The GRAVITY young stellar object survey
Authors:   GRAVITY Collaboration, Nowacki H. , Perraut K. , Labadie L. , Bouvier J. , Dougados C. , Benisty M. , Wojtczak J. A. , Soulain A. , Alecian E. , Brandner W. , Caratti o Garatti A. , Garcia Lopez R. , Ganci V. , Sánchez-Bermúdez J. , Berger J.-P. , Bourdarot G. , Caselli P. , Clénet Y. , Davies R. , Drescher A. , Eckart A. , Eisenhauer F. , Fabricius M. , Feuchtgruber H. , Förster-Schreiber N. M. , Garcia P. , Gendron E. , Genzel R. , Gillessen S. , Grant S. , Henning T. , Jocou L. , Kervella P. , Kurtovic N. , Lacour S. , Lapeyrère V. , Le Bouquin J.-B. , Lutz D. , Mang F. , Ott T. , Paumard T. , Perrin G. , Rabien S. , Ribeiro D. , Sadun Bordoni M. , Scheithauer S. , Shangguan J. , Shimizu T. , Spezzano S. , Straubmeier C. , Sturm E. , Tacconi L. , van Dishoeck E. , Vincent F. , Widmann F. 
Published: August 2024

Context. The dust- and gas-rich protoplanetary disks around young stellar systems play a key role in star and planet formation. While considerable progress has recently been made in probing these disks on large scales of a few tens of astronomical units (au), the central au requires further investigation.
Aims.We aim to unveil the physical processes at play in the innermost regions of the strongly accreting T Tauri Star S CrA N by means of near-infrared interferometric observations. As recent spectropolarimetric observations suggest that S CrA N might undergo intense ejection processes, we focus on the accretion–ejection phenomena and on the star–disk interaction region.
Methods. We obtained interferometric observations with VLTI/GRAVITY in the K-band during two consecutive nights in August 2022. The analysis of the continuum emission, coupled with the differential analysis across the Brγ line, allows us to constrain the morphology of the dust and the gas distribution in the innermost regions of S CrA N and to investigate their temporal variability. These observations are compared to magnetospheric accretion–ejection models of T Tauri stars and to previous observations in order to elucidate the physical processes operating in these regions.
Results. The K-band continuum emission is well reproduced with an azimuthally modulated dusty ring with a half-light radius of 0.24 au (∼20 R*), an inclination of ∼30°, and a position angle of ∼150°. As the star alone cannot explain such a large sublimation front, we propose that magnetospheric accretion is an important dust-heating mechanism leading to this continuum emission. The Brγ-emitting region (0.05–0.06 au; 5–7 R*) is found to be more compact than the continuum, to be similar in size or larger than the magnetospheric truncation radius. The on-sky displacements across the Brγ spectral channels are aligned along a position angle offset by 45° from the disk, and extend up to 2 R*. This is in agreement with radiative transfer models combining magnetospheric accretion and disk winds. These on-sky displacements remain unchanged from one night to another, while the line flux decreases by 13%, suggesting a dominant contribution of wind to the origin of the Brγ line.
Conclusions. Our observations support the scenario where the Brγ line originates from a combination of (variable) accretion–ejection processes in the inner disk region.