Flows along cometary tails in the Helix planetary nebula NGC 7293

Previous velocity images which reveal flows of ionized gas along the most prominent cometary tail (from Knot 38) in the Helix planetary nebula are compared with that taken at optical wavelengths with the Hubble Space Telescope and with an image in the emission from molecular hydrogen. The flows from the second most prominent tail from Knot 14 are also considered. The kinematics of the tail from the more complex Knot 32, shown here for the first time, also reveals an acceleration away from the central star. All of the tails are explained as accelerating ionized flows of ablated material driven by the previous, mildly supersonic, AGB wind from the central star. The longest tail of ionized gas, even though formed by this mechanism in a very clumpy medium, as revealed by the emission from molecular hydrogen, appears to be a coherent outflowing feature.Comment: 8 pages, 4 figures, accepted for publication in MNRA

Towards an explanation for the 30 Dor (LMC) Honeycomb nebula - the impact of recent observations and spectral analysis

The unique Honeycomb nebula, most likely a peculiar supernova remnant, lies in 30 Doradus in the Large Magellanic Cloud. Due to its proximity to SN1987A, it has been serendipitously and intentionally observed at many wavelengths. Here, an optical spectral analysis of forbidden line ratios is performed in order to compare the Honeycomb high-speed gas with supernova remnants in the Galaxy and the LMC, with galactic Wolf-Rayet nebulae and with the optical line emission from the interaction zone of the SS433 microquasar and W50 supernova remnant system. An empirical spatiokinematic model of the images and spectra for the Honeycomb reveals that its striking appearance is most likely due to a fortuitous viewing angle. The Honeycomb nebula is more extended in soft X-ray emission and could in fact be a small part of the edge of a giant LMC shell revealed for the first time in this short wavelength domain. It is also suggested that a previously unnoticed region of optical emission may in fact be an extension of the Honeycomb around the edge of this giant shell. A secondary supernova explosion in the edge of a giant shell is considered for the creation of the Honeycomb nebula. A microquasar origin of the Honeycomb nebula as opposed to a simple supernova origin is also evaluated.Comment: 12 pages, 9 figures, accepted for publication in MNRA

Unraveling the Helix Nebula: Its Structure and Knots

Through HST imaging of the inner part of the main-ring of the Helix Nebula together with CTIO 4-m images of the fainter outer parts, we have an unprecedented-quality view of the nearest bright planetary nebula. These images have allowed determination that the main-ring of the nebula is composed of an inner-disk of about 499\arcsec diameter (0.52 pc) surrounded by an outer-ring (in reality a torus) of 742\arcsec diameter (0.77 pc) whose plane is highly inclined to the plane of the disk. This outer-ring is surrounded by an outermost-ring of 1500\arcsec (1.76 pc) diameter which is flattened on the side colliding with the ambient interstellar medium. The inner-disk has an extended distribution of low density gas along its rotational axis of symmetry and the disk is optically thick to ionizing radiation, as is the outer-ring. Published radial velocities of the knots provides support for the two-component structure of the main-ring of the nebula and to the idea that the knots found there are expanding along with the nebular material from which it recently originated. There is a change in the morphology of the knots as a function of the distance from the local ionization front. This supports a scenario in which the knots are formed in or near the ionization front and are then sculpted by the stellar radiation from the central star as the ionization front advances beyond them.Comment: 30 pages, 20 figures, many figures have reduce fidelity for astroph preprint. Note: URLs in preprint were change

The tails in the Helix Nebula NGC 7293

We have examined a stream-source model for the production of the cometary tails observed in the Helix Nebula NGC 7293 in which a transonic or moderately supersonic stream of ionized gas overruns a source of ionized gas. Hydrodynamic calculations reveal velocity structures which are in good agreement with the observational data on tail velocities and are consistent with observations of the nebular structure. The results also are indicative of a stellar atmosphere origin for the cometary globules. Tail remnants persist for timescales long enough for their identification with faint striations visible in the nebula gas to be plausible.Comment: 7 pages, 6 figures, accepted for publication in A&

