Готові списки джерел за темами / Nebular abundances

Добірка наукової літератури з теми "Nebular abundances"

Автор: Grafiati
Опубліковано: 10 грудня 2022
Оновлено: 28 січня 2023

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Статті в журналах з теми "Nebular abundances"

1

Pollacco, D. L., and S. A. Bell. "Imaging and spectroscopy of ejected common envelopes." Symposium - International Astronomical Union 180 (1997): 271. http://dx.doi.org/10.1017/s007418090013089x.

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Imaging and spectroscopy are presented for four planetary nebulae known to contain close binary central stars resulting from a recent phase of common envelope evolution. These objects are Abell 41, Abell 46, Abell 63 and Abell 65. Determinations of the nebula abundances show that He is significantly enhanced in all of the objects. These results are in agreement with theoretical expectations. Uncertainties in the nebular electron temperature constrain other abundances less well. The line fluxes indicate that N is unexpectedly under-abundant. This effect is probably not real and may be an artifact of electron temperature fluctuations within the nebulae.
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2

Peña, Miriam, Grazyna Stasińska, César Esteban, Lars Koesterke, Selene Medina, and Robin Kingsburgh. "Spectroscopy of planetary nebulae with [WR] nuclei." Symposium - International Astronomical Union 193 (1999): 382–83. http://dx.doi.org/10.1017/s0074180900205846.

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We have started an extensive program of systematic observations of planetary nebulae excited by [WR] nuclei with the aim of understanding the evolutionary status of the central stars. Detailed analysis of the nebular and stellar properties might reveal the presence of abundance variations across the nebulae, and allows to detect possible interactions between the massive stellar wind and the nebula. Such an analysis requires spatially resolved spectra, together with a reliable procedure to derive chemical abundances. This is best achieved by constructing individual photo-ionization models that reproduce the main observed properties. Here we present the spectroscopic analysis made for different knots of PB6, NGC2452, NGC2867, NGC6905 and He2–55. All these nebulae are ionized by [WC 2–3] stars and present very high ionization degrees.
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3

Walton, N. A., M. J. Barlow, D. J. Monk, and R. E. S. Clegg. "Abundances and nebular and central star masses for Magellanic Cloud planetary nebulae." Symposium - International Astronomical Union 148 (1991): 334–36. http://dx.doi.org/10.1017/s0074180900200727.

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We present the results of a spectroscopic study of planetary nebulae (PN) in the Magellanic Clouds. The optical survey of He, N, O, and Ne abundances by Monk et al. (1988) has been updated by higher S/N AAT optical data. In addition, carbon and other elemental abundances have been derived from the IUE spectra of 38 PN. Ionized nebular masses have been derived for 80 PN. The ionised mass versus nebular electron density plot shows that planetary nebulae become optically thin when their electron densities drop below 4500 cm--3. Below this density, the mean nebular hydrogen mass found for non-Type I PN is 0.22±0.08 M⊙. Using Zanstra and energy-balance methods, the mean central star mass found for 14 SMC and LMC PN is 0.59±0.02 M⊙.
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4

Pagomenos, G. J. S., J. Bernard-Salas, and S. R. Pottasch. "Neon, sulphur, and argon abundances of planetary nebulae in the sub-solar metallicity Galactic anti-centre." Astronomy & Astrophysics 615 (July 2018): A29. http://dx.doi.org/10.1051/0004-6361/201730861.

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Context. Spectra of planetary nebulae show numerous fine structure emission lines from ionic species, enabling us to study the overall abundances of the nebular material that is ejected into the interstellar medium. The abundances derived from planetary nebula emission show the presence of a metallicity gradient within the disk of the Milky Way up to Galactocentric distances of ~10 kpc, which are consistent with findings from studies of different types of sources, including H II regions and young B-type stars. The radial dependence of these abundances further from the Galactic centre is in dispute. Aims. We aim to derive the abundances of neon, sulphur and argon from a sample of planetary nebulae towards the Galactic anti-centre, which represent the abundances of the clouds from which they were formed, as they remain unchanged throughout the course of stellar evolution. We then aim to compare these values with similarly analysed data from elsewhere in the Milky Way in order to observe whether the abundance gradient continues in the outskirts of our Galaxy. Methods. We have observed 23 planetary nebulae at Galactocentric distances of 8–21 kpc with Spitzer IRS. The abundances were calculated from infrared emission lines, for which we observed the main ionisation states of neon, sulphur, and argon, which are little affected by extinction and uncertainties in temperature measurements or fluctuations within the planetary nebula. We have complemented these observations with others from optical studies in the literature, in order to reduce or avoid the need for ionisation correction factors in abundance calculations. Results. The overall abundances of our sample of planetary nebulae in the Galactic anti-centre are lower than those in the solar neighbourhood. The abundances of neon, sulphur, and argon from these stars are consistent with a metallicity gradient from the solar neighbourhood up to Galactocentric distances of ~20 kpc, albeit with varying degrees of dispersion within the data.
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5

Flynn, G. J., S. Bajt, S. R. Sutton, M. E. Zolensky, K. L. Thomas, and L. P. Keller. "The Abundance Pattern of Elements Having Low Nebular Condensation Temperatures in Interplanetary Dust Particles: Evidence for a New Chemical Type of Chondritic Material." International Astronomical Union Colloquium 150 (1996): 291–94. http://dx.doi.org/10.1017/s0252921100501717.

