ALBERT

Description: HFG1 is the first well-observed planetary nebula (PN) which reveals a cometary-like structure. Its main morphological features consist of a bow-shaped shell, which surrounds the central star, accompanied by a long collimated tail. In this study, we perform two-dimensional hydrodynamic simulations modelling the formation of HFG1 from the interaction of the local ambient medium with the mass outflows of its asymptotic giant branch (AGB) progenitor star. We attribute the cometary appearance of HFG1 to the systemic motion of the PN with respect to the local ambient medium. Due to its vital importance, we re-estimate the distance of HFG1 by modelling the spectral energy distribution of its central star, V664 Cas, and we find a distance of 490 ± 50 pc. Our simulations show that none of our models with time invariant stellar wind and ambient medium properties are able to reproduce simultaneously the extended bow shock and the collimated tail observed in HFG1. Given this, we increase the complexity of our modelling considering that the stellar wind is time variable. The wind description is based on the predictions of the AGB and post-AGB evolution models. Testing a grid of models, we find that the properties of HFG1 are best reproduced by the mass outflows of a 3 M AGB star. Such a scenario is consistent with the current observed properties of V664 Cas primary star, an O-type subdwarf, and bridges the evolutionary history of HFG1 central star with the observables of the PN. We discuss the implications of our study in the understanding of the evolution of AGB/post-AGB stars towards the formation of O-type subdwarfs surrounded by PNe.

Description: Abell 14 is a poorly studied object despite being considered a born-again planetary nebula. We performed a detailed study of its 3D morphology and ionization structure using the shape and mocassin codes. We found that Abell 14 is a highly evolved, bipolar nebula with a kinematical age of ~19 400 yr for a distance of 4 kpc. The high He abundance, and N/O ratio indicate a progenitor of 5 M that has experienced the third dredge-up and hot bottom burning phases. The stellar parameters of the central source reveal a star at a highly evolved stage near to the white dwarf cooling track, being inconsistent with the born-again scenario. The nebula shows unexpectedly strong [N i ] 5200 and [O i ] 6300 emission lines indicating possible shock interactions. Abell 14 appears to be a member of a small group of highly evolved, extreme type-I planetary nebulae (PNe). The members of this group lie at the lower-left corner of the PNe regime on the [N ii ]/Hα versus [S ii ]/Hα diagnostic diagram, where shock-excited regions/objects are also placed. The low luminosity of their central stars, in conjunction with the large physical size of the nebulae, result in a very low photoionization rate, which can make any contribution of shock interaction easily perceptible, even for small velocities.

Description: In previous, very deep, optical images of NGC 7293, both a feature that has the morphology of a bow-shock and one with that of a jet, were discovered in the faint 40 arcmin diameter halo of the nebula. Spatially resolved longslit profiles of the Hα and [N ii ] 6548, 6584 Å nebular emission lines from both features have now been obtained. The bow-shaped feature has been found to have Hα radial velocities close to the systemic heliocentric radial velocity, –27 km s –1 , of NGC 7293 and is faint in the [N ii ] 6548, 6584 Å emission lines. Furthermore, the full width of these profiles matches the relative motion of NGC 7293 with its ambient interstellar medium consequently it is deduced that the feature is a real bow-shock caused by the motion of NGC 7293 as it ploughs through this medium. The proper motion of the central star also points towards this halo feature which substantiates this interpretation of its origin. Similarly [N ii ] 6584 Å line profiles reveal that the jet-like filament is indeed a collimated outflow, as suggested by its morphology, at around 300 km s –1 with turbulent widths of around 50 km s –1 . Its low Hα/[N ii ] 6548, 6584 Å brightness ratio suggests collisional ionization as expected in a high-speed jet.

Description: We present 3D hydrodynamical simulations of an isotropic fast wind interacting with a previously ejected toroidally shaped slow wind in order to model both the observed morphology and the kinematics of the planetary nebula (PN) NGC 6302. This source, also known as the Butterfly nebula, presents one of the most complex morphologies ever observed in PNe. From our numerical simulations, we have obtained an intensity map for the Hα emission to make a comparison with the Hubble Space Telescope ( HST ) observations of this object. We have also carried out a proper motion (PM) study from our numerical results, in order to compare with previous observational studies. We have found that the two interacting stellar wind model reproduce well the morphology of NGC 6302, and while the PMs in the models are similar to the observations, our results suggest that an acceleration mechanism is needed to explain the Hubble-type expansion found in HST observations.

