We analyze the evolution of nitrogen resulting from a set of spiral and irregular galaxy models computed for a large number of input mass radial distributions and with various star formation efficiencies. We show that our models produce a nitrogen abundance evolution in good agreement with the observational data. Differences in the star formation histories of the regions and galaxies modeled are essential to reproduce the observational data in the N/O-O/H plane and the corresponding dispersion.
We present the results of nitrogen and oxygen abundance measurements for 185 HII regions spanning a range of radius in 13 spiral galaxies. As expected, the nitrogen-to-oxygen ratio increases linearly with the oxygen abundance for high metallicity HII regions, indicating that nitrogen is predominately a secondary element. However, the nitrogen-to-oxygen ratio plateaus for oxygen abundances less than 1/3 solar (12+log(O/H) < 8.45), as is also seen in low metallicity dwarf galaxies. This result suggests that the observed trend in dwarf galaxies is not due to outflow of enriched material in a shal…
We present a detailed spectroscopic analysis of nitrogen abundances in 91 solar-type stars, 66 with and 25 without known planetary mass companions. All comparison sample stars and 28 planet hosts were analysed by spectral synthesis of the near-UV NH band at 3360 Åobserved at high resolution with the VLT/UVES,while the near-IR NI 7468 Åwas measured in 31 objects. These two abundance indicators are in good agreement. We found that nitrogen abundance scales with that of iron in the metallicity range -0.6 <[Fe/H]< +0.4 with the slope 1.08 \pm 0.05. Our results show that the bulk of nitrogen produc…
We analyze the impact on the Galactic nitrogen abundances of using a new set of low and intermediate mass star yields. These yields have a significant yield of primary nitrogen from intermediate mass stars. We use these yields as an input to a Galactic Chemical Evolution model and study the nitrogen abundances in the halo and in the disc, and compare them with models obtained using other yield sets and with a large amount of observational data. We find that, using these new yields, our model adequately reproduce the observed trends. In particular, these yields solve the historical problem of t…
Models of galactic chemical evolution (CEMs) show that the shape of the stellar initial mass function (IMF) and other assumptions regarding star formation affect the resultant abundance gradients in models of late-type galaxies. Furthermore, intermediate mass (IM) stars undeniably play an important role in the buildup of nitrogen abundances in galaxies. Here I specifically discuss the nitrogen contribution from IM/AGB stars and how it affects the N/O-gradient. For this purpose I have modelled the chemical evolution of a few nearby disc galaxies using different IMFs and star formation prescript…
The oxygen and nitrogen abundances in the HII regions of the nine Virgo spirals of the sample from Skillman et al (1996) and in nine field spiral galaxies are re-determined with the recently suggested P - method. We confirm that there is an abundance segregation in the sample of Virgo spirals in the sense that the HI deficient Virgo spirals near the core of the cluster have higher oxygen abundances in comparison to the spirals at the periphery of the Virgo cluster. At the same time both the Virgo periphery and core spirals have counterparts among field spirals. We conclude that if there is a d…
We investigate whether the observed high number of carbon- and nitrogen-enhanced extremely metal-poor stars could be explained by peculiar evolutionary properties during the core He flash at the tip of the red giant branch. For this purpose we compute a series of detailed stellar models expanding upon our previous work; in particular, we investigate if during the major He flash the penetration of the helium convective zone into the overlying hydrogen-rich layers can produce carbon- and nitrogen-rich abundances in agreement with current spectroscopic observations. The dependence of this phenome…
Using the HST Goddard High Resolution Spectrograph (GHRS), we have obtained high S/N echelle observations of the weak interstellar N I 1160, 1161 A absorption doublet toward the stars Gamma Cas, Lambda Ori, Iota Ori, Kappa Ori, Delta Sco, and Kappa Sco. In combination with a previous GHRS measurement of N I toward Zeta Oph, these new observations yield a mean interstellar gas phase nitrogen abundance (per 10$^6$ H atoms) of 10$^6$ N/H = 75 +/- 4. There are no statistically significant variations in the measured N abundances from sightline to sightline and no evidence of density-dependent deple…
We show the dependence of the Bayesian and the N2-derived oxygen abundances on the N-enrichment history of the star-forming galaxies. We select 531 metal-poor and ~20,000 metal-rich galaxies from the SDSS database for this study. Their "accurate" O/H abundances are obtained from Te and P-method, respectively. The discrepancies of the Bayesian and N2-derived abundances from these two "accurate" abundances show obvious correlations with log(N/O) abundance ratios.
