The Hungarian research network has recently been involved in several projects of particular importance.Continue reading
Researchers from the German Leibniz-Institute for Astrophysics Potsdam (AIP) and the Hungarian HUN-REN Research Center for Astronomy and Earth Sciences (HUN-REN RCAES) have reconstructed the temporal changes in the distribution of surface spots on the red giant star XX Trianguli. The groundbreaking study, published in the prestigious Nature Communications journal, is based on a unique series of spectroscopic observations carried out by the STELLA robotic observatory over 16 years.
One of the main findings of the study is that the surface changes of XX Tri do not show Sun-like magnetic cycles, based on which the authors conclude that the star’s dynamo is non-periodic in nature, most likely chaotic, reads the website of the HUN-REN Research Center.
“Sunspots are the most well-known manifestations of solar magnetic activity, which, together with many other phenomena, such as solar flares or the solar cycle, can be linked to the dynamo mechanism operating inside the Sun. Starspots are phenomena similar to sunspots, but on the surface of distant stars.
However, usually we cannot observe the surface of stars directly, therefore we applied an indirect tomographic technique called Doppler imaging to the data of XX Tri,”
the Research Center quotes Dr. Zsolt Kővári, the Hungarian member of the research team.
Data visualization experts at Moholy-Nagy University of Art and Design Budapest (MOME) have created a spectacular movie from the Doppler images.
The large-amplitude variations in the brightness of the red giant XX Tri have been observed before, thus it was known that the variations were caused by dark spots that move in and out of view as the star rotates on its axis in 24 days.
These spots are even larger than the entire surface of our Sun – which is why XX Tri has been dubbed “the most spotted star in the sky.”
This study is the first to show how the giant starspots cause a tiny displacement of XX Tri in the sky, which appears virtually as a point source when observed from Earth. The reason for this is that while the photocenter of a homogeneous (=unspotted) disk is the same as the geometric center of the star, giant starspots on the disk repel the photocenter in the opposite direction to the spots. In the case of XX Tri, that is 630 light-years away, the photocenter of the stellar disk can shift by up to 10% of the star’s radius relative to the geometric center, causing an apparent shift in the celestial position of the star of 24 microarcseconds (the diameter of a human hair at a distance of 1,000 km).
However, with the help of the Gaia astrometric space observatory, it is now possible to measure even such small displacements.
This is similar to the expected astrometric displacement caused by a Saturn-mass planet in a one-year orbit around a Sun about 300 light-years away. Therefore, separating the effects of spots and exoplanets seems very difficult, if not impossible, especially in cases of similar periodicity, the researchers conclude.
Observations of XX Tri using STELLA are continuing, and according to Dr. Kővári, new data may reveal more about how the star’s dynamo works.
Via hun-ren.hu, Featured image: Pixabay