Reference-star differential imaging on SPHERE/IRDIS

Abstract

Context. Reference-star differential imaging (RDI) is a promising technique in high-contrast imaging that is thought to be more sensitive to exoplanets and disks than angular differential imaging (ADI) at short angular separations (i.e., <0.3 ). However, it is unknown whether the performance of RDI on ground-based instruments can be improved by using all the archival data to optimize the subtraction of stellar contributions. Aims. We characterize the performance of RDI on SPHERE/IRDIS data in direct imaging of exoplanets and disks. Methods. We made use of all the archival data in H23 obtained by SPHERE/IRDIS in the past five years to build a master reference library and perform RDI. To avoid biases caused by limited test targets under specific conditions, 32 targets were selected to obtain the average performances of RDI under different conditions, and we compared the performances with those of ADI. Results. In the point-source detection, RDI can outperform ADI at small angular separations (<0.4 ) if the observing conditions are around the median conditions of our master reference library. On average, RDI has a gain of ∼0.8 mag over ADI at 0.15 separation for observations under median conditions. We demonstrate that including more reference targets in the master reference library can indeed help to improve the performance of RDI. In disk imaging, RDI can reveal more disk features and provide a more robust recovery of the disk morphology. We resolve 33 disks in total intensity (19 planet-forming disks and 14 debris disks), and 4 of them can only be detected with RDI. Two disks are resolved in scattered light for the first time. Three disks are detected in total intensity for the first time. Conclusions. RDI is a promising imaging technique for ground-based instruments such as SPHERE. The master reference library we built in this work can be easily implemented into legacy or future SPHERE surveys to perform RDI, achieving better performance than that of ADI. To obtain optimal RDI gains over ADI, we recommend future observations be carried out under seeing conditions of 0.6 -0.8 .

Observations of circumstellar disks in scattered light with SPHERE at the VLT

“…The method was generalized later to using a set of reference stars, with for instance linear combinations of frames and Principal Component Analysis, which allowed to discover a few more disks left undetected in archival HST data [47,48]. On the ground, because of the atmospheric turbulence, but also due to the inevitable gravity related variations of the optical wavefront, RDI has been much less effective until recently [49]. However, advanced numerical techniques, like artificial intelligence, are now being deployed to tackle this challenge since the amount of data, hence potentially of reference frames, is just gigantic.…”

Planet search with the Keck/NIRC2 vortex coronagraph in the Ms band for Vega

“…3 of https://jwst-docs.stsci.edu/jwst-nearinfrared-camera/nircam-instrumentation/nircamcoronagraphic-occulting-masks-and-lyot-stops expected to yield the most thorough discovery of planets (e.g., Nielsen et al 2019;Fulton et al 2021). In fact, for the detection of far-separation planets, existing direct imaging surveys equipped with extreme AO systems have experienced a degradation of contrast close to the central sources (e.g., Nielsen et al 2019;Vigan et al 2021;Xie et al 2022). In comparison, for the detection of close-in planets, existing radial velocity surveys have less completeness for long period planets (e.g., Wittenmyer et al 2020;Fulton et al 2021).…”

Planet Search with the Keck/NIRC2 Vortex Coronagraph in Ms-band for Vega

“…2 https://www2.keck.hawaii.edu/inst/nirc2/filters.html 3 https://jwst-docs.stsci.edu/ jwst-near-infrared-camera/nircam-instrumentation/ nircam-filters 4 Fig. 3 of https://jwst-docs.stsci.edu/ jwst-near-infrared-camera/nircam-instrumentation/ nircam-coronagraphic-occulting-masks-and-lyot-stops 2019; Vigan et al 2021;Xie et al 2022). In comparison, for the detection of close-in planets, existing radial velocity surveys have less completeness for long orbital period planets (e.g., Wittenmyer et al 2020;Fulton et al 2021).…”