2. [OIII ] observations and sample selection
2.1. Bulge, disk and halo membership
We present [OIII ] observations of 44 PNe, located primarily in the direction of the Galactic Bulge. However, this region also includes foreground disk objects, objects belonging to the inner halo, and two background PNe belonging to the Sagittarius Dwarf Galaxy (Sgr). Criteria for Bulge membership are: (1) within 15 degrees of the Galactic Centre; (2) distance ; (3) metallicity greater than 0.1 of Solar. (Stellar kinematics in the centre of the galaxy indicates that stars with metallicity less than 0.1 of Solar belong to the inner halo (Minniti 1996).)
Abundances for PNe in our sample are given by Dudziak et al. (2000) for the two objects in Sgr, and by Cuisinier et al. (2000), Ratag et al. (1997), Costa et al. (1996), Webster (1988) and Aller & Keyes (1987) for most of the Galactic PNe. The Bulge membership criteria are satisfied by 26 objects. 14 objects appear to belong to the Galactic disk. The two Sgr objects Zijlstra & Walsh 1996) are He 2-436 (004.8-22.7) and Wray 16-423 (006.8-19.8).
Two objects are suggested to be halo PN: Hb8 because of its large indicated distance (see Sect. 3.1) and high latitude and M2-29 because of its very low metallicity.
The observations were carried out with the ESO 1.4m CAT telescope in July 1993. The so-called short camera was used in the blue arm of the echelle spectrograph, with a resolution of 30000, corresponding to . The [OIII ] 5007 Å line was observed. Integration times varied from a few to 30 minutes depending on the line flux. Faint nebulae could not be observed because they were not visible on the finder due to the brightness of the Moon. The slit had a width of and a length of . The pixel scale corresponded to . The wavelength calibration was done with ThAr spectra, and also checked by observing well-known planetary nebulae as velocity standards.
The data reduction involved flat fielding, cosmic-ray removal and wavelength calibration. The line profiles were summed over the slit to obtain an integrated spectrum, but for resolved nebulae the profile variation along the slit was also analyzed. Radial velocities determined from the spectra have been presented in Zijlstra et al. (1997).
© European Southern Observatory (ESO) 2000
Online publication: June 20, 2000