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.

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.

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.

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.

Searching for the pulsar in SN1987A

NASA Astrophysics Data System (ADS)

Staveley-Smith, Lister; Manchester, Dick; Zanardo, Giovanna

2013-10-01

We propose to search for a pulsar in the remnant of SN1987A. The existence of a neutron star formed after the explosion of the progenitor, Sk -69-202, is predicted by stellar evolution theory. Early neutrino detection by three separate ground-based detectors appears to confirm the formation of neutrons. Moreover, recent Compact Array observations hint at the presence of a flat-spectrum component near the centre of the remnant, possibly the result of synchrotron emission from a pulsar-powered nebula. However, the initial mass of the SN1987A progenitor is close to the limit where collapse into a black hole is predicted. It is therefore possible that fallback of matter onto the neutron star resulted in later formation of a black hole, or even a quark star. Detection or otherwise of the SN1987A pulsar would make a powerful contribution to stellar evolution theory.

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.

1961-2011: Fifty years of Hayashi tracks

NASA Astrophysics Data System (ADS)

Palla, Francesco

2012-09-01

Fifty years after the seminal paper by Prof. C. Hayashi, the field of pre-main sequence (PMS) evolution still plays a fundamental role in observational and theoretical astrophysics. In this contribution, I highlight the contribution made by Hayashi in establishing the theoretical foundation of early stellar evolution. Then, I discuss the changes of the classical theory introduced by the inclusion of protostellar evolution in PMS models and present selected results on young stars.

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.

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.

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

An Era of Precision Astrophysics for Exoplanets, Stars, and the Milky Way

NASA Astrophysics Data System (ADS)

Stassun, Keivan G.; Kilodegree Extremely Little Telescope (KELT); Transiting Exoplanet Survey Satellite (TESS); Sloan Digital Sky Survey (SDSS)

2018-06-01

While observing stars teaches us about the physical properties of the stars themselves, that knowledge also is the key to measuring the properties of nearly all exoplanets, and also the history of the Galaxy. Combining data from current and upcoming all-sky surveys, including Gaia, TESS, and the fifth Sloan Digital Sky Survey (SDSS-V), will enable accurate, empirical measurements of fundamental properties for millions of stars throughout the Milky Way—including an increase by four orders of magnitude in the number of stars with reliable parallaxes, two orders of magnitude in the number with ultraprecise light curves, and two orders of magnitude in the number with detailed chemical abundances. We demonstrate that stellar masses, radii, temperatures, distances, space motions, and detailed chemical abundances can now be measured with precisions of order 1%, and with systematics better than ∼5% in most cases. We discuss the transformational advances that such precise stellar measurements promise for exoplanet science, including studies of planetary system architectures, forensic analyses of planet evolution pathways, testing planet formation theories, and even efforts to infer the mineralogy of planets. We also discuss the similarly transformational advances at hand for Galactic archaeology, including studies of stellar micro-populations, testing theories of star formation and of galaxy assembly, and even efforts to trace the chemical "family tree" of the Galaxy through stellar phylogenics. Finally, we discuss the revolution in stellar astrophysics represented by ultraprecise light curves of stars, specifically as probes of stellar interiors and therefore as stress-tests of stellar theory across the Hertzsprung-Russell diagram.

Extrasolar planetary systems.

NASA Technical Reports Server (NTRS)

Huang, S.-S.

1973-01-01

The terms 'planet' and 'planet-like objects' are defined. The observational search for extrasolar planetary systems is described, as performable by earthbound optical telescopes, by space probes, by long baseline radio interferometry, and finally by inference from the reception of signals sent by intelligent beings in other worlds. It is shown that any planetary system must be preceded by a rotating disk of gas and dust around a central mass. A brief review of the theories of the formation of the solar system is given, along with a proposed scheme for classification of these theories. The evidence for magnetic activity in the early stages of stellar evolution is presented. The magnetic braking theories of solar and stellar rotation are discussed, and an estimate is made for the frequency of occurrence of planetary systems in the universe.

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.

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

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.

White dwarf evolution - Cradle-to-grave constraints via pulsation

NASA Technical Reports Server (NTRS)

Kawaler, Steven D.

1990-01-01

White dwarf evolution, particularly in the early phases, is not very strongly constrained by observation. Fortunately, white dwarfs undergo nonradial pulsation in three distinct regions of the H-R diagram. These pulsations provide accurate masses, surface compositional structure and rotation velocities, and help constrain other important physical properties. We demonstrate the application of the tools of stellar seismology to white dwarf evolution using the hot white dwarf star PG 1159-035 and the cool DAV (or ZZ Ceti) stars as examples. From pulsation studies, significant challenges to the theory of white dwarf evolution emerge.

The evolution of kicked stellar-mass black holes in star cluster environments

NASA Astrophysics Data System (ADS)

Webb, Jeremy J.; Leigh, Nathan W. C.; Singh, Abhishek; Ford, K. E. Saavik; McKernan, Barry; Bellovary, Jillian

2018-03-01

We consider how dynamical friction acts on black holes that receive a velocity kick while located at the centre of a gravitational potential, analogous to a star cluster, due to either a natal kick or the anisotropic emission of gravitational waves during a black hole-black hole merger. Our investigation specifically focuses on how well various Chandrasekhar-based dynamical friction models can predict the orbital decay of kicked black holes with mbh ≲ 100 M⊙ due to an inhomogeneous background stellar field. In general, the orbital evolution of a kicked black hole follows that of a damped oscillator where two-body encounters and dynamical friction serve as sources of damping. However, we find models for approximating the effects of dynamical friction do not accurately predict the amount of energy lost by the black hole if the initial kick velocity vk is greater than the stellar velocity dispersion σ. For all kick velocities, we also find that two-body encounters with nearby stars can cause the energy evolution of a kicked BH to stray significantly from standard dynamical friction theory as encounters can sometimes lead to an energy gain. For larger kick velocities, we find the orbital decay of a black hole departs from classical theory completely as the black hole's orbital amplitude decays linearly with time as opposed to exponentially. Therefore, we have developed a linear decay formalism, which scales linearly with black hole mass and v_k/σ in order to account for the variations in the local gravitational potential.

Quantitative results of stellar evolution and pulsation theories.

NASA Technical Reports Server (NTRS)

Fricke, K.; Stobie, R. S.; Strittmatter, P. A.

1971-01-01

The discrepancy between the masses of Cepheid variables deduced from evolution theory and pulsation theory is examined. The effect of input physics on evolutionary tracks is first discussed; in particular, changes in the opacity are considered. The sensitivity of pulsation masses to opacity changes and to the ascribed values of luminosity and effective temperature are then analyzed. The Cepheid mass discrepancy is discussed in the light of the results already obtained. Other astronomical evidence, including the mass-luminosity relation for main sequence stars, the solar neutrino flux, and cluster ages are also considered in an attempt to determine the most likely source of error in the event that substantial mass loss has not occurred.

Stellar dynamics around a massive black hole - II. Resonant relaxation

NASA Astrophysics Data System (ADS)

Sridhar, S.; Touma, Jihad R.

2016-06-01

We present a first-principles theory of resonant relaxation (RR) of a low-mass stellar system orbiting a more massive black hole (MBH). We first extend the kinetic theory of Gilbert to include the Keplerian field of a black hole of mass M•. Specializing to a Keplerian stellar system of mass M ≪ M•, we use the orbit-averaging method of Sridhar & Touma to derive a kinetic equation for RR. This describes the collisional evolution of a system of N ≫ 1 Gaussian rings in a reduced 5-dim space, under the combined actions of self-gravity, 1 post-Newtonian (PN) and 1.5 PN relativistic effects of the MBH and an arbitrary external potential. In general geometries, RR is driven by both apsidal and nodal resonances, so the distinction between scalar RR and vector RR disappears. The system passes through a sequence of quasi-steady secular collisionless equilibria, driven by irreversible two-ring correlations that accrue through gravitational interactions, both direct and collective. This correlation function is related to a `wake function', which is the linear response of the system to the perturbation of a chosen ring. The wake function is easier to appreciate, and satisfies a simpler equation, than the correlation function. We discuss general implications for the interplay of secular dynamics and non-equilibrium statistical mechanics in the evolution of Keplerian stellar systems towards secular thermodynamic equilibria, and set the stage for applications to the RR of axisymmetric discs in Paper III.

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.

Not Alone: Tracing the Origins of Very-Low-Mass Stars and Brown Dwarfs Through Multiplicity Studies

NASA Astrophysics Data System (ADS)

Burgasser, A. J.; Reid, I. N.; Siegler, N.; Close, L.; Allen, P.; Lowrance, P.; Gizis, J.

The properties of multiple stellar systems have long provided important empirical constraints for star-formation theories, enabling (along with several other lines of evidence) a concrete, qualitative picture of the birth and early evolution of normal stars. At very low masses (VLM; M ? 0.1 solar mass), down to and below the hydrogen-burning minimum mass, our understanding of formation processes is not as clear, with several competing theories now under consideration. One means of testing these theories is through the empirical characterization of VLM multiple systems. Here, we review the results of various VLM multiplicity studies to date. These systems can be generally characterized as closely separated (93% have projected separations ? < 20 AU), near equal-mass (77% have M2/M1 ? 0.8) and occurring infrequently (perhaps 10-30% of systems are binary). Both the frequency and maximum separation of stellar and brown dwarf binaries steadily decrease for lower system masses, suggesting that VLM binary formation and/or evolution may be a mass-dependent process. There is evidence for a fairly rapid decline in the number of loosely bound systems below ~0.3 solar mass, corresponding to a factor of 10-20 increase in the minimum binding energy of VLM binaries as compared to more massive stellar binaries. This wide-separation "desert" is present among both field (~1-5 G.y.) and older (>100 m.y.) cluster systems, while the youngest (<10 m.y.) VLM binaries, particularly those in nearby, low-density star-forming regions, appear to have somewhat different systemic properties. We compare these empirical trends to predictions laid out by current formation theories, and outline future observational studies needed to probe the full parameter space of the lowest-mass multiple systems.

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 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

Which evolutionary status does the Blue Large-Amplitude Pulsators stay at?

NASA Astrophysics Data System (ADS)

Wu, Tao; Li, Yan

2018-05-01

Asteroseismology is a very useful tool for exploring the stellar interiors and evolutionary status and for determining stellar fundamental parameters, such as stellar mass, radius, surface gravity, and the stellar mean density. In the present work, we use it to preliminarily analyze the 14 new-type pulsating stars: Blue Large-Amplitude Pulsators (BLAPs) which is observed by OGLE project, to roughly analyze their evolutionary status. We adopt the theory of single star evolution and artificially set the mass loss rate of \\dot{M}=-2× 10^{-4} M_{⊙}/year and mass loss beginning at the radius of R = 40 R_{⊙} on red giant branch to generate a series of theoretical models. Based on these theoretical models and the corresponding observations, we find that those BLAP stars are more likely to be the core helium burning stars. Most of them are in the middle and late phase of the helium burning.

White dwarf stars with carbon atmospheres.

PubMed

Dufour, P; Liebert, J; Fontaine, G; Behara, N

2007-11-22

White dwarfs represent the endpoint of stellar evolution for stars with initial masses between approximately 0.07 and 8-10, where is the mass of the Sun (more massive stars end their life as either black holes or neutron stars). The theory of stellar evolution predicts that the majority of white dwarfs have a core made of carbon and oxygen, which itself is surrounded by a helium layer and, for approximately 80 per cent of known white dwarfs, by an additional hydrogen layer. All white dwarfs therefore have been traditionally found to belong to one of two categories: those with a hydrogen-rich atmosphere (the DA spectral type) and those with a helium-rich atmosphere (the non-DAs). Here we report the discovery of several white dwarfs with atmospheres primarily composed of carbon, with little or no trace of hydrogen or helium. Our analysis shows that the atmospheric parameters found for these stars do not fit satisfactorily in any of the currently known theories of post-asymptotic giant branch evolution, although these objects might be the cooler counterpart of the unique and extensively studied PG 1159 star H1504+65 (refs 4-7). These stars, together with H1504+65, might accordingly form a new evolutionary sequence that follows the asymptotic giant branch.

Dwarf spheroidal galaxies: Keystones of galaxy evolution

NASA Technical Reports Server (NTRS)

Gallagher, John S., III; Wyse, Rosemary F. G.

1994-01-01

Dwarf spheroidal galaxies are the most insignificant extragalactic stellar systems in terms of their visibility, but potentially very significant in terms of their role in the formation and evolution of much more luminous galaxies. We discuss the present observational data and their implications for theories of the formation and evolution of both dwarf and giant galaxies. The putative dark-matter content of these low-surface-brightness systems is of particular interest, as is their chemical evolution. Surveys for new dwarf spheroidals hidden behind the stars of our Galaxy and those which are not bound to giant galaxies may give new clues as to the origins of this unique class of galaxy.

A formulation of convection for stellar structure and evolution calculations without the mixing-length theory approximations. I - Application to the sun

NASA Technical Reports Server (NTRS)

Lydon, Thomas J.; Fox, Peter A.; Sofia, Sabatino

1992-01-01

The problem of treating convective energy transport without MLT approximations is approached here by formulating the results of numerical simulations of convection in terms of energy fluxes. This revised treatment of convective transport can be easily incorporated within existing stellar structure codes. As an example, the technique is applied to the sun. The treatment does not include any free parameters, making the models extremely sensitive to the accuracy of the treatments of opacities, chemical abundances, treatments of the solar atmosphere, and the equation of state.

Precision Astrophysics Experiments with the Kepler Satellite

NASA Astrophysics Data System (ADS)

Jackiewicz, Jason

2012-10-01

Long photometric observations from space of tens of thousands of stars, such as those provided by Kepler, offer unique opportunities to carry out ensemble astrophysics as well as detailed studies of individual objects. One of the primary tools at our disposal for understanding pulsating stars is asteroseismology, which uses observed stellar oscillation frequencies to determine interior properties. This can provide very strict constraints on theories of stellar evolution, structure, and the population characteristics of stars in the Milky Way galaxy. This talk will focus on several of the exciting insights Kepler has enabled through asteroseismology of stars across the H-R diagram.

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.

Tidal Interaction among Red Giants Close Binary Systems in APOGEE Database

NASA Astrophysics Data System (ADS)

Sun, Meng; Arras, Phil; Majewski, Steven R.; Troup, Nicholas William; Weinberg, Nevin N.

2017-01-01

Motivated by the newly discovered close binary systems in the Apache Point Observatory Galactic Evolution Experiment (APOGEE-1), the tidal evolution of binaries containing a red giant branch (RGB) star with a stellar or substellar companion was investigated. The tide raised by the companion in the RGB star leads to exchange of angular momentum between the orbit and the stellar spin, causing the orbit to contract. The tidal dissipation rate is computed using turbulent viscosity acting on the equilibrium tidal flow, where careful attention is paid to the effects of reduced viscosity for close-in companions. Evolutionary models for the RGB stars, from the zero-age main sequence to the present, were acquired from the MESA code. "Standard" turbulent viscosity gives rise to such a large orbital decay that many observed systems have decay times much shorter than the RGB evolution time. Several theories for "reduced" turbulent viscosity are investigated, and reduce the number of systems with uncomfortably short decay times.

Spheroidal Populated Star Systems

NASA Astrophysics Data System (ADS)

Angeletti, Lucio; Giannone, Pietro

2008-10-01

Globular clusters and low-ellipticity early-type galaxies can be treated as systems populated by a large number of stars and whose structures can be schematized as spherically symmetric. Their studies profit from the synthesis of stellar populations. The computation of synthetic models makes use of various contributions from star evolution and stellar dynamics. In the first sections of the paper we present a short review of our results on the occurrence of galactic winds in star systems ranging from globular clusters to elliptical galaxies, and the dynamical evolution of a typical massive globular cluster. In the subsequent sections we describe our approach to the problem of the stellar populations in elliptical galaxies. The projected radial behaviours of spectro-photometric indices for a sample of eleven galaxies are compared with preliminary model results. The best agreement between observation and theory shows that our galaxies share a certain degree of heterogeneity. The gas energy dissipation varies from moderate to large, the metal yield ranges from solar to significantly oversolar, the dispersion of velocities is isotropic in most of the cases and anisotropic in the remaining instances.

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

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.

Like grandfather, like grandson: Erasmus and Charles Darwin on evolution.

PubMed

Smith, C U M

2010-01-01

Last year (2009) marked the bicentenary of Charles Darwin's birth and the sesquicentenary of The Origin of Species. This article examines the influence of Erasmus Darwin on Charles's evolutionary thought and shows how, in many ways, Erasmus anticipated his much better-known grandson. It discusses the similarity in the mindsets of the two Darwins, asks how far the younger Darwin was exposed to the elder's evolutionary thought, examines the similarities and differences in their theories of evolution, and ends by showing the surprising similarity between their theories of inheritance. Erasmus's influence on Charles is greater than customarily acknowledged, and now is an opportune time to bring the grandfather out from behind the glare of his stellar grandson.

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.

Schwarzschild, Martin (1912-97)

NASA Astrophysics Data System (ADS)

Murdin, P.

2000-11-01

Astrophysicist, born in Potsdam, Germany, the son of KARL SCHWARZSCHILD, left Germany, became professor at Princeton University. Working with John von Neumann, Schwarzschild used the powers of the newly developed electronic digital computers to work on the theory of stellar structure and evolution. He uncovered phenomena in red giant stars, including how they evolve off the main sequence in the H...

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.

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 of galaxies

NASA Technical Reports Server (NTRS)

Gunn, J. E.

1982-01-01

The recent observational evidence on the evolution of galaxies is reviewed and related to the framework of current ideas for galaxy formation from primordial density fluctuations. Recent strong evidence for the evolution of the stellar population in ellipticals is presented, as well as evidence that not all ellipticals behave as predicted by any simple theory. The status of counts of faint galaxies and the implications for the evolution of spirals is discussed, together with a discussion of recent work on the redshift distribution of galaxies at faint magnitudes and a spectroscopic investigation of the Butcher-Oemler blue cluster galaxies. Finally a new picture for the formation and evolution of disk galaxies which may explain most of the features of the Hubble sequence is outlined.

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.

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.

Cosmic rays from supernovae and comments on the Vela X pre-supernova

NASA Technical Reports Server (NTRS)

Cameron, A. G. W.

1971-01-01

A possible history of the production of elements in the galaxy is presented, based on assumptions about the end points of stellar evolution and of the general evolution of the galaxy. A wide range of quantities involving the relative abundances of nucleosynthesis products observed in the solar system, and various galactic quantities such as the current rate of supernova production and the present gas content of the galaxy, were considered. These assumptions were utilized in a computer program in which the gas content of the galaxy is gradually turned into stars. The stars are continually enriched in the products of nucleosynthesis as they approach the ends of their evolutionary lifetimes. It is suggested that supernova explosions are associated with the mass range of about 4-8 solar masses. Possible theories on the type of stellar explosive event represented by the Vela supernova are discussed.

Primordial nucleosynthesis

PubMed Central

Schramm, David N.

1998-01-01

With the advent of the new extragalactic deuterium observations, Big Bang nucleosynthesis (BBN) is on the verge of undergoing a transformation. In the past, the emphasis has been on demonstrating the concordance of the BBN model with the abundances of the light isotopes extrapolated back to their primordial values by using stellar and galactic evolution theories. As a direct measure of primordial deuterium is converged upon, the nature of the field will shift to using the much more precise primordial D/H to constrain the more flexible stellar and galactic evolution models (although the question of potential systematic error in 4He abundance determinations remains open). The remarkable success of the theory to date in establishing the concordance has led to the very robust conclusion of BBN regarding the baryon density. This robustness remains even through major model variations such as an assumed first-order quark-hadron phase transition. The BBN constraints on the cosmological baryon density are reviewed and demonstrate that the bulk of the baryons are dark and also that the bulk of the matter in the universe is nonbaryonic. Comparison of baryonic density arguments from Lyman-α clouds, x-ray gas in clusters, and the microwave anisotropy are made. PMID:9419322

Primordial nucleosynthesis.

PubMed

Schramm, D N

1998-01-06

With the advent of the new extragalactic deuterium observations, Big Bang nucleosynthesis (BBN) is on the verge of undergoing a transformation. In the past, the emphasis has been on demonstrating the concordance of the BBN model with the abundances of the light isotopes extrapolated back to their primordial values by using stellar and galactic evolution theories. As a direct measure of primordial deuterium is converged upon, the nature of the field will shift to using the much more precise primordial D/H to constrain the more flexible stellar and galactic evolution models (although the question of potential systematic error in 4He abundance determinations remains open). The remarkable success of the theory to date in establishing the concordance has led to the very robust conclusion of BBN regarding the baryon density. This robustness remains even through major model variations such as an assumed first-order quark-hadron phase transition. The BBN constraints on the cosmological baryon density are reviewed and demonstrate that the bulk of the baryons are dark and also that the bulk of the matter in the universe is nonbaryonic. Comparison of baryonic density arguments from Lyman-alpha clouds, x-ray gas in clusters, and the microwave anisotropy are made.

Star clusters in evolving galaxies

NASA Astrophysics Data System (ADS)

Renaud, Florent

2018-04-01

Their ubiquity and extreme densities make star clusters probes of prime importance of galaxy evolution. Old globular clusters keep imprints of the physical conditions of their assembly in the early Universe, and younger stellar objects, observationally resolved, tell us about the mechanisms at stake in their formation. Yet, we still do not understand the diversity involved: why is star cluster formation limited to 105M⊙ objects in the Milky Way, while some dwarf galaxies like NGC 1705 are able to produce clusters 10 times more massive? Why do dwarfs generally host a higher specific frequency of clusters than larger galaxies? How to connect the present-day, often resolved, stellar systems to the formation of globular clusters at high redshift? And how do these links depend on the galactic and cosmological environments of these clusters? In this review, I present recent advances on star cluster formation and evolution, in galactic and cosmological context. The emphasis is put on the theory, formation scenarios and the effects of the environment on the evolution of the global properties of clusters. A few open questions are identified.

Evolution of the universe

NASA Astrophysics Data System (ADS)

Novikov, I. D.

The underlying principles and discoveries of cosmology are presented in a qualitative form. The General Theory of Relativity is the basis for the science of the structure of the Universe, and Friedmann in 1922-4 demonstrated that the Universe is either expanding or contracting; Hubble in 1929 provided evidence for expansion. The physical processes of the evolution of the Universe to date have been projected to include origins in a superdense, superhot state with violent reactions between elementary particles. The resulting matter fragmented into the stellar systems and agglomerations presently observed. Observational data of the most distant galaxies now covers a range of 10 Gpc. Current studies focus on the missing matter in the Universe and the mean density of matter, the gravitation of vacuum, relict radiation from the Big Bang, the curvature of space-time, and theories for the earliest moments of the Universe, including pancake theories, the synthesis of light elements, and black and white holes.

Microlensing Signature of Binary Black Holes

NASA Technical Reports Server (NTRS)

Schnittman, Jeremy; Sahu, Kailash; Littenberg, Tyson

2012-01-01

We calculate the light curves of galactic bulge stars magnified via microlensing by stellar-mass binary black holes along the line-of-sight. We show the sensitivity to measuring various lens parameters for a range of survey cadences and photometric precision. Using public data from the OGLE collaboration, we identify two candidates for massive binary systems, and discuss implications for theories of star formation and binary evolution.

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

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.

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.

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.

SECULAR EVOLUTION OF BINARIES NEAR MASSIVE BLACK HOLES: FORMATION OF COMPACT BINARIES, MERGER/COLLISION PRODUCTS AND G2-LIKE OBJECTS

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

Prodan, Snezana; Antonini, Fabio; Perets, Hagai B., E-mail: sprodan@cita.utoronto.ca, E-mail: antonini@cita.utoronto.ca

2015-02-01

Here we discuss the evolution of binaries around massive black holes (MBHs) in nuclear stellar clusters. We focus on their secular evolution due to the perturbation by the MBHs, while simplistically accounting for their collisional evolution. Binaries with highly inclined orbits with respect to their orbits around MBHs are strongly affected by secular processes, which periodically change their eccentricities and inclinations (e.g., Kozai-Lidov cycles). During periapsis approach, dissipative processes such as tidal friction may become highly efficient, and may lead to shrinkage of a binary orbit and even to its merger. Binaries in this environment can therefore significantly change theirmore » orbital evolution due to the MBH third-body perturbative effects. Such orbital evolution may impinge on their later stellar evolution. Here we follow the secular dynamics of such binaries and its coupling to tidal evolution, as well as the stellar evolution of such binaries on longer timescales. We find that stellar binaries in the central parts of nuclear stellar clusters (NSCs) are highly likely to evolve into eccentric and/or short-period binaries, and become strongly interacting binaries either on the main sequence (at which point they may even merge), or through their later binary stellar evolution. The central parts of NSCs therefore catalyze the formation and evolution of strongly interacting binaries, and lead to the enhanced formation of blue stragglers, X-ray binaries, gravitational wave sources, and possible supernova progenitors. Induced mergers/collisions may also lead to the formation of G2-like cloud-like objects such as the one recently observed in the Galactic center.« less

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.

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.

Unravelling the role of the SW Sextantis stars in the evolution of cataclysmic variables

NASA Astrophysics Data System (ADS)

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

2007-08-01

SW Sextantis stars are a relatively large group of cataclysmic variables (CVs) whose properties contradict all predictions made by the current CV evolution theories. 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 mass ratio of the system which, combined with the orbital inclination derived from modelling of either the disc eclipses in the high state or the ellipsoidal modulation in the low state, will eventually provide the first detailed system parameters for any SW Sex star.

Unravelling the role of the SW Sextantis stars in the evolution of cataclysmic variables

NASA Astrophysics Data System (ADS)

Torres, Manuel

2007-02-01

SW Sextantis stars are a relatively large group of cataclysmic variables (CVs) whose properties contradict all predictions made by the current CV evolution theories. 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 mass ratio of the system which, combined with the orbital inclination derived from modelling of either the disc eclipses in the high state or the ellipsoidal modulation in the low state, will eventually provide the first detailed system parameters for any SW Sex star.

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.

