The federally threatened northern spotted owl (Strix occidentalis caurina) is the focus of intensive conservation efforts that have led to much forested land being reserved as habitat for the owl and associated wildlife species throughout the Pacific Northwest of the United States. Recently, however, a relatively new threat to spotted owls has emerged in the form of an invasive competitor: the congeneric barred owl (Strix varia). As barred owls have rapidly expanded their populations into the entire range of the northern spotted owl, mounting evidence indicates that they are displacing, hybridizing with, and even killing spotted owls. The barred owl invasion into western North America has made an already complex conservation issue even more contentious, and a lack of information on the ecological relationships between the 2 species has hampered conservation efforts. During 2007–2009 I investigated spatial relationships, habitat selection, diets, survival, and reproduction of sympatric spotted owls and barred owls in western Oregon, USA. My overall objective was to determine the potential for and possible consequences of competition for space, habitat, and food between the 2 species. My study included 29 spotted owls and 28 barred owls that were radio-marked in 36 neighboring territories and monitored over a 24-month tracking period. Based on repeated surveys of both species, the number of territories occupied by pairs of barred owls in the 745 km² study area (82) greatly outnumbered those occupied by pairs of spotted owls (15). Estimates of mean size of home-ranges and core-use areas of spotted owls (1,843 ha and 305 ha, respectively) were 2–4 times larger than those of barred owls (581 ha and 188 ha, respectively). Individual spotted and barred owls in adjacent territories often had overlapping home ranges, but inter-specific space sharing was largely restricted to broader foraging areas in the home range with minimal spatial overlap among core-use areas. I used an information-theoretic approach to rank discrete choice models representing alternative hypotheses about the influence of forest conditions and interspecific interactions on species-specific patterns of nighttime habitat selection. Spotted owls spent a disproportionate amount of time foraging on steep slopes in ravines dominated by old (>120 yrs old) conifer trees. Barred owls used available forest types more evenly than spotted owls, and were most strongly associated with patches of large hardwood and conifer trees that occupied relatively flat areas along streams. Spotted and barred owls differed in the relative use of old conifer forest (higher for spotted owls) and slope conditions (steeper slopes for spotted owls). I found no evidence that the 2 species differed in their use of young, mature, and riparian-hardwood forest types, and both species avoided forest-nonforest edges. The best resource selection function for spotted owls indicated that the relative probability of a location being selected was reduced if the location was within or in close proximity to a core-use area of a barred owl. I used pellet analysis and measures of food niche overlap to examine the potential for dietary competition between spatially associated pairs of spotted owls and barred owls. I identified 1,223 prey items from 15 territories occupied by pairs of spotted owls and 4,299 prey items from 24 territories occupied by pairs of barred owls. Diets of both species were dominated by nocturnal mammals, but diets of barred owls included many terrestrial, aquatic, and diurnal prey species that were rare or absent in diets of spotted owls. Northern flying squirrels (Glaucomys sabrinus), woodrats (Neotoma fuscipes, N. cinerea), and lagomorphs (Lepus americanus, Sylvilagus bachmani) were particularly important prey for both owl species, accounting for 81% and 49% of total dietary biomass for spotted owls and barred owls, respectively. Dietary overlap between pairs of spotted and barred owls in adjacent territories ranged from 28–70% (mean = 42%) In addition to overlap in resource use, I also identified strong associations between the presence of barred owls and the behavior of spotted owls, as shown by changes in space-use, habitat selection, and reproductive output of spotted owls exposed to different levels of spatial overlap with barred owls in adjacent territories. Barred owls in my study area displayed both numeric and demographic superiority over spotted owls; the annual survival probability of radio-marked spotted owls from known-fate analyses (0.81, SE = 0.05) was lower than that of barred owls (0.92, SE = 0.04), and barred owls produced over 6 times as many young over a 3-year period as spotted owls. Survival of both species was positively associated with an increasing proportion of old (>120 yrs old) conifer forest within the home range, which suggested that availability of old forest was a potential limiting factor in the competitive relationship between the 2 species. When viewed collectively, my results support the hypothesis that interference competition with a high density of barred owls for territorial space can act to constrain the availability of critical resources required for successful recruitment and reproduction of spotted owls. My findings have broad implications for the conservation of spotted owls, as they suggest that spatial heterogeneity in survival and reproduction may arise not only because of differences among territories in the quality of forest habitat, but also because of the spatial distribution of an invasive competitor. / Graduation date: 2012 / This pdf will not be made available until April 12th, 2012.

