We present spectra of five ultra-diffuse galaxies (UDGs) in the vicinity of the Coma cluster obtained with the Multi-object Double Spectrograph on the Large Binocular Telescope. We confirm four of these as members of the cluster, quintupling the number of spectroscopically confirmed systems. Like the previously confirmed large (projected half-light radius > 4.6 kpc) UDG, DF44, the systems we targeted all have projected half-light radii > 2.9 kpc. As such, we spectroscopically confirm a population of physically large UDGs in the Coma cluster. The remaining UDG is located in the field, about 45 Mpc behind the cluster. We observe Balmer and Ca II H and K absorption lines in all of our UDG spectra. By comparing the stacked UDG spectrum against stellar population synthesis models, we conclude that, on average, these UDGs are composed of metal-poor stars ([Fe/H] less than or similar to -1.5). We also discover the first UDG with [O II] and [O III] emission lines within a clustered environment, demonstrating that not all cluster UDGs are devoid of gas and sources of ionizing radiation.

Although there has been much progress in understanding how galaxies evolve, we still do not understand how and when they stop forming stars and become quiescent. We address this by applying our galaxy spectral energy distribution models, which incorporate physically motivated star formation histories (SFHs) from cosmological simulations, to a sample of quiescent galaxies at 0.2 < z < 2.1. A total of 845 quiescent galaxies with multi-band photometry spanning rest-frame ultraviolet through near-infrared wavelengths are selected from the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS) data set. We compute median SFHs of these galaxies in bins of stellar mass and redshift. At all redshifts and stellar masses, the median SFHs rise, reach a peak, and then decline to reach quiescence. At high redshift, we find that the rise and decline are fast, as expected, because the universe is young. At low redshift, the duration of these phases depends strongly on stellar mass. Low-mass galaxies (log(M*/M-circle dot) similar to 9.5) grow on average slowly, take a long time to reach their peak of star formation (greater than or similar to 4 Gyr), and then the declining phase is fast (less than or similar to 2 Gyr). Conversely, high-mass galaxies (log(M*/M-circle dot) similar to 11) grow on average fast (less than or similar to 2 Gyr), and, after reaching their peak, decrease the star formation slowly (greater than or similar to 3). These findings are consistent with galaxy stellar mass being a driving factor in determining how evolved galaxies are, with high-mass galaxies being the most evolved at any time (i.e., downsizing). The different durations we observe in the declining phases also suggest that low- and high-mass galaxies experience different quenching mechanisms, which operate on different timescales.

Há uma concentração de aglomerados globulares moderadamente pobres em metais no bojo galáctico, e muitos deles mostram um Ramo Horizontal Azul (BHB). Essas características juntas apontam para uma idade antiga. Para entender melhor a origem desses aglomerados, o estudo de seu padrão de abundâncias pode ajudar a identificar o tipo das primeiras supernovas nas partes centrais da Galáxia. O NGC 6522 na janela do Baade é um representante desta classe de aglomerados. Análises de abundância de estrelas individuais nesses aglomerados confirmaram sua metalicidade de [Fe/H] -1.0, enriquecimento em elementos-$\\alpha$ e detectaram uma variação nas abundâncias dos elementos pesados de processo-s. Entre os maiores enriquecimentos em Y e Ba, a explicação usual da transferência de massa de uma companheira do ramo assintótico das gigantes pode não se aplicar, e um enriquecimento por estrelas massivas de alta rotação foi sugerido. A fim de estudar melhor as