Spatio-kinematical Model Research Articles

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 spatio-kinematical 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. Deep narrowband imaging in the light of [O III] {\lambda}5007A 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 narrowband imaging in the light of H{\alpha}+[NII] {\lambda}6584A combined with longslit observations of the H{\alpha} emission have been used to develop a spatio-kinematical 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. Sp 1 is one of very few nebulae to have this link, between nebular symmetry axis and binary plane, shown observationally.

The influence of binarity on the morpho-kinematics of planetary nebulae

AbstractThe role of central star binarity in the shaping of planetary nebulae (PNe) has been the subject of much debate, with single stars believed to be incapable of producing the most highly collimated morphologies. However, observational support for binary-induced shaping has been sadly lacking. Here, we highlight the results of a continuing programme to spatio-kinematically model the morphologies of all PNe known to contain a close binary central star. Spatio-kinematical modelling is imperative for these objects, as it circumvents the degeneracy between morphology and orientation which can adversely affect determinations of morphology based on imaging alone. Furthermore, spatio-kinematical modelling accurately determines the orientation of the nebular shell, allowing the theoretically predicted perpendicular alignment, between nebular symmetry axis and binary orbital plane, to be tested. To date, every PN subjected to this investigation has displayed the predicted alignment, indicating that binarity has played an important role in the formation and evolution of these nebulae. The further results from this programme will be key, not only in determining whether binary interaction is responsible for shaping the studied PNe, but also in assessing the importance of binarity in the formation and evolution of all PNe in general.

A detailed spatiokinematic model of the multipolar planetary nebula NGC 7026

AbstractWe present the most extensive, long-slit, high-resolution coverage of the complex planetary nebula (PN), NGC 7026. Ten spectra were acquired using the Manchester Echelle Spectrometer at San Pedro Martir Observatory in Baja California, Mexico, and each shows exquisite detail, revealing the intricate structure of this object. Incorporating these spectra into the 3-dimensional visualization and kinematic program, Shape, and using HST images of NGC 7026, we have produced a detailed structural and kinematic model of this PN. Knowledge of the 3-D structure of this nebula is relevant to understand the physics behind the extended X-ray emission in this object.

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

We present the first detailed spatio-kinematical 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 narrowband imaging in the light of [NII], [OIII] and [SII], obtained using ACAM on the William Herschel Telescope, has been used to investigate the ionisation structure of Abell 41. Longslit observations of the H-alpha and [NII] emission were obtained using the Manchester Echelle Spectrometer on the 2.1-m San Pedro M\'artir Telescope. These spectra, combined with the narrowband imagery, were used to develop a spatio-kinematical model of [NII] emission from Abell 41. The best fitting model reveals Abell 41 to have a waisted, bipolar structure with an expansion velocity of ~40km\s at the waist. The symmetry axis of the model nebula is within 5$\degr$ 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.

The kinematics of the quadrupolar nebula M 1–75 and the identification of its central star

Context. The link between the shaping of bipolar planetary nebulae and their central stars is still poorly understood. Aims. The kinematics and shaping of the multipolar nebula M 1-75 are hereby investigated, and the location and nature of its central star are briefly discussed. Methods. Fabry-Perot data from GHFAS on the WHT sampling the Doppler shift of the (Nii) 658.3 nm line are used to study the dynamics of the nebula, by means of a detailed 3-D spatio-kinematical model. Multi-wavelength images and spectra from the WFC and IDS on the INT, and from ACAM on the WHT, allowed us to constrain the parameters of the central star. Results. The two pairs of lobes, angularly separated by� 22 � , were ejected simultaneously approx.� 3500-5000 years ago, at the adopted distance range from 3.5 to 5.0 kpc. The larger lobes show evidence of a slight degree of point symmetry. The shaping of the nebula could be explained by wind interaction in a system consisting of a post-AGB star surrounded by a disc warped by radiative instabilities. This requires the system to be a close binary or a single star which engulfed a planet as it died. On the other hand, we present broad- and narrow-band images and a low S/N optical spectrum of the highly-reddened, previously unnoticed star which is likely the nebular progenitor. Its estimated V− I colour allows us to derive a rough estimate of the parameters and nature of the central star.

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.