We present N abundances for 21 bright giants in the globular cluster NGC 6752 based on high-resolution UVES spectra of the 3360A NH lines. We confirm that the Stromgren c1 index traces the N abundance and find that the star-to-star N abundance variation is 1.95 dex, at the sample's luminosity. We find statistically significant correlations, but small amplitude variations, between the abundances of N and alpha-, Fe-peak, and s-process elements. Analyses using model atmospheres with appropriate N, O, Na, and Al abundances would strengthen, rather than mute, these correlations. If the small varia…
Abundance ratios of carbon, nitrogen and strontium relative to iron, calculated using spectrum synthesis techniques, are given for a sample of main sequence and turnoff stars that belong to the globular cluster omega Centauri. The variations of carbon, nitrogen and/or strontium show several different abundance patterns as a function of [Fe/H]. The source of the enhancements/depletions in carbon, nitrogen and/or strontium may be enrichment from asymptotic giant branch stars of low (1--3 solar masses) and intermediate (3--8 solar masses) mass. Massive rotating stars which produce excess nitrogen…
Nitrogen abundances have been derived in Damped Ly alpha (DLA) galaxies at Zabs = 2.309, 2.827 and 3.025 toward the QSOs 0100+1300, 1425+6039 and 0347-3819 respectively. The behaviour of nitrogen relative to iron-peak and alpha-elements has been investigated by considering all the extant NI determinations for a total of 9 DLA galaxies. We have estimated the fraction of iron locked into dust grains to convert the observed [N/Fe] ratios into overall (dust plus gas) relative abundances, [N/Fe]corr. The ratios [N/alpha] have been mostly determined by using sulphur as a tracer of alpha-elements whi…
For the first time, we undertake a systematic examination of the nitrogen abundances for a sample of 35 early-type galaxies spanning a range of masses and local environment. The nitrogen-sensitive molecular feature at 3360Åhas been employed in conjunction with a suite of atomic- and molecular-sensitive indices to provide unique and definitive constraints on the chemical content of these systems. By employing NH3360, we are now able to break the carbon, nitrogen, and oxygen degeneracies inherent to the use of the CN-index. We demonstrate that the NH3360 feature shows little dependency upon the …
The 12C14N/12C15N and 12C14N/13C14N isotopic ratios have been determined in comets C/1995 O1 (Hale-Bopp), C/2001 Q4 (NEAT) and C/2003 K4 (LINEAR) at heliocentric distances of, respectively, 2.7, 3.7 and 2.6 AU. These ratios have also been measured at r ~ 1 AU. No significant differences were found between all determinations, nor with the value obtained for other comets. If confirmed, the discrepancy between the nitrogen isotopic ratios from optical and millimeter measurements on CN and HCN would rule out HCN as a major parent of the cometary CN radicals.
