High temperature plasma in solar and low-mass stars. The study: “Empirical prediction of plasma emission measure distributions and X-EUV spectra of late-type stars” of A. Maggio (INAF-OAPA) recently appeared on The Astrophysical Journal

Measured the amount of plasma between 10000 and 30 million degrees—responsible for the emission of extreme UV radiation and soft X-rays—in a sample of Sun-like and low-mass stars.

Sun-like stars (spectral classes FGK) and low-mass stars (spectral class M) host in their outer atmospheres (the corona) plasma at temperatures of millions of degrees. Such high temperatures are reached through processes governed by the stellar magnetic field, and are therefore grouped under the category of magnetic activity. At these temperatures, the plasma emits high-energy ultraviolet radiation (EUV, Extreme Ultraviolet) and low-energy X-rays (soft X-rays).

Measuring the emission levels of stars in these bands, and how they vary with stellar properties, is of great interest due to the strong impact that EUV and soft X-ray radiation have on the surrounding environment. This radiation interacts with the atmospheres of any orbiting planets and with the gas in the circumstellar environment, heating them and altering their chemical and physical properties.

Nevertheless, the study of stars in the EUV and soft X-ray bands is complicated by two major issues: the scarcity of instruments capable of measuring such emissions, and absorption by the interstellar medium. Currently, the most effective instruments available to the astronomical community are the Hubble Space Telescope in the UV band and the NASA Chandra and ESA XMM-Newton satellites in X-rays—each with more than 30 years of service.

A research team led by astrophysicist A. Maggio (INAF – Astronomical Observatory of Palermo) tackled this problem by analyzing observations of a large sample of FGK (Sun-like) and M (low-mass) stars obtained with these instruments. The aim of the study was to quantify the amount of plasma at temperatures between 10000 and 30 million K—known as the emission measure—as a function of X-ray emission, which traces the level of stellar magnetic activity. This was made possible through spectroscopic analyses, which isolate the contribution of highly ionized chemical elements, and through physical modeling of how X-ray emission varies with energy.

The authors obtained a grid of emission measure values for all the analyzed stars, finding that low-mass stars systematically show a smaller emission measure at low temperatures (below 100000 K) and a larger one at high temperatures (above 3 million K). Measurements of this kind are essential for understanding how high-energy stellar radiation can influence the evolution of planets and the circumstellar environment in stars of different types.

The study is described in the article “Empirical prediction of plasma emission measure distributions and X–EUV spectra of late-type stars”, published in The Astrophysical Journal.

The cover image shows an X-ray view from XMM-Newton of V1298 Tau, a young star hosting four planets and with a complex circumstellar environment.

"Giuseppe Salvatore Vaiana"

High temperature plasma in solar and low-mass stars. The study: “Empirical prediction of plasma emission measure distributions and X-EUV spectra of late-type stars” of A. Maggio (INAF-OAPA) recently appeared on The Astrophysical Journal

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