Bow-shocks and possible jet-shell interaction in the planetary nebula M 2-48 (original) (raw)

Fast, low-ionization emission regions of the planetary nebula M2-42

The Astronomical Journal, 2016

Spatially resolved observations of the planetary nebula M2-42 (PN G008.2−04.8) obtained with the Wide Field Spectrograph on the Australian National University 2.3 m telescope have revealed the remarkable features of bipolar collimated jets emerging from its main structure. Velocity-resolved channel maps derived from the [N ii] λ6584 emission line disentangle different morphological components of the nebula. This information is used to develop a three-dimensional morpho-kinematic model, which consists of an equatorial dense torus and a pair of asymmetric bipolar outflows. The expansion velocity of about 20 km s −1 is measured from the spectrum integrated over the main shell. However, the deprojected velocities of the jets are found to be in the range of 80–160 km s −1 with respect to the nebular center. It is found that the mean density of the collimated outflows, 595 ± 125 cm −3 , is five times lower than that of the main shell, 3150 cm −3 , whereas their singly ionized nitrogen and sulfur abundances are about three times higher than those determined from the dense shell. The results indicate that the features of the collimated jets are typical of fast, low-ionization emission regions.

The shock structure in the protoplanetary nebula M1-92: imaging of atomic and H_2 line emission

1998

We present HST imaging of continuum (5500Å) and atomic line (Hα, [OI] 6300Å, [SII] 6717 and 6731Å, and [OIII] 5007Å) emissions in the protoplanetary nebula M 1-92. Ground based imaging of 2µm continuum and H 2 ro-vibrational (S(1) v=1-0 and v=2-1 lines) emission has been also performed. The 5500Å continuum is due to scattering of the stellar light by grains in a double-lobed structure comparable in extent and total density with the molecular envelope detected at mm wavelengths, which consists of two empty shells with a clear axis of symmetry. On the other hand, the optical line emission comes mainly from two chains of shocked knots placed along the symmetry axis of the nebula and inside those cavities, for which relatively high excitation is deduced (shock velocities of about 200 km s −1 ). The H 2 emission probably comes from more extended regions with representative temperature and density of 1600 K and 6 10 3 cm −3 , intermediate in location and excitation between the atomic line knots and the very cold region detected in CO emission. We argue that the chains of knots emitting in atomic lines correspond to shocks taking place in the post-AGB bipolar flow. The models for interstellar Herbig-Haro objects seem to agree with the observations, at least qualitatively, explaining in particular that the atomic emission from the bipolar flow dominates over that from shocks propagating in the AGB shell. Models developed for protoplanetary nebula dynamics fail, however, to explain the strong concentration of the atomic emission along the symmetry axis.

HST observations of the protoplanetary nebula OH?231.8+4.2: The structure of the jets and shocks

Astronomy and Astrophysics, 2002

We present high-resolution images obtained with the WFPC2, on board the HST, of the protoplanetary nebula (PPN) OH 231.8+4.2. Hα and NII line emission and scattered light in the continuum at 6750 and 7910Å were observed. We also discuss NIR NICMOS images from the HST archive. The images show with high accuracy the shape and excitation state of the shocks developed in the nebula. Our high-resolution images (and data from other works) allow a very detailed and quantitative description of the different nebular components and of the physical conditions in them. We interpret specific structures identified in our images using existing models of shock interaction. In the center of the nebula, there is a dense torus-or disk-like condensation continued by an hourglass-like structure, with relatively high densities (∼10 5-10 6 cm −3) and temperatures (∼30 K). Inside this torus we have identified the location of the central star, from SiO maser observations. Two shock regions are detected from the optical line emission images, respectively in the north and south lobes. In both regions, a forward and a backward shock are identified. The densities of this hot gas vary between 40 and 250 cm −3 , with the densest clumps being placed in the reverse shocks. The total mass of the shocked hot gas is ∼2×10 −3 M , both lobes showing similar masses in spite of their different extents. The relatively collimated jet that impinges on an originally slow shell, so producing the shocks, is identified from the scattered light images and in CO maps. This flow is significantly denser and cooler than the shocked Hα regions. Its density decreases with the distance to the star, with typical values ∼10 5-10 4 cm −3 , and its temperature ranges between about 25 and 8 K. We explain the high Hα emission of the backward shock assuming that it propagates in a diffuse gas component, entrained by the observed collimated flow and sharing its axial movement. The existence of shocks also in the collimated densest flow is suggested by the high abundance of some molecules like HCO + and its structure and kinematics in certain regions, but they are not seen in Hα emission, probably because of the absence of (well developed) hot components in this dense flow. We think that the exceptionally detailed and quantitative image derived for the wind interaction regions in OH 231.8+4.2 is a challenge to check and improve hydrodynamical models of wind interaction in PPNe.

