arXiv subjects

J. A. Lopez

Publications and source records attributed to J. A. Lopez.

29 records · Page 2Linked to original sources

arXiv2005

The kinematics of the large western knot in the halo of the young planetary nebula NGC 6543

A detailed analysis is presented of the dominant ionised knot in the halo of the planetary nebula NGC 6543. Observations were made at high spectral and spatial resolution of the [OIII] 5007 line using the Manchester echelle spectrometer combined with the 2.1-m San Pedro Martir Telescope. A 20-element multislit was stepped across the field to give almost complete spatial coverage of the knot and surrounding halo. The spectra reveal, for the first time, gas flows around the kinematically inert knot. The gas flows are found to have velocities comparable to the sound speed as gas is photo-evaporated off an ionised surface. No evidence is found of fast wind interaction with the knot and we find it likely that the fast wind is still contained in a pressure-driven bubble in the core of the nebula. This rules out the possibility of the knot having its origin in instabilities at the interface of the fast and AGB winds. We suggest that the knot is embedded in the slowly expanding Red Giant wind and that its surfaces are being continually photoionised by the central star.

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arXiv2005

The creation of the Helix planetary nebula (NGC 7293) by multiple events

A deep, continuum-subtracted, image of NGC 7293 has been obtained in the light of the Halpha+[N II] emission lines. New images of two filamentary halo stuctures have been obtained and the possible detection of a collimated outflow made. Spatially resolved, longslit profiles of the Halpha+[N II] lines have been observed across several of these features with the MES combined with the SPM 2.1m telescope; these are compared with the [N II]6584, [O III]5007, HeII 6560 and Halpha profiles obtained over the nebular core. The central HeII emission is originating in a ~0.34pc diameter spherical volume expanding at <=12km/s which is surrounded, and partially coincident with an [O III] emitting inner shell expanding at 12km/s. The bright helical structure surrounding this inner region is modelled as a bi-polar nebula with lobe expansions of 25km/s whose axis is tilted at 37deg to the sight line but with a toroidal waist itself expanding at 14 km/s. These observations are compared with the expectations of the interacting two winds model for the formation of PNe. Only after the fast wind has switched off could this global velocity structure be generated. Ablated flows must complicate any interpretation. It is suggested that the clumpy nature of much of the material could play a part in creating the radial `spokes' shown here to be apparently present close to the central star. These `spokes' could in fact be the persistant tails of cometary globules whose heads have now photo-evaporated completely. A halo arc projecting from the north-east of the bright core has a conterpart to the south-east. Anomolies in the position-velocity arrays of line profiles could suggest that these are part of an expanding disc not aligned with the central helical structure though expanding bi-polar lobes along a tilted axis are not ruled out.

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arXiv2005

The global kinematics of the Dumbbell planetary nebula (NGC 6853, M27, PN G060.8-03.6)

Spatially resolved profiles of the HeII 6560 A, Halpha and [N II] 6548 & 6584 A nebular emission lines have been obtained in two orthogonal long cuts over the Dumbbell planetary nebula. The central HeII 6560 A emitting volume of the bright dumbbell structure is shown to be particularly inert with an expansion velocity of <= 7 km/s. This is enveloped by an inner [O III] 5007 A emitting shell expanding at 13 km/s, an outer [O III] 5007 A shell expanding at 31 km/s which is on the inside of the outer [N II] 6584 A emitting shell expanding at 35 km/s. A new Halpha + [N II] 6548 & 6584 A continuum-subtracted image of the 15' diameter halo has also been compared with recent proper motion measurements of the central star and the present line profiles from the halo's inner edge. Interaction with the ambient interstellar medium is suggested. The bright [N II] 6584 A emitting shell must be running into this relatively inert halo with a differential velocity of >= 25 km/s. The present results are compared with currents models for the creation of planetary nebulae.

astro-ph↗

arXiv2004

The kinematics of the bi-lobal supernova remnant G 65.3+5.7 - Paper II

Further deep, narrow-band images in the light of [O III] 5007 A have been added to the previous mosaic of the faint galactic supernova remnant G 65.3+5.7. Additionally longslit spatially resolved [O III] 5007 A line profiles have been obtained at sample positions using the Manchester Echelle Spectrometer at the San Pedro Martir observatory. The remnant is shown to be predominantly bi-lobal with an EW axis for this structure. However, a faint additional northern lobe has now been revealed. Splitting of the profiles along the slit lengths, when extrapolated to the remnant's centre, although uncertain suggests that the expansion velocity of this remnant is between 124 and 187 km/s ie much lower than the 400 km/s previously predicted for the forward shock velocity from the X-ray emission. An expansion proper motion measurement of 2.1+-0.4 arcsec in 48 years for the remnant's filamentary edge in the light of Halpha+[N II] has also been made. When combined with an expansion velocity of ~155 km/s, a distance of ~800 pc to G 65.3+5.7 is derived. Several possibilities are considered for the large difference in the expansion velocity measured here and the 400 km/s shock velocity required to generate the X-ray emission. It is also suggested that the morphology of the remnant may be created by a tilt in the galactic magnetic field in this vicinity.

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arXiv2004

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.

