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Astron. Astrophys. 322, L25-L28 (1997)

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3. Results

3.1. The VLA 1 outflow

Figure 2 shows the spectra at the central position and at two offset positions in the direction of VLA 1. The spectrum at the top corresponds to the peak of the red emission and the one in the middle shows the peak of the blue emission. The spectrum at the bottom is the one taken at the central position.

[FIGURE] Fig. 2. Spectra of 12 CO J [FORMULA] 3-2 emission in the direction of VLA 1. The offset positions are shown at the top left corner in arcseconds relatively to VLA 1. For clarity, the top and the middle spectra are offset by 30 K and 15 K, respectively. The dashed lines show the velocity ranges over which we have integrated the high velocity emission

A map of the high-velocity 12 CO J [FORMULA] 3-2 emission in the direction of VLA 1 is shown in Fig. 3. The map is centered on VLA 1 (R.A. (1950) [FORMULA], DEC. (1950) [FORMULA] [FORMULA]), covering an area of approximately [FORMULA]. A half beam spacing ([FORMULA]) was used to cover the area and 49 positions were observed.

[FIGURE] Fig. 3. CO J [FORMULA] 3-2 map in the direction of VLA 1. Red-shifted emission is shown by dashed lines and corresponds to an integrated intensity between 14-20 km s-1. Blue-shifted emission is shown by solid lines and corresponds to an integration between 0-5 km s-1. The contour interval and the lowest contour are 0.5 K km s-1. The dots show the 49 positions observed

From the map we can see that the peaks of red- and blue-shifted emission are separated by only [FORMULA]. However, the two lobes are clearly distinct from each other which suggests that the axis of the outflow is close to the plane of the sky. This axis is very well aligned with the HH 1-2 axis and VLA 1 is in the center of the two lobes. Taking into account our [FORMULA] beam size, we derive an angular diameter for the red lobe of [FORMULA] along the outflow direction and [FORMULA] along the direction perpendicular to it. The blue lobe has an angular diameter of [FORMULA] along the outflow direction but it is not resolved along the perpendicular direction.

We have also detected faint blue emission associated with the red lobe as well as faint red emission close to the blue lobe. This can be evidence for an interaction between the outflowing material and the ambient medium. An interaction between the outflow and the jet could lead to a re-direction of the outflowing material at the working surface of the jet (e.g. Padman et al. 1994), producing a component of emission in the opposite direction to the respective outflow lobe. Alternatively, this ca n be explained if we consider the outflow axis very close to the plane of the sky, as it seems to be the case. If the angle between the outflow axis and the plane of the sky is smaller than the outflow opening angle then we should expect to see, close to the blue lobe, some material receding from us; and for the same reason we should see some material approaching us when we look into the direction of the redshifted lobe.

Our 13 CO J [FORMULA] 3-2 observations were performed at the central position of VLA 1 and at the two offset positions corresponding to the peaks of the red and blue lobes in the 12 CO J [FORMULA] 3-2 map (([FORMULA]) and ([FORMULA]), respectively). We did not find any evidence for emission in the wings of the lines at a level of 0.02 K. The noise level achieved did not allow us to make an accurate estimative of the optical depth. However, 3 [FORMULA] upper limits were estimated and the results are: [FORMULA] and [FORMULA] fo r the red and blue lobes, respectively.

The mass, momentum and the energy of the CO J [FORMULA] 3-2 outflow associated with each lobe have been calculated using the same approach taken by Scoville et al. (1986). We have adopted an excitation temperature ([FORMULA]) of 30 K and we have considered optically thin emission. The results are summarized in Table 1. If the emission is optically thick, then these values increase by roughly a factor of [FORMULA]. The dependence on the excitation temperature is weak (less than 1 6 % for 20 [FORMULA] [FORMULA] K). The momentum and energy values were calculated assuming that [FORMULA], the angle between the line of sight and the outflow axis, is [FORMULA] (Noriega-Crespo et al. 1991). The total mass associated with the outflow is 1.1 [FORMULA] [FORMULA] which is in accordance with the predictions made by Chernin and Masson (1995). This outflow is approximately 75 times less massive than the least massive outflow listed by Fukui et al. (1993). The existence of this outflow suggests that other sources that are currently classified as non-outflow sources might have very weak and compact outflows not yet detected (Saraceno et al. 1996).


[TABLE]

Table 1. VLA 1 outflow physical parameters


From the outflow extent and the maximum velocity detected, we have estimated a dynamical timescale of [FORMULA] 1 [FORMULA] yr for the outflow making this one of the youngest outflows ever detected.

3.2. The VLA 3 outflow

The spectrum obtained at the central position in the direction of VLA 3 is shown in Fig. 4 (bottom spectrum). This position was identified as the position for which the blue emission achieves its peak. Fig. 4 also shows the spectrum for the offset position ([FORMULA]) where we clearly see very strong redshifted emission.

[FIGURE] Fig. 4. Spectra of 12 CO J [FORMULA] 3-2 emission in the direction of VLA 3. The offset positions are shown at the top left corner in arcseconds. The upper spectrum is offset by 15 K for clarity. The dashed lines show the velocity ranges over which we have integrated the high velocity emission

Figure 5 shows a map of the CO J [FORMULA] 3-2 emission in the direction of VLA 3 . It is clear that this outflow is much stronger and extended than the VLA 1 outflow. The blue peak is very close to VLA 3 and the two peaks are separated by only [FORMULA]. The large overlap suggests that [FORMULA] must be smaller than [FORMULA].

[FIGURE] Fig. 5. Map of the CO J [FORMULA] 3-2 emission in the direction of VLA 3. The red-shifted emission is shown as a dashed line and corresponds to an integrated intensity between 12 km s-1 and 30 km s-1. The blue-shifted emission is shown as a solid line and corresponds to an integration between -10 km s-1 and 5 km s-1. In the blue lobe, the lowest contour is 1 K km s-1 and the contour interval is 1 K km s-1 and in the red lobe the lowest contour is 2 K k m s-1 and the contour interval is 2.5 K km s-1. The dots show the 56 positions observed

We have taken 13 CO J [FORMULA] 3-2 spectra at the central position of VLA 3 and at the red peak position of the 12 CO J [FORMULA] 3-2 emission and, once again, we did not find any evidence of emission in the wings of the lines at a level of 0.02 K. The 3 [FORMULA] upper limits for the optical depth of the 12 CO emission are: [FORMULA] and [FORMULA] for the red and blue lobes, respectively. The strong restriction achieved for the red lobe is explained by the fact that ver y strong emission was detected in 12 CO (see Fig. 4) and no emission was detected in 13 CO; this supports the hypothesis that the emission is also optically thin in the other lobes of both outflows.

The estimated physical parameters of the VLA 3 outflow are summarized in Table 2. We have again used [FORMULA] K and we have considered optically thin emission. The momentum and energy values were calculated assuming [FORMULA]. We estimate a dynamical timescale of 2.1 [FORMULA] yr.


[TABLE]

Table 2. VLA 3 outflow physical parameters


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© European Southern Observatory (ESO) 1997

Online publication: June 5, 1998

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