2. Observations and data reductions
The observations where carried out on the nights of 12 - 14 December, 1992, using the ESO 3.5m NTT telescope. We used the red arm of the EMMI (ESO Multi-Mode Instrument) in its Echelle mode using grating No. 10 with grism No. 6 as a cross-disperser. A 20 decker was mounted in order to limit the length of the slit, and the slit width was set to 2. This slit width was selected as a compromise, in order to cover as much as possible of the object in the allotted time. This combination resulted in a mean resolution of / 28000 in the wavelength interval of 6200Å to 8100Å, equivalent to a velocity resolution of 10.7 km s-1 at the wavelength of H . The detector utilized was ESO CCD No. 18, with 1060 1040 19 µm pixels. The image scale translates as 0.44 pixel-1 and 4.5 km s-1 pixel-1 respectively.
On the first night we obtained spectra at 3 positions, with the slit in an E-W orientation. The exposure time for these spectra was 3 0.5 hours per position. The first spectrum was centered on the intensity maximum of HH 29a, and the two following spectra were obtained by moving the telescope 2 due north and 2 due south of this position. The seeing was measured as 0 7. On the second night we obtained 5 spectra with the slit in a N-S orientation. The integration time for these were 2 0.5 hours per position. The seeing was worse than on the previous night - 1 5 - but still matched to the slit width utilized. We centered the first exposure 1 W of the intensity maximum in HH 29a and each subsequent spectrum was obtained by moving the telescope 2 W from the previous position. The final spectrum (No. 8) was obtained by centering the slit on the small knot/filament, towards the east of HH 29 and exposing for 0.5 hour at this position. In Fig. 1, we show two H -images of HH 29, with the slit positions superposed.
In order to facilitate the interpretation, we will use the same nomenclature as FLP, as what regards the identification of different condensations in HH 29. We have added the designations HH 29e for the emission knot SW of HH 29a, and HH 29f for the small emission `knot' following HH 29 `proper' in hour angle (see Fig. 1).
The reduction was performed utilizing the ESO MIDAS package (ver. 92NOV and 95NOV) and the context ECHELLE and proceeded in a standard fashion.
The instrument profile was determined from Th-Ar comparison lines. From an analysis of 8 - 9 lines in each of three Th-Ar spectra obtained during both nights, we find the average full width at zero intensity of the instrument profile, FWZII to be 43.3 4.8 km s-1.
Flux calibration was achieved by observing HD74721 (Davis Philips & Hayes, 1983) on the first night and HR 718 (Hamuy et al. , 1992) on the second night. Standard extinction coefficients were extrapolated from data found on the ESO web site, taking into account also the anomalous atmospheric extinction introduced by the Mount Pinatoubo volcanic eruption. We have compared our flux calibration with the results of FLP, and it is found that the level of accuracy for H , [SII] and [OI] is of the order of 10 %. The results from the second night are not quite as good, but since some of the same areas of HH 29 are covered on both nights, an internal adjustment leads to the same level of accuracy. One have also to take into account the probable variability of the object (LHFC). Our observations reported in this paper was however, carried out within a few months of the relevant imaging observations reported in FLP.
© European Southern Observatory (ESO) 1998
Online publication: January 8, 1998