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Sample records for non-rotating stellar core

  1. Core Collapse Supernovae Using CHIMERA: Gravitational Radiation from Non-Rotating Progenitors

    SciTech Connect

    Yakunin, Konstantin; Marronetti, Pedro; Mezzacappa, Anthony; Bruenn, S. W.; Lee, Ching-Tsai; Chertkow, Merek A; Hix, William Raphael; Blondin, J. M.; Lentz, Eric J; Messer, Bronson; Yoshida, S.

    2011-01-01

    The CHIMERA code is a multi-dimensional multi-physics engine dedicated primarily to the simulation of core collapse supernova explosions. One of the most important aspects of these explosions is their capacity to produce gravitational radiation that is detectable by earth-based laser-interferometric gravitational wave observatories such as LIGO and VIRGO. We present here preliminary gravitational signatures of two-dimensional models with non-rotating progenitors. These simulations exhibit explosions, which are followed for more than half a second after stellar core bounce.

  2. Computer simulations of stellar collapse and supernovae explosions - Non-rotating and rotating models

    NASA Astrophysics Data System (ADS)

    Hillebrandt, W.

    1982-11-01

    Computer simulation models of type II supernova explosions are reviewed. For nonrotating models, it is discussed whether or not a shock wave generated from the rebounding core by itself causes mass ejection. Both adiabatic and nonadiabatic models are discussed in detail. In the former, entropy is strictly conserved and weak interaction reactions are ignored. Consequently, the electron concentration stays high and a very energetic supernova explosion results. In the nonadiabatic model, most of the shock energy is consumed in dissociating heavy nuclei on the way out, the rest being radiated away by neutrinos. In none of the recent computations does a supernova explosion result; possibilities to overcome these difficulties are discussed. Then, computation in which the assumption of spherical symmetry is omitted are addressed. Rotating models are considered, and it is shown that even initially moderately rotating stellar cores add important modifications to the simple core-bounce picture. Finally, processes resulting from the presence of magnetic fields, lepton number, entropy gradients, and unburned nuclear fuel are treated.

  3. Observations of Pre-Stellar Cores

    NASA Astrophysics Data System (ADS)

    Tafalla, M.

    2005-08-01

    Our understanding of the physical and chemical structure of pre-stellar cores, the simplest star-forming sites, has significantly improved since the last IAU Symposium on Astrochemistry (South Korea, 1999). Research done over these years has revealed that major molecular species like CO and CS systematically deplete onto dust grains in the interior of pre-stellar cores, while species like N2H+ and NH3 survive in the gas phase and can usually be detected toward the core centers. Such a selective behavior of molecular species gives rise to a differentiated (onion-like) chemical composition, and manifests itself in molecular maps as a dichotomy between centrally peaked and ring-shaped distributions. From the point of view of star-formation studies, the identification of molecular inhomogeneities in cores helps to resolve past discrepancies between observations made using different tracers, and brings the possibility of self-consistent modelling of the core internal structure. Here I present recent work on determining the physical and chemical structure of two pre-stellar cores, L1498 and L1517B, using observations in a large number of molecules and Monte Carlo radiative transfer analysis. These two cores are typical examples of the pre-stellar core population, and their chemical composition is characterized by the presence of large `freeze out holes' in most molecular species. In contrast with these chemically processed objects, a new population of chemically young cores has begun to emerge. The characteristics of its most extreme representative, L1521E, are briefly reviewed.

  4. Effects of stellar rotation on star formation rates and comparison to core-collapse supernova rates

    SciTech Connect

    Horiuchi, Shunsaku; Beacom, John F.; Bothwell, Matt S.; Thompson, Todd A.

    2013-06-01

    We investigate star formation rate (SFR) calibrations in light of recent developments in the modeling of stellar rotation. Using new published non-rotating and rotating stellar tracks, we study the integrated properties of synthetic stellar populations and find that the UV to SFR calibration for the rotating stellar population is 30% smaller than for the non-rotating stellar population, and 40% smaller for the Hα to SFR calibration. These reductions translate to smaller SFR estimates made from observed UV and Hα luminosities. Using the UV and Hα fluxes of a sample of ∼300 local galaxies, we derive a total (i.e., sky-coverage corrected) SFR within 11 Mpc of 120-170 M {sub ☉} yr{sup –1} and 80-130 M {sub ☉} yr{sup –1} for the non-rotating and rotating estimators, respectively. Independently, the number of core-collapse supernovae discovered in the same volume requires a total SFR of 270{sub −80}{sup +110} M{sub ⊙} yr{sup −1}, suggesting a tension with the SFR estimates made with rotating calibrations. More generally, when compared with the directly estimated SFR, the local supernova discoveries strongly constrain any physical effects that might increase the energy output of massive stars, including, but not limited to, stellar rotation. The cosmic SFR and cosmic supernova rate data, on the other hand, show the opposite trend, with the cosmic SFR higher than that inferred from cosmic supernovae, constraining a significant decrease in the energy output of massive stars. Together, these lines of evidence suggest that the true SFR calibration factors cannot be too far from their canonical values.

  5. Core density turbulence in the HSX Stellarator

    DOE PAGESBeta

    Deng, C. B.; Brower, D. L.; Anderson, D. T.; Anderson, F. S. B.; Briesemeister, Alexis R.; Likin, K. M.

    2015-10-23

    Broadband turbulent density fluctuations are explored in the helically symmetric stellarator experiment (HSX) by investigating changes related to plasma heating power and location. No fluctuation response is observed to occur with large changes in electron temperature and its gradient, thereby eliminating temperature gradient as a driving mechanism. Instead, measurements reveal that density turbulence varies inversely with electron density scale length. This response is consistent with density gradient drive as one might expect for trapped electron mode (TEM) turbulence. In general, the plasma stored energy and particle confinement are higher for discharges with reduced fluctuations in the plasma core. When themore » density fluctuation amplitude is reduced, increased plasma rotation is also evident suggesting a role is being played by intrinsic plasma flow.« less

  6. Core density turbulence in the HSX Stellarator

    SciTech Connect

    Deng, C. B.; Brower, D. L.; Anderson, D. T.; Anderson, F. S. B.; Briesemeister, Alexis R.; Likin, K. M.

    2015-10-23

    Broadband turbulent density fluctuations are explored in the helically symmetric stellarator experiment (HSX) by investigating changes related to plasma heating power and location. No fluctuation response is observed to occur with large changes in electron temperature and its gradient, thereby eliminating temperature gradient as a driving mechanism. Instead, measurements reveal that density turbulence varies inversely with electron density scale length. This response is consistent with density gradient drive as one might expect for trapped electron mode (TEM) turbulence. In general, the plasma stored energy and particle confinement are higher for discharges with reduced fluctuations in the plasma core. When the density fluctuation amplitude is reduced, increased plasma rotation is also evident suggesting a role is being played by intrinsic plasma flow.

  7. The CHESS Spectral Survey of Pre-stellar Cores

    NASA Astrophysics Data System (ADS)

    Bacmann, A.; Caselli, P.; Ceccarelli, C.; Pagani, L.; Vastel, C.

