Astronomers have discovered three new rare magnetic and helium-enriched hot subdwarf stars, expanding our understanding of these intriguing celestial objects. These findings shed light on the formation of these stars, which are thought to be the result of white dwarf mergers. Subdwarf stars, especially the helium-rich variety, provide valuable clues about the evolution of binary star systems and the fate of white dwarfs.
Unveiling the Secrets of Magnetic Hot Subdwarfs
In a groundbreaking discovery, an international team of astronomers has reported the detection of three new helium-enriched hot subdwarf stars with strong magnetic fields. These rare celestial objects, known as magnetic helium-rich hot subdwarfs (He-sdOs), were identified using the Southern African Large Telescope (SALT).
Helium-rich subdwarf O stars (He-sdOs) are a unique class of hot, compact stars that are in a pre-white dwarf evolutionary stage. They are typically dominated by helium and have effective temperatures ranging from 40,000 to 50,000 Kelvin. Observations in recent years have revealed a select group of these He-sdOs that possess magnetic fields, with strengths ranging from 300 to 500 kilogauss (kG).
Unraveling the Formation of Magnetic He-sdOs
The discovery by the research team led by Matti Dorsch of the University of Potsdam expands the total number of known magnetic hot subdwarfs to seven. Interestingly, the newly found magnetic He-sdOs have somewhat weaker magnetic fields, measuring around 200 kG.
According to the study, the researchers propose that these magnetic He-sdOs are the result of mergers between helium white dwarfs and hydrogen/helium white dwarfs. As these white dwarfs merge, the hydrogen-rich white dwarf is destroyed and fully mixed, with most of its mass condensing onto the surface of the helium white dwarf. This process is thought to be responsible for the generation of the strong magnetic fields observed in these rare stars.
Exploring the Diversity of Hot Subdwarf Stars
The newly discovered magnetic He-sdOs exhibit a range of physical properties, with masses ranging from approximately 0.48 to 0.74 solar masses and radii between 0.175 and 2.1 solar radii. Interestingly, all three stars have comparable effective temperatures, falling within the 46,000 to 47,680 Kelvin range.
These findings contribute to our growing understanding of the diversity and formation mechanisms of hot subdwarf stars. The presence of magnetic fields in a small subset of these stars suggests that the merger of white dwarfs can indeed generate strong magnetic fields, though the reasons why most He-sdOs do not exhibit this feature remain unclear. Further research is needed to fully unravel the complex evolutionary paths of these intriguing stellar objects.
