According to the most widely held theory, planetary systems form from large clouds of dust and gas forming disks around young stars. Over time, these disks accumulate, forming planets of varying sizes, compositions, and distances from their parent star. Over the past few decades, observations in the mid- and far-infrared have led to the discovery of debris disks around young stars (less than 100 million years old). This has allowed astronomers to study planetary systems throughout their early history and gain new insights into the formation and evolution of systems.
These include the SpHere INfrared Survey for Exoplanets (SHINE) consortium, an international team of astronomers dedicated to studying stellar systems in formation. Using ESO’s Very Large Telescope (VLT), the SHINE collaboration recently observed and characterized the debris disk of a nearby star (HD 114082) in visible and infrared wavelengths. Combined with data from NASA’s Transiting Exoplanet Space Satellite (TESS), they were able to directly image a gas giant many times the size of Jupiter (a “super Jupiter”) embedded in the disk.
The SHINE team was founded by Dr. Natalia Engler from the Institute for Particle Physics and Astrophysics (IPA) at ETH Zurich. She was joined by astronomers from the European Southern Observatory (ESO), the Space Telescope Science Institute (STScI), the Max Planck Institute for Astronomy, the Academia Sinica Institute of Astronomy and Astrophysics, and several observatories and universities. The paper describing their findings is scheduled to appear in the journal Astronomy & Astrophysics and currently available on the arXiv preprint server.
As they state in their publication, the team relied on the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument at the VLT to acquire optical and near-IR images of HD 114082, an F-type star (a yellow -white dwarf) ) in the Scorpius-Centaurus Association – a star cluster located about 310 light-years from Earth. Like the 500 stars studied by the SHINE team, HD 114082 is a young star surrounded by a protoplanetary debris disk (from which planets form). Observations of these disks over the last few decades have shown that they are an integral part of planetary systems:
like dr Engler emailed Universe Today, these polls date back to 1983 and the discovery of the first hard drive around Vega. Since then, dozens of investigations into infrared wavelengths and scattered light have been conducted using space-based telescopes such as the Herschel Space Observatory and the venerable Hubble, and ground-based telescopes such as the Atacama Large Millimeter-Submillimeter Array (ALMA), the Gemini Planet Imager (GMI) and SPHERE/VLT. As she explained:
“These studies provided valuable information about the formation and evolution of planetary systems, as planets are formed from, live within, and interact with dusty material. Young debris discs (first hundred million years) trace the processes of terrestrial planet formation, and therefore their study helps us to understand the dynamic interaction and evolution of terrestrial planets, especially Earth, in the young solar system.”
Using Sphere, Engler and her team observed HD 114082 in the optical and near-infrared using angular differential imaging (ADI) and polarimetric differential imaging (PDI) techniques. The former consists of acquiring high-contrast images from an altitude-azimuth telescope while the instrument rotator is turned off, which allows the instrument and the telescope’s optics to remain aligned and allows the field of view to rotate relative to the instrument. The latter involves combining different incident light polarizations and measuring the specific polarization components transmitted or scattered by the object.
Both techniques have been used extensively in studying circumstellar debris disks, and revealed (according to Engler) some interesting things about HD 114082:
“Our images revealed a bright planetesimal belt at a distance of 35 AU from the parent star, which is very similar to the Kuiper belt in the solar system. The debris belt is inclined at 83° and has a wide internal cavity. The dust particles we track in this observation have sizes around 5 micrometers and a relatively high scattering albedo of 0.65; this means that they scatter nearly two-thirds of the incoming stellar radiation and absorb only a third of it. The scattered light has a relatively low degree of polarization linearity, at a maximum of 17%, but this is comparable to the polarization values for cometary dust in the Solar System.”
The team also consulted data from TESS to confirm the presence of a Super Jupiter companion, first detected by the observatory in 2021 using transit photometry (also known as the transit method). Consistent with this data, Engler and her colleagues confirmed that the planet orbits its parent star at about 0.7 AU – about the same distance between Venus and the Sun. Recent observations based on radial velocity measurements confirmed this planet and gave mass estimates of about eight times that of Jupiter.
“HD 114082 is an example of young planetary systems where the presence of planetary companions of the host star has been inferred from the discovery of a debris disk,” Engler added. “This confirms the theoretical considerations on debris systems as signposts for young planets. The study of this and other similar planetary systems will make it possible [astronomers] to establish a connection between the properties of extrasolar Kuiper belts and the planets living in them.”
The implications of this study go beyond the study of young stars and planetary systems that are still forming. They are also relevant to the study of our solar system, which shows some interesting parallels with these protoplanetary environments.
Engler said: “The direct imaging studies of the last decade show that the circumstellar material in many debris disks is confined to ring-like structures, similar to two debris belts in the Solar System: the Edgeworth-Kuiper belt and the main asteroid belt. The voids within the extrasolar Kuiper Belts are curved by invisible planets that leave their mark on the debris distribution, such as faults, clumps, and belt eccentricities.”
Finally, this study demonstrates the growing use and effectiveness of direct imaging studies, made possible by improved instrumentation, imaging capabilities, and data-sharing methods. In the near future, next-generation instruments will allow even more accurate and detailed direct studies of the imagination. These include space-based observatories such as the JWST and the Roman Nancy Grace Space Telescope, and ground-based telescopes such as the Extremely Large Telescope (ELT), the Giant Magellan Telescope and the Thirty Meter Telescope (TMT).
By studying the geometry and asymmetric features in debris disks, astronomers can predict the positions and masses of planets that are not yet detectable with current instruments. “Direct imaging makes it possible to study the scattering properties of dust particles around distant stars,” Engler added. “These properties contain information about particle composition, shape and size, and so we can gain insight into the composition of the building blocks of exoplanets.”
N. Engler et al., The high-albedo, low-polarization disk around HD 114082, harboring a Jupiter-sized transiting planet, arXiv (2022). DOI: 10.48550/arxiv.2211.11767
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