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AbstractThe abundances of Ni, Fe, Cr, Mn, P, Cu, K, Na, Ga, Ge, Se, Zn, S, Br, and C were measured in interplanetary dust particles (IDPs) collected from the Earth's stratosphere. All elements with nebular condensation temperatures lower than Mn, except S, were enriched relative to the most volatile-rich type of meteorite while the refractory elements Cr and Ni were present at chondritic abundances. This element abundance pattern is consistent with nebular condensation, suggesting the IDPs condensed at either a different location or time in the evolving solar nebula than do the meteorites. The enrichments of the major elements C, Na, P, and K exclude the possibility that the volatile enrichment in IDPs results from a minor amount of contamination.
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6

Monk, D. J., M. J. Barlow, and R. E. S. Clegg. "Chemical Abundances in Magellanic Cloud Planetary Nebulae." Symposium - International Astronomical Union 131 (1989): 354. http://dx.doi.org/10.1017/s0074180900138732.

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Optical spectroscopic data for 71 Planetary Nebulae (PN) in the Large and Small Magellanic Clouds have been analysed. The line fluxes have been used to determine nebular temperatures, densities, and the abundances of He, N, O, Ne and Ar, relative to H. In our sample there are 12 nebulae with N/O ≥ 0.5, resembling Peimbert's Type I PN; 6 low excitation (LE) objects (1 ≤ I(5007)/I(Hβ) ≤ 4); and 4 very-low-excitation (VLE) nebulae (I(Hβ) > I(5007), similar to the Galactic VLE class. Mean abundances have been calculated for the nebulae not in these special groups.
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7

Zhang, C. Y., and S. Kwok. "Chemical abundances and metallicity of Planetary Nebulae." Symposium - International Astronomical Union 180 (1997): 291. http://dx.doi.org/10.1017/s0074180900131080.

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Анотація:
Confrontations of the dredge-up theory with observed patterns of chemical abundances of planetary nebulae (PNs) have been carried out by many authors (see, e.g., Kaler & Jacoby 1990, 1991; Stasińska & Tylenda 1990). Although these studies suggest that the observational abundance ratios of PNs can qualitatively be explained by the current dredge-up theory, scatters around the theoretical predictions in their diagrams are always large. This has led Ratag (1991) to conclude that there is no correlation at all between the nebular abundances and the core mass of CSPNs (see also Pottasch 1993).
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8

Conlon, E. S., P. L. Dufton, F. P. Keenan, and R. J. H. McCausland. "LSIV −12° 111 – A Newly Emerging Halo Planetary Nebula." Symposium - International Astronomical Union 155 (1993): 356. http://dx.doi.org/10.1017/s0074180900171451.

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We report on multi-wavelength observations of a young halo planetary nebula, LSIV −12° 111. This object was previously classified as an emission-line young B-type star but a model atmosphere abundance analysis of high resolution optical spectra revealed it to be an evolved object, probably in the post-asymptotic giant branch (post-AGB) evolutionary phase. The presence of an infrared excess and low excitation nebular emission lines implies that the central star may have just started to photoionize the remnant (AGB) circumstellar material. Here we discuss the nebular and dust properties of LSIV −12° 111 and re-determine some metal abundances for the central star. These results are used to constrain the evolutionary status of this unique halo planetary nebula.
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9

Skillman, Evan D. "Uncertainties in nebular helium abundances." Proceedings of the International Astronomical Union 5, S268 (November 2009): 113–18. http://dx.doi.org/10.1017/s1743921310003947.

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AbstractEfforts to determine the primordial helium abundance via observations of metal poor HII regions have been limited by significant uncertainties. Because of a degeneracy between the solutions for density and temperature, the precision of the helium abundance determinations is limited. Spectra from the literature are used to show the effects of new atomic data and to demonstrate the challenges of determining precise He abundances. Several suggestions are made for meeting these challenges.
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10

Stasińska, Grażyna. "Nebular abundances in galaxies: Beware of biases." Proceedings of the International Astronomical Union 5, S262 (August 2009): 93–96. http://dx.doi.org/10.1017/s1743921310002590.

