We investigate the dual-dust chemistry (DDC) phenomenon in PNe and discuss reasons for its occurrence, by analyzing Spitzer/IRS spectra of a sample of 40 Galactic PNe among which 26 belong to the Galactic Bulge (GB). The mixed chemistry is derived from the simultaneous detection of PAH features in the 6-14 micron range and crystalline silicates (CS) beyond 20 microns in the Spitzer/IRS spectra. Out of the 26 PNe observed in the GB, 21 show signatures of DDC. Our observations reveal that the simultaneous presence of O- and C-rich dust features in the IR spectra of [WC]-type PNe is not restricted to late/cool [WC]-type stars, as previously suggested in the literature, but is a common feature associated with all [WC]-type PNe. Surprisingly, we found that the DDC is seen also in all observed wels, as well as in other PNe with central stars being neither [WC] nor wels. Most sources observed display CS features in their spectra, with only a few PNe exhibiting, in addition, amorphous silicate bands. We appear to detect a recent change of chemistry at the end of the AGB evolution in the low-mass, high-metallicity population of GB PNe observed. The deficit of C-rich AGB stars in this environment suggests that the process of PAH formation in PNe occurs at the very end of the AGB phase. In addition, the population of low-mass, O-rich AGB stars in the GB, do not exhibit CS features in their spectra. Thus, the high detection rate of DDC that we find cannot be explained by long-lived O-rich (primordial or circumbinary) disks. Our most plausible scenario is a final thermal pulse on the AGB (or just after), which could produce enhanced mass loss, capable of removing/mixing (sometimes completely) the remaining H-rich envelope and exposing the internal C-rich layers, and generating shocks responsible for the silicate crystallization.
Planetary nebulae (PNe) constitute an important tool to study the chemical evolution of the Milky Way and other galaxies, probing the nucleosynthesis processes, abundance gradients and the chemical enrichment of the interstellar medium. In particular, Galactic bulge PNe (GBPNe) have been extensively used in the literature to study the chemical properties of this Galactic structure. However, the presently available GBPNe chemical composition studies are strongly biased, since they were focused on brighter objects, predominantly located in Galactic regions of low interstellar reddening. In this …
We present nucleosynthesis predictions (HeCNOCl) from asymptotic giant branch (AGB) models, with diffusive overshooting from all the convective borders, in the metallicity range Z/4 < Z < 2Zsun. They are compared to recent precise nebular abundances in a sample of Galactic planetary nebulae (PNe) that is divided among double-dust chemistry (DC) and oxygen-dust chemistry (OC) according to the infrared dust features. Unlike the similar subsample of Galactic carbon-dust chemistry PNe recently analysed by us, here the individual abundance errors, the higher metallicity spread, and the uncertain du…
We present deep high-resolution (R~15,000) and high-quality UVES optical spectrophotometry of nine planetary nebulae with dual-dust chemistry. We compute physical conditions from several diagnostics. Ionic abundances for a large number of ions of N, O, Ne, S, Cl, Ar, K, Fe and Kr are derived from collisionally excited lines. Elemental abundances are computed using state-of-the-art ionization correction factors. We derive accurate C/O ratios from optical recombination lines. We have re-analyzed additional high-quality spectra of 14 PNe from the literature following the same methodology. Compari…
Chemistry and kinematic studies can determine the origins of stellar population across the Milky Way. The metallicity distribution function of the bulge indicates that it comprises multiple populations, the more metal-poor end of which is particularly poorly understood. It is currently unknown if metal-poor bulge stars ([Fe/H] $<$ -1 dex) are part of the stellar halo in the inner most region, or a distinct bulge population or a combination of these. Cosmological simulations also indicate that the metal-poor bulge stars may be the oldest stars in the Galaxy. In this study, we successfully targe…
Circumstellar envelopes (CEs) around evolved stars are an active site for the production of molecules. After evolving through the Asymptotic Giant Branch (AGB), proto-planetary nebula (PPN), to planetary nebula (PN) phases, CEs ultimately merge with the interstellar medium (ISM). The study of molecules in PNe, therefore, is essential to understanding the transition from stellar to interstellar materials. So far, over 20 molecular species have been discovered in PNe. The molecular composition of PNe is rather different from those of AGB and PPNe, suggesting that the molecules synthesized in PN …