    2012-03-01

    We present the results of the HIFI observations of the pre-stellar cores L1544 and 16293E, as part of the CHESS Key Program. Pre-stellar cores, being cold and dense, have a chemistry dominated by the freeze-out of molecular species and enhanced deuteration, both phenomena being linked. L1544 is a well-studied prototypical pre-stellar core and 16293E is one of the very few source where the species para-D_2H^+ and ortho-H_2D^+ were both detected. These ions play a key role in the deuteration process. We report here the detection of HDO and ND in 16293E (together with their hydrogenated counterparts H_2O and NH). This is the first time these species have been observed in pre-stellar cores. Both species represent particularly interesting cases since they have completely different behaviours with respect to freeze-out. In L1544, we report the detection of high critical density transitions of NH_2D, tracing the very inner parts of the core. We discuss the implications of the species' abundances and deuterium fractionation on our understanding of pre-stellar core chemistry.

  8. Hydrodynamic Simulations of Shell Convection in Stellar Cores

    NASA Astrophysics Data System (ADS)

    Mocák, Miroslav; Müller, Ewald; Siess, Lionel

    Shell convection driven by nuclear burning in a stellar core is a common hydrodynamic event in the evolution of many types of stars. We encounter and simulate this convection (1) in the helium core of a low-mass red giant during core helium flash leading to a dredge-down of protons across an entropy barrier, (2) in a carbon-oxygen core of an intermediate-mass star during core carbon flash, and (3) in the oxygen and carbon burning shell above the silicon-sulfur rich core of a massive star prior to supernova explosion. Our results, which were obtained with the hydrodynamics code HERAKLES, suggest that both entropy gradients and entropy barriers are less important for stellar structure than commonly assumed. Our simulations further reveal a new dynamic mixing process operating below the base of shell convection zones.

  9. The compactness of presupernova stellar cores

    SciTech Connect

    Sukhbold, Tuguldur; Woosley, S. E.

    2014-03-01

    The success or failure of the neutrino-transport mechanism for producing a supernova in an evolved massive star is known to be sensitive not only to the mass of the iron core that collapses, but also to the density gradient in the silicon and oxygen shells surrounding that core. Here we study the systematics of a presupernova core's 'compactness' as a function of the mass of the star and the physics used in its calculation. Fine-meshed surveys of presupernova evolution are calculated for stars from 15 to 65 M {sub ☉}. The metallicity and the efficiency of semiconvection and overshoot mixing are both varied and bare carbon-oxygen cores are explored as well as full hydrogenic stars. Two different codes, KEPLER and MESA, are used for the study. A complex interplay of carbon and oxygen burning, especially in shells, can cause rapid variations in the compactness for stars of very nearly the same mass. On larger scales, the distribution of compactness with main sequence mass is found to be robustly non-monotonic, implying islands of 'explodabilty,' particularly around 8-20 M {sub ☉} and 25-30 M {sub ☉}. The carbon-oxygen (CO) core mass of a presupernova star is a better, (though still ambiguous) discriminant of its core structure than the main sequence mass.

  10. Perturbation analysis of a general polytropic homologously collapsing stellar core

    NASA Astrophysics Data System (ADS)

    Cao, Yi; Lou, Yu-Qing

    2009-12-01

    For dynamic background models of Goldreich & Weber and Lou & Cao, we examine three-dimensional perturbation properties of oscillations and instabilities in a general polytropic homologously collapsing stellar core of a relativistically hot medium with a polytropic index γ = 4/3. Perturbation behaviours, especially internal gravity g modes, depend on the variation of specific entropy in the collapsing core. Among possible perturbations, we identify acoustic p modes and surface f modes as well as internal gravity g+ and g- modes. As in stellar oscillations of a static star, we define g+ and g- modes by the sign of the Brunt-Väisälä buoyancy frequency squared for a collapsing stellar core. A new criterion for the onset of instabilities is established for a homologous stellar core collapse. We demonstrate that the global energy criterion of Chandrasekhar is insufficient to warrant the stability of general polytropic equilibria. We confirm the acoustic p-mode stability of Goldreich & Weber, even though their p-mode eigenvalues appear in systematic errors. Unstable modes include g- modes and sufficiently high-order g+ modes, corresponding to core instabilities. Such instabilities occur before the stellar core bounce, in contrast to instabilities in other models of supernova (SN) explosions. The breakdown of spherical symmetry happens earlier than expected in numerical simulations so far. The formation and motion of the central compact object are speculated to be much affected by such g-mode instabilities. By estimates of typical parameters, unstable low-order l = 1 g-modes may produce initial kicks of the central compact object. Other high-order and high-degree unstable g modes may shred the nascent neutron core into pieces without an eventual compact remnant (e.g. SN 1987A). Formation of binary pulsars and planets around neutron stars might originate from unstable l = 2 g-modes and high-order high-degree g modes, respectively.

  11. Stellar evolution at high mass with convective core overshooting

    NASA Technical Reports Server (NTRS)

    Stothers, R. B.; Chin, C.-W.

    1985-01-01

    The transition from stellar evolution models with no convective core overshooting (CCO) at all to models in which homogeneous mixing due to CCO reaches far beyond the formal convective core boundary is systematically explored. Overshooting is parameterized in terms of the ratio d/H(p), where d is the distance of convective overshoot beyond the formal convective core boundary and H(p) is the local pressure scale height. It is concluded that CCO in very massive main sequence stars produces a great expansion of the stellar envelope if d/H(p) is large but not excessively large. CCO does not entirely suppress convective instability above the overshoot zone in the envelopes of main sequence stars more massive than about 15 solar masses. A general comparison of theoretically constructed isochrones for young stars with observed main sequence turnups indicates that the observed turnups are longer, brighter, and cooler at the tip than those expected on thfe basis of standard evolutionary theory.

  12. AKARI Mapping of an Externally Heated Pre-Stellar Core

    NASA Astrophysics Data System (ADS)

    Nutter, D.; Ward-Thompson, D.; Stamatellos, D.

    2009-12-01

    We present observations of the L1155C pre-stellar core in the Cepheus molecular cloud, taken using the FIS instrument on the AKARI satellite. We compare these data to SCUBA and ISOPHOT data. All of the data show a relation between the position of the emission peak and wavelength, which we interpret as a temperature gradient. We fit modified blackbody curves to the spectral energy distributions at two positions in the core and find that the core is approximately 2 K warmer at one edge than in the centre. We carry out radiative transfer modelling and include the effects from the nearby A6V star BD+67 1263. We generate a good fit to the observed data at all wavelengths, and demonstrate that the appearance of the core at different wavelengths can be explained by the observed temperature gradient, caused by BD+67 1263. Our findings illustrate very clearly that the apparent morphology of a pre-stellar core can be highly dependent on the wavelength of the observation, and that temperature gradients must be taken into account before converting images into column density distributions. This is important to note when interpreting AKARI and Spitzer data and will also be significant for Herschel data.

  13. Magnetic braking of stellar cores in red giants and supergiants

    SciTech Connect

    Maeder, André; Meynet, Georges E-mail: georges.meynet@unige.ch

    2014-10-01

    Magnetic configurations, stable on the long term, appear to exist in various evolutionary phases, from main-sequence stars to white dwarfs and neutron stars. The large-scale ordered nature of these fields, often approximately dipolar, and their scaling according to the flux conservation scenario favor a fossil field model. We make some first estimates of the magnetic coupling between the stellar cores and the outer layers in red giants and supergiants. Analytical expressions of the truncation radius of the field coupling are established for a convective envelope and for a rotating radiative zone with horizontal turbulence. The timescales of the internal exchanges of angular momentum are considered. Numerical estimates are made on the basis of recent model grids. The direct magnetic coupling of the core to the extended convective envelope of red giants and supergiants appears unlikely. However, we find that the intermediate radiative zone is fully coupled to the core during the He-burning and later phases. This coupling is able to produce a strong spin down of the core of red giants and supergiants, also leading to relatively slowly rotating stellar remnants such as white dwarfs and pulsars. Some angular momentum is also transferred to the outer convective envelope of red giants and supergiants during the He-burning phase and later.