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arXiv2003

The kinematics of the most oxygen-poor planetary nebula PN G135.9+55.9

PN G135.9+55.9 is a compact, high excitation nebula that has been identified recently as the most oxygen-poor halo planetary nebula. Given its very peculiar characteristics and potential implications in the realms of stellar and Galactic evolution, additional data are needed to firmly establish its true nature and evolutionary history. Here we present the first long-slit, high spectral resolution observations of this object in the lines of H$α$ and He II 4686. The position-velocity data are shown to be compatible with the interpretation of PN G135.9+55.9 being a halo planetary nebula. In both emission lines, we find the same two velocity components that characterize the kinematics as that of an expanding elliptical envelope. The kinematics is consistent with a prolate ellipsoidal model with axis ratio about 2:1, a radially decreasing emissivity distribution, a velocity distribution that is radial, and an expansion velocity of 30 km/s for the bulk of the material. To fit the observed line profiles, this model requires an asymmetric matter distribution, with the blue-shifted emission considerably stronger than the red-shifted emission. We find that the widths of the two velocity components are substantially wider than those expected due to thermal motions, but kinematic structure in the projected area covered by the slit appears to be sufficient to explain the line widths. The present data also rule out the possible presence of an accretion disk in the system that could have been responsible for a fraction of the H$α$ flux, further supporting the planetary nebula nature of PN G135.9+55.9.

astro-ph↗

arXiv2002

Unveiling the structure of the planetary nebula M 2-48: Kinematics and physical conditions

The kinematics and physical conditions of the bipolar planetary nebula M 2-48 are analysed from high and low dispersion long-slit spectra. Previous CCD narrow-band optical observations have suggested that this nebula is mainly formed by a pair of symmetric bow-shocks, an off-center semi-circular shell, and an internal bipolar structure. The bipolar outflow has a complex structure, characterised by a series of shocked regions located between the bright core and the polar tips. There is an apparent kinematic discontinuity between the bright bipolar core and the outer regions. The fragmented ring around the bright bipolar region presents a low expansion velocity and could be associated to ejection in the AGB-PN transition phase, although its nature remains unclear. The chemical abundances of the central region are derived, showing that M 2-48 is a Type I planetary nebula (PN).

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arXiv2001

FLIERs as stagnation knots from post-AGB winds with polar momentum deficiency

We present an alternative model for the formation of fast low-ionization emission regions (FLIERs) in planetary nebulae that is able to account for many of their attendant characteristics and circumvent the problems on the collimation/formation mechanisms found in previous studies. In this model, the section of the stellar wind flowing along the symmetry axis carries less mechanical momentum than at higher latitudes, and temporarily develops a concave or inverted shock geometry. The shocked ambient material is thus refracted towards the symmetry axis, instead of away from it, and accumulates in the concave section. The reverse is true for the outflowing stellar wind, which in the reverse shock is refracted away from the axis. It surrounds the stagnation region of the bow-shock and confines the trapped ambient gas. The latter has time to cool and is then compressed into a dense "stagnation knot" or "stagnation jet". In the presence of a variable stellar wind these features may eventually overrun the expanding nebular shell and appear as detached FLIERs. We present representative two and three-dimensional hydrodynamic simulations of the formation and early evolution of stagnation knots and jets and compare their dynamical properties with those of FLIERs in planetary nebulae. Subject Headings: hydrodynamics - ISM: jets and outflows - ISM: kinematics and dynamics - planetary nebulae: FLIERs and stagnation knots

astro-ph↗

arXiv2000

Deep Halpha imagery of the Eridanus shells

A deep \ha image of interlocking filamentary arcs of nebulosity has been obtained with a wide-field ($\approx$ 30\degree diameter) narrow-band filter camera combined with a CCD as a detector. The resultant mosaic of images, extending to a galactic latitude of 65$^{o}$, has been corrected for field distortions and had galactic coordinates superimposed on it to permit accurate correlations with the most recent H{\sc i} (21 cm), X-ray (0.75 kev) and FIR (IRAS 100 $μ$m) maps. Furthermore, an upper limit of 0.13 arcsec/yr to the expansion proper motion of the primary 25\degree long nebulous arc has been obtained by comparing a recent \ha image obtained with the San Pedro Martir telescope of its filamentary edge with that on a POSS E plate obtained in 1951. It is concluded that these filamentary arcs are the superimposed images of separate shells (driven by supernova explosions and/or stellar winds) rather than the edges of a single `superbubble' stretching from Barnard's Arc (and the Orion Nebula) to these high galactic latitudes. The proper motion measurement argues against the primary \ha emitting arc being associated with the giant radio loop (Loop 2) except in extraordinary circumstances.

astro-ph↗

arXiv2000

Spin Observables and Path Integrals

We discuss the formulation of spin observables associated to a non-relativistic spinning particles in terms of grassmanian differential operators. We use as configuration space variables for the pseudo-classical description of this system the positions $x$ and a Grassmanian vector $\vecε$. We consider an explicit discretization procedure to obtain the quantum amplitudes as path integrals in this superspace. We compute the quantum action necessary for this description including an explicit expression for the boundary terms. Finally we shown how for simple examples, the path integral may be performed in the semi-classical approximation, leading to the correct quantum propagator.

hep-th↗

arXiv2000

HST/WFPC2 observations of the core of KjPn 8

Narrow-band images of the core of the extraordinary poly-polar planetary nebula KjPn 8 have been obtained with the WFPC2 camera on board the Hubble Space Telescope. Spasmodic bipolar ejections, in changing directions have occurred over thousands of years to create KjPn 8. The central star is finally revealed in these observations and its compact nebular core is resolved into a remarkably young, aprox. 500 years old, elliptical ring. The highest speed bipolar outflows are perpendicular to this central ring which is identified as the latest event in the creation of this nebula. The formation history of KjPn 8 has involved two distinct planetary nebula-like events, probably originating froma a binary core evolution with components of similar mass.

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