A general theory for the lifetimes of giant molecular clouds under the influence of galactic dynamics

NASA Astrophysics Data System (ADS)

Jeffreson, Sarah M. R.; Kruijssen, J. M. Diederik

2018-05-01

We propose a simple analytic theory for environmentally dependent molecular cloud lifetimes, based on the large-scale (galactic) dynamics of the interstellar medium. Within this theory, the cloud lifetime is set by the time-scales for gravitational collapse, galactic shear, spiral arm interactions, epicyclic perturbations, and cloud-cloud collisions. It is dependent on five observable quantities, accessible through measurements of the galactic rotation curve, the gas and stellar surface densities, and the gas and stellar velocity dispersions of the host galaxy. We determine how the relative importance of each dynamical mechanism varies throughout the space of observable galactic properties, and conclude that gravitational collapse and galactic shear play the greatest role in setting the cloud lifetime for the considered range of galaxy properties, while cloud-cloud collisions exert a much lesser influence. All five environmental mechanisms are nevertheless required to obtain a complete picture of cloud evolution. We apply our theory to the galaxies M31, M51, M83, and the Milky Way, and find a strong dependence of the cloud lifetime upon galactocentric radius in each case, with a typical cloud lifetime between 10 and 50 Myr. Our theory is ideally suited for systematic observational tests with the Atacama Large Millimetre/submillimetre array.

Sub-1% accuracy in fundamental stellar parameters from triply eclipsing systems

NASA Astrophysics Data System (ADS)

Prsa, Andrej

The current state-of-the-art level of accuracy in fundamental stellar parameters from eclipsing binary stars is 2-3%. Here we propose to use eclipsing triple stars to reduce the error bars by an entire order of magnitude, i.e. to 0.2-0.3%. This can be done because a presence of the third component breaks most of the degeneracy inherent in binary systems between the inclination and stellar sizes. We detail the feasibility arguments and foresee that these results will provide exceptional benchmark objects for stringent tests of stellar evolution and population models. The formation channel of close binary stars (with separations of several stellar radii) is a matter of debate. It is clear that close binaries cannot form in situ because (1) the physical radius of a star shrinks by a large factor between birth and the main sequence, yet many main-sequence stars have companions orbiting at a distance of only a few stellar radii, and (2) in current theories of planet formation, the region within 0.1 AU of a protostar is too hot and rarefied for a Jupiter-mass planet to form, yet many hot jupiters are observed at such distances. Current theories of dynamic orbital evolution attribute orbital shrinking to Kozai cycles and tidal friction, which are long-lasting, perturbative effects that take Gyrs to shrink orbits by 1-2 orders of magnitude. This implies that, if a binary star system has a tertiary companion, it will be in a hierarchical structure, and any disruptive orbital encounters should be exceedingly rare after a certain period. The Kepler satellite observed continuously over 2800 eclipsing binary stars over 4 years of its mission lifetime. The ultra-high precision photometry and essentially uninterrupted time coverage enables us to time the eclipses to a 6 second precision. Because of the well understood physics that governs the orbital motion of two bodies around the center of mass, the expected times of eclipses can be predicted to a fraction of a second. When other physical processes interplay, such as apsidal motion, mass transfer or third body interactions, the times of eclipses deviate from predictions: they either come early or late. These deviations are called eclipse timing variations (ETVs) and can range from a few seconds to a few hours. Our team measured ETVs for the entire Kepler data-set of eclipsing binaries and found 516 that demonstrate significant deviations. Of those, 16 show strong interactions between the binary system and the tertiary component that significantly affects the binary orbit within a single encounter. This observed rate of dynamical perturbation events is unexpectedly high and at odds with current theories. We propose to study these objects in great detail: (1) to apply a developed photodynamical code to model multiple body interactions; (2) to fully solve orbital dynamics of these interacting bodies using all available Kepler data, deriving masses of all objects to better than 1%; (3) to measure the occurrence rate of strong orbital interactions in multiple systems and compare it to the predicted rates; (4) to hypothesize and simulate additional evolution channels that could potentially lead to such a high occurrence rate of disruptive events; and (5) to integrate these systems over time and test whether this dynamic evolution can cause efficient orbital tightening and the creation of short period binaries. The team consists of a PI who has experience with Kepler satellite's idiosyncrasies, two postdoctoral fellows, one graduate student, and six undergraduate students that will invest their summer months to learn about multiple body interactions. The proposed study has far-reaching research goals in stellar and planetary science astrophysics, a strong educational/training component and is aligned with NASA's objectives as outlined in the NRA call. Kepler is the only instrument that can provide the accuracy and temporal coverage required for the execution of this project.

Accretion and Magnetic Reconnection in the Pre-Main Sequence Binary DQ Tau as Revealed through High-Cadence Optical Photometry

NASA Astrophysics Data System (ADS)

Tofflemire, Benjamin M.; Mathieu, Robert D.; Ardila, David R.; Akeson, Rachel L.; Ciardi, David R.; Herczeg, Gregory; Johns-Krull, Christopher M.; Vodniza, Alberto

2016-01-01

Protostellar disks are integral to the formation and evolution of low-mass stars and planets. A paradigm for the star-disk interaction has been extensively developed through theory and observation in the case of single stars. Most stars, however, form in binaries or higher order systems where the distribution of disk material and mass flows are more complex. Pre-main sequence (PMS) binary stars can have up to three accretion disks: two circumstellar disks and a circumbinary disk separated by a dynamically cleared gap. Theory suggests that mass may periodically flow in an accretion stream from a circumbinary disk across the gap onto circumstellar disks or stellar surfaces.The archetype for this theory is the eccentric, PMS binary DQ Tau. Moderate-cadence broadband photometry (~10 observations per orbital period) has shown pulsed brightening events near most periastron passages, just as numerical simulations would predict for a binary of similar orbital parameters. While this observed behavior supports the accretion stream theory, it is not exclusive to variable accretion rates. Magnetic reconnection events (flares) during the collision of stellar magnetospheres at periastron (when separated by 8 stellar radii) could produce the same periodic, broadband behavior when observed at a one-day cadence. Further evidence for magnetic activity comes from gyrosynchrotron, radio flares (typical of stellar flares) observed near multiple periastron passages. To reveal the physical mechanism seen in DQ Tau's moderate-cadence observations, we have obtained continuous, moderate-cadence, multi-band photometry over 10 orbital periods (LCOGT 1m network), supplemented with 32 nights of minute-cadence photometry centered on 4 separate periastron passages (WIYN 0.9m; APO ARCSAT). With detailed lightcurve morphologies we distinguish between the gradual rise and fall on multi-day time-scales predicted by the accretion stream theory and the hour time-scale, rapid-rise and exponential-decay typical of flares. While both are present, accretion dominates the observed variability providing evidence for the accretion stream theory and detailed mass accretion rates for comparison with numerical simulations.

The Mass Function in h+(chi) Persei

NASA Astrophysics Data System (ADS)

Bragg, Ann; Kenyon, Scott

2000-08-01

Knowledge of the stellar initial mass function (IMF) is critical to understanding star formation and galaxy evolution. Past studies of the IMF in open clusters have primarily used luminosity functions to determine mass functions, frequently in relatively sparse clusters. Our goal with this project is to derive a reliable, well- sampled IMF for a pair of very dense young clusters (h+(chi) Persei) with ages, 1-2 × 10^7 yr (e.g., Vogt A& A 11:359), where stellar evolution theory is robust. We will construct the HR diagram using both photometry and spectral types to derive more accurate stellar masses and ages than are possible using photometry alone. Results from the two clusters will be compared to examine the universality of the IMF. We currently have a spectroscopic sample covering an area within 9 arc-minutes of the center of each cluster taken with the FAST Spectrograph. The sample is complete to V=15.4 and contains ~ 1000 stars. We request 2 nights at WIYN/HYDRA to extend this sample to deeper magnitudes, allowing us to determine the IMF of the clusters to a lower limiting mass and to search for a pre-main sequence, theoretically predicted to be present for clusters of this age. Note that both clusters are contained within a single HYDRA field.

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.

A Study of The Binary and Anomalous Stellar Populations in Two Intermediate-Aged Open Clusters

NASA Astrophysics Data System (ADS)

Mathieu, Robert D.; Milliman, Katelyn; Geller, Aaron M.; Gosnell, Natalie

2010-08-01

``Anomalous'' stars, such as blue stragglers and more recently sub- subgiants, have been an enduring challenge for stellar evolution theory. It is now clear that in star clusters these systems are closely linked to the binary star populations. Furthermore, sophisticated N-body models show that stellar dynamical processes play a central role in the formation of such anomalous stars. These stars trace the interface between the classical fields of stellar evolution and stellar dynamics. We propose to expand our highly successful radial-velocity survey to include two new rich open clusters NGC 7789 (1.8 Gyr, -0.1 dex) and NGC 2506 (2.1 Gyr, -0.4 dex) as part of the WIYN Open Cluster Study (WOCS). Though these two clusters are both of intermediate age and of similar richness, they have quite different blue straggler populations. NGC 2506 has only 10 known blue stragglers, while NGC 7789 has at least 27, among the largest known populations of blue stragglers in an open cluster. Defining the hard-binary populations in these two clusters is critical for understanding the factors that determine blue straggler production rates. Our proposed observations will establish the hard- binary fraction and frequency distributions of orbital parameters (periods, eccentricities, mass-ratios, etc.) for orbital periods approaching the hard-soft boundary, and will provide a comprehensive survey of the blue stragglers and other anomalous stars, including secure cluster memberships and binary properties. These data will then form direct constraints for detailed N-body open cluster simulations from which we will study the impact of the hard-binary population on the production rates and mechanisms of blue stragglers.

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.

CALIBRATION OF EQUILIBRIUM TIDE THEORY FOR EXTRASOLAR PLANET SYSTEMS

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

Hansen, Brad M. S., E-mail: hansen@astro.ucla.ed

2010-11-01

We provide an 'effective theory' of tidal dissipation in extrasolar planet systems by empirically calibrating a model for the equilibrium tide. The model is valid to high order in eccentricity and parameterized by two constants of bulk dissipation-one for dissipation in the planet and one for dissipation in the host star. We are able to consistently describe the distribution of extrasolar planetary systems in terms of period, eccentricity, and mass (with a lower limit of a Saturn mass) with this simple model. Our model is consistent with the survival of short-period exoplanet systems, but not with the circularization period ofmore » equal mass stellar binaries, suggesting that the latter systems experience a higher level of dissipation than exoplanet host stars. Our model is also not consistent with the explanation of inflated planetary radii as resulting from tidal dissipation. The paucity of short-period planets around evolved A stars is explained as the result of enhanced tidal inspiral resulting from the increase in stellar radius with evolution.« less

Dynamical Asteroseismology: towards improving the theories of stellar structure and (tidal) evolution

NASA Astrophysics Data System (ADS)

Tkachenko, Andrew

2017-10-01

The potential of the dynamical asteroseismology, the research area that builds upon the synergies between the asteroseismology and binary stars research fields, is discussed in this manuscript. We touch upon the following topics: i) the mass discrepancy observed in intermediate-to high-mass main-sequence and evolved binaries as well as in the low mass systems that are still in the pre-main sequence phase of their evolution; ii) the rotationally induced mixing in high-mass stars, in particular how the most recent theoretical predictions and spectroscopic findings compare to the results of asteroseismic investigations; iii) internal gravity waves and their potential role in the evolution of binary star systems and surface nitrogen enrichment in high-mass stars; iv) the tidal evolution theory, in particular how its predictions of spin-orbit synchronisation and orbital circularisation compare to the present-day high-quality observations; v) the tidally-induced pulsations and their role in the angular momentum transport within binary star systems; vi) the scaling relations between fundamental and seismic properties of stars across the entire HR-diagram.

On the theory of group generation of stars

NASA Technical Reports Server (NTRS)

Zhilyayev, B. Y.; Porfiryev, V. V.; Shulman, L. M.

1973-01-01

The hypothesis proposed is that topology of a rotating gaseous cloud can be variable in the contraction process. Due to rotation an originally spherical cloud is transformed into a toroidal body. The contraction of a thin torus is considered with different suppositions on cooling the gas. In the determined time the torus will become gravitationally unstable. The excitation of Jeans' waves is shown to result in the disintegration of the torus into fragments. The number of the fragments and their mass distributions are calculated. The proposed hypothesis on toroidal stages in stellar evolution can remove some difficulties in the theory of structure and evolution of stars, such as absence of limitary stars, distribution of rotation velocities of early-type stars, origin of poloidal magnetic fields and decline rotators with the magnetic axis orthogonal to the axis of rotation.

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).

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

Cegla, H. M.; Watson, C. A.; Oshagh, M.

Observations of the Rossiter–McLaughlin (RM) effect provide information on star–planet alignments, which can inform planetary migration and evolution theories. Here, we go beyond the classical RM modeling and explore the impact of a convective blueshift that varies across the stellar disk and non-Gaussian stellar photospheric profiles. We simulated an aligned hot Jupiter with a four-day orbit about a Sun-like star and injected center-to-limb velocity (and profile shape) variations based on radiative 3D magnetohydrodynamic simulations of solar surface convection. The residuals between our modeling and classical RM modeling were dependent on the intrinsic profile width and v sin i; the amplitudemore » of the residuals increased with increasing v sin i and with decreasing intrinsic profile width. For slowly rotating stars the center-to-limb convective variation dominated the residuals (with amplitudes of 10 s of cm s{sup −1} to ∼1 m s{sup −1}); however, for faster rotating stars the dominant residual signature was due a non-Gaussian intrinsic profile (with amplitudes from 0.5 to 9 m s{sup −1}). When the impact factor was 0, neglecting to account for the convective center-to-limb variation led to an uncertainty in the obliquity of ∼10°–20°, even though the true v sin i was known. Additionally, neglecting to properly model an asymmetric intrinsic profile had a greater impact for more rapidly rotating stars (e.g., v sin i = 6 km s{sup −1}) and caused systematic errors on the order of ∼20° in the measured obliquities. Hence, neglecting the impact of stellar surface convection may bias star–planet alignment measurements and consequently theories on planetary migration and evolution.« less

Turbulence closure for mixing length theories

NASA Astrophysics Data System (ADS)

Jermyn, Adam S.; Lesaffre, Pierre; Tout, Christopher A.; Chitre, Shashikumar M.

2018-05-01

We present an approach to turbulence closure based on mixing length theory with three-dimensional fluctuations against a two-dimensional background. This model is intended to be rapidly computable for implementation in stellar evolution software and to capture a wide range of relevant phenomena with just a single free parameter, namely the mixing length. We incorporate magnetic, rotational, baroclinic, and buoyancy effects exactly within the formalism of linear growth theories with non-linear decay. We treat differential rotation effects perturbatively in the corotating frame using a novel controlled approximation, which matches the time evolution of the reference frame to arbitrary order. We then implement this model in an efficient open source code and discuss the resulting turbulent stresses and transport coefficients. We demonstrate that this model exhibits convective, baroclinic, and shear instabilities as well as the magnetorotational instability. It also exhibits non-linear saturation behaviour, and we use this to extract the asymptotic scaling of various transport coefficients in physically interesting limits.

The evolution of galaxies. III - Metal-enhanced star formation

NASA Technical Reports Server (NTRS)

Talbot, R. J., Jr.; Arnett, W. D.

1973-01-01

The problem of the paucity of low-metal-abundance low-mass stars is discussed. One alternative to the variable-initial-mass-function (VIMF) solution is proposed. It is shown that this solution - metal-enhanced star formation - satisfies the classical test which prompted the VIMF hypothesis. Furthermore, with no additional parameters it provides improved fits to other tests - e.g., inhomogeneities in the abundances in young stars, concordance of all nucleo-cosmochronologies, and a required yield of heavy-element production which is consistent with current stellar evolution theory. In this model the age of the Galaxy is 18.6 plus or minus 5.7 b.y.

Study of the Evolutions of the Universe, Stars and the Solar System ---Personal Retrospect and Prospect---

NASA Astrophysics Data System (ADS)

Hayakawa, S.

The universe, stars and the solar system belong to different hierarchies but have been studied in Jpn. by a common group with close mutual contact. Collaborative effort is not restricted within theoretical astrophysics but is extended to a variety of fields of science. In the present article the author describes on the basis of his personal recollection how the collaborate research has stimulated new fields of observational astronomy using infrared radiation and X-rays. A fee-back from these observational studies has given several inputs to the theory of stellar evolution and will provide important means in the study of cosmology.

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

The Secular Evolution Of Disc Galaxies And The Origin Of Exponential And Double Exponential Surface Density Profiles

NASA Astrophysics Data System (ADS)

Elmegreen, Bruce G.

2016-10-01

Exponential radial profiles are ubiquitous in spiral and dwarf Irregular galaxies, but the origin of this structural form is not understood. This talk will review the observations of exponential and double exponential disks, considering both the light and the mass profiles, and the contributions from stars and gas. Several theories for this structure will also be reviewed, including primordial collapse, bar and spiral torques, clump torques, galaxy interactions, disk viscosity and other internal processes of angular momentum exchange, and stellar scattering off of clumpy structure. The only process currently known that can account for this structure in the most theoretically difficult case is stellar scattering off disks clumps. Stellar orbit models suggest that such scattering can produce exponentials even in isolated dwarf irregulars that have no bars or spirals, little shear or viscosity, and profiles that go out too far for the classical Mestel case of primordial collapse with specific angular momentum conservation.

Results from the APOGEE IN-SYNC Orion: parameters and radial velocities for thousands of young stars in the Orion Complex.

NASA Astrophysics Data System (ADS)

Da Rio, Nicola; SDSS Apogee IN-SYNC ancillary program Team

2015-01-01

I will present the results of our characterization of the dynamical status of the young stellar population in the Orion A star forming region. This is based on radial velocity measurements obtained within the SDSS-III Apogee IN-SYNC Orion Survey, which obtained high-resolution spectroscopy of ~3000 objects in the region, from the dense Orion Nebula Cluster - the prototypical nearby region of active massive star formation - to the low-density environments of the L1641 region. We find evidence for kinematic subclustering along the star forming filament, where the stellar component remains kinematically associated to the gas; in the ONC we find that the stellar population is supervirial and currently expanding. We rule out the existence of a controversial candidate foreground cluster to the south of the ONC. These results, complemented with an analysis of the spatial structure of the population, enables critical tests of theories that describe the formation and early evolution of Orion and young clusters in general.

O-star parameters from line profiles of wind-blanketed model atmospheres

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

Voels, S.A.

1989-01-01

The basic stellar parameters (i.e. effective temperature, gravity, helium content, bolometric correction, etc...) of several O-stars are determined by matching high signal-to-noise observed line profiles of optical hydrogen and helium line transitions with theoretical line profiles from a core-halo model of the stellar atmosphere. The core-halo atmosphere includes the effect of radiation backscattered from a stellar wind by incorporating the stellar wind model of Abbott and Lucy as a reflective upper boundary condition in the Mihalas atmosphere model. Three of the four supergiants analyzed showed an enhanced surface abundance of helium. Using a large sample of equivalent width data frommore » Conti a simple argument is made that surface enhancement of helium may be a common property of the most luminous supergiants. The stellar atmosphere theory is sufficient to determine the stellar parameters only if careful attention is paid to the detection and exclusion of lines which are not accurately modeled by the physical processes included. It was found that some strong lines which form entirely below the sonic point are not well modeled due to effects of atmospheric extension. For spectral class 09.5, one of these lines is the classification line He I {lambda}4471{angstrom}. For supergiant, the gravity determined could be systematically low by up to 0.05 dex as the radiation pressure due to lines is neglected. Within the error ranges, the stellar parameters determined, including helium abundance, agree with those from the stellar evolution calculations of Maeder and Maynet.« less

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.

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.

A Study Of Anomalous Stars and Binary Populations Within Open Clusters: Tests Of Theoretical Models

NASA Astrophysics Data System (ADS)

Geller, Aaron M.; Mathieu, Robert D.; Braden, Ella; Latham, David W.

2008-08-01

``Anomalous'' stars, such as blue stragglers and more recently sub- subgiants, have been an enduring challenge for stellar evolution theory. Recently it has become clear that in star clusters these systems are closely linked to the binary star populations. Furthermore, through advances in N-body modeling, we have come to realize that stellar dynamical processes play a central role in the formation of such anomalous stars. Indeed, these stars trace the interface between the classical fields of stellar evolution and stellar dynamics. We propose a thesis study to directly probe this interface through high-precision radial-velocity measurements of the anomalous stars and the binary populations in four open clusters. We have selected NGC 188 (7 Gyr), M67 (NGC 2682; 4 Gyr), NGC 6819 (2.4 Gyr), and M35 (NGC 2168; 150 Myr), as these span a wide range in age, are rich enough to provide statistically significant conclusions, and already have an extensive base of kinematic, spectroscopic, and photometric observations from the WIYN Open Cluster Study. Our proposed observations will define the spectroscopic hard binary populations (fraction, frequency distributions of orbital parameters, mass ratios) for orbital periods approaching the hard-soft boundary. These observations will also provide a comprehensive survey for anomalous stars, including secure establishment of their cluster membership. These data will allow us to perform the first detailed comparison to predictions from open cluster simulations of the binary populations among normal and anomalous stars, and thereby to constrain the evolutionary paths from one to the other.

A Study Of Anomalous Stars and Binary Populations Within Open Clusters: Tests Of Theoretical Models

NASA Astrophysics Data System (ADS)

Geller, Aaron M.; Mathieu, Robert D.; Gosnell, Natalie; Latham, David W.

2009-02-01

``Anomalous'' stars, such as blue stragglers and more recently sub- subgiants, have been an enduring challenge for stellar evolution theory. Recently it has become clear that in star clusters these systems are closely linked to the binary star populations. Furthermore, through advances in N-body modeling, we have come to realize that stellar dynamical processes play a central role in the formation of such anomalous stars. Indeed, these stars trace the interface between the classical fields of stellar evolution and stellar dynamics. We propose a thesis study to directly probe this interface through high-precision radial-velocity measurements of the anomalous stars and the binary populations in four open clusters. We have selected NGC 188 (7 Gyr), M67 (NGC 2682; 4 Gyr), NGC 6819 (2.4 Gyr), and M35 (NGC 2168; 150 Myr), as these span a wide range in age, are rich enough to provide statistically significant conclusions, and already have an extensive base of kinematic, spectroscopic, and photometric observations from the WIYN Open Cluster Study. Our proposed observations will define the spectroscopic hard binary populations (fraction, frequency distributions of orbital parameters, mass ratios) for orbital periods approaching the hard-soft boundary. These observations will also provide a comprehensive survey for anomalous stars, including secure establishment of their cluster membership. These data will allow us to perform the first detailed comparison to predictions from open cluster simulations of the binary populations among normal and anomalous stars, and thereby to constrain the evolutionary paths from one to the other.

A Study Of Anomalous Stars and Binary Populations Within Open Clusters: Tests Of Theoretical Models

NASA Astrophysics Data System (ADS)

Geller, Aaron M.; Mathieu, Robert D.; Braden, Ella; Latham, David W.

2008-02-01

``Anomalous'' stars, such as blue stragglers and more recently sub- subgiants, have been an enduring challenge for stellar evolution theory. Recently it has become clear that in star clusters these systems are closely linked to the binary star populations. Furthermore, through advances in N-body modeling, we have come to realize that stellar dynamical processes play a central role in the formation of such anomalous stars. Indeed, these stars trace the interface between the classical fields of stellar evolution and stellar dynamics. We propose a thesis study to directly probe this interface through high-precision radial-velocity measurements of the anomalous stars and the binary populations in four open clusters. We have selected NGC 188 (7 Gyr), M67 (NGC 2682; 4 Gyr), NGC 6819 (2.4 Gyr), and M35 (NGC 2168; 150 Myr), as these span a wide range in age, are rich enough to provide statistically significant conclusions, and already have an extensive base of kinematic, spectroscopic, and photometric observations from the WIYN Open Cluster Study. Our proposed observations will define the spectroscopic hard binary populations (fraction, frequency distributions of orbital parameters, mass ratios) for orbital periods approaching the hard-soft boundary. These observations will also provide a comprehensive survey for anomalous stars, including secure establishment of their cluster membership. These data will allow us to perform the first detailed comparison to predictions from open cluster simulations of the binary populations among normal and anomalous stars, and thereby to constrain the evolutionary paths from one to the other.

Binary Black Hole Mergers from Field Triples: Properties, Rates, and the Impact of Stellar Evolution

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

Antonini, Fabio; Toonen, Silvia; Hamers, Adrian S.

We consider the formation of binary black hole (BH) mergers through the evolution of field massive triple stars. In this scenario, favorable conditions for the inspiral of a BH binary are initiated by its gravitational interaction with a distant companion, rather than by a common-envelope phase invoked in standard binary evolution models. We use a code that follows self-consistently the evolution of massive triple stars, combining the secular triple dynamics (Lidov–Kozai cycles) with stellar evolution. After a BH triple is formed, its dynamical evolution is computed using either the orbit-averaged equations of motion, or a high-precision direct integrator for triplesmore » with weaker hierarchies for which the secular perturbation theory breaks down. Most BH mergers in our models are produced in the latter non-secular dynamical regime. We derive the properties of the merging binaries and compute a BH merger rate in the range (0.3–1.3) Gpc{sup −3} yr{sup −1}, or up to ≈2.5 Gpc{sup −3} yr{sup −1} if the BH orbital planes have initially random orientation. Finally, we show that BH mergers from the triple channel have significantly higher eccentricities than those formed through the evolution of massive binaries or in dense star clusters. Measured eccentricities could therefore be used to uniquely identify binary mergers formed through the evolution of triple stars. While our results suggest up to ≈10 detections per year with Advanced-LIGO, the high eccentricities could render the merging binaries harder to detect with planned space based interferometers such as LISA.« less

Analyzing the Formation of Ultra-compact Dwarfs through Stellar Populations

NASA Astrophysics Data System (ADS)

Seshadri, Anish; Wang, Carolyn; Romanowsky, Aaron J.; Martin-navarro, Ignacio

2017-01-01

Since their discovery in 1999, ultra-compact dwarfs (UCDs) have been the subjects of intense study. Their small size, yet tremendous mass, brings into question their place among celestial objects. Are they galaxies or globular clusters? The answer to this question could come from analyzing how they formed. Thus, the goal of this project is to test one of the theories for the formation of UCDs, the theory of tidal stripping.This project approaches the issue by looking at dwarf galaxies currently in the process of stripping to understand formation history. Over twenty such dwarf galaxies were identified and their stellar populations analyzed. Using modeling techniques on spectroscopic and photometric data, the age, metallicity, and color of each object was identified. By objectively categorizing each object into a stage of evolution in the process of tidal stripping, a virtual timeline was built for the formation of UCDs. Data for each object were plotted vs. stage of formation, with pristine dwarfs and UCDs signifying the endpoints. Trends in the data revealed a natural progression over all stages of evolution, showing that tidally stripped dwarfs likely represent an intermediate stage in the formation of UCDs.This research was supported by NSF Grant AST-1515084. 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 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.