  14. Three-dimensional hydrodynamic instabilities in stellar core collapses

    NASA Astrophysics Data System (ADS)

    Lou, Yu-Qing; Lian, Biao

    2012-03-01

    A spherically symmetric hydrodynamic stellar core collapse process under gravity is time-dependent and may become unstable once disturbed. Subsequent non-linear evolutions of such growth of hydrodynamic instabilities may lead to various physical consequences. Specifically for a homologous collapse of a stellar core characterized by a polytropic exponent Γ= 4/3, we examine oscillations and/or instabilities of three-dimensional (3D) general polytropic perturbations. Being incompressible, the radial component of vorticity perturbation always grows unstably during the same homologous core collapse. For compressible 3D perturbations, the polytropic index γ of perturbations can differ from Γ= 4/3 of the general polytropic hydrodynamic background flow, where the background specific entropy is conserved along streamlines and can vary in radius and time. Our model formulation here is more general than previous ones. The Brunt-Väisälä buoyancy frequency ? does not vanish, allowing for the existence of internal gravity g- modes and/or g+ modes, depending on the sign of ? respectively. Eigenvalues and eigenfunctions of various oscillatory and unstable perturbation modes are computed, given asymptotic boundary conditions. As studied in several specialized cases of Goldreich & Weber and of Lou & Cao and Cao & Lou, we further confirm that acoustic p modes and surface f modes remain stable in the current more general situations. In comparison, g- modes and sufficiently high radial order g+ modes are unstable, leading to inevitable convective motions within the collapsing stellar interior; meanwhile, sufficiently low radial order g+ modes remain stably trapped in the collapsing core. Unstable growths of 3D g-mode disturbances are governed dominantly by the angular momentum conservation and modified by the gas pressure restoring force. We note in particular that unstable temporal growths of 3D vortical perturbations exist even when the specific entropy distribution becomes

  15. The Impact of Nuclear Physics During Stellar Core Collapse

    SciTech Connect

    Hix, William Raphael; Baird, Mark L; Lentz, Eric J; Messer, Bronson; Mezzacappa, Anthony

    2008-01-01

    Nuclear electron capture and the nuclear equation of state play important roles during the collapse of a massive star and the subsequent supernova. The nuclear equation of state controls the nature of the bounce which initially forms the supernova shock while electron capture determines the location where the shock forms. Advances in nuclear structure theory have allowed a more realistic treatment of electron capture on heavy nuclei to be developed. We will review how this improvement has led to a change in our understanding of stellar core collapse, with electron capture on nuclei with masses larger than 50 found to dominate electron capture on free protons, resulting is significant changes in the hydrodynamics of core collapse and bounce. We will also demonstrate the impact of a variety of nuclear equations of state on supernova shock propagation. Of particular note is the interplay between the nuclear composition determined by the equation of state and nuclear electron capture.

  16. The dependence of convective core overshooting on stellar mass

    NASA Astrophysics Data System (ADS)

    Claret, A.; Torres, G.

    2016-07-01

    Context. Convective core overshooting extends the main-sequence lifetime of a star. Evolutionary tracks computed with overshooting are very different from those that use the classical Schwarzschild criterion, which leads to rather different predictions for the stellar properties. Attempts over the last two decades to calibrate the degree of overshooting with stellar mass using detached double-lined eclipsing binaries have been largely inconclusive, mainly because of a lack of suitable observational data. Aims: We revisit the question of a possible mass dependence of overshooting with a more complete sample of binaries, and examine any additional relation there might be with evolutionary state or metal abundance Z. Methods: We used a carefully selected sample of 33 double-lined eclipsing binaries strategically positioned in the H-R diagram with accurate absolute dimensions and component masses ranging from 1.2 to 4.4 M⊙. We compared their measured properties with stellar evolution calculations to infer semi-empirical values of the overshooting parameter αov for each star. Our models use the common prescription for the overshoot distance dov = αovHp, where Hp is the pressure scale height at the edge of the convective core as given by the Schwarzschild criterion, and αov is a free parameter. Results: We find a relation between αov and mass, which is defined much more clearly than in previous work, and indicates a significant rise up to about 2 M⊙ followed by little or no change beyond this mass. No appreciable dependence is seen with evolutionary state at a given mass, or with metallicity at a given mass although the stars in our sample span a range of a factor of ten in [Fe/H], from -1.01 to + 0.01.

  17. Gravitational wave extraction in simulations of rotating stellar core collapse

    SciTech Connect

    Reisswig, C.; Ott, C. D.; Sperhake, U.; Schnetter, E.

    2011-03-15

    We perform simulations of general relativistic rotating stellar core collapse and compute the gravitational waves (GWs) emitted in the core-bounce phase of three representative models via multiple techniques. The simplest technique, the quadrupole formula (QF), estimates the GW content in the spacetime from the mass-quadrupole tensor only. It is strictly valid only in the weak-field and slow-motion approximation. For the first time, we apply GW extraction methods in core collapse that are fully curvature based and valid for strongly radiating and highly relativistic sources. These techniques are not restricted to weak-field and slow-motion assumptions. We employ three extraction methods computing (i) the Newman-Penrose (NP) scalar {Psi}{sub 4}, (ii) Regge-Wheeler-Zerilli-Moncrief master functions, and (iii) Cauchy-characteristic extraction (CCE) allowing for the extraction of GWs at future null infinity, where the spacetime is asymptotically flat and the GW content is unambiguously defined. The latter technique is the only one not suffering from residual gauge and finite-radius effects. All curvature-based methods suffer from strong nonlinear drifts. We employ the fixed-frequency integration technique as a high-pass waveform filter. Using the CCE results as a benchmark, we find that finite-radius NP extraction yields results that agree nearly perfectly in phase, but differ in amplitude by {approx}1%-7% at core bounce, depending on the model. Regge-Wheeler-Zerilli-Moncrief waveforms, while, in general, agreeing in phase, contain spurious high-frequency noise of comparable amplitudes to those of the relatively weak GWs emitted in core collapse. We also find remarkably good agreement of the waveforms obtained from the QF with those obtained from CCE. The results from QF agree very well in phase and systematically underpredict peak amplitudes by {approx}5%-11%, which is comparable to the NP results and is certainly within the uncertainties associated with core collapse

  18. Deuterated methanol in the pre-stellar core L1544

    NASA Astrophysics Data System (ADS)

    Bizzocchi, L.; Caselli, P.; Spezzano, S.; Leonardo, E.

