High-excitation Planetary Nebula Research Articles

Morphokinematical study of the planetary nebula Me2-1: Unveiling its point-symmetric and unusual physical structure

Me 2-1 is a high-excitation planetary nebula whose morphology and physical structure have not yet been investigated. We present narrow-band images in several emission lines, and high- and intermediate-resolution long-slit spectra aimed at investigating its morphology and 3D structure, and its physical parameters and chemical abundances. By applying deconvolution techniques to the images, we identified in Me 2-1: an elliptical ring; two elongated, curved structures (caps) that contain three pairs of bright point-symmetric (PS) knots; a shell interior of the ring; and a faint halo or attached shell. The caps are observed in all images, while the PS knots are only observed in the low-excitation emission line ones. These structures are also identified in the high-resolution long-slit spectra, allowing us to study their morphokinematics. The 3D reconstruction shows that Me 2-1 consists of a ring seen almost pole-on, and a virtually spherical shell, to which the caps and PS knots are attached. Caps and PS knots most probably trace the sites where high-velocity collimated bipolar outflows, ejected along a wobbling axis, collide with the spherical shell, are slowed down, and remain attached to it. Although the main excitation mechanism in Me 2-1 is found to be photoionization, a contribution of shocks in the PS knots is suggested by their emission line ratios. The combination of collimated outflows and a ring with a spherical shell is unusual among planetary nebulae. We speculate that two planets, each with less than one Jupiter mass, could be involved in the formation of Me 2-1 if both enter a common envelope evolution during the asymptotic giant branch phase of the progenitor. One planet is tidally disrupted, forming an accretion disk around the central star, from which collimated bipolar outflows are ejected; the other planet survives, causing wobbling of the accretion disk. The physical parameters and chemical abundances obtained from our intermediate-resolution spectrum are similar to those obtained in previous analyses, with the abundances also pointing to a low-mass progenitor of Me 2-1.

FAST Search for Circumstellar Atomic Hydrogen. II. Is BD+30°3639 an Interacting Planetary Nebula?

The young, compact, very high surface brightness but low excitation planetary nebula (PN) BD+30°3639 is one of the very few PNe that have been reported to exhibit the 21 cm H i emission line. As part of a long-term program to search for circumstellar atomic hydrogen, we observed the 21 cm feature toward BD+30°3639 with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Assuming a direct association between the PN and the detected H i emission, these new observations show that this surrounding emission is significantly more spatially extended than indicated by previous interferometric observations and can be resolved into two velocity components. The estimated H i mass is larger than 100 M ⊙, invalidating an origin from the host star itself or its ejecta for the emitting material. We discuss the possibility that the extended H i emission stems from the interstellar medium (ISM) swept out over time by the stellar wind. Moreover, we report tentative detections of H i absorption features lying near and blueward of the systemic velocity of this PN, which are probably from a stalled asterosphere at the outer boundary of the expanding ionized region. The mass of the gas producing the H i absorption is insufficient to solve the so-called “PN missing mass problem.” We demonstrate the capability of FAST to investigate the interaction process between a PN and the surrounding ISM.

WHTZ 1: a high excitation Planetary Nebula not a gaseous cocoon from runaway star HD 185806

ABSTRACT We present evidence that the nebular cocoon and bow-shock emission nebula putatively and recently reported as deriving from the 9th magnitude ‘runaway’ star HD 185806 is the previously discovered but obscure Planetary Nebula WHTZ 1 (Ra 7). It has a Gaia DR3 G∼16 blue ionizing star at its geometric centre. We present imagery, spectroscopy, other data and arguments to support that this emission source is a high excitation Planetary Nebula not a stellar wind bow shock.