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.

Planetary nebulae as standard candles. IV - A test in the Leo I group

NASA Technical Reports Server (NTRS)

Ciardullo, Robin; Jacoby, George H.; Ford, Holland C.

1989-01-01

In this paper, PN are used to determine accurate distances to three galaxies in the Leo I group - The E0 giant elliptical NGC 3379, its optical companion, the SB0 spiral NGC 3384, and the smaller E6 elliptical NGC 3377. In all three galaxies, the luminosity-specific PN number densities are roughly the same, and the derived stellar death rates are in remarkable agreement with the predictions of stellar evolution theory. It is shown that the shape of the forbidden O III 5007 A PN luminosity function is the same in each galaxy and indistinguishable from that observed in M31 and M81. It is concluded that the PN luminosity function is an excellent standard candle for early-type galaxies.

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 probable stellar solution to the cosmological lithium discrepancy.

PubMed

Korn, A J; Grundahl, F; Richard, O; Barklem, P S; Mashonkina, L; Collet, R; Piskunov, N; Gustafsson, B

2006-08-10

The measurement of the cosmic microwave background has strongly constrained the cosmological parameters of the Universe. When the measured density of baryons (ordinary matter) is combined with standard Big Bang nucleosynthesis calculations, the amounts of hydrogen, helium and lithium produced shortly after the Big Bang can be predicted with unprecedented precision. The predicted primordial lithium abundance is a factor of two to three higher than the value measured in the atmospheres of old stars. With estimated errors of 10 to 25%, this cosmological lithium discrepancy seriously challenges our understanding of stellar physics, Big Bang nucleosynthesis or both. Certain modifications to nucleosynthesis have been proposed, but found experimentally not to be viable. Diffusion theory, however, predicts atmospheric abundances of stars to vary with time, which offers a possible explanation of the discrepancy. Here we report spectroscopic observations of stars in the metal-poor globular cluster NGC 6397 that reveal trends of atmospheric abundance with evolutionary stage for various elements. These element-specific trends are reproduced by stellar-evolution models with diffusion and turbulent mixing. We thus conclude that diffusion is predominantly responsible for the low apparent stellar lithium abundance in the atmospheres of old stars by transporting the lithium deep into the star.

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

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.

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.

New theory of stellar convection without the mixing-length parameter: new stellar atmosphere model

NASA Astrophysics Data System (ADS)

Pasetto, Stefano; Chiosi, Cesare; Cropper, Mark; Grebel, Eva K.

2018-01-01

Stellar convection is usually described by the mixing-length theory, which makes use of the mixing-length scale factor to express the convective flux, velocity, and temperature gradients of the convective elements and stellar medium. The mixing-length scale is proportional to the local pressure scale height of the star, and the proportionality factor (i.e. mixing-length parameter) is determined by comparing the stellar models to some calibrator, i.e. the Sun. No strong arguments exist to suggest that the mixing-length parameter is the same in all stars and all evolutionary phases and because of this, all stellar models in the literature are hampered by this basic uncertainty. In a recent paper [1] we presented a new theory that does not require the mixing length parameter. Our self-consistent analytical formulation of stellar convection determines all the properties of stellar convection as a function of the physical behavior of the convective elements themselves and the surrounding medium. The new theory of stellar convection is formulated starting from a conventional solution of the Navier-Stokes/Euler equations expressed in a non-inertial reference frame co-moving with the convective elements. The motion of stellar convective cells inside convective-unstable layers is fully determined by a new system of equations for convection in a non-local and time-dependent formalism. The predictions of the new theory are compared with those from the standard mixing-length paradigm with positive results for atmosphere models of the Sun and all the stars in the Hertzsprung-Russell diagram.

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.

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.

Biography of Professor Hayashi

NASA Astrophysics Data System (ADS)

Sato, Humitaka

2012-09-01

Biography of Chushiro Hayashi(1920-2010) is described with an emphasis on his early career as a theoretical physicist. In spite of his well-recognized achievements in theoretical astrophysics, such as Hayashi phase, p/n-ratio at Big Bang, stellar evolution and nucleosynthesis and Kyoto Model on the origin of solar system, Hayashi had once wished to devote in study of non-local field theory of particle physics. However, the various changes of situation around Hideki Yukawa(Nobel prize laureate in 1949) had guided him to the study of astrophysics.

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).

A formulation of convection for stellar structure and evolution calculations without the mixing-length theory approximations. II - Application to Alpha Centauri A and B

NASA Technical Reports Server (NTRS)

Lydon, Thomas J.; Fox, Peter A.; Sofia, Sabatino

1993-01-01

We have constructed a series of models of Alpha Centauri A and Alpha Centauri B for the purposes of testing the effects of convection modeling both by means of the mixing-length theory (MLT), and by means of parameterization of energy fluxes based upon numerical simulations of turbulent compressible convection. We demonstrate that while MLT, through its adjustable parameter alpha, can be used to match any given values of luminosities and radii, our treatment of convection, which lacks any adjustable parameters, makes specific predictions of stellar radii. Since the predicted radii of the Alpha Centauri system fall within the errors of the observed radii, our treatment of convection is applicable to other stars in the H-R diagram in addition to the sun. A second set of models is constructed using MLT, adjusting alpha to yield not the 'measured' radii but, instead, the radii predictions of our revised treatment of convection. We conclude by assessing the appropriateness of using a single value of alpha to model a wide variety of stars.

CALIBRATION OF EQUILIBRIUM TIDE THEORY FOR EXTRASOLAR PLANET SYSTEMS. II

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

Hansen, Brad M. S., E-mail: hansen@astro.ucla.edu

2012-09-20

We present a new empirical calibration of equilibrium tidal theory for extrasolar planet systems, extending a prior study by incorporating detailed physical models for the internal structure of planets and host stars. The resulting strength of the stellar tide produces a coupling that is strong enough to reorient the spins of some host stars without causing catastrophic orbital evolution, thereby potentially explaining the observed trend in alignment between stellar spin and planetary orbital angular momentum. By isolating the sample whose spins should not have been altered in this model, we also show evidence for two different processes that contribute tomore » the population of planets with short orbital periods. We apply our results to estimate the remaining lifetimes for short-period planets, examine the survival of planets around evolving stars, and determine the limits for circularization of planets with highly eccentric orbits. Our analysis suggests that the survival of circularized planets is strongly affected by the amount of heat dissipated, which is often large enough to lead to runaway orbital inflation and Roche lobe overflow.« less

Constraints on modified gravity models from white dwarfs

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

Banerjee, Srimanta; Singh, Tejinder P.; Shankar, Swapnil, E-mail: srimanta.banerjee@tifr.res.in, E-mail: swapnil.shankar@cbs.ac.in, E-mail: tpsingh@tifr.res.in

Modified gravity theories can introduce modifications to the Poisson equation in the Newtonian limit. As a result, we expect to see interesting features of these modifications inside stellar objects. White dwarf stars are one of the most well studied stars in stellar astrophysics. We explore the effect of modified gravity theories inside white dwarfs. We derive the modified stellar structure equations and solve them to study the mass-radius relationships for various modified gravity theories. We also constrain the parameter space of these theories from observations.

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.

The evolution in the stellar mass of brightest cluster galaxies over the past 10 billion years

NASA Astrophysics Data System (ADS)

Bellstedt, Sabine; Lidman, Chris; Muzzin, Adam; Franx, Marijn; Guatelli, Susanna; Hill, Allison R.; Hoekstra, Henk; Kurinsky, Noah; Labbe, Ivo; Marchesini, Danilo; Marsan, Z. Cemile; Safavi-Naeini, Mitra; Sifón, Cristóbal; Stefanon, Mauro; van de Sande, Jesse; van Dokkum, Pieter; Weigel, Catherine

2016-08-01

Using a sample of 98 galaxy clusters recently imaged in the near-infrared with the European Southern Observatory (ESO) New Technology Telescope, WIYN telescope and William Herschel Telescope, supplemented with 33 clusters from the ESO archive, we measure how the stellar mass of the most massive galaxies in the universe, namely brightest cluster galaxies (BCGs), increases with time. Most of the BCGs in this new sample lie in the redshift range 0.2 < z < 0.6, which has been noted in recent works to mark an epoch over which the growth in the stellar mass of BCGs stalls. From this sample of 132 clusters, we create a subsample of 102 systems that includes only those clusters that have estimates of the cluster mass. We combine the BCGs in this subsample with BCGs from the literature, and find that the growth in stellar mass of BCGs from 10 billion years ago to the present epoch is broadly consistent with recent semi-analytic and semi-empirical models. As in other recent studies, tentative evidence indicates that the stellar mass growth rate of BCGs may be slowing in the past 3.5 billion years. Further work in collecting larger samples, and in better comparing observations with theory using mock images, is required if a more detailed comparison between the models and the data is to be made.

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.

WHY ARE RAPIDLY ROTATING M DWARFS IN THE PLEIADES SO (INFRA)RED? NEW PERIOD MEASUREMENTS CONFIRM ROTATION-DEPENDENT COLOR OFFSETS FROM THE CLUSTER SEQUENCE

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

Covey, Kevin R.; Agüeros, Marcel A.; Liu, Jiyu

2016-05-10

Stellar rotation periods ( P {sub rot}) measured in open clusters have proved to be extremely useful for studying stars’ angular momentum content and rotationally driven magnetic activity, which are both age- and mass-dependent processes. While P {sub rot} measurements have been obtained for hundreds of solar-mass members of the Pleiades, measurements exist for only a few low-mass (<0.5 M {sub ⊙}) members of this key laboratory for stellar evolution theory. To fill this gap, we report P {sub rot} for 132 low-mass Pleiades members (including nearly 100 with M ≤ 0.45 M {sub ⊙}), measured from photometric monitoring ofmore » the cluster conducted by the Palomar Transient Factory in late 2011 and early 2012. These periods extend the portrait of stellar rotation at 125 Myr to the lowest-mass stars and re-establish the Pleiades as a key benchmark for models of the transport and evolution of stellar angular momentum. Combining our new P {sub rot} with precise BVIJHK photometry reported by Stauffer et al. and Kamai et al., we investigate known anomalies in the photometric properties of K and M Pleiades members. We confirm the correlation detected by Kamai et al. between a star's P {sub rot} and position relative to the main sequence in the cluster's color–magnitude diagram. We find that rapid rotators have redder ( V − K ) colors than slower rotators at the same V , indicating that rapid and slow rotators have different binary frequencies and/or photospheric properties. We find no difference in the photometric amplitudes of rapid and slow rotators, indicating that asymmetries in the longitudinal distribution of starspots do not scale grossly with rotation rate.« less

Bayesian inference of galaxy formation from the K-band luminosity function of galaxies: tensions between theory and observation

NASA Astrophysics Data System (ADS)

Lu, Yu; Mo, H. J.; Katz, Neal; Weinberg, Martin D.

2012-04-01

We conduct Bayesian model inferences from the observed K-band luminosity function of galaxies in the local Universe, using the semi-analytic model (SAM) of galaxy formation introduced in Lu et al. The prior distributions for the 14 free parameters include a large range of possible models. We find that some of the free parameters, e.g. the characteristic scales for quenching star formation in both high-mass and low-mass haloes, are already tightly constrained by the single data set. The posterior distribution includes the model parameters adopted in other SAMs. By marginalizing over the posterior distribution, we make predictions that include the full inferential uncertainties for the colour-magnitude relation, the Tully-Fisher relation, the conditional stellar mass function of galaxies in haloes of different masses, the H I mass function, the redshift evolution of the stellar mass function of galaxies and the global star formation history. Using posterior predictive checking with the available observational results, we find that the model family (i) predicts a Tully-Fisher relation that is curved; (ii) significantly overpredicts the satellite fraction; (iii) vastly overpredicts the H I mass function; (iv) predicts high-z stellar mass functions that have too many low-mass galaxies and too few high-mass ones and (v) predicts a redshift evolution of the stellar mass density and the star formation history that are in moderate disagreement. These results suggest that some important processes are still missing in the current model family, and we discuss a number of possible solutions to solve the discrepancies, such as interactions between galaxies and dark matter haloes, tidal stripping, the bimodal accretion of gas, preheating and a redshift-dependent initial mass function.

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

Contact Binaries on Their Way Towards Merging

NASA Astrophysics Data System (ADS)

Gazeas, K.

2015-07-01

Contact binaries are the most frequently observed type of eclipsing star system. They are small, cool, low-mass binaries belonging to a relatively old stellar population. They follow certain empirical relationships that closely connect a number of physical parameters with each other, largely because of constraints coming from the Roche geometry. As a result, contact binaries provide an excellent test of stellar evolution, specifically for stellar merger scenarios. Observing campaigns by many authors have led to the cataloging of thousands of contact binaries and enabled statistical studies of many of their properties. A large number of contact binaries have been found to exhibit extraordinary behavior, requiring follow-up observations to study their peculiarities in detail. For example, a doubly-eclipsing quadruple system consisting of a contact binary and a detached binary is a highly constrained system offering an excellent laboratory to test evolutionary theories for binaries. A new observing project was initiated at the University of Athens in 2012 in order to investigate the possible lower limit for the orbital period of binary systems before coalescence, prior to merging.

The dynamical mass of a classical Cepheid variable star in an eclipsing binary system.

PubMed

Pietrzyński, G; Thompson, I B; Gieren, W; Graczyk, D; Bono, G; Udalski, A; Soszyński, I; Minniti, D; Pilecki, B

2010-11-25

Stellar pulsation theory provides a means of determining the masses of pulsating classical Cepheid supergiants-it is the pulsation that causes their luminosity to vary. Such pulsational masses are found to be smaller than the masses derived from stellar evolution theory: this is the Cepheid mass discrepancy problem, for which a solution is missing. An independent, accurate dynamical mass determination for a classical Cepheid variable star (as opposed to type-II Cepheids, low-mass stars with a very different evolutionary history) in a binary system is needed in order to determine which is correct. The accuracy of previous efforts to establish a dynamical Cepheid mass from Galactic single-lined non-eclipsing binaries was typically about 15-30% (refs 6, 7), which is not good enough to resolve the mass discrepancy problem. In spite of many observational efforts, no firm detection of a classical Cepheid in an eclipsing double-lined binary has hitherto been reported. Here we report the discovery of a classical Cepheid in a well detached, double-lined eclipsing binary in the Large Magellanic Cloud. We determine the mass to a precision of 1% and show that it agrees with its pulsation mass, providing strong evidence that pulsation theory correctly and precisely predicts the masses of classical Cepheids.

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.

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 Teaching Module about Stellar Structure and Evolution

ERIC Educational Resources Information Center

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…

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

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

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

Testing galaxy quenching theories with scatter in the stellar-to-halo mass relation

NASA Astrophysics Data System (ADS)

Tinker, Jeremy L.

2017-05-01

We use the scatter in the stellar-to-halo mass relation to constrain galaxy evolution models. If the efficiency of converting accreted baryons into stars varies with time, haloes of the same present-day mass but different formation histories will have different z = 0 galaxy stellar mass. This is one of the sources of scatter in stellar mass at fixed halo mass, σlog M*. For massive haloes that undergo rapid quenching of star formation at z ˜ 2, different mechanisms that trigger this quenching yield different values of σlog M*. We use this framework to test various models in which quenching begins after a galaxy crosses a threshold in one of the following physical quantities: redshift, halo mass, stellar mass and stellar-to-halo mass ratio. Our model is highly idealized, with other sources of scatter likely to arise as more physics is included. Thus, our test is whether a model can produce scatter lower than observational bounds, leaving room for other sources. Recent measurements find σlog M* = 0.16 dex for 1011 M⊙ galaxies. Under the assumption that the threshold is constant with time, such a low value of σlog M* rules out all of these models with the exception of quenching by a stellar mass threshold. Most physical quantities, such as metallicity, will increase scatter if they are uncorrelated with halo formation history. Thus, to decrease the scatter of a given model, galaxy properties would correlate tightly with formation history, creating testable predictions for their clustering. Understanding why σlog M* is so small may be key to understanding the physics of galaxy formation.

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.

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.

On the universal stellar law

NASA Astrophysics Data System (ADS)

Krot, Alexander

In this work, we consider a statistical theory of gravitating spheroidal bodies to derive and develop the universal stellar law for extrasolar systems. Previously, the statistical theory for a cosmogonic body forming (so-called spheroidal body)has been proposed [1-3]. This theory starts from the conception for forming a spheroidal body inside a gas-dust protoplanetary nebula; it permits us to derive the form of distribution functions, mass density, gravitational potentials and strengths both for immovable and rotating spheroidal bodies as well as to find the distribution function of specific angular momentum[1-3]. If we start from the conception for forming a spheroidal body as a protostar (in particular, proto-Sun) inside a prestellar (presolar) nebula then the derived distribution functions of particle (as well as the mass density of an immovable spheroidal body) characterizes the first stage of evolution: from a prestellar molecular cloud (the presolar nebula) to the forming core of protostar (the proto-Sun) together with its shell as a stellar nebula (the solar nebula). This work derives the equation of state of an ideal stellar substance based on conception of gravitating spheroidal body. Using this equation, we obtain the universal stellar law (USL) for the planetary systems connecting temperature, size and mass of each of stars. This work also considers the Solar corona in the connection with USL. Then it is accounting under calculation of the ratio of temperature of the Solar corona to effective temperature of the Sun’ surfaceand modification of USL. To test justice of the modified USLfor different types of stars, the temperature of stellar corona is estimated. The prediction of parameters of stars is carrying out by means of the modified USL,as well as the Hertzsprung-Russell’s dependence [5-7]is derivedby means of USL directly. This paper also shows that knowledge of some characteristics for multi-planet extrasolar systems refines own parameters of stars. In this connection, comparison with estimations of temperatures using of the regression dependences for multi-planet extrasolar systems [8] testifies the obtained results entirely. References 1. Krot, A.M.:2009, A statistical approach to investigate the formation of the solar system. Chaos, Solitons and Fractals41(3), 1481-1500. 2. Krot, A.M.:2012, A models of forming planets and distribution of planetary distances and orbits in the solar system based on the statistical theory of spheroidal bodies. In:Solar System: Structure, Formation and Exploration, ch.9 (Ed. by Matteo de Rossi). New York, Nova Science Publishers, pp. 201-264. - ISBN: 978-1-62100-057-0. 3. Krot, A. M.:2012, A statistical theory of formation of gravitating cosmogonicbodies. Minsk,Bel. Navuka, 4. 448 p. - ISBN 978-985-08-1442-5 [monograph in Russian]. 5. Eddington, A.S.: 1916,On the radiative equilibrium of the stars.Mon. Not. Roy. Astron. Soc.84 (7), 525-528. 6. Jeans, J.: 1929, Astronomy and cosmogony. Cambridge, University Press. 7. Chandrasekhar, S.:1939, An introduction to the study of stellar structure.Cambridge, University Press. 8. Pintr, P., Peřinová, V., Lukš, A., Pathak, A.:2013, Statistical and regression analyses of detected extrasolar systems. Planetary and Space Science, 75(1), 37-45.

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.

Dark gamma-ray bursts

NASA Astrophysics Data System (ADS)

Brdar, Vedran; Kopp, Joachim; Liu, Jia

2017-03-01

Many theories of dark matter (DM) predict that DM particles can be captured by stars via scattering on ordinary matter. They subsequently condense into a DM core close to the center of the star and eventually annihilate. In this work, we trace DM capture and annihilation rates throughout the life of a massive star and show that this evolution culminates in an intense annihilation burst coincident with the death of the star in a core collapse supernova. The reason is that, along with the stellar interior, also its DM core heats up and contracts, so that the DM density increases rapidly during the final stages of stellar evolution. We argue that, counterintuitively, the annihilation burst is more intense if DM annihilation is a p -wave process than for s -wave annihilation because in the former case, more DM particles survive until the supernova. If among the DM annihilation products are particles like dark photons that can escape the exploding star and decay to standard model particles later, the annihilation burst results in a flash of gamma rays accompanying the supernova. For a galactic supernova, this "dark gamma-ray burst" may be observable in the Čerenkov Telescope Array.

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.

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.

White dwarf stars: cosmic chronometers and dark matter probes

NASA Astrophysics Data System (ADS)

Salaris, Maurizio; Cassisi, Santi

2018-04-01

White dwarfs (WD) are the endpoint of the evolution of the large majority of stars formed in our galaxy. In the last two decades observations and theory have improved to a level that makes it possible to employ WD for determining ages of the stellar populations in the disk of the Milky Way and in the nearest star clusters, and constrain the existence and properties of dark matter (DM) candidates. This review is centred on WD models, age-dating, and DM identification methods, recent results and future developments of the field.

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.

Red supergiants as supernova progenitors

NASA Astrophysics Data System (ADS)

Davies, Ben

2017-09-01

It is now well-established from pre-explosion imaging that red supergiants (RSGs) are the direct progenitors of Type-IIP supernovae. These images have been used to infer the physical properties of the exploding stars, yielding some surprising results. In particular, the differences between the observed and predicted mass spectrum has provided a challenge to our view of stellar evolutionary theory. However, turning what is typically a small number of pre-explosion photometric points into the physical quantities of stellar luminosity and mass requires a number of assumptions about the spectral appearance of RSGs, as well as their evolution in the last few years of life. Here I will review what we know about RSGs, with a few recent updates on how they look and how their appearance changes as they approach supernova. This article is part of the themed issue 'Bridging the gap: from massive stars to supernovae'.

Red supergiants as supernova progenitors.

PubMed

Davies, Ben

2017-10-28

It is now well-established from pre-explosion imaging that red supergiants (RSGs) are the direct progenitors of Type-IIP supernovae. These images have been used to infer the physical properties of the exploding stars, yielding some surprising results. In particular, the differences between the observed and predicted mass spectrum has provided a challenge to our view of stellar evolutionary theory. However, turning what is typically a small number of pre-explosion photometric points into the physical quantities of stellar luminosity and mass requires a number of assumptions about the spectral appearance of RSGs, as well as their evolution in the last few years of life. Here I will review what we know about RSGs, with a few recent updates on how they look and how their appearance changes as they approach supernova.This article is part of the themed issue 'Bridging the gap: from massive stars to supernovae'. © 2017 The Author(s).

Radial Velocities of 41 Kepler Eclipsing Binaries

NASA Astrophysics Data System (ADS)

Matson, Rachel A.; Gies, Douglas R.; Guo, Zhao; Williams, Stephen J.

2017-12-01

Eclipsing binaries are vital for directly determining stellar parameters without reliance on models or scaling relations. Spectroscopically derived parameters of detached and semi-detached binaries allow us to determine component masses that can inform theories of stellar and binary evolution. Here we present moderate resolution ground-based spectra of stars in close binary systems with and without (detected) tertiary companions observed by NASA’s Kepler mission and analyzed for eclipse timing variations. We obtain radial velocities and spectroscopic orbits for five single-lined and 35 double-lined systems, and confirm one false positive eclipsing binary. For the double-lined spectroscopic binaries, we also determine individual component masses and examine the mass ratio {M}2/{M}1 distribution, which is dominated by binaries with like-mass pairs and semi-detached classical Algol systems that have undergone mass transfer. Finally, we constrain the mass of the tertiary component for five double-lined binaries with previously detected companions.

Solving puzzles of GW150914 by primordial black holes

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

Blinnikov, S.; Dolgov, A.; Porayko, N.K.

The black hole binary properties inferred from the LIGO gravitational wave signal GW150914 posed several serious problems. The high masses and low effective spin of black hole binary can be explained if they are primordial (PBH) rather than the products of the stellar binary evolution. Such PBH properties are postulated ad hoc but not derived from fundamental theory. We show that the necessary features of PBHs naturally follow from the slightly modified Affleck-Dine (AD) mechanism of baryogenesis. The log-normal distribution of PBHs, predicted within the AD paradigm, is adjusted to provide an abundant population of low-spin stellar mass black holes.more » The same distribution gives a sufficient number of quickly growing seeds of supermassive black holes observed at high redshifts and may comprise an appreciable fraction of Dark Matter which does not contradict any existing observational limits. Testable predictions of this scenario are discussed.« less

Tidal capture of stars by a massive black hole

NASA Technical Reports Server (NTRS)

Novikov, I. D.; Pethick, C. J.; Polnarev, A. G.

1992-01-01

The processes leading to tidal capture of stars by a massive black hole and the consequences of these processes in a dense stellar cluster are discussed in detail. When the amplitude of a tide and the subsequent oscillations are sufficiently large, the energy deposited in a star after periastron passage and formation of a bound orbit cannot be estimated directly using the linear theory of oscillations of a spherical star, but rather numerical estimates must be used. The evolution of a star after tidal capture is discussed. The maximum ratio R of the cross-section for tidal capture to that for tidal disruption is about 3 for real systems. For the case of a stellar system with an empty capture loss cone, even in the case when the impact parameter for tidal capture only slightly exceeds the impact parameter for direct tidal disruption, tidal capture would be much more important than tidal disruption.

High surface magnetic field in red giants as a new signature of planet engulfment?

NASA Astrophysics Data System (ADS)

Privitera, Giovanni; Meynet, Georges; Eggenberger, Patrick; Georgy, Cyril; Ekström, Sylvia; Vidotto, Aline A.; Bianda, Michele; Villaver, Eva; ud-Doula, Asif

2016-09-01

Context. Red giant stars may engulf planets. This may increase the rotation rate of their convective envelope, which could lead to strong dynamo-triggered magnetic fields. Aims: We explore the possibility of generating magnetic fields in red giants that have gone through the process of a planet engulfment. We compare them with similar models that evolve without any planets. We discuss the impact of magnetic braking through stellar wind on the evolution of the surface velocity of the parent star. Methods: By studying rotating stellar models with and without planets and an empirical relation between the Rossby number and the surface magnetic field, we deduced the evolution of the surface magnetic field along the red giant branch. The effects of stellar wind magnetic braking were explored using a relation deduced from magnetohydrodynamics simulations. Results: The stellar evolution model of a red giant with 1.7 M⊙ without planet engulfment and with a time-averaged rotation velocity during the main sequence equal to 100 km s-1 shows a surface magnetic field triggered by convection that is stronger than 10 G only at the base of the red giant branch, that is, for gravities log g> 3. When a planet engulfment occurs, this magnetic field can also appear at much lower gravities, that is, at much higher luminosities along the red giant branch. The engulfment of a 15 MJ planet typically produces a dynamo-triggered magnetic field stronger than 10 G for gravities between 2.5 and 1.9. We show that for reasonable magnetic braking laws for the wind, the high surface velocity reached after a planet engulfment may be maintained sufficiently long to be observable. Conclusions: High surface magnetic fields for red giants in the upper part of the red giant branch are a strong indication of a planet engulfment or of an interaction with a companion. Our theory can be tested by observing fast-rotating red giants such as HD 31994, Tyc 0347-00762-1, Tyc 5904-00513-1, and Tyc 6054-01204-1 and by determining whether they show magnetic fields.

