Jesse Bublitz

We present results from a program of Atacama Large Millimeter Array (ALMA) 1.3 mm (Band 6) molecular line mapping of a sample of nearby, bipolar/pinched-waist, molecule-rich planetary nebulae (PNs; NGC 6302, Hubble 5, NGC 2440, NGC 6445, NGC 2899, and NGC 2818). Maps of ¹² CO(2–1) and ¹³ CO(2–1) emission as well as emission lines of HCN, HNC, HCO ⁺ , CN, and CS—many of these detected in these PNs for the first time—reveal the molecular mass distributions, compositions, and velocity fields of the equatorial and, in some cases, polar regions of the sample PNs. In each case, the bulk of the molecular gas traces an expanding equatorial torus, with torus expansion velocities ranging from ∼15 to ∼50 km s ⁻¹ and molecular masses from ∼0.002 to ∼0.1 M _⊙ . The inferred molecular torus dynamical ages, which span the range ∼500 yr (Hb 5) to ∼11,000 yr (NGC 2818), provide support for a model wherein molecular torus ejection precedes bipolar lobe formation. Collectively, these ALMA survey results provide insight into the rapid structural evolution as well as the zones of irradiated molecular gas within bipolar PNs that are descended from relatively massive progenitors, likely residing in interacting binary systems, over ∼10 kyr of the post-asymptotic giant branch evolution of such systems.

We present Submillimeter Array (SMA) mapping of ¹²CO J = 2 → 1, ¹³CO J = 2 → 1, and CN N = 2 → 1 emission from the ring-like planetary nebula NGC 3132, one of the subjects of JWST Early Release Observation near-infrared imaging. The ∼5″ resolution SMA data demonstrate that the Southern Ring’s main, bright, molecule-rich ring is indeed an expanding ring, as opposed to a limb-brightened shell, in terms of its intrinsic (physical) structure. This suggests that NGC 3132 is a bipolar nebula viewed more or less pole-on (inclination ∼15°–30°). The SMA data furthermore reveal that the nebula harbors a second expanding molecular ring that is aligned almost orthogonally to the main, bright molecular ring. We propose that this two-ring structure is the remnant of an ellipsoidal molecular envelope of ejecta that terminated the progenitor star’s asymptotic giant branch evolution and was subsequently disrupted by a series of misaligned fast, collimated outflows or jets resulting from interactions between the progenitor and one or more companions.

The young and well-studied planetary nebula (PN) NGC 7027 harbors significant molecular gas that is irradiated by luminous, pointlike UV (central star) and diffuse (shocked nebular) X-ray emission. This nebula represents an excellent subject to investigate the molecular chemistry and physical conditions within photon- and X-ray-dominated regions (PDRs and XDRs). As yet, the exact formation routes of CO⁺ and HCO⁺ in PN environments remain uncertain. Here we present ∼2″ resolution maps of NGC 7027 in the irradiation tracers CO⁺ and HCO⁺ obtained with the IRAM NOEMA interferometer, along with SMA CO and HST 2.12 μm H₂ data for context. The CO⁺ map constitutes the first interferometric map of this molecular ion in any PN. Comparison of CO⁺ and HCO⁺ maps reveals strikingly different emission morphologies, as well as a systematic spatial displacement between the two molecules; the regions of brightest HCO⁺, found along the central waist of the nebula, are radially offset by ∼1″ (∼900 au) outside the corresponding CO⁺ emission peaks. The CO⁺ emission furthermore precisely traces the inner boundaries of the nebula’s PDR (as delineated by near-IR H₂ emission), suggesting that central star UV emission drives CO⁺ formation. The displacement of HCO⁺ radially outward with respect to CO⁺ is indicative that dust-penetrating soft X-rays are responsible for enhancing the HCO⁺ abundance in the surrounding molecular envelope, forming an XDR. These interferometric CO⁺ and HCO⁺ observations of NGC 7027 thus clearly establish the spatial distinction between the PDR and XDR formed (respectively) by intense UV and X-ray irradiation of molecular gas.