We performed a compilation of more than 1000 published spectra of HII regions in spiral galaxies. The oxygen and nitrogen abundances in each HII region were recomputed in a homogeneous way, using the P-method. The radial distributions of oxygen and nitrogen abundances were derived. The correlations between oxygen abundance and macroscopic properties are examined. There is a significant difference between the L-Z relationship obtained here and that based on the oxygen abundances determined through the R_23-calibrations. The oxygen abundance of NGC 5457 recently determined using direct measureme…
Boron abundances have been derived for seven main sequence B-type stars from HST STIS spectra around the B III 2066 A line. In two stars, boron appears to be undepleted with respect to the presumed initial abundance. In one star, boron is detectable but it is clearly depleted. In the other four stars, boron is undetectable implying depletions of 1 to 2 dex. Three of these four stars are nitrogen enriched, but the fourth shows no enrichment of nitrogen. Only rotationally induced mixing predicts that boron depletions are unaccompanied by nitrogen enrichments. The inferred rate of boron depletion…
The 12C14N/12C15N and 12C14N/13C14N isotopic ratios are determined for the first time in a Jupiter-family comet, 88P/1981 Q1 Howell, and in the chemically peculiar Oort Cloud comet C/1999 S4 (LINEAR). By comparing these measurements to previous ones derived for six other Oort Cloud comets (including one of Halley-type), we find that both the carbon and nitrogen isotopic ratios are constant within the uncertainties. The mean values are 12C/13C ~ 90 and 14N/15N \~ 145 for the eight comets. These results strengthen the view that CN radicals originate from refractory organics formed in the protoso…
High-resolution UVES/VLT spectra of B12, an extreme pole-on Be star in the SMC cluster NGC330, have been analysed using non-LTE model atmospheres to obtain its chemical composition relative to the SMC standard star AV304. We find a general underabundance of metals which can be understood in terms of an extra contribution to the stellar continuum due to emission from a disk which we estimate to be at the ~25% level. When this is corrected for, the nitrogen abundance for B12 shows no evidence of enhancement by rotational mixing as has been found in other non-Be B-type stars in NGC330, and is inc…
The AF-supergiants in the Galaxy and the SMC allow us to examine predictions from evolution models through their CNO abundances. In these proceedings, we recalculate the NLTE nitrogen abundances in 22 Galactic and 9 SMC A-supergiants using improved atomic data and model atmospheres to compare with new evolution models. The new abundances are higher than previously published values, and suggest that most of these stars have undergone substantial mixing with CN-cycled gas. While there is no clear relationship with mass, there is an apparent relation with metallicity since the SMC stars (includin…
The quasar Q0353-383 has long been known to have extremely strong nitrogen intercombination lines at 1486 and 1750 Angstroms, implying an anomalously high nitrogen abundance of ~15 times solar. A search for similar nitrogen-rich quasars in the Sloan Digital Sky Survey First Data Release catalog has yielded 20 candidates, including four with nitrogen emission as strong or stronger than that seen in Q0353-383. Our results indicate that only about 1 in 1700 of quasars have nitrogen abundances similar to Q0353-383, while up to 1 in 130 may be in the process of extreme nitrogen enrichment.
We present long slit optical spectroscopy of 67 HII regions in 21 dwarf irregular galaxies to investigate the enrichment of oxygen, nitrogen, neon, sulfur, and argon in low mass galaxies. Oxygen abundances are obtained via direct detection of the temperature sensitive emission lines for 25 HII regions; for the remainder of the sample, oxygen abundances are estimated from strong line calibrations. The direct abundance determinations are compared to the strong-line abundance calibrations of both McGaugh (1991) and Pilyugin (2000). Global oxygen and nitrogen abundances for this sample of dwarf ir…
We present optical spectra of the ionized `Outer Ejecta' of Eta Carinae that reveal differences in chemical composition at various positions. In particular, young condensations just outside the dusty Homunculus Nebula show strong nitrogen lines and little or no oxygen -- but farther away, nitrogen lines weaken and oxygen lines become stronger. The observed variations in the apparent N/O ratio may signify either that the various blobs were ejected with different abundances, or more likely, that the more distant condensations are interacting with normal-composition material. The second hypothesi…
