Chemical Evolution of Binary Stars

NASA Astrophysics Data System (ADS)

Izzard, R. G.

2013-02-01

Energy generation by nuclear fusion is the fundamental process that prevents stars from collapsing under their own gravity. Fusion in the core of a star converts hydrogen to heavier elements from helium to uranium. The signature of this nucleosynthesis is often visible in a single star only for a very short time, for example while the star is a red giant or, in massive stars, when it explodes. Contrarily, in a binary system nuclear-processed matter can captured by a secondary star which remains chemically polluted long after its more massive companion star has evolved and died. By probing old, low-mass stars we gain vital insight into the complex nucleosynthesis that occurred when our Galaxy was much younger than it is today. Stellar evolution itself is also affected by the presence of a companion star. Thermonuclear novae and type Ia supernovae result from mass transfer in binary stars, but big questions still surround the nature of their progenitors. Stars may even merge and one of the challenges for the future of stellar astrophysics is to quantitatively understand what happens in such extreme systems. Binary stars offer unique insights into stellar, galactic and extragalactic astrophysics through their plethora of exciting phenomena. Understanding the chemical evolution of binary stars is thus of high priority in modern astrophysics.

Rotation and magnetism in intermediate-mass stars

NASA Astrophysics Data System (ADS)

Quentin, Léo G.; Tout, Christopher A.

2018-06-01

Rotation and magnetism are increasingly recognized as important phenomena in stellar evolution. Surface magnetic fields from a few to 20 000 G have been observed and models have suggested that magnetohydrodynamic transport of angular momentum and chemical composition could explain the peculiar composition of some stars. Stellar remnants such as white dwarfs have been observed with fields from a few to more than 109 G. We investigate the origin of and the evolution, on thermal and nuclear rather than dynamical time-scales, of an averaged large-scale magnetic field throughout a star's life and its coupling to stellar rotation. Large-scale magnetic fields sustained until late stages of stellar evolution with conservation of magnetic flux could explain the very high fields observed in white dwarfs. We include these effects in the Cambridge stellar evolution code using three time-dependant advection-diffusion equations coupled to the structural and composition equations of stars to model the evolution of angular momentum and the two components of the magnetic field. We present the evolution in various cases for a 3 M_{⊙} star from the beginning to the late stages of its life. Our particular model assumes that turbulent motions, including convection, favour small-scale field at the expense of large-scale field. As a result, the large-scale field concentrates in radiative zones of the star and so is exchanged between the core and the envelope of the star as it evolves. The field is sustained until the end of the asymptotic giant branch, when it concentrates in the degenerate core.

Nuclear physics: Close encounters of the alpha kind

DOE PAGES

Quaglioni, Sofia

2015-12-02

Here, breakthrough calculations of collisions between two helium nuclei pave the way to a quantitative understanding of how the elements carbon and oxygen were made in stars — and to improved models of stellar evolution.

Latest results from LUNA

NASA Astrophysics Data System (ADS)

Depalo, Rosanna; LUNA Collaboration

2018-01-01

A precise knowledge of the cross section of nuclear fusion reactions is a crucial ingredient in understanding stellar evolution and nucleosynthesis. At stellar temperatures, fusion cross sections are extremely small and difficult to measure. Measuring nuclear cross sections at astrophysical energies is a challenge that triggered a huge amount of experimental work. A breakthrough in this direction was the first operation of an underground accelerator at the Laboratory for Underground Nuclear Astrophysics (LUNA) in Gran Sasso, Italy. The 1400 meters of rocks above the laboratory act as a natural shield against cosmic radiation, suppressing the background by orders of magnitude. The latest results achieved at LUNA are discussed, with special emphasis on the 22Ne(p,γ)23Na reaction. Future perspectives of the LUNA experiment are also illustrated.

Understanding Stellar Evolution

NASA Astrophysics Data System (ADS)

Lamers, Henny J. G. L. M.; Levesque, Emily M.

2017-12-01

'Understanding Stellar Evolution' is based on a series of graduate-level courses taught at the University of Washington since 2004, and is written for physics and astronomy students and for anyone with a physics background who is interested in stars. It describes the structure and evolution of stars, with emphasis on the basic physical principles and the interplay between the different processes inside stars such as nuclear reactions, energy transport, chemical mixing, pulsation, mass loss, and rotation. Based on these principles, the evolution of low- and high-mass stars is explained from their formation to their death. In addition to homework exercises for each chapter, the text contains a large number of questions that are meant to stimulate the understanding of the physical principles. An extensive set of accompanying lecture slides is available for teachers in both Keynote® and PowerPoint® formats.

Confronting Models of Massive Star Evolution and Explosions with Remnant Mass Measurements

NASA Astrophysics Data System (ADS)

Raithel, Carolyn A.; Sukhbold, Tuguldur; Özel, Feryal

2018-03-01

The mass distribution of compact objects provides a fossil record that can be studied to uncover information on the late stages of massive star evolution, the supernova explosion mechanism, and the dense matter equation of state. Observations of neutron star masses indicate a bimodal Gaussian distribution, while the observed black hole mass distribution decays exponentially for stellar-mass black holes. We use these observed distributions to directly confront the predictions of stellar evolution models and the neutrino-driven supernova simulations of Sukhbold et al. We find strong agreement between the black hole and low-mass neutron star distributions created by these simulations and the observations. We show that a large fraction of the stellar envelope must be ejected, either during the formation of stellar-mass black holes or prior to the implosion through tidal stripping due to a binary companion, in order to reproduce the observed black hole mass distribution. We also determine the origins of the bimodal peaks of the neutron star mass distribution, finding that the low-mass peak (centered at ∼1.4 M ⊙) originates from progenitors with M ZAMS ≈ 9–18 M ⊙. The simulations fail to reproduce the observed peak of high-mass neutron stars (centered at ∼1.8 M ⊙) and we explore several possible explanations. We argue that the close agreement between the observed and predicted black hole and low-mass neutron star mass distributions provides new, promising evidence that these stellar evolution and explosion models capture the majority of relevant stellar, nuclear, and explosion physics involved in the formation of compact objects.

ON THE FATE OF THE MATTER REINSERTED WITHIN YOUNG NUCLEAR STELLAR CLUSTERS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hueyotl-Zahuantitla, Filiberto; Palous, Jan; Wuensch, Richard

2013-04-01

This paper presents a hydrodynamical model describing the evolution of the gas reinserted by stars within a rotating young nuclear star cluster (NSC). We explicitly consider the impact of the stellar component on the flow by means of a uniform insertion of mass and energy within the stellar cluster. The model includes the gravity force of the stellar component and a central supermassive black hole (SMBH), and accounts for the heating from the central source of radiation and the radiative cooling of the thermalized gas. By using a set of parameters typical for NSCs and SMBHs in Seyfert galaxies, ourmore » simulations show that a filamentary/clumpy structure is formed in the inner part of the cluster. This 'torus' is Compton-thick and covers a large fraction of the sky (as seen from the SMBH). In the outer parts of the cluster a powerful wind is produced that inhibits the infall of matter from larger scales and thus the NSC-SMBH interplay occurs in isolation.« less

Roles of nuclear weak rates on the evolution of degenerate cores in stars

NASA Astrophysics Data System (ADS)

Suzuki, Toshio; Tsunodaa, Naofumi; Tsunoda, Yuhsuke; Shimizu, Noritaka; Otsuka, Takaharu

2018-01-01

Electron-capture and β-decay rates in stellar environments are evaluated with the use of new shell-model Hamiltonians for sd-shell and pf-shell nuclei as well as for nuclei belonging to the island of inversion. Important role of the nuclear weak rates on the final evolution of stellar degenerate cores is presented. The weak interaction rates for sd-shell nuclei are calculated to study nuclear Urca processes in O-Ne-Mg cores of stars with 8-10 M⊙ (solar mass) and their effects on the final fate of the stars. Nucleosynthesis of iron-group elements in Type Ia supernova explosions are studied with the weak rates for pf-shell nuclei. The problem of the neutron-rich iron-group isotope over-production compared to the solar abundances is shown to be nearly solved with the use of the new rates and explosion model of slow defraglation with delayed detonation. Evaluation of the weak rates is extended to the island of inversion and the region of neutron-rich nuclei near 78Ni, where two major shells contribute to their configurations.

Stellar helium burning in other universes: A solution to the triple alpha fine-tuning problem

NASA Astrophysics Data System (ADS)

Adams, Fred C.; Grohs, Evan

2017-01-01

Motivated by the possible existence of other universes, with different values for the fundamental constants, this paper considers stellar models in universes where 8Be is stable. Many previous authors have noted that stars in our universe would have difficulty producing carbon and other heavy elements in the absence of the well-known 12C resonance at 7.6 MeV. This resonance is necessary because 8Be is unstable in our universe, so that carbon must be produced via the triple alpha reaction to achieve the requisite abundance. Although a moderate change in the energy of the resonance (200-300 keV) will indeed affect carbon production, an even smaller change in the binding energy of beryllium (∼100 keV) would allow 8Be to be stable. A stable isotope with A = 8 would obviate the need for the triple alpha process in general, and the 12C resonance in particular, for carbon production. This paper explores the possibility that 8Be can be stable in other universes. Simple nuclear considerations indicate that bound states can be realized, with binding energy ∼ 0.1 - 1 MeV, if the fundamental constants vary by a ∼ few - 10 %. In such cases, 8Be can be synthesized through helium burning, and 12C can be produced later through nuclear burning of beryllium. This paper focuses on stellar models that burn helium into beryllium; once the universe in question has a supply of stable beryllium, carbon production can take place during subsequent evolution in the same star or in later stellar generations. Using both a semi-analytic stellar structure model as well as a state-of-the-art stellar evolution code, we find that viable stellar configurations that produce beryllium exist over a wide range of parameter space. Finally, we demonstrate that carbon can be produced during later evolutionary stages.

Meteoritic Stardust and the Presolar History of the Solar Neighborhood

NASA Astrophysics Data System (ADS)

Nittler, Larry R.

Presolar stardust is present at low levels in meteorites and cometary dust and identified as ancient stellar matter by unusual isotopic compositions reflecting nuclear processes in stellar interiors and galactic chemical evolution. Most grains originated in winds from asymptotic giant branch (AGB) stars and supernova and their isotopic compositions provide important constraints on models of evolution and nucleosynthesis in these environments. The presolar grains from AGB stars appear to have formed in a lower-mass population of stars than predicted by GCE models. A merger of the Milky Way with a dwarf galaxy some 1 Gyr before the birth of the Solar System may explain this and other grain observations and the data thus can provide a unique window into the presolar history of the solar neighborhood.

The life cycle of starbursting circumnuclear gas discs

NASA Astrophysics Data System (ADS)

Schartmann, M.; Mould, J.; Wada, K.; Burkert, A.; Durré, M.; Behrendt, M.; Davies, R. I.; Burtscher, L.

2018-01-01

High-resolution observations from the submm to the optical wavelength regime resolve the central few 100 pc region of nearby galaxies in great detail. They reveal a large diversity of features: thick gas and stellar discs, nuclear starbursts, inflows and outflows, central activity, jet interaction, etc. Concentrating on the role circumnuclear discs play in the life cycles of galactic nuclei, we employ 3D adaptive mesh refinement hydrodynamical simulations with the RAMSES code to self-consistently trace the evolution from a quasi-stable gas disc, undergoing gravitational (Toomre) instability, the formation of clumps and stars and the disc's subsequent, partial dispersal via stellar feedback. Our approach builds upon the observational finding that many nearby Seyfert galaxies have undergone intense nuclear starbursts in their recent past and in many nearby sources star formation is concentrated in a handful of clumps on a few 100 pc distant from the galactic centre. We show that such observations can be understood as the result of gravitational instabilities in dense circumnuclear discs. By comparing these simulations to available integral field unit observations of a sample of nearby galactic nuclei, we find consistent gas and stellar masses, kinematics, star formation and outflow properties. Important ingredients in the simulations are the self-consistent treatment of star formation and the dynamical evolution of the stellar distribution as well as the modelling of a delay time distribution for the supernova feedback. The knowledge of the resulting simulated density structure and kinematics on pc scale is vital for understanding inflow and feedback processes towards galactic scales.

The Updated BaSTI Stellar Evolution Models and Isochrones. I. Solar-scaled Calculations

NASA Astrophysics Data System (ADS)

Hidalgo, Sebastian L.; Pietrinferni, Adriano; Cassisi, Santi; Salaris, Maurizio; Mucciarelli, Alessio; Savino, Alessandro; Aparicio, Antonio; Silva Aguirre, Victor; Verma, Kuldeep

2018-04-01

We present an updated release of the BaSTI (a Bag of Stellar Tracks and Isochrones) stellar model and isochrone library for a solar-scaled heavy element distribution. The main input physics that have been changed from the previous BaSTI release include the solar metal mixture, electron conduction opacities, a few nuclear reaction rates, bolometric corrections, and the treatment of the overshooting efficiency for shrinking convective cores. The new model calculations cover a mass range between 0.1 and 15 M ⊙, 22 initial chemical compositions between [Fe/H] = ‑3.20 and +0.45, with helium to metal enrichment ratio dY/dZ = 1.31. The isochrones cover an age range between 20 Myr and 14.5 Gyr, consistently take into account the pre-main-sequence phase, and have been translated to a large number of popular photometric systems. Asteroseismic properties of the theoretical models have also been calculated. We compare our isochrones with results from independent databases and with several sets of observations to test the accuracy of the calculations. All stellar evolution tracks, asteroseismic properties, and isochrones are made available through a dedicated web site.

Entropy of the Universe

NASA Astrophysics Data System (ADS)

Sato, Humitaka

2010-06-01

Charles Darwin's calculation of a life of Earth had ignited Kelvin's insight on a life of Sun, which had eventually inherited to the physical study of stellar structure and energy source. Nuclear energy had secured a longevity of the universe and the goal of the cosmic evolution has been secured by the entropy of black holes.

The Impact of Nuclear Reaction Rate Uncertainties on the Evolution of Core-collapse Supernova Progenitors

NASA Astrophysics Data System (ADS)

Fields, C. E.; Timmes, F. X.; Farmer, R.; Petermann, I.; Wolf, William M.; Couch, S. M.

2018-02-01

We explore properties of core-collapse supernova progenitors with respect to the composite uncertainties in the thermonuclear reaction rates by coupling the probability density functions of the reaction rates provided by the STARLIB reaction rate library with MESA stellar models. We evolve 1000 models of 15{M}ȯ from the pre-main sequence to core O-depletion at solar and subsolar metallicities for a total of 2000 Monte Carlo stellar models. For each stellar model, we independently and simultaneously sample 665 thermonuclear reaction rates and use them in a MESA in situ reaction network that follows 127 isotopes from 1H to 64Zn. With this framework we survey the core mass, burning lifetime, composition, and structural properties at five different evolutionary epochs. At each epoch we measure the probability distribution function of the variations of each property and calculate Spearman rank-order correlation coefficients for each sampled reaction rate to identify which reaction rate has the largest impact on the variations on each property. We find that uncertainties in the reaction rates of {}14{{N}}{({{p}},γ )}15{{O}}, triple-α, {}12{{C}}{(α ,γ )}16{{O}}, 12C(12C,p)23Na, 12C(16O, p)27Al, 16O(16O,n)31S, 16O(16O, p)31P, and 16O(16O,α)28Si dominate the variations of the properties surveyed. We find that variations induced by uncertainties in nuclear reaction rates grow with each passing phase of evolution, and at core H-, He-depletion they are of comparable magnitude to the variations induced by choices of mass resolution and network resolution. However, at core C-, Ne-, and O-depletion, the reaction rate uncertainties can dominate the variation, causing uncertainty in various properties of the stellar model in the evolution toward iron core-collapse.

Beta-decay rates of FP shell nuclei with A greater than 60 in massive stars at the presupernova stage

NASA Astrophysics Data System (ADS)

Kar, K.; Ray, A.; Sarkar, S.

1994-10-01

Beta decay and electron capture on a number of neutron-rich nuclei with A greater than 60 at the presupernova stage may play an important role in determining the hydrostatic core structure of massive presupernova stars and, through this, affect the subsequent evolution during the gravitational collapse and supernova explosion phases. In particular, some isotopes of cobalt and copper can make a substantial contribution to the overall changes in the lepton fraction and entropy of the stellar core during its very late stage of evolution. In the stellar evolution calculations to date, many of these nuclei could not be appropriately tracked in the reaction network, since reliable rates for these have not been available so far. We describe a model to calculate the beta-decay rates using an average beta strength function and an electron phase-space factor evaluated for typical presupernova matter density (rho = 3 x 107-3 x 109 g/cu cm) and temperature (T = (2-5) x 109 K). For the Gamnow-Teller (GT) strength function we use a sum rule calculated by the spectral distribution theory, and the centroid of the distribution is obtained from experimental data on (p, n) reactions. The width sigma of the GT strength function has two parts (sigma2 = (sigmaN exp 2 + (sigmaC exp 2, with sigmaC = 0.157ZA-1/3). The parameter sigmaN is fixed by a best fit to the observed half-lives for the free decays of a number of A greater than 60 nuclei. In the calculation of rates we include contributions from the excited states of the mother nucleus wherever they are known experimentally. For the excited states one uses the same form of the GT strength function, but shifted in energy using the extended isobaric analog state argument. The method is particularly suited for calculating contributions from the excited states important at high temperatures relevant at the presupernova stellar evolution phase. We also include the contributions to the transition rates from the Gamow-Teller resonance states (e.g., the GTR+ state) in the mother nucleus, which may be thermally populated. The beta-decay rates for nuclei having A greater than 60 reported here can be inputs for presupernova stellar evolution and nucleosynthesis calculations employing detailed nuclear reaction networks relevant in the advanced phases of hydrostatic nuclear burning.

Frontiers of stellar evolution

NASA Technical Reports Server (NTRS)

Lambert, David L. (Editor)

1991-01-01

The present conference discusses theoretical and observational views of star formation, spectroscopic constraints on the evolution of massive stars, very low mass stars and brown dwarfs, asteroseismology, globular clusters as tests of stellar evolution, observational tests of stellar evolution, and mass loss from cool evolved giant stars. Also discussed are white dwarfs and hot subdwarfs, neutron stars and black holes, supernovae from single stars, close binaries with evolved components, accretion disks in interacting binaries, supernovae in binary systems, stellar evolution and galactic chemical evolution, and interacting binaries containing compact components.

Eight luminous early-type galaxies in nearby pairs and sparse groups. I. Stellar populations spatially analysed

NASA Astrophysics Data System (ADS)

Rosa, D. A.; Milone, A. C.; Krabbe, A. C.; Rodrigues, I.

2018-06-01

We present a detailed spatial analysis of stellar populations based on long-slit optical spectra in a sample of eight luminous early-type galaxies selected from nearby sparse groups and pairs, three of them may have interaction with another galaxy of similar mass. We have spatially measured luminosity-weighted averages of age, [M/H], [Fe/H], and [α /Fe] in the sample galaxies to add empirical data relative to the influence of galaxy mass, environment, interaction, and AGN feedback in their formation and evolution. The stellar population of the individual galaxies were determined through the well-established stellar population synthesis code starlight using semi-empirical simple stellar population models. Radial variations of luminosity- weighted means of age, [M/H], [Fe/H], and [α /Fe] were quantified up to half of the effective radius of each galaxy. We found trends between representative values of age, [M/H], [α /Fe], and the nuclear stellar velocity dispersion. There are also relations between the metallicity/age gradients and the velocity dispersion. Contributions of 1-4 Gyr old stellar populations were quantified in IC 5328 and NGC 6758 as well as 4-8 Gyr old ones in NGC 5812. Extended gas is present in IC 5328, NGC 1052, NGC 1209, and NGC 6758, and the presence of a LINER is identified in all these galaxies. The regions up to one effective radius of all galaxies are basically dominated by α -enhanced metal-rich old stellar populations likely due to rapid star formation episodes that induced efficient chemical enrichment. On average, the age and [α /Fe] gradients are null and the [M/H] gradients are negative, although discordant cases were found. We found no correlation between the stellar population properties and the LINER presence as well as between the stellar properties and environment or gravitational interaction, suggesting that the influence of progenitor mass cannot be discarded in the formation and evolution of early-type galaxies.

The fate of the Antennae galaxies

NASA Astrophysics Data System (ADS)

Lahén, Natalia; Johansson, Peter H.; Rantala, Antti; Naab, Thorsten; Frigo, Matteo

2018-04-01

We present a high-resolution smoothed particle hydrodynamic simulation of the Antennae galaxies (NGC 4038/4039) and follow the evolution 3 Gyr beyond the final coalescence. The simulation includes metallicity-dependent cooling, star formation, and both stellar feedback and chemical enrichment. The simulated best-match Antennae reproduce well both the observed morphology and the off-nuclear starburst. We also produce for the first time a simulated two-dimensional (2D) metallicity map of the Antennae and find good agreement with the observed metallicity of off-nuclear stellar clusters; however, the nuclear metallicities are overproduced by ˜0.5 dex. Using the radiative transfer code SKIRT, we produce multiwavelength observations of both the Antennae and the merger remnant. The 1-Gyr-old remnant is well fitted with a Sérsic profile of n = 7.07, and with an r-band effective radius of re = 1.6 kpc and velocity dispersion of σe = 180 km s-1 the remnant is located on the Fundamental Plane of early-type galaxies (ETGs). The initially blue Antennae remnant evolves on to the red sequence after ˜2.5 Gyr of secular evolution. The remnant would be classified as a fast rotator, as the specific angular momentum evolves from λRe ≈ 0.11 to 0.14 during its evolution. The remnant shows ordered rotation and a double peaked maximum in the mean 2D line-of-sight velocity. These kinematical features are relatively common amongst local ETGs and we specifically identify three local ETGs (NGC 3226, NGC 3379, and NGC 4494) in the atlas3D sample, whose photometric and kinematic properties most resemble the Antennae remnant.

Foreword

NASA Astrophysics Data System (ADS)

Jorissen, A.; Goriely, S.; Rayet, M.; Siess, L.; Boffin, H.

The international conference The Future Astronuclear Physics was held at the Université Libre de Bruxelles (ULB) from August 20 to 22, 2003, to celebrate Marcel Arnould on the occasion of his sixtieth birthday. Marcel Arnould is full professor at ULB and was appointed director of the Institut d'Astronomie et d'Astrophysique (IAA) of this university in 1983, when he was still a Research Associate of the National Fund for Scientific Research (FNRS). Since the late sixties he has played a leading role in the development of a trans-disciplinary field of research, the object of which is the study of nuclear phenomena in astrophysics. Those phenomena being the main source of energy in stellar interiors and being also responsible for the synthesis of the chemical elements, the study of the often peculiar, sometimes exotic, nuclear physics in a rich variety of astrophysical conditions, is crucial to understand almost all stages of stellar evolution as well as the chemical and isotopic content of the neighboring and remote places of our universe. All along his scientific career, Marcel Arnould has worked to give the so-called nuclear astrophysics, born in the second half of the twentieth century and marked by a few prominent physicists in the United States and in Canada, a fertile ground for development inside Europe as a fully grown discipline, collecting the knowledge on the infinitely small with that on the infinitely large, a true interdisciplinary science that ought to be more appropriately called “astronuclear physics". We like to remind that to achieve this goal, Marcel Arnould has promoted and directed two important projects in the framework of the EU scientific programs. The first one (1989 1992), “Nuclear Astrophysics: experimental and theoretical studies", involved 11 European research centers and led to the first measurement, at the Louvain-la-Neuve cyclotron facility, of a nuclear reaction rate involving a short-lived nuclide, ^{13}N. This experiment was performed using a radioactive ion beam technique, a new and powerful tool of investigation in nuclear astrophysics, which has since been developed worldwide. The second program, “Nuclear Astrophysics: measurement, evaluation and compilation of reaction rates, and their impact on stellar evolution and nucleosynthesis" (1992 1997), gave the scientific community the first European compilation of astrophysical reaction rates. This work was meant to supersede the compilations performed during more than forty years by a team led by the late Nobel Prize winner, William A. Fowler, at the California Institute of Technology. A relentless scientific advisor amongst astrophysicists as well as nuclear physicists, Marcel deplores the persistent lack of communication between those two communities. For years, his hope has been to see the rise of a generation of true astronuclear physicists, but one has to admit with him that this goal is far from being achieved yet and that one still has to fight, despite all the expressions of good intentions, against the barriers that, as is usual, separate scientific disciplines. It is therefore in tribute to the transdisciplinary and visionary nature of Marcel Arnould's scientific work that his close collaborators at the IAA decided to organize this conference, which is explicitely devoted to future developments in the field of astronuclear physics and not, as is often the case, to already completed, or even published, works. The audience has been limited from the start to invited participants chosen for the quality of their human and scientific relations with Marcel, as well as for their contribution to the domains he is exceptionally found of. The conference program was on purpose centered on a few fields that for many years now have been central to the activities of the IAA: the stellar nucleosynthesis and its relations to stellar physics, to nuclear physics and to cosmochemistry. The organizers' choice was to concentrate on a few challenging problems: abundance determinations in stars and modeling of atmospheres, special topics in stellar evolution (rotation, mixing, binarity), multi-D modeling of stellar explosions, future progress in experimental and theoretical nuclear physics for astrophysics. The speakers were asked to give, starting from their own topic, a prospective (or “visionary") view on the evolution of astronuclear physics for the next twenty years. Of course this demand requires time and explains why the organizers chose to limit the number of speeches rather than the time allocated to each speaker. In each of the four sessions, round tables gave the participants plenty of time for discussions or for more formal contributions, some of which have been included in the present proceedings. We hope that the reader will find the same pleasure in reading these proceedings as those who lived the three days of the Conference in a studious and friendly enthusiasm. Scientific Organizing Committee: H. Boffin (Observatoire Royal de Belgique/European Southern Observatory), S. Goriely (IAA), A. Jorissen (IAA), P. Leleux (Université Catholique de Louvain, Institut de Physique Nucléaire), M. Rayet (IAA). Local Organizing Committee: S. Goriely, S. Jancart, A. Jorissen, Y. Levasseur, D. Pourbaix, M. Rayet, L. Siess, S. Van Eck.

Supernova Explosions, Nucleosynthesis, and Cosmic Chemical Evolution

NASA Astrophysics Data System (ADS)

Truran, James W.

2006-08-01

The Universe emerged from its first three minutes with a composition consisting of hydrogen, deuterium, 3He, 4He, and 7Li. These isotopes constitute the primordial compositions of galaxies. Within galaxies, the synthesis of heavier elements from carbon through uranium is understood to occur during the normal evolution of stars and in supernova explosions of Types I and II. This history is written in the compositions of the stars and gas in our Milky Way Galaxy and other galaxies. The contributions both from massive stars (M>10 Msolar) and associated Type II supernovae and from Type Ia (thermonuclear) supernovae are particularly noteworthy. We review both the nuclear processes by which this occurs and the compositions of the stellar components of our Galaxy as a function of time which reflect these nucleosynthesis processes. We then discuss how such observations inform us of the nature of the earliest stellar populations and of the abundance history of the Cosmos.

A teaching module about stellar structure and evolution

NASA Astrophysics Data System (ADS)

Colantonio, Arturo; Galano, Silvia; Leccia, Silvio; Puddu, Emanuella; Testa, Italo

2017-01-01

In this paper, we present a teaching module about stellar structure, functioning and evolution. Drawing from literature in astronomy education, we designed the activities around three key ideas: spectral analysis, mechanical and thermal equilibrium, energy and nuclear reactions. The module is divided into four phases, in which the key ideas for describing stars' functioning and physical mechanisms are gradually introduced. The activities (20 hours) build on previously learned laws in mechanics, thermodynamics, and electromagnetism and help students combine them meaningfully in order to get a complete picture of processes that happens in stars. The module was piloted with two intact classes of secondary school students (N = 59 students, 17-18 years old), using a ten-question multiple-choice questionnaire as research instrument. Results support the effectiveness of the proposed activities. Implications for the teaching of advanced physics topics using stars as fruitful context are briefly discussed.

BULGES OF NEARBY GALAXIES WITH SPITZER: THE GROWTH OF PSEUDOBULGES IN DISK GALAXIES AND ITS CONNECTION TO OUTER DISKS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fisher, David B.; Drory, Niv; Fabricius, Maximilian H.

2009-05-20

We study star formation rates (SFRs) and stellar masses in bulges of nearby disk galaxies. For this we construct a new SFR indicator that linearly combines data from the Spitzer Space Telescope and the Galaxy Evolution Explorer. All bulges are found to be forming stars irrespective of bulge type (pseudobulge or classical bulge). At present-day SFR the median pseudobulge could have grown the present-day stellar mass in 8 Gyr. Classical bulges have the lowest specific SFR implying a growth times that are longer than a Hubble time, and thus the present-day SFR does not likely play a major role inmore » the evolution of classical bulges. In almost all galaxies in our sample the specific SFR (SFR per unit stellar mass) of the bulge is higher than that of the outer disk. This suggests that almost all galaxies are increasing their B/T through internal star formation. The SFR in pseudobulges correlates with their structure. More massive pseudobulges have higher SFR density, this is consistent with that stellar mass being formed by moderate, extended star formation. Bulges in late-type galaxies have similar SFRs as pseudobulges in intermediate-type galaxies, and are similar in radial size. However, they are deficient in mass; thus, they have much shorter growth times, {approx}2 Gyr. We identify a class of bulges that have nuclear morphology similar to pseudobulges, significantly lower specific SFR than pseudobulges, and are closer to classical bulges in structural parameter correlations. These are possibly composite objects, evolved pseudobulges or classical bulges experiencing transient, enhanced nuclear star formation. Our results are consistent with a scenario in which bulge growth via internal star formation is a natural, and near ubiquitous phenomenon in disk galaxies. Those galaxies with large classical bulges are not affected by the in situ bulge growth, likely because the majority of their stellar mass comes from some other phenomenon. Yet, those galaxies without a classical bulge, over long periods of extended star formation are able to growth a pseudobulge. Though cold accretion is not ruled out, for pseudobulge galaxies an addition of stellar mass from mergers or accretion is not required to explain the bulge mass. In this sense, galaxies with pseudobulges may very well be bulgeless (or 'quasi-bulgeless') galaxies, and galaxies with classical bulges are galaxies in which both internal evolution and hierarchical merging are responsible for the bulge mass by fractions that vary from galaxy to galaxy.« less

Triple-α reaction rate constrained by stellar evolution models

NASA Astrophysics Data System (ADS)

Suda, Takuma; Hirschi, Raphael; Fujimoto, Masayuki Y.

2012-11-01

We investigate the quantitative constraint on the triple-α reaction rate based on stellar evolution theory, motivated by the recent significant revision of the rate proposed by nuclear physics calculations. Targeted stellar models were computed in order to investigate the impact of that rate in the mass range of 0.8<=M/Msolar<=25 and in the metallicity range between Z = 0 and Z = 0.02. The revised rate has a significant impact on the evolution of low-and intermediate-mass stars, while its influence on the evolution of massive stars (M > 10Msolar) is minimal. We find that employing the revised rate suppresses helium shell flashes on AGB phase for stars in the initial mass range 0.8<=M/Msolar<=6, which is contradictory to what is observed. The absence of helium shell flashes is due to the weak temperature dependence of the revised triple-α reaction cross section at the temperature involved. In our models, it is suggested that the temperature dependence of the cross section should have at least ν > 10 at T = 1-1.2×108K where the cross section is proportional to Tν. We also derive the helium ignition curve to estimate the maximum cross section to retain the low-mass first red giants. The semi-analytically derived ignition curves suggest that the reaction rate should be less than ~ 10-29 cm6 s-1 mole-2 at ~ 107.8 K, which corresponds to about three orders of magnitude larger than that of the NACRE compilation.

Capturing Neutrinos from a Star's Final Hours

NASA Astrophysics Data System (ADS)

Hensley, Kerry

2018-04-01

What happens on the last day of a massive stars life? In the hours before the star collapses and explodes as a supernova, the rapid evolution of material in its core creates swarms of neutrinos. Observing these neutrinos may help us understand the final stages of a massive stars life but theyve never been detected.A view of some of the 1,520 phototubes within the MiniBooNE neutrino detector. Observations from this and other detectors are helping to illuminate the nature of the mysterious neutrino. [Fred Ullrich/FNAL]Silent Signposts of Stellar EvolutionThe nuclear fusion that powers stars generates tremendous amounts of energy. Much of this energy is emitted as photons, but a curious and elusive particle the neutrino carries away most of the energy in the late stages of stellar evolution.Stellar neutrinos can be created through two processes: thermal processesand beta processes. Thermal processes e.g.,pair production, in which a particle/antiparticle pair are created depend on the temperature and pressure of the stellar core. Beta processes i.e.,when a proton converts to a neutron, or vice versa are instead linked to the isotopic makeup of the stars core. This means that, if we can observe them, beta-process neutrinos may be able to tell us about the last steps of stellar nucleosynthesis in a dying star.But observing these neutrinos is not so easilydone. Neutrinos arenearly massless, neutral particles that interact only feebly with matter; out of the whopping 1060neutrinos released in a supernova explosion, even the most sensitive detectors only record the passage of just a few. Do we have a chance of detectingthe beta-process neutrinos that are released in the final few hours of a stars life, beforethe collapse?Neutrino luminosities leading up to core collapse. Shortly before collapse, the luminosity of beta-process neutrinos outshines that of any other neutrino flavor or origin. [Adapted from Patton et al. 2017]Modeling Stellar CoresTo answer this question, Kelly Patton (University of Washington) and collaborators first used a stellar evolution model to explore neutrino production in massive stars. They modeled the evolution of two massive stars 15 and 30 times the mass of our Sun from the onset of nuclear fusion to the moment of collapse.The authors found that in the last few hours before collapse, during which the material in the stars cores is rapidly upcycled into heavier elements, the flux from beta-process neutrinos rivals that of thermal neutrinos and even exceeds it at high energies. So now we know there are many beta-process neutrinos but can we spot them?Neutrino and antineutrino fluxes at Earth from the last 2 hours of a 30-solar-mass stars life compared to the flux from background sources. The rows represent calculations using two different neutrino mass hierarchies. Click to enlarge. [Patton et al. 2017]Observing Elusive NeutrinosFor an imminent supernova at a distance of 1 kiloparsec, the authors find that the presupernova electron neutrino flux rises above the background noise from the Sun, nuclear reactors, and radioactive decay within the Earth in the final two hours before collapse.Based on these calculations, current and future neutrino observatories should be able to detect tens of neutrinos from a supernova within 1 kiloparsec, about 30% of which would be beta-process neutrinos. As the distance to the star increases, the time and energy window within which neutrinos can be observed gradually narrows, until it closes for stars at a distance of about 30 kiloparsecs.Are there any nearby supergiants soon to go supernova so these predictions can be tested? At a distance of only 650 light-years, the red supergiant star Betelgeuse should produce detectable neutrinos when it explodes an exciting opportunity for astronomers in the far future!CitationKelly M. Patton et al 2017ApJ8516. doi:10.3847/1538-4357/aa95c4

POET: Planetary Orbital Evolution due to Tides

NASA Astrophysics Data System (ADS)

Penev, Kaloyan

2014-08-01

POET (Planetary Orbital Evolution due to Tides) calculates the orbital evolution of a system consisting of a single star with a single planet in orbit under the influence of tides. The following effects are The evolutions of the semimajor axis of the orbit due to the tidal dissipation in the star and the angular momentum of the stellar convective envelope by the tidal coupling are taken into account. In addition, the evolution includes the transfer of angular momentum between the stellar convective and radiative zones, effect of the stellar evolution on the tidal dissipation efficiency, and stellar core and envelope spins and loss of stellar convective zone angular momentum to a magnetically launched wind. POET can be used out of the box, and can also be extended and modified.

Astrophysical factors: Zero energy vs most effective energy

NASA Astrophysics Data System (ADS)

Liolios, Theodore E.

2001-07-01

Effective astrophysical factors for nonresonant astrophysical nuclear reaction are usually calculated with respect to a zero-energy limit. In the present work that limit is shown to be very disadvantageous compared to the more natural effective-energy limit. The latter is used in order to modify the thermonuclear reaction rate formula in stellar evolution codes so that it takes into account both plasma and laboratory screening effects.

Nuclear planetology: understanding habitable planets as Galactic bulge stellar remnants (black dwarfs) in a Hertzsprung-Russell (HR) diagram

NASA Astrophysics Data System (ADS)

Roller, Goetz

2016-04-01

The Hertzsprung-Russell (HR) diagram is one of the most important diagrams in astronomy. In a HR diagram, the luminosity of stars and/or stellar remnants (white dwarf stars, WD's), relative to the luminosity of the sun, is plotted versus their surface temperatures (Teff). The Earth shows a striking similarity in size (radius ≈ 6.370 km) and Teff of its outer core surface (Teff ≈ 3800 K at the core-mantle-boundary) with old WD's (radius ≈ 6.300 km) like WD0346+246 (Teff ≈ 3820 K after ≈ 12.7 Ga [1]), which plot in the HR diagram close to the low-mass extension of the stellar population or main sequence. In the light of nuclear planetology [2], Earth-like planets are regarded as old, down-cooled and differentiated black dwarfs (Fe-C BLD's) after massive decompression, the most important nuclear reactions involved being 56Fe(γ,α)52Cr (etc.), possibly responsible for extreme terrestrial glaciations events ("snowball" Earth), together with (γ,n), (γ,p) and fusion reactions like 12C(α,γ)16O. The latter reaction might have caused oxidation of the planet from inside out. Nuclear planetology is a new research field, tightly constrained by a coupled 187Re-232Th-238U systematics. By means of nuclear/quantum physics and taking the theory of relativity into account, it aims at understanding the thermal and chemical evolution of Fe-C BLD's after gravitational contraction (e.g. Mercury) or Fermi-pressure controlled collapse (e.g. Earth) events after massive decompression, leading possibly to an r-process event, towards the end of their cooling period [2]. So far and based upon 187Re-232Th-238U nuclear geochronometry, the Fe-C BLD hypothesis can successfully explain the global terrestrial MORB 232Th/238U signature [3]. Thus, it may help to elucidate the DM (depleted mantle), EMI (enriched mantle 1), EMII (enriched mantle 2) or HIMU (high U/Pb) reservoirs, and the 187Os/188Os isotopic dichotomy in Archean magmatic rocks and sediments [4]. Here I present a conceptual model constraining the evolution of a rocky planet like Earth or Mercury from a stellar precursor of the oldest population to a Fe-C BLD, shifting through different spectral classes in a HR diagram after massive decompression and tremendous energy losses. In the light of WD/BLD cosmochronology [1], solar system bodies like Earth, Mercury and Moon are regarded as captured interlopers from the Galactic bulge, Earth and Moon possibly representing remnants of an old binary system. Such a preliminary scenario is supported by similar ages obtained from WD's for the Galactic halo [1] and, independently, by means of 187Re-232Th-238U nuclear geochronometry [2, 4, 5], together with recent observations extremely metal-poor stars from the cosmic dawn in the bulge of the Milky Way [6]. This might be further elucidated in the near future by Th/U cosmochronometry based upon a nuclear production ratio Th/U = 0.96 [5] and additionally by means of a newly developed nucleogeochronometric age dating method for stellar spectroscopy, which will be presented in a forthcoming paper. The model shall stimulate geochemical data interpretation from a different perspective to constrain the (thermal) evolution of a habitable planet as to its geo-, bio-, hydro- and atmosphere. [1] Fontaine et al. (2001), Public. Astron. Soc. of the Pacific 113, 409-435. [2] Roller (2015), Abstract T34B-0407, AGU Spring Meeting 2015. [3] Arevalo et al. (2010), Chem. Geol. 271, 70-85. [4] Roller (2015), Geophys. Res. Abstr. 17, EGU2015-2399. [5] Roller (2015), 78th Annu. Meeting Met. Soc., Abstract #5041. [6] Howes et al. (2015), Nature 527, 484-487.

Galactic Bulge Giants: Probing Stellar and Galactic Evolution. 1. Catalogue of Spitzer IRAC and MIPS Sources (PREPRINT)

NASA Technical Reports Server (NTRS)

Uttenthaler, Stefan; Stute, Matthias; Sahai, Raghvendra; Blommaert, Joris A.; Schultheis, Mathias; Kraemer, Kathleen E.; Groenewegen, Martin A.; Price, Stephan D.

2010-01-01

Aims. We aim at measuring mass-loss rates and the luminosities of a statistically large sample of Galactic bulge stars at several galactocentric radii. The sensitivity of previous infrared surveys of the bulge has been rather limited, thus fundamental questions for late stellar evolution, such as the stage at which substantial mass-loss begins on the red giant branch and its dependence on fundamental stellar properties, remain unanswered. We aim at providing evidence and answers to these questions. Methods. To this end, we observed seven 15 15 arcmin2 fields in the nuclear bulge and its vicinity with unprecedented sensitivity using the IRAC and MIPS imaging instruments on-board the Spitzer Space Telescope. In each of the fields, tens of thousands of point sources were detected. Results. In the first paper based on this data set, we present the observations, data reduction, the final catalogue of sources, and a detailed comparison to previous mid-IR surveys of the Galactic bulge, as well as to theoretical isochrones. We find in general good agreement with other surveys and the isochrones, supporting the high quality of our catalogue.

Exploring stellar evolution with gravitational-wave observations

NASA Astrophysics Data System (ADS)

Dvorkin, Irina; Uzan, Jean-Philippe; Vangioni, Elisabeth; Silk, Joseph

2018-05-01

Recent detections of gravitational waves from merging binary black holes opened new possibilities to study the evolution of massive stars and black hole formation. In particular, stellar evolution models may be constrained on the basis of the differences in the predicted distribution of black hole masses and redshifts. In this work we propose a framework that combines galaxy and stellar evolution models and use it to predict the detection rates of merging binary black holes for various stellar evolution models. We discuss the prospects of constraining the shape of the time delay distribution of merging binaries using just the observed distribution of chirp masses. Finally, we consider a generic model of primordial black hole formation and discuss the possibility of distinguishing it from stellar-origin black holes.

Advances in stellar evolution; Proceedings of the Workshop on Stellar Ecology, Marciana Marina, Italy, June 23-29, 1996

NASA Astrophysics Data System (ADS)

Rood, R. T.; Renzini, A.

1997-01-01

The present volume on stellar evolution discusses fundamentals of stellar evolution and star clusters, variable stars, AGB stars and planetary nebulae, white dwarfs, binary star evolution, and stars in galaxies. Attention is given to the stellar population in the Galactic bulge, a photometric study of NGC 458, and HST observations of high-density globular clusters. Other topics addressed include the Cepheid instability strip in external galaxies, Hyades cluster white dwarfs and the initial-final mass relation, element diffusion in novae, mass function of the stars in the solar neighborhood, synthetic spectral indices for elliptical galaxies, and stars at the Galactic center.

Merging black holes in non-spherical nuclear star clusters

NASA Astrophysics Data System (ADS)

Petrovich, Cristobal

2018-04-01

The Milky Way and a significant fraction of galaxies are observed to host a central Massive Black Hole (MBH) embedded in a non-spherical nuclear star cluster. I will discuss the orbital evolution of stellar binaries in these environments and argue that their merger rates are expected to be greatly enhanced when the effect from cluster potential is taken into account in the binary-MBH triple system. I will apply our results to compact-object binary mergers mediated by gravitational wave radiation and show that this merger channel can contribute significantly to the LIGO/Virgo detections.

Estimating precise metallicity and stellar mass evolution of galaxies

NASA Astrophysics Data System (ADS)

Mosby, Gregory

2018-01-01

The evolution of galaxies can be conveniently broken down into the evolution of their contents. The changing dust, gas, and stellar content in addition to the changing dark matter potential and periodic feedback from a super-massive blackhole are some of the key ingredients. We focus on the stellar content that can be observed, as the stars reflect information about the galaxy when they were formed. We approximate the stellar content and star formation histories of unresolved galaxies using stellar population modeling. Though simplistic, this approach allows us to reconstruct the star formation histories of galaxies that can be used to test models of galaxy formation and evolution. These models, however, suffer from degeneracies at large lookback times (t > 1 Gyr) as red, low luminosity stars begin to dominate a galaxy’s spectrum. Additionally, degeneracies between stellar populations at different ages and metallicities often make stellar population modeling less precise. The machine learning technique diffusion k-means has been shown to increase the precision in stellar population modeling using a mono-metallicity basis set. However, as galaxies evolve, we expect the metallicity of stellar populations to vary. We use diffusion k-means to generate a multi-metallicity basis set to estimate the stellar mass and chemical evolution of unresolved galaxies. Two basis sets are formed from the Bruzual & Charlot 2003 and MILES stellar population models. We then compare the accuracy and precision of these models in recovering complete (stellar mass and metallicity) histories of mock data. Similarities in the groupings of stellar population spectra in the diffusion maps for each metallicity hint at fundamental age transitions common to both basis sets that can be used to identify stellar populations in a given age range.

ASTEC—the Aarhus STellar Evolution Code

NASA Astrophysics Data System (ADS)

Christensen-Dalsgaard, Jørgen

2008-08-01

The Aarhus code is the result of a long development, starting in 1974, and still ongoing. A novel feature is the integration of the computation of adiabatic oscillations for specified models as part of the code. It offers substantial flexibility in terms of microphysics and has been carefully tested for the computation of solar models. However, considerable development is still required in the treatment of nuclear reactions, diffusion and convective mixing.

Chemical element transport in stellar evolution models

PubMed Central

Cassisi, Santi

2017-01-01

Stellar evolution computations provide the foundation of several methods applied to study the evolutionary properties of stars and stellar populations, both Galactic and extragalactic. The accuracy of the results obtained with these techniques is linked to the accuracy of the stellar models, and in this context the correct treatment of the transport of chemical elements is crucial. Unfortunately, in many respects calculations of the evolution of the chemical abundance profiles in stars are still affected by sometimes sizable uncertainties. Here, we review the various mechanisms of element transport included in the current generation of stellar evolution calculations, how they are implemented, the free parameters and uncertainties involved, the impact on the models and the observational constraints. PMID:28878972

Chemical element transport in stellar evolution models.

PubMed

Salaris, Maurizio; Cassisi, Santi

2017-08-01

Stellar evolution computations provide the foundation of several methods applied to study the evolutionary properties of stars and stellar populations, both Galactic and extragalactic. The accuracy of the results obtained with these techniques is linked to the accuracy of the stellar models, and in this context the correct treatment of the transport of chemical elements is crucial. Unfortunately, in many respects calculations of the evolution of the chemical abundance profiles in stars are still affected by sometimes sizable uncertainties. Here, we review the various mechanisms of element transport included in the current generation of stellar evolution calculations, how they are implemented, the free parameters and uncertainties involved, the impact on the models and the observational constraints.

The Evolution and Stability of Massive Stars

NASA Astrophysics Data System (ADS)

Shiode, Joshua Hajime

Massive stars are the ultimate source for nearly all the elements necessary for life. The first stars forge these elements from the sparse set of ingredients supplied by the Big Bang, and distribute enriched ashes throughout their galactic homes via their winds and explosive deaths. Subsequent generations follow suit, assembling from the enriched ashes of their predecessors. Over the last several decades, the astrophysics community has developed a sophisticated theoretical picture of the evolution of these stars, but it remains an incomplete accounting of the rich set of observations. Using state of the art models of massive stars, I have investigated the internal processes taking place throughout the life-cycles of stars spanning those from the first generation ("Population III") to the present-day ("Population I"). I will argue that early-generation stars were not highly unstable to perturbations, contrary to a host of past investigations, if a correct accounting is made for the viscous effect of convection. For later generations, those with near solar metallicity, I find that this very same convection may excite gravity-mode oscillations that produce observable brightness variations at the stellar surface when the stars are near the main sequence. If confirmed with modern high-precision monitoring experiments, like Kepler and CoRoT, the properties of observed gravity modes in massive stars could provide a direct probe of the poorly constrained physics of gravity mode excitation by convection. Finally, jumping forward in stellar evolutionary time, I propose and explore an entirely new mechanism to explain the giant eruptions observed and inferred to occur during the final phases of massive stellar evolution. This mechanism taps into the vast nuclear fusion luminosity, and accompanying convective luminosity, in the stellar core to excite waves capable of carrying a super-Eddington luminosity out to the stellar envelope. This energy transfer from the core to the envelope has the potential to unbind a significant amount of mass in close proximity to a star's eventual explosion as a core collapse supernova.

Modules for Experiments in Stellar Astrophysics (MESA): Planets, Oscillations, Rotation, and Massive Stars

NASA Astrophysics Data System (ADS)

Paxton, Bill; Cantiello, Matteo; Arras, Phil; Bildsten, Lars; Brown, Edward F.; Dotter, Aaron; Mankovich, Christopher; Montgomery, M. H.; Stello, Dennis; Timmes, F. X.; Townsend, Richard

2013-09-01

We substantially update the capabilities of the open source software package Modules for Experiments in Stellar Astrophysics (MESA), and its one-dimensional stellar evolution module, MESA star. Improvements in MESA star's ability to model the evolution of giant planets now extends its applicability down to masses as low as one-tenth that of Jupiter. The dramatic improvement in asteroseismology enabled by the space-based Kepler and CoRoT missions motivates our full coupling of the ADIPLS adiabatic pulsation code with MESA star. This also motivates a numerical recasting of the Ledoux criterion that is more easily implemented when many nuclei are present at non-negligible abundances. This impacts the way in which MESA star calculates semi-convective and thermohaline mixing. We exhibit the evolution of 3-8 M ⊙ stars through the end of core He burning, the onset of He thermal pulses, and arrival on the white dwarf cooling sequence. We implement diffusion of angular momentum and chemical abundances that enable calculations of rotating-star models, which we compare thoroughly with earlier work. We introduce a new treatment of radiation-dominated envelopes that allows the uninterrupted evolution of massive stars to core collapse. This enables the generation of new sets of supernovae, long gamma-ray burst, and pair-instability progenitor models. We substantially modify the way in which MESA star solves the fully coupled stellar structure and composition equations, and we show how this has improved the scaling of MESA's calculational speed on multi-core processors. Updates to the modules for equation of state, opacity, nuclear reaction rates, and atmospheric boundary conditions are also provided. We describe the MESA Software Development Kit that packages all the required components needed to form a unified, maintained, and well-validated build environment for MESA. We also highlight a few tools developed by the community for rapid visualization of MESA star results.

Astrophysics with Presolar Stardust

NASA Astrophysics Data System (ADS)

Clayton, Donald D.; Nittler, Larry R.

2004-09-01

Meteorites and interplanetary dust particles contain presolar stardust grains: solid samples of stars that can be studied in the laboratory. The stellar origin of the grains is indicated by enormous isotopic ratio variations compared with Solar System materials, explainable only by nuclear reactions occurring in stars. Known presolar phases include diamond, SiC, graphite, Si3N4, Al2O3, MgAl2O4, CaAl12O19, TiO2, Mg(Cr,Al)2O4, and most recently, silicates. Subgrains of refractory carbides (e.g., TiC), and Fe-Ni metal have also been observed within individual presolar graphite grains. We review the astrophysical implications of these grains for the sciences of nucleosynthesis, stellar evolution, grain condensation, and the chemical and dynamic evolution of the Galaxy. Unique scientific information derives primarily from the high precision (in some cases <1%) of the measured isotopic ratios of large numbers of elements in single stardust grains. Stardust science is just now reaching maturity and will play an increasingly important role in nucleosynthesis applications.

On the Li and Be tests for brown dwarfs

NASA Technical Reports Server (NTRS)

Nelson, L. A.; Rappaport, S.; Chiang, E.

1993-01-01

We present the results of stellar evolution calculations which show quantitatively how the measured abundances of Li and Be in low-mass stellar objects can be used to discriminate between brown dwarfs and low-mass main-sequence stars. The evolution of B, although less useful, is also studied. We define a transition mass range, below which at least 50 percent of the light element remains at the end of nuclear burning, and above which no more than 10 percent remains. We find that the transition mass range for Li burning is 0.059-0.062 solar mass, while for Be the range is 0.075-0.077 solar mass. Using these results, we then examine the factors (e.g., age and luminosity) that affect our ability to identify low-luminosity objects as brown dwarfs. In particular, we show that the Li test would be well suited for brown dwarf candidates located in nearby open clusters with ages in the range of 2 x 10 exp 8 to 5 x 10 exp 8 yr.

Pre-supernova models for massive stars produced with large nuclear reaction network by MESA

NASA Astrophysics Data System (ADS)

Park, Byeongchan; Kwak, Kyujin

2018-04-01

Core-collapsed Supernova (CCSN) is one of violent phenomena in the universe. CCSN generates heavy elements and leaves a neutron star behind. It has been known that the physical properties of CCSN depend on those of pre-supernova such as mass, metallicities including distribution of elements, and the density and temperature profile which are obtained from the stellar evolution calculation. In particular, the production of heavy elements in CCSN is sensitive to the abundance profiles in the pre-supernova models. In this study, we evolve a massive main sequence star with 15Msun and solar metallicity to the pre-supernova stage by using two different networks, small and large. The large nuclear reaction network includes more than four times isotopes than the small network. Our calculations were done by MESA (Modules for Experiments in Stellar Astrophysics) which allowed us to use the large network containing about a hundred isotopes. We compare the results obtained with two networks.

Stellar Populations. A User Guide from Low to High Redshift

NASA Astrophysics Data System (ADS)

Greggio, Laura; Renzini, Alvio

2011-09-01

This textbook is meant to illustrate the specific role played by stellar population diagnostics in our attempt to understand galaxy formation and evolution. The book starts with a rather unconventional summary of the results of stellar evolution theory (Chapter 1), as they provide the basis for the construction of synthetic stellar populations. Current limitations of stellar models are highlighted, which arise from the necessity to parametrize all those physical processes that involve bulk mass motions, such as convection, mixing, mass loss, etc. Chapter 2 deals with the foundations of the theory of synthetic stellar populations, and illustrates their energetics and metabolic functions, providing basic tools that will be used in subsequent chapters. Chapters 3 and 4 deal with resolved stellar populations, first addressing some general problems encountered in photometric studies of stellar fields. Then some highlights are presented illustrating our current capacity of measuring stellar ages in Galactic globular clusters, in the Galactic bulge and in nearby galaxies. Chapter 5 is dedicated to the exemplification of synthetic spectra of simple as well as composite stellar populations, drawing attention to those spectral features that may depend on less secure results of stellar evolution models. Chapter 6 illustrates how synthetic stellar populations are used to derive basic galaxy properties, such as star formation rates, stellar masses, ages and metallicities, and does so for galaxies at low as well as at high redshifts. Chapter 7 is dedicated to supernovae, distinguishing them in core collapse and thermonuclear cases, describing the evolution of their rates for various star formation histories, and estimating the supernova productivity of stellar populations and their chemical yields. In Chapter 8 the stellar initial mass function (IMF) is discussed, first showing how even apparently small IMF variations may have large effects on the demo! graphy of stellar populations, and then using galaxies at low ! and high redshifts and clusters of galaxies to set tight constraints on possible IMF variations in space or time. In Chapter 9 a phenomenological model of galaxy evolution is presented which illustrates a concrete application of the stellar population tools described in the previous chapters. Finally, Chapter 10 is dedicated to the chemical evolution on the scale of galaxies, clusters of galaxies and the whole Universe.

Evolving R Coronae Borealis Stars with MESA

NASA Astrophysics Data System (ADS)

Clayton, Geoffrey C.; Lauer, Amber; Chatzopoulos, Emmanouil; Frank, Juhan

2018-01-01

R Coronae Borealis (RCB) stars form a small class of cool, carbon-rich supergiants that have almost no hydrogen. They undergo extreme, irregular declines in brightness of up to 8 magnitudes due to the formation of thick clouds of carbon dust. Two scenarios have been proposed for the origin of an RCB star: the merger of a CO/He white dwarf (WD) binary and a final helium-shell flash. We are using a combination of 3D hydrodynamics codes and the 1D MESA (Modules for Experiments in Stellar Astrophysics) stellar evolution code including nucleosynthesis to construct post-merger spherical models based on realistic merger progenitor models and on our hydrodynamical simulations, and then following the evolution into the region of the HR diagram where RCB stars are located. We are investigating nucleosynthesis in the dynamically accreting material of CO/He WD mergers which may provide a suitable environment for significant production of 18O and the very low 16O/18O values observed.Our MESA modeling consists of two steps: first mimicking the WD merger event using two different techniques, (a) by choosing a very high mass accretion rate with appropriate abundances and (b) by applying "stellar engineering" to an initial CO WD model to account for the newly merged material by applying an entropy adjusting procedure. Second, we follow the post-merger evolution using a large nuclear reaction network including the effects of convective and rotational instabilities to the mixing of material in order to match the observed RCB abundances. MESA follows the evolution of the merger product as it expands and cools to become an RCB star. We then examine the surface abundances and compare them to the observed RCB abundances. We also investigate how long fusion continues in the He shell near the core and how this processed material is mixed up to the surface of the star. We then model the later evolution of RCB stars to determine their likely lifetimes and endpoints when they have returned to being a WD. Solving the mystery of how the RCB stars evolve will lead to a better understanding of other important types of stellar merger events such as Type Ia SNe.

Direct measurements of astrophysically important α-induced reactions

NASA Astrophysics Data System (ADS)

Avila, Melina

2016-03-01

Understanding stellar evolution is one of the primary objectives of nuclear astrophysics. Reaction rates involving α-particles are often key nuclear physics inputs in stellar models. For instance, there are numerous (α , p) reactions fundamental for the understanding of X-ray bursts and the production of 44Ti in core-collapse supernovae. Furthermore, some (α , n) reactions are considered as one of the main neutron sources in the s-process. However, direct measurements of these reactions at relevant astrophysical energies are experimentally challenging because of their small cross section and intensity limitation of radioactive beams. The active target system MUSIC offers a unique opportunity to study (α , p) and (α , n) reactions because its segmented anode allows the investigation of a large energy range in the excitation function with a single measurement. Recent results on the direct measurement of (α , n) and (α , p) measurements in the MUSIC detector will be discussed. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, under Contract Number DE-AC02-06CH11357. This research used resources of ANL's ATLAS facility, which is a DOE Office of Science User.

Nuclear structure properties and stellar weak rates for 76Se: Unblocking of the Gamow Teller strength

NASA Astrophysics Data System (ADS)

Nabi, Jameel-Un; Ishfaq, Mavra; Böyükata, Mahmut; Riaz, Muhammad

2017-10-01

At finite temperatures (≥ 107K), 76Se is abundant in the core of massive stars and electron capture on 76Se has a consequential role to play in the dynamics of core-collapse. The present work may be classified into two main categories. In the first phase we study the nuclear structure properties of 76Se using the interacting boson model-1 (IBM-1). The IBM-1 investigations include the energy levels, B (E 2) values and the prediction of the geometry. We performed the extended consistent-Q formalism (ECQF) calculation and later the triaxial formalism calculation (constructed by adding the cubic term to the ECQF). The geometry of 76Se can be envisioned within the formalism of the potential energy surface based on the classical limit of IBM-1 model. In the second phase, we reconfirm the unblocking of the Gamow-Teller (GT) strength in 76Se (a test case for nuclei having N > 40 and Z < 40). Using the deformed pn-QRPA model we calculate GT transitions, stellar electron capture cross section (within the limit of low momentum transfer) and stellar weak rates for 76Se. The distinguishing feature of our calculation is a state-by-state evaluation of stellar weak rates in a fully microscopic fashion. Results are compared with experimental data and previous calculations. The calculated GT distribution fulfills the Ikeda sum rule. Rates for β-delayed neutrons and emission probabilities are also calculated. Our study suggests that at high stellar temperatures and low densities, the β+-decay on 76Se should not be neglected and needs to be taken into consideration along with electron capture rates for simulation of presupernova evolution of massive stars.

The Effects of Stellar Dynamics on the Evolution of Young, Dense Stellar Systems

NASA Astrophysics Data System (ADS)

Belkus, H.; van Bever, J.; Vanbeveren, D.

In this paper, we report on first results of a project in Brussels in which we study the effects of stellar dynamics on the evolution of young dense stellar systems using 3 decades of expertise in massive-star evolution and our population (number and spectral) synthesis code. We highlight an unconventionally formed object scenario (UFO-scenario) for Wolf Rayet binaries and study the effects of a luminous blue variable-type instability wind mass-loss formalism on the formation of intermediate-mass black holes.

Cluster galaxy population evolution from the Subaru Hyper Suprime-Cam survey: brightest cluster galaxies, stellar mass distribution, and active galaxies

NASA Astrophysics Data System (ADS)

Lin, Yen-Ting; Hsieh, Bau-Ching; Lin, Sheng-Chieh; Oguri, Masamune; Chen, Kai-Feng; Tanaka, Masayuki; Chiu, I.-non; Huang, Song; Kodama, Tadayuki; Leauthaud, Alexie; More, Surhud; Nishizawa, Atsushi J.; Bundy, Kevin; Lin, Lihwai; Miyazaki, Satoshi; HSC Collaboration

2018-01-01

The unprecedented depth and area surveyed by the Subaru Strategic Program with the Hyper Suprime-Cam (HSC-SSP) have enabled us to construct and publish the largest distant cluster sample out to z~1 to date. In this exploratory study of cluster galaxy evolution from z=1 to z=0.3, we investigate the stellar mass assembly history of brightest cluster galaxies (BCGs), and evolution of stellar mass and luminosity distributions, stellar mass surface density profile, as well as the population of radio galaxies. Our analysis is the first high redshift application of the top N richest cluster selection, which is shown to allow us to trace the cluster galaxy evolution faithfully. Our stellar mass is derived from a machine-learning algorithm, which we show to be unbiased and accurate with respect to the COSMOS data. We find very mild stellar mass growth in BCGs, and no evidence for evolution in both the total stellar mass-cluster mass correlation and the shape of the stellar mass surface density profile. The clusters are found to contain more red galaxies compared to the expectations from the field, even after the differences in density between the two environments have been taken into account. We also present the first measurement of the radio luminosity distribution in clusters out to z~1.

Evolution of the Stellar Mass–Metallicity Relation. I. Galaxies in the z ∼ 0.4 Cluster Cl0024

NASA Astrophysics Data System (ADS)

Leethochawalit, Nicha; Kirby, Evan N.; Moran, Sean M.; Ellis, Richard S.; Treu, Tommaso

2018-03-01

We present the stellar mass–stellar metallicity relationship (MZR) in the galaxy cluster Cl0024+1654 at z ∼ 0.4 using full-spectrum stellar population synthesis modeling of individual quiescent galaxies. The lower limit of our stellar mass range is M * = 109.7 M ⊙, the lowest galaxy mass at which individual stellar metallicity has been measured beyond the local universe. We report a detection of an evolution of the stellar MZR with observed redshift at 0.037 ± 0.007 dex per Gyr, consistent with the predictions from hydrodynamical simulations. Additionally, we find that the evolution of the stellar MZR with observed redshift can be explained by an evolution of the stellar MZR with the formation time of galaxies, i.e., when the single stellar population (SSP)-equivalent ages of galaxies are taken into account. This behavior is consistent with stars forming out of gas that also has an MZR with a normalization that decreases with redshift. Lastly, we find that over the observed mass range, the MZR can be described by a linear function with a shallow slope ([{Fe}/{{H}}]\\propto (0.16+/- 0.03){log}{M}* ). The slope suggests that galaxy feedback, in terms of mass-loading factor, might be mass-independent over the observed mass and redshift range.

Galactic evolution. I - Single-zone models. [encompassing stellar evolution and gas-star dynamic theories

NASA Technical Reports Server (NTRS)

Thuan, T. X.; Hart, M. H.; Ostriker, J. P.

1975-01-01

The two basic approaches of physical theory required to calculate the evolution of a galactic system are considered, taking into account stellar evolution theory and the dynamics of a gas-star system. Attention is given to intrinsic (stellar) physics, extrinsic (dynamical) physics, and computations concerning the fractionation of an initial mass of gas into stars. The characteristics of a 'standard' model and its variants are discussed along with the results obtained with the aid of these models.

Improving 1D Stellar Models with 3D Atmospheres

NASA Astrophysics Data System (ADS)

Mosumgaard, Jakob Rørsted; Silva Aguirre, Víctor; Weiss, Achim; Christensen-Dalsgaard, Jørgen; Trampedach, Regner

2017-10-01

Stellar evolution codes play a major role in present-day astrophysics, yet they share common issues. In this work we seek to remedy some of those by the use of results from realistic and highly detailed 3D hydrodynamical simulations of stellar atmospheres. We have implemented a new temperature stratification extracted directly from the 3D simulations into the Garching Stellar Evolution Code to replace the simplified atmosphere normally used. Secondly, we have implemented the use of a variable mixing-length parameter, which changes as a function of the stellar surface gravity and temperature - also derived from the 3D simulations. Furthermore, to make our models consistent, we have calculated new opacity tables to match the atmospheric simulations. Here, we present the modified code and initial results on stellar evolution using it.

The Cosmic Century

NASA Astrophysics Data System (ADS)

Longair, Malcolm S.

2013-04-01

Part I. Stars and Stellar Evolution up to the Second World War: 1. The legacy of the nineteenth century; 2. The classification of stellar spectra; 3. Stellar structure and evolution; 4. The end points of stellar evolution; Part II. The Large-Scale Structure of the Universe, 1900-1939: 5. The Galaxy and the nature of spiral nebulae; 6. The origins of astrophysical cosmology; Part III. The Opening up of the Electromagnetic Spectrum: 7. The opening up of the electromagnetic spectrum and the new astronomies; Part IV. The Astrophysics of Stars and Galaxies since 1945: 8. Stars and stellar evolution; 9. The physics of the interstellar medium; 10. The physics of galaxies and clusters of galaxies; 11. High-energy astrophysics; Part V. Astrophysical Cosmology since 1945: 12. Astrophysical cosmology; 13. The determination of cosmological parameters; 14. The evolution of galaxies and active galaxies with cosmic epoch; 15. The origin of galaxies and the large-scale structure of the Universe; 16. The very early Universe; References; Name index; Object index; Subject index.

Stellar models for a wide range of initial chemical compositions until helium burning IV. From X = 0.65 to X = 0.80, for Z = 0.004

NASA Astrophysics Data System (ADS)

Claret, A.; Gimenez, A.

1998-11-01

As a continuation of previous papers in a series devoted to the computation of stellar structure and evolution models we present a grid specifically obtained for detailed studies of the stellar content of the Small Magellanic Cloud. The initial metal content has thus been adopted to be Z = 0.004 while the hydrogen content varies from 0.65 to 0.80 leaving as an intermediate value that given by standard laws of enrichment, X = 0.744. Interpolation for different environment is therefore possible with these new models. Other input physics parameters, e.g. convective overshooting, mixing-length, opacities or nuclear reaction rates, have been adopted to be homogeneous with the previously published models in order to facilitate comparative studies. Tables 1-72 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html}

II Zw 40 - 30 Doradus on Steroids

NASA Astrophysics Data System (ADS)

Leitherer, Claus; Lee, Janice C.; Levesque, Emily M.

2017-11-01

We obtained HST COS G140L spectra of the enigmatic nearby blue compact dwarf galaxy II Zw 40. The galaxy hosts a nuclear super star cluster embedded in a radio-bright nebula, similar to those observed in the related blue compact dwarfs NGC 5253 and Henize 2-10. The ultraviolet spectrum of II Zw 40 is exceptional in terms of the strength of He II 1640, O III] 1666 and C III] 1909. We determined reddening, age, and the cluster mass from the ultraviolet data. The super nebula and the ionizing cluster exceed the ionizing luminosity and stellar mass of the local benchmark 30 Doradus by an order of magnitude. Comparison with stellar evolution models accounting for rotation reveals serious short-comings: these models do not account for the presence of Wolf-Rayet-like stars at young ages observed in II Zw 40. Photoionization modeling is used to probe the origin of the nebular lines and determine gas phase abundances. C/O is solar, in agreement with the result of the stellar-wind modeling.

Tidal dissipation in rotating low-mass stars and implications for the orbital evolution of close-in massive planets. II. Effect of stellar metallicity

NASA Astrophysics Data System (ADS)

Bolmont, E.; Gallet, F.; Mathis, S.; Charbonnel, C.; Amard, L.; Alibert, Y.

2017-08-01

Observations of hot-Jupiter exoplanets suggest that their orbital period distribution depends on the metallicity of the host stars. We investigate here whether the impact of the stellar metallicity on the evolution of the tidal dissipation inside the convective envelope of rotating stars and its resulting effect on the planetary migration might be a possible explanation for this observed statistical trend. We use a frequency-averaged tidal dissipation formalism coupled to an orbital evolution code and to rotating stellar evolution models in order to estimate the effect of a change of stellar metallicity on the evolution of close-in planets. We consider here two different stellar masses: 0.4 M⊙ and 1.0 M⊙ evolving from the early pre-main sequence phase up to the red-giant branch. We show that the metallicity of a star has a strong effect on the stellar parameters, which in turn strongly influence the tidal dissipation in the convective region. While on the pre-main sequence, the dissipation of a metal-poor Sun-like star is higher than the dissipation of a metal-rich Sun-like star; on the main sequence it is the opposite. However, for the 0.4 M⊙ star, the dependence of the dissipation with metallicity is much less visible. Using an orbital evolution model, we show that changing the metallicity leads to different orbital evolutions (e.g., planets migrate farther out from an initially fast-rotating metal-rich star). Using this model, we qualitatively reproduced the observational trends of the population of hot Jupiters with the metallicity of their host stars. However, more steps are needed to improve our model to try to quantitatively fit our results to the observations. Specifically, we need to improve the treatment of the rotation evolution in the orbital evolution model, and ultimately we need to consistently couple the orbital model to the stellar evolution model.

Testing stellar evolution models with detached eclipsing binaries

NASA Astrophysics Data System (ADS)

Higl, J.; Weiss, A.

2017-12-01

Stellar evolution codes, as all other numerical tools, need to be verified. One of the standard stellar objects that allow stringent tests of stellar evolution theory and models, are detached eclipsing binaries. We have used 19 such objects to test our stellar evolution code, in order to see whether standard methods and assumptions suffice to reproduce the observed global properties. In this paper we concentrate on three effects that contain a specific uncertainty: atomic diffusion as used for standard solar model calculations, overshooting from convective regions, and a simple model for the effect of stellar spots on stellar radius, which is one of the possible solutions for the radius problem of M dwarfs. We find that in general old systems need diffusion to allow for, or at least improve, an acceptable fit, and that systems with convective cores indeed need overshooting. Only one system (AI Phe) requires the absence of it for a successful fit. To match stellar radii for very low-mass stars, the spot model proved to be an effective approach, but depending on model details, requires a high percentage of the surface being covered by spots. We briefly discuss improvements needed to further reduce the freedom in modelling and to allow an even more restrictive test by using these objects.

Reevaluating Old Stellar Populations

NASA Astrophysics Data System (ADS)

Stanway, E. R.; Eldridge, J. J.

2018-05-01

Determining the properties of old stellar populations (those with age >1 Gyr) has long involved the comparison of their integrated light, either in the form of photometry or spectroscopic indexes, with empirical or synthetic templates. Here we reevaluate the properties of old stellar populations using a new set of stellar population synthesis models, designed to incorporate the effects of binary stellar evolution pathways as a function of stellar mass and age. We find that single-aged stellar population models incorporating binary stars, as well as new stellar evolution and atmosphere models, can reproduce the colours and spectral indices observed in both globular clusters and quiescent galaxies. The best fitting model populations are often younger than those derived from older spectral synthesis models, and may also lie at slightly higher metallicities.

Biological damage of UV radiation in environments of F-type stars

NASA Astrophysics Data System (ADS)

Sato, Satoko

I investigate the general astrobiological significance of F-type main-sequence stars with special consideration to stellar evolutionary aspects due to nuclear evolution. DNA is taken as a proxy for carbon-based macromolecules following the assumption that exobiology is most likely based on hydrocarbons. The DNA action spectrum is utilized to represent the relative damage of the stellar UV radiation. Planetary atmospheric attenuation is taken into account in the form of parameterized attenuation functions. My work is motivated by previous studies indicating that the UV environment of solar-like stars is one of the most critical elements in determining the habitability of exoplanets and exomoons. It contributes further to the exploration of the exobiological suitability of stars that are hotter and emit much higher photospheric UV fluxes than the Sun. I found that the damage inflicted on DNA for planets at Earth-equivalent positions is between 2.5 and 7.1 times higher than for solar-like stars, and there are intricate relations for the time-dependence of damage during stellar main-sequence evolution. If atmospheric attenuation is included, however, less damage is obtained in alignment to the attenuation parameters. Also, the outer part of late F-type stars have similar UV conditions to Earth. Therefore, F-type circumstellar environments should not be excluded from candidates for habitable places on the grounds of higher stellar UV emission than the Sun. Besides the extensive theoretical component of this study, emphasis is furthermore placed on applications to observed planetary systems including CoRoT-3, WASP-14, HD 197286, HD 179949, upsilon And, and HD 86264.

The planetary nebulae population in the nuclear regions of M31: the SAURON view

NASA Astrophysics Data System (ADS)

Pastorello, Nicola; Sarzi, Marc; Cappellari, Michele; Emsellem, Eric; Mamon, Gary A.; Bacon, Roland; Davies, Roger L.; de Zeeuw, P. Tim

2013-04-01

The study of extragalactic planetary nebulae (PNe) in the optical regions of galaxies, where the properties of their stellar population can be best characterized, is a promising ground to better understand the late evolution of stars across different galactic environments. Following a first study of the central regions of M32 that illustrated the power of integral field spectroscopy (IFS) in detecting and measuring the [O III] λ5007 emission of PNe against a strong stellar background, we turn to the very nuclear PN population of M31, within ˜80 pc of its centre. We show that PNe can also be found in the presence of emission from diffuse gas, as commonly observed in early-type galaxies and in the bulge of spirals, and further illustrate the excellent sensitivity of IFS in detecting extragalactic PNe through a comparison with narrow-band images obtained with the Hubble Space Telescope. Contrary to the case of the central regions of M32, the nuclear PNe population of M31 is only marginally consistent with the generally adopted form of the PNe luminosity function (PNLF). In particular, this is due to a lack of PNe with absolute magnitude M5007 brighter than -3, which would only result from a rather unfortunate draw from such a model PNLF. The nuclear stellar population of M31 is quite different from that of the central regions of M32, which is characterized in particular by a larger metallicity and a remarkable ultraviolet (UV) upturn. We suggest that the observed lack of bright PNe in the nuclear regions of M31 is due to a horizontal-branch population that is more tilted towards less massive and hotter He-burning stars, so that its progeny consists mostly of UV-bright stars that fail to climb back up the asymptotic giant branch (AGB) and only a few, if any, bright PNe powered by central post-AGB stars. These results are also consistent with recent reports on a dearth of bright post-AGB stars towards the nucleus of M31, and lend further support to the idea that the metallicity of a stellar population has an impact on the way the horizontal branch is populated and to the loose anticorrelation between the strength of the UV upturn and the specific number of PNe that is observed in early-type galaxies. Finally, our investigation also serves to stress the importance of considering the same spatial scales when comparing the PNe population of galaxies with the properties of their stellar populations.

Gamma-ray bursts appear simpler than expected?

NASA Astrophysics Data System (ADS)

Chardonnet, P.; Filina, A. A.; Popov, M. V.; Chechetkin, V. M.; Baranov, A. A.

The cosmic gamma-ray bursts are certainly an enigma in astrophysics. The "standard fireball" scenario developed during many years has provided a possible explanation of this phenomenon. The aim of this work is simply to explore a new possible interpretation by developing a coherent scenario inside the global picture of stellar evolution. At the basis of our scenario is the fact that maybe we have not fully understood how the core of a pair instability supernovae explode. In such a way, we have proposed a new paradigm assuming that the core of such massive star, instead of doing a symmetrical explosion, is completely fragmented in hot spots of burning nuclear matter. We have tested our scenario using some observational data like GRB spectrum, light curves, Amati relation and GRB-SN connection, and for each set of data we have proposed a possible physical interpretation. We have also suggested some possible tests of this scenario by measurement at high redshift. If this scenario is correct, it tells us simply that cosmic gamma-ray bursts are simply a missing link in stellar evolution.

Cosmic gamma-ray bursts from primordial stars: A new renaissance in astrophysics?

NASA Astrophysics Data System (ADS)

Chardonnet, Pascal; Filina, Anastasia; Chechetkin, Valery; Popov, Mikhail; Baranov, Andrey

2015-10-01

The cosmic gamma-ray bursts are certainly an enigma in astrophysics. The “standard fireball” scenario developed during many years has provided a possible explanation of this phenomena. The aim of this work is simply to explore a new possible interpretation by developing a coherent scenario inside the global picture of stellar evolution. At the basis of our scenario, is the fact that maybe we have not fully understood how the core of a pair instability supernova explodes. In such way, we have proposed a new paradigm assuming that the core of such massive star, instead of doing a symmetrical explosion, is completely fragmented in hot spots of burning nuclear matter. We have tested our scenario with observational data like GRB spectra, lightcurves, Amati relation and GRB-SN connection, and for each set of data we have proposed a possible physical interpretation. We have also suggested some possible test of this scenario by measurement at high redshifts. If this scenario is correct, it tells us simply that the cosmic gamma-ray bursts are a missing link in stellar evolution, related to an unusual explosion.

Stellar structure and compact objects before 1940: Towards relativistic astrophysics

NASA Astrophysics Data System (ADS)

Bonolis, Luisa

2017-06-01

Since the mid-1920s, different strands of research used stars as "physics laboratories" for investigating the nature of matter under extreme densities and pressures, impossible to realize on Earth. To trace this process this paper is following the evolution of the concept of a dense core in stars, which was important both for an understanding of stellar evolution and as a testing ground for the fast-evolving field of nuclear physics. In spite of the divide between physicists and astrophysicists, some key actors working in the cross-fertilized soil of overlapping but different scientific cultures formulated models and tentative theories that gradually evolved into more realistic and structured astrophysical objects. These investigations culminated in the first contact with general relativity in 1939, when J. Robert Oppenheimer and his students George Volkoff and Hartland Snyder systematically applied the theory to the dense core of a collapsing neutron star. This pioneering application of Einstein's theory to an astrophysical compact object can be regarded as a milestone in the path eventually leading to the emergence of relativistic astrophysics in the early 1960s.

Direct measurement of nuclear cross-section of astrophysical interest: Results and perspectives

NASA Astrophysics Data System (ADS)

Cavanna, Francesca; Prati, Paolo

2018-03-01

Stellar evolution and nucleosynthesis are interconnected by a wide network of nuclear reactions: the study of such connection is usually known as nuclear astrophysics. The main task of this discipline is the determination of nuclear cross-section and hence of the reaction rate in different scenarios, i.e. from the synthesis of a few very light isotopes just after the Big Bang to the heavy element production in the violent explosive end of massive stars. The experimental determination of reaction cross-section at the astrophysical relevant energies is extremely difficult, sometime impossible, due to the Coulomb repulsion between the interacting nuclei which turns out in cross-section values down to the fbar level. To overcome these obstacles, several experimental approaches have been developed and the adopted techniques can be roughly divided into two categories, i.e. direct and indirect methods. In this review paper, the general problem of nuclear astrophysics is introduced and discussed from the point of view of experimental approach. We focus on direct methods and in particular on the features of low-background experiments performed at underground laboratory facilities. The present knowledge of reactions involved in the Big Bang and stellar hydrogen-burning scenarios is discussed as well as the ongoing projects aiming to investigate mainly the helium- and carbon-burning phases. Worldwide, a new generation of experiment in the MeV range is in the design phase or at the very first steps and decisive progresses are expected to come in the next years.