The iconic planetary nebula (PN) NGC 7027 is bright, nearby (D ∼ 1 kpc), highly ionized, intricately structured, and well observed. This nebula is hence an ideal case study for understanding PN shaping and evolution processes. Accordingly, we have conducted a comprehensive imaging survey of NGC 7027 comprised of 12 HST Wide Field Camera 3 images in narrow-band and continuum filters spanning the wavelength range 0.243–1.67 μm. The resulting panchromatic image suite reveals the spatial distributions of emission lines covering low-ionization species such as singly ionized Fe, N, and Si, through H recombination lines, to more highly ionized O and Ne. These images, combined with available X-ray and radio data, provide the most extensive view of the structure of NGC 7027 obtained to date. Among other findings, we have traced the ionization structure and dust extinction within the nebula in subarcsecond detail; uncovered multipolar structures actively driven by collimated winds that protrude through and beyond the PN’s bright inner core; compared the ionization patterns in the WFC3 images to X-ray and radio images of its interior hot gas and to its molecular outflows; pinpointed the loci of thin, shocked interfaces deep inside the nebula; and more precisely characterized the central star. We use these results to describe the recent history of this young and rapidly evolving PN in terms of a series of shaping events. This evolutionary sequence involves both thermal and ram pressures, and is far more complex than predicted by extant models of UV photoionization or winds from a single central progenitor star, thereby highlighting the likely influence of an unseen binary companion.

Context. Observations of molecular clouds, prestellar cores, and protoplanetary disks have established that the HNC/HCN ratio may be a potent diagnostic of molecular gas physical conditions. The processes that govern the relative abundances of these molecules nevertheless remain poorly understood. Aims. We seek to exploit the wide range of UV irradiation strengths within the ∼pc diameter Helix planetary nebula to explore the potential role of UV radiation in driving HNC/HCN. Methods. We performed IRAM 30 m and APEX 12 m radio line observations across six positions within the Helix Nebula, making use of radiative transfer and photodissociation modeling codes to interpret the results for line intensities and line ratios in terms of the molecular gas properties. Results. We have obtained the first detections of the plasma-embedded Helix molecular knots (globules) in HCN, HNC, HCO⁺, and other trace molecules. Analysis of the HNC/HCN integrated line intensity ratio reveals an increase with radial distance from the Helix central star. In the context of molecular line ratios of other planetary nebulae from the literature, the HNC/HCN ratio appears to be anticorrelated with UV emission over four orders of magnitude in incident flux. Models of the photodissociation regions within the Helix using the RADEX and Meudon codes reveal strong constraints on the column density (1.5–2.5 × 10¹² cm⁻²) of the molecular gas, as well as pressure and temperature. Analysis of the molecular ion HCO⁺ across the Helix indicates that X-ray irradiation is likely driving HCO⁺ production in the outer regions of planetary nebulae, where photodissociation is limited but cold gas and ionized molecules are abundant. Conclusions. Although the observational results clearly indicate that UV irradiation is important in determining the HNC/HCN ratio, our photodissociation region modeling indicates that the UV flux gradient alone cannot reproduce the observed variation in HNC/HCN across the Helix Nebula. Instead, HNC/HCN appears to be dependent on both UV irradiation and gas pressure and density.

We present the results of a comprehensive, near-UV-to-near-IR Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) imaging study of the young planetary nebula (PN) NGC 6302, the archetype of the class of extreme bilobed, pinched-waist PNe that are rich in dust and molecular gas. The new WFC3 emission-line image suite clearly defines the dusty toroidal equatorial structure that bisects NGC 6302's polar lobes, and the fine structures (clumps, knots, and filaments) within the lobes. The most striking aspect of the new WFC3 image suite is the bright, S-shaped 1.64 μm [Fe ii] emission that traces the southern interior of the east lobe rim and the northern interior of the west lobe rim, in point-symmetric fashion. We interpret this [Fe ii] emitting region as a zone of shocks caused by ongoing, fast (∼100 km s⁻¹), collimated, off-axis winds from NGC 6302's central star(s). The [Fe ii] emission and a zone of dusty, N- and S-rich clumps near the nebular symmetry axis form wedge-shaped structures on opposite sides of the core, with boundaries marked by sharp azimuthal ionization gradients. Comparison of our new images with earlier HST/WFC3 imaging reveals that the object previously identified as NGC 6302's central star is a foreground field star. Shell-like inner lobe features may instead pinpoint the obscured central star’s actual position within the nebula’s dusty central torus. The juxtaposition of structures revealed in this HST/WFC3 imaging study of NGC 6302 presents a daunting challenge for models of the origin and evolution of bipolar PNe.