Nós realizamos um estudo estatístico do comportamento de perfis de cor em bandas largas (UBV) para 257 galáxias espirais do tipo Sbc, ordinárias e barradas, utilizando dados obtidos através de fotometria fotoelétrica de abertura, disponíveis na literatura (Longo & de Vaucouleurs 1983,1985). Nós determinamos os gradientes de cor (B-V) e (U-B) para as galáxias da amostra total, bem como os índices de cor (B-V) e (U-B) de bojos e discos separadamente, utilizando métodos estatísticos robustos. Utilizamos uma técnica de decomposição bi-dimensional para modelar os perfis de brilho de bojos e discos em imagens dos arquivos do ``Digitised Sky Survey' (DSS), obtendo parâmetros estruturais característicos para 39 galáxias. A aquisição de imagens de 14 galáxias no Laboratório Nacional de Astrofísica permitiu-nos realizar um estudo fotométrico comparativo, e atestar a validade dos resultados obtidos neste estudo. Entre os principais resultados obtidos, destacam-se: (i) - 65% das galáxias possuem gradientes de cor negativos (mais vermelhos no centro), 25% possuem gradientes nulos, e 10% apresentam gradientes positivos; (ii) - galáxias que apresentam gradientes de cor nulos tendem a ser barradas; (iii) - os índices de cor ao longo das galáxias com gradientes nulos são similares aos índices de cor dos discos das galáxias com gradientes negativos; (iv) - confirmamos a correlação entre os índices de cor de bojos e discos, já obtida por outros autores; (v) - a ausência de correlação entre os gradientes de cor e de metalicidade sugere que o excesso de galáxias barradas com gradientes de cor nulos ou positivos reflete uma diferença no comportamento da idade média da população estelar ao longo de galáxias barradas e ordinárias; (vi) - galáxias com gradientes de cor nulos ou positivos têm uma leve tendência a apresentar bojos maiores e com maior concentração central de luz; e (vii) - confirmamos a correlação entre as escalas de comprimento de bojos e discos, já obtida por outros autores. Estes resultados são compatíveis e favoráveis ao cenário de evolução secular, no qual barras produzem fluxos radiais de massa para as regiões centrais de galáxias, não somente homogeneizando as populações estelares ao longo de galáxias, produzindo discos e bojos com índices de cor semelhantes, mas também contribuindo para a formação e/ou construção de bojos. / We have done a statistical study of the behaviour of the broadband color profiles (UBV) for 257 Sbc galaxies, barred and unbarred, collecting data obtained through photoeletric aperture photometry, available in the literature (Longo & de Vaucouleurs 1983,1985). We have determined (B-V) and (U-B) color gradients for the total sample of galaxies, as well as (B-V) and (U-B) color indices of bulges and disks separately, using robust statistical methods. Applying a bi-dimensional decomposition technique to model the brightness profiles of bulges and disks in images from the Digitised Sky Survey (DSS), we obtained characteristic structural parameters for 39 galaxies. The acquisition of images for 14 galaxies in the Laboratório Nacional de Astrofísica (Astrophysics National Laboratory) allowed us to do a comparative photometric study, and verify the validity of the results obtained in this work. Among the main results obtained, we point out: (i) - 65% of the galaxies have negative color gradients (reddish inward), 25% have zero gradients, and 10% show positive gradients; (ii) - galaxies that show zero color gradients tend to be barred; (iii) - the color indices along the galaxies with zero color gradients are similar to the color indices of the disks of the galaxies with negative color gradients; (iv) - we confirm the correlation between the color indices of bulges and disks, already found by other authors; (v) - the absence of correlation between color and metallicity gradients suggests that the excess of barred galaxies with zero or positive color gradients reflects a difference in the behaviour of the mean age of the stellar population along barred and unbarred galaxies; (vi) - galaxies with zero or positive color gradients show a slight tendency of having larger bulges, with a greater central concentration of light; and (vii) - we confirm the correlation between the scale lenghts of bulges and disks, already found by other authors. These results are compatible and favourable to the secular evolutionary scenario, in which stellar bars induce radial mass fluxes to the central regions of galaxies, not only turning homogeneous the stellar populations along the galaxies, producing disks and bulges with similar color indices, but also contributing to the formation and/or building of galactic bulges.