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.

Unsolved problems. [the physics of B stars

NASA Technical Reports Server (NTRS)

1982-01-01

The level of understanding of the physics of single, isolated B stars is assessed and unresolved problems are defined. The significant observational results concerning the effective temperatures, radii, masses and mantles are summarized. The results of the theory of the evolution of massive stars are confronted with the observed luminosities and effective temperatures of B stars. In addition the implications of stellar spectra theory are compared with observed spectra and a heuristic model for a mantle is developed. The chief unresolved problems for B stars concern developing detailed models for (1) the internal structure of massive stars which are beginning to evolve rapidly as they complete burning hydrogen in their cores; (2) mantles; and (3) the transfer of radiation in high temperature inhomogeneous moving bodies of gas.

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.

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.

Minicourses in Astrophysics, Modular Approach, Vol. II.

ERIC Educational Resources Information Center

Illinois Univ., Chicago.

This is the second of a two-volume minicourse in astrophysics. It contains chapters on the following topics: stellar nuclear energy sources and nucleosynthesis; stellar evolution; stellar structure and its determination; and pulsars. Each chapter gives much technical discussion, mathematical treatment, diagrams, and examples. References are…

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.

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.

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.

On the Origin and Evolution of Stellar Chromospheres, Coronae and Winds

NASA Technical Reports Server (NTRS)

Musielak, Z. E.

2000-01-01

This grant was awarded by NASA to The University of Alabama in Huntsville (UAH) to construct state-of-the-art, theoretical, two-component, chromospheric models for single stars of different spectral types and different evolutionary status. In our proposal, we suggested to use these models to predict the level of the "basal flux", the observed range of variation of chromospheric activity for a given spectral type, and the decrease of this activity with stellar age. In addition, for red giants and supergiants, we also proposed to construct self-consistent, purely theoretical wind models, and used these models to investigate the origin of "dividing lines" in the H-R diagram. In the following, we describe our completed work. We have accomplished the first main goal of our proposal by constructing first purely theoretical, time-dependent and two-component models of stellar chromospheres.1 The models require specifying only three basic stellar parameters, namely, the effective temperature, gravity and rotation rate, and they take into account non-magnetic and magnetic regions in stellar chromospheres. The non-magnetic regions are heated by acoustic waves generated by the turbulent convection in the stellar subphotospheric layers. The magnetic regions are identified with magnetic flux tubes uniformly distributed over the entire stellar surface and they are heated by longitudinal tube waves generated by turbulent motions in the subphotospheric and photospheric layers. The coverage of stellar surface by magnetic regions (the so-called filling factor) is estimated for a given rotation rate from an observational relationship. The constructed models are time-dependent and are based on the energy balance between the amount of mechanical energy supplied by waves and radiative losses in strong Ca II and Mg II emission lines. To calculate the amount of wave energy in the non-magnetic regions, we have used the Lighthill-Stein theory for sound generation.

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.

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.

Unravelling the Role of the SW Sextantis Stars in the Evolution of Cataclysmic Variables

NASA Astrophysics Data System (ADS)

Torres, Manuel; Steeghs, D.; Rodriguez-Gil, P.; Gansicke, B.; Marsh Warwick, T. R.; Araujo-Betancor, S.; Long, K.

2006-08-01

SW Sextantis stars are a relatively large group of cataclysmic variables whose properties contradict all predictions made by the current CV evolution theories. 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 33 SW Sex stars, and request here Gemini/GMOS-N time to obtain orbital phase-resolved spectroscopy if one of them enters a low state. These data will be used to accurately measure the mass ratio, white dwarf temperature, and distance of the system, eventually providing the first detailed system parameters for any SW Sex star.

UV-optical from space

NASA Technical Reports Server (NTRS)

Illingworth, Garth; Savage, Blair; Angel, J. Roger; Blandford, Roger D.; Boggess, Albert; Bowyer, C. Stuart; Carruthers, George R.; Cowie, Lennox L.; Doschek, George A.; Dupree, Andrea K.

1991-01-01

The following subject areas are covered: (1) the science program (star formation and origins of planetary systems; structure and evolution of the interstellar medium; stellar population; the galactic and extragalactic distance scale; nature of galaxy nuclei, AGNs, and QSOs; formation and evolution of galaxies at high redshifts; and cosmology); (2) implementation of the science program; (3) the observatory-class missions (HST; LST - the 6m successor to HST; and next-generation 16m telescope); (4) moderate and small missions (Delta-class Explorers; imaging astrometric interferometer; small Explorers; optics development and demonstrations; and supporting ground-based capabilities); (5) prerequisites - the current science program (Lyman-FUSE; HTS optimization; the near-term science program; data analysis, modeling, and theory funding; and archives); (6) technologies for the next century; and (7) lunar-based telescopes and instruments.

Pulsars in binary systems: probing binary stellar evolution and general relativity.

PubMed

Stairs, Ingrid H

2004-04-23

Radio pulsars in binary orbits often have short millisecond spin periods as a result of mass transfer from their companion stars. They therefore act as very precise, stable, moving clocks that allow us to investigate a large set of otherwise inaccessible astrophysical problems. The orbital parameters derived from high-precision binary pulsar timing provide constraints on binary evolution, characteristics of the binary pulsar population, and the masses of neutron stars with different mass-transfer histories. These binary systems also test gravitational theories, setting strong limits on deviations from general relativity. Surveys for new pulsars yield new binary systems that increase our understanding of all these fields and may open up whole new areas of physics, as most spectacularly evidenced by the recent discovery of an extremely relativistic double-pulsar system.

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.

Observation of interstellar lithium in the low-metallicity Small Magellanic Cloud.

PubMed

Howk, J Christopher; Lehner, Nicolas; Fields, Brian D; Mathews, Grant J

2012-09-06

The primordial abundances of light elements produced in the standard theory of Big Bang nucleosynthesis (BBN) depend only on the cosmic ratio of baryons to photons, a quantity inferred from observations of the microwave background. The predicted primordial (7)Li abundance is four times that measured in the atmospheres of Galactic halo stars. This discrepancy could be caused by modification of surface lithium abundances during the stars' lifetimes or by physics beyond the Standard Model that affects early nucleosynthesis. The lithium abundance of low-metallicity gas provides an alternative constraint on the primordial abundance and cosmic evolution of lithium that is not susceptible to the in situ modifications that may affect stellar atmospheres. Here we report observations of interstellar (7)Li in the low-metallicity gas of the Small Magellanic Cloud, a nearby galaxy with a quarter the Sun's metallicity. The present-day (7)Li abundance of the Small Magellanic Cloud is nearly equal to the BBN predictions, severely constraining the amount of possible subsequent enrichment of the gas by stellar and cosmic-ray nucleosynthesis. Our measurements can be reconciled with standard BBN with an extremely fine-tuned depletion of stellar Li with metallicity. They are also consistent with non-standard BBN.

Chemical Evolution and the Formation of Dwarf Galaxies in the Early Universe

NASA Astrophysics Data System (ADS)

Cote, Benoit; JINA-CEE, NuGrid, ChETEC

2018-06-01

Stellar abundances in local dwarf galaxies offer a unique window into the nature and nucleosynthesis of the first stars. They also contain clues regarding how galaxies formed and assembled in the early stages of the universe. In this talk, I will present our effort to connect nuclear astrophysics with the field of galaxy formation in order to define what can be learned about galaxy evolution using stellar abundances. In particular, I will describe the current state of our numerical chemical evolution pipeline which accounts for the mass assembly history of galaxies, present how we use high-redshift cosmological hydrodynamic simulations to calibrate our models and to learn about the formation of dwarf galaxies, and address the challenge of identifying the dominant r-process site(s) using stellar abundances.

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.

Mass loss of stars on the asymptotic giant branch. Mechanisms, models and measurements

NASA Astrophysics Data System (ADS)

Höfner, Susanne; Olofsson, Hans

2018-01-01

As low- and intermediate-mass stars reach the asymptotic giant branch (AGB), they have developed into intriguing and complex objects that are major players in the cosmic gas/dust cycle. At this stage, their appearance and evolution are strongly affected by a range of dynamical processes. Large-scale convective flows bring newly-formed chemical elements to the stellar surface and, together with pulsations, they trigger shock waves in the extended stellar atmosphere. There, massive outflows of gas and dust have their origin, which enrich the interstellar medium and, eventually, lead to a transformation of the cool luminous giants into white dwarfs. Dust grains forming in the upper atmospheric layers play a critical role in the wind acceleration process, by scattering and absorbing stellar photons and transferring their outward-directed momentum to the surrounding gas through collisions. Recent progress in high-angular-resolution instrumentation, from the visual to the radio regime, is leading to valuable new insights into the complex dynamical atmospheres of AGB stars and their wind-forming regions. Observations are revealing asymmetries and inhomogeneities in the photospheric and dust-forming layers which vary on time-scales of months, as well as more long-lived large-scale structures in the circumstellar envelopes. High-angular-resolution observations indicate at what distances from the stars dust condensation occurs, and they give information on the chemical composition and sizes of dust grains in the close vicinity of cool giants. These are essential constraints for building realistic models of wind acceleration and developing a predictive theory of mass loss for AGB stars, which is a crucial ingredient of stellar and galactic chemical evolution models. At present, it is still not fully possible to model all these phenomena from first principles, and to predict the mass-loss rate based on fundamental stellar parameters only. However, much progress has been made in recent years, which is described in this review. We complement this by discussing how observations of emission from circumstellar molecules and dust can be used to estimate the characteristics of the mass loss along the AGB, and in different environments. We also briefly touch upon the issue of binarity.

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.

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

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.

Lithium in Stellar Atmospheres: Observations and Theory

NASA Astrophysics Data System (ADS)

Lyubimkov, L. S.

2016-09-01

Of all the light elements, lithium is the most sensitive indicator of stellar evolution. This review discusses current data on the abundance of lithium in the atmospheres of A-, F-, G-, and K-stars of different types, as well as the consistency of these data with theoretical predictions. The variety of observed Li abundances is illustrated by the following objects in different stages of evolution: (1) Old stars in the galactic halo, which have a lithium abundance logɛ(Li)=2.2 (the "lithium plateau") that appears to be 0.5 dex lower than the primordial abundance predicted by cosmological models. (2) Young stars in the galactic disk, which have been used to estimate the contemporary initial lithium abundance logɛ(Li)=3.2±0.1 for stars in the Main sequence. Possible sources of lithium enrichment in the interstellar medium during evolution of the galaxy are discussed. (3) Evolving FGK dwarfs in the galactic disk, which have lower logɛ(Li) for lower effective temperature T eff and mass M. The "lithium dip" near T eff ~6600 K in the distribution of logɛ(Li) with respect to T eff in old clusters is discussed. (4) FGK giants and supergiants, of which most have no lithium at all. This phenomenon is consistent with rotating star model calculations. (5) Lithium rich cold giants with logɛ(Li) ≥ 2.0, which form a small, enigmatic group. Theoretical models with rotation can explain the existence of these stars only in the case of low initial rotation velocities V 0 <50 km/s. In all other cases it is necessary to assume recent synthesis of lithium (capture of a giant planet is an alternative). (6) Magnetic Ap-stars, where lithium is concentrated in spots located at the magnetic poles. There the lithium abundance reaches logɛ(Li)=6. Discrepancies between observations and theory are noted for almost all the stars discussed in this review.

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.

The slowly pulsating B-star 18 Pegasi: A testbed for upper main sequence stellar evolution

NASA Astrophysics Data System (ADS)

Irrgang, A.; Desphande, A.; Moehler, S.; Mugrauer, M.; Janousch, D.

2016-06-01

The predicted width of the upper main sequence in stellar evolution models depends on the empirical calibration of the convective overshooting parameter. Despite decades of discussions, its precise value is still unknown and further observational constraints are required to gauge it. Based on a photometric and preliminary asteroseismic analysis, we show that the mid B-type giant 18 Peg is one of the most evolved members of the rare class of slowly pulsating B-stars and, thus, bears tremendous potential to derive a tight lower limit for the width of the upper main sequence. In addition, 18 Peg turns out to be part of a single-lined spectroscopic binary system with an eccentric orbit that is greater than 6 years. Further spectroscopic and photometric monitoring and a sophisticated asteroseismic investigation are required to exploit the full potential of this star as a benchmark object for stellar evolution theory. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programmes 265.C-5038(A), 069.C-0263(A), and 073.D-0024(A). Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC), proposals H2005-2.2-016 and H2015-3.5-008. Based on observations made with the William Herschel Telescope operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, proposal W15BN015. Based on observations obtained with telescopes of the University Observatory Jena, which is operated by the Astrophysical Institute of the Friedrich-Schiller-University.

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.

MUSEing about the SHAPE of eta Car's outer ejecta

NASA Astrophysics Data System (ADS)

Mehner, A.; Steffen, W.; Groh, J.; Vogt, F. P. A.; Baade, D.; Boffin, H. M. J.; de Wit, W. J.; Oudmaijer, R. D.; Rivinius, T.; Selman, F.

2017-11-01

The role of episodic mass loss in evolved massive stars is one of the outstanding questions in stellar evolution theory. Integral field spectroscopy of nebulae around massive stars provide information on their recent mass-loss history. η Car is one of the most massive evolved stars and is surrounded by a complex circumstellar environment. We have conducted a three-dimensional morpho-kinematic analysis of η Car's ejecta outside its famous Homunculus nebula. SHAPE modelling of VLT MUSE data establish unequivocally the spatial cohesion of the outer ejecta and the correlation of ejecta with the soft X-ray emission.

Evidence of a primordial solar wind. [T Tauri-type evolution model

NASA Technical Reports Server (NTRS)

Sonett, C. P.

1974-01-01

A model is reviewed which requires a T Tauri 'wind' and at the same time encompasses certain early-object stellar features. The theory rests on electromagnetic induction driven by the 'wind'. Plasma confinement of the induced field prohibits a scattered field, and all energy loss is via ohmic heating in the scatterer (i.e., planetary objects). Two modes, one caused by the interplanetary electric field (transverse magnetic) and the other by time variations in the interplanetary magnetic field (transverse electric) are present. Parent body melting, lunar surface melting, and a primordial magnetic field are components of the proposed model.

Detection of a Red Supergiant Progenitor Star of a Type II-Plateau Supernova

NASA Astrophysics Data System (ADS)

Smartt, Stephen J.; Maund, Justyn R.; Hendry, Margaret A.; Tout, Christopher A.; Gilmore, Gerard F.; Mattila, Seppo; Benn, Chris R.

2004-01-01

We present the discovery of a red supergiant star that exploded as supernova 2003gd in the nearby spiral galaxy M74. The Hubble Space Telescope (HST) and the Gemini Telescope imaged this galaxy 6 to 9 months before the supernova explosion, and subsequent HST images confirm the positional coincidence of the supernova with a single resolved star that is a red supergiant of 8+4-2 solar masses. This confirms both stellar evolution models and supernova theories predicting that cool red supergiants are the immediate progenitor stars of type II-plateau supernovae.

3D Simulations of Convection: From the Sun Toward Evolved Stars

NASA Astrophysics Data System (ADS)

Höfner, Susanne

2018-04-01

Basic physical considerations and detailed numerical simulations predict a dramatic increase in the sizes of convection cells during late phases of stellar evolution. The recent progress in high-angular-resolution techniques has made it possible to observe surface structures on several nearby giants and supergiants for a wide range of wavelengths. Such observations provide much-needed checkpoints for convection theory, in addition to the detailed comparisons of models and observations for the sun. In this talk I will give an overview of current 3D convection models for different types of stars and discuss related observable phenomena.

The hubble constant.

PubMed

Huchra, J P

1992-04-17

The Hubble constant is the constant of proportionality between recession velocity and distance in the expanding universe. It is a fundamental property of cosmology that sets both the scale and the expansion age of the universe. It is determined by measurement of galaxy The Hubble constant is the constant of proportionality between recession velocity and development of new techniques for the measurements of galaxy distances, both calibration uncertainties and debates over systematic errors remain. Current determinations still range over nearly a factor of 2; the higher values favored by most local measurements are not consistent with many theories of the origin of large-scale structure and stellar evolution.

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 BLUE HOOK POPULATIONS OF MASSIVE GLOBULAR CLUSTERS

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

Brown, Thomas M.; Smith, Ed; Sweigart, Allen V.

2010-08-01

We present new Hubble Space Telescope ultraviolet color-magnitude diagrams of five massive Galactic globular clusters: NGC 2419, NGC 6273, NGC 6715, NGC 6388, and NGC 6441. These observations were obtained to investigate the 'blue hook' (BH) phenomenon previously observed in UV images of the globular clusters {omega} Cen and NGC 2808. Blue hook stars are a class of hot (approximately 35,000 K) subluminous horizontal branch stars that occupy a region of the HR diagram that is unexplained by canonical stellar evolution theory. By coupling new stellar evolution models to appropriate non-LTE synthetic spectra, we investigate various theoretical explanations for thesemore » stars. Specifically, we compare our photometry to canonical models at standard cluster abundances, canonical models with enhanced helium (consistent with cluster self-enrichment at early times), and flash-mixed models formed via a late helium-core flash on the white dwarf cooling curve. We find that flash-mixed models are required to explain the faint luminosity of the BH stars, although neither the canonical models nor the flash-mixed models can explain the range of color observed in such stars, especially those in the most metal-rich clusters. Aside from the variation in the color range, no clear trends emerge in the morphology of the BH population with respect to metallicity.« less

Songlines from Direct Collapse Seed Black Holes

NASA Astrophysics Data System (ADS)

Aykutalp, Aycin; Wise, John; Spaans, Marco; Meijerink, Rowin

2015-01-01

In the last decade, the growth of supermassive black holes (SMBHs) has been intricately linked to galaxy formation and evolution, and is a key ingredient in the assembly of galaxies. Observations of SMBHs with masses of 109 solar at high redshifts (z~7) poses challenges to the theory of seed black hole formation and their growth in young galaxies. Fundamental to understanding their existence within the first billion years after the Big Bang, is the identification of their formation processes, growth rate and evolution through cosmic time. We perform cosmological hydrodynamic simulations following the growth of direct collapse seed black holes (DCBH) including X-ray irradiation from the central black hole, stellar feedback both from metal-free and metal-rich stars and H2 self-shielding. These simulations demonstrate that X-ray irradiation from the central black hole regulates its growth and influence the formation of stellar population in the host halo. In particular, X-ray radiation enhances H2 formation in metal-free gas and initially induces the star formation in the halo. However, in the long term, X-ray irradiation from the accreting seed DCBH stifles the initial growth relative to the Eddington rate argument. This further complicates the explanation for the existence of SMBHs in the early universe.

Stellar nucleosynthesis and chemical evolution of the solar neighborhood

NASA Technical Reports Server (NTRS)

Clayton, Donald D.

1988-01-01

Current theoretical models of nucleosynthesis (N) in stars are reviewed, with an emphasis on their implications for Galactic chemical evolution. Topics addressed include the Galactic population II red giants and early N; N in the big bang; star formation, stellar evolution, and the ejection of thermonuclearly evolved debris; the chemical evolution of an idealized disk galaxy; analytical solutions for a closed-box model with continuous infall; and nuclear burning processes and yields. Consideration is given to shell N in massive stars, N related to degenerate cores, and the types of observational data used to constrain N models. Extensive diagrams, graphs, and tables of numerical data are provided.

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.

Stars and Nuclei. Part II

ERIC Educational Resources Information Center

Ames, Oakes

1972-01-01

A brief review of the evidence that nuclear reactions are the main source of stellar energy, how nuclear reactions synthesize the elements, and how nuclear reactions determine the course of stellar evolution. (Author/CP)

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

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.

Thermodynamics, Life, the Universe and Everything

NASA Astrophysics Data System (ADS)

Neswald, Elizabeth

2015-01-01

The laws of thermodynamics were developed in the first half of the nineteenth century to describe processes governing the working of steam engines. The mechanical equivalent of heat, which quantified the relationship between heat and motion, enabled the quantification and comparison of all energy transformation processes. The energy laws and the mechanical equivalent of heat quickly moved out of the narrower field of physics to form the basis of a cosmic narrative that began with stellar evolution and continued to universal heat death. Newer physiological theories turned to the energy laws to explain life processes, energy and entropy were integrated into theories of biological evolution and degeneration, and economists and cultural theorists turned to thermodynamics to explore both the limits of natural resources and economic expansion and the contradictions of industrial modernity. This paper discusses the career of thermodynamics as an explanatory model and cultural commonplace in the late nineteenth and early twentieth centuries, and the different scientific, religious, and social perspectives that could be expressed through this model. Connected through the entropy law intimately to irreversible processes and time, thermodynamics provided an arena to debate which way the world was going.

On the r-mode spectrum of relativistic stars: the inclusion of the radiation reaction

NASA Astrophysics Data System (ADS)

Ruoff, Johannes; Kokkotas, Kostas D.

2002-03-01

We consider both mode calculations and time-evolutions of axial r modes for relativistic uniformly rotating non-barotropic neutron stars, using the slow-rotation formalism, in which rotational corrections are considered up to linear order in the angular velocity Ω. We study various stellar models, such as uniform density models, polytropic models with different polytropic indices n, and some models based on realistic equations of state. For weakly relativistic uniform density models and polytropes with small values of n, we can recover the growth times predicted from Newtonian theory when standard multipole formulae for the gravitational radiation are used. However, for more compact models, we find that relativistic linear perturbation theory predicts a weakening of the instability compared to the Newtonian results. When turning to polytropic equations of state, we find that for certain ranges of the polytropic index n, the r mode disappears, and instead of a growth, the time-evolutions show a rapid decay of the amplitude. This is clearly at variance with the Newtonian predictions. It is, however, fully consistent with our previous results obtained in the low-frequency approximation.

The MACHO Project LMC Variable Star Inventory. VIII. The Recent Star Formation History of the Large Magellanic Cloud from the Cepheid Period Distribution

NASA Astrophysics Data System (ADS)

Alcock, C.; Allsman, R. A.; Alves, D. R.; Axelrod, T. S.; Becker, A. C.; Bennett, D. P.; Bersier, D. F.; Cook, K. H.; Freeman, K. C.; Griest, K.; Guern, J. A.; Lehner, M.; Marshall, S. L.; Minniti, D.; Peterson, B. A.; Pratt, M. R.; Quinn, P. J.; Rodgers, A. W.; Stubbs, C. W.; Sutherland, W.; Tomaney, A.; Vandehei, T.; Welch, D. L.

1999-02-01

We present an analysis of the period distribution of about 1800 Cepheids in the LMC, based on data obtained by the MACHO microlensing experiment and on a previous catalog by C. H. Payne Gaposchkin. Using stellar evolution and pulsation models, we construct theoretical period-frequency distributions that are compared with the observations. These models reveal that a significant burst of star formation has occurred recently in the LMC (~1.15x10^8 yr). We also show that during the last ~10^8 yr, the main center of star formation has been propagating from southeast to northwest along the bar. We find that the evolutionary masses of Cepheids are still smaller than pulsation masses by ~7% and that the red edge of the Cepheid instability strip could be slightly bluer than indicated by theory. There are approximately 600 Cepheids with periods below ~2.5 days that cannot be explained by evolution theory. We suggest that they are anomalous Cepheids and that a number of these stars are double-mode Cepheids.

Laboratory Astrophysics Prize: Laboratory Astrophysics with Nuclei

NASA Astrophysics Data System (ADS)

Wiescher, Michael

2018-06-01

Nuclear astrophysics is concerned with nuclear reaction and decay processes from the Big Bang to the present star generation controlling the chemical evolution of our universe. Such nuclear reactions maintain stellar life, determine stellar evolution, and finally drive stellar explosion in the circle of stellar life. Laboratory nuclear astrophysics seeks to simulate and understand the underlying processes using a broad portfolio of nuclear instrumentation, from reactor to accelerator from stable to radioactive beams to map the broad spectrum of nucleosynthesis processes. This talk focuses on only two aspects of the broad field, the need of deep underground accelerator facilities in cosmic ray free environments in order to understand the nucleosynthesis in stars, and the need for high intensity radioactive beam facilities to recreate the conditions found in stellar explosions. Both concepts represent the two main frontiers of the field, which are being pursued in the US with the CASPAR accelerator at the Sanford Underground Research Facility in South Dakota and the FRIB facility at Michigan State University.

Tests of two convection theories for red giant and red supergiant envelopes

NASA Technical Reports Server (NTRS)

Stothers, Richard B.; Chin, Chao-Wen

1995-01-01

Two theories of stellar envelope convection are considered here in the context of red giants and red supergiants of intermediate to high mass: Boehm-Vitense's standard mixing-length theory (MLT) and Canuto & Mazzitelli's new theory incorporating the full spectrum of turbulence (FST). Both theories assume incompressible convection. Two formulations of the convective mixing length are also evaluated: l proportional to the local pressure scale height (H(sub P)) and l proportional to the distance from the upper boundary of the convection zone (z). Applications to test both theories are made by calculating stellar evolutionary sequences into the red zone (z). Applications to test both theories are made by calculating stellar evolutionary sequences into the red phase of core helium burning. Since the theoretically predicted effective temperatures for cool stars are known to be sensitive to the assigned value of the mixing length, this quantity has been individually calibrated for each evolutionary sequence. The calibration is done in a composite Hertzsprung-Russell diagram for the red giant and red supergiant members of well-observed Galactic open clusters. The MLT model requires the constant of proportionality for the convective mixing length to vary by a small but statistically significant amount with stellar mass, whereas the FST model succeeds in all cases with the mixing lenghth simply set equal to z. The structure of the deep stellar interior, however, remains very nearly unaffected by the choices of convection theory and mixing lenghth. Inside the convective envelope itself, a density inversion always occurs, but is somewhat smaller for the convectively more efficient MLT model. On physical grounds the FST model is preferable, and seems to alleviate the problem of finding the proper mixing length.

