A young and low-density planet for DS Tucanae A. The study: “Constraints on the mass and atmospheric composition and evolution of the low-density young planet DS Tuc A b” of S. Benatti (INAF – OAPa) recently appeared on A&A

The study of planets orbiting around young stars (younger than 100 million years) can help astronomers understanding the physical processes setting the early evolution of planetary systems. However, young stars are typically characterized by rapid rotation and intense magnetic activity, phenomena which produce photometric and spectroscopic signals that can mimic and confuse those due to the presence of planets. It is thus quite difficult to discover and characterize planets around young stars.

 

The intense magnetic activity in young stars also produces a high level of emission in X-rays and UV bands. This radiation can seriously impact the atmospheres of planets, especially those orbiting close to the parent star. Young planets have in fact primordial atmospheres which are mainly constituted by hydrogen. The stellar energetic radiation dissociate and ionize the molecules in the gas, and thus it deposits a large amount of energy in the atmospheric layers. Under these conditions, the atmospheres inflate and evaporate, which affects both the main planetary properties (such as mass and radius) and their entire evolution.

 

One of the few young planets discovered so far orbits around the star DS Tuc A, which is the main component of a binary system 40 million years old, member of the stellar association Tucana-Horologium. The team led by the astronomer S. Benatti (INAF – Astronomical Observatory of Palermo) has analyzed data acquired with the optical spectrographs HARPS and ESPRESSO of the European Southern Observatory in order to better determine the mass of this planet. Despite the intense magnetic activity of the star, it was possible to estimate a mass upper limit of 14.4 Earth masses. Thanks to spectroscopic data acquired during a transit, the authors have studied the orbit of the planet, which is not perfectly aligned. In principle, these observations would have allowed the authors also to study the chemical composition of the atmosphere, ma the intense magnetic activity of the star hampered this possibility. The authors have also analyzed X-ray observations of the binary system acquired with the satellite XMM-Newton of the European Space Agency, achieving to estimate the X-ray luminosity of DS Tuc A (9.57×1029 erg s−1). Thanks to these results, and by applying models describing the evaporating atmosphere of the planet, it was possible to demonstrate that  about 10% of the entire mass of the planet will evaporate by the end of the process, reducing its radius by a factor of about three. The study is describer in the paper “Constraints on the mass and atmospheric composition and evolution of the low-density young planet DS Tuc A b“, recently appeared on Astronomy & Astrophysics.

 

The figure (click here to visualize the entire figure) shows the X-ray image of DS Tuc acquired with the instrument MOS1 on board of XMM-Newton. The binary system is only partially resolved. The position of the two stars according to the SIMBAD database is marked with the red crosses. The small offset with respect the X-ray emission contours (shown in light blue) is due to the proper motion of the system. The circles have a radius of 30 arcsec (purple) and 10 arcsec (yellow).

 

Mario Giuseppe Guarcello  ( follow mguarce) ( youtube)

 

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