Rogue's gallery of dusty star systems reveals exoplanet nurseries
Systematic survey of 104 nearby stars turns up 25 dust disks with
evidence of planets

Date:
June 24, 2020
Source:
University of California - Berkeley
Summary:
The Gemini Planet Imager on the Gemini South telescope looked at
104 young, nearby stars, 10-100 million years old, in search of
debris disks.

It found 26, 25 of which had inner holes indicating a planet. These
debris rings, similar to the Kuiper Belt in our solar system,
display amazing diversity in size and distance from the star. Such
studies help astronomers understand the formation of planets and
shed light on our system's early history.



FULL STORY ========================================================================== Astronomers this month released the largest collection of sharp, detailed images of debris disks around young stars, showcasing the great variety
of shapes and sizes of stellar systems during their prime planet-forming
years.

Surprisingly, nearly all showed evidence of planets.


==========================================================================
The images were obtained over a period of four years by a precision
instrument, the Gemini Planet Imager (GPI), mounted on the 8-meter Gemini
South telescope in Chile. The GPI uses a state-of-the-art adaptive optics system to remove atmospheric blur, providing the sharpest images to date
of many of these disks.

Ground-based instruments like GPI, which is being upgraded to conduct
similar observations in the northern sky from the Gemini North Telescope
in Hawaii, can be a way to screen stars with suspected debris disks to determine which are worth targeting by more powerful, but expensive,
telescopes to find planets - - in particular, habitable planets. Several
20-, 30- and 40-meter telescopes, such as the Giant Magellan Telescope
and the Extremely Large Telescope, will come online in the next couple
of decades, while the orbiting James Webb Space Telescope is expected
to be launched in 2021.

"It is often easier to detect the dust-filled disk than the planets, so
you detect the dust first and then you know to point your James Webb Space Telescope or your Nancy Grace Roman Space Telescope at those systems,
cutting down the number of stars you have to sift through to find these
planets in the first place," said Tom Esposito, a postdoctoral fellow
at the University of California, Berkeley.

Esposito is first author of a paper describing the results that appeared
June 15 in The Astronomical Journal.

Comet belts around other stars The debris disks in the images are the equivalent of the Kuiper Belt in our solar system, a frigid realm about
40 times farther from the sun than Earth - - beyond the orbit of Neptune
-- and full of rocks, dust and ice that never became part of any planet
in our solar system. Comets from the belt -- balls of ice and rock -- periodically sweep through the inner solar system, occasionally wreaking
havoc on Earth, but also delivering life-related materials like water,
carbon and oxygen.



==========================================================================
Of the 26 images of debris disks obtained by the Gemini Planet Imager
(GPI), 25 had "holes" around the central star that likely were created
by planets sweeping up rocks and dust. Seven of the 26 were previously
unknown; earlier images of the other 19 were not as sharp as those from
GPI and often didn't have the resolution to detect an inner hole. The
survey doubles the number of debris disks imaged at such high resolution.

"One of the things we found is that these so-called disks are really
rings with inner clearings," said Esposito, who is also a researcher
at the SETI Institute in Mountain View, California. "GPI had a clear
view of the inner regions close to the star, whereas in the past,
observations by the Hubble Space Telescope and older instruments from the ground couldn't see close enough to the star to see the hole around it."
The GPI incorporates a coronagraph that blocks the light from the star, allowing it to see as close as one astronomical unit (AU) from the star,
or the distance of the Earth from our sun: 93 million miles.

The GPI targeted 104 stars that were unusually bright in infrared light, indicating they were surrounded by debris reflecting the light of the star
or warmed by the star. The instrument recorded polarized near-infrared
light scattered by small dust particles, about a thousandth of a
millimeter (1 micron) in size, likely the result of collisions among
larger rocks in a debris disk.

"There has been no systematic survey of young debris disks nearly this
large, looking with the same instrument, using the same observing modes
and methods," Esposito said. "We detected these 26 debris disks with very consistent data quality, where we can really compare the observations, something that is unique in terms of debris disk surveys." The seven
debris disks never before imaged in this manner were among 13 disks
around stars moving together though the Milky Way, members of a group
called the Scorpius-Centaurus stellar association, which is located
between 100 and 140 parsecs from Earth, or some 400 light years.