abundâncias em NGC 6522, obtivemos um programa com o FLAMES em 2012, a partir da qual, com os dados de UVES, mostramos que o enriquecimento em elementos-s ainda poderia ser acomodado com o modelo de transferência de massa de uma estrela companheira. Além disso, obtivemos novos dados com o FLAMES em 2016. No presente trabalho analisamos outras 6 estrelas observadas em alta resolução com UVES, e 32 estrelas em resolução média-alta observadas com GIRAFFE, onde foram selecionadas por suas velocidades radiais em torno de -14,3 km/s com uma abrangência de ±15 km/s. Os parâmetros atmosféricos e as abundâncias dos elementos leves C, N, O, elementos de Z ímpar Na e Al, elementos-$alpha$ Mg, Si, Ca, Ti, elementos de pico de ferro Mn, Cu, Zn, elementos de processo-s Y, Zr, Ba, La, Ce, Nd e o elemento de processo-r Eu são derivados para a amostra UVES e preliminarmente para a amostra GIRAFFE. Entre as estrelas UVES, duas delas mostram um enriquecimento significativo nos elementos do processo-s e uma com alto valor nas razões [Y/Ba] e [Zr/Ba], sugerindo um enriquecimento por estrelas massivas de alta rotação. / There is a concentration of moderately metal-poor globular clusters in the Galactic bulge, and many of them show a Blue Horizontal Branch (BHB). These characteristics together point to an old age. In order to better understand the origin of these clusters, the study of their abundance pattern can help identifying the kind of the earliest supernovae in the central parts of the Galaxy. NGC 6522 in Baades Window is a representative of this class of clusters. Abundance analyses of individual stars in this clusters have confirmed its metallicity of [Fe/H]-1.0, enhanced -elements, and detected a variation in the abundances of the s-process heavy elements. Among the highest enhancements of Y and Ba, the usual explanation of mass transfer from a companion in the Asymptotic Giant Branch might not apply, and an enrichment by early fast-rotating massive stars was suggested. In order to further study the abundances in NGC 6522 we obtained a run with FLAMES- UVES in 2012, from which with the UVES data we have shown that the enhancement in s-elements could still be accommodated with the companion transfer model. We further obtained new data with FLAMES-UVES in 2016. In the present work we analyze another 6 stars observed at high resolution with UVES, and 32 stars at medium-high resolution observed with GIRAFFE. The latter were selected from their radial velocities of -14.3±15 km/s. The abundances of the light elements C, N, O, odd-Z elements Na, Al, -elements Mg, Si, Ca, Ti, iron-peak elements Mn, Cu, Zn, s-process elements Y, Zr, Ba, La, Ce, Nd and r-process element Eu are derived. Among the UVES stars, two of them show a significant enrichment in s-process elements and one of them show high [Y/Ba] and [Zr/Ba] ratios, suggesting that an early enrichment by fast rotating massive stars is a probable scenario.

Há uma concentração de aglomerados globulares moderadamente pobres em metais no bojo galáctico, e muitos deles mostram um Ramo Horizontal Azul (BHB). Essas características juntas apontam para uma idade antiga. Para entender melhor a origem desses aglomerados, o estudo de seu padrão de abundâncias pode ajudar a identificar o tipo das primeiras supernovas nas partes centrais da Galáxia. O NGC 6522 na janela do Baade é um representante desta classe de aglomerados. Análises de abundância de estrelas individuais nesses aglomerados confirmaram sua metalicidade de [Fe/H] -1.0, enriquecimento em elementos-$\\alpha$ e detectaram uma variação nas abundâncias dos elementos pesados de processo-s. Entre os maiores enriquecimentos em Y e Ba, a explicação usual da transferência de massa de uma companheira do ramo assintótico das gigantes pode não se aplicar, e um enriquecimento por estrelas massivas de alta rotação foi sugerido. A fim de estudar