The History and Impact of the CNO Cycles in Nuclear Astrophysics

NASA Astrophysics Data System (ADS)

Wiescher, Michael

2018-03-01

The carbon cycle, or Bethe-Weizsäcker cycle, plays an important role in astrophysics as one of the most important energy sources for quiescent and explosive hydrogen burning in stars. This paper presents the intellectual and historical background of the idea of the correlation between stellar energy production and the synthesis of the chemical elements in stars on the example of this cycle. In particular, it addresses the contributions of Carl Friedrich von Weizsäcker and Hans Bethe, who provided the first predictions of the carbon cycle. Further, the experimental verification of the predicted process as it developed over the following decades is discussed, as well as the extension of the initial carbon cycle to the carbon-nitrogen-oxygen (CNO) multi-cycles and the hot CNO cycles. This development emerged from the detailed experimental studies of the associated nuclear reactions over more than seven decades. Finally, the impact of the experimental and theoretical results on our present understanding of hydrogen burning in different stellar environments is presented, as well as the impact on our understanding of the chemical evolution of our universe.

Resonant Proton Capture on Sodium-23 and Elemental Variations in Globular Cluster Stars

NASA Astrophysics Data System (ADS)

Cesaratto, John Michael

Globular clusters represent some of the oldest stellar bodies in the universe. As such, they are used as testing grounds for theories of stellar evolution and nucleosynthesis. Astronomical observations have shown star-to-star abundance variation in light-mass elements in all Galactic globular clusters. Standard stellar evolution models do not predict these variations. For instance, there exists a pronounced anticorrelation between Na and O in the cluster stars that is not observed in similar, isolated field stars. The current explanations for these observations are that a preexisting massive star could have polluted the interstellar medium where a younger star was born, or that stars undergo some additional mixing beyond dredge-up. Theoreticians rely on nuclear physics input in the form of thermonuclear reaction rates to edit or propose new theories predicting these abundance anomalies. The 23Na + p reaction is a bridge between the NeNa cycle and the MgAl cycle, but large uncertainties exist in the 23Na(p, gamma)24Mg reaction rate for burning temperatures relevant to red giant branch and asymptotic giant branch stars. The uncertainties arise from an expected, but unobserved resonance at Ecmr = 138 keV. A new high-intensity, low-energy electron cyclotron resonance (ECR) ion source at the Laboratory for Experimental Nuclear Astrophysics (LENA) has increased sensitivity for measuring this reaction. After many attempts and long measurement periods, a marginal signal (90% confidence level) has been observed from the resonance and a new strength has been established. This new strength marks a factor of 70 reduction from the previous strength upper limit. The strength has also been calculated as an upper limit at 95% confidence level. New reaction rates have been calculated for the 23Na(p, gamma)24Mg and 23 Na(p, alpha)20Ne reactions and the recommended value for the 23Na(p, gamma) 24Mg rate has been reduced by over an order of magnitude at T 9 = 0.07. This will have implications for the processing of material between the NeNa and MgAl cycles in stellar models.

Observing Stellar Clusters in the Computer

NASA Astrophysics Data System (ADS)

Borch, A.; Spurzem, R.; Hurley, J.

2006-08-01

We present a new approach to combine direct N-body simulations to stellar population synthesis modeling in order to model the dynamical evolution and color evolution of globular clusters at the same time. This allows us to model the spectrum, colors and luminosities of each star in the simulated cluster. For this purpose the NBODY6++ code (Spurzem 1999) is used, which is a parallel version of the NBODY code. J. Hurley implemented simple recipes to follow the changes of stellar masses, radii, and luminosities due to stellar evolution into the NBODY6++ code (Hurley et al. 2001), in the sense that each simulation particle represents one star. These prescriptions cover all evolutionary phases and solar to globular cluster metallicities. We used the stellar parameters obtained by this stellar evolution routine and coupled them to the stellar library BaSeL 2.0 (Lejeune et al. 1997). As a first application we investigated the integrated broad band colors of simulated clusters. We modeled tidally disrupted globular clusters and compared the results with isolated globular clusters. Due to energy equipartition we expected a relative blueing of tidally disrupted clusters, because of the higher escape probability of red, low-mass stars. This behaviour we actually observe for concentrated globular clusters. The mass-to-light ratio of isolated clusters follows exactly a color-M/L correlation, similar as described in Bell and de Jong (2001) in the case of spiral galaxies. At variance to this correlation, in tidally disrupted clusters the M/L ratio becomes significantly lower at the time of cluster dissolution. Hence, for isolated clusters the behavior of the stellar population is not influenced by dynamical evolution, whereas the stellar population of tidally disrupted clusters is strongly influenced by dynamical effects.

A new technique for calculations of binary stellar evolution, with application to magnetic braking

NASA Technical Reports Server (NTRS)

Rappaport, S.; Joss, P. C.; Verbunt, F.

1983-01-01

The development of appropriate computer programs has made it possible to conduct studies of stellar evolution which are more detailed and accurate than the investigations previously feasible. However, the use of such programs can also entail some serious drawbacks which are related to the time and expense required for the work. One approach for overcoming these drawbacks involves the employment of simplified stellar evolution codes which incorporate the essential physics of the problem of interest without attempting either great generality or maximal accuracy. Rappaport et al. (1982) have developed a simplified code to study the evolution of close binary stellar systems composed of a collapsed object and a low-mass secondary. The present investigation is concerned with a more general, but still simplified, technique for calculating the evolution of close binary systems with collapsed binaries and mass-losing secondaries.

Habitable Zone Evolution

NASA Astrophysics Data System (ADS)

Waltham, D.; Lota, J.

2012-12-01

The location of the habitable zone around a star depends upon stellar luminosity and upon the properties of a potentially habitable planet such as its mass and near-surface volatile inventory. Stellar luminosity generally increases as a star ages whilst planetary properties change through time as a consequence of biological and geological evolution. Hence, the location of the habitable zone changes through time as a result of both stellar evolution and planetary evolution. Using the Earth's Phanerozoic temperature history as a constraint, it is shown that changes in our own habitable zone over the last 540 My have been dominated by planetary evolution rather than solar evolution. Furthermore, sparse data from earlier times suggests that planetary evolution may have dominated habitable zone development throughout our biosphere's history. Hence, the existence of a continuously habitable zone depends upon accidents of complex bio-geochemical evolution more than it does upon relatively simple stellar-evolution. Evolution of the inner margin of the habitable zone through time using three different estimates for climate sensitivity. The dashed line shows a typical predicted evolution assuming this was driven simply by a steady increase in solar luminosity. Solar evolution does not account for the observations. Evolution of the outer margin of the habitable zone through time using three different estimates for climate sensitivity. The dashed line shows a typical predicted evolution assuming this was driven simply by a steady increase in solar luminosity. Solar evolution does not account for the observations.

LINER galaxy properties and the local environment

NASA Astrophysics Data System (ADS)

Coldwell, Georgina V.; Alonso, Sol; Duplancic, Fernanda; Mesa, Valeria

2018-05-01

We analyse the properties of a sample of 5560 low-ionization nuclear emission-line region (LINER) galaxies selected from SDSS-DR12 at low red shift, for a complete range of local density environments. The host LINER galaxies were studied and compared with a well-defined control sample of 5553 non-LINER galaxies matched in red shift, luminosity, morphology and local density. By studying the distributions of galaxy colours and the stellar age population, we find that LINERs are redder and older than the control sample over a wide range of densities. In addition, LINERs are older than the control sample, at a given galaxy colour, indicating that some external process could have accelerated the evolution of the stellar population. The analysis of the host properties shows that the control sample exhibits a strong relation between colours, ages and the local density, while more than 90 per cent of the LINERs are redder and older than the mean values, independently of the neighbourhood density. Furthermore, a detailed study in three local density ranges shows that, while control sample galaxies are redder and older as a function of stellar mass and density, LINER galaxies mismatch the known morphology-density relation of galaxies without low-ionization features. The results support the contribution of hot and old stars to the low-ionization emission although the contribution of nuclear activity is not discarded.

Modelling the molecular composition and nuclear-spin chemistryof collapsing pre-stellar sources

NASA Astrophysics Data System (ADS)

Hily-Blant, P.; Faure, A.; Rist, C.; Pineau des Forêts, G.; Flower, D. R.

2018-07-01

We study the gravitational collapse of pre-stellar sources and the associated evolution of their chemical composition. We use the University of Grenoble Alpes Astrochemical Network (UGAN), which includes reactions involving the different nuclear-spin states of H2, H_3^+, and of the hydrides of carbon, nitrogen, oxygen, and sulphur, for reactions involving up to seven protons. In addition, species-to-species rate coefficients are provided for the ortho/para interconversion of the H_3^+ + H2 system and isotopic variants. The composition of the medium is followed from an initial steady state through the early phase of isothermal gravitational collapse. Both the freeze-out of the molecules on to grains and the coagulation of the grains were incorporated in the model. The predicted abundances and column densities of the spin isomers of ammonia and its deuterated forms are compared with those measured recently towards the pre-stellar cores H-MM1, L16293E, and Barnard B1. We find that gas-phase processes alone account satisfactorily for the observations, without recourse to grain-surface reactions. In particular, our model reproduces both the isotopologue abundance ratios and the ortho:para ratios of NH2D and NHD2 within observational uncertainties. More accurate observations are necessary to distinguish between full scrambling processes - as assumed in our gas-phase network - and direct nucleus- or atom-exchange reactions.

Advancing Nucleosynthesis in Core-Collapse Supernovae Models Using 2D CHIMERA Simulations

NASA Astrophysics Data System (ADS)

Harris, J. A.; Hix, W. R.; Chertkow, M. A.; Bruenn, S. W.; Lentz, E. J.; Messer, O. B.; Mezzacappa, A.; Blondin, J. M.; Marronetti, P.; Yakunin, K.

2014-01-01

The deaths of massive stars as core-collapse supernovae (CCSN) serve as a crucial link in understanding galactic chemical evolution since the birth of the universe via the Big Bang. We investigate CCSN in polar axisymmetric simulations using the multidimensional radiation hydrodynamics code CHIMERA. Computational costs have traditionally constrained the evolution of the nuclear composition in CCSN models to, at best, a 14-species α-network. However, the limited capacity of the α-network to accurately evolve detailed composition, the neutronization and the nuclear energy generation rate has fettered the ability of prior CCSN simulations to accurately reproduce the chemical abundances and energy distributions as known from observations. These deficits can be partially ameliorated by "post-processing" with a more realistic network. Lagrangian tracer particles placed throughout the star record the temporal evolution of the initial simulation and enable the extension of the nuclear network evolution by incorporating larger systems in post-processing nucleosynthesis calculations. We present post-processing results of the four ab initio axisymmetric CCSN 2D models of Bruenn et al. (2013) evolved with the smaller α-network, and initiated from stellar metallicity, non-rotating progenitors of mass 12, 15, 20, and 25 M⊙ from Woosley & Heger (2007). As a test of the limitations of post-processing, we provide preliminary results from an ongoing simulation of the 15 M⊙ model evolved with a realistic 150 species nuclear reaction network in situ. With more accurate energy generation rates and an improved determination of the thermodynamic trajectories of the tracer particles, we can better unravel the complicated multidimensional "mass-cut" in CCSN simulations and probe for less energetically significant nuclear processes like the νp-process and the r-process, which require still larger networks.

Constraints on the Evolution of the Galaxy Stellar Mass Function I: Role of Star Formation, Mergers, and Stellar Stripping

NASA Astrophysics Data System (ADS)

Contini, E.; Kang, Xi; Romeo, A. D.; Xia, Q.

2017-03-01

We study the connection between the observed star formation rate-stellar mass (SFR-M *) relation and the evolution of the stellar mass function (SMF) by means of a subhalo abundance matching technique coupled to merger trees extracted from an N-body simulation. Our approach, which considers both galaxy mergers and stellar stripping, is to force the model to match the observed SMF at redshift z> 2, and let it evolve down to the present time according to the observed SFR-M * relation. In this study, we use two different sets of SMFs and two SFR-M * relations: a simple power law and a relation with a mass-dependent slope. Our analysis shows that the evolution of the SMF is more consistent with an SFR-M * relation with a mass-dependent slope, in agreement with predictions from other models of galaxy evolution and recent observations. In order to fully and realistically describe the evolution of the SMF, both mergers and stellar stripping must be considered, and we find that both have almost equal effects on the evolution of SMF at the massive end. Taking into account the systematic uncertainties in the observed data, the high-mass end of the SMF obtained by considering stellar stripping results in good agreement with recent observational data from the Sloan Digital Sky Survey. At {log} {M}* < 11.2, our prediction at z = 0.1 is close to Li & White data, but the high-mass end ({log} {M}* > 11.2) is in better agreement with D’Souza et al. data which account for more massive galaxies.

DISCOVERY OF RR LYRAE STARS IN THE NUCLEAR BULGE OF THE MILKY WAY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Minniti, Dante; Ramos, Rodrigo Contreras; Zoccali, Manuela

Galactic nuclei, such as that of the Milky Way, are extreme regions with high stellar densities, and in most cases, the hosts of a supermassive black hole. One of the scenarios proposed for the formation of the Galactic nucleus is merging of primordial globular clusters. An implication of this model is that this region should host stars that are characteristically found in old Milky Way globular clusters. RR Lyrae stars are primary distance indicators, well known representatives of old and metal-poor stellar populations, and therefore are regularly found in globular clusters. Here we report the discovery of a dozen RRmore » Lyrae type ab stars in the vicinity of the Galactic center, i.e., in the so-called nuclear stellar bulge of the Milky Way. This discovery provides the first direct observational evidence that the Galactic nuclear stellar bulge contains ancient stars (>10 Gyr old). Based on this we conclude that merging globular clusters likely contributed to the build-up of the high stellar density in the nuclear stellar bulge of the Milky Way.« less

VizieR Online Data Catalog: Evolution of rotating very massive LC stars (Kohler, 2015)

NASA Astrophysics Data System (ADS)

Kohler, K.; Langer, N.; de Koter, A.; de Mink, S. E.; Crowther, P. A.; Evans, C. J.; Grafener, G.; Sana, H.; Sanyal, D.; Schneider, F. R. N.; Vink, J. S.

2014-11-01

A dense model grid with chemical composition appropriate for the Large Magellanic Cloud is presented. A one-dimensional hydrodynamic stellar evolution code was used to compute our models on the main sequence, taking into account rotation, transport of angular momentum by magnetic fields and stellar wind mass loss. We present stellar evolution models with initial masses of 70-500M⊙ and with initial surface rotational velocities of 0-550km/s. (2 data files).

Origin of the Elements

NASA Astrophysics Data System (ADS)

Truran, J. W., Jr.; Heger, A.

2003-12-01

Nucleosynthesis is the study of the nuclear processes responsible for the formation of the elements which constitute the baryonic matter of the Universe. The elements of which the Universe is composed indeed have a quite complicated nucleosynthesis history, which extends from the first three minutes of the Big Bang through to the present. Contemporary nucleosynthesis theory associates the production of certain elements/isotopes or groups of elements with a number of specific astrophysical settings, the most significant of which are: (i) the cosmological Big Bang, (ii) stars, and (iii) supernovae.Cosmological nucleosynthesis studies predict that the conditions characterizing the Big Bang are consistent with the synthesis only of the lightest elements: 1H, 2H, 3He, 4He, and 7Li (Burles et al., 2001; Cyburt et al., 2002). These contributions define the primordial compositions both of galaxies and of the first stars formed therein. Within galaxies, stars and supernovae play the dominant role both in synthesizing the elements from carbon to uranium and in returning heavy-element-enriched matter to the interstellar gas from which new stars are formed. The mass fraction of our solar system (formed ˜4.6 Gyr ago) in the form of heavy elements is ˜1.8%, and stars formed today in our galaxy can be a factor 2 or 3 more enriched (Edvardsson et al., 1993). It is the processes of nucleosynthesis operating in stars and supernovae that we will review in this chapter. We will confine our attention to three broad categories of stellar and supernova site with which specific nucleosynthesis products are understood to be identified: (i) intermediate mass stars, (ii) massive stars and associated type II supernovae, and (iii) type Ia supernovae. The first two of these sites are the straightforward consequence of the evolution of single stars, while type Ia supernovae are understood to result from binary stellar evolution.Stellar nucleosynthesis resulting from the evolution of single stars is a strong function of stellar mass (Woosley et al., 2002). Following phases of hydrogen and helium burning, all stars consist of a carbon-oxygen core. In the mass range of the so-called "intermediate mass" stars (1<˜M/M⊙<˜10), the temperatures realized in their degenerate cores never reach levels at which carbon ignition can occur. Substantial element production occurs in such stars during the asymptotic giant branch (AGB) phase of evolution, accompanied by significant mass loss, and they evolve to white dwarfs of carbon-oxygen (or, less commonly, oxygen-neon) composition. In contrast, the increased pressures that are experienced in the cores of stars of masses M>˜10M⊙ yield higher core temperatures that enable subsequent phases of carbon, neon, oxygen, and silicon burning to proceed. Collapse of an iron core devoid of further nuclear energy then gives rise to a type II supernova and the formation of a neutron star or black hole remnant (Heger et al., 2003). The ejecta of type IIs contain the ashes of nuclear burning of the entire life of the star, but are also modified by the explosion itself. They are the source of most material (by mass) heavier than helium.Observations reveal that binary stellar systems comprise roughly half of all stars in our galaxy. Single star evolution, as noted above, can leave in its wake compact stellar remnants: white dwarfs, neutron stars, and black holes. Indeed, we have evidence for the occurrence of all three types of condensed remnant in binaries. In close binary systems, mass transfer can take place from an evolving companion onto a compact object. This naturally gives rise to a variety of interesting phenomena: classical novae (involving hydrogen thermonuclear runaways in accreted shells on white dwarfs (Gehrz et al., 1998)), X-ray bursts (hydrogen/helium thermonuclear runaways on neutron stars (Strohmayer and Bildsten, 2003)), and X-ray binaries (accretion onto black holes). For some range of conditions, accretion onto carbon-oxygen white dwarfs will permit growth of the CO core to the Chandrasekhar limit MCh=1.4M⊙, and a thermonuclear runaway in to core leads to a type Ia supernova.In this chapter, we will review the characteristics of thermonuclear processing in the three environments we have identified: (i) intermediate-mass stars; (ii) massive stars and type II supernovae; and (iii) type Ia supernovae. This will be followed by a brief discussion of galactic chemical evolution, which illustrates how the contributions from each of these environments are first introduced into the interstellar media of galaxies. Reviews of nucleosynthesis processes include those by Arnett (1995), Trimble (1975), Truran (1984), Wallerstein et al. (1997), and Woosley et al. (2002). An overview of galactic chemical evolution is presented by Tinsley (1980).

A large oxygen-dominated core from the seismic cartography of a pulsating white dwarf

NASA Astrophysics Data System (ADS)

Giammichele, N.; Charpinet, S.; Fontaine, G.; Brassard, P.; Green, E. M.; Van Grootel, V.; Bergeron, P.; Zong, W.; Dupret, M.-A.

2018-02-01

White-dwarf stars are the end product of stellar evolution for most stars in the Universe. Their interiors bear the imprint of fundamental mechanisms that occur during stellar evolution. Moreover, they are important chronometers for dating galactic stellar populations, and their mergers with other white dwarfs now appear to be responsible for producing the type Ia supernovae that are used as standard cosmological candles. However, the internal structure of white-dwarf stars—in particular their oxygen content and the stratification of their cores—is still poorly known, because of remaining uncertainties in the physics involved in stellar modelling codes. Here we report a measurement of the radial chemical stratification (of oxygen, carbon and helium) in the hydrogen-deficient white-dwarf star KIC08626021 (J192904.6+444708), independently of stellar-evolution calculations. We use archival data coupled with asteroseismic sounding techniques to determine the internal constitution of this star. We find that the oxygen content and extent of its core exceed the predictions of existing models of stellar evolution. The central homogeneous core has a mass of 0.45 solar masses, and is composed of about 86 per cent oxygen by mass. These values are respectively 40 per cent and 15 per cent greater than those expected from typical white-dwarf models. These findings challenge present theories of stellar evolution and their constitutive physics, and open up an avenue for calibrating white-dwarf cosmochronology.

A large oxygen-dominated core from the seismic cartography of a pulsating white dwarf.

PubMed

Giammichele, N; Charpinet, S; Fontaine, G; Brassard, P; Green, E M; Van Grootel, V; Bergeron, P; Zong, W; Dupret, M-A

2018-02-01

White-dwarf stars are the end product of stellar evolution for most stars in the Universe. Their interiors bear the imprint of fundamental mechanisms that occur during stellar evolution. Moreover, they are important chronometers for dating galactic stellar populations, and their mergers with other white dwarfs now appear to be responsible for producing the type Ia supernovae that are used as standard cosmological candles. However, the internal structure of white-dwarf stars-in particular their oxygen content and the stratification of their cores-is still poorly known, because of remaining uncertainties in the physics involved in stellar modelling codes. Here we report a measurement of the radial chemical stratification (of oxygen, carbon and helium) in the hydrogen-deficient white-dwarf star KIC08626021 (J192904.6+444708), independently of stellar-evolution calculations. We use archival data coupled with asteroseismic sounding techniques to determine the internal constitution of this star. We find that the oxygen content and extent of its core exceed the predictions of existing models of stellar evolution. The central homogeneous core has a mass of 0.45 solar masses, and is composed of about 86 per cent oxygen by mass. These values are respectively 40 per cent and 15 per cent greater than those expected from typical white-dwarf models. These findings challenge present theories of stellar evolution and their constitutive physics, and open up an avenue for calibrating white-dwarf cosmochronology.

Organic compounds in circumstellar and interstellar environments.

PubMed

Kwok, Sun

2015-06-01

Recent research has discovered that complex organic matter is prevalent throughout the Universe. In the Solar System, it is found in meteorites, comets, interplanetary dust particles, and planetary satellites. Spectroscopic signatures of organics with aromatic/aliphatic structures are also found in stellar ejecta, diffuse interstellar medium, and external galaxies. From space infrared spectroscopic observations, we have found that complex organics can be synthesized in the late stages of stellar evolution. Shortly after the nuclear synthesis of the element carbon, organic gas-phase molecules are formed in the stellar winds, which later condense into solid organic particles. This organic synthesis occurs over very short time scales of about a thousand years. In order to determine the chemical structures of these stellar organics, comparisons are made with particles produced in the laboratory. Using the technique of chemical vapor deposition, artificial organic particles have been created by injecting energy into gas-phase hydrocarbon molecules. These comparisons led us to believe that the stellar organics are best described as amorphous carbonaceous nanoparticles with mixed aromatic and aliphatic components. The chemical structures of the stellar organics show strong similarity to the insoluble organic matter found in meteorites. Isotopic analysis of meteorites and interplanetary dust collected in the upper atmospheres have revealed the presence of pre-solar grains similar to those formed in old stars. This provides a direct link between star dust and the Solar System and raises the possibility that the early Solar System was chemically enriched by stellar ejecta with the potential of influencing the origin of life on Earth.

Impact of pairing on clustering and neutrino transport properties in low-density stellar matter

NASA Astrophysics Data System (ADS)

Burrello, S.; Colonna, M.; Matera, F.

2017-11-01

We analyze the effects of pairing correlations on the behavior of stellar matter, focusing on thermodynamical conditions close to the onset of the liquid-gas phase transition, which are characterized by quite large density fluctuations and where clustering phenomena occur. We concentrate on the neutrino transport properties and we show, within a thermodynamical treatment, that at moderate temperatures, where pairing effects are still active, the scattering of neutrinos in the nuclear medium is significantly affected by the matter superfluidity. The pairing correlations can indeed enhance neutrino trapping and reduce the energy flux carried out by neutrino emission. New hints about an important impact of pairing on the cooling mechanism, by neutrino emission, are so envisaged and therefore this study could be of relevant interest for the evolution of proto-neutron stars and in modelization of supernova explosions.

Posters also presented at the Symposium

NASA Astrophysics Data System (ADS)

Eldridge, J. J.; Bray, J. C.; McClelland, L. A. S.; Xiao, L.

2017-11-01

I am reporting on our team's progress in investigating fundamental properties of convective shells in the deep stellar interior during advanced stages of stellar evolution. We have performed a series of 3D hydrodynamic simulations of convection in conditions similar to those in the O-shell burning phase of massive stars. We focus on characterizing the convective boundary and the mixing of material across this boundary. Results from 7683 and 15363 grids are encouragingly similar (typically within 20%). Several global quantities, including the rate of mass entrainment at the convective boundary and the driving luminosity, are related by scaling laws. We investigate the effect of several of our assumptions, including the treatment of the nuclear burning driving the convection or that of neutrino cooling. The burning of the entrained material from above the convection zone could have important implications for pre-supernova nucleosynthesis.

The next generation of galaxy evolution models: A symbiosis of stellar populations and chemical abundances

NASA Astrophysics Data System (ADS)

Kotulla, Ralf

2012-10-01

Over its lifespan Hubble has invested significant effort into detailed observations of galaxies both in the local and distant universe. To extract the physical information from the observed {spectro-}photometry requires detailed and accurate models. Stellar population synthesis models are frequently used to obtain stellar masses, star formation rate, galaxy ages and star formation histories. Chemical evolution models offer another valuable and complementary approach to gain insight into many of the same aspects, yet these two methods have rarely been used in combination.Our proposed next generation of galaxy evolution models will help us improve our understanding of how galaxies form and evolve. Building on GALEV evolutionary synthesis models we incorporate state-of-the-art input physics for stellar evolution of binaries and rotating stars as well as new spectral libraries well matched to the modern observational capabilities. Our improved chemical evolution model allows us to self-consistently trace abundances of individual elements, fully accounting for the increasing initial abundances of successive stellar generations. GALEV will support variable Initial Mass Functions {IMF}, enabling us to test recent observational findings of a non-universal IMF by predicting chemical properties and integrated spectra in an integrated and consistent manner.HST is the perfect instrument for testing this approach. Its wide wavelength coverage from UV to NIR enables precise SED fitting, and with its spatial resolution we can compare the inferred chemical evolution to studies of star clusters and resolved stellar populations in nearby galaxies.

POET: A Model for Planetary Orbital Evolution Due to Tides on Evolving Stars

NASA Astrophysics Data System (ADS)

Penev, Kaloyan; Zhang, Michael; Jackson, Brian

2014-06-01

We make publicly available an efficient, versatile, easy to use and extend tool for calculating the evolution of circular aligned planetary orbits due to the tidal dissipation in the host star. This is the first model to fully account for the evolution of the angular momentum of the stellar convective envelope by the tidal coupling, the transfer of angular momentum between the stellar convective and radiative zones, the effects of the stellar evolution on the tidal dissipation efficiency and stellar core and envelope spins, the loss of stellar convective zone angular momentum to a magnetically launched wind and frequency dependent tidal dissipation. This is only a first release and further development is under way to allow calculating the evolution of inclined and eccentric orbits, with the latter including the tidal dissipation in the planet and its feedback on planetary structure. Considerable effort has been devoted to providing extensive documentation detailing both the usage and the complete implementation details, in order to make it as easy as possible for independent groups to use and/or extend the code for their purposes. POET represents a significant improvement over some previous models for planetary tidal evolution and so has many astrophysical applications. In this article, we describe and illustrate several key examples.

The universal relation of galactic chemical evolution: the origin of the mass-metallicity relation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zahid, H. Jabran; Dima, Gabriel I.; Kudritzki, Rolf-Peter

2014-08-20

We examine the mass-metallicity relation for z ≲ 1.6. The mass-metallicity relation follows a steep slope with a turnover, or 'knee', at stellar masses around 10{sup 10} M {sub ☉}. At stellar masses higher than the characteristic turnover mass, the mass-metallicity relation flattens as metallicities begin to saturate. We show that the redshift evolution of the mass-metallicity relation depends only on the evolution of the characteristic turnover mass. The relationship between metallicity and the stellar mass normalized to the characteristic turnover mass is independent of redshift. We find that the redshift-independent slope of the mass-metallicity relation is set by themore » slope of the relationship between gas mass and stellar mass. The turnover in the mass-metallicity relation occurs when the gas-phase oxygen abundance is high enough that the amount of oxygen locked up in low-mass stars is an appreciable fraction of the amount of oxygen produced by massive stars. The characteristic turnover mass is the stellar mass, where the stellar-to-gas mass ratio is unity. Numerical modeling suggests that the relationship between metallicity and the stellar-to-gas mass ratio is a redshift-independent, universal relationship followed by all galaxies as they evolve. The mass-metallicity relation originates from this more fundamental universal relationship between metallicity and the stellar-to-gas mass ratio. We test the validity of this universal metallicity relation in local galaxies where stellar mass, metallicity, and gas mass measurements are available. The data are consistent with a universal metallicity relation. We derive an equation for estimating the hydrogen gas mass from measurements of stellar mass and metallicity valid for z ≲ 1.6 and predict the cosmological evolution of galactic gas masses.« less

TRACING THE EVOLUTION OF HIGH-REDSHIFT GALAXIES USING STELLAR ABUNDANCES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Crosby, Brian D.; O’Shea, Brian W.; Beers, Timothy C.

2016-03-20

This paper presents the first results from a model for chemical evolution that can be applied to N-body cosmological simulations and quantitatively compared to measured stellar abundances from large astronomical surveys. This model convolves the chemical yield sets from a range of stellar nucleosynthesis calculations (including asymptotic giant branch stars, Type Ia and II supernovae, and stellar wind models) with a user-specified stellar initial mass function (IMF) and metallicity to calculate the time-dependent chemical evolution model for a “simple stellar population” (SSP) of uniform metallicity and formation time. These SSP models are combined with a semianalytic model for galaxy formation andmore » evolution that uses merger trees from N-body cosmological simulations to track several α- and iron-peak elements for the stellar and multiphase interstellar medium components of several thousand galaxies in the early (z ≥ 6) universe. The simulated galaxy population is then quantitatively compared to two complementary data sets of abundances in the Milky Way stellar halo and is capable of reproducing many of the observed abundance trends. The observed abundance ratio distributions are best reproduced with a Chabrier IMF, a chemically enriched star formation efficiency of 0.2, and a redshift of reionization of 7. Many abundances are qualitatively well matched by our model, but our model consistently overpredicts the carbon-enhanced fraction of stars at low metallicities, likely owing to incomplete coverage of Population III stellar yields and supernova models and the lack of dust as a component of our model.« less

Nuclear Neutrino Spectra in Late Stellar Evolution

NASA Astrophysics Data System (ADS)

Misch, G. Wendell; Sun, Yang; Fuller, George

2018-05-01

Neutrinos are the principle carriers of energy in massive stars, beginning from core carbon burning and continuing through core collapse and after the core bounce. In fact, it may be possible to detect neutrinos from nearby pre-supernova stars. Therefore, it is of great interest to understand the neutrino energy spectra from these stars. Leading up to core collapse, beginning around core silicon burning, nuclei become dominant producers of neutrinos, particularly at high neutrino energy, so a systematic study of nuclear neutrino spectra is desirable. We have done such a study, and we present our sd-shell model calculations of nuclear neutrino energy spectra for nuclei in the mass number range A = 21 - 35. Our study includes neutrinos produced by charged lepton capture, charged lepton emission, and neutral current nuclear deexcitation. Previous authors have tabulated the rates of charged current nuclear weak interactions in astrophysical conditions, but the present work expands on this not only by providing neutrino energy spectra, but also by including the heretofore untabulated neutral current de-excitation neutrino pairs.

Effect of the stellar spin history on the tidal evolution of close-in planets

NASA Astrophysics Data System (ADS)

Bolmont, E.; Raymond, S. N.; Leconte, J.; Matt, S. P.

2012-08-01

Context. The spin rate of stars evolves substantially during their lifetime, owing to the evolution of their internal structure and to external torques arising from the interaction of stars with their environments and stellar winds. Aims: We investigate how the evolution of the stellar spin rate affects, and is affected by, planets in close orbits via star-planet tidal interactions. Methods: We used a standard equilibrium tidal model to compute the orbital evolution of single planets orbiting both Sun-like stars and very low-mass stars (0.1 M⊙). We tested two stellar spin evolution profiles, one with fast initial rotation (1.2 day rotation period) and one with slow initial rotation (8 day period). We tested the effect of varying the stellar and planetary dissipations, and the planet's mass and initial orbital radius. Results: For Sun-like stars, the different tidal evolution between initially rapidly and slowly rotating stars is only evident for extremely close-in gas giants orbiting highly dissipative stars. However, for very low-mass stars the effect of the initial rotation of the star on the planet's evolution is apparent for less massive (1 M⊕) planets and typical dissipation values. We also find that planetary evolution can have significant effects on the stellar spin history. In particular, when a planet falls onto the star, it can cause the star to spin up. Conclusions: Tidal evolution allows us to differentiate between the early behaviors of extremely close-in planets orbiting either a rapidly rotating star or a slowly rotating star. The early spin-up of the star allows the close-in planets around fast rotators to survive the early evolution. For planets around M-dwarfs, surviving the early evolution means surviving on Gyr timescales, whereas for Sun-like stars the spin-down brings about late mergers of Jupiter planets. In the light of this study, we can say that differentiating one type of spin evolution from another given the present position of planets can be very tricky. Unless we can observe some markers of former evolution, it is nearly impossible to distinguish the two very different spin profiles, let alone intermediate spin-profiles. Nevertheless, some conclusions can still be drawn about statistical distributions of planets around fully convective M-dwarfs. If tidal evolution brings about a merger late in the stellar history, it can also entail a noticeable acceleration of the star at late ages, so that it is possible to have old stars that spin rapidly. This raises the question of how the age of stars can be more tightly constrained.

STRUCTURAL GLITCHES NEAR THE CORES OF RED GIANTS REVEALED BY OSCILLATIONS IN G-MODE PERIOD SPACINGS FROM STELLAR MODELS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cunha, M. S.; Avelino, P. P.; Stello, D.

2015-06-01

With recent advances in asteroseismology it is now possible to peer into the cores of red giants, potentially providing a way to study processes such as nuclear burning and mixing through their imprint as sharp structural variations—glitches—in the stellar cores. Here we show how such core glitches can affect the oscillations we observe in red giants. We derive an analytical expression describing the expected frequency pattern in the presence of a glitch. This formulation also accounts for the coupling between acoustic and gravity waves. From an extensive set of canonical stellar models we find glitch-induced variation in the period spacingmore » and inertia of non-radial modes during several phases of red giant evolution. Significant changes are seen in the appearance of mode amplitude and frequency patterns in asteroseismic diagrams such as the power spectrum and the échelle diagram. Interestingly, along the red giant branch glitch-induced variation occurs only at the luminosity bump, potentially providing a direct seismic indicator of stars in that particular evolution stage. Similarly, we find the variation at only certain post-helium-ignition evolution stages, namely, in the early phases of helium core burning and at the beginning of helium shell burning, signifying the asymptotic giant branch bump. Based on our results, we note that assuming stars to be glitch-free, while they are not, can result in an incorrect estimate of the period spacing. We further note that including diffusion and mixing beyond classical Schwarzschild could affect the characteristics of the glitches, potentially providing a way to study these physical processes.« less

Merger-driven evolution of the effective stellar initial mass function of massive early-type galaxies

NASA Astrophysics Data System (ADS)

Sonnenfeld, Alessandro; Nipoti, Carlo; Treu, Tommaso

2017-02-01

The stellar initial mass function (IMF) of early-type galaxies is the combination of the IMF of the stellar population formed in situ and that of accreted stellar populations. Using as an observable the effective IMF αIMF, defined as the ratio between the true stellar mass of a galaxy and the stellar mass inferred assuming a Salpeter IMF, we present a theoretical model for its evolution as a result of dry mergers. We use a simple dry-merger evolution model, based on cosmological N-body simulations, together with empirically motivated prescriptions for the IMF to make predictions on how the effective IMF of massive early-type galaxies changes from z = 2 to z = 0. We find that the IMF normalization of individual galaxies becomes lighter with time. At fixed velocity dispersion, αIMF is predicted to be constant with redshift. Current dynamical constraints on the evolution of the IMF are in slight tension with this prediction, even though systematic uncertainties, including the effect of radial gradients in the IMF, prevent a conclusive statement. The correlation of αIMF with stellar mass becomes shallower with time, while the correlation between αIMF and velocity dispersion is mostly preserved by dry mergers. We also find that dry mergers can mix the dependence of the IMF on stellar mass and velocity dispersion, making it challenging to infer, from z = 0 observations of global galactic properties, what is the quantity that is originally coupled with the IMF.

Hypercompact Stellar Systems Around Recoiling Supermassive Black Holes

NASA Astrophysics Data System (ADS)

Merritt, David; Schnittman, Jeremy D.; Komossa, S.

2009-07-01

A supermassive black hole ejected from the center of a galaxy by gravitational-wave recoil carries a retinue of bound stars—a "hypercompact stellar system" (HCSS). The numbers and properties of HCSSs contain information about the merger histories of galaxies, the late evolution of binary black holes, and the distribution of gravitational-wave kicks. We relate the structural properties (size, mass, density profile) of HCSSs to the properties of their host galaxies and to the size of the kick in two regimes: collisional (M BH lsim 107 M sun), i.e., short nuclear relaxation times, and collisionless (M BH gsim 107 M sun), i.e., long nuclear relaxation times. HCSSs are expected to be similar in size and luminosity to globular clusters, but in extreme cases (large galaxies, kicks just above escape velocity) their stellar mass can approach that of ultracompact dwarf galaxies. However, they differ from all other classes of compact stellar system in having very high internal velocities. We show that the kick velocity is encoded in the velocity dispersion of the bound stars. Given a large enough sample of HCSSs, the distribution of gravitational-wave kicks can therefore be empirically determined. We combine a hierarchical merger algorithm with stellar population models to compute the rate of production of HCSSs over time and the probability of observing HCSSs in the local universe as a function of their apparent magnitude, color, size, and velocity dispersion, under two different assumptions about the star formation history prior to the kick. We predict that ~102 HCSSs should be detectable within 2 Mpc of the center of the Virgo cluster, and that many of these should be bright enough that their kick velocities (i.e., velocity dispersions) could be measured with reasonable exposure times. We discuss other strategies for detecting HCSSs and speculate on some exotic manifestations.

The Effects of Single and Close Binary Evolution on the Stellar Mass Function

NASA Astrophysics Data System (ADS)

Schneider, R. N. F.; Izzard, G. R.; de Mink, S.; Langer, N., Stolte, A., de Koter, A.; Gvaramadze, V. V.; Hussmann, B.; Liermann, A.; Sana, H.

2013-06-01

Massive stars are almost exclusively born in star clusters, where stars in a cluster are expected to be born quasi-simultaneously and with the same chemical composition. The distribution of their birth masses favors lower over higher stellar masses, such that the most massive stars are rare, and the existence of an stellar upper mass limit is still debated. The majority of massive stars are born as members of close binary systems and most of them will exchange mass with a close companion during their lifetime. We explore the influence of single and binary star evolution on the high mass end of the stellar mass function using a rapid binary evolution code. We apply our results to two massive Galactic star clusters and show how the shape of their mass functions can be used to determine cluster ages and comment on the stellar upper mass limit in view of our new findings.

Supermassive Black Holes and Galaxy Evolution

NASA Technical Reports Server (NTRS)

Merritt, D.

2004-01-01

Supermassive black holes appear to be generic components of galactic nuclei. The formation and growth of black holes is intimately connected with the evolution of galaxies on a wide range of scales. For instance, mergers between galaxies containing nuclear black holes would produce supermassive binaries which eventually coalesce via the emission of gravitational radiation. The formation and decay of these binaries is expected to produce a number of observable signatures in the stellar distribution. Black holes can also affect the large-scale structure of galaxies by perturbing the orbits of stars that pass through the nucleus. Large-scale N-body simulations are beginning to generate testable predictions about these processes which will allow us to draw inferences about the formation history of supermassive black holes.

Rotational stellar structures based on the Lagrangian variational principle

NASA Astrophysics Data System (ADS)

Yasutake, Nobutoshi; Fujisawa, Kotaro; Yamada, Shoichi

2017-06-01

A new method for multi-dimensional stellar structures is proposed in this study. As for stellar evolution calculations, the Heney method is the defacto standard now, but basically assumed to be spherical symmetric. It is one of the difficulties for deformed stellar-evolution calculations to trace the potentially complex movements of each fluid element. On the other hand, our new method is very suitable to follow such movements, since it is based on the Lagrange coordinate. This scheme is also based on the variational principle, which is adopted to the studies for the pasta structures inside of neutron stars. Our scheme could be a major break through for evolution calculations of any types of deformed stars: proto-planets, proto-stars, and proto-neutron stars, etc.

Electron capture rates in stars studied with heavy ion charge exchange reactions

NASA Astrophysics Data System (ADS)

Bertulani, C. A.

2018-01-01

Indirect methods using nucleus-nucleus reactions at high energies (here, high energies mean ~ 50 MeV/nucleon and higher) are now routinely used to extract information of interest for nuclear astrophysics. This is of extreme relevance as many of the nuclei involved in stellar evolution are short-lived. Therefore, indirect methods became the focus of recent studies carried out in major nuclear physics facilities. Among such methods, heavy ion charge exchange is thought to be a useful tool to infer Gamow-Teller matrix elements needed to describe electron capture rates in stars and also double beta-decay experiments. In this short review, I provide a theoretical guidance based on a simple reaction model for charge exchange reactions.

Photodisintegration reactions for nuclear astrophysics studies at ELI-NP

NASA Astrophysics Data System (ADS)

Matei, C.; Balabanski, D.; Filipescu, D. M.; Tesileanu, O.

2018-01-01

Extreme Light Infrastructure - Nuclear Physics facility will come online in Bucharest-Magurele, Romania, in 2018 and will deliver high intensity laser and brilliant gamma beams. We present the physics cases and instruments proposed at ELI-NP to measure capture reactions by means of the inverse photodisintegration reaction. We propose to study the 16O(γ, α)12C reaction using a Time Projection Chamber detector with electronic readout. Several other reactions, such as 24Mg(γ, α)20Ne and reactions on heavy nuclei relevant in the p-process, are central to stellar evolution and will be investigated with a proposed Silicon Strip Detector array and a 4π neutron detector. The status of the experimental facilities and first-day experiments will be presented in detail.

Stellar mass and velocity functions of galaxies. Backward evolution and the fate of Milky Way siblings

NASA Astrophysics Data System (ADS)

Boissier, S.; Buat, V.; Ilbert, O.

2010-11-01

Context. In recent years, stellar mass functions of both star-forming and quiescent galaxies have been observed at different redshifts in various fields. In addition, star formation rate (SFR) distributions (e.g. in the form of far infrared luminosity functions) were also obtained. Taken together, they offer complementary pieces of information concerning the evolution of galaxies. Aims: We attempt in this paper to check the consistency of the observed stellar mass functions, SFR functions, and the cosmic SFR density with simple backward evolutionary models. Methods: Starting from observed stellar mass functions for star-forming galaxies, we use backwards models to predict the evolution of a number of quantities, such as the SFR function, the cosmic SFR density and the velocity function. Because the velocity is a parameter attached to a galaxy during its history (contrary to the stellar mass), this approach allows us to quantify the number density evolution of galaxies of a given velocity, e.g. of the Milky Way siblings. Results: Observations suggest that the stellar mass function of star-forming galaxies is constant between redshift 0 and 1. To reproduce this result, we must quench star formation in a number of star-forming galaxies. The stellar mass function of these “quenched” galaxies is consistent with available data concerning the increase in the population of quiescent galaxies in the same redshift interval. The stellar mass function of quiescent galaxies is then mainly determined by the distribution of active galaxies that must stop star formation, with a modest mass redistribution during mergers. The cosmic SFR density and the evolution of the SFR functions are recovered relatively well, although they provide some clues to a minor evolution of the stellar mass function of star forming galaxies at the lowest redshifts. We thus consider that we have obtained in a simple way a relatively consistent picture of the evolution of galaxies at intermediate redshifts. If this picture is correct, 50% of the Milky-Way sisters (galaxies with the same velocity as our Galaxy, i.e. 220 km s-1) have quenched their star formation since redshift 1 (and an even higher fraction for higher velocities). We discuss the processes that might be responsible for this transformation.

Cyberhubs: Virtual Research Environments for Astronomy

NASA Astrophysics Data System (ADS)

Herwig, Falk; Andrassy, Robert; Annau, Nic; Clarkson, Ondrea; Côté, Benoit; D’Sa, Aaron; Jones, Sam; Moa, Belaid; O’Connell, Jericho; Porter, David; Ritter, Christian; Woodward, Paul

2018-05-01

Collaborations in astronomy and astrophysics are faced with numerous cyber-infrastructure challenges, such as large data sets, the need to combine heterogeneous data sets, and the challenge to effectively collaborate on those large, heterogeneous data sets with significant processing requirements and complex science software tools. The cyberhubs system is an easy-to-deploy package for small- to medium-sized collaborations based on the Jupyter and Docker technology, which allows web-browser-enabled, remote, interactive analytic access to shared data. It offers an initial step to address these challenges. The features and deployment steps of the system are described, as well as the requirements collection through an account of the different approaches to data structuring, handling, and available analytic tools for the NuGrid and PPMstar collaborations. NuGrid is an international collaboration that creates stellar evolution and explosion physics and nucleosynthesis simulation data. The PPMstar collaboration performs large-scale 3D stellar hydrodynamics simulations of interior convection in the late phases of stellar evolution. Examples of science that is currently performed on cyberhubs, in the areas of 3D stellar hydrodynamic simulations, stellar evolution and nucleosynthesis, and Galactic chemical evolution, are presented.

A High Resolution View of Galactic Centers: Arp 220 and M31

NASA Astrophysics Data System (ADS)

Lockhart, Kelly E.

The centers of galaxy are small in size and yet incredibly complex. They play host to supermassive black holes and nuclear star clusters (NSCs) and are subject to large gas inows, nuclear starbursts, and active galactic nuclear (AGN) activity. They can also be the launching site for large-scale galactic outows. However, though these systems are quite important to galactic evolution, observations are quite difficult due to their small size. Using high spatial resolution narrowband imaging with HST/WFC3 of Arp 220, a latestage galaxy merger, I discover an ionized gas bubble feature ( r = 600 pc) just off the nucleus. The bubble is aligned with both the western nucleus and with the large-scale galactic outflow. Using energetics arguments, I link the bubble with a young, obscured AGN or with an intense nuclear starburst. Given its alignment along the large-scale outflow axis, I argue that the bubble presents evidence for a link between the galactic center and the large-scale outflow. I also present new observations of the NSC in M31, the closest large spiral galaxy to our own. Using the OSIRIS near-infrared integral field spectrograph (IFS) on Keck, I map the kinematics of the old stellar population in the eccentric disk of the NSC. I compare the observations to models to derive a precession speed of the disk of 0+/-5 km s-1 pc-1 , and hence confirm that winds from the old stellar population may be the source of gas needed to form the young stellar population in the NSC. Studies of galactic centers are dependent on high spatial resolution observations. In particular, IFSs are ideal instruments for these studies as they provide two-dimensional spectroscopy of the field of view, enabling 2D kinematic studies. I report on work to characterize and improve the data reduction pipeline of the OSIRIS IFS, and discuss implications for future generations of IFS instrumentation.

Nuclear planetology: understanding planetary mantle and crust formation in the light of nuclear and particle physics

NASA Astrophysics Data System (ADS)

Roller, Goetz

2017-04-01

The Hertzsprung-Russell (HR) diagram is one of the most important diagrams in astronomy. In a HR diagram, the luminosity of stars and/or stellar remnants (white dwarf stars, WD's), relative to the luminosity of the sun, is plotted versus their surface temperatures (Teff). The Earth shows a striking similarity in size (radius ≈ 6.371 km) and Teff of its outer core surface (Teff ≈ 3800 K at the core-mantle-boundary) with old WD's (radius ≈ 6.300 km) like WD0346+246 (Teff ≈ 3820 K after ≈ 12.7 Ga [1]), which plot in the HR diagram close to the low-mass extension of the stellar population or main sequence. In the light of nuclear planetology [2], Earth-like planets are regarded as old, down-cooled and differentiated black dwarfs (Fe-C BLD's) after massive decompression, the most important nuclear reactions involved being 56Fe(γ,α)52Cr (etc.), possibly responsible for extreme terrestrial glaciations events ("snowball" Earth), together with (γ,n), (γ,p) and fusion reactions like 12C(α,γ)16O. The latter reaction might have caused oxidation of the planet from inside out. Nuclear planetology is a new research field, tightly constrained by a coupled 187Re-232Th-238U systematics [3-5]. By means of nuclear/quantum physics and taking the theory of relativity into account, it aims at understanding the thermal and chemical evolution of Fe-C BLD's after gravitational contraction (e.g. Mercury) or Fermi-pressure controlled collapse (e.g. Earth) events after massive decompression, leading possibly to an r-process event, towards the end of their cooling period [2]. So far and based upon 187Re-232Th-238U nuclear geochronometry, the Fe-C BLD hypothesis can successfully explain the global terrestrial MORB 232Th/238U signature [5]. Thus, it may help to elucidate the DM (depleted mantle), EMI (enriched mantle 1), EMII (enriched mantle 2) or HIMU (high U/Pb) reservoirs [6], and the 187Os/188Os isotopic dichotomy in Archean magmatic rocks and sediments [7]. Here I present a conceptual model constraining the evolution of a rocky planet like Earth or Mercury from a stellar precursor of the oldest population to a Fe-C BLD, shifting through different spectral classes in a HR diagram after massive decompression and tremendous energy losses. In the light of WD/BLD cosmochronology [1], solar system bodies like Earth, Mercury and Moon are regarded as captured interlopers from the Galactic bulge, Earth and Moon possibly representing remnants of an old binary system. Such a preliminary scenario is supported by similar ages obtained from WD's for the Galactic halo [1] and, independently, by means of 187Re-232Th-238U nuclear geochronometry [3, 4], together with recent observations extremely metal-poor stars from the cosmic dawn in the bulge of the Milky Way [8]. This might be further elucidated in the near future by Th/U cosmochronometry based upon a nuclear production ratio Th/U = 0.96 [9] and additionally by means of a newly developed nucleogeochronometric age dating method for stellar spectroscopy [9-11]. The model shall stimulate geochemical data interpretation from a different perspective, to constrain the evolution and differentiation of planetary or lunar crusts and mantles in general. [1] Fontaine et al. (2001), Public. Astron. Soc. of the Pacific 113, 409-435. [2] Roller (2015), Abstract T34B-0407, AGU Spring Meeting 2015. [3] Roller (2016), Goldschmidt Conf. Abstr. 26, 2642. [4] Roller (2015), Goldschmidt Conf. Abstr. 25, 2672. [5] Roller (2015), Geophys. Res. Abstr. 18, EGU2016-33. [6] Arevalo et al. (2010), Chem. Geol. 271, 70-85. [7] Roller (2015), Geophys. Res. Abstr. 17, EGU2015-2399. [8] Howes et al. (2015), Nature 527, 484-487. [9] Roller (2016), JPS Conf. Proc., Nuclei in the Cosmos (NIC XIV), Niigata, Japan, subm. (NICXIV-001); NICXIV Abstr. #1570244284. [10] Roller (2016), JPS Conf. Proc., Nuclei in the Cosmos (NIC XIV), Niigata, Japan, subm. (NICXIV-002); NICXIV Abstr. #1570244285. [11] Roller (2016), JPS Conf. Proc., Nuclei in the Cosmos (NIC XIV), Niigata, Japan, subm. (NICXIV-003); NICXIV Abstr. #1570244281.

Globular-cluster stars - Results of theoretical evolution and pulsation studies compared with the observations.

NASA Technical Reports Server (NTRS)

Iben, I., Jr.

1971-01-01

Survey of recently published studies on globular clusters, and comparison of stellar evolution and pulsation theory with reported observations. The theory of stellar evolution is shown to be capable of describing, in principle, the behavior of a star through all quasi-static stages. Yet, as might be expected, estimates of bulk properties obtained by comparing observations with results of pulsation and stellar atmosphere theory differ somewhat from estimates of these same properties obtained by comparing observations with results of evolution theory. A description is given of how such estimates are obtained, and suggestions are offered as to where the weak points in each theory may lie.

Tidal dissipation in rotating low-mass stars and implications for the orbital evolution of close-in planets. I. From the PMS to the RGB at solar metallicity

NASA Astrophysics Data System (ADS)

Gallet, F.; Bolmont, E.; Mathis, S.; Charbonnel, C.; Amard, L.

2017-08-01

Context. Star-planet interactions must be taken into account in stellar models to understand the dynamical evolution of close-in planets. The dependence of the tidal interactions on the structural and rotational evolution of the star is of particular importance and should be correctly treated. Aims: We quantify how tidal dissipation in the convective envelope of rotating low-mass stars evolves from the pre-main sequence up to the red-giant branch depending on the initial stellar mass. We investigate the consequences of this evolution on planetary orbital evolution. Methods: We couple the tidal dissipation formalism previously described to the stellar evolution code STAREVOL and apply this coupling to rotating stars with masses between 0.3 and 1.4 M⊙. As a first step, this formalism assumes a simplified bi-layer stellar structure with corresponding averaged densities for the radiative core and the convective envelope. We use a frequency-averaged treatment of the dissipation of tidal inertial waves in the convection zone (but neglect the dissipation of tidal gravity waves in the radiation zone). In addition, we generalize a recent work by following the orbital evolution of close-in planets using the new tidal dissipation predictions for advanced phases of stellar evolution. Results: On the pre-main sequence the evolution of tidal dissipation is controlled by the evolution of the internal structure of the contracting star. On the main sequence it is strongly driven by the variation of surface rotation that is impacted by magnetized stellar winds braking. The main effect of taking into account the rotational evolution of the stars is to lower the tidal dissipation strength by about four orders of magnitude on the main sequence, compared to a normalized dissipation rate that only takes into account structural changes. Conclusions: The evolution of the dissipation strongly depends on the evolution of the internal structure and rotation of the star. From the pre-main sequence up to the tip of the red-giant branch, it varies by several orders of magnitude, with strong consequences for the orbital evolution of close-in massive planets. These effects are the strongest during the pre-main sequence, implying that the planets are mainly sensitive to the star's early history.

Strong Stellar-driven Outflows Shape the Evolution of Galaxies at Cosmic Dawn

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fontanot, Fabio; De Lucia, Gabriella; Hirschmann, Michaela

We study galaxy mass assembly and cosmic star formation rate (SFR) at high redshift (z ≳ 4), by comparing data from multiwavelength surveys with predictions from the GAlaxy Evolution and Assembly (gaea) model. gaea implements a stellar feedback scheme partially based on cosmological hydrodynamical simulations, which features strong stellar-driven outflows and mass-dependent timescales for the re-accretion of ejected gas. In previous work, we have shown that this scheme is able to correctly reproduce the evolution of the galaxy stellar mass function (GSMF) up to z ∼ 3. We contrast model predictions with both rest-frame ultraviolet (UV) and optical luminosity functionsmore » (LFs), which are mostly sensitive to the SFR and stellar mass, respectively. We show that gaea is able to reproduce the shape and redshift evolution of both sets of LFs. We study the impact of dust on the predicted LFs, and we find that the required level of dust attenuation is in qualitative agreement with recent estimates based on the UV continuum slope. The consistency between data and model predictions holds for the redshift evolution of the physical quantities well beyond the redshift range considered for the calibration of the original model. In particular, we show that gaea is able to recover the evolution of the GSMF up to z ∼ 7 and the cosmic SFR density up to z ∼ 10.« less

X-raying galaxies: a Chandra legacy.

PubMed

Wang, Q Daniel

2010-04-20

This presentation reviews Chandra's major contribution to the understanding of nearby galaxies. After a brief summary on significant advances in characterizing various types of discrete x-ray sources, the presentation focuses on the global hot gas in and around galaxies, especially normal ones like our own. The hot gas is a product of stellar and active galactic nuclear feedback--the least understood part in theories of galaxy formation and evolution. Chandra observations have led to the first characterization of the spatial, thermal, chemical, and kinetic properties of the gas in our galaxy. The gas is concentrated around the galactic bulge and disk on scales of a few kiloparsec. The column density of chemically enriched hot gas on larger scales is at least an order magnitude smaller, indicating that it may not account for the bulk of the missing baryon matter predicted for the galactic halo according to the standard cosmology. Similar results have also been obtained for other nearby galaxies. The x-ray emission from hot gas is well correlated with the star formation rate and stellar mass, indicating that the heating is primarily due to the stellar feedback. However, the observed x-ray luminosity of the gas is typically less than a few percent of the feedback energy. Thus the bulk of the feedback (including injected heavy elements) is likely lost in galaxy-wide outflows. The results are compared with simulations of the feedback to infer its dynamics and interplay with the circumgalactic medium, hence the evolution of galaxies.

X-raying galaxies: A Chandra legacy

PubMed Central

Wang, Q. Daniel

2010-01-01

This presentation reviews Chandra’s major contribution to the understanding of nearby galaxies. After a brief summary on significant advances in characterizing various types of discrete x-ray sources, the presentation focuses on the global hot gas in and around galaxies, especially normal ones like our own. The hot gas is a product of stellar and active galactic nuclear feedback—the least understood part in theories of galaxy formation and evolution. Chandra observations have led to the first characterization of the spatial, thermal, chemical, and kinetic properties of the gas in our galaxy. The gas is concentrated around the galactic bulge and disk on scales of a few kiloparsec. The column density of chemically enriched hot gas on larger scales is at least an order magnitude smaller, indicating that it may not account for the bulk of the missing baryon matter predicted for the galactic halo according to the standard cosmology. Similar results have also been obtained for other nearby galaxies. The x-ray emission from hot gas is well correlated with the star formation rate and stellar mass, indicating that the heating is primarily due to the stellar feedback. However, the observed x-ray luminosity of the gas is typically less than a few percent of the feedback energy. Thus the bulk of the feedback (including injected heavy elements) is likely lost in galaxy-wide outflows. The results are compared with simulations of the feedback to infer its dynamics and interplay with the circumgalactic medium, hence the evolution of galaxies. PMID:20212160

Lithium in halo stars from standard stellar evolution

NASA Technical Reports Server (NTRS)

Deliyannis, Constantine P.; Demarque, Pierre; Kawaler, Steven D.

1990-01-01

A grid has been constructed of theoretical evolution sequences of models for low-metallicity stars from the premain-sequence to the giant branch phases. The grid is used to study the history of surface Li abundance during standard stellar evolution. The Li-7 observations of halo stars by Spite and Spite (1982) and subsequent observations are synthesized to separate the halo stars by age. The theory of surface Li abundance is illustrated by following the evolution of a reference halo star model from the contracting fully convective premain sequence to the giant branch phase. The theoretical models are compared with observed Li abundances. The results show that the halo star lithium abundances can be explained in the context of standard stellar evolution theory using completely standard assumptions and physics.

An Extension of the EDGES Survey: Stellar Populations in Dark Matter Halos

NASA Astrophysics Data System (ADS)

van Zee, Liese

The formation and evolution of galactic disks is one of the key questions in extragalactic astronomy today. We plan to use archival data from GALEX, Spitzer, and WISE to investigate the growth and evolution of the stellar component in a statistical sample of nearby galaxies. Data covering a broad wavelength range are critical for measurement of current star formation activity, stellar populations, and stellar distributions in nearby galaxies. In order to investigate the timescales associated with the growth of galactic disks, we will (1) investigate the structure of the underlying stellar distribution, (2) measure the ratio of current-to-past star formation activity as a function of radius, and (3) investigate the growth of the stellar disk as a function of baryon fraction and total dynamical mass. The proposed projects leverage the existing deep wide field-of-view near infrared imaging observations obtained with the Spitzer Space Telescope as part of the EDGES Survey, a Cycle 8 Exploration Science Program. The proposed analysis of multiwavelength imaging observations of a well-defined statistical sample will place strong constraints on hierarchical models of galaxy formation and evolution and will further our understanding of the stellar component of nearby galaxies.

Blue Stragglers in Clusters and Integrated Spectral Properties of Stellar Populations

NASA Astrophysics Data System (ADS)

Xin, Yu; Deng, Licai

Blue straggler stars are the most prominent bright objects in the colour-magnitude diagram of a star cluster that challenges the theory of stellar evolution. Star clusters are the closest counterparts of the theoretical concept of simple stellar populations (SSPs) in the Universe. SSPs are widely used as the basic building blocks to interpret stellar contents in galaxies. The concept of an SSP is a group of coeval stars which follows a given distribution in mass, and has the same chemical property and age. In practice, SSPs are more conveniently made by the latest stellar evolutionary models of single stars. In reality, however, stars can be more complicated than just single either at birth time or during the course of evolution in a typical environment. Observations of star clusters show that there are always exotic objects which do not follow the predictions of standard theory of stellar evolution. Blue straggler stars (BSSs), as discussed intensively in this book both observationally and theoretically, are very important in our context when considering the integrated spectral properties of a cluster, or a simple stellar population. In this chapter, we are going to describe how important the contribution of BSSs is to the total light of a cluster.

INTEGRAL-FIELD STELLAR AND IONIZED GAS KINEMATICS OF PECULIAR VIRGO CLUSTER SPIRAL GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cortés, Juan R.; Hardy, Eduardo; Kenney, Jeffrey D. P., E-mail: jcortes@alma.cl, E-mail: ehardy@nrao.cl, E-mail: jeff.kenney@yale.edu

2015-01-01

We present the stellar and ionized gas kinematics of 13 bright peculiar Virgo cluster galaxies observed with the DensePak Integral Field Unit at the WIYN 3.5 m telescope in order to look for kinematic evidence that these galaxies have experienced gravitational interactions or gas stripping. Two-dimensional maps of the stellar velocity V, stellar velocity dispersion σ, and the ionized gas velocity (Hβ and/or [O III]) are presented for the galaxies in the sample. The stellar rotation curves and velocity dispersion profiles are determined for 13 galaxies, and the ionized gas rotation curves are determined for 6 galaxies. Misalignments between themore » optical and kinematical major axes are found in several galaxies. While in some cases this is due to a bar, in other cases it seems to be associated with gravitational interaction or ongoing ram pressure stripping. Non-circular gas motions are found in nine galaxies, with various causes including bars, nuclear outflows, or gravitational disturbances. Several galaxies have signatures of kinematically distinct stellar components, which are likely signatures of accretion or mergers. For all of our galaxies, we compute the angular momentum parameter λ {sub R}. An evaluation of the galaxies in the λ {sub R} ellipticity plane shows that all but two of the galaxies have significant support from random stellar motions, and have likely experienced gravitational interactions. This includes some galaxies with very small bulges and truncated/compact Hα morphologies, indicating that such galaxies cannot be fully explained by simple ram pressure stripping, but must have had significant gravitational encounters. Most of the sample galaxies show evidence for ICM-ISM stripping as well as gravitational interactions, indicating that the evolution of a significant fraction of cluster galaxies is likely strongly impacted by both effects.« less

The stellar content of the nuclear regions of Sc galaxies

NASA Technical Reports Server (NTRS)

Turnrose, B. E.

1976-01-01

Stellar-population syntheses based on absolute spectral energy distributions over the wavelength range from 3300 to 10,400 A are used to determine the stellar content of the nuclear regions of seven nearby Sc galaxies (NGC 628, 1073, 1084, 1637, 2903, 4321, and 5194). A linear-programming procedure is employed to construct models of the overall stellar populations whose spectra closely match those of the seven galaxies. Absolute measurements of the emission-line spectra of the nuclear regions are also provided. It is found that: (1) intrinsic reddening is probably present in each nuclear region; (2) the upper main sequence is substantially populated in most of the models; (3) the lower main sequence contributes insignificantly to the luminosity in all optimal solutions; (4) substantial contributions are made by evolved M stars at long wavelengths in all the models; (5) the model photometric M/L ratios are low, of the order of unity; and (6) the O-B stars arising naturally in the population models are just sufficient to provide the observed nuclear ionization in all the galaxies except NGC 5194, which may be collisionally ionized. The properties of the nuclear regions are shown to be consistent with the existence of a common initial mass function for star formation and a variety of time dependences for the star-formation process. A possibly significant correlation is noted between nuclear stellar content and overall dynamical properties in four of the galaxies.

Astrophysical dust grains in stars, the interstellar medium, and the solar system

NASA Technical Reports Server (NTRS)

Gehrz, Robert D.

1991-01-01

Studies of astrophysical dust grains in circumstellar shells, the interstellar medium, and the solar system may provide information about stellar evolution and about physical conditions in the primitive solar nebula. The following subject areas are covered: (1) the cycling of dust in stellar evolution and the formation of planetary systems; (2) astrophysical dust grains in circumstellar environments; (3) circumstellar grain formation and mass loss; (4) interstellar dust grains; (5) comet dust and the zodiacal cloud; (6) the survival of dust grains during stellar evolution; and (7) establishing connections between stardust and dust in the solar system.

Dust formation at low metallicity

NASA Astrophysics Data System (ADS)

Ferrarotti, A. S.; Gail, H.-P.

Stars between 3Modot and 25Modot reach their final stages of stellar evolution either as AGB (asymptotic giant branch) stars and finally become white dwarfs, or end in a supernova explosion. The last evolutionary stages, shortly before the final state, are regularly accompanied by stellar winds which lead to substantial mass loss and develop optically very thick dust shells. Mass loss for smaller and medium sized stars higher up on the AGB depends predominantly on the metallicity of the star. For Pop I metallicity, the mass loss is caused by dust condensation. This process is not possible for stars of small Z. Thus, their final evolution strongly depends on the possibility of dust formation. Our research focuses on the dependence of dust formation of the first stellar generation on Z and on the initial mass of the star. Furthermore, we investigate when dust formation becomes possible in stellar winds and the effects this process has on the evolution of the star at the final evolutionary stages. With synthetic AGB evolution models some important issues in stellar evolution can tried to be answered: (1) mass loss on the AGB, (2) the shift of the limit (γ>1) for the onset of dust driven winds with Z and (3) the critical Z when dust formation becomes possible.

Large Magellanic Cloud Planetary Nebula Morphology: Probing Stellar Populations and Evolution.

PubMed

Stanghellini; Shaw; Balick; Blades

2000-05-10

Planetary nebulae (PNe) in the Large Magellanic Cloud (LMC) offer the unique opportunity to study both the population and evolution of low- and intermediate-mass stars, by means of the morphological type of the nebula. Using observations from our LMC PN morphological survey, and including images available in the Hubble Space Telescope Data Archive and published chemical abundances, we find that asymmetry in PNe is strongly correlated with a younger stellar population, as indicated by the abundance of elements that are unaltered by stellar evolution (Ne, Ar, and S). While similar results have been obtained for Galactic PNe, this is the first demonstration of the relationship for extragalactic PNe. We also examine the relation between morphology and abundance of the products of stellar evolution. We found that asymmetric PNe have higher nitrogen and lower carbon abundances than symmetric PNe. Our two main results are broadly consistent with the predictions of stellar evolution if the progenitors of asymmetric PNe have on average larger masses than the progenitors of symmetric PNe. The results bear on the question of formation mechanisms for asymmetric PNe-specifically, that the genesis of PNe structure should relate strongly to the population type, and by inference the mass, of the progenitor star and less strongly on whether the central star is a member of a close binary system.

Nucleosynthesis in the early Galaxy: Progress and challenges.

NASA Astrophysics Data System (ADS)

Montes, Fernando

2015-10-01

Chemical imprints left by the first stars in the oldest stars of the Milky Way gives clues of the stellar nucleosynthesis responsible for the creation of elements heavier than iron. Recent progress in astronomical observations and in the modeling of the chemical evolution of the Galaxy have shown that multiple nucleosynthesis processes may operate at those early times. In this talk I will review some of that evidence along with the important role that nuclear reactions play in those processes. I will focus in progress in our understanding of the rapid neutron capture process (r-process) and in new results on nucleosynthesis in core-collapse supernovae and neutrino-driven winds that produce elements up to silver. I will show some examples of recent nuclear physics measurements addressing the need for better nuclear data and give an outlook of the remaining challenges and future plans to continue those measurements.

LLAMA: nuclear stellar properties of Swift-BAT AGN and matched inactive galaxies

NASA Astrophysics Data System (ADS)

Lin, Ming-Yi; Davies, R. I.; Hicks, E. K. S.; Burtscher, L.; Contursi, A.; Genzel, R.; Koss, M.; Lutz, D.; Maciejewski, W.; Müller-Sánchez, F.; Orban de Xivry, G.; Ricci, C.; Riffel, R.; Riffel, R. A.; Rosario, D.; Schartmann, M.; Schnorr-Müller, A.; Shimizu, T.; Sternberg, A.; Sturm, E.; Storchi-Bergmann, T.; Tacconi, L.; Veilleux, S.

2018-02-01

In a complete sample of local 14-195 keV selected active galactic nuclei (AGNs) and inactive galaxies, matched by their host galaxy properties, we study the spatially resolved stellar kinematics and luminosity distributions at near-infrared wavelengths on scales of 10-150 pc, using SINFONI on the VLT. In this paper, we present the first half of the sample, which comprises 13 galaxies, eight AGNs and five inactive galaxies. The stellar velocity fields show a disc-like rotating pattern, for which the kinematic position angle is in agreement with the photometric position angle obtained from large scale images. For this set of galaxies, the stellar surface brightness of the inactive galaxy sample is generally comparable to the matched sample of AGN, but extends to lower surface brightness. After removal of the bulge contribution, we find a nuclear stellar light excess with an extended nuclear disc structure, which exhibits a size-luminosity relation. While we expect the excess luminosity to be associated with a dynamically cooler young stellar population, we do not typically see a matching drop in dispersion. This may be because these galaxies have pseudo-bulges in which the intrinsic dispersion increases towards the centre. And although the young stars may have an impact in the observed kinematics, their fraction is too small to dominate over the bulge and compensate the increase in dispersion at small radii, so no dispersion drop is seen. Finally, we find no evidence for a difference in the stellar kinematics and nuclear stellar luminosity excess between these active and inactive galaxies.

Introduction to Galactic Chemical Evolution

NASA Astrophysics Data System (ADS)

Matteucci, Francesca

2016-04-01

In this lecture I will introduce the concept of galactic chemical evolution, namely the study of how and where the chemical elements formed and how they were distributed in the stars and gas in galaxies. The main ingredients to build models of galactic chemical evolution will be described. They include: initial conditions, star formation history, stellar nucleosynthesis and gas flows in and out of galaxies. Then some simple analytical models and their solutions will be discussed together with the main criticisms associated to them. The yield per stellar generation will be defined and the hypothesis of instantaneous recycling approximation will be critically discussed. Detailed numerical models of chemical evolution of galaxies of different morphological type, able to follow the time evolution of the abundances of single elements, will be discussed and their predictions will be compared to observational data. The comparisons will include stellar abundances as well as interstellar medium ones, measured in galaxies. I will show how, from these comparisons, one can derive important constraints on stellar nucleosynthesis and galaxy formation mechanisms. Most of the concepts described in this lecture can be found in the monograph by Matteucci (2012).

Physics with gamma-beams and charged particle detectors: I) Nuclear structure II) Nuclear astrophysics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gai, Moshe

The Charged Particle Working Group (CPWG) is proposing to construct large area Silicon Strip Detector (SSD), a gas Time Projection Chamber detector read by an electronic readout system (eTPC) and a Bubble Chamber (BC) containing superheated high purity water to be used in measurements utilizing intense gamma-ray beams from the newly constructed ELI-NP facility at Magurele, Bucharest in Romania. We intend to use the SSD and eTPC detectors to address essential problems in nuclear structure physics, such as clustering and the many alpha-decay of light nuclei such as {sup 12}C and {sup 16}O. All three detectors (SSD, eTPC and BC)more » will be used to address central problems in nuclear astrophysics such as the astrophysical cross section factor of the {sup 12}C(α,γ) reaction and other processes central to stellar evolution. The CPWG intends to submit to the ELI-NP facility a Technical Design Report (TDR) for the proposed detectors.« less

MODULES FOR EXPERIMENTS IN STELLAR ASTROPHYSICS (MESA): BINARIES, PULSATIONS, AND EXPLOSIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paxton, Bill; Bildsten, Lars; Cantiello, Matteo

We substantially update the capabilities of the open-source software instrument Modules for Experiments in Stellar Astrophysics (MESA). MESA can now simultaneously evolve an interacting pair of differentially rotating stars undergoing transfer and loss of mass and angular momentum, greatly enhancing the prior ability to model binary evolution. New MESA capabilities in fully coupled calculation of nuclear networks with hundreds of isotopes now allow MESA to accurately simulate the advanced burning stages needed to construct supernova progenitor models. Implicit hydrodynamics with shocks can now be treated with MESA, enabling modeling of the entire massive star lifecycle, from pre-main-sequence evolution to themore » onset of core collapse and nucleosynthesis from the resulting explosion. Coupling of the GYRE non-adiabatic pulsation instrument with MESA allows for new explorations of the instability strips for massive stars while also accelerating the astrophysical use of asteroseismology data. We improve the treatment of mass accretion, giving more accurate and robust near-surface profiles. A new MESA capability to calculate weak reaction rates “on-the-fly” from input nuclear data allows better simulation of accretion induced collapse of massive white dwarfs and the fate of some massive stars. We discuss the ongoing challenge of chemical diffusion in the strongly coupled plasma regime, and exhibit improvements in MESA that now allow for the simulation of radiative levitation of heavy elements in hot stars. We close by noting that the MESA software infrastructure provides bit-for-bit consistency for all results across all the supported platforms, a profound enabling capability for accelerating MESA's development.« less

What we learn from eclipsing binaries in the ultraviolet

NASA Technical Reports Server (NTRS)

Guinan, Edward F.

1990-01-01

Recent results on stars and stellar physics from IUE (International Ultraviolet Explorer) observations of eclipsing binaries are discussed. Several case studies are presented, including V 444 Cyg, Aur stars, V 471 Tau and AR Lac. Topics include stellar winds and mass loss, stellar atmospheres, stellar dynamos, and surface activity. Studies of binary star dynamics and evolution are discussed. The progress made with IUE in understanding the complex dynamical and evolutionary processes taking place in W UMa-type binaries and Algol systems is highlighted. The initial results of intensive studies of the W UMa star VW Cep and three representative Algol-type binaries (in different stages of evolution) focused on gas flows and accretion, are included. The future prospects of eclipsing binary research are explored. Remaining problems are surveyed and the next challenges are presented. The roles that eclipsing binaries could play in studies of stellar evolution, cluster dynamics, galactic structure, mass luminosity relations for extra galactic systems, cosmology, and even possible detection of extra solar system planets using eclipsing binaries are discussed.

Comparisons between stellar models and reliability of the theoretical models

NASA Astrophysics Data System (ADS)

Lebreton, Yveline; Montalbán, Josefina

2010-07-01

The high quality of the asteroseismic data provided by space missions such as CoRoT (Michel et al. in The CoRoT Mission, ESA Spec. Publ. vol. 1306, p. 39, 2006) or expected from new operating missions such as Kepler (Christensen-Dalsgaard et al. in Commun. Asteroseismol. 150:350, 2007) requires the capacity of stellar evolution codes to provide accurate models whose numerical precision is better than the expected observational errors (i.e. below 0.1 μHz on the frequencies in the case of CoRoT). We present a review of some thorough comparisons of stellar models produced by different evolution codes, involved in the CoRoT/ESTA activities (Monteiro in Evolution and Seismic Tools for Stellar Astrophysics, 2009). We examine the numerical aspects of the computations as well as the effects of different implementations of the same physics on the global quantities, physical structure and oscillations properties of the stellar models. We also discuss a few aspects of the input physics.

Exploring the cosmic evolution of habitability with galaxy merger trees

NASA Astrophysics Data System (ADS)

Stanway, E. R.; Hoskin, M. J.; Lane, M. A.; Brown, G. C.; Childs, H. J. T.; Greis, S. M. L.; Levan, A. J.

2018-04-01

We combine inferred galaxy properties from a semi-analytic galaxy evolution model incorporating dark matter halo merger trees with new estimates of supernova and gamma-ray burst rates as a function of metallicity from stellar population synthesis models incorporating binary interactions. We use these to explore the stellar-mass fraction of galaxies irradiated by energetic astrophysical transients and its evolution over cosmic time, and thus the fraction which is potentially habitable by life like our own. We find that 18 per cent of the stellar mass in the Universe is likely to have been irradiated within the last 260 Myr, with GRBs dominating that fraction. We do not see a strong dependence of irradiated stellar-mass fraction on stellar mass or richness of the galaxy environment. We consider a representative merger tree as a Local Group analogue, and find that there are galaxies at all masses which have retained a high habitable fraction (>40 per cent) over the last 6 Gyr, but also that there are galaxies at all masses where the merger history and associated star formation have rendered galaxies effectively uninhabitable. This illustrates the need to consider detailed merger trees when evaluating the cosmic evolution of habitability.

Spin Evolution of Stellar Progenitors in Compact Binaries

NASA Astrophysics Data System (ADS)

Steinle, Nathan; Kesden, Michael

2018-01-01

Understanding the effects of various processes on the spins of stellar progenitors in compact binary systems is important for modeling the binary’s evolution and thus for interpreting the gravitational radiation emitted during inspiral and merger. Tides, winds, and natal kicks can drastically modify the binary parameters: tidal interactions increase the spin magnitudes, align the spins with the orbital angular momentum, and circularize the orbit; stellar winds decrease the spin magnitudes and cause mass loss; and natal kicks can misalign the spins and orbital angular momentum or even disrupt the binary. Also, during Roche lobe overflow, the binary may experience either stable mass transfer or common envelope evolution. The former can lead to a mass ratio reversal and alter the component spins, while the latter can dramatically shrink the binary separation. For a wide range of physically reasonable stellar-evolution scenarios, we compare the timescales of these processes to assess their relative contributions in determining the initial spins of compact binary systems.

First Results on the Cluster Galaxy Population from the Subaru Hyper Suprime-Cam Survey. III. Brightest Cluster Galaxies, Stellar Mass Distribution, and Active Galaxies

NASA Astrophysics Data System (ADS)

Lin, Yen-Ting; Hsieh, Bau-Ching; Lin, Sheng-Chieh; Oguri, Masamune; Chen, Kai-Feng; Tanaka, Masayuki; Chiu, I.-Non; Huang, Song; Kodama, Tadayuki; Leauthaud, Alexie; More, Surhud; Nishizawa, Atsushi J.; Bundy, Kevin; Lin, Lihwai; Miyazaki, Satoshi

2017-12-01

The unprecedented depth and area surveyed by the Subaru Strategic Program with the Hyper Suprime-Cam (HSC-SSP) have enabled us to construct and publish the largest distant cluster sample out to z∼ 1 to date. In this exploratory study of cluster galaxy evolution from z = 1 to z = 0.3, we investigate the stellar mass assembly history of brightest cluster galaxies (BCGs), the evolution of stellar mass and luminosity distributions, the stellar mass surface density profile, as well as the population of radio galaxies. Our analysis is the first high-redshift application of the top N richest cluster selection, which is shown to allow us to trace the cluster galaxy evolution faithfully. Over the 230 deg2 area of the current HSC-SSP footprint, selecting the top 100 clusters in each of the four redshift bins allows us to observe the buildup of galaxy population in descendants of clusters whose z≈ 1 mass is about 2× {10}14 {M}ȯ . Our stellar mass is derived from a machine-learning algorithm, which is found to be unbiased and accurate with respect to the COSMOS data. We find very mild stellar mass growth in BCGs (about 35% between z = 1 and 0.3), and no evidence for evolution in both the total stellar mass–cluster mass correlation and the shape of the stellar mass surface density profile. We also present the first measurement of the radio luminosity distribution in clusters out to z∼ 1, and show hints of changes in the dominant accretion mode powering the cluster radio galaxies at z∼ 0.8.

