In our Scorpion Survey we are using the VLT/SPHERE extreme adaptive optics system – one of the most capable high-contrast imaging instruments in the world – to measure the occurrence rates of long-period jovian planets around intermediate-mass (A-type) stars. Scorpion has already led to three exciting discoveries, making it one of the most productive SPHERE surveys. Furthermore, it also led to the first SPHERE-discovered exoplanet!
About 99% of the known exoplanets have been discovered indirectly – their presence deduced only through the movement or dimming of their host stars. The atmospheres of most such planets are impossible or impractical to study directly. In contrast, directly imaged exoplanets can be studied via a plethora of methods – astrometry, photometry, spectroscopy, polarimetry – and thus, they provide goldmines for exoplanet scientists.
Intriguingly, as of now most of the directly imaged planets (on planet-like orbits) have been found to orbit intermediate-mass stars (A-type), raising the question whether they are intrinsically more common around slightly more massive stars than around sun-like stars.
The Scorpion Survey (PI: D. Apai) is a multi-semester survey of A-type stars located in the Upper Scorpio/Centaurus region. Our goal is to obtain sensitive, high-contrast images on at least ~70 young and co-eval A-type stars. Our team includes UA astronomy graduate student Kevin Wagner, who is leading the data reduction and planet candidate follow-up, and ESO Adaptive Optics Scientist Markus Kasper, an expert on the SPHERE instrument.
Scorpion has been extremely productive: although still underway, it already produced three exciting discoveries:
In a study published in Science and widely covered in the media, our team presented the discovery of a 3-4 Jupiter mass and about 850 K temperature gas giant exoplanet. This is the second lowest-mass and coolest planet imaged, which makes it an excellent benchmark object for exoplanet atmosphere studies. Even more intriguingly, the planet – HD131399Ab – orbits within a triple star system! This is a very unusual and unexpected dynamical configuration and, as the first planet discovered on such an orbit, it provides exciting insights into the formation of giant planets in multi-star systems and also demonstrates that such multi-star systems are promising hunting grounds for exoplanets! This discovery was led by Kevin Wagner, UA Astronomy graduate student and NSF Graduate Student Research Fellow.
This artist’s impression shows a view of the triple star system HD 131399 from close to the giant planet orbiting in the system. The planet is known as HD 131399Ab and appears at the lower-left of the picture. Located about 320 light-years from Earth in the constellation of Centaurus (The Centaur), HD 131399Ab is about 16 million years old, making it also one of the youngest exoplanets discovered to date, and one of very few directly-imaged planets. With a temperature of around 580 degrees Celsius and having an estimated mass of four Jupiter masses, it is also one of the coldest and least massive directly-imaged exoplanets.
Check out the Science paper. or check out the media coverage: CNN, The Guardian, History Channel, National Geographic, Spiegel, New York Times, Washington Post, Arizona Daily Star, USA Today, Forbes, Huffington Post, UA News,
Discovery of Two-armed Spiral Structure in a Planet-forming Disk
During our Scorpion Survey we also discovered a rare and spectacular two-armed spiral structure in a previously unresolved planet-forming disk. The structure seen here may be driven by a nearby red dwarf stellar companion, may be the induced by self-shadowing disk structures, or may be driven by giant planets forming in the interior of the disk. Follow-up observations with SPHERE and other instruments will allow us to disentangle these possibilities.
Discovery of a Debris Disk with Warped Disk Structure