We have used the Cornish radio catalogue combined with the use of multi-wavelength data to identify 62 new Planetary Nebula (PN) candidates close to the Galactic mid-plane. Of this sample 11 have weak optical counterparts in deep narrow band H$α$ imaging that allows their spectroscopic follow-up. We have observed eight of these candidates spectroscopically, leading to the confirmation of 7 out of 8 as PNe. All but one of our sample of newly detected PNe appear to be of Type I chemistry with very large [NII]/H$α$ ratios. This indicates that our selection method heavily favours detection of this…
The characteristics of the stellar populations in the Galactic Bulge inform and constrain the Milky Way's formation and evolution. The metal-poor population is particularly important in light of cosmological simulations, which predict that some of the oldest stars in the Galaxy now reside in its center. The metal-poor bulge appears to consist of multiple stellar populations that require dynamical analyses to disentangle. In this work, we undertake a detailed chemodynamical study of the metal-poor stars in the inner Galaxy. Using R$\sim$ 20,000 VLT/GIRAFFE spectra of 319 metal-poor (-2.55 dex$\…
Cosmological models predict the oldest stars in the Galaxy should be found closest to the centre of the potential well, in the bulge. The EMBLA Survey successfully searched for these old, metal-poor stars by making use of the distinctive SkyMapper photometric filters to discover candidate metal-poor stars in the bulge. Their metal-poor nature was then confirmed using the AAOmega spectrograph on the AAT. Here we present an abundance analysis of 10 bulge stars with -2.8<[Fe/H]<-1.7 from MIKE/Magellan observations, in total determining the abundances of 22 elements. Combining these results with o…
We present the identification of 34 likely binary central stars (CSs) of planetary nebulae (PNe) from {\it Kepler/K2} data, seven of which show eclipses. Of these, 29 are new discoveries. Two additional CSs with more complicated variability are also presented. We examined the light curves of all `possible', `likely' and `true' PNe in every {\it Kepler/K2} campaign (0 through 19) to identify CS variability that may indicate a binary CS. For Campaigns 0, 2, 7, 15, and 16 we find 6 likely or confirmed variables among 21 PNe. Our primary effort, though, was focused on Campaign 11 which targeted a …
Planetary nebulae (PNe) represent the near endpoints of evolution for stars of initial mass $\sim$1-8 $M_\odot$, wherein the envelope of an asymptotic giant branch (AGB) star becomes photodissociated and ionized by high-energy radiation from a newly emerging white dwarf that was the progenitor star's core. It is increasingly evident that most PNe are descended from binary systems. PNe hence provide unique insight into a diverse range of astrophysical phenomena, including the influence of companion stars on the late stages of stellar evolution; stellar wind interactions and shocks; the physics …
We report the detection of a large sample of high-$α$-metal-rich stars on the low giant branch with $2.6<logg<3.3$ dex in the LAMOST-MRS survey. This special group corresponds to an intermediate-age population of $5-9$ Gyr based on the $[Fe/H]$-$[C/N]$ diagram and age-$[C/N]$ calibration. A comparison group is selected to have solar $α$ ratio at super metallicity, which is young and has a narrow age range around 3 Gyr. Both groups have thin-disk like kinematics but the former shows slightly large velocity dispersions. The special group shows a larger extension in vertical distance toward 1.2 k…
The separation of oxygen- and carbon-rich AGB sources is crucial for their accurate use as local and cosmological distance and age/metallicity indicators. We investigate the use of unsupervised learning algorithms for classifying the chemistry of long-period variables from Gaia DR3's BP/RP spectra. Even in the presence of significant interstellar dust, the spectra separate into two groups attributable to O-rich and C-rich sources. Given these classifications, we utilise a supervised approach to separate O-rich and C-rich sources without BP/RP spectra but instead given broadband optical and inf…
For 32 central stars of PNe we present their parameters interpolated among the new evolutionary sequences. The derived stellar final masses are confined between 0.53 and 0.58 $M_\odot$ in good agreement with the peak in the white dwarf mass distribution. Consequently, the inferred star formation history of the Galactic bulge is well restricted between 3 and 11 Gyr and is compatible with other published studies. The new evolutionary tracks proved a very good as a tool for analysis of late stages of stars life. The result provide a compelling confirmation of the accelerated post-AGB evolution.