We show that the excess of nitrogen emission observed in a large sample of Starburst Nucleus Galaxies (SBNGs) can only be explained at a given metallicity by an overabundance of nitrogen with respect to normal HII regions in the disks of late-type spirals. The N/O ratios in the SBNGs are comparable to the values found in the bulges of normal early-type spirals, which suggests that what we observe could be the main production of nitrogen in the bulges of these galaxies. The variation of the N/O ratio as a function of metallicity in SBNGs follows a primary + secondary relation, but the increase …
We study the Oxygen and Nitrogen abundances in the interstellar medium of high-redshift galaxies. We use high resolution and high signal-to-noise ratio spectra of Damped Lyman-alpha (DLA) systems detected along the line-of-sight to quasars to derive robust abundance measurements from unsaturated metal absorption lines. We present results for a sample of 16 high-redshift DLAs and strong sub-DLAs (log N(HI)>19.5, 2.4<zabs<3.6) including 13 new measurements. We find that the Oxygen to Iron abundance ratio is pretty much constant with [O/Fe]=+0.32+-0.10 for -2.5<[O/H]<-1.0 with a small scatter aro…
We present the results of a detailed NLTE abundance study of nine beta Cephei stars, all of them being prime targets for theoretical modelling: gamma Peg, delta Cet, nu Eri, beta CMa, xi1 CMa, V836 Cen, V2052 Oph, beta Cep and DD (12) Lac. The following chemical elements are considered: He, C, N, O, Mg, Al, Si, S and Fe. Our abundance analysis is based on a large number of time-resolved, high-resolution optical spectra covering in most cases the entire oscillation cycle of the stars. Nitrogen is found to be enhanced by up to 0.6 dex in four stars, three of which have severe constraints on thei…
We attempt to produce low temperature opacity data incorporating the effects of varied abundances of the elements carbon and nitrogen. For our temperature range of interest, molecules represent the dominant opacity source. Our dataset covers a wide metallicity range and is meant to provide important input data for stellar evolution models and other applications. We conduct chemical equilibrium calculations to evaluate the partial pressures of neutral atoms, ions, and molecules. Based on a large dataset containing atomic line and continuum data and, most importantly, a plethora of molecular lin…
We take a fresh look at the abundance of nitrogen in DLAs with oxygen abundances between 1/10 and 1/100 of solar. This is a metallicity regime poorly sampled in the local universe and where QSO absorbers may hold clues to both the nucleosynthetic origin of N and the chemical evolution of high redshift galaxies. We combine new VLT UVES observations with others from the literature to form a sample of 10 DLAs in which the abundances of N and of one of the two alpha-capture elements O or S have been measured. We confirm earlier reports that the (N/O) ratio exhibits a larger range of values than ot…
The combined enrichment of Supernovae II and I in a hierarchical clustering scenario could produce regions with low N content respect to $α$-elements consistent with observed values measured in Damped Ly-$α$ (DLAs). We have studied the formation of DLAs in a hierarchical clustering scenario under the hypothesis that the building blocks of current field galaxies could be part of the structures mapped by DLAs. In our models the effects of the non-linear evolution of the structure (which produces bursty star formation histories, gas infall, etc.) and the contributions of SNIa and SNII are found t…
We have studied the chemistry of nitrogen--bearing species during the initial stages of protostellar collapse, with a view to explaining the observed longevity of N2H+ and NH3 and the high levels of deuteration of these species. We followed the chemical evolution of a medium comprising gas and dust as it underwent free--fall gravitational collapse. Chemical processes which determine the relative populations of the nuclear spin states of molecules and molecular ions were included explicitly, as were reactions which lead ultimately to the deuteration of the nitrogen--containing species N2H+ and …
