610 research outputs found
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 ~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
Optical line profiles of the Helix planetary nebula (NGC 7293) to large radii
New, very long (25'), cuts of spatially resolved profiles of the Halpha and
[N II] optical emission lines have been obtained over the face of the Helix
planetary nebula, NGC 7293. These directions were chosen to supplement previous
similar, though shorter, cuts as well as crossing interesting phenomena in this
nebular envelope. In particular one new cut crosses the extremes of the
proposed CO J=2-1 emitting outer "torus" shown by Huggins and his co-workers to
be nearly orthogonal to its inner counterpart. The second new cut crosses the
extensive outer filamentary arcs on either side of the bright nebular core. It
is shown that NGC 7293 is composed of multiple bipolar outflows along different
axes. Hubble-type outflows over a dynamical timescale of 11,000 years are shown
to be occurring for all the phenomena from the smallest He II emitting core out
to the largest outer filamentary structure. All must then have been ejected
over a short timescale but with a range of ejection velocitiesComment: 14 pages, 7 figures, MNRAS in pres
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