Spectroscopy of southern Galactic disk planetary nebulae. Notes on chemical composition and emission-line stars

We present low resolution spectroscopic observations for a sample of 53 planetary nebulae (PNe) located in the southern sky between Vela and Norma constellations and pertaining to the Galactic disk with expected Galactocentric distance range of 5 to 10 kpc. We derive nebular chemical composition and plasma parameters with the classical empirical method. For most of the observed objects, this has been done for the first time. The distributions of the chemical abundances of the observed disk sample are generally indistinguishable from Galactic bulge and inner-disk PNe populations. The exceptions are possible differences in the He/H distribution, as compared to bulge PNe and Ne/Ar, compared to inner-disk PNe sample. The derived O/H ratios for the observed disk PNe fit to the concept of flattening of the chemical gradient in the inner parts of the Milky Way. We use the spectra to search for emission-line central stars in the observed sample. We found 6 new emission-line central stars comprising examples of all known types: WEL, VL and [WR]. We confirm that these types represent three evolutionary unconnected forms of enhanced mass-loss in the central stars of PNe. We note on the problem of high ionisation PNe with nebular CIV emission that can mimic the presence of WEL central stars in 1D spectra.Comment: 35 pages, 19 figures, 4 tables (Note: corrected error in measured flux of [O II] 7325 lines in Table B.1

New groups of planetary nebulae with peculiar dust chemistry towards the Galactic bulge

We investigate Galactic bulge planetary nebulae without emission-line central stars for which peculiar infrared spectra have been obtained with the Spitzer Space Telescope, including the simultaneous signs of oxygen and carbon based dust. Three separate sub-groups can be defined characterized by the different chemical composition of the dust and the presence of crystalline and amorphous silicates. We find that the classification based on the dust properties is reflected in the more general properties of these planetary nebulae. However, some observed properties are difficult to relate to the common view of planetary nebulae. In particular, it is challenging to interpret the peculiar gas chemical composition of many analyzed objects in the standard picture of the evolution of planetary nebulae progenitors. We confirm that the dual-dust chemistry phenomenon is not limited to planetary nebulae with emission-line central stars.Comment: 17 pages, 13 figure

Copper-catalysed selective hydroamination reactions of alkynes

The development of selective reactions that utilize easily available and abundant precursors for the efficient synthesis of amines is a long-standing goal of chemical research. Despite the centrality of amines in a number of important research areas, including medicinal chemistry, total synthesis and materials science, a general, selective and step-efficient synthesis of amines is still needed. Here, we describe a set of mild catalytic conditions utilizing a single copper-based catalyst that enables the direct preparation of three distinct and important amine classes (enamines, α-chiral branched alkylamines and linear alkylamines) from readily available alkyne starting materials with high levels of chemo-, regio- and stereoselectivity. This methodology was applied to the asymmetric synthesis of ​rivastigmine and the formal synthesis of several other pharmaceutical agents, including ​duloxetine, ​atomoxetine, ​fluoxetine and ​tolterodine.National Institutes of Health (U.S.) (GM58160

Optical spectroscopy of long polyenes

We have synthesized a homologous series of soluble, linearly conjugated oligomers and related polymers using molybdenum alkylidene catalysts. We have developed HPLC procedures to isolate the oligomers according to their chain lengths and have obtained the absorption spectra of the purified oligomers in room temperature solutions and in 77 K glasses. The oligomer absorption spectra are structured and remarkably similar to those of simple polyenes with comparable numbers of conjugated double bonds (N). Furthermore, the electronic origins of the low-energy, strongly allowed 11Ag- f 11Bu+ transitions follow the E(0-0) ) A + B/N behavior previously noted in simple polyenes and carotenoids. Extrapolation of data for oligomers with N) 3-15 suggests E(0-0) 14 000 cm-1 (ì 700 nm) in the long polyene limit. The oligomer spectra exhibit modest red shifts on cooling, suggesting minimal conformational disorder in the room temperature samples. In contrast, the absorption spectrum of the longest soluble polymer (N> 100) in this series undergoes a significant red shift and sharpening upon cooling from 300 to 77 K. This indicates that the room temperature polymer is disordered due to relatively low thermal barriers for torsional motion about carbon-carbon single bonds. Unlike the longer oligomers, the low-temperature absorption of the polymer shows well-defined vibronic structure. The polymerization reactions lead to a distribution of conjugation lengths in the unpurified polymer sample. However, the vibronically resolved, red-shifted absorption at low temperature (ì(0-0) ) 630 nm) indicates that this distribution is dominated by species with very long conjugation lengths. The resolution of the low-temperature spectrum argues that the absorption is due to the superposition of almost identical 11Ag- f 11Bu+ spectra and that all conjugated segments in this sample absorb near the asymptotic limit (1/N 0)

Central stars of planetary nebulae in the Galactic bulge

Context.Optical high-resolution spectra of five central stars of planetary nebulae (CSPN) in the Galactic bulge have been obtained with Keck/HIRES in order to derive their parameters. Since the distance of the objects is quite well known, such a method has the advantage that stellar luminosities and masses can in principle be determined without relying on theoretical relations between both quantities. Aims.By alternatively combining the results of our spectroscopic investigation with evolutionary tracks, we obtain so-called spectroscopic distances, which can be compared with the known (average) distance of the bulge-CSPN. This offers the possibility to test the validity of model atmospheres and present date post-AGB evolution. Methods.We analyze optical H/He profiles of five Galactic bulge CSPN (plus one comparison object) by means of profile fitting based on state of the art non-LTE modeling tools, to constrain their basic atmospheric parameters (${\rm T}_{\it eff}$, $\log g$, helium abundance and wind strength). Masses and other stellar radius dependent quantities are obtained from both the known distances and from evolutionary tracks, and the results from both approaches are compared. Results.The major result of the present investigation is that the derived spectroscopic distances depend crucially on the applied reddening law. Assuming either standard reddening or values based on radio-Hβ extinctions, we find a mean distance of 9.0±1.6 kpc and 12.2±2.1 kpc, respectively. An “average extinction law” leads to a distance of 10.7±1.2 kpc, which is still considerably larger than the Galactic center distance of 8 kpc. In all cases, however, we find a remarkable internal agreement of the individual spectroscopic distances of our sample objects, within ±10% to ±15% for the different reddening laws. Conclusions.Due to the uncertain reddening correction, the analysis presented here cannot yet be regarded as a consistency check for our method, and a rigorous test of the CSPN evolution theory becomes only possible if this problem has been solved