A Multiband Study of the HR 4796A Disk in the Optical Using MagAO-X

Abstract We present total intensity images of the debris disk around HR 4796A from observations spanning 2023 to 2025 with the Magellan extreme adaptive optics instrument (MagAO-X). We detected the disk at high signal-to-noise ratios at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>g</mml:mi> <mml:mo accent="false">′</mml:mo> <mml:mspace width="1em"/> <mml:mo stretchy="false">(</mml:mo> <mml:mn>527</mml:mn> </mml:math> nm), <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>r</mml:mi> <mml:mo accent="false">′</mml:mo> <mml:mspace width="1em"/> <mml:mo stretchy="false">(</mml:mo> <mml:mn>615</mml:mn> </mml:math> nm), <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>i</mml:mi> <mml:mo accent="false">′</mml:mo> <mml:mspace width="1em"/> <mml:mo stretchy="false">(</mml:mo> <mml:mn>762</mml:mn> </mml:math> nm), and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>z</mml:mi> <mml:mo accent="false">′</mml:mo> <mml:mspace width="1em"/> <mml:mo stretchy="false">(</mml:mo> <mml:mn>909</mml:mn> </mml:math> nm). Additionally, we present images collected using the “star-hopping” technique that show the entirety of the disk, including the dramatic forward-scattering at the minor axis. We subjected our images to a battery of modeling techniques to constrain the geometry and photometry of the disk. Leveraging our clear detections of the disk’s minor axis, we modeled the scattering phase function (SPF) using a basis of the Legendre polynomials. To mitigate self-subtraction artifacts in our angular differential imaging, we implemented a forward-modeling pipeline that generates a pixel-based freeform disk forward model leading to a deconvolved image of the disk. Our best-fit disk models reveal (1) highly forward-scattering SPFs with a minimum at the ∼65 ∘ scattering angle, (2) a faint halo of dust just exterior to the spine of the disk that is not well-described by a broken power-law density profile, (3) a red spectral slope for the dust, and finally (4) a compact, clump-like feature in the freeform disk models. Our empirically measured SPFs suggest that the scattering is dominated by large, highly absorptive grains. However, we emphasize the need for testing advanced irregular grain models using our SPFs to learn more about the physical and chemical properties of this complex system.