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AbstractThe derivation of nebular abundances in galaxies using strong line methods is simple and quick. Various indices have been designed and calibrated for this purpose, and they are widely used. However, abundances derived with such methods may be significantly biased, if the objects under study have different structural properties (hardness of the ionizing radiation field, morphology of the nebulae) than those used to calibrate the methods. Special caution is required when comparing the metallicities of different samples, like, for example, blue compact galaxies and other emission line dwarf galaxies, or samples at different redshifts.
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Більше джерел

Дисертації з теми "Nebular abundances"

1

Wesson, Roger. "Heavy element abundances in emission line nebulae." Thesis, University College London (University of London), 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.430104.

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2

Tsamis, Ionnis. "Heavy element abundance in ionized nebulae." Thesis, University College London (University of London), 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270150.

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3

Armour, Mary-Helen. "A multicomponent echelle spectral data analysis of four planetary nebulae." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/MQ56161.pdf.

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4

Smith, Christina Louise. "Spectroscopic studies of evolved stars and planetary nebulae." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/spectroscopic-studies-of-evolved-stars-and-planetary-nebulae(c01465c8-a7dd-4471-a37b-cc4ee01a9905).html.

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Evolved stars and planetary nebulae are rich and varied sites of molecule and dust formation. These objects undergo dramatic mass loss which ultimately enriches the interstellar medium. In this thesis, a number of studies, outlined below, have been undertaken to better understand the chemical and physical properties of these diverse objects. A molecular line survey of a sample of evolved stars and planetary nebulae has been carried out using the Mopra radio telescope, Australia. Transitions with hyperfine structure have been fitted to constrain optical depths. The population diagram method was applied to determine the rotation temperatures of molecules which had multiple transitions available. Column densities have been calculated for all detected species and isotopic ratios measured where possible. The results include the corroboration of the classification of II Lup as a J-type star. The 89.087 GHz HCN maser was detected in IRAS 15082-4808 for the first time from the aforementioned survey, bringing the total number of detections of this maser to ten. The velocity shift of this maser has been measured at −2.0+/-0.9 km/s. Drawing on literature data in addition to the survey data, the variation of maser intensity with pulsation phase has been investigated across all sources for the first time. Comparing these masers with model atmospheres constrains the formation region to between 2 and 4 stellar radii. CO in the circumstellar envelope of II Lup has been modelled using the radiative transfer codes GASTRoNOoM, and ComboCode. The models have demonstrated that a ‘standard’ smooth model does not satisfactorily reproduce the combined CO observations of PACS, JCMT, Mopra and APEX. Two potential solutions are proposed: a discontinuous temperature model, requiring the presence of an efficient cooling molecule that is most effective in the region 75-200 R*, or a variable mass loss model that requires a factor of ten increase inmass loss in the same region. Zinc abundances, a proxy for iron abundances, have been determined for a sample of Galactic planetary nebulae using the [Zn IV] 3.625 μm line. O++/O has been shown to be a reliable ionisation correction factor for Zn3+ from Cloudy photoionisation models. The majority of the sample are sub-solar in [Zn/H] and enriched in [O/Zn]. Zinc abundances as functions of Galactocentric distance have also been investigated and no evidence for a trend has been found.
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5

Moraes, Oscar Cavichia de. "Populações e evolução do bojo e região central da Galáxia." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/14/14131/tde-30012013-113804/.

