Unveiling a protoplanet candidate embedded in the HD 135344B disk with VLT/ERIS

Context. High-angular-resolution observations in infrared and millimeter wavelengths of protoplanetary disks have revealed cavities, gaps, and spirals. One proposed mechanism to explain these structures is the dynamical perturbation caused by giant protoplanets. Aims. The purpose of this study is to detect and characterize potential protoplanets in the HD 135344B system. The star is located at ∼136 pc, and hosts a protoplanetary disk characterized by a 40 au cavity, multiple spiral arms detected in the optical/near-infrared, and a large-scale azimuthal asymmetry at millimeter wavelengths. Methods. We conducted deep high-contrast imaging observations using VLT/ERIS in the L′-band with the annular groove phase mask coronagraph (vortex coronagraph). Angular differential imaging with principal component analysis (ADI-PCA) was applied for the point spread function (PSF) subtraction to highlight the presence of point sources in the system. Results. We identified the previously detected S1, S2, S2a spiral arms and the “blob” features southward of the star. Besides this, we also identified a new point source at the base of the spiral arm (S2) embedded in the inner part of the disk at a separation of ∼ 0.″21, corresponding to a projected separation of ∼28 au, and a position angle of ∼87° (west of north). The point source has a contrast of ∼3 × 10−3. Our multiwavelength analysis implies a planetary mass of ≳2 MJup and large dust extinction (AV ≳ 10 mag). Moreover, the L′-band flux of the candidate protoplanet and the upper limits at shorter wavelengths hint at the presence of a circumplanetary disk. Additionally, we report the detection of a previously unrecognized spiral arm located northwest of the star at a separation of ∼ 0.″77. No planets are detected in the outer disk with an upper limit of ∼600 K. Conclusions. These results suggest a physical link between the newly identified planet candidate and the observed disk substructures, supporting the scenario of a planet-driven origin for the cavity and spirals in the HD 135344B disk.