Photoionization Models Applied to Planetary Nebulae

Abstract

Good to excellent photoionization models based on the Cloudy code (from Ferland and coworkers) were obtained for 13 out of 19 spectra of planetary nebulae (PNs). Results are deficient when the slit is missing most of the in-depth extent of the ionized region. Features that can be associated to shock excitation and abnormally large helium abundances are found when this is the case. Models assume that the exciting star is a Rauch photosphere illuminating a static uniform density spherical shell. Model central stars lie close to a 2.5 M post-AGB theoretical evolutionary track in the H-R diagram (from Vassiliadis and Wood), with implied PN ages between 1000 and 7000 yr. Observed and modeled nebular temperatures derived from [N ii] kk(6548 þ 6584)/k5755 agree within 10%, but models usually underestimate temperatures found from [O iii] kk(4959 þ 5007)/k4363, more so when the slit does not cover the in-depth extent of the ionized region. Helium, nitrogen, oxygen, neon, sulfur, chlorine, and argon model abundances are uncertain at the 15%, 15%, 10%, 7%, 30%, 5%, and 7% levels, respectively. The following relationships between chemical elements are found: He tends to be more abundant when N/O is large; there is a loose anticorrelation between N/O and O/H; N/C and C/H are anticorrelated; and the sum of the carbon, nitrogen, and oxygen abundances is larger in carbon-rich objects. Finally, it is shown that neon abundance in PNs has been overestimated, and an alternative ionization correction factor is provided.

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

“…The size of the nebula (r out ) is ∼10 17 cm with a low electron density (<100 cm 3 ). All these parameters are consistent with the results from our previous study of Abell 14 Bohigas 2008), but it does not explain the observed discrepancy, and ii) the high O abundance of the 3MdB cloudy models, ∼1 dex more abundant than the observations indicate. Such difference in O abundance, the most important coolant element, will significantly alter the ionization structure of the model and the rest of the emission-lines ratios.…”

The H surface brightness-radius relation: a robust statistical distance indicator for planetary nebulae

“…However, we have not utilised the distance for Mz 1 (Monteiro et al 2005), owing to the lack of a reliable CSPN magnitude needed for modelling. Additionally, Bohigas (2008) presented photoionization models for 19 PNe, deriving two distances per object by comparing the model output with the observed Hα flux and the angular size respectively. We only used PNe which had the model distances consistent to better than ±25%, with the additional requirement that the input parameters agreed with those in our database (Parker et al, in prep.).…”

Introducing PyCross: PyCloudy Rendering Of Shape Software for pseudo 3D ionisation modelling of nebulae

“…While spectroscopic data can be used to yield approximate values for temperature, velocity, and density along the line of sight of the object, a photoionisation model is required to determine the chemical structure of a nebula (Bohigas, 2008). As discussed in Harvey et al (2018), photoionisation modelling of ejected nova shells during their nebular stage of evolution can contribute to estimates of the total mass and abundances of heavy elements ejected during nova events (Helton et al, 2011).…”