N. M. H. Vaytet

Proof of polar ejection from the close-binary core of the planetary nebula Abell 63

We present the first detailed kinematical analysis of the planetary nebula Abell 63, which is known to contain the eclipsing close-binary nucleus UU Sge. Abell 63 provides an important test case in investigating the role of close-binary central stars on the evolution of planetary nebulae. n n n nLongslit observations were obtained using the Manchester echelle spectrometer combined with the 2.1-m San Pedro Martir Telescope. The spectra reveal that the central bright rim of Abell 63 has a tube-like structure. A deep image shows collimated lobes extending from the nebula, which are shown to be high-velocity outflows. The kinematic ages of the nebular rim and the extended lobes are calculated to be 8400 ± 500 and 12xa0900 ± 2800 yr, respectively, which suggests that the lobes were formed at an earlier stage than the nebular rim. This is consistent with expectations that disc-generated jets form immediately after the common envelope phase. n n n nA morphological–kinematical model of the central nebula is presented and the best-fitting model is found to have the same inclination as the orbital plane of the central binary system; this is the first proof that a close-binary system directly affects the shaping of its nebula. A Hubble-type flow is well-established in the morphological–kinematical modelling of the observed line profiles and imagery. n n n nTwo possible formation models for the elongated lobes of Abell 63 are considered, (i) a low-density, pressure-driven jet excavates a cavity in the remnant asymptotic giant branch (AGB) envelope; (ii) high-density bullets form the lobes in a single ballistic ejection event.

Abell 41: shaping of a planetary nebula by a binary central star★

We present the first detailed spatiokinematical analysis and modelling of the planetary nebula Abell 41, which is known to contain the well-studied close-binary system MT Ser. This object represents an important test case in the study of the evolution of planetary nebulae with binary central stars as current evolutionary theories predict that the binary plane should be aligned perpendicular to the symmetry axis of the nebula. Deep narrow-band imaging in the light of [N II] 6584 A, [O III] 5007 A and [S II] 6717+ 6731 A, obtained using ACAM on the William Herschel Telescope, has been used to investigate the ionization structure of Abell 41. Long-slit observations of the Hα and [N II] 6584 A emission were obtained using the Manchester Echelle Spectrometer on the 2.1-m San Pedro M´ artir Telescope. These spectra, combined with the narrow-band imagery, were used to develop a spatiokinematical model of [N II] 6584 A emission from Abell 41. The best-fitting model reveals Abell 41 to have a waisted, bipolar structure with an expansion velocity of ∼40 km s −1 at the waist. The symmetry axis of the model nebula is within 5 ◦ of perpendicular to the orbital plane of the central binary system. This provides strong evidence that the close-binary system, MT Ser, has directly affected the shaping of its nebula, Abell 41. Although the theoretical link between bipolar planetary nebulae and binary central stars is long established, this nebula is only the second to have this link, between nebular symmetry axis and binary plane, proved observationally.

Hubble-type outflows of the high-excitation poly-polar planetary nebula NGC 6302 – from expansion proper motions

The outflowing proper motions of 15 knots in the dominant northwestern lobe of the high-excitation poly-polar planetary nebula NGC 6302 have been determined by comparing their positions relative to those of faint stars in an image taken at the San Pedro Martir Observatory in 2007 to those in a South African Astronomical Observatory archival plate obtained by Evans in 1956. The Hubble-type expansion of this lobe is now directly confirmed in a model-independent way from these measurements. Furthermore, an unambigous distance to NGC 6302 of 1.17 ± 0.14 kpc is now determined. Also, all the velocity vectors of the 15 knots (and two others) point back to the central source. An eruptive event from within the central torus ≈2200 yr previously must have created the high-speed lobes of NGC 6302.

A numerical model for multigroup radiation hydrodynamics

Abstract We present in this paper a multigroup model for radiation hydrodynamics to account for variations of the gas opacity as a function of frequency. The entropy closure model (M1) is applied to multigroup radiation transfer in a radiation hydrodynamics code. In difference from the previous grey model, we are able to reproduce the crucial effects of frequency-variable gas opacities, a situation omnipresent in physics and astrophysics. We also account for the energy exchange between neighbouring groups which is important in flows with strong velocity divergence. These terms were computed using a finite volume method in the frequency domain. The radiative transfer aspect of the method was first tested separately for global consistency (reversion to grey model) and against a well-established kinetic model through Marshak wave tests with frequency-dependent opacities. Very good agreement between the multigroup M1 and kinetic models was observed in all tests. The successful coupling of the multigroup radiative transfer to the hydrodynamics was then confirmed through a second series of tests. Finally, the model was linked to a database of opacities for a Xe gas in order to simulate realistic multigroup radiative shocks in Xe. The differences with the previous grey models are discussed.

The morphology and kinematics of the Fine Ring Nebula, planetary nebula Sp 1, and the shaping influence of its binary central star

We present the first detailed spatiokinematical analysis and modelling of the planetary nebula Shapley 1 (Sp 1), which is known to contain a close-binary central star system. Close-binary central stars have been identified as a likely source of shaping in planetary nebulae, but with little observational support to date. n n n nDeep narrow-band imaging in the light of [Oxa0iii]xa0λ5007xa0A suggests the presence of a large bow shock to the west of the nebula, indicating that it is undergoing the first stages of an interaction with the interstellar medium. Further narrow-band imaging in the light of Hα+ [Nxa0ii]xa0λ6584xa0A combined with long-slit observations of the Hα emission have been used to develop a spatiokinematical model of Sp 1. The model clearly reveals Sp 1 to be a bipolar, axisymmetric structure viewed almost pole-on. The symmetry axis of the model nebula is within a few degrees of perpendicular to the orbital plane of the central binary system – strong evidence that the central close-binary system has played an important role in shaping the nebula. n n n nSp 1 is one of the very few nebulae to have this link, between nebular symmetry axis and binary plane, shown observationally.