Central line-strength indices were measured in the blue spectral region for a sample of 98 early-type galaxies in different environments. For most indices (Mgb and <Fe> in particular) ellipticals in rich clusters and in low-density regions follow the same index-sigma relations. However, striking spectral differences between field ellipticals and their counterparts in the central region of the Coma cluster are found for the first time, with galaxies in the denser environment showing significantly lower C4668 and CN2 absorption strengths. The most convincing interpretation of these results is a …
Determination of chemical abundances for elements produced mainly by Type I SNae and intermediate mass stars in high redshift DLAs probes the early chemical build-up on time-scales comparable with their production. Nitrogen shows a peculiar behaviour never detected before in any other class of objects. For [N/H] < -3 there is a plateau with [N/Si]= -1.45(\pm 0.05). We interpret this as empirical evidence for primary N production by massive stars in young systems where AGB stars have not yet had time to make their contribution. The plateau provides the observational integrated yields for N prod…
We report on 293 quasars with strong NIV] lambda 1486 or NIII] lambda 1750 emission lines (rest-frame equivalent width > 3 Å) at 1.7 < z < 4.0 selected from the Sloan Digital Sky Survey (SDSS) Fifth Data Release. These nitrogen-rich (N-rich) objects comprise ~1.1% of the SDSS quasars. The comparison between the N-rich quasars and other quasars shows that the two quasar subsets share many common properties. We also confirm previous results that N-rich quasars have much stronger Lya and NV lambda 1240 emission lines. Strong nitrogen emission in all ionization states indicates high overall nitrog…
Recent new high-precision abundance data for Galactic halo stars suggest important primary nitrogen production in very metal-poor massive stars. Here, we compute a new model for the chemical evolution of the Milky Way aimed at explaining these new abundance data. The new data can be explained by adopting: a) the stellar yields obtained from stellar models that take into account rotation and b) an extra production of nitrogen in the very metal-poor massive stars. In particular, we suggest an increase of nearly a factor of 200 in 14N for a star of 60 Msun and 40 for a star of 9Msun, for metallic…
We present measurements of the column densities of interstellar DI, OI, NI, and H2 made with FUSE, and of HI made with IUE toward the sdO star LSE 44, at a distance of 554+/-66 pc. This target is among the seven most distant Galactic sight lines for which these abundance ratios have been measured. The column densities were estimated by profile fitting and curve of growth analyses. We find D/H = (2.24 +1.39 -1.32)E-5, D/O = (1.99 +1.30 -0.67)E-2, D/N = (2.75 +1.19 -0.89)E-1, and O/H = (1.13 +0.96 -0.71)E-3 (2 sigma). Of the most distant Galactic sight lines for which the deuterium abundance has…
The interstellar abundances of D I, N I, and O I in the local ISM are studied us ing high-resolution spectra of four hot white dwarfs. The spectra of GD 246, WD 2331$-$475, HZ 21, and Lan 23 were obtained with the {\it Far Ultraviolet Spectroscopic Explorer} FUSE in the wavelength range 905-1187 A. The line of sight to GD 246 probes the Local Interstellar Cloud and at least one other H I cloud inside the Local Bubble, which contains most of the gas seen al ong this line of sight. The column densities of H I, C II*, S II, and Si II are measured using archival STIS echelle-mode observations. The…
We have constructed a 3D photoionisation model of a planetary nebula (PN) similar in structure to NGC 7009 with its outer pair of knots (also known as FLIERs --fast, low-ionization emission regions). The work is motivated by the fact that the strong [N II]6583A line emission from FLIERs in many planetary nebulae has been attributed to a significant local overabundance of nitrogen. We explore the possibility that the apparent enhanced nitrogen abundance previously reported in the FLIERs may be due to ionization effects. Our model is indeed able to reproduce the main spectroscopic and imaging ch…
We present results on carbon, nitrogen, and oxygen abundances for a sample of unevolved metal-poor stars with metallicities in the range -0.3< [Fe/H]< -3. Oxygen abundances derived from different indicators are compared showing consistently that in the range 0.3 >[Fe/H]>-3.0, the [O/Fe] ratio increases from approximately 0 to 1. We find a good agreement between abundances based on the forbidden line, the OH and IR triplet lines when gravities based on Hipparcos} parallaxes are considered for the sample stars. Gravities derived from LTE ionization balance in metal-poor stars with [Fe/H]< -1 are…