melhor as abundâncias em NGC 6522, obtivemos um programa com o FLAMES em 2012, a partir da qual, com os dados de UVES, mostramos que o enriquecimento em elementos-s ainda poderia ser acomodado com o modelo de transferência de massa de uma estrela companheira. Além disso, obtivemos novos dados com o FLAMES em 2016. No presente trabalho analisamos outras 6 estrelas observadas em alta resolução com UVES, e 32 estrelas em resolução média-alta observadas com GIRAFFE, onde foram selecionadas por suas velocidades radiais em torno de -14,3 km/s com uma abrangência de ±15 km/s. Os parâmetros atmosféricos e as abundâncias dos elementos leves C, N, O, elementos de Z ímpar Na e Al, elementos-$alpha$ Mg, Si, Ca, Ti, elementos de pico de ferro Mn, Cu, Zn, elementos de processo-s Y, Zr, Ba, La, Ce, Nd e o elemento de processo-r Eu são derivados para a amostra UVES e preliminarmente para a amostra GIRAFFE. Entre as estrelas UVES, duas delas mostram um enriquecimento significativo nos elementos do processo-s e uma com alto valor nas razões [Y/Ba] e [Zr/Ba], sugerindo um enriquecimento por estrelas massivas de alta rotação. / There is a concentration of moderately metal-poor globular clusters in the Galactic bulge, and many of them show a Blue Horizontal Branch (BHB). These characteristics together point to an old age. In order to better understand the origin of these clusters, the study of their abundance pattern can help identifying the kind of the earliest supernovae in the central parts of the Galaxy. NGC 6522 in Baades Window is a representative of this class of clusters. Abundance analyses of individual stars in this clusters have confirmed its metallicity of [Fe/H]-1.0, enhanced -elements, and detected a variation in the abundances of the s-process heavy elements. Among the highest enhancements of Y and Ba, the usual explanation of mass transfer from a companion in the Asymptotic Giant Branch might not apply, and an enrichment by early fast-rotating massive stars was suggested. In order to further study the abundances in NGC 6522 we obtained a run with FLAMES- UVES in 2012, from which with the UVES data we have shown that the enhancement in s-elements could still be accommodated with the companion transfer model. We further obtained new data with FLAMES-UVES in 2016. In the present work we analyze another 6 stars observed at high resolution with UVES, and 32 stars at medium-high resolution observed with GIRAFFE. The latter were selected from their radial velocities of -14.3±15 km/s. The abundances of the light elements C, N, O, odd-Z elements Na, Al, -elements Mg, Si, Ca, Ti, iron-peak elements Mn, Cu, Zn, s-process elements Y, Zr, Ba, La, Ce, Nd and r-process element Eu are derived. Among the UVES stars, two of them show a significant enrichment in s-process elements and one of them show high [Y/Ba] and [Zr/Ba] ratios, suggesting that an early enrichment by fast rotating massive stars is a probable scenario.

Zhang, Yaojun = / "November 2009." / Thesis (M.Phil.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (p. 109-111). / Abstracts in English and Chinese. / Zhang, Yaojun = / Abstract --- p.i / Acknowledgement --- p.iv / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Quasi-Normal Modes of Neutron Stars --- p.6 / Chapter 2.1 --- Equilibrium State of a Neutron Star --- p.6 / Chapter 2.2 --- Fluid Displacement and Metric Perturbation --- p.8 / Chapter 2.3 --- Axial Oscillations of Neutron Stars --- p.9 / Chapter 2.3.1 --- Wave Equation inside the Star --- p.9 / Chapter 2.3.2 --- Wave Equation outside the Star --- p.10 / Chapter 2.3.3 --- Location of Quasi-normal Modes --- p.10 / Chapter 2.4 --- Polar Oscillations of Neutron Stars - LD Formalism --- p.12 / Chapter 2.4.1 --- Equations inside the Star --- p.12 / Chapter 2.4.2 --- Equations outside the Star --- p.14 / Chapter 2.4.3 --- Location of Quasi-normal Modes --- p.16 / Chapter 2.5 --- Polar Oscillations of Neutron Stars - AAKS Formalism --- p.16 / Chapter 2.5.1 --- Equations inside the Star --- p.16 / Chapter 2.5.2 --- Equations outside the Star --- p.19 / Chapter 2.5.3 --- Location of Quasi-normal Modes --- p.19 / Chapter 3 --- Decoupling of Spacetime Oscillations and Fluid Motion --- p.21 / Chapter 3.1 --- Motivation of Decoupling --- p.21 / Chapter 3.2 --- Expressing F in terms of S and H --- p.21 / Chapter 3.2.1 --- Inside the Star --- p.22 / Chapter 3.2.2 --- Outside the Star --- p.25 / Chapter 3.3 --- Constraint-free AAKS Formalism --- p.25 / Chapter 3.3.1 --- Equations inside the Star --- p.25 / Chapter 3.3.2 --- Equations outside the Star --- p.27 / Chapter 3.4 --- Cowling Approximation for Polar p-Mode --- p.29 / Chapter 3.4.1 --- Independent Fluid Motion --- p.29 / Chapter 3.4.2 --- Location of Polar p-Modes --- p.30 / Chapter 3.4.3 --- Numerical Results and Discussion --- p.31 / Chapter 3.5 --- Inverse-Cowling approximation for ω-Mode --- p.33 / Chapter 3.5.1 --- Independent Spacetime Oscillations --- p.33 / Chapter 3.5.2 --- Location of ω-Modes --- p.34 / Chapter 3.5.3 --- Numerical Results and Discussion --- p.34 / Chapter 4 --- Interplay between Matter and Spacetime --- p.37 / Chapter 4.1 --- Physical Insight --- p.37 / Chapter 4.2 --- Sturm-Liouville Eigenvalue Problem --- p.39 / Chapter 4.3 --- Energy of the Fluid --- p.40 / Chapter 4.4 --- Spacetime Oscillation Driven by Fluid Motion --- p.45 / Chapter 4.5 --- Damped Oscillation Caused by Radiation of Gravitational Wave --- p.46 / Chapter 4.6 --- Calculation of δωn in a Perturbative Way --- p.48 / Chapter 4.7 --- Numerical Results and Discussion --- p.49 / Chapter 5 --- Asymptotic Behavior of Spacetime Modes --- p.61 / Chapter 5.1 --- Motivation --- p.61 / Chapter 5.2 --- Asymptotic Behavior of Axial ω-modes for One-Layered Stars --- p.62 / Chapter 5.2.1 --- "Asymptotic Form of g(r*,ω)" --- p.63 / Chapter 5.2.2 --- "Asymptotic Form of f(r*, ω)" --- p.67 / Chapter 5.2.3 --- Asymptotic Behavior of Axial Quasi-Normal Modes --- p.69 / Chapter 5.3 --- Asymptotic Behavior of Polar ω-modes for One-Layered Stars --- p.71 / Chapter 5.3.1 --- High-Frequency Approximation --- p.71 / Chapter 5.3.2 --- Asymptotic Behavior of Polar Quasi-Normal Modes --- p.73 / Chapter 5.4 --- Relationship between Axial and Polar ω-Modes --- p.74 / Chapter 5.4.1 --- Application 1:ω-Modes of Quark Stars --- p.75 / Chapter 5.4.2 --- Application 2:ω-Modes of Polytropic Stars --- p.80 / Chapter 5.4.3 --- Application 3: The Influence of Surface Discontinuities --- p.89 / Chapter 5.4.4 --- Application 4:ω-Modes of Realistic Neutron Stars --- p.92 / Chapter 6 --- Conclusion and Outlook --- p.99 / Chapter A --- From Einstein Equation to LD Formalism --- p.101 / Chapter A.l --- The Linearized Perturbation Equations --- p.101 / Chapter A.1.1 --- The Perturbation of the Einstein Tensor --- p.102 / Chapter A.1.2 --- The Perturbation of the Energy-momentum Tensor --- p.103 / Chapter A.1.3 --- The Perturbed Einstein Equations --- p.104 / Chapter A.2 --- Some Symbolic Operation Results --- p.105 / Chapter A.3 --- Simplifications --- p.106

The objective of this thesis is to study the fluid oscillation modes in compact stars, understand their properties and infer stellar structures from their frequencies. The first part of the thesis focuses on the Newtonian theory of stellar pulsation and the Cowling approximation (CA), which neglects the change in gravitational potential. We modify the conventional CA, devise a more accurate version of the CA and calculate the first-order correction to the conventional CA. In the second part, we apply the variational approximation method proposed by Chandrasekhar [Astrophys. J. 139,664 (1963)] and δ-perturbation expansion proposed by Bender et. al. [J. Maths. Phys. 30, 1447 (1989)] to explain the universality