Bars are common in disc galaxies along with many associated structures such as disc-like bulges, boxy/peanut bulges, rings, etc. They are a sign of maturity of disc galaxies and can play an important role in their evolution. In this thesis, I investigate the specific role bars play in quenching the star formation in, and shaping of their host galaxies. In order to test how bars affect their host galaxies, I study the discs, bars and bulges of what is currently the largest sample of barred galaxies (~3,500), selected with visual morphologies from the Galaxy Zoo project. I perform multi-wavelength and multi-component photometric decomposition, with the novel GALFITM software. With the detailed structural analysis I obtain physical quantities such as the bar- and bulge-to-total luminosity ratios, effective radii, Sérsic indices and colours of the individual components. I find a clear difference in the colours of the components, the discs being bluer than the bars and bulges. An overwhelming fraction of bulge components have Sérsic indices consistent with being disc-like bulges. I compare the barred galaxies with a mass- and environment-matched volume-limited sample of unbarred galaxies, finding that the discs of unbarred galaxies are bluer compared to the discs of barred galaxies, while there is only a small difference in the colours of the bulges. I suggest that this is evidence for secular evolution via bars that leads to the build-up of disc-like bulges and to the quenching of star formation in the galaxy discs. I identify a subsample of unbarred galaxies that are better fitted with an additional component, identified as an inner lens/oval. I find that their structural properties are similar to barred galaxies, and speculate that lenses might be former bars. Using the decompositions, I identify a sample of 271 late-type galaxies with curious bars that are off-centre from the disc. I measure offsets up to 2.5 kpc between the photometric centres of the stellar disc and stellar bar, which are in good agreement with predictions from simulations of dwarf-dwarf tidal interactions. The median mass of these galaxies is 10^9.6 M_⊙, and they are similar to the Large Magellanic Cloud, which also has an offset bar. Very few high mass galaxies with significant bulges show offsets, thus I suggest that the self-gravity of a significant bulge prevents the disc and bar from getting displaced with respect to each other. I conduct a search for companions to test the hypothesis of tidal interactions, but find that a similar fraction of galaxies with offset bars have companions within 100 kpc as galaxies with centred bars. Since many of these galaxies appear isolated, interactions might not be the only way to produce an offset bar. One suggested alternative is that the dark matter haloes surrounding the galaxies are lopsided, which distorts the potential, and imprints the lopsidedness and offsets onto the galaxy discs. I investigate the asymmetries in the kinematics of a subsample of such galaxies using data from the MaNGA survey, and find that the perturbations in the haloes are ~ 6% for both galaxies with off-centre and centred bars. I also measure the amplitude of non-circular motions in the outer discs due to an oval potential and find only minor departures from circularity, suggesting that the dark matter haloes are consistent with being spherical (axis ratio q ≳ 0.96). Therefore, the lopsidedness of the dark matter haloes cannot be the origin of the offsets. Either small companions are missed due to the incompleteness of the Sloan Digital Sky Survey spectroscopic survey, or interactions with dark matter satellites might explain the offsets. Modeling the kinematics of these galaxies, I find that the Hα gas rotation is centred closer to the centre of the bar than the centre of stellar rotation, suggesting that, in general, the bars are located closer to the dynamical centres of these galaxies than the discs. This implies that the discs are offset in these galaxies, not the bars. If offsets are characteristic of low mass galaxies only, high mass galaxies show