SWIFT OBSERVATIONS OF THE 2006 OUTBURST OF THE RECURRENT NOVA RS OPHIUCHI. III. X-RAY SPECTRAL MODELING

Following the Swift X-ray observations of the 2006 outburst of the recurrent nova RS Ophiuchi, we developed hydrodynamical models of mass ejection from which the forward shock velocities were used to estimate the ejecta mass and velocity. In order to further constrain our model parameters, we present synthetic X-ray spectra from our hydrodynamical calculations, which we compare to the Swift data. An extensive set of simulations was carried out to find a model that best fits the spectra up to 100 days after outburst. We find a good fit at high energies but require additional absorption to match the low energy emission. We estimate the ejecta mass to be in the range (2-5) × 10–7 M ☉ and the ejection velocity to be greater than 6000 km s–1 (and probably closer to 10, 000 km s–1). We also find that estimates of shock velocity derived from gas temperatures via standard model fits to the X-ray spectra are much lower than those of the true shock velocities.

Kinematics of the ring-like nebula SuWt 2

We present the first detailed spatio-kinematical analysis and modelling of the southern planetary nebula SuWt 2. This object presents a problem for current theories of planetary nebula formation and evolution, as it is not known to contain a central post-main-sequence star. n n n nDeep narrow-band [Nxa0ii]6584xa0A images reveal the presence of faint bipolar lobes emanating from the edges of the nebular ring. Long-slit observations of the Hα and [Nxa0ii]6584xa0A emission lines were obtained using the ESO (European Southern Observatory) Multi-Mode Instrument on the 3.6-m ESO New Technology Telescope. The spectra reveal the nebular morphology as a bright torus encircling the waist of an extended bipolar structure. By deprojection, the inclination of the ring is found to be 68°± 2° (cf. ∼90° for the double A-type binary believed to lie at the centre of the nebula), and the ring expansion velocity is found to be 28 kmxa0s−1. n n n nOur findings are discussed with relation to possible formation scenarios for SuWt 2. Through comparison of the nebular heliocentric systemic velocity, found here to be −25 ± 5xa0km s−1, and the heliocentric systemic velocity of the double A-type binary, we conclude that neither component of the binary could have been the nebular progenitor. However, we are unable to rule out the presence of a third component to the system, which would have been the nebula progenitor.

Swift Observations of the 2006 Outburst of the Recurrent Nova RS Ophiuchi. II. One-dimensional Hydrodynamical Models of Wind-driven Shocks

Following the early Swift X-ray observations of the latest outburst of the recurrent nova RS Ophiuchi in 2006 February (Paper I), we present new one-dimensional hydrodynamical models of the system that take into account all three phases of the remnant evolution. The models suggest a novel way of modeling the system by treating the outburst as a sudden increase followed by a decrease in wind mass-loss rate and velocity. The differences between this wind model and previous Primakoff-type simulations are described. A more complex structure, even in one-dimension, is revealed through the presence of both forward and reverse shocks, with a separating contact discontinuity. The effects of radiative cooling are investigated, and key outburst parameters such as mass-loss rate and ejecta velocity and mass are varied. The shock velocities as a function of time are compared to the ones derived in Paper I. We show how the manner in which the matter is ejected controls the evolution of the shock and that for a well-cooled remnant, the shock deceleration rate depends on the amount of energy that is radiated away.

Evidence for ablated flows in the shell of the nova DQ Herculis

High-resolution longslit Halpha spectra of the shell of the old nova DQ Her have been obtained with the William Herschel Telescope using the ISIS spectrograph. An equatorial expansion velocity of 370+/-14 km/s is derived from the spectra which, in conjunction with a narrowband Halpha image of the remnant, allows a distance estimate of 525+/-28 pc. An equatorial ring which exhibits enhanced [NII] emission has also been detected and the inclination angle of the shell is found to be 86.8+/-0.2 degrees with respect to the line of sight. The spectra also reveal tails extending from the clumps in the shell, which have a radial velocity increasing along their length. This suggests the presence of a stellar wind, collimated in the polar direction, which ablates fragments of material from the clumps and accelerates them into its stream up to a terminal velocity of order 800-900 km/s.

High-speed knots in the hourglass-shaped planetary nebula Hubble 12

We present a detailed kinematical analysis of the young compact hourglass-shaped planetary nebula Hb 12. We performed optical imaging and long-slit spectroscopy of Hb 12 using the Manchester echelle spectrometer with the 2.1-m San Pedro Martir telescope. We reveal, for the first time, the presence of end caps (or knots) aligned with the bipolar lobes of the planetary nebula shell in a deep [Nxa0ii]λ6584 image of Hb 12. We measured from our spectroscopy radial velocities of ∼120xa0kmxa0s−1 for these knots. n n n nWe have derived the inclination angle of the hourglass-shaped nebular shell to be ∼65° to the line of sight. It has been suggested that Hb 12s central star system is an eclipsing binary which would imply a binary inclination of at least 80°. However, if the central binary has been the major shaping influence on the nebula, then both nebula and binary would be expected to share a common inclination angle. n n n nFinally, we report the discovery of high-velocity knots with Hubble-type velocities, close to the core of Hb 12, observed in Hα and oriented in the same direction as the end caps. Very different velocities and kinematical ages were calculated for the outer and inner knots showing that they may originate from different outburst events.