Here we study 16 planetary nebulae (PNe) in the dwarf irregular galaxy NGC 205 by using GMOS@Gemini spectra to derive their physical and chemical parameters. The chemical patterns and evolutionary tracks for 14 of our PNe suggest that there are no ty
pe I PNe among them. These PNe have an average oxygen abundance of 12+log(O/H)=8.08$pm$0.28, progenitor masses of 2-2.5M$_{odot}$ and thus were born ~1.0-1.7Gyr ago. Our results are in good agreement with previous PN studies in NGC 205. The present 12+log(O/H) is combined with our previous works and with the literature to study the PN metallicity trends of the Local Group (LG) dwarf galaxies, in an effort to establish the PN luminosity- and mass-metallicity relations (LZR and MZR) for the LG dwarf irregulars (dIrrs) and dwarf spheroidals (dSphs). Previous attempts to obtain such relations failed to provide correct conclusions because were based on limited samples (Richer & McCall 1995; Gonc{c}calves et al. 2007). As far as we are able to compare stellar with nebular metallicities, our MZR is in very good agreement with the slope of the MZR recently obtained for LG dwarf galaxies using spectroscopic stellar metallicities (Kirby et al. 2013). Actually, we found that both dIrr and dSph galaxies follow the same MZR, at variance with the differences claimed in the past. Moreover our MZR is also consistent with the global MZR of star-forming galaxies, which span a wider stellar mass range ($sim10^6$ - $sim10^{11}$M$odot$).
Using Herschel data from the Open Time Key Project the Herschel Virgo Cluster Survey (HeViCS), we investigated the relationship between the metallicity gradients expressed by metal abundances in the gas phase as traced by the chemical composition of
HII regions, and in the solid phase, as traced by the dust-to-gas mass ratio. We derived the radial gradient of the dust-to-gas mass ratio for all galaxies observed by HeViCS whose metallicity gradients are available in the literature. They are all late type Sbc galaxies, namely NGC4254, NGC4303, NGC4321, and NGC4501. We examined different dependencies on metallicity of the CO-to-H$_2$ conversion factor (xco), used to transform the $^{12}$CO observations into the amount of molecular hydrogen. We found that in these galaxies the dust-to-gas mass ratio radial profile is extremely sensitive to choice of the xco value, since the molecular gas is the dominant component in the inner parts. We found that for three galaxies of our sample, namely NGC4254, NGC4321, and NGC4501, the slopes of the oxygen and of the dust-to-gas radial gradients agree up to $sim$0.6-0.7R$_{25}$ using xco values in the range 1/3-1/2 Galactic xco. For NGC4303 a lower value of xco$sim0.1times$ 10$^{20}$ is necessary. We suggest that such low xco values might be due to a metallicity dependence of xco (from close to linear for NGC4254, NGC4321, and NGC4501 to superlinear for NGC4303), especially in the radial regions R$_G<$0.6-0.7R$_{25}$ where the molecular gas dominates. On the other hand, the outer regions, where the atomic gas component is dominant, are less affected by the choice of xco, and thus we cannot put constraints on its value.
Nearby galaxies are ideal places to study in detail metallicity gradients and their time evolution. We consider chemical abundances of a new sample of hii regions complemented with previous literature data-sets. We compare hii region and PN abundance
s obtained with a common set of observations taken at MMT. With an updated theoretical model, we follow the time evolution of the baryonic components and chemical abundances in the disk of M33, assuming that the galaxy is accreting gas from an external reservoir. Supported by a uniform sample of nebular spectroscopic observations, we conclude that: {em i}) the metallicity distribution in M33 is very complex, showing a central depression in metallicity probably due to observational bias; {em ii}) the metallicity gradient in the disk of M33 has a slope of -0.037$pm$ 0.009 dex kpc$^{-1}$ in the whole radial range up to $sim$8 kpc, and -0.044$pm$ 0.009 dex kpc$^{-1}$ excluding the central kpc; {em iii}) there is a small evolution of the slope with time from the epoch of PN progenitor formation to the present-time.}
We report the results of spectroscopic observations, obtained with the Gemini North Multi-Object Spectrograph, of 9 planetary nebulae (PNe) and 15 hii regions located in the 5.5arcmin $times$5.5arcmin inner region of the nearby starburst galaxy IC10.
Twelve new candidate PNe have been discovered during our pre-imaging phase. Nine of them have been spectroscopically confirmed. The direct availability of the electron temperature diagnostics in several nebulae allowed an accurate determination of the metallicity map of IC10 at two epochs: the present-time from hii regions and the old/intermediate-age from PNe. We found a non-homogeneous distribution of metals at both epochs, but similar average abundances were found for the two populations. The derived age-metallicity relation shows a little global enrichment interpreted as the loss of metals by SN winds and to differential gas outflows. Finally, we analyzed the production of oxygen --through the third dredge-up-- in the chemical abundance patterns of the PN populations belonging to several dwarf irregular galaxies. We found that the third dredge-up of oxygen is a metallicity dependent phenomenon occurring mainly for 12+$log$(O/H)$leq$7.7 and substantially absent in IC10 PNe.
We report the discovery of a trend of increasing barium abundance with decreasing age for a large sample of Galactic open clusters. The observed pattern of [Ba/Fe] vs. age can be reproduced with a Galactic chemical evolution model only assuming a hig
her Ba yield from the $s$-process in low-mass stars than the average one suggested by parametrized models of neutron-capture nucleosynthesis. We show that this is possible in a scenario where the efficiency of the extra-mixing processes producing the neutron source $^{13}$C is anti-correlated with the initial mass, with a larger efficiency for lower masses. This is similar to the known trend of extended mixing episodes acting in H-rich layers and might suggest a common physical mechanism.
We report the discovery of the first known symbiotic star in IC10, a starburst galaxy belonging to the Local Group, at a distance of ~750kpc. The symbiotic star was identified during a survey of emission-line objects. It shines at V = 24.62+-0.04, V
- R_C = 2.77+-0.05 and R_C - I_C = 2.39+-0.02 and suffers from E(B-V) = 0.85+-0.05 reddening. The spectrum of the cool component well matches that of solar neighborhood M8III giants. The observed emission lines belong to Balmer series, [SII], [NII] and [OIII]. They suggest a low electronic density, negligible optical depth effects and 35,000K < T_eff < 90,000K for the ionizing source. The spectrum of the new symbiotic star in IC10 is an almost perfect copy of that of Hen 2-147, a well known Galactic symbiotic star and Mira.
