Shadows on the young binary system V4046 Sgr

The V4046 Sgr system (Image V. D’Orazi/Sphere/Inaf)
The V4046 Sgr system (Image V. D’Orazi/Sphere/Inaf)

An article published in the journal “Nature Astronomy” describes a study of the V4046 Sagittarii, or simply V4046 Sgr, binary system. A team of researchers led by Valentina D’Orazi of INAF, Padua, Italy, used the SPHERE instrument on ESO’s Very Large Telescope (VLT) to examine the rotating shadows projected on the protoplanetary disk that orbits the two young stars. The mapping of the shadows’ movements made it possible to better understand that system’s characteristics thanks to the motion of the two stars, which orbit each other in almost 2.5 days.

About 271 light years away from Earth, the V4046 Sgr system is very young, with an estimated age of about 20 million years. The two stars are at least for now both a little smaller and less massive than the Sun and, because of their young age, are variable in the sense that their brightness hasn’t yet reached stability so they’re classified in the T Tauri category.

Another consequence of the V4046 Sgr system’s young age is that the two stars are surrounded by a protoplanetary disk of dust and gas. Actually we already see a certain evolution within the disk with the presence of two rings distant from the stars about 14 and 29 times the distance of the Earth from the Sun. This suggests the formation of planets, perhaps gas giants, is underway, but one would expect it to be in a more advanced stage for its age. Perhaps the problem is in the presence of two stars and this hypothesis could stimulate more research.

For these reasons the V4046 Sgr system was already studied a number of times, recently also using the SPHERE (Spectro-Polarimetric High-contrast Exoplanet REsearch) instrument, activated in June 2014, mainly an exoplanet hunter but also useful in the study of very young systems. The results were described in an article published in April 2018 in the journal “Astronomy & Astrophysics” by a team led by Elena Sissa of INAF, Padua, who is also part of the team that carried out the new research on the shadows projected on V4046 Sgr’s protoplanetary disk.

The various observations of the V4046 Sgr system carried out using the SPHERE instrument highlighted the movements the shadows on the protoplanetary disk. This phenomenon is due to the nature of the system, in which there are two stars that periodically eclipse each other. The light of the two stars takes many minutes to reach the rings in the disk since they’re billions of kilometers away from them, a delay useful to measure the distance of the system.

These shadows, which are what was called a reverse lighthouse, have a depth linked to what’s called in jargon flaring angle, and to its thickness. Together with the measure of the distance, they’re independent ways to obtain data concerning a system of this type. The importance of this study is above all in this technique since having those measures allows to obtain better models of protoplanetary disks and consequently to improve our knowledge of the early phases of star systems’ evolution.

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