Hen 2–104: a close-up look at the Southern Crab

Aims. The kinematics, shaping, density distribution, expansion distance, and ionized mass of the nebula Hen 2–104, and the nature of its symbiotic Mira are investigated. Methods. A combination of multi-epoch HST images and VLT integral field high-resolution spectroscopy is used to study the nebular dynamics both along the line of sight and in the plane of the sky. These observations enable a 3-D spatio-kinematical model of the nebula to be constructed, which, with the measurement of its apparent expansion in the plane of the sky over a period of 4 years, provides the expansion parallax for the nebula. The integral-field data featuring the [Sii] λλ671.7, 673.1 emission line doublet provide a density map of the inner lobes of the nebula, which with the distance estimation provide a measurement of its ionized mass. Results. We measure densities ranging from ne = 500 to 1000 cm −3 in the inner lobes, and from 300 to 500 cm −3 in the outer lobes. We determine an expansion-parallax distance of 3.3 ± 0.9 kpc to Hen 2–104, which implies an unexpectedly large ionized mass for the nebula of approximately one tenth of a solar mass.

HST and VLT observations of the symbiotic star Hen 2–147

Aims. We investigate the dynamics of the nebula around the symbiotic star Hen 2-147, determine its expansion parallax, and compare it with the distance obtained via the period-luminosity relation for its Mira variable. Methods. A combination of multi-epoch HST images and VLT integral field high-resolution spectroscopy is used to study the nebular dynamics both along the line of sight and in the plane of the sky. These observations allow us to build a 3D spatio-kinematical model of the nebula, which, together with the measurement of its apparent expansion in the plane of the sky over a period of 3 years, provides the expansion parallax for the nebula. Additionally, SAAO near-infrared photometry obtained over 25 years is used to determine the Mira pulsation period and derive an independent distance estimation via the period-luminosity relationship for Mira variables. Results. The geometry of the nebula is found to be that of a knotty annulus of ionized gas inclined to the plane of sky and expanding with a velocity of ∼90 km s -1 . A straightforward application of the expansion parallax method provides a distance of 1.5 ± 0.4 kpc, which is a factor of two lower than the distance of 3.0 ± 0.4 kpc obtained from the period-luminosity relationship for the Mira (which has a pulsation period of 373 days). The discrepancy is removed if, instead of expanding matter, we are observing the expansion of a shock front in the plane of the sky. This shock interpretation is further supported by the broadening of the nebular emission lines.

Interferometric COJ= 2–1 Emission Mapping of the Protoplanetary Nebula IRAS 19475+3119

We present ~2'' resolution interferometric maps of the 12CO J = 2-1 emission in the PPN IRAS 19475+3119 obtained with OVRO. These data probe two distinct molecular components, namely, a slowly expanding shell and a fast bipolar outflow.We have used a spatiokinematic model of the 12CO J = 2-1 emission to constrain the properties of these two components. The shell has inner and outer radii of Rin ~ 6.5 × 1016 cm and Rout ~ 2 × 1017 cm and expands at Vexp ~ 11 km s-1. The 12CO J = 2-1 line wing emission arises in a bipolar structure that emerges from two diametrically opposite holes in the slow shell. The bipolar outflow is aligned with one of the two lobe pairs of the quadrupolar optical nebula (at P.A. ≈ 80°). Both the holes and the bipolar outflow are most likely the result of the interaction of fast, collimated post-AGB winds with the shell. The quadrupolar morphology of the optical nebula indicates two distinct bipolar post-AGB winds ejected in two different directions. The elongation of the optical counterpart of the shell (at P.A. ≈ -45°) and two similarly aligned CO clumps suggest that the slow shell has also been affected by the wind interaction. The expansion velocity in the bipolar outflow increases linearly with the distance from the nebula center and reaches Vexp = 30 km s-1 (projected) at the tips of the lobes. This velocity gradient yields a relatively long kinematical age of ~1900 yr, assuming an outflow inclination of i = 30° with respect to the plane of the sky; this age is comparable with the post-AGB lifetime estimated from the shell expansion velocity and inner radius. We derive a mean kinetic temperature of ~14 K and a total mass of ~0.4 M☉. The collimation and linear momentum (P ~ 4 × 1038 g cm s-1) of the outflow are unlikely to result from radiation pressure on dust grains.

