Integral field spectroscopy of planetary nebulae: mapping the line diagnostics and hydrogen-poor zones with VLT FLAMES

Abstract

Results from the first dedicated study of Galactic planetary nebulae (PNe) by means of optical integral field spectroscopy with the Very Large Telescope Fibre Large Array Multi Element Spectrograph Argus integral field unit are presented. Three typical Galactic disc PNe have been mapped with the 11.5 × 7.2‐arcsec2 Argus array: 2D spectral maps of the main shell of NGC 5882 and of large areas of NGC 6153 and NGC 7009 with 297 spatial pixels per target were obtained at subarcsec resolutions. A corresponding number of 297 spectra per target were obtained in the 396.4–507.8 nm range. Spatially resolved maps of emission lines and of nebular physical properties such as electron temperatures, densities and ionic abundances were produced. The abundances of helium and of doubly ionized carbon and oxygen, relative to hydrogen, were derived from optical recombination lines (ORLs), while those of O2+ were also derived from the classic collisionally excited lines (CELs). The occurrence of the abundance discrepancy problem, pertaining to oxygen, was investigated by mapping the ratio of ORL/CEL abundances for O2+[the abundance discrepancy factor (ADF)] across the face of the PNe. The ADF varies between targets and also with position within the targets, attaining values of ∼40 in the case of NGC 6153 and ∼30 in the case of NGC 7009. Correlations of the ADF with geometric distance from the central star and plasma surface brightness (for NGC 6153), as well as with [O iii] electron temperature, plasma ionization state and other physical properties of the targets are established. Very small values of the temperature fluctuation parameter in the plane of the sky, t2A(O2+), are found in all cases. It is argued that these results provide further evidence for the existence in run‐of‐the‐mill PNe of a distinct nebular component consisting of hydrogen‐deficient, super‐metal‐rich plasma. The zones containing this posited component appear as undulations in the C ii and O ii ORL abundance diagnostics of about 2 spatial pixels across, and so any associated structures should have physical sizes of less than ∼1000 astronomical units. Regarding the origin of the inferred zones, we propose that circumstellar discs, Abell 30‐type knots, or Helix‐type cometary globules may be involved. Implications for emission‐line studies of nebulae are discussed.

Characterization of the planetary nebula Tc 1 based on VLT X-shooter observations

“…Their analysis indicates that part of the extinction is internal to the nebula. This is also observed in the PNe extinction maps derived by Tsamis et al (2008) and by Leal-Ferreira et al (2011). Integrated line fluxes corrected for extinction (using c(Hβ) = 0.40) are presented in Appendix A.…”

Evolution of Planetary Nebulae with WR-type Central Stars

“…We can detect them in nearby PNe through very deep observations, due to their extremely weak intensities relative to the hydrogen recombination line Hβ . However, the abundances of carbon, nitrogen, oxygen and neon derived from ORLs are found to be systematically higher than those derived from CELs in many PNe (Rola & Stasińska 1994;Liu et al 1995Liu et al , 2000Liu et al , 2001Luo et al 2001;Wesson et al 2003;Tsamis et al 2004;Wesson et al 2005;Tsamis et al 2008;García-Rojas et al 2009). This problem was already found in gaseous nebulae over seventy years ago (Wyse 1942;Aller & Menzel 1945).…”

“…Tsamis et al 2003b;Peimbert et al 2005;García-Rojas et al 2007;López-Sánchez et al 2007;Peña-Guerrero et al 2012). However, the recent studies of ORLs indicated that the abundances derived using the ORL method are systematically higher than those derived from CELs in many PNe (Liu et al 2000(Liu et al , 2001Luo et al 2001;Wesson et al 2003;Tsamis et al 2004;Wesson et al 2005;Tsamis et al 2008;García-Rojas et al 2009). Such discrepancies are commonly described using the so-called abundance discrepancy factor (ADF): ADF(X i+ ) = (X i+ /H + ) ORLs / (X i+ /H + ) CELs , where X i+ is the i+ ionic abundance of element X and H + is the abundance of ionized hydrogen.…”

Exploring the differences of integrated and spatially resolved analysis using integral field unit data: the case of Abell 14

“…However, only a few PNe had been observed and studied with IFS, the majority of them during the last 5-6 yr (e.g. Tsamis et al 2008;Danehkar et al 2013;Monteiro et al 2013;Danehkar et al 2014;Ali et al 2015Ali et al , 2016Danehkar 2015;Danehkar & Parker 2015;Basurah et al 2016;Danehkar et al 2016;Walsh et al 2016;Dopita et al 2017Dopita et al , 2018Walsh et al 2018;Ali & Dopita 2019) and imaging fourier transform spectroscopy (Lagrois et al 2015).…”