Planetary nebulae with UVIT

The high excitation planetary nebula, NGC 6302, has been imaged in two far-ultraviolet (FUV) filters, F169M (Sapphire; λeff: 1608 Å) and F172M (Silica; λeff: 1717 Å) and two near-UV (NUV) filters, N219M (B15; λeff: 2196 Å) and N279N (N2; λeff: 2792 Å) with the Ultra Violet Imaging Telescope (UVIT). The FUV F169M image shows faint emission lobes that extend to about 5 arcmin on either side of the central source. Faint orthogonal collimated jet-like structures are present on either side of the FUV lobes through the central source. These structures are not present in the two NUV filters or in the FUV F172M filter. Optical and infrared (IR) images of NGC 6302 show bright emission bipolar lobes in the east-west direction with a massive torus of molecular gas and dust seen as a dark lane in the north-south direction. The FUV lobes are much more extended and oriented at a position angle of 113°. They and the jet-like structures might be remnants of an earlier evolutionary phase, prior to the dramatic explosive event that triggered the Hubble type bipolar flows approximately 2200 years ago. The source of the FUV lobe and jet emission is not known, but is likely due to fluorescent emission from H2 molecules. The cause of the difference in orientation of optical and FUV lobes is not clear and, we speculate, could be related to two binary interactions.

The H surface brightness-radius relation: a robust statistical distance indicator for planetary nebulae

Measuring the distances to Galactic planetary nebulae (PNe) has been an intractable problem for many decades. We have now established a robust optical statistical distance indicator, the H$\alpha$ surface brightness- radius or S-r relation, which addresses this problem. We developed this relation from a critically evaluated sample of primary calibrating PNe. The robust nature of the method results from our revised calibrating distances with significantly reduced systematic uncertainties, and the recent availability of high-quality data, including updated nebular diameters and integrated H$\alpha$ fluxes. The S-r technique is simple in its application, requiring only an angular size, an integrated H\alpha\ flux, and the reddening to the PN. From these quantities, an intrinsic radius is calculated, which when combined with the angular size, yields the distance directly. Furthermore, we have found that optically thick PNe tend to populate the upper bound of the trend, while optically-thin PNe fall along the lower boundary in the S-r plane. This enables sub-trends to be developed which offer even better precision in the determination of distances, as good as 18 per cent in the case of optically-thin, high-excitation PNe. This is significantly better than any previous statistical indicator. We use this technique to create a catalogue of statistical distances for over 1100 Galactic PNe, the largest such compilation in the literature to date. Finally, in an appendix, we investigate both a set of transitional PNe and a range of PN mimics in the S-r plane, to demonstrate its use as a diagnostic tool. Interestingly, stellar ejecta around massive stars plot on a tight locus in S-r space with the potential to act as a separate distance indicator for these objects.

THE REMARKABLE MOLECULAR CONTENT OF THE RED SPIDER NEBULA (NGC 6537)

Millimeter and sub-millimeter molecular-line observations of planetary nebula (PN) NGC 6537 (Red Spider) have been carried out using the Sub-Millimeter Telescope and the 12 m antenna of the Arizona Radio Observatory in the frequency range 86-692 GHz. CN, HCN, HNC, CCH, CS, SO, H2CO, HCO+ and N2H+, along with the J = 3 → 2 and 6 → 5 lines of CO and those of several isotopologues, were detected toward the Red Spider, estimated to be ~1600 yr old. This extremely high excitation PN evidently fosters a rich molecular environment. The presence of CS and SO suggest that sulfur may be sequestered in molecular form in such nebulae. A radiative transfer analysis of the CO and CS spectra indicate a kinetic temperature of T K ~ 60-80 K and gas densities of n(H2) ~ 1-8 × 105 cm–3 in NGC 6537. Column densities of the molecules in the nebula and their fractional abundances relative to H2 ranged from N tot ~ 1016 cm–2 and f ~ 10–4 for CO, to ~7 × 1011 cm–2 and f ~ 8 × 10–9 for the least abundant species, N2H+. For SO and CS, N tot ~ 2 × 1012 cm–2 and 1013 cm–2, respectively, with f ~ 10–7 and 2 × 10–8. It was also found that HCN/HNC 2. A low 12C/13C ratio of ~4 was measured, indicative of hot-bottom burning. These results, coupled with past observations, suggest that molecular abundances in PNe are governed principally by the physical and chemical properties of the individual object and its progenitor star, rather than nebular age.

