ALBERT

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: In this paper we discuss the photometric and spectroscopic observations of newly discovered (symbiotic) systems in the dwarf spheroidal galaxy NGC 205. The Gemini Multi-Object Spectrograph on–off band [O  iii ] 5007 Å emission imaging highlighted several [O iii ] line emitters, for which optical spectra were then obtained. The detailed study of the spectra of three objects allows us to identify them as true, likely and possible symbiotic systems (SySts), the first ones discovered in this galaxy. SySt-1 is unambiguously classified as a symbiotic star, because of the presence of unique emission lines which belong only to symbiotic spectra, the well-known O vi Raman-scattered lines. SySt-2 is only possibly a SySt because the Ne vii Raman-scattered line at 4881 Å, recently identified in a well-studied Galactic symbiotic as another very conspicuous property of symbiotic, could as well be identified as N iii or [Fe iii ]. Finally, SySt-3 is likely a symbiotic binary because in the red part of the spectrum it shows the continuum of a late giant, and forbidden lines of moderate to high ionization, like [Fe v ] 4180 Å. The main source for scepticism on the symbiotic nature of the latter systems is their location in the planetary nebula region in the [O iii ]4363/H versus [O iii ]5007/Hβ diagnostic diagram. It is worth mentioning that at least another two confirmed symbiotics, one of the Local Group dwarf spheroidal IC 10 and the other of the Galaxy, are also misplaced in this diagram.

Description: In this paper we discuss the photometric and spectroscopic observations of newly discovered (symbiotic) systems in the dwarf spheroidal galaxy NGC 205. The Gemini Multi-Object Spectrograph on–off band [O  iii ] 5007 Å emission imaging highlighted several [O iii ] line emitters, for which optical spectra were then obtained. The detailed study of the spectra of three objects allows us to identify them as true, likely and possible symbiotic systems (SySts), the first ones discovered in this galaxy. SySt-1 is unambiguously classified as a symbiotic star, because of the presence of unique emission lines which belong only to symbiotic spectra, the well-known O vi Raman-scattered lines. SySt-2 is only possibly a SySt because the Ne vii Raman-scattered line at 4881 Å, recently identified in a well-studied Galactic symbiotic as another very conspicuous property of symbiotic, could as well be identified as N iii or [Fe iii ]. Finally, SySt-3 is likely a symbiotic binary because in the red part of the spectrum it shows the continuum of a late giant, and forbidden lines of moderate to high ionization, like [Fe v ] 4180 Å. The main source for scepticism on the symbiotic nature of the latter systems is their location in the planetary nebula region in the [O iii ]4363/H versus [O iii ]5007/Hβ diagnostic diagram. It is worth mentioning that at least another two confirmed symbiotics, one of the Local Group dwarf spheroidal IC 10 and the other of the Galaxy, are also misplaced in this diagram.

Description: We present high-dispersion spectroscopic data of the compact planetary nebula Vy 1-2, where high expansion velocities up to 100 km s –1 are found in the Hα, [N ii ] and [O iii ] emission lines. Hubble Space Telescope images reveal a bipolar structure. Vy 1-2 displays a bright ring-like structure with a size of 2.4 arcsec  x  3.2 arcsec and two faint bipolar lobes in the east–west direction. A faint pair of knots is also found, located almost symmetrically on opposite sides of the nebula at position angle = 305°. Furthermore, deep low-dispersion spectra are also presented and several emission lines are detected for the first time in this nebula, such as the doublet [Cl iii ] 5517, 5537, [K iv ] 6101, C ii 6461 and the doublet C iv 5801, 5812Å. By comparison with the solar abundances, we find enhanced N, depleted C and solar O. The central star must have experienced the hot-bottom burning (CN-cycle) during the second dredge-up phase, implying a progenitor star of M  ≥ 3 M . The very low C/O and N/O abundance ratios suggest a likely post-common envelope close binary system. A simple spherically symmetric geometry with either a blackbody or an H-deficient stellar atmosphere model is not able to reproduce the ionization structure of Vy 1-2. The effective temperature and luminosity of its central star indicate a young nebula located at a distance of ~9.7 kpc with an age of ~3500 yr. The detection of stellar emission lines, C ii 6461, the doublet C iv 5801, 5812 and O iii 5592 Å, emitted from an H-deficient star, indicates the presence of a late-type Wolf–Rayet or a WEL-type central star.

