A. J. Holloway

The Morphology and Kinematics of the Complex Polypolar Planetary Nebula NGC 2440

Spatially resolved profiles of the Hα, [N II] 6584 A, and [O III] 5007 A lines have been obtained with the Manchester echelle spectrometer combined with the 2.1 m San Pedro Martir telescope over the planetary nebula NGC 2440. The resulting position-velocity (PV) arrays are compared with ground-based and HST archival imagery, revealing the complex structure that prevails in this object. This work represents the first detailed kinematical study of NGC 2440. Several bipolar structures are shown to be emerging at different position angles from the core, as expected from bipolar, rotating, episodic outflows with different degrees of collimation. Line splitting reaches main peak to peak separations of 175 km s-1 and 145 km s-1 in the western and eastern main lobes, respectively. The FWZI values of the complex profiles span a range of 250 km s-1 near the core and 150 km s-1 in the outer regions. The nebular core is found to be a toroid expanding radially at ≥22 km s-1, and the systemic heliocentric radial velocity of NGC 2440 is found to be 65 km s-1. When combined with existing measurements of the upper limit to the angular expansion, and assuming a tilt for the axis of the central toroid of 40° in the plane of the sky, this lower limit for the expansion velocity implies a distance of ≥1.45 kpc to NGC 2440. Puzzling kinematical features are the faint velocity components receding with radial velocity differences of 150 km s-1 with respect to the systemic radial velocity from prominent knots at both ends of the brightest bipolar configuration. Scattering by dust in these knots of the line profiles from the bright nebular core is a likely explanation for this curious phenomenon.

The Hypersonic, Bipolar, Knotty Outflow from the Engraved Hourglass Planetary Nebula MyCn 18

The remarkable velocity structure of the different components of the young planetary nebula MyCn 18 have been revealed by obtaining imagery and spatially resolved spectrometry of the Hα and [N II] λλ6548, 6584 lines with the Manchester echelle spectrometer combined with the 3.9 m Anglo-Australian telescope. The bright, bipolar, nebular core is shown to be composed of two extended hemispherical cavities whose axes are tilted at 52° to the plane of the sky. Ionized flows, at ≤90 km s-1 and parallel to the walls of these cavities, are occurring. The full extent of the elongated bipolar assembly of high-speed knots which apparently lie along the same axis is now revealed in a continuum-subtracted image in the light of the Hα and [N II] λλ6548, 6584 nebular emission lines. Complete spatial coverage of line profiles from these knots is also presented for the first time. In their most likely configuration, these knots are shown to have a range of outflowing speeds of ≤630 km s-1 that are proportional to their distance from the central star. There is some degree of point/velocity symmetry, indicating that some pairs of knots have been ejected in opposing directions at the same speed. Curiously, the line profiles from the knots are very narrow, i.e., from 15 to 30 km s-1. Among several possible explanations of the origin of these hypersonic knots is a recurrent nova-like ejection from a central binary star.

Observations of the neutral gas and dust in the radio galaxy 3C 305

We present MERLIN and Hubble Space Telescope (HST) observations of the central region of the nearby radio galaxy 3C 305 and use them to study the gas and dust in this object. The MERLIN observations are of neutral hydrogen (H I) absorption against the strong non-thermal 20 cm continuum seen towards the central 4 kpc of 3C 305. Our ∼0.2 arcsec (160 pc) resolution observations show that the H I absorption is highly localized against the south-western radio-emission with column densities ∼1.9 x 10 2 1 cm - 2 . The absorption is broad (full width at half maximum, FWHM, of 145 ′ 26 km s - 1 ) and redshifted by 130 km s - 1 relative to the systemic velocity. The HST images in multiple optical and infrared filters (430 nm, 702 nm, [O III] 500.7 nm, [Fe II] 1.64 μm and K-band polarization) are presented. Evidence is seen for coincidence of the [Fe n] emission with the knot at the end of the radio jet, which is evidence for the presence of shocks. We compare the optical and radio images in order to investigate the relationship between the dust and neutral gas distributions. An unresolved (0.07 arcsec) nucleus is detected in H and K and its properties are consistent with a quasar reddened by A V > 4. We propose that the absorption arises in a region of neutral gas and dust. Its structure is complex but is broadly consistent with an inclined disc of gas and dust encircling, but not covering, the active galactic nucleus. A comparison of the neutral gas observations and previous emission-line observations suggests that both the neutral and ionized gas are undergoing galactic rotation towards the observer in the north-east and away from the observer in the south-west. We propose that the outflow giving rise to the radio emission has a component towards the observer in the north-east and away from the observer in the south-west. Unfortunately, as we do not detect radio emission from the compact nucleus, we cannot set limits to neutral hydrogen absorption from a circumnuclear obscuring torus.

