Kinematical analysis of PNe with high ADF: Hf 2-2 and M 1-42

TL;DR

Two planetary nebulae with large ADFs, Hf 2-2 and M 1-42, are analyzed with high-resolution PV diagrams to test the two-plasma-component hypothesis. The study identifies a normal nebular plasma that emits both CELs and ORLs and an additional, denser, cooler plasma that predominantly emits permitted lines, spatially closer to the central star. The ADFs arise mainly from the mass of $O^{2+}$ in the additional plasma, reaching values up to ~300 in Hf 2-2 and >100 in M 1-42, rather than from the physical conditions alone. The results imply that accurately determining chemical abundances in high-ADF PNe requires modeling hydrogen-poor, cold, dense plasma and that the ADF reflects ion-mass distribution within multi-component ejected material.

Abstract

We use deep Echelle spectroscopy of the planetary nebulae Hf 2-2 and M1-42 to study the characteristics of the plasma that gives rise to their high abundance discrepancy factors (70 and 20, respectively). We analyze position-velocity diagrams for forbidden and permitted lines (92 and 93 lines in Hf 2-2 and M 1-42, respectively), to compare their kinematic behaviour and to determine the physical characteristics of the emitting plasma. We confirm that there are two plasma components in both nebulae: a normal nebular plasma that emits both forbidden and permitted lines and an additional plasma component that emits the permitted lines of O I, C II, N II, O II, and Ne II. These plasma components have different spatial distributions, with the additional plasma component being the more centrally concentrated. Their physical conditions are also different, with the additional plasma component being denser and cooler. We find that, in these objects, the additional plasma component contains masses of N$^{2}$ and O$^{2}$ ions that are at least as large as the normal nebular plasma. In both objects, we find strong gradients in the electron temperature in small volumes near the central star. Compared to NGC 6153, we find that the larger ADFs in Hf 2-2 and M 1-42 are due to larger masses of ions that emit only in the permitted lines, and not due to the physical conditions.

Figures (26)

• Figure 1: These images of Hf 2-2 (left) and M 1-42 (right) indicate the slit position for the red spectra. The slit size is $15.75\arcsec \times 2\arcsec$ but the decker limits the silt length to $13\arcsec$ for red spectra and 10 for blue. The arrows show the image orientation. The slit position angle is $45^\circ$ for Hf 2-2 and $120^\circ$ for M 1-42.
• Figure 2: Left: We present RGB composite images based upon MUSE data cubes for Hf 2-2 (top) and M 1-42 (bottom) with the spectrograph slit superposed garciarojas2022. Emission from Heii $\lambda$4686 is shown in blue, [Oiii] $\lambda$4959 in green, and [Nii] $\lambda$6548 in red, all displayed on a logarithmic scale. Right: We present the PV diagrams of the H$\beta$ line for each object at the same spatial scale as the images on the left. Here, and in subsequent PV diagrams, the line intensity runs from zero (white) to its maximum value (red), given in the box at upper left. The vertical (spatial) scale is in arc seconds, with a resolution of $0.36 \arcsec/$pixel, and the horizontal scale is the velocity in km s$^{-1}$, centred at the systemic velocity of each object. The horizontal black line indicates the position of the central star. The blank space at the bottom of the PV diagram for Hf 2-2 is the spatial region seen only in the red slit. The PV diagrams have the nebular and stellar continua subtracted. Two schematic ellipses have been drawn to describe the inner and outer shells in Hf 2-2.
• Figure 3: These PV diagrams illustrate the ionization structure of Hf 2-2. The left column shows commonly observed strong forbidden lines as well Heii $\lambda$4686. The right column displays weak permitted lines of C$^+$, N$^+$, and O$^+$. In [Oi] $\lambda$6300, the bright vertical band is a sky line. The PV diagrams are arranged in order of ionization potential, from lowest (bottom) to highest (top). Here, the ionization energy corresponding to the ion that initiates the line emission process is shown in the box at upper left.
• Figure 4: We present the Wilson diagram of Hf 2-2 in two parts. The upper diagram displays forbidden nebular, recombination, and fluorescence lines. The lower diagram repeats the results from the upper panel, but adds the data for forbidden auroral lines and the permitted lines of Oi, Cii, Nii, Oii, and Neii. The blue and black dotted lines represent linear fits to the collisionally excited lines and to the Oi, Cii, Nii, Oii, and Neii lines, respectively.
• Figure 5: We present the PV diagrams of the [Sii] $\lambda\lambda$6716,6731 (left) and [Oii] $\lambda\lambda$3726,3729 lines (right) and the density derived from their ratios (bottom row) for Hf 2-2. The contour lines in the bottom row correspond to the intensities of [Sii] $\lambda$6716 and [Oii] $\lambda$3726 lines, respectively. Here, and in subsequent PV diagrams, the contours are drawn at 10%, 20%, ..., 90% of the maximum intensity, shown in the box at upper left.