Long-slit spectroscopy of the bipolar planetary nebula ESO\,428$-$05

RESUMO

The results of detailed long-slit spectroscopy of the bipolar planetary nebula \ESO\ are presented. The observations were obtained with the facility spectrograph RSS of the SALT telescope. The total measured extent of the nebula reaches $\approx$55$^{\prime\prime}$, and the kinematics along the slit directly confirms its bipolar structure. The inclination of the nebula to the line of sight is estimated as $i\approx 45^{\circ}$, and the kinematic ages of two morphological structures are measured: the expanding ring and the polar outflow in the direction perpendicular to the ring. The age of the former is $\approx$1.5$\times$10$^4$~yr and that of the latter is $\approx$(3--4)$\times$10$^4$~yr, i.e. the polar outflow is 2--3 times older than the central ring. The ratio of these ages does not depend on the adopted distance. The weighted mean heliocentric velocity of \ESO\ is V$_{\rm hel}$=74.7$\pm$1.6~\kms. Chemical abundances are obtained for 19 regions along the major axis of the nebula, over an extent of 40$^{\prime\prime}$, i.e. for different morphological parts of \ESO. The abundances were derived with the T$_{\rm e}$--method, where the electron temperature was calculated directly using the measured faint auroral lines [\ion{O}{iii}]~$\lambda$4363~Å and [\ion{N}{ii}]~$\lambda$5755~Å. The abundances of O, N, Ne, S, Ar, Cl and He were determined. Despite a significant stratification, the measured abundances along the slit can be considered nearly constant.