Description: Though the low-ionization small-scale structures (LISs) such as knots, filaments and jets of planetary nebulae (PNe) are known for ~30 yr, some of their observational properties are not well established. In consequence, our ability to include them in the wider context of the formation and evolution of PNe is directly affected. Why most structures have lower densities than the PN shells hosting them? Is their intense emission in low-ionization lines the key to their main excitation mechanism? Therefore, if considered altogether, can LISs line ratios, chemical abundances and kinematics enlighten the interplay between the different excitation and formation processes? Here we present a spectroscopic analysis of five PNe that possess LISs confirming that all nebular components have comparable electron temperatures, whereas the electron density is systematically lower in LISs than in the surrounding nebula. Chemical abundances of LISs versus other PN components do not show significant differences as well. By using diagnostic diagrams from shock models, we demonstrate that LISs’ main excitation is due to shocks, whereas the other components are mainly photoionized. We also propose new diagnostic diagrams involving a few emission lines ([N ii ], [O iii ], [S ii ]) and log( f shocks / f * ), where f shocks and f * are the ionization photon fluxes due to the shocks and the central star ionizing continuum, respectively. A robust relation differentiating the structures is found, with the shock-excited clearly having log( f shocks / f * ) 〉 –1; while the photoionized structures have log( f shocks / f * ) 〈 –2. A transition zone, with –2 〈 log( f shocks / f * ) 〈 –1, where both mechanisms are equally important, is also defined.

Description: We report the detection of near-IR H 2 emission from the low-ionization structures (knots) in two planetary nebulae. The deepest ever high-angular-resolution H 2 (1–0) S(1) at 2.122 μm, H 2 (2–1) S(1) at 2.248 μm and Br images of K 4-47 and NGC 7662, obtained using the Near InfraRed Imager and Spectrometer (NIRI) at Gemini-North, are analysed here. K 4-47 reveals a remarkable highly collimated bipolar structure not only in the optical but also in the molecular hydrogen emission. The H 2 emission emanates from the walls of the bipolar outflows and also from the pair of knots at the tip of the outflows. The H 2 (1–0) S(1)/(2–1) S(1) line ratio ranges from ~7 to ~10, suggesting the presence of shock interactions. Our findings can be explained by the interaction of a jet/bullet ejected from the central star with the surrounding asymptotic giant branch material. The strongest H 2 line, (1–0) S(1), is also detected in several low-ionization knots located at the periphery of the elliptical planetary nebula NGC 7662, but only four of these knots are detected in the H 2 (2–1) S(1) line. These four knots exhibit an H 2 line ratio between 2 and 3.5, which suggests that the emission is caused by the UV ionizing flux of the central star. Our data confirm the presence of H 2 gas in both fast- and slow-moving low-ionization knots, which has only been confirmed before in the nearby Helix nebula and Hu 1-2. Overall, the low-ionization structures of planetary nebulae are found to have similar traits to photodissociation regions.

Description: Context. We present a new methodology for the estimation of stellar atmospheric parameters from narrow- and intermediate-band photometry of the Javalambre Photometric Local Universe Survey (J-PLUS), and propose a method for target pre-selection of low-metallicity stars for follow-up spectroscopic studies. Photometric metallicity estimates for stars in the globular cluster M15 are determined using this method. Aims. By development of a neural-network-based photometry pipeline, we aim to produce estimates of effective temperature, Teff, and metallicity, [Fe/H], for a large subset of stars in the J-PLUS footprint. Methods. The Stellar Photometric Index Network Explorer, SPHINX, was developed to produce estimates of Teff and [Fe/H], after training on a combination of J-PLUS photometric inputs and synthetic magnitudes computed for medium-resolution (R ~ 2000) spectra of the Sloan Digital Sky Survey. This methodology was applied to J-PLUS photometry of the globular cluster M15. Results. Effective temperature estimates made with J-PLUS Early Data Release photometry exhibit low scatter, σ(Teff) = 91 K, over the temperature range 4500 〈 Teff (K) 〈 8500. For stars from the J-PLUS First Data Release with 4500 〈 Teff (K) 〈 6200, 85 ± 3% of stars known to have [Fe/H] 〈 −2.0 are recovered by SPHINX. A mean metallicity of [Fe/H] = − 2.32 ± 0.01, with a residual spread of 0.3 dex, is determined for M15 using J-PLUS photometry of 664 likely cluster members. Conclusions. We confirm the performance of SPHINX within the ranges specified, and verify its utility as a stand-alone tool for photometric estimation of effective temperature and metallicity, and for pre-selection of metal-poor spectroscopic targets.