    2014-09-01

    Context. High methanol (CH3OH) deuteration has been revealed in Class 0 protostars with the detection of singly, doubly, and even triply D-substituted forms. Methanol is believed to form during the pre-collapse phase via gas-grain chemistry and then eventually injected into the gas when the heating produced by the newly formed protostar sublimates the grain mantles. The molecular deuterium fraction of the warm gas is thus a relic of the cold pre-stellar era and provides hints of the past history of the protostars. Aims: Pre-stellar cores represent the preceding stages in the process of star formation. We aim at measuring methanol deuteration in L1544, a prototypical dense and cold core on the verge of gravitational collapse. The aim is to probe the deuterium fractionation process while the "frozen" molecular reservoir is accumulated onto dust grains. Methods: Using the IRAM 30 m telescope, we mapped the methanol emission in the pre-stellar core L1544 and observed singly deuterated methanol (CH2DOH and CH3OD) towards the dust peak of L1544. Non-LTE radiative transfer modelling was performed on three CH3OH emissions lines at 96.7 GHz, using a Bonnor-Ebert sphere as a model for the source. We have also assumed a centrally decreasing abundance profile to take the molecule freeze-out in the inner core into account. The column density of CH2DOH was derived assuming LTE excitation and optically thin emission. Results: The CH3OH emission has a highly asymmetric morphology, resembling a non-uniform ring surrounding the dust peak, where CO is mainly frozen onto dust grains. The observations provide an accurate measure of methanol deuteration in the cold pre-stellar gas. The derived abundance ratio is [CH2DOH]/[CH3OH] = 0.10 ± 0.03, which is significantly smaller than the ones found in low-mass Class 0 protostars and smaller than the deuterium fraction measured in other molecules towards L1544. The singly-deuterated form CH3OD was not detected at 3σ sensitivity of 7 mK km s

  19. The stellar population in the core of M15

    NASA Technical Reports Server (NTRS)

    De Marchi, Guido; Paresce, Francesco

    1994-01-01

    The inner core of the globular cluster M15 within approximately 2 sec of the geometrical center has been explored with high-resolution images taken through several broad-band UV filter with the Faint Object Camera (FOC) on board the Hubble Space Telescope (HST). Approximately 210 stars in this region down to a 5 sigma detection limit of m(sub 220) = 21.5 were reliably identified and located on a UV - U color magnitude diagram for the first time. A majority of stars (about 70% of the total) observed this way lie above the expected main-sequence turn-off of this cluster and below the sparsely populated horizontal branch. The extension of the main sequence above the turn-off separates this population in two roughly equal components situated to the right and left of this line. Most of the former must be classical blue stragglers while the rest belong to a new, as yet unidentified, population of very blue stars. Possibilities include, but are not restricted to, well-mixed single stars, subdwarfs, and helium white dwarfs. Similar objects are also found just outside the core out to approximately 6 sec from the center, but the brighter, presumably more massive ones, are sharply confined to the core itself. The measured excess of bright blue stars and the relative deficiency of bright red giants in the core are consistent with the blue inward color gradient measured from the ground and imply that dynamical evolution can significantly affect the stellar population in the very dense central regions of a high-concentration globular cluster like M15.

  20. Relativistic MHD simulations of stellar core collapse and magnetars

    NASA Astrophysics Data System (ADS)

    Font, José A.; Cerdá-Durán, Pablo; Gabler, Michael; Müller, Ewald; Stergioulas, Nikolaos

    2011-02-01

    We present results from simulations of magneto-rotational stellar core collapse along with Alfvén oscillations in magnetars. These simulations are performed with the CoCoA/CoCoNuT code, which is able to handle ideal MHD flows in dynamical spacetimes in general relativity. Our core collapse simulations highlight the importance of genuine magnetic effects, like the magneto-rotational instability, for the dynamics of the flow. For the modelling of magnetars we use the anelastic approximation to general relativistic MHD, which allows for an effective suppression of fluid modes and an accurate description of Alfvén waves. We further compute Alfvén oscillation frequencies along individual magnetic field lines with a semi-analytic approach. Our work confirms previous results based on perturbative approaches regarding the existence of two families of quasi-periodic oscillations (QPOs), with harmonics at integer multiples of the fundamental frequency. Additional material is presented in the accompanying contribution by Gabler et al (2010b) in these proceedings.

  1. CORE-COLLAPSE SUPERNOVAE AND HOST GALAXY STELLAR POPULATIONS

    SciTech Connect

    Kelly, Patrick L.; Kirshner, Robert P.

    2012-11-10

    We have used images and spectra of the Sloan Digital Sky Survey to examine the host galaxies of 519 nearby supernovae (SN). The colors at the sites of the explosions, as well as chemical abundances, and specific star formation rates (SFRs) of the host galaxies provide circumstantial evidence on the origin of each SN type. We examine separately SN II, SN IIn, SN IIb, SN Ib, SN Ic, and SN Ic with broad lines (SN Ic-BL). For host galaxies that have multiple spectroscopic fibers, we select the fiber with host radial offset most similar to that of the SN. Type Ic SN explode at small host offsets, and their hosts have exceptionally strongly star-forming, metal-rich, and dusty stellar populations near their centers. The SN Ic-BL and SN IIb explode in exceptionally blue locations, and, in our sample, we find that the host spectra for SN Ic-BL show lower average oxygen abundances than those for SN Ic. SN IIb host fiber spectra are also more metal-poor than those for SN Ib, although a significant difference exists for only one of two strong-line diagnostics. SN Ic-BL host galaxy emission lines show strong central specific SFRs. In contrast, we find no strong evidence for different environments for SN IIn compared to the sites of SN II. Because our SN sample is constructed from a variety of sources, there is always a risk that sampling methods can produce misleading results. We have separated the SN discovered by targeted surveys from those discovered by galaxy-impartial searches to examine these questions and show that our results do not depend sensitively on the discovery technique.

  2. Improved models of stellar core collapse and still no explosions: what is missing?

    PubMed

    Buras, R; Rampp, M; Janka, H-Th; Kifonidis, K

    2003-06-20

    Two-dimensional hydrodynamic simulations of stellar core collapse are presented which for the first time were performed by solving the Boltzmann equation for the neutrino transport including a state-of-the-art description of neutrino interactions. Stellar rotation is also taken into account. Although convection develops below the neutrinosphere and in the neutrino-heated region behind the supernova shock, the models do not explode. This suggests missing physics, possibly with respect to the nuclear equation of state and weak interactions in the subnuclear regime. However, it might also indicate a fundamental problem with the neutrino-driven explosion mechanism. PMID:12857181

  3. A 3D view of the Hydra I cluster core- II. Stellar populations

    NASA Astrophysics Data System (ADS)

    Barbosa, Carlos Eduardo; Arnaboldi, Magda; Hilker, Michael; Coccato, Lodovico; Richtler, Tom; Mendes de Oliveira, Cláudia

    2015-02-01

    Several observations of the central region of the Hydra I galaxy cluster point to a multi-epoch assembly history. Using our novel FORS2/VLT spectroscopic data set, we were able to map the luminosity-weighted age, [Fe/H] and [α/Fe] distributions for the stellar populations around the cD galaxy NGC 3311. Our results indicate that the stellar populations follow the trends of the photometric substructures, with distinct properties that may aid to constrain the evolutionary scenarios for the formation of the cluster core.

  4. Stellar encounters involving neutron stars in globular cluster cores

    NASA Technical Reports Server (NTRS)

    Davies, M. B.; Benz, W.; Hills, J. G.

    1992-01-01

    Encounters between a 1.4 solar mass neutron star and a 0.8 solar mass red giant (RG) and between a 1.4 solar mass neutron star (NS) and an 0.8 solar mass main-sequence (MS) star have been successfully simulated. In the case of encounters involving an RG, bound systems are produced when the separation at periastron passage R(MIN) is less than about 2.5 R(RG). At least 70 percent of these bound systems are composed of the RG core and NS forming a binary engulfed in a common envelope of what remains of the former RG envelope. Once the envelope is ejected, a tight white dwarf-NS binary remains. For MS stars, encounters with NSs will produce bound systems when R(MIN) is less than about 3.5 R(MS). Some 50 percent of these systems will be single objects with the NS engulfed in a thick disk of gas almost as massive as the original MS star. The ultimate fate of such systems is unclear.