Cosmic reionization on computers. Ultraviolet continuum slopes and dust opacities in high redshift galaxies

DOE PAGES

Khakhaleva-Li, Zimu; Gnedin, Nickolay Y.

2016-03-30

In this study, we compare the properties of stellar populations of model galaxies from the Cosmic Reionization On Computers (CROC) project with the exiting UV and IR data. Since CROC simulations do not follow cosmic dust directly, we adopt two variants of the dust-follows-metals ansatz to populate model galaxies with dust. Using the dust radiative transfer code Hyperion, we compute synthetic stellar spectra, UV continuum slopes, and IR fluxes for simulated galaxies. We find that the simulation results generally match observational measurements, but, perhaps, not in full detail. The differences seem to indicate that our adopted dust-follows-metals ansatzes are notmore » fully sufficient. While the discrepancies with the exiting data are marginal, the future JWST data will be of much higher precision, rendering highly significant any tentative difference between theory and observations. It is, therefore, likely, that in order to fully utilize the precision of JWST observations, fully dynamical modeling of dust formation, evolution, and destruction may be required.« less

Cosmic reionization on computers. Ultraviolet continuum slopes and dust opacities in high redshift galaxies

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

Khakhaleva-Li, Zimu; Gnedin, Nickolay Y.

In this study, we compare the properties of stellar populations of model galaxies from the Cosmic Reionization On Computers (CROC) project with the exiting UV and IR data. Since CROC simulations do not follow cosmic dust directly, we adopt two variants of the dust-follows-metals ansatz to populate model galaxies with dust. Using the dust radiative transfer code Hyperion, we compute synthetic stellar spectra, UV continuum slopes, and IR fluxes for simulated galaxies. We find that the simulation results generally match observational measurements, but, perhaps, not in full detail. The differences seem to indicate that our adopted dust-follows-metals ansatzes are notmore » fully sufficient. While the discrepancies with the exiting data are marginal, the future JWST data will be of much higher precision, rendering highly significant any tentative difference between theory and observations. It is, therefore, likely, that in order to fully utilize the precision of JWST observations, fully dynamical modeling of dust formation, evolution, and destruction may be required.« less

Quantum Tunnelling to the Origin and Evolution of Life

PubMed Central

Trixler, Frank

2013-01-01

Quantum tunnelling is a phenomenon which becomes relevant at the nanoscale and below. It is a paradox from the classical point of view as it enables elementary particles and atoms to permeate an energetic barrier without the need for sufficient energy to overcome it. Tunnelling might seem to be an exotic process only important for special physical effects and applications such as the Tunnel Diode, Scanning Tunnelling Microscopy (electron tunnelling) or Near-field Optical Microscopy operating in photon tunnelling mode. However, this review demonstrates that tunnelling can do far more, being of vital importance for life: physical and chemical processes which are crucial in theories about the origin and evolution of life can be traced directly back to the effects of quantum tunnelling. These processes include the chemical evolution in stellar interiors and within the cold interstellar medium, prebiotic chemistry in the atmosphere and subsurface of planetary bodies, planetary habitability via insolation and geothermal heat as well as the function of biomolecular nanomachines. This review shows that quantum tunnelling has many highly important implications to the field of molecular and biological evolution, prebiotic chemistry and astrobiology. PMID:24039543

The 100 brigthest Blue Straggler Stars.

NASA Astrophysics Data System (ADS)

Morales Durán, C.; Llorente de Andrés, F.; Ahumada, J. A.

2015-05-01

Blue straggler stars (BSS) are characterized by their appearance in the CMD of globular and open clusters, in the Main Sequence extension, above the turn-off and blueward of this. In accordance with the Standard Theory of stellar evolution, BSS should be out of the Main Sequence and over the Giant Branch if they really belong to the cluster and are formed at the same time than the rest of cluster stars. There are several theories that try to explain the existence of BSS but at present prevails the idea that they can be the product of mass transfer in binaries (McCrea, 1964), and the luminosity of the receiver star is incremented in such a way that now it is over the Main Sequence turn-off point of its cluster. Also it is believed that they are the result of stellar fussion of two or several stars, specially in dense systems as the globular cluster nucleus. This work is focalised in all the BSS brihgter the V = 10 mag. that we have been able to identify in open clusters. It is a sample unprecedented by its number and as well it is a sample with plentiful observational information, it is why we hope to be able to assure their membership to the parent cluster and obtain reliable information about their possible origin.

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.;

Nuclear Structure Aspects in Nuclear Astrophysics

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

Smith, Michael Scott

2006-12-01

Nuclear Astrophysics as a broad and diverse field of study can be viewed as a magnifier of the impact of microscopic processes on the evolution of macroscopic events. One of the primary goals in Nuclear Astrophysics is the understanding of the nucleosynthesis processes that take place in the cosmos and the simulation of the correlated stellar and explosive burning scenarios. These simulations are strongly dependent on the input from Nuclear Physics which sets the time scale for all stellar dynamic processes--from giga-years of stellar evolution to milliseconds of stellar explosions--and provides the basis for most of the signatures that wemore » have for the interpretation of these events--from stellar luminosities, elemental and isotopic abundances to neutrino flux from distant supernovae. The Nuclear Physics input comes through nuclear structure, low energy reaction rates, nuclear masses, and decay rates. There is a common perception that low energy reaction rates are the most important component of the required nuclear physics input; however, in this article we take a broader approach and present an overview of the close correlation between various nuclear structure aspects and their impact on nuclear astrophysics. We discuss the interplay between the weak and the strong forces on stellar time scales due to the limitations they provide for the evolution of slow and rapid burning processes. The effects of shell structure in nuclei on stellar burning processes as well as the impact of clustering in nuclei is outlined. Furthermore we illustrate the effects of the various nuclear structure aspects on the major nucleosynthesis processes that have been identified in the last few decades. We summarize and provide a coherent overview of the impact of all aspects of nuclear structure on nuclear astrophysics.« less

Stellar Evolution in NGC 6791: Mass Loss on the Red Giant Branch and the Formation of Low-Mass White Dwarfs

NASA Astrophysics Data System (ADS)

Kalirai, Jasonjot S.; Bergeron, P.; Hansen, Brad M. S.; Kelson, Daniel D.; Reitzel, David B.; Rich, R. Michael; Richer, Harvey B.

2007-12-01

We present the first detailed study of the properties (temperatures, gravities, and masses) of the NGC 6791 white dwarf population. This unique stellar system is both one of the oldest (8 Gyr) and most metal-rich ([Fe/H]~+0.4) open clusters in our Galaxy and has a color-magnitude diagram (CMD) that exhibits both a red giant clump and a much hotter extreme horizontal branch. Fitting the Balmer lines of the white dwarfs in the cluster using Keck/LRIS spectra suggests that most of these stars are undermassive, =0.43+/-0.06 Msolar, and therefore could not have formed from canonical stellar evolution involving the helium flash at the tip of the red giant branch. We show that at least 40% of NGC 6791's evolved stars must have lost enough mass on the red giant branch to avoid the flash and therefore did not convert helium into carbon-oxygen in their core. Such increased mass loss in the evolution of the progenitors of these stars is consistent with the presence of the extreme horizontal branch in the CMD. This unique stellar evolutionary channel also naturally explains the recent finding of a very young age (2.4 Gyr) for NGC 6791 from white dwarf cooling theory; helium-core white dwarfs in this cluster will cool ~3 times slower than carbon-oxygen-core stars, and therefore the corrected white dwarf cooling age is in fact >~7 Gyr, consistent with the well-measured main-sequence turnoff age. These results provide direct empirical evidence that mass loss is much more efficient in high-metallicity environments and therefore may be critical in interpreting the ultraviolet upturn in elliptical galaxies. Data presented herein were 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 the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. Based on observations obtained at the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii.

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.

Constraining Core-collapse Supernova Theory Predictions with 400 Progenitor Masses

NASA Astrophysics Data System (ADS)

Murphy, Jeremiah

2017-08-01

A new era is emerging in which we will have hundreds of progenitor masses for supernovae (SNe) and supernova remnants (SNRs); we propose to develop the statistical and theoretical tools needed to interpret this data. Two of the fundamental predictions of stellar evolution theory are that stars more massive than about 8 solar masses will explode and that some of these stars will not explode and form black holes. These statements are clear and simple, yet constraining them with observations has remained elusive until recently. For many years, the rate of progenitor discovery was steady but slow; each progenitor discovery required rare serendipitous pre-cursor imaging. With this steady drip of direct imaging, the number of progenitor masses numbered no more than 20. Recently, we developed a technique that increased the number of progenitor masses by a factor of 10 or more. In this new technique, we use HST photometry to age-date the stellar populations surrounding SNRs. From this age, we derive a progenitor mass for each SNR. We currently have progenitor masses for 115 SNRs in M31 and M33, soon we will have 300 more from M83, and there are hundreds more SNRs that could be analyzed in other nearby galaxies. To prepare for this watershed, we propose to develop the Bayesian framework needed to properly infer the progenitor mass distribution. This work will culminate in a direct constraint on the predictions of core-collapse supernova theory.

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.

Calibrating Detailed Chemical Analysis of M dwarfs

NASA Astrophysics Data System (ADS)

Veyette, Mark; Muirhead, Philip Steven; Mann, Andrew; Brewer, John; Allard, France; Homeier, Derek

2018-01-01

The ability to perform detailed chemical analysis of Sun-like F-, G-, and K-type stars is a powerful tool with many applications including studying the chemical evolution of the Galaxy, assessing membership in stellar kinematic groups, and constraining planet formation theories. Unfortunately, complications in modeling cooler stellar atmospheres has hindered similar analysis of M-dwarf stars. Large surveys of FGK abundances play an important role in developing methods to measure the compositions of M dwarfs by providing benchmark FGK stars that have widely-separated M dwarf companions. These systems allow us to empirically calibrate metallicity-sensitive features in M dwarf spectra. However, current methods to measure metallicity in M dwarfs from moderate-resolution spectra are limited to measuring overall metallicity and largely rely on astrophysical abundance correlations in stellar populations. In this talk, I will discuss how large, homogeneous catalogs of precise FGK abundances are crucial to advancing chemical analysis of M dwarfs beyond overall metallicity to direct measurements of individual elemental abundances. I will present a new method to analyze high-resolution, NIR spectra of M dwarfs that employs an empirical calibration of synthetic M dwarf spectra to infer effective temperature, Fe abundance, and Ti abundance. This work is a step toward detailed chemical analysis of M dwarfs at a similar precision achieved for FGK stars.

Unique first-forbidden β-decay rates for neutron-rich nickel isotopes in stellar environment

NASA Astrophysics Data System (ADS)

Nabi, Jameel-Un; Stoica, Sabin

2014-02-01

In astrophysical environments, allowed Gamow-Teller (GT) transitions are important, particularly for β-decay rates in presupernova evolution of massive stars, since they contribute to the fine-tuning of the lepton-to-baryon content of the stellar matter prior to and during the collapse of a heavy star. In environments where GT transitions are unfavored, first-forbidden transitions become important especially in medium heavy and heavy nuclei. Particularly in case of neutron-rich nuclei, first-forbidden transitions are favored primarily due to the phase-space amplification for these transitions. In this work the total β-decay half-lives and the unique first-forbidden (U1F) β-decay rates for a number of neutron-rich nickel isotopes, 72-78Ni, are calculated using the proton-neutron quasi-particle random phase approximation (pn-QRPA) theory in stellar environment for the first time. For the calculation of the β-decay half-lives both allowed and unique first-forbidden transitions were considered. Comparison of the total half-lives is made with measurements and other theoretical calculations where it was found that the pn-QRPA results are in better agreement with experiments and at the same time are suggestive of inclusion of rank 0 and rank 1 operators in first-forbidden rates for still better results.

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

The seven sisters DANCe. II. Proper motions and the lithium rotation-activity connection for G and K Pleiades

NASA Astrophysics Data System (ADS)

Barrado, D.; Bouy, H.; Bouvier, J.; Moraux, E.; Sarro, L. M.; Bertin, E.; Cuillandre, J.-C.; Stauffer, J. R.; Lillo-Box, J.; Pollock, A.

2016-12-01

Context. Stellar clusters open the window to understanding stellar evolution and, in particular, the change with time and the dependence on mass of different stellar properties. As such, stellar clusters act as laboratories where different theories can be tested. Aims: We try to understand the origin of the connection between lithium depletion in F, G, and K stars, rotation and activity in the Pleiades open cluster. Methods: We have collected all the relevant data in the literature, including information regarding rotation period, binarity, and activity, and cross-matched this data with proper motions, multiwavelength photometry, and membership probability from the DANCe database. To avoid biases, we only included single members of the Pleiades with probabilities larger than 75% in the discussion. Results: The analysis confirms that there is a strong link between activity, rotation, and the lithium equivalent width excess, especially for the range Lum(bol) = 0.5-0.2L⊙ (about K2-K7 spectral types or 0.75-0.95 M⊙). Conclusions: It is not possible to disentangle these effects, but we cannot exclude that the observed lithium overabundance is partially an observational effect from enhanced activity owing to a large coverage by stellar spots induced by high rotation rates. Since a bona fide lithium enhancement is present in young, fast rotators, both activity and rotation should play a role in the lithium problem. Tables 1-3 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/596/A113

NuGrid Stellar Data Set. I.Stellar Yields from H to Bi for Stars with Metallicities Z = 0.02 and Z = 0.01

NASA Astrophysics Data System (ADS)

Pignatari, M.; Herwig, F.; Hirschi, R.; Bennett, M.; Rockefeller, G.; Fryer, C.; Timmes, F. X.; Ritter, C.; Heger, A.; Jones, S.; Battino, U.; Dotter, A.; Trappitsch, R.; Diehl, S.; Frischknecht, U.; Hungerford, A.; Magkotsios, G.; Travaglio, C.; Young, P.

2016-08-01

We provide a set of stellar evolution and nucleosynthesis calculations that applies established physics assumptions simultaneously to low- and intermediate-mass and massive star models. Our goal is to provide an internally consistent and comprehensive nuclear production and yield database for applications in areas such as presolar grain studies. Our non-rotating models assume convective boundary mixing (CBM) where it has been adopted before. We include 8 (12) initial masses for Z = 0.01 (0.02). Models are followed either until the end of the asymptotic giant branch phase or the end of Si burning, complemented by simple analytic core-collapse supernova (SN) models with two options for fallback and shock velocities. The explosions show which pre-SN yields will most strongly be effected by the explosive nucleosynthesis. We discuss how these two explosion parameters impact the light elements and the s and p process. For low- and intermediate-mass models, our stellar yields from H to Bi include the effect of CBM at the He-intershell boundaries and the stellar evolution feedback of the mixing process that produces the {}13{{C}} pocket. All post-processing nucleosynthesis calculations use the same nuclear reaction rate network and nuclear physics input. We provide a discussion of the nuclear production across the entire mass range organized by element group. The entirety of our stellar nucleosynthesis profile and time evolution output are available electronically, and tools to explore the data on the NuGrid VOspace hosted by the Canadian Astronomical Data Centre are introduced.

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.

Identification of binary and multiple systems in TGAS using the Virtual Observatory

NASA Astrophysics Data System (ADS)

Jiménez-Esteban, F.; Solano, E.

2018-04-01

Binary and multiple stars have long provided an effective method of testing stellar formation and evolution theories. In particular, wide binary systems with separations > 20,000 au are particularly challenging as their physical separations are beyond the typical size of a collapsing cloud core (5,000 - 10,000 au). We present here a preliminary work in which we make use of the TGAS catalogue and Virtual Observatory tools and services (Aladin, TOPCAT, STILTS, VOSA, VizieR) to identify binary and multiple star candidate systems. The catalogue will be available from the Spanish VO portal (http://svo.cab.inta-csic.es) in the coming months.

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

Adiabatic Mass Loss Model in Binary Stars

NASA Astrophysics Data System (ADS)

Ge, H. W.

2012-07-01

Rapid mass transfer process in the interacting binary systems is very complicated. It relates to two basic problems in the binary star evolution, i.e., the dynamically unstable Roche-lobe overflow and the common envelope evolution. Both of the problems are very important and difficult to be modeled. In this PhD thesis, we focus on the rapid mass loss process of the donor in interacting binary systems. The application to the criterion of dynamically unstable mass transfer and the common envelope evolution are also included. Our results based on the adiabatic mass loss model could be used to improve the binary evolution theory, the binary population synthetic method, and other related aspects. We build up the adiabatic mass loss model. In this model, two approximations are included. The first one is that the energy generation and heat flow through the stellar interior can be neglected, hence the restructuring is adiabatic. The second one is that he stellar interior remains in hydrostatic equilibrium. We model this response by constructing model sequences, beginning with a donor star filling its Roche lobe at an arbitrary point in its evolution, holding its specific entropy and composition profiles fixed. These approximations are validated by the comparison with the time-dependent binary mass transfer calculations and the polytropic model for low mass zero-age main-sequence stars. In the dynamical time scale mass transfer, the adiabatic response of the donor star drives it to expand beyond its Roche lobe, leading to runaway mass transfer and the formation of a common envelope with its companion star. For donor stars with surface convection zones of any significant depth, this runaway condition is encountered early in mass transfer, if at all; but for main sequence stars with radiative envelopes, it may be encountered after a prolonged phase of thermal time scale mass transfer, so-called delayed dynamical instability. We identify the critical binary mass ratio for the onset of dynamical time scale mass transfer; if the ratio of donor to accretor masses exceeds this critical value, the dynamical time scale mass transfer ensues. The grid of criterion for all stars can be used to be the basic input as the binary population synthetic method, which will be improved absolutely. In common envelope evolution, the dissipation of orbital energy of the binary provides the energy to eject the common envelope; the energy budget for this process essentially consists of the initial orbital energy of the binary and the initial binding energies of the binary components. We emphasize that, because stellar core and envelope contribute mutually to each other's gravitational potential energy, proper evaluation of the total energy of a star requires integration over the entire stellar interior, not the ejected envelope alone as commonly assumed. We show that the change in total energy of the donor star, as a function of its remaining mass along an adiabatic mass-loss sequence, can be calculated. This change in total energy of the donor star, combined with the requirement that both remnant donor and its companion star fit within their respective Roche lobes, then circumscribes energetically possible survivors of common envelope evolution. It is the first time that we can calculate the accurate total energy of the donor star in common envelope evolution, while the results with the old method are inconsistent with observations.

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.

Relaxational effects in radiating stellar collapse

NASA Astrophysics Data System (ADS)

Govender, Megan; Maartens, Roy; Maharaj, Sunil D.

1999-12-01

Relaxational effects in stellar heat transport can in many cases be significant. Relativistic Fourier-Eckart theory is inherently quasi-stationary, and cannot incorporate these effects. The effects are naturally accounted for in causal relativistic thermodynamics, which provides an improved approximation to kinetic theory. Recent results, based on perturbations of a static star, show that relaxation effects can produce a significant increase in the central temperature and temperature gradient for a given luminosity. We use a simple stellar model that allows for non-perturbative deviations from staticity, and confirms qualitatively the predictions of the perturbative models.

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

Baqui, P.O.; Fabris, J.C.; Piattella, O.F., E-mail: pedrobaqui@gmail.com, E-mail: fabris@pq.cnpq.br, E-mail: oliver.piattella@pq.cnpq.br

We revisit the analysis made by Hwang and Noh [JCAP 1310 (2013)] aiming the construction of a Newtonian set of equations incorporating pressure effects typical of the General Relativity theory. We explicitly derive the Hwang-Noh equations, comparing them with similar computations found in the literature. Then, we investigate i ) the cosmological expansion, ii ) linear cosmological perturbations theory and iii ) stellar equilibrium by using the new set of equations and comparing the results with those coming from the usual Newtonian theory, from the Neo-Newtonian theory and from the General Relativity theory. We show that the predictions for themore » background evolution of the Universe are deeply changed with respect to the General Relativity theory: the acceleration of the Universe is achieved with positive pressure. On the other hand, the behaviour of small cosmological perturbations reproduces the one found in the relativistic context, even if only at small scales. We argue that this last result may open new possibilities for numerical simulations for structure formation in the Universe. Finally, the properties of neutron stars are qualitatively reproduced by Hwang-Noh equations, but the upper mass limit is at least one order of magnitude higher than the one obtained in General Relativity.« less

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.

The evolution of stable magnetic fields in stars: an analytical approach

NASA Astrophysics Data System (ADS)

Mestel, Leon; Moss, David

2010-07-01

The absence of a rigorous proof of the existence of dynamically stable, large-scale magnetic fields in radiative stars has been for many years a missing element in the fossil field theory for the magnetic Ap/Bp stars. Recent numerical simulations, by Braithwaite & Spruit and Braithwaite & Nordlund, have largely filled this gap, demonstrating convincingly that coherent global scale fields can survive for times of the order of the main-sequence lifetimes of A stars. These dynamically stable configurations take the form of magnetic tori, with linked poloidal and toroidal fields, that slowly rise towards the stellar surface. This paper studies a simple analytical model of such a torus, designed to elucidate the physical processes that govern its evolution. It is found that one-dimensional numerical calculations reproduce some key features of the numerical simulations, with radiative heat transfer, Archimedes' principle, Lorentz force and Ohmic decay all playing significant roles.

The SOAPS project - Spin-orbit alignment of planetary systems. Exoplanets' evolution histories in systems with different architectures

NASA Astrophysics Data System (ADS)

Faedi, F.; Gómez Maqueo Chew, Y.; Fossati, L.; Pollacco, D.; McQuillan, A.; Hebb, L.; Chaplin, W. J.; Aigrain, S.

2013-04-01

The wealth of information rendered by Kepler planets and planet candidates is indispensable for statistically significant studies of distinct planet populations, in both single and multiple systems. Empirical evidences suggest that Kepler's planet population shows different physical properties as compared to the bulk of known exoplanets. The SOAPS project, aims to shed light on Kepler's planets formation, their migration and architecture. By measuring v sini accurately for Kepler hosts with rotation periods measured from their high-precision light curves, we will assess the alignment of the planetary orbit with respect to the stellar spin axis. This degree of alignment traces the formation history and evolution of the planetary systems, and thus, allows to distinguish between different proposed migration theories. SOAPS will increase by a factor of 2 the number of spin-orbit alignment measurements pushing the parameters space down to the SuperEarth domain. Here we present our preliminary results.

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.

Lithium in a short-period tidally locked binary of M67: Implications for stellar evolution, Galactic Lithium evolution, and cosmology

NASA Technical Reports Server (NTRS)

Deliyannis, Constantine P.; King, Jeremy R.; Boesgaard, Ann M.; Ryan, Sean G.

1994-01-01

In open clusters, late-F stars exhibit a Li maximum (the Li 'peak' region) at lower abundance with age, which could be due either to stellar depletion or Galactic Li enrichment (or some other cause). We have observed a short-period tidally locked binary (SPTLB) on the Li peak region in the old cluster M67 to distinguish between alternatives. SPTLBs which synchronized in the early pre-main sequence would avoid the rotational mixing which, according to Yale models, may be responsible for depleting Li with age in open cluster dwarfs. We find that both components of the M67 SPTLB have a Li abundance lying about a factor of 2 or more above any other M67 single star and about a factor of 3 or more above the mean Li peak region abundance in M67. Our results suggest that the initial Li abundance in M67 is at least as high as approximately 3.0 = 12 + log (N(sub Li)/N(sub H)). Our high M67 SPTLB Li abundance and those in other clusters support the combination of Zahn's tidal circularization and the Yale rotational mixing theories and may indicate that the halo Li plateau (analogous to the cluster Li peak region) abundance has been depleted from a higher primordial value. Implications are discussed.

Evolution of the Mass and Luminosity Functions of Globular Star Clusters

NASA Astrophysics Data System (ADS)

Goudfrooij, Paul; Fall, S. Michael

2016-12-01

We reexamine the dynamical evolution of the mass and luminosity functions of globular star clusters (GCMF and GCLF). Fall & Zhang (2001, FZ01) showed that a power-law MF, as commonly seen among young cluster systems, would evolve by dynamical processes over a Hubble time into a peaked MF with a shape very similar to the observed GCMF in the Milky Way and other galaxies. To simplify the calculations, the semi-analytical FZ01 model adopted the “classical” theory of stellar escape from clusters, and neglected variations in the M/L ratios of clusters. Kruijssen & Portegies Zwart (2009, KPZ09) modified the FZ01 model to include “retarded” and mass-dependent stellar escape, the latter causing significant M/L variations. KPZ09 asserted that their model was compatible with observations, whereas the FZ01 model was not. We show here that this claim is not correct; the FZ01 and KPZ09 models fit the observed Galactic GCLF equally well. We also show that there is no detectable correlation between M/L and L for GCs in the Milky Way and Andromeda galaxies, in contradiction with the KPZ09 model. Our comparisons of the FZ01 and KPZ09 models with observations can be explained most simply if stars escape at rates approaching the classical limit for high-mass clusters, as expected on theoretical grounds.

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.

A model for the wind of the M supergiant VX Sagittarii

NASA Astrophysics Data System (ADS)

Pijpers, F. P.

1990-11-01

The velocity distribution of the stellar wind from the M supergiant VX Sgr deduced from interferometric measurements of maser lines by Chapman and Cohen (1986) has been modeled using the linearized theory of stellar winds driven by short period sound waves proposed by Pijpers and Hearn (1989) and the theory of stellar winds driven by short period shocks proposed by Pijpers and Habing (1989). The effect of the radiative forces on the dust formed in the wind is included in a simple way. Good agreement with the observations is obtained by a range of parameters in the theory. A series of observations of the maser lines at invervals of one or a few days may provide additional constraints on the interpretation.

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).