in the relationships between the fundamental mode frequency and the moment of inertia of neutron stars, which was discovered by Lau et. al. [Astrophys. J. 714, 1234 (2010)]. We reveal that stiff equations of state are the conditions for the observed universality. In the third part, we consider the relativistic pulsation formulation and relativistic CAs for compact stars. We unify several known CAs with a single second-order differential equation. We also extend the modified CA derived from the formalism established by Allen et. al. [Phys. Rev. D 58, 124012 (1998)] to include the effect of buoyancy. Finally, we find the first-order and the second-order post-Newtonian expansions for the nonradial pulsations in quark stars. We derive an analytic formula expressing the fundamental mode frequency in terms of the compactness of quark stars. As a result, we are able to verify the universality mentioned above for quark stars. / 這論文是對在牛頓力學以及相對論框架下緻密星流體振盪的研究結果。論文第一部分集中討論牛頓力學下流體振盪以及近似方法。這近似方法忽略重力勢的擾動，令系統由四階微分方程減少為二階微分方程。我們修正了已往的近似方法和提出一個更精準的近似方法。第二部分包括變分近似方法。我們利用該方法和δ微擾理論解釋基本模式頻率的普通性。第三部分包括相對論框架下緻密星流體振盪和近似方法。我們以一條二階微分方程總結之前出現的近似方法並且在近似方法中加入浮力。最後，我們執行一階和二階的後牛頓展開，以分析夸克星的基本模式。我們驗證了展開的準確度和發現了基本模式頻率的方程。 / Chan, Tsang Keung = 有關在緻密星中流體振盪的研究 / 陳增強. / Thesis M.Phil. Chinese University of Hong Kong 2013. / Abstracts also in Chinese. / Title from PDF title page (viewed on 07, October, 2016). / Chan, Tsang Keung = You guan zai zhi mi xing zhong liu ti zhen dang de yan jiu / Chen Zengqiang. / Detailed summary in vernacular field only.

We analyse the properties of extrasolar planets, other close companions and their hosts. We start by identifying a sample of the detected extrasolar planets that is minimally affected by the selection effects of the Doppler detection method. With a simple analysis we quantify trends in the surface density of this sample in the Msini-period plane. A modest extrapolation of these trends puts Jupiter in the most densely occupied region of this parameter space, thus suggesting that Jupiter is a typical massive planet rather than an outlier. We then examine what fraction of Sun-like (~ FGK) stars have planets. We find that at least ~25% of stars possess planets when we limit our analysis to stars that have been monitored the longest and whose low surface activity allow the most precise radial velocity measurements. The true fraction of stars with planets may be as large as ~100%. We construct a sample of nearby Sun-like stars with close companions (period < 5 years). By using the same sample to extract the relative numbers of stellar, brown dwarf and planetary companions, we verify the existence of a very dry brown dwarf desert and describe it quantitatively. Approximately 16% of Sun-like stars have close companions more massive than Jupiter: 11% +- 3% are stellar, <1% are brown dwarf and 5% +- 2% are giant planets. A comparison with the initial mass function of individual stars and free-floating brown dwarfs, suggests either a different spectrum of gravitational fragmentation in the formation environment or post-formation migratory processes disinclined to leave brown dwarfs in close orbits. Finally we examine the relationship between the frequency of close companions and the metallicity of their Sun-like hosts. We confirm and quantify a ~4 sigma positive correlation between host metallicity and planetary companions. In contrast we find a ~2 sigma anti-correlation between host metallicity and the presence of a stellar companion. Upon dividing our sample into FG and K sub-samples, we find a negligible anti-correlation in the FG sub-sample and a ~3 sigma anti-correlation in the K sub-sample. A kinematic analysis suggests that this anti-correlation is produced by a combination of low-metallicity, high-binarity thick disk stars and higher-metallicity, lower-binarity thin disk stars.

No description available.

