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Astron. Astrophys. 357, L61-L64 (2000)

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3. Results on individual objects

3.1. RW Aur jet (HH 229)

RW Aur is a hierarchical triple system with the primary A separated by 1.4"  at P.A. = 256o from the close binary B & C (separation 0.12" ; Ghez et al.   1993). Both RW Aur A and B are actively accreting T Tauri stars (EW(H[FORMULA])[FORMULA] 40 Å; Duchêne et al 1999). Component C has only been detected at 2 µm so far. Using long-slit spectroscopy, Hirth et al.   (1994a) first detected bipolar collimated forbidden line emission extending over [FORMULA] 10" . A detailed analysis of these data is presented in Bacciotti et al.   (1996). Deep [S II ] images at 1" resolution (Mundt & Eislöffel, 1998, hereafter ME98) trace the flow beyond 5" from the star and out to 100".

Our [S II ] and [O I ] images reveal for the first time the morphology of the flow at a resolution of 15 AU inside the central 15"  (Figs. 1 & 2). They clearly confirm RW Aur-A as the source of the jet. The jet is resolved transversally down to 0.4" (56 AU) from the star and shows a FWHM slowly increasing with distance from 0.18" at 56 AU to 0.56" at 700 AU (Fig. 3). The intrinsic jet width (subtracted in quadrature by the psf FWHM) remains [FORMULA] 35 AU over the central 420 AU. We infer a total opening angle over the central 5" of 3.9o. The jet axis also appears remarkably straight with angle variations [FORMULA]. We derive for the inner regions a PA of 130o [FORMULA] 2o, identical within quoted uncertainties to the previous estimates of H97 and ME98 on larger scales. Morphologically, the emission is dominated by a bright inner jet body out to 5"  on the redshifted side, and breaks up into a series of knots (Fig. 1). Four major knots with spacings ranging from 3 to 5"  can be identified on the redshifted side. The brightest two have roughly symmetrical counterparts on the blueshifted side. Inside the bright inner jet body, fainter knots with typical spacing [FORMULA] 1"  are strongly suggested. The detection of redshifted emission as close as 0.4" from RW Aur-A implies an upper limit of 56 AU for the projected radius of its opaque circumstellar disk.

[FIGURE] Fig. 1. [S II ][FORMULA]6716+6731Å+Continuum deconvolved map of the jet from RW Aur-A. The resolution (core FWHM) and dynamical range are 0.1"  and 106 (1 [FORMULA]). Tick marks show the identified knots along the jet. The white cross locates the continuum centroid from RW Aur-A. RW Aur-B and a field star are also indicated. The faint 3"  radius annulus around RW Aur-A is a deconvolution residual. The gap between the continuum and the jet emission is apparent and due to strong psf wing oscillations. In effect the jet emission is detected down to 0.4". Details of the bright inner redshifted jet are shown in Fig. 2.

[FIGURE] Fig. 2. [O I ] (top ) and [S II ] (bottom ) + Continuum deconvolved maps of the CW Tau DG Tau and RW Aur jets at the same spatial scale. Spatial resolutions (core FWHM) range from 0.1 to 0.12". Contours increase by factors of 2 starting at typically 10-5 of the peak image intensity (except RW Aur [S II ]: [FORMULA]). Crosses locate the position of the unresolved continuum sources. White dashed lines show the variation of the jet centroid position. The dates of observation are indicated. The faint extended emission up and left from RW Aur-A in the [O I ] image is a deconvolution artefact arising from the spider of the telescope.

[FIGURE] Fig. 3. Variation with distance of the measured jet transverse FWHM in CW Tau (open circles), DG Tau (filled triangles) and RW Aur (filled circles). Also shown are HST measurements of the HH30 (grey dashed curve), HL Tau (full grey curve) and HH 34 (grey star) jet FWHM.

3.2. CW Tau jet (HH 220)

[S II ] and [N II ] images obtained by Gomez de Castro (1993) with medium spatial resolution (0.5-0.9" ) provided first evidence for collimated emission around CW Tau, further studied with long-slit spectroscopy by Hirth et al.   (1994b).

Our high resolution [S II ] and [O I ] images fully resolve for the first time the line emission and show a highly collimated jet body pointing towards a strong knot (Fig. 2). The CW Tau jet is resolved transversally down to 0.4" and shows a global slow increase of FWHM with distance from 0.22" at 56 AU to [FORMULA] 0.35" at 400 AU. The derived full opening angle is 3.3o. As in the case of RW Aur, jet axis angle variations are small ([FORMULA]). We infer the same PA of 144o [FORMULA] 2o as Gomez de Castro (1993). Because of lower signal to noise ratio, the jet body is not detected in [O I ]. The counterjet is detected in the [S II ] image but its irregular shape prevents a reliable estimate of its width.

3.3. DG Tau jet (HH 158)

The presence of a collimated outflow around DG Tau was first inferred from long-slit spectroscopy (Mundt & Fried, 1983; Solf & Böhm, 1993). From imaging at 1"  resolution, Eislöffel & Mundt (1998, hereafter EM98) detect four knots beyond 2.5" . HST observations of DG Tau were obtained by Kepner et al.   (1993) and Stapelfeldt et al.   (1997) in [O I ] and broad band R filters. Strong psf residuals in these data prevented however a reliable study of the inner jet regions. Lavalley et al.   (1997, hereafter L97), using spectro-imaging techniques, imaged the DG Tau jet in [O I ] and definitely confirmed the jet-like morphology of the emission. A knot at 2.7" with morphology and kinematics strongly suggestive of a bow-shock was identified.

Our new PUEO images improve by a factor 2.5 the spatial resolution of our previous study. The DG Tau jet looks far more perturbed than the previous two jets. Its FWHM increases from 0.21"  at 56 AU to 1.25" at 335 AU (Fig. 3). Beyond 90 AU, strong contamination by the bow-shock wings are likely, preventing reliable estimate of intrinsic jet width. It also shows a more sinuous beam (maximum [FORMULA] [FORMULA] 5 o) suggesting strong interaction with the ambient medium and/or jet axis variation. As in the previous two jets, the emission appears knotty. The outer knot is fully resolved and shows a clear bow morphology. Comparing with the TIGER data obtained 2 years earlier, we detect for this knot a proper motion of 194 [FORMULA] 20 km s-1 (Fig. 4), in complete agreement with our new January 1998 spectro-imaging observations (Lavalley et al.   2000). If the tangential velocity has been conserved, the corresponding ejection date is 1985, thus corresponding to a more recent ejection event than those identified by EM98.

[FIGURE] Fig. 4. Proper motion of the bow-shaped knot in DG Tau. Comparison of our [O I ] map obtained in 11-1994 (top) with the new PUEO image (bottom). The displacement of the bow-shaped knot between these 2 epochs is 0.65" [FORMULA] 0.07" corresponding to a proper motion of 0.29" [FORMULA] 0.03 "/yr.

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© European Southern Observatory (ESO) 2000

Online publication: June 5, 2000