Using the Near-Infrared Camera (NIRC2) on the Keck II telescope at W. M. Keck Observatory on Maunakea in Hawaii, astronomers have directly imaged two infant gas giants PDS 70b and PDS 70c.
This image shows protoplanets PDS 70b and PDS 70c (labeled with white arrows) with the circumstellar disk removed. Image credit: J. Wang, Caltech.
PDS 70 is a K7-type pre-main sequence star located 370 light-years away in the constellation of Centaurus.
Also known as V* V1032 Cen and IRAS 14050-4109, the star is only 5.4 million years old.
It hosts two protoplanets, PDS 70b and c, and a circumstellar disk in which a large region from 20 to 40 AU is cleared of dust.
PDS 70b is located within the disk gap at a distance of about 21 AU from the star, similar to the orbit of Uranus in our Solar System. The planet has a mass of between 4 and 17 times that of Jupiter.
PDS 70c is located near the outer edge of the disk gap at 34.5 AU from the star, similar to Neptune’s distance from our Sun. It is less massive than PDS 70b, weighing between 1 and 10 times as much as Jupiter.
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 PDS 70c in 2019.
“There was some confusion when the two protoplanets were first imaged,” said Dr. Jason Wang, an astronomer in the Department of Astronomy at Caltech.
“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, Dr. Wang and colleagues 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,” Dr. Wang said.
“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.”
The study was published in the Astronomical Journal.
_____
Jason J. Wang et al. 2020. Keck/NIRC2 L’-band Imaging of Jovian-mass Accreting Protoplanets around PDS 70. AJ 159, 263; doi: 10.3847/1538-3881/ab8aef