THECHANDRAX-RAY SURVEY OF PLANETARY NEBULAE (CHANPLANS): PROBING BINARITY, MAGNETIC FIELDS, AND WIND COLLISIONS

We present an overview of the initial results from the Chandra Planetary Nebula Survey (ChanPlaNS), the first systematic (volume-limited) Chandra X-ray Observatory survey of planetary nebulae (PNe) in the solar neighborhood. The first phase of ChanPlaNS targeted 21 mostly high-excitation PNe within ~1.5 kpc of Earth, yielding 4 detections of diffuse X-ray emission and 9 detections of X-ray-luminous point sources at the central stars (CSPNe) of these objects. Combining these results with those obtained from Chandra archival data for all (14) other PNe within ~1.5 kpc that have been observed to date, we find an overall X-ray detection rate of ~70%. Roughly 50% of the PNe observed by Chandra harbor X-ray-luminous CSPNe, while soft, diffuse X-ray emission tracing shocks formed by energetic wind collisions is detected in ~30%; five objects display both diffuse and point-like emission components. The presence of X-ray sources appears correlated with PN density structure, in that molecule-poor, elliptical nebulae are more likely to display X-ray emission (either point-like or diffuse) than molecule-rich, bipolar or Ring-like nebulae. All but one of the X-ray point sources detected at CSPNe display X-ray spectra that are harder than expected from hot (~100 kK) central star photospheres, possibly indicating a high frequency of binary companions to CSPNe. Other potential explanations include self-shocking winds or PN mass fallback. Most PNe detected as diffuse X-ray sources are elliptical nebulae that display a nested shell/halo structure and bright ansae; the diffuse X-ray emission regions are confined within inner, sharp-rimmed shells. All sample PNe that display diffuse X-ray emission have inner shell dynamical ages <~5x10^3 yr, placing firm constraints on the timescale for strong shocks due to wind interactions in PNe.

Early results from ChanPLaNS: Mystery of hard X-ray emitting CSPNe

AbstractWe are presently using the Chandra X-ray Observatory to conduct the first systematic X-ray survey of planetary nebulae (PNe) in the solar neighborhood. The Chandra Planetary Nebula Survey (ChanPlaNS) is a 570 ks Chandra Cycle 12 Large Program targeting 21 high-excitation PNe within ~1.5 kpc of Earth. When complete, this survey will provide a suite of new X-ray diagnostics that will inform the study of late stellar evolution, binary star astrophysics, and wind interactions. Among the early results of ChanPlaNS (when combined with archival Chandra data) is a surprisingly high detection rate of relatively hard X-ray emission from CSPNe. Specifically, X-ray point sources are clearly detected in roughly half of the ~30 high-excitation PNe observed thus far by Chandra, and all but one of these X-ray-emitting CSPNe display evidence for a hard (few MK) component in their Chandra spectra. Only the central star of the Dumbbell appears to display “pure” hot blackbody emission from a ~200 kK hot white dwarf photosphere in the X-ray band. Potential explanations for the“excess” hard X-ray emission detected from the other CSPNe include late-type companions (heretofore undetected, in most cases) whose coronae have been rejuvenated by recent interactions with the mass-losing WD progenitor, non-LTE effects in hot white dwarf photospheres, self-shocking variable winds from the central star, and slow (re-)accretion of previously ejected red giant envelope mass.

The Necklace: equatorial and polar outflows from the binary central star of the new planetary nebula IPHASX J194359.5+170901

IPHASXJ194359.5+170901 is a new high-excitation planetary nebula with remarkable characteristics. It consists of a knotty ring expanding at a speed of 28 km/s, and a fast collimated outflow in the form of faint lobes and caps along the direction perpendicular to the ring. The expansion speed of the polar caps is 100 km/s, and their kinematical age is twice as large as the age of the ring. Time-resolved photometry of the central star of IPHASXJ194359.5+170901 reveals a sinusoidal modulation with a period of 1.16 days. This is interpreted as evidence for binarity of the central star, the brightness variations being related to the orbital motion of an irradiated companion. This is supported by the spectrum of the central star in the visible range, which appears to be dominated by emission from the irradiated zone, consisting of a warm (6000-7000 K) continuum, narrow C III, C IV, and N III emission lines, and broader lines from a flat H I Balmer sequence in emission. IPHASXJ194359.5+170901 helps to clarify the role of (close) binaries in the formation and shaping of planetary nebulae. The output of the common-envelope evolution of the system is a strongly flattened circumstellar mass deposition, a feature that seems to be distinctive of this kind of binary system. Also, IPHASXJ194359.5+170901 is among the first post-CE PNe for which the existence of a high-velocity polar outflow has been demonstrated. Its kinematical age might indicate that the polar outflow is formed before the common-envelope phase. This points to mass transfer onto the secondary as the origin, but alternative explanations are also considered.