  5. Collapse and fragmentation of molecular cloud cores. 2: Collapse induced by stellar shock waves

    NASA Technical Reports Server (NTRS)

    Boss, Alan P.

    1995-01-01

    The standard scenario for low-mass star formation involves 'inside-out' collapse of a dense molecular cloud core following loss of magnetic field support through ambipolar diffusion. However, isotopic anomalies in presolar grains and meteoritical inclusions imply that the collapse of the presolar cloud may have been triggered by a stellar shock wave. This paper explores 'outside-in' collapse, that is, protostellar collapse initiated directly by the compression of quiescent dense cloud cores impacted by relatively slow stellar shock waves. A second-order accurate, gravitational hydrodynamics code has been used to study both the spherically symmetrical and three-dimensional evolution of initially centrally condensed, isothermal, self-gravitating, solar-mass cloud cores that are struck by stellar shock waves with velocities up to 25 km/s and postshock temperatures of 10 to 10,000 K. The models show that such mild shock waves do not completely shred and destroy the cloud, and that the dynamical ram pressure can compress the cloud to the verge of self-gravitational collapse. However, compression caused by a high postshock temperature is a considerably more effective means of inducing collapse. Shock-induced collapse produces high initial mass accretion rates (greater than 10(exp -4) solar mass/yr in a solar-mass cloud) that decline rapidly to much lower values, depending on the presence (approximately 10(exp -6) solar mass/yr) or absence (approximately 10(exp -8) to 10(exp -7) solar mass/yr) of an infinite reservoir of mass. Stellar mass accretion rates approximately 10(exp -7) solar mass/yr have been previously inferred from the luminosities of T Tauri stars; balanced mass accretion (stellar rate = envelope rate) at approximately 10(exp -7) solar mass/yr could then be possible if accretion occurs from a finite mass reservoir. Fluid tracers are used to determine what fraction of the stellar shock material is incorporated into the resulting protostellar object and disk

  6. Non-rotated midgut in a dog.

    PubMed

    Kirk, E J; Nutman, A W; Murray, S L

    2009-02-01

    Macroscopic observations of the partly-dissected abdomen of the preserved cadaver of a Labrador bitch were recorded and photographs taken. Neither the duodenum nor the colon looped around the root of the great (jejuno-ileal) mesentery, but both were long enough to have done so. The abdominal organs appeared to be otherwise normal, as did the other parts of the body. The condition appeared to have resulted from non-rotation of the midgut during embryonic development and to have no adverse effect on the animal. PMID:18983624

  7. THE AGE, STELLAR CONTENT, AND STAR FORMATION TIMESCALE OF THE B59 DENSE CORE

    SciTech Connect

    Covey, K. R.; Lada, C. J.; Muench, A. A.; Forbrich, J.; Ascenso, J.; Roman-Zuniga, C.

    2010-10-20

    We have investigated the stellar content of Barnard 59 (B59), the most active star-forming core in the Pipe Nebula. Using the SpeX spectrograph on the NASA Infrared Telescope Facility, we obtained moderate resolution, near-infrared (NIR) spectra for 20 candidate young stellar objects (YSOs) in B59 and a representative sample of NIR and mid-IR bright sources distributed throughout the Pipe. Measuring luminosity and temperature sensitive features in these spectra, we identified likely background giant stars and measured each star's spectral type, extinction, and NIR continuum excess. To measure B59's age, we place its candidate YSOs in the Hertzsprung-Russell diagram and compare their location to YSOs in several well-studied star-forming regions, as well as predictions of pre-main-sequence (PMS) evolutionary models. We find that B59 is composed of late-type (K4-M6) low-mass (0.9-0.1 M{sub sun}) YSOs whose median stellar age is comparable to, if not slightly older than, that of YSOs within the {rho} Oph, Taurus, and Chameleon star-forming regions. Deriving absolute age estimates from PMS models computed by D'Antona et al., and accounting only for statistical uncertainties, we measure B59's median stellar age to be 2.6 {+-} 0.8 Myr. Including potential systematic effects increases the error budget for B59's median (DM98) stellar age to 2.6{sup +4.1}{sub -2.6} Myr. We also find that the relative age orderings implied by PMS evolutionary tracks depend on the range of stellar masses sampled, as model isochrones possess significantly different mass dependences. The maximum likelihood median stellar age we measure for B59, and the region's observed gas properties, suggests that the B59 dense core has been stable against global collapse for roughly six dynamical timescales and is actively forming stars with a star formation efficiency per dynamical time of {approx}6%. While the {approx}150% uncertainties associated with our age measurement propagate directly into these

  8. Asteroseismic analysis of solar-like star KIC 6225718: constraints on stellar parameters and core overshooting

    NASA Astrophysics Data System (ADS)

    Tian, Z. J.; Bi, S. L.; Yang, W. M.; Chen, Y. Q.; Liu, Z. E.; Liu, K.; Li, T. D.; Ge, Z. S.; Yu, J.

    2014-12-01

    We analyse five seasons of short-cadence data of a solar-type star of spectral type F: KIC 6225718 observed by Kepler. We obtain the power spectrum of this star by applying the Lomb-Scargle periodogram to the smoothed time series. By applying the autocorrelation technique to the power spectrum, we derive the large-frequency separation Δν = 105.78 ± 0.65 μHz and the frequency of maximum power νmax = 2301 ± 21 μHz. We identify 33 p modes with angular degrees of l = 0-2 in the frequency range 1600-2800 μHz of the power spectrum with Bayesian Markov Chain Monte Carlo algorithms. In order to determine the parameters of the star accurately, we construct a grid of stellar models with core overshooting using the Yale stellar evolution code and then perform preliminary seismological analysis. With both asteroseismic and non-asteroseismic constraints, the following range of stellar parameters is estimated: mass M=1.10^{+0.04}_{-0.03} M_{{{odot }}}, radius R = 1.22^{+0.01}_{-0.01} R_{{{odot }}} and age t=3.35^{+0.36}_{-0.75} Gyr for this star. In addition, we analyse the effects of overshooting on stellar interiors and find that the upper limit of the overshooting parameter αov is approximately 0.2 for this star.

  9. Bayesian reconstruction of gravitational wave burst signals from simulations of rotating stellar core collapse and bounce

    SciTech Connect

    Roever, Christian; Bizouard, Marie-Anne; Christensen, Nelson; Dimmelmeier, Harald; Heng, Ik Siong; Meyer, Renate

    2009-11-15

    Presented in this paper is a technique that we propose for extracting the physical parameters of a rotating stellar core collapse from the observation of the associated gravitational wave signal from the collapse and core bounce. Data from interferometric gravitational wave detectors can be used to provide information on the mass of the progenitor model, precollapse rotation, and the nuclear equation of state. We use waveform libraries provided by the latest numerical simulations of rotating stellar core collapse models in general relativity, and from them create an orthogonal set of eigenvectors using principal component analysis. Bayesian inference techniques are then used to reconstruct the associated gravitational wave signal that is assumed to be detected by an interferometric detector. Posterior probability distribution functions are derived for the amplitudes of the principal component analysis eigenvectors, and the pulse arrival time. We show how the reconstructed signal and the principal component analysis eigenvector amplitude estimates may provide information on the physical parameters associated with the core collapse event.