We present an analysis of interstellar absorption along the line of sight to the nearby white dwarf star HZ43A. The distance to this star is 68+/-13 pc, and the line of sight extends toward the north Galactic pole. Column densities of OI, NI, and NII were derived from spectra obtained by the Far Ultraviolet Spectroscopic Explorer (FUSE), the column density of DI was derived from a combination of our FUSE spectra and an archival HST GHRS spectrum, and the column density of HI was derived from a combination of the GHRS spectrum and values derived from EUVE data obtained from the literature. We f…
The intensity of the strong N V 1240 line relative to C IV 1549 or to He II 1640 has been proposed as an indicator of the metallicity of QSO broad emission line regions, allowing abundance measurements in a large number of QSOs out to the highest redshifts. Previously, it had been shown that the (normally) much weaker lines N III] 1750 and N IV] 1486 could be used in the same way. The redshift 1.96 QSO 0353-383 has long been known to have N III] and N IV] lines that are far stronger relative to Ly-alpha or C IV than in any other QSO. Because in this particular case these intercombination lines…
We investigate the production of nitrogen in star forming galaxies with ultraviolet (UV) radiation detected by the Galaxy Evolution Explorer Satellite (GALEX). We use a sample of 8,745 GALEX emission line galaxies matched to the Sloan Digital Sky Survey (SDSS) spectroscopic sample. We derive both gas-phase oxygen and nitrogen abundances for the sample, and apply stellar population synthesis models to derive stellar masses and star formation histories of the galaxies. We compare oxygen abundances derived using three different diagnostics. We derive the specific star formation rates of the galax…
Stromgren indices v and b are combined with broad-band index I, and a new index p, the short wavelength half of the v band, to estimate CN 4215A molecular absorption in a sample of stars in M22. The results have been used to estimate carbon and nitrogen abundances and suggest groups of stars within this cluster, each with a characteristic nitrogen abundance, but with a range of carbon abundances. The results suggest the possibility of stars consisting of material which has undergone CNO recycling two or three times. The method can be subsequently used for other globular clusters.
The main objective of the present work is to ckeck if the star formation efficiency plays a relevant role in the evolution of the relative abundance N/O. We analyze the evolution of the nitrogen-to-oxygen ratio as predicted by a set of computed theoretical models of simulated galaxies with different total masses which are evolved assuming different collapse time scales and different star formation efficiencies, thus producing different star formation histories. The stellar yield set we use for all of them (Gavilán et al. 2005) have an important contribution of primary nitrogen proceeding from …
The aim of this paper is to provide the fundamental parameters and abundances for a large sample of local clump giants with a high accuracy. The selection of clump stars for the sample group was made applying a color - absolute magnitude window to nearby Hipparcos stars. The abundances of carbon and nitrogen were obtained from molecular synthetic spectrum, the Mg and Na abundances were derived using the non-LTE approximation. The "classical" models of stellar evolution without atomic diffusion and rotation-induced mixing were employed. The atmospheric parameters (Teff, log g, [Fe/H], Vt) and L…
High redshift DLA systems suggest that the relative abundances of elements might be roughly solar, although with absolute abundances of more than two orders of magnitude below solar. The result comes from observations of the [SII/ZnII] ratio, which is a reliable diagnostic of the true abundance, and from DLA absorbers with small dust depletion and negligible HII contamination. In particular, in two DLA systems nitrogen is detected and at remarkably high levels (Vladilo et al. 1995, Molaro et al. 1995, Green et al. 1995, Kulkarni et al. 1996). Here we compare the predictions from chemical evolu…
We measure the nitrogen abundance in 5 Turn Off(TO) stars of the Globular Clusters NGC 6397 and NGC 6752, and compare the cluster abundances with those of field stars of comparable metallicity. We determine the nitrogen abundance from the band head system at 3360 Å, using spectra of resolution R=45000 obtained with the UVES spectrograph on the VLT. We apply the same method previously used on field stars, to allow a direct comparison of the results. Nitrogen is found to have the same abundance in two of the NGC 6397 stars, in spite of a difference of one order of magnitude in oxygen abundance b…
