Special star is a Rosetta Stone for understanding the sun's variability and climate effect

January 8, 2018, Aarhus University
A picture of dark sunspots and bright diffuse faculae (best seen around the edges). The study shows how the larger mix of heavy elements leave the spots unchanged, while increasing the contrast of the bright diffuse faculae. Credit: NASA/SDO

The spots on the surface on the sun come and go with an 11-year periodicity known as the solar cycle. The solar cycle is driven by the solar dynamo, which is an interplay between magnetic fields, convection and rotation. However, our understanding of the physics underlying the solar dynamo is far from complete. One example is the so-called Maunder Minimum, a period in the 17th century, where spots almost disappeared from the surface of the sun for a period of over 50 years.

Now, a large international team led by Christoffer Karoff from Aarhus University has found a star that can shed light on the physics underlying the solar dynamo. The star is located 120 light years away in the constellation of Cygnus, and on the surface, it looks just like the sun. It has the same mass, radius and ageā€”but the of the star is very different. It consists of around twice as many as in the sun.

The team has succeeded in combining observations from the Kepler spacecraft with ground-based observations dating as far back as 1978, thereby reconstructing a 7.4-year cycle in this star. "The unique combination of a star almost identical to the sun, except for the chemical composition, with a cycle that has been observed from both the Kepler spacecraft and from ground makes this star a Rosetta Stone for the study of stellar dynamos," explains Karoff.

Heavy elements make the star more variable

By combining photometric, spectroscopic and asteroseismic data, the team collected the most detailed set of observations for a solar-like cycle in any star other than the sun. The observations revealed that the amplitude of the cycle seen in the star's is more than twice as strong as what is seen on the sun, and the cycle is even stronger in visible light.

This allowed the team to conclude that more heavy elements make a stronger cycle. Based on models of the physics taking place in the deep interior and the atmosphere of the star, the team was also able to propose an explanation of the stronger cycle. Actually, they came up with a two-part explanation. First, the heavy elements make the star more opaque, which changes the energy transport deep inside the star from radiation to convection. This makes the dynamo stronger, affecting both the amplitude of the variability in the magnetic field and the rotation pattern near the surface. The latter effect was also measured. Second, the heavy elements affect the processes on the and in the atmosphere of the star. Specifically, the contrast between diffuse bright regions called faculae and the quiet solar background increases as the mix of heavy elements is increased. This makes the cyclic photometric variability of the star stronger.

Can help us understand how the sun affects our climate

The new study can help us understand how the irradiance of the sun has changed over time, which is likely to have an effect on our climate. In general special attention is paid to the Maunder Minimum, which coincided with a period of relatively cold climate, especially in Northern Europe. The new measurements offer an important constraint on the models trying to explain the weak activity and possible reduced brightness of the sun during the Maunder minimum.

Explore further: New clue to solving the mystery of the Sun's hot atmosphere

More information: Christoffer Karoff et al, The Influence of Metallicity on Stellar Differential Rotation and Magnetic Activity, The Astrophysical Journal (2018). DOI: 10.3847/1538-4357/aaa026

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4 comments

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Chris_Reeve
Jan 08, 2018
This comment has been removed by a moderator.
jonesdave
4.2 / 5 (5) Jan 09, 2018
It is sloppy to assume an internal dynamo origin for this cycling. Cycling can also possibly be imposed externally, and may perhaps represent an interaction between the star and its environment.


Really? Interaction between the star and.....what exactly? And where has this been written up, so that we may learn about it?
cantdrive85
2 / 5 (4) Jan 09, 2018
Really? Interaction between the star and.....what exactly?

This is obviously an individual who hasn't a clue of plasma physics nor electric circuitry which is of primary importance to the physics of plasmas. He is jonesdumb though, and still believes in dirty snowballs and other pre-space-age conjectures.
Captain Stumpy
5 / 5 (2) Jan 09, 2018
@illiterate pseudoscience cultist idiot
This is obviously an individual who hasn't a clue of
so, you can't actually provide a scientific reference that can't be validated?

imagine that

.

@hannes/reeve the eu pseudoscience idiot
It is sloppy to assume an
it is far, far sloppier to ASSume external actions when there are absolutely no possible influences nearby to make said external actions, especially when your ASSumptions are based entirely off of an unproven pseudoscience that can't actually produce any viable provable claims in any reputable journals

blogs and web pages are not equivalent to science - if they were, we would literally be surrounded by vampire zombies and unicorn farts

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