Elemental Abundances of Solar Sibling Candidates

Abstract: Dynamical information along with survey data on metallicity and in some cases age have been used recently by some authors to search for candidates of stars that were born in the cluster where the Sun formed. We have acquired high resolution, high signal-to-noise ratio spectra for 30 of these objects to determine, using detailed elemental abundance analysis, if they could be true solar siblings. Only two of the candidates are found to have solar chemical composition. Updated modeling of the stars' past orbits in a realistic Galactic potential reveals that one of them, HD162826, satisfies both chemical and dynamical conditions for being a sibling of the Sun. Measurements of rare-element abundances for this star further confirm its solar composition, with the only possible exception of Sm. Analysis of long-term high-precision radial velocity data rules out the presence of hot Jupiters and confirms that this star is not in a binary system. We find that chemical tagging does not necessarily benefit from studying as many elements as possible, but instead from identifying and carefully measuring the abundances of those elements which show large star-to-star scatter at a given metallicity. Future searches employing data products from ongoing massive astrometric and spectroscopic surveys can be optimized by acknowledging this fact.

• The paper uses high-resolution spectroscopy and dynamical modeling to analyze elemental abundances and past orbits of 30 solar sibling candidates.
• Spectroscopic analysis revealed that only HD 154747 and HD 162826 had solar-like chemical compositions among the candidates studied.
• Combining chemistry and dynamics, the study identified HD 162826 as the most promising solar sibling candidate due to its solar-like composition and past orbital proximity to the Sun.

Elemental Abundances of Solar Sibling Candidates

The paper under review explores the intriguing possibility of identifying solar sibling stars — stars that were born in the same cluster as our Sun. The authors employ high-resolution and high signal-to-noise ratio spectroscopy to analyze the elemental abundances of 30 candidate stars previously suggested by various authors based on their dynamical properties. This approach seeks to establish whether any of these stars share a birth cluster with our Sun, utilizing both chemical tagging and dynamical modeling in the context of the current understanding of the Galaxy's evolution and star formation.

Spectroscopic Analysis and Chemical Tagging

The research presents a rigorous chemical analysis, noting that not all elemental abundances are useful for identifying stars with a common origin. The study distinguishes elements with typically low scatter across different stars at a given metallicity, from those with significant star-to-star variations. For example, while elements like Si, Ca, Sc, Ti, and Ni often reflect a uniform distribution due to their production in supernovae, elements such as Na, Y, and Ba exhibit significant and informative variance. This variance suggests sensitivity to the specific conditions in the formation environment, making them key elements for detailed chemical tagging.

The spectroscopic analysis reveals that, despite being high in solar abundance, only two stars from the initial list — HD 154747 and HD 162826 — exhibit chemical compositions resembling solar values within measurement errors. This insight underscores the importance of discerning specific elemental abundance signatures when tracing stellar lineages to a common birthplace.

Dynamical Modeling

The authors employ the Galactic potential model akin to that proposed by Bobylev et al. (2011), including a spiral arm model, to reconstruct the possible past Galactic orbits of the stars and determine their proximity to the Sun over time. Such modeling complements the chemical analysis by verifying the likelihood of stars having shared a point of origin with the Sun. This combined chemical-dynamical methodology is crucial as it highlights the criticality of both spatial associations and shared chemical signatures in sibling identification.

The dynamical examination reveals that of the two stars with solar-like chemical compositions, only HD 162826 has a past orbit suggesting potential close encounters with the solar orbit. The results of detailed orbital reconstruction suggest that HD 162826 had several close approaches to the Sun at relative velocities conducive to shared formation scenarios. This candidate, thus, satisfies the dual criteria of chemistry and proximity in historical Galactic orbits necessary for sibling identification.

Practical Implications and Future Directions

The findings emphasize the need for comprehensive surveys involving both high-quality spectroscopic and dynamical data to identify solar siblings. Given the capabilities of ongoing and forthcoming surveys, such as Gaia, this research strategy can be expanded to actively trace solar siblings across the Milky Way, offering potential insights into our solar system's formation environment and enriching our understanding of Galactic chemical evolution.

Furthermore, the prospect of identifying solar siblings poses interesting implications for studies on the dissemination of life across stellar systems, the dynamical evolution of early open clusters, and identifying the starting conditions of the solar system's formation region. The paper's methodology could form a blueprint for targeted searches that strategically integrate chemical and dynamical data, making it a valuable contribution to both stellar astrophysics and broader astronomical studies.