Stellar Mass and 3.4 μm M/L Ratio Evolution of Brightest Cluster Galaxies in COSMOS since z ∼ 1.0

NASA Astrophysics Data System (ADS)

Cooke, Kevin C.; Fogarty, Kevin; Kartaltepe, Jeyhan S.; Moustakas, John; O’Dea, Christopher P.; Postman, Marc

2018-04-01

We investigate the evolution of star formation rates (SFRs), stellar masses, and M/L 3.4 μm ratios of brightest cluster galaxies (BCGs) in the COSMOS survey since z ∼ 1 to determine the contribution of star formation to the growth-rate of BCG stellar mass over time. Through the spectral energy density (SED) fitting of the GALEX, CFHT, Subaru, Vista, Spitzer, and Herschel photometric data available in the COSMOS2015 catalog, we estimate the stellar mass and SFR of each BCG. We use a modified version of the iSEDfit package to fit the SEDs of our sample with both stellar and dust emission models, as well as constrain the impact of star formation history assumptions on our results. We find that in our sample of COSMOS BCGs, star formation evolves similarly to that in BCGs in samples of more massive galaxy clusters. However, compared to the latter, the magnitude of star formation in our sample is lower by ∼1 dex. Additionally, we find an evolution of BCG baryonic mass-to-light ratio (M/L 3.4 μm) with redshift which is consistent with a passively aging stellar population. We use this to build upon Wen et al.'s low-redshift νL 3.4 μm–M Stellar relation, quantifying a correlation between νL 3.4 μm and M Stellar to z ∼ 1. By comparing our results to BCGs in Sunyaev–Zel’dovich and X-ray-selected samples of galaxy clusters, we find evidence that the normalization of star formation evolution in a cluster sample is driven by the mass range of the sample and may be biased upwards by cool cores.

Stellar Parameters, Chemical composition and Models of chemical evolution

NASA Astrophysics Data System (ADS)

Mishenina, T.; Pignatari, M.; Côté, B.; Thielemann, F.-K.; Soubiran, C.; Basak, N.; Gorbaneva, T.; Korotin, S. A.; Kovtyukh, V. V.; Wehmeyer, B.; Bisterzo, S.; Travaglio, C.; Gibson, B. K.; Jordan, C.; Paul, A.; Ritter, C.; Herwig, F.

2018-04-01

We present an in-depth study of metal-poor stars, based high resolution spectra combined with newly released astrometric data from Gaia, with special attention to observational uncertainties. The results are compared to those of other studies, including Gaia benchmark stars. Chemical evolution models are discussed, highlighting few puzzles that are still affecting our understanding of stellar nucleosynthesis and of the evolution of our Galaxy.

The Evolution of Massive Stars: a Selection of Facts and Questions

NASA Astrophysics Data System (ADS)

Vanbeveren, D.

In the present paper we discuss a selection of facts and questions related to observations and evolutionary calculations of massive single stars and massive stars in interacting binaries. We focus on the surface chemical abundances, the role of stellar winds, the early Be-stars, the high mass X-ray binaries and the effects of rotation on stellar evolution. Finally, we present an unconventionally formed object scenario (UFO-scenario) of WR binaries in dense stellar environments.

Stellar models with calibrated convection and temperature stratification from 3D hydrodynamics simulations

NASA Astrophysics Data System (ADS)

Mosumgaard, Jakob Rørsted; Ball, Warrick H.; Aguirre, Víctor Silva; Weiss, Achim; Christensen-Dalsgaard, Jørgen

2018-06-01

Stellar evolution codes play a major role in present-day astrophysics, yet they share common simplifications related to the outer layers of stars. We seek to improve on this by the use of results from realistic and highly detailed 3D hydrodynamics simulations of stellar convection. We implement a temperature stratification extracted directly from the 3D simulations into two stellar evolution codes to replace the simplified atmosphere normally used. Our implementation also contains a non-constant mixing-length parameter, which varies as a function of the stellar surface gravity and temperature - also derived from the 3D simulations. We give a detailed account of our fully consistent implementation and compare to earlier works, and also provide a freely available MESA-module. The evolution of low-mass stars with different masses is investigated, and we present for the first time an asteroseismic analysis of a standard solar model utilising calibrated convection and temperature stratification from 3D simulations. We show that the inclusion of 3D results have an almost insignificant impact on the evolution and structure of stellar models - the largest effect are changes in effective temperature of order 30 K seen in the pre-main sequence and in the red-giant branch. However, this work provides the first step for producing self-consistent evolutionary calculations using fully incorporated 3D atmospheres from on-the-fly interpolation in grids of simulations.

Scale covariant gravitation. V - Kinetic theory. VI - Stellar structure and evolution

NASA Technical Reports Server (NTRS)

Hsieh, S.-H.; Canuto, V. M.

1981-01-01

A scale covariant kinetic theory for particles and photons is developed. The mathematical framework of the theory is given by the tangent bundle of a Weyl manifold. The Liouville equation is derived, and solutions to corresponding equilibrium distributions are presented and shown to yield thermodynamic results identical to the ones obtained previously. The scale covariant theory is then used to derive results of interest to stellar structure and evolution. A radiative transfer equation is derived that can be used to study stellar evolution with a variable gravitational constant. In addition, it is shown that the sun's absolute luminosity scales as L approximately equal to GM/kappa, where kappa is the stellar opacity. Finally, a formula is derived for the age of globular clusters as a function of the gravitational constant using a previously derived expression for the absolute luminosity.

Yonsei Evolutionary Population Synthesis (YEPS). II. Spectro-photometric Evolution of Helium-enhanced Stellar Populations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chung, Chul; Yoon, Suk-Jin; Lee, Young-Wook, E-mail: chulchung@yonsei.ac.kr, E-mail: sjyoon0691@yonsei.ac.kr

The discovery of multiple stellar populations in Milky Way globular clusters (GCs) has stimulated various follow-up studies on helium-enhanced stellar populations. Here we present the evolutionary population synthesis models for the spectro-photometric evolution of simple stellar populations (SSPs) with varying initial helium abundance ( Y {sub ini}). We show that Y {sub ini} brings about dramatic changes in spectro-photometric properties of SSPs. Like the normal-helium SSPs, the integrated spectro-photometric evolution of helium-enhanced SSPs is also dependent on metallicity and age for a given Y {sub ini}. We discuss the implications and prospects for the helium-enhanced populations in relation to themore » second-generation populations found in the Milky Way GCs. All of the models are available at http://web.yonsei.ac.kr/cosmic/data/YEPS.htm.« less

Online Tools for Astronomy and Cosmochemistry

NASA Technical Reports Server (NTRS)

Meyer, B. S.

2005-01-01

Over the past year, the Webnucleo Group at Clemson University has been developing a web site with a number of interactive online tools for astronomy and cosmochemistry applications. The site uses SHP (Simplified Hypertext Preprocessor), which, because of its flexibility, allows us to embed almost any computer language into our web pages. For a description of SHP, please see http://www.joeldenny.com/ At our web site, an internet user may mine large and complex data sets, such as our stellar evolution models, and make graphs or tables of the results. The user may also run some of our detailed nuclear physics and astrophysics codes, such as our nuclear statistical equilibrium code, which is written in fortran and C. Again, the user may make graphs and tables and download the results.

Some Unanswered Questions in Astronomy: Are There More than Nine Planets in the Universe? Is the Theory of Stellar Evolution Wrong?

ERIC Educational Resources Information Center

Field, George

1982-01-01

Based on the premise that discoveries raise more questions than they answer, explores various research questions related to the discovery of the planets and discoveries related to the theory of stellar evolution. (SK)

Star-disc interaction in galactic nuclei: formation of a central stellar disc

NASA Astrophysics Data System (ADS)

Panamarev, Taras; Shukirgaliyev, Bekdaulet; Meiron, Yohai; Berczik, Peter; Just, Andreas; Spurzem, Rainer; Omarov, Chingis; Vilkoviskij, Emmanuil

2018-05-01

We perform high-resolution direct N-body simulations to study the effect of an accretion disc on stellar dynamics in an active galactic nucleus (AGN). We show that the interaction of the nuclear stellar cluster (NSC) with the gaseous accretion disc (AD) leads to formation of a stellar disc in the central part of the NSC. The accretion of stars from the stellar disc on to the super-massive black hole is balanced by the capture of stars from the NSC into the stellar disc, yielding a stationary density profile. We derive the migration time through the AD to be 3 per cent of the half-mass relaxation time of the NSC. The mass and size of the stellar disc are 0.7 per cent of the mass and 5 per cent of the influence radius of the super-massive black hole. An AD lifetime shorter than the migration time would result in a less massive nuclear stellar disc. The detection of such a stellar disc could point to past activity of the hosting galactic nucleus.

Determining the Stellar Initial Mass by Means of the 17O/18O Ratio on the AGB

NASA Astrophysics Data System (ADS)

De Nutte, Rutger; Decin, Leen; Olofsson, Hans; de Koter, Alex; Karakas, Amanda; Lombaert, Robin; Milam, Stefanie; Ramstedt, Sofia; Stancliffe, Richard; Homan, Ward; Van de Sande, Marie

2016-07-01

This poster presentsnewly obtainedcircumstellar 12C17O and 12C18O line observations, from which theline intensity are then related directly tothe 17O/18O surface abundance ratiofor a sample of nine AGB stars covering the three spectral types ().These ratios are evaluated in relation to a fundamental stellar evolution parameters: the stellar initial mass. The17O/18O ratio is shown to function as an effective method of determining the initial stellar mass. Through comparison with predictions bystellar evolution models, accurate initial mass estimates are calculated for all nine sources.

Trajectories of Cepheid variable stars in the Galactic nuclear bulge

NASA Astrophysics Data System (ADS)

Matsunaga, Noriyuki

2012-06-01

The central region of our Galaxy provides us with a good opportunity to study the evolution of galactic nuclei and bulges because we can observe various phenomena in detail at the proximity of 8 kpc. There is a hierarchical alignment of stellar systems with different sizes; from the extended bulge, the nuclear bulge, down to the compact cluster around the central supermassive blackhole. The nuclear bulge contains stars as young as a few Myr, and even hosts the ongoing star formation. These are in contrast to the more extended bulge which are dominated by old stars, 10Gyr. It is considered that the star formation in the nuclear bulge is caused by fresh gas provided from the inner disk. In this picture, the nuclear bulge plays an important role as the interface between the gas supplier, the inner disk, and the galactic nucleus. Kinematics of young stars in the nuclear bulge is important to discuss the star forming process and the gas circulation in the Galactic Center. We here propose spectroscopic observations of Cepheid variable stars, 25 Myr, which we recently discovered in the nuclear bulge. The spectra taken in this proposal will allow timely estimates of the systemic velocities of the variable stars.

Our Cosmic Connection

ERIC Educational Resources Information Center

Young, Donna L.

2005-01-01

To help students understand the connection that Earth and the solar system have with the cosmic cycles of stellar evolution, and to give students an appreciation of the beauty and elegance of celestial phenomena, the Chandra X-Ray Center (CXC) educational website contains a stellar evolution module that is available free to teachers. In this…

A Census of Broad-line Active Galactic Nuclei in Nearby Galaxies: Coeval Star Formation and Rapid Black Hole Growth

NASA Astrophysics Data System (ADS)

Trump, Jonathan R.; Hsu, Alexander D.; Fang, Jerome J.; Faber, S. M.; Koo, David C.; Kocevski, Dale D.

2013-02-01

We present the first quantified, statistical map of broad-line active galactic nucleus (AGN) frequency with host galaxy color and stellar mass in nearby (0.01 < z < 0.11) galaxies. Aperture photometry and z-band concentration measurements from the Sloan Digital Sky Survey are used to disentangle AGN and galaxy emission, resulting in estimates of uncontaminated galaxy rest-frame color, luminosity, and stellar mass. Broad-line AGNs are distributed throughout the blue cloud and green valley at a given stellar mass, and are much rarer in quiescent (red sequence) galaxies. This is in contrast to the published host galaxy properties of weaker narrow-line AGNs, indicating that broad-line AGNs occur during a different phase in galaxy evolution. More luminous broad-line AGNs have bluer host galaxies, even at fixed mass, suggesting that the same processes that fuel nuclear activity also efficiently form stars. The data favor processes that simultaneously fuel both star formation activity and rapid supermassive black hole accretion. If AGNs cause feedback on their host galaxies in the nearby universe, the evidence of galaxy-wide quenching must be delayed until after the broad-line AGN phase.

Planetary nebula progenitors that swallow binary systems

NASA Astrophysics Data System (ADS)

Soker, Noam

2016-01-01

I propose that some irregular messy planetary nebulae (PNe) owe their morphologies to triple-stellar evolution where tight binary systems evolve inside and/or on the outskirts of the envelope of asymptotic giant branch (AGB) stars. In some cases, the tight binary system can survive, in others, it is destroyed. The tight binary system might break up with one star leaving the system. In an alternative evolution, one of the stars of the broken-up tight binary system falls towards the AGB envelope with low specific angular momentum, and drowns in the envelope. In a different type of destruction process, the drag inside the AGB envelope causes the tight binary system to merge. This releases gravitational energy within the AGB envelope, leading to a very asymmetrical envelope ejection, with an irregular and messy PN as a descendant. The evolution of the triple-stellar system can be in a full common envelope evolution or in a grazing envelope evolution. Both before and after destruction (if destruction takes place), the system might launch pairs of opposite jets. One pronounced signature of triple-stellar evolution might be a large departure from axisymmetrical morphology of the descendant PN. I estimate that about one in eight non-spherical PNe is shaped by one of these triple-stellar evolutionary routes.

Stellar Absorption Line Analysis of Local Star-forming Galaxies: The Relation between Stellar Mass, Metallicity, Dust Attenuation, and Star Formation Rate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jabran Zahid, H.; Kudritzki, Rolf-Peter; Ho, I-Ting

We analyze the optical continuum of star-forming galaxies in the Sloan Digital Sky Survey by fitting stacked spectra with stellar population synthesis models to investigate the relation between stellar mass, stellar metallicity, dust attenuation, and star formation rate. We fit models calculated with star formation and chemical evolution histories that are derived empirically from multi-epoch observations of the stellar mass–star formation rate and the stellar mass–gas-phase metallicity relations, respectively. We also fit linear combinations of single-burst models with a range of metallicities and ages. Star formation and chemical evolution histories are unconstrained for these models. The stellar mass–stellar metallicity relationsmore » obtained from the two methods agree with the relation measured from individual supergiant stars in nearby galaxies. These relations are also consistent with the relation obtained from emission-line analysis of gas-phase metallicity after accounting for systematic offsets in the gas-phase metallicity. We measure dust attenuation of the stellar continuum and show that its dependence on stellar mass and star formation rate is consistent with previously reported results derived from nebular emission lines. However, stellar continuum attenuation is smaller than nebular emission line attenuation. The continuum-to-nebular attenuation ratio depends on stellar mass and is smaller in more massive galaxies. Our consistent analysis of stellar continuum and nebular emission lines paves the way for a comprehensive investigation of stellar metallicities of star-forming and quiescent galaxies.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bekki, Kenji

We propose that there is an evolutionary link between ultra-compact blue dwarf galaxies (UCBDs) with active star formation and nucleated dwarfs based on the results of numerical simulations of dwarf–dwarf merging. We consider the observational fact that low-mass dwarfs can be very gas-rich, and thereby investigate the dynamical and chemical evolution of very gas-rich, dissipative dwarf–dwarf mergers. We find that the remnants of dwarf–dwarf mergers can be dominated by new stellar populations formed from the triggered starbursts and consequently can have blue colors and higher metallicities (Z ∼ [0.2–1]Z{sub ⊙}). We also find that the remnants of these mergers canmore » have rather high mass densities (10{sup 4} M{sub ⊙} pc{sup −3}) within the central 10 pc and small half-light radii (40−100 pc). The radial stellar structures of some merger remnants are similar to those of nucleated dwarfs. Star formation can continue in nuclear gas disks (R < 100 pc) surrounding stellar galactic nuclei (SGNs) so that the SGNs can finally have multiple stellar populations with different ages and metallicities. These very compact blue remnants can be identified as UCBDs soon after merging and as nucleated dwarfs after the young stars fade. We discuss these results in the context of the origins of metal-rich ultra-compact dwarfs and SGNs.« less

MERIDIONAL TILT OF THE STELLAR VELOCITY ELLIPSOID DURING BAR BUCKLING INSTABILITY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saha, Kanak; Pfenniger, Daniel; Taam, Ronald E., E-mail: saha@mpe.mpg.de

2013-02-20

The structure and evolution of the stellar velocity ellipsoid play an important role in shaping galaxies undergoing bar-driven secular evolution and the eventual formation of a boxy/peanut bulge such as is present in the Milky Way. Using collisionless N-body simulations, we show that during the formation of such a boxy/peanut bulge, the meridional shear stress of stars, which can be measured by the meridional tilt of the velocity ellipsoid, reaches a characteristic peak in its time evolution. It is shown that the onset of a bar buckling instability is closely connected to the maximum meridional tilt of the stellar velocitymore » ellipsoid. Our findings bring a new insight to this complex gravitational instability of the bar which complements the buckling instability studies based on orbital models. We briefly discuss the observed diagnostics of the stellar velocity ellipsoid during such a phenomenon.« less

The Evolution of the Tully-Fisher Relation between z ˜ 2.3 and z ˜ 0.9 with KMOS3D

NASA Astrophysics Data System (ADS)

Übler, H.; Förster Schreiber, N. M.; Genzel, R.; Wisnioski, E.; Wuyts, S.; Lang, P.; Naab, T.; Burkert, A.; van Dokkum, P. G.; Tacconi, L. J.; Wilman, D. J.; Fossati, M.; Mendel, J. T.; Beifiori, A.; Belli, S.; Bender, R.; Brammer, G. B.; Chan, J.; Davies, R.; Fabricius, M.; Galametz, A.; Lutz, D.; Momcheva, I. G.; Nelson, E. J.; Saglia, R. P.; Seitz, S.; Tadaki, K.

2017-06-01

We investigate the stellar mass and baryonic mass Tully-Fisher relations (TFRs) of massive star-forming disk galaxies at redshift z˜ 2.3 and z˜ 0.9 as part of the {{KMOS}}3{{D}} integral field spectroscopy survey. Our spatially resolved data allow reliable modeling of individual galaxies, including the effect of pressure support on the inferred gravitational potential. At fixed circular velocity, we find higher baryonic masses and similar stellar masses at z˜ 2.3 as compared to z˜ 0.9. Together with the decreasing gas-to-stellar mass ratios with decreasing redshift, this implies that the contribution of dark matter to the dynamical mass on the galaxy scale increases toward lower redshift. A comparison to local relations reveals a negative evolution of the stellar and baryonic TFR zero points from z = 0 to z˜ 0.9, no evolution of the stellar TFR zero point from z˜ 0.9 to z˜ 2.3, and a positive evolution of the baryonic TFR zero point from z˜ 0.9 to z˜ 2.3. We discuss a toy model of disk galaxy evolution to explain the observed nonmonotonic TFR evolution, taking into account the empirically motivated redshift dependencies of galactic gas fractions and the relative amount of baryons to dark matter on galaxy and halo scales. Based on observations collected at the European Organization for Astronomical Research in the Southern Hemisphere under ESO programs 092.A-0091, 093.A-0079, 094.A-0217, 095.A-0047, and 096.A-0025.

Failures no More: The Radical Consequences of Realistic Stellar Feedback for Dwarf Galaxies, the Milky Way, and Reionization

NASA Astrophysics Data System (ADS)

Hopkins, Philip F.

2016-06-01

Many of the most fundamental unsolved questions in star and galaxy formation revolve around star formation and "feedback" from massive stars, in-extricably linking galaxy formation and stellar evolution. I'll present simulations with un-precedented resolution of Milky-Way (MW) mass galaxies, followed cosmologically to redshift zero. For the first time, these simulations resolve the internal structure of small dwarf satellites around a MW-like host, with detailed models for stellar evolution including radiation pressure, supernovae, stellar winds, and photo-heating. I'll show that, without fine-tuning, these feedback processes naturally resolve the "missing satellites," "too big to fail," and "cusp-core" problems, and produce realistic galaxy populations. At high redshifts however, the realistic ISM structure predicted, coupled to standard stellar population models, naively leads to the prediction that only ~1-2% of ionizing photons can ever escape galaxies, insufficient to ionize the Universe. But these models assume all stars are single: if we account for binary evolution, the escape fraction increases dramatically to ~20% for the small, low-metallicity galaxies believed to ionize the Universe.

Asteroseismic Constraints on the Models of Hot B Subdwarfs: Convective Helium-Burning Cores

NASA Astrophysics Data System (ADS)

Schindler, Jan-Torge; Green, Elizabeth M.; Arnett, W. David

2017-10-01

Asteroseismology of non-radial pulsations in Hot B Subdwarfs (sdB stars) offers a unique view into the interior of core-helium-burning stars. Ground-based and space-borne high precision light curves allow for the analysis of pressure and gravity mode pulsations to probe the structure of sdB stars deep into the convective core. As such asteroseismological analysis provides an excellent opportunity to test our understanding of stellar evolution. In light of the newest constraints from asteroseismology of sdB and red clump stars, standard approaches of convective mixing in 1D stellar evolution models are called into question. The problem lies in the current treatment of overshooting and the entrainment at the convective boundary. Unfortunately no consistent algorithm of convective mixing exists to solve the problem, introducing uncertainties to the estimates of stellar ages. Three dimensional simulations of stellar convection show the natural development of an overshooting region and a boundary layer. In search for a consistent prescription of convection in one dimensional stellar evolution models, guidance from three dimensional simulations and asteroseismological results is indispensable.

Redshift evolution of the dynamical properties of massive galaxies from SDSS-III/BOSS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beifiori, Alessandra; Saglia, Roberto P.; Bender, Ralf

2014-07-10

We study the redshift evolution of the dynamical properties of ∼180, 000 massive galaxies from SDSS-III/BOSS combined with a local early-type galaxy sample from SDSS-II in the redshift range 0.1 ≤ z ≤ 0.6. The typical stellar mass of this sample is M{sub *} ∼2 × 10{sup 11} M{sub ☉}. We analyze the evolution of the galaxy parameters effective radius, stellar velocity dispersion, and the dynamical to stellar mass ratio with redshift. As the effective radii of BOSS galaxies at these redshifts are not well resolved in the Sloan Digital Sky Survey (SDSS) imaging we calibrate the SDSS size measurementsmore » with Hubble Space Telescope/COSMOS photometry for a sub-sample of galaxies. We further apply a correction for progenitor bias to build a sample which consists of a coeval, passively evolving population. Systematic errors due to size correction and the calculation of dynamical mass are assessed through Monte Carlo simulations. At fixed stellar or dynamical mass, we find moderate evolution in galaxy size and stellar velocity dispersion, in agreement with previous studies. We show that this results in a decrease of the dynamical to stellar mass ratio with redshift at >2σ significance. By combining our sample with high-redshift literature data, we find that this evolution of the dynamical to stellar mass ratio continues beyond z ∼ 0.7 up to z > 2 as M{sub dyn}/M{sub *} ∼(1 + z){sup –0.30±0.12}, further strengthening the evidence for an increase of M{sub dyn}/M{sub *} with cosmic time. This result is in line with recent predictions from galaxy formation simulations based on minor merger driven mass growth, in which the dark matter fraction within the half-light radius increases with cosmic time.« less

Status and future of MUSE

NASA Astrophysics Data System (ADS)

Harfst, S.; Portegies Zwart, S.; McMillan, S.

2008-12-01

We present MUSE, a software framework for combining existing computational tools from different astrophysical domains into a single multi-physics, multi-scale application. MUSE facilitates the coupling of existing codes written in different languages by providing inter-language tools and by specifying an interface between each module and the framework that represents a balance between generality and computational efficiency. This approach allows scientists to use combinations of codes to solve highly-coupled problems without the need to write new codes for other domains or significantly alter their existing codes. MUSE currently incorporates the domains of stellar dynamics, stellar evolution and stellar hydrodynamics for studying generalized stellar systems. We have now reached a ``Noah's Ark'' milestone, with (at least) two available numerical solvers for each domain. MUSE can treat multi-scale and multi-physics systems in which the time- and size-scales are well separated, like simulating the evolution of planetary systems, small stellar associations, dense stellar clusters, galaxies and galactic nuclei. In this paper we describe two examples calculated using MUSE: the merger of two galaxies and an N-body simulation with live stellar evolution. In addition, we demonstrate an implementation of MUSE on a distributed computer which may also include special-purpose hardware, such as GRAPEs or GPUs, to accelerate computations. The current MUSE code base is publicly available as open source at http://muse.li.

The Apache Point Observatory Galactic Evolution Experiment (APOGEE) and its successor, APOGEE-2

NASA Astrophysics Data System (ADS)

Majewski, S. R.; APOGEE Team; APOGEE-2 Team

2016-09-01

The Apache Point Observatory Galactic Evolution Experiment (APOGEE) of Sloan Digital Sky Survey III (SDSS-III) has produced a large catalog of high resolution ({R = 22 500}), high quality (S/N > 100), infrared (H-band) spectra for stars throughout all stellar populations of the Milky Way, including in regions veiled by significant dust opacity. APOGEE's half million spectra collected on > 163 000 unique stars, with time series information via repeat visits to each star, are being applied to numerous problems in stellar populations, Galactic astronomy, and stellar astrophysics. From among the early results of the APOGEE project - which span from measurements of Galactic dynamics, to multi-element chemical maps of the disk and bulge, new views of the interstellar medium, explorations of stellar companions, the chemistry of star clusters, and the discovery of rare stellar species - I highlight a few results that demonstrate APOGEE's unique ability to sample and characterize the Galactic disk and bulge. Plans are now under way for an even more ambitious successor to APOGEE: the six-year, dual-hemisphere APOGEE-2 project. Both phases of APOGEE feature a strong focus on targets having asteroseismological measurements from either Kepler or {CoRoT}, from which it is possible to derive relatively precise stellar ages. The combined APOGEE and APOGEE-2 databases of stellar chemistry, dynamics and ages constitute an unusually comprehensive, systematic and homogeneous resource for constraining models of Galactic evolution.

MY Cam: can homogeneous evolution produce gravitational-wave progenitors?

NASA Astrophysics Data System (ADS)

Negueruela, Ignacio

2016-10-01

Besides opening the era of gravitational-wave astrophysics, GW150914 has revolutionized the field of massive stars. GW150914 proves the existence of stellar-mass black holes in a configuration that current models for stellar evolution can only reproduce in special conditions of homogeneous evolution and/or low metallicity.Only a handful of very-massive binaries that could lead to a binary black hole are known. We request UV spectroscopy of MY Cam (38Msun+32Msun), the best laboratory to test several predictions by current models, in order to derive stellar abundances and wind parameters that are inaccessible from the ground. Together with our previous photometric and spectroscopic exhaustive coverage, the STIS spectra will be key to characterize the pre-common envelope phase and test the homogeneous evolution hypothesis, critical ingredients of the different progenitor scenarios proposed to explain GW15091.

Preface (for CUP)

NASA Technical Reports Server (NTRS)

Pap, Judit

1993-01-01

Study of changes in solar and stellar irradiances has been of high interest for a long time. Determining the absolute value of the luminosity of stars with different ages is a crucial question for the theory of stellar evolution and energy production in stellar interiors.

What makes the family of barred disc galaxies so rich: damping stellar bars in spinning haloes

NASA Astrophysics Data System (ADS)

Collier, Angela; Shlosman, Isaac; Heller, Clayton

2018-05-01

We model and analyse the secular evolution of stellar bars in spinning dark matter (DM) haloes with the cosmological spin λ ˜ 0-0.09. Using high-resolution stellar and DM numerical simulations, we focus on angular momentum exchange between stellar discs and DM haloes of various axisymmetric shapes - spherical, oblate, and prolate. We find that stellar bars experience a diverse evolution that is guided by the ability of parent haloes to absorb angular momentum, J, lost by the disc through the action of gravitational torques, resonant and non-resonant. We confirm that dynamical bar instability is accelerated via resonant J-transfer to the halo. Our main findings relate to the long-term secular evolution of disc-halo systems: with an increasing λ, bars experience less growth and basically dissolve after they pass through vertical buckling instability. Specifically, with increasing λ, (1) the vertical buckling instability in stellar bars colludes with inability of the inner halo to absorb J - this emerges as the main factor weakening or destroying bars in spinning haloes; (2) bars lose progressively less J, and their pattern speeds level off; (3) bars are smaller, and for λ ≳ 0.06 cease their growth completely following buckling; (4) bars in λ > 0.03 haloes have ratio of corotation-to-bar radii, RCR/Rb > 2, and represent so-called slow bars without offset dust lanes. We provide a quantitative analysis of J-transfer in disc-halo systems, and explain the reasons for absence of growth in fast spinning haloes and its observational corollaries. We conclude that stellar bar evolution is substantially more complex than anticipated, and bars are not as resilient as has been considered so far.

Delayed Gratification Habitable Zones (DG-HZs): When Deep Outer Solar System Regions Become Balmy During Post-Main Sequence Stellar Evolution

NASA Astrophysics Data System (ADS)

Stern, S. A.

2002-09-01

Late in the Sun's evolution it, like all low and moderate mass stars, it will burn as a red giant, generating 1000s of solar luminosities for a few tens of millions of years. A dozen years ago this stage of stellar evolution was predicted to create observable sublimation signatures in systems where Kuiper Belts (KBs) are extant (Stern et al. 1990, Nature, 345, 305); recently, the SWAS spacecraft detected such systems (Melnick et al. 2001, 412, 160). During the red giant phase, the habitable zone of our solar system will lie in the region where Triton, Pluto-Charon, and KBOs orbit. Compared to the 1 AU habitable zone where Earth resided early in the solar system's history, this "delayed gratification habitable zone (DG-HZ)" will enjoy a far less biologically hazardous environment-- with far lower harmful UV radiation levels from the Sun, and a far quieter collisional environment. Objects like Triton, Pluto-Charon, and KBOs, which are known to be rich in both water and organics, will then become possible sites for biochemical and perhaps even biological evolution. The Sun's DG-HZ may only be of academic interest owing to its great separation from us in time. However, several 108 approximately solar-type Milky Way stars burn as luminous red giants today. Thus, if icy-organic objects are common in the 20-50 AU zones of these stars, as they are in our solar system (and as inferred in numerous main sequence stellar disk systems), then DG-HZs form a kind of niche habitable zone that is likely to be numerically common in the galaxy. I will show the calculated temporal evolution of DG-HZs around various stellar types using modern stellar evolution luminosity tracks, and then discuss various aspects of DG-HZs, including the effects of stellar pulsations and mass loss winds. This work was supported by NASA's Origins of Solar Systems Program.

The Galaxy mass function up to z =4 in the GOODS-MUSIC sample: into the epoch of formation of massive galaxies

NASA Astrophysics Data System (ADS)

Fontana, A.; Salimbeni, S.; Grazian, A.; Giallongo, E.; Pentericci, L.; Nonino, M.; Fontanot, F.; Menci, N.; Monaco, P.; Cristiani, S.; Vanzella, E.; de Santis, C.; Gallozzi, S.

2006-12-01

Aims.The goal of this work is to measure the evolution of the Galaxy Stellar Mass Function and of the resulting Stellar Mass Density up to redshift ≃4, in order to study the assembly of massive galaxies in the high redshift Universe. Methods: .We have used the GOODS-MUSIC catalog, containing 3000 Ks-selected galaxies with multi-wavelength coverage extending from the U band to the Spitzer 8 μm band, of which 27% have spectroscopic redshifts and the remaining fraction have accurate photometric redshifts. On this sample we have applied a standard fitting procedure to measure stellar masses. We compute the Galaxy Stellar Mass Function and the resulting Stellar Mass Density up to redshift ≃4, taking into proper account the biases and incompleteness effects. Results: .Within the well known trend of global decline of the Stellar Mass Density with redshift, we show that the decline of the more massive galaxies may be described by an exponential timescale of ≃6 Gyr up to z≃ 1.5, and proceeds much faster thereafter, with an exponential timescale of ≃0.6 Gyr. We also show that there is some evidence for a differential evolution of the Galaxy Stellar Mass Function, with low mass galaxies evolving faster than more massive ones up to z≃ 1{-}1.5 and that the Galaxy Stellar Mass Function remains remarkably flat (i.e. with a slope close to the local one) up to z≃ 1{-}1.3. Conclusions: .The observed behaviour of the Galaxy Stellar Mass Function is consistent with a scenario where about 50% of present-day massive galaxies formed at a vigorous rate in the epoch between redshift 4 and 1.5, followed by a milder evolution until the present-day epoch.

The relativistic equations of stellar structure and evolution

NASA Technical Reports Server (NTRS)

Thorne, K. S.

1975-01-01

The general relativistic equations of stellar structure and evolution are reformulated in a notation which makes easy contact with Newtonian theory. A general relativistic version of the mixing-length formalism for convection is presented. It is argued that in work on spherical systems, general relativity theorists have identified the wrong quantity as total mass-energy inside radius r.

Weak-interaction rates in stellar conditions

NASA Astrophysics Data System (ADS)

Sarriguren, Pedro

2018-05-01

Weak-interaction rates, including β-decay and electron captures, are studied in several mass regions at various densities and temperatures of astrophysical interest. In particular, we study odd-A nuclei in the pf-shell region, which are involved in presupernova formations. Weak rates are relevant to understand the late stages of the stellar evolution, as well as the nucleosynthesis of heavy nuclei. The nuclear structure involved in the weak processes is studied within a quasiparticle proton-neutron random-phase approximation with residual interactions in both particle-hole and particle-particle channels on top of a deformed Skyrme Hartree-Fock mean field with pairing correlations. First, the energy distributions of the Gamow-Teller strength are discussed and compared with the available experimental information, measured under terrestrial conditions from charge-exchange reactions. Then, the sensitivity of the weak-interaction rates to both astrophysical densities and temperatures is studied. Special attention is paid to the relative contribution to these rates of thermally populated excited states in the decaying nucleus and to the electron captures from the degenerate electron plasma.

An Integrated Picture of Star Formation, Metallicity Evolution, and Galactic Stellar Mass Assembly

NASA Astrophysics Data System (ADS)

Cowie, L. L.; Barger, A. J.

2008-10-01

We present an integrated study of star formation and galactic stellar mass assembly from z = 0.05 to 1.5 and galactic metallicity evolution from z = 0.05 to 0.9 using a very large and highly spectroscopically complete sample selected by rest-frame NIR bolometric flux in the GOODS-N. We assume a Salpeter IMF and fit Bruzual & Charlot models to compute the galactic stellar masses and extinctions. We determine the expected formed stellar mass density growth rates produced by star formation and compare them with the growth rates measured from the formed stellar mass functions by mass interval. We show that the growth rates match if the IMF is slightly increased from the Salpeter IMF at intermediate masses (~10 M⊙). We investigate the evolution of galaxy color, spectral type, and morphology with mass and redshift and the evolution of mass with environment. We find that applying extinction corrections is critical when analyzing galaxy colors; e.g., nearly all of the galaxies in the green valley are 24 μm sources, but after correcting for extinction, the bulk of the 24 μm sources lie in the blue cloud. We find an evolution of the metallicity-mass relation corresponding to a decrease of 0.21 +/- 0.03 dex between the local value and the value at z = 0.77 in the 1010-1011 M⊙ range. We use the metallicity evolution to estimate the gas mass of the galaxies, which we compare with the galactic stellar mass assembly and star formation histories. Overall, our measurements are consistent with a galaxy evolution process dominated by episodic bursts of star formation and where star formation in the most massive galaxies (gtrsim1011 M⊙) ceases at z < 1.5 because of gas starvation. Based in part on data obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA and was made possible by the generous financial support of the W. M. Keck Foundation.

High Energy Density Plasmas (HEDP) for studies of basic nuclear science relevant to Stellar and Big Bang Nucleosynthesis

NASA Astrophysics Data System (ADS)

Frenje, Johan

2014-06-01

Thermonuclear reaction rates and nuclear processes have been explored traditionally by means of conventional accelerator experiments, which are difficult to execute at conditions relevant to stellar nucleosynthesis. Thus, nuclear reactions at stellar energies are often studied through extrapolations from higher-energy data or in low-background underground experiments. Even when measurements are possible using accelerators at relevant energies, thermonuclear reaction rates in stars are inherently different from those in accelerator experiments. The fusing nuclei are surrounded by bound electrons in accelerator experiments, whereas electrons occupy mainly continuum states in a stellar environment. Nuclear astrophysics research will therefore benefit from an enlarged toolkit for studies of nuclear reactions. In this presentation, we report on the first use of High Energy Density Plasmas for studies of nuclear reactions relevant to basic nuclear science, stellar and Big Bang nucleosynthesis. These experiments were carried out at the OMEGA laser facility at University of Rochester and the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory, in which spherical capsules were irradiated with powerful lasers to compress and heat the fuel to high enough temperatures and densities for nuclear reactions to occur. Four experiments will be highlighted in this presentation. In the first experiment, the differential cross section for the elastic neutron-triton (n-T) scattering at 14.1 MeV was measured with significantly higher accuracy than achieved in accelerator experiments. In the second experiment, the T(t,2n)4He reaction, a mirror reaction to the 3He(3He,2p)4He reaction that plays an important role in the proton-proton chain that transforms hydrogen into ordinary 4He in stars like our Sun, was studied at energies in the range 15-40 keV. In the third experiment, the 3He+3He solar fusion reaction was studied directly, and in the fourth experiment, we probed the T+3He reaction, possibly relevant to Big Bang nucleosynthesis.

Abundance Patterns in S-type AGB Stars: Setting Constraints on Nucleosynthesis and Stellar Evolution Models

NASA Astrophysics Data System (ADS)

Neyskens, P.; van Eck, S.; Plez, B.; Goriely, S.; Siess, L.; Jorissen, A.

2011-09-01

During evolution on the AGB, stars of type S are the first to experience s-process nucleosynthesis and the third dredge-up, and therefore to exhibit s-process signatures in their atmospheres. Their high mass-loss rates (10-7 to 10-6 M⊙/year) make them major contributors to the AGB nucleosynthesis yields at solar metallicity. Precise abundance determinations in S stars are of the utmost importance for constraining e.g. the third dredge-up luminosity and efficiency (which has been only crudely parameterized in current nucleosynthetic models so far). Here, dedicated S-star model atmospheres are used to determine precise abundances of key s-process elements, and to set constraints on nucleosynthesis and stellar evolution models. Special interest is paid to technetium, an element with no stable isotopes. Its detection is considered the best signature that the star effectively populates the thermally-pulsing AGB phase of evolution. The derived Tc/Zr abundances are compared, as a function of the derived [Zr/Fe] overabundances, with AGB stellar model predictions. The [Zr/Fe] overabundances are in good agreement with model predictions, while the Tc/Zr abundances are slightly overpredicted. This discrepancy can help to set better constraints on nucleosynthesis and stellar evolution models of AGB stars.

Not-so-simple stellar populations in nearby, resolved massive star clusters

NASA Astrophysics Data System (ADS)

de Grijs, Richard; Li, Chengyuan

2018-02-01

Around the turn of the last century, star clusters of all kinds were considered ‘simple’ stellar populations. Over the past decade, this situation has changed dramatically. At the same time, star clusters are among the brightest stellar population components and, as such, they are visible out to much greater distances than individual stars, even the brightest, so that understanding the intricacies of star cluster composition and their evolution is imperative for understanding stellar populations and the evolution of galaxies as a whole. In this review of where the field has moved to in recent years, we place particular emphasis on the properties and importance of binary systems, the effects of rapid stellar rotation, and the presence of multiple populations in Magellanic Cloud star clusters across the full age range. Our most recent results imply a reverse paradigm shift, back to the old simple stellar population picture for at least some intermediate-age (˜1-3 Gyr old) star clusters, opening up exciting avenues for future research efforts.

Influence of Stellar Multiplicity On Planet Formation. III. Adaptive Optics Imaging of Kepler Stars With Gas Giant Planets

NASA Astrophysics Data System (ADS)

Wang, Ji; Fischer, Debra A.; Horch, Elliott P.; Xie, Ji-Wei

2015-06-01

As hundreds of gas giant planets have been discovered, we study how these planets form and evolve in different stellar environments, specifically in multiple stellar systems. In such systems, stellar companions may have a profound influence on gas giant planet formation and evolution via several dynamical effects such as truncation and perturbation. We select 84 Kepler Objects of Interest (KOIs) with gas giant planet candidates. We obtain high-angular resolution images using telescopes with adaptive optics (AO) systems. Together with the AO data, we use archival radial velocity data and dynamical analysis to constrain the presence of stellar companions. We detect 59 stellar companions around 40 KOIs for which we develop methods of testing their physical association. These methods are based on color information and galactic stellar population statistics. We find evidence of suppressive planet formation within 20 AU by comparing stellar multiplicity. The stellar multiplicity rate (MR) for planet host stars is {0}-0+5% within 20 AU. In comparison, the stellar MR is 18% ± 2% for the control sample, i.e., field stars in the solar neighborhood. The stellar MR for planet host stars is 34% ± 8% for separations between 20 and 200 AU, which is higher than the control sample at 12% ± 2%. Beyond 200 AU, stellar MRs are comparable between planet host stars and the control sample. We discuss the implications of the results on gas giant planet formation and evolution.

Ion traps for precision experiments at rare-isotope-beam facilities

NASA Astrophysics Data System (ADS)

Kwiatkowski, Anna

2016-09-01

Ion traps first entered experimental nuclear physics when the ISOLTRAP team demonstrated Penning trap mass spectrometry of radionuclides. From then on, the demand for ion traps has grown at radioactive-ion-beam (RIB) facilities since beams can be tailored for the desired experiment. Ion traps have been deployed for beam preparation, from bunching (thereby allowing time coincidences) to beam purification. Isomerically pure beams needed for nuclear-structure investigations can be prepared for trap-assisted or in-trap decay spectroscopy. The latter permits studies of highly charged ions for stellar evolution, which would be impossible with traditional experimental nuclear-physics methods. Moreover, the textbook-like conditions and advanced ion manipulation - even of a single ion - permit high-precision experiments. Consequently, the most accurate and precise mass measurements are now performed in Penning traps. After a brief introduction to ion trapping, I will focus on examples which showcase the versatility and utility of the technique at RIB facilities. I will demonstrate how this atomic-physics technique has been integrated into nuclear science, accelerator physics, and chemistry. DOE.

The effect of stellar evolution uncertainties on the rest-frame ultraviolet stellar lines of C IV and He II in high-redshift Lyman-break galaxies

NASA Astrophysics Data System (ADS)

Eldridge, John J.; Stanway, Elizabeth R.

2012-01-01

Young, massive stars dominate the rest-frame ultraviolet (UV) spectra of star-forming galaxies. At high redshifts (z > 2), these rest-frame UV features are shifted into the observed-frame optical and a combination of gravitational lensing, deep spectroscopy and spectral stacking analysis allows the stellar population characteristics of these sources to be investigated. We use our stellar population synthesis code Binary Population and Spectral Synthesis (BPASS) to fit two strong rest-frame UV spectral features in published Lyman-break galaxy spectra, taking into account the effects of binary evolution on the stellar spectrum. In particular, we consider the effects of quasi-homogeneous evolution (arising from the rotational mixing of rapidly rotating stars), metallicity and the relative abundance of carbon and oxygen on the observed strengths of He IIλ1640 Å and C IVλ1548, 1551 Å spectral lines. We find that Lyman-break galaxy spectra at z ˜ 2-3 are best fitted with moderately sub-solar metallicities, and with a depleted carbon-to-oxygen ratio. We also find that the spectra of the lowest metallicity sources are best fitted with model spectra in which the He II emission line is boosted by the inclusion of the effect of massive stars being spun-up during binary mass transfer so these rapidly rotating stars experience quasi-homogeneous evolution.

The Origin of Stellar Species: constraining stellar evolution scenarios with Local Group galaxy surveys

NASA Astrophysics Data System (ADS)

Sarbadhicary, Sumit; Badenes, Carles; Chomiuk, Laura; Maldonado, Jessica; Caprioli, Damiano; Heger, Mairead; Huizenga, Daniel

2018-01-01

Our understanding of the progenitors of many stellar species, such as supernovae, massive and low-mass He-burning stars, is limited because of many poorly constrained aspects of stellar evolution theory. For my dissertation, I have focused on using Local Group galaxy surveys to constrain stellar evolution scenarios by measuring delay-time distributions (DTD). The DTD is the hypothetical occurrence rate of a stellar object per elapsed time after a brief burst of star formation. It is the measured distribution of timescales on which stars evolve, and therefore serves as a powerful observational constraint on theoretical progenitor models. The DTD can be measured from a survey of stellar objects and a set of star-formation histories of the host galaxy, and is particularly effective in the Local Group, where high-quality star-formation histories are available from resolved stellar populations. I am currently calculating a SN DTD with supernova remnants (SNRs) in order to provide the strongest constraints on the progenitors of thermonuclear and core-collapse supernovae. However, most SNRs do not have reliable age measurements and their evolution depends on the ambient environment. For this reason, I wrote a radio light curve model of an SNR population to extract the visibility times and rates of supernovae - crucial ingredients for the DTD - from an SNR survey. The model uses observational constraints on the local environments from multi-wavelength surveys, accounts for missing SNRs and employs the latest models of shock-driven particle acceleration. The final calculation of the SN DTD in the Local Group is awaiting completion of a systematic SNR catalog from deep radio-continuum images, now in preparation by a group led by Dr. Laura Chomiuk. I have also calculated DTDs for the LMC population of RR Lyrae and Cepheid variables, which serve as important distance calibrators and stellar population tracers. We find that Cepheids can have delay-times between 10 Myrs - 1 Gyr, while RR Lyrae can have delay-times < 10 Gyrs. These observations cannot be explained by models using mass and metallicity alone. In future projects, I will apply the DTD technique to constrain the supergiant and pre-supernova evolutionary models.

The GALAH Survey and Galactic Archaeology in the Next Decade

NASA Astrophysics Data System (ADS)

Martell, S. L.

2016-10-01

The field of Galactic Archaeology aims to understand the origins and evolution of the stellar populations in the Milky Way, as a way to understand galaxy formation and evolution in general. The GALAH (Galactic Archaeology with HERMES) Survey is an ambitious Australian-led project to explore the Galactic history of star formation, chemical evolution, minor mergers and stellar migration. GALAH is using the HERMES spectrograph, a novel, highly multiplexed, four-channel high-resolution optical spectrograph, to collect high-quality R˜28,000 spectra for one million stars in the Milky Way. From these data we will determine stellar parameters, radial velocities and abundances for up to 29 elements per star, and carry out a thorough chemical tagging study of the nearby Galaxy. There are clear complementarities between GALAH and other ongoing and planned Galactic Archaeology surveys, and also with ancillary stellar data collected by major cosmological surveys. Combined, these data sets will provide a revolutionary view of the structure and history of the Milky Way.

ABUNDANCES IN THE LOCAL REGION. I. G AND K GIANTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luck, R. Earle, E-mail: rel2@case.edu

2015-09-15

Parameters and abundances for 1133 stars of spectral types F, G, and K of luminosity class III have been derived. In terms of stellar parameters, the primary point of interest is the disagreement between gravities derived with masses determined from isochrones, and gravities determined from an ionization balance. This is not a new result per se, but the size of this sample emphasizes the severity of the problem. A variety of arguments led to the selection of the ionization-balance gravity as the working value. The derived abundances indicate that the giants in the solar region have Sun-like total abundances andmore » abundance ratios. Stellar evolution indicators have also been investigated with the Li abundances and the [C/Fe] and C/O ratios, indicating that standard processing has been operating in these stars. The more salient result for stellar evolution is that the [C/Fe] data across the red-giant clump indicates the presence of mass-dependent mixing in accord with standard stellar evolution predictions.« less

The great escape - III. Placing post-main-sequence evolution of planetary and binary systems in a Galactic context

NASA Astrophysics Data System (ADS)

Veras, Dimitri; Evans, N. Wyn; Wyatt, Mark C.; Tout, Christopher A.

2014-01-01

Our improving understanding of the life cycle of planetary systems prompts investigations of the role of the Galenvironment before, during and after asymptotic giant branch (AGB) stellar evolution. Here, we investigate the interplay between stellar mass-loss, Galactic tidal perturbations and stellar flybys for evolving stars which host one planet, smaller body or stellar binary companion and reside in the Milky Way's bulge or disc. We find that the potential evolutionary pathways from a main sequence (MS) to a white dwarf (WD) planetary system are a strong function of Galactocentric distance only with respect to the prevalence of stellar flybys. Planetary ejection and collision with the parent star should be more common towards the bulge. At a given location anywhere in the Galaxy, if the mass-loss is adiabatic, then the secondary is likely to avoid close flybys during AGB evolution, and cannot eventually escape the resulting WD because of Galactic tides alone. Partly because AGB mass-loss will shrink a planetary system's Hill ellipsoid axes by about 20 to 40 per cent, Oort clouds orbiting WDs are likely to be more depleted and dynamically excited than on the MS.

UV Astronomy: Stars from Birth to Death

NASA Astrophysics Data System (ADS)

Gómez de Castro, Ana I.; Barstow, Martin A.

The Joint Discussion on UV Astronmy: Stars from Birth to Death was held during the IAU General Assembly of 2006, in August 2006. It was aimed to provide a forum where the accomplishments of UV astrophysics could be highlighted and a new roadmap for the future discussed. This meeting focussed in particular on stellar astrophysics. The understanding of stellar physics is at the very base of our understanding of the Universe. The chemical evolution of the Universe is controlled by stars. Supernovae are prime distance indicators that have allowed to measure the evolution of the curvature of the Universe and to detect the existence of dark energy. The development of life sustaining system depends strongly on the evolution of stars like our Sun. Some of the most extreme forms of matter in the Universe, the densest and more strongly magnetized, are the magnetars, debris of stellar evolution. The excellent contributions presented in this Joint Discussion dealt with the many aspects of stellar astrophysics from the analysis of dissipative processes in the atmosphere of cool stars and their impact on the evolution of the planetary systems to the study of the atmospheres and winds of the hot massive stars or the determination of the abundances in white dwarfs. The physics of disks, its role in the evolution of binary systems, and the formation of supernovae were among the main topics treated in the meeting. We should also not forget the role of starbursts and, in general, high mass stars in the chemical evolution of galaxies. The metallicity gradient in the Galaxy is traced in the UV spectrum of planetary nebulae. The evolution of young planetary disks and the role of the central stars in the photoevaporation of the giant gaseous planets that have been detected recently. The book contains a summary of the numerous and high quality contributions to this Joint Discussion classified in five chapters: * Chapter 1: Star Formation and Young Stellar Objects * Chapter 2: Life in Main Sequence * Chapter 3: Star Death * Chapter 4: Compact Objects * Chapter 5: The impact of stellar astrophysics in understanding the formation of life sustainable systems; That correspond to the five sessions held during the meeting. A summary of the current status of UV astronomy and the discussions that took place during the XXVIth I. A. U. General Assembly can be found in Highlights of Astronomy, Volume 14.

Rotational evolution of slow-rotator sequence stars

NASA Astrophysics Data System (ADS)

Lanzafame, A. C.; Spada, F.

2015-12-01

Context. The observed relationship between mass, age and rotation in open clusters shows the progressive development of a slow-rotator sequence among stars possessing a radiative interior and a convective envelope during their pre-main sequence and main-sequence evolution. After 0.6 Gyr, most cluster members of this type have settled on this sequence. Aims: The observed clustering on this sequence suggests that it corresponds to some equilibrium or asymptotic condition that still lacks a complete theoretical interpretation, and which is crucial to our understanding of the stellar angular momentum evolution. Methods: We couple a rotational evolution model, which takes internal differential rotation into account, with classical and new proposals for the wind braking law, and fit models to the data using a Monte Carlo Markov chain (MCMC) method tailored to the problem at hand. We explore to what extent these models are able to reproduce the mass and time dependence of the stellar rotational evolution on the slow-rotator sequence. Results: The description of the evolution of the slow-rotator sequence requires taking the transfer of angular momentum from the radiative core to the convective envelope into account. We find that, in the mass range 0.85-1.10 M⊙, the core-envelope coupling timescale for stars in the slow-rotator sequence scales as M-7.28. Quasi-solid body rotation is achieved only after 1-2 Gyr, depending on stellar mass, which implies that observing small deviations from the Skumanich law (P ∝ √{t}) would require period data of older open clusters than is available to date. The observed evolution in the 0.1-2.5 Gyr age range and in the 0.85-1.10 M⊙ mass range is best reproduced by assuming an empirical mass dependence of the wind angular momentum loss proportional to the convective turnover timescale and to the stellar moment of inertia. Period isochrones based on our MCMC fit provide a tool for inferring stellar ages of solar-like main-sequence stars from their mass and rotation period that is largely independent of the wind braking model adopted. These effectively represent gyro-chronology relationships that take the physics of the two-zone model for the stellar angular momentum evolution into account.

Stellar Explosions: Hydrodynamics and Nucleosynthesis

NASA Astrophysics Data System (ADS)

Jose, Jordi

2016-01-01

Stars are the main factories of element production in the universe through a suite of complex and intertwined physical processes. Such stellar alchemy is driven by multiple nuclear interactions that through eons have transformed the pristine, metal-poor ashes leftover by the Big Bang into a cosmos with 100 distinct chemical species. The products of stellar nucleosynthesis frequently get mixed inside stars by convective transport or through hydrodynamic instabilities, and a fraction of them is eventually ejected into the interstellar medium, thus polluting the cosmos with gas and dust. The study of the physics of the stars and their role as nucleosynthesis factories owes much to cross-fertilization of different, somehow disconnected fields, ranging from observational astronomy, computational astrophysics, and cosmochemistry to experimental and theoretical nuclear physics. Few books have simultaneously addressed the multidisciplinary nature of this field in an engaging way suitable for students and young scientists. Providing the required multidisciplinary background in a coherent way has been the driving force for Stellar Explosions: Hydrodynamics and Nucleosynthesis. Written by a specialist in stellar astrophysics, this book presents a rigorous but accessible treatment of the physics of stellar explosions from a multidisciplinary perspective at the crossroads of computational astrophysics, observational astronomy, cosmochemistry, and nuclear physics. Basic concepts from all these different fields are applied to the study of classical and recurrent novae, type I and II supernovae, X-ray bursts and superbursts, and stellar mergers. The book shows how a multidisciplinary approach has been instrumental in our understanding of nucleosynthesis in stars, particularly during explosive events.

Stellar Explosions: Hydrodynamics and Nucleosynthesis

NASA Astrophysics Data System (ADS)

José, Jordi

2015-12-01

Stars are the main factories of element production in the universe through a suite of complex and intertwined physical processes. Such stellar alchemy is driven by multiple nuclear interactions that through eons have transformed the pristine, metal-poor ashes leftover by the Big Bang into a cosmos with 100 distinct chemical species. The products of stellar nucleosynthesis frequently get mixed inside stars by convective transport or through hydrodynamic instabilities, and a fraction of them is eventually ejected into the interstellar medium, thus polluting the cosmos with gas and dust. The study of the physics of the stars and their role as nucleosynthesis factories owes much to cross-fertilization of different, somehow disconnected fields, ranging from observational astronomy, computational astrophysics, and cosmochemistry to experimental and theoretical nuclear physics. Few books have simultaneously addressed the multidisciplinary nature of this field in an engaging way suitable for students and young scientists. Providing the required multidisciplinary background in a coherent way has been the driving force for Stellar Explosions: Hydrodynamics and Nucleosynthesis. Written by a specialist in stellar astrophysics, this book presents a rigorous but accessible treatment of the physics of stellar explosions from a multidisciplinary perspective at the crossroads of computational astrophysics, observational astronomy, cosmochemistry, and nuclear physics. Basic concepts from all these different fields are applied to the study of classical and recurrent novae, type I and II supernovae, X-ray bursts and superbursts, and stellar mergers. The book shows how a multidisciplinary approach has been instrumental in our understanding of nucleosynthesis in stars, particularly during explosive events.

The Multiplicity of Wolf-Rayet Stars

NASA Technical Reports Server (NTRS)

Wallace, Debra J.

2004-01-01

The most massive stars drastically reconfigure their surroundings via their strong stellar winds and powerful ionizing radiation. With this mass fueling their large luminosities, these stars are frequently used as standard candles in distance determination, and as tracers of stellar evolution in different regions and epochs. In their dieing burst, some of the once massive stars will enter a Wolf-Rayet (WR) phase lasting approx.10% of the stellar lifetime. This phase is particularly useful for study because these stars have strong spectroscopic signatures that allow them to be easily identified at great distances. But how accurate are these identifications? Increasingly, the relatively nearby stars we once assumed to be single are revealing themselves to be binary or multiple. New techniques, such as high-resolution imaging and interferometry, are changing our knowledge of these objects. I will discuss recent results in the literature and how this affects the binary distribution of WR stars. I will also discuss the implications of binary vs. single star evolution on evolution through the WR phase. Finally, I will discuss the implications of these revised numbers on both massive stellar evolution itself, and the impact that this has on the role of WR stars as calibrators.

DEPENDENCE OF X-RAY BURST MODELS ON NUCLEAR REACTION RATES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cyburt, R. H.; Keek, L.; Schatz, H.

2016-10-20

X-ray bursts are thermonuclear flashes on the surface of accreting neutron stars, and reliable burst models are needed to interpret observations in terms of properties of the neutron star and the binary system. We investigate the dependence of X-ray burst models on uncertainties in (p, γ ), ( α , γ ), and ( α , p) nuclear reaction rates using fully self-consistent burst models that account for the feedbacks between changes in nuclear energy generation and changes in astrophysical conditions. A two-step approach first identified sensitive nuclear reaction rates in a single-zone model with ignition conditions chosen to matchmore » calculations with a state-of-the-art 1D multi-zone model based on the Kepler stellar evolution code. All relevant reaction rates on neutron-deficient isotopes up to mass 106 were individually varied by a factor of 100 up and down. Calculations of the 84 changes in reaction rate with the highest impact were then repeated in the 1D multi-zone model. We find a number of uncertain reaction rates that affect predictions of light curves and burst ashes significantly. The results provide insights into the nuclear processes that shape observables from X-ray bursts, and guidance for future nuclear physics work to reduce nuclear uncertainties in X-ray burst models.« less

Second Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun, volume 1

NASA Technical Reports Server (NTRS)

Giampapa, M. S. (Editor); Golub, L. (Editor)

1981-01-01

Solar and stellar atmospheric phenomena and their fundamental physical properties such as gravity, effective temperature and rotation rate, which provides the range in parameter space required to test various theoretical models were investigated. The similarity between solar activity and stellar activity is documented. Some of the topics discussed are: atmospheric structure, magnetic fields, solar and stellar activity, and evolution.

Abundance anomalies in RGB stars as probes of galactic chemical evolution

NASA Astrophysics Data System (ADS)

Charbonnel, C.; Palacios, A.

During the last two decades, extensive spectroscopic studies have revealed chemical abundance anomalies exhibited by low mass RGB stars which bring a new light on some important aspects of stellar nucleosynthesis and chemical evolution. We underline the differences between field and globular cluster populations and discuss their possible origin both in terms of primordial pollution and stellar internal nucleosynthesis and mixing. We suggest some tests to help to understand the influence of metallicity and of a dense environment on abundance anomalies in connection with the second parameter problem and with the stellar yields.

ON POTASSIUM AND OTHER ABUNDANCE ANOMALIES OF RED GIANTS IN NGC 2419

DOE Office of Scientific and Technical Information (OSTI.GOV)

Iliadis, C.; Karakas, A. I.; Prantzos, N.

2016-02-10

Globular clusters are of paramount importance for testing theories of stellar evolution and early galaxy formation. Strong evidence for multiple populations of stars in globular clusters derives from observed abundance anomalies. A puzzling example is the recently detected Mg–K anticorrelation in NGC 2419. We perform Monte Carlo nuclear reaction network calculations to constrain the temperature–density conditions that gave rise to the elemental abundances observed in this elusive cluster. We find a correlation between stellar temperature and density values that provide a satisfactory match between simulated and observed abundances in NGC 2419 for all relevant elements (Mg, Si, K, Ca, Sc,more » Ti, and V). Except at the highest densities (ρ ≳ 10{sup 8} g cm{sup −3}), the acceptable conditions range from ≈100 MK at ≈10{sup 8} g cm{sup −3} to ≈200 MK at ≈10{sup −4} g cm{sup −3}. This result accounts for uncertainties in nuclear reaction rates and variations in the assumed initial composition. We review hydrogen-burning sites and find that low-mass stars, asymptotic giant branch (AGB) stars, massive stars, or supermassive stars cannot account for the observed abundance anomalies in NGC 2419. Super-AGB stars could be viable candidates for the polluter stars if stellar model parameters can be fine-tuned to produce higher temperatures. Novae, involving either CO or ONe white dwarfs, could be interesting polluter candidates, but a current lack of low-metallicity nova models precludes firmer conclusions. We also discuss whether additional constraints for the first-generation polluters can be obtained by future measurements of oxygen, or by evolving models of second-generation low-mass stars with a non-canonical initial composition.« less

Gravitational wave sources from inspiralling globular clusters in the Galactic Centre and similar environments

NASA Astrophysics Data System (ADS)

Arca-Sedda, Manuel; Gualandris, Alessia

2018-07-01

We model the inspiral of globular clusters (GCs) towards a galactic nucleus harbouring a supermassive black hole (SMBH), a leading scenario for the formation of nuclear star clusters. We consider the case of GCs containing either an intermediate-mass black hole (IMBH) or a population of stellar-mass black holes (BHs), and study the formation of gravitational wave (GW) sources. We perform direct summation N-body simulations of the infall of GCs with different orbital eccentricities in the live background of a galaxy with either a shallow or steep density profile. We find that the GC acts as an efficient carrier for the IMBH, facilitating the formation of a bound pair. The hardening and evolution of the binary depends sensitively on the galaxy's density profile. If the host galaxy has a shallow profile, the hardening is too slow to allow for coalescence within a Hubble time, unless the initial cluster orbit is highly eccentric. If the galaxy hosts a nuclear star cluster, the hardening leads to coalescence by emission of GWs within 3-4 Gyr. In this case, we find an IMBH-SMBH merger rate of ΓIMBH-SMBH = 2.8 × 10-3 yr-1 Gpc3. If the GC hosts a population of stellar BHs, these are deposited close enough to the SMBH to form extreme mass ratio inspirals with a merger rate of ΓEMRI = 0.25 yr-1 Gpc3. Finally, the SMBH tidal field can boost the coalescence of stellar black hole binaries delivered from the infalling GCs. The merger rate for this merging channel is ΓBHB = 0.4-4 yr-1 Gpc3.

Evolution of Optical Binary Fraction in Sparse Stellar Systems

NASA Astrophysics Data System (ADS)

Li, Zhongmu; Mao, Caiyan

2018-05-01

This work studies the evolution of the fraction of optical binary stars (OBF; not including components such as neutron stars and black holes), which is caused by stellar evolution, and the contributions of various binaries to OBF via the stellar population synthesis technique. It is shown that OBF decreases from 1 to about 0.81 for stellar populations with the Salpeter initial mass function (IMF), and to about 0.85 for the case of the Kroupa IMF, on a timescale of 15 Gyr. This result depends on metallicity, slightly. The contributions of binaries varying with mass ratio, orbital period, separation, spectral types of primary and secondary, contact degree, and pair type to OBF are calculated for stellar populations with different ages and metallicities. The contribution of different kinds of binaries to OBF depends on age and metallicity. The results can be used for estimating the global OBF of star clusters or galaxies from the fraction of a kind of binary. It is also helpful for estimating the primordial and future binary fractions of sparse stellar systems from the present observations. Our results are suitable for studying field stars, open clusters, and the outer part of globular clusters, because the OBF of such objects is affected by dynamical processes, relatively slightly, but they can also be used for giving some limits for other populations.

The Diversity of Chemical Composition and the Effects on Stellar Evolution and Planetary Habitability

NASA Astrophysics Data System (ADS)

Truitt, Amanda R.

2017-08-01

I present a catalog of 1,794 stellar evolution models for solar-type and low-mass stars, which is intended to help characterize real host-stars of interest during the ongoing search for potentially habitable exoplanets. The main grid is composed of 904 tracks, for 0.5-1.2 M solar masses at scaled metallicity values of 0.1-1.5 Z solar masses and specific elemental abundance ratio values of 0.44-2.28 O/Fe solar masses, 0.58-1.72 C/Fe solar masses, 0.54-1.84 Mg/Fe solar masses, and 0.5-2.0 Ne/Fe solar masses. The catalog includes a small grid of late stage evolutionary tracks (25 models), as well as a grid of M-dwarf stars for 0.1-0.45 M solar masses (856 models). The time-dependent habitable zone evolution is calculated for each track, and is strongly dependent on stellar mass, effective temperature, and luminosity parameterizations. I have also developed a subroutine for the stellar evolution code TYCHO that implements a minimalist coupled model for estimating changes in the stellar X-ray luminosity, mass loss, rotational velocity, and magnetic activity over time; to test the utility of the updated code, I created a small grid (9 models) for solar-mass stars, with variations in rotational velocity and scaled metallicity. Including this kind of information in the catalog will ultimately allow for a more robust consideration of the long-term conditions that orbiting planets may experience. In order to gauge the true habitability potential of a given planetary system, it is extremely important to characterize the host-star's mass, specific chemical composition, and thus the timescale over which the star will evolve. It is also necessary to assess the likelihood that a planet found in the "instantaneous" habitable zone has actually had sufficient time to become "detectably" habitable. This catalog provides accurate stellar evolution predictions for a large collection of theoretical host-stars; the models are of particular utility in that they represent the real variation in stellar parameters that have been observed in nearby stars.

Exploring the luminosity evolution and stellar mass assembly of 2SLAQ luminous red galaxies between redshifts 0.4 and 0.8

NASA Astrophysics Data System (ADS)

Banerji, Manda; Ferreras, Ignacio; Abdalla, Filipe B.; Hewett, Paul; Lahav, Ofer

2010-03-01

We present an analysis of the evolution of 8625 luminous red galaxies (LRGs) between z = 0.4 and 0.8 in the 2dF and Sloan Digital Sky Survey LRG and QSO (2SLAQ) survey. The LRGs are split into redshift bins and the evolution of both the luminosity and stellar mass function with redshift is considered and compared to the assumptions of a passive evolution scenario. We draw attention to several sources of systematic error that could bias the evolutionary predictions made in this paper. While the inferred evolution is found to be relatively unaffected by the exact choice of spectral evolution model used to compute K + e corrections, we conclude that photometric errors could be a source of significant bias in colour-selected samples such as this, in particular when using parametric maximum likelihood based estimators. We find that the evolution of the most massive LRGs is consistent with the assumptions of passive evolution and that the stellar mass assembly of the LRGs is largely complete by z ~ 0.8. Our findings suggest that massive galaxies with stellar masses above 1011Msolar must have undergone merging and star formation processes at a very early stage (z >~ 1). This supports the emerging picture of downsizing in both the star formation as well as the mass assembly of early-type galaxies. Given that our spectroscopic sample covers an unprecedentedly large volume and probes the most massive end of the galaxy mass function, we find that these observational results present a significant challenge for many current models of galaxy formation.

A close nuclear black-hole pair in the spiral galaxy NGC 3393.

PubMed

Fabbiano, G; Wang, Junfeng; Elvis, M; Risaliti, G

2011-08-31

The current picture of galaxy evolution advocates co-evolution of galaxies and their nuclear massive black holes, through accretion and galactic merging. Pairs of quasars, each with a massive black hole at the centre of its galaxy, have separations of 6,000 to 300,000 light years (refs 2 and 3; 1 parsec = 3.26 light years) and exemplify the first stages of this gravitational interaction. The final stages of the black-hole merging process, through binary black holes and final collapse into a single black hole with gravitational wave emission, are consistent with the sub-light-year separation inferred from the optical spectra and light-variability of two such quasars. The double active nuclei of a few nearby galaxies with disrupted morphology and intense star formation (such as NGC 6240 with a separation of about 2,600 light years and Mrk 463 with a separation of about 13,000 light years between the nuclei) demonstrate the importance of major mergers of equal-mass spiral galaxies in this evolution; such mergers lead to an elliptical galaxy, as in the case of the double-radio-nucleus elliptical galaxy 0402+379 (with a separation of about 24 light years between the nuclei). Minor mergers of a spiral galaxy with a smaller companion should be a more common occurrence, evolving into spiral galaxies with active massive black-hole pairs, but have hitherto not been seen. Here we report the presence of two active massive black holes, separated by about 490 light years, in the Seyfert galaxy NGC 3393 (50 Mpc, about 160 million light years). The regular spiral morphology and predominantly old circum-nuclear stellar population of this galaxy, and the closeness of the black holes embedded in the bulge, provide a hitherto missing observational point to the study of galaxy/black hole evolution. Comparison of our observations with current theoretical models of mergers suggests that they are the result of minor merger evolution. © 2011 Macmillan Publishers Limited. All rights reserved

Stellar feedback as the origin of an extended molecular outflow in a starburst galaxy.

PubMed

Geach, J E; Hickox, R C; Diamond-Stanic, A M; Krips, M; Rudnick, G H; Tremonti, C A; Sell, P H; Coil, A L; Moustakas, J

2014-12-04

Recent observations have revealed that starburst galaxies can drive molecular gas outflows through stellar radiation pressure. Molecular gas is the phase of the interstellar medium from which stars form, so these outflows curtail stellar mass growth in galaxies. Previously known outflows, however, involve small fractions of the total molecular gas content and have typical scales of less than a kiloparsec. In at least some cases, input from active galactic nuclei is dynamically important, so pure stellar feedback (the momentum return into the interstellar medium) has been considered incapable of rapidly terminating star formation on galactic scales. Molecular gas has been detected outside the galactic plane of the archetypal starburst galaxy M82 (refs 4 and 5), but so far there has been no evidence that starbursts can propel substantial quantities of cold molecular gas to the same galactocentric radius (about 10 kiloparsecs) as the warmer gas that has been traced by metal ion absorbers in the circumgalactic medium. Here we report observations of molecular gas in a compact (effective radius 100 parsecs) massive starburst galaxy at redshift 0.7, which is known to drive a fast outflow of ionized gas. We find that 35 per cent of the total molecular gas extends approximately 10 kiloparsecs, and one-third of this extended gas has a velocity of up to 1,000 kilometres per second. The kinetic energy associated with this high-velocity component is consistent with the momentum flux available from stellar radiation pressure. This demonstrates that nuclear bursts of star formation are capable of ejecting large amounts of cold gas from the central regions of galaxies, thereby strongly affecting their evolution by truncating star formation and redistributing matter.

Evolution of Galaxy Luminosity and Stellar-Mass Functions since $z=1$ with the Dark Energy Survey Science Verification Data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Capozzi, D.; et al.

We present the first study of the evolution of the galaxy luminosity and stellar-mass functions (GLF and GSMF) carried out by the Dark Energy Survey (DES). We describe the COMMODORE galaxy catalogue selected from Science Verification images. This catalogue is made ofmore » $$\\sim 4\\times 10^{6}$$ galaxies at $$0« less

THE EVOLUTION OF EARLY- AND LATE-TYPE GALAXIES IN THE COSMIC EVOLUTION SURVEY UP TO z {approx} 1.2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pannella, Maurilio; Gabasch, Armin; Drory, Niv

2009-08-10

The Cosmic Evolution Survey (COSMOS) allows for the first time a highly significant census of environments and structures up to redshift 1, as well as a full morphological description of the galaxy population. In this paper we present a study aimed to constrain the evolution, in the redshift range 0.2 < z < 1.2, of the mass content of different morphological types and its dependence on the environmental density. We use a deep multicolor catalog, covering an area of {approx}0.7 deg{sup 2} inside the COSMOS field, with accurate photometric redshifts (i {approx}< 26.5 and {delta}z/(z {sub spec} + 1) {approx}more » 0.035). We estimate galaxy stellar masses by fitting the multicolor photometry to a grid of composite stellar population models. We quantitatively describe the galaxy morphology by fitting point-spread function convolved Sersic profiles to the galaxy surface brightness distributions down to F814 = 24 mag for a sample of 41,300 objects. We confirm an evolution of the morphological mix with redshift: the higher the redshift the more disk-dominated galaxies become important. We find that the morphological mix is a function of the local comoving density: the morphology density relation extends up to the highest redshift explored. The stellar mass function of disk-dominated galaxies is consistent with being constant with redshift. Conversely, the stellar mass function of bulge-dominated systems shows a decline in normalization with redshift. Such different behaviors of late-types and early-types stellar mass functions naturally set the redshift evolution of the transition mass. We find a population of relatively massive, early-type galaxies, having high specific star formation rate (SSFR) and blue colors which live preferentially in low-density environments. The bulk of massive (>7 x 10{sup 10} M {sub sun}) early-type galaxies have similar characteristic ages, colors, and SSFRs independently of the environment they belong to, with those hosting the oldest stars in the universe preferentially belonging to the highest density regions. The whole catalog including morphological information and stellar mass estimates analyzed in this work is made publicly available.« less

Inflow, Outflow, Yields, and Stellar Population Mixing in Chemical Evolution Models

NASA Astrophysics Data System (ADS)

Andrews, Brett H.; Weinberg, David H.; Schönrich, Ralph; Johnson, Jennifer A.

2017-02-01

Chemical evolution models are powerful tools for interpreting stellar abundance surveys and understanding galaxy evolution. However, their predictions depend heavily on the treatment of inflow, outflow, star formation efficiency (SFE), the stellar initial mass function, the SN Ia delay time distribution, stellar yields, and stellar population mixing. Using flexCE, a flexible one-zone chemical evolution code, we investigate the effects of and trade-offs between parameters. Two critical parameters are SFE and the outflow mass-loading parameter, which shift the knee in [O/Fe]-[Fe/H] and the equilibrium abundances that the simulations asymptotically approach, respectively. One-zone models with simple star formation histories follow narrow tracks in [O/Fe]-[Fe/H] unlike the observed bimodality (separate high-α and low-α sequences) in this plane. A mix of one-zone models with inflow timescale and outflow mass-loading parameter variations, motivated by the inside-out galaxy formation scenario with radial mixing, reproduces the two sequences better than a one-zone model with two infall epochs. We present [X/Fe]-[Fe/H] tracks for 20 elements assuming three different supernova yield models and find some significant discrepancies with solar neighborhood observations, especially for elements with strongly metallicity-dependent yields. We apply principal component abundance analysis to the simulations and existing data to reveal the main correlations among abundances and quantify their contributions to variation in abundance space. For the stellar population mixing scenario, the abundances of α-elements and elements with metallicity-dependent yields dominate the first and second principal components, respectively, and collectively explain 99% of the variance in the model. flexCE is a python package available at https://github.com/bretthandrews/flexCE.

Inflow, Outflow, Yields, and Stellar Population Mixing in Chemical Evolution Models

DOE Office of Scientific and Technical Information (OSTI.GOV)

Andrews, Brett H.; Weinberg, David H.; Schönrich, Ralph

Chemical evolution models are powerful tools for interpreting stellar abundance surveys and understanding galaxy evolution. However, their predictions depend heavily on the treatment of inflow, outflow, star formation efficiency (SFE), the stellar initial mass function, the SN Ia delay time distribution, stellar yields, and stellar population mixing. Using flexCE, a flexible one-zone chemical evolution code, we investigate the effects of and trade-offs between parameters. Two critical parameters are SFE and the outflow mass-loading parameter, which shift the knee in [O/Fe]–[Fe/H] and the equilibrium abundances that the simulations asymptotically approach, respectively. One-zone models with simple star formation histories follow narrow tracksmore » in [O/Fe]–[Fe/H] unlike the observed bimodality (separate high- α and low- α sequences) in this plane. A mix of one-zone models with inflow timescale and outflow mass-loading parameter variations, motivated by the inside-out galaxy formation scenario with radial mixing, reproduces the two sequences better than a one-zone model with two infall epochs. We present [X/Fe]–[Fe/H] tracks for 20 elements assuming three different supernova yield models and find some significant discrepancies with solar neighborhood observations, especially for elements with strongly metallicity-dependent yields. We apply principal component abundance analysis to the simulations and existing data to reveal the main correlations among abundances and quantify their contributions to variation in abundance space. For the stellar population mixing scenario, the abundances of α -elements and elements with metallicity-dependent yields dominate the first and second principal components, respectively, and collectively explain 99% of the variance in the model. flexCE is a python package available at https://github.com/bretthandrews/flexCE.« less

On the Maximum Mass of Accreting Primordial Supermassive Stars

NASA Astrophysics Data System (ADS)

Woods, T. E.; Heger, Alexander; Whalen, Daniel J.; Haemmerlé, Lionel; Klessen, Ralf S.

2017-06-01

Supermassive primordial stars are suspected to be the progenitors of the most massive quasars at z ˜ 6. Previous studies of such stars were either unable to resolve hydrodynamical timescales or considered stars in isolation, not in the extreme accretion flows in which they actually form. Therefore, they could not self-consistently predict their final masses at collapse, or those of the resulting supermassive black hole seeds, but rather invoked comparison to simple polytropic models. Here, we systematically examine the birth, evolution, and collapse of accreting, non-rotating supermassive stars under accretion rates of 0.01-10 M ⊙ yr-1 using the stellar evolution code Kepler. Our approach includes post-Newtonian corrections to the stellar structure and an adaptive nuclear network and can transition to following the hydrodynamic evolution of supermassive stars after they encounter the general relativistic instability. We find that this instability triggers the collapse of the star at masses of 150,000-330,000 M ⊙ for accretion rates of 0.1-10 M ⊙ yr-1, and that the final mass of the star scales roughly logarithmically with the rate. The structure of the star, and thus its stability against collapse, is sensitive to the treatment of convection and the heat content of the outer accreted envelope. Comparison with other codes suggests differences here may lead to small deviations in the evolutionary state of the star as a function of time, that worsen with accretion rate. Since the general relativistic instability leads to the immediate death of these stars, our models place an upper limit on the masses of the first quasars at birth.

Binary Population and Spectral Synthesis Version 2.1: Construction, Observational Verification, and New Results

NASA Astrophysics Data System (ADS)

Eldridge, J. J.; Stanway, E. R.; Xiao, L.; McClelland, L. A. S.; Taylor, G.; Ng, M.; Greis, S. M. L.; Bray, J. C.

