According to the most widely accepted theory, planetary systems form from large clouds of dust and gas that form disks around young stars. Over time, these disks accumulate to create planets of varying size, composition, and distance from their parent star. In recent decades, mid- and far-infrared observations have led to the discovery of debris disks around young stars (less than 100 million years old). This allowed astronomers to study planetary systems early in their history, providing new insight into how systems form and evolve.
This includes the SpHere INfrared Survey for Exoplanets (SHINE) consortium, an international team of astronomers dedicated to the study of star systems in formation. Using ESO’s Very Large Telescope (VLT), the SHINE collaboration recently directly imaged 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 detect a gas giant several times the size of Jupiter (a “Super-Jupiter”) embedded in the disk.
The SHINE team was led 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 article describing their findings recently appeared in the journal Astronomy & Astrophysics.
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As they state in their paper, the team relied on the VLT’s Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument to take optical and near-IR images of HD 114082, a star type F (a yellow-white dwarf) located in the Scorpius-Centaurus association – a star cluster located approximately 310 light-years from Earth. Like the 500 stars surveyed by the SHINE team, HD 114082 is a young star surrounded by a disk of protoplanetary debris (from which planets form). Observations of these disks over the past few decades have shown that they are an integral part of planetary systems:
As Dr. Engler told Universe Today via email, these investigations date back to 1983 and the discovery of the first disc around Vega. Since then, dozens of readings have been made in infrared wavelengths and scattered light using space telescopes like the Herschel Space Observatory and the venerable Hubble and ground-based telescopes like the Atacama Large Millimeter-submillimeter Array (ALMA), Gemini Planet Imager (GMI), and SPHERE/VLT. As she explained:
“These studies have provided valuable insight into the formation and evolution of planetary systems since planets are formed from, reside in, and interact with dust material. Young debris disks (during the first hundred million years) trace the formation processes of the terrestrial planets, and thus studying them helps us to understand the dynamic interaction and evolution of the terrestrial planets, in particular the Earth, in the young solar system.
Using Sphere, Engler and his team observed HD 114082 in optical and near-infrared using Angular Differential Imaging (ADI) and Polarimetric Differential Imaging (PDI) techniques. The first is to acquire high-contrast images from an altitude-azimuth telescope while the instrument’s rotator is turned off, allowing the instrument and telescope optics to remain aligned and in field vision to rotate relative to the instrument. The latter consists of combining different incident polarizations of light and measuring the specific polarization components transmitted or scattered by the object.
Both techniques have been used extensively in the study of circumstellar debris disks and (according to Engler) revealed some interesting things about HD 114082:
“Our images revealed a bright planetesimal belt at a distance of 35 AU from the host star, very similar to the Kuiper belt in the solar system. The debris belt is tilted at 83° and has a large internal cavity. dust particles, which we trace in this observation, have sizes around 5 microns and a relatively high scattering albedo of 0.65; this means that they scatter nearly two-thirds of the incoming stellar radiation and only absorb it. The scattered light has a relatively low degree of linear polarization with a maximum of 17%, which is however comparable to the polarization values of cometary dust in the solar system.
The team also consulted data from TESS to confirm the presence of a super-Jupiter companion, which was first detected by the observatory in 2021 using transit photometry (aka the method of transit). Consistent with this data, Engler and his colleagues confirmed that the planet orbits its parent star at around 0.7 AU, roughly the same distance between Venus and the Sun. Recent observations based on radial velocity measurements have confirmed this planet and produced mass estimates about eight times that of Jupiter.
“HD 114082 provides an example for young planetary systems, where the presence of planetary companions to the host star has been inferred from the discovery of a debris disk,” Engler added. “This confirms theoretical considerations about debris systems as beacons for young planets. The study of this system and other similar planetary systems will allow [astronomers] relate the properties of extrasolar Kuiper belts to the planets residing there.
The implications of this study go beyond the study of young stars and planetary systems still in formation. They are also important for the study of our solar system, which has interesting parallels with these protoplanetary environments. Said Engler:
“Direct imaging studies over the past decade show that the circumstellar material of many debris disks is confined to ring-like structures, similar to two Solar System debris belts: the Edgeworth-Kuiper Belt and the main asteroid belt.The cavities inside the extrasolar Kuiper belts are curved by invisible planets, which leave their imprints in the dust distribution of debris, such as deformations, clusters and eccentricities of the belt.
Finally, this study demonstrates the increasing use and effectiveness of direct imaging studies, made possible by improved instruments, imaging capabilities, and data sharing methods. In the near future, next-generation instruments will enable even more precise and detailed direct imaging studies. These include space observatories such as the JWST and the Nancy Grace Roman Space Telescope and ground-based telescopes like the Extremely Large Telescope (ELT), the Giant Magellan Telescope, and the Thirty Meter Telescope (TMT).
By studying the geometry and asymmetric characteristics of debris disks, astronomers can predict the location and masses of planets 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 the composition, shape and size of particles, and thus we can better understand the composition of the building blocks of exoplanets.”
Further reading: arXiv
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