  10. FIRST DETECTION OF WATER VAPOR IN A PRE-STELLAR CORE

    SciTech Connect

    Caselli, Paola; Douglas, Thomas; Keto, Eric; Bergin, Edwin A.; Tafalla, Mario; Aikawa, Yuri; Pagani, Laurent; Yildiz, Umut A.; Kristensen, Lars E.; Van Dishoeck, Ewine F.; Van der Tak, Floris F. S.; Walmsley, C. Malcolm; Codella, Claudio; Nisini, Brunella

    2012-11-10

    Water is a crucial molecule in molecular astrophysics as it controls much of the gas/grain chemistry, including the formation and evolution of more complex organic molecules in ices. Pre-stellar cores provide the original reservoir of material from which future planetary systems are built, but few observational constraints exist on the formation of water and its partitioning between gas and ice in the densest cores. Thanks to the high sensitivity of the Herschel Space Observatory, we report on the first detection of water vapor at high spectral resolution toward a dense cloud on the verge of star formation, the pre-stellar core L1544. The line shows an inverse P-Cygni profile, characteristic of gravitational contraction. To reproduce the observations, water vapor has to be present in the cold and dense central few thousand AU of L1544, where species heavier than helium are expected to freeze out onto dust grains, and the ortho:para H{sub 2} ratio has to be around 1:1 or larger. The observed amount of water vapor within the core (about 1.5 Multiplication-Sign 10{sup -6} M{sub Sun }) can be maintained by far-UV photons locally produced by the impact of galactic cosmic rays with H{sub 2} molecules. Such FUV photons irradiate the icy mantles, liberating water vapor in the core center. Our Herschel data, combined with radiative transfer and chemical/dynamical models, shed light on the interplay between gas and solids in dense interstellar clouds and provide the first measurement of the water vapor abundance profile across the parent cloud of a future solar-type star and its potential planetary system.

  11. Protostellar collapse of rotating cloud cores. Covering the complete first accretion period of the stellar core

    NASA Astrophysics Data System (ADS)

    Schönke, J.; Tscharnuter, W. M.

    2011-02-01

    Aims: We investigate the influence of turbulent viscosity on the collapse of a rotating molecular cloud core with axial symmetry, in particular, on the first and second collapse phase, as well as the evolution of the second (protostellar) core during its first accretion period. By using extensive numerical calculations, we monitor the intricate interactions between the newly formed protostar and the surrounding accretion disk (the first core) in which the star is embedded. Methods: We use a grid-based radiation-hydrodynamics code with a spatial grid designed to meet the high resolution required to study the second core. The radiative transfer is treated in the flux-limited diffusion approximation. A slightly supercritical Bonnor-Ebert sphere of 1 Msun and uniform rotation according to a fixed centrifugal radius of 100 AU serves as the initial condition without exception. In a parameter study, we vary the β-viscosity driving the angular momentum transport. Results: Without viscosity (β=0), a highly flattened accretion disk forms that fragments into several "cold" rings. For β = 10-4, a single "warm" ring forms that undergoes collapse due to hydrogen dissociation. For β = 10-3, ring formation is suppressed completely. The second collapse proceeds on the local thermal timescale, which is in contrast to the current view of a generally dynamical second collapse. During the first accretion period of the second core, the first core heats up globally and, as a consequence, a nearly spherical outflow occurs, destroying the structure of the former accretion disk completely. Finally, for β = 10-2, we see the classical dynamical second collapse and a shorter but more rapid accretion phase. The impact on the surrounding accretion disk is even more pronounced. We follow the resulting massive outflow up to several kyr after the second collapse, where the central parts (R < 0.7 AU) are now cut out and replaced with an appropriate inner boundary condition. Matter is found to

  12. Stellar

    NASA Technical Reports Server (NTRS)

    1995-01-01

    This eerie, dark structure, resembling an imaginary sea serpent's head, is a column of cool molecular hydrogen gas (two atoms of hydrogen in each molecule) and dust that is an incubator for new stars. The stars are embedded inside finger-like protrusions extending from the top of the nebula. Each 'fingertip' is somewhat larger than our own solar system. The pillar is slowly eroding away by the ultraviolet light from nearby hot stars, a process called 'photoevaporation.' As it does, small globules of especially dense gas buried within the cloud is uncovered. These globules have been dubbed 'EGGs' -- an acronym for 'Evaporating Gaseous Globules.' The shadows of the EGGs protect gas behind them, resulting in the finger-like structures at the top of the cloud. Forming inside at least some of the EGGs are embryonic stars -- stars that abruptly stop growing when the EGGs are uncovered and they are separated from the larger reservoir of gas from which they were drawing mass. Eventually the stars emerge, as the EGGs themselves succumb to photoevaporation. The stellar EGGS are found, appropriately enough, in the 'Eagle Nebula' (also called M16 -- the 16th object in Charles Messier's 18th century catalog of 'fuzzy' permanent objects in the sky), a nearby star-forming region 7,000 light-years away in the constellation Serpens. The picture was taken on April 1, 1995 with the Hubble Space Telescope Wide Field and Planetary Camera 2. The color image is constructed from three separate images taken in the light of emission from different types of atoms. Red shows emission from singly-ionized sulfur atoms. Green shows emission from hydrogen. Blue shows light emitted by doubly-ionized oxygen atoms.

  13. Observation results by the TAMA300 detector on gravitational wave bursts from stellar-core collapses

    SciTech Connect

    Ando, Masaki; Aso, Youichi; Iida, Yukiyoshi; Nishi, Yuhiko; Otsuka, Shigemi; Seki, Hidetsugu; Soida, Kenji; Taniguchi, Shinsuke; Tochikubo, Kuniharu; Tsubono, Kimio; Yoda, Tatsuo; Arai, Koji; Beyersdorf, Peter; Kawamura, Seiji; Sato, Shuichi; Takahashi, Ryutaro; Tatsumi, Daisuke; Tsunesada, Yoshiki; Zhu, Zong-Hong; Fujimoto, Masa-Katsu

    2005-04-15

    We present data-analysis schemes and results of observations with the TAMA300 gravitational wave detector, targeting burst signals from stellar-core collapse events. In analyses for burst gravitational waves, the detection and fake-reduction schemes are different from well-investigated ones for a chirp wave analysis, because precise waveform templates are not available. We used an excess -power filter for the extraction of gravitational wave candidates, and developed two methods for the reduction of fake events caused by nonstationary noises of the detector. These analysis schemes were applied to real data from the TAMA300 interferometric gravitational wave detector. As a result, fake events were reduced by a factor of about 1000 in the best cases. In addition, in order to interpret the event candidates from an astronomical viewpoint, we performed a Monte-Carlo simulation with an assumed Galactic event distribution model and with burst waveforms obtained from numerical simulations of stellar-core collapses. We set an upper limit of 5.0x10{sup 3} events/sec on the burst gravitational wave event rate in our Galaxy with a confidence level of 90%. This work shows prospects on the search for burst gravitational waves, by establishing an analysis scheme for the observation data from an interferometric gravitational wave detector.