2017-11-01

The Binary Population and Spectral Synthesis suite of binary stellar evolution models and synthetic stellar populations provides a framework for the physically motivated analysis of both the integrated light from distant stellar populations and the detailed properties of those nearby. We present a new version 2.1 data release of these models, detailing the methodology by which Binary Population and Spectral Synthesis incorporates binary mass transfer and its effect on stellar evolution pathways, as well as the construction of simple stellar populations. We demonstrate key tests of the latest Binary Population and Spectral Synthesis model suite demonstrating its ability to reproduce the colours and derived properties of resolved stellar populations, including well-constrained eclipsing binaries. We consider observational constraints on the ratio of massive star types and the distribution of stellar remnant masses. We describe the identification of supernova progenitors in our models, and demonstrate a good agreement to the properties of observed progenitors. We also test our models against photometric and spectroscopic observations of unresolved stellar populations, both in the local and distant Universe, finding that binary models provide a self-consistent explanation for observed galaxy properties across a broad redshift range. Finally, we carefully describe the limitations of our models, and areas where we expect to see significant improvement in future versions.

The Class of Jsolated Stars and Luminous Planetary Nebulae in old stellar populations

NASA Astrophysics Data System (ADS)

Sabach, Efrat; Soker, Noam

2018-06-01

We suggest that stars whose angular momentum (J) does not increase by a companion, star or planet, along their post-main sequence evolution have much lower mass loss rates along their giant branches. Their classification to a separate group can bring insight on their late evolution stages. We here term these Jsolated stars. We argue that the mass loss rate of Jsolated stars is poorly determined because the mass loss rate expressions on the giant branches are empirically based on samples containing stars that experience strong binary interaction, with stellar or sub-stellar companions, e.g., planetary nebula (PN) progenitors. We use our earlier claim for a low mass loss rate of asymptotic giant branch (AGB) stars that are not spun-up by a stellar or substellar companion to show that we can account for the enigmatic finding that the brightest PNe in old stellar populations reach the same luminosity as the brightest PNe in young populations. It is quite likely that the best solution to the existence of bright PNe in old stellar populations is the combination of higher AGB luminosities, as obtained in some new stellar models, and the lower mass loss rates invoked here.

Feedback Driven Chemical Evolution in Simulations of Low Mass Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Emerick, Andrew; Bryan, Greg; Mac Low, Mordecai-Mark

2018-06-01

Galaxy chemical properties place some of the best constraints on models of galaxy evolution. Both gas and stellar metal abundances in galaxies depend upon the integrated star formation history of the galaxy, gas accretion, outflows, and the effectiveness of metal mixing within the interstellar medium (ISM). Capturing the physics that governs these processes in detail, however, is challenging, in part due to the difficulty in self-consistently modelling stellar feedback physics that impacts each of these processes. Using high resolution hydrodynamics simulations of isolated dwarf galaxies where we follow stars as individual star particles, we examine the role of feedback in driving dwarf galaxy chemical evolution. This star-by-star method allows us to directly follow feedback from stellar winds from massive and AGB stars, stellar ionizing radiation and photoelectric heating, and supernovae. Additionally, we track 15 individual metal species yields from these stars as they pollute the ISM and enrich new stellar populations. I will present initial results from these simulations in the context of observational constraints on the retention/ejection of metals from Local Group dwarf galaxies. In addition, I will discuss the variations with which individual elements evolve in the various phases of the ISM, as they progress from hot, ionized gas down to cold, star forming regions. I will conclude by outlining the implications of these results on interpretations of observed chemical abundances in dwarf galaxies and on standard assumptions made in semi-analytic chemical evolution models of these galaxies.

The massive end of the luminosity and stellar mass functions and clustering from CMASS to SDSS: evidence for and against passive evolution

NASA Astrophysics Data System (ADS)

Bernardi, M.; Meert, A.; Sheth, R. K.; Huertas-Company, M.; Maraston, C.; Shankar, F.; Vikram, V.

2016-02-01

We describe the luminosity function, based on Sérsic fits to the light profiles, of CMASS galaxies at z ˜ 0.55. Compared to previous estimates, our Sérsic-based reductions imply more luminous, massive galaxies, consistent with the effects of Sérsic- rather than Petrosian or de Vaucouleur-based photometry on the Sloan Digital Sky Survey (SDSS) main galaxy sample at z ˜ 0.1. This implies a significant revision of the high-mass end of the correlation between stellar and halo mass. Inferences about the evolution of the luminosity and stellar mass functions depend strongly on the assumed, and uncertain, k + e corrections. In turn, these depend on the assumed age of the population. Applying k + e corrections taken from fitting the models of Maraston et al. to the colours of both SDSS and CMASS galaxies, the evolution of the luminosity and stellar mass functions appears impressively passive, provided that the fits are required to return old ages. However, when matched in comoving number- or luminosity-density, the SDSS galaxies are less strongly clustered compared to their counterparts in CMASS. This rules out the passive evolution scenario, and, indeed, any minor merger scenarios which preserve the rank ordering in stellar mass of the population. Potential incompletenesses in the CMASS sample would further enhance this mismatch. Our analysis highlights the virtue of combining clustering measurements with number counts.

Infrared surface photometry of 3C 65: Stellar evolution and the Tolman signal

NASA Astrophysics Data System (ADS)

Rigler, M. A.; Lilly, S. J.

1994-06-01

We present an analysis of the infrared surface brightness profile of the high-redshift radio galaxy 3C 65 (z = 1.176), which is well fitted by a de Vaucouleurs r1/4 law. A model surface fitting routine yields characteristic photometric parameters comparable to those of low-redshift radio galaxies and brightest cluster members (BCMs) in standard cosmologies. The small displacement of this galaxy from the locus of low-redshift systems on the mur - log(re) plane suggests that little or no luminosity evolution is required in a cosmological model with (Omega0, lambda0 = (1,0), while a modest degree of luminosity evolution, accountable by passive evolution of the stellar population, is implied in models with (0, 0) or (0.1, 0.9). A nonexpanding cosmology is unlikely because it would require 3C 65 to lie at the extreme end of the distribution of properties of local gE galaxies, and the effects of plausible stellar and/or dynamic evolution would make 3C 65 even more extreme by the present epoch.

The evolution of rotating very massive stars with LMC composition

NASA Astrophysics Data System (ADS)

Köhler, K.; Langer, N.; de Koter, A.; de Mink, S. E.; Crowther, P. A.; Evans, C. J.; Gräfener, G.; Sana, H.; Sanyal, D.; Schneider, F. R. N.; Vink, J. S.

2015-01-01

Context. With growing evidence for the existence of very massive stars at subsolar metallicity, there is an increased need for corresponding stellar evolution models. Aims: We present a dense model grid with a tailored input chemical composition appropriate for the Large Magellanic Cloud (LMC). Methods: We use a one-dimensional hydrodynamic stellar evolution code, which accounts for rotation, transport of angular momentum by magnetic fields, and stellar wind mass loss to compute our detailed models. We calculate stellar evolution models with initial masses from 70 to 500 M⊙ and with initial surface rotational velocities from 0 to 550 km s-1, covering the core-hydrogen burning phase of evolution. Results: We find our rapid rotators to be strongly influenced by rotationally induced mixing of helium, with quasi-chemically homogeneous evolution occurring for the fastest rotating models. Above 160 M⊙, homogeneous evolution is also established through mass loss, producing pure helium stars at core hydrogen exhaustion independent of the initial rotation rate. Surface nitrogen enrichment is also found for slower rotators, even for stars that lose only a small fraction of their initial mass. For models above ~150 M⊙ at zero age, and for models in the whole considered mass range later on, we find a considerable envelope inflation due to the proximity of these models to their Eddington limit. This leads to a maximum ZAMS surface temperature of ~56 000 K, at ~180 M⊙, and to an evolution of stars in the mass range 50 M⊙...100 M⊙ to the regime of luminous blue variables in the Hertzsprung-Russell diagram with high internal Eddington factors. Inflation also leads to decreasing surface temperatures during the chemically homogeneous evolution of stars above ~180 M⊙. Conclusions: The cool surface temperatures due to the envelope inflation in our models lead to an enhanced mass loss, which prevents stars at LMC metallicity from evolving into pair-instability supernovae. The corresponding spin-down will also prevent very massive LMC stars to produce long-duration gamma-ray bursts, which might, however, originate from lower masses. The dataset of the presented stellar evolution models is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/573/A71Appendices are available in electronic form at http://www.aanda.org

Effect of the rotation and tidal dissipation history of stars on the evolution of close-in planets

NASA Astrophysics Data System (ADS)

Bolmont, Emeline; Mathis, Stéphane

2016-11-01

Since 20 years, a large population of close-in planets orbiting various classes of low-mass stars (from M-type to A-type stars) has been discovered. In such systems, the dissipation of the kinetic energy of tidal flows in the host star may modify its rotational evolution and shape the orbital architecture of the surrounding planetary system. In this context, recent observational and theoretical works demonstrated that the amplitude of this dissipation can vary over several orders of magnitude as a function of stellar mass, age and rotation. In addition, stellar spin-up occurring during the Pre-Main-Sequence (PMS) phase because of the contraction of stars and their spin-down because of the torque applied by magnetized stellar winds strongly impact angular momentum exchanges within star-planet systems. Therefore, it is now necessary to take into account the structural and rotational evolution of stars when studying the orbital evolution of close-in planets. At the same time, the presence of planets may modify the rotational dynamics of the host stars and as a consequence their evolution, magnetic activity and mixing. In this work, we present the first study of the dynamics of close-in planets of various masses orbiting low-mass stars (from 0.6~M_⊙ to 1.2~M_⊙) where we compute the simultaneous evolution of the star's structure, rotation and tidal dissipation in its external convective envelope. We demonstrate that tidal friction due to the stellar dynamical tide, i.e. tidal inertial waves excited in the convection zone, can be larger by several orders of magnitude than the one of the equilibrium tide currently used in Celestial Mechanics, especially during the PMS phase. Moreover, because of this stronger tidal friction in the star, the orbital migration of the planet is now more pronounced and depends more on the stellar mass, rotation and age. This would very weakly affect the planets in the habitable zone because they are located at orbital distances such that stellar tide-induced migration happens on very long timescales. We also demonstrate that the rotational evolution of host stars is only weakly affected by the presence of planets except for massive companions.

A New Fokker-Planck Approach for the Relaxation-driven Evolution of Galactic Nuclei

NASA Astrophysics Data System (ADS)

Vasiliev, Eugene

2017-10-01

We present an approach for simulating the collisional evolution of spherical isotropic stellar systems based on the one-dimensional Fokker-Planck equation. A novel aspect is that we use the phase volume as the argument of the distribution function instead of the traditionally used energy, which facilitates the solution. The publicly available code PhaseFlow implements a high-accuracy finite-element method for the Fokker-Planck equation, and can handle multiple-component systems, optionally with the central black hole and taking into account loss-cone effects and star formation. We discuss the energy balance in the general setting, and in application to the Bahcall-Wolf cusp around a central black hole, for which we derive a perturbative solution. We stress that the cusp is not a steady-state structure, but rather evolves in amplitude while retaining an approximately ρ \\propto {r}-7/4 density profile. Finally, we apply the method to the nuclear star cluster of the milky Way, and illustrate a possible evolutionary scenario in which a two-component system of lighter main-sequence stars and stellar-mass black holes develops a Bahcall-Wolf cusp in the heavier component and a weaker ρ \\propto {r}-3/2 cusp in the lighter, visible component, over the period of several Gyr. The present-day density profile is consistent with the recently detected mild cusp inside the central parsec, and is weakly sensitive to initial conditions.

Influence of Non-spherical Initial Stellar Structure on the Core-Collapse Supernova Mechanism

NASA Astrophysics Data System (ADS)

Couch, Sean M.

I review the state of investigation into the impact that nonspherical stellar progenitor structure has on the core-collapse supernova mechanism. Although modeling stellar evolution relies on 1D spherically symmetric calculations, massive stars are not truly spherical. In the stellar evolution codes, this fact is accounted for by "fixes" such as mixing length theory and attendant modifications. Of particular relevance to the supernova mechanism, the Si- and O-burning shells surrounding the iron core at the point of collapse can be violently convective, with convective speeds of hundreds of km s-1. It has recently been shown by a number of groups that the presence of nonspherical perturbations in the layers surrounding the collapsing iron core can have a favorable impact on the likelihood for shock revival and explosion via the neutrino heating mechanism. This is due in large part to the strengthening of turbulence behind the stalled shock due to the presence of finite amplitude seed perturbations to speed the growth of convection which drives the post-shock turbulence. Efforts are now underway to simulate the final minutes of stellar evolution to core-collapse in 3D with the aim to generate realistic multidimensional initial conditions for use in simulations of the supernova mechanism.

TRACING REJUVENATION EVENTS IN NEARBY S0 GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marino, Antonietta; Bianchi, Luciana; Thilker, David A.

2011-08-01

With the aim of characterizing rejuvenation processes in early-type galaxies, we analyzed five barred S0 galaxies showing a prominent outer ring in ultraviolet (UV) imaging. We analyzed Galaxy Evolution Explorer far-UV (FUV) and near-UV (NUV), and optical data using stellar population models and estimated the age and the stellar mass of the entire galaxies and the UV-bright ring structures. Outer rings consist of young ({approx}<200 Myr old) stellar populations, accounting for up to 70% of the FUV flux but containing only a few percent of the total stellar mass. Integrated photometry of the whole galaxies places four of these objectsmore » on the green valley, indicating a globally evolving nature. We suggest such galaxy evolution is likely driven by bar-induced instabilities, i.e., inner secular evolution, that conveys gas to the nucleus and the outer rings. At the same time, H I observations of NGC 1533 and NGC 2962 suggest external gas re-fueling can play a role in the rejuvenation processes of such galaxies.« less

The relativistic equations of stellar structure and evolution. Stars with degenerate neutron cores. 1: Structure of equilibrium models

NASA Technical Reports Server (NTRS)

Thorne, K. S.; Zytkow, A. N.

1976-01-01

The general relativistic equations of stellar structure and evolution are reformulated in a notation which makes easy contact with Newtonian theory. Also, a general relativistic version of the mixing-length formalism for convection is presented. Finally, it is argued that in previous work on spherical systems general relativity theorists have identified the wrong quantity as "total mass-energy inside radius r."

Stellar Evolution and Modelling Stars

NASA Astrophysics Data System (ADS)

Silva Aguirre, Víctor

In this chapter I give an overall description of the structure and evolution of stars of different masses, and review the main ingredients included in state-of-the-art calculations aiming at reproducing observational features. I give particular emphasis to processes where large uncertainties still exist as they have strong impact on stellar properties derived from large compilations of tracks and isochrones, and are therefore of fundamental importance in many fields of astrophysics.

The cosmological density of baryons from observations of 3He+ in the Milky Way.

PubMed

Bania, T M; Rood, Robert T; Balser, Dana S

2002-01-03

Primordial nucleosynthesis after the Big Bang can be constrained by the abundances of the light elements and isotopes 2H, 3He, 4He and 7Li (ref. 1). The standard theory of stellar evolution predicts that 3He is also produced by solar-type stars, so its abundance is of interest not only for cosmology, but also for understanding stellar evolution and the chemical evolution of the Galaxy. The 3He abundance in star-forming (H II) regions agrees with the present value for the local interstellar medium, but seems to be incompatible with the stellar production rates inferred from observations of planetary nebulae, which provide a direct test of stellar evolution theory. Here we develop our earlier observations, which, when combined with recent theoretical developments in our understanding of light-element synthesis and destruction in stars, allow us to determine an upper limit for the primordial abundance of 3He relative to hydrogen: 3He/H = (1.1 +/- 0.2) x 10(-5). The primordial density of all baryons determined from the 3He data is in excellent agreement with the densities calculated from other cosmological probes. The previous conflict is resolved because most solar-mass stars do not produce enough 3He to enrich the interstellar medium significantly.

The Structural Evolution of Milky-Way-Like Star-Forming Galaxies zeta is approximately 1.3

NASA Technical Reports Server (NTRS)

Patel, Shannon G.; Fumagalli, Mattia; Franx, Marun; VanDokkum, Pieter G.; VanDerWel, Arjen; Leja, Joel; Labbe, Ivo; Brammr, Gabriel; Whitaker, Katherine E.; Skelton, Rosalind E.;

Solar astrophysics - Ghettosis from, or symbiosis with, stellar and galactic astrophysics

NASA Technical Reports Server (NTRS)

Pecker, J.-C.; Thomas, R. N.

1976-01-01

The purpose of the paper is to show how the solar-stellar symbiotic approach has led to the modeling of a star as a concentration of matter and energy. By 'solar-stellar symbiosis' is meant the philosophy of investigation according to which one asks what change in our general understanding of stellar structure and of stellar spectroscopic diagnostics is required to satisfy both the sun and an unusual star when, for example, some feature of an unusual star is discovered. The evolution of stellar models is traced, from walled, thermodynamic-equilibrium models to de-isolated models featuring transition zones and nonlocal thermodynamic equilibrium.

The evolution of magnetic hot massive stars: Implementation of the quantitative influence of surface magnetic fields in modern models of stellar evolution

NASA Astrophysics Data System (ADS)

Keszthelyi, Zsolt; Wade, Gregg A.; Petit, Veronique

2017-11-01

Large-scale dipolar surface magnetic fields have been detected in a fraction of OB stars, however only few stellar evolution models of massive stars have considered the impact of these fossil fields. We are performing 1D hydrodynamical model calculations taking into account evolutionary consequences of the magnetospheric-wind interactions in a simplified parametric way. Two effects are considered: i) the global mass-loss rates are reduced due to mass-loss quenching, and ii) the surface angular momentum loss is enhanced due to magnetic braking. As a result of the magnetic mass-loss quenching, the mass of magnetic massive stars remains close to their initial masses. Thus magnetic massive stars - even at Galactic metallicity - have the potential to be progenitors of "heavy" stellar mass black holes. Similarly, at Galactic metallicity, the formation of pair instability supernovae is plausible with a magnetic progenitor.

Not All Stars Are the Sun: Empirical Calibration of the Mixing Length for Metal-poor Stars Using One-dimensional Stellar Evolution Models

NASA Astrophysics Data System (ADS)

Joyce, M.; Chaboyer, B.

2018-03-01

Theoretical stellar evolution models are constructed and tailored to the best known, observationally derived characteristics of metal-poor ([Fe/H] ∼ ‑2.3) stars representing a range of evolutionary phases: subgiant HD 140283, globular cluster M92, and four single, main sequence stars with well-determined parallaxes: HIP 46120, HIP 54639, HIP 106924, and WOLF 1137. It is found that the use of a solar-calibrated value of the mixing length parameter α MLT in models of these objects is ineffective at reproducing their observed properties. Empirically calibrated values of α MLT are presented for each object, accounting for uncertainties in the input physics employed in the models. It is advocated that the implementation of an adaptive mixing length is necessary in order for stellar evolution models to maintain fidelity in the era of high-precision observations.

Physical Orbit for Lam Vir and Testing of Stellar Evolution Models

NASA Astrophysics Data System (ADS)

Zhao, M.; Monnier, J. D.; Torres, G.; Pedretti, E.; Millan-Gabet, R.; Berger, J.-P.; Traub, W. A.; Schloerb, F. P.

2005-12-01

Lambda Virginis is a well-known double-lined spectroscopic Am binary with the interesting property that both stars are very similar in abundance but one is sharp-lined and the other is broad-lined. The differing rotation rates and the unusual metallic-lined nature of this system presents a unique opportunity to test stellar evolution models. In this poster, we present high resolution observations of Lam Vir, taken with the Infrared-Optical Telescopes Array (IOTA) between 2003 and 2005. By combining our interferometric data with double-lined radial velocity data, we determined for the first time the physical orbit of Lam Vir, as well as the orbital parallax of the system. In addition, the masses of the two components are determined with 1% and 1.5% errors respectively. Our preliminary result from comparison with stellar evolution models suggests a discrepancy between Lam Vir and standard models.

Study of Gamow-Teller strength and associated weak-rates on odd-A nuclei in stellar matter

NASA Astrophysics Data System (ADS)

Majid, Muhammad; Nabi, Jameel-Un; Riaz, Muhammad

In a recent study by Cole et al. [A. L. Cole et al., Phys. Rev. C 86 (2012) 015809], it was concluded that quasi-particle random phase approximation (QRPA) calculations show larger deviations and overestimate the total experimental Gamow-Teller (GT) strength. It was also concluded that QRPA calculated electron capture rates exhibit larger deviation than those derived from the measured GT strength distributions. The main purpose of this study is to probe the findings of the Cole et al. paper. This study gives useful information on the performance of QRPA-based nuclear models. As per simulation results, the capturing of electrons that occur on medium heavy isotopes have a significant role in decreasing the ratio of electron-to-baryon content of the stellar interior during the late stages of core evolution. We report the calculation of allowed charge-changing transitions strength for odd-A fp-shell nuclei (45Sc and 55Mn) by employing the deformed pn-QRPA approach. The computed GT transition strength is compared with previous theoretical calculations and measured data. For stellar applications, the corresponding electron capture rates are computed and compared with rates using previously calculated and measured GT values. Our finding shows that our calculated results are in decent accordance with measured data. At higher stellar temperature, our calculated electron capture rates are larger than those calculated by independent particle model (IPM) and shell model. It was further concluded that at low temperature and high density regions, the positron emission weak-rates from 45Sc and 55Mn may be neglected in simulation codes.

The Trojan Horse method for nuclear astrophysics: Recent results on resonance reactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cognata, M. La; Pizzone, R. G.; Spitaleri, C.

Nuclear astrophysics aims to measure nuclear-reaction cross sections of astrophysical interest to be included into models to study stellar evolution and nucleosynthesis. Low energies, < 1 MeV or even < 10 keV, are requested for this is the window where these processes are more effective. Two effects have prevented to achieve a satisfactory knowledge of the relevant nuclear processes, namely, the Coulomb barrier exponentially suppressing the cross section and the presence of atomic electrons. These difficulties have triggered theoretical and experimental investigations to extend our knowledge down to astrophysical energies. For instance, indirect techniques such as the Trojan Horse Methodmore » have been devised yielding new cutting-edge results. In particular, I will focus on the application of this indirect method to resonance reactions. Resonances might dramatically enhance the astrophysical S(E)-factor so, when they occur right at astrophysical energies, their measurement is crucial to pin down the astrophysical scenario. Unknown or unpredicted resonances might introduce large systematic errors in nucleosynthesis models. These considerations apply to low-energy resonances and to sub-threshold resonances as well, as they may produce sizable modifications of the S-factor due to, for instance, destructive interference with another resonance.« less

Numeric simulation of relativistic stellar core collapse and the formation of Reissner-Nordstroem black holes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ghezzi, Cristian R.; Letelier, Patricio S.

2007-01-15

The time evolution of a set of 22M{sub {center_dot}} unstable charged stars that collapse is computed integrating the Einstein-Maxwell equations. The model simulates the collapse of a spherical star that had exhausted its nuclear fuel and has or acquires a net electric charge in its core while collapsing. When the charge-to-mass ratio is Q/{radical}(G)M{>=}1, the star does not collapse but spreads. On the other hand, a different physical behavior is observed with a charge-to-mass ratio of 1>Q/{radical}(G)M>0.1. In this case, the collapsing matter forms a bubble enclosing a lower density core. We discuss an immediate astrophysical consequence of these resultsmore » that is a more efficient neutrino trapping during the stellar collapse and an alternative mechanism for powerful supernova explosions. The outer space-time of the star is the Reissner-Nordstroem solution that matches smoothly with our interior numerical solution; thus the collapsing models form Reissner-Nordstroem black holes.« less

Evolution and nucleosynthesis of extremely metal-poor and metal-free low- and intermediate-mass stars. II. s-process nucleosynthesis during the core He flash

NASA Astrophysics Data System (ADS)

Campbell, S. W.; Lugaro, M.; Karakas, A. I.

2010-11-01

Context. Models of primordial and hyper-metal-poor stars that have masses similar to the Sun are known to experience an ingestion of protons into the hot core during the core helium flash phase at the end of their red giant branch evolution. This produces a concurrent secondary flash powered by hydrogen burning that gives rise to further nucleosynthesis in the core. Aims: We aim to model the nucleosynthesis occurring during the proton ingestion event to ascertain if any significant neutron-capture nucleosynthesis occurs. Methods: We perform post-process nucleosynthesis calculations on a one-dimensional stellar evolution calculation of a star with mass 1 M_⊙ and a metallicity of [Fe/H] = -6.5 that suffers a proton ingestion episode. Our network includes 320 nuclear species and 2366 reactions and treats mixing and burning simultaneously. Results: We find that the mixing and burning of protons into the hot convective core leads to the production of 13C, which then burns via the 13C(α, n)16O reaction, releasing a large number of free neutrons. During the first two years of neutron production the neutron poison 14N abundance is low, allowing the prodigious production of heavy elements such as strontium, barium, and lead via slow neutron captures (the s process). These nucleosynthetic products are later carried to the stellar surface and ejected via stellar winds. We compare our results with observations of the hyper-metal-poor halo star HE 1327-2326, which shows a strong Sr overabundance. Conclusions: Our model provides the possibility of self-consistently explaining the Sr overabundance in HE 1327-2326 together with its C, N, and O overabundances (all within a factor of ˜ ~4) if the material were heavily diluted, for example, via mass transfer in a wide binary system. The model produces at least 18 times too much Ba than observed, but this may be within the large modelling uncertainties. In this scenario, binary systems of low mass must have formed in the early Universe. If this is true, it puts constraints on the primordial initial mass function.

Protomagnetar and black hole formation in high-mass stars

NASA Astrophysics Data System (ADS)

Obergaulinger, M.; Aloy, M. Á.

2017-07-01

Using axisymmetric simulations coupling special relativistic magnetohydrodynamics (MHD), an approximate post-Newtonian gravitational potential and two-moment neutrino transport, we show different paths for the formation of either protomagnetars or stellar mass black holes. The fraction of prototypical stellar cores which should result in collapsars depends on a combination of several factors, among which the structure of the progenitor star and the profile of specific angular momentum are probably the foremost. Along with the implosion of the stellar core, we also obtain supernova-like explosions driven by neutrino heating and hydrodynamic instabilities or by magneto-rotational effects in cores of high-mass stars. In the latter case, highly collimated, mildly relativistic outflows are generated. We find that after a rather long post-collapse phase (lasting ≳1 s) black holes may form in cases both of successful and failed supernova-like explosions. A basic trend is that cores with a specific angular momentum smaller than that obtained by standard, one-dimensional stellar evolution calculations form black holes (and eventually collapsars). Complementary, protomagnetars result from stellar cores with the standard distribution of specific angular momentum obtained from prototypical stellar evolution calculations including magnetic torques and moderate to large mass-loss rates.

Exponential Stellar Disks in Low Surface Brightness Galaxies: A Critical Test of Viscous Evolution

NASA Astrophysics Data System (ADS)

Bell, Eric F.

2002-12-01

Viscous redistribution of mass in Milky Way-type galactic disks is an appealing way of generating an exponential stellar profile over many scale lengths, almost independent of initial conditions, requiring only that the viscous timescale and star formation timescale are approximately equal. However, galaxies with solid-body rotation curves cannot undergo viscous evolution. Low surface brightness (LSB) galaxies have exponential surface brightness profiles, yet have slowly rising, nearly solid-body rotation curves. Because of this, viscous evolution may be inefficient in LSB galaxies: the exponential profiles, instead, would give important insight into initial conditions for galaxy disk formation. Using star formation laws from the literature and tuning the efficiency of viscous processes to reproduce an exponential stellar profile in Milky Way-type galaxies, I test the role of viscous evolution in LSB galaxies. Under the conservative and not unreasonable condition that LSB galaxies are gravitationally unstable for at least a part of their lives, I find that it is impossible to rule out a significant role for viscous evolution. This type of model still offers an attractive way of producing exponential disks, even in LSB galaxies with slowly rising rotation curves.

The XMM-Newton View of Wolf-Rayet Bubbles

NASA Astrophysics Data System (ADS)

Guerrero, M.; Toala, J.

2017-10-01

The powerful stellar winds of Wolf-Rayet (WR) stars blow large bubble into the circumstellar material ejected in previous phases of stellar evolution. The shock of those stellar winds produces X-ray-emitting hot plasmas which tells us about the diffusion of processed material onto the interstellar medium, about processes of heat conduction and turbulent mixing at the interface, about the late stages of stellar evolution, and about the shaping of the circumstellar environment, just before supernova explosions. The unique sensitivity of XMM-Newton has been key for the detection, mapping and spectral analysis of the X-ray emission from the hot bubbles around WR stars. These observations underscore the importance of the structure of the interstellar medium around massive stars, but they have also unveiled unknown phenomena, such as blowouts of hot gas into the interstellar medium or spatially-resolved spectral properties of the hot gas, which disclose inhomogeneous chemical abundances and physical properties across these bubbles.

What Makes Red Giants Tick? Linking Tidal Forces, Activity, and Solar-Like Oscillations via Eclipsing Binaries

NASA Astrophysics Data System (ADS)

Rawls, Meredith L.; Gaulme, Patrick; McKeever, Jean; Jackiewicz, Jason

2016-01-01

Thanks to advances in asteroseismology, red giants have become astrophysical laboratories for studying stellar evolution and probing the Milky Way. However, not all red giants show solar-like oscillations. It has been proposed that stronger tidal interactions from short-period binaries and increased magnetic activity on spotty giants are linked to absent or damped solar-like oscillations, yet each star tells a nuanced story. In this work, we characterize a subset of red giants in eclipsing binaries observed by Kepler. The binaries exhibit a range of orbital periods, solar-like oscillation behavior, and stellar activity. We use orbital solutions together with a suite of modeling tools to combine photometry and spectroscopy in a detailed analysis of tidal synchronization timescales, star spot activity, and stellar evolution histories. These red giants offer an unprecedented opportunity to test stellar physics and are important benchmarks for ensemble asteroseismology.

The shock-heated atmosphere of an asymptotic giant branch star resolved by ALMA

NASA Astrophysics Data System (ADS)

Vlemmings, Wouter; Khouri, Theo; O'Gorman, Eamon; De Beck, Elvire; Humphreys, Elizabeth; Lankhaar, Boy; Maercker, Matthias; Olofsson, Hans; Ramstedt, Sofia; Tafoya, Daniel; Takigawa, Aki

2017-12-01

Our current understanding of the chemistry and mass-loss processes in Sun-like stars at the end of their evolution depends critically on the description of convection, pulsations and shocks in the extended stellar atmosphere1. Three-dimensional hydrodynamical stellar atmosphere models provide observational predictions2, but so far the resolution to constrain the complex temperature and velocity structures seen in the models has been lacking. Here we present submillimetre continuum and line observations that resolve the atmosphere of the asymptotic giant branch star W Hydrae. We show that hot gas with chromospheric characteristics exists around the star. Its filling factor is shown to be small. The existence of such gas requires shocks with a cooling time longer than commonly assumed. A shocked hot layer will be an important ingredient in current models of stellar convection, pulsation and chemistry at the late stages of stellar evolution.

ACCURATE LOW-MASS STELLAR MODELS OF KOI-126

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feiden, Gregory A.; Chaboyer, Brian; Dotter, Aaron, E-mail: gregory.a.feiden@dartmouth.edu

2011-10-10

The recent discovery of an eclipsing hierarchical triple system with two low-mass stars in a close orbit (KOI-126) by Carter et al. appeared to reinforce the evidence that theoretical stellar evolution models are not able to reproduce the observational mass-radius relation for low-mass stars. We present a set of stellar models for the three stars in the KOI-126 system that show excellent agreement with the observed radii. This agreement appears to be due to the equation of state implemented by our code. A significant dispersion in the observed mass-radius relation for fully convective stars is demonstrated; indicative of the influencemore » of physics currently not incorporated in standard stellar evolution models. We also predict apsidal motion constants for the two M dwarf companions. These values should be observationally determined to within 1% by the end of the Kepler mission.« less

Constructing and Monitoring the Infrared SED of the First Known Recent Stellar Merger

NASA Astrophysics Data System (ADS)

McCollum, Bruce; Laine, Seppo; Bruhweiler, Frederick; Rottler, Lee

2012-12-01

Stellar mergers have long been thought to be astrophysically important to the evolution and global properties of dense stellar aggregates and even open clusters. However, the study of this phenomenon has until now been severely impeded by the lack of any definite, recent merger with which to compare models. It was recently realized that a 2008 nova was in fact a contact binary which erupted when the two stars finally merged. We have obtained post-merger infrared observations which show a large IR excess and a nonstellar SED which have changed subsantially over time, and near-IR emission lines from shocked material. This object is an important opportunity to learn about the nature and time evolution of recent merger products, and to assemble a unique data set which will be used for many years as a basis for modeling stellar mergers.

ZFOURGE/CANDELS: On the Evolution of M* Galaxy Progenitors from z = 3 to 0.5

NASA Astrophysics Data System (ADS)

Papovich, C.; Labbé, I.; Quadri, R.; Tilvi, V.; Behroozi, P.; Bell, E. F.; Glazebrook, K.; Spitler, L.; Straatman, C. M. S.; Tran, K.-V.; Cowley, M.; Davé, R.; Dekel, A.; Dickinson, M.; Ferguson, H. C.; Finkelstein, S. L.; Gawiser, E.; Inami, H.; Faber, S. M.; Kacprzak, G. G.; Kawinwanichakij, L.; Kocevski, D.; Koekemoer, A.; Koo, D. C.; Kurczynski, P.; Lotz, J. M.; Lu, Y.; Lucas, R. A.; McIntosh, D.; Mehrtens, N.; Mobasher, B.; Monson, A.; Morrison, G.; Nanayakkara, T.; Persson, S. E.; Salmon, B.; Simons, R.; Tomczak, A.; van Dokkum, P.; Weiner, B.; Willner, S. P.

2015-04-01

Galaxies with stellar masses near M* contain the majority of stellar mass in the universe, and are therefore of special interest in the study of galaxy evolution. The Milky Way (MW) and Andromeda (M31) have present-day stellar masses near M*, at 5 × 1010 M ⊙ (defined here to be MW-mass) and 1011 M ⊙ (defined to be M31-mass). We study the typical progenitors of these galaxies using the FOURSTAR Galaxy Evolution Survey (ZFOURGE). ZFOURGE is a deep medium-band near-IR imaging survey, which is sensitive to the progenitors of these galaxies out to z ~ 3. We use abundance-matching techniques to identify the main progenitors of these galaxies at higher redshifts. We measure the evolution in the stellar mass, rest-frame colors, morphologies, far-IR luminosities, and star formation rates, combining our deep multiwavelength imaging with near-IR Hubble Space Telescope imaging from Cosmic Near-IR Deep Extragalactic Legacy Survey (CANDELS), and Spitzer and Herschel far-IR imaging from Great Observatories Origins Deep Survey-Herschel and CANDELS-Herschel. The typical MW-mass and M31-mass progenitors passed through the same evolution stages, evolving from blue, star-forming disk galaxies at the earliest stages to redder dust-obscured IR-luminous galaxies in intermediate stages and to red, more quiescent galaxies at their latest stages. The progenitors of the MW-mass galaxies reached each evolutionary stage at later times (lower redshifts) and with stellar masses that are a factor of two to three lower than the progenitors of the M31-mass galaxies. The process driving this evolution, including the suppression of star formation in present-day M* galaxies, requires an evolving stellar-mass/halo-mass ratio and/or evolving halo-mass threshold for quiescent galaxies. The effective size and SFRs imply that the baryonic cold-gas fractions drop as galaxies evolve from high redshift to z ~ 0 and are strongly anticorrelated with an increase in the Sérsic index. Therefore, the growth of galaxy bulges in M* galaxies corresponds to a rapid decline in the galaxy gas fractions and/or a decrease in the star formation efficiency. This paper contains data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

The birth of gravitational evolutionary dynamics of stellar systems (from Th. Wright to W. Herschel).

NASA Astrophysics Data System (ADS)

Eremeeva, A. J.

1995-05-01

Th. Wright, I. Kant and I. H. Lambert used well-known ideas about the structure and dynamics of the Solar system as a basis of their concepts of the stellar Universe. W. Herschel discovered the main features of the true, non-hierarchical large-scale structure of the Universe. He was also a pioneer of stellar dynamics with its new statistical laws and also of the theory of dynamical evolution in stellar systems at different scales.

Stellar activity and coronal heating: an overview of recent results

PubMed Central

Testa, Paola; Saar, Steven H.; Drake, Jeremy J.

2015-01-01

Observations of the coronae of the Sun and of solar-like stars provide complementary information to advance our understanding of stellar magnetic activity, and of the processes leading to the heating of their outer atmospheres. While solar observations allow us to study the corona at high spatial and temporal resolution, the study of stellar coronae allows us to probe stellar activity over a wide range of ages and stellar parameters. Stellar studies therefore provide us with additional tools for understanding coronal heating processes, as well as the long-term evolution of solar X-ray activity. We discuss how recent studies of stellar magnetic fields and coronae contribute to our understanding of the phenomenon of activity and coronal heating in late-type stars. PMID:25897087

On the Maximum Mass of Accreting Primordial Supermassive Stars

DOE Office of Scientific and Technical Information (OSTI.GOV)

Woods, T. E.; Heger, Alexander; Whalen, Daniel J.

Supermassive primordial stars are suspected to be the progenitors of the most massive quasars at z ∼ 6. Previous studies of such stars were either unable to resolve hydrodynamical timescales or considered stars in isolation, not in the extreme accretion flows in which they actually form. Therefore, they could not self-consistently predict their final masses at collapse, or those of the resulting supermassive black hole seeds, but rather invoked comparison to simple polytropic models. Here, we systematically examine the birth, evolution, and collapse of accreting, non-rotating supermassive stars under accretion rates of 0.01–10 M {sub ⊙} yr{sup −1} using themore » stellar evolution code Kepler . Our approach includes post-Newtonian corrections to the stellar structure and an adaptive nuclear network and can transition to following the hydrodynamic evolution of supermassive stars after they encounter the general relativistic instability. We find that this instability triggers the collapse of the star at masses of 150,000–330,000 M {sub ⊙} for accretion rates of 0.1–10 M {sub ⊙} yr{sup −1}, and that the final mass of the star scales roughly logarithmically with the rate. The structure of the star, and thus its stability against collapse, is sensitive to the treatment of convection and the heat content of the outer accreted envelope. Comparison with other codes suggests differences here may lead to small deviations in the evolutionary state of the star as a function of time, that worsen with accretion rate. Since the general relativistic instability leads to the immediate death of these stars, our models place an upper limit on the masses of the first quasars at birth.« less

Stellar and Binary Evolution in Star Clusters

NASA Technical Reports Server (NTRS)

McMillan, Stephen L. W.

2001-01-01

This paper presents a final report on research activities covered on Stellar and Binary Evolution in Star Clusters. Substantial progress was made in the development and dissemination of the "Starlab" software environment. Significant improvements were made to "kira," an N-body simulation program tailored to the study of dense stellar systems such as star clusters and galactic nuclei. Key advances include (1) the inclusion of stellar and binary evolution in a self-consistent manner, (2) proper treatment of the anisotropic Galactic tidal field, (3) numerous technical enhancements in the treatment of binary dynamics and interactions, and (4) full support for the special-purpose GRAPE-4 hardware, boosting the program's performance by a factor of 10-100 over the accelerated version. The data-reduction and analysis tools in Starlab were also substantially expanded. A Starlab Web site (http://www.sns.ias.edu/-starlab) was created and developed. The site contains detailed information on the structure and function of the various tools that comprise the package, as well as download information, "how to" tips and examples of common operations, demonstration programs, animations, etc. All versions of the software are freely distributed to all interested users, along with detailed installation instructions.

The History of the M31 Disk from Resolved Stellar Populations as Seen by PHAT

NASA Astrophysics Data System (ADS)

Lewis, A. R.; Dalcanton, J. J.; Dolphin, A. E.; Weisz, D. R.; Williams, B. F.; PHAT Collaboration

2014-03-01

The Panchromatic Hubble Andromeda Treasury (PHAT) is an HST multi-cycle treasury program that is mapping the resolved stellar populations of ˜1/3 of M31 from the UV through the near-IR. These data provide color and luminosity information for more than 150 million stars in the M31 disk. We use stellar evolution models to fit the luminous main sequence to derive spatially-resolved recent star formation histories (SFHs) over large areas of M31 with 50-100 pc resolution. These include individual star-forming regions as well as quiescent portions of the disk. We use the gridded SFHs to create movies of star formation activity to study the evolution of individual star-forming events across the disk. Outside of the star-forming regions, we use our resolved stellar photometry to derive the full SFHs of larger regions. These allow us to probe spatial and temporal trends in age and metallicity across a large radial baseline, providing constraints on the global formation and evolution of the disk over a Hubble time. M31 is the only large disk galaxy that is close enough to obtain the photometry necessary for this type of spatially-resolved SFH mapping.

ELECTRON-CAPTURE AND β-DECAY RATES FOR sd-SHELL NUCLEI IN STELLAR ENVIRONMENTS RELEVANT TO HIGH-DENSITY O–NE–MG CORES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Suzuki, Toshio; Toki, Hiroshi; Nomoto, Ken’ichi, E-mail: suzuki@phys.chs.nihon-u.ac.jp

Electron-capture and β-decay rates for nuclear pairs in the sd-shell are evaluated at high densities and high temperatures relevant to the final evolution of electron-degenerate O–Ne–Mg cores of stars with initial masses of 8–10 M{sub ⊙}. Electron capture induces a rapid contraction of the electron-degenerate O–Ne–Mg core. The outcome of rapid contraction depends on the evolutionary changes in the central density and temperature, which are determined by the competing processes of contraction, cooling, and heating. The fate of the stars is determined by these competitions, whether they end up with electron-capture supernovae or Fe core-collapse supernovae. Since the competing processes aremore » induced by electron capture and β-decay, the accurate weak rates are crucially important. The rates are obtained for pairs with A = 20, 23, 24, 25, and 27 by shell-model calculations in the sd-shell with the USDB Hamiltonian. Effects of Coulomb corrections on the rates are evaluated. The rates for pairs with A = 23 and 25 are important for nuclear Urca processes that determine the cooling rate of the O–Ne–Mg core, while those for pairs with A = 20 and 24 are important for the core contraction and heat generation rates in the core. We provide these nuclear rates at stellar environments in tables with fine enough meshes at various densities and temperatures for studies of astrophysical processes sensitive to the rates. In particular, the accurate rate tables are crucially important for the final fates of not only O–Ne–Mg cores but also a wider range of stars, such as C–O cores of lower-mass stars.« less

Dynamical Processes Near the Super Massive Black Hole at the Galactic Center

NASA Astrophysics Data System (ADS)

Antonini, Fabio

2011-01-01

Observations of the stellar environment near the Galactic center provide the strongest empirical evidence for the existence of massive black holes in the Universe. Theoretical models of the Milky Way nuclear star cluster fail to explain numerous properties of such environment, including the presence of very young stars close to the super massive black hole (SMBH) and the more recent discovery of a parsec-scale core in the central distribution of the bright late-type (old) stars. In this thesis we present a theoretical study of dynamical processes near the Galactic center, strongly related to these issues. Using different numerical techniques we explore the close environment of a SMBH as catalyst for stellar collisions and mergers. We study binary stars that remain bound for several revolutions around the SMBH, finding that in the case of highly inclined binaries the Kozai resonance can lead to large periodic oscillations in the internal binary eccentricity and inclination. Collisions and mergers of the binary elements are found to increase significantly for multiple orbits around the SMBH. In collisions involving a low-mass and a high-mass star, the merger product acquires a high core hydrogen abundance from the smaller star, effectively resetting the nuclear evolution clock to a younger age. This process could serve as an important source of young stars at the Galactic center. We then show that a core in the old stars can be naturally explained in a scenario in which the Milky Way nuclear star cluster (NSC) is formed via repeated inspiral of globular clusters into the Galactic center. We present results from a set of N -body simulations of this process, which show that the fundamental properties of the NSC, including its mass, outer density profile and velocity structure, are also reproduced. Chandrasekhar's dynamical friction formula predicts no frictional force on a test body in a low-density core, regardless of its density, due to the absence of stars moving more slowly than the local circular velocity. We have tested this prediction using large-scale N -body experiments. The rate of orbital decay never drops precisely to zero, because stars moving faster than the test body also contribute to the frictional force. When the contribution from the fast-moving stars is included in the expression for the dynamical friction force, and the changes induced by the massive body on the stellar distribution are taken into account, Chandrasekhar's theory is found to reproduce the rate of orbital decay remarkably well. However, this rate is still substantially smaller than the rate predicted by Chandrasekhar's formula in its most widely-used forms, implying longer time scales for inspiral. Motivated by recent observations that suggest a parsec-scale core around the Galactic center SMBH, we investigated the evolution of a population of stellar-mass black holes (BHs) as they spiral in to the center of the Galaxy. After ˜ 10 Gyr, we find that the density of BHs can remain substantially less than the density in stars at all radii; we conclude that it would be unjustified to assume that the spatial distribution of BHs at the Galactic center is well described by steady-state models.

The Gaia-ESO Survey: Sodium and aluminium abundances in giants and dwarfs. Implications for stellar and Galactic chemical evolution

NASA Astrophysics Data System (ADS)

Smiljanic, R.; Romano, D.; Bragaglia, A.; Donati, P.; Magrini, L.; Friel, E.; Jacobson, H.; Randich, S.; Ventura, P.; Lind, K.; Bergemann, M.; Nordlander, T.; Morel, T.; Pancino, E.; Tautvaišienė, G.; Adibekyan, V.; Tosi, M.; Vallenari, A.; Gilmore, G.; Bensby, T.; François, P.; Koposov, S.; Lanzafame, A. C.; Recio-Blanco, A.; Bayo, A.; Carraro, G.; Casey, A. R.; Costado, M. T.; Franciosini, E.; Heiter, U.; Hill, V.; Hourihane, A.; Jofré, P.; Lardo, C.; de Laverny, P.; Lewis, J.; Monaco, L.; Morbidelli, L.; Sacco, G. G.; Sbordone, L.; Sousa, S. G.; Worley, C. C.; Zaggia, S.

2016-05-01

Context. Stellar evolution models predict that internal mixing should cause some sodium overabundance at the surface of red giants more massive than ~1.5-2.0 M⊙. The surface aluminium abundance should not be affected. Nevertheless, observational results disagree about the presence and/or the degree of Na and Al overabundances. In addition, Galactic chemical evolution models adopting different stellar yields lead to very different predictions for the behavior of [Na/Fe] and [Al/Fe] versus [Fe/H]. Overall, the observed trends of these abundances with metallicity are not well reproduced. Aims: We readdress both issues, using new Na and Al abundances determined within the Gaia-ESO Survey. Our aim is to obtain better observational constraints on the behavior of these elements using two samples: I) more than 600 dwarfs of the solar neighborhood and of open clusters and II) low- and intermediate-mass clump giants in six open clusters. Methods: Abundances were determined using high-resolution UVES spectra. The individual Na abundances were corrected for nonlocal thermodynamic equilibrium effects. For the Al abundances, the order of magnitude of the corrections was estimated for a few representative cases. For giants, the abundance trends with stellar mass are compared to stellar evolution models. For dwarfs, the abundance trends with metallicity and age are compared to detailed chemical evolution models. Results: Abundances of Na in stars with mass below ~2.0 M⊙, and of Al in stars below ~3.0 M⊙, seem to be unaffected by internal mixing processes. For more massive stars, the Na overabundance increases with stellar mass. This trend agrees well with predictions of stellar evolutionary models. For Al, our only cluster with giants more massive than 3.0 M⊙, NGC 6705, is Al enriched. However, this might be related to the environment where the cluster was formed. Chemical evolution models that well fit the observed [Na/Fe] vs. [Fe/H] trend in solar neighborhood dwarfs cannot simultaneously explain the run of [Al/Fe] with [Fe/H], and vice versa. The comparison with stellar ages is hampered by severe uncertainties. Indeed, reliable age estimates are available for only a half of the stars of the sample. We conclude that Al is underproduced by the models, except for stellar ages younger than about 7 Gyr. In addition, some significant source of late Na production seems to be missing in the models. Either current Na and Al yields are affected by large uncertainties, and/or some important Galactic source(s) of these elements has as yet not been taken into account. Based on observations made with the ESO/VLT, at Paranal Observatory, under program 188.B-3002 (The Gaia-ESO Public Spectroscopic Survey), and on data obtained from the ESO Archive originally observed under programs 60.A-9143, 076.B-0263 and 082.D-0726.Table 1 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/589/A115

Nuclear reaction rate uncertainties and the 22Ne( p,gamma)23Na reaction: Classical novae and globular clusters

NASA Astrophysics Data System (ADS)

Kelly, Keegan John

The overall theme of this thesis is the advancement of nuclear astrophysics via the analysis of stellar processes in the presence of varying levels of precision in the available nuclear data. With regard to classical novae, the level of mixing that occurs between the outer layers of the white dwarf core and the solar accreted material in oxygen-neon novae is presently undetermined by stellar models, but the nuclear data relevant to these explosive phenomena are fairly precise. This precision allowed for the identification of a series of elemental ratios indicative of the level of mixing occurring in novae. Direct comparisons of the modelled elemental ratios to observations showed that there is likely to be much less of this mixing than was previously assumed. Thus, our understanding of classical novae was altered via the investigation of the nuclear reactions relevant to this phenomenon. However, this level of experimental precision is rare and large nuclear reaction uncertainties can hinder our understanding of certain astrophysical phenomena. For example, it is commonly believed that uncertainties in the 22Ne(p,g)23Na reaction rate at temperatures relevant to thermally-pulsing asymptotic giant branch stars are largely responsible for our inability to explain the observed sodium-oxygen anti-correlation in globular clusters. With this motivation, resonances in the 22Ne(p,g) 23Na reaction at E_{c.m.} = 458, 417, 178, and 151 keV were measured. The direct-capture contribution was also measured at E_{lab} = 425 keV. It was determined that the 22Ne(p,g)23Na reaction rate in the astrophysically relevant temperature range is dominated by the resonances at 178 and 151 keV and that the total reaction rate is greater than the previously assumed rate by a factor of approximately ˜40 at 0.15 GK. This increased reaction rate impacts the expected nucleosynthesis that occurs in these stars and will shed light onto the origin of this anti-correlation as it is incorporated into sophisticated stellar models in the future. In both of these cases the available nuclear data were used to probe stellar processes. This analysis of stellar processes through nuclear reactions is an extremely useful technique that is crucial for the advancement of astrophysics.

Progenitors of Core-Collapse Supernovae

NASA Astrophysics Data System (ADS)

Hirschi, R.; Arnett, D.; Cristini, A.; Georgy, C.; Meakin, C.; Walkington, I.

2017-02-01

Massive stars have a strong impact on their surroundings, in particular when they produce a core-collapse supernova at the end of their evolution. In these proceedings, we review the general evolution of massive stars and their properties at collapse as well as the transition between massive and intermediate-mass stars. We also summarise the effects of metallicity and rotation. We then discuss some of the major uncertainties in the modelling of massive stars, with a particular emphasis on the treatment of convection in 1D stellar evolution codes. Finally, we present new 3D hydrodynamic simulations of convection in carbon burning and list key points to take from 3D hydrodynamic studies for the development of new prescriptions for convective boundary mixing in 1D stellar evolution codes.

Origin and Evolution of Magnetic Field in PMS Stars: Influence of Rotation and Structural Changes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Emeriau-Viard, Constance; Brun, Allan Sacha, E-mail: constance.emeriau@cea.fr, E-mail: sacha.brun@cea.fr

During stellar evolution, especially in the pre-main-sequence phase, stellar structure and rotation evolve significantly, causing major changes in the dynamics and global flows of the star. We wish to assess the consequences of these changes on stellar dynamo, internal magnetic field topology, and activity level. To do so, we have performed a series of 3D HD and MHD simulations with the ASH code. We choose five different models characterized by the radius of their radiative zone following an evolutionary track computed by a 1D stellar evolution code. These models characterized stellar evolution from 1 to 50 Myr. By introducing amore » seed magnetic field in the fully convective model and spreading its evolved state through all four remaining cases, we observe systematic variations in the dynamical properties and magnetic field amplitude and topology of the models. The five MHD simulations develop a strong dynamo field that can reach an equipartition state between the kinetic and magnetic energies and even superequipartition levels in the faster-rotating cases. We find that the magnetic field amplitude increases as it evolves toward the zero-age main sequence. Moreover, the magnetic field topology becomes more complex, with a decreasing axisymmetric component and a nonaxisymmetric one becoming predominant. The dipolar components decrease as the rotation rate and the size of the radiative core increase. The magnetic fields possess a mixed poloidal-toroidal topology with no obvious dominant component. Moreover, the relaxation of the vestige dynamo magnetic field within the radiative core is found to satisfy MHD stability criteria. Hence, it does not experience a global reconfiguration but slowly relaxes by retaining its mixed stable poloidal-toroidal topology.« less

A complex approach to the blue-loop problem

NASA Astrophysics Data System (ADS)

Ostrowski, Jakub; Daszynska-Daszkiewicz, Jadwiga

2015-08-01

The problem of the blue loops during the core helium burning, outstanding for almost fifty years, is one of the most difficult and poorly understood problems in stellar astrophysics. Most of the work focused on the blue loops done so far has been performed with old stellar evolution codes and with limited computational resources. In the end the obtained conclusions were based on a small sample of models and could not have taken into account more advanced effects and interactions between them.The emergence of the blue loops depends on many details of the evolution calculations, in particular on chemical composition, opacity, mixing processes etc. The non-linear interactions between these factors contribute to the statement that in most cases it is hard to predict without a precise stellar modeling whether a loop will emerge or not. The high sensitivity of the blue loops to even small changes of the internal structure of a star yields one more issue: a sensitivity to numerical problems, which are common in calculations of stellar models on advanced stages of the evolution.To tackle this problem we used a modern stellar evolution code MESA. We calculated a large grid of evolutionary tracks (about 8000 models) with masses in the range of 3.0 - 25.0 solar masses from the zero age main sequence to the depletion of helium in the core. In order to make a comparative analysis, we varied metallicity, helium abundance and different mixing parameters resulting from convective overshooting, rotation etc.The better understanding of the properties of the blue loops is crucial for our knowledge of the population of blue supergiants or pulsating variables such as Cepheids, α-Cygni or Slowly Pulsating B-type supergiants. In case of more massive models it is also of great importance for studies of the progenitors of supernovae.

Super Star Clusters and H II Regions in Nuclear Rings

NASA Astrophysics Data System (ADS)

Filippenko, Alex

1996-07-01

We propose to obtain WFPC2 optical broad-band {F547M and F814W} and narrow-band Halpha+ionN2 {F658N} images of nuclear starburst rings in four nearby galaxies for which we already have ultraviolet {F220W} FOC data. Nuclear rings {or ``hot- spot'' regions} in barred spirals are some of the nearest and least obscured starburst regions, and HST images of nuclear rings in several galaxies show that the rings contain large populations of super star clusters similar to those recently discovered in other types of starburst systems. These compact clusters, many having luminosities exceeding that of the R136 cluster in 30 Doradus, represent a violent mode of star formation distinct from that seen in ordinary disk ionH2 regions, and the nuclear rings present us with an opportunity to study large numbers of these extreme clusters in relatively unobscured starburst environments. It has been suggested that super star clusters are present-day versions of young globular clusters. To evaluate this hypothesis, it is important to understand the physical properties and stellar contents of the clusters, but previous HST studies of nuclear ring galaxies have only used single-filter observations. Together with our UV data, new WFPC2 images will enable us to determine the H II region and cluster luminosity functions within nuclear rings, measure cluster radii, derive age and mass estimates for the clusters by comparison with evolutionary synthesis models, and study the structure and evolution of nuclear rings.

The impact and evolution of magnetic confinement in hot stars

NASA Astrophysics Data System (ADS)

Keszthelyi, Z.; Wade, G. A.; Petit, V.; Meynet, G.; Georgy, C.

2018-01-01

Magnetic confinement of the winds of hot, massive stars has far-reaching consequences on timescales ranging from hours to Myr. Understanding the long-term effects of this interplay has already led to the identification of two new evolutionary pathways to form `heavy' stellar mass black holes and pair-instability supernova even at galactic metallicity. We are performing 1D stellar evolution model calculations that, for the first time, account for the surface effects and the time evolution of fossil magnetic fields. These models will be thoroughly confronted with observations and will potentially lead to a significant revision of the derived parameters of observed magnetic massive stars.

Tidal Dissipation In Rotating Low Mass Stars: Implications For The Orbital Evolution Of Close In Planets

NASA Astrophysics Data System (ADS)

Gallet, Florian; Bolmont, Emeline; Mathis, Stéphane; Charbonnel, Corinne; Amard, Louis; Alibert, Yann

2017-10-01

Close-in planets represent a large fraction of the population of confirmed exoplanets. To understand the dynamical evolution of these planets, star-planet interactions must be taken into account. In particular, the dependence of the tidal interactions on the structural parameters of the star, its rotation, and its metallicity should be treated in the models. We quantify how the tidal dissipation in the convective envelope of rotating low-mass stars evolves in time. We also investigate the possible consequences of this evolution on planetary orbital evolution. In Gallet et al. (2017) and Bolmont et al. (2017) we generalized the work of Bolmont & Mathis (2016) by following the orbital evolution of close-in planets using the new tidal dissipation predictions for advanced phases of stellar evolution and non-solar metallicity. We find that during the pre-main sequence the evolution of tidal dissipation is controlled by the evolution of the internal structure of the star through the stellar contraction. On the main-sequence tidal dissipation is strongly driven by the evolution of the surface rotation that is impacted by magnetized stellar winds braking. Finally, during the more evolved phases, the tidal dissipation sharply decreases as radiative core retreats in mass and radius towards the red-giant branch. Using an orbital evolution model, we also show that changing the metallicity leads to diUerent orbital evolutions (e.g., planets migrate farther out from an initially fast rotating metal rich star). By using this model, we qualitatively reproduced the observational trends of the population of hot Jupiters with the metallicity of their host stars. However, more work still remain to be do so as to be able to quantitatively fit our results to the observations.

MASSIVE STARS IN THE LOCAL GROUP: Implications for Stellar Evolution and Star Formation

NASA Astrophysics Data System (ADS)

Massey, Philip

The galaxies of the Local Group serve as important laboratories for understanding the physics of massive stars. Here I discuss what is involved in identifying various kinds of massive stars in nearby galaxies: the hydrogen-burning O-type stars and their evolved He-burning evolutionary descendants, the luminous blue variables, red supergiants, and Wolf-Rayet stars. Primarily I review what our knowledge of the massive star population in nearby galaxies has taught us about stellar evolution and star formation. I show that the current generation of stellar evolutionary models do well at matching some of the observed features and provide a look at the sort of new observational data that will provide a benchmark against which new models can be evaluated.

Stellar Populations in BL Lac type Objects

NASA Astrophysics Data System (ADS)

Serote Roos, Margarida

The relationship between an Active Galactic Nucleus (AGN) and its host galaxy is a crucial question in the study of galaxy evolution. We present an estimate of the stellar contribution in a sample of low luminosity BL Lac type objects. We have performed stellar population synthesis for a sample of 19 objects selected from Marchã et al. (1996, MNRAS 281, 425). The stellar content is quantified using the equivalent widths of all absorption features available throughout the spectrum. The synthesis is done by a variant of the GPG method (Pelat: 1997, MNRAS 284, 365).

Ensemble asteroseismology of solar-type stars with the NASA Kepler mission.

PubMed

Chaplin, W J; Kjeldsen, H; Christensen-Dalsgaard, J; Basu, S; Miglio, A; Appourchaux, T; Bedding, T R; Elsworth, Y; García, R A; Gilliland, R L; Girardi, L; Houdek, G; Karoff, C; Kawaler, S D; Metcalfe, T S; Molenda-Żakowicz, J; Monteiro, M J P F G; Thompson, M J; Verner, G A; Ballot, J; Bonanno, A; Brandão, I M; Broomhall, A-M; Bruntt, H; Campante, T L; Corsaro, E; Creevey, O L; Doğan, G; Esch, L; Gai, N; Gaulme, P; Hale, S J; Handberg, R; Hekker, S; Huber, D; Jiménez, A; Mathur, S; Mazumdar, A; Mosser, B; New, R; Pinsonneault, M H; Pricopi, D; Quirion, P-O; Régulo, C; Salabert, D; Serenelli, A M; Silva Aguirre, V; Sousa, S G; Stello, D; Stevens, I R; Suran, M D; Uytterhoeven, K; White, T R; Borucki, W J; Brown, T M; Jenkins, J M; Kinemuchi, K; Van Cleve, J; Klaus, T C

2011-04-08

In addition to its search for extrasolar planets, the NASA Kepler mission provides exquisite data on stellar oscillations. We report the detections of oscillations in 500 solar-type stars in the Kepler field of view, an ensemble that is large enough to allow statistical studies of intrinsic stellar properties (such as mass, radius, and age) and to test theories of stellar evolution. We find that the distribution of observed masses of these stars shows intriguing differences to predictions from models of synthetic stellar populations in the Galaxy.

Stellar Parameter Determination With J-Plus Using Artificial Neural Networks

NASA Astrophysics Data System (ADS)

Whitten, Devin D.

2017-10-01

The J-PLUS narrow-band filter system provides a unique opportunity for the determination of stellar parameters and chemical abundances from photometry alone. Mapping stellar magnitudes to estimates of surface temperature, [Fe/H], and [C/Fe] is an excellent application of machine learning and in particular, artificial neural networks (ANN). The logistics and performance of this ANN methodology is explored with the J-PLUS Early Data Release, as well as the potential impact of stellar parameters from J-PLUS on the field of Galactic chemical evolution.

The growth of discs and bulges during hierarchical galaxy formation - II. Metallicity, stellar populations and dynamical evolution

NASA Astrophysics Data System (ADS)

Tonini, C.; Mutch, S. J.; Wyithe, J. S. B.; Croton, D. J.

2017-03-01

We investigate the properties of the stellar populations of model galaxies as a function of galaxy evolutionary history and angular momentum content. We use the new semi-analytic model presented in Tonini et al. This new model follows the angular momentum evolution of gas and stars, providing the base for a new star formation recipe, and treatment of the effects of mergers that depends on the central galaxy dynamical structure. We find that the new recipes have the effect of boosting the efficiency of the baryonic cycle in producing and recycling metals, as well as preventing minor mergers from diluting the metallicity of bulges and ellipticals. The model reproduces the stellar mass-stellar metallicity relation for galaxies above 1010 solar masses, including Brightest Cluster Galaxies. Model discs, galaxies dominated by instability-driven components, and merger-driven objects each stem from different evolutionary channels. These model galaxies therefore occupy different loci in the galaxy mass-size relation, which we find to be in accord with the ATLAS 3D classification of disc galaxies, fast rotators and slow rotators. We find that the stellar populations' properties depend on the galaxy evolutionary type, with more evolved stellar populations being part of systems that have lost or dissipated more angular momentum during their assembly history.

COUPLED EVOLUTIONS OF THE STELLAR OBLIQUITY, ORBITAL DISTANCE, AND PLANET'S RADIUS DUE TO THE OHMIC DISSIPATION INDUCED IN A DIAMAGNETIC HOT JUPITER AROUND A MAGNETIC T TAURI STAR

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chang, Yu-Ling; Gu, Pin-Gao; Bodenheimer, Peter H.

We revisit the calculation of the ohmic dissipation in a hot Jupiter presented by Laine et al. by considering more realistic interior structures, stellar obliquity, and the resulting orbital evolution. In this simplified approach, the young hot Jupiter of one Jupiter mass is modeled as a diamagnetic sphere with a finite resistivity, orbiting across tilted stellar magnetic dipole fields in vacuum. Since the induced ohmic dissipation occurs mostly near the planet's surface, we find that the dissipation is unable to significantly expand the young hot Jupiter. Nevertheless, the planet inside a small corotation orbital radius can undergo orbital decay bymore » the dissipation torque and finally overfill its Roche lobe during the T Tauri star phase. The stellar obliquity can evolve significantly if the magnetic dipole is parallel/antiparallel to the stellar spin. Our results are validated by the general torque-dissipation relation in the presence of the stellar obliquity. We also run the fiducial model of Laine et al. and find that the planet's radius is sustained at a nearly constant value by the ohmic heating, rather than being thermally expanded to the Roche radius as suggested by the authors.« less

Supernova 1987A - the evolution from blue to red

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tuchman, Y.; Wheeler, J.C.

1989-09-01

The evolution of stars with mass comparable to that of the progenitor of SN 1987A from the main sequence to the Hayashi track is critically examined to determine why some models evolve to the red on nuclear time scales, some on thermal time scales, and some not at all. Thermal equilibrium solutions to a parametrized series of structural models with active hydrogen burning shells have two stable solutions with different T(eff) for the same helium core M(He) mass and a minimum M(He) below which no blue thermal equlibrium solution is possible. The dependence of the equilibrium solutions on stellar mass,more » envelope composition, and mass loss are investigated. The solutions quantitatively account for the 'gap' in the HR diagrams of massive stars in the Galaxy and LMC and suggest that the outer envelopes are not substantially enriched in helium during the first passage from the main sequence to the Hayashi track. 23 refs.« less

The primary role of the SW Sextantis stars in the evolution of cataclysmic variables

NASA Astrophysics Data System (ADS)

Torres, Manuel; Gaensicke, Boris; Rodriguez-Gil, Pablo; Long, Knox; Marsh, Tom; Steeghs, Danny; Munoz-Darias, Teodoro; Shahbaz, Tariq; Schmidtobreick, Linda; Schreiber, Matthias

2009-02-01

SW Sextantis stars are a relatively large group of cataclysmic variables (CVs) which plays a fundamental role in our understanding of CV structure and evolution. Very little is known about the properties of their accreting white dwarfs and their donor stars, as the stellar components are usually outshone by an extremely bright accretion flow. Consequently, a proper assesment of their evolutionary state is illusionary. We are monitoring the brightness of a number of SW Sex stars and request here Gemini/GMOS-N ToO time to obtain orbital phase-resolved spectroscopy if one of them enters a low state, since this is the only opportunity for studying the stellar components individually. These data will be used to accurately measure the binary parameters, white dwarf temperature, and distance to the system for a SW Sex star for the first time. The measured stellar masses and radii will especially be a precious input to the theory of compact binary evolution as a whole.

Adiabatic invariants in stellar dynamics, 3: Application to globular cluster evolution

NASA Technical Reports Server (NTRS)

Weinberg, Martin D.

1994-01-01

The previous two companion papers demonstrate that slowly varying perturbations may not result in adiabatic cutoffs and provide a formalism for computing the long-term effects of time-dependent perturbations on stellar systems. Here, the theory is implemented in a Fokker-Planck code and a suite of runs illustrating the effects of shock heating on globular cluster evolution are described. Shock heating alone results in considerable mass loss for clusters with R(sub g) less than or approximately 8 kpc: a concentration c = 1.5 cluster with R(sub g) kpc loses up to 95% of its initial mass in 15 Gyr. Only those with concentration c greater than or approximately 1.3 survive disk shocks inside of this radius. Other effects, such as mass loss by stellar evolution, will decrease this survival bound. Loss of the initial halo together with mass segregation leads to mass spectral indices, x, which may be considerably larger than their initial values.

Evolution of massive stars in very young clusters and associations

NASA Technical Reports Server (NTRS)

Stothers, R. B.

1985-01-01

Statistics concerning the stellar content of young galactic clusters and associations which show well defined main sequence turnups have been analyzed in order to derive information about stellar evolution in high-mass galaxies. The analytical approach is semiempirical and uses natural spectroscopic groups of stars on the H-R diagram together with the stars' apparent magnitudes. The new approach does not depend on absolute luminosities and requires only the most basic elements of stellar evolution theory. The following conclusions are offered on the basis of the statistical analysis: (1) O-tupe main-sequence stars evolve to a spectral type of B1 during core hydrogen burning; (2) most O-type blue stragglers are newly formed massive stars burning core hydrogen; (3) supergiants lying redward of the main-sequence turnup are burning core helium; and most Wolf-Rayet stars are burning core helium and originally had masses greater than 30-40 solar mass. The statistics of the natural spectroscopic stars in young galactic clusters and associations are given in a table.

RADIUS-DEPENDENT ANGULAR MOMENTUM EVOLUTION IN LOW-MASS STARS. I

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reiners, Ansgar; Mohanty, Subhanjoy, E-mail: Ansgar.Reiners@phys.uni-goettingen.de

2012-02-10

Angular momentum evolution in low-mass stars is determined by initial conditions during star formation, stellar structure evolution, and the behavior of stellar magnetic fields. Here we show that the empirical picture of angular momentum evolution arises naturally if rotation is related to magnetic field strength instead of to magnetic flux and formulate a corrected braking law based on this. Angular momentum evolution then becomes a strong function of stellar radius, explaining the main trends observed in open clusters and field stars at a few Gyr: the steep transition in rotation at the boundary to full convection arises primarily from themore » large change in radius across this boundary and does not require changes in dynamo mode or field topology. Additionally, the data suggest transient core-envelope decoupling among solar-type stars and field saturation at longer periods in very low mass stars. For solar-type stars, our model is also in good agreement with the empirical Skumanich law. Finally, in further support of the theory, we show that the predicted age at which low-mass stars spin down from the saturated to unsaturated field regimes in our model corresponds remarkably well to the observed lifetime of magnetic activity in these stars.« less

Cosmic evolution of stellar quenching by AGN feedback: clues from the Horizon-AGN simulation

NASA Astrophysics Data System (ADS)

Beckmann, R. S.; Devriendt, J.; Slyz, A.; Peirani, S.; Richardson, M. L. A.; Dubois, Y.; Pichon, C.; Chisari, N. E.; Kaviraj, S.; Laigle, C.; Volonteri, M.

2017-11-01

The observed massive end of the galaxy stellar mass function is steeper than its predicted dark matter halo counterpart in the standard Λ cold dark matter paradigm. In this paper, we investigate the impact of active galactic nuclei (AGN) feedback on star formation in massive galaxies. We isolate the impact of AGN by comparing two simulations from the HORIZON suite, which are identical except that one also includes supermassive black holes (SMBHs) and related feedback models. This allows us to cross-identify individual galaxies between simulations and quantify the effect of AGN feedback on their properties, including stellar mass and gas outflows. We find that massive galaxies (M* ≥ 1011 M⊙) are quenched by AGN feedback to the extent that their stellar masses decrease by up to 80 per cent at z = 0. SMBHs affect their host halo through a combination of outflows that reduce their baryonic mass, particularly for galaxies in the mass range 109 M⊙ ≤ M* ≤ 1011 M⊙, and a disruption of central gas inflows, which limits in situ star formation. As a result, net gas inflows on to massive galaxies, M* ≥ 1011 M⊙, drop by up to 70 per cent. We measure a redshift evolution in the stellar mass ratio of twin galaxies with and without AGN feedback, with galaxies of a given stellar mass showing stronger signs of quenching earlier on. This evolution is driven by a progressive flattening of the MSMBH-M* relation with redshift, particularly for galaxies with M* ≤ 1010 M⊙. MSMBH/M* ratios decrease over time, as falling average gas densities in galaxies curb SMBH growth.

Quenching of Star-formation Activity of High-redshift Galaxies in Cluster and Field

NASA Astrophysics Data System (ADS)

Lee, Seong-Kook; Im, Myungshin; Kim, Jae-Woo; Lotz, Jennifer; McPartland, Conor; Peth, Michael; Koekemoer, Anton M.

2015-08-01

How the galaxy evolution differs at different environment is one of intriguing questions in the study of structure formation. At local, galaxy properties are well known to be clearly different in different environments. However, it is still an open question how this environment-dependent trend has been shaped.In this presentation, we will present the results of our investigation about the evolution of star-formation properties of galaxies over a wide redshift range, from z~ 2 to z~0.5, focusing its dependence on their stellar mass and environment. In the UKIDSS/UDS region, covering ~2800 arcmin2, we estimated photometric redshifts and stellar population properties, such as stellar masses and star-formation rates, using the deep optical and near-infrared data available in this field. Then, we identified galaxy cluster candidates within the given redshift range.Through the analysis and comparison of star-formation (SF) properties of galaxies in clusters and in field, we found interesting results regarding the evolution of SF properties of galaxies: (1) regardless of redshifts, stellar mass is a key parameter controlling quenching of star formation in galaxies; (2) At z<1, environmental effects become important at quenching star formation regardless of stellar mass of galaxies; and (3) However, the result of the environmental quenching is prominent only for low mass galaxies (M* < 1010 M⊙) since the star formation in most of high mass galaxies are already quenched at z > 1.

Molecular Diagnostics of the Interstellar Medium and Star Forming Regions

NASA Astrophysics Data System (ADS)

Hartquist, T. W.; Dalgarno, A.

1996-03-01

Selected examples of the use of observationally inferred molecular level populations and chemical compositions in the diagnosis of interstellar sources and processes important in them (and in other diffuse astrophysical sources) are given. The sources considered include the interclump medium of a giant molecular cloud, dark cores which are the progenitors of star formation, material responding to recent star formation and which may form further stars, and stellar ejecta (including those of supernovae) about to merge with the interstellar medium. The measurement of the microwave background, mixing of material between different nuclear burning zones in evolved stars and turbulent boundary layers (which are present in and influence the structures and evolution of all diffuse astrophysical sources) are treated.

THE VIRUS-P EXPLORATION OF NEARBY GALAXIES (VENGA): SURVEY DESIGN, DATA PROCESSING, AND SPECTRAL ANALYSIS METHODS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Blanc, Guillermo A.; Weinzirl, Tim; Song, Mimi

2013-05-15

We present the survey design, data reduction, and spectral fitting pipeline for the VIRUS-P Exploration of Nearby Galaxies (VENGA). VENGA is an integral field spectroscopic survey, which maps the disks of 30 nearby spiral galaxies. Targets span a wide range in Hubble type, star formation activity, morphology, and inclination. The VENGA data cubes have 5.''6 FWHM spatial resolution, {approx}5 A FWHM spectral resolution, sample the 3600 A-6800 A range, and cover large areas typically sampling galaxies out to {approx}0.7R{sub 25}. These data cubes can be used to produce two-dimensional maps of the star formation rate, dust extinction, electron density, stellarmore » population parameters, the kinematics and chemical abundances of both stars and ionized gas, and other physical quantities derived from the fitting of the stellar spectrum and the measurement of nebular emission lines. To exemplify our methods and the quality of the data, we present the VENGA data cube on the face-on Sc galaxy NGC 628 (a.k.a. M 74). The VENGA observations of NGC 628 are described, as well as the construction of the data cube, our spectral fitting method, and the fitting of the stellar and ionized gas velocity fields. We also propose a new method to measure the inclination of nearly face-on systems based on the matching of the stellar and gas rotation curves using asymmetric drift corrections. VENGA will measure relevant physical parameters across different environments within these galaxies, allowing a series of studies on star formation, structure assembly, stellar populations, chemical evolution, galactic feedback, nuclear activity, and the properties of the interstellar medium in massive disk galaxies.« less

Introduction

NASA Astrophysics Data System (ADS)

Kirby, Evan N.

2018-06-01

Dwarf galaxies are excellent laboratories of chemical evolution. Many dwarf galaxies have simple star formation histories with very low average star formation rates. These conditions simplify models of chemical evolution and facilitate the identification of sites of nucleosynthesis. Dwarf galaxies also host extremely metal-poor stars, which sample the ejecta of the first generations of supernovae in the universe. This meeting-in-a-meeting, "Stellar Abundances in Dwarf Galasxies," will recognize the importance of dwarf galaxies in learning about the creation and evolution of the elements. Topics include: * the most metal-poor stars * the connection between dwarf galaxies and the Milky Way halo * dwarf galaxies as the paragons of r-process nucleosynthesis * modern techniques in stellar abundance measurements * recent advances in chemical evolution modelingI will give a very brief introduction to set the stage for the meeting.

From Luminous Hot Stars to Starburst Galaxies

NASA Astrophysics Data System (ADS)

Conti, Peter S.; Crowther, Paul A.; Leitherer, Claus

2012-10-01

1. Introduction; 2. Observed properties; 3. Stellar atmospheres; 4. Stellar winds; 5. Evolution of single stars; 6. Binaries; 7. Birth of massive stars and star clusters; 8. The interstellar environment; 9. From giant HII regions to HII galaxies; 10. Starburst phenomena; 11. Cosmological implications; References; Index.

Nuclear Astrophysics in underground laboratories: the LUNA experiment

NASA Astrophysics Data System (ADS)

2017-11-01

One of the main ingredients of nuclear astrophysics is the knowledge of the thermonuclear reactions responsible for powering the stellar engine and for the synthesis of the chemical elements. At astrophysical energies the cross section of nuclear processes is extremely reduced by the effect of the Coulomb barrier. The low value of cross sections prevents their measurement at stellar energies on Earth surface and often extrapolations are needed. The Laboratory for Underground Nuclear Astrophysics (LUNA) is placed under the Gran Sasso mountain and thanks to the cosmic-ray background reduction provided by its position can investigate cross sections at energies close to the Gamow peak in stellar scenarios. Many crucial reactions involved in hydrogen burning has been measured directly at astrophysical energies with both the LUNA-50kV and the LUNA-400kV accelerators, and this intense work will continue with the installation of a MV machine able to explore helium and carbon burnings. Based on this progress, currently there are efforts in several countries to construct new underground accelerators. In this talk, the typical techniques adopted in underground nuclear astrophysics will be described and the most relevant results achieved by LUNA will be reviewed. The exciting science that can be probed with the new facilities will be highlighted.

Influence of stellar multiplicity on planet formation. I. Evidence of suppressed planet formation due to stellar companions within 20 au and validation of four planets from the Kepler multiple planet candidates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Ji; Fischer, Debra A.; Xie, Ji-Wei

2014-03-01

The planet occurrence rate for multiple stars is important in two aspects. First, almost half of stellar systems in the solar neighborhood are multiple systems. Second, the comparison of the planet occurrence rate for multiple stars to that for single stars sheds light on the influence of stellar multiplicity on planet formation and evolution. We developed a method of distinguishing planet occurrence rates for single and multiple stars. From a sample of 138 bright (K{sub P} < 13.5) Kepler multi-planet candidate systems, we compared the stellar multiplicity rate of these planet host stars to that of field stars. Using dynamicalmore » stability analyses and archival Doppler measurements, we find that the stellar multiplicity rate of planet host stars is significantly lower than field stars for semimajor axes less than 20 AU, suggesting that planet formation and evolution are suppressed by the presence of a close-in companion star at these separations. The influence of stellar multiplicity at larger separations is uncertain because of search incompleteness due to a limited Doppler observation time baseline and a lack of high-resolution imaging observation. We calculated the planet confidence for the sample of multi-planet candidates and find that the planet confidences for KOI 82.01, KOI 115.01, KOI 282.01, and KOI 1781.02 are higher than 99.7% and thus validate the planetary nature of these four planet candidates. This sample of bright Kepler multi-planet candidates with refined stellar and orbital parameters, planet confidence estimation, and nearby stellar companion identification offers a well-characterized sample for future theoretical and observational study.« less

THE CENTRAL MOLECULAR GAS STRUCTURE IN LINERS WITH LOW-LUMINOSITY ACTIVE GALACTIC NUCLEI: EVIDENCE FOR GRADUAL DISAPPEARANCE OF THE TORUS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mueller-Sanchez, F.; Prieto, M. A.; Mezcua, M.