vertically extended bars, known as boxy/peanut bulges. I investigate, for the first time, the formation and evolution of these structures associated to bars, from z≈0 to z=1. I compare two samples of moderately inclined galaxies with masses M_* > 10¹⁰ M_⊙, imaged by the Sloan Digital Sky Survey and the Hubble Space Telescope. Using a novel technique to classify bar isophotes, and based on the visual inspection of three expert astronomers, I find an evolving fraction of galaxies having boxy/peanut bulges from 30% at z≈0 to ~ 0% at z=1, and a strong correlation with stellar mass. I find 26 galaxies (15 at higher redshifts) in the phase of bar buckling, the mechanism proposed to form boxy/peanut bulges. The peak redshift of buckling is z≈0.75, where the bar buckling fraction is 4 times higher than in the local Universe. My observations suggest that many, if not all, of the boxy/peanut bulges are formed via buckling, ~ 2 Gyr after bar formation, with the buckling phase lasting for approximately 0.8 Gyr. I discuss my findings in the context of the evolution of barred galaxies and propose ideas for future work - applying similar decomposition techniques to higher redshift, and better resolution datasets, using integral field spectroscopic data to study the stellar populations of barred galaxies in greater detail, as well as a novel project to identify large nuclear discs in galaxies.

The present study investigates longshore sediment transport for a variety of bathymetric and wave conditions using the National Oceanic Partnership Program (NOPP) NearCoM Model. The model is used to determine the effects of wave shape and bathymetry changes on the resulting longshore sediment transport. The wave drivers, REF/DIF 1 and REF/DIF S, are used to assess the effects of monochromatic and spectral waves on longshore sediment transport, respectively. SHORECIRC is used as the circulation module and four different sediment transport models are used. Longshore transport comparisons are made with and without skewed orbital velocities in the shear stress and current velocities. It is found that the addition of skewed orbital velocities in shear stress and transport formulations increases longshore sediment transport by increasing time-varying effective shear stress. The addition of skewed orbital velocities greatly increases the transport due to advection by waves. The localized longshore sediment transport is calculated using a generic physics based method and formulas by Bagnold, Bailard, and Bowen, Watanabe, and Ribberink. The transport results for each scenario are compared to the total transport CERC, Kamphuis, and GENESIS formulas. The bathymetries tested include an equilibrium beach profile, cusped beach profiles, and barred beach profiles with different bar locations. The longshore transport on an equilibrium beach profile is modeled for a 0.2 mm and 0.4 mm grain size and transport is compared to the CERC formula. The longshore sediment transport for d=0.2 mm is larger than d=0.4 mm when wave power is small, but as wave power increases the transport for the larger grain size dominates. The transport is also affected by the addition of cusps and bars on an equilibrium beach profile. The barred beach is modified to compare transport between waves breaking at the bar, before the bar, and after the bar. The features affect the transport when the wave powers are small, but as wave heights increase the cusp and bar features induce little change on the longshore sediment transport.

My study was aimed to describe the antipredator behaviour of Barred Warbler against five avian mounted dummies differing in the level of threat they represent for the Barred Warbler: Eurasian Sparrowhawk (Accipiter nisus), Eurasian Jay (Garrulus glandarius), Black-billed Magpie (Pica pica), Red-backed Shrike (Lanius collurio), and Domastic Pigeon (Columba livia f. domestica) using the experiments carried in the vicinity of the nests with fledglings of Barred Warbler. The next goal of my study was to discover the relationship between the Barred Warbler and the Red-backed Shrike nesting together.