The latest edition of the APOGEE-2/DR14 survey catalogue and the first \texttt{Payne} data release of APOGEE abundance determinations by Ting et al. are examined. We identify 31 previously unremarked metal-poor giant stars with anomalously high levels of nitrogen in the chemical space defined by [Fe/H] and [N/Fe]. The APOGEE chemical abundance patterns of such objects revealed that these are chemically distinct from the Milky Way (MW) in most chemical elements. We have found all these objects have a [N/Fe]$>+0.5$, and are thus identified here as nitrogen-rich stars. An orbital analysis of thes…
The planetary nebula (PN) PB 8 around a [WN/WC]-hybrid central star is one of PNe with moderate abundance discrepancy factors (ADFs ~ 2-3), which could be an indication of a tiny fraction of metal-rich inclusions embedded in the nebula (bi-abundance). In this work, we have constructed photoionization models to reproduce the optical and infrared observations of the PN PB 8 using a non-LTE stellar model atmosphere ionizing source. A chemically homogeneous model initially used cannot predict the optical recombination lines (ORLs). However, a bi-abundance model provides a better fit to most of the…
The Pristine Inner Galaxy Survey (PIGS) V: a chemo-dynamical investigation of the early assembly of the Milky Way with the most metal-poor stars in the bulge
The AKARI/IRC color combining the S9W and L18W bands is useful for distinguishing between oxygen-rich and carbon-rich circumstellar dust. Ishihara and collaborators found in 2011 that this color, used together with the near-IR color J-Ks, can be used to classify two groups of dust-enshrouded stars with different chemistry. They investigated the distributions of such dusty AGB stars in the Galaxy and found that those with oxygen-rich dust are more centrally concentrated. While this is consistent with previous studies, the map in Ishihara et al. shows that carbon-rich stars are also present in t…
Detection of unidentified molecular pure rotational lines in C-rich PNe I. The fullerene-containing PN IC 418
Instituto de Astrofísica de Canarias (IAC)（加那利天体物理研究所）；Universidad de La Laguna (ULL)（拉各鲁纳大学）；Instituto de Física Fundamental (IFF, CSIC)（基础物理研究所）；Observatorio Astronómico Nacional (OAN, IGN/CNIG)（国家天文台）；Universidad de Valladolid（巴利亚多利德大学）；Consejo Superior de Investigaciones Científicas (CSIC)（西班牙高等科学研究委员会）；Universitat de Barcelona (UB)（巴塞罗那大学）
A high-resolution spectrum of the helium-rich `hot subdwarf' GALEX J184559.8-413827 (J1845-4138) obtained with SALT HRS demonstrates it to be the first extreme helium (EHe) star to be discovered in nearly 40 years. A quantitative analysis demonstrates it to have an atmosphere described by Teff = 26 170 +/- 750 K, log g /(cm s^-2) = 4.22 +/- 0.10, and a surface chemistry characterised by CNO-processed helium, a 1% contamination of hydrogen (by number), and a metallicity 0.4 dex subsolar. Its distance and position are consistent with membership of the Galactic bulge. Its sharp absorption lines p…