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O presente trabalho propõe uma abordagem abrangente para descrever a evolução da região central da Via Láctea, compreendendo-se aí o bojo, a barra e as interfaces dos mesmos com o limite interno do disco e com a região central do halo. Pretende-se investigar as propriedades químicas e cinemáticas destas estruturas, que são interconectadas, com o objetivo de separá-las e aplicar os resultados daí obtidos a um modelo de formação e evolução do bojo e da região interna do disco que descreva simultaneamente distintos aspectos da evolução da região central da Galáxia. Na primeira parte do trabalho, uma amostra de nebulosas planetárias (NPs) localizadas no disco interno e no bojo da Galáxia é utilizada para encontrar a distância galactocêntrica que melhor separa estas duas populações, do ponto de vista das abundâncias. Foram utilizadas escalas de distâncias estatísticas para o estudo da distribuição das abundâncias na interface bojo-disco. A aplicação do teste Kolmogorov-Smirnov mostrou que, em média, a população interna não segue o gradiente radial de abundâncias do disco na direção do centro galáctico. Baseado neste estudo, propõe-se uma distância galactocêntrica de 1.5 kpc para definir a interface bojo-disco. Na segunda parte do trabalho, foram realizadas observações espectrofotométricas de 21 NPs localizadas na direção do centro da Galáxia com o telescópio SOAR. Estes objetos estão localizados bem próximos ao plano galáctico na direção central da Via Láctea, onde não existem dados de NPs na literatura. Os resultados mostram que as NPs localizadas nesta região apresentam baixas abundâncias de oxigênio comparadas com as NPs do disco interno e de outras regiões do bojo. Os resultados indicam que o bojo apresenta uma complexa composição de populações estelares. Por um lado, a presença de nebulosas com baixas abundâncias mostra que o bojo pode ter se formado a partir de um disco galáctico antigo através de uma evolução secular. Por outro lado, existem alguns objetos do bojo para os quais as abundâncias coincidem com o limite do gradiente radial do disco nesta região. Esta é uma evidência para um bojo composto por duas ou mais populações: uma originada do disco fino, e outra originada do disco espesso. Na última parte do trabalho propõe-se a inclusão de fluxos radiais de gás em um modelo de evolução química para simular os efeitos de uma barra localizada no centro da Galáxia nas distribuições de abundâncias, densidade de gás e taxa de formação estelar (SFR). Os resultados das simulações indicam que os modelos com fluxos de gás apresentam uma SFR mais alta no bojo e que os perfis da SFR e da densidade de gás na região central são melhor reproduzidos após a inclusão dos fluxos radiais no modelo. As simulações indicam ainda que o gradiente de abundâncias do disco é mais plano para o caso da inclusão da barra. Estes resultados indicam que a barra e os fluxos de gás exercem um importante papel na formação de estrelas no centro das galáxias espirais barradas.
This project proposes a comprehensive approach to describe the evolution of the central region of the Galaxy, comprising the bulge, the bar and their interfaces with the inner disk and the central region of the halo. We intend to investigate the chemical and kinematic properties of these structures, which are interconnected, aiming to separate them and apply these results to a model for the formation and evolution of the bulge and inner disk, capable to describe simultaneously distinct aspects of the evolution of the central region of the Galaxy. First, a sample of planetary nebulae (PNe) located in the inner-disk and bulge of the Galaxy is used in order to find the galactocentric distance that better separates these two populations, from the point of view of abundances. Statistical distance scales were used to study the distribution of abundances across the disk-bulge interface. A Kolmogorov-Smirnov test was used to find the distance in which the chemical properties of these regions better separates. The results of the statistical analysis indicate that, on the average, the inner population has lower abundances than the outer. Additionally, for the $\\alpha$-elements abundances, the inner population does not follow the disk radial gradient towards the galactic centre. Based on our results, we suggest a bulge-disk interface at 1.5 kpc, marking the transition between the bulge and inner-disk of the Galaxy, as defined by the intermediate mass population. Second, we present spectrophotometric observations for a sample of 21 PNe located towards the galactic centre of the Galaxy. The abundances are derived based on observations in the optical domain made at the SOAR telescope. Their location is interesting since there are no observations of PNe in this region. The data show lower oxygen abundances compared to those from PNe located in the inner disk and other bulge regions. The results show that the bulge has a complex composition of stellar populations. The presence of PNe with low abundances indicates that the bulge might be formed from an old galactic disk through secular evolution. On the other hand, other objects from our sample have abundances compared to those from inner disk PNe. This is evidence that two or more populations might compose the bulge: one originated from the thin disk, and the other from the thick disk. Last, we propose a chemical evolution model that includes radial gas flows. This is done in order to mimic the effects of the galactic bar on the chemical abundances distributions and the gas density profiles and the star formation rate (SFR). The results of the models with radial flows point to a high SFR in the bulge and, additionally, the SFR and gas density profiles in the inner Galaxy are better reproduced after the inclusion of radial gas flows in the model. After including a specific velocity pattern for the bar, the results show a flattening of the radial abundance gradient. Our results indicate that radial gas flows may play an important role in the star formation near the centre of barred spiral galaxies.
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6

Nicholls, David Conway. "Nebular metallicities in isolated dwarf irregular galaxies." Phd thesis, 2014. http://hdl.handle.net/1885/11923.