The origin of the strings in the outer regions of η Carinae

The narrow optical filaments (‘strings’ or ‘spikes’) emerging from the Homunculus of η Carinae are modelled as resulting from the passage of ballistic ‘bullets’ of material through the dense circumstellar environment. In this explanation, the string is the decelerating flow of ablated gas from the bullet. An archive Hubble Space Telescope image and new forbidden-line profiles of the most distinct of the strings are presented and discussed in terms of this simple model.

IRAS 04210+0400 : MODELLING THE OPTICAL SPECTRA FROM FLARING LARGE-SCALE JETS

The emission-lines in the active galaxy IRAS0421+0400 show a dramatic (�900kms 1 ) increase in the velocity spread at the position of radio hot-spots which are located at the beginning of extended radio lobes. We study a simple geometric model of an opening outflow which reproduces the structure found in the long-slit emission-line spectrum of the hot-spot regions. The predicted bifurcations in the optical image structure of these regions is confirmed by deep [Oiii]-5007u line-imaging. We propose that this phenomenon is the result of a jet emerging from the galaxy through the boundary between the interstellar and intergalactic medium. A similar model has previously been suggested as an explanation for wide angle tail radio sources (WAT’s). If our model proves to be correct in more detailed future observations, then IRAS0421+0400 provides the unique possibility to study the flaring jet phenomenon at optical wavelengths.

An Optical Nebula Associated with a Young X-Ray Supernova Remnant in Vela

A remarkable filamentary nebula (RCW 37) in the close vicinity of the newly discovered X-ray-emitting supernova remnant in Vela (RX J0852.0-4622) is investigated. This supernova explosion is arguably the nearest in recent history. A comparison is made between deep United Kingdom Schmidt Telescope optical images of the region and the ROSAT X-ray data in which the remnant was discovered. This reveals that RCW 37 is most likely directly associated with an X-ray projection from RX J0852.0-4622. This interpretation is strengthened by new long-slit echelle spectrometry of the edge of RCW 37 in the light of [S II] λ6716. A systematic increase in the velocity splitting of the line profiles, from the nebular edge toward its center, of 100 km s-1 is found. The structure bears morphological and kinematical similarities to the famous Crab Nebula funnel.

Smoke Rings Around Supernova 1987A

Detailed observations of the [Oiii]5007 Å emission from the elliptical rings around SN 1987A suggest a model wherein the two faint, outer rings are due to emission from two circular toroids moving outwards (at ≤ 25 km s−1) along a bipolar cone centred on the site of the supernova. The brighter, central ring is expanding radially outward at 8.3 km s−1. The rings must have been created ∼ 2-3 × 104 years before the supernova explosion and are thought to be a consequence of the interaction of stellar winds emanating from the progenitor system during the final stages of its evolution to a supernova.

IRAS 0421+0400: A Curious Spiral with Flaring Jets

We present new VLA observations of IRAS 0421+0400 at 1.4 and 5 GHz, providing dual frequency information and higher resolution than previously available. We find extremely accurate alignment of the central double with the closest (though not brightest) feature in the southern kiloparsec hotspot region. There is a tight relation between the symmetric radio structure and emission line gas in the hotspot regions of this Seyfert 2 type galaxy.