The near- through mid-infrared offers a unique and, as this thesis aims to show, essential view of extragalactic stellar populations both nearby, at intermediate redshifts and at very high redshift. In chapter 2, I demonstrate that rest-frame near-IR photometry obtained by the Spitzer Space Telescope provides more robust stellar mass estimates for a spectroscopic sample of ~100 galaxies in the redshift desert (0.5<z<2), and is crucial for modeling galaxies with young star-forming populations. From this analysis, a surprising result emerges in the data. Although the rest-frame light short of 2 micron improves stellar mass estimates, the models and observations disagree beyond 2 micron and emission from non-stellar sources becomes significant. At wavelengths from 1-30 micron, stellar and non-stellar emission contribute equally to a galaxy's global spectral energy distribution. This is unlike visible wavelengths where stellar emission dominates or the far-IR where dust emission provides the bulk of a galaxy's luminosity. Using the sample of high-z galaxies, in chapter 3, I quantify the statistical significance of the excess emission at 2-5 micron and find the emission to correlate with the OII luminosity, suggesting a link between the excess emission and star formation. The origin of the excess emission is not clear, although I explore a number of non-stellar candidates in this chapter. Nearby resolved observations provide a clearer picture of the excess by spatially resolving 68 nearby galaxies. By analyzing the pixel-by-pixel near-IR colours within each galaxy at ~1-5 micron, increasingly red near-IR colors are mapped to spatial regions in chapter 4. For regions with red NIR colors and high star formation rates, I find the broad near- through mid-IR spectrum is constant, varying only in amplitude as a function of the intensity of star formation, suggesting the infrared emission of a young, dusty stellar populations can be added to stellar population synthesis models as an additional component tied to the star formation rate. In closing the thesis, the focus is moved to the detection of stellar populations in the earliest star-forming galaxies. By z>6, all visible wavelength emission is redshifted into near-IR wavelengths. In chapter 5, I show how a tunable near-IR filter I have helped develop holds promise for finding bright Lyman alpha emitting galaxies at redshifts of 8<z<11.

The near- through mid-infrared offers a unique and, as this thesis aims to show, essential view of extragalactic stellar populations both nearby, at intermediate redshifts and at very high redshift. In chapter 2, I demonstrate that rest-frame near-IR photometry obtained by the Spitzer Space Telescope provides more robust stellar mass estimates for a spectroscopic sample of ~100 galaxies in the redshift desert (0.5<z<2), and is crucial for modeling galaxies with young star-forming populations. From this analysis, a surprising result emerges in the data. Although the rest-frame light short of 2 micron improves stellar mass estimates, the models and observations disagree beyond 2 micron and emission from non-stellar sources becomes significant. At wavelengths from 1-30 micron, stellar and non-stellar emission contribute equally to a galaxy's global spectral energy distribution. This is unlike visible wavelengths where stellar emission dominates or the far-IR where dust emission provides the bulk of a galaxy's luminosity. Using the sample of high-z galaxies, in chapter 3, I quantify the statistical significance of the excess emission at 2-5 micron and find the emission to correlate with the OII luminosity, suggesting a link between the excess emission and star formation. The origin of the excess emission is not clear, although I explore a number of non-stellar candidates in this chapter. Nearby resolved observations provide a clearer picture of the excess by spatially resolving 68 nearby galaxies. By analyzing the pixel-by-pixel near-IR colours within each galaxy at ~1-5 micron, increasingly red near-IR colors are mapped to spatial regions in chapter 4. For regions with red NIR colors and high star formation rates, I find the broad near- through mid-IR spectrum is constant, varying only in amplitude as a function of the intensity of star formation, suggesting the infrared emission of a young, dusty stellar populations can be added to stellar population synthesis models as an additional component tied to the star formation rate. In closing the thesis, the focus is moved to the detection of stellar populations in the earliest star-forming galaxies. By z>6, all visible wavelength emission is redshifted into near-IR wavelengths. In chapter 5, I show how a tunable near-IR filter I have helped develop holds promise for finding bright Lyman alpha emitting galaxies at redshifts of 8<z<11.