Gaia's Astrometry Discovers Binaries with Peculiar Chemical Enrichment
The ESA's Gaia mission is revolutionizing our view of the galaxy. Its high-precision astrometric measurements have identified thousands of binary systems formed by a normal star and a white dwarf. A surprising finding is a group of these white dwarfs with masses exceeding 0.8 solar masses, an unusually high value. According to stellar evolution models, stars that massive should not produce certain heavy elements, such as barium. This contradiction points to systems with exceptional evolutionary histories. 🔭
Barium as Evidence of Stellar Merger
The key to solving this mystery lies in the chemical composition of the companion star. When it shows an excess of elements created in the s-process, the scenario changes completely. This chemical enrichment indicates that the massive white dwarf did not form in isolation. Astronomers propose that it formed after merging with another star within an original triple system. The violent interaction and material transfer during that internal merger can contaminate the surviving star, creating a system similar to the well-known IK Pegasi.
Characteristics of these peculiar systems:- Presence of a massive white dwarf (more than 0.8 solar masses).
- A main-sequence companion star enriched in barium.
- A probable origin in a hierarchical triple system that underwent instability.
To understand how a solitary star explodes, sometimes you have to look for systems where three stars danced a waltz that was too tight.
Candidates for Supernova Progenitors
By applying these criteria to public spectroscopic catalogs, researchers have identified new candidates besides IK Pegasi. It is estimated that there could be several dozen of these systems in Gaia's current data. Their importance goes beyond the peculiar: if they are truly the result of mergers in triples, they represent an observable intermediate phase in an explosive pathway.
Implications for stellar astrophysics:- They provide test cases for models of multiple system evolution.
- They are possible links in the chain of the double merger (double fusion).