2024-04-16 16:10:33
Infrared image of the shock wave (red arc) created by the massive giant star Zeta Ophiuchi in a cloud of interstellar dust. The light winds of sun-like stars are much harder to see. Credit: NASA/JPL-Caltech; NASA and the Hubble Legacy Team (STScI/AURA); CR O’Dell, Vanderbilt University
Astrophysicists quantify the mass loss of stars using their stellar winds
An international research team led by a researcher from the University of Vienna has for the first time detected stellar winds from three Sun-like stars by recording the X-ray emission from their astrospheres, placing limits on the stars’ rate of mass loss. through the spirits of their stars. The study was published in Astronomy of nature.
Astrospheres, stellar analogs of the heliosphere surrounding our solar system, are very hot plasma bubbles blown by stellar winds into the interstellar medium, a space filled with gas and dust. Studying the stellar winds of low-mass stars similar to the Sun allows us to understand the evolution of stars and stars, and ultimately the history and future of our star and solar system. Stellar winds drive many processes that evaporate planetary atmospheres into space and therefore lead to atmospheric mass loss.
Although the escape rates of planets over an hour or even a year are tiny, they operate over long geological periods. The losses add up and can be a decisive factor in a planet evolving into a habitable world or airless rock. Despite their importance to the evolution of stars and planets alike, the winds of Sun-like stars are notoriously difficult to constrain. Consisting mainly of protons and electrons, they also contain a small amount of heavier ions (such as oxygen, carbon). It is these ions that, by capturing electrons from the neutrals of the interstellar medium around the star, emit X-rays.
X-ray emission from astrospheres has been detected
An international research team led by Kristina Kislyakova, a senior scientist at the Department of Astrophysics of the University of Vienna, has for the first time detected the X-ray emission from the astrospheres around three Sun-like stars, so-called main sequence stars which are stars at the peak of their lives, and thus recorded such winds for the first time directly, allowing them Place constraints on the mass loss rate of stars using their stellar winds.
These results, based on observations with the XMM-Newton space telescope, are now published in Astronomy of nature. The researchers observed the spectral fingerprints (so-called spectral lines) of the oxygen ions with XMM-Newton and were able to determine the amount of oxygen and ultimately the total mass of the stellar wind emitted by the stars. For the three stars with identified astrospheres, named 70 Ophiuchi, epsilon Eridani and 61 Cygni, the researchers estimated their mass loss rates to be 66.5±11.1, 15.6±4.4 and 9.6±4.1 times the solar mass loss rate, respectively. This means that the winds from these stars are much stronger than the solar wind, which may be explained by the stronger magnetic activity of these stars.
The XMM-Newton image of the star 70 Ophiuchi (left) and the X-ray emission from the region (“annulus”) surrounding the star represented by the spectrum over the energy of X-ray photons (right). Most of the emission consists of X-ray photons from the star itself but scattered within the observing telescope and across the camera (approximately according to the model shown with the blue line), but there is a significant contribution around the K-alpha oxygen line at an energy of 0.56 keV that originates from the extended astrosphere and not from the star (this contribution is included in the model the red). Credit: Kislyakova et al. Nature Astronomy, 10.1038/s41550-024-02222-x, 2024
“In the Solar System, charge-exchange emission of solar wind has been observed from planets, comets and the heliosphere and provides a natural laboratory to study the composition of the solar wind,” explains the study’s lead author, Kristina Kislyakova. “Observing this emission from distant stars is much more complicated because of the fading of the signal. In addition, the distance to the stars makes it very difficult to separate the signal emitted from the astrosphere from the actual X-ray emission of the star itself, which is “scattered” across the field of view of the star itself. Telescope due to instrumental effects .
“We developed a new algorithm to separate the stellar from the astrospheric contributions to the charge-exchange signal emission detected from stellar wind oxygen ions and the surrounding neutral interstellar medium of three main-sequence stars. This was the first time X-ray charge-exchange emission from the astrospheres of such stars has been detected . Our estimated mass-loss rates can serve as a benchmark for stellar wind models and extend our limited observational evidence for solar-like stellar winds.”
Future prospects and technological progress
Co-author Manuel Goodell, also from the University of Vienna, adds: “There have been three decades of worldwide efforts to establish the presence of winds around Sun-like stars and measure their strength, but so far only indirect evidence based on their secondary effects on the star or its environment has hinted at the existence of Such winds; our group previously tried to detect radio emission from the winds, but could only place upper limits on the winds without detecting the winds themselves. Our new results, based on X-rays, pave the way for finding these winds and even studying their interactions with stars. Go around.”
“In the future, this method of directly detecting X-ray stellar winds will be possible thanks to future high-resolution instruments, such as the X-IFU spectrometer of the European Athena mission. The high spectral resolution of the X-IFU will resolve the finer structure and emission ratio of the oxygen lines (as well as other faint lines), which are difficult to discern at XMM’s CCD resolution, and will provide additional constraints on the emission mechanism; thermal emission from the stars, or non-thermal charge exchange from the astrosphere.” – explains CNRS researcher Dimitra Kotrompah, co-author of the study.
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