An amazingly wide variety of planet-forming disks

New images from the SPHERE instrument on ESO’s Very Large
Telescope are revealing the dusty discs surrounding nearby
young stars in greater detail than previously achieved.
They show a bizarre variety of shapes, sizes and
structures, including the likely effects of planets still
in the process of forming. Credit: Photographs: ESO/H.
Avenhaus et al./DARTT-S collaboration

With an instrument at the Very Large Telescope in Chile
scientists of ETH Zurich observed planet-forming disks around
young stars similar to the sun 4,5 billion years ago.
Surprisingly, the disks are very different. The data will
help to shed more light on the formation processes of
planets.


An instrument, which was partially developed and built at ETH
Zurich, has now been particularly successful at studying new
born still surrounded by gas and dust. With
SPHERE (Spectro-Polarimetric High-contrast Exoplanet REsearch)
at the European Southern Observatory (ESO), astronomers of ETH
Zurich and Max Planck Institute for Astronomy in Heidelberg
were able to take images of around the : these disks, called , exist around so-called
TTauri stars – the progenitors to our Sun – as well as around
the more massive siblings called Herbig Ae/Be stars. So far
astronomers focussed mostly on Herbig Ae/Be stars in their
studies, but with a new, ambitious program called DARTTS-S
(Disks Around TTauri Stars with SPHERE), Henning Avenhaus and
Sascha Quanz, former and current members of the NCCR PlanetS at
ETH Zurich, have now been able to use the capabilities of
SPHERE to undertake a survey of TTauri disks.

The results for the first eight stars are released in a paper
published by the Astronomical Journal. “Not only were we
able to clearly detect all eight disks,” summarizes Henning
Avenhaus, “but, surprisingly, they looked all very different in
particular with respect to their size.” While some of them
could only be detected with a radius of 80 au (80 times the
distance Sun-Earth and about twice the average distance
Sun-Pluto), others could be traced out to an astounding 700 au.
“Most of the disks were found to display rings, a phenomenon
known from previous observations of more massive stars,”
explains Sascha Quanz: “However, none of them displayed spiral
structures, which is a phenomenon seen regularly in Herbig
disks.” A key question is now to understand where this
difference is coming from and what it means for planet
formation around different types of stars.

Start on a bad footing

As successful as the project was, it started on a bad footing,
as Henning Avenhaus remembers: “While the first proposal to
undertake such observations was already written in March 2013
and highly rated (back then using the older NACO instrument),
unexpected works that had to be performed on the instrument
made it impossible to take data.” The same happened again in
September 2013. Again, the instrument was not available. A
third attempt in March 2014 did yield the requested
scheduling—in March 2015, when Henning Avenhaus flew to the
telescope just to find out that the instrument (still NACO) had
a malfunction the night before the observations were scheduled
to start. Not that it mattered: Wind and clouds made it
impossible to observe anyway.

At this point, the team decided to switch to the new
instrument—SPHERE—and got their first observations scheduled in
March 2016. This time, it worked: Both the and the weather were well-behaved, as
Henning Avenhaus remembers: “I was present at Cerro Paranal,
the location of the Very Large Telescope, working through the
nights to perform the observations and occasionally peaking out
of the control room to head to the telescope platform and
marvel at the impressive display of stars.”

The data taken over the course of several nights in March 2016
and in the following year were of very high quality. More than
five years after the idea for the program, the researchers are
now rewarded with results that will help to shed more light on
the formation processes for planets. “This high-quality dataset
impressively shows the power of SPHERE for these observations
and significantly increases the number of planetary nurseries
studied at high resolution enabling us to eventually get a
statistical grasp on planet formation,” summarizes Sascha
Quanz. Further results of the DARTTS-S programme and similar
observations with the ALMA radio telescope in Chile should
contribute to this.

Explore further:

SPHERE reveals fascinating zoo of discs around young stars

More information: Disks ARound TTauri Stars with Sphere
(DARTTS-S) I: Sphere / IRDIS Polarimetric Imaging of 8
prominent TTauri Disks: arxiv.org/abs/1803.10882v2

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