The spectrum of the variable planetary nebula IC 4997

The identification of PM 1-322 as a new young high-density planetary nebulae

“…But since in PM 1-322 we do not observe any absorption line or TiO band nor an increase of the continuum towards the red, which would indicate the presence of a companion, it is unlikely to be a binary symbiotic system The most likely explanation of why the position of PM 1-322 in this diagram is the same as that of the symbiotics, is that it is a young high-density planetary nebula. Figure 3 also shows the positions of other objects already classified as young high-density planetary-nebulae; Hen 2-57 from KB94 and IC 4997 from Hyung et al (1994). The other object, Hen 2-25 from Corradi (1995) might be a symbiotic or a PNe.…”

“…Using this procedure and from the observed line ratios Hα/Hβ and Hγ/Hβ we obtain E(B − V) = 0.17. It was assumed that the reddening law can be represented by the standard interstellar extinction curve f (λ), (Seaton 1979 (Pereira et al 1998;Schmid & Schild 1990;Gutiérrez-Moreno & Moreno 1996); and in the very young planetary nebulae Hen 2-57 (Kingsburgh & Barlow 1994, hereafter KB94), Hen 2-35 (Corradi 1995) and IC 4997 (Hyung et al 1994). …”

Study of electron density in planetary nebulae

“…The data used were taken from the electronic emissionline catalogue for planetary nebulae by Kaler et al (1997), from Kingsburgh & English (1992) and from the spectral survey of high surface brightness planetaries by Hyung, Aller, Feibelman and collaborators (Aller & Hyung 1995;Aller et al 1996;Feibelman et al 1994Feibelman et al , 1996Hyung 1994;Hyung & Aller 1995a,b, 1996, 1997a,b, 1998Hyung et al 1993Hyung et al , 1994aHyung et al ,b,c, 1995Hyung et al , 1997Hyung et al , 1999aHyung et al ,b, 2000Hyung et al , 2001Keyes et al 1990). Instead of comparing directly the derived densities, as has been done by other authors, what implies in discarding all line ratios close or beyond the saturation limits at low and high densities, we have compared the line ratios themselves with one another.…”

A Reexamination of Electron Density Diagnostics for Ionized Gaseous Nebulae

“…On the other hand, a very different result was obtained by Meatheringham & Dopita (1991) who found that for a sample of 44 PNe in the Magellanic Clouds, [S ] densities were systematically lower than those determined from the [O ] doublet ratio. Using high resolution spectroscopic data obtained with an echelle spectrograph, mostly by the group led by Aller Aller et al 1996;Feibelman et al 1994Feibelman et al , 1996Hyung 1994;Hyung & Aller 1995a,b, 1996, 1997a,b, 1998Hyung et al 1993Hyung et al , 1994aHyung et al ,b,c, 1995Hyung et al , 1997Hyung et al , 1999aHyung et al ,b, 2000Hyung et al , 2001Keyes et al 1990;Keenan et al 1993Keenan et al , 1996Keenan et al , 1997 they determined simultaneously electron densities and temperatures using a number of plasma diagnostic lines in the optical and ultraviolet and found that overall the data yielded compatible and consistent results. More recently, Copetti & Writzl (2002), using data published in the literature, compared the observed line ratios for a number of density-diagnostics, instead of densities deduced from them, thus avoiding discarding measurements that yield ratios close to or beyond the the low-or high-N e limits.…”