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The motive for this work was to investigate whether small, isolated gas-rich galaxies show evidence of chemical evolution, by studying their nebular metallicities. I have identified a sample of 83 objects chosen for low luminosity and mass, the presence of active star formation, and isolation from other galaxies and galaxy clusters that might generate tidal effects or enrich the intergalactic medium. From these I have measured the spectra of 35 objects, using theWiFeS IFU spectrograph on the ANU 2.3m telescope at Siding Spring. In analysing spectra extracted from the WiFeS data cubes, I found that standard ‘strong line’ methods using emission line ratios to measure atomic abundances, gave either erratic or no results. I found that for those galaxies showing the [O iii] 4363Å auroral line, the metallicities determined using the standard ‘electron temperature’ methodwere inconsistent with previous published work. This led me to investigate the conventional assumption that electrons in Hii regions are in thermal equilibrium. I show that the non-equilibrium ‘ ’ electron energy distribution, found almost universally in solar system plasmas, can explain the long recognised ‘abundance discrepancy’ between recombination line and collisional line abundance calculations in nebular metallicity measurements. This has added an important new dimension to the analysis of nebular spectra. Using the extensively revised Mappings photoionisation modelling code and new atomic data to analyse the spectra of two exceptionally isolated dwarf galaxies, I find that they exhibit metallicities similar to galaxies in more crowded environments, and appear to have evolved quite normally, through periodic star formation and subsequent enrichment of their interstellar media. I present a new approach for calculating total oxygen abundance using electron temperatures that appears to give more consistent results than earlier methods. I apply this to my measured spectra, together with the revised Mappings photoionisation modelling code, to explore the physical parameters affecting the measurement of nebular metallicities. In particular, I find strong evidence for several of the observed nebulae being—in part—optically thin. I use the models to show that nebular optical depth affects measured abundances and temperatures, and that electron densities also have an important role. I develop models that give a very good match to the observations. I conclude that the measurement of abundances and temperatures in Hii regions is a more complex question than had generally been assumed, and important physical parameters affecting the measurement processes have in the past not been taken fully into account.
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7

Sterling, Nicholas Craig. "Light neutron-capture element abundances in planetary nebulae." Thesis, 2006. http://hdl.handle.net/2152/3503.

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8

Hwang, Sehyun. "Integral field spectroscopy of optical recombination lines in the planetary nebula NGC 7009: implications for dual-abundance models." Thesis, 2009. http://hdl.handle.net/2152/ETD-UT-2009-08-386.

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9

Άκρας, Σταύρος. "Ανίχνευση και μελέτη φαινομένων μεσοαστρική ύλης". Thesis, 2010. http://nemertes.lis.upatras.gr/jspui/handle/10889/3289.

