Although it might sound strange to question if the Sun is a sun-like star, Angela Santos, a researcher on IA's "Towards a comprehensive study of stars" team at the University of Porto, explains the issue: "Within the community, there is an ongoing debate about whether the Sun is a 'sun-like' star, especially regarding its magnetic activity. Some studies have suggested that stars similar to the Sun exhibit significantly more activity."
However, Santos believes that the issue lies not with the Sun itself, but rather with the classification of "sun-like" stars, due to various limitations and biases in observational data and inferred stellar properties.
For their study, the team selected several stars with properties similar to the Sun, using a new catalog of stellar properties derived from Kepler data, along with Gaia data and the team's rotation period and magnetic activity index catalog. They compared this stellar data with activity data from the last two solar cycles, obtained from the VIRGO/SPM instrument aboard the SOHO spacecraft.
One star in the study, affectionately named "Doris" by the astronomers and chosen from the Kepler catalog, had previously been observed to have a cycle amplitude twice that of the Sun's latest solar cycles, despite having similar properties. Santos explains that "the difference was the metallicity. Our interpretation is that the effect of metallicity, which results in a deeper convection zone, produces a more effective dynamo, leading to a stronger activity cycle."
When the team selected stars similar to Doris without considering metallicity, they found an excess of high-metallicity stars. "In our selection, the only parameter that could lead to this excess is the rotation period. Specifically, Doris had a longer period than the Sun. Indeed, we found evidence of a correlation between the rotation period and metallicity," says Santos.
The two studies' findings are consistent because stronger magnetic activity implies that the magnetic braking process results in a slower rotation period. This explains why Doris rotates more slowly than the Sun, even though it is very similar and slightly younger.
In conclusion, Angela Santos says, "What we discovered is that, although there are stars more active than the Sun, the Sun is indeed a completely normal sun-like star."
The findings have been published in Astronomy and Astrophysics.
Related Links
Instituto de Astrofisica e Ciencias do Espaco
Stellar Chemistry, The Universe And All Within It
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