Planetary Nebulae

Abstract

Planetary nebulae are formed by the matter ejected by low-to-intermediate mass stars (~0.8-8 times the mass of the Sun) towards the end of their lives. As hydrogen and then helium fuel sources run out, stars expand. During these giant phases stars also lose sizable amounts of mass. During the second giant phase, after the exhaustion of core helium, the mass loss is so great that stars lose a large fraction of their mass (50 - 90%), leaving behind a small, hot core, known as a white dwarf, surrounded by a nebula. Planetary nebulae are the result of many processes that shape and alter their ionization structure and chemical composition. The resulting nebula, illuminated by the ultraviolet-rich spectrum of the remnant very hot stellar core, is a spectacle of beauty and science. In this chapter, we show that these objects are invaluable laboratories for astrophysics, astrochemistry, and astromineralogy studies, with impact in many areas of Astronomy.

Figures (25)

• Figure 1: The planetary nebula NGC 6302 observed by the Hubble Space Telescope Wide Field Camera. This nebula is approximately 3300 light years away and is approximately 3 light years across. Colors are white for [S ii], orange for [N ii], brown for H$\alpha$, cyan for [O iii], blue for He ii, and purple for [O ii]. Credit: NASA, ESA.
• Figure 2: The Hertzsprung-Russell diagram for the Sun, a representation of the change in effective temperature and luminosity over the Sun's life, from today ("Sun Now") to when it will become a white dwarf. The thick blue line is instead the '' main sequence'', the locus where stars that burn hydrogen in their core, with lower mass stars occupying the bottom right side and more massive stars the top left. The red line is the Sun's evolution till the end of the AGB phase, the brown line is the post-AGB, pre-PN phase, the pink line is the PN phase while the purple line is the time when the PN has faded and the star cools as a white dwarf.
• Figure 3: Observed planetary nebulae with different shapes. Credits for the PN images: NASA, ESA, HEIC, WIYN, NOIRLab, NSF, The Hubble Heritage Team STScI/AURA, the ERO team (STScI + ST-ECF), C. R. O’Dell, J. Kastner, K. Noll, J. Schmidt, M. Canale, A. Fruchter, M. Meixner, P. McCullough, G. Bacon, G. Jacoby, J. Barrington, and A. Zijlstra.
• Figure 4: Main structures often seen in a planetary nebula. Left panel: the rim, shell and the much fainter halo nebular structures are indicated on the optical [O iii] emission line image of NGC 2022 Corradi_etal_2003. The central part of the image (shell and rim) and the outer part (halo) are shown in different intensity scales (separated by the white gap) to better represent the very different emission intensities. Right panel: concentric rings are observed in the halo of NGC 7009 Guerrero_etal_2020.
• Figure 5: Four PNe with different types of small scale structures obtained from the Hubble Space Telescope archive.