Constrained Reference Star Differential Imaging: Enabling High-fidelity Imagery of Highly Structured Circumstellar Disks ^*

Abstract

High-contrast imaging presents us with the opportunity to study circumstellar disks and the planets still embedded within them, providing key insights into the formation and evolution of planetary systems. However, the postprocessing techniques that are often needed to suppress stellar halo light typically result in significant and variable loss of circumstellar light, even when using relatively conservative approaches like reference star differential imaging (RDI). We introduce “constrained reference star differential imaging” (constrained RDI), a new class of RDI point-spread-function (PSF) subtraction techniques for systems with circumstellar disks. Constrained RDI utilizes either high-resolution polarized-intensity (PI) images or disk models to severely limit or even eliminate the signal loss due to oversubtraction that is common to RDI. We demonstrate the ability of constrained RDI utilizing polarimetric data to yield an oversubtraction-free detection of the AB Aurigae protoplanetary disk in total intensity. PI-constrained RDI allows us to decisively recover the spectral signature of the confirmed, recently discovered protoplanet, AB Aurigae b. We further demonstrate that constrained RDI can be a powerful analysis tool for soon-to-be-acquired James Webb Space Telescope coronagraphic imaging of disks. In both cases, constrained RDI provides analysis-ready products that enable more detailed studies of disks and more robust verification of embedded exoplanets.

The Giant Accreting Protoplanet Survey (GAPlanetS)—Results from a 6 yr Campaign to Image Accreting Protoplanets

“…We also overplot an ellipse in Figure 11 at the edge of the imaged inner disk rim. While the LkCa 15 "c" and "d" candidates are coincident with the inner disk rim, the "b" candidate lies significantly inside of it and is less likely to be a scattered light artifact, though we note that disk signals at similar separation to planet candidates can influence extracted KL modes (Lawson et al 2022), and further vetting of this candidate is warranted.…”

JWST-TST High Contrast: Asymmetries, Dust Populations, and Hints of a Collision in the β Pictoris Disk with NIRCam and MIRI

“…This effect, known as "oversubtraction," varies both spatially and spectrally (e.g., Pueyo et al 2012;Betti et al 2022), and thus introduces significant barriers for disk studies. MCRDI (Lawson et al 2022) remedies this by suppressing the impact of circumstellar flux during construction of the stellar PSF model using a synthetic model of the circumstellar scene.…”

JWST/NIRCam Coronagraphy of the Young Planet-hosting Debris Disk AU Microscopii

“…To attain image products free of significant oversubtraction, we also carry out model-constrained RDI (MCRDI), as described in Lawson et al (2022), in which a model of the CSS is optimized alongside the model of the starlight. By subtracting the CSS estimate from the data during optimization of the stellar model, the contribution to the stellar model resulting from the projection of the underlying disk signal onto the reference images (or reference eigenimages, in the case of KLIP), the cause of RDI oversubtraction, can be eliminated.…”

“…For a LOCI or KLIP reduction that does not account for the presence of the disk, simply forward modeling point sources would not be appropriate for assessing the faintest recoverable companions. If not suppressed, the disk will serve to significantly reduce the throughput circumstellar flux throughout the field of view (FOV)-including that of any companions (e.g., Lawson et al 2022). To accurately account for the effects of starlight subtraction using any technique in which the stellar model is optimized by comparison with the data itself or in which the target data are used to build the PSF model (e.g., any common technique besides classical RDI), the entire circumstellar scene must be considered holistically in forward modeling.…”

“…That is, computing the RDI residuals after first subtracting the CSS estimate from the data; seeLawson et al (2022) for more information regarding this equivalency.27 Because oversubtraction is entirely the result of the presence of the disk itself, the brightness of the forward-modeled result scales linearly with that of the input. For example, if I M ¢ is the forward-modeled result for an input disk model I M , then sI M ¢ will be the result for the input model sI M for any scalar constant s. The value of s producing the best fit can therefore be computed after forward modeling.…”