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Ο σκοπός της παρούσας διδακτορικής διατριβής ήταν η μελέτη δύο σημαντικών φαινομένων μεσοαστρική ύλης όπως είναι τα Πλανητικά Νεφελώμάτα (ΠΝ) και η ράβδος των σπειροειδών γαλαξιών. Πιο συγκεκριμένα, μελετήθηκαν 44 ΠΝ στην περιοχή του Γαλαξιακού σφαιροειδούς (Boumis et al. 2003; 2006) και προσδιορίστηκαν οι φυσικοί παράμετροι τους, όπως είναι η ενεργός θερμοκρασία και η λαμπρότητα του κεντρικού αστεριού, η πυκνότητα και η θερμοκρασία των ηλεκτρονίων, η αφθονία των Ηe, N, O, S κτλ., χρησιμοποιώντας το μοντέλο φωτο-ιονισμού Cloudy (Akras et al. 2010a). Επίσης, μελετήθηκε η ράβδος των γαλαξιών, χρησιμοποιώντας το μοντέλο διάδοσης ακτινοβολίας CRETE, με σκοπό να ερευνηθεί πώς η ύπαρξη της ράβδου επηρεάζει την μορφολογία των γαλαξιών και την σκόνη τους. Ταυτόχρονα, προσδιορίστηκαν οι παράμετροι της ράβδου, όπως το μήκος, το ύψος, η γωνία κλίσης και η γωνία θέσης της για 4 ραβδωτούς σπειροειδείς γαλαξίες (NGC 4013, UGC 2048, IC 2531 και το Γαλαξία μας). Στο πρώτο μέρος της μελέτης, διαχωρίστηκαν τα ΠΝ ανάλογα με την μορφολογία τους σε σφαιρικά, ελλειπτικά και διπολικά και βρέθηκε ότι η αφθονία του Ηe και του Ν είναι μεγαλύτερη στην τελευταία κατηγορία σε σχέση με τις υπόλοιπες. Επιπλέον, η χρήση του στατιστικού εργαλείου PCA, έδειξε ότι τα κυκλικά και τα ελλειπτικά ΠΝ διαχωρίζονται από τα διπολικά, βάσει της τιμής του λόγου log(Ν/Ο), ο οποίος παίρνει αρνητικές και θετικές τιμές για τα διπολικά, ενώ μόνο αρνητικές τιμές στις υπόλοιπες κατηγορίες. Η κρίσιμη τιμή βρέθηκε ίση με -0.18 dex και αντιστοιχεί σε μάζα προγενέστερου αστεριού ίση με 2.6 (Akras & Boumis 2007). Στο δεύτερο μέρος, περιγράφηκε η ράβδος των γαλαξιών χρησιμοποιώντας την συναρτησιακή ελλειψοειδής υπερβολής. Μεταβάλλοντας την γωνία κλίσης του γαλαξία, η δομή σχήματος «Χ», η οποία παρατηρείται στις ράβδους, μπορεί να παρατηρηθεί μόνο για γωνίες μεγαλύτερες από 60ο. Επιπρόσθετα, στην περίπτωση του Γαλαξία μας, βρέθηκε ότι η γωνία θέσης της ράβδου είναι γύρω στις 25ο και το μήκος της 3.75 kpc (Akras et al. 2010b). Λαμβάνοντας υπόψη ότι η μέση τιμή του μήκους της ράβδου στους γαλαξίες είναι μεταξύ 3.0 και 4.0 kpc, προκύπτει ότι για τον NGC 4013 η γωνία θέσης του είναι μεταξύ 5 και 10 μοίρες, για τον UGC 2048 μεταξύ 40 και 50 μοίρες, για τον IC 2531 35 και 45 μοίρες ενώ τέλος για το Γαλαξία μας υπολογίζεται μεταξύ 20 και 30 μοίρες (Akras et al. 2010b).
The aim of this PhD thesis was the study of two very important interstellar medium phenomena like the Planetary Nebulae (PNe) and the stellar bar in spiral galaxies. In particular, we studied 44 PNe in the Galactic bulge region and we determined their physical parameters, like the effective temperature and luminosity of the central star, the electron temperature and density, the abundance of He, N, O, S etc., using the photo-ionization model “Cloudy” (Akras et al. 2010a). It was also pursued to study the stellar bar component using the 3D radiative transfer model CRETE, in order to investigate the effects of a stellar bar component to the morphology of the galaxy and its dust content. In addition, the parameters of the bar component such as the length, the height, the inclination angle and the position angle were determined for four spiral galaxies (NGC 4013, UGC 2048, IC 2531 and our Galaxy). In the first part of the thesis, the PNe were separated according to their morphology (spherical, elliptical and bipolar shape) and we found that the He and N abundances are greater in bipolar PNe. Moreover, by using the statistical tool PCA, it was found that the circular and the elliptical PNe are different from the bipolar, since the log(O/N) takes negative values in the first two and positive or negative values in the bipolar PNe. The critical value was found at -0.18 dex, which corresponds to a stellar mass of 2.6 (Akras & Boumis 2007). In the second part, we managed to accurately describe the morphology of the bar component by using the function of hyperbolic ellipse. For different inclination angles of the observed galaxies, it was found that the “X-shape" feature can be seen only in the case where the inclination angle is greater than 60 degrees. In the case of Milky Way, it was found that the position angle of the bar is approximately 25 degrees and the length equals to 3.75 kpc (Akras et al. 2010b). Considering that the mean length of the bar component is equal to 3.0-4.0 kpc, it was determined that the position angle of a) NGC 4013 takes values between 5 and 10 degrees, b) UGC 2048 takes values between 40 and 50 degrees, c) IC 2531 takes values between 35 and 45 degrees, and our Galaxy takes values between 20 and 30 degrees (Akras et al. 2010b).
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Книги з теми "Nebular abundances"

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Planetary nebular carbon-to-oxygen ratios, morphology and evolution: Final technical report for NASA grant no. NSG 5358 : period covered by report, May 9, 1979 - July 14, 1987. [Washington, DC: National Aeronautics and Space Administration, 1987.

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2

United States. National Aeronautics and Space Administration, ed. Planetary nebular carbon-to-oxygen ratios, morphology and evolution: Final technical report for NASA grant no. NSG 5358 : period covered by report, May 9, 1979 - July 14, 1987. [Washington, DC: National Aeronautics and Space Administration, 1987.

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3

United States. National Aeronautics and Space Administration., ed. Planetary nebular carbon-to-oxygen ratios, morphology and evolution: Final technical report for NASA grant no. NSG 5358 : period covered by report, May 9, 1979 - July 14, 1987. [Washington, DC: National Aeronautics and Space Administration, 1987.

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4

Planetary nebular carbon-to-oxygen ratios, morphology and evolution: Final technical report for NASA grant no. NSG 5358 : period covered by report, May 9, 1979 - July 14, 1987. [Washington, DC: National Aeronautics and Space Administration, 1987.

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5

Trieloff, Mario. Noble Gases. Oxford University Press, 2017. http://dx.doi.org/10.1093/acrefore/9780190647926.013.30.