We present V, B-V, and DDO C(41-42) and C(42-45) photometry for a sample of 75 red giants down to M_V = +2 in the relatively metal-rich Galactic globular cluster M71. The C(41-42) colors reveal a bimodal distribution of CN band strengths generally anticorrelated with CH band strength as measured by the C(42-45) color. Both DDO colors agree well with those found in 47 Tucanae -- a nearby globular cluster of similar metallicity -- and suggest nearly identical C and N abundance patterns among the giants of both clusters. A comparison with synthetic DDO colors demonstrates that little change in su…
High resolution far-ultraviolet spectra of the O-type subdwarf BD +28 4211 were obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) to measure the interstellar deuterium, nitrogen, and oxygen abundances in this direction. The interstellar D I transitions are analyzed down to Lyman iota at 920.7 A. The star was observed several times at different target offsets in the direction of spectral dispersion. The aligned and coadded spectra have high signal-to-noise ratios (S/N =50-100). D I, N I, and O I transitions were analyzed with curve-of-growth and profile fitting techniques. A model…
Abundance ratios relative to iron for carbon, nitrogen, strontium and barium are presented for a metal-rich main sequence star ([Fe/H]=--0.74) in the globular cluster omega Centauri. This star, designated 2015448, shows depleted carbon and solar nitrogen, but more interestingly, shows an enhanced abundance ratio of strontium [Sr/Fe] ~ 1.6 dex, while the barium abundance ratio is [Ba/Fe]<0.6 dex. At this metallicity one usually sees strontium and barium abundance ratios that are roughly equal. Possible formation scenarios of this peculiar object are considered.
We present results for the chemical evolution of the Galactic bulge in the context of an inside-out formation model of the Galaxy. A supernova-driven wind was also included in analogy with elliptical galaxies. New observations of chemical abundance ratios and metallicity distribution have been employed in order to check the model results. We confirm previous findings that the bulge formed on a very short timescale with a quite high star formation efficiency and an initial mass function more skewed toward high masses than the one suitable for the solar neighbourhood. A certain amount of primary…
We present detailed spectroscopic analysis of nitrogen abundances in 31 unevolved metal-poor stars analysed by spectral synthesis of the near-UV NH band at 3360 A observed at high resolution with various telescopes. We found that [N/Fe] scales with that of iron in the metallicity range -3.1 < [Fe/H] <0 with the slope 0.01+-0.02. Furthermore, we derive uniform and accurate (N/O) ratios using oxygen abundances from near-UV OH lines obtained in our previous studies. We find that a primary component of nitrogen is required to explain the observations. The NH lines are discovered in the VLT/UVES sp…
Galactic chemical evolution model calculations indicate that there should be considerable scatter in the observed N/O ratios at a fixed metallicity (O/H) for galaxies with very low metallicities due to the delayed release of primary N from intermediate mass stars relative to that of O from short-lived massive stars. Moreover, the scatter should increase progressively toward decreasing metallicity. Such effects have not been convincingly demonstrated by observations of H II regions in nearby metal-poor galaxies, raising doubts about the time-delay model of primary N production. Pettini et al an…
We present elemental abundances for multiple HII regions in Leo A and GR 8 obtained from long slit optical spectroscopy of these two nearby low luminosity dwarf irregular galaxies. As expected from their luminosities, and in agreement with previous observations, the derived oxygen abundances are extremely low in both galaxies. High signal-to-noise ratio observations of a planetary nebula in Leo A yield 12 + log(O/H) = 7.30 +/- 0.05; "semi-empirical" calculations of the oxygen abundance in four HII regions in Leo A indicate 12 + log(O/H) = 7.38 +/- 0.10. These results confirm that Leo A has one…
