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Astron. Astrophys. 347, 169-177 (1999)

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2. Observations

The target selection for this programme followed two criteria: First, the PN should have a very high EC; second, the spectral type of the CSPN should be unknown. Nine objects were observed in two observation campaigns in February and June 1996 at ESO with the 3.6m telescope and EFOSC 1. The targets are summarized in Table 1. Data reduction had been performed using IRAF 1.

2.1. Narrow-band imaging of the planetary nebulae

We took H [FORMULA] and [O III ] [FORMULA] 5007 Å images (exposure time 900 sec each) of all PN from Table 1 with EFOSC 1 (CCD ESO #26, TEK 512M, [FORMULA] px, 1 px = 0.609" projected at the sky). The images are flatfielded with suitable sky flats.

The field size of the presented PN images as well as the nebula diameters are summarized in Table 2. Comments on the morphology of the PN are given in the figure captions. The intensity of the presented images is following a grayscale. H [FORMULA] images are on the left, [O III ] [FORMULA] 5007 Å images on the right side; North is up and East is right.


Table 1. List of our targets. Given are the visual magnitudes of the CSPN (Acker et al. 1992) and the EC of the PN, determined from Stenholm's survey spectra (Sect. 3)


Table 2. Measured angular diameters (faintest visible H [FORMULA] emissions) of our nebulae. Given are the field sizes of the images shown here, the diameters in West-East ([FORMULA]) and North-South direction ([FORMULA]) compared to the values given by Acker et al. 1992 ([FORMULA])

We like to mention that the selection of our targets had nothing to do with their morphology. Thus it is interesting to note that we have a quite wide variety of different types in our sample.

2.2. Spectroscopy of the central stars

U, B, V, and R images have been taken in order to unambiguously identify the exciting stars in case of doubt (e.g. PN G277.1-03.8, Fig. 6). In the case of PN G257.5+00.6 two stars appear at equal brightness. While the 1st star is almost in the geometrical center of the PN, the 2nd is about 15" South-East of the other, next to the inner edge of the [O III ] blob. We took spectra of both of these stars (Fig. 12).

Medium-resolution (6 - 8 Å) spectra of all targets but PN G324.1+09.0 (Table 1) have been taken with EFOSC 1 and the B 150 grism (Fig. 12). The exposure times were one hour. In the data reduction it has been impossible to subtract completely the nebula emission lines [O III ] [FORMULA] 4959, 5007 Å due to strong asymmetries. However, the other nebula emission lines could sufficiently be eliminated.

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© European Southern Observatory (ESO) 1999

Online publication: June 18, 1999