November 7th, 2024
A COBREX article named ” The COBREX archival survey: Improved constraints on the occurrence rate of wide-orbit substellar companions - I. A uniform re-analysis of 400 stars from the GPIES survey” and led by Vito Squicciarini, a postdoctoral researcher at the Observatory of Paris, is now published in Astronomy & Astrophysics.
One of the main goals of COBREX was the complete re-analysis, performed in a uniform way, of thousand of archival high-contrast imaging observations obtained from the SPHERE (Spectro-Polarimetric High-contrast Exoplanet REsearch) instrument installed at the VLT and the GPI (Gemini Planet Imager) instrument installed at Gemini South. Over the last ten years, SPHERE and GPI have provided the exoplanet community with the two largest direct imaging campaigns looking for wide giant exoplanets around young close-by stars: SHINE@SPHERE and GPIES@GPI. Thanks to PACO, a novel post-processing technique, COBREX had the unique potential to identify new companions that had previously escaped detection.
The paper describes the re-reduction of observations for 400 stars coming from the GPIES survey, the attained performances and the derived statistical constraints on the frequency of wide giant planets and brown dwarf companions to main sequence stars. Despite no new detection, a few candidates awaiting confirmation emerged.
The image shows a comparison of the occurrence frequency of giant planets obtained by our team, as compared to previous direct imaging studies of similar sample size. Owing to the large sensitivity gain compared to previous analyses, the new rates come with a much smaller uncertainty than previous GPI works – comparable to that of SPHERE works despite a much smaller instrumental field of view.
This study is a first step towards a full analysis of the COBREX sample, that will deliver the tightest constraints to planet formation models ever provided by direct imaging; this information will be, in turn, crucial in the context of the coveted combination of different detection techniques for the scope of understanding how planetary formation works at all scales and around all stars.
September 18th, 2023
The ESO website publishes a new "Picture of the Week" on one of the Cobrex team’s results
The image shows the HIP 81208 star system observed by the Very Large Telescope (VLT) in Chile. HIP 81208 was thought to be a multiple system made up of a massive star (A, the bright central spot), a brown dwarf (B) orbiting A, and a low-mass star (C) located a little further away. However, a new study reveals a new object never observed before: a component Cb orbiting C and about 15 times more massive than Jupiter.
The discovery of Cb means that HIP 81208 is a peculiar system with two stars and two low-mass bodies orbiting each of these stars, in other words a quadruple hierarchical system.
The mass of the new Cb component places it on the borderline between planets and brown dwarfs, "failed" stars that are not massive enough and not hot enough to fuse hydrogen into helium.
The Cb component was discovered by a team led by A. Chomez, a doctoral student at Paris Observatory, by re-analysing archive data from the SPHERE (Spectro-Polarimetric High-contrast Exoplanet REsearch) instrument installed at the VLT. While most instruments use indirect methods to hunt for exoplanets, SPHERE uses direct imaging. Here we see a true image of this multiple system. It is the first hierarchical quadruple system to be discovered by direct imaging, and represents proof of the complexity of exoplanetary systems.
Link to Picture of the Week https://www.eso.org/public/images/p...
Credit:
ESO/A. Chomez et al.