Abstract In this thesis we shed light on the formation and evolution of disk galaxies, which often host a stellar bar (about 2/3 of cases). In particular, we address the bar-driven secular evolution, that is, the steady redistribution of stellar and gaseous material through the disk induced by the bar torques and resonances. We characterize the mass distribution of the disks in the Spitzer Survey of Stellar Structure in Galaxies (S4G, Sheth et al. 2010) and study the properties of the different stellar structure components and the interplay between them. We use 3.6µm photometry for ~ 1300 face-on and moderately inclined disk galaxies to analyze the frequency, dimensions, orientations and shapes of stellar bars, spiral arms, rings, (ring)lenses, and barlenses (i.e. lens-like structures embedded in the bars). We calculate the strength of the bars in the S4G via ellipse fitting, Fourier decomposition of the galaxy images, and from the gravitational tangential-to-radial forces. We also estimate the stellar contribution to the circular velocity, allowing us to analyze the coupling between non-baryonic and stellar matter within the optical disk. We average stellar density profiles (1D), the disk(+bulge) component of the rotation curve, and stellar bars (2D) as a function of fundamental galaxy parameters. We complement the study with integral-field unit kinematic data from Seidel et al. (2015b) for a subsample of 16 S4G barred galaxies. We quantify the bar-induced perturbation strengths in the stellar and gaseous disk from the kinematics, and show that they agree with the estimates obtained from the images. We also use Hα Fabry-Perot observations from Erroz-Ferrer et al. (2015) for 29 S4G disk galaxies to study the inner slope of the rotation curves. We provide possible observational evidence for the growth of bars in a Hubble time. We demonstrate the role of bars causing the spreading of the disk and the enhancement of the central stellar concentration. Our observations support the idea that Boxy/Peanut bulges in face-on perspective manifest as barlenses, that are often identfied in early-type galaxies hosting strong bars, and some of them also as inner lenses. We find that the amount of dark matter within the optical disk scales with the total stellar mass, as expected in the ΛCDM models. We also confirm that the observed inner velocity gradient is correlated with the central surface brightness, showing a strong connection between the inner shape of the potential well and the central stellar density. We show that disks and bars in early-type (T < 5 ≡ Sc) and late-type (T ≥ 5) disk galaxies, or alternatively in galaxies having total stellar masses greater or smaller than 1010M☉, are characterized by very distinct properties. Late-type disks are less centrally concentrated (many galaxies are bulge-less) and present a larger halo-to-stellar mass ratio, what probably affects the disk stability properties. The detection of bars in late-type galaxies is strongly dependent on the identification criteria. On average, bars in early-type spirals (T = 0 − 2) are longer (both in physical units and relative to the disk) and have larger density amplitudes than the intermediate-type spirals (T ≈ 5), and the bar lengths among the latest-types in the S4G are also larger. In comparison to earlier types, the bars in late-type systems show larger tangential-to-radial force ratios. This result holds even when the estimated dark halo effect is included.

