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Register a new userSpatio-kinematic modelling: Testing the link between planetary nebulae and close binaries
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David Jones
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It is widely believed that central star binarity plays an important role in the formation and evolution of aspherical planetary nebulae, however observational support for this hypothesis is lacking. Here, we present the most recent results of a continuing programme to model the morphologies of all planetary nebulae known to host a close binary central star. Initially, this programme allows us to compare the inclination of the nebular symmetry axis to that of the binary plane, testing the theoretical expectation that they will lie perpendicular - to date, all have satisfied this expectation, indicating that each nebula has been shaped by its central binary star. As a greater sample of nebulae are modelled, it will be possible to search for trends connecting the parameters of both nebula and central binary, strengthening our understanding of the processes at work in these objects. I will discuss some of the more obvious comparisons, and their current statuses, as well as the obvious links to common envelope evolution.
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We present kinematic data for 211 bright planetary nebulae in eleven Local Group galaxies: M31 (137 PNe), M32 (13), M33 (33), Fornax (1), Sagittarius (3), NGC 147 (2), NGC 185 (5), NGC 205 (9), NGC 6822 (5), Leo A (1), and Sextans A (1). The data were acquired at the Observatorio Astronomico Nacional in the Sierra de San Pedro Martir using the 2.1m telescope and the Manchester Echelle Spectrometer in the light of [ion{O}{3}]$lambda$5007 at a resolution of 11 km/s. A few objects were observed in H$alpha$. The internal kinematics of bright planetary nebulae do not depend strongly upon the metallicity or age of their progenitor stellar populations, though small systematic differences exist. The nebular kinematics and H$beta$ luminosity require that the nebular shells be accelerated during the early evolution of their central stars. Thus, kinematics provides an additional argument favoring similar stellar progenitors for bright planetary nebulae in all galaxies.
We investigate the possible progenitors of the planetary nebulae (PNs) which populate the top 0.5 mag of the [O III] 5007 planetary nebula luminosity function (PNLF). We show that the absolute luminosity of the PNLF cutoff demands that the central stars of these most luminous planetaries be greater than 0.6 Msun, and that such high-mass PN cores must exist in every galaxy. We also use the bolometric-luminosity specific PN number density to show that in early-type galaxies, [O III]-bright planetaries are relatively rare, with only about 10% of stars evolving to these bright magnitudes. We demonstrate that the combination of these two facts implies that either all early-type systems contain a small, smoothly distributed component of young (< 1 Gyr old) stars, or another mechanism exists for creating high-core mass planetaries. We argue that binary-star evolution is this second mechanism, and demonstrate that blue stragglers have the appropriate core properties and number density to explain the observations. We discuss the implications of this alternative mode of stellar evolution, and speculate on how coalesced binaries might affect the use of PNs for measuring a galaxys star-formation history and chemical evolution.
It has recently been noted that there seems to be a strong correlation between planetary nebulae with close binary central stars, and highly enhanced recombination line abundances. We present new deep spectra of seven objects known to have close binary central stars, and find that the heavy element abundances derived from recombination lines exceed those from collisionally excited lines by factors of 5-95, placing several of these nebulae among the most extreme known abundance discrepancies. This study nearly doubles the number of nebulae known to have a binary central star and an extreme abundance discrepancy. A statistical analysis of all nebulae with measured recombination line abundances reveals no link between central star surface chemistry and nebular abundance discrepancy, but a clear link between binarity and the abundance discrepancy, as well as an anticorrelation between abundance discrepancies and nebular electron densities: all nebulae with a binary central star with a period of less than 1.15 days have an abundance discrepancy factor exceeding 10, and an electron density less than $sim$1000 cm$^{-3}$; those with longer period binaries have abundance discrepancy factors less than 10 and much higher electron densities. We find that [O~{sc ii}] density diagnostic lines can be strongly enhanced by recombination excitation, while [S~{sc ii}] lines are not. These findings give weight to the idea that extreme abundance discrepancies are caused by a nova-like eruption from the central star system, occurring soon after the common-envelope phase, which ejects material depleted in hydrogen, and enhanced in CNONe but not in third-row elements.
The age distribution of the central stars of planetary nebulae (CSPN) is estimated using two methods based on their kinematic properties. First, the expected rotation velocities of the nebulae at their Galactocentric distances are compared with the predicted values for the rotation curve, and the differences are attributed to the different ages of the evolved stars. Adopting the relation between the ages and the velocity dispersions determined by the Geneva-Copenhagen survey, the age distribution can be derived. Second, the U, V, W, velocity components of the stars are determined, and the corresponding age-velocity dispersion relations are used to infer the age distribution. These methods have been applied to two samples of PN in the Galaxy. The results are similar for both samples, and show that the age distribution of the PN central stars concentrates in ages lower than 5 Gyr, peaking at about 1 to 3 Gyr.
The majority of planetary nebulae (PNe) show axisymmetric morphologies, whose causes are not well understood. In this work, we present spatially resolved kinematic observations of 14 Galactic PNe surrounding Wolf-Rayet ([WR]) and weak emission-line stars ($wels$) based on the H$alpha$ and [N II] emission taken with the Wide Field Spectrograph on the ANU 2.3-m telescope. Velocity-resolved channel maps and position--velocity diagrams, together with archival Hubble Space Telescope ($HST$) and ground-based images, are employed to construct three-dimensional morpho-kinematic models of 12 objects using the program SHAPE. Our results indicate that these 12 PNe have elliptical morphologies with either open or closed outer ends. Kinematic maps also illustrate on-sky orientations of elliptically symmetric morphologies of the interior shells in NGC 6578 and NGC 6629, and the compact ($leq 6$ arcsec) PNe Pe1-1, M3-15, M1-25, Hen2-142, and NGC 6567, in agreement with the high-resolution $HST$ images containing morphological details. Point-symmetric knots in Hb4 exhibit deceleration with distance from the nebular center that could be due to shock collisions with the ambient medium. Velocity dispersion maps of Pe1-1 disclose point-symmetric knots similar to those in Hb4. Collimated outflows are also visible in the position--velocity diagrams of M3-30, M1-32, M3-15, and K2-16, which are reconstructed by tenuous prolate ellipsoids extending upwardly from thick toroidal shells in our models.
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