Unveiling shocks in planetary nebulae (original) (raw)

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.

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.

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.

Investigating the Near-Infrared Properties of Planetary Nebulae. I. Narrowband Images

The Astrophysical Journal Supplement Series, 1995

We present medium-resolution (R ∼ 700) near-infrared (λ = 1 − 2.5 µm) spectra of a sample of planetary nebulae (PNe). A narrow slit was used which sampled discrete locations within the nebulae; observations were obtained at one or more positions in the 41 objects included in the survey. The PN spectra fall into one of four general categories: H I emission line-dominated PNe, H I and H 2 emission line PNe, H 2 emission line-dominated PNe, and continuum-dominated PNe. These categories correlate with morphological type, with the elliptical PNe falling into the first group, and the bipolar PNe primarily in the H 2 and continuum emission groups. The categories also correlate with C/O ratio, with the O-rich objects generally falling into the first group and the C-rich objects in the other groups. Other spectral features were observed in all categories, such as continuum emission from the central star, C 2 , CN, and CO emission, and warm dust continuum emission towards the long wavelength end of the spectra.

Investigating the Near‐Infrared Properties of Planetary Nebulae. II. Medium‐Resolution Spectra

The Astrophysical Journal Supplement Series, 1999

Shock-Enhanced Ammonia Emission in the Egg Nebula

The Astrophysical Journal, 2009

We present high angular resolution observations of the NH 3 (1,1), (2,2) and (3,3) inversion transitions from the Egg Nebula, the archetypical proto-planetary nebula. The spatial distribution and kinematics of the emission in all three lines show four distinct components or lobes that are aligned with the polar and equatorial directions. The kinematics of the NH 3 emission is also found to follow a clear pattern: redshifted emission in the South and West and blueshifted emission in the North and East. The morphology and spatial kinematics of NH 3 emission are shown to have strong similarity to that observed previously in molecular hydrogen emission and CO emission which arise from the shocked molecular gas. We also find that the higher lying inversion transition NH 3 (2,2) and (3,3) are stronger in the polar direction in comparison to the lower transition NH 3 (1,1). We conclude that the NH 3 emission traces the warm molecular gas, which is shocked and heated by the interaction between the high velocity outflows and the surrounding envelope. The presence of strong ammonia emission associated with the shock fronts and the lack of the emission at the center of the nebula indicate that the abundance of ammonia is significantly enhanced by shocks, a situation very similar to that found in outflows from protostars.

On the relationship between the H2 emission and the physical structure of planetary nebulae

Monthly Notices of the Royal Astronomical Society, 2013

Mid-IR observations of planetary nebulae (PNe) have revealed diffuse emission associated to their main nebular shells and outer envelopes or haloes. The interpretation of this emission is uncertain because the broad-band mid-IR images may include contributions of different components. In particular, the Spitzer IRAC 8 µm images, that best reveal these nebular features, can include contributions not only of H 2 lines, but also those of ionic species, PAH features, and thermal dust continuum emission. To investigate the nature of the emission detected in mid-IR observations of a sample of 10 PNe, we have obtained narrow-band near-IR H 2 λ2.122 µm and optical [N ii] λ6584Å images. The comparison between these images confirm that a significant fraction of the emission detected in the IRAC 8 µm images can be attributed to molecular hydrogen, thus confirming the utility of these mid-IR images to investigate the molecular component of PNe. We have also detected H 2 emission from PNe whose physical structure cannot be described as bipolar, but rather as ellipsoidal or barrel-like. These detections suggest that, as more sensitive observations of PNe in the H 2 λ2.122 line are acquired, the detection of H 2 emission is not exclusive of bipolar PNe, although objects with this morphology are still the brightest H 2 emitters. Finally, we remark that the bright H 2 emission from the equatorial ring of a bipolar PN does not arise from a photo-dissociation region shielded from the UV stellar radiation by the ring itself, but from dense knots and clumps embedded within the ionized material of the ring.

Near-infrared echelle spectroscopy of protoplanetary nebulae: probing the fast wind in H 2

Monthly Notices of the Royal Astronomical Society, 2005

Echelle spectroscopy of H 2 2.122 µm, [FeII] 1.644 µm and Brγ line emission from a very young planetary nebula, IRAS 21282+5050, and from four proto-planetary nebulae, IRAS 19343+2926 (M 1-92), IRAS 17150-3224 (AFGL 6815), IRAS 17423-1755 (Hen 3-1475), and IRAS 17441-2411 is presented. H 2 line emission is detected in discrete shock fronts in the lobes of each nebula, regardless of source spectral type (although non-detections in IRAS 09371+1212 (Frosty Leo) support claims that late spectral types do not produce bright H 2 line emission). In IRAS 17150-3224 we also uncover possible signs of rotation, as would be expected if the H 2 features were excited in a magneto-centrifugal disk wind.

An Atlas of [N ii ] and [O iii ] Images and Spectra of Planetary Nebulae

The Astrophysical Journal Supplement Series, 2007

We present an atlas of Hubble Space Telescope images and ground-based, long-slit, narrowband spectra centered on the 6584 8 line of [N ii] and the 5007 8 line of [O iii]. The spectra were obtained for a variety of slit positions across each target (as shown on the images) in an effort to account for nonspherical nebular geometries in a robust manner. We have extended the prolate ellipsoidal shell model originally devised by Aaquist, Zhang, and Kwok to generate synthetic images, as well as long-slit spectra. Using this model, we have derived basic parameters for the subsample of PNe that present ellipsoidal appearances and regular kinematic patterns. We find differences between our parameters for the target PNe as compared to those of previous studies, which we attribute to increased spatial resolution for our image data and the inclusion of kinematic data in the model fits. The data and analysis presented in this paper can be combined with detections of nebular angular expansion rates to determine precise distances to the PN targets.

Unveiling shocks in planetary nebulae (original) (raw)

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