Results appeared since the last APN meeting on the relation between abundances and PNe morphological features are reviewed here. Statistical analyses of round, elliptical, and bipolar PNe clearly separate the latter group as having larger He and N/O abundances. Studies of individual PNe, including the UV and IR domains, allow a detailed comparison with evolutionary models for the AGB phase; the abundances of most important elements can be matched but an 'age-metallicity' problem for the progenitors of He-rich PNe is implied. Halo abundances do not show strong chemical differences with respect …
New abundances of N, O, Na, Mg, Si, Ca, Sc, Ti, Cr, Fe, Sr, Zr, and Ba are presented for 10 A-type supergiants in the SMC, plus upper limits for C. In interpreting the CNO results for constraints on stellar evolution theories, careful attention has been paid to the comparison abundances, i.e., the present day abundances of SMC nebulae and B-dwarf stars. These new results are also compared to published results from F-K supergiant analyses, and found to be in good agreement when both sets of data are carefully examined as differential (SMC minus Galactic standard) abundances. With the exception …
High resolution spectra of seven early B-type giant/supergiant stars in the SMC cluster NGC330 are analysed to obtain their chemical compositions relative to SMC field and Galactic B-type stars. It is found that all seven stars are nitrogen rich with an abundance approximately 1.3 dex higher than an SMC main-sequence field B-type star, AV304. They also display evidence for deficiencies in carbon, but other metals have abundances typical of the SMC. Given the number of B-type stars with low rotational projected velocities in NGC330 (all our targets have vsini < 50 km/s), we suggest that it is u…
We present chemical abundances for planetary nebulae in M32, NGC 185, and NGC 205 based upon spectroscopy obtained at the Canada-France-Hawaii Telescope using the Multi-Object Spectrograph. From these and similar data compiled from the literature for other Local Group galaxies, we consider the origin and evolution of the stellar progenitors of bright planetary nebulae in galaxies where star formation ceased long ago. The ratio of neon to oxygen abundances in bright planetary nebulae is either identical to that measured in the interstellar medium of star-forming dwarf galaxies or at most change…
Evolutionary models for massive stars, accounting for rotational mixing effects, do not predict any core-processed material at the surface of B dwarfs with low rotational velocities. Contrary to theoretical expectations, we present a detailed and fully-homogeneous, NLTE abundance analysis of 20 early B-type dwarfs and (sub)giants that reveals the existence of a population of nitrogen-rich and boron-depleted, yet intrinsically slowly-rotating objects. The low-rotation rate of several of these stars is firmly established, either from the occurrence of phase-locked UV wind line-profile variations…
We present 14 N^0 measurements from our HIRES/Keck database of damped Lya abundances. These data are combined with measurements from the recent and past literature to build an homogeneous, uniform set of observations. We examine photoionization diagnostics like Fe^++ and Ar^0 in the majority of the complete sample and assess the impact of ionization corrections on N/alpha and alpha/H values derived from observed ionic column densities of N^0, Si^+, H^0, and S^+. Our final sample of 19 N/alpha, alpha/H pairs appears bimodal; the majority of systems show N/alpha values consistent with metal-poor…
The blue supergiant Sher 25 is surrounded by an asymmetric, hourglass-shaped circumstellar nebula. Its structure and dynamics have been studied previously through high-resolution imaging and spectroscopy, and it appears dynamically similar to the ring structure around SN 1987A. Here we present long-slit spectroscopy of the circumstellar nebula around Sher 25, and of the background nebula of the host cluster NGC 3603. We perform a detailed nebular abundance analysis to measure the gas-phase abundances of oxygen, nitrogen, sulphur, neon and argon. The oxygen abundance in the circumstellar nebula…
We compute the ozone distribution for a model terrestrial paleoatmosphere in which the present oxygen abundance is largely replaced by carbon dioxide, which we argue is a reasonable working assumption. In principle, the presence of carbon dioxide might supplement the ozone shield as compared with models based on nitrogen without high carbon dioxide abundance so that early life need not have been as UV-resistant as often assumed. An extrasolar planet with a high-CO2 atmosphere might contain enough O3 to be a source of false positive biomarkers. We find that the globally averaged O3 column densi…
