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Astron. Astrophys. 348, 584-593 (1999)

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3. Results

The data were analysed using the Figaro packages Twodspec and Longslit. Spectra at three positions along the jet are shown in Fig. 2. The spectra from all positions along the jet are dominated by the v=1-0 lines, particularly the S(1), S(3) and Q lines. Also present in the spectra are weaker lines from the v=2-1 and v=3-2 bands. The emission from lines with v[FORMULA]1 is weak compared to the 1-0S(1) lines. The appearance of apparent absorption lines is not significant, as these are due to poorly subtracted atmospheric lines. The apparent weak emission feature close to [FORMULA] in the spectrum of the nebula (Fig. 2c) is probably due to Brackett gamma absorption in the standard stars.

[FIGURE] Fig. 2a-c. [FORMULA] emission lines from: a  The head of the jet (Slit 1), taken across row 19 where the emission from the jet head peaks. The strongest [FORMULA] lines are marked. b  The main body of the jet (Slit 2), taken across row 32. c  The jet near the source (Slit 2), taken across row 64.

A comparison of Figs. 2a and 2b shows that the lines are an order of magnitude brighter at the head of the jet than in the body of the jet. The general pattern of the emission lines is, however, the same. The v=1-0 lines are visible at all positions along the jet. The v=2-1 lines and v=3-2 lines can clearly be seen at the head of the jet, but as the intensity of the lines falls along the jet, these higher excitation level lines fall below the RMS noise in the spectra. The v=2-1 and v=3-2 lines are detectable at points along the jet where the emission is stronger, but at positions where the intensity of the v=1-0 lines falls by 2 orders of magnitude, the higher excitation lines are not detectable above the RMS noise.

Near the source, the jet is coincident with a bright nebula, which is seen in the K-band continuum. The K-band continuum can be explained as light from the central source scattered from the edge of the cavity excavated by the outflow. Fig. 2c shows [FORMULA] lines superimposed on this continuum. The continuum is rather red in colour, rising towards longer wavelengths, indicating that the source is indeed young and deeply embedded. As scattering would be expected to make a spectrum more blue, the light being scattered by the cavity walls must be very red, indicating that there is dust between the source and the scattering location, or that the source has an intrinsically red spectrum.

The extinction can be calculated from the ratio of the [FORMULA] lines, which originate from the same upper state (Fernandes & Brand 1995). The observed ratio of the line intensities towards the nebula gives [FORMULA]=3.8 mag at this position, which corresponds to an extinction of [FORMULA] 38 mag at visual wavelengths, assuming that the extinction scales as the wavelength to the power -1.7. Towards both the jet and jet head, the extinction is about 3 times less.

Fig. 3a shows a cut along the length of the jet in the 1-0S(1) line at 2.12 µm. Fig. 3b shows the same cut in a line free part of the spectrum. These figures show that the jet has knots of brighter emission (labelled Peaks 1, 2 and 3) between the head of the jet, at row 20, and the rise in the continuum at row 60. These peaks are coincident with the knots of [FORMULA] emission seen in Fig. 1. The approximate distances between the peaks, starting from the head of the jet are 2400 AU to peak 1, 1000 AU to peak 2, and 3400 AU to peak 3. The off axis slit (slit 3) shows a fourth emission peak near the nebulosity, which is between the peaks labelled 2 and 3 in slit 2. This emission peak lies between the two knots of emission shown in Fig. 1, just below the central cross of slit 1. As can been seen from Fig. 3, [FORMULA] emission is also seen between the emission peaks. Two of these positions have been labelled as Troughs 1 and 2. This is inter-clump emission detected in the other strong [FORMULA] lines, and in the off-axis slit. The emission from the troughs, between the peaks, is an order of magnitude less bright than the emission from the knot peaks, but it is present at all positions in the jet.

[FIGURE] Fig. 3. a  Cut along the jet axis in the 1-0S(1) line. Arrows mark the emission peaks, and lines mark the emission troughs. The head of the jet peaks at row 20. b  Cut along the jet axis in a line free part of the spectrum. Emission is seen only from the nebulosity.

From the long slit observations, the length and width of the jet can be estimated, assuming a distance of 200 pc to the L483 system. The jet is 14400 AU long, from the start of the nebulosity, near the source, to the head of the jet. From Slit 1, which goes through the centre of the head of the jet, this has a width of 1400 AU. Slit 3 is placed 2 " below Slit 2, and, from the observations, is still placed within the jet. Assuming that the jet is symmetric about its axis, this gives a minimum width to the jet body of 400 AU.

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© European Southern Observatory (ESO) 1999

Online publication: July 26, 1999
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