2013-01-20

We present observations of the molecular gas in the nuclear environment of three prototypical low-luminosity active galactic nuclei (LLAGNs), based on VLT/SINFONI AO-assisted integral-field spectroscopy of H{sub 2} 1-0 S(1) emission at angular resolutions of {approx}0.''17. On scales of 50-150 pc, the spatial distribution and kinematics of the molecular gas are consistent with a rotating thin disk, where the ratio of rotation (V) to dispersion ({sigma}) exceeds unity. However, in the central 50 pc, the observations reveal a geometrically and optically thick structure of molecular gas (V/{sigma} < 1 and N{sub H} > 10{sup 23} cm{sup -2}) that is likelymore » to be associated with the outer extent of any smaller scale obscuring structure. In contrast to Seyfert galaxies, the molecular gas in LLAGNs has a V/{sigma} < 1 over an area that is {approx}9 times smaller and column densities that are on average {approx}3 times smaller. We interpret these results as evidence for a gradual disappearance of the nuclear obscuring structure. While a disk wind may not be able to maintain a thick rotating structure at these luminosities, inflow of material into the nuclear region could provide sufficient energy to sustain it. In this context, LLAGNs may represent the final phase of accretion in current theories of torus evolution. While the inflow rate is considerable during the Seyfert phase, it is slowly decreasing, and the collisional disk is gradually transitioning to become geometrically thin. Furthermore, the nuclear region of these LLAGNs is dominated by intermediate-age/old stellar populations (with little or no ongoing star formation), consistent with a late stage of evolution.« less

The new semi-analytic code GalICS 2.0 - reproducing the galaxy stellar mass function and the Tully-Fisher relation simultaneously

NASA Astrophysics Data System (ADS)

Cattaneo, A.; Blaizot, J.; Devriendt, J. E. G.; Mamon, G. A.; Tollet, E.; Dekel, A.; Guiderdoni, B.; Kucukbas, M.; Thob, A. C. R.

2017-10-01

GalICS 2.0 is a new semi-analytic code to model the formation and evolution of galaxies in a cosmological context. N-body simulations based on a Planck cosmology are used to construct halo merger trees, track subhaloes, compute spins and measure concentrations. The accretion of gas on to galaxies and the morphological evolution of galaxies are modelled with prescriptions derived from hydrodynamic simulations. Star formation and stellar feedback are described with phenomenological models (as in other semi-analytic codes). GalICS 2.0 computes rotation speeds from the gravitational potential of the dark matter, the disc and the central bulge. As the rotation speed depends not only on the virial velocity but also on the ratio of baryons to dark matter within a galaxy, our calculation predicts a different Tully-Fisher relation from models in which vrot ∝ vvir. This is why, GalICS 2.0 is able to reproduce the galaxy stellar mass function and the Tully-Fisher relation simultaneously. Our results are also in agreement with halo masses from weak lensing and satellite kinematics, gas fractions, the relation between star formation rate (SFR) and stellar mass, the evolution of the cosmic SFR density, bulge-to-disc ratios, disc sizes and the Faber-Jackson relation.

An examination of astrophysical habitats for targeted SETI

NASA Technical Reports Server (NTRS)

Doyle, Laurance R.; Mckay, Christopher P.; Reynolds, Ray T.; Whitmire, Daniel P.; Matese, John J.

1991-01-01

Planetary atmospheric radiative transfer models have recently given valuable insights into the definition of the solar system's ecoshell. In addition, however, results have indicated that constraints on solar evolution also need to be addressed, with even minor solar variations, (mass loss, for example), having important consequences from an exobiological standpoint. Following the definition of the solar system's ecoshell evolution, the ecoshells around different stellar spectral types can then be modeled. In this study the astrophysical constraints on the definition of ecoshells and possible exobiological habitats includes: (1) the investigation of the evolution of the solar system's ecoshell under different initial solar/stellar model conditions as indicated by both solar abundance considerations as well as planetary evidence; (2) an outline of considerations necessary to define the ecoshells around the most abundant spectral-type stars, the K and M stars looking at the effects on exobiological habitats of planetary rotational tidal locking effects, and stellar flare/chromospheric-activity cycles, among other effects; (3) a preliminary examination of the factors defining the expected ecoshells around binary stars determining the of regular stellar eclipses, and the expected shortening of the semi-major axis. These results can then be applied to the targeted microwave search for extraterrestrial intelligent signals by constraining the ecoshell space in the solar neighborhood.

Accuracy of inference on the physics of binary evolution from gravitational-wave observations

NASA Astrophysics Data System (ADS)

Barrett, Jim W.; Gaebel, Sebastian M.; Neijssel, Coenraad J.; Vigna-Gómez, Alejandro; Stevenson, Simon; Berry, Christopher P. L.; Farr, Will M.; Mandel, Ilya

2018-04-01

The properties of the population of merging binary black holes encode some of the uncertain physics underlying the evolution of massive stars in binaries. The binary black hole merger rate and chirp-mass distribution are being measured by ground-based gravitational-wave detectors. We consider isolated binary evolution, and explore how accurately the physical model can be constrained with such observations by applying the Fisher information matrix to the merging black hole population simulated with the rapid binary-population synthesis code COMPAS. We investigate variations in four COMPAS parameters: common-envelope efficiency, kick-velocity dispersion, and mass-loss rates during the luminous blue variable and Wolf-Rayet stellar-evolutionary phases. We find that ˜1000 observations would constrain these model parameters to a fractional accuracy of a few per cent. Given the empirically determined binary black hole merger rate, we can expect gravitational-wave observations alone to place strong constraints on the physics of stellar and binary evolution within a few years. Our approach can be extended to use other observational data sets; combining observations at different evolutionary stages will lead to a better understanding of stellar and binary physics.

Dynamical evolution of stars and gas of young embedded stellar sub-clusters

NASA Astrophysics Data System (ADS)

Sills, Alison; Rieder, Steven; Scora, Jennifer; McCloskey, Jessica; Jaffa, Sarah

2018-06-01

We present simulations of the dynamical evolution of young embedded star clusters. Our initial conditions are directly derived from X-ray, infrared, and radio observations of local systems, and our models evolve both gas and stars simultaneously. Our regions begin with both clustered and extended distributions of stars, and a gas distribution that can include a filamentary structure in addition to gas surrounding the stellar sub-clusters. We find that the regions become spherical, monolithic, and smooth quite quickly, and that the dynamical evolution is dominated by the gravitational interactions between the stars. In the absence of stellar feedback, the gas moves gently out of the centre of our regions but does not have a significant impact on the motions of the stars at the earliest stages of cluster formation. Our models at later times are consistent with observations of similar regions in the local neighbourhood. We conclude that the evolution of young protostar clusters is relatively insensitive to reasonable choices of initial conditions. Models with more realism, such as an initial population of binary and multiple stars and ongoing star formation, are the next step needed to confirm these findings.

Accuracy of inference on the physics of binary evolution from gravitational-wave observations

NASA Astrophysics Data System (ADS)

Barrett, Jim W.; Gaebel, Sebastian M.; Neijssel, Coenraad J.; Vigna-Gómez, Alejandro; Stevenson, Simon; Berry, Christopher P. L.; Farr, Will M.; Mandel, Ilya

2018-07-01

The properties of the population of merging binary black holes encode some of the uncertain physics underlying the evolution of massive stars in binaries. The binary black hole merger rate and chirp-mass distribution are being measured by ground-based gravitational-wave detectors. We consider isolated binary evolution, and explore how accurately the physical model can be constrained with such observations by applying the Fisher information matrix to the merging black hole population simulated with the rapid binary-population synthesis code COMPAS. We investigate variations in four COMPAS parameters: common-envelope efficiency, kick-velocity dispersion and mass-loss rates during the luminous blue variable, and Wolf-Rayet stellar-evolutionary phases. We find that ˜1000 observations would constrain these model parameters to a fractional accuracy of a few per cent. Given the empirically determined binary black hole merger rate, we can expect gravitational-wave observations alone to place strong constraints on the physics of stellar and binary evolution within a few years. Our approach can be extended to use other observational data sets; combining observations at different evolutionary stages will lead to a better understanding of stellar and binary physics.

Multiplicity in Early Stellar Evolution

NASA Astrophysics Data System (ADS)

Reipurth, B.; Clarke, C. J.; Boss, A. P.; Goodwin, S. P.; Rodríguez, L. F.; Stassun, K. G.; Tokovinin, A.; Zinnecker, H.

Observations from optical to centimeter wavelengths have demonstrated that multiple systems of two or more bodies is the norm at all stellar evolutionary stages. Multiple systems are widely agreed to result from the collapse and fragmentation of cloud cores, despite the inhibiting influence of magnetic fields. Surveys of class 0 protostars with millimeter interferometers have revealed a very high multiplicity frequency of about 2/3, even though there are observational difficulties in resolving close protobinaries, thus supporting the possibility that all stars could be born in multiple systems. Near-infrared adaptive optics observations of class I protostars show a lower binary frequency relative to the class 0 phase, a declining trend that continues through the class II/III stages to the field population. This loss of companions is a natural consequence of dynamical interplay in small multiple systems, leading to ejection of members. We discuss observational consequences of this dynamical evolution, and its influence on circumstellar disks, and we review the evolution of circumbinary disks and their role in defining binary mass ratios. Special attention is paid to eclipsing PMS binaries, which allow for observational tests of evolutionary models of early stellar evolution. Many stars are born in clusters and small groups, and we discuss how interactions in dense stellar environments can significantly alter the distribution of binary separations through dissolution of wider binaries. The binaries and multiples we find in the field are the survivors of these internal and external destructive processes, and we provide a detailed overview of the multiplicity statistics of the field, which form a boundary condition for all models of binary evolution. Finally, we discuss various formation mechanisms for massive binaries, and the properties of massive trapezia.

Convective penetration in a young sun

NASA Astrophysics Data System (ADS)

Pratt, Jane; Baraffe, Isabelle; Goffrey, Tom; MUSIC developers group

2018-01-01

To interpret the high-quality data produced from recent space-missions it is necessary to study convection under realistic stellar conditions. We describe the multi-dimensional, time implicit, fully compressible, hydrodynamic, implicit large eddy simulation code MUSIC. We use MUSIC to study convection during an early stage in the evolution of our sun where the convection zone covers approximately half of the solar radius. This model of the young sun possesses a realistic stratification in density, temperature, and luminosity. We approach convection in a stellar context using extreme value theory and derive a new model for convective penetration, targeted for one-dimensional stellar evolution calculations. This model provides a scenario that can explain the observed lithium abundance in the sun and in solar-like stars at a range of ages.

Circumstellar shells, the formation of grains, and radiation transfer

NASA Technical Reports Server (NTRS)

Lefevre, Jean

1987-01-01

Advances in infrared astronomy during the last decade have firmly established the presence of dust around a large number of cold giant and supergiant stars. To describe the properties of stars and to understand their evolution, it is necessary to know the nature of the giants and their influence on stellar radiation. Two questions are considered: the formation of grains around cold stars and the modification of stellar radiation by the stellar shell.

STELLAR ATMOSPHERES, ATMOSPHERIC EXTENSION, AND FUNDAMENTAL PARAMETERS: WEIGHING STARS USING THE STELLAR MASS INDEX

DOE Office of Scientific and Technical Information (OSTI.GOV)

Neilson, Hilding R.; Lester, John B.; Baron, Fabien

2016-10-20

One of the great challenges of understanding stars is measuring their masses. The best methods for measuring stellar masses include binary interaction, asteroseismology, and stellar evolution models, but these methods are not ideal for red giant and supergiant stars. In this work, we propose a novel method for inferring stellar masses of evolved red giant and supergiant stars using interferometric and spectrophotometric observations combined with spherical model stellar atmospheres to measure what we call the stellar mass index, defined as the ratio between the stellar radius and mass. The method is based on the correlation between different measurements of angularmore » diameter, used as a proxy for atmospheric extension, and fundamental stellar parameters. For a given star, spectrophotometry measures the Rosseland angular diameter while interferometric observations generally probe a larger limb-darkened angular diameter. The ratio of these two angular diameters is proportional to the relative extension of the stellar atmosphere, which is strongly correlated to the star’s effective temperature, radius, and mass. We show that these correlations are strong and can lead to precise measurements of stellar masses.« less

COS Spectroscopy of White Dwarf Companions to Blue Stragglers

NASA Astrophysics Data System (ADS)

Gosnell, Natalie M.; Geller, Aaron M.; Knigge, Christian; Mathieu, Robert D.; Sills, Alison; Leiner, Emily; Leigh, Nathan

2017-01-01

Complete membership studies of open stellar clusters reveal that 25% of the evolved stars follow alternative pathways in stellar evolution, meaning something in the history of these stars changed their composition or mass (or both). In order to draw a complete picture of stellar evolution we must include these canonically "strange" stars in our definition of standard stellar populations. The formation mechanism of blue straggler stars, traditionally defined to be brighter and bluer than the main sequence turnoff in a star cluster, has been an outstanding question for almost six decades. Recent Hubble Space Telescope (HST) far-ultraviolet (far-UV) observations directly reveal that the blue straggler stars in the old (7 Gyr) open cluster NGC 188 are predominantly formed through mass transfer. We will present HST far-UV COS spectroscopy of white dwarf companions to blue stragglers. These white dwarfs are the remnants of the mass transfer formation process. The effective temperatures and surface gravities of the white dwarfs delineate the timeline of blue straggler formation in this cluster. The existence of these binaries in a well-studied cluster environment provides an unprecedented opportunity to observationally constrain mass transfer models and inform our understanding of many other alternative pathway stellar products.

Active Galactic Nuclei Feedback and the Origin and Fate of the Hot Gas in Early-type Galaxies

NASA Astrophysics Data System (ADS)

Pellegrini, Silvia; Ciotti, Luca; Negri, Andrea; Ostriker, Jeremiah P.

2018-04-01

A recent determination of the relationships between the X-ray luminosity of the ISM (L X) and the stellar and total mass for a sample of nearby early-type galaxies (ETGs) is used to investigate the origin of the hot gas, via a comparison with the results of hydrodynamical simulations of the ISM evolution for a large set of isolated ETGs. After the epoch of major galaxy formation (after z ≃ 2), the ISM is replenished by stellar mass losses and SN ejecta, at the rate predicted by stellar evolution, and is depleted by star formation; it is heated by the thermalization of stellar motions, SNe explosions, and the mechanical (from winds) and radiative AGN feedback. The models agree well with the observed relations, even for the largely different L X values at the same mass, thanks to the sensitivity of the gas flow to many galaxy properties; this holds for models including AGN feedback, and those without. Therefore, the mass input from the stellar population is able to account for a major part of the observed L X; and AGN feedback, while very important to maintain massive ETGs in a time-averaged quasi-steady state, keeping low star formation and the black hole mass, does not dramatically alter the gas content originating in stellar recycled material. These conclusions are based on theoretical predictions for the stellar population contributions in mass and energy, and on a self-consistent modeling of AGN feedback.

Ubiquitous time variability of integrated stellar populations.

PubMed

Conroy, Charlie; van Dokkum, Pieter G; Choi, Jieun

2015-11-26

Long-period variable stars arise in the final stages of the asymptotic giant branch phase of stellar evolution. They have periods of up to about 1,000 days and amplitudes that can exceed a factor of three in the I-band flux. These stars pulsate predominantly in their fundamental mode, which is a function of mass and radius, and so the pulsation periods are sensitive to the age of the underlying stellar population. The overall number of long-period variables in a population is directly related to their lifetimes, which is difficult to predict from first principles because of uncertainties associated with stellar mass-loss and convective mixing. The time variability of these stars has not previously been taken into account when modelling the spectral energy distributions of galaxies. Here we construct time-dependent stellar population models that include the effects of long-period variable stars, and report the ubiquitous detection of this expected 'pixel shimmer' in the massive metal-rich galaxy M87. The pixel light curves display a variety of behaviours. The observed variation of 0.1 to 1 per cent is very well matched to the predictions of our models. The data provide a strong constraint on the properties of variable stars in an old and metal-rich stellar population, and we infer that the lifetime of long-period variables in M87 is shorter by approximately 30 per cent compared to predictions from the latest stellar evolution models.

The Universe, Two by Two.

ERIC Educational Resources Information Center

Metz, William

1983-01-01

Discusses the nature of and current research related to binary stars, indicating that the knowledge that most stars come in pairs is critical to the understanding of stellar phenomena. Subjects addressed include aberrant stellar behavior, x-ray binaries, lobes/disks, close binaries, planetary nebulas, and formation/evolution of binaries. (JN)

The applicability of the viscous α-parameterization of gravitational instability in circumstellar disks

NASA Astrophysics Data System (ADS)

Vorobyov, E. I.

2010-01-01

We study numerically the applicability of the effective-viscosity approach for simulating the effect of gravitational instability (GI) in disks of young stellar objects with different disk-to-star mass ratios ξ . We adopt two α-parameterizations for the effective viscosity based on Lin and Pringle [Lin, D.N.C., Pringle, J.E., 1990. ApJ 358, 515] and Kratter et al. [Kratter, K.M., Matzner, Ch.D., Krumholz, M.R., 2008. ApJ 681, 375] and compare the resultant disk structure, disk and stellar masses, and mass accretion rates with those obtained directly from numerical simulations of self-gravitating disks around low-mass (M∗ ∼ 1.0M⊙) protostars. We find that the effective viscosity can, in principle, simulate the effect of GI in stellar systems with ξ≲ 0.2- 0.3 , thus corroborating a similar conclusion by Lodato and Rice [Lodato, G., Rice, W.K.M., 2004. MNRAS 351, 630] that was based on a different α-parameterization. In particular, the Kratter et al.'s α-parameterization has proven superior to that of Lin and Pringle's, because the success of the latter depends crucially on the proper choice of the α-parameter. However, the α-parameterization generally fails in stellar systems with ξ≳ 0.3 , particularly in the Classes 0 and I phases of stellar evolution, yielding too small stellar masses and too large disk-to-star mass ratios. In addition, the time-averaged mass accretion rates onto the star are underestimated in the early disk evolution and greatly overestimated in the late evolution. The failure of the α-parameterization in the case of large ξ is caused by a growing strength of low-order spiral modes in massive disks. Only in the late Class II phase, when the magnitude of spiral modes diminishes and the mode-to-mode interaction ensues, may the effective viscosity be used to simulate the effect of GI in stellar systems with ξ≳ 0.3 . A simple modification of the effective viscosity that takes into account disk fragmentation can somewhat improve the performance of α-models in the case of large ξ and even approximately reproduce the mass accretion burst phenomenon, the latter being a signature of the early gravitationally unstable stage of stellar evolution [Vorobyov, E.I., Basu, S., 2006. ApJ 650, 956]. However, further numerical experiments are needed to explore this issue.

Global Clusters as Laboratories for Stellar Evolution

NASA Technical Reports Server (NTRS)

Catelan, Marcio; Valcarce, Aldo A. R.; Sweigart, Allen V.

2010-01-01

Globular clusters have long been considered the closest approximation to a physicist's laboratory in astrophysics, and as such a near-ideal laboratory for (low-mass) stellar evolution, However, recent observations have cast a shadow on this long-standing paradigm, suggesting the presence of multiple populations with widely different abundance patterns, and - crucially - with widely different helium abundances as welL In this review we discuss which features of the Hertzsprung-Russell diagram may be used as helium abundance indicators, and present an overview of available constraints on the helium abundance in globular clusters,

Generation and Characterization of States of Matter at Solar Core Conditions

NASA Astrophysics Data System (ADS)

Bachmann, Benjamin

2016-10-01

The equation-of-state (EOS) of matter at solar core conditions is important to stellar evolution models and understanding the origin of high Z elements. Temperatures, densities and pressures of stellar cores are, however, orders of magnitude greater than those obtained in state-of-the-art laboratory EOS experiments and therefore such conditions have been limited to observational astronomy and theoretical models. Here we present a method to generate and diagnose these conditions in the laboratory, which is the first step towards characterizing the EOS of such extreme states of matter. By launching a converging shock wave into a deuterated plastic sphere (CD2) we produce solar core conditions (R /RSun < 0.2) which are initiated when the shock reaches the center of the CD2 sphere and extends during transit of the reflected wave until the temperature drops to a level where the neutron production and x-ray self emission drop below threshold levels of the detectors. These conditions are diagnosed by both, the neutron spectral data from D-D nuclear reactions, and temporal, spatial, and spectral x-ray emission data. We will discuss how these observables can be measured and used to help our understanding of dense plasma states that reach well into the thermonuclear regime of stellar cores. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and was supported by Laboratory Directed Research and Development Grant No. 13-ERD-073.

The stellar metallicity gradients in galaxy discs in a cosmological scenario

NASA Astrophysics Data System (ADS)

Tissera, Patricia B.; Machado, Rubens E. G.; Sanchez-Blazquez, Patricia; Pedrosa, Susana E.; Sánchez, Sebastián F.; Snaith, Owain; Vilchez, Jose

2016-08-01

Context. The stellar metallicity gradients of disc galaxies provide information on disc assembly, star formation processes, and chemical evolution. They also might store information on dynamical processes that could affect the distribution of chemical elements in the gas phase and the stellar components. Understanding their joint effects within a hierarchical clustering scenario is of paramount importance. Aims: We studied the stellar metallicity gradients of simulated discs in a cosmological simulation. We explored the dependence of the stellar metallicity gradients on stellar age and on the size and mass of the stellar discs. Methods: We used a catalogue of galaxies with disc components selected from a cosmological hydrodynamical simulation performed including a physically motivated supernova feedback and chemical evolution. Disc components were defined based on angular momentum and binding energy criteria. The metallicity profiles were estimated for stars with different ages. We confront our numerical findings with results from the Calar Alto Legacy Integral Field Area (CALIFA) Survey. Results: The simulated stellar discs are found to have metallicity profiles with slopes in global agreement with observations. Low stellar mass galaxies tend to have a larger variety of metallicity slopes. When normalized by the half-mass radius, the stellar metallicity gradients do not show any dependence and the dispersion increases significantly, regardless of the galaxy mass. Galaxies with stellar masses o f around 1010M⊙ show steeper negative metallicity gradients. The stellar metallicity gradients correlate with the half-mass radius. However, the correlation signal is not present when they are normalized by the half-mass radius. Stellar discs with positive age gradients are detected to have negative and positive metallicity gradients, depending on the relative importance of recent star formation activity in the central regions. Conclusions: Our results suggest that inside-out formation is the main process responsible for the metallicity and age profiles. The large dispersions in the metallicity gradients as a function of stellar mass could be ascribed to the effects of dynamical processes such as mergers, interactions and/or migration as well as those regulating the conversion of gas into stars. The fingerprints of the inside-out formation seem better preserved by the stellar metallicity gradients as a function of the half-mass radius.

Numerical simulations of relativistic heavy-ion reactions

NASA Astrophysics Data System (ADS)

Daffin, Frank Cecil

Bulk quantities of nuclear matter exist only in the compact bodies of the universe. There the crushing gravitational forces overcome the Coulomb repulsion in massive stellar collapses. Nuclear matter is subjected to high pressures and temperatures as shock waves propagate and burn their way through stellar cores. The bulk properties of nuclear matter are important parameters in the evolution of these collapses, some of which lead to nucleosynthesis. The nucleus is rich in physical phenomena. Above the Coulomb barrier, complex interactions lead to the distortion of, and as collision energies increase, the destruction of the nuclear volume. Of critical importance to the understanding of these events is an understanding of the aggregate microscopic processes which govern them. In an effort to understand relativistic heavy-ion reactions, the Boltzmann-Uehling-Uhlenbeck (Ueh33) (BUU) transport equation is used as the framework for a numerical model. In the years since its introduction, the numerical model has been instrumental in providing a coherent, microscopic, physical description of these complex, highly non-linear events. This treatise describes the background leading to the creation of our numerical model of the BUU transport equation, details of its numerical implementation, its application to the study of relativistic heavy-ion collisions, and some of the experimental observables used to compare calculated results to empirical results. The formalism evolves the one-body Wigner phase-space distribution of nucleons in time under the influence of a single-particle nuclear mean field interaction and a collision source term. This is essentially the familiar Boltzmann transport equation whose source term has been modified to address the Pauli exclusion principle. Two elements of the model allow extrapolation from the study of nuclear collisions to bulk quantities of nuclear matter: the modification of nucleon scattering cross sections in nuclear matter, and the compressibility of nuclear matter. Both are primarily subject to the short- range portion of the inter-nucleon potential, and do not show strong finite-size effects. To that end, several useful observables are introduced and their behavior, as BUU model parameters are changed, explored. The average, directed, in-plane, transverse momentum distribution in rapidity is the oldest of the observables presented in this work. Its slope at mid- rapidity is called the flow of the event, and well characterizes the interplay of repulsive and attractive elements of the dynamics of the events. The BUU model has been quite successful in its role of illuminating the physics of intermediate energy heavy-ion collisions. Though current numerical implementations suffer from some shortcomings they have nonetheless served the community well.

The Dramatic Size and Kinematic Evolution of Massive Early-type Galaxies

NASA Astrophysics Data System (ADS)

Lapi, A.; Pantoni, L.; Zanisi, L.; Shi, J.; Mancuso, C.; Massardi, M.; Shankar, F.; Bressan, A.; Danese, L.

2018-04-01

We aim to provide a holistic view on the typical size and kinematic evolution of massive early-type galaxies (ETGs) that encompasses their high-z star-forming progenitors, their high-z quiescent counterparts, and their configurations in the local Universe. Our investigation covers the main processes playing a relevant role in the cosmic evolution of ETGs. Specifically, their early fast evolution comprises biased collapse of the low angular momentum gaseous baryons located in the inner regions of the host dark matter halo; cooling, fragmentation, and infall of the gas down to the radius set by the centrifugal barrier; further rapid compaction via clump/gas migration toward the galaxy center, where strong heavily dust-enshrouded star formation takes place and most of the stellar mass is accumulated; and ejection of substantial gas amount from the inner regions by feedback processes, which causes a dramatic puffing-up of the stellar component. In the late slow evolution, passive aging of stellar populations and mass additions by dry merger events occur. We describe these processes relying on prescriptions inspired by basic physical arguments and by numerical simulations to derive new analytical estimates of the relevant sizes, timescales, and kinematic properties for individual galaxies along their evolution. Then we obtain quantitative results as a function of galaxy mass and redshift, and compare them to recent observational constraints on half-light size R e , on the ratio v/σ between rotation velocity and velocity dispersion (for gas and stars) and on the specific angular momentum j ⋆ of the stellar component; we find good consistency with the available multiband data in average values and dispersion, both for local ETGs and for their z ∼ 1–2 star-forming and quiescent progenitors. The outcomes of our analysis can provide hints to gauge sub-grid recipes implemented in simulations, to tune numerical experiments focused on specific processes, and to plan future multiband, high-resolution observations on high-redshift star-forming and quiescent galaxies with next-generation facilities.

Mass-loss rates of cool stars

NASA Astrophysics Data System (ADS)

Katrien Els Decin, Leen

2015-08-01

Over much of the initial mass function, stars lose a significant fraction of their mass through a stellar wind during the late stages of their evolution when being a (super)giant star. As of today, we can not yet predict the mass-loss rate during the (super)giant phase for a given star with specific stellar parameters from first principles. This uncertainty directly impacts the accuracy of current stellar evolution and population synthesis models that predict the enrichment of the interstellar medium by these stellar winds. Efforts to establish the link between the initial physical and chemical conditions at stellar birth and the mass-loss rate during the (super)giant phase have proceeded on two separate tracks: (1) more detailed studies of the chemical and morpho-kinematical structure of the stellar winds of (super)giant stars in our own Milky Way by virtue of the proximity, and (2) large scale and statistical studies of a (large) sample of stars in other galaxies (such as the LMC and SMC) and globular clusters eliminating the uncertainty on the distance estimate and providing insight into the dependence of the mass-loss rate on the metallicity. In this review, I will present recent results of both tracks, will show how recent measurements confirm (some) theoretical predictions, but also how results from the first track admonish of common misconceptions inherent in the often more simplified analysis used to analyse the large samples from track 2.

A multiphysics and multiscale software environment for modeling astrophysical systems

NASA Astrophysics Data System (ADS)

Portegies Zwart, Simon; McMillan, Steve; Harfst, Stefan; Groen, Derek; Fujii, Michiko; Nualláin, Breanndán Ó.; Glebbeek, Evert; Heggie, Douglas; Lombardi, James; Hut, Piet; Angelou, Vangelis; Banerjee, Sambaran; Belkus, Houria; Fragos, Tassos; Fregeau, John; Gaburov, Evghenii; Izzard, Rob; Jurić, Mario; Justham, Stephen; Sottoriva, Andrea; Teuben, Peter; van Bever, Joris; Yaron, Ofer; Zemp, Marcel

2009-05-01

We present MUSE, a software framework for combining existing computational tools for different astrophysical domains into a single multiphysics, multiscale application. MUSE facilitates the coupling of existing codes written in different languages by providing inter-language tools and by specifying an interface between each module and the framework that represents a balance between generality and computational efficiency. This approach allows scientists to use combinations of codes to solve highly coupled problems without the need to write new codes for other domains or significantly alter their existing codes. MUSE currently incorporates the domains of stellar dynamics, stellar evolution and stellar hydrodynamics for studying generalized stellar systems. We have now reached a "Noah's Ark" milestone, with (at least) two available numerical solvers for each domain. MUSE can treat multiscale and multiphysics systems in which the time- and size-scales are well separated, like simulating the evolution of planetary systems, small stellar associations, dense stellar clusters, galaxies and galactic nuclei. In this paper we describe three examples calculated using MUSE: the merger of two galaxies, the merger of two evolving stars, and a hybrid N-body simulation. In addition, we demonstrate an implementation of MUSE on a distributed computer which may also include special-purpose hardware, such as GRAPEs or GPUs, to accelerate computations. The current MUSE code base is publicly available as open source at http://muse.li.

AN EXPLORATION OF THE STATISTICAL SIGNATURES OF STELLAR FEEDBACK

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boyden, Ryan D.; Offner, Stella S. R.; Koch, Eric W.

2016-12-20

All molecular clouds are observed to be turbulent, but the origin, means of sustenance, and evolution of the turbulence remain debated. One possibility is that stellar feedback injects enough energy into the cloud to drive observed motions on parsec scales. Recent numerical studies of molecular clouds have found that feedback from stars, such as protostellar outflows and winds, injects energy and impacts turbulence. We expand upon these studies by analyzing magnetohydrodynamic simulations of molecular clouds, including stellar winds, with a range of stellar mass-loss rates and magnetic field strengths. We generate synthetic {sup 12}CO(1–0) maps assuming that the simulations aremore » at the distance of the nearby Perseus molecular cloud. By comparing the outputs from different initial conditions and evolutionary times, we identify differences in the synthetic observations and characterize these using common astrostatistics. We quantify the different statistical responses using a variety of metrics proposed in the literature. We find that multiple astrostatistics, including the principal component analysis, the spectral correlation function, and the velocity coordinate spectrum (VCS), are sensitive to changes in stellar mass-loss rates and/or time evolution. A few statistics, including the Cramer statistic and VCS, are sensitive to the magnetic field strength. These findings demonstrate that stellar feedback influences molecular cloud turbulence and can be identified and quantified observationally using such statistics.« less

Clear Evidence for the Presence of Second-generation Asymptotic Giant Branch Stars in Metal-poor Galactic Globular Clusters

NASA Astrophysics Data System (ADS)

García-Hernández, D. A.; Mészáros, Sz.; Monelli, M.; Cassisi, S.; Stetson, P. B.; Zamora, O.; Shetrone, M.; Lucatello, S.

2015-12-01

Galactic globular clusters (GCs) are known to host multiple stellar populations: a first generation (FG) with a chemical pattern typical of halo field stars and a second generation (SG) enriched in Na and Al and depleted in O and Mg. Both stellar generations are found at different evolutionary stages (e.g., the main-sequence turnoff, the subgiant branch, and the red giant branch (RGB)). The non detection of SG asymptotic giant branch (AGB) stars in several metal-poor ([Fe/H] < -1) GCs suggests that not all SG stars ascend the AGB phase, and that failed AGB stars may be very common in metal-poor GCs. This observation represents a serious problem for stellar evolution and GC formation/evolution theories. We report fourteen SG-AGB stars in four metal-poor GCs (M13, M5, M3, and M2) with different observational properties: horizontal branch (HB) morphology, metallicity, and age. By combining the H-band Al abundances obtained by the Apache Point Observatory Galactic Evolution Experiment survey with ground-based optical photometry, we identify SG Al-rich AGB stars in these four GCs and show that Al-rich RGB/AGB GC stars should be Na-rich. Our observations provide strong support for present, standard stellar models, i.e., without including a strong mass-loss efficiency, for low-mass HB stars. In fact, current empirical evidence is in agreement with the predicted distribution of FG and SG stars during the He-burning stages based on these standard stellar models.

The signatures of the parental cluster on field planetary systems

NASA Astrophysics Data System (ADS)

Cai, Maxwell Xu; Portegies Zwart, Simon; van Elteren, Arjen

2018-03-01

Due to the high stellar densities in young clusters, planetary systems formed in these environments are likely to have experienced perturbations from encounters with other stars. We carry out direct N-body simulations of multiplanet systems in star clusters to study the combined effects of stellar encounters and internal planetary dynamics. These planetary systems eventually become part of the Galactic field population as the parental cluster dissolves, which is where most presently known exoplanets are observed. We show that perturbations induced by stellar encounters lead to distinct signatures in the field planetary systems, most prominently, the excited orbital inclinations and eccentricities. Planetary systems that form within the cluster's half-mass radius are more prone to such perturbations. The orbital elements are most strongly excited in the outermost orbit, but the effect propagates to the entire planetary system through secular evolution. Planet ejections may occur long after a stellar encounter. The surviving planets in these reduced systems tend to have, on average, higher inclinations and larger eccentricities compared to systems that were perturbed less strongly. As soon as the parental star cluster dissolves, external perturbations stop affecting the escaped planetary systems, and further evolution proceeds on a relaxation time-scale. The outer regions of these ejected planetary systems tend to relax so slowly that their state carries the memory of their last strong encounter in the star cluster. Regardless of the stellar density, we observe a robust anticorrelation between multiplicity and mean inclination/eccentricity. We speculate that the `Kepler dichotomy' observed in field planetary systems is a natural consequence of their early evolution in the parental cluster.

A Double Zone Dynamical Model For The Tidal Evolution Of The Obliquity

NASA Astrophysics Data System (ADS)

Damiani, Cilia

2017-10-01

It is debated wether close-in giants planets can form in-situ and if not, which mechanisms are responsible for their migration. One of the observable tests for migration theories is the current value of the obliquity. But after the main migration mechanism has ended, the combined effects of tidal dissipation and the magnetic braking of the star lead to the evolution of both the obliquity and the semi-major axis. The observed correlation between effective temperature and measured projected obliquity has been taken as evidence of such mechanisms being at play. Here I present an improved model for the tidal evolution of the obliquity. It includes all the components of the dynamical tide for circular misaligned systems. It uses an analytical formulation for the frequency-averaged dissipation for each mode, depending only on global stellar parameters, giving a measure of the dissipative properties of the convective zone of the host as it evolves in time. The model also includes the effect of magnetic braking in the framework of the double zone model. This results in the estimation of different tidal evolution timescales for the evolution of the planet's semi-major axis and obliquity depending on the properties of the stellar host. This model can be used to test migration theories, provided that a good determination of stellar radii, masses and ages can be obtained.

Revealing the Location of the Mixing Layer in a Hot Bubble

NASA Astrophysics Data System (ADS)

Guerrero, M. A.; Fang, X.; Chu, Y.-H.; Toalá, J. A.; Gruendl, R. A.

2017-10-01

The fast stellar winds can blow bubbles in the circumstellar material ejected from previous phases of stellar evolution. These are found at different scales, from planetary nebulae (PNe) around stars evolving to the white dwarf stage, to Wolf-Rayet (WR) bubbles and up to large-scale bubbles around massive star clusters. In all cases, the fast stellar wind is shock-heated and a hot bubble is produced. Processes of mass evaporation and mixing of nebular material and heat conduction occurring at the mixing layer between the hot bubble and the optical nebula are key to determine the thermal structure of these bubbles and their evolution. In this contribution we review our current understanding of the X-ray observations of hot bubbles in PNe and present the first spatially-resolved study of a mixing layer in a PN.

Convective penetration in stars

NASA Astrophysics Data System (ADS)

Pratt, Jane; Baraffe, Isabelle; Goffrey, Tom; Constantino, Tom; Popov, M. V.; Walder, Rolf; Folini, Doris; TOFU Collaboration

To interpret the high-quality data produced from recent space-missions it is necessary to study convection under realistic stellar conditions. We describe the multi-dimensional, time implicit, fully compressible, hydrodynamic, implicit large eddy simulation code MUSIC, currently being developed at the University of Exeter. We use MUSIC to study convection during an early stage in the evolution of our sun where the convection zone covers approximately half of the solar radius. This model of the young sun possesses a realistic stratification in density, temperature, and luminosity. We approach convection in a stellar context using extreme value theory and derive a new model for convective penetration, targeted for one-dimensional stellar evolution calculations. The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework (FP7/2007-2013)/ERC Grant agreement no. 320478.

Adiabatic invariants in stellar dynamics. 1: Basic concepts

NASA Technical Reports Server (NTRS)

Weinberg, Martin D.

1994-01-01

The adiabatic criterion, widely used in astronomical dynamics, is based on the harmonic oscillator. It asserts that the change in action under a slowly varying perturbation is exponentially small. Recent mathematical results that precisely define the conditions for invariance show that this model does not apply in general. In particular, a slowly varying perturbation may cause significant evolution stellar dynamical systems even if its time scale is longer than any internal orbital time scale. This additional 'heating' may have serious implications for the evolution of star clusters and dwarf galaxies which are subject to long-term environmental forces. The mathematical developments leading to these results are reviewed, and the conditions for applicability to and further implications for stellar systems are discussed. Companion papers present a computational method for a general time-dependent disturbance and detailed example.

Pervasive orbital eccentricities dictate the habitability of extrasolar earths.

PubMed

Kita, Ryosuke; Rasio, Frederic; Takeda, Genya

2010-09-01

The long-term habitability of Earth-like planets requires low orbital eccentricities. A secular perturbation from a distant stellar companion is a very important mechanism in exciting planetary eccentricities, as many of the extrasolar planetary systems are associated with stellar companions. Although the orbital evolution of an Earth-like planet in a stellar binary system is well understood, the effect of a binary perturbation on a more realistic system containing additional gas-giant planets has been very little studied. Here, we provide analytic criteria confirmed by a large ensemble of numerical integrations that identify the initial orbital parameters leading to eccentric orbits. We show that an extrasolar earth is likely to experience a broad range of orbital evolution dictated by the location of a gas-giant planet, which necessitates more focused studies on the effect of eccentricity on the potential for life.

Infrared Extinction and Stellar Populations in the Milky Way Midplane

NASA Astrophysics Data System (ADS)

Zasowski, Gail; Majewski, S. R.; Benjamin, R. A.; Nidever, D. L.; Skrutskie, M. F.; Indebetouw, R.; Patterson, R. J.; Meade, M. R.; Whitney, B. A.; Babler, B.; Churchwell, E.; Watson, C.

2012-01-01

The primary laboratory for developing and testing models of galaxy formation, structure, and evolution is our own Milky Way, the closest large galaxy and the only one in which we can resolve large numbers of individual stars. The recent availability of extensive stellar surveys, particularly infrared ones, has enabled precise, contiguous measurement of large-scale Galactic properties, a major improvement over inferences based on selected, but scattered, sightlines. However, our ability to fully exploit the Milky Way as a galactic laboratory is severely hampered by the fact that its midplane and central bulge -- where most of the Galactic stellar mass lies -- is heavily obscured by interstellar dust. Therefore, proper consideration of the interstellar extinction is crucial. This thesis describes a new extinction-correction method (the RJCE method) that measures the foreground extinction towards each star and, in many cases, enables recovery of its intrinsic stellar type. We have demonstrated the RJCE Method's validity and used it to produce new, reliable extinction maps of the heavily-reddened Galactic midplane. Taking advantage of the recovered stellar type information, we have generated maps probing the extinction at different heliocentric distances, thus yielding information on the elusive three-dimensional distribution of the interstellar dust. We also performed a study of the interstellar extinction law itself which revealed variations previously undetected in the diffuse ISM and established constraints on models of ISM grain formation and evolution. Furthermore, we undertook a study of large-scale stellar structure in the inner Galaxy -- the bar(s), bulge(s), and inner spiral arms. We used observed and extinction-corrected infrared photometry to map the coherent stellar features in these heavily-obscured parts of the Galaxy, placing constraints on models of the central stellar mass distribution.

The FMOS-COSMOS survey of star-forming galaxies at z ∼ 1.6. II. The mass-metallicity relation and the dependence on star formation rate and dust extinction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zahid, H. J.; Sanders, D. B.; Chu, J.

We investigate the relationships between stellar mass, gas-phase oxygen abundance (metallicity), star formation rate (SFR), and dust content of star-forming galaxies at z ∼ 1.6 using Subaru/FMOS spectroscopy in the COSMOS field. The mass-metallicity (MZ) relation at z ∼ 1.6 is steeper than the relation observed in the local universe. The steeper MZ relation at z ∼ 1.6 is mainly due to evolution in the stellar mass where the MZ relation begins to turnover and flatten. This turnover mass is 1.2 dex larger at z ∼ 1.6. The most massive galaxies at z ∼ 1.6 (∼10{sup 11} M {sub ☉})more » are enriched to the level observed in massive galaxies in the local universe. The MZ relation we measure at z ∼ 1.6 supports the suggestion of an empirical upper metallicity limit that does not significantly evolve with redshift. We find an anti-correlation between metallicity and SFR for galaxies at a fixed stellar mass at z ∼ 1.6, which is similar to trends observed in the local universe. We do not find a relation between stellar mass, metallicity, and SFR that is independent of redshift; rather, our data suggest that there is redshift evolution in this relation. We examine the relation between stellar mass, metallicity, and dust extinction, and find that at a fixed stellar mass, dustier galaxies tend to be more metal rich. From examination of the stellar masses, metallicities, SFRs, and dust extinctions, we conclude that stellar mass is most closely related to dust extinction.« less

Secular Evolution of Galaxies

NASA Astrophysics Data System (ADS)

Falcón-Barroso, Jesús; Knapen, Johan H.

2013-10-01

Preface; 1. Secular evolution in disk galaxies John Kormendy; 2. Galaxy morphology Ronald J. Buta; 3. Dynamics of secular evolution James Binney; 4. Bars and secular evolution in disk galaxies: theoretical input E. Athanassoula; 5. Stellar populations Reynier F. Peletier; 6. Star formation rate indicators Daniela Calzetti; 7. The evolving interstellar medium Jacqueline van Gorkom; 8. Evolution of star formation and gas Nick Z. Scoville; 9. Cosmological evolution of galaxies Isaac Shlosman.

Extrasolar comets: The origin of dust in exozodiacal disks?

NASA Astrophysics Data System (ADS)

Marboeuf, U.; Bonsor, A.; Augereau, J.-C.

2016-11-01

Comets have been invoked in numerous studies as a potentially important source of dust and gas around stars, but none has studied the thermo-physical evolution, out-gassing rate, and dust ejection of these objects in such stellar systems. In this paper we investigate the thermo-physical evolution of comets in exo-planetary systems in order to provide valuable theoretical data required to interpret observations of gas and dust. We use a quasi-3D model of cometary nucleus to study the thermo-physical evolution of comets evolving around a single star from 0.1 to 50 AU, whose homogeneous luminosity varies from 0.1 to 70L⊙. This paper provides thermal evolution, physical alteration, mass ejection, lifetimes, and the rate of dust and water gas mass productions for comets as a function of the distance to the star and stellar luminosity. Results show significant physical changes to comets at high stellar luminosities. The mass loss per revolution and the lifetime of comets depend on their initial size, orbital parameters and follow a power law with stellar luminosity. The models are presented in such a manner that they can be readily applied to any planetary system. By considering the examples of the Solar System, Vega and HD 69830, we show that dust grains released from sublimating comets have the potential to create the observed (exo)zodiacal emission. We show that observations can be reproduced by 1 to 2 massive comets or by a large number of comets whose orbits approach close to the star. Our conclusions depend on the stellar luminosity and the uncertain lifetime of the dust grains. We find, as in previous studies, that exozodiacal dust disks can only survive if replenished by a population of typically sized comets renewed from a large and cold reservoir of cometary bodies beyond the water ice line. These comets could reach the inner regions of the planetary system following scattering by a (giant) planet.

Fingering convection induced by atomic diffusion in stars: 3D numerical computations and applications to stellar models

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zemskova, Varvara; Garaud, Pascale; Deal, Morgan

2014-11-10

Iron-rich layers are known to form in the stellar subsurface through a combination of gravitational settling and radiative levitation. Their presence, nature, and detailed structure can affect the excitation process of various stellar pulsation modes and must therefore be modeled carefully in order to better interpret Kepler asteroseismic data. In this paper, we study the interplay between atomic diffusion and fingering convection in A-type stars, as well as its role in the establishment and evolution of iron accumulation layers. To do so, we use a combination of three-dimensional idealized numerical simulations of fingering convection (which neglect radiative transfer and complexmore » opacity effects) and one-dimensional realistic stellar models. Using the three-dimensional simulations, we first validate the mixing prescription for fingering convection recently proposed by Brown et al. (within the scope of the aforementioned approximation) and identify what system parameters (total mass of iron, iron diffusivity, thermal diffusivity, etc.) play a role in the overall evolution of the layer. We then implement the Brown et al. prescription in the Toulouse-Geneva Evolution Code to study the evolution of the iron abundance profile beneath the stellar surface. We find, as first discussed by Théado et al., that when the concurrent settling of helium is ignored, this accumulation rapidly causes an inversion in the mean molecular weight profile, which then drives fingering convection. The latter mixes iron with the surrounding material very efficiently, and the resulting iron layer is very weak. However, taking helium settling into account partially stabilizes the iron profile against fingering convection, and a large iron overabundance can accumulate. The opacity also increases significantly as a result, and in some cases it ultimately triggers dynamical convection. The direct effects of radiative acceleration on the dynamics of fingering convection (especially in the nonlinear regime) remain to be added in the future to improve the quantitative predictions of the model.« less

Dark stars: a review.

PubMed

Freese, Katherine; Rindler-Daller, Tanja; Spolyar, Douglas; Valluri, Monica

2016-06-01

Dark stars are stellar objects made (almost entirely) of hydrogen and helium, but powered by the heat from dark matter annihilation, rather than by fusion. They are in hydrostatic and thermal equilibrium, but with an unusual power source. Weakly interacting massive particles (WIMPs), among the best candidates for dark matter, can be their own antimatter and can annihilate inside the star, thereby providing a heat source. Although dark matter constitutes only [Formula: see text]0.1% of the stellar mass, this amount is sufficient to power the star for millions to billions of years. Thus, the first phase of stellar evolution in the history of the Universe may have been dark stars. We review how dark stars come into existence, how they grow as long as dark matter fuel persists, and their stellar structure and evolution. The studies were done in two different ways, first assuming polytropic interiors and more recently using the MESA stellar evolution code; the basic results are the same. Dark stars are giant, puffy (∼10 AU) and cool (surface temperatures  ∼10 000 K) objects. We follow the evolution of dark stars from their inception at  ∼[Formula: see text] as they accrete mass from their surroundings to become supermassive stars, some even reaching masses  >[Formula: see text] and luminosities  >[Formula: see text], making them detectable with the upcoming James Webb Space Telescope. Once the dark matter runs out and the dark star dies, it may collapse to a black hole; thus dark stars may provide seeds for the supermassive black holes observed throughout the Universe and at early times. Other sites for dark star formation may exist in the Universe today in regions of high dark matter density such as the centers of galaxies. The current review briefly discusses dark stars existing today, but focuses on the early generation of dark stars.

Dark stars: a review

NASA Astrophysics Data System (ADS)

Freese, Katherine; Rindler-Daller, Tanja; Spolyar, Douglas; Valluri, Monica

2016-06-01

Dark stars are stellar objects made (almost entirely) of hydrogen and helium, but powered by the heat from dark matter annihilation, rather than by fusion. They are in hydrostatic and thermal equilibrium, but with an unusual power source. Weakly interacting massive particles (WIMPs), among the best candidates for dark matter, can be their own antimatter and can annihilate inside the star, thereby providing a heat source. Although dark matter constitutes only ≲ 0.1% of the stellar mass, this amount is sufficient to power the star for millions to billions of years. Thus, the first phase of stellar evolution in the history of the Universe may have been dark stars. We review how dark stars come into existence, how they grow as long as dark matter fuel persists, and their stellar structure and evolution. The studies were done in two different ways, first assuming polytropic interiors and more recently using the MESA stellar evolution code; the basic results are the same. Dark stars are giant, puffy (˜10 AU) and cool (surface temperatures  ˜10 000 K) objects. We follow the evolution of dark stars from their inception at  ˜1{{M}⊙} as they accrete mass from their surroundings to become supermassive stars, some even reaching masses  >{{10}6}{{M}⊙} and luminosities  >{{10}10}{{L}⊙} , making them detectable with the upcoming James Webb Space Telescope. Once the dark matter runs out and the dark star dies, it may collapse to a black hole; thus dark stars may provide seeds for the supermassive black holes observed throughout the Universe and at early times. Other sites for dark star formation may exist in the Universe today in regions of high dark matter density such as the centers of galaxies. The current review briefly discusses dark stars existing today, but focuses on the early generation of dark stars.

Accounting for planet-shaped planetary nebulae

NASA Astrophysics Data System (ADS)

Sabach, Efrat; Soker, Noam

2018-01-01

By following the evolution of several observed exoplanetary systems, we show that by lowering the mass-loss rate of single solar-like stars during their two giant branches, these stars will swallow their planets at the tip of their asymptotic giant branch (AGB) phase. This will most likely lead the stars to form elliptical planetary nebulae (PNe). Under the traditional mass-loss rate these stars will hardly form observable PNe. Stars with a lower mass-loss rate as we propose, about 15 per cent of the traditional mass-loss rate of single stars, leave the AGB with much higher luminosities than what traditional evolution produces. Hence, the assumed lower mass-loss rate might also account for the presence of bright PNe in old stellar populations. We present the evolution of four exoplanetary systems that represent stellar masses in the range of 0.9-1.3 M⊙. The justification for this low mass-loss rate is our assumption that the stellar samples that were used to derive the traditional average single-star mass-loss rate were contaminated by stars that suffer binary interaction.

Effects of Combined Stellar Feedback on Star Formation in Stellar Clusters

NASA Astrophysics Data System (ADS)

Wall, Joshua Edward; McMillan, Stephen; Pellegrino, Andrew; Mac Low, Mordecai; Klessen, Ralf; Portegies Zwart, Simon

2018-01-01

We present results of hybrid MHD+N-body simulations of star cluster formation and evolution including self consistent feedback from the stars in the form of radiation, winds, and supernovae from all stars more massive than 7 solar masses. The MHD is modeled with the adaptive mesh refinement code FLASH, while the N-body computations are done with a direct algorithm. Radiation is modeled using ray tracing along long characteristics in directions distributed using the HEALPIX algorithm, and causes ionization and momentum deposition, while winds and supernova conserve momentum and energy during injection. Stellar evolution is followed using power-law fits to evolution models in SeBa. We use a gravity bridge within the AMUSE framework to couple the N-body dynamics of the stars to the gas dynamics in FLASH. Feedback from the massive stars alters the structure of young clusters as gas ejection occurs. We diagnose this behavior by distinguishing between fractal distribution and central clustering using a Q parameter computed from the minimum spanning tree of each model cluster. Global effects of feedback in our simulations will also be discussed.

The Cosmic Abundance of 3He: Green Bank Telescope Observations

NASA Astrophysics Data System (ADS)

Balser, Dana; Bania, Thomas

2018-01-01

The Big Bang theory for the origin of the Universe predicts that during the first ~1,000 seconds significant amounts of the light elements (2H, 3He, 4He, and 7Li) were produced. Many generations of stellar evolution in the Galaxy modifies these primordial abundances. Observations of the 3He+ hyperfine transition in Galactic HII regions reveals a 3He/H abundance ratio that is constant with Galactocentric radius to within the uncertainties, and is consistent with the primordial value as determined from cosmic microwave background experiments (e.g., WMAP). This "3He Plateau" indicates that the net production and destruction of 3He in stars is approximately zero. Recent stellar evolution models that include thermohaline mixing, however, predict that 3He/H abundance ratios should slightly decrease with Galactocentric radius, or in places in the Galaxy with lower star formation rates. Here we discuss sensitive Green Bank Telescope (GBT) observations of 3He+ at 3.46 cm in a subset of our HII region sample. We develop HII region models and derive accurate 3He/H abundance ratios to better constrain these new stellar evolution models.

Constraining Star Formation in Old Stellar Populations from Theoretical Spectra

NASA Astrophysics Data System (ADS)

Peterson, R. C.

2007-12-01

We are calculating stellar spectra using Kurucz codes, Castelli models, and Kurucz laboratory lines plus guesses; but must first finish adjusting gf values to match stars of solar metallicity and higher. We show that even now, 1D LTE spectral calculations fit a wide range of stellar spectra (from A to K types) over 2200 Å-9000Å once gf values are set to optimize them. Moreover, weighted coadditions of spectral calculations can be constructed that match M31 globular clusters over this entire wavelength range. Both stellar and composite grids will be archived on MAST. The age-metallicity degeneracy can be broken, but only with high-quality data, and only if rare stages of stellar evolution are incorporated where necessary.

Merging Black Hole Binaries in Galactic Nuclei: Implications for Advanced-LIGO Detections

NASA Astrophysics Data System (ADS)

Antonini, Fabio; Rasio, Frederic A.

2016-11-01

Motivated by the recent detection of gravitational waves from the black hole binary merger GW150914, we study the dynamical evolution of (stellar-mass) black holes in galactic nuclei, where massive star clusters reside. With masses of ˜ {10}7 {M}⊙ and sizes of only a few parsecs, nuclear star clusters (NSCs) are the densest stellar systems observed in the local universe and represent a robust environment where black hole binaries can dynamically form, harden, and merge. We show that due to their large escape speeds, NSCs can retain a large fraction of their merger remnants. Successive mergers can then lead to significant growth and produce black hole mergers of several tens of solar masses similar to GW150914 and up to a few hundreds of solar masses, without the need to invoke extremely low metallicity environments. We use a semi-analytical approach to describe the dynamics of black holes in massive star clusters. Our models give a black hole binary merger rate of ≈ 1.5 {{Gpc}}-3 {{yr}}-1 from NSCs, implying up to a few tens of possible detections per year with Advanced LIGO. Moreover, we find a local merger rate of ˜ 1 {{Gpc}}-3 {{yr}}-1 for high mass black hole binaries similar to GW150914; a merger rate comparable to or higher than that of similar binaries assembled dynamically in globular clusters (GCs). Finally, we show that if all black holes receive high natal kicks, ≳ 50 {km} {{{s}}}-1, then NSCs will dominate the local merger rate of binary black holes compared to either GCs or isolated binary evolution.

Dynamical effects of stellar companions

NASA Astrophysics Data System (ADS)

Naoz, Smadar

2015-08-01

The fraction of stellar binaries in the field is extremely high (about 40% - 70% for > 1 Msun stars), and thus, given this frequency, a large fraction of all exoplanetary systems may reside in binaries. While close-in giant planets tend to be found preferentially in binary stellar systems it seems that the frequency of giant planets in close binaries (<100 AU) is significantly lower than in the overall population. Stellar companions’ gravitational perturbations may significantly alter the planetary orbits around their partner on secular timescales. They can drive planets to large eccentric orbits which can either result in plunging these planets into the star or shrinking their orbits and forming short period planets. I will review the dynamical effects stellar binaries have on a planetary systems. I will also present new results on the influence that stellar evolution has on the dynamical processes in these systems.

Chandra stacking analysis of CANDELS galaxies at z>1.5

NASA Astrophysics Data System (ADS)

Civano, Francesca

2016-09-01

The goal of this proposal is to study the X-ray emission of non-X-ray detected galaxies at z>1.5, beyond the peak of stellar and nuclear activity, in combination with galaxy global properties, such as stellar mass and star formation activity and their morphological classification. To achieve this goal, we will select galaxies in CANDELS. Making use of the 5 X-ray surveys with different depths (160 ks for COSMOS, 800 ks for AEGIS-XD and X-UDS, 2 Ms for GOODS-N and 4 (8) Ms GOODS-S) available in these famous fields, we will be able to reach X-ray luminosities where stellar emission dominate the nuclear one. This analysis will extend to z>1.5, the results obtained performing stacking analysis solely using the Chandra COSMOS Legacy Survey at lower redshift.

The Dynamical Evolution of Stellar-Mass Black Holes in Dense Star Clusters

NASA Astrophysics Data System (ADS)

Morscher, Maggie

Globular clusters are gravitationally bound systems containing up to millions of stars, and are found ubiquitously in massive galaxies, including the Milky Way. With densities as high as a million stars per cubic parsec, they are one of the few places in the Universe where stars interact with one another. They therefore provide us with a unique laboratory for studying how gravitational interactions can facilitate the formation of exotic systems, such as X-ray binaries containing black holes, and merging double black hole binaries, which are produced much less efficiently in isolation. While telescopes can provide us with a snapshot of what these dense clusters look like at present, we must rely on detailed numerical simulations to learn about their evolution. These simulations are quite challenging, however, since dense star clusters are described by a complicated set of physical processes occurring on many different length and time scales, including stellar and binary evolution, weak gravitational scattering encounters, strong resonant binary interactions, and tidal stripping by the host galaxy. Until very recently, it was not possible to model the evolution of systems with millions of stars, the actual number contained in the largest clusters, including all the relevant physics required describe these systems accurately. The Northwestern Group's Henon Monte Carlo code, CMC, which has been in development for over a decade, is a powerful tool that can be used to construct detailed evolutionary models of large star clusters. With its recent parallelization, CMC is now capable of addressing a particularly interesting unsolved problem in astrophysics: the dynamical evolution of stellar black holes in dense star clusters. Our current understanding of the stellar initial mass function and massive star evolution suggests that young globular clusters may have formed hundreds to thousands of stellar-mass black holes, the remnants of stars with initial masses from 20 - 100 Solar masses. Birth kicks from supernova explosions may eject some black holes from their birth clusters, but most should be retained initially. Using our Monte Carlo code, we have investigated the long-term dynamical evolution of globular clusters containing large numbers of stellar black holes. Our study is the first to explore in detail the dynamics of BHs in clusters through a large number of realistic simulations covering a wide range of initial conditions (cluster masses from 105 -- 106 Solar masses, as well as variation in other key parameters, such as the virial radius, central concentration, and metallicity), that also includes all the required physics. In almost all of our models we find that significant numbers of black holes (up to about a 1000) are retained all the way to the present. This is in contrast to previous theoretical expectations that most black holes should be ejected dynamically within a few Gyr. The main reason for this difference is that core collapse driven by black holes (through the Spitzer "mass segregation instability'') is easily reverted through three-body processes, and involves only a small number of the most massive black holes, while lower-mass black holes remain well-mixed with ordinary stars far from the central cusp. Thus the rapid segregation of stellar black holes does not lead to a long-term physical separation of most black holes into a dynamically decoupled inner core, as often assumed previously; this is one of the most important results of this dissertation. Combined with the recent detections of several black hole X-ray binary candidates in Galactic globular clusters, our results suggest that stellar black holes could still be present in large numbers in many globular clusters today, and that they may play a significant role in shaping the long-term dynamical evolution and the present-day dynamical structure of many clusters.

Stochastic 2-D galaxy disk evolution models. Resolved stellar populations in the galaxy M33

NASA Astrophysics Data System (ADS)

Mineikis, T.; Vansevičius, V.

We improved the stochastic 2-D galaxy disk models (Mineikis & Vansevičius 2014a) by introducing enriched gas outflows from galaxies and synthetic color-magnitude diagrams of stellar populations. To test the models, we use the HST/ACS stellar photometry data in four fields located along the major axis of the galaxy M33 (Williams et al. 2009) and demonstrate the potential of the models to derive 2-D star formation histories in the resolved disk galaxies.

Evidence of a Supermassive Black Hole in the Galaxy NGC 1023 From The Nuclear Stellar Dynamics

NASA Technical Reports Server (NTRS)

Bower, G. A.; Green, R. F.; Bender, R.; Gebhardt, K.; Lauer, T. R.; Magorrian, J.; Richstone, D. O.; Danks, A.; Gull, T.; Hutchings, J.

2000-01-01

We analyze the nuclear stellar dynamics of the SBO galaxy NGC 1023, utilizing observational data both from the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope and from the ground. The stellar kinematics measured from these long-slit spectra show rapid rotation (V equals approx. 70 km/s at a distance of O.1 deg = 4.9 pc from the nucleus) and increasing velocity dispersion toward the nucleus (where sigma = 295 +/- 30 km/s). We model the observed stellar kinematics assuming an axisymmetric mass distribution with both two and three integrals of motion. Both modeling techniques point to the presence of a central dark compact mass (which presumably is a supermassive black hole) with confidence > 99%. The isotropic two-integral models yield a best-fitting black hole mass of (6.0 +/- 0.4) x 10(exp 7) solar masses and mass-to-light ratio (M/L(sub v)) of 5.38 +/- 0.08, and the goodness-of-fit (CHI(exp 2)) is insensitive to reasonable values for the galaxy's inclination. The three-integral models, which non-parametrically fit the observed line-of-sight velocity distribution as a function of position in the galaxy, suggest a black hole mass of (3.9 +/- 0.4) x 10(exp 7) solar masses and M/L(sub v) of 5.56 +/- 0.02 (internal errors), and the edge-on models are vastly superior fits over models at other inclinations. The internal dynamics in NGC 1023 as suggested by our best-fit three-integral model shows that the velocity distribution function at the nucleus is tangentially anisotropic, suggesting the presence of a nuclear stellar disk. The nuclear line of sight velocity distribution has enhanced wings at velocities >= 600 km/s from systemic, suggesting that perhaps we have detected a group of stars very close to the central dark mass.

Young LMC clusters: the role of red supergiants and multiple stellar populations in their integrated light and CMDs

NASA Astrophysics Data System (ADS)

Asa'd, Randa S.; Vazdekis, Alexandre; Cerviño, Miguel; Noël, Noelia E. D.; Beasley, Michael A.; Kassab, Mahmoud

2017-11-01

The optical integrated spectra of three Large Magellanic Cloud young stellar clusters (NGC 1984, NGC 1994 and NGC 2011) exhibit concave continua and prominent molecular bands which deviate significantly from the predictions of single stellar population (SSP) models. In order to understand the appearance of these spectra, we create a set of young stellar population (MILES) models, which we make available to the community. We use archival International Ultraviolet Explorer integrated UV spectra to independently constrain the cluster masses and extinction, and rule out strong stochastic effects in the optical spectra. In addition, we also analyse deep colour-magnitude diagrams of the clusters to provide independent age determinations based on isochrone fitting. We explore hypotheses, including age spreads in the clusters, a top-heavy initial mass function, different SSP models and the role of red supergiant stars (RSG). We find that the strong molecular features in the optical spectra can be only reproduced by modelling an increased fraction of about ˜20 per cent by luminosity of RSG above what is predicted by canonical stellar evolution models. Given the uncertainties in stellar evolution at Myr ages, we cannot presently rule out the presence of Myr age spreads in these clusters. Our work combines different wavelengths as well as different approaches (resolved data as well as integrated spectra for the same sample) in order to reveal the complete picture. We show that each approach provides important information but in combination we can better understand the cluster stellar populations.

INTRODUCING CAFein, A NEW COMPUTATIONAL TOOL FOR STELLAR PULSATIONS AND DYNAMIC TIDES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Valsecchi, F.; Farr, W. M.; Willems, B.

2013-08-10

Here we present CAFein, a new computational tool for investigating radiative dissipation of dynamic tides in close binaries and of non-adiabatic, non-radial stellar oscillations in isolated stars in the linear regime. For the latter, CAFein computes the non-adiabatic eigenfrequencies and eigenfunctions of detailed stellar models. The code is based on the so-called Riccati method, a numerical algorithm that has been successfully applied to a variety of stellar pulsators, and which does not suffer from the major drawbacks of commonly used shooting and relaxation schemes. Here we present an extension of the Riccati method to investigate dynamic tides in close binaries.more » We demonstrate CAFein's capabilities as a stellar pulsation code both in the adiabatic and non-adiabatic regimes, by reproducing previously published eigenfrequencies of a polytrope, and by successfully identifying the unstable modes of a stellar model in the {beta} Cephei/SPB region of the Hertzsprung-Russell diagram. Finally, we verify CAFein's behavior in the dynamic tides regime by investigating the effects of dynamic tides on the eigenfunctions and orbital and spin evolution of massive main sequence stars in eccentric binaries, and of hot Jupiter host stars. The plethora of asteroseismic data provided by NASA's Kepler satellite, some of which include the direct detection of tidally excited stellar oscillations, make CAFein quite timely. Furthermore, the increasing number of observed short-period detached double white dwarfs (WDs) and the observed orbital decay in the tightest of such binaries open up a new possibility of investigating WD interiors through the effects of tides on their orbital evolution.« less

The Galaxy–Halo Connection for 1.5\\lesssim z\\lesssim 5 as Revealed by the Spitzer Matching Survey of the UltraVISTA Ultra-deep Stripes

NASA Astrophysics Data System (ADS)

Cowley, William I.; Caputi, Karina I.; Deshmukh, Smaran; Ashby, Matthew L. N.; Fazio, Giovanni G.; Le Fèvre, Olivier; Fynbo, Johan P. U.; Ilbert, Olivier; McCracken, Henry J.; Milvang-Jensen, Bo; Somerville, Rachel S.

2018-01-01

The Spitzer Matching Survey of the UltraVISTA ultra-deep Stripes (SMUVS) provides unparalleled depth at 3.6 and 4.5 μm over ∼0.66 deg2 of the COSMOS field, allowing precise photometric determinations of redshift and stellar mass. From this unique data set we can connect galaxy samples, selected by stellar mass, to their host dark matter halos for 1.5< z< 5.0, filling in a large hitherto unexplored region of the parameter space. To interpret the observed galaxy clustering, we use a phenomenological halo model, combined with a novel method to account for uncertainties arising from the use of photometric redshifts. We find that the satellite fraction decreases with increasing redshift and that the clustering amplitude (e.g., comoving correlation length/large-scale bias) displays monotonic trends with redshift and stellar mass. Applying ΛCDM halo mass accretion histories and cumulative abundance arguments for the evolution of stellar mass content, we propose pathways for the coevolution of dark matter and stellar mass assembly. Additionally, we are able to estimate that the halo mass at which the ratio of stellar-to-halo mass is maximized is {10}{12.5-0.08+0.10} {M}ȯ at z∼ 2.5. This peak halo mass is here inferred for the first time from stellar mass-selected clustering measurements at z≳ 2, and it implies a mild evolution of this quantity for z≲ 3, consistent with constraints from abundance-matching techniques.

A Review of Stellar Abundance Databases and the Hypatia Catalog Database

NASA Astrophysics Data System (ADS)

Hinkel, Natalie Rose

2018-01-01

The astronomical community is interested in elements from lithium to thorium, from solar twins to peculiarities of stellar evolution, because they give insight into different regimes of star formation and evolution. However, while some trends between elements and other stellar or planetary properties are well known, many other trends are not as obvious and are a point of conflict. For example, stars that host giant planets are found to be consistently enriched in iron, but the same cannot be definitively said for any other element. Therefore, it is time to take advantage of large stellar abundance databases in order to better understand not only the large-scale patterns, but also the more subtle, small-scale trends within the data.In this overview to the special session, I will present a review of large stellar abundance databases that are both currently available (i.e. RAVE, APOGEE) and those that will soon be online (i.e. Gaia-ESO, GALAH). Additionally, I will discuss the Hypatia Catalog Database (www.hypatiacatalog.com) -- which includes abundances from individual literature sources that observed stars within 150pc. The Hypatia Catalog currently contains 72 elements as measured within ~6000 stars, with a total of ~240,000 unique abundance determinations. The online database offers a variety of solar normalizations, stellar properties, and planetary properties (where applicable) that can all be viewed through multiple interactive plotting interfaces as well as in a tabular format. By analyzing stellar abundances for large populations of stars and from a variety of different perspectives, a wealth of information can be revealed on both large and small scales.

Stellar alchemy. The celestial origin of atoms

NASA Astrophysics Data System (ADS)

Cassé, Michel

Why do the stars shine? What messages can we read in the light they send to us from the depths of the night? Nuclear astrophysics is a fascinating discipline, and enables connections to be made between atoms, stars, and human beings. Through modern astronomy, scientists have managed to unravel the full history of the chemical elements, and to understand how they originated and evolved into all the elements that compose our surroundings today. The transformation of metals into gold, something once dreamed of by alchemists, is a process commonly occurring in the cores of massive stars. But the most exciting revelation is the intimate connection that humanity itself has with the debris of exploded stars. This engaging account of nucleosynthesis in stars, and the associated chemical evolution of the Universe, is suitable for the general reader.

Fates of the most massive primordial stars

NASA Astrophysics Data System (ADS)

Chen, Ke-Jung; Heger, Alexander; Almgren, Ann; Woosley, Stan

2012-09-01

We present our results of numerical simulations of the most massive primordial stars. For the extremely massive non-rotating Pop III stars over 300Msolar, they would simply die as black holes. But the Pop III stars with initial masses 140 - 260Msolar may have died as gigantic explosions called pair-instability supernovae (PSNe). We use a new radiation-hydrodynamics code CASTRO to study evolution of PSNe. Our models follow the entire explosive burning and the explosion until the shock breaks out from the stellar surface. In our simulations, we find that fluid instabilities occurred during the explosion. These instabilities are driven by both nuclear burning and hydrodynamical instability. In the red supergiant models, fluid instabilities can lead to significant mixing of supernova ejecta and alter the observational signature.

Stellar MHD and Nuclear Physics Coupled Together Solve the Puzzle of Oxide Grain Composition

NASA Astrophysics Data System (ADS)

Palmerini, Sara; Trippella, Oscar; Busso, Maurizio; La Cognata, Marco; Petrelli, Maurizio; Zucchini, Azzurra

Oxide grains, enclosed in meteorites, give us very precise information about the stars in which they formed. Grains belonging to group 1 and 2 are characterized by values of 17O/16O and 18O/16O inconsistent with explosive nucleosynthesis scenarios, and are then believed to form in low mass stars. Nowadays, models of non convective mixing coupled with nuclear burning succeed in reproducing the oxygen isotopic mix found in these ancient solids thanks to the more accurate nuclear physics inputs employed in calculations. However, a large part of oxide grains shows values of the 26Al/27Al isotopic ratio too high to be accounted for by the mixing models mentioned above. Recently, [1] demonstrated that the stellar magnetic field might promote the transport of material across the stellar radiative layers. We apply this magnetic mixing model to a 1.2M ⊙ AGB star of solar metallicity. It turns out that the oxygen and aluminum isotopic ratios shown by group 1 and 2 grains are perfectly reproduced.

Direct Reactions at the Facility for Experiments on Nuclear Reactions in Stars (FENRIS)

NASA Astrophysics Data System (ADS)

Longland, Richard; Kelley, John; Marshall, Caleb; Portillo, Federico; Setoodehnia, Kiana

2017-09-01

Nuclear cross sections are a key ingredient in stellar models designed to understand how stars evolve. Determining these cross sections, therefore, is critical for obtaining reliable predictions from stellar models. While many charged-particle reaction cross sections can be measured in the laboratory, the Coulomb barrier means that they cannot always be measured at the low energies relevant to astrophysics. In other cases, radioactive targets make the measurements unfeasible. Radioactive ion beam experiments in inverse kinematics are one solution, but low beam intensities mean that cross sections plague these attempts further. Direct measurements, particularly particle transfer experiments, are one tool in our inventory that provides us with the necessary information to infer reaction cross sections at stellar energies. I will present an overview of one facility: the Facility for Experiments on Nuclear Reactions in Stars (FENRIS), which is dedicated to performing particle transfer measurements for astrophysical cross sections. Over the past few years, FENRIS has been fully upgraded and characterized. I will show highlights of our upgrade activities and current capabilities. I will also highlight our recent experimental results and discuss current upgrade efforts.

Astrostatistical Analysis in Solar and Stellar Physics

NASA Astrophysics Data System (ADS)

Stenning, David Craig

This dissertation focuses on developing statistical models and methods to address data-analytic challenges in astrostatistics---a growing interdisciplinary field fostering collaborations between statisticians and astrophysicists. The astrostatistics projects we tackle can be divided into two main categories: modeling solar activity and Bayesian analysis of stellar evolution. These categories from Part I and Part II of this dissertation, respectively. The first line of research we pursue involves classification and modeling of evolving solar features. Advances in space-based observatories are increasing both the quality and quantity of solar data, primarily in the form of high-resolution images. To analyze massive streams of solar image data, we develop a science-driven dimension reduction methodology to extract scientifically meaningful features from images. This methodology utilizes mathematical morphology to produce a concise numerical summary of the magnetic flux distribution in solar "active regions'' that (i) is far easier to work with than the source images, (ii) encapsulates scientifically relevant information in a more informative manner than existing schemes (i.e., manual classification schemes), and (iii) is amenable to sophisticated statistical analyses. In a related line of research, we perform a Bayesian analysis of the solar cycle using multiple proxy variables, such as sunspot numbers. We take advantage of patterns and correlations among the proxy variables to model solar activity using data from proxies that have become available more recently, while also taking advantage of the long history of observations of sunspot numbers. This model is an extension of the Yu et al. (2012) Bayesian hierarchical model for the solar cycle that used the sunspot numbers alone. Since proxies have different temporal coverage, we devise a multiple imputation scheme to account for missing data. We find that incorporating multiple proxies reveals important features of the solar cycle that are missed when the model is fit using only the sunspot numbers. In Part II of this dissertation we focus on two related lines of research involving Bayesian analysis of stellar evolution. We first focus on modeling multiple stellar populations in star clusters. It has long been assumed that all star clusters are comprised of single stellar populations---stars that formed at roughly the same time from a common molecular cloud. However, recent studies have produced evidence that some clusters host multiple populations, which has far-reaching scientific implications. We develop a Bayesian hierarchical model for multiple-population star clusters, extending earlier statistical models of stellar evolution (e.g., van Dyk et al. 2009, Stein et al. 2013). We also devise an adaptive Markov chain Monte Carlo algorithm to explore the complex posterior distribution. We use numerical studies to demonstrate that our method can recover parameters of multiple-population clusters, and also show how model misspecification can be diagnosed. Our model and computational tools are incorporated into an open-source software suite known as BASE-9. We also explore statistical properties of the estimators and determine that the influence of the prior distribution does not diminish with larger sample sizes, leading to non-standard asymptotics. In a final line of research, we present the first-ever attempt to estimate the carbon fraction of white dwarfs. This quantity has important implications for both astrophysics and fundamental nuclear physics, but is currently unknown. We use a numerical study to demonstrate that assuming an incorrect value for the carbon fraction leads to incorrect white-dwarf ages of star clusters. Finally, we present our attempt to estimate the carbon fraction of the white dwarfs in the well-studied star cluster 47 Tucanae.

Kepler observations of the asteroseismic binary HD 176465

NASA Astrophysics Data System (ADS)

White, T. R.; Benomar, O.; Silva Aguirre, V.; Ball, W. H.; Bedding, T. R.; Chaplin, W. J.; Christensen-Dalsgaard, J.; Garcia, R. A.; Gizon, L.; Stello, D.; Aigrain, S.; Antia, H. M.; Appourchaux, T.; Bazot, M.; Campante, T. L.; Creevey, O. L.; Davies, G. R.; Elsworth, Y. P.; Gaulme, P.; Handberg, R.; Hekker, S.; Houdek, G.; Howe, R.; Huber, D.; Karoff, C.; Marques, J. P.; Mathur, S.; McQuillan, A.; Metcalfe, T. S.; Mosser, B.; Nielsen, M. B.; Régulo, C.; Salabert, D.; Stahn, T.

2017-05-01

Binary star systems are important for understanding stellar structure and evolution, and are especially useful when oscillations can be detected and analysed with asteroseismology. However, only four systems are known in which solar-like oscillations are detected in both components. Here, we analyse the fifth such system, HD 176465, which was observed by Kepler. We carefully analysed the system's power spectrum to measure individual mode frequencies, adapting our methods where necessary to accommodate the fact that both stars oscillate in a similar frequency range. We also modelled the two stars independently by fitting stellar models to the frequencies and complementaryparameters. We are able to cleanly separate the oscillation modes in both systems. The stellar models produce compatible ages and initial compositions for the stars, as is expected from their common and contemporaneous origin. Combining the individual ages, the system is about 3.0 ± 0.5 Gyr old. The two components of HD 176465 are young physically-similar oscillating solar analogues, the first such system to be found, and provide important constraints for stellar evolution and asteroseismology.

Surface density: a new parameter in the fundamental metallicity relation of star-forming galaxies

NASA Astrophysics Data System (ADS)

Hashimoto, Tetsuya; Goto, Tomotsugu; Momose, Rieko

2018-04-01

Star-forming galaxies display a close relation among stellar mass, metallicity, and star formation rate (or molecular-gas mass). This is known as the fundamental metallicity relation (FMR) (or molecular-gas FMR), and it has a profound implication on models of galaxy evolution. However, there still remains a significant residual scatter around the FMR. We show here that a fourth parameter, the surface density of stellar mass, reduces the dispersion around the molecular-gas FMR. In a principal component analysis of 29 physical parameters of 41 338 star-forming galaxies, the surface density of stellar mass is found to be the fourth most important parameter. The new 4D fundamental relation forms a tighter hypersurface that reduces the metallicity dispersion to 50 per cent of that of the molecular-gas FMR. We suggest that future analyses and models of galaxy evolution should consider the FMR in a 4D space that includes surface density. The dilution time-scale of gas inflow and the star-formation efficiency could explain the observational dependence on surface density of stellar mass.

Recent advances in non-LTE stellar atmosphere models

NASA Astrophysics Data System (ADS)

Sander, Andreas A. C.

2017-11-01

In the last decades, stellar atmosphere models have become a key tool in understanding massive stars. Applied for spectroscopic analysis, these models provide quantitative information on stellar wind properties as well as fundamental stellar parameters. The intricate non-LTE conditions in stellar winds dictate the development of adequate sophisticated model atmosphere codes. The increase in both, the computational power and our understanding of physical processes in stellar atmospheres, led to an increasing complexity in the models. As a result, codes emerged that can tackle a wide range of stellar and wind parameters. After a brief address of the fundamentals of stellar atmosphere modeling, the current stage of clumped and line-blanketed model atmospheres will be discussed. Finally, the path for the next generation of stellar atmosphere models will be outlined. Apart from discussing multi-dimensional approaches, I will emphasize on the coupling of hydrodynamics with a sophisticated treatment of the radiative transfer. This next generation of models will be able to predict wind parameters from first principles, which could open new doors for our understanding of the various facets of massive star physics, evolution, and death.

Binary stellar winds. [flow and magnetic field geometry

NASA Technical Reports Server (NTRS)

Siscoe, G. L.; Heinemann, M. A.

1974-01-01

Stellar winds from a binary star pair will interact with each other along a contact discontinuity. We discuss qualitatively the geometry of the flow and field resulting from this interaction in the simplest case where the stars and winds are identical. We consider the shape of the critical surface (defined as the surface where the flow speed is equal to the sound speed) as a function of stellar separation and the role of shock waves in the flow field. The effect of stellar spin and magnetic sectors on the field configuration is given. The relative roles of mass loss and magnetic torque in the evolution of orbital parameters is discussed.