  14. The core mass growth and stellar lifetime of thermally pulsing asymptotic giant branch stars

    SciTech Connect

    Kalirai, Jason S.; Tremblay, Pier-Emmanuel; Marigo, Paola E-mail: paola.marigo@unipd.it

    2014-02-10

    We establish new constraints on the intermediate-mass range of the initial-final mass relation, and apply the results to study the evolution of stars on the thermally pulsing asymptotic giant branch (TP-AGB). These constraints derive from newly discovered (bright) white dwarfs in the nearby Hyades and Praesepe star clusters, including a total of 18 high signal-to-noise ratio measurements with progenitor masses of M {sub initial} = 2.8-3.8 M {sub ☉}. We also include a new analysis of existing white dwarfs in the older NGC 6819 and NGC 7789 star clusters, M {sub initial} = 1.6 and 2.0 M {sub ☉}. Over this range of initial masses, stellar evolutionary models for metallicity Z {sub initial} = 0.02 predict the maximum growth of the core of TP-AGB stars. By comparing the newly measured remnant masses to the robust prediction of the core mass at the first thermal pulse on the AGB (i.e., from stellar interior models), we establish several findings. First, we show that the stellar core mass on the AGB grows rapidly from 10% to 30% for stars with M {sub initial} = 1.6 to 2.0 M {sub ☉}. At larger masses, the core-mass growth decreases steadily to ∼10% at M {sub initial} = 3.4 M {sub ☉}, after which there is a small hint of a upturn out to M {sub initial} = 3.8 M {sub ☉}. These observations are in excellent agreement with predictions from the latest TP-AGB evolutionary models in Marigo et al. We also compare to models with varying efficiencies of the third dredge-up and mass loss, and demonstrate that the process governing the growth of the core is largely the stellar wind, while the third dredge-up plays a secondary, but non-negligible role. Based on the new white dwarf measurements, we perform an exploratory calibration of the most popular mass-loss prescriptions in the literature, as well as of the third dredge-up efficiency as a function of the stellar mass. Finally, we estimate the lifetime and the integrated luminosity of stars on the TP-AGB to peak at t

  15. Maximal acceleration is non-rotating

    NASA Astrophysics Data System (ADS)

    Page, Don N.

    1998-06-01

    In a stationary axisymmetric spacetime, the angular velocity of a stationary observer whose acceleration vector is Fermi-Walker transported is also the angular velocity that locally extremizes the magnitude of the acceleration of such an observer. The converse is also true if the spacetime is symmetric under reversing both t and 0264-9381/15/6/020/img1 together. Thus a congruence of non-rotating acceleration worldlines (NAW) is equivalent to a stationary congruence accelerating locally extremely (SCALE). These congruences are defined completely locally, unlike the case of zero angular momentum observers (ZAMOs), which requires knowledge around a symmetry axis. The SCALE subcase of a stationary congruence accelerating maximally (SCAM) is made up of stationary worldlines that may be considered to be locally most nearly at rest in a stationary axisymmetric gravitational field. Formulae for the angular velocity and other properties of the SCALEs are given explicitly on a generalization of an equatorial plane, infinitesimally near a symmetry axis, and in a slowly rotating gravitational field, including the far-field limit, where the SCAM is shown to be counter-rotating relative to infinity. These formulae are evaluated in particular detail for the Kerr-Newman metric. Various other congruences are also defined, such as a stationary congruence rotating at minimum (SCRAM), and stationary worldlines accelerating radially maximally (SWARM), both of which coincide with a SCAM on an equatorial plane of reflection symmetry. Applications are also made to the gravitational fields of maximally rotating stars, the Sun and the Solar System.

  16. Global Rotation of Non-Rotating Origin

    NASA Astrophysics Data System (ADS)

    Fukushima, T.

    2001-11-01

    At its 24th General Assembly held at Manchester last year, the IAU has adopted the Celestial Ephemeris Origin (CEO) as a new longitude origin of the celestial coordinate system (Capitaine et al. 2000, IAU 2001). The CEO is the application of Guinot's non-rotating origin (NRO) to the Earth's equator (Guinot 1979, Capitaine et al. 1986, Capitaine 1990). By using the current IAU precession/nutation theory, we integrated the global orbit of CEO. It is a slightly curved zigzag pattern of the amplitude of around 23o moving secularly along the ecliptic. Among its kinematical features, we note that CEO has a large secular component of rotation with respect to the inertial reference frame. The current speed of this global rotation is as large as around -4.15 ''/yr. The negative sign shows that CEO rotates clockwise with respect to the inertial frame when viewed from the north celestial pole. Unfortunately this is a general property of NROs. On the other hand, such secular rotation does not exist for some geometrically-defined longitude origins like K, H, and Σ already discussed in Kovalevsky and McCarthy (1998). We think that the existence of a global secular rotaion means that the CEO, and NROs in general, is not appropriate to be specified as the x-axis of celestial coordinate systems.

  17. The Luminosity Function and Radial Profile of the Stellar Population in the Core of 47 Tucanae

    NASA Astrophysics Data System (ADS)

    Paresce, F.; de Marchi, G.; Jedrzejewski, R.; Gilliland, R.; Stratta, M. G.

    1994-12-01

    The core of the galactic globular cluster 47 Tucanae was observed by the Faint Object Camera on the refurbished Hubble Space Telescope for the first time through narrow band F253M and F346M filters centered at 253 nm and 346 nm. A total of 511 stars down to the detection limit at m346 =~ 24 in the 7('') times 7('') field were accurately placed on a m346 vs m253-m346 color magnitude diagram to characterize the stellar populations in the core. Approximately 100 objects above and to the right of the main sequence turn-off are the same as those classified earlier with the aberrated HST but the rest below it are new objects seen now for the first time thanks to the substantial improvement in sensitivity. The new objects form a well defined main sequence whose luminosity function turns over dramatically at m346 =~ 20 well before the completeness limit and well before the end of the slowly increasing luminosity function for the outer fields measured from the ground by Hesser et al. (1987). We interpret this premature drop in the number of stars below ~ 0.7 M_sun in the core as the effect of mass segregation due to two body relaxation. The position of 9 objects in the range 20< m346<24 and -1.5core of 47 Tuc obtained with the WFPC1 before refurbishment in the U band to study with the highest possible accuracy the radial profile of stellar density around the geometrical center of the cluster. This data set fully confirms and extends further the results published by Calzetti et al. (1993) that showed that the radial density profile of 47 Tuc is not consistent with a King model of core radius 25('') extending all the way to the center but requires a central density enhancement of radius ~ 8('') = 0.02 parsec superimposed on the former. This result provides fresh evidence that this cluster may have suffered

  18. Stellar Forensics IV: A post-explosion view of the progenitors of core-collapse supernovae

    NASA Astrophysics Data System (ADS)

    Maund, Justyn

    2012-10-01

    Recent studies have used high spatial resolution HST observations of supernova {SN} sites to directly identify the progenitors of core-collapse SNe on pre-explosion images. These studies have set constraints about the nature of massive stars and their evolution just prior to their explosion as SNe. Now, at late-times when the SNe have faded sufficiently, it is possible to return to the sites of these core-collapse supernovae to search for clues about the nature of their progenitors.We request time to conduct deep, late-time, high-resolution imaging with WFC3 UVIS of the site of the core-collapse SN 2009hd. We aim to: 1} Confirm our original identification, made in pre-explosion images, by confirming that the progenitor is now missing; 2} Apply image subtraction techniques for the pre-explosion images with this late-time imaging to determine accurate photometry of the progenitor to constrain its temperature and luminosity; and 3} use the stellar population in the immediate vicinity of the SN to determine the reddening and extinction that affected the progenitor. HST provides the unique combination of high-resolution optical/IR imaging at very faint magnitudes that will facilitate this study.

