New advances in the field of planetary nebulae from ultraviolet observations

Abstract

Abstract. The ultraviolet (UV) domain, in particular shortwards of Lyα, provides unique information to unravel the physical parameters of Central Stars of Planetary Nebulae (CSPNe) and the paths for this elusive final stage of stellar evolution, thanks to a wealth of diagnostic transitions from ionic species not observable at other wavelengths. Intermediate mass stars are the major providers of important elements like C and N. Understanding how they shed most of their initial mass is critical for understanding the chemical enrichment of the ISM. Mass-loss diagnostic lines abound at UV wavelengths, and when the CSPN reaches the hottest T eff before turning on the WD-cooling sequence, and the wind fades, the last wind lines to disappear are found in the far-UV, as well as diagnostic lines for elements such as Ne. This domain also offers a host of H 2 transitions, tracing the circum-stellar material expelled in previous phases. UV images and spectra of PNe add critical constraints to their ionization structure and to some abundances. Finally, the recent GALEX sky surveys in two UV bands afforded the first unbiased census of hot white dwarfs (WD) and post-AGB objects in the Milky Way, significantly expanding known catalogs and providing statistical constraints to the initial-final mass relation.

The effective temperatures of O-type stars from UV spectroscopy

“…by Puls, Vink & Najarro (2008), Najarro, Hanson, & Puls, J. (2011), see also also Bianchi 2012and references therein, Herald & Bianchi 2011, Keller et al 2011, Kaschinski et al 2012 for discussions on the importance of a consistent modeling, and on the effects on treatement of clumping in UV line analysis in evolved hot stellar objects, where similar issues are at play as those recalled in this work for massive stars, and e.g. Oskinova et al 2007 for additional discussion.…”

The ultraviolet sky: An overview from the GALEX surveys

“…Not surprisingly, many unexpected discoveries and results have emerged, beyond the original science goals of the GALEX mission (e.g. Bianchi 2011 for a partial review, Martin et al 2007, Wyder et al 2009, Thilker et al 2007a, Bianchi 2012.…”

Ultraviolet imaging of planetary nebulae with $\mathit{GALEX}$

“…The expanding layers of gas, shed in the previous Red Giant phases and then ionized by the hot central star (CSPN), offer clues about the progenitor's evolution, in particular about the chemical elements produced by nucleosynthesis and brought up to outer layers, about the temperature and luminosity of the stellar remnant, through their ionization, and about massloss and wind momentum in subsequent phases, through their complex expansion kinematics and density structure. Studies of both the nebula and the central star benefit by observations in the Ultraviolet (UV), where crucial diagnostic transitions of important chemical elements, and trace elements, abound (e.g., Bianchi 2016Bianchi , 2012. CSPNe, the hottest stars known, emit most of their light at UV wavelengths or shortwards.…”

“…The lower panel shows a zoomedin portion of the image, and a plot of archival IUE spectra taken in the bright part of the nebula, with the GALEX transmission bands overplotted, suggesting that the FUV flux mostly originates from HeII emission in the inner regions ald and Bianchi 2004Bianchi , 2007. For a review of the role of UV observations in the understanding of CSPNe see Bianchi (2012).…”