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

From “White Fathers” to “Black Fathers” in Kasama and Mpika Dioceses in Zambia

Employing the missiological theory of Henry Venn (1796-1873) and Rufus Anderson (1796-1880) on indigenisation of churches, this article explores the lived experiences of black Zambian Catholic clergymen, nuns, catechists and lay people at some of the mission stations that were once in the hands of Missionaries of Africa, popularly known as White Fathers, from 1891to1991 in the Archdiocese of Kasama and Diocese of Mpika. To write about the White Fathers from the point of view of our interviewees accords us an auspicious opportunity to pay tribute to Fr. Hugo Hinfelaar to whom this article and this particular issue of the Zambia Journal of Social Sciences is dedicated. Having arrived in Zambia as a young Dutch White Father missionary in 1958, Fr. Hinfelaar desired to understand the culture of the Bemba people among whom he was working. He, therefore, became a serious field worker – an anthropologist, historian and theologian. He retired and returned home in 2014, after having contributed to the efforts of indigenising the Catholic Church’s clergy and inculturation of the Catholic faith in the country. The article demonstrates that the indigenisation of Kasama and Mpika Dioceses was incomplete. This is because, of the “three selves”: self-propagating church, self-sustaining church and self-governing church in the indigenisation theory, the self-sustaining church has not been realised according to the respondents, although some of them spoke of the White Fathers having accomplished their mission. This article proposes a reengagement with the discourse of ‘self-sustainability’ which has largely been abandoned by local Catholic theologians. However, it is now an issue which has become all too apparent to be ignored as the Catholic Church becomes more and more indigenised, at least in terms of its clergy. This article proposes a new theme in Church history in Zambia, namely, the localisation of the personnel and self-sustainability in the Catholic Church in Zambia

Abundances in planetary nebulae: NGC1535, NGC6629, He2-108, and Tc1

The aim of the paper is to determine abundances in a group of PNe with uniform morphology. The PNe discussed are circular excited by rather low-temperature central stars. The relation between abundance and evolution is discussed. The mid-infrared spectra of NGC1535, NGC6629, He2-108 and Tc1 taken with the Spitzer Space Telescope are presented. These spectra are combined with IUE and visual spectra to obtain complete extinction-corrected spectra from which the abundances are determined. These abundances are more accurate for several reasons, the most important is that the inclusion of the far infrared spectra increases the number of observed ions and makes it possible to include the nebular temperature gradient in the abundance calculation. The abundances of these PNe are compared to those found in five other PNe of similar properties and are further compared with predictions of evolutionary models. From this comparison we conclude that these PNe originated from low mass stars, probably between 1 and 2.5 solar masses and at present have core masses between 0.56 and 0.63 solar masses. A consistent description of the evolution of this class of PNe is found that agrees with the predictions of the present nebular abundances, the individual masses and the luminosities of these PNe. The distances to these nebulae can be found as well.Comment: 17 pages, 18 tables, 1 figure, Accepted for publication in A&

The Galactic structure and chemical evolution traced by the population of planetary nebulae

We use an extended and homogeneous data set of Galactic planetary nebulae (PNe) to study the metallicity gradients and the Galactic structure and evolution. The most up-to-date abundances, distances (calibrated with Magellanic Cloud PNe) have been employed, together with a novel homogeneous morphological classification, to characterize the different PN populations. We confirm that morphological classes have a strong correlation with PN Peimbert's Type, and also with their distribution on the Galactic landscape. We studied the alpha-element distribution within the Galactic disk, and found that the best selected disk population, together with the most reliable PN distance scale yields to a radial oxygen gradient of d[log(O/H)]/dR=-0.023 +- 0.006 dex/ kpc for the whole disk sample, and of d[log(O/H)]/dR= -0.035+-0.024, -0.023+-0.005, and -0.011+-0.013 dex/kpc respectively for Type I, II, and III PNe. Neon gradients for the same PN types confirm the trend. Accurate statistical analysis show moderately high uncertainties in the slopes, but also confirm the trend of steeper gradient for PNe with more massive progenitors, indicating a possible steepening with time of the Galactic disk metallicity gradient. The PN metallicity gradients presented here are consistent with the local metallicity distribution; furthermore, oxygen gradients determined with young and intermediate age PNe show good consistency with oxygen gradients derived respectively from other young (OB stars, HII regions) and intermediate (open cluster) Galactic populations. We also extend the Galactic metallicity gradient comparison by revisiting the open cluster [Fe/H] data from high resolution spectroscopy. The analysis suggests that they could be compliant with the same general picture of a steepening of gradient with time.Comment: ApJ, in pres