Nós realizamos um estudo estatístico do comportamento de perfis de cor em bandas largas (UBV) para 257 galáxias espirais do tipo Sbc, ordinárias e barradas, utilizando dados obtidos através de fotometria fotoelétrica de abertura, disponíveis na literatura (Longo & de Vaucouleurs 1983,1985). Nós determinamos os gradientes de cor (B-V) e (U-B) para as galáxias da amostra total, bem como os índices de cor (B-V) e (U-B) de bojos e discos separadamente, utilizando métodos estatísticos robustos. Utilizamos uma técnica de decomposição bi-dimensional para modelar os perfis de brilho de bojos e discos em imagens dos arquivos do ``Digitised Sky Survey' (DSS), obtendo parâmetros estruturais característicos para 39 galáxias. A aquisição de imagens de 14 galáxias no Laboratório Nacional de Astrofísica permitiu-nos realizar um estudo fotométrico comparativo, e atestar a validade dos resultados obtidos neste estudo. Entre os principais resultados obtidos, destacam-se: (i) - 65% das galáxias possuem gradientes de cor negativos (mais vermelhos no centro), 25% possuem gradientes nulos, e 10% apresentam gradientes positivos; (ii) - galáxias que apresentam gradientes de cor nulos tendem a ser barradas; (iii) - os índices de cor ao longo das galáxias com gradientes nulos são similares aos índices de cor dos discos das galáxias com gradientes negativos; (iv) - confirmamos a correlação entre os índices de cor de bojos e discos, já obtida por outros autores; (v) - a ausência de correlação entre os gradientes de cor e de metalicidade sugere que o excesso de galáxias barradas com gradientes de cor nulos ou positivos reflete uma diferença no comportamento da idade média da população estelar ao longo de galáxias barradas e ordinárias; (vi) - galáxias com gradientes de cor nulos ou positivos têm uma leve tendência a apresentar bojos maiores e com maior concentração central de luz; e (vii) - confirmamos a correlação entre as escalas de comprimento de bojos e discos, já obtida por outros autores. Estes resultados são compatíveis e favoráveis ao cenário de evolução secular, no qual barras produzem fluxos radiais de massa para as regiões centrais de galáxias, não somente homogeneizando as populações estelares ao longo de galáxias, produzindo discos e bojos com índices de cor semelhantes, mas também contribuindo para a formação e/ou construção de bojos. / We have done a statistical study of the behaviour of the broadband color profiles (UBV) for 257 Sbc galaxies, barred and unbarred, collecting data obtained through photoeletric aperture photometry, available in the literature (Longo & de Vaucouleurs 1983,1985). We have determined (B-V) and (U-B) color gradients for the total sample of galaxies, as well as (B-V) and (U-B) color indices of bulges and disks separately, using robust statistical methods. Applying a bi-dimensional decomposition technique to model the brightness profiles of bulges and disks in images from the Digitised Sky Survey (DSS), we obtained characteristic structural parameters for 39 galaxies. The acquisition of images for 14 galaxies in the Laboratório Nacional de Astrofísica (Astrophysics National Laboratory) allowed us to do a comparative photometric study, and verify the validity of the results obtained in this work. Among the main results obtained, we point out: (i) - 65% of the galaxies have negative color gradients (reddish inward), 25% have zero gradients, and 10% show positive gradients; (ii) - galaxies that show zero color gradients tend to be barred; (iii) - the color indices along the galaxies with zero color gradients are similar to the color indices of the disks of the galaxies with negative color gradients; (iv) - we confirm the correlation between the color indices of bulges and disks, already found by other authors; (v) - the absence of correlation between color and metallicity gradients suggests that the excess of barred galaxies with zero or positive color gradients reflects a difference in the behaviour of the mean age of the stellar population along barred and unbarred galaxies; (vi) - galaxies with zero or positive color gradients show a slight tendency of having larger bulges, with a greater central concentration of light; and (vii) - we confirm the correlation between the scale lenghts of bulges and disks, already found by other authors. These results are compatible and favourable to the secular evolutionary scenario, in which stellar bars induce radial mass fluxes to the central regions of galaxies, not only turning homogeneous the stellar populations along the galaxies, producing disks and bulges with similar color indices, but also contributing to the formation and/or building of galactic bulges.

A collection of eight nonfiction stories by Missy Bowen about the Minnesota State Fair, owls, winter, summer, stairs, lumber, and the rock and roll life.

Alarm calls are one of the essential components of antipredator behaviour in birds. In this study I recorded and analysed alarm responses of the barred warbler (Sylvia nisoria) to different mounts of avian predators and nonpredators. The information about danger is encoded through graded structure in its unspecific alarm call type.

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).