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This is an advance summary of a forthcoming article in the Oxford Encyclopedia of Planetary Science. Please check back later for the full article.Although the second most abundant element in the cosmos is helium, noble gases are also called rare gases. The reason is that they are not abundant on terrestrial planets like our Earth, which is characterized by orders of magnitude depletion of—particularly light—noble gases when compared to the cosmic element abundance pattern. Indeed, such geochemical depletion and enrichment processes make noble gases so versatile concerning planetary formation and evolution: When our solar system formed, the first small grains started to adsorb small amounts of noble gases from the protosolar nebula, resulting in depletion of light He and Ne when compared to heavy noble gases Ar, Kr, and Xe: the so-called planetary type abundance pattern. Subsequent flash heating of the first small mm to cm-sized objects (chondrules and calcium, aluminum rich inclusions) resulted in further depletion, as well as heating—and occasionally differentiation—on small planetesimals, which were precursors of larger planets and which we still find in the asteroid belt today from where we get rocky fragments in form of meteorites. In most primitive meteorites, we even can find tiny rare grains that are older than our solar system and condensed billions of years ago in circumstellar atmospheres of, for example, red giant stars. These grains are characterized by nucleosynthetic anomalies and particularly identified by noble gases, for example, so-called s-process xenon.While planetesimals acquired a depleted noble gas component strongly fractionated in favor of heavy noble gases, the sun and also gas giants like Jupiter attracted a much larger amount of gas from the protosolar nebula by gravitational capture. This resulted in a cosmic or “solar type” abundance pattern, containing the full complement of light noble gases. Contrary to Jupiter or the sun, terrestrial planets accreted from planetesimals with only minor contributions from the protosolar nebula, which explains their high degree of depletion and basically “planetary” elemental abundance pattern. Indeed this depletion enables another tool to be applied in noble gas geo- and cosmochemistry: ingrowth of radiogenic nuclides. Due to heavy depletion of primordial nuclides like 36Ar and 130Xe, radiogenic ingrowth of 40Ar by 40K decay, 129Xe by 129I decay, or fission Xe from 238U or 244Pu decay are precisely measurable, and allow insight in the chronology of fractionation of lithophile parent nuclides and atmophile noble gas daughters, mainly caused by mantle degassing and formation of the atmosphere.Already the dominance of 40Ar in the terrestrial atmosphere allowed C. F v. Weizsäcker to conclude that most of the terrestrial atmosphere originated by degassing of the solid Earth, which is an ongoing process today at mid ocean ridges, where primordial helium leaves the lithosphere for the first time. Mantle degassing was much more massive in the past; in fact, most of the terrestrial atmosphere formed during the first 100 million years of Earth´s history, and was completed at about the same time when the terrestrial core formed and accretion was terminated by a giant impact that also formed our moon. However, before that time, somehow also tiny amounts of solar noble gases managed to find their way into the mantle, presumably by solar wind irradiation of small planetesimals or dust accreting to Earth. While the moon-forming impact likely dissipated the primordial atmosphere, today´s atmosphere originated by mantle degassing and a late veneer with asteroidal and possibly cometary contributions. As other atmophile elements behave similar to noble gases, they also trace the origin of major volatiles on Earth, for example, water, nitrogen, sulfur, and carbon.
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6

United States. National Aeronautics and Space Administration., ed. Theoretical studies of interstellar processes: Final report, December 1, 1991-February 28, 1995. Lexington, MA: Institute for Scientific Research, 1995.

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Частини книг з теми "Nebular abundances"

1

Liu, X. W., M. J. Barlow, I. J. Danziger, and P. J. Storey. "Nebular Abundances from Recombination Lines." In Chemical Evolution from Zero to High Redshift, 39–43. Berlin, Heidelberg: Springer Berlin Heidelberg, 1999. http://dx.doi.org/10.1007/978-3-540-48360-1_5.

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Díaz, Angeles I., and Enrique Pérez-Montero. "Empirical Calibrations of Nebular Abundances: The Sulphur Abundance Parameter." In Chemical Evolution from Zero to High Redshift, 134–38. Berlin, Heidelberg: Springer Berlin Heidelberg, 1999. http://dx.doi.org/10.1007/978-3-540-48360-1_31.

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Walton, N. A., M. J. Barlow, D. J. Monk, and R. E. S. Clegg. "Abundances and Nebular and Central Star Masses for Magellanic Cloud Planetary Nebulae." In The Magellanic Clouds, 334–36. Dordrecht: Springer Netherlands, 1991. http://dx.doi.org/10.1007/978-94-011-3432-3_79.

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Maciel, W. J. "Planetary Nebulae: Abundances and Abundance Gradients." In The Evolution of The Milky Way, 81–92. Dordrecht: Springer Netherlands, 2000. http://dx.doi.org/10.1007/978-94-010-0938-6_8.

