Research on the exoplanet WASP-39b has uncovered the need to include stellar magnetic fields in models to match observations with theoretical predictions, significantly advancing exoplanet study accuracy. (Artist’s concept.) Credit: SciTechDaily.com
From the brightness variations of its host star, an
Stars with low magnetic field strength exhibit a more pronounced limb darkening than those with a strong magnetic field. This affects the shape of the light curve. Credit: MPS / hormesdesign.de
Researchers define a light curve as a measurement of the brightness of a star over a longer period of time. The brightness of a star fluctuates constantly, for example because its luminosity is subject to natural fluctuations. Exoplanets can also leave traces in the light curve. If an exoplanet passes in front of its star as seen by an observer, it dims the starlight. This is reflected in the light curve as a regularly recurring drop in brightness. Precise evaluations of such curves provide information about the size and orbital period of the planet. Researchers can also obtain information about the composition of the planet’s atmosphere, if the light from the star is split into its different wavelengths or colours.
A close look at a star’s brightness distribution
The limb of a star, the edge of the stellar disk, plays a decisive role in the interpretation of its light curve. Just as in the case of the Sun, the limb appears darker to the observer than the inner area. However, the star does not actually shine less brightly further out. “As the star is a sphere and its surface curved, we look into higher and therefore cooler layers at the limb than in the center,” explains coauthor and MPS-Director Prof. Dr. Laurent Gizon. “This area therefore appears darker to us,” he adds.
It is known that the limb darkening affects the exact shape of the exoplanet signal in the light curve: The dimming determines how steeply the brightness of a star falls during a planetary transit and then rises again. However, it has not been possible to reproduce observational data accurately using conventional models of the stellar atmosphere. The decrease of brightness was always less abrupt than the model calculations suggested. “It was clear that we were missing a crucial piece of the puzzle to precisely understand the exoplanets’ signal,” says MPS-Director Prof. Dr. Sami Solanki, coauthor of the current study.
Magnetic field is the missing piece of the puzzle
As the calculations published today show, the missing piece of the puzzle is the stellar magnetic field. Like the Sun, many stars generate a magnetic field deep in their interior through enormous flows of hot Related Post The many problems of a fragmenting world wide web
The researchers were also able to prove that the discrepancy between observational data and model calculations disappears if the star’s magnetic field is included in the computations. To this end, the team turned to selected data from Related Post The Hidden Detail NASA Didn't Show in New Spacesuits : ScienceAlert
James Webb Space Telescope
The James Webb Space Telescope (JWST or Webb) is an orbiting infrared observatory that will complement and extend the discoveries of the Hubble Space Telescope. It covers longer wavelengths of light, with greatly improved sensitivity, allowing it to see inside dust clouds where stars and planetary systems are forming today as well as looking further back in time to observe the first galaxies that formed in the early universe.
” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]” tabindex=”0″ role=”link”>James Webb Space Telescope. The telescope is able to split the light of distant stars into its various wavelengths and thus search for the characteristic signs of certain molecules in the atmosphere of the discovered planets. As it turns out, the magnetic field of the parent star influences the stellar limb darkening differently at different wavelengths – and should therefore be taken into account in future evaluations in order to achieve even more precise results.
From telescopes to models
“In the past decades and years, the way to move forward in exoplanet research was to improve the hardware, the space telescopes designed to search for and characterize new worlds. The James Webb Space Telescope has pushed this development to new limits,” says Dr. Alexander Shapiro, coauthor of the current study and head of an ERC-funded research group at the MPS. “The next step is now to improve and refine the models to interpret this excellent data,” he adds.
To further advance this development, the researchers now want to extend their analyses to stars that are clearly different from the Sun. In addition, their findings offer the possibility of using the light curves of stars with exoplanets to infer the strength of the stellar magnetic field, which is otherwise often hard to measure.
Reference: “Magnetic origin of the discrepancy between stellar limb-darkening models and observations” by Nadiia M. Kostogryz, Alexander I. Shapiro, Veronika Witzke, Robert H. Cameron, Laurent Gizon, Natalie A. Krivova, Hans-G. Ludwig, Pierre F. L. Maxted, Sara Seager, Sami K. Solanki and Jeff Valenti, 12 April 2024, Nature Astronomy.
DOI: 10.1038/s41550-024-02252-5