Photoionization Modeling of Planetary Nebulae in the Galactic Bulge

TL;DR

This study presents the most comprehensive photoionization modeling to date for 124 Galactic bulge PNe using Cloudy, constraining central-star temperatures ($T_{\mathrm{eff}}$) near $10^{5}$ K, luminosities around $3\times10^{3}\,L_\odot$, and inner nebular radii up to $0.31$ pc. The authors employ Gaia distances and multi-wavelength photometry (IRAS/WISE, radio) with a homogeneous spherical-shell assumption to infer gas/dust properties and elemental abundances, finding general agreement with Tan24 ($\lesssim0.5$ dex) and a robust Cl/H concordance but larger scatter in He/H and S/H. Evolutionary inferences from post-AGB tracks yield progenitor masses $M_i$ between $0.8$ and $4.2\,M_\odot$, final masses $M_f$ between $0.53$ and $0.87\,M_\odot$, substantial mass loss, and post-AGB ages from $\sim$150 to $2\times10^{4}$ yr, with most PNe in an intermediate evolutionary stage. The work enhances our understanding of CSPN evolution, nebular gas/dust content, and bulge chemical evolution, and highlights the influence of infrared photometry on fit quality. Overall, it provides a valuable, expansive dataset for refining PN physics in the Galactic bulge.

Abstract

In this study, we present the results of photoionization modeling for 124 planetary nebulae (PNe) in the Galactic bulge. Utilizing the {\scshape cloudy} code, we derived the effective temperatures (T$_{eff}$) of the central stars, with a peak distribution around $\sim$ 100,000 K, and luminosities clustering around $\sim$ 3,000 L$\odot$. The inner radii of the ionized regions range from 0.003 to 0.31 pc, with nebula diameters varying from 1.8" to 34", averaging 7\% larger than the observed visible diameters. Elemental abundances for Helium, Nitrogen, Oxygen, Neon, Sulphur, Chlorine and Argon relative to hydrogen derived from the models show consistency within 0.5 dex, with notable variations in Sulphur, Nitrogen, and Chlorine. The study also compares elemental abundances from photoionization models with previous observations, showing overall good agreement, particularly for Cl/H, but notable discrepancies in He/H and S/H ratios. The models' goodness of fit, quantified by $χ^{2}$ values, varies widely, with higher values linked to discrepancies in WISE photometric data. The evolutionary tracks of the central stars from H-R diagrams suggest progenitor masses ranging from 0.8 to 4.2 $M_\odot$ and progenitor final masses between 0.53 and 0.87 $M_\odot$, indicating significant mass loss during evolution. These PNe have post-AGB ages ranging from 150 to 20,000 years, consistent with the Galactic PNe distribution. Most of the PNe are in an intermediate evolutionary stage with larger nebular sizes. Our results provide the most comprehensive photoionization modeling to date, with key implications for central stars of PNe, gas, and dust.

Figures (6)

• Figure 1: RGB composite images of PN G002.8+01.7, PN G352.1+05.1, PN G007.6+06.9, and PN G359.3$-$01.8 generated using WISE data. The images are composed with Red: W4, Green: W3, and Blue: W2 channels, and are arranged according to the PN G designations listed in Table \ref{['T:obslog']}. Each planetary nebula is located at the center of its panel, typically exhibiting a reddish hue. Each image spans $500\hbox{$^{\prime\prime}$} \times 500\hbox{$^{\prime\prime}$}$, with north up and east to the left. Remaining PNe images have given as supplementary data.
• Figure 2: SED of PN G356.8+03.3. The SED, generated from the best cloudy model with a $\chi^2 = 0.55$ among all PNe, is represented by the orange lines. Key parameters derived from the model are shown in the upper left corner. Blue circles denote IRAS data, the black circle represents radio data, and the blue inverted triangles indicate the upper limit of the IRAS data.
• Figure 5: The histograms of parameters output from the cloudy model are presented in Table \ref{['T:cloudy_out']}. The element abundances are shown in the form of log(X/H) + 12. The red dashed lines indicate the median for each value. The median and bin size are provided at the corresponding location on the plot.
• Figure 6: Box plot of abundance ratios of He/H, N/H, O/H, Ne/H, S/H, Cl/H and Ar/H between observed data and cloudy model. The y-axis indicates deviations in abundance ratios, with the red line at zero representing no difference between observations and the model. The plot highlights the median, interquartile range, and outliers for each element of PNe.
• Figure 7: The distribution of 124 planetary nebulae (black filled circles) in the H-R diagram is shown using their effective temperatures, $T_{\mathrm{eff}}$, and luminosities, $L/L_{\odot}$. Post-AGB evolutionary tracks are adopted from 2016AA...588A..25M. Gray dashed curves denote linearly interpolated tracks at $0.1\,M_{\odot}$ increments (solar metallicity $Z=0.02$). The blue dashed line marks the beginning of the post-AGB phase, defined at $\log T_{\mathrm{eff}}=3.85$ as $\tau=0$. Blue squares indicate ages of $10\,000$ yr measured from $\tau=0$. Black shaded regions are reproduced from 2020Galax...8...29G.