Abstract:
We conducted NOrthern Extended Millimeter Array (NOEMA) observations toward the Class 0/I protobinary system SVS13A as part of the PROtostars & DIsks: Global Evolution (PRODIGE) program. SVS13A is composed of two protostars VLA4A and VLA4B with a separation of ∼90 au, for which VLA4A is undergoing an accretion burst that enriches the chemistry of the surrounding gas. This gives us an excellent opportunity to probe the chemical and physical conditions as well as the accretion process. We study the kinematic structures of SVS13A via DCN (3–2) line, and the C18O (2–1) line at about hundred au scale. By combining our observations with previous ALMA high-angular-resolution observations, we find that the binary system (or VLA4A) might be fed by an infalling streamer from envelope scales (∼700 au). If this is the case, this streamer contributes to the accretion of material onto the system with a rate of at least 1.4 × 10−6 Msun yr−1. We further analyzed 12- 11 lines of CH CN and CH 13CN and six selected O-bearing COMs: CH3OH, aGg’-(CH2OH)2, C2H5OH, CH2(OH)CHO, CH3CHO, and CH3OCHO. Although the COM emission is not spatially resolved, we constrained the source sizes to ~0.3 − 0.4 arcsec (90−120 au) by conducting uv-domain Gaussian fitting. Interestingly, the high-spectral-resolution data reveal complex line profiles with multiple peaks; although the line emission is likely dominated by the secondary,VLA4A,at Vlsr = 7.36 kms−1,the numbers of peaks (∼2−5), the velocities, and the linewidths of these six O-bearing COMs are different. The local thermodynamic equilibrium (LTE) fitting unveils differences in excitation temperatures and emitting areas among these COMs. We further conducted multiple-velocity-component LTE fitting to decompose the line emission into different kinematic components. As a result, the emission of these COMs is decomposed into up to six velocity components from the LTE modeling. The physical conditions (temperature, column density, and source size) of these components from each COM are obtained. We conclude that accretion shocks induced by the large-scale infalling streamer likely exist and contribute to the complexity of the COM emission. This underlines the importance of high-spectral-resolution data when analyzing COM emission in protostars and deriving relative COM abundances.