The structures and kinematics of planetary nebulae with close-binary central stars

A programme is currently underway to study the structures and kinematics of planetary nebulae known to contain close-binary central stars. Images and high-resolution spectroscopy are presented of the collimated nebula Abell 63 and the ring-like nebula Sp 1. A spatio-kinematical model shows that Abell 63 has a tube-like structure, which has the same inclination as the orbital plane of the central binary system. Kinematic data reveal that Sp 1 is not a hollow sphere, but a tube-like nebula viewed pole-on.

The evolution of planetary nebulae

A detailed theoretical study of the basic internal kinematics of planetary nebulae is presented, based on 1D radiation-hydrodynamics simulations of circumstellar envelopes around central stars of 0.595 and 0.696 . By means of observable quantities like radial surface-brightness distributions and emission-line profiles computed from the models, a comparison with real objects was performed and revealed a reasonable agreement. This allowed to draw important conclusions by investigating the kinematics of these models in detail. Firstly, it is shown that the determination of kinematical ages, normally considered to be simple if size and expansion rate of an object are given, can seriously be flawed. Secondly, the expansion law of a planetary nebula is different from what is assumed for deriving spatio-kinematical models. Thirdly and most importantly, our hydrodynamical models help to correctly use existing angular expansion measurements for distance determinations. The mere combination of the angular expansion rates with the spectroscopic expansion velocities leads always to a serious underestimate of the distance, the degree of which depends on the evolutionary state of the object. The necessary correction factor varies between 3 and 1.3. Individual correction factors can be estimated with an accuracy of about 10% by matching our hydrodynamical models to real objects. As a result, revised distances for a few objects with reliable angular expansion rates are presented. But even these corrected distances are not always satisfying: they still appear to be inconsistent with other distance determinations and, even more disturbing, with the accepted theory of post-asymptotic giant branch evolution. As a byproduct of the angular expansion measurements, the transition times from the vicinity of the asymptotic giant branch to the planetary-nebula regime could be estimated. They appear to be shorter than assumed in the present evolutionary calculations.

1″ Resolution Mapping of the Molecular Envelope of the Protoplanetary Nebula CRL 618

We present 1 00 resolution interferometric maps of the CO J ¼ 2 1a nd HC3N J ¼ 25 24 emission in the protoplanetary nebula CRL 618 obtained with the millimeter array of the Owens Valley Radio Observatory (OVRO). Our CO data trace with high accuracy the spatio-kinematic structure of different molecular components: (1) the fast, bipolar outflow, which is observed up to axial distances of � 2B 5( � 2:7 ; 10 16 cm) from the nebula center with a maximal deprojected expansion velocity of Vexp � 340 km s � 1 ; (2) the roughly round outer halo, which is slowly expanding at Vexp � 17 km s � 1 ; (3) an extended structure that is elongated in the polar direction � 6 00 (� 8:1 ; 10 16 cm),surroundingtheopticallobes,andthatexpandsatVexp � 22kms � 1 (slowaxialcomponent); and(4)a dense, inner torus-likecore (Rout � 1:6 ; 10 16 cm) expanding atVexpP12kms � 1 . Components (3) and (4) have been revealed for the first time by our high angular resolution data. The geometry, kinematics, density, and temperaturedistributionoftheindividualcomponentsofthemolecularenvelopeofCRL618havebeenconstrained by fitting a spatio-kinematic model to the data. We interpret our results in terms of nebular evolution as follows. In the last k2500 yr, there have been at least two distinct episodes of mass loss at a large scale in the form of a slow wind. The firsttookplace at a rate of ˙

Physical Structure of Planetary Nebulae. III. The Large and Evolved NGC 1360

NGC 1360 is a large planetary nebula (PN) without an obvious shell morphology. We have analyzed Hα images and high-dispersion echelle spectra of NGC 1360 in order to construct spatio-kinematic models and to determine its density distribution. The best-fit model indicates that NGC 1360 is a prolate ellipsoidal shell whose major axis is twice as long as its minor axis and is tilted by 60° with respect to the line of sight. The large kinematic age of the shell, ~10,000 yr, and the low density of the nebula, ≤130 H atom cm-3, imply that NGC 1360 is an evolved PN and has begun to merge with the interstellar medium. The observed morphology and surface brightness profiles of NGC 1360 can be described well as a thick shell with a Gaussian radial density profile without a sharp inner edge, indicating a lack of ongoing compression by a fast stellar wind. The fast, low-ionization emission regions observed in NGC 1360 near the end of its major axis expand faster than the shell and are younger than the nebular shell.

