Searching for H$_��$ emitting sources around MWC758: SPHERE/ZIMPOL high-contrast imaging

MWC758 is a young star surrounded by a transitional disk. Recently, a protoplanet candidate has been detected around MWC758 through high-resolution $L'$-band observations. The candidate is located inside the disk cavity at a separation of $\sim$111 mas from the central star, and at an average position angle of $\sim$165.5 degrees. We have performed simultaneous adaptive optics observations of MWC758 in the H$_��$ line and the adjacent continuum using SPHERE/ZIMPOL at the Very Large Telescope (VLT). We aim at detecting accreting protoplanet candidates through spectral angular differential imaging observations. The data analysis does not reveal any H$_��$ signal around the target. The derived contrast curve in the B_Ha filter allows us to derive a 5$��$ upper limit of $\sim$7.6 mag at 111 mas, the separation of the previously detected planet candidate. This contrast translates into a H$_��$ line luminosity of $L_{\rm H_��}\lesssim$ 5$\times$10$^{-5}$ $L_{\odot}$ at 111 mas, and an accretion luminosity of $L_{acc}
5 pages, accepted for publication in A&A letters