An XMM-Newton view of planetary nebulae in the Small Magellanic Cloud

During an X-ray survey of the Small Magellanic Cloud, carried out with the XMM-Newton satellite, we detected significant soft X-ray emission from the central star of the high-excitation planetary nebula SMP SMC 22. Its very soft spectrum is well fit with a non local thermodynamical equilibrium model atmosphere composed of H, He, C, N, and O, with abundances equal to those inferred from studies of its nebular lines. The derived effective temperature of 1.5x10^5 K is in good agreement with that found from the optical/UV data. The unabsorbed flux in the 0.1-0.5 keV range is about 3x10^{-11} erg cm^-2 s^-1, corresponding to a luminosity of 1.2x10^37 erg/s at the distance of 60 kpc. We also searched for X-ray emission from a large number of SMC planetary nebulae, confirming the previous detection of SMP SMC 25 with a luminosity of (0.2-6)x10^35 erg/s (0.1-1 keV). For the remaining objects that were not detected, we derived flux upper limits corresponding to luminosity values from several tens to hundreds times smaller than that of SMP SMC 22. The exceptionally high X-ray luminosity of SMP SMC 22 is probably due to the high mass of its central star, quickly evolving toward the white dwarf's cooling branch, and to a small intrinsic absorption in the nebula itself.

THE NATURE OF THE STRONG 24 μmSPITZERSOURCE J222557+601148: NOT A YOUNG GALACTIC SUPERNOVA REMNANT

The nebula J222557+601148, tentatively identified by Morris et al. (2006) as a young Galactic supernova remnant (SNR) from Spitzer Galactic First Look Survey images and a follow-up mid-infrared spectrum, is unlikely to be a SNR remnant based on Halpha, [O III], [S II] images and low dispersion optical spectra. The object is seen in Halpha and [O III] 5007 images as a faint, roughly circular ring nebula with dimensions matching that seen in 24 micron Spitzer images. Low-dispersion optical spectra show it to have narrow Halpha and [N II] 6548, 6583 line emissions with no evidence of broad or high-velocity (v > 300 km/s) line emissions. The absence of any high-velocity optical features, the presence of relatively strong [N II] emissions, a lack of detected [S II] emission which would indicate the presence of shock-heated gas, plus no coincident X-ray or nonthermal radio emissions indicate the nebula is unlikely to be a SNR, young or old. Instead, it is likely a faint, high-excitation planetary nebula (PN) as its elliptical morphology would suggest, lying at a distance of approximately 2 - 3 kpc with unusual but not extraordinary mid-IR colors and spectrum. We have identified a m_r' = 22.4 +/- 0.2 star as a PN central star candidate.

SPECTROSCOPIC CONFIRMATION OF THE PLANETARY NEBULA NATURE OF PM 1-242, PM 1-318, AND PM 1-333 AND MORPHOLOGICAL ANALYSIS OF THE NEBULAE

We present intermediate resolution long-slit spectra and narrowband H{alpha}, [N II], and [O III] images of PM 1-242, PM 318, and PM 1-333, three IRAS sources classified as possible planetary nebulae. The spectra show that the three objects are true planetary nebulae and allow us to study their physical properties; the images provide a detailed view of their morphology. PM 1-242 is a medium- to high-excitation (e.g., He II{lambda}4686/H{beta} {approx} 0.4; [N II]{lambda}6584/H{alpha} {approx} 0.3) planetary nebula with an elliptical shape containing [N II] enhanced point-symmetric arcs. An electron temperature [T {sub e}([S III])] of {approx} 10250 K and an electron density [N {sub e}([S II])] of {approx} 2300 cm{sup -3} are derived for PM 1-242. Abundance calculations suggest a large helium abundance (He/H {approx} 0.29) in PM 1-242. PM 1-318 is a high-excitation (He II{lambda}4686/H{beta} {approx} 1) planetary nebula with a ring-like inner shell containing two enhanced opposite regions, surrounded by a fainter round attached shell brighter in the light of [O III]. PM 1-333 is an extended planetary nebula with a high-excitation (He II{lambda}4686/H{beta} up to {approx} 0.9) patchy circular main body containing two low-excitation knotty arcs. A low N {sub e}([S II]) of {approx} 450 cm{sup -3}more » and T {sub e}([O III]) of {approx} 15000 K are derived for this nebula. Abundance calculations suggest that PM 1-333 is a type I planetary nebula. The lack of a sharp shell morphology, low electron density, and high excitation strongly suggest that PM 1-333 is an evolved planetary nebula. PM 1-333 also shows two low-ionization polar structures whose morphology and emission properties are reminiscent of collimated outflows. We compare PM 1-333 with other evolved planetary nebulae with collimated outflows and find that outflows among evolved planetary nebulae exhibit a large variety of properties, in accordance with these observed in younger planetary nebula.« less

