Planetary nebulae in the galactic bulge

Abstract

Planetary Nebulae (PNe) are gaseous layers and dust shrouding dying stars with low- and intermediate-masses, showing predominant emission lines. With the advancement of wide-field and high-precision telescopes, for example, the HST and the ESO VLT, both high-resolution images and long-slit spectra became available for a growing sample of PNe. This allows an improvement in our understanding of both the formation of PNe, including the evolutionary his- tory, mass-loss physics, and chemical abundances of their progenitors, furthermore, to analyse the chemical environment in which their progenitors were born. This may give powerful insights into the chemical evolution of the galaxy they reside. The main purpose of this project is to make full use of the observation of 138 PNe in the Galactic bulge from the 8.2m ESO VLT. This set of observational data is comprised of high-resolution images and long-slit spectroscopic observations covering a wavelength range from 3660 to 8450 Å. With the imaging data, the morphologies, position angles, as well as central star visibilities of PNe in the sample, were investigated in combination with the HSTobservations where avail- able. The excellent resolving power of the VLT reveals many never-seen-before morphological features and central stars of PNe in previous studies. With the long-slit spectroscopic observations, the chemical abundances of PNe in this sample were derived after a careful data reduction. The oxygen abundance was then used as a metallicity indicator of the central stars of PNe to trace the chemical evolution in the Galactic bulge. An analysis of PN spatial distribution, oxygen abundance gradient and abundance distribution func- tion was carried out. Combining with the previous studies on different stellar populations in the bulge, these results add pieces of evidence to the origin of the bulge as a pseudo-bulge formed through disk instabilities in the inner thin disk. Besides, weak optical recombination lines were also detected in the spectroscopic observations which allow a determination of the abundance discrepancy in these objects. Different nebular and central star properties were investigated to find possible links to the abundance discrepancy in these objects. Our results confirm the relationship between abundance discrepancy factors (ADFs) and central star binarity, chemical abundances as well as electron densities noticed in previous studies.