Binary stellar winds. [flow and magnetic field interactions

NASA Technical Reports Server (NTRS)

Siscoe, G. L.; Heinemann, M. A.

1974-01-01

Stellar winds from a binary star will interact with each other along a contact discontinuity. We discuss qualitatively the geometry of the flow and field resulting from this interaction in the simplest case where the stars and winds are identical. We consider the shape of the critical surface (defined as the surface where the flow speed is equal to the sound speed) as a function of stellar separation and the role of shock waves in the flow field. The effect of stellar spin and magnetic sectors on the field configuration is given. The relative roles of mass loss and magnetic torque in the evolution of orbital parameters are discussed.

Patrick Moore's Data Book of Astronomy

NASA Astrophysics Data System (ADS)

Moore, Patrick; Rees, Robin

2014-01-01

1. The Solar System; 2. The Sun; 3. The Moon; 4. Mercury; 5. Venus; 6. Earth; 7. Mars; 8. The asteroid belt; 9. Jupiter; 10. Saturn; 11. Uranus; 12. Neptune; 13. Beyond Neptune: the Kuiper Belt; 14. Comets; 15. Meteors; 16. Meteorites; 17. Glows and atmospheric effects; 18. The stars; 19. Stellar spectra and evolution; 20. Extrasolar planets; 21. Double stars; 22. Variable stars; 23. Stellar clusters; 24. Nebulae; 25. The Galaxy; 26. The evolution of the Universe; 27. The constellations; 28. The star catalogue; 29. Telescopes and observatories; 30. Non-optical astronomy; 31. The history of astronomy; 32. Astronomers; 33. Glossary; Index.

Variance in binary stellar population synthesis

NASA Astrophysics Data System (ADS)

Breivik, Katelyn; Larson, Shane L.

2016-03-01

In the years preceding LISA, Milky Way compact binary population simulations can be used to inform the science capabilities of the mission. Galactic population simulation efforts generally focus on high fidelity models that require extensive computational power to produce a single simulated population for each model. Each simulated population represents an incomplete sample of the functions governing compact binary evolution, thus introducing variance from one simulation to another. We present a rapid Monte Carlo population simulation technique that can simulate thousands of populations in less than a week, thus allowing a full exploration of the variance associated with a binary stellar evolution model.

Planetary geology, stellar evolution and galactic cosmology

NASA Technical Reports Server (NTRS)

1972-01-01

Field studies of selected basalt flows in the Snake River Plain, Idaho, were made for comparative lunar and Mars geological investigations. Studies of basalt lava tubes were also initiated in Washington, Oregon, Hawaii, and northern California. The main effort in the stellar evolution research is toward the development of a computer code to calculate hydrodynamic flow coupled with radiative energy transport. Estimates of the rotation effects on a collapsing cloud indicate that the total angular momentum is the critical parameter. The study of Paschen and Balmer alpha lines of positronium atoms in the center of a galaxy is mentioned.

Quenching of Star-formation Activity of High-redshift Galaxies in Clusters and Field

NASA Astrophysics Data System (ADS)

Lee, Seong-Kook; Im, Myungshin; Kim, Jae-Woo; Lotz, Jennifer; McPartland, Conor; Peth, Michael; Koekemoer, Anton

At local, galaxy properties are well known to be clearly different in different environments. However, it is still an open question how this environment-dependent trend has been shaped. We present the results of our investigation about the evolution of star-formation properties of galaxies over a wide redshift range, from z ~ 2 to z ~ 0.5, focusing its dependence on their stellar mass and environment (Lee et al. 2015). In the UKIDSS/UDS region, covering ~2800 square arcmin, we estimated photometric redshifts and stellar population properties, such as stellar masses and star-formation rates, using the deep optical and near-infrared data available in this field. Then, we identified galaxy cluster candidates within the given redshift range. Through the analysis and comparison of star-formation (SF) properties of galaxies in clusters and in field, we found interesting results regarding the evolution of SF properties of galaxies: (1) regardless of redshifts, stellar mass is a key parameter controlling quenching of star formation in galaxies; (2) At z < 1, environmental effects become important at quenching star formation regardless of stellar mass of galaxies; and (3) However, the result of the environmental quenching is prominent only for low mass galaxies (M* < 1010 M⊙) since the star formation in most of high mass galaxies are already quenched at z > 1.

Snapshots in X-ray binary evolution: Using Hα Emitters and post-starburst galaxies to study the age-dependence of XRB populations

NASA Astrophysics Data System (ADS)

Basu-Zych, Antara; Hornschemeier, Ann; Fragkos, Anastasios; Lehmer, Bret; Zezas, Andreas; Yukita, Mihoko; Tzanavaris, Panayiotis

2018-01-01

The X-ray emission in galaxies, due to X-ray binaries (XRBs), appears to depend on global galaxy properties such as stellar mass (M*), star formation rate (SFR), metallicity, and stellar age. This poster will present unique galaxy populations with well-defined stellar ages to test current relations and models. Specifically, Hα emitters (HAEs), which are nearby analogs of galaxies in the early universe, trace how XRBs form and evolve in young, metal-poor environments. We find that HAEs have lower X-ray luminosities per SFR and metallicity compared to other normal galaxies. At such young ages (<10Myr), XRBs may not have fully formed. Therefore, these observations provide constraints for the expected X-ray emission from XRBs in the early Universe. Post-starburst galaxies, selected by the strength of the Hδ equivalent width (> 500 Å), probe the XRB population related to stellar ages of 0.1-1 Gyr. At these ages, the donor star is expected to be an A-star whose mass is ~2 M⊙ and similar to that of the compact object, which may potentially lead to high mass transfer rates and high X-ray luminosities. Together, these samples offer important constraints for the evolution of XRBs with stellar age.

The Role of Stellar Feedback on the Structure of the ISM and Star Formation in Galaxies

NASA Astrophysics Data System (ADS)

Grisdale, Kearn Michael

2017-08-01

Stellar feedback refers to the injection of energy, momentum and mass into the interstellar medium (ISM) by massive stars. This feedback owes to a combination of ionising radiation, radiation pressure, stellar winds and supernovae and is likely responsible both for the inefficiency of star formation in galaxies, and the observed super-sonic turbulence of the ISM. In this thesis, I study how stellar feedback shapes the ISM thereby regulating galaxy evolution. In particular, I focus on three key questions: (i) How does stellar feedback shape the gas density distribution of the ISM? (ii) How does feedback change or influence the distribution of the kinetic energy in the ISM? and (iii) What role does feedback play in determining the star formation efficiency of giant molecular clouds (GMCs)? To answer these questions, I run high resolution (Deltax 4.6 pc) numerical simulations of three isolated galaxies, both with and without stellar feedback. I compare these simulations to observations of six galaxies from The HI Nearby Galaxy Survey (THINGS) using power spectra, and I use clump finding techniques to identify GMCs in my simulations and calculate their properties. I find that the kinetic energy power spectra in stellar feedback- regulated galaxies, regardless of the galaxy's mass and size, show scalings in excellent agreement with supersonic turbulence on scales below the thickness of the HI layer. I show that feedback influences the gas density field, and drives gas turbulence, up to large (kiloparsec) scales. This is in stark contrast to the density fields generated by large-scale gravity-only driven turbulence (i.e. without stellar feedback). Simulations with stellar feedback are able to reproduce the internal properties of GMCs such as: mass, size and velocity dispersion. Finally, I demonstrate that my simulations naturally reproduce the observed scatter (3.5-4 dex) in the star formation efficiency per free-fall time of GMCs, despite only employing a simple Schmidt star formation law. I conclude that the neutral gas content of galaxies carries signatures of stellar feedback on all scales and that stellar feedback is, therefore, key to regulating the evolution of galaxies over cosmic time.

Star and Dust Formation Activities in AzTEC-3, a Starburst Galaxy at z = 5.3

NASA Astrophysics Data System (ADS)

Dwek, Eli; Staguhn, Johannes G.; Arendt, Richard G.; Capak, Peter L.; Kovacs, Attila; Benford, Dominic J.; Fixsen, Dale; Karim, Alexander; Leclercq, Samuel; Maher, Stephen F.; Moseley, Samuel H.; Schinnerer, Eva; Sharp, Elmer H.

2011-09-01

Analyses of high-redshift ultraluminous infrared (IR) galaxies traditionally use the observed optical to submillimeter spectral energy distribution (SED) and estimates of the dynamical mass as observational constraints to derive the star formation rate (SFR), the stellar mass, and age of these objects. An important observational constraint neglected in the analysis is the mass of dust giving rise to the IR emission. In this paper we add this constraint to the analysis of AzTEC-3. Adopting an upper limit to the mass of stars and a bolometric luminosity for this object, we construct different stellar and chemical evolutionary scenarios, constrained to produce the inferred dust mass and observed luminosity before the associated stellar mass exceeds the observational limit. We use the PÉGASE population synthesis code and a chemical evolution model to follow the evolution of the galaxy's SED and its stellar and dust masses as a function of galactic age for seven different stellar initial mass functions (IMFs). We find that the model with a Top Heavy IMF provided the most plausible scenario consistent with the observational constraints. In this scenario the dust formed over a period of ~200 Myr, with an SFR of ~500 M sun yr-1. These values for the age and SFR in AzTEC-3 are significantly higher and lower, respectively, from those derived without the dust mass constraint. However, this scenario is not unique, and others cannot be completely ruled out because of the prevailing uncertainties in the age of the galaxy, its bolometric luminosity, and its stellar and dust masses. A robust result of our models is that all scenarios require most of the radiating dust mass to have been accreted in molecular clouds. Our new procedure highlights the importance of a multiwavelength approach, and of the use of dust evolution models in constraining the age and the star formation activity and history in galaxies.

STAR AND DUST FORMATION ACTIVITIES IN AzTEC-3, A STARBURST GALAXY AT z = 5.3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dwek, Eli; Staguhn, Johannes G.; Arendt, Richard G.

2011-09-01

Analyses of high-redshift ultraluminous infrared (IR) galaxies traditionally use the observed optical to submillimeter spectral energy distribution (SED) and estimates of the dynamical mass as observational constraints to derive the star formation rate (SFR), the stellar mass, and age of these objects. An important observational constraint neglected in the analysis is the mass of dust giving rise to the IR emission. In this paper we add this constraint to the analysis of AzTEC-3. Adopting an upper limit to the mass of stars and a bolometric luminosity for this object, we construct different stellar and chemical evolutionary scenarios, constrained to producemore » the inferred dust mass and observed luminosity before the associated stellar mass exceeds the observational limit. We use the PEGASE population synthesis code and a chemical evolution model to follow the evolution of the galaxy's SED and its stellar and dust masses as a function of galactic age for seven different stellar initial mass functions (IMFs). We find that the model with a Top Heavy IMF provided the most plausible scenario consistent with the observational constraints. In this scenario the dust formed over a period of {approx}200 Myr, with an SFR of {approx}500 M{sub sun} yr{sup -1}. These values for the age and SFR in AzTEC-3 are significantly higher and lower, respectively, from those derived without the dust mass constraint. However, this scenario is not unique, and others cannot be completely ruled out because of the prevailing uncertainties in the age of the galaxy, its bolometric luminosity, and its stellar and dust masses. A robust result of our models is that all scenarios require most of the radiating dust mass to have been accreted in molecular clouds. Our new procedure highlights the importance of a multiwavelength approach, and of the use of dust evolution models in constraining the age and the star formation activity and history in galaxies.« less

A Comprehensive Stellar Astrophysical Study of the Old Open Cluster M67 with Kepler

NASA Astrophysics Data System (ADS)

Mathieu, Robert D.; Vanderburg, Andrew; K2 M67 Team

2016-06-01

M67 is among the best studied of all star clusters. Being at an age and metallicity very near solar, at an accessible distance of 850 pc with low reddening, and rich in content (over 1000 members including main-sequence dwarfs, a well populated subgiant branch and red giant branch, white dwarfs, blue stragglers, sub-subgiants, X-ray sources and CVs), M67 is a cornerstone of stellar astrophysics.The K2 mission (Campaign 5) has obtained long-cadence observations for 2373 stars, both within an optimized central superaperture and as specified targets outside the superaperture. 1,432 of these stars are likely cluster members based on kinematic and photometric criteria.We have extracted light curves and corrected for K2 roll systematics, producing light curves with noise characteristics qualitatively similar to Kepler light curves of stars of similar magnitudes. The data quality is slightly poorer than for field stars observed by K2 due to crowding near the cluster core, but the data are of sufficient quality to detect seismic oscillations, binary star eclipses, flares, and candidate transit events. We are in the process of uploading light curves and various diagnostic files to MAST; light curves and supporting data will also be made available on ExoFOP.Importantly, several investigators within the M67 K2 team are independently doing light curve extractions and analyses for confirmation of science results. We also are adding extensive ground-based supporting data, including APOGEE near-infrared spectra, TRES and WIYN optical spectra, LCOGT photometry, and more.Our science goals encompass asteroseismology and stellar evolution, alternative stellar evolution pathways in binary stars, stellar rotation and angular momentum evolution, stellar activity, eclipsing binaries and beaming, and exoplanets. We will present early science results as available by the time of the meeting, and certainly including asteroseismology, blue stragglers and sub-subgiants, and newly discovered eclipsing binaries.This work is supported by NASA grant NNX15AW24A to the University of Wisconsin - Madison.

The assembly histories of quiescent galaxies since z = 0.7 from absorption line spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Choi, Jieun; Conroy, Charlie; Moustakas, John

2014-09-10

We present results from modeling the optical spectra of a large sample of quiescent galaxies between 0.1 < z < 0.7 from the Sloan Digital Sky Survey (SDSS) and the AGN and Galaxy Evolution Survey (AGES). We examine how the stellar ages and abundance patterns of galaxies evolve over time as a function of stellar mass from 10{sup 9.6}-10{sup 11.8} M {sub ☉}. Galaxy spectra are stacked in bins of mass and redshift and modeled over a wavelength range from 4000 Å to 5500 Å. Full spectrum stellar population synthesis modeling provides estimates of the age and the abundances ofmore » the elements Fe, Mg, C, N, and Ca. We find negligible evolution in elemental abundances at fixed stellar mass over roughly 7 Gyr of cosmic time. In addition, the increase in stellar ages with time for massive galaxies is consistent with passive evolution since z = 0.7. Taken together, these results favor a scenario in which the inner ∼0.3-3 R {sub e} of massive quiescent galaxies have been passively evolving over the last half of cosmic time. Interestingly, the derived stellar ages are considerably younger than the age of the universe at all epochs, consistent with an equivalent single-burst star formation epoch of z ≲ 1.5. These young stellar population ages coupled with the existence of massive quiescent galaxies at z > 1 indicate the inhomogeneous nature of the z ≲ 0.7 quiescent population. The data also permit the addition of newly quenched galaxies at masses below ∼10{sup 10.5} M {sub ☉} at z < 0.7. Additionally, we analyze very deep Keck DEIMOS spectra of the two brightest quiescent galaxies in a cluster at z = 0.83. There is tentative evidence that these galaxies are older than their counterparts in low-density environments. In the Appendix, we demonstrate that our full spectrum modeling technique allows for accurate and reliable modeling of galaxy spectra to low S/N (∼20 Å{sup –1}) and/or low spectral resolution (R ∼ 500).« less

Binary black hole mergers from globular clusters: Masses, merger rates, and the impact of stellar evolution

NASA Astrophysics Data System (ADS)

Rodriguez, Carl L.; Chatterjee, Sourav; Rasio, Frederic A.

2016-04-01

The recent discovery of GW150914, the binary black hole merger detected by Advanced LIGO, has the potential to revolutionize observational astrophysics. But to fully utilize this new window into the Universe, we must compare these new observations to detailed models of binary black hole formation throughout cosmic time. Expanding upon our previous work [C. L. Rodriguez, M. Morscher, B. Pattabiraman, S. Chatterjee, C.-J. Haster, and F. A. Rasio, Phys. Rev. Lett. 115, 051101 (2015).], we study merging binary black holes formed in globular clusters using our Monte Carlo approach to stellar dynamics. We have created a new set of 52 cluster models with different masses, metallicities, and radii to fully characterize the binary black hole merger rate. These models include all the relevant dynamical processes (such as two-body relaxation, strong encounters, and three-body binary formation) and agree well with detailed direct N -body simulations. In addition, we have enhanced our stellar evolution algorithms with updated metallicity-dependent stellar wind and supernova prescriptions, allowing us to compare our results directly to the most recent population synthesis predictions for merger rates from isolated binary evolution. We explore the relationship between a cluster's global properties and the population of binary black holes that it produces. In particular, we derive a numerically calibrated relationship between the merger times of ejected black hole binaries and a cluster's mass and radius. With our improved treatment of stellar evolution, we find that globular clusters can produce a significant population of massive black hole binaries that merge in the local Universe. We explore the masses and mass ratios of these binaries as a function of redshift, and find a merger rate of ˜5 Gpc-3yr-1 in the local Universe, with 80% of sources having total masses from 32 M⊙ to 64 M⊙. Under standard assumptions, approximately one out of every seven binary black hole mergers in the local Universe will have originated in a globular cluster, but we also explore the sensitivity of this result to different assumptions for binary stellar evolution. If black holes were born with significant natal kicks, comparable to those of neutron stars, then the merger rate of binary black holes from globular clusters would be comparable to that from the field, with approximately 1 /2 of mergers originating in clusters. Finally we point out that population synthesis results for the field may also be modified by dynamical interactions of binaries taking place in dense star clusters which, unlike globular clusters, dissolved before the present day.

Stellar populations dominated by massive stars in dusty starburst galaxies across cosmic time

NASA Astrophysics Data System (ADS)

Zhang, Zhi-Yu; Romano, D.; Ivison, R. J.; Papadopoulos, Padelis P.; Matteucci, F.

2018-06-01

All measurements of cosmic star formation must assume an initial distribution of stellar masses—the stellar initial mass function—in order to extrapolate from the star-formation rate measured for typically rare, massive stars (of more than eight solar masses) to the total star-formation rate across the full stellar mass spectrum1. The shape of the stellar initial mass function in various galaxy populations underpins our understanding of the formation and evolution of galaxies across cosmic time2. Classical determinations of the stellar initial mass function in local galaxies are traditionally made at ultraviolet, optical and near-infrared wavelengths, which cannot be probed in dust-obscured galaxies2,3, especially distant starbursts, whose apparent star-formation rates are hundreds to thousands of times higher than in the Milky Way, selected at submillimetre (rest-frame far-infrared) wavelengths4,5. The 13C/18O isotope abundance ratio in the cold molecular gas—which can be probed via the rotational transitions of the 13CO and C18O isotopologues—is a very sensitive index of the stellar initial mass function, with its determination immune to the pernicious effects of dust. Here we report observations of 13CO and C18O emission for a sample of four dust-enshrouded starbursts at redshifts of approximately two to three, and find unambiguous evidence for a top-heavy stellar initial mass function in all of them. A low 13CO/C18O ratio for all our targets—alongside a well tested, detailed chemical evolution model benchmarked on the Milky Way6—implies that there are considerably more massive stars in starburst events than in ordinary star-forming spiral galaxies. This can bring these extraordinary starbursts closer to the `main sequence' of star-forming galaxies7, although such main-sequence galaxies may not be immune to changes in initial stellar mass function, depending on their star-formation densities.

The rise and fall of stellar across the peak of cosmic star formation history: effects of mergers versus diffuse stellar mass acquisition

NASA Astrophysics Data System (ADS)

Welker, C.; Dubois, Y.; Devriendt, J.; Pichon, C.; Kaviraj, S.; Peirani, S.

2017-02-01

Building galaxy merger trees from a state-of-the-art cosmological hydrodynamical simulation, Horizon-AGN, we perform a statistical study of how mergers and diffuse stellar mass acquisition processes drive galaxy morphologic properties above z > 1. By diffuse mass acquisition here, we mean both accretion of stars by unresolved mergers (relative stellar mass growth smaller than 4.5 per cent) as well as in situ star formation when no resolved mergers are detected along the main progenitor branch of a galaxy. We investigate how stellar densities, galaxy sizes and galaxy morphologies (defined via shape parameters derived from the inertia tensor of the stellar density) depend on mergers of different mass ratios. We investigate how stellar densities, effective radii and shape parameters derived from the inertia tensor depend on mergers of different mass ratios. We find strong evidence that diffuse stellar accretion and in situ formation tend to flatten small galaxies over cosmic time, leading to the formation of discs. On the other hand, mergers, and not only the major ones, exhibit a propensity to puff up and destroy stellar discs, confirming the origin of elliptical galaxies. We confirm that mergers grow galaxy sizes more efficiently than diffuse processes (r_{0.5}∝ M_s^{0.85} and r_{0.5}∝ M_s^{0.1} on average, respectively) and we also find that elliptical galaxies are more susceptible to grow in size through mergers than disc galaxies with a size-mass evolution r_{0.5}∝ M_s^{1.2} instead of r_{0.5}∝ M_s^{-0.5}-M^{0.5} for discs depending on the merger mass ratio. The gas content drives the size-mass evolution due to merger with a faster size growth for gas-poor galaxies r_{0.5}∝ M_s2 than for gas-rich galaxies r0.5 ∝ Ms.

Stellar populations dominated by massive stars in dusty starburst galaxies across cosmic time.

PubMed

Zhang, Zhi-Yu; Romano, D; Ivison, R J; Papadopoulos, Padelis P; Matteucci, F

2018-06-01

All measurements of cosmic star formation must assume an initial distribution of stellar masses-the stellar initial mass function-in order to extrapolate from the star-formation rate measured for typically rare, massive stars (of more than eight solar masses) to the total star-formation rate across the full stellar mass spectrum 1 . The shape of the stellar initial mass function in various galaxy populations underpins our understanding of the formation and evolution of galaxies across cosmic time 2 . Classical determinations of the stellar initial mass function in local galaxies are traditionally made at ultraviolet, optical and near-infrared wavelengths, which cannot be probed in dust-obscured galaxies 2,3 , especially distant starbursts, whose apparent star-formation rates are hundreds to thousands of times higher than in the Milky Way, selected at submillimetre (rest-frame far-infrared) wavelengths 4,5 . The 13 C/ 18 O isotope abundance ratio in the cold molecular gas-which can be probed via the rotational transitions of the 13 CO and C 18 O isotopologues-is a very sensitive index of the stellar initial mass function, with its determination immune to the pernicious effects of dust. Here we report observations of 13 CO and C 18 O emission for a sample of four dust-enshrouded starbursts at redshifts of approximately two to three, and find unambiguous evidence for a top-heavy stellar initial mass function in all of them. A low 13 CO/C 18 O ratio for all our targets-alongside a well tested, detailed chemical evolution model benchmarked on the Milky Way 6 -implies that there are considerably more massive stars in starburst events than in ordinary star-forming spiral galaxies. This can bring these extraordinary starbursts closer to the 'main sequence' of star-forming galaxies 7 , although such main-sequence galaxies may not be immune to changes in initial stellar mass function, depending on their star-formation densities.

A COMPREHENSIVE ANALYSIS OF UNCERTAINTIES AFFECTING THE STELLAR MASS-HALO MASS RELATION FOR 0 < z < 4

DOE Office of Scientific and Technical Information (OSTI.GOV)

Behroozi, Peter S.; Wechsler, Risa H.; Conroy, Charlie

2010-07-01

We conduct a comprehensive analysis of the relationship between central galaxies and their host dark matter halos, as characterized by the stellar mass-halo mass (SM-HM) relation, with rigorous consideration of uncertainties. Our analysis focuses on results from the abundance matching technique, which assumes that every dark matter halo or subhalo above a specific mass threshold hosts one galaxy. We provide a robust estimate of the SM-HM relation for 0 < z < 1 and discuss the quantitative effects of uncertainties in observed galaxy stellar mass functions (including stellar mass estimates and counting uncertainties), halo mass functions (including cosmology and uncertaintiesmore » from substructure), and the abundance matching technique used to link galaxies to halos (including scatter in this connection). Our analysis results in a robust estimate of the SM-HM relation and its evolution from z = 0 to z = 4. The shape and the evolution are well constrained for z < 1. The largest uncertainties at these redshifts are due to stellar mass estimates (0.25 dex uncertainty in normalization); however, failure to account for scatter in stellar masses at fixed halo mass can lead to errors of similar magnitude in the SM-HM relation for central galaxies in massive halos. We also investigate the SM-HM relation to z = 4, although the shape of the relation at higher redshifts remains fairly unconstrained when uncertainties are taken into account. We find that the integrated star formation at a given halo mass peaks at 10%-20% of available baryons for all redshifts from 0 to 4. This peak occurs at a halo mass of 7 x 10{sup 11} M{sub sun} at z = 0 and this mass increases by a factor of 5 to z = 4. At lower and higher masses, star formation is substantially less efficient, with stellar mass scaling as M{sub *} {approx} M {sup 2.3}{sub h} at low masses and M{sub *} {approx} M {sup 0.29}{sub h} at high masses. The typical stellar mass for halos with mass less than 10{sup 12} M{sub sun} has increased by 0.3-0.45 dex for halos since z {approx} 1. These results will provide a powerful tool to inform galaxy evolution models.« less

A Comprehensive Analysis of Uncertainties Affecting the Stellar Mass-Halo Mass Relation for 0

DOE Office of Scientific and Technical Information (OSTI.GOV)

Behroozi, Peter S.; Conroy, Charlie; Wechsler, Risa H.

2010-06-07

We conduct a comprehensive analysis of the relationship between central galaxies and their host dark matter halos, as characterized by the stellar mass - halo mass (SM-HM) relation, with rigorous consideration of uncertainties. Our analysis focuses on results from the abundance matching technique, which assumes that every dark matter halo or subhalo above a specific mass threshold hosts one galaxy. We provide a robust estimate of the SM-HM relation for 0 < z < 1 and discuss the quantitative effects of uncertainties in observed galaxy stellar mass functions (GSMFs) (including stellar mass estimates and counting uncertainties), halo mass functions (includingmore » cosmology and uncertainties from substructure), and the abundance matching technique used to link galaxies to halos (including scatter in this connection). Our analysis results in a robust estimate of the SM-HM relation and its evolution from z=0 to z=4. The shape and evolution are well constrained for z < 1. The largest uncertainties at these redshifts are due to stellar mass estimates (0.25 dex uncertainty in normalization); however, failure to account for scatter in stellar masses at fixed halo mass can lead to errors of similar magnitude in the SM-HM relation for central galaxies in massive halos. We also investigate the SM-HM relation to z = 4, although the shape of the relation at higher redshifts remains fairly unconstrained when uncertainties are taken into account. We find that the integrated star formation at a given halo mass peaks at 10-20% of available baryons for all redshifts from 0 to 4. This peak occurs at a halo mass of 7 x 10{sup 11} M{sub {circle_dot}} at z = 0 and this mass increases by a factor of 5 to z = 4. At lower and higher masses, star formation is substantially less efficient, with stellar mass scaling as M{sub *} {approx} M{sub h}{sup 2.3} at low masses and M{sub *} {approx} M{sub h}{sup 0.29} at high masses. The typical stellar mass for halos with mass less than 10{sup 12} M{sub {circle_dot}} has increased by 0.3-0.45 dex for halos since z {approx} 1. These results will provide a powerful tool to inform galaxy evolution models.« less

An Unexpected Detection of Bifurcated Blue Straggler Sequences in the Young Globular Cluster NGC 2173

NASA Astrophysics Data System (ADS)

Li, Chengyuan; Deng, Licai; de Grijs, Richard; Jiang, Dengkai; Xin, Yu

2018-03-01

The bifurcated patterns in the color–magnitude diagrams of blue straggler stars (BSSs) have attracted significant attention. This type of special (but rare) pattern of two distinct blue straggler sequences is commonly interpreted as evidence that cluster core-collapse-driven stellar collisions are an efficient formation mechanism. Here, we report the detection of a bifurcated blue straggler distribution in a young Large Magellanic Cloud cluster, NGC 2173. Because of the cluster’s low central stellar number density and its young age, dynamical analysis shows that stellar collisions alone cannot explain the observed BSSs. Therefore, binary evolution is instead the most viable explanation of the origin of these BSSs. However, the reason why binary evolution would render the color–magnitude distribution of BSSs bifurcated remains unclear. C. Li, L. Deng, and R. de Grijs jointly designed this project.

INFRARED OBSERVATIONAL MANIFESTATIONS OF YOUNG DUSTY SUPER STAR CLUSTERS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martínez-González, Sergio; Tenorio-Tagle, Guillermo; Silich, Sergiy, E-mail: sergiomtz@inaoep.mx

The growing evidence pointing at core-collapse supernovae as large dust producers makes young massive stellar clusters ideal laboratories to study the evolution of dust immersed in a hot plasma. Here we address the stochastic injection of dust by supernovae, and follow its evolution due to thermal sputtering within the hot and dense plasma generated by young stellar clusters. Under these considerations, dust grains are heated by means of random collisions with gas particles which result in the appearance of  infrared spectral signatures. We present time-dependent infrared spectral energy distributions that are to be expected from young stellar clusters. Our results aremore » based on hydrodynamic calculations that account for the stochastic injection of dust by supernovae. These also consider gas and dust radiative cooling, stochastic dust temperature fluctuations, the exit of dust grains out of the cluster volume due to the cluster wind, and a time-dependent grain size distribution.« less

The Resolved Stellar Populations Early Release Science Program

NASA Astrophysics Data System (ADS)

Gilbert, Karoline; Weisz, Daniel; Resolved Stellar Populations ERS Program Team

2018-06-01

The Resolved Stellar Populations Early Release Science Program (PI D. Weisz) will observe Local Group targets covering a range of stellar density and star formation histories, including a globular cluster, and ultra-faint dwarf galaxy, and a star-forming dwarf galaxy. Using observations of these diverse targets we will explore a broad science program: we will measure star formation histories, the sub-solar stellar initial mass function, and proper motions, perform studies of evolved stars, and map extinction in the target fields. Our observations will be of high archival value for other science such as calibrating stellar evolution models, studying variable stars, and searching for metal-poor stars. We will determine optimal observational setups and develop data reduction techniques that will be common to JWST studies of resolved stellar populations. We will also design, test, and release point spread function (PSF) fitting software specific to NIRCam and NIRISS, required for the crowded stellar regime. Prior to the Cycle 2 Call for Proposals, we will release PSF fitting software, matched HST and JWST catalogs, and clear documentation and step-by-step tutorials (such as Jupyter notebooks) for reducing crowded stellar field data and producing resolved stellar photometry catalogs, as well as for specific resolved stellar photometry science applications.

THE IMPACT OF STELLAR FEEDBACK ON THE STRUCTURE, SIZE, AND MORPHOLOGY OF GALAXIES IN MILKY-WAY-SIZED DARK MATTER HALOS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Agertz, Oscar; Kravtsov, Andrey V., E-mail: o.agertz@surrey.ac.uk

We use cosmological zoom-in simulations of galaxy formation in a Milky-Way-sized halo started from identical initial conditions to investigate the evolution of galaxy sizes, baryon fractions, morphologies, and angular momenta in runs with different parameters of the star formation–feedback cycle. Our fiducial model with a high local star formation efficiency, which results in efficient feedback, produces a realistic late-type galaxy that matches the evolution of basic properties of late-type galaxies: stellar mass, disk size, morphology dominated by a kinematically cold disk, stellar and gas surface density profiles, and specific angular momentum. We argue that feedback’s role in this success ismore » twofold: (1) removal of low angular momentum gas, and (2) maintaining a low disk-to-halo mass fraction, which suppresses disk instabilities that lead to angular momentum redistribution and a central concentration of baryons. However, our model with a low local star formation efficiency, but large energy input per supernova, chosen to produce a galaxy with a similar star formation history as our fiducial model, leads to a highly irregular galaxy with no kinematically cold component, overly extended stellar distribution, and low angular momentum. This indicates that only when feedback is allowed to become vigorous via locally efficient star formation in dense cold gas do resulting galaxy sizes, gas/stellar surface density profiles, and stellar disk angular momenta agree with observed z = 0 galaxies.« less

Kinematics of Hα Emitting Stars in Andromeda

NASA Astrophysics Data System (ADS)

Ilango, Megha; Ilango, Anita; Damon, Gabriel; Prichard, Laura; Guhathakurta, Puragra; PHAT Collaboration; SPLASH Collaboration

2017-01-01

Studying emission line stars helps improve our understanding of stellar evolution, types of stars, and their environments. In this study, we analyzed stars exhibiting Hα emission (Hα stars) in the Andromeda Galaxy. We used a combination of spectroscopic and photometric diagnostic methods to remove a population of foreground Milky Way (MW) star contaminants from our data set. The Hα stars were selected from a sample of 5295 spectra from the Spectroscopic and Photometric Landscape of Andromeda’s Stellar Halo (SPLASH) survey and accompanying photometric data from the Panchromatic Hubble Andromeda Treasury (PHAT) survey. Velocities of two classes of Hα stars, main sequence (MS) stars and asymptotic giant branch (AGB) stars, were analyzed through a novel Age-Velocity Difference Correlation (AVDC) method, which utilizes line-of-sight velocity differences (LOSVDs) in order to estimate the age of a rare stellar population. Histograms, weighted means, and weighted standard deviations of the LOSVDs were used to conclude that MS stars are more kinematically coherent than AGB stars, and that Hα stars are kinematically comparable and thus close in age to their non-Hα counterparts. With these results, it can definitively be inferred that mass loss is important in two stages of stellar evolution: massive MS and intermediate mass AGB. We hypothesized that this mass loss could either occur as a normal part of MS and AGB evolution, or that it could be emitted by only a subpopulation of MS and AGB stars throughout their life cycle. Our use of the novel AVDC method sets a precedent for the use of similar methods in predicting the ages of rare stellar subgroups.This research was supported by NASA and the National Science Foundation. Most of this work was carried out by high school students working under the auspices of the Science Internship Program at UC Santa Cruz.

The Distinct Build-Up Of Dense And Normal Massive Passive Galaxies In Vipers

NASA Astrophysics Data System (ADS)

Gargiulo, Adriana; Vipers Team

2017-06-01

At fixed stellar mass, the population of passive galaxies has increased its mean effective radius < Re > by a factor 5 in the last 10 Gyr, decreasing its mean stellar mass density (S = Mstar/(2πRe 2 ) by a factor >> 10. Whether this increase in < Re > is mainly due to the size-growth of individual galaxies through dry mergers, or to the fact that newly quenched galaxies have a larger size, is still matter of debate. A promising approach to shed light on this issue is to investigate the evolution of the number density of passive galaxies as a function of their mass density. In this context, massive (Mstar >10^11 Msun) passive galaxies are the most intriguing systems to study, since, in a hierarchical scenario, they are expected to accrete their stellar mass mainly by mergers. The wide area (˜ 16 sq. deg) and high sampling rate (˜ 40%) of the spectroscopic survey VIPERS allowed us to collect a sample of ˜ 2000 passive massive galaxies over the redshift range 0.5 < z < 1.0 and to study, with unprecedented statistics, the evolution of their number density as function of their mean stellar mass density in this redshift range. Taking advantage of both spectroscopic (D4000) and photometric (SED fitting) data available, we studied the age of the stellar population of passive galaxies as function both of redshift and mass density. This information, combined with the evolution of the number density allowed us to put constraints on the mass accretion scenarios of passive galaxies. In this talk I will present our results and conclusions and how they depend on the environment in which the galaxies reside.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morscher, Meagan; Pattabiraman, Bharath; Rodriguez, Carl

Our current understanding of the stellar initial mass function and massive star evolution suggests that young globular clusters (GCs) may have formed hundreds to thousands of stellar-mass black holes (BHs), the remnants of stars with initial masses from ∼20-100 M {sub ☉}. Birth kicks from supernova explosions may eject some BHs from their birth clusters, but most should be retained. Using a Monte Carlo method we investigate the long-term dynamical evolution of GCs containing large numbers of stellar BHs. We describe numerical results for 42 models, covering a broad range of realistic initial conditions, including up to 1.6 × 10{supmore » 6} stars. In almost all models we find that significant numbers of BHs (up to ∼10{sup 3}) are retained all the way to the present. This is in contrast to previous theoretical expectations that most BHs should be ejected dynamically within a few gigayears The main reason for this difference is that core collapse driven by BHs (through the Spitzer {sup m}ass segregation instability{sup )} is easily reverted through three-body processes, and involves only a small number of the most massive BHs, while lower-mass BHs remain well-mixed with ordinary stars far from the central cusp. Thus the rapid segregation of stellar BHs does not lead to a long-term physical separation of most BHs into a dynamically decoupled inner core, as often assumed previously. Combined with the recent detections of several BH X-ray binary candidates in Galactic GCs, our results suggest that stellar BHs could still be present in large numbers in many GCs today, and that they may play a significant role in shaping the long-term dynamical evolution and the present-day dynamical structure of many clusters.« less

Role of Massive Stars in the Evolution of Primitive Galaxies

NASA Technical Reports Server (NTRS)

Heap, Sara

2012-01-01

An important factor controlling galaxy evolution is feedback from massive stars. It is believed that the nature and intensity of stellar feedback changes as a function of galaxy mass and metallicity. At low mass and metallicity, feedback from massive stars is mainly in the form of photoionizing radiation. At higher mass and metallicity, it is in stellar winds. IZw 18 is a local blue, compact dwarf galaxy that meets the requirements for a primitive galaxy: low halo mass greater than 10(exp 9)Msun, strong photoionizing radiation, no galactic outflow, and very low metallicity,log(O/H)+12=7.2. We will describe the properties of massive stars and their role in the evolution of IZw 18, based on analysis of ultraviolet images and spectra obtained with HST.

The Mass, Color, and Structural Evolution of Today’s Massive Galaxies Since z ˜ 5

NASA Astrophysics Data System (ADS)

Hill, Allison R.; Muzzin, Adam; Franx, Marijn; Clauwens, Bart; Schreiber, Corentin; Marchesini, Danilo; Stefanon, Mauro; Labbe, Ivo; Brammer, Gabriel; Caputi, Karina; Fynbo, Johan; Milvang-Jensen, Bo; Skelton, Rosalind E.; van Dokkum, Pieter; Whitaker, Katherine E.

2017-03-01

In this paper, we use stacking analysis to trace the mass growth, color evolution, and structural evolution of present-day massive galaxies ({log}({M}* /{M}⊙ )=11.5) out to z = 5. We utilize the exceptional depth and area of the latest UltraVISTA data release, combined with the depth and unparalleled seeing of CANDELS to gather a large, mass-selected sample of galaxies in the NIR (rest-frame optical to UV). Progenitors of present-day massive galaxies are identified via an evolving cumulative number density selection, which accounts for the effects of merging to correct for the systematic biases introduced using a fixed cumulative number density selection, and find progenitors grow in stellar mass by ≈ 1.5 {dex} since z = 5. Using stacking, we analyze the structural parameters of the progenitors and find that most of the stellar mass content in the central regions was in place by z˜ 2, and while galaxies continue to assemble mass at all radii, the outskirts experience the largest fractional increase in stellar mass. However, we find evidence of significant stellar mass build-up at r< 3 {kpc} beyond z> 4 probing an era of significant mass assembly in the interiors of present-day massive galaxies. We also compare mass assembly from progenitors in this study to the EAGLE simulation and find qualitatively similar assembly with z at r< 3 {kpc}. We identify z˜ 1.5 as a distinct epoch in the evolution of massive galaxies where progenitors transitioned from growing in mass and size primarily through in situ star formation in disks to a period of efficient growth in r e consistent with the minor merger scenario.

Evolution of the stellar mass function in multiple-population globular clusters

NASA Astrophysics Data System (ADS)

Vesperini, Enrico; Hong, Jongsuk; Webb, Jeremy J.; D'Antona, Franca; D'Ercole, Annibale

2018-05-01

We present the results of a survey of N-body simulations aimed at studying the effects of the long-term dynamical evolution on the stellar mass function (MF) of multiple stellar populations in globular clusters. Our simulations show that if first-(1G) and second-generation (2G) stars have the same initial MF (IMF), the global MFs of the two populations are affected similarly by dynamical evolution and no significant differences between the 1G and 2G MFs arise during the cluster's evolution. If the two populations have different IMFs, dynamical effects do not completely erase memory of the initial differences. Should observations find differences between the global 1G and 2G MFs, these would reveal the fingerprints of differences in their IMFs. Irrespective of whether the 1G and 2G populations have the same global IMF or not, dynamical effects can produce differences between the local (measured at various distances from the cluster centre) 1G and 2G MFs; these differences are a manifestation of the process of mass segregation in populations with different initial structural properties. In dynamically old and spatially mixed clusters, however, differences between the local 1G and 2G MFs can reveal differences between the 1G and 2G global MFs. In general, for clusters with any dynamical age, large differences between the local 1G and 2G MFs are more likely to be associated with differences in the global MF. Our study also reveals a dependence of the spatial mixing rate on the stellar mass, another dynamical consequence of the multiscale nature of multiple-population clusters.

KPC-SCALE STUDY OF SUBSTRUCTURES INSIDE GALAXIES out to z ~ 1.3

NASA Astrophysics Data System (ADS)

Hemmati, Shoubaneh; Mobasher, B.; Miller, S.; Nayyeri, H.

2014-01-01

Studying the resolved properties of galaxies in kpc scale has the capability to address major questions in galaxy structure formation and stellar properties evolution. We use a unique sample of 129 morphologically inclusive disk-like galaxies in the redshift range 0.2

Evolution of the fraction of clumpy galaxies at 0.2 < z < 1.0 in the cosmos field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Murata, K. L.; Kajisawa, M.; Taniguchi, Y.

2014-05-01

Using the Hubble Space Telescope/Advanced Camera for Surveys data in the COSMOS field, we systematically searched clumpy galaxies at 0.2 < z < 1.0 and investigated the fraction of clumpy galaxies and its evolution as a function of stellar mass, star formation rate (SFR), and specific SFR (SSFR). The fraction of clumpy galaxies in star-forming galaxies with M {sub star} > 10{sup 9.5} M {sub ☉} decreases with time from ∼0.35 at 0.8 < z < 1.0 to ∼0.05 at 0.2 < z < 0.4, irrespective of the stellar mass, although the fraction tends to be slightly lower for massivemore » galaxies with M {sub star} > 10{sup 10.5} M {sub ☉} at each redshift. On the other hand, the fraction of clumpy galaxies increases with increasing both SFR and SSFR in all the redshift ranges we investigated. In particular, we found that the SSFR dependences of the fractions are similar among galaxies with different stellar masses, and the fraction at a given SSFR does not depend on the stellar mass in each redshift bin. The evolution of the fraction of clumpy galaxies from z ∼ 0.9 to z ∼ 0.3 seems to be explained by such SSFR dependence of the fraction and the evolution of SSFRs of star-forming galaxies. The fraction at a given SSFR also appears to decrease with time, but this can be due to the effect of the morphological k correction. We suggest that these results are understood by the gravitational fragmentation model for the formation of giant clumps in disk galaxies, where the gas mass fraction is a crucial parameter.« less

A GRID OF THREE-DIMENSIONAL STELLAR ATMOSPHERE MODELS OF SOLAR METALLICITY. I. GENERAL PROPERTIES, GRANULATION, AND ATMOSPHERIC EXPANSION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Trampedach, Regner; Asplund, Martin; Collet, Remo

2013-05-20

Present grids of stellar atmosphere models are the workhorses in interpreting stellar observations and determining their fundamental parameters. These models rely on greatly simplified models of convection, however, lending less predictive power to such models of late-type stars. We present a grid of improved and more reliable stellar atmosphere models of late-type stars, based on deep, three-dimensional (3D), convective, stellar atmosphere simulations. This grid is to be used in general for interpreting observations and improving stellar and asteroseismic modeling. We solve the Navier Stokes equations in 3D and concurrent with the radiative transfer equation, for a range of atmospheric parameters,more » covering most of stellar evolution with convection at the surface. We emphasize the use of the best available atomic physics for quantitative predictions and comparisons with observations. We present granulation size, convective expansion of the acoustic cavity, and asymptotic adiabat as functions of atmospheric parameters.« less

Cosmochemistry

NASA Astrophysics Data System (ADS)

Esteban, C.; García López, R. J.; Herrero, A.; Sánchez, F.

2004-03-01

1. Primordial alchemy: from the Big Bang to the present Universe G. Steigman; 2. Stellar nucleosynthesis N. Langer; 3. Obervational aspects of stellar nucleosynthesis D. L. Lambert; 4. Abundance determinations in HII regions and planetary nebulae G. Stasinska; 5. Element abundances in nearby galaxies D. R. Garnett; 6. Chemical evolution of galaxies and intracluster medium F.Matteucci; 7. Element abundances through the cosmic ages M. Pettini.

Cosmochemistry

NASA Astrophysics Data System (ADS)

Esteban, C.; García López, R. J.; Herrero, A.; Sánchez, F.

2011-01-01

1. Primordial alchemy: from the Big Bang to the present Universe G. Steigman; 2. Stellar nucleosynthesis N. Langer; 3. Obervational aspects of stellar nucleosynthesis D. L. Lambert; 4. Abundance determinations in HII regions and planetary nebulae G. Stasinska; 5. Element abundances in nearby galaxies D. R. Garnett; 6. Chemical evolution of galaxies and intracluster medium F.Matteucci; 7. Element abundances through the cosmic ages M. Pettini.

Heat capacity of the neutron star inner crust within an extended nuclear statistical equilibrium model

NASA Astrophysics Data System (ADS)

Burrello, S.; Gulminelli, F.; Aymard, F.; Colonna, M.; Raduta, Ad. R.

2015-11-01

Background: Superfluidity in the crust is a key ingredient for the cooling properties of proto-neutron stars. Present theoretical calculations employ the quasiparticle mean-field Hartree-Fock-Bogoliubov theory with temperature-dependent occupation numbers for the quasiparticle states. Purpose: Finite temperature stellar matter is characterized by a whole distribution of different nuclear species. We want to assess the importance of this distribution on the calculation of heat capacity in the inner crust. Method: Following a recent work, the Wigner-Seitz cell is mapped into a model with cluster degrees of freedom. The finite temperature distribution is then given by a statistical collection of Wigner-Seitz cells. We additionally introduce pairing correlations in the local density BCS approximation both in the homogeneous unbound neutron component, and in the interface region between clusters and neutrons. Results: The heat capacity is calculated in the different baryonic density conditions corresponding to the inner crust, and in a temperature range varying from 100 KeV to 2 MeV. We show that accounting for the cluster distribution has a small effect at intermediate densities, but it considerably affects the heat capacity both close to the outer crust and close to the core. We additionally show that it is very important to consider the temperature evolution of the proton fraction for a quantitatively reliable estimation of the heat capacity. Conclusions: We present the first modelization of stellar matter containing at the same time a statistical distribution of clusters at finite temperature, and pairing correlations in the unbound neutron component. The effect of the nuclear distribution on the superfluid properties can be easily added in future calculations of the neutron star cooling curves. A strong influence of resonance population on the heat capacity at high temperature is observed, which deserves to be further studied within more microscopic calculations.

Asteroseismology of ZZ Ceti stars with full evolutionary white dwarf models. II. The impact of AGB thermal pulses on the asteroseismic inferences of ZZ Ceti stars

NASA Astrophysics Data System (ADS)

De Gerónimo, F. C.; Althaus, L. G.; Córsico, A. H.; Romero, A. D.; Kepler, S. O.

2018-05-01

Context. The thermally pulsing phase on the asymptotic giant branch (TP-AGB) is the last nuclear burning phase experienced by most low- and intermediate-mass stars. During this phase, the outer chemical stratification above the C/O core of the emerging white dwarf (WD) is built up. The chemical structure resulting from progenitor evolution strongly impacts the whole pulsation spectrum exhibited by ZZ Ceti stars, which are pulsating C/O core white dwarfs located on a narrow instability strip at Teff 12 000 K. Several physical processes occurring during progenitor evolution strongly affect the chemical structure of these stars; those found during the TP-AGB phase are the most relevant for the pulsational properties of ZZ Ceti stars. Aims: We present a study of the impact of the chemical structure built up during the TP-AGB evolution on the stellar parameters inferred from asteroseismological fits of ZZ Ceti stars. Methods: Our analysis is based on a set of carbon-oxygen core white dwarf models with masses from 0.534 to 0.6463 M⊙ derived from full evolutionary computations from the ZAMS to the ZZ Ceti domain. We computed evolutionary sequences that experience different number of thermal pulses (TP). Results: We find that the occurrence or not of thermal pulses during AGB evolution implies an average deviation in the asteroseimological effective temperature of ZZ Ceti stars of at most 8% and on the order of ≲5% in the stellar mass. For the mass of the hydrogen envelope, however, we find deviations up to 2 orders of magnitude in the case of cool ZZ Ceti stars. Hot and intermediate temperature ZZ Ceti stars show no differences in the hydrogen envelope mass in most cases. Conclusions: Our results show that, in general, the impact of the occurrence or not of thermal pulses in the progenitor stars is not negligible and must be taken into account in asteroseismological studies of ZZ Ceti stars.

Irradiation-driven Mass Transfer Cycles in Compact Binaries

NASA Astrophysics Data System (ADS)

Büning, A.; Ritter, H.

2005-08-01

We elaborate on the analytical model of Ritter, Zhang, & Kolb (2000) which describes the basic physics of irradiation-driven mass transfer cycles in semi-detached compact binary systems. In particular, we take into account a contribution to the thermal relaxation of the donor star which is unrelated to irradiation and which was neglected in previous studies. We present results of simulations of the evolution of compact binaries undergoing mass transfer cycles, in particular also of systems with a nuclear evolved donor star. These computations have been carried out with a stellar evolution code which computes mass transfer implicitly and models irradiation of the donor star in a point source approximation, thereby allowing for much more realistic simulations than were hitherto possible. We find that low-mass X-ray binaries (LMXBs) and cataclysmic variables (CVs) with orbital periods ⪉ 6hr can undergo mass transfer cycles only for low angular momentum loss rates. CVs containing a giant donor or one near the terminal age main sequence are more stable than previously thought, but can possibly also undergo mass transfer cycles.

Nuclear astrophysics at Gran Sasso Laboratory: the LUNA experiment

NASA Astrophysics Data System (ADS)

Cavanna, Francesca

2018-05-01

LUNA is an experimental approach for the study of nuclear fusion reactions based on an underground accelerator laboratory. Aim of the experiment is the direct measurement of the cross section of nuclear reactions relevant for stellar and primordial nucleosynthesis. In the following the latest results and the future goals will be presented.

Rare isotopes and the sound of dilute nuclear matter

NASA Astrophysics Data System (ADS)

Papakonstantinou, P.

2018-04-01

Dilute baryonic matter, at densities below the normal saturation density of symmetric matter, is found on the crust of neutron stars and in collapsing supernova matter, its properties determining the evolution of those stellar objects. It is also readily found on the surface of ordinary and exotic atomic nuclei and lives fleetingly in the form of space-extended resonances of excited nucleons. Liminal states of nuclear matter, between saturation and full evaporation or clusterization, are manifest in the structure of symmetric nuclei through clustering and of very asymmetric rare species in haloes and the neutron skin; they stand literally at the threshold of a nucleus's response to hadronic probes, including processes which hinder or enable fusion. In this contribution I focus on excited states, and in particular exotic or not-so-exotic dipole excitation modes of N = Z nuclei and neutron-rich species, including new theoretical results on threshold strength. Modes of special interest are vibrations of and within diffuse surface layers and alpha-cluster oscillations. The modeling of such processes is relevant, directly or indirectly, for the description of reactions at astrophysical energies.

CNO isotopes in red giant stars

NASA Technical Reports Server (NTRS)

Wannier, P. G.

1985-01-01

The production and distribution of the CNO nuclides is discussed in light of observed abundance ratios in red giants and in the interstellar medium. Isotope abundances have been measured in the atmospheres and in the recent ejecta of cool giants, including carbon stars, S-type stars and red supergiants as well as in oxygen-rich giants making their first ascent of the giant branch. Several of the observations suggest revision of currently accepted nuclear cross-sections and of the mixing processes operating in giant envelopes. By comparing red giant abundances with high-quality observations of the interstellar medium, conclusions are reached about the contribution of intermediate-mass stars to galactic nuclear evolution. The three oxygen isotopes, O-16, -17 and -18, are particularly valuable for such comparison because they reflect three different stages of stellar nucleosynthesis. One remarkable result comes from observations of O-17/O-18 in several classes of red giant stars. The observed range of values for red giants excludes the entire range of values seen in interstellar molecular clouds. Furthermore, both the observations of stars and interstellar clouds exclude the isotopic ratio found in the solar system.

Moving Towards a State of the Art Charge-Exchange Reaction Code

NASA Astrophysics Data System (ADS)

Poxon-Pearson, Terri; Nunes, Filomena; Potel, Gregory

2017-09-01

Charge-exchange reactions have a wide range of applications, including late stellar evolution, constraining the matrix elements for neutrinoless double β-decay, and exploring symmetry energy and other aspects of exotic nuclear matter. Still, much of the reaction theory needed to describe these transitions is underdeveloped and relies on assumptions and simplifications that are often extended outside of their region of validity. In this work, we have begun to move towards a state of the art charge-exchange reaction code. As a first step, we focus on Fermi transitions using a Lane potential in a few body, Distorted Wave Born Approximation (DWBA) framework. We have focused on maintaining a modular structure for the code so we can later incorporate complications such as nonlocality, breakup, and microscopic inputs. Results using this new charge-exchange code will be shown compared to the analysis in for the case of 48Ca(p,n)48Sc. This work was supported in part by the National Nuclear Security Administration under the Stewardship Science Academic Alliances program through the U.S. DOE Cooperative Agreement No. DE- FG52-08NA2855.

THE EVOLUTION OF THE STELLAR MASS FUNCTION OF GALAXIES FROM z = 4.0 AND THE FIRST COMPREHENSIVE ANALYSIS OF ITS UNCERTAINTIES: EVIDENCE FOR MASS-DEPENDENT EVOLUTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marchesini, Danilo; Van Dokkum, Pieter G.; Foerster Schreiber, Natascha M.

2009-08-20

We present the evolution of the stellar mass function (SMF) of galaxies from z = 4.0 to z = 1.3 measured from a sample constructed from the deep near-infrared Multi-wavelength Survey by Yale-Chile, the Faint Infrared Extragalactic Survey, and the Great Observatories Origins Deep Survey-Chandra Deep Field South surveys, all having very high-quality optical to mid-infrared data. This sample, unique in that it combines data from surveys with a large range of depths and areas in a self-consistent way, allowed us to (1) minimize the uncertainty due to cosmic variance and empirically quantify its contribution to the total error budget;more » (2) simultaneously probe the high-mass end and the low-mass end (down to {approx}0.05 times the characteristic stellar mass) of the SMF with good statistics; and (3) empirically derive the redshift-dependent completeness limits in stellar mass. We provide, for the first time, a comprehensive analysis of random and systematic uncertainties affecting the derived SMFs, including the effect of metallicity, extinction law, stellar population synthesis model, and initial mass function. We find that the mass density evolves by a factor of {approx}17{sup +7}{sub -10} since z = 4.0, mostly driven by a change in the normalization {phi}*. If only random errors are taken into account, we find evidence for mass-dependent evolution, with the low-mass end evolving more rapidly than the high-mass end. However, we show that this result is no longer robust when systematic uncertainties due to the SED-modeling assumptions are taken into account. Another significant uncertainty is the contribution to the overall stellar mass density of galaxies below our mass limit; future studies with WFC3 will provide better constraints on the SMF at masses below 10{sup 10} M{sub sun} at z>2. Taking our results at face value, we find that they are in conflict with semianalytic models of galaxy formation. The models predict SMFs that are in general too steep, with too many low-mass galaxies and too few high-mass galaxies. The discrepancy at the high-mass end is susceptible to uncertainties in the models and the data, but the discrepancy at the low-mass end may be more difficult to explain.« less

The Diversity of Chemical Composition: The Impact of Stellar Abundances on the Evolution of Stars and Habitable Zones

NASA Astrophysics Data System (ADS)

Truitt, Amanda R.; Young, Patrick A.

2018-01-01

I have investigated how stars of different mass and composition evolve, and how stellar evolution impacts the location of the habitable zone around a star. Current research into habitability of exoplanets focuses mostly on the concept of a “classical” HZ, the range of distances from a star over which liquid water could exist on a planet's surface. This is determined by the host star's luminosity and spectral characteristics; in order to gauge the habitability potential of a given system, both the evolutionary history and the detailed chemical characterization of the host star must be considered. With the ever-accelerating discovery of new exoplanets, it is imperative to develop a better understanding of what factors play a role in creating “habitable” conditions of a planet. I will discuss how stellar evolution is integral to how we define the HZ, and how this work will apply to the search for Earth-like planets in the future.I have developed a catalog of stellar evolution models for Sun-like stars with variable compositions; masses range from 0.1-1.2 Msol (spectral types M4-F4) at scaled metallicities (Z) of 0.1-1.5 Zsol, and O/Fe, C/Fe, and Mg/Fe values of 0.44-2.28, 0.58-1.72, and 0.54-1.84, respectively. I use a spread in abundance values based on observations of variability in nearby stars. It is important to understand how specific elements, not just total Z, impacts stellar lifetime. Time-dependent HZ boundaries are calculated for each track. I have also created a grid of M-dwarfs, and I am currently working to estimate stellar activity vs. age for each model.This catalog is meant to characterize potential host stars of interest. I have explored how to use existing observational data (i.e. Hypatia Catalog) for a more robust comparison to my grid of theoretical models, and I will discuss a new statistical analysis of the catalog to further refine our definition of “continuous” habitability. This work is an important step to assess whether a planet discovered in the HZ of its star has had sufficient time to develop a biosphere capable of producing detectable biosignatures. The catalog is designed for use by the astrobiology and exoplanet communities to characterize any real planetary systems of interest.

The Diversity of Chemical Composition and the Effects on Stellar Evolution and Planetary Habitability

NASA Astrophysics Data System (ADS)

Truitt, Amanda; Young, Patrick A.

2017-01-01

For my dissertation under the supervision of Dr. Young, I investigate how stars of different mass and composition evolve, and how stellar evolution impacts the location of the habitable zone around a star. Current research into habitability of exoplanets focuses mostly on the concept of the classical HZ - the range of distances from a star over which liquid water could exist on a planet's surface - determined primarily by the host star's luminosity and spectral characteristics. With the ever-accelerating discovery of new exoplanets, it is imperative to develop a more complete understanding of what factors play a role in creating the “habitable” conditions of a planet. I discuss how stellar evolution is integral to how we define a HZ, and how this work will apply to the search for habitable Earth-like planets in the future.I developed a catalog of stellar evolution models for Sun-like stars with variable compositions; masses range from 0.1-1.2 Msol (spectral types M4-F4) at scaled metallicities of 0.1-1.5 Zsol, and O/Fe, C/Fe, and Mg/Fe values of 0.44-2.28, 0.58-1.72, and 0.54-1.84, respectively. I use a spread in abundance values based on observations of variability in nearby stars. It is important to understand how specific elements (and not just total metallicity) can impact evolutionary lifetime. The time-dependent HZ boundaries have also been calculated for each stellar track. Additionally, I recently created a grid of models for M-dwarfs, and I am currently working to make preliminary estimates of stellar activity vs. age for each representative star in the catalog.My results indicate that to gauge the habitability potential of a given system, both the evolutionary history as well as the detailed chemical characterization of the host star must be considered. This work can be used to assess whether a planet discovered in the HZ of its star has had sufficient time to develop a biosphere capable of producing detectable biosignatures. The catalog is designed for use by the astrobiology and exoplanet communities to characterize stars and their surrounding HZs for real planetary candidates of interest.

Scalar Resonant Relaxation of Stars around a Massive Black Hole

NASA Astrophysics Data System (ADS)

Bar-Or, Ben; Fouvry, Jean-Baptiste

2018-06-01

In nuclear star clusters, the potential is governed by the central massive black hole (MBH), so that stars move on nearly Keplerian orbits and the total potential is almost stationary in time. Yet, the deviations of the potential from the Keplerian one, due to the enclosed stellar mass and general relativity, will cause the stellar orbits to precess. Moreover, as a result of the finite number of stars, small deviations of the potential from spherical symmetry induce residual torques that can change the stars’ angular momentum faster than the standard two-body relaxation. The combination of these two effects drives a stochastic evolution of orbital angular momentum, a process named “resonant relaxation” (RR). Owing to recent developments in the description of the relaxation of self-gravitating systems, we can now fully describe scalar resonant relaxation (relaxation of the magnitude of the angular momentum) as a diffusion process. In this framework, the potential fluctuations due to the complex orbital motion of the stars are described by a random correlated noise with statistical properties that are fully characterized by the stars’ mean field motion. On long timescales, the cluster can be regarded as a diffusive system with diffusion coefficients that depend explicitly on the mean field stellar distribution through the properties of the noise. We show here, for the first time, how the diffusion coefficients of scalar RR, for a spherically symmetric system, can be fully calculated from first principles, without any free parameters. We also provide an open source code that evaluates these diffusion coefficients numerically.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Antonini, Fabio, E-mail: antonini@cita.utoronto.ca

We use N-body simulations as well as analytical techniques to study the long-term dynamical evolution of stellar black holes (BHs) at the Galactic center (GC) and to put constraints on their number and mass distribution. Starting from models that have not yet achieved a state of collisional equilibrium, we find that timescales associated with cusp regrowth can be longer than the Hubble time. Our results cast doubts on standard models that postulate high densities of BHs near the GC and motivate studies that start from initial conditions that correspond to well-defined physical models. For the first time, we consider themore » distribution of BHs in a dissipationless model for the formation of the Milky Way nuclear cluster (NC), in which massive stellar clusters merge to form a compact nucleus. We simulate the consecutive merger of ∼10 clusters containing an inner dense sub-cluster of BHs. After the formed NC is evolved for ∼5 Gyr, the BHs do form a steep central cusp, while the stellar distribution maintains properties that resemble those of the GC NC. Finally, we investigate the effect of BH perturbations on the motion of the GC S-stars as a means of constraining the number of the perturbers. We find that reproducing the quasi-thermal character of the S-star orbital eccentricities requires ≳ 1000 BHs within 0.1 pc of Sgr A*. A dissipationless formation scenario for the GC NC is consistent with this lower limit and therefore could reconcile the need for high central densities of BHs (to explain the S-stars orbits) with the 'missing-cusp' problem of the GC giant star population.« less

Near-infrared variability study of the central 2.3 × 2.3 arcmin2 of the Galactic Centre - II. Identification of RR Lyrae stars in the Milky Way nuclear star cluster

NASA Astrophysics Data System (ADS)

Dong, Hui; Schödel, Rainer; Williams, Benjamin F.; Nogueras-Lara, Francisco; Gallego-Cano, Eulalia; Gallego-Calvente, Teresa; Wang, Q. Daniel; Rich, R. Michael; Morris, Mark R.; Do, Tuan; Ghez, Andrea

2017-11-01

Because of strong and spatially highly variable interstellar extinction and extreme source crowding, the faint (K ≥ 15) stellar population in the Milky Way's nuclear star cluster is still poorly studied. RR Lyrae stars provide us with a tool to estimate the mass of the oldest, relative dim stellar population. Recently, we analysed HST/WFC3/IR observations of the central 2.3 × 2.3 arcmin2 of the Milky Way and found 21 variable stars with periods between 0.2 and 1 d. Here, we present a further comprehensive analysis of these stars. The period-luminosity relationship of RR Lyrae is used to derive their extinctions and distances. Using multiple approaches, we classify our sample as 4 RRc stars, 4 RRab stars, 3 RRab candidates and 10 binaries. Especially, the four RRab stars show sawtooth light curves and fall exactly on to the Oosterhoff I division in the Bailey diagram. Compared to the RRab stars reported by Minniti et al., our new RRab stars have higher extinction (AK > 1.8) and should be closer to the Galactic Centre. The extinction and distance of one RRab stars match those for the Milky Way's nuclear star cluster given in previous works. We perform simulations and find that after correcting for incompleteness, there could be not more than 40 RRab stars within the Milky Way's nuclear star cluster and in our field of view. Through comparing with the known globular clusters of the Milky Way, we estimate that if there exists an old, metal-poor (-1.5 < [Fe/H] < -1) stellar population in the Milky Way nuclear star cluster on a scale of 5 × 5 pc, then it contributes at most 4.7 × 105 M⊙, I.e. ˜18 per cent of the stellar mass.

The assembly of stellar haloes in massive Early-Type Galaxies

NASA Astrophysics Data System (ADS)

Buitrago, F.

2017-03-01

Massive (Mstellar >= 5×1010 M⊙) Early-Type Galaxies (ETGs) must build an outer stellar envelope over cosmic time in order to account for their remarkable size evolution. This is similar to what occurs to nearby Late-Type Galaxies (LTGs), which create their stellar haloes out of the debris of lower mass systems. We analysed the outer parts of massive ETGs at z < 1 by exploiting the Hubble Ultra Deep Field imaging. These galaxies store 10-30% of their stellar mass at distances 10 < R/kpc < 50, in contrast to the low percentages (< 5%) found for LTGs. We find evidence for a progressive outskirt development with redshift driven solely via merging.

Strong stellar winds.

PubMed

Conti, P S; McCray, R

1980-04-04

The hottest and most luminous stars lose a substantial fraction of their mass in strong stellar winds. These winds not only affect the evolution of the star, they also carve huge expanding cavities in the surrounding interstellar medium, possibly affecting star formation. The winds are probably driven by radiation pressure, but uncertainties persist in their theoretical description. Strong x-ray sources associated with a few of these hot stars may be used to probe the stellar winds. The nature of the weak x-ray sources recently observed to be associated with many of these stars is uncertain. It is suggested that roughly 10 percent of the luminous hot stars may have as companions neutron stars or black holes orbiting within the stellar winds.

Photometric Follow-up of Eclipsing Binary Candidates from KELT and Kepler

NASA Astrophysics Data System (ADS)

Garcia Soto, Aylin; Rodriguez, Joseph E.; Bieryla, Allyson; KELT survey

2018-01-01

Eclipsing binaries (EBs) are incredibly valuable, as they provide the opportunity to precisely measure fundamental stellar parameters without the need for stellar models. Therefore, we can use EBs to directly test stellar evolution models. Constraining the stellar properties of stars is important since they directly influence our understanding of any planets orbiting them. Using the Harvard University's Clay 0.4m telescope and Fred Lawrence Whipple Observatory’s 1.2m telescope on Mount Hopkins, Arizona, we conducted follow-up multi-band photometric observations of EB candidates from the Kilodegree Extremely Little Telescope (KELT) survey and the Kepler mission. We will present our follow-up observations and AstroImageJ analysis on these 5 EB systems.

Chempy: A flexible chemical evolution model for abundance fitting. Do the Sun's abundances alone constrain chemical evolution models?

NASA Astrophysics Data System (ADS)

Rybizki, Jan; Just, Andreas; Rix, Hans-Walter

2017-09-01

Elemental abundances of stars are the result of the complex enrichment history of their galaxy. Interpretation of observed abundances requires flexible modeling tools to explore and quantify the information about Galactic chemical evolution (GCE) stored in such data. Here we present Chempy, a newly developed code for GCE modeling, representing a parametrized open one-zone model within a Bayesian framework. A Chempy model is specified by a set of five to ten parameters that describe the effective galaxy evolution along with the stellar and star-formation physics: for example, the star-formation history (SFH), the feedback efficiency, the stellar initial mass function (IMF), and the incidence of supernova of type Ia (SN Ia). Unlike established approaches, Chempy can sample the posterior probability distribution in the full model parameter space and test data-model matches for different nucleosynthetic yield sets. It is essentially a chemical evolution fitting tool. We straightforwardly extend Chempy to a multi-zone scheme. As an illustrative application, we show that interesting parameter constraints result from only the ages and elemental abundances of the Sun, Arcturus, and the present-day interstellar medium (ISM). For the first time, we use such information to infer the IMF parameter via GCE modeling, where we properly marginalize over nuisance parameters and account for different yield sets. We find that 11.6+ 2.1-1.6% of the IMF explodes as core-collapse supernova (CC-SN), compatible with Salpeter (1955, ApJ, 121, 161). We also constrain the incidence of SN Ia per 103M⊙ to 0.5-1.4. At the same time, this Chempy application shows persistent discrepancies between predicted and observed abundances for some elements, irrespective of the chosen yield set. These cannot be remedied by any variations of Chempy's parameters and could be an indication of missing nucleosynthetic channels. Chempy could be a powerful tool to confront predictions from stellar nucleosynthesis with far more complex abundance data sets and to refine the physical processes governing the chemical evolution of stellar systems.

From protostellar to pre-main-sequence evolution

NASA Astrophysics Data System (ADS)

D'Antona, F.

I summarize the status of pre-main-sequence evolutionary tracks starting from the first steps dating back to the concept of Hayashi track. Understanding of the dynamical protostellar phase in the vision of Palla & Stahler, who introduced the concept of the deuterium burning thermostat and of stellar birthline, provided for a long time a link between the dynamical and hydrostatic evolution. Disk accretion however changed considerably the view, but re-introducing some ambiguities which must still be solved. The limitations and uncertainties in the mass and age determination from models for young stellar objects are summarized, but the burning of light elements is still a powerful observational signature.

Pulsating Stars

NASA Astrophysics Data System (ADS)

Catelan, M.; Smith, H. A.

2015-03-01

This book surveys our understanding of stars which change in brightness because they pulsate. Pulsating variable stars are keys to distance scales inside and beyond the Milky Way galaxy. They test our understanding not only of stellar pulsation theory but also of stellar structure and evolution theory. Moreover, pulsating stars are important probes of the formation and evolution of our own and neighboring galaxies. Our understanding of pulsating stars has greatly increased in recent years as large-scale surveys of pulsating stars in the Milky Way and other Local Group galaxies have provided a wealth of new observations and as space-based instruments have studied particular pulsating stars in unprecedented detail.

High Resolution X-ray Spectroscopy and Star Formation: HETG Observations of the Pre-Main Sequence Stellar Cluster IC 348

NASA Astrophysics Data System (ADS)

Principe, David; Huenemoerder, David P.; Schulz, Norbert; Kastner, Joel H.; Weintraub, David; Preibisch, Thomas

2018-01-01

We present Chandra High Energy Transmission Grating (HETG) observations of the ∼3 Myr old pre-main sequence (pre-MS) stellar cluster IC 348. With 400-500 cluster members at a distance of ∼300 pc, IC 348 is an ideal target to observe a large number of X-ray sources in a single pointing and is thus an extremely efficient use of Chandra-HETG. High resolution X-ray spectroscopy offers a means to investigate detailed spectral characteristic of X-ray emitting plasmas and their surrounding environments. We present preliminary results where we compare X-ray spectral signatures (e.g., luminosity, temperature, column density, abundance) of the X-ray brightest pre-MS stars in IC 348 with spectral type, multiwavelength signatures of accretion, and the presence of circumstellar disks at multiple stages of pre-MS stellar evolution. Assuming all IC 348 members formed from the same primordial molecular cloud, any disparity between coronal abundances of individual members, as constrained by the identification and strength of emission lines, will constrain the source(s) of coronal chemical evolution at a stage of pre-MS evolution vital to the formation of planets.

Investigating the Consistency of Stellar Evolution Models with Globular Cluster Observations via the Red Giant Branch Bump

NASA Astrophysics Data System (ADS)

Joyce, Meridith; Chaboyer, Brian

2016-01-01

Synthetic Red Giant Branch Bump (RGBB) magnitudes are generated with the most recent theoretical stellar evolution models computed with the Dartmouth Stellar Evolution Program (DSEP) code. They are compared to the observational work of Nataf et al. (2013), who present RGBB magnitudes for 72 globular clusters. A DSEP model using a chemical composition with enhanced α capture [α/Fe] =+0.4 and an age of 13 Gyr shows agreement with observations over metallicities ranging from [Fe/H] = 0 to [Fe/H] ≈-1.5, with discrepancy emerging at lower metallicities. A model-independent, density-based outlier detection routine known as the Local Outlying Factor (LOF) algorithm is applied to the observations in order to identify clusters that deviate most in magnitude-metallicity space from the bulk of the observations. Our model's fit is scrutinized with a series of χ^2 routines performed on subsets of the data from which highly anomalous clusters have been selectively removed based on LOF identification. In particular, NGCs 6254, 6681, 6218, and 1904 are tagged recurrently as outliers. The effects of systematic and non-systematic error in metallicity are assessed, and the robustness of observational error bars is investigated.

Do We Really Have an Age/H_0 Conflict?

NASA Astrophysics Data System (ADS)

Baum, W. A.

1997-12-01

Two independent methods for estimating the age of the universe can both be linked to the absolute magnitudes of the RR Lyrae stars, one based on stellar evolution in globular clusters and the other based on the Hubble Constant derived from globular clusters as distance indicators. The latter has recently been extracted from HST-WFPC2 data for globular clusters in the Coma Cluster galaxy IC 4051 (Baum et al. 1997, AJ, 113, 1483). If RR Lyrae stars are brighter than we have previously thought, the stellar-evolution age estimate is shortened whereas the Hubble age is increased, so we can ask a very simple question: For what RR Lyrae magnitude zero point would the stellar-evolution age coincide with the Hubble age, and is it a reasonable value? Allowing 1 Gyr for globular clusters to have formed, and assuming a classical Einstein-deSitter universe with Lambda = 0, I find the two ages to coincide if M_V(RR) ~ 0.16[Fe/H] + 0.46, which (among other things) puts the Large Magellanic Cloud at (m-M) = 18.78 +/- 0.17 mag. The implied age of the universe is 11.0 +/- 1.4 Gyr, and the corresponding H_0 = 59 +/- 8 km/s per Mpc.

The Evolution of Low-Metallicity Massive Stars

NASA Astrophysics Data System (ADS)

Szécsi, Dorottya

2016-07-01

Massive star evolution taking place in astrophysical environments consisting almost entirely of hydrogen and helium - in other words, low-metallicity environments - is responsible for some of the most intriguing and energetic cosmic phenomena, including supernovae, gamma-ray bursts and gravitational waves. This thesis aims to investigate the life and death of metal-poor massive stars, using theoretical simulations of the stellar structure and evolution. Evolutionary models of rotating, massive stars (9-600 Msun) with an initial metal composition appropriate for the low-metallicity dwarf galaxy I Zwicky 18 are presented and analyzed. We find that the fast rotating models (300 km/s) become a particular type of objects predicted only at low-metallicity: the so-called Transparent Wind Ultraviolet INtense (TWUIN) stars. TWUIN stars are fast rotating massive stars that are extremely hot (90 kK), very bright and as compact as Wolf-Rayet stars. However, as opposed to Wolf-Rayet stars, their stellar winds are optically thin. As these hot objects emit intense UV radiation, we show that they can explain the unusually high number of ionizing photons of the dwarf galaxy I Zwicky 18, an observational quantity that cannot be understood solely based on the normal stellar population of this galaxy. On the other hand, we find that the most massive, slowly rotating models become another special type of object predicted only at low-metallicity: core-hydrogen-burning cool supergiant stars. Having a slow but strong stellar wind, these supergiants may be important contributors in the chemical evolution of young galactic globular clusters. In particular, we suggest that the low mass stars observed today could form in a dense, massive and cool shell around these, now dead, supergiants. This scenario is shown to explain the anomalous surface abundances observed in these low mass stars, since the shell itself, having been made of the mass ejected by the supergiant’s wind, contains nuclear burning products in the same ratio as observed today in globular clusters stars. Further elaborating the fast rotating TWUIN star models, we predict that some of them will become Wolf-Rayet stars near the end of their lives. From this we show that our models can self-consistently explain both the high ionizing flux and the number of Wolf-Rayet stars in I Zwicky 18. Moreover, some of our models are predicted to explode as long-duration gamma-ray bursts. Thus, we speculate that the high ionizing flux observed can be a signpost for upcoming gamma-ray bursts in dwarf galaxies. Although our models have been applied to interpret observations of globular clusters and dwarf galaxies, we point out that they could also be used in the context of other low-metallicity environments as well. Understanding the early Universe, for example, requires to have a solid knowledge of how massive stars at low-metallicity live and interact with their environments. Thus, we expect that the models and results presented in this thesis will be beneficial for not only the massive star community, but for the broader astronomy and cosmology community as well.

Stellar Alchemy

NASA Astrophysics Data System (ADS)

Cassé, Michel; Lyle, Translated by Stephen

2003-08-01

Preface; 1. Nuclear astrophysics: defence and illustration; 2. Light from atoms, light from the sky; 3. Visions; 4. Contents of the sky: atomic sources and fountains; 5. Nuclear suns; 6. Sociology of stars and clouds; 7. Histories; 8. Ancient stars in the galactic halo; 9. Conclusion; Appendices.

THE OBSERVED RELATION BETWEEN STELLAR MASS, DUST EXTINCTION, AND STAR FORMATION RATE IN LOCAL GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zahid, H. J.; Kewley, L. J.; Kudritzki, R. P.

In this study, we investigate the relation between stellar mass, dust extinction, and star formation rate (SFR) using {approx}150,000 star-forming galaxies from SDSS DR7. We show that the relation between dust extinction and SFR changes with stellar mass. For galaxies at the same stellar mass, dust extinction is anti-correlated with the SFR at stellar masses <10{sup 10} M {sub Sun }. There is a sharp transition in the relation at a stellar mass of 10{sup 10} M {sub Sun }. At larger stellar masses, dust extinction is positively correlated with the SFR for galaxies at the same stellar mass. Themore » observed relation between stellar mass, dust extinction, and SFR presented in this study helps to confirm similar trends observed in the relation between stellar mass, metallicity, and SFR. The relation reported in this study provides important new constraints on the physical processes governing the chemical evolution of galaxies. The correlation between SFR and dust extinction for galaxies with stellar masses >10{sup 10} M {sub Sun} is shown to extend to the population of quiescent galaxies suggesting that the physical processes responsible for the observed relation between stellar mass, dust extinction, and SFR may be related to the processes leading to the shutdown of star formation in galaxies.« less

The Dearth of UV-bright Stars in M32: Implications for Stellar Evolution Theory

NASA Technical Reports Server (NTRS)

Sweigart, Allen V.; Kimble, Randy A.; Bowers, Charles W.

2008-01-01

Using the Space Telescope Imaging Spectrograph on the Hubble Space Telescope, we have obtained deep far ultraviolet images of the compact elliptical galaxy M32. When combined with earlier near-ultraviolet images of the same field, these data enable the construction of an ultraviolet color-magnitude diagram of the hot horizontal branch (HB) population and other hot stars in late phases of stellar evolution. We find few post-asymptotic giant branch (PAGB) stars in the galaxy, implying that these stars either cross the HR diagram more rapidly than expected, and/or that they spend a significant fraction of their time enshrouded in circumstellar material. The predicted luminosity gap between the hot HB and its AGB-Manque (AGBM) progeny is less pronounced than expected, especially when compared to evolutionary tracks with enhanced helium abundances, implying that the presence of hot HB stars in this metal-rich population is not due to (Delta)Y/(Delta)Z greater than or approx. 4. Only a small fraction (approx. 2%) of the HB population is hot enough to produce significant UV emission, yet most of the W emission in this galaxy comes from the hot HB and AGBM stars, implying that PAGB stars are not a significant source of W emission even in those elliptical galaxies with a weak W excess. Subject headings: galaxies: evolution - galaxies: stellar content - galaxies: individual (M32) - stars: evolution - stars: horizontal branch

Planet Formation in Disks with Inclined Binary Companions: Can Primordial Spin-Orbit Misalignment be Produced?

