The Galactic distribution of planetary nebulae with different types of dust

Abstract

We identify different dust features in our compilation of infrared spectra for 267 planetary nebulae (PNe) from the Spitzer, ISO, and IRAS telescopes. We classify 206 objects according to their dust type: mixed dust (MD), oxygen-rich dust (ORD), carbon-rich dust (CRD), PNe with only polycyclic aromatic hydrocarbons (PAHs) in their spectra (oPAH), and featureless (F) PNe. We study statistically the distributions of surface brightness and diameter of PNe with different types of dust as well as their distributions in the Galaxy.We find that both MD and ORD PNe are closer to the Galactic centre than CRD and oPAH PNe, and that the Galactic distributions of each pair of groups are statistically compatible, suggesting that they have similar progenitors. Since oPAH PNe have, on average, larger diameters and lower surface brightness than CRD PNe, we suggest that oPAH PNe are evolved CRD PNe. On the other hand, F PNe have the lowest surface brightness and the largest diameters, suggesting they could contain evolved PNe from any initial type of dust. Among the PNe with silicates, we find that only a few ORD PNe have just amorphous silicates in their spectra, and their distributions of Galactocentric distances and Galactic heights suggest that they had low-mass progenitors. MD PNe with both amorphous and crystalline silicates have the largest surface brightness and the smallest diameters and might be the earliest stages of PNe with the most massive and metal-rich progenitors.

Figures (10)

• Figure 1: Example of a spectrum with PAH features, whose expected positions are indicated with pink stripes. The green dotted lines show the wavelengths of nebular emission lines: MgV] 5.60 , H$_2$ S(6) 6.10 , H$_2$ S(5) 6.90 , HeI 6.99 , [NaIII] 7.31 , HI 7.48 , [NeIV] 7.65 , [ArV] 7.90 , H$_2$ S(4) 8.03 , [NeIV] 8.56 , H$_2$ S(3) 9.66 , [SIV] at 10.51 , HI 11.30 , H$_2$ S(2) 12.28 , HeI 12.39 , [NeII] 12.82 , [ArV] 13.10 , and [MgV] 13.52 .
• Figure 2: Top panel: spectrum of IC 4776, which shows features of amorphous silicates at $\sim10$ and crystalline silicates at $\sim23$, 28 and 33 , as indicated with the blue stripes. Middle panel: spectrum of Hen 2-26 showing the SiC feature at around 11 and the 30 feature, both marked with pink stripes. Bottom panel: spectrum of GJJC 1, a PN with no apparent dust features.
• Figure 3: Distributions (left panels) and $p$-values (right panels) of: a) the H$\alpha$ surface brightness of PNe, and b) the PN diameters, for different types of dust. The dashed lines in the left panels indicate the medians of the distributions. The right panels show the results of Kolmogorov-Smirnov (K-S) tests between each pair of dust types, with the lightest cells indicating similar distributions, and the darkest cells indicating significantly different distributions.
• Figure 4: Distributions of Galactic longitude ($l$) and latitude ($b$) of PNe with different types of dust. The numbers in the parentheses indicate the sample sizes. Five PNe lie outside the range plotted for $b$: MaC 2-1 (PN G205.8$-$26.7, CRD), NGC 6210 (PN G043.1+37.7, ORD), BoBn 1 (PN G108.4$-$76.1, oPAH), NGC 246 (PN G118.8$-$74.7, F), and NGC 7094 (PN G066.7$-$28.2, F).
• Figure 5: Distributions (right panels) and $p$-values (left panels) of a) heliocentric distances; b) Galactocentric distances; and c) projection on the Galactic plane of PNe with different types of dust. The dashed lines in the top and middle left panels indicate the medians of the distributions. In the bottom left panel, the positions of the Sun (0, 0) and the Galactic centre (8, 0) are marked in green as "$\odot$" and "GC", and the lines show the distance uncertainties. The right panels show the $p$-values obtained from one dimensional K-S tests that compare each pair of distributions. The darkest cells in these panels indicate significant differences between the distributions. The $p$-values that are based on an insufficient number of data are enclosed in parentheses