Nebular Abundance Errors

The errors inherent to the use of the standard "ionization correction factor" ("i_CF") method of calculating nebular conditions and relative abundances of H, He, N, O, Ne, S, and Ar in emission line nebulae have been investigated under conditions typical for planetary nebulae. The photoionization code CLOUDY was used to construct a series of model nebulae with properties spanning the range typical of PNe. Its radial "profiles" of bright, frequently observed optical emission lines were then summed over a variety of "apertures" to generate sets of emission line measurements. These resulting line ratios were processed using the i_CF method to "derive" nebular conditions and abundances. We find that for lines which are summed over the entire nebula the i_CF-derived abundances differ from the input abundances by less than 5% for He and O up to 25% or more for Ne, S, and Ar. For resolved observations, however, the discrepancies are often much larger and are systematically variable with radius. This effect is especially pronounced in low-ionization zones where nitrogen and oxygen are neutral or once-ionized such as in FLIERs, ansae and ionization fronts. We argue that the reports of stellar-enriched N in the FLIERs of several PNe are probably specious.Comment: 22 pages, 4 tables, and 1 figure. Accepted for publication in the Astronomical Journal. Replaced to correct a referenc

Abundances of Disk Planetary Nebulae in M31 and the Radial Oxygen Gradient

We have obtained spectra of 16 planetary nebulae in the disk of M31 and determined the abundances of He, N, O, Ne, S and Ar. Here we present the median abundances and compare them with previous M31 PN disk measurements and with PNe in the Milky Way. We also derive the radial oxygen gradient in M31, which is shallower than that in the Milky Way, even accounting for M31's larger disk scale length.Comment: 2 pages, 1 figure, 1 table, to appear in the proceedings of IAU Symposium No. 283, Planetary Nebulae: An Eye to the Futur

The evolution of M 2-9 from 2000 to 2010

M 2-9, the Butterfly nebula, is an outstanding representative of extreme aspherical flows. It presents unique features such as a pair of high-velocity dusty polar blobs and a mirror-symmetric rotating pattern in the inner lobes. Imaging monitoring of the evolution of the nebula in the past decade is presented. We determine the proper motions of the dusty blobs, which infer a new distance estimate of 1.3+-0.2 kpc, a total nebular size of 0.8 pc, a speed of 147 km/s, and a kinematical age of 2500 yr. The corkscrew geometry of the inner rotating pattern is quantified. Different recombination timescales for different ions explain the observed surface brightness distribution. According to the images taken after 1999, the pattern rotates with a period of 92+-4 yr. On the other hand, the analysis of images taken between 1952 and 1977 measures a faster angular velocity. If the phenomenon were related to orbital motion, this would correspond to a modest orbital eccentricity (e=0.10+-0.05), and a slightly shorter period (86+-5 yr). New features have appeared after 2005 on the west side of the lobes and at the base of the pattern. The geometry and travelling times of the rotating pattern support our previous proposal that the phenomenon is produced by a collimated spray of high velocity particles (jet) from the central source, which excites the walls of the inner cavity of M 2-9, rather than by a ionizing photon beam. The speed of such a jet would be remarkable: between 11000 and 16000 km/s. The rotating-jet scenario may explain the formation and excitation of most of the features observed in the inner nebula, with no need for additional mechanisms, winds, or ionization sources. All properties point to a symbiotic-like interacting binary as the central source of M 2-9.Comment: Accepted for publication on Astronomy and Astrophysics (10 pages, 8 figures

Abundances of PNe in the Outer Disk of M31

We present spectroscopic observations and chemical abundances of 16 planetary nebulae (PNe) in the outer disk of M31. The [O III] 4363 line is detected in all objects, allowing a direct measurement of the nebular temperature essential for accurate abundance determinations. Our results show that the abundances in these M31 PNe display the same correlations and general behaviors as Type II PNe in the Milky Way Galaxy. We also calculate photoionization models to derive estimates of central star properties. From these we infer that our sample PNe, all near the peak of the Planetary Nebula Luminosity Function, originated from stars near 2 M_sun. Finally, under the assumption that these PNe are located in M31's disk, we plot the oxygen abundance gradient, which appears shallower than the gradient in the Milky Way.Comment: 48 pages, including 12 figures and 8 tables, accepted by Astrophysical Journa

Rings and arcs around evolved stars. II. The Carbon Star AFGL 3068 and the Planetary Nebulae NGC 6543, NGC 7009 and NGC 7027

We present a detailed comparative study of the arcs and fragmented ring-like features in the haloes of the planetary nebulae (PNe) NGC 6543, NGC 7009, and NGC 7027 and the spiral pattern around the carbon star AFGL 3068 using high-quality multi-epoch HST images. This comparison allows us to investigate the connection and possible evolution between the regular patterns surrounding AGB stars and the irregular concentric patterns around PNe. The radial proper motion of these features, ~15 km/s, are found to be consistent with the AGB wind and their linear sizes and inter-lapse times (500-1900 yr) also agree with those found around AGB stars, suggesting a common origin. We find evidence using radiative-hydrodynamic simulations that regular patterns produced at the end of the AGB phase become highly distorted by their interactions with the expanding PN and the anisotropic illumination and ionization patterns caused by shadow instabilities. These processes will disrupt the regular (mostly spiral) patterns around AGB stars, plausibly becoming the arcs and fragmented rings observed in the haloes of PNe.Comment: 13 pages, 9 figures, accepted for publication in MNRA

Spectroscopic confirmation of the planetary nebula nature of PM1-242, PM1-318 and PM1-333 and morphological analysis of the nebulae

We present intermediate resolution long-slit spectra and narrow-band Halpha, [NII] and [OIII] images of PM1-242, PM318 and PM1-333, three IRAS sources classified as possible planetary nebulae. The spectra show that the three objects are true planetary nebulae and allow us to study their physical properties; the images provide a detailed view of their morphology. PM1-242 is a medium-to-high-excitation (e.g., HeII4686/Hbeta ~0.4; [NII]6584/Halpha ~0.3) planetary nebula with an elliptical shape containing [NII] enhanced point-symmetric arcs. An electron temperature [Te([SIII])] of ~10250 K and an electron density [Ne([SII])] of ~2300 cm-3 are derived for PM1-242. Abundance calculations suggest a large helium abundance (He/H ~0.29) in PM1-242. PM1-318 is a high-excitation (HeII4686/Hbeta ~1) planetary nebula with a ring-like inner shell containing two enhanced opposite regions, surrounded by a fainter round attached shell brighter in the light of [OIII]. PM1-333 is an extended planetary nebula with a high-excitation (HeII4686/Hbeta up to ~0.9) patchy circular main body containing two low-excitation knotty arcs. A low Ne([SII]) of ~450 cm-3 and Te([OIII]) of ~15000 K are derived for this nebula. Abundance calculations suggest that PM1-333 is a type I planetary nebula. The lack of a sharp shell morphology, low electron density, and high-excitation strongly suggest that PM1-333 is an evolved planetary nebula. PM1-333 also shows two low-ionization polar structures whose morphology and emission properties are reminiscent of collimated outflows. We compare PM1-333 with other evolved planetary nebulae with collimated outflows and find that outflows among evolved planetary nebulae exhibit a large variety of properties, in accordance with these observed in younger planetary nebula.Comment: Accepted in The Astronomical Journal, 23 pages, 6 figure