NASA Astrophysics Data System (ADS)

Zanazzi, J. J.; Lai, Dong

2018-04-01

Many hot Jupiter (HJ) systems have been observed to have their stellar spin axis misaligned with the planet's orbital angular momentum axis. The origin of this spin-orbit misalignment and the formation mechanism of HJs remain poorly understood. A number of recent works have suggested that gravitational interactions between host stars, protoplanetary disks, and inclined binary companions may tilt the stellar spin axis with respect to the disk's angular angular momentum axis, producing planetary systems with misaligned orbits. These previous works considered idealized disk evolution models and neglected the gravitational influence of newly formed planets. In this paper, we explore how disk photoevaporation and planet formation and migration affect the inclination evolution of planet-star-disk-binary systems. We take into account planet-disk interactions and the gravitational spin-orbit coupling between the host star and the planet. We find that the rapid depletion of the inner disk via photoevaporation reduces the excitation of stellar obliquities. Depending on the formation and migration history of HJs, the spin-orbit coupling between the star and the planet may reduces and even completely suppress the excitation of stellar obliquities. Our work constrains the formation/migration history of HJs. On the other hand, planetary systems with "cold" Jupiters or close-in super-earths may experience excitation of stellar obliquities in the presence of distant inclined companions.

Planet formation in discs with inclined binary companions: can primordial spin-orbit misalignment be produced?

NASA Astrophysics Data System (ADS)

Zanazzi, J. J.; Lai, Dong

2018-07-01

Many hot Jupiter (HJ) systems have been observed to have their stellar spin axis misaligned with the planet's orbital angular momentum axis. The origin of this spin-orbit misalignment and the formation mechanism of HJs remain poorly understood. A number of recent works have suggested that gravitational interactions between host stars, protoplanetary discs, and inclined binary companions may tilt the stellar spin axis with respect to the disc's angular angular momentum axis, producing planetary systems with misaligned orbits. These previous works considered idealized disc evolution models and neglected the gravitational influence of newly formed planets. In this paper, we explore how disc photoevaporation and planet formation and migration affect the inclination evolution of planet-star-disc-binary systems. We take into account planet-disc interactions and the gravitational spin-orbit coupling between the host star and the planet. We find that the rapid depletion of the inner disc via photoevaporation reduces the excitation of stellar obliquities. Depending on the formation and migration history of HJs, the spin-orbit coupling between the star and the planet may reduces and even completely suppress the excitation of stellar obliquities. Our work constrains the formation/migration history of HJs. On the other hand, planetary systems with `cold' Jupiters or close-in super-earths may experience excitation of stellar obliquities in the presence of distant inclined companions.

Single rotating stars and the formation of bipolar planetary nebula

DOE Office of Scientific and Technical Information (OSTI.GOV)

García-Segura, G.; Villaver, E.; Langer, N.

2014-03-10

We have computed new stellar evolution models that include the effects of rotation and magnetic torques under different hypotheses. The goal is to test whether a single star can sustain the rotational velocities needed in the envelope for magnetohydrodynamical(MHD) simulations to shape bipolar planetary nebulae (PNe) when high mass-loss rates take place. Stellar evolution models with main sequence masses of 2.5 and 5 M {sub ☉} and initial rotational velocities of 250 km s{sup –1} have been followed through the PNe formation phase. We find that stellar cores have to be spun down using magnetic torques in order to reproducemore » the rotation rates observed for white dwarfs. During the asymptotic giant branch phase and beyond, the magnetic braking of the core has a practically null effect on increasing the rotational velocity of the envelope since the stellar angular momentum is efficiently removed by the wind. We have also tested the best possible case scenarios in rather non-physical contexts to give enough angular momentum to the envelope. We find that we cannot get the envelope of a single star to rotate at the speeds needed for MHD simulations to form bipolar PNe. We conclude that single stellar rotators are unlikely to be the progenitors of bipolar PNe under the current MHD model paradigm.« less

Deep spectroscopy of the dwarf spheroidal NGC 185

NASA Astrophysics Data System (ADS)

Gonçalves, Denise R.; Magrini, Laura; Martins, Lucimara P.; Teodorescu, Ana M.; Quireza, Cintia; Lanfranchi, Gaia

2012-08-01

Dwarf galaxies are crucial to understand the formation and evolution of galaxies, since they constitute the most abundant galaxy population. Abundance ratios and their variations due to star formation and inflow/outflow of gas are key constraints to chemical evolution models. The determination of these abundances in the dwarf galaxies of the Local Universe is thus of extreme importance. NGC 185 is one of the four brightest dwarf companions of M31, but unlike the other three it has an important content of gas and dust. Interestingly enough, in an optical survey of bright nearby galaxies NGC 185 was classified as a Seyfert galaxy based on its integrated emission-line ratios in the nuclear regions. However, although its emission lines formally place it in the category of Seyfert it is probable that this galaxy does not contain a genuine active nucleus. In this contribution, we resume, firstly, our results of an empirical study of the galaxy, on which we characterise its emission-line population and obtain planetary nebulae abundance ratios (Gonçalves et al. 2012). And, secondly, we discuss our attempt to identify the possible ionization mechanisms for NGC 185 enlighting the controversial classification of this galaxy dwarf spheroidal (dSph) as well as Seyfert, via stellar population synthesis and chemical evolution modelling (Martins et al. 2011).

Protoplanetary Nebulae

NASA Astrophysics Data System (ADS)

Kwok, S.; Murdin, P.

2000-11-01

Protoplanetary nebulae (or pre-planetary nebulae, PPNs) are defined as objects that are in transition between the asymptotic giant branch (AGB) and planetary nebula phases of STELLAR EVOLUTION. Stars on the AGB lose mass at a high rate ((10-7-10-4)M⊙ yr-1) in the form of a stellar wind. Such mass loss eventually depletes the hydrogen envelope of the star and exposes the electron-degenerate carbon...

Evolutionary synthesis of simple stellar populations. Colours and indices

NASA Astrophysics Data System (ADS)

Kurth, O. M.; Fritze-v. Alvensleben, U.; Fricke, K. J.

1999-07-01

We construct evolutionary synthesis models for simple stellar populations using the evolutionary tracks from the Padova group (1993, 1994), theoretical colour calibrations from \\cite[Lejeune et al. (1997, 1998)]{lejeune} and fit functions for stellar atmospheric indices from \\cite[Worthey et al. (1994)]{worthey}. A Monte-Carlo technique allows us to obtain a smooth time evolution of both broad band colours in UBVRIK and a series of stellar absorption features for Single Burst Stellar Populations (SSPs). We present colours and indices for SSPs with ages from 1 \\ 10(9) yrs to 1.6 \\ 10(10) yrs and metallicities [M/H]=-2.3, -1.7, -0.7, -0.4, 0.0 and 0.4. Model colours and indices at an age of about a Hubble time are in good agreement with observed colours and indices of the Galactic and M 31 GCs.

A Panchromatic View of Star-Forming Regions in the Magellanic Clouds: Characterizing Physical and Evolutionary Parameters of 1,000 Young Stellar Objects

NASA Astrophysics Data System (ADS)

Carlson, Lynn R.

2010-01-01

I discuss newly discovered Young Stellar Objects (YSOs) in several star-forming regions in the Magellanic Clouds. I exploit the synergy between infrared photometry from the Spitzer SAGE (Surveying the Agents of Galaxy Evolution) legacy programs, near-infrared and optical photometry from ground-based surveys, and HST imaging to characterize young stellar populations. This reveals a variety of Main Sequence Stars and Proto-Stars over a wide range of evolutionary stages. Through SED fitting, I characterize the youngest, embedded, infrared-bright YSOs. Complementary color-Magnitude analysis and isochrone fitting of optical data allows a statistical description of more evolved, unembedded stellar and protostellar populations within these same regions. I examine the early evolution of Magellanic star clusters, including propagating and triggered star formation, and take a step toward characterizing evolutionary timescales for YSOs. In this talk, I present an overview of the project and exemplify the analysis by focusing on NGC 602 in the SMC and Henize 206 in the LMC as examples. The SAGE Project is supported by NASA/Spitzer grant 1275598 and NASA NAG5-12595.

STAR FORMATION IN DISK GALAXIES. III. DOES STELLAR FEEDBACK RESULT IN CLOUD DEATH?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tasker, Elizabeth J.; Wadsley, James; Pudritz, Ralph

2015-03-01

Stellar feedback, star formation, and gravitational interactions are major controlling forces in the evolution of giant molecular clouds (GMCs). To explore their relative roles, we examine the properties and evolution of GMCs forming in an isolated galactic disk simulation that includes both localized thermal feedback and photoelectric heating. The results are compared with the three previous simulations in this series, which consists of a model with no star formation, star formation but no form of feedback, and star formation with photoelectric heating in a set with steadily increasing physical effects. We find that the addition of localized thermal feedback greatlymore » suppresses star formation but does not destroy the surrounding GMC, giving cloud properties closely resembling the run in which no stellar physics is included. The outflows from the feedback reduce the mass of the cloud but do not destroy it, allowing the cloud to survive its stellar children. This suggests that weak thermal feedback such as the lower bound expected for a supernova may play a relatively minor role in the galactic structure of quiescent Milky-Way-type galaxies, compared to gravitational interactions and disk shear.« less

The U/Th production ratio and the age of the Milky Way from meteorites and Galactic halo stars

NASA Astrophysics Data System (ADS)

Dauphas, Nicolas

2005-06-01

Some heavy elements (with atomic number A > 69) are produced by the `rapid' (r)-process of nucleosynthesis, where lighter elements are bombarded with a massive flux of neutrons. Although this is characteristic of supernovae and neutron star mergers, uncertainties in where the r-process occurs persist because stellar models are too crude to allow precise quantification of this phenomenon. As a result, there are many uncertainties and assumptions in the models used to calculate the production ratios of actinides (like uranium-238 and thorium-232). Current estimates of the U/Th production ratio range from ~0.4 to 0.7. Here I show that the U/Th abundance ratio in meteorites can be used, in conjunction with observations of low-metallicity stars in the halo of the Milky Way, to determine the U/Th production ratio very precisely . This value can be used in future studies to constrain the possible nuclear mass formulae used in r-process calculations, to help determine the source of Galactic cosmic rays, and to date circumstellar grains. I also estimate the age of the Milky Way ( in a way that is independent of the uncertainties associated with fluctuations in the microwave background or models of stellar evolution.

The Stellar-Solar Connection

NASA Astrophysics Data System (ADS)

Ayres, T. R.

2004-05-01

Many solar-stellar astronomers believe that the solar-stellar connection primarily is a one-way street: the exquisitely detailed studies of the solar surface, interior, and heliosphere strongly mold our views of the distant, unresolved stars. Perhaps many solar physicists have gone so far as to adopt the myopic view that stellar astronomy, by and large, is merely sponging up the fabulous insights from ever deeper examinations of our local star, but the ``dark side'' is not really capable of returning the favor. What could we possibly learn from the stars, that we don't already know from much better observations of the Sun? In my Introduction to this Topical Session, I will discuss two broad issues: (1) the present divergence between solar and stellar physics (driven by the different goals and tools of the two disciplines); and (2) the diversity of stars in the H-R diagram, to help inform our understanding of solar processes. Today, there are observations of stars that greatly exceed the quality of analogous solar measurements: e.g., HST/STIS UV echelle spectra of Alpha Cen A; Chandra transmission grating spectra of solar-type stars; and only recently have we obtained a definitive understanding of the Sun's soft X-ray luminosity in the key ROSAT/PSPC band. The lack of equivalent solar observations hinders practical applications of the solar-stellar connection. On the more informative side, the evolutionary paths of other stars can be quite different from the Sun's, with potentially dramatic influences on phenomena such as magnetic activity. Equally important, examples of Sun-like stars can be found at all stages of evolution, from proplyds to red giants, in the volume of nearby space out to 500 pc. In short, the solar-stellar connection need not be a one-way street, but rather a powerful tool to explore solar processes within the broader context of stars and stellar evolution. This work was supported by NASA grant NAG5-13058.

A Generalist Looks Back

NASA Astrophysics Data System (ADS)

Salpeter, Edwin E.

I fled with my parents from Hitler's Austria to Australia and studied physics at Sydney University. I obtained my Ph.D. in quantum electrodynamics with Rudolf Peierls at Birmingham University and came to Cornell to work with Hans Bethe. I have stayed at Cornell ever since, and I have essentially had only a single job in my whole life, but have switched fields quite often. I worked in nuclear astrophysics and in late-stellar evolution, estimated the Initial Mass Function for star formation and the metal enrichment of the interstellar medium. I suggested black hole accretion as the energy source for quasars, worked on molecule formation on dust grain surfaces, and was involved in 21-cm studies of gas clouds and disk galaxies. I collaborated with my wife on the neurobiology of the neuromuscular junction and with one of my daughters on the epidemiology of tuberculosis.

[Carl Friedrich von Weizsäcker and the Bethe-Weizsäcker cycle].

PubMed

Wiescher, Michael

2014-01-01

The Carbon- or Bethe-Weizsäcker Cycle plays an important role in astrophysics as one of the most important energy sources for a quiescent and explosive hydrogen burning in stars. This paper presents the historical background and the contributions by Carl Friedrich von Weizsäcker and Hans Bethe who provided the first predictions of the cycle. Furthermore, it discussed the experimental verification of the predicted process in the following decades. Also discussed is the extension of the initial Carbon cycle to the CNO multi-cycles and the hot CNO cycles which followed from the detailed experimental studies of the associated nuclear reactions. Finally discussed is the impact of the experimental and theoretical results on our present understanding of hydrogen burning in different stellar environments and on our understanding of the chemical evolution of our universe.

Estimation of distances to stars with stellar parameters from LAMOST

DOE PAGES

Carlin, Jeffrey L.; Liu, Chao; Newberg, Heidi Jo; ...

2015-06-05

Here, we present a method to estimate distances to stars with spectroscopically derived stellar parameters. The technique is a Bayesian approach with likelihood estimated via comparison of measured parameters to a grid of stellar isochrones, and returns a posterior probability density function for each star's absolute magnitude. We tailor this technique specifically to data from the Large Sky Area Multi-object Fiber Spectroscopic Telescope (LAMOST) survey. Because LAMOST obtains roughly 3000 stellar spectra simultaneously within each ~5-degree diameter "plate" that is observed, we can use the stellar parameters of the observed stars to account for the stellar luminosity function and targetmore » selection effects. This removes biasing assumptions about the underlying populations, both due to predictions of the luminosity function from stellar evolution modeling, and from Galactic models of stellar populations along each line of sight. Using calibration data of stars with known distances and stellar parameters, we show that our method recovers distances for most stars within ~20%, but with some systematic overestimation of distances to halo giants. We apply our code to the LAMOST database, and show that the current precision of LAMOST stellar parameters permits measurements of distances with ~40% error bars. This precision should improve as the LAMOST data pipelines continue to be refined.« less

Estimation of distances to stars with stellar parameters from LAMOST

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carlin, Jeffrey L.; Liu, Chao; Newberg, Heidi Jo

Here, we present a method to estimate distances to stars with spectroscopically derived stellar parameters. The technique is a Bayesian approach with likelihood estimated via comparison of measured parameters to a grid of stellar isochrones, and returns a posterior probability density function for each star's absolute magnitude. We tailor this technique specifically to data from the Large Sky Area Multi-object Fiber Spectroscopic Telescope (LAMOST) survey. Because LAMOST obtains roughly 3000 stellar spectra simultaneously within each ~5-degree diameter "plate" that is observed, we can use the stellar parameters of the observed stars to account for the stellar luminosity function and targetmore » selection effects. This removes biasing assumptions about the underlying populations, both due to predictions of the luminosity function from stellar evolution modeling, and from Galactic models of stellar populations along each line of sight. Using calibration data of stars with known distances and stellar parameters, we show that our method recovers distances for most stars within ~20%, but with some systematic overestimation of distances to halo giants. We apply our code to the LAMOST database, and show that the current precision of LAMOST stellar parameters permits measurements of distances with ~40% error bars. This precision should improve as the LAMOST data pipelines continue to be refined.« less

The Size Evolution of Passive Galaxies: Observations From the Wide-Field Camera 3 Early Release Science Program

NASA Technical Reports Server (NTRS)

Ryan, R. E., Jr.; Mccarthy, P.J.; Cohen, S. H.; Yan, H.; Hathi, N. P.; Koekemoer, A. M.; Rutkowski, M. J.; Mechtley, M. R.; Windhorst, R. A.; O’Connell, R. W.;

Testing a one-dimensional prescription of dynamical shear mixing with a two-dimensional hydrodynamic simulation

NASA Astrophysics Data System (ADS)

Edelmann, P. V. F.; Röpke, F. K.; Hirschi, R.; Georgy, C.; Jones, S.

2017-07-01

Context. The treatment of mixing processes is still one of the major uncertainties in 1D stellar evolution models. This is mostly due to the need to parametrize and approximate aspects of hydrodynamics in hydrostatic codes. In particular, the effect of hydrodynamic instabilities in rotating stars, for example, dynamical shear instability, evades consistent description. Aims: We intend to study the accuracy of the diffusion approximation to dynamical shear in hydrostatic stellar evolution models by comparing 1D models to a first-principle hydrodynamics simulation starting from the same initial conditions. Methods: We chose an initial model calculated with the stellar evolution code GENEC that is just at the onset of a dynamical shear instability but does not show any other instabilities (e.g., convection). This was mapped to the hydrodynamics code SLH to perform a 2D simulation in the equatorial plane. We compare the resulting profiles in the two codes and compute an effective diffusion coefficient for the hydro simulation. Results: Shear instabilities develop in the 2D simulation in the regions predicted by linear theory to become unstable in the 1D stellar evolution model. Angular velocity and chemical composition is redistributed in the unstable region, thereby creating new unstable regions. After a period of time, the system settles in a symmetric, steady state, which is Richardson stable everywhere in the 2D simulation, whereas the instability remains for longer in the 1D model due to the limitations of the current implementation in the 1D code. A spatially resolved diffusion coefficient is extracted by comparing the initial and final profiles of mean atomic mass. Conclusions: The presented simulation gives a first insight on hydrodynamics of shear instabilities in a real stellar environment and even allows us to directly extract an effective diffusion coefficient. We see evidence for a critical Richardson number of 0.25 as regions above this threshold remain stable for the course of the simulation. The movie of the simulation is available at http://www.aanda.org

Stellar Models of Rotating, PMS Stars with Magnetic Fields

NASA Astrophysics Data System (ADS)

Mendes, L. T. S.; Landin, N. R.; Vaz, L. P. R.

2014-10-01

We report our ongoing studies of the magnetic field effects on the structure and evolution of low-mass stars, using a method first proposed by Lydon & Sofia (1995, ApJS 101, 357) which treats the magnetic field as a perturbation on the stellar structure equations. The ATON 2.3 stellar evolution code (Ventura et al. 1998, A&A 334, 953) now includes, via this method, the effects of an imposed, parametric magnetic field whose surface strength scales throughout the stellar interior according to one of the three following laws: (a) the ratio between the magnetic and gas energy densities, β_{mg}, is kept at its surface value across the stellar interior, (b) β_{mg} has a shallower decrease in deeper layers, or (c) β_{mg} decays as [m(r)/M_{*}]^{2/3}. We then computed rotating stellar models, starting at the pre-main sequence phase, of 0.4, 0.6, 0.8 and 1.0 M_{odot} with solar chemical composition, mixing-length convection treatment with &alpha=λ/H_{P}=1.5 and surface magnetic field strength of 50 G. Summarizing our main findings: (1) we confirm that the magnetic field inhibits convection and so reduces the convective envelope; (2) the magnetic perturbation effect dominates over that of rotation for 0.8 and 1.0 M_{odot} masses, but their relative impact shows a reversal during the Hayashi tracks at lower masses (0.4 and 0.6 M_{odot}); in any case, the magnetic perturbation makes the tracks cooler; and (3) the magnetic field contributes to higher surface lithium abundances.

On the Red Giant Branch: Ambiguity in the Surface Boundary Condition Leads to ≈100 K Uncertainty in Model Effective Temperatures

NASA Astrophysics Data System (ADS)

Choi, Jieun; Dotter, Aaron; Conroy, Charlie; Ting, Yuan-Sen

2018-06-01

The effective temperature (T eff) distribution of stellar evolution models along the red giant branch (RGB) is sensitive to a number of parameters including the overall metallicity, elemental abundance patterns, the efficiency of convection, and the treatment of the surface boundary condition (BC). Recently there has been interest in using observational estimates of the RGB T eff to place constraints on the mixing length parameter, α MLT, and possible variation with metallicity. Here we use 1D Modules for Experiments in Stellar Astrophysics (MESA) stellar evolution models to explore the sensitivity of the RGB T eff to the treatment of the surface BC. We find that different surface BCs can lead to ±100 K metallicity-dependent offsets on the RGB relative to one another in spite of the fact that all models can reproduce the properties of the Sun. Moreover, for a given atmosphere T–τ relation, we find that the RGB T eff is also sensitive to the optical depth at which the surface BC is applied in the stellar model. Nearly all models adopt the photosphere as the location of the surface BC, but this choice is somewhat arbitrary. We compare our models to stellar parameters derived from the APOGEE-Kepler sample of first ascent red giants and find that systematic uncertainties in the models due to treatment of the surface BC place a limit of ≈100 K below which it is not possible to make firm conclusions regarding the fidelity of the current generation of stellar models.

The Dependence of Convective Core Overshooting on Stellar Mass: Additional Binary Systems and Improved Calibration

NASA Astrophysics Data System (ADS)

Claret, Antonio; Torres, Guillermo

2018-06-01

Many current stellar evolution models assume some dependence of the strength of convective core overshooting on mass for stars more massive than 1.1–1.2 M ⊙, but the adopted shapes for that relation have remained somewhat arbitrary for lack of strong observational constraints. In previous work, we compared stellar evolution models to well-measured eclipsing binaries to show that, when overshooting is implemented as a diffusive process, the fitted free parameter f ov rises sharply up to about 2 M ⊙, and remains largely constant thereafter. Here, we analyze a new sample of eight binaries selected to be in the critical mass range below 2 M ⊙ where f ov is changing the most, nearly doubling the number of individual stars in this regime. This interval is important because the precise way in which f ov changes determines the shape of isochrones in the turnoff region of ∼1–5 Gyr clusters, and can thus affect their inferred ages. It also has a significant influence on estimates of stellar properties for exoplanet hosts, on stellar population synthesis, and on the detailed modeling of interior stellar structures, including the calculation of oscillation frequencies that are observable with asteroseismic techniques. We find that the derived f ov values for our new sample are consistent with the trend defined by our earlier determinations, and strengthen the relation. This provides an opportunity for future series of models to test the new prescription, grounded on observations, against independent observations that may constrain overshooting in a different way.

SFR bulge-to-disk ratios from the CALIFA IFS nearby galaxies survey

NASA Astrophysics Data System (ADS)

Catalán-Torrecilla, Cristina; Gil de Paz, Armando; Castillo-Morales, Africa; Iglesias Páramo, Jorge; Sanchez, Sebastian

2015-08-01

Our ultimate aim is to study the evolution of the Star Formation Rate (SFR) by components (nuclei, bulges, disks) as a key constraint for the models of galaxy formation and evolution. In order to provide a local benchmark, we start from the analysis of a sample of nearby galaxies from the CALIFA Integral Field Spectroscopy (IFS) survey. Prior to this study, we have verified that the extinction-corrected Halpha luminosity provided by CALIFA IFS data recovers the total SFR by means of comparing measurements from this estimator with single-band (22μm, TIR and FUV) and hybrid tracers (FUV+22μm, FUV+TIR, Halpha+22μm, Halpha+TIR) for our sample of 272 CALIFA galaxies (Catalán-Torrecilla et al. 2015). We focus here on the study of the SFR bulge-to-disk ratio in nearby galaxies, something achievable in large numbers thanks to the good spatial resolution of our optical stellar-absorption and extinction corrected IFS-based Halpha maps. The results of the photometric decomposition of SDSS images of our sample is used as a prior is this analysis. The CALIFA objects analyzed range from galaxies that have all the SFR concentrated in the nuclear part to cases in which the SFR is spread over the disk and include both barred and unbarred galaxies. In summary, we are able to explore the distribution of the SFR in scales of 0.3-1.6 kpc for a rather large and well-characterized galaxy sample in the Local Universe.This and similar studies at higher redshifts will be key to understand how and at what rate galaxies assemble their stellar masses, either through mergers and/or secular processes.

X-shooter study of accretion in Chamaeleon I. II. A steeper increase of accretion with stellar mass for very low-mass stars?

NASA Astrophysics Data System (ADS)

Manara, C. F.; Testi, L.; Herczeg, G. J.; Pascucci, I.; Alcalá, J. M.; Natta, A.; Antoniucci, S.; Fedele, D.; Mulders, G. D.; Henning, T.; Mohanty, S.; Prusti, T.; Rigliaco, E.

2017-08-01

The dependence of the mass accretion rate on the stellar properties is a key constraint for star formation and disk evolution studies. Here we present a study of a sample of stars in the Chamaeleon I star-forming region carried out using spectra taken with the ESO VLT/X-shooter spectrograph. The sample is nearly complete down to stellar masses (M⋆) 0.1 M⊙ for the young stars still harboring a disk in this region. We derive the stellar and accretion parameters using a self-consistent method to fit the broadband flux-calibrated medium resolution spectrum. The correlation between accretion luminosity to stellar luminosity, and of mass accretion rate to stellar mass in the logarithmic plane yields slopes of 1.9 ± 0.1 and 2.3 ± 0.3, respectively. These slopes and the accretion rates are consistent with previous results in various star-forming regions and with different theoretical frameworks. However, we find that a broken power-law fit, with a steeper slope for stellar luminosity lower than 0.45 L⊙ and for stellar masses lower than 0.3 M⊙ is slightly preferred according to different statistical tests, but the single power-law model is not excluded. The steeper relation for lower mass stars can be interpreted as a faster evolution in the past for accretion in disks around these objects, or as different accretion regimes in different stellar mass ranges. Finally, we find two regions on the mass accretion versus stellar mass plane that are empty of objects: one region at high mass accretion rates and low stellar masses, which is related to the steeper dependence of the two parameters we derived. The second region is located just above the observational limits imposed by chromospheric emission, at M⋆ 0.3 - 0.4 M⊙. These are typical masses where photoevaporation is known to be effective. The mass accretion rates of this region are 10-10M⊙/yr, which is compatible with the value expected for photoevaporation to rapidly dissipate the inner disk. This work is based on observations made with ESO Telescopes at the Paranal Observatory under programme ID 090.C-0253 and 095.C-0378.

Constraining the evolution of the Hubble Parameter using cosmic chronometer

NASA Astrophysics Data System (ADS)

Scarlata, Claudia; Dickinson, Hugh

2018-01-01

The Lambda-CDM model of Big Bang cosmology relies heavily on the assumption that two components - dark energy and dark matter - encompass 95% of the energy density of the Universe. Despite the dominant influence of these components, their nature is still entirely unknown.We present the initial results from a project that aims to provide new insights regarding the Dark Energy component. We do this by deriving independent constraints on the time-evolution of the Hubble parameter (H_0) using the “cosmic chronometer” method.By analyzing the HST NIR spectra from a large archival sample of passively evolving galaxies in distinct redshift bins between 1.3 and 2 we measure the typical stellar population ages (A) for the galaxies in each bin. The differential evolution of stellar population age with redshift (dA/dz) can be used to infer the corresponding evolution of H_0 which will provide important constraints on the nature of Dark Energy and its equation of state.

Core Collapse: The Race Between Stellar Evolution and Binary Heating

NASA Astrophysics Data System (ADS)

Converse, Joseph M.; Chandar, R.

2012-01-01

The dynamical formation of binary stars can dramatically affect the evolution of their host star clusters. In relatively small clusters (M < 6000 Msun) the most massive stars rapidly form binaries, heating the cluster and preventing any significant contraction of the core. The situation in much larger globular clusters (M 105 Msun) is quite different, with many showing collapsed cores, implying that binary formation did not affect them as severely as lower mass clusters. More massive clusters, however, should take longer to form their binaries, allowing stellar evolution more time to prevent the heating by causing the larger stars to die off. Here, we simulate the evolution of clusters between those of open and globular clusters in order to find at what size a star cluster is able to experience true core collapse. Our simulations make use of a new GPU-based computing cluster recently purchased at the University of Toledo. We also present some benchmarks of this new computational resource.

VizieR Online Data Catalog: Stellar yields and the initial mass function (Molla+, 2015)

NASA Astrophysics Data System (ADS)

Molla, M.; Cavichia, O.; Gavilan, M.; Gibson, B. K.

2017-10-01

These tables give the theoretical chemical evolution models applied for the Milky Way Galaxy (MWG) from the cited paper. Basically give tables 2, 4 of stellar yields used and results of table 6 for the 144 models computed that work. Tables 2 and 4 give the stellar yields q_i(m) and remmnant mass for low and intermediate stars and massive stars, respectively, in a similar format for all authors. Table 6 gives the value of Chi2 for the 144 models computed for MWG using those stellar yields and different Initial Mass Function (see paper). Moreover, we give the table with results of the present time state of the Galactic disk for these 144 models. (12 data files).

On the optically thick winds of Wolf-Rayet stars

NASA Astrophysics Data System (ADS)

Gräfener, G.; Owocki, S. P.; Grassitelli, L.; Langer, N.

2017-12-01

Context. The classical Wolf-Rayet (WR) phase is believed to mark the end stage of the evolution of massive stars with initial masses higher than 25M⊙. Stars in this phase expose their stripped cores with the products of H- or He-burning at their surface. They develop strong, optically thick stellar winds that are important for the mechanical and chemical feedback of massive stars, and that determine whether the most massive stars end their lives as neutron stars or black holes. The winds of WR stars are currently not well understood, and their inclusion in stellar evolution models relies on uncertain empirical mass-loss relations. Aims: We investigate theoretically the mass-loss properties of H-free WR stars of the nitrogen sequence (WN stars). Methods: We connected stellar structure models for He stars with wind models for optically thick winds and assessed the degree to which these two types of models can simultaneously fulfil their respective sonic-point conditions. Results: Fixing the outer wind law and terminal wind velocity ν∞, we obtain unique solutions for the mass-loss rates of optically thick, radiation-driven winds of WR stars in the phase of core He-burning. The resulting mass-loss relations as a function of stellar parameters agree well with previous empirical relations. Furthermore, we encounter stellar mass limits below which no continuous solutions exist. While these mass limits agree with observations of WR stars in the Galaxy, they contradict observations in the LMC. Conclusions: While our results in particular confirm the slope of often-used empirical mass-loss relations, they imply that only part of the observed WN population can be understood in the framework of the standard assumptions of a smooth transonic flow and compact stellar core. This means that alternative approaches such as a clumped and inflated wind structure or deviations from the diffusion limit at the sonic point may have to be invoked. Qualitatively, the existence of mass limits for the formation of WR-type winds may be relevant for the non-detection of low-mass WR stars in binary systems, which are believed to be progenitors of Type Ib/c supernovae. The sonic-point conditions derived in this work may provide a possibility to include optically thick winds in stellar evolution models in a more physically motivated form than in current models.

Scaling Stellar Mass Estimates of Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Carr, Brandon Michael; McQuinn, Kristen B.; Cannon, John M.; Dalcanton, Julianne; Dolphin, Andrew E.; Skillman, Evan D.; Williams, Benjamin F.; van Zee, Liese

2017-01-01

Hubble Space Telescope (HST) optical imaging of resolved stellar populations has been used to constrain the star formation history (SFH) and chemical evolution of many nearby dwarf galaxies. However, even for dwarf galaxies, the angle subtended by nearby systems can be greater than the HST field of view. Thus, estimates of stellar mass from the HST footprint do not accurately represent the total mass of the system, impacting how SFH results can be used in holistic comparisons of galaxy properties. Here, we use the SFHs of dwarfs combined with stellar population synthesis models to determine mass-to-light ratios for individual galaxies, and compare these values with measured infrared luminosities from Spitzer IRAC data. In this way, we determine what fraction of mass is not included in the HST field of view. To test our methodology, we focus on dwarfs whose stellar disks are contained within the HST observations. Then, we also apply this method to galaxies with larger angular sizes to scale the stellar masses accordingly.

The make-up of stars

DOE Office of Scientific and Technical Information (OSTI.GOV)

Asplund, Martin

2014-11-20

The chemical composition of stars contain vital clues not only about the stars themselves but also about the conditions prevailing before their births. As such, stellar spectroscopy plays a key role in contemporary astrophysics and cosmology by probing cosmic, galactic, stellar and planetary evolution. In this review I will describe the theoretical foundations of quantitative stellar spectroscopy: stellar atmosphere models and spectral line formation. I will focus mainly on more recent advances in the field, in particular the advent of realistic time-dependent, 3D, (magneto-)hydrodynamical simulations of stellar surface convection and atmospheres and non-LTE radiative transfer relevant for stars like themore » Sun. I will also discuss some particular applications of this type of modelling which have resulted in some exciting break-throughs in our understanding and with wider implications: the solar chemical composition, the chemical signatures of planet formation imprinted in stellar abundances, the cosmological Li problem(s) and where the first stars may be residing today.« less

Multi-scale, Hierarchically Nested Young Stellar Structures in LEGUS Galaxies

NASA Astrophysics Data System (ADS)

Thilker, David A.; LEGUS Team

2017-01-01

The study of star formation in galaxies has predominantly been limited to either young stellar clusters and HII regions, or much larger kpc-scale morphological features such as spiral arms. The HST Legacy ExtraGalactic UV Survey (LEGUS) provides a rare opportunity to link these scales in a diverse sample of nearby galaxies and obtain a more comprehensive understanding of their co-evolution for comparison against model predictions. We have utilized LEGUS stellar photometry to identify young, resolved stellar populations belonging to several age bins and then defined nested hierarchical structures as traced by these subsamples of stars. Analagous hierarchical structures were also defined using LEGUS catalogs of unresolved young stellar clusters. We will present our emerging results concerning the physical properties (e.g. area, star counts, stellar mass, star formation rate, ISM characteristics), occupancy statistics (e.g. clusters per substructure versus age and scale, parent/child demographics) and relation to overall galaxy morphology/mass for these building blocks of hierarchical star-forming structure.

Cosmic Catastrophes

NASA Astrophysics Data System (ADS)

Wheeler, J. Craig

2014-08-01

Preface; 1. Setting the stage: star formation and hydrogen burning in single stars; 2. Stellar death: the inexorable grip of gravity; 3. Dancing with stars: binary stellar evolution; 4. Accretion disks: flat stars; 5. White Dwarfs: quantum dots; 6. Supernovae: stellar catastrophes; 7. Supernova 1987A: lessons and enigmas; 8. Neutron stars: atoms with attitude; 9. Black holes in theory: into the abyss; 10. Black holes in fact: exploring the reality; 11. Gamma-ray bursts, black holes and the universe: long, long ago and far, far away; 12. Supernovae and the universe; 13. Worm holes and time machines: tunnels in space and time; 14. Beyond: the frontiers; Index.

Cosmic Catastrophes

NASA Astrophysics Data System (ADS)

Wheeler, J. Craig

2007-01-01

Preface; 1. Setting the stage: star formation and hydrogen burning in single stars; 2. Stellar death: the inexorable grip of gravity; 3. Dancing with stars: binary stellar evolution; 4. Accretion disks: flat stars; 5. White Dwarfs: quantum dots; 6. Supernovae: stellar catastrophes; 7. Supernova 1987A: lessons and enigmas; 8. Neutron stars: atoms with attitude; 9. Black holes in theory: into the abyss; 10. Black holes in fact: exploring the reality; 11. Gamma-ray bursts, black holes and the universe: long, long ago and far, far away; 12. Supernovae and the universe; 13. Worm holes and time machines: tunnels in space and time; 14. Beyond: the frontiers; Index.

AK Sco: a tidally induced atmospheric dynamo in a pre-main sequence binary?

NASA Astrophysics Data System (ADS)

Gómez de Castro, A. I.

2009-02-01

AK Sco is a unique source: a 10-30 Myrs old pre-main sequence spectroscopic binary composed by two nearly equal F5 stars that at periastron are separated by barely eleven stellar radii so, the stellar magnetospheres fill the Roche lobe at periastron. The orbit is not yet circularized (e = 0.47) and very strong tides are expected. This makes of AK Sco, the ideal laboratory to study the effect of gravitational tides in the stellar magnetic field building up during pre-main sequence evolution. Evidence of this effect is reported in this contribution.

Dynamics of Dwarf Galaxies Disfavor Stellar-Mass Black Holes as Dark Matter.

PubMed

Koushiappas, Savvas M; Loeb, Abraham

2017-07-28

We study the effects of black hole dark matter on the dynamical evolution of stars in dwarf galaxies. We find that mass segregation leads to a depletion of stars in the center of dwarf galaxies and the appearance of a ring in the projected stellar surface density profile. Using Segue 1 as an example we show that current observations of the projected surface stellar density rule out at the 99.9% confidence level the possibility that more than 6% of the dark matter is composed of black holes with a mass of few tens of solar masses.

Rediscovering the Giant Low Surface Brightness Spiral Galaxy Malin 1

NASA Astrophysics Data System (ADS)

Galaz, Gaspar

2018-01-01

I summarize the latest discoveries regarding this ramarkable diffuse and giant galaxy, the largest single spiral in the universe so far. I describe how the latest discoveries could have been done easily 20 years ago, but an incredible summation of facts and some astronomical sociology, keeped many of them undisclosed. I present the most conspicuous features of the giant spiral arms of Malin 1, including stellar density, colors, stellar populations and some modeling describing their past evolution to the current state. I conclude with pending issues regarding stellar formation in Malin 1, and the efforts to detect its elusive molecular gas.

Discovering astronomy

NASA Technical Reports Server (NTRS)

Chapman, R. D.

1978-01-01

An overview of basic astronomical knowledge is presented with attention to the structure and dynamics of the stars and planets. Also dealt with are techniques of astronomical measurement, e.g., stellar spectrometry, radio astronomy, star catalogs, etc. Basic physical principles as they pertain to astronomy are reviewed, including the nature of light, gravitation, and electromagnetism. Finally, stellar evolution and cosmology are discussed with reference to the possibility of life elsewhere in the universe.

A Model Connecting Galaxy Masses, Star Formation Rates, and Dust Temperatures across Cosmic Time

NASA Astrophysics Data System (ADS)

Imara, Nia; Loeb, Abraham; Johnson, Benjamin D.; Conroy, Charlie; Behroozi, Peter

2018-02-01

We investigate the evolution of dust content in galaxies from redshifts z = 0 to z = 9.5. Using empirically motivated prescriptions, we model galactic-scale properties—including halo mass, stellar mass, star formation rate, gas mass, and metallicity—to make predictions for the galactic evolution of dust mass and dust temperature in main-sequence galaxies. Our simple analytic model, which predicts that galaxies in the early universe had greater quantities of dust than their low-redshift counterparts, does a good job of reproducing observed trends between galaxy dust and stellar mass out to z ≈ 6. We find that for fixed galaxy stellar mass, the dust temperature increases from z = 0 to z = 6. Our model forecasts a population of low-mass, high-redshift galaxies with interstellar dust as hot as, or hotter than, their more massive counterparts; but this prediction needs to be constrained by observations. Finally, we make predictions for observing 1.1 mm flux density arising from interstellar dust emission with the Atacama Large Millimeter Array.

Evolutionary models of rotating dense stellar systems: challenges in software and hardware

NASA Astrophysics Data System (ADS)

Fiestas, Jose

2016-02-01

We present evolutionary models of rotating self-gravitating systems (e.g. globular clusters, galaxy cores). These models are characterized by the presence of initial axisymmetry due to rotation. Central black hole seeds are alternatively included in our models, and black hole growth due to consumption of stellar matter is simulated until the central potential dominates the kinematics in the core. Goal is to study the long-term evolution (~ Gyr) of relaxed dense stellar systems, which deviate from spherical symmetry, their morphology and final kinematics. With this purpose, we developed a 2D Fokker-Planck analytical code, which results we confirm by detailed N-Body techniques, applying a high performance code, developed for GPU machines. We compare our models to available observations of galactic rotating globular clusters, and conclude that initial rotation modifies significantly the shape and lifetime of these systems, and can not be neglected in studying the evolution of globular clusters, and the galaxy itself.

The circumstellar disk response to the motion of the host star

NASA Astrophysics Data System (ADS)

Regály, Zs.; Vorobyov, E.

2017-05-01

Context. Grid-based hydrodynamics simulations of circumstellar disks are often performed in the curvilinear coordinate system, in which the center of the computational domain coincides with the motionless star. However, the center of mass may be shifted from the star due to the presence of any non-axisymmetric mass distribution. As a result, the system exerts a non-zero gravity force on the star, causing the star to move in response, which can in turn affect the evolution of the circumstellar disk. Aims: We aim at studying the effects of stellar motion on the evolution of protostellar and protoplanetary disks. In protostellar disks, a non-axisymmetric distribution of matter in the form of spiral arms and/or massive clumps can form due to gravitational instability. Protoplanetary disks can also feature non-axisymmetric structures caused by an embedded high-mass planet or a large-scale vortex formed at viscosity transitions. Methods: We use 2D grid-based numerical hydrodynamic simulations to explore the effect of stellar motion. We adopt a non-inertial polar coordinate system centered on the star, in which the stellar motion is taken into account by calculating the indirect potential caused by the non-axisymmetric disk, a high-mass planet, or a large-scale vortex. We compare the results of numerical simulations with and without stellar motion. Results: We found that the stellar motion has a moderate effect on the evolution history and the mass accretion rate in protostellar disks, reducing somewhat the disk size and mass, while having a profound effect on the collapsing envelope, changing its inner shape from an initially axisymmetric to a non-axisymmetric configuration. Protoplanetary disk simulations show that the stellar motion slightly reduces the width of the gap opened by a high-mass planet, decreases the planet migration rate, and strengthens the large-scale vortices formed at the viscosity transition. Conclusions: We conclude that the inclusion of the indirect potential is recommended in grid-based hydrodynamics simulations of circumstellar disks which use the curvilinear coordinate system.

Social stars: Modeling the interactive lives of stars in dense clusters and binary systems in the era of time domain astronomy

NASA Astrophysics Data System (ADS)

MacLeod, Morgan Elowe

This thesis uses computational modeling to study of phases of dramatic interaction that intersperse stellar lifetimes. In galactic centers stars trace dangerously wandering orbits dictated by the combined gravitational force of a central, supermassive black hole and all of the surrounding stars. In binary systems, stars' evolution -- which causes their radii to increase substantially -- can bring initially non-interacting systems into contact. Moments of strong stellar interaction transform stars, their subsequent evolution, and the stellar environments they inhabit. In tidal disruption events, a star is partially or completely destroyed as tidal forces from a supermassive black hole overwhelm the star's self gravity. A portion of the stellar debris falls back to the black hole powering a luminous flare as it accretes. This thesis studies the relative event rates and properties of tidal disruption events for stars across the stellar evolutionary spectrum. Tidal disruptions of giant stars occur with high specific frequency; these objects' extended envelopes make them vulnerable to disruption. More-compact white dwarf stars are tidally disrupted relatively rarely. Their transients are also of very different duration and luminosity. Giant star disruptions power accretion flares with timescales of tens to hundreds of years; white dwarf disruption flares take hours to days. White dwarf tidal interactions can additionally trigger thermonuclear burning and lead to transients with signatures similar to type I supernovae. In binary star systems, a phase of hydrodynamic interaction called a common envelope episode occurs when one star evolves to swallow its companion. Dragged by the surrounding gas, the companion star spirals through the envelope to tighter orbits. This thesis studies accretion and flow morphologies during this phase. Density gradients across the gravitationally-focussed material lead to a strong angular momentum barrier to accretion during common envelope. Typical accretion efficiencies are in the range of 1 percent the Hoyle-Lyttleton accretion rate. This implies that compact objects embedded in common envelopes do not grow significantly during this phase, increasing their mass by at most a few percent. This thesis models the properties of a recent stellar-merger powered transient to derive constraints on this long-uncertain phase of binary star evolution.

Radii and Orbits of Hot Jupiters

NASA Astrophysics Data System (ADS)

Wu, Yanqin

2011-09-01

Hot jupiters suffer extreme external (stellar) and internal (tidal, Ohmic and wind-power) heating. These lead to peculiar thermal evolution, which is potentially self-destrutive. For instance, the amount of energy deposited during tidal dissipation far exceeds the planets' binding energy. If this energy is mostly deposited in shallow layers, it does little damage to the planet. However, the presence of stellar insolation changes the picture, and Ohmic/wind-power heating further modifies the subsequent evolution of these jupiters. A diversity of planetary sizes results. We tie these thermodynamical processes together with the migration history of hot jupiters to explain the orbital distribution and physical radii of hot jupiters. Moreover, we constrain the location of tidal heating inside the planet.

Análisis de la evolución química de los cúmulos abiertos de la Galaxia a través de simulaciones dinámicas con procesos de destrucción

NASA Astrophysics Data System (ADS)

Bignone, L. A.; Pellizza, L. J.; Piatti, A. E.; Tecce, T. E.

It is well known that open clusters are excellent tracers (in time and space) of the metallicity of the Galactic disk. We analyze the history of stellar for- mation of the Galactic disk using numerical simulations of the dynamical evolution of the open cluster system. We have included the effects of clus- ter disruption caused by stellar evolution, tidal fields, and the interaction with the spiral arms. We model the present astrophysical properties of open clusters from initial hypothesis regarding their formation history. FULL TEXT IN SPANISH

Binaries in globular clusters

NASA Technical Reports Server (NTRS)

Hut, Piet; Mcmillan, Steve; Goodman, Jeremy; Mateo, Mario; Phinney, E. S.; Pryor, Carlton; Richer, Harvey B.; Verbunt, Frank; Weinberg, Martin

1992-01-01

Recent observations have shown that globular clusters contain a substantial number of binaries most of which are believed to be primordial. We discuss different successful optical search techniques, based on radial-velocity variables, photometric variables, and the positions of stars in the color-magnitude diagram. In addition, we review searches in other wavelengths, which have turned up low-mass X-ray binaries and more recently a variety of radio pulsars. On the theoretical side, we give an overview of the different physical mechanisms through which individual binaries evolve. We discuss the various simulation techniques which recently have been employed to study the effects of a primordial binary population, and the fascinating interplay between stellar evolution and stellar dynamics which drives globular-cluster evolution.

New Directions in Giant Planet Formation

NASA Astrophysics Data System (ADS)

Youdin, Andrew

The proposed research will explore the limits of the core accretion mechanism for forming giant planets, both in terms of timescale and orbital distance. This theoretical research will be useful in interpreting the results of ongoing exoplanet searches. The effects of radiogenic heating and aerodynamic accretion of pebbles and boulders will be included in time-dependent models of atmospheric structure and growth. To investigate these issues, we will develop and publicly share a protoplanet atmospheric evolution code as an extension of the MESA stellar evolution code. By focusing on relevant processes in the early stages of giant planet formation, we can refine model predictions for exoplanet searches at a wide range of stellar ages and distances from the host star.

The First 3D Simulations of Carbon Burning in a Massive Star

NASA Astrophysics Data System (ADS)

Cristini, A.; Meakin, C.; Hirschi, R.; Arnett, D.; Georgy, C.; Viallet, M.

2017-11-01

We present the first detailed three-dimensional hydrodynamic implicit large eddy simulations of turbulent convection for carbon burning. The simulations start with an initial radial profile mapped from a carbon burning shell within a 15 M⊙ stellar evolution model. We considered 4 resolutions from 1283 to 10243 zones. These simulations confirm that convective boundary mixing (CBM) occurs via turbulent entrainment as in the case of oxygen burning. The expansion of the boundary into the surrounding stable region and the entrainment rate are smaller at the bottom boundary because it is stiffer than the upper boundary. The results of this and similar studies call for improved CBM prescriptions in 1D stellar evolution models.

The nature, origin and evolution of embedded star clusters

NASA Technical Reports Server (NTRS)

Lada, Charles J.; Lada, Elizabeth A.

1991-01-01

The recent development of imaging infrared array cameras has enabled the first systematic studies of embedded protoclusters in the galaxy. Initial investigations suggest that rich embedded clusters are quite numerous and that a significant fraction of all stars formed in the galaxy may begin their lives in such stellar systems. These clusters contain extremely young stellar objects and are important laboratories for star formation research. However, observational and theoretical considerations suggest that most embedded clusters do not survive emergence from molecular clouds as bound clusters. Understanding the origin, nature, and evolution of embedded clusters requires understanding the intimate physical relation between embedded clusters and the dense molecular cloud cores from which they form.

Improved models of stellar core collapse and still no explosions: what is missing?

PubMed

Buras, R; Rampp, M; Janka, H-Th; Kifonidis, K

2003-06-20

Two-dimensional hydrodynamic simulations of stellar core collapse are presented which for the first time were performed by solving the Boltzmann equation for the neutrino transport including a state-of-the-art description of neutrino interactions. Stellar rotation is also taken into account. Although convection develops below the neutrinosphere and in the neutrino-heated region behind the supernova shock, the models do not explode. This suggests missing physics, possibly with respect to the nuclear equation of state and weak interactions in the subnuclear regime. However, it might also indicate a fundamental problem with the neutrino-driven explosion mechanism.

Constraining the Radiation and Plasma Environment of the Kepler Circumbinary Habitable-zone Planets

NASA Astrophysics Data System (ADS)

Zuluaga, Jorge I.; Mason, Paul A.; Cuartas-Restrepo, Pablo A.

2016-02-01

The discovery of many planets using the Kepler telescope includes 10 planets orbiting eight binary stars. Three binaries, Kepler-16, Kepler-47, and Kepler-453, have at least one planet in the circumbinary habitable zone (BHZ). We constrain the level of high-energy radiation and the plasma environment in the BHZ of these systems. With this aim, BHZ limits in these Kepler binaries are calculated as a function of time, and the habitability lifetimes are estimated for hypothetical terrestrial planets and/or moons within the BHZ. With the time-dependent BHZ limits established, a self-consistent model is developed describing the evolution of stellar activity and radiation properties as proxies for stellar aggression toward planetary atmospheres. Modeling binary stellar rotation evolution, including the effect of tidal interaction between stars in binaries, is key to establishing the environment around these systems. We find that Kepler-16 and its binary analogs provide a plasma environment favorable for the survival of atmospheres of putative Mars-sized planets and exomoons. Tides have modified the rotation of the stars in Kepler-47, making its radiation environment less harsh in comparison to the solar system. This is a good example of the mechanism first proposed by Mason et al. Kepler-453 has an environment similar to that of the solar system with slightly better than Earth radiation conditions at the inner edge of the BHZ. These results can be reproduced and even reparameterized as stellar evolution and binary tidal models progress, using our online tool http://bhmcalc.net.

CONSTRAINING THE RADIATION AND PLASMA ENVIRONMENT OF THE KEPLER CIRCUMBINARY HABITABLE-ZONE PLANETS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zuluaga, Jorge I.; Mason, Paul A.; Cuartas-Restrepo, Pablo A.

The discovery of many planets using the Kepler telescope includes 10 planets orbiting eight binary stars. Three binaries, Kepler-16, Kepler-47, and Kepler-453, have at least one planet in the circumbinary habitable zone (BHZ). We constrain the level of high-energy radiation and the plasma environment in the BHZ of these systems. With this aim, BHZ limits in these Kepler binaries are calculated as a function of time, and the habitability lifetimes are estimated for hypothetical terrestrial planets and/or moons within the BHZ. With the time-dependent BHZ limits established, a self-consistent model is developed describing the evolution of stellar activity and radiation propertiesmore » as proxies for stellar aggression toward planetary atmospheres. Modeling binary stellar rotation evolution, including the effect of tidal interaction between stars in binaries, is key to establishing the environment around these systems. We find that Kepler-16 and its binary analogs provide a plasma environment favorable for the survival of atmospheres of putative Mars-sized planets and exomoons. Tides have modified the rotation of the stars in Kepler-47, making its radiation environment less harsh in comparison to the solar system. This is a good example of the mechanism first proposed by Mason et al. Kepler-453 has an environment similar to that of the solar system with slightly better than Earth radiation conditions at the inner edge of the BHZ. These results can be reproduced and even reparameterized as stellar evolution and binary tidal models progress, using our online tool http://bhmcalc.net.« less

LITHIUM DEPLETION IS A STRONG TEST OF CORE-ENVELOPE RECOUPLING

DOE Office of Scientific and Technical Information (OSTI.GOV)

Somers, Garrett; Pinsonneault, Marc H., E-mail: somers@astronomy.ohio-state.edu

2016-09-20

Rotational mixing is a prime candidate for explaining the gradual depletion of lithium from the photospheres of cool stars during the main sequence. However, previous mixing calculations have relied primarily on treatments of angular momentum transport in stellar interiors incompatible with solar and stellar data in the sense that they overestimate the internal differential rotation. Instead, recent studies suggest that stars are strongly differentially rotating at young ages but approach a solid body rotation during their lifetimes. We modify our rotating stellar evolution code to include an additional source of angular momentum transport, a necessary ingredient for explaining the openmore » cluster rotation pattern, and examine the consequences for mixing. We confirm that core-envelope recoupling with a ∼20 Myr timescale is required to explain the evolution of the mean rotation pattern along the main sequence, and demonstrate that it also provides a more accurate description of the Li depletion pattern seen in open clusters. Recoupling produces a characteristic pattern of efficient mixing at early ages and little mixing at late ages, thus predicting a flattening of Li depletion at a few Gyr, in agreement with the observed late-time evolution. Using Li abundances we argue that the timescale for core-envelope recoupling during the main sequence decreases sharply with increasing mass. We discuss the implications of this finding for stellar physics, including the viability of gravity waves and magnetic fields as agents of angular momentum transport. We also raise the possibility of intrinsic differences in initial conditions in star clusters using M67 as an example.« less

The mass-metallicity relations for gas and stars in star-forming galaxies: strong outflow versus variable IMF

NASA Astrophysics Data System (ADS)

Lian, Jianhui; Thomas, Daniel; Maraston, Claudia; Goddard, Daniel; Comparat, Johan; Gonzalez-Perez, Violeta; Ventura, Paolo

2018-02-01

We investigate the mass-metallicity relations for the gaseous (MZRgas) and stellar components (MZRstar) of local star-forming galaxies based on a representative sample from Sloan Digital Sky Survey Data Release 12. The mass-weighted average stellar metallicities are systematically lower than the gas metallicities. This difference in metallicity increases towards galaxies with lower masses and reaches 0.4-0.8 dex at 109 M⊙ (depending on the gas metallicity calibration). As a result, the MZRstar is much steeper than the MZRgas. The much lower metallicities in stars compared to the gas in low-mass galaxies imply dramatic metallicity evolution with suppressed metal enrichment at early times. The aim of this paper is to explain the observed large difference in gas and stellar metallicity and to infer the origin of the mass-metallicity relations. To this end we develop a galactic chemical evolution model accounting for star formation, gas inflow and outflow. By combining the observed mass-metallicity relation for both gas and stellar components to constrain the models, we find that only two scenarios are able to reproduce the observations. Either strong metal outflow or a steep initial mass function (IMF) slope at early epochs of galaxy evolution is needed. Based on these two scenarios, for the first time we successfully reproduce the observed MZRgas and MZRstar simultaneously, together with other independent observational constraints in the local Universe. Our model also naturally reproduces the flattening of the MZRgas at the high-mass end leaving the MZRstar intact, as seen in observational data.

CFHTLenS: co-evolution of galaxies and their dark matter haloes

NASA Astrophysics Data System (ADS)

Hudson, Michael J.; Gillis, Bryan R.; Coupon, Jean; Hildebrandt, Hendrik; Erben, Thomas; Heymans, Catherine; Hoekstra, Henk; Kitching, Thomas D.; Mellier, Yannick; Miller, Lance; Van Waerbeke, Ludovic; Bonnett, Christopher; Fu, Liping; Kuijken, Konrad; Rowe, Barnaby; Schrabback, Tim; Semboloni, Elisabetta; van Uitert, Edo; Velander, Malin

2015-02-01

Galaxy-galaxy weak lensing is a direct probe of the mean matter distribution around galaxies. The depth and sky coverage of the Canada-France-Hawaii Telescope Legacy Survey yield statistically significant galaxy halo mass measurements over a much wider range of stellar masses (108.75 to 1011.3 M⊙) and redshifts (0.2 < z < 0.8) than previous weak lensing studies. At redshift z ˜ 0.5, the stellar-to-halo mass ratio (SHMR) reaches a maximum of 4.0 ± 0.2 per cent as a function of halo mass at ˜1012.25 M⊙. We find, for the first time from weak lensing alone, evidence for significant evolution in the SHMR: the peak ratio falls as a function of cosmic time from 4.5 ± 0.3 per cent at z ˜ 0.7 to 3.4 ± 0.2 per cent at z ˜ 0.3, and shifts to lower stellar mass haloes. These evolutionary trends are dominated by red galaxies, and are consistent with a model in which the stellar mass above which star formation is quenched `downsizes' with cosmic time. In contrast, the SHMR of blue, star-forming galaxies is well fitted by a power law that does not evolve with time. This suggests that blue galaxies form stars at a rate that is balanced with their dark matter accretion in such a way that they evolve along the SHMR locus. The redshift dependence of the SHMR can be used to constrain the evolution of the galaxy population over cosmic time.

Galactic bulge preferred over dark matter for the Galactic centre gamma-ray excess

NASA Astrophysics Data System (ADS)

Macias, Oscar; Gordon, Chris; Crocker, Roland M.; Coleman, Brendan; Paterson, Dylan; Horiuchi, Shunsaku; Pohl, Martin

2018-05-01

An anomalous gamma-ray excess emission has been found in the Fermi Large Area Telescope data1 covering the centre of the Galaxy2,3. Several theories have been proposed for this `Galactic centre excess'. They include self-annihilation of dark-matter particles4, an unresolved population of millisecond pulsars5, an unresolved population of young pulsars6, or a series of burst events7. Here, we report on an analysis that exploits hydrodynamical modelling to register the position of interstellar gas associated with diffuse Galactic gamma-ray emission. We find evidence that the Galactic centre excess gamma rays are statistically better described by the stellar over-density in the Galactic bulge and the nuclear stellar bulge, rather than a spherical excess. Given its non-spherical nature, we argue that the Galactic centre excess is not a dark-matter phenomenon but rather associated with the stellar population of the Galactic bulge and the nuclear bulge.

The Impact of Modeling Assumptions in Galactic Chemical Evolution Models

NASA Astrophysics Data System (ADS)

Côté, Benoit; O'Shea, Brian W.; Ritter, Christian; Herwig, Falk; Venn, Kim A.

2017-02-01

We use the OMEGA galactic chemical evolution code to investigate how the assumptions used for the treatment of galactic inflows and outflows impact numerical predictions. The goal is to determine how our capacity to reproduce the chemical evolution trends of a galaxy is affected by the choice of implementation used to include those physical processes. In pursuit of this goal, we experiment with three different prescriptions for galactic inflows and outflows and use OMEGA within a Markov Chain Monte Carlo code to recover the set of input parameters that best reproduces the chemical evolution of nine elements in the dwarf spheroidal galaxy Sculptor. This provides a consistent framework for comparing the best-fit solutions generated by our different models. Despite their different degrees of intended physical realism, we found that all three prescriptions can reproduce in an almost identical way the stellar abundance trends observed in Sculptor. This result supports the similar conclusions originally claimed by Romano & Starkenburg for Sculptor. While the three models have the same capacity to fit the data, the best values recovered for the parameters controlling the number of SNe Ia and the strength of galactic outflows, are substantially different and in fact mutually exclusive from one model to another. For the purpose of understanding how a galaxy evolves, we conclude that only reproducing the evolution of a limited number of elements is insufficient and can lead to misleading conclusions. More elements or additional constraints such as the Galaxy’s star-formation efficiency and the gas fraction are needed in order to break the degeneracy between the different modeling assumptions. Our results show that the successes and failures of chemical evolution models are predominantly driven by the input stellar yields, rather than by the complexity of the Galaxy model itself. Simple models such as OMEGA are therefore sufficient to test and validate stellar yields. OMEGA is part of the NuGrid chemical evolution package and is publicly available online at http://nugrid.github.io/NuPyCEE.

Rare Isotopes in Cosmic Explosions and Accelerators on Earth

ScienceCinema

Schatz, Hendrick

2017-12-28

Rare isotopes are nature’s stepping stones to produce the heavy elements, and they are produced in large quantities in stellar explosions. Despite their fleeting existence, they shape the composition of the universe and the observable features of stellar explosions. The challenge for nuclear science is to produce and study the very same rare isotopes so as to understand the origin of the elements and a range of astronomical observations. I will review the progress that has been made to date in astronomy and nuclear physics, and the prospects of finally addressing many of the outstanding issues with the future Facility for Rare Isotope Beams (FRIB), which DOE will build at Michigan State University.

Dancing to CHANGA: a self-consistent prediction for close SMBH pair formation time-scales following galaxy mergers

NASA Astrophysics Data System (ADS)

Tremmel, M.; Governato, F.; Volonteri, M.; Quinn, T. R.; Pontzen, A.

2018-04-01

We present the first self-consistent prediction for the distribution of formation time-scales for close supermassive black hole (SMBH) pairs following galaxy mergers. Using ROMULUS25, the first large-scale cosmological simulation to accurately track the orbital evolution of SMBHs within their host galaxies down to sub-kpc scales, we predict an average formation rate density of close SMBH pairs of 0.013 cMpc-3 Gyr-1. We find that it is relatively rare for galaxy mergers to result in the formation of close SMBH pairs with sub-kpc separation and those that do form are often the result of Gyr of orbital evolution following the galaxy merger. The likelihood and time-scale to form a close SMBH pair depends strongly on the mass ratio of the merging galaxies, as well as the presence of dense stellar cores. Low stellar mass ratio mergers with galaxies that lack a dense stellar core are more likely to become tidally disrupted and deposit their SMBH at large radii without any stellar core to aid in their orbital decay, resulting in a population of long-lived `wandering' SMBHs. Conversely, SMBHs in galaxies that remain embedded within a stellar core form close pairs in much shorter time-scales on average. This time-scale is a crucial, though often ignored or very simplified, ingredient to models predicting SMBH mergers rates and the connection between SMBH and star formation activity.

Magnetic fields driven by tidal mixing in radiative stars

NASA Astrophysics Data System (ADS)

Vidal, Jérémie; Cébron, David; Schaeffer, Nathanaël; Hollerbach, Rainer

2018-04-01

Stellar magnetism plays an important role in stellar evolution theory. Approximatively 10 per cent of observed main sequence (MS) and pre-main-sequence (PMS) radiative stars exhibit surface magnetic fields above the detection limit, raising the question of their origin. These stars host outer radiative envelopes, which are stably stratified. Therefore, they are assumed to be motionless in standard models of stellar structure and evolution. We focus on rapidly rotating, radiative stars which may be prone to the tidal instability, due to an orbital companion. Using direct numerical simulations in a sphere, we study the interplay between a stable stratification and the tidal instability, and assess its dynamo capability. We show that the tidal instability is triggered regardless of the strength of the stratification (Brunt-Väisälä frequency). Furthermore, the tidal instability can lead to both mixing and self-induced magnetic fields in stably stratified layers (provided that the Brunt-Väisälä frequency does not exceed the stellar spin rate in the simulations too much). The application to stars suggests that the resulting magnetic fields could be observable at the stellar surfaces. Indeed, we expect magnetic field strengths up to several Gauss. Consequently, tidally driven dynamos should be considered as a (complementary) dynamo mechanism, possibly operating in radiative MS and PMS stars hosting orbital companions. In particular, tidally driven dynamos may explain the observed magnetism of tidally deformed and rapidly rotating Vega-like stars.

DEMOGRAPHICS OF BULGE TYPES WITHIN 11 Mpc AND IMPLICATIONS FOR GALAXY EVOLUTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fisher, David B.; Drory, Niv, E-mail: dbfisher@astro.umd.edu

2011-06-01

We present an inventory of galaxy bulge types (elliptical galaxy, classical bulge, pseudobulge, and bulgeless galaxy) in a volume-limited sample within the local 11 Mpc sphere using Spitzer 3.6 {mu}m and Hubble Space Telescope data. We find that whether counting by number, star formation rate, or stellar mass, the dominant galaxy type in the local universe has pure disk characteristics (either hosting a pseudobulge or being bulgeless). Galaxies that contain either a pseudobulge or no bulge combine to account for over 80% of the number of galaxies above a stellar mass of 10{sup 9} M{sub sun}. Classical bulges and ellipticalmore » galaxies account for {approx}1/4, and disks for {approx}3/4 of the stellar mass in the local 11 Mpc. About 2/3 of all star formation in the local volume takes place in galaxies with pseudobulges. Looking at the fraction of galaxies with different bulge types as a function of stellar mass, we find that the frequency of classical bulges strongly increases with stellar mass, and comes to dominate above 10{sup 10.5} M{sub sun}. Galaxies with pseudobulges dominate at 10{sup 9.5}-10{sup 10.5} M{sub sun}. Yet lower-mass galaxies are most likely to be bulgeless. If pseudobulges are not a product of mergers, then the frequency of pseudobulges in the local universe poses a challenge for galaxy evolution models.« less

Dust cloud evolution in sub-stellar atmospheres via plasma deposition and plasma sputtering

NASA Astrophysics Data System (ADS)

Stark, C. R.; Diver, D. A.

2018-04-01

Context. In contemporary sub-stellar model atmospheres, dust growth occurs through neutral gas-phase surface chemistry. Recently, there has been a growing body of theoretical and observational evidence suggesting that ionisation processes can also occur. As a result, atmospheres are populated by regions composed of plasma, gas and dust, and the consequent influence of plasma processes on dust evolution is enhanced. Aim. This paper aims to introduce a new model of dust growth and destruction in sub-stellar atmospheres via plasma deposition and plasma sputtering. Methods: Using example sub-stellar atmospheres from DRIFT-PHOENIX, we have compared plasma deposition and sputtering timescales to those from neutral gas-phase surface chemistry to ascertain their regimes of influence. We calculated the plasma sputtering yield and discuss the circumstances where plasma sputtering dominates over deposition. Results: Within the highest dust density cloud regions, plasma deposition and sputtering dominates over neutral gas-phase surface chemistry if the degree of ionisation is ≳10-4. Loosely bound grains with surface binding energies of the order of 0.1-1 eV are susceptible to destruction through plasma sputtering for feasible degrees of ionisation and electron temperatures; whereas, strong crystalline grains with binding energies of the order 10 eV are resistant to sputtering. Conclusions: The mathematical framework outlined sets the foundation for the inclusion of plasma deposition and plasma sputtering in global dust cloud formation models of sub-stellar atmospheres.

Evolución de estrellas de varias masas: Cálculo de los pulsos térmicos

NASA Astrophysics Data System (ADS)

Panei, J. A.; Althaus, L. G.; Benvenuto, O. G.; Serenelli, A. M.

We present stellar evolutionary calculations for models with stellar masses ranging from 1.2 to 20 Msolar. We follow the calculations from the Main Sequence up to the phase of thermal pulses. The emphasis is placed mainly on the analysis of the behaviour of a 5 Msolar model. The evolutionary code is based on the Kippenhahn, Weigert, & Hofmeister (1967) method to compute stellar evolution. The structure and stellar evolution equations for the stellar interior are integrated using the standard Henyey method. The degree of superadiabaticity is computed from the mixing length theory of convection (Böhm - Vitense 1958). The equation of state we employed takes into account partial ionization, radiation pressure and relativistic degeneracy for electrons at finite temperature. Radiative opacities with metallicity Z=0.02 are taken from Rogers & Iglesias (1996). Conductive opacities for the low - density regime are from the fits of Iben (1975) to the calculations of Hubbard & Lampe (1969). For higher densities we use the results of Itoh et. al (1983). The molecular opacities are those of Alexander & Ferguson (1994). The different mechanisms of neutrino emission are also taken account. In particular, photo and pair neutrinos are from Itoh et al. (1989); plasma neutrinos from Itoh et al. (1989) and Bremsstrahlung from Itoh et al. (1992). Because the aim in this work has been to calculate the stages corresponding to the thermal pulses, particular attention has been devoted to the treatment of the numerical difficulties appearing in this kind of calculation. To this end, we solve the equations describing the structure and evolution of a star in terms of differences with respect to time, instead of iterating the value of the physical variables directly. This change has allowed us to calculate advanced evolutionary stages such as the thermal pulses. In this regard, we find that our models experiencies up to 10 thermal flashes.

The Magellanic Bridge Cluster NGC 796: Deep Optical AO Imaging Reveals the Stellar Content and Initial Mass Function of a Massive Open Cluster

NASA Astrophysics Data System (ADS)

Kalari, Venu M.; Carraro, Giovanni; Evans, Christopher J.; Rubio, Monica

2018-04-01

NGC 796 is a massive young cluster located 59 kpc from us in the diffuse intergalactic medium of the 1/5–1/10 Z⊙ Magellanic Bridge, allowing us to probe variations in star formation and stellar evolution processes as a function of metallicity in a resolved fashion, and providing a link between resolved studies of nearby solar-metallicity and unresolved distant metal-poor clusters located in high-redshift galaxies. In this paper, we present adaptive optics griHα imaging of NGC 796 (at 0.″5, which is ∼0.14 pc at the cluster distance) along with optical spectroscopy of two bright members to quantify the cluster properties. Our aim is to explore whether star formation and stellar evolution vary as a function of metallicity by comparing the properties of NGC 796 to higher-metallicity clusters. We find an age of {20}-5+12 Myr from isochronal fitting of the cluster main sequence in the color–magnitude diagram. Based on the cluster luminosity function, we derive a top-heavy stellar initial mass function (IMF) with a slope α = 1.99 ± 0.2, hinting at a metallicity and/or environmental dependence of the IMF, which may lead to a top-heavy IMF in the early universe. Study of the Hα emission-line stars reveals that classical Be stars constitute a higher fraction of the total B-type stars when compared with similar clusters at greater metallicity, providing some support to the chemically homogeneous theory of stellar evolution. Overall, NGC 796 has a total estimated mass of 990 ± 200 M⊙, and a core radius of 1.4 ± 0.3 pc, which classifies it as a massive young open cluster, unique in the diffuse interstellar medium of the Magellanic Bridge.

Purely Dry Mergers do not Explain the Observed Evolution of Massive Early-type Galaxies since z ~ 1

NASA Astrophysics Data System (ADS)

Sonnenfeld, Alessandro; Nipoti, Carlo; Treu, Tommaso

2014-05-01

Several studies have suggested that the observed size evolution of massive early-type galaxies (ETGs) can be explained as a combination of dry mergers and progenitor bias, at least since z ~ 1. In this paper we carry out a new test of the dry-merger scenario based on recent lensing measurements of the evolution of the mass density profile of ETGs. We construct a theoretical model for the joint evolution of the size and mass density profile slope γ' driven by dry mergers occurring at rates given by cosmological simulations. Such dry-merger model predicts a strong decrease of γ' with cosmic time, inconsistent with the almost constant γ' inferred from observations in the redshift range 0 < z < 1. We then show with a simple toy model that a modest amount of cold gas in the mergers—consistent with the upper limits on recent star formation in ETGs—is sufficient to reconcile the model with measurements of γ'. By fitting for the amount of gas accreted during mergers, we find that models with dissipation are consistent with observations of the evolution in both size and density slope, if ~4% of the total final stellar mass arises from the gas accreted since z ~ 1. Purely dry merger models are ruled out at >99% CL. We thus suggest a scenario where the outer regions of massive ETGs grow by accretion of stars and dark matter, while small amounts of dissipation and nuclear star formation conspire to keep the mass density profile constant and approximately isothermal.

Stellar differential rotation and coronal time-scales

NASA Astrophysics Data System (ADS)

Gibb, G. P. S.; Jardine, M. M.; Mackay, D. H.

2014-10-01

We investigate the time-scales of evolution of stellar coronae in response to surface differential rotation and diffusion. To quantify this, we study both the formation time and lifetime of a magnetic flux rope in a decaying bipolar active region. We apply a magnetic flux transport model to prescribe the evolution of the stellar photospheric field, and use this to drive the evolution of the coronal magnetic field via a magnetofrictional technique. Increasing the differential rotation (i.e. decreasing the equator-pole lap time) decreases the flux rope formation time. We find that the formation time is dependent upon the lap time and the surface diffusion time-scale through the relation τ_Form ∝ √{τ_Lapτ_Diff}. In contrast, the lifetimes of flux ropes are proportional to the lap time (τLife∝τLap). With this, flux ropes on stars with a differential rotation of more than eight times the solar value have a lifetime of less than 2 d. As a consequence, we propose that features such as solar-like quiescent prominences may not be easily observable on such stars, as the lifetimes of the flux ropes which host the cool plasma are very short. We conclude that such high differential rotation stars may have very dynamical coronae.

N-body simulations of star clusters

NASA Astrophysics Data System (ADS)

Engle, Kimberly Anne

1999-10-01

We investigate the structure and evolution of underfilling (i.e. non-Roche-lobe-filling) King model globular star clusters using N-body simulations. We model clusters with various underfilling factors and mass distributions to determine their evolutionary tracks and lifetimes. These models include a self-consistent galactic tidal field, mass loss due to stellar evolution, ejection, and evaporation, and binary evolution. We find that a star cluster that initially does not fill its Roche lobe can live many times longer than one that does initially fill its Roche lobe. After a few relaxation times, the cluster expands to fill its Roche lobe. We also find that the choice of initial mass function significantly affects the lifetime of the cluster. These simulations were performed on the GRAPE-4 (GRAvity PipE) special-purpose hardware with the stellar dynamics package ``Starlab.'' The GRAPE-4 system is a massively-parallel computer designed to calculate the force (and its first time derivative) due to N particles. Starlab's integrator ``kira'' employs a 4th- order Hermite scheme with hierarchical (block) time steps to evolve the stellar system. We discuss, in some detail, the design of the GRAPE-4 system and the manner in which the Hermite integration scheme with block time steps is implemented in the hardware.

UPDATED MASS SCALING RELATIONS FOR NUCLEAR STAR CLUSTERS AND A COMPARISON TO SUPERMASSIVE BLACK HOLES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scott, Nicholas; Graham, Alister W.

2013-02-15

We investigate whether or not nuclear star clusters and supermassive black holes (SMBHs) follow a common set of mass scaling relations with their host galaxy's properties, and hence can be considered to form a single class of central massive object (CMO). We have compiled a large sample of galaxies with measured nuclear star cluster masses and host galaxy properties from the literature and fit log-linear scaling relations. We find that nuclear star cluster mass, M {sub NC}, correlates most tightly with the host galaxy's velocity dispersion: log M {sub NC} = (2.11 {+-} 0.31)log ({sigma}/54) + (6.63 {+-} 0.09), butmore » has a slope dramatically shallower than the relation defined by SMBHs. We find that the nuclear star cluster mass relations involving host galaxy (and spheroid) luminosity and stellar and dynamical mass, intercept with but are in general shallower than the corresponding black hole scaling relations. In particular, M {sub NC}{proportional_to}M {sup 0.55{+-}0.15} {sub Gal,dyn}; the nuclear cluster mass is not a constant fraction of its host galaxy or spheroid mass. We conclude that nuclear stellar clusters and SMBHs do not form a single family of CMOs.« less

The SILCC project - III. Regulation of star formation and outflows by stellar winds and supernovae

NASA Astrophysics Data System (ADS)

Gatto, Andrea; Walch, Stefanie; Naab, Thorsten; Girichidis, Philipp; Wünsch, Richard; Glover, Simon C. O.; Klessen, Ralf S.; Clark, Paul C.; Peters, Thomas; Derigs, Dominik; Baczynski, Christian; Puls, Joachim

2017-04-01

We study the impact of stellar winds and supernovae on the multiphase interstellar medium using three-dimensional hydrodynamical simulations carried out with FLASH. The selected galactic disc region has a size of (500 pc)2 × ±5 kpc and a gas surface density of 10 M⊙ pc-2. The simulations include an external stellar potential and gas self-gravity, radiative cooling and diffuse heating, sink particles representing star clusters, stellar winds from these clusters that combine the winds from individual massive stars by following their evolution tracks, and subsequent supernova explosions. Dust and gas (self-) shielding is followed to compute the chemical state of the gas with a chemical network. We find that stellar winds can regulate star (cluster) formation. Since the winds suppress the accretion of fresh gas soon after the cluster has formed, they lead to clusters that have lower average masses (102-104.3 M⊙) and form on shorter time-scales (10-3-10 Myr). In particular, we find an anticorrelation of cluster mass and accretion time-scale. Without winds, the star clusters easily grow to larger masses for ˜5 Myr until the first supernova explodes. Overall, the most massive stars provide the most wind energy input, while objects beginning their evolution as B-type stars contribute most of the supernova energy input. A significant outflow from the disc (mass loading ≳1 at 1 kpc) can be launched by thermal gas pressure if more than 50 per cent of the volume near the disc mid-plane can be heated to T > 3 × 105 K. Stellar winds alone cannot create a hot volume-filling phase. The models that are in best agreement with observed star formation rates drive either no outflows or weak outflows.

Correlations among Galaxy Properties from the Sloan Digital Sky Survey

NASA Astrophysics Data System (ADS)

Li, Zhongmu; Mao, Caiyan

2013-07-01

Galaxies are complex systems with many properties. Correlations among galaxy properties can supply important clues for studying the formation and evolution of galaxies. Using principal component analysis and least-squares fitting, this paper investigates the correlations among galactic parameters involving more properties (color, morphology, stellar population, and absolute magnitude) than previous studies. We use a volume-limited sample (whole sample) of 75,423 galaxies that was selected from the Sloan Digital Sky Survey Data Release 2 and divided into two subsamples (blue and red samples) using a critical color of (g - r) = 0.70 mag. In addition to recovering some previous results, we also obtain some new results. First, all separators for dividing galaxies into two groups can be related via good parameter-first principal component (PC1) correlations. A critical PC1 that indicates whether or not stellar age (or the evolution of a stellar population over time) is important can be used to separate galaxies. This suggests that a statistical parameter, PC1, is helpful in understanding the physical separators of galaxies. In addition, stellar age is shown to be unimportant for red galaxies, while both stellar age and mass are dominating parameters of blue galaxies. This suggests that the various numbers of dominating parameters of galaxies may result from the use of different samples. Finally, some parameters are shown to be correlated, and quantitative fits for a few correlations are obtained, e.g., log(t) = 8.57 + 1.65 (g - r) for the age (log t) and color (g - r) of blue galaxies and log (M *) = 4.31 - 0.30 M r for the stellar mass (log M *) and absolute magnitude (M r) of red galaxies. The median relationships between various parameter pairs are also presented for comparison.

The evolution of CNO isotopes: a new window on cosmic star formation history and the stellar IMF in the age of ALMA

NASA Astrophysics Data System (ADS)

Romano, D.; Matteucci, F.; Zhang, Z.-Y.; Papadopoulos, P. P.; Ivison, R. J.

