The kinematic evolution of the ionized shells of planetary nebulae

Abstract

Abstract. In this contribution we present the results of measuring the bulk outflow, or global expansion velocities for a large number of planetary nebulae (PNe) that span a wide range of evolutionary stages and different stellar populations. The sample comprises 133 PNe from the galactic bulge, 100 mature and highly evolved PNe from the disk, 11 PNe from the galactic halo and 15 PNe with very low central star masses and low metallicities, for a total of 259 PNe. The long-slit, echelle data are drawn from the SPM Kinematic Catalogue of Galactic Planetary Nebulae. These results reveal from a statistical perspective the kinematic evolution of the expansion velocities of PNe in relation with the changing characteristics of the central star's wind and ionizing luminosity and as a function of the evolutionary rate determined by the central star (CS) mass. The large number of PNe utilized in this work for each group of PNe under study and the homogeneity of the data provide for the first time a solid benchmark from observations for models predictions. This project is still in progress and aims at measuring expansion velocities for about 300 more galactic PNe with the aim of providing a reliable parametric description of their expansion velocity in terms of different populations, morphologies, evolutionary stages and CS masses. IntroductionPlanetary Nebulae are expanding ionized shells evolving from the mass loss process in the previous AGB stage. The expanding nature of PNe was recognized nearly 70 years ago [1]. It was then inferred [2] that PNe should descend from fast-evolving, mass-losing red giant stars to eventually become white dwarfs. These ideas led to the concept of PNe originating in the ejected envelope of red giants [3] and shortly after the first basic post-AGB evolutionary model track was calculated [4] starting with an AGB star with an electron degenerate core and a H shell burning envelope. The times were ripe to realize then that the AGB envelope is the precursor of the PN [5]. However, the shells of AGB stars need additional pressure to keep an expanding motion after being ejected and various mechanisms involving ionization fronts and radiation pressure on gas and dust were explored with unsatisfactory results, until it was concluded [6] that mass loss from active stellar winds was needed to maintain the shell expansion. This problem was originally solved through the interacting stellar winds model (ISW) [7] [8] where after the initial AGB mass loss phase the exposed core of the now much smaller star becomes hotter and mass loss through radiation pressure develops a faster wind that interacts with the previous slower wind from the AGB producing a shocked interface between the two. The ISW model provides

Deconstructing the Characteristics of the Ionized Gas Component in Planetary Nebulae From Their Internal Motions

“…They analysed the populations in the bulge, disk and halo, including in these groups stages of early, evolved, mature, and PNe with lowmass central stars. The result of these works are summarized in López et al (2016) and essentially show for the first time from observations how the kinematic evolution of the ionized shell correlates closely with the central star mass and its evolutionary stage during this last phase of stellar evolution (see Figure 5).…”

Euclid preparation

“…They have sufficiently many, bright near-infrared lines, and typical spectral expansion velocities of 10-50 km s −1 (e.g. Gesicki & Zijlstra 2000;Marigo et al 2001;Jacob et al 2013;López et al 2016;Schönberner 2016), at least a factor five below the NISP spectral resolution. PNe are also used to provide absolute wavelength calibration for instruments flying on other missions, such as the James Webb Space Telescope (JWST; Labiano et al 2021).…”