Physical Structure of the Protoplanetary Nebula CRL 618. II. Interferometric Mapping of Millimeter‐Wavelength HCNJ= 1–0, HCO+J= 1–0, and Continuum Emission

We present interferometric maps with high angular resolution, 11 to 19, of the HCO + J = 1-0 and HCN J = 1-0 emission lines in the protoplanetary nebula CRL 618. These molecules are present in both the slowly (~10-20 km s-1) and rapidly (~200 km s-1) outflowing components of the molecular envelope of CRL 618. The high-velocity (HV) molecular outflow is composed of two compact (mean size ~1'') clumps aligned with the optical lobes and separated by 21. The distance between these clumps is now 05 larger than 11 yr ago, which is consistent with rapid expansion of the HV clumps. The expansion velocity in the HV outflow increases linearly with the distance to the nebular center, from which we derive a kinematical age of ~60 yr. Our data reveal that part of the low-velocity (LV) molecular gas in CRL 618 arises in a extended structure elongated ~11'' in the direction perpendicular to the outflow, which is consistent with a dense, equatorial torus expanding at Vexp ~ 17.5 km s-1. We have used a two-dimensional spatio-kinematical model to better constrain the structure, kinematics, and density distribution of the HV and LV components that are probed by HCN J = 1-0 and HCO + J = 1-0 emission. The central H II region of CRL 618, which is traced by free-free mm-continuum emission, is unresolved in these observations. We report (1) a recent decrease of the mm-continuum flux and (2) a 3 mm-to-1 mm flux ratio consistent with optically thin free-free emission in the millimeter wavelength range. The continuum flux at 3 mm (1 mm) was 1.6 ± 0.15 Jy (1.2 ± 0.3 Jy) in 2000, when our observations were performed. The weakening of the millimeter continuum, as well as the decrease of the free-free turnover frequency, could result from a recent cessation of the post-AGB wind or the growth of the cavity of the central H II region (or both). From a consideration of multiwavelength datasets on CRL 618, we provide a comprehensive view of the temporal evolution of its nebular material.

SiO Emission in the Multilobe Outflow Associated with IRAS 16293−2422

We have mapped the thermal emission line of SiO (v = 0; J = 2-1) associated with the quadrupolar molecular outflow driven by the very cold far-infrared source IRAS 16293-2422. The SiO emission is significantly enhanced in the northeastern red lobe and at the position ~50'' east of the IRAS source. Strong SiO emission observed at ~50'' east of the IRAS source presents evidence for a dynamical interaction between a part of the eastern blue lobe and the dense ambient gas condensation; however, such an interaction is unlikely to be responsible for producing the quadrupolar morphology. The SiO emission in the northeastern red lobe shows spatial and velocity structure similar to those of the CO outflow, suggesting that the SiO emission comes from the molecular outflow in the northeastern red lobe itself. The observed velocity structure is reproduced by a simple spatiokinematic model of bow shock with a shock velocity of 19-24 km s-1 inclined by 30°-45° from the plane of the sky. This implies that the northeastern red lobe is independent of the eastern blue lobe and that the quadrupolar structure is due to two separate bipolar outflows. The SiO emission observed in the western red lobe has a broad pedestal shape with low intensity. Unlike the SiO emission in the northeastern red lobe, the spatial extent of the SiO emission in the western red lobe is restricted to its central region. The spatial and velocity structures and the line profiles suggest that three different types of SiO emission are observed in this outflow: the SiO emission arising from the interface between the outflowing gas and the dense ambient gas clump, the SiO emission coming from the outflow lobe itself, and the broad SiO emission with low intensity observed at the central region of the outflow lobe.

Knots in the Outer Shells of the Planetary Nebulae IC 2553 and NGC 5882

We present images and high-resolution spectra of the planetary nebulae IC 2553 and NGC 5882. Spatio-kinematic modeling of the nebulae shows that they are composed of a markedly elongated inner shell, and of a less aspherical outer shell expanding at a considerably higher velocity than the inner one. Embedded in the outer shells of both nebulae are found several low-ionization knots. In IC 2553, the knots show a point-symmetric distribution with respect to the central star: one possible explanation for their formation is that they are the survivors of pre-existing point-symmetric condensations in the AGB wind, a fact which would imply a quite peculiar mass-loss geometry from the giant progenitor. In the case of NGC 5882, the lack of symmetry in the distribution of the observed low-ionization structures makes it possible that they are the result of in situ instabilities.

