New Direct Images Captured with W. M. Keck Observatory’s Upgraded Adaptive Optics System Lead to First Independent Confirmation of PDS 70 Protoplanets

Maunakea, Hawaii – New evidence shows the first-ever pictures capturing the birth of a pair of planets orbiting the star PDS 70 are in fact authentic.

Using a new infrared pyramid wavefront sensor for adaptive optics (AO) correction at W. M. Keck Observatory on Maunakea in Hawaii, a Caltech-led team of astronomers applied a new method of taking family photos of the baby planets, or protoplanets, and confirmed their existence.

The team’s results are published in today’s issue of The Astronomical Journal.

PDS 70 is the first known multiplanetary system where astronomers can witness planet formation in action. The first direct image of one of its planets, PDS 70b, was taken in 2018 followed by multiple images taken at different wavelengths of its sibling, PDS 70c, in 2019. Both Jupiter-like protoplanets were discovered by the European Southern Observatory’s Very Large Telescope (VLT).

“There was some confusion when the two protoplanets were first imaged,” said Jason Wang, a Heising-Simons Foundation 51 Pegasi b Fellow at Caltech and lead author of the study. “Planet embryos form from a disk of dust and gas surrounding a newborn star. This circumstellar material accretes onto the protoplanet, creating a kind of smokescreen that makes it difficult to differentiate the dusty, gaseous disk from the developing planet in an image.”

To help provide clarity, Wang and his team developed a method to disentangle the image signals from the circumstellar disk and the protoplanets.

“We know the disk’s shape should be a symmetrical ring around the star whereas a planet should be a single point in the image,” said Wang. “So even if a planet appears to sit on top of the disk, which is the case with PDS 70c, based on our knowledge of how the disk looks throughout the whole image, we can infer how bright the disk should be at the location of the protoplanet and remove the disk signal. All that’s left over is the planet’s emission.”

Artist’s impression of the PDS 70 system. The two planets are seen clearing a gap in the protoplanetary disk from which they were born. The planets are heated by infalling material that they are actively accreting and are glowing red. Note that the planets and star are not to scale and would be much smaller in size compared to their relative separations. Image Credit: W. M. Keck Observatory/Adam Makarenko

The team snapped images of PDS 70 with the Near-Infrared Camera (NIRC2) on the Keck II telescope, marking first science for a vortex coronagraph installed in NIRC2 as part of a recent upgrade, combined with the Observatory’s upgraded AO system consisting of a new infrared pyramid wavefront sensor and real-time control computer.

“The new infrared detector technology used in our pyramid wavefront sensor has dramatically improved our ability to study exoplanets, especially those around low-mass stars where planet formation is actively occurring,” said Sylvain Cetre, software engineer at Keck Observatory and one of the lead developers of the AO upgrade. “It will also allow us to improve the quality of our AO correction for harder to image targets like the center of our galaxy.”

This project benefited from the innovative infrared sensor that measures distortions in light caused by the Earth’s atmosphere.

“New technology is a science multiplier,” says Peter Kurczynski, program director at the National Science Foundation, which contributed funding to this project. “It enables investigations that were never before possible.”

AO is a technique used to remove the atmospheric blurring that distorts astronomical images. With the new infrared pyramid wavefront sensor and real-time controller installed, Keck Observatory’s AO system is able to deliver sharper, more detailed images.

“The PDS 70 imagery Jason’s team captured was among the first tests of the scientific quality produced by Keck’s pyramid wavefront sensor,” said AO scientist Charlotte Bond, who played a key role in the design and installation of the technology. “It’s exciting to see just how precise the new AO system corrects for the atmospheric turbulence of dusty objects like the young stars where protoplanets are expected to reside, allowing for the clearest, sharpest view of baby versions of our solar system.”  

The W. M. Keck Observatory Adaptive Optics Near-Infrared Pyramid Wavefront Sensor development was supported by a grant from the National Science Foundation Advanced Telescopes and Instrumentation program and conducted in collaboration with the University of Hawaii and Caltech, as well as colleages from the Subaru Telescope, Arcetri Astrophysical Observatory, and the Laboratoire d’Astrophysique de Marseille.

ABOUT ADAPTIVE OPTICS

 W. M. Keck Observatory is a distinguished leader in the field of adaptive optics (AO), a breakthrough technology that removes the distortions caused by the turbulence in the Earth’s atmosphere. Keck Observatory pioneered the astronomical use of both natural guide star (NGS) and laser guide star adaptive optics (LGS AO) and current systems now deliver images three to four times sharper than the Hubble Space Telescope. Keck AO has imaged the four massive planets orbiting the star HR8799, measured the mass of the giant black hole at the center of our Milky Way Galaxy, discovered new supernovae in distant galaxies, and identified the specific stars that were their progenitors.

The original Keck II AO system was built with funding from the W. M. Keck Foundation and NASA. The new RTC will build on a laser guide star facility upgrade completed in 2016 with the generous financial support of the Gordon and Betty Moore Foundation, W. M. Keck Foundation, the National Science Foundation, and other Friends of Keck including The Bob and Renee Parsons Foundation, Change Happens Foundation, Mt. Cuba Astronomical Foundation, and Sanford and Jeanne Robertson.

ABOUT NIRC2

The Near-Infrared Camera, second generation (NIRC2) works in combination with the Keck II adaptive optics system to obtain very sharp images at near-infrared wavelengths, achieving spatial resolutions comparable to or better than those achieved by the Hubble Space Telescope at optical wavelengths. NIRC2 is probably best known for helping to provide definitive proof of a central massive black hole at the center of our galaxy. Astronomers also use NIRC2 to map surface features of solar system bodies, detect planets orbiting other stars, and study detailed morphology of distant galaxies.

ABOUT W. M. KECK OBSERVATORY

The W. M. Keck Observatory telescopes are among the most scientifically productive on Earth. The two, 10-meter optical/infrared telescopes on the summit of Maunakea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometers, and world-leading laser guide star adaptive optics systems. Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c) 3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community.  We are most fortunate to have the opportunity to conduct observations from this mountain.

Quelle: Keck Observatory