Astron. Astrophys. 342, 823-830 (1999)

3. Results

The image in the H₂ 1-0S(1) line is shown in Fig. 1. As verified with the spectra, the continuum emission is everywhere negligible but at the position of the central star, i.e. in a radius region centered on the star.

The H₂ 1-0S(1) image of Fig. 1 shows the well-known NGC 2346 morphology, with a bright central region of size and two very extended lobes of weaker emission (Kastner et al. 1994). The central region has two peaks of emission, to the east and west of the star and matches well the bright torus, tilted with respect to the line of sight, seen in optical tracers and in CO (Walsh 1983; Bachiller et al. 1989). The H₂ 1-0S(1) intensity is erg cm^-2 s^-1 sr^-1 on both peaks. The total luminosity of the nebula in this line is about 0.06 L (for pc), of which about 48% is contributed by the torus. The average line intensity over the torus (defined as the central region of size ) is erg cm^-2 s^-1 sr^-1. These numbers are very similar (within 10-20%) to those derived by Zuckerman and Gatley (1988).

The K band spectra in the three positions E, S and W are shown in Fig. 2. The spectra have been averaged over a region of (12 pix) along the slit centered on the torus midplane. The line intensities are given in Table 1, which gives in Column 1 the line identification, in Column 2 the wavelength of the line, in Column 3 the intensity in the W position, in Column 4 that on the E position, in Column 5 that in the S position of the slit. The lines are normalized to the 1-0S(1) line set equal to 100; the intensity of the 1-0S(1) line is given in the table's note. Typical uncertainties on the line ratios are 10% for ratios 50, and 30% for the others. Lines whose intensity is particularly uncertain are marked with a semicolon.

Fig. 2. K-band spectra in the W, E and S positions. The lines have been averaged over a slit section of centered on the peak of the emission (the torus mid-plane). The small gap at 2-2.04 µm corresponds to a region of very poor atmospheric transmission.

Table 1. K-Band spectrum of the central torus
Note: 1-0S(1) intensity 100 corresponds to erg cm^{- 2} s^-1 sr^-1 in the W position, erg cm^-2s^-1 sr^-1 in the E position and erg cm^-2 s^{- 1} sr^-1 in the S position. The spectra have been averaged over a slit portion centred on the torus midplane.

The variations in intensity along the slit positions E and W and S of the H₂ 1-0S(1) and 2-1S(1) lines and of Br is shown in Fig. 3. The intensity profiles show that the H₂ emission in the 1-0S(1) line peaks in the torus (i.e., for ) and has extended emission with intensity that declines more sharply toward the north than toward the south, possibly due to the tilt in the plane of the sky. Some of the inhomogeneities seen in the two-dimensional image can also be seen in these profiles. The ratio of the 2-1S(1) over the 1-0S(1) intensity varies between about 0.1 in the W and E peaks of emission to about 0.04 in the condensation detected in the W position south of the midplane. Another interesting result which emerges from the spectra and the intensity profiles is that the emission in Br extends over the whole central torus. However, Br is quite weak, 10% of the 1-0S(1).

Fig. 3. Top panel: variation with declination offset of the intensity of the H2 1-0S(1) and 2-1S(1) lines and of Br (dotted curve) for the slit position E. Middle panel: same for slit position W. Bottom panel: same for slit position S. All intensity profiles have been smoothed over three pixels. The offset is measured with respect to the central star.

© European Southern Observatory (ESO) 1999

Online publication: February 23, 1999
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