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

A spectroscopic and photometric study of the unique pre- main sequence system KH 15D

NASA Astrophysics Data System (ADS)

Hamilton, Catrina Marie

2004-09-01

As a class, T Tauri stars are YSOs, some which are surrounded by circumstellar disks, and are recognized as the final stage of low-mass star formation. They also represent the earliest stage of stellar evolution that is optically visible, and, therefore, can be easily studied in detail. Understanding the processes through which these young stars interact with and eventually disperse their circumstellar disks is critical for understanding how they evolve from the T Tauri phase to the zero age main sequence (ZAMS), and how this affects the formation of planets, as well as their rotational evolution. KH 15D is a unique eclipsing system that could provide invaluable insight into the evolution of circumstellar disk material, as well as clues to the close stellar environment. Discovered in 1997, this star system has been observed to undergo an eclipse every 48 days in which the star's light is diminished by 3.5 magnitudes. What is so unusual about the eclipse is that the length of the eclipse has evolved over time, growing in length from 16 days initially, to ˜25 days in 2002/2003. Evolution of disk material on these timescales has never been observed before, and therefore provides us with a unique opportunity to refine our theories about remnant disks around young stars, how they transition, possibly into planets, and what role they play as the star matures and arrives on the zero age main sequence. Additionally, high resolution spectra obtained at specific phases during the December 2001 eclipse showed that as the obscuring matter cut across the star, dramatic spectral changes in the Hα and Hβ lines were seen. Its unique eclipse produces a “natural coronographic” effect in which the stellar photosphere is occulted, revealing details of its magnetosphere and surroundings during eclipse. There is evidence that the weak-lined T Tauri star (WTTS) central to the system is actively accreting gas, although probably not at the rate of a typical classical T Tauri star, calling into question the common practice of associating WTTS characteristics with the absence of an accretion disk. Here I present an investigation of the photometric and spectroscopic properties of the KH 15D eclipsing system, and discuss the implications that this system holds for the future research of T Tauri stars.

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.

Preface

NASA Astrophysics Data System (ADS)

Schuh, S.; Handler, G.

2009-03-01

The Joint European and National Astronomy Meeting 2008 (JENAM 2008) was held from September 8-12, 2008 in Vienna, Austria, as the joint meeting of the Austrian Society of Astronomy and Astrophysics (ÖGAA), the Astronomische Gesellschaft (AG), and the European Astronomical Society (EAS). It hosted nine symposia under the overall topic ''New Challenges To European Astronomy''. This special volume of Communications in Asteroseismology holds the proceedings of the JENAM 2008 Symposium No 4: ''Asteroseismology and Stellar Evolution''. The Asteroseismology and Stellar Evolution Symposium has been generously sponsored by the ÖGAA, by the HELAS Forum (an activity of the European Helio- and Asteroseismology Network, initiative funded by the European Commission since April 1st, 2006, as a Co-ordination Action under its Sixth Framework Programme, FP6), and by the Kulturabteilung der Stadt Wien (Magistratsabteilung 7). The Symposium program was put together by the Scientific Organizing Committee consisting of Conny Aerts (University of Leuven, Belgium), Annie Baglin (Observatoire de Paris, France), Wolfgang Glatzel (University of Göttingen, Germany), Gerald Handler (University of Vienna, Austria, Co-convener), Uli Heber (University of Erlangen-Nürnberg, Germany), Katrien Kolenberg (University of Vienna, Austria), Suzanna Randall (European Southern Observatory) and Sonja Schuh (University of Göttingen, Germany, Convener). Out of a total of 60 oral and poster contributions, 15 contributed talks were selected for presentation during the three half-day session program, with ample time for questions and discussion. There also was an opportunity to introduce the poster contributions during 2-min oral presentations. The scientific topics covered diverse object classes divided into Stochastically excited pulsators (main sequence, red giants, AGB supergiants), Heat-driven pulsators along the main sequence, and Compact pulsators, as well as additional topics that we have summarized as contributions on Eruptive variable and binary stars, and contributions presenting Methods and tools. The three session topics were introduced by two invited review speakers per field. In the first session, Jadwiga Daszynska-Daszkiewicz summarized current ''Challenges for stellar pulsation and evolution theory'', and Konstanze Zwintz reported ''A preliminary glimpse on CoRoT results and expectations'' (for Eric Michel), together giving an overview of the observational and theoretical status of the field. Anne Thoul and Oleg Kochukhov presented the state of the art in ''Asteroseismology of B stars'' and ''Asteroseismology of chemically peculiar stars'', respectively, in the second session, highlighting the hot issues in understanding and interpreting the pulsational behaviour of these groups. The stellar evolution aspect was given special consideration in ''Asteroseismology and Evolution of EHB stars'' by Roy Østensen and ''Asteroseismology and evolution of GW Vir stars'' by Pierre-Oliver Quirion in the concluding third session. A dedicated audience (on average 45 participants in each session), the excellent speakers, and our colleague Patrick Lenz who acted as the friendly and competent technician made this Symposium a highly interesting, enjoyable and successful event. We would like to thank all speakers, poster authors, and participants for coming to Vienna, the SOC and the referees for their work, the local organizers at Vienna for providing all the necessary infrastructure, and all sponsors for having made possible this event and the proceedings at hand.

Proto-planetary disc evolution and dispersal

NASA Astrophysics Data System (ADS)

Rosotti, Giovanni Pietro

2015-05-01

Planets form from gas and dust discs in orbit around young stars. The timescale for planet formation is constrained by the lifetime of these discs. The properties of the formed planetary systems depend thus on the evolution and final dispersal of the discs, which is the main topic of this thesis. Observations reveal the existence of a class of discs called "transitional", which lack dust in their inner regions. They are thought to be the last stage before the complete disc dispersal, and hence they may provide the key to understanding the mechanisms behind disc evolution. X-ray photoevaporation and planet formation have been studied as possible physical mechanisms responsible for the final dispersal of discs. However up to now, these two phenomena have been studied separately, neglecting any possible feedback or interaction. In this thesis we have investigated what is the interplay between these two processes. We show that the presence of a giant planet in a photo-evaporating disc can significantly shorten its lifetime, by cutting the inner regions from the mass reservoir in the exterior of the disc. This mechanism produces transition discs that for a given mass accretion rate have larger holes than in models considering only X-ray photo-evaporation, constituting a possible route to the formation of accreting transition discs with large holes. These discs are found in observations and still constitute a puzzle for the theory. Inclusion of the phenomenon called "thermal sweeping", a violent instability that can destroy a whole disc in as little as 10 4 years, shows that the outer disc left can be very short-lived (depending on the X-ray luminosity of the star), possibly explaining why very few non accreting transition discs are observed. However the mechanism does not seem to be efficient enough to reconcile with observations. In this thesis we also show that X-ray photo-evaporation naturally explains the observed correlation between stellar masses and accretion rates and is therefore the ideal candidate for driving disc evolution. Another process that can influence discs is a close encounter with another star. In this thesis we develop a model to study the effect of stellar dynamics in the natal stellar cluster on the discs, following for the first time at the same time the stellar dynamics together with the evolution of the discs. We find that, although close encounters with stars are unlikely to change significantly the mass of a disc, they can change substantially its size, hence imposing an upper limit on the observed disc radii. Finally, we investigated in this thesis whether discs can be reformed after their dispersal. If a star happens to be in a region that is currently forming stars, it can accrete material from the interstellar medium. This mechanism may result in the production of "second generation" discs such that in a given star forming region a few percent of stars may still possess a disc, in tentative agreement with observations of so called "old accretors", which are difficult to explain within the current paradigm of disc evolution and dispersal.

The formation and evolution of galaxies in an expanding universe

NASA Astrophysics Data System (ADS)

Ceverino-Rodriguez, Daniel

This PhD thesis is part of an ongoing effort in improving the theory of galaxy formation in a LCDM Universe. We include more realistic models of radiative cooling, star formation, and stellar feedback. A special attention has been given to the role of supernova explosions and stellar winds in the galaxy assembly. These processes happen at very small scales (parsecs), but they affect the inter-stellar medium (ISM) at Kpc-scales and regulate the formation of a whole galaxy. Previous attempts of mimicking these effects in simulations of galaxy formation use very simplified assumptions. We develop a much more realistic prescription for modeling the feedback, which minimizes any ad hoc sub-grid physics. We start with developing high resolution models of the ISM and formulate the conditions required for its realistic functionality: formation of a multi-phase medium with hot chimneys, super-bubbles, cold molecular phase, and very slow consumption of gas. We find that this can be achieved only by doing what the real Universe does: formation of dense (> 10 H atoms cm -3 ), cold ( T [approximate] 100 K) molecular phase, where star formation happens, and which young stars disrupt. Another important ingredient is the effect of runaway stars: massive binary stars ejected from molecular clouds when one of the companions becomes a supernova. These stars can move to 10-100 parsecs away from molecular clouds before exploding themselves as supernovae. This greatly facilitates the feedback. Once those effects are implemented into cosmological simulations, galaxy formation proceeds more realistically. For example, we do not have the overcooling problem. The angular momentum problem (resulting in a too massive bulge) is also reduced substantially: the rotation curves are nearly flat. The galaxy formation also becomes more violent. Just as often observed in absorption lines studies, there are substantial outflows from forming and active galaxies. At high redshifts we routinely find gas with few hundred km s -1 and occasionally 1000 - 2000 kms - 1 . The gas has high metallicity, which may exceed the solar metallicity. The temperature of the gas in the outflows and in chimneys can be very high: T = 10 7 - 10^8 K. The density profile of dark matter is still consistent with a cuspy profile. The simulations reproduce this picture only if the resolution is very high: better than 50 pc, which is 10 times better than the typical resolution in previous cosmological simulations. Our simulations of galaxy formation reach a resolution of 35 pc. At the time in which most of the mass is assembled into a galaxy, a big fraction of the gas in the galactic disk has already been converted into stars. Therefore, we can assume that the remaining gas does not affect the evolution of the stellar distribution. In this approximation, all gasdynamical processes are neglected and we treat a galaxy as a pure collisionless system. Then we use N-body-only models to study the long-term evolution of an already formed stellar disk. During this evolution, the disk develops a bar at the center through disk instabilities. We find dynamical resonances between the bar and disk or halo material. These resonances can capture stars near certain resonant orbits. As a result, resonances prevent the evolution of the stars trapped around these orbits.

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.

A footnote on the prehistory of interpretation of stellar colours

NASA Astrophysics Data System (ADS)

Brosche, P.

2001-10-01

Father Maximilian Hell S.J. (1720-92) was one of the first astronomers to formulate a theory of aurorae. This paper speculates on the possibility that Hell somehow could have associated his theory with the colours of stars, possibly by assuming that in some stellar atmospheres frozen particles are prevailing whereas in other stellar atmospheres water droplets dominate; the first would be more white-yellow, the others could show all colours of the rainbow. Our main point consists in the fact that somebody had seen and recorded colours of stars as an intrinsic phenomenon which called for an explanation.

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.

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 spectroscopic indistinguishability of red giant branch and red clump stars

NASA Astrophysics Data System (ADS)

Masseron, T.; Hawkins, K.

2017-01-01

Context. Stellar spectroscopy provides useful information on the physical properties of stars such as effective temperature, metallicity and surface gravity. However, those photospheric characteristics are often hampered by systematic uncertainties. The joint spectro-sismo project (APOGEE+Kepler, aka APOKASC) of field red giants has revealed a puzzling offset between the surface gravities (log g) determined spectroscopically and those determined using asteroseismology, which is largely dependent on the stellar evolutionary status. Aims: Therefore, in this letter, we aim to shed light on the spectroscopic source of the offset. Methods: We used the APOKASC sample to analyse the dependencies of the log g discrepancy as a function of stellar mass and stellar evolutionary status. We discuss and study the impact of some neglected abundances on spectral analysis of red giants, such as He and carbon isotopic ratio. Results: We first show that, for stars at the bottom of the red giant branch where the first dredge-up had occurred, the discrepancy between spectroscopic log g and asteroseismic log g depends on stellar mass. This seems to indicate that the log g discrepancy is related to CN cycling. Among the CN-cycled elements, we demonstrate that the carbon isotopic ratio (12C /13C) has the largest impact on stellar spectrum. In parallel, we observe that this log g discrepancy shows a similar trend as the 12C /13C ratios as expected by stellar evolution theory. Although we did not detect a direct spectroscopic signature of 13C, other corroborating evidences suggest that the discrepancy in log g is tightly correlated to the production of 13C in red giants. Moreover, by running the data-driven algorithm (the Cannon) on a synthetic grid trained on the APOGEE data, we try to evaluate more quantitatively the impact of various 12C /13C ratios. Conclusions: While we have demonstrated that 13C indeed impacts all parameters, the size of the impact is smaller than the observed offset in log g. If further tests confirm that 13C is not the main element responsible of the log g problem, the number of spectroscopic effects remaining to be investigated is now relatively limited (if any).

On Lithium-rich Red Giants. I. Engulfment of Substellar Companions

NASA Astrophysics Data System (ADS)

Aguilera-Gómez, Claudia; Chanamé, Julio; Pinsonneault, Marc H.; Carlberg, Joleen K.

2016-10-01

A small fraction of red giants are known to be lithium (Li) rich, in contradiction with expectations from stellar evolutionary theory. A possible explanation for these atypical giants is the engulfment of an Li-rich planet or brown dwarf by the star. In this work, we model the evolution of Li abundance in canonical red giants including the accretion of a substellar mass companion. We consider a wide range of stellar and companion masses, Li abundances, stellar metallicities, and planetary orbital periods. Based on our calculations, companions with masses lower than 15 {M}J dissolve in the convective envelope and can induce Li enrichment in regimes where extra mixing does not operate. Our models indicate that the accretion of a substellar companion can explain abundances up to A(Li) ≈ 2.2, setting an upper limit for Li-rich giants formed by this mechanism. Giants with higher abundances need another mechanism to be explained. For reasonable planetary distributions, we predict the Li abundance distribution of low-mass giants undergoing planet engulfment, finding that between 1% and 3% of them should have {{A}}({Li})≥slant 1.5. We show that depending on the stellar mass range, this traditional definition of Li-rich giants is misleading, as isolated massive stars would be considered anomalous while giants engulfing a companion would be set aside, flagged as normal. We explore the detectability of companion engulfment, finding that planets with masses higher than ∼ 7 {M}J produce a distinct signature, and that descendants of stars originating in the Li dip and low-luminosity red giants are ideal tests of this channel.

Improved solar models constructed with a formulation of convection for stellar structure and evolution calculations without the mixing-length theory approximations

NASA Technical Reports Server (NTRS)

Lydon, Thomas J.; Fox, Peter A.; Sofia, Sabatino

1993-01-01

We have updated a previous attempt to incorporate within a solar model a treatment of convection based upon numerical simulations of convection rather than mixing-length theory (MLT). We have modified our formulation of convection for a better treatment of the kinetic energy flux. Our solar model has been updated to include a complete range of OPAL opacities, the Debye-Hueckel correction to the equation of state, helium diffusion due to gravitational settling, and atmospheres by Kurucz. We construct a series of models using both MLT and our revised formulation of convection and the compared results to measurements of the solar radius, the solar luminosity, and the depth of the solar convection zone as inferred from helioseismology. We find X(solar) = 0.702 +/- 0.005, Y(solar) = 0.278 +/- 0.005, and Z(solar) = 0.0193 +/- 0.0005.

Massive stars in their death throes.

PubMed

Eldridge, John J

2008-12-13

The study of the stars that explode as supernovae used to be a forensic study, working backwards from the remnants of the star. This changed in 1987 when the first progenitor star was identified in pre-explosion images. Currently, there are eight detected progenitors with another 21 non-detections, for which only a limit on the pre-explosion luminosity can be placed. This new avenue of supernova research has led to many interesting conclusions, most importantly that the progenitors of the most common supernovae, type IIP, are red supergiants, as theory has long predicted. However, no progenitors have been detected thus far for the hydrogen-free type Ib/c supernovae, which, given the expected progenitors, is an unlikely result. Also, observations have begun to show evidence that luminous blue variables, which are among the most massive stars, may directly explode as supernovae. These results contradict the current stellar evolution theory. This suggests that we may need to update our understanding.

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.

Chemical evolution in spiral and irregular galaxies

NASA Technical Reports Server (NTRS)

Torres-Peimbert, S.

1986-01-01

A brief review of models of chemical evolution of the interstellar medium in our galaxy and other galaxies is presented. These models predict the time variation and radial dependence of chemical composition in the gas as function of the input parameters; initial mass function, stellar birth rate, chemical composition of mass lost by stars during their evolution (yields), and the existence of large scale mass flows, like infall from the halo, outflow to the intergalactic medium or radial flows within a galaxy. At present there is a considerable wealth of observational data on the composition of HII regions in spiral and irregular galaxies to constrain the models. Comparisons are made between theory and the observed physical conditions. In particular, studies of helium, carbon, nitrogen and oxygen abundances are reviewed. In many molecular clouds the information we have on the amount of H2 is derived from the observed CO column density, and a standard CO/H2 ratio derived for the solar neighborhood. Chemical evolution models and the observed variations in O/H and N/O values, point out the need to include these results in a CO/H2 relation that should be, at least, a function of the O/H ratio. This aspect is also discussed.

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.

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)

Special Features of Galactic Dynamics

NASA Astrophysics Data System (ADS)

Efthymiopoulos, Christos; Voglis, Nikos; Kalapotharakos, Constantinos

This is an introductory article to some basic notions and currently open problems of galactic dynamics. The focus is on topics mostly relevant to the so-called `new methods' of celestial mechanics or Hamiltonian dynamics, as applied to the ellipsoidal components of galaxies, i.e., to the elliptical galaxies and to the dark halos and bulges of disk galaxies. Traditional topics such as Jeans theorem, the role of a `third integral' of motion, Nekhoroshev theory, violent relaxation, and the statistical mechanics of collisionless stellar systems are first discussed. The emphasis is on modern extrapolations of these old topics. Recent results from orbital and global dynamical studies of galaxies are then shortly reviewed. The role of various families of orbits in supporting self-consistency, as well as the role of chaos in galaxies, are stressed. A description is then given of the main numerical techniques of integration of the N-body problem in the framework of stellar dynamics and of the results obtained via N-Body experiments. A final topic is the secular evolution and self-organization of galactic systems.

COSMIC REIONIZATION ON COMPUTERS. ULTRAVIOLET CONTINUUM SLOPES AND DUST OPACITIES IN HIGH REDSHIFT GALAXIES

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

Khakhaleva-Li, Zimu; Gnedin, Nickolay Y., E-mail: zimu@uchicago.edu, E-mail: gnedin@fnal.gov

We compare the properties of stellar populations of model galaxies from the Cosmic Reionization On Computers (CROC) project with the exiting ultraviolet (UV) and IR data. Since CROC simulations do not follow cosmic dust directly, we adopt two variants of the dust-follows-metals ansatz to populate model galaxies with dust. Using the dust radiative transfer code Hyperion, we compute synthetic stellar spectra, UV continuum slopes, and IR fluxes for simulated galaxies. We find that the simulation results generally match observational measurements, but, perhaps, not in full detail. The differences seem to indicate that our adopted dust-follows-metals ansatzes are not fully sufficient.more » While the discrepancies with the exiting data are marginal, the future James Webb Space Telescope (JWST) data will be of much higher precision, rendering highly significant any tentative difference between theory and observations. It is, therefore, likely, that in order to fully utilize the precision of JWST observations, fully dynamical modeling of dust formation, evolution, and destruction may be required.« less

STELLAR EVIDENCE THAT THE SOLAR DYNAMO MAY BE IN TRANSITION

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

Metcalfe, Travis S.; Egeland, Ricky; Van Saders, Jennifer

2016-07-20

Precise photometry from the Kepler space telescope allows not only the measurement of rotation in solar-type field stars, but also the determination of reliable masses and ages from asteroseismology. These critical data have recently provided the first opportunity to calibrate rotation–age relations for stars older than the Sun. The evolutionary picture that emerges is surprising: beyond middle-age the efficiency of magnetic braking is dramatically reduced, implying a fundamental change in angular momentum loss beyond a critical Rossby number (Ro ∼ 2). We compile published chromospheric activity measurements for the sample of Kepler asteroseismic targets that were used to establish themore » new rotation–age relations. We use these data along with a sample of well-characterized solar analogs from the Mount Wilson HK survey to develop a qualitative scenario connecting the evolution of chromospheric activity to a fundamental shift in the character of differential rotation. We conclude that the Sun may be in a transitional evolutionary phase, and that its magnetic cycle might represent a special case of stellar dynamo theory.« less

Formation of the Galactic Stellar Halo: Origin of the Metallicity-Eccentricity Relation.

PubMed

Bekki; Chiba

2000-05-01

Motivated by the recently improved knowledge on the kinematic and chemical properties of the Galactic metal-poor stars, we present the numerical simulation for the formation of the Galactic stellar halo to interpret the observational results. As a model for the Galaxy contraction, we adopt the currently standard theory of galaxy formation based on the hierarchical assembly of the cold dark matter fluctuations. We find, for the simulated stars with &sqbl0;Fe&solm0;H&sqbr0;

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,

On the Origin of Sub-subgiant Stars. II. Binary Mass Transfer, Envelope Stripping, and Magnetic Activity

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

Leiner, Emily; Mathieu, Robert D.; Geller, Aaron M., E-mail: leiner@astro.wisc.edu

Sub-subgiant stars (SSGs) lie to the red of the main sequence and fainter than the red giant branch in cluster color–magnitude diagrams (CMDs), a region not easily populated by standard stellar evolution pathways. While there has been speculation on what mechanisms may create these unusual stars, no well-developed theory exists to explain their origins. Here we discuss three hypotheses of SSG formation: (1) mass transfer in a binary system, (2) stripping of a subgiant’s envelope, perhaps during a dynamical encounter, and (3) reduced luminosity due to magnetic fields that lower convective efficiency and produce large starspots. Using the stellar evolutionmore » code MESA, we develop evolutionary tracks for each of these hypotheses, and compare the expected stellar and orbital properties of these models with six known SSGs in the two open clusters M67 and NGC 6791. All three of these mechanisms can create stars or binary systems in the SSG CMD domain. We also calculate the frequency with which each of these mechanisms may create SSG systems, and find that the magnetic field hypothesis is expected to create SSGs with the highest frequency in open clusters. Mass transfer and envelope stripping have lower expected formation frequencies, but may nevertheless create occasional SSGs in open clusters. They may also be important mechanisms to create SSGs in higher mass globular clusters.« less

Observational properties of pulsars.

PubMed

Manchester, R N

2004-04-23

Pulsars are remarkable clocklike celestial sources that are believed to be rotating neutron stars formed in supernova explosions. They are valuable tools for investigations into topics such as neutron star interiors, globular cluster dynamics, the structure of the interstellar medium, and gravitational physics. Searches at radio and x-ray wavelengths over the past 5 years have resulted in a large increase in the number of known pulsars and the discovery of new populations of pulsars, posing challenges to theories of binary and stellar evolution. Recent images at radio, optical, and x-ray wavelengths have revealed structures resulting from the interaction of pulsar winds with the surrounding interstellar medium, giving new insights into the physics of pulsars.

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.

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.

Theory of Stellar Oscillations

NASA Astrophysics Data System (ADS)

Cunha, Margarida S.

In recent years, astronomers have witnessed major progresses in the field of stellar physics. This was made possible thanks to the combination of a solid theoretical understanding of the phenomena of stellar pulsations and the availability of a tremendous amount of exquisite space-based asteroseismic data. In this context, this chapter reviews the basic theory of stellar pulsations, considering small, adiabatic perturbations to a static, spherically symmetric equilibrium. It starts with a brief discussion of the solar oscillation spectrum, followed by the setting of the theoretical problem, including the presentation of the equations of hydrodynamics, their perturbation, and a discussion of the functional form of the solutions. Emphasis is put on the physical properties of the different types of modes, in particular acoustic (p-) and gravity (g-) modes and their propagation cavities. The surface (f-) mode solutions are also discussed. While not attempting to be comprehensive, it is hoped that the summary presented in this chapter addresses the most important theoretical aspects that are required for a solid start in stellar pulsations research.

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.

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

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.

VizieR Online Data Catalog: NuGrid stellar data set I. Yields from H to Bi (Pignatari+, 2016)

NASA Astrophysics Data System (ADS)

Pignatari, M.; Herwig, F.; Hirschi, R.; Bennett, M.; Rockefeller, G.; Fryer, C.; Timmes, F. X.; Ritter, C.; Heger, A.; Jones, S.; Battino, U.; Dotter, A.; Trappitsch, R.; Diehl, S.; Frischknecht, U.; Hungerford, A.; Magkotsios, G.; Travaglio, C.; Young, P.

2016-10-01

We provide a set of stellar evolution and nucleosynthesis calculations that applies established physics assumptions simultaneously to low- and intermediate-mass and massive star models. Our goal is to provide an internally consistent and comprehensive nuclear production and yield database for applications in areas such as presolar grain studies. Our non-rotating models assume convective boundary mixing (CBM) where it has been adopted before. We include 8 (12) initial masses for Z=0.01 (0.02). Models are followed either until the end of the asymptotic giant branch phase or the end of Si burning, complemented by simple analytic core-collapse supernova (SN) models with two options for fallback and shock velocities. The explosions show which pre-SN yields will most strongly be effected by the explosive nucleosynthesis. We discuss how these two explosion parameters impact the light elements and the s and p process. For low- and intermediate-mass models, our stellar yields from H to Bi include the effect of CBM at the He-intershell boundaries and the stellar evolution feedback of the mixing process that produces the 13C pocket. All post-processing nucleosynthesis calculations use the same nuclear reaction rate network and nuclear physics input. We provide a discussion of the nuclear production across the entire mass range organized by element group. The entirety of our stellar nucleosynthesis profile and time evolution output are available electronically, and tools to explore the data on the NuGrid VOspace hosted by the Canadian Astronomical Data Centre are introduced. (12 data files).

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.

The Development of Early Pulsation Theory, or, How Cepheids Are Like Steam Engines

NASA Astrophysics Data System (ADS)

Stanley, M.

2012-06-01

The pulsation theory of Cepheid variable stars was a major breakthrough of early twentieth-century astrophysics. At the beginning of that century, the basic physics of normal stars was very poorly understood, and variable stars were even more mysterious. Breaking with accepted explanations in terms of eclipsing binaries, Harlow Shapley and A. S. Eddington pioneered novel theories that considered Cepheids as pulsating spheres of gas. Surprisingly, the pulsation theory not only depended on novel developments in stellar physics, but the theory also drove many of those developments. In particular, models of stars in radiative balance and theories of stellar energy were heavily inspired and shaped by ideas about variable stars. Further, the success of the pulsation theory helped justify the new approaches to astrophysics being developed before World War II.