2017-09-01

We use state-of-the-art chemical models to track the cosmic evolution of the CNO isotopes in the interstellar medium of galaxies, yielding powerful constraints on their stellar initial mass function (IMF). We re-assess the relative roles of massive stars, asymptotic giant branch (AGB) stars and novae in the production of rare isotopes such as 13C, 15N, 17O and 18O, along with 12C, 14N and 16O. The CNO isotope yields of super-AGB stars, novae and fast-rotating massive stars are included. Having reproduced the available isotope enrichment data in the solar neighbourhood, and across the Galaxy, and having assessed the sensitivity of our models to the remaining uncertainties, e.g. nova yields and star formation history, we show that we can meaningfully constrain the stellar IMF in galaxies using C, O and N isotope abundance ratios. In starburst galaxies, where data for multiple isotopologue lines are available, we find compelling new evidence for a top-heavy stellar IMF, with profound implications for their star formation rates and efficiencies, perhaps also their stellar masses. Neither chemical fractionation nor selective photodissociation can significantly perturb globally averaged isotopologue abundance ratios away from the corresponding isotope ones, as both these processes will typically affect only small mass fractions of molecular clouds in galaxies. Thus, the Atacama Large Millimeter Array now stands ready to probe the stellar IMF, and even the ages of specific starburst events in star-forming galaxies across cosmic time unaffected by the dust obscuration effects that plague optical/near-infrared studies.

GAMA/G10-COSMOS/3D-HST: the 0 < z < 5 cosmic star formation history, stellar-mass, and dust-mass densities

NASA Astrophysics Data System (ADS)

Driver, Simon P.; Andrews, Stephen K.; da Cunha, Elisabete; Davies, Luke J.; Lagos, Claudia; Robotham, Aaron S. G.; Vinsen, Kevin; Wright, Angus H.; Alpaslan, Mehmet; Bland-Hawthorn, Joss; Bourne, Nathan; Brough, Sarah; Bremer, Malcolm N.; Cluver, Michelle; Colless, Matthew; Conselice, Christopher J.; Dunne, Loretta; Eales, Steve A.; Gomez, Haley; Holwerda, Benne; Hopkins, Andrew M.; Kafle, Prajwal R.; Kelvin, Lee S.; Loveday, Jon; Liske, Jochen; Maddox, Steve J.; Phillipps, Steven; Pimbblet, Kevin; Rowlands, Kate; Sansom, Anne E.; Taylor, Edward; Wang, Lingyu; Wilkins, Stephen M.

2018-04-01

We use the energy-balance code MAGPHYS to determine stellar and dust masses, and dust corrected star formation rates for over 200 000 GAMA galaxies, 170 000 G10-COSMOS galaxies, and 200 000 3D-HST galaxies. Our values agree well with previously reported measurements and constitute a representative and homogeneous data set spanning a broad range in stellar-mass (108-1012 M⊙), dust-mass (106-109 M⊙), and star formation rates (0.01-100 M⊙yr-1), and over a broad redshift range (0.0 < z < 5.0). We combine these data to measure the cosmic star formation history (CSFH), the stellar-mass density (SMD), and the dust-mass density (DMD) over a 12 Gyr timeline. The data mostly agree with previous estimates, where they exist, and provide a quasi-homogeneous data set using consistent mass and star formation estimators with consistent underlying assumptions over the full time range. As a consequence our formal errors are significantly reduced when compared to the historic literature. Integrating our CSFH we precisely reproduce the SMD with an interstellar medium replenishment factor of 0.50 ± 0.07, consistent with our choice of Chabrier initial mass function plus some modest amount of stripped stellar mass. Exploring the cosmic dust density evolution, we find a gradual increase in dust density with lookback time. We build a simple phenomenological model from the CSFH to account for the dust-mass evolution, and infer two key conclusions: (1) For every unit of stellar mass which is formed 0.0065-0.004 units of dust mass is also formed. (2) Over the history of the Universe approximately 90-95 per cent of all dust formed has been destroyed and/or ejected.

Chemical Abundances of Main-sequence, Turnoff, Subgiant, and Red Giant Stars from APOGEE Spectra. I. Signatures of Diffusion in the Open Cluster M67

NASA Astrophysics Data System (ADS)

Souto, Diogo; Cunha, Katia; Smith, Verne V.; Allende Prieto, C.; García-Hernández, D. A.; Pinsonneault, Marc; Holzer, Parker; Frinchaboy, Peter; Holtzman, Jon; Johnson, J. A.; Jönsson, Henrik; Majewski, Steven R.; Shetrone, Matthew; Sobeck, Jennifer; Stringfellow, Guy; Teske, Johanna; Zamora, Olga; Zasowski, Gail; Carrera, Ricardo; Stassun, Keivan; Fernandez-Trincado, J. G.; Villanova, Sandro; Minniti, Dante; Santana, Felipe

2018-04-01

Detailed chemical abundance distributions for 14 elements are derived for eight high-probability stellar members of the solar metallicity old open cluster M67 with an age of ∼4 Gyr. The eight stars consist of four pairs, with each pair occupying a distinct phase of stellar evolution: two G dwarfs, two turnoff stars, two G subgiants, and two red clump (RC) K giants. The abundance analysis uses near-IR high-resolution spectra (λ1.5–1.7 μm) from the Apache Point Observatory Galactic Evolution Experiment survey and derives abundances for C, N, O, Na, Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, and Fe. Our derived stellar parameters and metallicity for 2M08510076+1153115 suggest that this star is a solar twin, exhibiting abundance differences relative to the Sun of ≤0.04 dex for all elements. Chemical homogeneity is found within each class of stars (∼0.02 dex), while significant abundance variations (∼0.05–0.20 dex) are found across the different evolutionary phases; the turnoff stars typically have the lowest abundances, while the RCs tend to have the largest. Non-LTE corrections to the LTE-derived abundances are unlikely to explain the differences. A detailed comparison of the derived Fe, Mg, Si, and Ca abundances with recently published surface abundances from stellar models that include chemical diffusion provides a good match between the observed and predicted abundances as a function of stellar mass. Such agreement would indicate the detection of chemical diffusion processes in the stellar members of M67.

Origin and Evolution of the Elements

NASA Astrophysics Data System (ADS)

McWilliam, Andrew; Rauch, Michael

2004-09-01

Introduction; List of participants; 1. Mount Wilson Observatory contributions to the study of cosmic abundances of the chemical elements George W. Preston; 2. Synthesis of the elements in stars: B2FH and beyond E. Margaret Burbidge; 3. Stellar nucleosynthesis: a status report 2003 David Arnett; 4. Advances in r-process nucleosynthesis John J. Cowan and Christopher Sneden; 5. Element yields of intermediate-mass stars Richard B. C. Henry; 6. The impact of rotation on chemical abundances in red giant branch stars Corinne Charbonnel; 7. s-processing in AGB stars and the composition of carbon stars Maurizio Busso, Oscar Straniero, Roberto Gallino, and Carlos Abia; 8. Models of chemical evolution Francesca Matteucci; 9. Model atmospheres and stellar abundance analysis Bengt Gustafsson; 10. The light elements: lithium, beryllium, and boron Ann Merchant Boesgaard; 11. Extremely metal-poor stars John E. Norris; 12. Thin and thick galactic disks Poul E. Nissen; 13. Globular clusters and halo field stars Christopher Sneden, Inese I. Ivans and Jon P. Fulbright; 14. Chemical evolution in ω Centauri Verne V. Smith; 15. Chemical composition of the Magellanic Clouds, from young to old stars Vanessa Hill; 16. Detailed composition of stars in dwarf spheroidal galaxies Matthew D. Shetrone; 17. The evolutionary history of Local Group irregular galaxies Eva K. Grebel; 18. Chemical evolution of the old stellar populations of M31 R. Michael Rich; 19. Stellar winds of hot massive stars nearby and beyond the Local Group Fabio Bresolin and Rolf P. Kudritzki; 20. Presolar stardust grains Donald D. Clayton and Larry R. Nittler; 21. Interstellar dust B. T. Draine; 22. Interstellar atomic abundances Edward B. Jenkins; 23. Molecules in the interstellar medium Tommy Wiklind; 24. Metal ejection by galactic winds Crystal L. Martin; 25. Abundances from the integrated light of globular clusters and galaxies Scott C. Trager; 26. Abundances in spiral and irregular galaxies Donald R. Garnett; 27. Chemical composition of the intracluster medium Michael Loewenstein; 28. Quasar elemental abundances and host galaxy evolution Fred Hamann, Matthias Dietrich, Bassem M. Sabra, and Craig Warner; 29. Chemical abundances in the damped Lyα systems Jason X. Prochaska; 30. Intergalactic medium abundances Robert F. Carswell; 31. Conference summary Bernard E. J. Pagel.

Synthetic nebular emission from massive galaxies - I: origin of the cosmic evolution of optical emission-line ratios

NASA Astrophysics Data System (ADS)

Hirschmann, Michaela; Charlot, Stephane; Feltre, Anna; Naab, Thorsten; Choi, Ena; Ostriker, Jeremiah P.; Somerville, Rachel S.

2017-12-01

Galaxies occupy different regions of the [O III]λ5007/H β-versus-[N II]λ6584/H α emission-line ratio diagram in the distant and local Universe. We investigate the origin of this intriguing result by modelling self-consistently, for the first time, nebular emission from young stars, accreting black holes (BHs) and older, post-asymptotic giant branch (post-AGB) stellar populations in galaxy formation simulations in a full cosmological context. In post-processing, we couple new-generation nebular-emission models with high-resolution, cosmological zoom-in simulations of massive galaxies to explore which galaxy physical properties drive the redshift evolution of the optical-line ratios [O III]λ5007/H β, [N II]λ6584/H α, [S II]λλ6717, 6731/H α and [O I]λ6300/H α. The line ratios of simulated galaxies agree well with observations of both star-forming and active local Sloan Digital Sky Survey galaxies. Towards higher redshifts, at fixed galaxy stellar mass, the average [O III]/H β is predicted to increase and [N II]/H α, [S II]/H α and [O I]/H α to decrease - widely consistent with observations. At fixed stellar mass, we identify star formation history, which controls nebular emission from young stars via the ionization parameter, as the primary driver of the cosmic evolution of [O III]/H β and [N II]/H α. For [S II]/H α and [O I]/H α, this applies only to redshifts greater than z = 1.5, the evolution at lower redshift being driven in roughly equal parts by nebular emission from active galactic nuclei and post-AGB stellar populations. Instead, changes in the hardness of ionizing radiation, ionized-gas density, the prevalence of BH accretion relative to star formation and the dust-to-metal mass ratio (whose impact on the gas-phase N/O ratio we model at fixed O/H) play at most a minor role in the cosmic evolution of simulated galaxy line ratios.

Uncertainties in Galactic Chemical Evolution Models

DOE PAGES

Cote, Benoit; Ritter, Christian; Oshea, Brian W.; ...

2016-06-15

Here we use a simple one-zone galactic chemical evolution model to quantify the uncertainties generated by the input parameters in numerical predictions for a galaxy with properties similar to those of the Milky Way. We compiled several studies from the literature to gather the current constraints for our simulations regarding the typical value and uncertainty of the following seven basic parameters: the lower and upper mass limits of the stellar initial mass function (IMF), the slope of the high-mass end of the stellar IMF, the slope of the delay-time distribution function of Type Ia supernovae (SNe Ia), the number ofmore » SNe Ia per M ⊙ formed, the total stellar mass formed, and the final mass of gas. We derived a probability distribution function to express the range of likely values for every parameter, which were then included in a Monte Carlo code to run several hundred simulations with randomly selected input parameters. This approach enables us to analyze the predicted chemical evolution of 16 elements in a statistical manner by identifying the most probable solutions along with their 68% and 95% confidence levels. Our results show that the overall uncertainties are shaped by several input parameters that individually contribute at different metallicities, and thus at different galactic ages. The level of uncertainty then depends on the metallicity and is different from one element to another. Among the seven input parameters considered in this work, the slope of the IMF and the number of SNe Ia are currently the two main sources of uncertainty. The thicknesses of the uncertainty bands bounded by the 68% and 95% confidence levels are generally within 0.3 and 0.6 dex, respectively. When looking at the evolution of individual elements as a function of galactic age instead of metallicity, those same thicknesses range from 0.1 to 0.6 dex for the 68% confidence levels and from 0.3 to 1.0 dex for the 95% confidence levels. The uncertainty in our chemical evolution model does not include uncertainties relating to stellar yields, star formation and merger histories, and modeling assumptions.« less

Presupernova Evolution of Differentially Rotating Massive Stars Including Magnetic Fields

NASA Astrophysics Data System (ADS)

Heger, A.; Woosley, S. E.; Spruit, H. C.

2005-06-01

As a massive star evolves through multiple stages of nuclear burning on its way to becoming a supernova, a complex, differentially rotating structure is set up. Angular momentum is transported by a variety of classic instabilities and also by magnetic torques from fields generated by the differential rotation. We present the first stellar evolution calculations to follow the evolution of rotating massive stars including, at least approximately, all these effects, magnetic and nonmagnetic, from the zero-age main sequence until the onset of iron-core collapse. The evolution and action of the magnetic fields is as described by Spruit in 2002, and a range of uncertain parameters is explored. In general, we find that magnetic torques decrease the final rotation rate of the collapsing iron core by about a factor of 30-50 when compared with the nonmagnetic counterparts. Angular momentum in that part of the presupernova star destined to become a neutron star is an increasing function of main-sequence mass. That is, pulsars derived from more massive stars rotate faster and rotation plays a more important role in the star's explosion. The final angular momentum of the core has been determined-to within a factor of 2-by the time the star ignites carbon burning. For the lighter stars studied, around 15 Msolar, we predict pulsar periods at birth near 15 ms, though a factor of 2 range is easily tolerated by the uncertainties. Several mechanisms for additional braking in a young neutron star, especially by fallback, are explored.

Bar formation as driver of gas inflows in isolated disc galaxies

NASA Astrophysics Data System (ADS)

Fanali, R.; Dotti, M.; Fiacconi, D.; Haardt, F.

2015-12-01

Stellar bars are a common feature in massive disc galaxies. On a theoretical ground, the response of gas to a bar is generally thought to cause nuclear starbursts and, possibly, AGN activity once the perturbed gas reaches the central supermassive black hole. By means of high-resolution numerical simulations, we detail the purely dynamical effects that a forming bar exerts on the gas of an isolated disc galaxy. The galaxy is initially unstable to the formation of non-axisymmetric structures, and within ˜1 Gyr it develops spiral arms that eventually evolve into a central stellar bar on kpc scale. A first major episode of gas inflow occurs during the formation of the spiral arms while at later times, when the stellar bar is establishing, a low-density region is carved between the bar corotational and inner Lindblad resonance radii. The development of such `dead zone' inhibits further massive gas inflows. Indeed, the gas inflow reaches its maximum during the relatively fast bar-formation phase and not, as often assumed, when the bar is fully formed. We conclude that the low efficiency of long-lived, evolved bars in driving gas towards galactic nuclei is the reason why observational studies have failed to establish an indisputable link between bars and AGNs. On the other hand, the high efficiency in driving strong gas inflows of the intrinsically transient process of bar formation suggests that the importance of bars as drivers of AGN activity in disc galaxies has been overlooked so far. We finally prove that our conclusions are robust against different numerical implementations of the hydrodynamics routinely used in galaxy evolution studies.

Three-dimensional simulations of the interaction between the nova ejecta, accretion disk, and companion star

NASA Astrophysics Data System (ADS)

Figueira, Joana; José, Jordi; García-Berro, Enrique; Campbell, Simon W.; García-Senz, Domingo; Mohamed, Shazrene

2018-05-01

Context. Classical novae are thermonuclear explosions hosted by accreting white dwarfs in stellar binary systems. Material piles up on top of the white dwarf star under mildly degenerate conditions, driving a thermonuclear runaway. The energy released by the suite of nuclear processes operating at the envelope, mostly proton-capture reactions and β+-decays, heats the material up to peak temperatures ranging from 100 to 400 MK. In these events, about 10-3-10-7 M⊙, enriched in CNO and, sometimes, other intermediate-mass elements (e.g., Ne, Na, Mg, and Al) are ejected into the interstellar medium. Aims: To date, most of the efforts undertaken in the modeling of classical nova outbursts have focused on the early stages of the explosion and ejection, ignoring the interaction of the ejecta, first with the accretion disk orbiting the white dwarf and ultimately with the secondary star. Methods: A suite of 3D, smoothed-particle hydrodynamics (SPH) simulations of the interaction between the nova ejecta, accretion disk, and stellar companion were performed to fill this gap; these simulations were aimed at testing the influence of the model parameters—that is, the mass and velocity of the ejecta, mass and the geometry of the accretion disk—on the dynamical and chemical properties of the system. Results: We discuss the conditions that lead to the disruption of the accretion disk and to mass loss from the binary system. In addition, we discuss the likelihood of chemical contamination of the stellar secondary induced by the impact with the nova ejecta and its potential effect on the next nova cycle. Movies showing the full evolution of several models are available online at http://https://www.aanda.org and at http://www.fen.upc.edu/users/jjose/Downloads.html

Centennial History of the Carnegie Institution of Washington

NASA Astrophysics Data System (ADS)

Sandage, Allan

2013-01-01

Foreword Richard A. Meserve; Acknowledgements; Prologue; Part I. Before the Beginning (1542-1904): 1. A telegram; 2. The origin of a name; 3. Three observatories for Mount Wilson before the real one; 4. The creation of the Carnegie Institution and its initial Astronomy Advisory Committee; Part II. Creation of the Observatory and the First Scientific Results: 5. The instruments of detection: solar telescopes, coelostats, spectrographs and spectra; 6. Snow, hale, frost and gale: just the right people to study storms on the sun; 7. Tower telescopes and magnetic fields and cycles; 8. Pioneers of peering: the scientific staff in the early years (1904-9); 9. Solar physics: the intermediate years (1910-30); 10. Yet more solar physics: motions on the surface, clocks in the gravity field and the reality of prominences; Part III. The Beginning of Nighttime Sidereal Astronomy at Mount Wilson: 11. The coming of the 60-inch and 100-inch reflectors; 12. Life on the mountain; 13. Anatomy of an observatory; Part IV. Preparation for an Understanding of Stellar Evolution and Galactic Structure: 14. Galactic structure in the raw; 15. Spectral classification and the invention of spectroscopic parallaxes; 16. Radial velocity; 17. Globular star clusters and the galactocentric revolution; 18. Galactic rotation: Stromberg, Lindblad and Oort; 19. The Carnegie Meridian Astrometry Department at the Dudley Observatory; 20. Absolute magnitudes from direct parallaxes and stellar motions; 21. Threads leading to the population concept that became the fabric of evolution; Part V. Physics of the Stars and the Interstellar Medium: 22. Five problems in astrophysics; 23. Long-term research associates and short-term visitors; 24. Interstellar gas, instruments and the spiral arms of the galaxy; Part VI. Observational Cosmology and the Code of Stellar Evolution: 25. Observational cosmology I: galaxy classification and the discovery of cepheids; 26. Observational cosmology II: the expansion of the universe and the search for the curvature of space; 27. Down more corridors of time; 28. The observational approach to stellar evolution; Epilogue; Abbreviations; Notes; Bibliography; Index.

Centennial History of the Carnegie Institution of Washington

NASA Astrophysics Data System (ADS)

Sandage, Allan

2005-03-01

Foreword Richard A. Meserve; Acknowledgements; Prologue; Part I. Before the Beginning (1542-1904): 1. A telegram; 2. The origin of a name; 3. Three observatories for Mount Wilson before the real one; 4. The creation of the Carnegie Institution and its initial Astronomy Advisory Committee; Part II. Creation of the Observatory and the First Scientific Results: 5. The instruments of detection: solar telescopes, coelostats, spectrographs and spectra; 6. Snow, hale, frost and gale: just the right people to study storms on the sun; 7. Tower telescopes and magnetic fields and cycles; 8. Pioneers of peering: the scientific staff in the early years (1904-9); 9. Solar physics: the intermediate years (1910-30); 10. Yet more solar physics: motions on the surface, clocks in the gravity field and the reality of prominences; Part III. The Beginning of Nighttime Sidereal Astronomy at Mount Wilson: 11. The coming of the 60-inch and 100-inch reflectors; 12. Life on the mountain; 13. Anatomy of an observatory; Part IV. Preparation for an Understanding of Stellar Evolution and Galactic Structure: 14. Galactic structure in the raw; 15. Spectral classification and the invention of spectroscopic parallaxes; 16. Radial velocity; 17. Globular star clusters and the galactocentric revolution; 18. Galactic rotation: Stromberg, Lindblad and Oort; 19. The Carnegie Meridian Astrometry Department at the Dudley Observatory; 20. Absolute magnitudes from direct parallaxes and stellar motions; 21. Threads leading to the population concept that became the fabric of evolution; Part V. Physics of the Stars and the Interstellar Medium: 22. Five problems in astrophysics; 23. Long-term research associates and short-term visitors; 24. Interstellar gas, instruments and the spiral arms of the galaxy; Part VI. Observational Cosmology and the Code of Stellar Evolution: 25. Observational cosmology I: galaxy classification and the discovery of cepheids; 26. Observational cosmology II: the expansion of the universe and the search for the curvature of space; 27. Down more corridors of time; 28. The observational approach to stellar evolution; Epilogue; Abbreviations; Notes; Bibliography; Index.

Effects of Dynamical Evolution on Globular Clusters’ Internal Kinematics

NASA Astrophysics Data System (ADS)

Tiongco, Maria; Vesperini, Enrico; Varri, Anna Lisa

2018-01-01

The synergy between recent photometric, spectroscopic, and astrometric studies is revealing that globular clusters deviate from the traditional picture of dynamically simple and single stellar population systems. Complex kinematical features such as velocity anisotropy and rotation, and the existence of multiple stellar populations are some of the key observational findings. My thesis work has aimed to build a theoretical framework to interpret these new observational results and to understand their link with a globular cluster’s dynamical history.I have focused on the study of the evolution of globular clusters' internal kinematics, as driven by two-body relaxation, and the interplay between internal angular momentum and the external Galactic tidal field. With a specifically-designed, large survey of direct N-body simulations, I have explored the three-dimensional structure of the velocity space of tidally-perturbed clusters, by characterizing their degree of anisotropy and their rotational properties. These studies have proved that a cluster's kinematical properties contain a distinct imprints of the cluster’s initial structural properties, dynamical history, and tidal environment. By relaxing a number of simplifying assumptions that are traditionally imposed, I have also showed how the interplay between a cluster's internal evolution and the interaction with the host galaxy can produce complex morphological and kinematical properties, such as a counter-rotating core and a twisting of the projected isodensity contours.Building on this fundamental understanding, I have then studied the dynamics of multiple stellar populations in globular clusters, with attention to the largely unexplored role of angular momentum. I have analyzed the evolution of clusters with stellar populations characterized by different initial structural and kinematical properties to determine how long these differences are preserved, and in what cases they could still be observable in present-day systems.This body of results provides essential guidance for a meaningful interpretation of the emerging dynamical complexity of globular clusters in the era of Gaia and other upcoming large spectroscopic surveys.

Photometrically-derived properties of massive-star clusters obtained with different massive-star evolution tracks and deterministic models

NASA Astrophysics Data System (ADS)

Wofford, Aida; Charlot, Stéphane; Eldridge, John

2015-08-01

We compute libraries of stellar + nebular spectra of populations of coeval stars with ages of <100 Myr and metallicities of Z=0.001 to 0.040, using different sets of massive-star evolution tracks, i.e., new Padova tracks for single non-rotating stars, the Geneva tracks for single non-rotating and rotating stars, and the Auckland tracks for single non-rotating and binary stars. For the stellar component, we use population synthesis codes galaxev, starburst99, and BPASS, depending on the set of tracks. For the nebular component we use photoionization code cloudy. From these spectra, we obtain magnitudes in filters F275W, F336W, F438W, F547M, F555W, F657N, and F814W of the Hubble Space Telescope (HST) Wide Field Camera Three. We use i) our computed magnitudes, ii) new multi-band photometry of massive-star clusters in nearby (<11 Mpc) galaxies spanning the metallicity range 12+log(O/H)=7.2-9.2, observed as part of HST programs 13364 (PI Calzetti) and 13773 (PI Chandar), and iii) Bayesian inference to a) establish how well the different models are able to constrain the metallicities, extinctions, ages, and masses of the star clusters, b) quantify differences in the cluster properties obtained with the different models, and c) assess how properties of lower-mass clusters are affected by the stochastic sampling of the IMF. In our models, the stellar evolution tracks, stellar atmospheres, and nebulae have similar chemical compositions. Different metallicities are available with different sets of tracks and we compare results from models of similar metallicities. Our results have implications for studies of the formation and evolution of star clusters, the cluster age and mass functions, and the star formation histories of galaxies.

Massive stars in advanced evolutionary stages, and the progenitor of GW150914

NASA Astrophysics Data System (ADS)

Hamann, Wolf-Rainer; Oskinova, Lidia; Todt, Helge; Sander, Andreas; Hainich, Rainer; Shenar, Tomer; Ramachandran, Varsha

2017-11-01

The recent discovery of a gravitational wave from the merging of two black holes of about 30 solar masses each challenges our incomplete understanding of massive stars and their evolution. Critical ingredients comprise mass-loss, rotation, magnetic fields, internal mixing, and mass transfer in close binary systems. The imperfect knowledge of these factors implies large uncertainties for models of stellar populations and their feedback. In this contribution we summarize our empirical studies of Wolf-Rayet populations at different metallicities by means of modern non-LTE stellar atmosphere models, and confront these results with the predictions of stellar evolution models. At the metallicity of our Galaxy, stellar winds are probably too strong to leave remnant masses as high as ~30 M⊙, but given the still poor agreement between evolutionary tracks and observation even this conclusion is debatable. At the low metallicity of the Small Magellanic Cloud, all WN stars which are (at least now) single are consistent with evolving quasi-homogeneously. O and B-type stars, in contrast, seem to comply with standard evolutionary models without strong internal mixing. Close binaries which avoided early merging could evolve quasi-homogeneously and lead to close compact remnants of relatively high masses that merge within a Hubble time.

Self-gravity, Resonances, and Orbital Diffusion in Stellar Disks

NASA Astrophysics Data System (ADS)

Fouvry, Jean-Baptiste; Binney, James; Pichon, Christophe

2015-06-01

Fluctuations in a stellar system's gravitational field cause the orbits of stars to evolve. The resulting evolution of the system can be computed with the orbit-averaged Fokker-Planck equation once the diffusion tensor is known. We present the formalism that enables one to compute the diffusion tensor from a given source of noise in the gravitational field when the system's dynamical response to that noise is included. In the case of a cool stellar disk we are able to reduce the computation of the diffusion tensor to a one-dimensional integral. We implement this formula for a tapered Mestel disk that is exposed to shot noise and find that we are able to explain analytically the principal features of a numerical simulation of such a disk. In particular the formation of narrow ridges of enhanced density in action space is recovered. As the disk's value of Toomre's Q is reduced and the disk becomes more responsive, there is a transition from a regime of heating in the inner regions of the disk through the inner Lindblad resonance to one of radial migration of near-circular orbits via the corotation resonance in the intermediate regions of the disk. The formalism developed here provides the ideal framework in which to study the long-term evolution of all kinds of stellar disks.

The edge of galaxy formation - I. Formation and evolution of MW-satellite analogues before accretion

NASA Astrophysics Data System (ADS)

Macciò, Andrea V.; Frings, Jonas; Buck, Tobias; Penzo, Camilla; Dutton, Aaron A.; Blank, Marvin; Obreja, Aura

2017-12-01

The satellites of the Milky Way and Andromeda represent the smallest galaxies we can observe in our Universe. In this series of papers, we aim to shed light on their formation and evolution using cosmological hydrodynamical simulations. In this first paper, we focus on the galaxy properties before accretion, by simulating 27 haloes with masses between 5 × 108 and 1010 M⊙. Out of this set 19 haloes successfully form stars, while 8 remain dark. The simulated galaxies match quite well present day observed scaling relations between stellar mass, size and metallicity, showing that such relations are in place before accretion. Our galaxies show a large variety of star formation histories, from extended star formation periods to single bursts. As in more massive galaxies, large star formation bursts are connected with major mergers events, which greatly contribute to the overall stellar mass build up. The intrinsic stochasticity of mergers induces a large scatter in the stellar mass-halo mass relation, up to two orders of magnitude. Despite the bursty star formation history, on these mass scales baryons are very ineffective in modifying the dark matter profiles, and galaxies with a stellar mass below ≈106 M⊙ retain their cuspy central dark matter distribution, very similar to results from pure N-body simulations.

The Mass-Size Relation of Quenched, Quiescent Galaxies in the WISP Survey

NASA Astrophysics Data System (ADS)

Pahl, Anthony; Scarlata, Claudia; Rutkowski, Michael J.; Zanella, Anita; Bagley, Micaela B.; Colbert, James W.; Baronchelli, Ivano; Henry, Alaina L.; Hathi, Nimish P.; Teplitz, Harry I.; Rafelski, Marc; Dai, Yu Sophia; Malkan, Matthew Arnold; Mehta, Vihang; Beck, Melanie

2016-01-01

The relation between the stellar mass and size, if measured for galaxies of similar types, can be a useful tool for studying galactic evolution. We study the mass-size relation of quenched, quiescent galaxies to determine the effect of star-formation history on the growth of these objects over time. The WFC3 Infrared Spectroscopic Parallels (WISP) survey is a large HST IR grism survey of over 385 fields of ~4 arcmin2 each, and it is ideal for studying the star-formation rate with its broad spectral coverage. Using a subset of these fields with deep IR data and measurements across both filters (28 fields), we perform a color selection and identify 83 quenched galaxies with a median z~1.6. With GALFIT, we measure their effective radius and sersic index on the 2-D surface brightness distribution in the F110W band. We perform fitting of grism spectra of the observed galaxies to derive redshift, stellar mass and age for all galaxies. We combine the size, stellar mass, and stellar age determinations to investigate whether the evolution of the mass-size relation over time is primarily driven by the entrance of newly quenched galaxies or by processes affecting the individual quenched galaxies.

A large difference in the progenitor masses of active and passive galaxies in the EAGLE simulation

NASA Astrophysics Data System (ADS)

Clauwens, Bart; Franx, Marijn; Schaye, Joop

2016-11-01

Cumulative number density matching of galaxies is a method to observationally connect descendent galaxies to their typical main progenitors at higher redshifts and thereby to assess the evolution of galaxy properties. The accuracy of this method is limited due to galaxy merging and scatter in the stellar mass growth history of individual galaxies. Behroozi et al. have introduced a refinement of the method, based on abundance matching of observed galaxies to the Bolshoi dark matter-only simulation. The EAGLE cosmological hydrosimulation is well suited to test this method, because it reproduces the observed evolution of the galaxy stellar mass function and the passive fraction. We find agreement with the Behroozi et al. method for the complete sample of main progenitors of z = 0 galaxies, but we also find a strong dependence on the current star formation rate. Passive galaxies with a stellar mass up to 1010.75 M⊙ have a completely different median mass history than active galaxies of the same mass. This difference persists if we only select central galaxies. This means that the cumulative number density method should be applied separately to active and passive galaxies. Even then, the typical main progenitor of a z = 0 galaxy already spans two orders of magnitude in stellar mass at z = 2.

A local leaky-box model for the local stellar surface density-gas surface density-gas phase metallicity relation

NASA Astrophysics Data System (ADS)

Zhu, Guangtun Ben; Barrera-Ballesteros, Jorge K.; Heckman, Timothy M.; Zakamska, Nadia L.; Sánchez, Sebastian F.; Yan, Renbin; Brinkmann, Jonathan

2017-07-01

We revisit the relation between the stellar surface density, the gas surface density and the gas-phase metallicity of typical disc galaxies in the local Universe with the SDSS-IV/MaNGA survey, using the star formation rate surface density as an indicator for the gas surface density. We show that these three local parameters form a tight relationship, confirming previous works (e.g. by the PINGS and CALIFA surveys), but with a larger sample. We present a new local leaky-box model, assuming star-formation history and chemical evolution is localized except for outflowing materials. We derive closed-form solutions for the evolution of stellar surface density, gas surface density and gas-phase metallicity, and show that these parameters form a tight relation independent of initial gas density and time. We show that, with canonical values of model parameters, this predicted relation match the observed one well. In addition, we briefly describe a pathway to improving the current semi-analytic models of galaxy formation by incorporating the local leaky-box model in the cosmological context, which can potentially explain simultaneously multiple properties of Milky Way-type disc galaxies, such as the size growth and the global stellar mass-gas metallicity relation.

The evolution of and starburst-agn connection in luminous and ultraluminous infrared galaxies and their link to globular cluster formation

NASA Astrophysics Data System (ADS)

Fiorenza, Stephanie Lynn

The evolutionary connection between nuclear starbursts and active galactic nuclei (AGN) in luminous infrared galaxies (LIRGs; 1011 < LIR < 1012 L[special character omitted]) and ultraluminous infrared galaxies (ULIRGs; 1012 < LIR < 1013 L[special character omitted]), which result from galaxy interactions and mergers and produce the bulk of their radiation as infrared (IR) emission, is not well understood. To this effort, I first spectroscopically examine U/LIRGs (1011 < LIR < 1013 L[special character omitted]) within the IRAS 2 Jansky Redshift Survey with 0.05 < z < 0.16. Using new spectrophotometric data, I classify the primary source of IR radiation as being a nuclear starburst or a type of AGN by using the Baldwin-Phillips-Terlevich (BPT) diagrams. I show that for the U/LIRGs in my sample the properties that describe their nuclear starbursts and AGN (e.g. star formation rate (SFR), L[O III], optical D parameter, D4000, and EW(Hdelta)) are independent of one another, ensuring that no biases affect correlations between these properties and objects' locations on the BPT diagrams. I then derive evolutionary paths on the BPT diagram involving [N II]/Halpha that are based on how these properties vary between two U/LIRGs positioned at the end-points. The paths involve U/LIRGs that decrease in SFR and increase in AGN activity. Paths with U/LIRGs that evolve into high luminosity AGN likely do so due to recent, strong starbursts. Second, to study how the properties of the IR power sources in U/LIRGs vary, I use a combination of photometric data points that I carefully measure (using photometry from SDSS, 2MASS, WISE, and Spitzer) and that I retrieve from catalogues (IRAS, AKARI, and ISO) to perform UV to FIR SED-fitting with CIGALE (Code Investigating GALaxy Emission) for 34 U/LIRGs from the IRAS 2 Jy Redshift Survey with 0.01 < z < 0.16. I find evidence that the nuclear starburst forms first in U/LIRGs, and also find that U/LIRGs with relatively similar SFRs show increased AGN activity if they are older. However, I also find that a young U/LIRG can show a relatively large amount of AGN activity if a very large starburst is present. Then, I quantify the timescales at which the starburst activity in my U/LIRGs evolves with the use of the Tukey-Kramer method of statistical analysis, and fit an exponential curve to the data to describe the expected amount of decrease in SFR seen for a U/LIRG in my sample over a given change in starburst age. Finally, I find evidence that the stellar mass and starburst mass fractions influence whether a U/LIRG in my sample will have a strong AGN and SFR, respectively. I compare the SFR-Mstar relationship seen in my sample with those predicted by models and found from previous observations. I find that the U/LIRGs with older starbursts (>125 Myr) agree with previous results, while those with younger starbursts show a large dispersion in Mstar. I conclude that this is supporting evidence that the star formation histories and timescales at which the IR power sources in U/LIRGs evolve are responsible for the scatter found for the SFR-Mstar relationship. U/LIRGs that form from merging gas-rich disk galaxies could also represent a stage of galaxy evolution involving heavy formation of globular clusters (GCs). It has been suggested that a large number of stellar clusters form during the merging of two gas-rich disk galaxies, leading to open and young massive clusters with the latter likely evolving into GCs. Furthering our understanding of GC formation can uncover the connection between GCs and their host galaxies, which could, at some point during their formation or evolution, be U/LIRGs. To understand GC formation in the context of hierarchical galaxy formation, it is necessary to understand the origin of their abundance patterns. To this effort, I use SDSS spectra from Data Release 8 and 9 to estimate carbon (C) abundances for five GCs by matching synthetic spectra, created with TURBOSPECTRUM using atmospheric parameters derived from the Segue Stellar Parameter Pipeline, with observed spectra at the CH G-band feature. I find large spreads in the C abundances throughout the color magnitude diagrams of the GCs, which serves as evidence for multiple stellar populations, in contrast to standard models of GC formation. (Abstract shortened by UMI.)

STANDARD BIG BANG NUCLEOSYNTHESIS UP TO CNO WITH AN IMPROVED EXTENDED NUCLEAR NETWORK

DOE Office of Scientific and Technical Information (OSTI.GOV)

Coc, Alain; Goriely, Stephane; Xu, Yi

Primordial or big bang nucleosynthesis (BBN) is one of the three strong pieces of evidence for the big bang model together with the expansion of the universe and cosmic microwave background radiation. In this study, we improve the standard BBN calculations taking into account new nuclear physics analyses and enlarge the nuclear network up to sodium. This is, in particular, important to evaluate the primitive value of CNO mass fraction that could affect Population III stellar evolution. For the first time we list the complete network of more than 400 reactions with references to the origin of the rates, includingmore » Almost-Equal-To 270 reaction rates calculated using the TALYS code. Together with the cosmological light elements, we calculate the primordial beryllium, boron, carbon, nitrogen, and oxygen nuclei. We performed a sensitivity study to identify the important reactions for CNO, {sup 9}Be, and boron nucleosynthesis. We re-evaluated those important reaction rates using experimental data and/or theoretical evaluations. The results are compared with precedent calculations: a primordial beryllium abundance increase by a factor of four compared to its previous evaluation, but we note a stability for B/H and for the CNO/H abundance ratio that remains close to its previous value of 0.7 Multiplication-Sign 10{sup -15}. On the other hand, the extension of the nuclear network has not changed the {sup 7}Li value, so its abundance is still 3-4 times greater than its observed spectroscopic value.« less

Reprint of: Reaction measurements with the Jet Experiments in Nuclear Structure and Astrophysics (JENSA) gas jet target

NASA Astrophysics Data System (ADS)

Chipps, K. A.

2018-01-01

Explosive stellar environments are sometimes driven by nuclear reactions on short-lived, radioactive nuclei. These reactions often drive the stellar explosion, alter the observable light curves produced, and dictate the final abundances of the isotopes created. Unfortunately, many reaction rates at stellar temperatures cannot be directly measured in the laboratory, due to the physical limitations of ultra-low cross sections and high background rates. An additional complication arises because many of the important reactions involve radioactive nuclei which have lifetimes too short to be made into a target. As such, direct reactions require very intense and pure beams of exotic nuclei. Indirect approaches with both stable and radioactive beams can, however, provide crucial information on the nuclei involved in these astrophysical reactions. A major development toward both direct and indirect studies of nuclear reactions rates is the commissioning of the Jet Experiments in Nuclear Structure and Astrophysics (JENSA) supersonic gas jet target. The JENSA system provides a pure, homogeneous, highly localized, dense, and robust gaseous target for radioactive ion beam studies. Charged-particle reactions measurements made with gas jet targets can be cleaner and display better resolution than with traditional targets. With the availability of pure and localized gas jet targets in combination with developments in exotic radioactive ion beams and next-generation detector systems, the range of reaction studies that are experimentally possible is vastly expanded. Various representative cases will be discussed.

Cross Section Measurements of the Reaction 23Na(p, γ)24Mg

NASA Astrophysics Data System (ADS)

Boeltzig, Axel; Deboer, Richard James; Macon, Kevin; Wiescher, Michael; Best, Andreas; Imbriani, Gianluca; Gyürky, György; Strieder, Frank

2017-09-01

The reaction 23Na(p, γ)24Mg can provide a link from the NeNa to the MgAl cycle in stellar burning and is therefore of interest in nuclear astrophysics. To determine the reaction rates at stellar temperatures, new cross section measurements at low proton energies have been performed recently, and further experiments are underway. The current cross section data implies that the reaction rate up to temperatures of 1 GK is determined by a few narrow resonances and direct capture. Complementary to these experimental efforts at low proton energies, cross section measurements at higher energies can help to constrain the direct capture and broad resonance contributions to the cross section and reduce the uncertainty of the extrapolation towards stellar energies. In this paper we report an experiment to measure the 23Na(p, γ)24Mg cross section with a solid target setup at the St. ANA 5U accelerator at the University of Notre Dame. The experiment and the current status of data analysis will be described. This work benefited from support by the National Science Foundation under Grant No. PHY-1430152 (JINA-CEE), the Nuclear Science Laboratory (NSL), the Istituto Nazionale di Fisica Nucleare (INFN), and the Gran Sasso Science Institute (GSSI).

The nature of very low luminosity objects (VeLLOs)

NASA Astrophysics Data System (ADS)

Vorobyov, Eduard I.; Elbakyan, Vardan; Dunham, Michael M.; Guedel, Manuel

2017-04-01

Aims: The nature of very low luminosity objects (VeLLOs) with the internal luminosity Lobj ≤ 0.1 L⊙ is investigated by means of numerical modeling coupling the core collapse simulations with the stellar evolution calculations. Methods: The gravitational collapse of a large sample of model cores in the mass range 0.1-2.0 M⊙ is investigated. Numerical simulations were started at the pre-stellar phase and terminated at the end of the embedded phase when 90% of the initial core mass had been accreted onto the forming protostar plus disk system. The disk formation and evolution was studied using numerical hydrodynamics simulations, while the formation and evolution of the central star was calculated using a stellar evolution code. Three scenarios for mass accretion from the disk onto the star were considered: hybrid accretion in which a fraction of accreted energy absorbed by the protostar depends on the accretion rate, hot accretion wherein a fraction of accreted energy is constant, and cold accretion wherein all accretion energy is radiated away. Results: Our conclusions on the nature of VeLLOs depend crucially on the character of protostellar accretion. In the hybrid accretion scenario, most VeLLOs (90.6%) are expected to be the first hydrostatic cores (FHSCs) and only a small fraction (9.4%) are true protostars. In the hot accretion scenario, all VeLLOs are FHSCs due to overly high photospheric luminosity of protostars. In the cold accretion scenario, on the contrary, the majority of VeLLOs belong to the Class I phase of stellar evolution. The reason is that the stellar photospheric luminosity, which sets the floor for the total internal luminosity of a young star, is lower in cold accretion, thus enabling more VeLLOs in the protostellar stage. VeLLOs are relatively rare objects occupying 7%-11% of the total duration of the embedded phase and their masses do not exceed 0.3 M⊙. When compared with published observations inferring a fraction of VeLLOs in the protostellar stage of 6.25%, we find that cold accretion provides a much better fit to observations than hybrid accretion (5.7% for cold accretion vs. 0.7% for hybrid accretion). Both accretion scenarios predict more VeLLOs in the Class I phase than in the Class 0 phase, in contrast to observations. Finally, when accretion variability with episodic bursts is artificially filtered out from our numerically derived accretion rates, the fraction of VeLLOs in the protostellar stage drops significantly, suggesting a causal link between the two phenomena.

A Physical Parameterization of the Evolution of X-ray Binary Emission

NASA Astrophysics Data System (ADS)

Gilbertson, Woodrow; Lehmer, Bret; Eufrasio, Rafael

2018-01-01

The Chandra Deep Field-South (CDF-S) and North (CDF-N) surveys, 7 Ms and 2 Ms respectively, contain measurements spanning a large redshift range of z = 0 to 7. These data-rich fields provide a unique window into the cosmic history of X-ray emission from normal galaxies (i.e., not dominated by AGN). Scaling relations between normal-galaxy X-ray luminosity and quantities, such as star formation rate (SFR) and stellar mass (M*), have been used to constrain the redshift evolution of the formation rates of low-mass X-ray binaries (LMXB) and high-mass X-ray binaries (HMXB). However, these measurements do not directly reveal the driving forces behind the redshift evolution of X-ray binaries (XRBs). We hypothesize that changes in the mean stellar age and metallicity of the Universe drive the evolution of LMXB and HMXB emission, respectively. We use star-formation histories, derived through fitting broad-band UV-to-far-IR spectra, to estimate the masses of stellar populations in various age bins for each galaxy. We then divide our galaxy samples into bins of metallicity, and use our star-formation history information and measured X-ray luminosities to determine for each metallicity bin a best model LX/M*(tage). We show that this physical model provides a more useful parameterization of the evolution of X-ray binary emission, as it can be extrapolated out to high redshifts with more sensible predictions. This meaningful relation can be used to better estimate the emission of XRBs in the early Universe, where XRBs are predicted to play an important role in heating the intergalactic medium.

Evolution and seismology of Procyon

NASA Technical Reports Server (NTRS)

Guenther, D. B.; Demarque, P.

1993-01-01

We have calculated an array of stellar models for Procyon A that are based on the best physics available to us, including the latest opacities and nuclear cross sections. The array of models spans the error space centered on Procyon's mass, chemical composition, effective temperature, and luminosity. We find that with OPAL opacities no convective overshoot is needed at the edge of the convective core to match Procyon's position in the H-R diagram. We discuss the discrepancy between the astrophysical mass and the astrometric mass, which is reduced by the more up-to-date physics in the models, and describe how oscillation data can be used to distinguish among the possible models and help resolve the discrepancy. We have calculated oscillation frequencies for the l = 0, 1, 2, and 3 p-modes and oscillation periods for the l = 1, 2, and 3 g-modes for several of these models.

PROBING WOLF–RAYET WINDS: CHANDRA/HETG X-RAY SPECTRA OF WR 6

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huenemoerder, David P.; Schulz, N. S.; Gayley, K. G.

With a deep Chandra/HETGS exposure of WR 6, we have resolved emission lines whose profiles show that the X-rays originate from a uniformly expanding spherical wind of high X-ray-continuum optical depth. The presence of strong helium-like forbidden lines places the source of X-ray emission at tens to hundreds of stellar radii from the photosphere. Variability was present in X-rays and simultaneous optical photometry, but neither were correlated with the known period of the system or with each other. An enhanced abundance of sodium revealed nuclear-processed material, a quantity related to the evolutionary state of the star. The characterization of themore » extent and nature of the hot plasma in WR 6 will help to pave the way to a more fundamental theoretical understanding of the winds and evolution of massive stars.« less

Hydrodynamic Studies of Turbulent AGN Tori

NASA Astrophysics Data System (ADS)

Schartmann, M.; Meisenheimer, K.; Klahr, H.; Camenzind, M.; Wolf, S.; Henning, Th.; Burkert, A.; Krause, M.

Recently, the MID-infrared Interferometric instrument (MIDI) at the VLTI has shown that dust tori in the two nearby Seyfert galaxies NGC 1068 and the Circinus galaxy are geometrically thick and can be well described by a thin, warm central disk, surrounded by a colder and fluffy torus component. By carrying out hydrodynamical simulations with the help of the TRAMP code (Klahr et al. 1999), we follow the evolution of a young nuclear star cluster in terms of discrete mass-loss and energy injection from stellar processes. This naturally leads to a filamentary large scale torus component, where cold gas is able to flow radially inwards. The filaments join into a dense and very turbulent disk structure. In a post-processing step, we calculate spectral energy distributions and images with the 3D radiative transfer code MC3D Wolf (2003) and compare them to observations. Turbulence in the dense disk component is investigated in a separate project.

The Multi-dimensional Character of Core-collapse Supernovae

DOE PAGES

Hix, W. R.; Lentz, E. J.; Bruenn, S. W.; ...

2016-03-01

Core-collapse supernovae, the culmination of massive stellar evolution, are spectacular astronomical events and the principle actors in the story of our elemental origins. Our understanding of these events, while still incomplete, centers around a neutrino-driven central engine that is highly hydrodynamically unstable. Increasingly sophisticated simulations reveal a shock that stalls for hundreds of milliseconds before reviving. Though brought back to life by neutrino heating, the development of the supernova explosion is inextricably linked to multi-dimensional fluid flows. In this paper, the outcomes of three-dimensional simulations that include sophisticated nuclear physics and spectral neutrino transport are juxtaposed to learn about themore » nature of the three-dimensional fluid flow that shapes the explosion. Comparison is also made between the results of simulations in spherical symmetry from several groups, to give ourselves confidence in the understanding derived from this juxtaposition.« less

The KONA Survey: A Near-IR Perspective of the Circumnuclear Environment of local Seyfert Galaxies

NASA Astrophysics Data System (ADS)

Hicks, Erin K. S.; Mueller Sanchez, Francisco; Malkan, Matthew Arnold

2018-06-01

With the Keck OSIRIS Nearby AGN, KONA, survey we simultaneously probe the stellar, molecular gas, and ionized gas kinematics within the central 400 pc of a sample of 40 local representative AGN. KONA's spatially resolved spectra enable an unprecedented study of the feeding and feedback processes in bona- fide AGN. We present a study the nuclear K-band properties of these local Seyferts, as well as the integrated molecular hydrogen and stellar distribution and kinematic at radii varying from 25 to 200 pc. We find that the luminosities of the unresolved Seyfert 1 sources at 2.1 microns are correlated with the hard X-ray luminosities over 3 orders of magnitude in both K-band and X-ray luminosities, implying that the majority of the emission is non-stellar. No correlation is found between the 2.1 microns luminosity and hard X-ray luminosity for the Seyfert 2 galaxies. The spatial extent and spectral slope of the Seyfert 2 galaxies indicates the presence of nuclear star formation and attenuating material (gas and dust), which is found to be compact in some galaxies and in others extended. A comparison of the circumnuclear stellar and molecular hydrogen properties (flux distribution, surface brightness, and velocity dispersion) in Seyfert 1 and 2 sources will also be presented.

sunstardb: A Database for the Study of Stellar Magnetism and the Solar-stellar Connection

NASA Astrophysics Data System (ADS)

Egeland, Ricky

2018-05-01

The “solar-stellar connection” began as a relatively small field of research focused on understanding the processes that generate magnetic fields in stars and sometimes lead to a cyclic pattern of long-term variability in activity, as demonstrated by our Sun. This area of study has recently become more broadly pertinent to questions of exoplanet habitability and exo-space weather, as well as stellar evolution. In contrast to other areas of stellar research, individual stars in the solar-stellar connection often have a distinct identity and character in the literature, due primarily to the rarity of the decades-long time-series that are necessary for studying stellar activity cycles. Furthermore, the underlying stellar dynamo is not well understood theoretically, and is thought to be sensitive to several stellar properties, e.g., luminosity, differential rotation, and the depth of the convection zone, which in turn are often parameterized by other more readily available properties. Relevant observations are scattered throughout the literature and existing stellar databases, and consolidating information for new studies is a tedious and laborious exercise. To accelerate research in this area I developed sunstardb, a relational database of stellar properties and magnetic activity proxy time-series keyed by individual named stars. The organization of the data eliminates the need for the problematic catalog cross-matching operations inherent when building an analysis data set from heterogeneous sources. In this article I describe the principles behind sunstardb, the data structures and programming interfaces, as well as use cases from solar-stellar connection research.

VEGAS-SSS: A VST Early-Type GAlaxy Survey: Analysis of Small Stellar System

NASA Astrophysics Data System (ADS)

Cantiello, M.

VEGAS-SSS is a program devoted to study the properties of small stellar systems (SSSs) around bright galaxies, built on the VEGAS survey. At completion, the survey will have collected detailed photometric information of ˜ 100 bright early-type galaxies to study the properties of diffuse light (surface brightness, colours, SBF, etc.) and the clustered light (compact stellar systems) out to previously unreached projected galactocentric radii. VEGAS-SSS will define an accurate and homogeneous dataset that will have an important legacy value for studies of the evolution and transformation processes taking place in galaxies through the fossil information provided by SSSs.

Understanding the Early Evolution of M dwarf Extreme Ultraviolet Radiation

NASA Astrophysics Data System (ADS)

Peacock, Sarah; Barman, Travis; Shkolnik, Evgenya

2015-11-01

The chemistry and evolution of planetary atmospheres depends on the evolution of high-energy radiation emitted by its host star. High levels of extreme ultraviolet (EUV) radiation can drastically alter the atmospheres of terrestrial planets through ionizing, heating, expanding, chemically modifying and eroding them during the first few billion years of a planetary lifetime. While there is evidence that stars emit their highest levels of far and near ultraviolet (FUV; NUV) radiation in the earliest stages of their evolution, we are currently unable to directly measure the EUV radiation. Most previous stellar atmosphere models under-predict FUV and EUV emission from M dwarfs; here we present new models for M stars that include prescriptions for the hot, lowest density atmospheric layers (chromosphere, transition region and corona), from which this radiation is emitted. By comparing our model spectra to GALEX near and far ultraviolet fluxes, we are able to predict the evolution of EUV radiation for M dwarfs from 10 Myr to a few Gyr. This research is the next major step in the HAZMAT (HAbitable Zones and M dwarf Activity across Time) project to analyze how the habitable zone evolves with the evolving properties of stellar and planetary atmospheres.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sonnenfeld, Alessandro; Treu, Tommaso; Marshall, Philip J.

Here, we investigate the cosmic evolution of the internal structure of massive early-type galaxies over half of the age of the universe. We also perform a joint lensing and stellar dynamics analysis of a sample of 81 strong lenses from the Strong Lensing Legacy Survey and Sloan ACS Lens Survey and combine the results with a hierarchical Bayesian inference method to measure the distribution of dark matter mass and stellar initial mass function (IMF) across the population of massive early-type galaxies. Lensing selection effects are taken into account. Furthermore, we found that the dark matter mass projected within the innermore » 5 kpc increases for increasing redshift, decreases for increasing stellar mass density, but is roughly constant along the evolutionary tracks of early-type galaxies. The average dark matter slope is consistent with that of a Navarro-Frenk-White profile, but is not well constrained. The stellar IMF normalization is close to a Salpeter IMF at log M * = 11.5 and scales strongly with increasing stellar mass. No dependence of the IMF on redshift or stellar mass density is detected. The anti-correlation between dark matter mass and stellar mass density supports the idea of mergers being more frequent in more massive dark matter halos.« less

Star Formation in the Central Regions of Galaxies

NASA Astrophysics Data System (ADS)

Tsai, Mengchun

2015-08-01

The galactic central region connects the galactic nucleus to the host galaxy. If the central black hole co-evolved with the host galaxies, there should be some evidence left in the central region. We use the environmental properties in the central regions such as star-forming activity, stellar population and molecular abundance to figure out a possible scenario of the evolution of galaxies. In this thesis at first we investigated the properties of the central regions in the host galaxies of active and normal galaxies. We used radio emission around the nuclei of the host galaxies to represent activity of active galactic nuclei (AGNs), and used infrared ray (IR) emission to represent the star-forming activity and stellar population of the host galaxies. We determined that active galaxies have higher stellar masses (SMs) within the central kiloparsec radius than normal galaxies do independent of the Hubble types of the host galaxies; but both active and normal galaxies exhibit similar specific star formation rates (SSFRs). We also discovered that certain AGNs exhibit substantial inner stellar structures in the IR images; most of the AGNs with inner structures are Seyferts, whereas only a few LINERs exhibit inner structures. We note that the AGNs with inner structures show a positive correlation between the radio activity of the AGNs and the SFRs of the host galaxies, but the sources without inner structures show a negative correlation between the radio power and the SFRs. These results might be explained with a scenario of starburst-AGN evolution. In this scenario, AGN activities are triggered following a nuclear starburst; during the evolution, AGN activities are accompanied by SF activity in the inner regions of the host galaxies; at the final stage of the evolution, the AGNs might transform into LINERs, exhibiting weak SF activity in the central regions of the host galaxies. For further investigation about the inner structure, we choose the most nearby and luminous Seyfert galaxy with inner structure as an example. In this thesis, we present CO(3-2) interferometric observations of the central region of the Seyfert 2 galaxy NGC1068 using the Submillimeter Array, together with CO(1-0) data taken with the Owens Valley Radio Observatory Millimeter Array. Both the CO(3-2) and CO(1-0) emission lines are mainly distributed within ~5 arcsec of the nucleus and along the spiral arms, but the intensity distributions show differences; the CO(3-2) map peaks in the nucleus, while the CO(1-0) emission is mainly located along the spiral arms. The CO(3-2)/CO(1-0) ratio is about 3.1 in the nucleus, which is four times as large as the average line ratio in the spiral arms, suggesting that the molecular gas there must be affected by the radiation arising from the AGN. On the other hand, the line ratios in the spiral arms vary over a wide range from 0.24 to 2.34 with a average value around 0.75, which is similar to the line ratios of star-formation regions, indicating that the molecular gas is affected by star formation. Besides, we see a tight correlation between CO(3-2)/(1-0) ratios in the spiral arms and star formation rate surface densities derived from Spitzer 8 micron dust flux densities. We also compare the CO(3-2)/(1-0) ratio and the star formation rate at different positions within the spiral arms; both are found to decrease as the radius from the nucleus increases.

Helium stars: Towards an understanding of Wolf-Rayet evolution

NASA Astrophysics Data System (ADS)

McClelland, Liam A. S.; Eldridge, J. J.

2017-11-01

Recent observational modelling of the atmospheres of hydrogen-free Wolf-Rayet stars have indicated that their stellar surfaces are cooler than those predicted by the latest stellar evolution models. We have created a large grid of pure helium star models to investigate the dependence of the surface temperatures on factors such as the rate of mass loss and the amount of clumping in the outer convection zone. Upon comparing our results with Galactic and LMC WR observations, we find that the outer convection zones should be clumped and that the mass-loss rates need to be slightly reduced. We discuss the implications of these findings in terms of the detectability of Type Ibc supernovae progenitors, and in terms of refining the Conti scenario.

Dynamical evolution of dense star clusters in galactic nuclei

NASA Astrophysics Data System (ADS)

Haas, Jaroslav; Šubr, Ladislav

2014-05-01

By means of direct numerical N-body modeling, we investigate the orbital evolution of an initially thin, central mass dominated stellar disk. We include the perturbative gravitational influence of an extended spherically symmetric star cluster and the mutual gravitational interaction of the stars within the disk. Our results show that the two-body relaxation of the disk leads to significant changes of its radial density profile. In particular, the disk naturally evolves, for a variety of initial configurations, a similar broken power-law surface density profile. Hence, it appears that the single power-law surface density profile ∝R -2 suggested by various authors to describe the young stellar disk observed in the Sgr A* region does not match theoretical expectations.

Astrophysics of Red Supergiants

NASA Astrophysics Data System (ADS)

Levesque, Emily M.

2017-12-01

'Astrophysics of Red Supergiants' is the first book of its kind devoted to our current knowledge of red supergiant stars, a key evolutionary phase that is critical to our larger understanding of massive stars. It provides a comprehensive overview of the fundamental physical properties of red supergiants, their evolution, and their extragalactic and cosmological applications. It serves as a reference for researchers from a broad range of fields (including stellar astrophysics, supernovae, and high-redshift galaxies) who are interested in red supergiants as extreme stages of stellar evolution, dust producers, supernova progenitors, extragalactic metallicity indicators, members of massive binaries and mergers, or simply as compelling objects in their own right. The book is accessible to a range of experience levels, from graduate students up to senior researchers.

SciDAC Computational Astrophysics Consortium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burrows, Adam

Supernova explosions are the central events in nuclear astrophysics. The core-collapse variety is a major source for the universe's heavy elements. The neutron stars, pulsars, and stellar-mass black holes of high-energy astrophysics are their products. Given their prodigious explosion energies, they are the major agencies of change in the interstellar medium, driving star formation and the evolution of galaxies. Their gas remnants are the birthplaces of the cosmic rays. Such is their brightness that they can be used as standard candles to measure the size and geometry of the universe. Recently, there is evidence that gamma-ray bursts (GRBs) originate inmore » a small fraction of core collapses, thereby connecting two of the most energetic phenomena in the universe. However, the mechanism by which core-collapse supernovae explode has not yet been unambiguously determined. Arguably, this is one of the great unsolved problems in modern astrophysics and its investigation draws on nuclear physics, particle physics, radiative transfer, kinetic theory, gravitational physics, thermodynamics, and the numerical arts. Hence, supernovae are unrivaled astrophysical laboratories. It is the quest for the mechanism and new insights our team has recently had that motivate this proposal.« less

A Multiphysics and Multiscale Software Environment for Modeling Astrophysical Systems

NASA Astrophysics Data System (ADS)

Portegies Zwart, Simon; McMillan, Steve; O'Nualláin, Breanndán; Heggie, Douglas; Lombardi, James; Hut, Piet; Banerjee, Sambaran; Belkus, Houria; Fragos, Tassos; Fregeau, John; Fuji, Michiko; Gaburov, Evghenii; Glebbeek, Evert; Groen, Derek; Harfst, Stefan; Izzard, Rob; Jurić, Mario; Justham, Stephen; Teuben, Peter; van Bever, Joris; Yaron, Ofer; Zemp, Marcel

We present MUSE, a software framework for tying together existing computational tools for different astrophysical domains into a single multiphysics, multiscale workload. MUSE facilitates the coupling of existing codes written in different languages by providing inter-language tools and by specifying an interface between each module and the framework that represents a balance between generality and computational efficiency. This approach allows scientists to use combinations of codes to solve highly-coupled problems without the need to write new codes for other domains or significantly alter their existing codes. MUSE currently incorporates the domains of stellar dynamics, stellar evolution and stellar hydrodynamics for a generalized stellar systems workload. MUSE has now reached a "Noah's Ark" milestone, with two available numerical solvers for each domain. MUSE can treat small stellar associations, galaxies and everything in between, including planetary systems, dense stellar clusters and galactic nuclei. Here we demonstrate an examples calculated with MUSE: the merger of two galaxies. In addition we demonstrate the working of MUSE on a distributed computer. The current MUSE code base is publicly available as open source at http://muse.li.

The resolved history of galaxy evolution.

PubMed

Brinchmann, Jarle

2002-12-15

We briefly review the study of the evolution of galaxies from an observational point of view, with particular emphasis on the role of the Hubble Space Telescope in probing the evolution of the different morphological types of galaxy. We show how using the stellar mass of galaxies as a tracer of evolution can improve our understanding of the physical process taking place before turning our eyes towards the future and giving an overview of what we can expect from future advances in technology.

Early dynamical evolution of young substructured clusters

NASA Astrophysics Data System (ADS)

Dorval, Julien; Boily, Christian

2017-03-01

Stellar clusters form with a high level of substructure, inherited from the molecular cloud and the star formation process. Evidence from observations and simulations also indicate the stars in such young clusters form a subvirial system. The subsequent dynamical evolution can cause important mass loss, ejecting a large part of the birth population in the field. It can also imprint the stellar population and still be inferred from observations of evolved clusters. Nbody simulations allow a better understanding of these early twists and turns, given realistic initial conditions. Nowadays, substructured, clumpy young clusters are usually obtained through pseudo-fractal growth and velocity inheritance. We introduce a new way to create clumpy initial conditions through a ''Hubble expansion'' which naturally produces self consistent clumps, velocity-wise. In depth analysis of the resulting clumps shows consistency with hydrodynamical simulations of young star clusters. We use these initial conditions to investigate the dynamical evolution of young subvirial clusters. We find the collapse to be soft, with hierarchical merging leading to a high level of mass segregation. The subsequent evolution is less pronounced than the equilibrium achieved from a cold collapse formation scenario.

Galactic Abundance Patterns via Peimbert Types I & II Planetary Nebulae

NASA Astrophysics Data System (ADS)

Milingo, J. B.; Barnes, K. L.; Kwitter, K. B.; Souza, S. P.; Henry, R. B. C.; Skinner, J. N.

2005-12-01

Planetary Nebulae (PNe) are well known fonts of information about both stellar evolution and galactic chemical evolution. Abundance patterns in PNe are used to note signatures and constraints of nuclear processing, and as tracers of the distribution of metals throughout galaxies. In this poster abundance gradients and heavy element ratios are presented based upon newly acquired spectrophotometry of a sample of Galactic Peimbert Type I PNe. This new data set is extracted from spectra that extend from λ 3600 - 9600Å allowing the use of [S III] features at λ 9069 and 9532Å. Since a significant portion of S in PNe resides in S+2 and higher ionization stages, including these features improves the extrapolation from observed ion abundances to total element abundance. An alternate metallicity tracer, Sulfur is precluded from enhancement and depletion across the range of PNe progenitor masses. Its stability in intermediate mass stars makes it a useful tool to probe the natal conditions as well as the evolution of PNe progenitors. This is a continuation of our Type II PNe work, the impetus being to compile a relatively large set of line strengths and abundances with internally consistent observation, reduction, calibration, and abundance determination, minimizing systematic affects that come from compiling various data sets. This research is supported by the AAS Small Research Grants program, the Franklin & Marshall Committee on Grants, and NSF grant AST-0307118.

CONVECTION THEORY AND SUB-PHOTOSPHERIC STRATIFICATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arnett, David; Meakin, Casey; Young, Patrick A., E-mail: darnett@as.arizona.ed, E-mail: casey.meakin@gmail.co, E-mail: patrick.young.1@asu.ed

2010-02-20

As a preliminary step toward a complete theoretical integration of three-dimensional compressible hydrodynamic simulations into stellar evolution, convection at the surface and sub-surface layers of the Sun is re-examined, from a restricted point of view, in the language of mixing-length theory (MLT). Requiring that MLT use a hydrodynamically realistic dissipation length gives a new constraint on solar models. While the stellar structure which results is similar to that obtained by Yale Rotational Evolution Code (Guenther et al.; Bahcall and Pinsonneault) and Garching models (Schlattl et al.), the theoretical picture differs. A new quantitative connection is made between macro-turbulence, micro-turbulence, andmore » the convective velocity scale at the photosphere, which has finite values. The 'geometric parameter' in MLT is found to correspond more reasonably with the thickness of the superadiabatic region (SAR), as it must for consistency in MLT, and its integrated effect may correspond to that of the strong downward plumes which drive convection (Stein and Nordlund), and thus has a physical interpretation even in MLT. If we crudely require the thickness of the SAR to be consistent with the 'geometric factor' used in MLT, there is no longer a free parameter, at least in principle. Use of three-dimensional simulations of both adiabatic convection and stellar atmospheres will allow the determination of the dissipation length and the geometric parameter (i.e., the entropy jump) more realistically, and with no astronomical calibration. A physically realistic treatment of convection in stellar evolution will require substantial additional modifications beyond MLT, including nonlocal effects of kinetic energy flux, entrainment (the most dramatic difference from MLT found by Meakin and Arnett), rotation, and magnetic fields.« less

The Metallicity Evolution of Low Mass Galaxies: New Contraints at Intermediate Redshift

NASA Technical Reports Server (NTRS)

Henry, Alaina; Martin, Crystal L.; Finlator, Kristian; Dressler, Alan

2013-01-01

We present abundance measurements from 26 emission-line-selected galaxies at z approx. 0.6-0.7. By reaching stellar masses as low as 10(exp 8) M stellar mass, these observations provide the first measurement of the intermediate-redshift mass-metallicity (MZ) relation below 10(exp 9)M stellar mass. For the portion of our sample above M is greater than 10(exp 9)M (8/26 galaxies), we find good agreement with previous measurements of the intermediate-redshift MZ relation. Compared to the local relation, we measure an evolution that corresponds to a 0.12 dex decrease in oxygen abundances at intermediate redshifts. This result confirms the trend that metallicity evolution becomes more significant toward lower stellar masses, in keeping with a downsizing scenario where low-mass galaxies evolve onto the local MZ relation at later cosmic times. We show that these galaxies follow the local fundamental metallicity relation, where objects with higher specific (mass-normalized) star formation rates (SFRs) have lower metallicities. Furthermore, we show that the galaxies in our sample lie on an extrapolation of the SFR-M* relation (the star-forming main sequence). Leveraging the MZ relation and star-forming main sequence (and combining our data with higher-mass measurements from the literature), we test models that assume an equilibrium between mass inflow, outflow, and star formation.We find that outflows are required to describe the data. By comparing different outflow prescriptions, we show that momentum, driven winds can describe the MZ relation; however, this model underpredicts the amount of star formation in low-mass galaxies. This disagreement may indicate that preventive feedback from gas heating has been overestimated, or it may signify a more fundamental deviation from the equilibrium assumption.

The Evolution of Normal Galaxy X-Ray Emission Through Cosmic History: Constraints from the 6 MS Chandra Deep Field-South

NASA Technical Reports Server (NTRS)

Lehmer, B. D.; Basu-Zych, A. R.; Mineo, S.; Brandt, W. N.; Eurfrasio, R. T.; Fragos, T.; Hornschemeier, A. E.; Lou, B.; Xue, Y. Q.; Bauer, F. E.;

Using dust, gas and stellar mass-selected samples to probe dust sources and sinks in low-metallicity galaxies

NASA Astrophysics Data System (ADS)

De Vis, P.; Gomez, H. L.; Schofield, S. P.; Maddox, S.; Dunne, L.; Baes, M.; Cigan, P.; Clark, C. J. R.; Gomez, E. L.; Lara-López, M.; Owers, M.

2017-10-01

We combine samples of nearby galaxies with Herschel photometry selected on their dust, metal, H I and stellar mass content, and compare these to chemical evolution models in order to discriminate between different dust sources. In a companion paper, we used an H I-selected sample of nearby galaxies to reveal a subsample of very gas-rich (gas fraction >80 per cent) sources with dust masses significantly below predictions from simple chemical evolution models, and well below Md/M* and Md/Mgas scaling relations seen in dust and stellar-selected samples of local galaxies. We use a chemical evolution model to explain these dust-poor, but gas-rich, sources as well as the observed star formation rates (SFRs) and dust-to-gas ratios. We find that (I) a delayed star formation history is required to model the observed SFRs; (II) inflows and outflows are required to model the observed metallicities at low gas fractions; (III) a reduced contribution of dust from supernovae (SNe) is needed to explain the dust-poor sources with high gas fractions. These dust-poor, low stellar mass galaxies require a typical core-collapse SN to produce 0.01-0.16 M⊙ of dust. To match the observed dust masses at lower gas fractions, significant grain growth is required to counteract the reduced contribution from dust in SNe and dust destruction from SN shocks. These findings are statistically robust, though due to intrinsic scatter it is not always possible to find one single model that successfully describes all the data. We also show that the dust-to-metal ratio decreases towards lower metallicity.

Variations of the stellar initial mass function in semi-analytical models - II. The impact of cosmic ray regulation

NASA Astrophysics Data System (ADS)

Fontanot, Fabio; De Lucia, Gabriella; Xie, Lizhi; Hirschmann, Michaela; Bruzual, Gustavo; Charlot, Stéphane

2018-04-01

Recent studies proposed that cosmic rays (CRs) are a key ingredient in setting the conditions for star formation, thanks to their ability to alter the thermal and chemical state of dense gas in the ultraviolet-shielded cores of molecular clouds. In this paper, we explore their role as regulators of the stellar initial mass function (IMF) variations, using the semi-analytic model for GAlaxy Evolution and Assembly (GAEA). The new model confirms our previous results obtained using the integrated galaxy-wide IMF (IGIMF) theory. Both variable IMF models reproduce the observed increase of α-enhancement as a function of stellar mass and the measured z = 0 excess of dynamical mass-to-light ratios with respect to photometric estimates assuming a universal IMF. We focus here on the mismatch between the photometrically derived (M^app_{\\star }) and intrinsic (M⋆) stellar masses, by analysing in detail the evolution of model galaxies with different values of M_{\\star }/M^app_{\\star }. We find that galaxies with small deviations (i.e. formally consistent with a universal IMF hypothesis) are characterized by more extended star formation histories and live in less massive haloes with respect to the bulk of the galaxy population. In particular, the IGIMF theory does not change significantly the mean evolution of model galaxies with respect to the reference model, a CR-regulated IMF instead implies shorter star formation histories and higher peaks of star formation for objects more massive than 1010.5 M⊙. However, we also show that it is difficult to unveil this behaviour from observations, as the key physical quantities are typically derived assuming a universal IMF.

Uncertainties in s-process nucleosynthesis in massive stars determined by Monte Carlo variations

NASA Astrophysics Data System (ADS)

Nishimura, N.; Hirschi, R.; Rauscher, T.; St. J. Murphy, A.; Cescutti, G.

2017-08-01

The s-process in massive stars produces the weak component of the s-process (nuclei up to A ˜ 90), in amounts that match solar abundances. For heavier isotopes, such as barium, production through neutron capture is significantly enhanced in very metal-poor stars with fast rotation. However, detailed theoretical predictions for the resulting final s-process abundances have important uncertainties caused both by the underlying uncertainties in the nuclear physics (principally neutron-capture reaction and β-decay rates) as well as by the stellar evolution modelling. In this work, we investigated the impact of nuclear-physics uncertainties relevant to the s-process in massive stars. Using a Monte Carlo based approach, we performed extensive nuclear reaction network calculations that include newly evaluated upper and lower limits for the individual temperature-dependent reaction rates. We found that most of the uncertainty in the final abundances is caused by uncertainties in the neutron-capture rates, while β-decay rate uncertainties affect only a few nuclei near s-process branchings. The s-process in rotating metal-poor stars shows quantitatively different uncertainties and key reactions, although the qualitative characteristics are similar. We confirmed that our results do not significantly change at different metallicities for fast rotating massive stars in the very low metallicity regime. We highlight which of the identified key reactions are realistic candidates for improved measurement by future experiments.

The U/Th production ratio and the age of the Milky Way from meteorites and Galactic halo stars.

PubMed

Dauphas, Nicolas

2005-06-30

Some heavy elements (with atomic number A > 69) are produced by the 'rapid' (r)-process of nucleosynthesis, where lighter elements are bombarded with a massive flux of neutrons. Although this is characteristic of supernovae and neutron star mergers, uncertainties in where the r-process occurs persist because stellar models are too crude to allow precise quantification of this phenomenon. As a result, there are many uncertainties and assumptions in the models used to calculate the production ratios of actinides (like uranium-238 and thorium-232). Current estimates of the U/Th production ratio range from approximately 0.4 to 0.7. Here I show that the U/Th abundance ratio in meteorites can be used, in conjunction with observations of low-metallicity stars in the halo of the Milky Way, to determine the U/Th production ratio very precisely (0.57(+0.037)(-0.031). This value can be used in future studies to constrain the possible nuclear mass formulae used in r-process calculations, to help determine the source of Galactic cosmic rays, and to date circumstellar grains. I also estimate the age of the Milky Way (14.5(+2.8)(-2.2)Gyr in a way that is independent of the uncertainties associated with fluctuations in the microwave background or models of stellar evolution.

Gas Flows in Dual Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Mueller Sanchez, Francisco; Comerford, Julia M.; Davies, Richard; Treister, Ezequiel; Privon, George C.; Nevin, Becky

2018-06-01

Dual Active Galactic Nuclei (AGN) are the Rosetta stone to understand the role of galaxy mergers in triggering nuclear activity and regulating black hole (BH) and galaxy growth. But very little is known about the physical processes required to effectively trigger AGN activity and regulate the growth of the two BHs. The work I will present here characterizes for the first time the properties of the stars, gas (molecular, ionized, and highly-ionized) and dust in all the confirmed dual AGN at z < 0.05, using Keck/OSIRIS, VLT/SINFONI, SOFIA/FORCAST, and HST data. I will focus on the interplay between the several complex processes observed in dual AGN, using as an example the prototypical merger system NGC 6240: vigorous star formation, two AGNs, outflowing winds of ionized gas, rippling dust and gas lanes, and tidal tails. In this galaxy, we observe for the first time a dual outflow of different species of gas: an AGN-driven outflow of highly-ionized gas to the northeast and a starburst-driven outflow of ionized hydrogen to the northwest. This shows that stellar feedback and supermassive black hole feedback can work in tandem to regulate the stellar growth of a galaxy after a merger event. These results open a new door to studies of dual AGN and AGN pairs in general, and enable dual AGN to be used, for the first time, for studies of galaxy evolution.

MUSE observations of the counter-rotating nuclear ring in NGC 7742

NASA Astrophysics Data System (ADS)

Martinsson, Thomas P. K.; Sarzi, Marc; Knapen, Johan H.; Coccato, Lodovico; Falcón-Barroso, Jesús; Elmegreen, Bruce G.; de Zeeuw, Tim

2018-04-01

Aims: We present results from MUSE observations of the nearly face-on disk galaxy NGC 7742. This galaxy hosts a spectacular nuclear ring of enhanced star formation, which is unusual in that it is hosted by a non-barred galaxy, and because this star formation is most likely fuelled by externally accreted gas that counter-rotates with respect to its main stellar body. Methods: We used the MUSE data to derive the star-formation history (SFH) and accurately measure the stellar and ionized-gas kinematics of NGC 7742 in its nuclear, bulge, ring, and disk regions. Results: We have mapped the previously known gas counter-rotation well outside the ring region and deduce the presence of a slightly warped inner disk, which is inclined at approximately 6° compared to the outer disk. The gas-disk inclination is well constrained from the kinematics; the derived inclination 13.7° ± 0.4° agrees well with that derived from photometry and from what one expects using the inverse Tully-Fisher relation. We find a prolonged SFH in the ring with stellar populations as old as 2-3 Gyr and an indication that the star formation triggered by the minor merger event was delayed in the disk compared to the ring. There are two separate stellar components: an old population that counter-rotates with the gas, and a young one, concentrated to the ring, that co-rotates with the gas. We recover the kinematics of the old stars from a two-component fit, and show that combining the old and young stellar populations results in the erroneous average velocity of nearly zero found from a one-component fit. Conclusions: The spatial resolution and field of view of MUSE allow us to establish the kinematics and SFH of the nuclear ring in NGC 7742. We show further evidence that this ring has its origin in a minor merger event, possibly 2-3 Gyr ago. Data used for the flux and kinematic maps (Figs. 1 and 3-5) are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/612/A66

Is the SDSS ZZ Ceti instability strip really pure?

NASA Astrophysics Data System (ADS)

de Souza Oliveira, Kepler

2006-08-01

We propose to obtain SNR > 60 optical spectra of the DA white dwarf stars for which the Sloan Digital Sky Survey spectra indicated temperatures inside de ZZ Ceti instability strip, but time series photometry show they are not variables. The Sloan spectra have insufficient SNR, specially below 4000A, where there are hydrogen lines whose strength can be used to measure surface gravity accurately. Theoretically and observationally, the location of the instability strip depends both on temperature and mass. To use the properties derived from the pulsating stars as applying to all white dwarf stars, and their progenitors, we must demonstrate pulsation is a normal evolutionary state. As the instability strip is only 1200K wide, accurate temperatures and log g must be obtained and therefore the spectra must include the log g sensitive lines Hgamma to H9. White dwarf stars, the objects of this proposal, are the end point of evolution of around 97% of all stars born. As they cool, they pass through instability strips, where they are seen as multi-periodic pulsators. Each pulsation is an independent measurement, placing another constraint on the stellar properties. Pulsations allow the determination of the stellar compositional layers, including the core, crucial to understand the progenitor's evolution, from AGB to planetary nebulae nuclei, "born again" phase, and their possible evolution to SNIa through accretion. As white dwarf progenitors lose at least half of their masses before turning into white dwarfs, they contribute to the interstellar medium enrichment, and measuring their structure in detail will allow us to decode nuclear reaction rates and convection, which determine their evolution. Pulsating white dwarf stars are also laboratories for physics at high densities as crystallization, neutrino cooling, and axion emission. White dwarf cooling, also measured through pulsations, allows an independent measurement of the age of the galactic components and was the first to indicate an age of 13 Gyr to the Universe, back in 1987. Now that we have observed white dwarf stars in all the components of our galaxy, possible differences in component ages are detectable. Our goal is to determine if the instalibity strip is pure, implying the information we obtain on the variables applies to white dwarf stars in general. As these stars are on average fainter than g=18.2, we require blue sensitive 8m class telescope.