Three elder sisters of the Sun with planets
by Staff Writers
Torun, Poland (SPX) Mar 03, 2021
An international team led by Prof. dr habil. Andrzej Niedzielski, an astronomer from the Nicolaus Copernicus University in Torun (Poland), has discovered yet another three extrasolar planets. These planets revolve around the stars that can be called elder sisters of our Sun.
You can read about the astronomers' success in Astronomy and Astrophysics. The prestigious European journal will publish the paper: Tracking Advanced Planetary Systems (TAPAS) with HARPS-N. VII. Elder suns with low-mass companions. Apart from Prof. Andrzej Niedzielski from the NCU Institute of Astronomy, the team which worked on the discovery includes Prof. dr habil. Gracjan Maciejewski, also from the NCU Faculty of Physics, Astronomy and Informatics, Prof. Aleksander Wolszczan (Pennsylvania State University), dr Eva Villaver (University of Madrid) as well as dr Monika Adamow and dr Kacper Kowalik (both from the University of Illinois).
Discoverers of planets
"The red giant is a star that has burnt out hydrogen in its interior as a result of nuclear reactions and is rebuilding its internal structure to ignite helium burning nuclear reactions" explains Prof. Niedzielski, "Such a star shrinks in its central part, where the temperature starts to rise. Its outer areas expand significantly and cool down. Initially a yellow star, like the Sun, becomes red and huge. Hence the name of this type of stars. These stars can reach a size comparable to that of Earth's orbit."
Sisters of the Sun
"These stars are red giants. They have masses exactly the same as our star, but they are a few billion years older, much bigger and cool" explains Prof. Niedzielski, "The planets that we have discovered are gas giants - without surfaces, similar to our Jupiter. They orbit far too close to their stars for conditions favourable for the origin of life to occur on them or in their vicinity"
Eldest sister: HD 4760
"A planet about 14 times more massive than Jupiter revolves around it. It is in an orbit similar in size to that of Earth around the Sun, at a distance of about 1.1 astronomical units. A year on this planet lasts 434 days" says Prof. Niedzielski.
The observations of the star that led to the discovery of the planet took 9 years. They were conducted first with the Hobby-Eberly telescope and the HRS spectrograph, then with the Galileo telescope and the Harps-N.
"The observations were so long because in the case of the search for planets near red giants it is necessary to study several periods of rotation of the star, which can reach hundreds of days+ - explains the astronomer from Toru, "The researchers must make sure that a planet is actually observed, and not a spot on the star's surface that pretends to be a planet.
Younger sisters: TYC 0434-04538-1 and HD 96992
"Interestingly, this planet orbits quite close to its star, at a distance of 0.66 astronomical units. In our Solar System it would be located between the orbits of Venus and Earth" explains Prof. Niedzielski, "A year on this gas planet lasts only 193 days. Observations of this star with both telescopes lasted 10 years. The third of the Sun's elder sisters, the HD 96992, is closest to us - "only" 1305 light years away. It is a star of the ninth magnitude in the Great Bear."
"This star, seven times bigger and almost 30 times more energetic than the Sun, has a planet with a mass only slightly bigger than that of Jupiter, in an orbit of 1.24 astronomical units. A year on this planet lasts 514 days," says Prof. Niedzielski.
This star has been observed with the use of two telescopes by astronomers for the longest time - 14 years.
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