R. D. D. Costa

An estimate of the time variation of the O/H radial gradient from planetary nebulae

Radial abundance gradients are a common feature of spiral galaxies, and in the case of the Galaxy both the magnitude of the gradients and their variations are among the most important constraints of chemical evolution models. Planetary nebulae (PN) are particularly interesting objects to study the gradients and their variations. Owing to their bright emission spectra, they can be observed even at large galactocentric distances, and the derived abundances are relatively accurate, with uncertainties of about 0.1 to 0.2 dex, particularly for the elements that are not synthesized in their progenitor stars. On the other hand, as the offspring of intermediate mass stars, with main sequence masses in the interval of 1 to 8 solar masses, they are representative of objects with a reasonable age span. In this paper, we present an estimate of the time variation of the O/H radial gradient in a sample containing over 200 nebulae with accurate abundances. Our results are consistent with a flattening of the O/H gradient roughly from −0.11 dex/kpc to −0.06 dex/kpc during the last 9 Gyr, or from −0.08 dex/kpc to −0.06 dex/kpc during the last 5 Gyr.

Chemical abundances of planetary nebulae towards the Galactic anticenter

In this paper we report new observations and derive chemical abundances for a sample of 26 planetary nebulae (PN) located in the anticenter direction. Most of these nebulae are far away objects, located at Galactocentric distances greater than about 8 kpc, so that they are particularly useful for the determination of the radial gradients at large distances from the galactic center. A comparison of the present results with previously determined abundances suggests that the radial abundance gradients flatten out at distances larger than about 10 kpc from the center.

An estimate of the time variation of the abundance gradient from planetary nebulae ⋆ III. O, S, Ar, and Ne: A comparison of PN samples

The time behaviour of the radial abundance gradients in the galactic disk is investigated on the basis of four different samples of planetary nebulae, comprising both smaller, homogeneous sets of data and larger, albeit non-homogeneous, samples. Four different chemical elements are considered, namely, oxygen, sulphur, argon, and neon. Our analysis supports our earlier conclusions that, on the average, the radial abundance gradients have flattened out in the last 6 to 8 Gyr.New results on the time variation of the radial abundance gradients in the galactic disk are presented on the basis of four different samples of planetary nebulae. These comprise both smaller, homogeneous sets of data, and larger but non-homogeneous samples. Four different chemical elements are considered, namely, O, S, Ar, and Ne. Other objects such as open clusters, cepheids and HII regions are also taken into account. Our analysis support our earlier conclusions in the sense that, on the average, the radial abundance gradients have flattened out during the last 6 to 8 Gyr, with important consequences for models of the chemical evolution of the Galaxy.

New abundances of planetary nebulae in the Galactic Bulge

New observations and derived chemical abundances are reported for a sample of 57 bulge planetary nebulae (PN). Together with our previous results, a total of over a hundred objects have been analyzed, which constitute one of the largest samples of bulge nebulae studied under homogeneous conditions, including equipment and reduction procedures. In general, our data show a good agreement with some recent results in the literature, in the sense that the average abundances of bulge PN are similar to those from disk objects, however showing a larger dispersion.

An estimate of the time variation of the abundance gradient from planetary nebulae II. Comparison with open clusters, cepheids and young objects

The temporal behaviour of the radial abundance gradients has important consequences for models of the chemical evolution of the Galaxy. We present a comparison of the time variation of the abundance gradients in the Milky Way disk as determined from a sample of planetary nebulae, open clusters, cepheids and young objects, such as stars in OB associ- ations and HII regions. We conclude that the (Fe/H) gradients as measured in open cluster stars strongly support the time flattening of the abundance gradient as determined from O/ Ha nd S/H measurements in planetary nebulae. This conclusion is also supported by the cepheid variables, for which very accurate gradients and ages can be determined, and also by some recent estimates for OB stars and HII regions. It is estimated that the average flattening rate for the last 8 Gyr is in the range 0.005−0.010 dex kpc −1 Gyr −1 .

Gas and dust release rates and color of dust in comets P/Halley (1986 III), P/Giacobini-Zinner (1985 XIII), and P/Hartley-Good (1985 XVII)

Abstract CN, C2, and C3 emission fluxes observed at wavelengths of 388, 516, and 405 nm in the spectra of the comae of comets P/Halley (1986 III), P/Giacobini-Zinner (1985 XIII), and P/Hartley-Good (1985 XVII) were analyzed within the framework of the Haser model (Haser, Bull. Acad. R. Belg., Classe de Sciences 43, 740, 1957). Column densities and production rates of these gaseous species are determined and compared with those from other observations. For pre-perihelion heliocentric distances it is found that production rates/expansion velocity ( Q ν ) for species vary proportional to r−n, where n is 3.7 ± 0.8, 1.7 ± 0.7, and 4.7 ± 1.4 for CN, C2, and C3, respectively. Continuum fluxes measured at wavelengths of 484.5 and 412.0 nm were analyzed, and dust release rates in the coma of these comets are determined. The dust release rates decrease with increase of heliocentric distance for comet Halley, and follow a r−3.0±0.7 power law. Color excesses of grains were determined in comets P/Halley (1986 III), P/Giacobini-Zinner (1985 XIII), and P/Hartley-Good (1985 XVII).

