Abundances and Gradients in the Milky Way Disk Based on Deep Spectroscopy of Compact Planetary Nebulae

As an important phase of the late-stage evolution of the low- and intermediate-mass stars (1 to 8 solar masses) that account for the absolute majority of the stellar populations in the universe, planetary nebulae (PNe) are probes of chemical evolution of the Milky Way. We carried out deep, optical long-slit spectroscopy of a sample of 24 compact PNe in the Milky Way disk using the OSIRIS spectrograph on the 10.4m Gran Telescopio Canarias (GTC, La Palma). The spatial distribution of this sample of PNe extends as far as 25 kpc from the Galactic centre. By analyzing the GTC optical spectra in combination with the available Spitzer/IRS MIR and HST/STIS UV data, we derived chemical abundances of carbon, oxygen, nitrogen and other heavy elements (neon, sulfur, chlorine, argon) of these PNe. Abundance gradients of the Galactic disk are also derived based on the PN sample using the accurate galactocentric distances available from Gaia, and compared with the gradients defined by the Galactic H II regions from the literature. Chemical evolution of the Milky Way is discussed based on these new results. [Note: This work is support by NSF grant AST-1616807.]