A Tentative Detection of a Point Source in the Disk Gap of HD 100546 with VLT/SPHERE-IRDIS Sparse Aperture Masking Interferometry*

Abstract We reanalyze VLT/SPHERE-IRDIS K- and H -band sparse aperture masking interferometry data of the transition disk HD 100546 observed in 2018 and 2021, respectively. We fit geometrical models to the closure phases extracted from both datasets. We compare three model classes: a forward scattering disk, a forward scattering disk plus an arbitrary asymmetric disk feature, and a forward scattering disk plus an unresolved point source in the disk gap. We find that the forward scattering disk plus point-source model is the best representation of the data. We find that this point-source candidate moved from a position of sep. = <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>39</mml:mn> <mml:mo>.</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>9</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3.3</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>2.8</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> mas, P.A. = <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>124</mml:mn> <mml:mo>.</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>1</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.0</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>1.0</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> degrees to a sep. = <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>50</mml:mn> <mml:mo>.</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.0</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>1.0</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> mas, P.A. = <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>106</mml:mn> <mml:mo>.</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>4</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.4</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>1.4</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> degrees between 2018 and 2021. Both of these positions are well within the ~13 au (~120 mas) disk gap, favouring the point-source interpretation. We explore the orbital parameter space that is consistent with the measured relative astrometry. We find orbits either with a similar orientation to the outer disk, with a high eccentricity e ≿ 0.65, or orbits with a large relative inclination (∼60°) to the outer disk, and any eccentricity. Despite the significance of the observed point-source signal, follow-up observations will be necessary to conclusively determine its nature.