A detailed X-ray study of the HD 189733 binary system variability

(ORDO NEWS) — Astronomers observed the binary known as HD 189733 using the European Space Agency’s XMM-Newton satellite. The results of this observational campaign provide valuable information about the unusual X-ray variability of this binary star.

Located about 63 light-years from Earth, the HD 189733 system is a wide binary system consisting of two dwarfs of spectral types K1 (HD 189733 A) and M (HD 189733 B).

The primary and secondary components of the system have masses of 0.8 and 0.2 solar masses, respectively, while the orbital period of the system is about 3200 years.

It is known that in orbit around the star HD 189733 A, a swollen and actively evaporating exoplanet of the hot Jupiter class circulates, making one revolution around the parent star within 2.2 days.

A detailed study of the X-ray spectrum of a binary system and its changes over time, for example, due to flare activity, provides valuable information about the formation and evolution of binary systems.

In the new work, a team led by Ignazio Pillitteri of the Astronomical Observatory of Palermo, Italy, analyzed an 8-year archive of observations from the XMM-Newton X-ray space observatory to study the X-ray emission from the HD 189733 A source.

According to the authors, the total duration of flares on the star HD 189733 A was 423,600 seconds out of a total of 958,000 seconds observed. It was found that the number of flares observed during the time the planet is outside the disk of the star does not differ statistically from the number of flares during transit periods.

The researchers also found that the average corona temperature of the star HD 189733 A is about 0.4 kiloelectronvolts (keV). During flares, the temperature of the star rises to 0.9 keV; however, the corona remains relatively cold, even during the most energetic flares.

Moreover, astronomers have found that, in general, the nature of changes in the brightness of the star HD 189733 A in the X-ray range differs sharply from the optical range.

To explain these differences, the authors proposed a hypothesis about the relationship between brightness changes and the transfer of angular momentum from the exoplanet to the parent star.

“We believe that the sharp differences between the activity of the star in the optical and X-ray ranges, as well as relatively cold outbursts, can be explained by the transfer of angular momentum from the planet to the parent star and the influence of such transfer on the magnetic dynamo mechanism that forms the stellar corona.

Moreover, the magnetic interaction between the star and the planet may be responsible for the formation of a significant part of the observed X-ray emission and its changes, ”the researchers conclude.


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