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Discovery of a point-like source and a third spiral arm in the transition disk around the Herbig Ae star MWC 758

2017; EDP Sciences; Volume: 611; Linguagem: Inglês

10.1051/0004-6361/201732016

1432-0746

Maddalena Reggiani, Valentin Christiaens, Olivier Absil, Dimitri Mawet, Elsa Huby, Élodie Choquet, Carlos Gómez González, Garreth Ruane, Bruno Femenía, Eugene Serabyn, K. Matthews, M. Barraza, Brunella Carlomagno, Denis Defrère, Christian Delacroix, Serge Habraken, Aïssa Jolivet, Mikael Karlsson, Gilles Orban de Xivry, Pierre Piron, Jean Surdej, E. Vargas Catalán, O. Wertz,

Stellar, planetary, and galactic studies

Transition disks offer the extraordinary opportunity to look for newly born planets and investigate the early stages of planet formation. In this context we observed the Herbig A5 star MWC 758 with the L band vector vortex coronagraph installed in the near-infrared camera and spectrograph NIRC2 at the Keck II telescope, with the aim of unveiling the nature of the spiral structure by constraining the presence of planetary companions in the system. Our high-contrast imaging observations show a bright (delta L=7.0+/-0.3 mag) point-like emission, south of MWC 758 at a deprojected separation of about 20 au (r=0.111+/- 0. 004 arcsec) from the central star. We also recover the two spiral arms (south-east and north-west), already imaged by previous studies in polarized light, and discover a third one to the south-west of the star. No additional companions were detected in the system down to 5 Jupiter masses beyond 0.6 arcsec from the star. We propose that the bright L band emission could be caused by the presence of an embedded and accreting protoplanet, although the possibility of it being an asymmetric disk feature cannot be excluded. The spiral structure is probably not related to the protoplanet candidate, unless on an inclined and eccentric orbit, and it could be due to one (or more) yet undetected planetary companions at the edge of or outside the spiral pattern. Future observations and additional simulations will be needed to shed light on the true nature of the point-like source and its link with the spiral arms.