06.05.2016 change 06.05.2016

Twentieth planet discovered by a Polish team of astronomers

The list of twenty extrasolar planets discovered by Prof. Andrzej Niedzielski's team from the Nicolaus Copernicus University Centre for Astronomy. The horizontal axis shows the distance of the planets from their stars (in astronomical units, not to scale). The symbol sizes indicate the masses of the planets. Source: Nicolaus Copernicus University. The list of twenty extrasolar planets discovered by Prof. Andrzej Niedzielski's team from the Nicolaus Copernicus University Centre for Astronomy. The horizontal axis shows the distance of the planets from their stars (in astronomical units, not to scale). The symbol sizes indicate the masses of the planets. Source: Nicolaus Copernicus University.

International research group led by Prof. Andrzej Niedzielski of Nicolaus Copernicus University Centre for Astronomy announced the discovery of their twentieth planet on April 26. Toruń astronomers specialize in the studies of planets orbiting red giants, which are stars in the late stage of evolution, which the Sun will reach in a few billion years.

The latest object studied by the scientists is the red giant designated TYC 3667-1280-1. This star is six times larger in diameter than the Sun, and 30 times brighter. In the sky it can be seen in the constellation Cassiopeia, and its distance from Earth is 1600 light-years.

In turn, the planet TYC 3667-1280-1 b is five times more massive than Jupiter, but unlike the largest planet of the solar system it orbits its star in a very tight orbit. One loop around the star takes the planet only 26.5 days. If this planet were in the solar system, it would have a twice lower orbit than Mercury, which is the closest planet to the Sun.

Planets with masses several times larger than the mass of Jupiter, orbiting very close to their stars, are called "hot Jupiters" because of very high temperatures that prevail on those planets. In the case of the planet TYC 3667-1280-1 b, the temperature is 1,100 degrees Celsius.

The discovery is a reason for celebration for Prof. Niedzielski\'s team, because this is the twentieth planet discovered by the team. Astronomers use large Hobby-Eberly telescope (abbreviated name: HET) in Texas in the United States. The effective primary mirror aperture of the telescope is 9.2 meters.

This instrument was used to carry out observations that led to the discovery of all 20 planets. In addition, in the case of the five most recent discoveries, astronomers also used the 3.6-meter telescope of Galileo, on which one of the world\'s most precise spectrographs HARPS-N is mounted, allowing to measure radial velocities of stars with accuracy better than 1 m/sec.

Prof. Niedzielski\'s team discovers planets with spectroscopy, measuring the so-called radial velocity. When planetary system consists of both a star and a planet, they interact gravitationally. The planet orbits the star, but the planet\'s gravity causes the star to orbit the system\'s centre of mass. Typically, the difference between the masses of the star and the planet is so large that this point is located within the star. The result of this movement is a situation in which the star regularly moves a little closer and a little farther from Earth. This small movement can be measured with spectroscopy and the Doppler effect. This phenomenon is a shift of the light wave toward longer wavelengths (the red side of the spectrum) when the subject is moving away from us and towards shorter wavelengths (the blue side of the spectrum) when the star is moving closer. A good analogy is a change of engine sound or the sound of siren when a car or ambulance passes by.

In the spectrum of star there are visible lines corresponding to different elements. By measuring the shift of these lines scientists can calculate the amplitude of star movement in km/s, and then determine the minimum mass of the planet. If astronomers have only spectroscopic observations, they do not know the inclination of the orbital plane of the planet to our line of sight, so they can only determine the lower limit of the mass of the planet.

The members of the research team are: Prof. Andrzej Niedzielski (Nicolaus Copernicus University Centre for Astronomy), Prof. Aleksander Wolszczan (Pennsylvania State University, USA), Dr. Eva Villaver (Autonomous University of Madrid, Spain), Grzegorz Nowak (Institute of Astrophysics of the Canary Islands, Spain), Dr. Monika Adamów (Texas State University and the McDonald Observatory, USA, as well as the Nicolaus Copernicus University), Dr. Gracjan Maciejewski (Nicolaus Copernicus University Centre for Astronomy), Dr. Kacper Kowalik (National Center for Supercomputing Applications in Illinois, USA) and Dr. Beata Deka-Szymankiewicz and Michalina Adamczyk from the Nicolaus Copernicus University. Prof. Niedzielski\'s research is financed by the National Science Centre.

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