Atomic Emission Lines in the Spectrum Observed after the Impact between the L-Fragment of Comet D/Shoemaker-Levy 9 and Jupiter

Emission lines of neutral Na, Fe, Ca, and Li atoms were detected in the wavelength range 575-700 nm in the spectra of the plume produced by the L-fragment impact of comet D/Shoemaker-Levy 9 with Jupiter. If the fluorescence mechanism is responsible for excitation of the Na I and Li I resonance lines, then the ratio Li/Na = (1.2 ± 0.3) × 10-3 is quite compatible with meteoritic values. A lower limit of about 1013 g was estimated for the mass of the L-fragment.

The population of planetary nebulae near the Galactic Centre: chemical abundances

In this work, we report physical parameters and abundances derived for a sample of high extinction planetary nebulae located in the Galactic bulge, near the Galactic Centre, based on low dispersion spectroscopy secured at the SOAR telescope using the Goodman spectrograph. The results show that the abundances of our sample are similar to those from other regions of the bulge. Nevertheless, the average abundances of the Galactic bulge do not follow the observed trend of the radial abundance gradient in the disk. Planetary nebulae (PNe) are the offspring of stars within a large mass interval (0.8−8M⊙). They 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 (ISM). The fact that PNe are originated from stars of different masses difficults the construction of representatives samples for unbiased chemical composition studies. So that, the presently available chemical composition studies of PNe are strongly biased, since they were focused on brighter objects, predominantly located in Galactic regions of low interstellar reddening. In this work, we report physical parameters and abundances derived for a sample of high extinction PNe located in the Galactic bulge, near the Galactic Centre (GC), based on low dispersion spectroscopy secured at the SOAR telescope using the Goodman spectrograph. The results point to weaker, highly obscured PNe, with E(B-V) roughly 2.3 on the average, that are at the faint end of the PNe luminosity function (PNLF). With such high extinction, no lines are seen in the blue part of the spectra, at wavelengths shorter than Hβ(486.1 nm). From the point of view of the abundances, Fig. 1 (top) shows sulfur as a function of oxygen abundances. Triangles and stars represent the data obtained with SOAR, and filled circles the data from Cavichia et al. (2010), hereafter CCM10. We assumed a temperature of 10000 K for PNe to which we could not

The time evolution of the Milky Way's oxygen abundance gradient

© 2018 The Author(s). We study the evolution of oxygen abundance radial gradients as a function of time for the Milky Way Galaxy obtained with our MulChem chemical evolution model. We review the recent data of abundances for different objects observed in our Galactic disc. We analyse with our models the role of the growth of the stellar disc, as well as the effect of infall rate and star formation prescriptions, or the pre-enrichment of the infall gas, on the time evolution of the oxygen abundance radial distribution. We compute the radial gradient of abundances within the disc, and its corresponding evolution, taking into account the disc growth along time. We compare our predictions with the data compilation, showing a good agreement. Our models predict a very smooth evolution when the radial gradient is measured within the optical disc with a slight flattening of the gradient from ∼-0.057 dex kpc-1 at z = 4 until values around ∼-0.015 dex kpc-1 at z = 1 and basically the same gradient until the present, with small differences between models. Moreover, some models show a steepening at the last times, from z = 1 until z = 0 in agreement with data which give a variation of the gradient in a range from -0.02 to -0.04 dex kpc-1 from t = 10 Gyr until now. The gradient measured as a function of the normalized radius R/Reff is in good agreement with findings by CALIFA and MUSE, and its evolution with redshift falls within the error bars of cosmological simulations.

Nucleosynthesis of intermediate mass stars: inferences from the observed abundances in photoionized nebulae of the Local Group

Photoionized nebulae, comprising HII regions and planetary nebulae, are excellent laboratories to investigate the nucleosynthesis and chemical evolution of several elements in the Galaxy and other galaxies of the Local Group. Our purpose in this investigation is threefold: (i) to compare the abundances of HII regions and planetary nebulae in each system in order to investigate the differences derived from the age and origin of these objects, (ii) to compare the chemical evolution in different systems, such as the Milky Way, the Magellanic Clouds, and other galaxies of the Local Group, and (iii) to investigate to what extent the nucleosynthesis contributions from the progenitor stars affect the observed abundances in planetary nebulae, especially for oxygen and neon, which places constraints on the amount of these elements that can be produced by intermediate mass stars.