Narrow band CCD imaging of four PNe

We present first results of a project to construct and study spatio-kinematical models of selected Planetary Nebulae (PNe). Deep monochromatic CCD images of A8, A4, M2-55, and J-320 were made with the Calar Alto 2.2m telescope and the two interference filters 5005/90 and 6574/104 for the [O III] and Hα+[N II] emission lines. The images were corrected for bias and dark, and flatfielded using MIDAS software, and also corrected for atmospheric extinction to derive the total flux in each emission line. The observed parameters are summarized in Table 1. – A8 (PNG167.0–00.9) has a very symmetric, round appearance with large diameter. The Hα+[N II] image clearly shows a round, limb-brightened ring which is less apparent in the [O III] image. Due to its appearance we can classify it as a late round type according to Balick (1987). −M2-55 (PN G116.2+08.5) has a box-like, quadratic and highly structured inner part (slightly more roundish in [O III]), with four maxima at the corners. The faint outer parts seem to consist of two ovals that are perpendicular to each other. Together, they again resemble a square tilted 45° against the inner one. The Hα+[N II] image is larger than [O III]: The square (distance of maxima) by some 20 percent, the faint ovals by about 10 percent. We can classify this PN as a middle elliptical type. – A4 (PNG144.3–15.5) is a spherical shell, with some definite structure in the brightest parts. This structure forms roughly a ring halfway between the center and the rim. A4 can be classified as an early round type. Both images are quite similar, the Hα+ [N II] maximum lying slightly, about 20 percent, farther from the center. In the very faint outer regions, the [O III]/(Hα+[N II]) ratio seems to increase by a factor of about 5 above the average which is otherwise constant within 10 percent over the whole image. -J-320 (PNG190.3–17.7) is elongated, with one maximum on the main axis, slightly off-center. The Hα+[N II] image has an interesting structure which is not present in [O III]: Two stripes of decreased intensity that are roughly parallel to and on both sides of the main axis. At present, we have no explanation for this feature. J-320 has ansae (small knots found in pairs on opposite sides and at equal distance from the nucleus) usually seen best in the light of low-ionization emission lines. Balick (1987) classified this PN as early type butterfly.

Nebular Density Distributions; A Critical Look

The symmetry of planetary nebulae demands an explanation. Underlying previous attempts to explain these objects is the inferred density distribution based on spatio-kinematic models such as those of Weedman (1968), Reay et al. (1983) and others. Although some observations suggest a linear velocity-radius relationship for planetaries, plausible hypothetical examples may be constructed which greatly violate a linear relationship, and hydrodynamic theory (Schmalz 1986) suggests it may not hold even when observations may be most easily interpreted as supporting a linear relationship. Therefore, an independent assessment of the nebular density distribution is needed.

The Structure and Kinematics of Bipolar Planetary Nebulae

We have obtained high-dispersion, long-slit echelle spectra at closely spaced intervals across the face of the bipolar planetary nebulae NGC 2440, NGC 6302 and Mz-3. Deep monochromatic images of these objects in lines from high (HeII, [OIII]), intermediate (HI, [OII]) and low ([NII], [SII]) excitation species have also been acquired. Taken together, these data permit us to construct self-consistent spatio-kinematic models of these nebulae and to investigate the spatial variations of excitation conditions within them.

Expansion Velocities and Characteristics of Galactic Planetary Nebulae

An up-to-date account of expansion data and their interpretation is provided.- the importance of spatiokine-matical models is underlined; bipolar outflows appear to be characteristic of very young objects and prolate spheroids (including toroids and rings) seem to be a useful approximation for many PN.- High-velocity features are much more frequent than previously assumed.- Expansion velocities vs. linear radii diagrams for [OIII], HI, and [NII], based on a new catalogue show a broad, rather homogeneous distribution and thus are of limited value for studies of the dynamical evolution or formation mechanisms of PN - future investigations of these relations should be pursued separately for groups of PN with similar physical properties; a difference in the kinematical properties of B and C nebulae could, however, be confirmed.- Several recommendations for work in this area are added.