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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents

ID: 710127.0, MPI für Astronomie / Publikationen_mpia
Physical properties of the jet from DG Tauri on sub-arcsecond scales with HST/STIS
Authors:Maurri, L.; Bacciotti, F.; Podio, L.; Eislöffel, J.; Ray, T. P.; Mundt, R.; Locatelli, U.; Coffey, D.
Date of Publication (YYYY-MM-DD):2014
Title of Journal:Astronomy and Astrophysics
Start Page:id. A110 (15 pp)
Audience:Not Specified
Abstract / Description:Context. Stellar jets are believed to play a key role in star formation, but the question of how they originate is still being debated. <BR /> Aims: We derive the physical properties at the base of the jet from DG Tau both along and across the flow and as a function of velocity. <BR /> Methods: We analysed seven optical spectra of the DG Tau jet, taken with the Hubble Space Telescope Imaging Spectrograph. The spectra were obtained by placing a long-slit parallel to the jet axis and stepping it across the jet width. The resulting position-velocity diagrams in optical forbidden emission lines allowed access to plasma conditions via calculation of emission line ratios. In this way, we produced a 3D map (2D in space and 1D in velocity) of the jet's physical parameters i.e. electron density ne, hydrogen ionisation fraction xe, and total hydrogen density nH. The method used is a new version of the BE-technique. <BR /> Results: A fundamental improvement is that the new diagnostic method allows us to overcome the upper density limit of the standard [S ii] diagnostics. As a result, we find at the base of the jet high electron density, ne ~ 105, and very low ionisation, xe ~ 0.02-0.05, which combine to give a total density up to nH ~ 3 × 106. This analysis confirms previous reports of variations in plasma parameters along the jet, (i.e. decrease in density by several orders of magnitude, increase of xe from 0.05 to a plateau at 0.7 downstream at 2'' from the star). Furthermore, a spatial coincidence is revealed between sharp gradients in the total density and supersonic velocity jumps. This strongly suggests that the emission is caused by shock excitation. No evidence was found of variations in the parameters across the jet, within a given velocity interval. The position-velocity diagrams indicate the presence of both fast accelerating gas and slower, less collimated material. We derive the mass outflow rate, Mj, in the blue-shifted lobe in different velocity channels, that contribute to a total of Mj ~ 8±4 × 10-9 M&sun; yr-1. We estimate that a symmetric bipolar jet would transport at the low and intermediate velocities probed by rotation measurements, an angular momentum flux of L&dot;j ~ 2.9 ± 1.5 × 10-6 M&sun; yr-1 AU km s-1. We discuss implications of these findings for jet launch theories. <BR /> Conclusions: The derived properties of the DG Tau jet are demonstrated to be consistent with magneto-centrifugal theory. However, non-stationary modelling is required in order to explain all of the features revealed at high resolution. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.Figures 16-18 are available in electronic form at <A href="http://www.aanda.org/10.1051/0004-6361/201117510/olm">http://www.aanda.org</A>
Free Keywords:stars: pre-main sequence; Herbig-Haro objects; ISM: jets and outflows; stars: formation
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie
Identifiers:ISSN:0004-6361 %R 10.1051/0004-6361/201117510
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