==========================================================================
"It is like the perfect fishing spot; our success rate was much greater
than anything else we have ever done," said Paul Kalas, a UC Berkeley
adjunct professor of astronomy who is second author of the paper. Because
all seven are around stars that were born in the same region at roughly
the same time, "that group itself is a mini-laboratory where we can
compare and contrast the architectures of many planetary nurseries
developing simultaneously under a range of conditions, something that
we really didn't have before," Esposito added.

Of the 104 stars observed, 75 had no disk of a size or density that GPI
could detect, though they may well be surrounded by debris left over
from planet formation. Three other stars were observed to host disks
belonging to the earlier "protoplanetary" phase of evolution.

What did our solar system look like in its infancy? The extent of the
debris disks varied widely, but most ranged between 20 and 100 AU. These
were around stars that ranged in age from tens of millions of years to
a few hundred million years, a very dynamic period for the evolution of planets. Most were larger and brighter than the sun.

The one star, HD 156623, that did not have a hole in the center of
the debris disk was one of the youngest in the group, which fits with
theories of how planets form. Initially, the protoplanetary disk should
be relatively uniform, but as the system ages, planets form and sweep
out the inner part of the disk.

"When we look at younger circumstellar disks, like protoplanetary disks
that are in an earlier phase of evolution, when planets are forming, or
before planets have started to form, there is a lot of gas and dust in
the areas where we find these holes in the older debris disks," Esposito
said. "Something has removed that material over time, and one of the ways
you can do that is with planets." Because polarized light from debris
disks can theoretically tell astronomers the composition of the dust,
Esposito is hoping to refine models to predict the composition -- in particular, to detect water, which is thought to be a condition for life.

Studies like these could help answer a lingering question about our own
solar system, Kalas said.

"If you dial back the clock for our own solar system by 4.5 billion years, which one of these disks were we? Were we a narrow ring, or were we a
fuzzy blob?" he said. "It would be great to know what we looked like
back then to understand our own origins. That is the great unanswered question."

========================================================================== Story Source: Materials provided by
University_of_California_-_Berkeley. Original written by Robert
Sanders. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Thomas M. Esposito, Paul Kalas, Michael P. Fitzgerald, Maxwell
A. Millar-
Blanchaer, Gaspard Duche^ne, Jennifer Patience, Justin Hom,
Marshall D.

Perrin, Robert J. De Rosa, Eugene Chiang, Ian Czekala, Bruce
Macintosh, James R. Graham, Megan Ansdell, Pauline Arriaga,
Sebastian Bruzzone, Joanna Bulger, Christine H. Chen, Tara Cotten,
Ruobing Dong, Zachary H.

Draper, Katherine B. Follette, Li-Wei Hung, Ronald Lopez, Brenda C.

Matthews, Johan Mazoyer, Stan Metchev, Julien Rameau, Bin Ren,
Malena Rice, Inseok Song, Kevin Stahl, Jason Wang, Schuyler
Wolff, Ben Zuckerman, S. Mark Ammons, Vanessa P. Bailey, Travis
Barman, Jeffrey Chilcote, Rene Doyon, Benjamin L. Gerard,
Stephen J. Goodsell, Alexandra Z. Greenbaum, Pascale Hibon,
Sasha Hinkley, Patrick Ingraham, Quinn Konopacky, Je'ro^me Maire,
Franck Marchis, Mark S. Marley, Christian Marois, Eric L. Nielsen,
Rebecca Oppenheimer, David Palmer, Lisa Poyneer, Laurent Pueyo,
Abhijith Rajan, Fredrik T. Rantakyro", Jean-Baptiste Ruffio,
Dmitry Savransky, Adam C. Schneider, Anand Sivaramakrishnan,
Re'mi Soummer, Sandrine Thomas, Kimberly Ward-Duong. Debris
Disk Results from the Gemini Planet Imager Exoplanet Survey's
Polarimetric Imaging Campaign. The Astronomical Journal, 2020;
160 (1): 24 DOI: 10.3847/1538- 3881/ab9199 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200624151553.htm

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