Towards a Comprehensive Understanding of Planet Occurrence Rates: Extending the Kepler Legacy Across a Wide Stellar Parameter Space with K2

NASA Astrophysics Data System (ADS)

Akeson, Rachel

Measuring the occurrence rate of extrasolar planets is one of the most fundamental constraints on our understanding of planets throughout the Galaxy. By studying planet populations across a wide parameter space in stellar age, type, metallicity, and multiplicity, we can inform planet formation, migration and evolution theories. The ground-based ELTs and the flagship space missions that NASA is planning in the next decades and beyond will be designed to make the first observations of potential biomarkers in the atmospheres of extrasolar planets understanding how common these planets and how they are distributed will be crucial for this effort. One of the most important results of the main Kepler mission was a measurement of the frequency of planets orbiting FGK dwarfs. Although that result is crucial for estimating the frequency of planetary systems orbiting middle-aged Sun-like stars, the majority of stars in the galaxy have lower masses. We propose to extend the Kepler occurrence rates to lower stellar masses by using publicly available data from the second-generation K2 mission to estimate the frequency of planets orbiting low-mass stars. The confluence of the lower temperature, smaller size, and relative abundance of M dwarfs makes them attractive and efficient targets for habitable planet detection and characterization. The archived K2 data contain nearly an order of magnitude more M dwarfs than the original Kepler data set ( 30,000 compared to 3700), allowing us to constrain occurrence rates both more precisely and with more granularity across the M dwarf parameter range. We will also take advantage of the wide variety of stellar environments sampled by the community-driven K2 mission to estimate the frequency of planets orbiting stars with a range of metallicities and ages. The K2 mission has observed several clusters across a wide range of ages, including the Upper Scorpius OB association (10My old), the Pleiades cluster (115My old), and the Hyades and Praesepe clusters (600My old). One goal of this proposal is to pinpoint when and if the planet occurrence rate converges with that of the Kepler field, whose stars have a median age of 4Gy. This will inform the timescales of the dominant formation and migration mechanisms, and improve our ability to discriminate between competing proposed theories. The proposed work encompasses the following tasks: (1) Generating and publishing a uniform, repeatable, robust catalogue of planet candidates using the publicly available K2 data comprising the first 33 months of observations; (2) Measuring the completeness (false negative rate) and reliability (false positive rate) of the resulting candidate catalogue; (3) Systematically and accurately characterizing the properties of the stellar sample (both exoplanet hosts and non-hosts); (4) Calculating the distribution of the underlying planet population across a wide range of stellar host parameters. The proposed work is relevant to several of NASA s strategic goals, including ascertaining the content, origin, and evolution of the solar system and the potential for life elsewhere , and discovering how the universe works, exploring how it began and evolved, and searching for life on planets around other stars . With respect to the Astrophysics Data Analysis Program call, the proposed work builds on the legacy of Kepler occurrence rate calculations by placing them in the wider context afforded by the publicly available K2 data.

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.

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.

Adiabatic invariants in stellar dynamics. 2: Gravitational shocking

NASA Technical Reports Server (NTRS)

Weinberg, Martin D.

1994-01-01

A new theory of gravitational shocking based on time-dependent perturbation theory shows that the changes in energy and angular momentum due to a slowly varying disturbance are not exponentially small for stellar dynamical systems in general. It predicts significant shock heating by slowly varying perturbations previously thought to be negligible according to the adiabatic criterion. The theory extends the scenarios traditionally computed only with the impulse approximation and is applicable to a wide class of disturbances. The approach is applied specifically to the problem of disk shocking of star clusters.

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.

Role of nuclear reactions on stellar evolution of intermediate-mass stars

NASA Astrophysics Data System (ADS)

Möller, H.; Jones, S.; Fischer, T.; Martínez-Pinedo, G.

2018-01-01

The evolution of intermediate-mass stars (8 - 12 solar masses) represents one of the most challenging subjects in nuclear astrophysics. Their final fate is highly uncertain and strongly model dependent. They can become white dwarfs, they can undergo electron-capture or core-collapse supernovae or they might even proceed towards explosive oxygen burning and a subsequent thermonuclear explosion. We believe that an accurate description of nuclear reactions is crucial for the determination of the pre-supernova structure of these stars. We argue that due to the possible development of an oxygen-deflagration, a hydrodynamic description has to be used. We implement a nuclear reaction network with ∼200 nuclear species into the implicit hydrodynamic code AGILE. The reaction network considers all relevant nuclear electron captures and beta-decays. For selected relevant nuclear species, we include a set of updated reaction rates, for which we discuss the role for the evolution of the stellar core, at the example of selected stellar models. We find that the final fate of these intermediate-mass stars depends sensitively on the density threshold for weak processes that deleptonize the core.

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.

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.

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.

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.

Asteroseismology with FRESIP: A meter class space telescope

NASA Technical Reports Server (NTRS)

Milford, Peter

1994-01-01

The requirements for asteroseismology and searching for occulting inner planets are similar. The FRESIP mission will be suited to making asteroseismology measurements. Recommendation: Use 30-60 second integrations from one or more CCD's in the FRESIP mosaic, sampled continuously for the entire mission to measure stellar non-radial oscillations with amplitudes of parts per million and frequencies of 0.1 to 10 MHz. These measurements lead to determination of stellar interior helium abundances, rotation rates, depth of convection zones and measuring stellar cycle frequency changes for a variety of stellar types, enabling major advances in stellar structure and evolutionary theories.

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.

On the Lack of Circumbinary Planets Orbiting Isolated Binary Stars

NASA Astrophysics Data System (ADS)

Fleming, David; Barnes, Rory; Graham, David E.; Luger, Rodrigo; Quinn, Thomas R.

2018-04-01

To date, no binary star system with an orbital period less than 7.5 days has been observed to host a circumbinary planet (CBP), a puzzling observation given the thousands of binary stars with orbital periods < 10 days discovered by the Kepler mission (Kirk et al., 2016) and the observational biases that favor their detection (Munoz & Lai, 2015). We outline a mechanism that explains the observed lack of CBPs via coupled stellar-tidal evolution of isolated binary stars. Tidal forces between low-mass, short-period binary stars on the pre-main sequence slow the stellar rotations, transferring rotational angular momentum to the orbit as the stars approach the tidally locked state. This transfer increases the binary orbital period, expanding the region of dynamical instability around the binary, and destabilizing CBPs that tend to preferentially orbit just beyond the initial dynamical stability limit. After the stars tidally lock, we find that angular momentum loss due to magnetic braking can significantly shrink the binary orbit, and hence the region of dynamical stability, over time impacting where surviving CBPs are observed relative to the boundary. We perform simulations over a wide range of parameter space and find that the expansion of the instability region occurs for most plausible initial conditions and that in some cases, the stability semi-major axis doubles from its initial value. We examine the dynamical and observable consequences of a CBP falling within the dynamical instability limit by running N-body simulations of circumbinary planetary systems and find that typically, at least one planet is ejected from the system. We apply our theory to the shortest period Kepler binary that possesses a CBP, Kepler-47, and find that its existence is consistent with our model. Under conservative assumptions, we find that coupled stellar-tidal evolution of pre-main sequence binary stars removes at least one close-in CBP in 87% of multi-planet circumbinary systems.

Accretion Disks and the Formation of Stellar Systems

NASA Astrophysics Data System (ADS)

Kratter, Kaitlin Michelle

2011-02-01

In this thesis, we examine the role of accretion disks in the formation of stellar systems, focusing on young massive disks which regulate the flow of material from the parent molecular core down to the star. We study the evolution of disks with high infall rates that develop strong gravitational instabilities. We begin in chapter 1 with a review of the observations and theory which underpin models for the earliest phases of star formation and provide a brief review of basic accretion disk physics, and the numerical methods that we employ. In chapter 2 we outline the current models of binary and multiple star formation, and review their successes and shortcomings from a theoretical and observational perspective. In chapter 3 we begin with a relatively simple analytic model for disks around young, high mass stars, showing that instability in these disks may be responsible for the higher multiplicity fraction of massive stars, and perhaps the upper mass to which they grow. We extend these models in chapter 4 to explore the properties of disks and the formation of binary companions across a broad range of stellar masses. In particular, we model the role of global and local mechanisms for angular momentum transport in regulating the relative masses of disks and stars. We follow the evolution of these disks throughout the main accretion phase of the system, and predict the trajectory of disks through parameter space. We follow up on the predictions made in our analytic models with a series of high resolution, global numerical experiments in chapter 5. Here we propose and test a new parameterization for describing rapidly accreting, gravitationally unstable disks. We find that disk properties and system multiplicity can be mapped out well in this parameter space. Finally, in chapter 6, we address whether our studies of unstable disks are relevant to recently detected massive planets on wide orbits around their central stars.

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.

Physical Properties of UV-bright Clumps in Star-forming Galaxies at 0.5 ≤ z < 3

NASA Astrophysics Data System (ADS)

Guo, Yicheng; Rafelski, Marc; Bell, Eric F.; Dekel, Avishai; Mandelker, Nir; Primack, Joel R.; CANDELS

2018-06-01

Studying giant star-forming clumps in distant galaxies is important to understand galaxy formation and evolution. At present, however, observers and theorists have not reached a consensus on whether the observed “clumps” in distant galaxies are the same phenomenon that is seen in simulations. As a step to establish a benchmark of direct comparisons between observations and theories, we publish a sample of clumps constructed to represent the commonly observed “clumps” in the literature. This sample contains 3193 clumps detected from the rest-frame images of 1270 galaxies at 0.5≤z<3.0. The physical properties of clumps (e.g., rest-frame color, stellar mass, star formation rate, age, and dust extinction) are measured by fitting the spectral energy distribution (SED) to synthetic stellar population models. We carefully test the procedures of measuring clump properties, especially the method of subtracting background fluxes from the diffuse component of galaxies. With our fiducial background subtraction, we find a radial clump U-V color variation, where clumps close to galactic centers are redder than those in outskirts. The slope of the color gradient (clump color as a function of their galactocentric distance scaled by the semimajor axis of galaxies) changes with redshift and stellar mass of the host galaxies: at a fixed stellar mass, the slope becomes steeper toward low redshift, and at a fixed redshift, it becomes slightly steeper with stellar mass. Based on our SED fitting, this observed color gradient can be explained by a combination of a negative age gradient, a negative E(B-V) gradient, and a positive specific star formation rate gradient of the clumps. We also find that the color gradients of clumps are steeper than those of intra-clump regions. Correspondingly, the radial gradients of the derived physical properties of clumps are different from those of the diffuse component or intra-clump regions.

THE STAR FORMATION HISTORIES OF z {approx} 2 DUST-OBSCURED GALAXIES AND SUBMILLIMETER-SELECTED GALAXIES

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

Bussmann, R. S.; Dey, Arjun; Jannuzi, B. T.

The Spitzer Space Telescope has identified a population of ultraluminous infrared galaxies (ULIRGs) at z {approx} 2 that may play an important role in the evolution of massive galaxies. We measure the stellar masses (M{sub *}) of two populations of Spitzer-selected ULIRGs that have extremely red R - [24] colors (dust-obscured galaxies, or DOGs) and compare our results with submillimeter-selected galaxies (SMGs). One set of 39 DOGs has a local maximum in their mid-infrared (mid-IR) spectral energy distribution (SED) at rest frame 1.6 {mu}m associated with stellar emission ({sup b}ump DOGs{sup )}, while the other set of 51 DOGs havemore » power-law mid-IR SEDs that are typical of obscured active galactic nuclei ({sup p}ower-law DOGs{sup )}. We measure M{sub *} by applying Charlot and Bruzual stellar population synthesis models to broadband photometry in the rest-frame ultraviolet, optical, and near-infrared of each of these populations. Assuming a simple stellar population and a Chabrier initial mass function, we find that power-law DOGs and bump DOGs are on average a factor of 2 and 1.5 more massive than SMGs, respectively (median and inter-quartile M{sub *} values for SMGs, bump DOGs, and power-law DOGs are log(M{sub *}/M{sub Sun }) = 10.42{sup +0.42}{sub -0.36}, 10.62{sup +0.36}{sub -0.32}, and 10.71{sup +0.40}{sub -0.34}, respectively). More realistic star formation histories drawn from two competing theories for the nature of ULIRGs at z {approx} 2 (major merger versus smooth accretion) can increase these mass estimates by up to 0.5 dex. A comparison of our stellar masses with the instantaneous star formation rate (SFR) in these z {approx} 2 ULIRGs provides a preliminary indication supporting high SFRs for a given M{sub *}, a situation that arises more naturally in major mergers than in smooth accretion-powered systems.« less

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

Hydrogen Balmer Line Broadening in Solar and Stellar Flares

NASA Technical Reports Server (NTRS)

Kowalski, Adam F.; Allred, Joel C.; Uitenbroek, Han; Tremblay, Pier-Emmanuel; Brown, Stephen; Carlsson, Mats; Osten, Rachel A.; Wisniewski, John P.; Hawley, Suzanne L.

2017-01-01

The broadening of the hydrogen lines during flares is thought to result from increased charge (electron, proton) density in the flare chromosphere. However, disagreements between theory and modeling prescriptions have precluded an accurate diagnostic of the degree of ionization and compression resulting from flare heating in the chromosphere. To resolve this issue, we have incorporated the unified theory of electric pressure broadening of the hydrogen lines into the non-LTE radiative-transfer code RH. This broadening prescription produces a much more realistic spectrum of the quiescent, A0 star Vega compared to the analytic approximations used as a damping parameter in the Voigt profiles. We test recent radiative-hydrodynamic (RHD) simulations of the atmospheric response to high nonthermal electron beam fluxes with the new broadening prescription and find that the Balmer lines are overbroadened at the densest times in the simulations. Adding many simultaneously heated and cooling model loops as a 'multithread' model improves the agreement with the observations. We revisit the three component phenomenological flare model of the YZ CMi Megaflare using recent and new RHD models. The evolution of the broadening, line flux ratios, and continuum flux ratios are well-reproduced by a multithread model with high-flux nonthermal electron beam heating, an extended decay phase model, and a 'hot spot' atmosphere heated by an ultra relativistic electron beam with reasonable filling factors: approximately 0.1%, 1%, and 0.1% of the visible stellar hemisphere, respectively. The new modeling motivates future work to understand the origin of the extended gradual phase emission.

The quest for novel modes of excitation in exotic nuclei

NASA Astrophysics Data System (ADS)

Paar, N.

2010-06-01

This paper provides an insight into several open problems in the quest for novel modes of excitation in nuclei with isospin asymmetry, deformation and finite-temperature characteristics in stellar environments. Major unsolved problems include the nature of pygmy dipole resonances, the quest for various multipole and spin-isospin excitations both in neutron-rich and proton drip-line nuclei mainly driven by loosely bound nucleons, excitations in unstable deformed nuclei and evolution of their properties with the shape phase transition. Exotic modes of excitation in nuclei at finite temperatures characteristic of supernova evolution present open problems with a possible impact in modeling astrophysically relevant weak interaction rates. All these issues challenge self-consistent many-body theory frameworks at the frontiers of on-going research, including nuclear energy density functionals, both phenomenological and constrained by the strong interaction physics of QCD, models based on low-momentum two-nucleon interaction Vlow-k and correlated realistic nucleon-nucleon interaction VUCOM, supplemented by three-body force, as well as two-nucleon and three-nucleon interactions derived from the chiral effective field theory. Joined theoretical and experimental efforts, including research with radioactive isotope beams, are needed to provide insight into dynamical properties of nuclei away from the valley of stability, involving the interplay of isospin asymmetry, deformation and finite temperature.

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.

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

Digging for substellar objects in the stellar graveyard

NASA Astrophysics Data System (ADS)

Debes, John H., IV

2005-11-01

White dwarfs, the endpoint of stellar evolution for stars with mass < 8 [Special characters omitted.] , possess several attributes favorable for studying planet and brown dwarf formation around stars with primordial masses 1 [Special characters omitted.] . This thesis explores the consequences of post-main-sequence evolution on the dynamics of a planetary system and the observational signatures that arise from such evolution. These signatures are then specifically tested with a direct imaging survey of nearby white dwarfs. Finally, new techniques for high contrast imaging are discussed and placed in the context of further searches for planets and brown dwarfs in the stellar graveyard. While planets closer than ~ 5 AU will most likely not survive the post-main sequence evolution of its parent star, any planet with semimajor axis > 5 AU will survive, and its semimajor axis will increase as the central star loses mass. The stability of adjacent orbits to mutual planet-planet perturbations depends on the ratio of the planet mass to the central star's mass, and I demonstrate that some planets in previously stable orbits around a star undergoing mass loss will become unstable. If pollution of a white dwarf's atmosphere is caused by relic planetary systems, any white dwarf with photospheric absorption due to metals can be searched for substellar companions. Hydrogen white dwarfs with metal absorption, so called DAZ white dwarfs, are hard to explain by simple ISM accretion, and present an opportunity to test the observational signatures of unstable planetary systems. Additionally, field white dwarfs can be searched for substellar companions as well. The search for planetary companions to stars requires further development of high contrast imaging techniques. This thesis studies Gaussian aperture pupil masks (GAPMs) which in theory can achieve the contrast requisite for directly imaging an extrasolar planet around a nearby solar type star. I outline the process of designing, fabricating, and testing a GAPM for use on current telescopes and specifically the Penn State near-IR Imager and Spectrograph (PIRIS) at the Mt. Wilson 100" telescope. I find that observations with a prototype are quite successful, achieving a contrast similar to a traditional Lyot coronagraph without blocking any light from a central object and useful for finding faint companions to nearby young solar analogues. In the lab I can reproduce the expected PSF reasonably well and with a single aperture design which achieves ~ 4 x 10 -5 contrast at 10l/ D . I find that small inaccuracies in the mask fabrication process and insufficient correction of the atmosphere contribute the most degradation to contrast at these levels. (Abstract shortened by UMI.)

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.

Observational tests for stellar evolution and pulsation theory. I - The globular clusters M 4 and M 15

NASA Astrophysics Data System (ADS)

Caputo, F.

1987-01-01

It is shown that the pulsational properties of RR Lyrae variables in globular clusters can be used together with the Red Giant Branch location to derive reliable information on the cluster reddening and distance modulus. By demanding full agreement with some key observables, the reddening and distance modulus of the globular clusters M4 and M15 are derived as a function of the mass of the variables and of the adopted cluster metallicity. Thus, from the comparison between observations and theoretical isochrones, the cluster age can be evaluated. A best guess for the age of M4 and M15 can be presented: 16×109yr, with a total uncertainty of 2 billion years.

Oscillation Mode Variability in Evolved Compact Pulsators from Kepler Photometry. I. The Hot B Subdwarf Star KIC 3527751

NASA Astrophysics Data System (ADS)

Zong, Weikai; Charpinet, Stéphane; Fu, Jian-Ning; Vauclair, Gérard; Niu, Jia-Shu; Su, Jie

2018-02-01

We present the first results of an ensemble and systematic survey of oscillation mode variability in pulsating hot B subdwarf (sdB) and white dwarf stars observed with the original Kepler mission. The satellite provides uninterrupted high-quality photometric data with a time baseline that can reach up to 4 yr collected on pulsating stars. This is a unique opportunity to characterize long-term behaviors of oscillation modes. A mode modulation in amplitude and frequency can be independently inferred by its fine structure in the Fourier spectrum, from the sLSP, or with prewhitening methods applied to various parts of the light curve. We apply all these techniques to the sdB star KIC 3527751, a long-period-dominated hybrid pulsator. We find that all the detected modes with sufficiently large amplitudes to be thoroughly studied show amplitude and/or frequency variations. Components of three identified quintuplets around 92, 114, and 253 μHz show signatures that can be linked to nonlinear interactions according to the resonant mode coupling theory. This interpretation is further supported by the fact that many oscillation modes are found to have amplitudes and frequencies showing correlated or anticorrelated variations, a behavior that can be linked to the amplitude equation formalism, where nonlinear frequency corrections are determined by their amplitude variations. Our results suggest that oscillation modes varying with diverse patterns are a very common phenomenon in pulsating sdB stars. Close structures around main frequencies therefore need to be carefully interpreted in light of this finding to secure a robust identification of real eigenfrequencies, which is crucial for seismic modeling. The various modulation patterns uncovered should encourage further developments in the field of nonlinear stellar oscillation theory. It also raises a warning to any long-term project aiming at measuring the rate of period change of pulsations caused by stellar evolution, or at discovering stellar (planetary) companions around pulsating stars using timing methods, as both require very stable pulsation modes.

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.

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.

Stellar pulsations in beyond Horndeski gravity theories

NASA Astrophysics Data System (ADS)

Sakstein, Jeremy; Kenna-Allison, Michael; Koyama, Kazuya

2017-03-01

Theories of gravity in the beyond Horndeski class recover the predictions of general relativity in the solar system whilst admitting novel cosmologies, including late-time de Sitter solutions in the absence of a cosmological constant. Deviations from Newton's law are predicted inside astrophysical bodies, which allow for falsifiable, smoking-gun tests of the theory. In this work we study the pulsations of stars by deriving and solving the wave equation governing linear adiabatic oscillations to find the modified period of pulsation. Using both semi-analytic and numerical models, we perform a preliminary survey of the stellar zoo in an attempt to identify the best candidate objects for testing the theory. Brown dwarfs and Cepheid stars are found to be particularly sensitive objects and we discuss the possibility of using both to test the theory.

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.

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.

Kepler-91b: a planet at the end of its life. Planet and giant host star properties via light-curve variations

NASA Astrophysics Data System (ADS)

Lillo-Box, J.; Barrado, D.; Moya, A.; Montesinos, B.; Montalbán, J.; Bayo, A.; Barbieri, M.; Régulo, C.; Mancini, L.; Bouy, H.; Henning, T.

2014-02-01

Context. The evolution of planetary systems is intimately linked to the evolution of their host stars. Our understanding of the whole planetary evolution process is based on the wide planet diversity observed so far. Only a few tens of planets have been discovered orbiting stars ascending the red giant branch. Although several theories have been proposed, the question of how planets die remains open owing to the small number statistics, making it clear that the sample of planets around post-main sequence stars needs to be enlarged. Aims: In this work we study the giant star Kepler-91 (KOI-2133) in order to determine the nature of a transiting companion. This system was detected by the Kepler Space Telescope, which identified small dims in its light curve with a period of 6.246580 ± 0.000082 days. However, its planetary confirmation is needed due to the large pixel size of the Kepler camera, which can hide other stellar configurations able to mimic planet-like transit events. Methods: We analysed Kepler photometry to 1) re-calculate transit parameters; 2) study the light-curve modulations; and 3) to perform an asteroseismic analysis (accurate stellar parameter determination) by identifying solar-like oscillations on the periodogram. We also used a high-resolution and high signal-to-noise ratio spectrum obtained with the Calar Alto Fiber-fed Échelle spectrograph (CAFE) to measure stellar properties. Additionally, false-positive scenarios were rejected by obtaining high-resolution images with the AstraLux lucky imaging camera on the 2.2 m telescope at the Calar Alto Observatory. Results: We confirm the planetary nature of the object transiting the star Kepler-91 by deriving a mass of Mp=0.88+0.17-0.33 MJup and a planetary radius of Rp=1.384+0.011-0.054 RJup. Asteroseismic analysis produces a stellar radius of R⋆ = 6.30 ± 0.16 R⊙ and a mass of M⋆ = 1.31 ± 0.10 M⊙. We find that its eccentric orbit (e=0.066+0.013-0.017) is just 1.32+0.07-0.22 R⋆ away from the stellar atmosphere at the pericentre. We also detected three small dims in the phase-folded light curve. The combination of two of them agrees with the theoretical characteristics expected for secondary eclipse. Conclusions: Kepler-91b could be the previous stage of the planet engulfment, which has recently been detected for BD+48 740. Our estimations show that Kepler-91b will be swallowed by its host star in less than 55 Myr. Among the confirmed planets around giant stars, this is the closest to its host star. At pericentre, the star subtends an angle of 48°, covering around 10% of the sky as seen from the planet. The planetary atmosphere seems to be inflated probably due to the high stellar irradiation. Based on observations collected at the German-Spanish Astronomical Center, Calar Alto, jointly operated by the Max-Planck-Institut fur Astronomie (Heidelberg) and the Instituto de Astrofísica de Andalucía (IAA-CSIC, Granada).Appendix A is available in electronic form at http://www.aanda.org

Locations of stationary/periodic solutions in mean motion resonances according to the properties of dust grains

NASA Astrophysics Data System (ADS)

Pástor, P.

2016-07-01

The equations of secular evolution for dust grains in mean motion resonances with a planet are solved for stationary points. Non-gravitational effects caused by stellar radiation (the Poynting-Robertson effect and the stellar wind) are taken into account. The solutions are stationary in the semimajor axis, eccentricity and resonant angle, but allow the pericentre to advance. The semimajor axis of stationary solutions can be slightly shifted from the exact resonant value. The periodicity of the stationary solutions in a reference frame orbiting with the planet is proved analytically. The existence of periodic solutions in mean motion resonances means that analytical theory enables infinitely long capture times for dust particles. The stationary solutions are periodic motions to which the eccentricity asymptotically approaches and around which the libration occurs. Initial conditions corresponding to the stationary solutions are successfully found by numerically integrating the equation of motion. Numerically and analytically determined shifts of the semimajor axis from the exact resonance for the stationary solutions are in excellent agreement. The stationary solutions can be plotted by the locations of pericentres in the reference frame orbiting with the planet. The pericentres are distributed in space according to the properties of the dust particles.

AN ASTEROSEISMIC MEMBERSHIP STUDY OF THE RED GIANTS IN THREE OPEN CLUSTERS OBSERVED BY KEPLER: NGC 6791, NGC 6819, AND NGC 6811

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

Stello, Dennis; Huber, Daniel; Bedding, Timothy R.

Studying star clusters offers significant advances in stellar astrophysics due to the combined power of having many stars with essentially the same distance, age, and initial composition. This makes clusters excellent test benches for verification of stellar evolution theory. To fully exploit this potential, it is vital that the star sample is uncontaminated by stars that are not members of the cluster. Techniques for determining cluster membership therefore play a key role in the investigation of clusters. We present results on three clusters in the Kepler field of view based on a newly established technique that uses asteroseismology to identifymore » fore- or background stars in the field, which demonstrates advantages over classical methods such as kinematic and photometry measurements. Four previously identified seismic non-members in NGC 6819 are confirmed in this study, and three additional non-members are found-two in NGC 6819 and one in NGC 6791. We further highlight which stars are, or might be, affected by blending, which needs to be taken into account when analyzing these Kepler data.« less

Origin of the DA and non-DA white dwarf stars

NASA Technical Reports Server (NTRS)

Shipman, Harry L.