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Clegg, R. E. S. "Abundances in Planetary Nebulae." In Planetary Nebulae, 139–56. Dordrecht: Springer Netherlands, 1989. http://dx.doi.org/10.1007/978-94-009-0865-9_30.

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Schmid, H. M., and H. Nussbaumer. "Elemental Abundances in Symbiotic Stars." In Planetary Nebulae, 402. Dordrecht: Springer Netherlands, 1993. http://dx.doi.org/10.1007/978-94-011-2088-3_201.

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Marigo, Paola. "Theoretical Abundances in Planetary Nebulae." In Planetary Nebulae, 257. Dordrecht: Springer Netherlands, 1997. http://dx.doi.org/10.1007/978-94-011-5244-0_111.

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Clegg, R. E. S., and J. P. Harrington. "Helium Abundances in Gaseous Nebulae." In Planetary Nebulae, 211. Dordrecht: Springer Netherlands, 1989. http://dx.doi.org/10.1007/978-94-009-0865-9_80.

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Vilchez, J. M., and C. Esteban. "Abundances in WR Nebulae." In Wolf-Rayet Stars and Interrelations with other Massive Stars in Galaxies, 379–84. Dordrecht: Springer Netherlands, 1991. http://dx.doi.org/10.1007/978-94-011-3306-7_70.

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Clegg, R. E. S. "PN Abundances in Different Galactic Systems." In Planetary Nebulae, 549–56. Dordrecht: Springer Netherlands, 1993. http://dx.doi.org/10.1007/978-94-011-2088-3_249.

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Тези доповідей конференцій з теми "Nebular abundances"

1

Frankowski, Adam. "Binary CSPN and PN Abundances." In PLANETARY NEBULAE AS ASTRONOMICAL TOOLS: International Conference on Planetary Nebulae as Astronomical Tools. AIP, 2005. http://dx.doi.org/10.1063/1.2146266.

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Leisy, P. "Local Group Galaxies: Abundances in NGC 3109." In PLANETARY NEBULAE AS ASTRONOMICAL TOOLS: International Conference on Planetary Nebulae as Astronomical Tools. AIP, 2005. http://dx.doi.org/10.1063/1.2146291.

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Tsamis, Yiannis. "Elemental Abundances in PNe and H II Regions: Lessons in Parallel." In PLANETARY NEBULAE AS ASTRONOMICAL TOOLS: International Conference on Planetary Nebulae as Astronomical Tools. AIP, 2005. http://dx.doi.org/10.1063/1.2146225.

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Werner, Klaus. "Light and Heavy Metal Abundances in Hot Central Stars of Planetary Nebulae." In PLANETARY NEBULAE AS ASTRONOMICAL TOOLS: International Conference on Planetary Nebulae as Astronomical Tools. AIP, 2005. http://dx.doi.org/10.1063/1.2146248.

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Maciel, W. J. "Planetary Nebulae as a Chemical Evolution Tool: Abundance Gradients." In PLANETARY NEBULAE AS ASTRONOMICAL TOOLS: International Conference on Planetary Nebulae as Astronomical Tools. AIP, 2005. http://dx.doi.org/10.1063/1.2146285.

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Stasińska, G. "Abundance Gradients in M33: the Use of Planetary Nebulae." In PLANETARY NEBULAE AS ASTRONOMICAL TOOLS: International Conference on Planetary Nebulae as Astronomical Tools. AIP, 2005. http://dx.doi.org/10.1063/1.2146290.

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Lorente-Espin, O. "Abundance Analysis of a Sample of Bipolar Type I Planetary Nebulae." In PLANETARY NEBULAE AS ASTRONOMICAL TOOLS: International Conference on Planetary Nebulae as Astronomical Tools. AIP, 2005. http://dx.doi.org/10.1063/1.2146227.

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Walsh, Jeremy R., George H. Jacoby, Reynier F. Petetier, and Nicholas A. Walton. "Using planetary nebulae as abundance probes of galaxies." In Astronomical Telescopes and Instrumentation, edited by Jacqueline Bergeron. SPIE, 2000. http://dx.doi.org/10.1117/12.390136.

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Peña, M. "Using Planetary Nebulae to Analyze the Abundance Gradient in the Milky Way." In PLANETARY NEBULAE AS ASTRONOMICAL TOOLS: International Conference on Planetary Nebulae as Astronomical Tools. AIP, 2005. http://dx.doi.org/10.1063/1.2146284.

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Torres-Peimbert, Silvia. "Chemical composition of planetary nebulae: The abundance discrepancy problem." In INTERNATIONAL CONFERENCE OF COMPUTATIONAL METHODS IN SCIENCES AND ENGINEERING 2015 (ICCMSE 2015). AIP Publishing LLC, 2015. http://dx.doi.org/10.1063/1.4937639.

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