Description: In this Letter, we explore the hypothesis that the smooth appearance of bow shocks around some red supergiants (RSGs) might be caused by the ionization of their winds by external sources of radiation. Our numerical simulations of the bow shock generated by IRC –10414 (the first-ever RSG with an optically detected bow shock) show that the ionization of the wind results in its acceleration by a factor of 2, which reduces the difference between the wind and space velocities of the star and makes the contact discontinuity of the bow shock stable for a range of stellar space velocities and mass-loss rates. Our best-fitting model reproduces the overall shape and surface brightness of the observed bow shock and suggests that the space velocity and mass-loss rate of IRC –10414 are 50 km s –1 and 10 –6 M yr –1 , respectively, and that the number density of the local interstellar medium is 3 cm –3 . It also shows that the bow shock emission comes mainly from the shocked stellar wind. This naturally explains the enhanced nitrogen abundance in the line-emitting material, derived from the spectroscopy of the bow shock. We found that photoionized bow shocks are 15–50 times brighter in optical line emission than their neutral counterparts, from which we conclude that the bow shock of IRC –10414 must be photoionized.

Description: We present simultaneous observations of H 2 O maser emission and radio continuum at 1.3 cm carried out with the Australia Telescope Compact Array towards two sources, IRAS 16333–4807 and IRAS 12405–6219, catalogued as planetary nebula (PN) candidates, and where single-dish detections of H 2 O masers have been previously reported. Our goal was to unambiguously confirm the spatial association of the H 2 O masers with these two PN candidates. We detected and mapped H 2 O maser emission in both fields, but only in IRAS 16333–4807 the maser emission is spatially associated with the radio continuum emission. The properties of IRAS 16333–4807 provide strong support for the PN nature of the object, hereby confirming it as the fifth known case of an H 2 O maser-emitting PN. This source is bipolar, like the other four known H 2 O maser-emitting PNe, indicating that these sources might pertain to a usual, but short phase in the evolution of bipolar PNe. In IRAS 12405–6219, the H 2 O maser and radio continuum emission are not associated with each other and, in addition, the available data indicate that this source is an H  ii region rather than a PN.

Description: LoTr 1 is a planetary nebula thought to contain an intermediate-period binary central star system (that is, a system with an orbital period, P , between 100 and, say, 1500 d). The system shows the signature of a K type, rapidly rotating giant and most likely constitutes an accretion-induced post-mass-transfer system similar to other PNe, such as LoTr 5, WeBo 1 and A70. Such systems represent rare opportunities to further the investigation into the formation of barium stars and intermediate-period post-asymptotic giant branch systems – a formation process still far from being understood. Here, we present the first detailed analyses of both the central star system and the surrounding nebula of LoTr 1 using a combination of spectra obtained with Very Large Telescope-Focal Reducer and low dispersion Spectrograph, Anglo-Australian Telescope-UCL Coudé Echelle Spectrograph and New Technology Telescope-European Southern Observatory Multi-Mode Instrument, as well as SuperWASP (Wide Angle Search for Planets) photometry. We confirm the binary nature of the central star of LoTr 1 that consists of a K1 III giant and a hot white dwarf. The cool giant does not present any sign of s-process enhancement but is shown to have a rotation period of 6.4 d, which is a possible sign of mass accretion. LoTr 1 also presents broad double-peaked Hα emission lines, whose origin is still unclear. The nebula of LoTr 1 consists in two slightly elongated shells, with ages of 17 000 and 35 000 yr, respectively, and with different orientations. As such, LoTr 1 present a very different nebular morphology than A70 and WeBo 1, which may be an indication of difference in the mass-transfer episodes.

Description: The primary aim is to establish a firm value for the distance to the extraordinary planetary nebula KjPn 8. Secondary aims are to measure the ages of the three giant lobes of this object as well as estimate the energy in the eruption, that caused the most energetic outflow, for comparison with that of an intermediate-luminosity optical transient (ILOT). For these purposes a mosaic of images in the Hα + [N ii ] optical emission lines has been obtained with the new Aristarchos telescope in 2011 for comparison with the images of the KjPn 8 giant lobes present on the Palomar Observatory Sky Survey (POSSI-R) 1954 and POSSII-R 1991 plates. Expansion proper motions of features over this 57 yr baseline in the outflows are present. Using these, a firm distance to KjPn 8 of 1.8 ± 0.3 kpc has been derived for now the angle of the latest outflow to the sky has been established from Hubble Space Telescope imagery of the nebular core. Previously, the uncertain predictions of a bow-shock model were used for this purpose. The dynamical ages of the three separate outflows that form the giant lobes of KjPn 8 are also directly measured as 3200, 7200 and ≥5  x 10 4  yr, respectively, which confirms their sequential ejection. Moreover, the kinetic energy of the youngest and most energetic of these is measured as 10 47 erg which is compatible with an ILOT origin.