The High‐Excitation Planetary Nebula NGC 246. II.FUSEandChandraObservations

This paper presents Far-Ultraviolet Spectroscopic Explorer (FUSE) medium-resolution slit and Chandra X-Ray Observatory ACIS-S observations of the high-excitation planetary nebula NGC 246. The Ne V λ1146 and [Ne V] λ3426 emission lines, the latter obtained in a previous investigation, indicate that the nebula is photoionized by the intense UV radiation of the central object and has a temperature of ~20,000 K. The O VI λ1032 and λ1037 emission lines are moderately optically thick and probably contain contributions from both collisional excitation and radiative scattering of the UV continuum of the central star. The Chandra observation did not detect any X-ray emission from the nebula, but did detect the central star. The absence of nebular X-ray emission and the photoionized nature of the nebula support the hypothesis that the nebula contains a biconical cavity, which extends to the edge of the nebula. In this geometry the stellar wind does not shock the nebular material, resulting only in a cool photoionized plasma. The X-ray spectrum of the central object is consistent with NLTE models for PG 1159-type stars.

Observations and a Model of NGC 2610

While photoionization codes have been carefully intercompared, a fundamental need for clean tests against real nebulae remains. NGC 2610 is a high-excitation planetary nebula which, even at HST resolution, is smooth and symmetric. Helium is He collision strengths.

Far Ultraviolet Emission from NGC 7009

The high-excitation planetary nebula NGC 7009 and its central star were observed with the Far Ultraviolet Spectroscopic Explorer (FUSE) through a 30 $\,{\times}\,$ 30 arcsec (LWRS) aperture, and with the HIRS narrow slit (1.25 $\,{\times}\,$ 20 arcsec) to isolate the inner and outer parts of the nebula from the central star. The high-resolution (15 km/s) nebular spectra (910-1187 A) show strong emission from C III] and permitted transitions of He II N II, N III, S III, S IV, S VI and O VI, with stronger emission closer to the central star. In this paper we present results obtained on the spatial variation of these tracers of highly ionized gas. The hot central star of NGC 7009 is discussed in a separate paper by Sonneborn et al.

Modelling of aspherical nebulae - I. A quick pseudo-3D photoionization code

We describe a pseudo-3D photoionization code, NEBU_3D and its associated visualization tool, VIS_NEB3D, which are able to easily and rapidly treat a wide variety of nebular geometries, by combining models obtained with a 1D photoionization code. The only requirement for the code to work is that the ionization source is uniqu e and not extended. It is applicable as long as the diffuse ionizing radiation f ield is not dominant and strongly inhomogeneous. As examples of the capabilities of these new tools, we consider two very differ ent theoretical cases. One is that of a high excitation planetary nebula that ha s an ellipsoidal shape with two polar density knots. The other one is that of a blister HII region, for which we have also constructed a spherical model (the sp herical impostor) which has exactly the same Hbeta surface brightness distrib ution as the blister model and the same ionizing star. These two examples warn against preconceived ideas when interpreting spectroscop ic and imaging data of HII regions and planetary nebulae. The tools NEBU_3D and VIS_NEB3D, which will be made publicly available in the future, should facilitat e the performance of numerical experiments, to yield a better understanding of t he physics of aspherical ionized nebulae.

FUSE Observations of Mass Loss in Planetary Nebulae

The Far Ultraviolet Spectroscopic Explorer (FUSE) satellite observed several high and low excitation planetary nebulae in the wavelength range 905–1187 Å at a spectral resolution of λ/Δλ ~ 15,000.