1989-01-01

Various proposals for the bifurcation of the white dwarf cooling sequence are reviewed. 'Primordial' theories, in which the basic bifurcation of the white dwarf sequence is rooted in events predating the white dwarf stage of stellar evolution, are discussed, along with the competing 'mixing' theories in which processes occurring during the white dwarf stage are responsible for the existence of DA or non-DA stars. A new proposal is suggested, representing a two-channel scenario. In the DA channel, some process reduces the hydrogen layer mass to the value of less than 10 to the -7th. The non-DA channel is similar to that in the primordial scenario. These considerations suggest that some mechanism operates in both channels to reduce the thickness of the outermost layer of the white dwarf. It is also noted that accretion from the interstellar medium has little to do with whether a particular white dwarf becomes a DA or a non-DA star.

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

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).

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

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.

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.

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 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.

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.;

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.

Spin-orbit coupling and tidal dissipation in hot Jupiter systems

NASA Astrophysics Data System (ADS)

Shabaltas, Natalia Igorevna

Hot Jupiters are giant planets located extremely close to their host stars, with orbital periods less than 5 days. Many aspects of hot Jupiter (HJ) formation remain unclear, but several clues, such as the observed misalignment between their orbital axes and their hosts' spin axes, point to a dynamical origin. In the first portion of this work we explore the stellar spin-orbit dynamics of one such dynamical formation channel, the Lidov-Kozai mechanism. We show that the coupling between the stellar spin and the planet orbit can lead to complex, and sometimes chaotic, behavior of the stellar spin vector. Many features of this behavior arise due to a set of resonances between the stellar spin axis precession timescale and the Lidov-Kozai timescale. Under the assumption that the stellar quadrupole does not induce precession in the planet's orbit, given a system with a set of initial parameters, we show that it is possible to predict whether the system can attain high spin-orbit misalignments. In the second portion of this work, we discuss tidal dissipation in giant planets, another aspect that is crucial to dynamical HJ formation theories. We show that tidal dissipation in the cores of giant planets can be significant, and can help reconcile inconsistencies in the tidal dissipation efficiencies inferred from observations of Jupiter's moons and from high-eccentricity HJ migration theories. Finally, we improve upon existing core tidal dissipation theories by presenting semi-analytical formulae for dissipation in a core surrounded by a polytropic n = 1 envelope.

Rotation curves of galaxies and the stellar mass-to-light ratio

NASA Astrophysics Data System (ADS)

Haghi, Hosein; Khodadadi, Aziz; Ghari, Amir; Zonoozi, Akram Hasani; Kroupa, Pavel

2018-03-01

Mass models of a sample of 171 low- and high-surface brightness galaxies are presented in the context of the cold dark matter (CDM) theory using the NFW dark matter halo density distribution to extract a new concentration-viral mass relation (c - Mvir). The rotation curves (RCs) are calculated from the total baryonic matter based on the 3.6 μm-band surface photometry, the observed distribution of neutral hydrogen, and the dark halo, in which the three adjustable parameters are the stellar mass-to-light ratio, halo concentration and virial mass. Although accounting for a NFW dark halo profile can explain rotation curve observations, the implied c - Mvir relation from RC analysis strongly disagrees with that resulting from different cosmological simulations. Also, the M/L -color correlation of the studied galaxies is inconsistent with that expected from stellar population synthesis models with different stellar initial mass functions. Moreover, we show that the best-fitting stellar M/L - ratios of 51 galaxies (30% of our sample) have unphysically negative values in the framework of the ΛCDM theory. This can be interpreted as a serious crisis for this theory. This suggests either that the commonly used NFW halo profile, which is a natural result of ΛCDM cosmological structure formation, is not an appropriate profile for the dark halos of galaxies, or, new dark matter physics or alternative gravity models are needed to explain the rotational velocities of disk galaxies.

Rotation curves of galaxies and the stellar mass-to-light ratio

NASA Astrophysics Data System (ADS)

Haghi, Hosein; Khodadadi, Aziz; Ghari, Amir; Zonoozi, Akram Hasani; Kroupa, Pavel

2018-07-01

Mass models of a sample of 171 low- and high-surface brightness galaxies are presented in the context of the cold dark matter (CDM) theory using the NFW dark matter halo density distribution to extract a new concentration-viral mass relation (c-Mvir). The rotation curves (RCs) are calculated from the total baryonic matter based on the 3.6 μm-band surface photometry, the observed distribution of neutral hydrogen, and the dark halo, in which the three adjustable parameters are the stellar mass-to-light ratio, halo concentration, and virial mass. Although accounting for a NFW dark halo profile can explain RC observations, the implied c-Mvir relation from RC analysis strongly disagrees with that resulting from different cosmological simulations. Also, the M/L-colour correlation of the studied galaxies is inconsistent with that expected from stellar population synthesis models with different stellar initial mass functions. Moreover, we show that the best-fitting stellar M/L ratios of 51 galaxies (30 per cent of our sample) have unphysically negative values in the framework of the ΛCDM theory. This can be interpreted as a serious crisis for this theory. This suggests either that the commonly used NFW halo profile, which is a natural result of ΛCDM cosmological structure formation, is not an appropriate profile for the dark haloes of galaxies, or, new dark matter physics or alternative gravity models are needed to explain the rotational velocities of disc galaxies.

Validating early stellar encounters as the cause of dynamically hot planetary systems

NASA Astrophysics Data System (ADS)

Kalas, Paul

2017-08-01

One of the key questions concerning exoplanetary systems is why some are dynamically cold, such as TRAPPIST-1, whereas others are dynamically hot, with highly eccentric planets and/or perturbed debris disks. Dynamical theory describes a variety of plausible mechanisms, but few can be empirically tested since the critical dynamical evolution that sets the final planetary architecture is short-lived. One rare system available for testing dynamical upheaval scenarios is the 400 Myr-old Fomalhaut system. In Cycle 22 we coronagraphically studied Fomalhaut C, which is a wide M-dwarf companion to Fomalhaut A, in order to test our prediction that the unresolved, Herschel-detected debris disk around Fomalhaut C may be highly perturbed because of a recent close interaction with Fomalhaut A. Using HST/STIS we discovered a highly asymmetric feature extending northward of Fomalhaut C by 3 that resembles our model of a dynamically hot disk. However, it may be a background galaxy and the definitive test of its physical relationship to Fomalhaut C is to demonstrate common proper motion. Using Keck adaptive optics follow-up observations in J band, we did not detect the feature, and hence follow-up HST observations are the only way to test for common proper motion. Here we request a very small program to revisit Fomalhaut C with STIS in order to validate the initial discovery as a debris disk (1 proper motion between HST epochs). The astrophysical significance is demonstrating that the Fomalhaut system is a valuable case for studying dynamical upheavals via stellar encounters that are inferred to occur in the evolution of many other planetary systems.

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.

A circumstellar disk associated with a massive protostellar object.

PubMed

Jiang, Zhibo; Tamura, Motohide; Fukagawa, Misato; Hough, Jim; Lucas, Phil; Suto, Hiroshi; Ishii, Miki; Yang, Ji

2005-09-01

The formation process for stars with masses several times that of the Sun is still unclear. The two main theories are mergers of several low-mass young stellar objects, which requires a high stellar density, or mass accretion from circumstellar disks in the same way as low-mass stars are formed, accompanied by outflows during the process of gravitational infall. Although a number of disks have been discovered around low- and intermediate-mass young stellar objects, the presence of disks around massive young stellar objects is still uncertain and the mass of the disk system detected around one such object, M17, is disputed. Here we report near-infrared imaging polarimetry that reveals an outflow/disk system around the Becklin-Neugebauer protostellar object, which has a mass of at least seven solar masses (M(o)). This strongly supports the theory that stars with masses of at least 7M(o) form in the same way as lower mass stars.

The development of early pulsation theory, or, how Cepheids are like steam engines"

NASA Astrophysics Data System (ADS)

Stanley, Matthew

2011-05-01

The pulsation theory of Cepheid variable stars was a major breakthrough of early twentieth-century astrophysics. At the beginning of that century, the basic physics of normal stars was very poorly understood, and variable stars were even more mysterious. Breaking with accepted explanations in terms of eclipsing binaries, Harlow Shapley and A.S. Eddington pioneered novel theories that considered Cepheids as pulsating spheres of gas. These theoretical models relied on highly speculative physics, but nonetheless returned very impressive results despite attacks from figures such as James Jeans. Surprisingly, the pulsation theory not only depended on developments in stellar physics, but also drove many of those developments. In particular, models of stars in radiative balance and theories of stellar energy were heavily inspired and shaped by ideas about variable stars. Further, the success of the pulsation theory helped justify the new approaches to astrophysics being developed before World War II.

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.

The galaxy-wide initial mass function of dwarf late-type to massive early-type galaxies

NASA Astrophysics Data System (ADS)

Weidner, C.; Kroupa, P.; Pflamm-Altenburg, J.; Vazdekis, A.

2013-12-01

Observational studies are showing that the galaxy-wide stellar initial mass function (IMF) is top-heavy in galaxies with high star formation rates (SFRs). Calculating the integrated galactic stellar initial mass function (IGIMF) as a function of the SFR of a galaxy, it follows that galaxies which have or which formed with SFRs >10 M⊙ yr-1 would have a top-heavy IGIMF in excellent consistency with the observations. Consequently and in agreement with observations, elliptical galaxies would have higher mass-to-light ratios as a result of the overabundance of stellar remnants compared to a stellar population that formed with an invariant canonical stellar IMF. For the Milky Way, the IGIMF yields very good agreement with the disc- and the bulge IMF determinations. Our conclusions are that purely stochastic descriptions of star formation on the scales of a parsec and above are falsified. Instead, star formation follows the laws, stated here as axioms, which define the IGIMF theory. We also find evidence that the power-law index β of the embedded cluster mass function decreases with increasing SFR. We propose further tests of the IGIMF theory through counting massive stars in dwarf galaxies.

Radiation-driven winds of hot stars. V - Wind models for central stars of planetary nebulae

NASA Technical Reports Server (NTRS)

Pauldrach, A.; Puls, J.; Kudritzki, R. P.; Mendez, R. H.; Heap, S. R.

1988-01-01

Wind models using the recent improvements of radiation driven wind theory by Pauldrach et al. (1986) and Pauldrach (1987) are presented for central stars of planetary nebulae. The models are computed along evolutionary tracks evolving with different stellar mass from the Asymptotic Giant Branch. We show that the calculated terminal wind velocities are in agreement with the observations and allow in principle an independent determination of stellar masses and radii. The computed mass-loss rates are in qualitative agreement with the occurrence of spectroscopic stellar wind features as a function of stellar effective temperature and gravity.

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).

Stellar pulsations in beyond Horndeski gravity theories

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

Sakstein, Jeremy; Kenna-Allison, Michael; Koyama, Kazuya, E-mail: sakstein@physics.upenn.edu, E-mail: mka1g13@soton.ac.uk, E-mail: kazuya.koyama@port.ac.uk

Theories of gravity in the beyond Horndeski class recover the predictions of general relativity in the solar system whilst admitting novel cosmologies, including late-time de Sitter solutions in the absence of a cosmological constant. Deviations from Newton's law are predicted inside astrophysical bodies, which allow for falsifiable, smoking-gun tests of the theory. In this work we study the pulsations of stars by deriving and solving the wave equation governing linear adiabatic oscillations to find the modified period of pulsation. Using both semi-analytic and numerical models, we perform a preliminary survey of the stellar zoo in an attempt to identify themore » best candidate objects for testing the theory. Brown dwarfs and Cepheid stars are found to be particularly sensitive objects and we discuss the possibility of using both to test the theory.« less

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.

The Supernova - A Stellar Spectacle.

ERIC Educational Resources Information Center

Straka, W. C.

This booklet is part of an American Astronomical Society curriculum project designed to provide teaching materials to teachers of secondary school chemistry, physics, and earth science. The following topics concerning supernovae are included: the outburst as observed and according to theory, the stellar remnant, the nebular remnant, and a summary…

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.

The Allegheny Observatory search for planetary systems

NASA Technical Reports Server (NTRS)

Gatewood, George D.

1989-01-01

The accomplishments of the observatory's search for planetary systems are summarized. Among these were the construction, implementation, and regular use of the Multichannel Astrometric Photometer (MAP), and the design, fabrication and use of the second largest refractor objective built since 1950. The MAP parallax and planetary observing programs are described. Various developments concerning alternate solid state photodetectors and telescope instrumentation are summarized. The extreme accuracy of the system is described in relation to a study of the position and velocity of the members of the open cluster Upgren 1. The binary star system stringently tests the theory of stellar evolution since it is composed of an evolved giant F5 III and a subgiant F5 IV star. A study that attempts to measure the luminosities, surface temperatures, and masses of these stars is discussed.

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.

Gravity, black holes, and the universe

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

Nicolson, I.

1981-01-01

The book treats current understandings of the nature and properties of gravity, with particular emphasis on its role in the physics of black holes and the structure and evolution of the universe as a whole. The development of modern ideas on force, motion and gravity is traced from the systems of Aristotle and Ptolemy through the work of Copernicus, Galileo and Kepler to Newton's law of universal gravitation and Einstein's general theory of relativity. Particular attention is then given to the role of gravity in stellar motions and to the phenomena determined by the immense gravitational forces associated with bodiesmore » of such great density, including relativistic effects, tidal forces, space-time effects, event horizons, rotation, mass and electrical charge, the existence of naked singularities and white holes, and black-hole thermodynamics. The existence of actual black holes in the universe is considered, and various black-hole candidates in the Galaxy, quasars and galactic nuclei are indicated. The role of gravity in cosmology is then examined, with attention given to the implications of general relativity, the Hubble law, the age of the universe, the density of the universe and its eventual fate. Possible alternative to general relativity as a theory of gravitation are considered, including theories of variable gravitational constant, grand unified theories, and quantum gravity.« less

Gravity, black holes and the universe

NASA Astrophysics Data System (ADS)

Nicolson, I.

The book treats current understandings of the nature and properties of gravity, with particular emphasis on its role in the physics of black holes and the structure and evolution of the universe as a whole. The development of modern ideas on force, motion and gravity is traced from the systems of Aristotle and Ptolemy through the work of Copernicus, Galileo and Kepler to Newton's law of universal gravitation and Einstein's general theory of relativity. Particular attention is then given to the role of gravity in stellar motions and to the phenomena determined by the immense gravitational forces associated with bodies of such great density, including relativistic effects, tidal forces, space-time effects, event horizons, rotation, mass and electrical charge, the existence of naked singularities and white holes, and black-hole thermodynamics. The existence of actual black holes in the universe is considered, and various black-hole candidates in the Galaxy, quasars and galactic nuclei are indicated. The role of gravity in cosmology is then examined, with attention given to the implications of general relativity, the Hubble law, the age of the universe, the density of the universe and its eventual fate. Possible alternative to general relativity as a theory of gravitation are considered, including theories of variable gravitational constant, grand unified theories, and quantum gravity.

REVIEWS OF TOPICAL PROBLEMS: The theory of nucleosynthesis in stars: the slow neutron capture process

NASA Astrophysics Data System (ADS)

Chechev, Valerii P.; Kramarovskiĭ, Ya M.

1981-07-01

The theory of the s process of nucleosynthesis has received considerable development during recent years, mainly as the result of more detailed physical and mathematical treatments and also as a result of the accumulation of new observational data on stellar evolution and the abundance of the elements in the solar system, and accumulation of experimental data on neutron-capture cross sections. The exact solution of the s process equations obtained recently by Newman (1978) is discussed. It confirms the correctness of the initial s process theory (Clayton, Fowler, Hull, and Zimmerman, 1961). At the same time for small neutron exposures the exact and initial solutions differ. The influence of branching of the s-process due to competition between β decay and neutron capture is analyzed; it is noted that at a temperature ~3·108 K and a density of free neutrons 1.6·107 cm-3 the s process theory is in good agreement with observational data on the yields of the various nuclides. Models are discussed for the pulsed neutron s process, which leads to formation of heavy elements in the interior of a star as the result of periodic flares of the helium shell and subsequent remixing of the material.

Evolution of CO lines in time-dependent models of protostellar disk formation

NASA Astrophysics Data System (ADS)

Harsono, D.; Visser, R.; Bruderer, S.; van Dishoeck, E. F.; Kristensen, L. E.

2013-07-01

Context. Star and planet formation theories predict an evolution in the density, temperature, and velocity structure as the envelope collapses and forms an accretion disk. While continuum emission can trace the dust evolution, spectrally resolved molecular lines are needed to determine the physical structure and collapse dynamics. Aims: The aim of this work is to model the evolution of the molecular excitation, line profiles, and related observables during low-mass star formation. Specifically, the signatures of disks during the deeply embedded stage (Menv > M⋆) are investigated. Methods: The semi-analytic 2D axisymmetric model of Visser and collaborators has been used to describe the evolution of the density, stellar mass, and luminosity from the pre-stellar to the T-Tauri phase. A full radiative transfer calculation is carried out to accurately determine the time-dependent dust temperatures. The time-dependent CO abundance is obtained from the adsorption and thermal desorption chemistry. Non-LTE near-IR (NIR), far-IR (FIR), and submm lines of CO have been simulated at a number of time steps. Results: In single dish (10-20'' beams), the dynamics during the collapse are best probed through highly excited 13CO and C18O lines, which are significantly broadened by the infall process. In contrast to the dust temperature, the CO excitation temperature derived from submm/FIR data does not vary during the protostellar evolution, consistent with C18O observations obtained with Herschel and from ground-based telescopes. The NIR spectra provide complementary information to the submm lines by probing not only the cold outer envelope but also the warm inner region. The NIR high-J (≥8) absorption lines are particularly sensitive to the physical structure of the inner few AU, which does show evolution. The models indicate that observations of 13CO and C18O low-J submm lines within a ≤1″ (at 140 pc) beam are well suited to probe embedded disks in Stage I (Menv < M⋆) sources, consistent with recent interferometric observations. High signal-to-noise ratio subarcsec resolution data with ALMA are needed to detect the presence of small rotationally supported disks during the Stage 0 phase and various diagnostics are discussed. The combination of spatially and spectrally resolved lines with ALMA and at NIR is a powerful method to probe the inner envelope and disk formation process during the embedded phase. Appendices are available in electronic form at http://www.aanda.org

Hydrogen Balmer Line Broadening in Solar and Stellar Flares

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

Kowalski, Adam F.; Allred, Joel C.; Uitenbroek, Han

2017-03-10

The broadening of the hydrogen lines during flares is thought to result from increased charge (electron, proton) density in the flare chromosphere. However, disagreements between theory and modeling prescriptions have precluded an accurate diagnostic of the degree of ionization and compression resulting from flare heating in the chromosphere. To resolve this issue, we have incorporated the unified theory of electric pressure broadening of the hydrogen lines into the non-LTE radiative-transfer code RH. This broadening prescription produces a much more realistic spectrum of the quiescent, A0 star Vega compared to the analytic approximations used as a damping parameter in the Voigtmore » profiles. We test recent radiative-hydrodynamic (RHD) simulations of the atmospheric response to high nonthermal electron beam fluxes with the new broadening prescription and find that the Balmer lines are overbroadened at the densest times in the simulations. Adding many simultaneously heated and cooling model loops as a “multithread” model improves the agreement with the observations. We revisit the three-component phenomenological flare model of the YZ CMi Megaflare using recent and new RHD models. The evolution of the broadening, line flux ratios, and continuum flux ratios are well-reproduced by a multithread model with high-flux nonthermal electron beam heating, an extended decay phase model, and a “hot spot” atmosphere heated by an ultrarelativistic electron beam with reasonable filling factors: ∼0.1%, 1%, and 0.1% of the visible stellar hemisphere, respectively. The new modeling motivates future work to understand the origin of the extended gradual phase emission.« less

Hydrogen Balmer Line Broadening in Solar and Stellar Flares

NASA Astrophysics Data System (ADS)

Kowalski, Adam F.; Allred, Joel C.; Uitenbroek, Han; Tremblay, Pier-Emmanuel; Brown, Stephen; Carlsson, Mats; Osten, Rachel A.; Wisniewski, John P.; Hawley, Suzanne L.

2017-03-01

The broadening of the hydrogen lines during flares is thought to result from increased charge (electron, proton) density in the flare chromosphere. However, disagreements between theory and modeling prescriptions have precluded an accurate diagnostic of the degree of ionization and compression resulting from flare heating in the chromosphere. To resolve this issue, we have incorporated the unified theory of electric pressure broadening of the hydrogen lines into the non-LTE radiative-transfer code RH. This broadening prescription produces a much more realistic spectrum of the quiescent, A0 star Vega compared to the analytic approximations used as a damping parameter in the Voigt profiles. We test recent radiative-hydrodynamic (RHD) simulations of the atmospheric response to high nonthermal electron beam fluxes with the new broadening prescription and find that the Balmer lines are overbroadened at the densest times in the simulations. Adding many simultaneously heated and cooling model loops as a “multithread” model improves the agreement with the observations. We revisit the three-component phenomenological flare model of the YZ CMi Megaflare using recent and new RHD models. The evolution of the broadening, line flux ratios, and continuum flux ratios are well-reproduced by a multithread model with high-flux nonthermal electron beam heating, an extended decay phase model, and a “hot spot” atmosphere heated by an ultrarelativistic electron beam with reasonable filling factors: ˜0.1%, 1%, and 0.1% of the visible stellar hemisphere, respectively. The new modeling motivates future work to understand the origin of the extended gradual phase emission.

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.

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.

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.

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.

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.

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.

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

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.

Arguments concerning Relativity and Cosmology.

PubMed

Klein, O

1971-01-29

In the first place I have reviewed the true foundation of Einstein's theory of general relativity, the so-called principle of equivalence, according to which there is no essential difference between "genuine" gravitation and inertial forces, well known from accelerated vehicles. By means of a comparison with Gaussian geometry of curved surfaces-the background of Riemannian geometry, the tool used by Einstein for the mathematical formulation of his theory-it is made clear that this principle is incompatible with the idea proposed by Mach and accepted by Einstein as an incitement to his attempt to describe the main situation in the universe as an analogy in three dimensions to the closed surface of a sphere. In the later attempts toward a mathematical description of the universe, where Einstein's cosmology was adapted to the discovery by Hubble that its observed part is expanding, the socalled cosmological postulate has been used as a kind of axiomatic background which, when analyzed, makes it probable that this expansion is shared by a very big, but still bounded system. This implies that our expanding metagalaxy is probably just one of a type of stellar objects in different phases of evolution, some expanding and some contracting. Some attempts toward the description of this evolution are sketched in the article with the hope that further investigation, theoretical and observational, may lead to an interesting advance in this part of astrophysics.

Relativistic stellar stability: An empirical approach

NASA Technical Reports Server (NTRS)

Ni, W.

1972-01-01

The PPN formalism which encompasses the post-Newtonian limit of nearly every metric theory of gravity is used to analyze stellar stability. This analysis enables one to infer, for any given gravitation theory, the extent to which post-Newtonian effects induce instabilities in white dwarfs, in neutron stars, and in supermassive stars. It also reveals the extent to which our current empirical knowledge of post-Newtonian gravity (based on solar-system experiments) actually guarantees that relativistic instabilities exist. In particular, it shows that: (1) for conservative theories of gravity, current solar-system experiments guarantee that the critical adiabatic index, for the stability of stars against radial pulsations exceeds the Newtonian value of 4/3 and (2) for nonconservative theories, current experiments do not permit any firm conclusion about the sign of the critical adiabatic index, and (3) in the PPN approximation to every metric theory, the standard Schwarzschild criterion for convection is valid.

Zodiacal Exoplanets in Time (ZEIT). IV. Seven Transiting Planets in the Praesepe Cluster

NASA Astrophysics Data System (ADS)

Mann, Andrew W.; Gaidos, Eric; Vanderburg, Andrew; Rizzuto, Aaron C.; Ansdell, Megan; Medina, Jennifer Vanessa; Mace, Gregory N.; Kraus, Adam L.; Sokal, Kimberly R.

2017-02-01

Open clusters and young stellar associations are attractive sites to search for planets and to test theories of planet formation, migration, and evolution. We present our search for, and characterization of, transiting planets in the 800 Myr old Praesepe (Beehive, M44) Cluster from K2 light curves. We identify seven planet candidates, six of which we statistically validate to be real planets, the last of which requires more data. For each host star, we obtain high-resolution NIR spectra to measure its projected rotational broadening and radial velocity, the latter of which we use to confirm cluster membership. We combine low-resolution spectra with the known cluster distance and metallicity to provide precise temperatures, masses, radii, and luminosities for the host stars. Combining our measurements of rotational broadening, rotation periods, and our derived stellar radii, we show that all planetary orbits are consistent with alignment to their host star’s rotation. We fit the K2 light curves, including priors on stellar density to put constraints on the planetary eccentricities, all of which are consistent with zero. The difference between the number of planets found in Praesepe and Hyades (8 planets, ≃ 800 Myr) and a similar data set for Pleiades (0 planets, ≃125 Myr) suggests a trend with age, but may be due to incompleteness of current search pipelines for younger, faster-rotating stars. We see increasing evidence that some planets continue to lose atmosphere past 800 Myr, as now two planets at this age have radii significantly larger than their older counterparts from Kepler.

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.

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.

Radiative Transfer in Stellar Atmospheres

NASA Astrophysics Data System (ADS)

Rutten, Robert J.

2003-05-01

The main topic treated in these graduate course notes is the classical theory of radiative transfer for explaining stellar spectra. It needs relatively much attention to be mastered. Radiative transfer in gaseous media that are neither optically thin nor fully opaque and scatter to boot is a key part of astrophysics but not a transparent subject. These course notes represent a middle road between Mihalas' "Stellar Atmospheres" (graduate level and up) and the books by Novotny and Boehm-Vitense (undergraduate level). They are at about the level of Gray's "The observation and analysis of stellar photospheres" but emphasize NLTE radiative transfer rather than observational techniques and data interpretation.

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.