Candidates for giant lobes projecting from the LBV stars P Cygni and R 143

Deep, wide-field, continuum-subtracted, images in the light of the Halpha+[NII] 6548 & 6584 A and [O III] 5007 A nebular emission lines have been obtained of the environment of the Luminous Blue Variable (LBV) star P Cygni. A previously discovered, receding, nebulous filament along PA 50 deg has now been shown to extend up to 12' from this star. Furthermore, in the light of [O III] 5007 A, a southern counterpart is discovered as well as irregular filaments on the opposite side of P Cygni. Line profiles from this nebulous complex indicate that this extended nebulosity is similar to that associated with middle-aged supernova remnants. However, there are several indications that it has originated in P Cygni and is not just a chance superposition along the same sight-line. This possibility is explored here and comparison is made with a new image of the LBV star R 143 in the LMC from which similar filaments appear to project. The dynamical age of the P Cygni giant lobe of ~5x10^{4} yr is consistent with both the predicted and observed durations of the LBV phases of 50M stars after they have left the main sequence. Its irregular shape may have been determined by the cavity formed in the ambient gas by the energetic wind of the star, and shaped by a dense torus, when on the main sequence. The proper motion and radial velocity of P Cygni, with respect to its local environment, could explain the observed angular and kinematical shifts of the star compared with the giant lobe.Comment: 7 pages, 3 figures, accepted for publication in A&

High speed outflows driven by the 30 Doradus starburst

Echelle spectroscopy has been carried out towards a sample region of the halo of the giant HII region 30 Doradus in the Large Magellanic Cloud. This new kinematical data is the amongst the most sensitive yet obtained for this nebula and reveals a wealth of faint, complex high speed features. These are interpreted in terms of localised shells due to individual stellar winds and supernova explosions, and collections of discrete knots of emission that still retain the velocity pattern of the giant shells from which they fragmented. The high speed velocity features may trace the base of the superwind that emanates from the 30 Doradus starburst, distributed around the super star cluster R136.Comment: 8 pages, 8 figures, accepted for publication in MNRA

A long trail behind the planetary nebula HFG1 (PK 136+05) and its precataclysmic binary central star V664 Cas

A deep wide-field image in the light of the Halpha+[N II] emission lines, of the planetary nebula HFG1 which surrounds the precataclysmic binary system V664 Cas, has revealed a tail of emission at least 20' long, at a position angle of 316deg. Evidence is presented which suggests that this is an ~10^5 y old trail of shocked material, left behind V664 Cas as it ejects matter whilst ploughing through its local interstellar media at anywhere between 29 and 59 km/s depending on its distance from the Sun.Comment: 3 pages, 1 figure, accepted for publication in MNRA

The Manchester occulting mask imager (MOMI) - first results on the environment of P Cygni

The design and first use of the Manchester occulting mask imager (MOMI) is described. This device, when combined with the Cassegrain or Ritchey-Chretien foci of large telescopes, is dedicated to the imagery of faint line emission regions around bright central sources. Initial observations, with MOMI on the Nordic Optical telescope (NOT), of the V=4.8 mag P~Cygni environment, have revealed a $\geq$~5~arcmin long [NII] 6584A emitting filament projecting from the outer nebular shell of this luminous blue variable (LBV) star. The presence of a mono-polar lobe older than both the inner (22 arcsec diameter) and outer (1.6 arcmin diameter) shells is suggested.Comment: 4 pages, 4 figures, accepted MNRAS 1998 June 1

MERLIN radio detection of an interaction zone within a binary Orion proplyd system

Presented here are high angular resolution MERLIN 5 GHz (6 cm) continuum observations of the binary proplyd system, LV 1 in the Orion nebula, which consists of proplyd 168--326SE and its binary proplyd companion 168--326NW (separation 0.4 arcsec). Accurate astrometric alignment allows a detailed comparison between these data and published HST PC Halpha and [Oiii] images. Thermal radio sources coincide with the two proplyds and originate in the ionized photoevaporating flows seen in the optical emission lines. Flow velocities of approx 50 km/s from the ionized proplyd surfaces and \geq 100 km/s from a possible micro-jet have been detected using the Manchester Echelle spectrometer. A third radio source is found to coincide with a region of extended, high excitation, optical line emission that lies between the binary proplyds 168--326SE/326NW . This is modelled as a bowshock due to the collision of the photoevaporating flows from the two proplyds. Both a thermal and a non-thermal origin for the radio emission in this collision zone are considered.Comment: 23 pages, 9 figures, accepted by Ap