Shadows on the protoplanetary disk surrounding the young star HD 135344B

The HD 135344B system
The HD 135344B system

An article published in the magazine “The Astrophysical Journal” describes a research on the protoplanetary disk surrounding the star HD 135344B. A team led by Tomas Stolker of the ETH in Zurich, Switzerland, used the SPHERE instrument mounted on ESO’s VLT (Very Large Telescope) to monitor the evolution of that dust and gas disk and of the dark bands that appear as shadows projected on it. Probably there are processes in the disk’s inner area that cause shadows on its outer area.

The SPHERE (Spectro-Polarimetric High-contrast Exoplanet REsearch) instrument was activated in June 2014. It’s primarily an exoplanet hunter but can also be used to take direct pictures of protoplanetary disks around young stars in which new planets are forming.

The protoplanetary disk surrounding the star HD 135344B, about 450 light years from Earth, was already studied in the past, also with the SPHERE instrument by a team also led by Tomas Stolker, whose research was described in an article published about a year ago on the magazine “Astronomy and Astrophysics”. Those observations already showed changes in the dark bands that indicated a possible protoplanet formation processes so the studies continued.

Using the SPHERE instrument again, the researchers got new images over time of the protoplanetary disk surrounding the star HD 135344B, its spiral arm structure and dark bands. One or more protoplanets could have created that type of structure and in some millions of years may form one or more gas giants.

The observations concern a very short time in astronomical terms, yet they’re enough to notice variations, such as those in the brighness on the protoplanetary disk’s outer area. The image (courtesy Tomas Stolker / University of Amsterdam) shows a sequence of observations made on May 3, 2015, May 4, 2016, May 12, 2016, June 22, 2016, and June 30, 2016.

According to the researchers, the cause of the variations is due to the high speed with which gas and dust rotate around the star HD 135344B. There’s some ongoing process that is still unclear: it may be winds, swirls, or collisions of more or less large objects that have already formed inside the disk.

The HD 135344B system is constantly evolving, so the observations must continue to monitor the possible formation of planets in real time. The researchers still want to use the SPHERE instrument at a intervals of a few days and carry out photometric and spectroscopic observations at the same time in order to at least exclude some hypotheses.

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