3-D ionization structure (in stereoscopic view) of planetary nebulae: the case of NGC 1501

Long-slit echellograms of the high excitation planetary nebula NGC1501, reduced according to the methodology developed by Sabbadin et al. (2000a, b), allowed us to obtain the ``true'' distribution of the ionized gas in the eight nebular slices covered by the spectroscopic slit. A 3-D rendering procedure is described and applied, which assembles the tomographic maps and rebuilds the spatial structure. The images of NGC 1501, as seen in 12 directions separated by 15 deg, form a series of stereoscopic pairs giving surprising 3-D views in as many directions. The main nebula consists of an almost oblate ellipsoid of moderate ellipticity (a=44 arcsec, a/b=1.02, a/c=1.11), brighter in the equatorial belt, deformed by several bumps, and embedded in a quite homogeneous, inwards extended cocoon. Some reliability tests are applied to the rebuilt nebula; the radial matter profile, the small scale density fluctuations and the 2-D (morphology) - 3-D (structure) correlation are presented and analysed. The wide applications of the 3-D reconstruction to the morphology, physical conditions, ionization parameters and evolutionary status of expanding nebulae in general (planetary nebulae, nova and supernova remnants, shells around Population I Wolf-Rayet stars, nebulae ejected by symbiotic stars, bubbles surrounding early spectral type main sequence stars etc.) are introduced.

Fluorescent Excitation of Spectral Lines in Planetary Nebulae

Fluorescent excitation of spectral lines is demonstrated as a function of temperature-luminosity and the distance of the emitting region from the central stars of planetary nebulae (PNs). The electron densities and temperatures are determined, and the method is exemplified through a detailed analysis of spectral observations of a high-excitation PN, NGC 6741. Fluorescence should also be important in the determination of element abundances. It is suggested that the method could be generally applied to determine or constrain the luminosity and the region of spectral emission in other intensively radiative sources such as novae, supernovae, and active galactic nuclei.

The Complex Environment of the High‐Excitation Planetary Nebula NGC 3242

Spatially resolved profiles of the Hα, [N II] λ6584, and [O III] λ5007 nebular emission lines, obtained with the Manchester echelle spectrometer combined with the 2.1 m San Pedro Martir telescope, have revealed the velocity structure of the nebular core and of one of the three (A, B, and C) inner of the high-excitation planetary nebula NGC 3242. The core is shown to have a cylindrical structure expanding at 25 km s-1. The bright, diffuse, line-emitting, inner spherical halo A surrounding the intensely bright elliptical core is shown to be limb brightened, but its expansion velocity is unclear. The surrounding diffuse, 2.5 pc diameter halo B is modeled by a thick shell expanding at 20 km s-1, although the contribution of scattered [O III] λ5007 emission is unknown at present. The origin of the broad profiles from the fainter, patchy, 0.44 pc diameter halo C is again somewhat uncertain and may originate in scattered core light. Far-infrared (FIR) observations with IRAS and the Infrared Space Observatory (ISO) reveal the presence of warm dust throughout the core and inner halos on NGC 3242. Alternatively, the split profiles could imply an expansion velocity of around 20 km s-1 for halo C if scattering is discounted. There is a large filamentary structure of line-emitting gas 1.7 pc to the west of the nebular core. This is shown to be the western boundary of extended FIR emission from warm dust. A patchy component associated with this filamentary nebulosity emits the [O III] λ5007 line with anomalously high intensity yet is shown here to be kinematically relatively inert. Likewise, [N II] λ6584 profiles from the filamentary edge are very narrow with turbulent motions of 8 km s-1. Certainly, the arc is being photoionized by leakage radiation from NGC 3242, but the radial velocities of the line profiles are inconsistent with its origin as a simple shell expanding radially from this planetary nebula. An asymmetric lobe remains a possibility, in which case the arc could be an ancient halo of NGC 3242. The more mundane possibility that the arc is simply photoionized ambient gas is not completely ruled out by the present observations. Strange, faint, broad [O III] λ5007 line profiles are found over the whole 15' diameter area being considered here. The extended FIR emission region implies the presence of hot dust and suggests therefore that these [O III] λ5007 line profiles could have a scattered origin.