e., the presence of lithium in its atmosphere and the existence of a magnetic field, are unexpected for post-FDU giants in terms of the standard theory, can be be explained in the framework of a single hypothesis: an engulfment by a star of the planet with a mass several times that of Jupiter. For the 11 giants examined here we found a distinct correlation between the [N/C] and [N/O] values. A comparison of the observed relation with the theoretical model computed with rotation included showed that the theory cannot explain the high values of [N/C]=1.0 – 1.4 obtained for the most of the giants. Apparently, the known hypothesis of extra mixing is needed here. The combined abundance of C+N+O, which, according to the theory, should remain constant from the star’s formation, showed a correlation with the metallicity index [Fe/H]. In this regard, for the stars with the normal metallicity [Fe/H] = ±0.1 a value of logε(C + N + O) = 8.97 was found that agrees perfectly with the solar value logε(C + N + O) = 8.94. For the giant m Leo with a high metallicity [Fe/H]=+0.26 the highest value of logε(C + N + O) = 9.31 was obtained. An anticorrelation was found between [RE/Fe], the mean abundance of rare earth (RE) elements (relative to Fe) and the index [Fe/H]. It is in good agreement with data for F- and G-dwarfs in the sun’s neighborhood and reflects the initial chemical composition of the giants studied here.