Unveiling shocks in planetary nebulae

Astronomy & Astrophysics, 2013

The propagation of a shock wave into a medium is expected to heat the material beyond the shock, producing noticeable effects in intensity line ratios such as [O iii]/Hα. To investigate the occurrence of shocks in planetary nebulae (PNe), we have used all narrowband [O iii] and Hα images of PNe available in the HST archive to build their [O iii]/Hα ratio maps and to search for regions where this ratio is enhanced. Regions with enhanced [O iii]/Hα emission ratio can be ascribed to two different types of morphological structures: bow-shock structures produced by fast collimated outflows and thin skins enveloping expanding nebular shells. Both collimated outflows and expanding shells are therefore confirmed to generate shocks in PNe. We also find regions with depressed values of the [O iii]/Hα ratio which are found mostly around density bounded PNe, where the local contribution of [N ii] emission into the F656N Hα filter cannot be neglected.

Unveiling the Structure of the Planetary Nebula M2-48

2002

The PN M2-48 is formed by three main structures, namely, a bipolar central region (CR), a set of knots tracing a semicircular shell surrounding CR, and two symmetric bow-shocks. CR shows a kinematic structure corresponding to a bipolar shell, with an expansion velocity of =~ 50kms-1. The semicircular shell appears to be expanding at =~ 20kms-1, except in the regions aligned with the bow-shocks, which are interpreted as jet-shell interaction zones at =~ 100kms-1. Finally, the bow-shocks have uncorrected velocities of =~ 80kms-1. An inclination angle of 10^o with respect to the plane of the sky is estimated using simple bow shock models.

New Observations of the High-Velocity Outflows of the Proto-Planetary Nebula Hen 3-1475

2002

The proto-planetary nebula Hen 3-1475 shows a remarkable highly collimated optical jet with a S-shaped string of shock-excited knots. Moreover, extremely high velocities have been observed in the innermost regions of its jet. We present a detailed analysis of the kinematic structure, and the excitation conditions in the shock-excited knots based on ground-based high dispersion spectroscopy and high angular resolution images obtained with the HST WFPC2. We discuss the similarities between the jet of Hen 3-1475 and the HH jets. Both exhibit double-peaked and extremely wide profiles, a decrease of the radial velocities with distance to the source in a step-like fashion, and high tangential velocities. The overall picture of Hen 3-1475 supports the description of the system as the result of time-dependent ejection velocity variability.

Collimation of Astrophysical Jets: The Proto–Planetary Nebula H[CLC]e[/CLC] [CSC]3-1475[/CSC]

The Astrophysical Journal, 1997

The proto-planetary nebula He 3-1475 was imaged in the [N II] 6584 line with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope. This image has revealed what appear to be large-scale flows being collimated into narrow bipolar jets. This is a unique object: we may be observing the actual collimation process of an astrophysical jet. Analytical models and hydrodynamical simulations suggest that the jet in He 3-1475 may be produced by purely hydrodynamical means, through focusing of a weakly collimated bipolar outflow into jets by oblique radiative shocks.

A New Diagnostic for Fast Outflows in Planetary Nebulae

… Planetary Nebulae IV, 2007

Fast collimated outflows have proven ubiquitous in planetary nebulae (PNe) and their dynamical action can be very important in the PNe formation and shaping. Using a database of HST WFPC2 images of 64 PNe, we explore in this work a new diagnostic for fast collimated outflows in PNe based on the effects that their shocks produce in the relative [O iii] and Hα emissions. We confirm that the [O iii]/Hα ratio is enhanced in thin skins associated to bow-shocks of fast collimated outflows, but we also find that low velocity shocks associated to expanding shells of multiple shell PNe produce similar effects. These results indicate that the occurence of a thin skin of bright [O iii]/Hα in a PN is not sufficient to confirm the presence of a fast collimated outflow, but it can always be connected with the effects of a shock.

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

Astronomy & Astrophysics, 2002

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).

A photo-ionised canopy for the shock-excited Criss-Cross nebula

Astronomy and Astrophysics, 2007

Aims. We study a new broad well-defined arc of optical nebulosity close to the cloud-shock interacting Criss-Cross Nebula, derive the basic physical properties of the former and revise those of the latter, and compare both objects to simulations of cloud-shock interactions from the literature. Methods. Deep optical, partly wide-field, images were used to reveal the intricate morphology and overall extent of the nebulosities. Optical spectroscopy enabled us to uncover their nature. Results. The two nebulosities obviously are physically linked, but are of different type; the Criss-Cross Nebula is, as was shown also in an earlier paper, excited via a slow shock from the expanding Orion-Eridanus Bubble, but the broad arc is definitely photoionized. The source for ionizing photons appears to be hot gas in this bubble. Some results of simulations of interactions of SNRs with interstellar clouds available from the literature bear a striking resemblance to our nebulae, which appear to represent an example -unrivalled in closeness and clarity -for an early to medium stage in the destruction of an isolated cloud over-run by a highly evolved SNR. Thereby the Criss-Cross Nebula is, when seen from the SNR, the rear disrupted part of the original small cloud, whereas the arc probably is its yet rather intact front part.