High-resolution visible spectroscopy of the jet-driving star Th 28

Abstract

Context. We present a study of the extreme T Tauri star Th 28, a young stellar object in the Lupus 3 cloud whose spectrum displays all the varieties of signposts associated with early stellar activity. Th 28 is the driving source of a fast jet, making it a very promising target to study the disk-jet connection. Aims. We try to identify and investigate the different structural components that contribute to the different emission lines in the spectrum of the Th 28 central source. Methods. We obtained high-resolution visible spectroscopy with the UVES spectrograph at the VLT, using the resolved profiles of both permitted and forbidden lines as tracers of gas with different kinematic and physical properties, complemented with other observations from the literature. Results. We identify four distinct structural components that contribute to the visible emission-line spectrum of Th 28. The first one, dominating most of the permitted and forbidden lines, is probably associated with the origin of the outflow that in the past produced the Herbig-Haro objects seen to the west of Th 28. The second one is an uncollimated stellar wind characterized by high excitation and temperature, as shown by the broad profile of the intense [OIII] lines. The third component, traced only by permitted lines, appears as a redshifted tail extending up to radial velocities of +450 km s −1 , which we attribute to magnetospheric accretion. From the latter component we obtain a rough estimate of 0.6−0.9 M for the mass of the central object. Using published equivalent widths of the CaII triplet lines, we estimate an accretion rate of 4.2−6.3 × 10 −8 M yr −1 , comparable to the values inferred for other T Tauri stars of similar mass. The last component, which appears most clearly in the [SII] lines and is hardly seen in any lines other than those of [OI], displays signatures that we interpret as coming from rotation, perhaps formed in a disk atmosphere. Following this interpretation, we estimate a disk central hole of 0.7 AU radius. Conclusions. Even though spatially unresolved, the spectrum of Th 28 is rich in emission lines whose shapes provide important information on the distinct structures where they form. In this way we were able to identify the existence of a stellar wind, an accretion flow, the basis of a collimated outflow, and possibly a rotating disk atmosphere, obtaining rough estimates of basic parameters of the central source and its environment that should be useful for further modeling.

ALMA observations of the Th 28 protostellar disk

“…The large proper motions derived for the distant knots are compatible with a close to edge-on geometry (e.g., Comerón & Fernández 2010). Th 28 is considered one of the best case for jet rotation detection in the HST sample, as transverse velocity gradients are well detected in both lobes of its optical atomic jet and are consistent in different optical lines (Coffey et al 2004).…”

“…Line-of-sight velocities (V rad ) of −62 km s −1 and +38 km s −1 were reported for the E1 and W knots, respectively (Comerón & Fernández 2010 • for the E1 and W knots, respectively. We therefore adopt a global inclination of the jet, from the knots analysis, of 82.3 ± 2…”

News on two jets in Lupus 3

“…Further probing of the innermost region of the jet using nearinfrared hydrogen and [FeII] lines was recently presented by the same authors (Coffey et al 2010). The different outflow and inflow components in the immediate circumstellar environments of Th 28 were discussed by Comerón & Fernández (2010) based on spatially unresolved high resolution spectroscopy of a variety of emission lines. An accretion rate of ∼6.3 × 10 −8 M yr −1 is inferred from these observations, which, with the caveat of the uncertainties in both estimates, suggests a high outflow-to-inflow mass ratio.…”

Signatures of Hot Molecular Hydrogen Absorption from Protoplanetary Disks. I. Non-thermal Populations

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