  19. Stellar Forensics III: A post-explosion view of the progenitors of core-collapse supernovae

    NASA Astrophysics Data System (ADS)

    Maund, Justyn

    2011-10-01

    Recent studies have used high spatial resolution HST observations of supernova {SN} sites to directly identify the progenitors of core-collapse SNe on pre-explosion images. These studies have set constraints about the nature of massive stars and their evolution just prior to their explosion as SNe. Now, at late-times when the SNe have faded sufficiently, it is possible to return to the sites of these core-collapse SNe to search for clues about the nature of their progenitors.We request time to conduct deep, late-time, high-resolution imaging with ACS/WFC of the sites of two core-collapse SNe 2009kr and 2009md. We aim to: 1} Confirm our original identifications, made in pre-explosion images, by confirming that the progenitors are now missing; 2} Apply image subtraction techniques for this late-time imaging with our pre-explosion images to determine accurate photometry of the progenitors to constrain their temperatures and luminosities; and 3} study the stellar populations in the immediate vicinities of these SNe, previously obscured by the progenitor and the SN, to provide a measure of the progenitor's age, as well. HST provides the unique combination of high-resolution optical/IR imaging at very faint magnitudes that will facilitate this study.

  20. Core-halo age gradients and star formation in the Orion Nebula and NGS 2024 young stellar clusters

    SciTech Connect

    Getman, Konstantin V.; Feigelson, Eric D.; Kuhn, Michael A.

    2014-06-01

    We analyze age distributions of two nearby rich stellar clusters, the NGC 2024 (Flame Nebula) and Orion Nebula cluster (ONC) in the Orion molecular cloud complex. Our analysis is based on samples from the MYStIX survey and a new estimator of pre-main sequence (PMS) stellar ages, Age{sub JX} , derived from X-ray and near-infrared photometric data. To overcome the problem of uncertain individual ages and large spreads of age distributions for entire clusters, we compute median ages and their confidence intervals of stellar samples within annular subregions of the clusters. We find core-halo age gradients in both the NGC 2024 cluster and ONC: PMS stars in cluster cores appear younger and thus were formed later than PMS stars in cluster peripheries. These findings are further supported by the spatial gradients in the disk fraction and K-band excess frequency. Our age analysis is based on Age{sub JX} estimates for PMS stars and is independent of any consideration of OB stars. The result has important implications for the formation of young stellar clusters. One basic implication is that clusters form slowly and the apparent age spreads in young stellar clusters, which are often controversial, are (at least in part) real. The result further implies that simple models where clusters form inside-out are incorrect and more complex models are needed. We provide several star formation scenarios that alone or in combination may lead to the observed core-halo age gradients.

  1. Stellar Forensics: A post-explosion view of the progenitors of core-collapse supernovae

    NASA Astrophysics Data System (ADS)

    Maund, Justyn

    2009-07-01

    Recent studies have used high spatial resolution HST observations of SN sites to identify the progenitors of core-collapse SNe on pre-explosion images. These studies have set constraints about the nature of massive stars and their evolution just prior to their explosion as SNe. Now, at late-times when the SNe have faded sufficiently, it is possible to return to the sites of these core-collapse SNe to search for clues about the nature of their progenitors.We request time to conduct deep, late-time, high-resolution imaging with ACS/HRC of the sites of six core-collapse SNe. In this program we aim to: 1} confirm our identifications, that were made with HST pre-explosion images, of the red supergiant progenitors of four Type IIP SNe {1999ev, 2003gd, 2004A and 2005cs}, by observing if the objects identified as the progenitors are now missing; 2} place precise constraints on the progenitor of the Type Ic SN 2007gr by studying its host cluster; and 3} confirm our identification of an LBV-like outburst of an unstable WR star as belonging to the progenitor of a Type Ib-n core-collapse SN {2006jc}, using broad and narrow-band imaging to search for emission line stars in its locality. The deep imaging will also allow to probe the stellar populations in the immediate vicinities of these SNe, that were previously obscured by the progenitors and the bright SNe. HST provides the unique combination of high-resolution optical imaging at very faint magnitudes that will facilitate this study.

  2. On the effects of solenoidal and compressive turbulence in pre-stellar cores

    NASA Astrophysics Data System (ADS)

    Lomax, O.; Whitworth, A. P.; Hubber, D. A.

    2015-05-01

    We present the results of an ensemble of SPH simulations that follow the evolution of pre-stellar cores for 0.2 Myr. All the cores have the same mass, and start with the same radius, density profile, thermal and turbulent energy. Our purpose is to explore the consequences of varying the fraction of turbulent energy, δsol, that is solenoidal, as opposed to compressive; specifically, we consider δsol = 1, 2/3, 1/3, 1/9 and 0. For each value of δsol, we follow 10 different realizations of the turbulent velocity field, in order also to have a measure of the stochastic variance blurring any systematic trends. With low δsol(<1/3), filament fragmentation dominates and delivers relatively high-mass stars. Conversely, with high values of δsol(>1/3) disc fragmentation dominates and delivers relatively low-mass stars. There are no discernible systematic trends in the multiplicity statistics obtained with different δsol.

  3. Stellar Forensics II: A post-explosion view of the progenitors of core-collapse supernovae

    NASA Astrophysics Data System (ADS)

    Maund, Justyn

    2010-09-01

    Recent studies have used high spatial resolution HST observations of supernova {SN} sites to directly identify the progenitors of core-collapse SNe on pre-explosion images. These studies have set constraints about the nature of massive stars and their evolution just prior to their explosion as SNe. Now, at late-times when the SNe have faded sufficiently, it is possible to return to the sites of these core-collapse SNe to search for clues about the nature of their progenitors.We request time to conduct deep, late-time, high-resolution imaging with WFC3/UVIS+IR and ACS/WFC of the sites of three core-collapse SNe 2008ax, 2008bk and 2008cn. We aim to: 1} Confirm our original identifications, made in pre-explosion images, by confirming that the progenitors are now missing; 2} Apply image subtraction techniques for this late-time imaging with our pre-explosion images to determine accurate photometry of the progenitors to constrain their temperatures and luminosities; and 3} study the stellar populations in the immediate vicinities of these SNe, previously obscured by the progenitor and the SN, to provide a measure of the progenitor's age, as well. For SN 2008ax we aim to determine the possible presence of a binary companion, as a persistent source at the SN location once the SN has faded and the progenitor has disappeared. HST provides the unique combination of high-resolution optical/IR imaging at very faint magnitudes that will facilitate this study.

  4. An ultraviolet-optical flare from the tidal disruption of a helium-rich stellar core.

    PubMed

    Gezari, S; Chornock, R; Rest, A; Huber, M E; Forster, K; Berger, E; Challis, P J; Neill, J D; Martin, D C; Heckman, T; Lawrence, A; Norman, C; Narayan, G; Foley, R J; Marion, G H; Scolnic, D; Chomiuk, L; Soderberg, A; Smith, K; Kirshner, R P; Riess, A G; Smartt, S J; Stubbs, C W; Tonry, J L; Wood-Vasey, W M; Burgett, W S; Chambers, K C; Grav, T; Heasley, J N; Kaiser, N; Kudritzki, R-P; Magnier, E A; Morgan, J S; Price, P A

    2012-05-10

    The flare of radiation from the tidal disruption and accretion of a star can be used as a marker for supermassive black holes that otherwise lie dormant and undetected in the centres of distant galaxies. Previous candidate flares have had declining light curves in good agreement with expectations, but with poor constraints on the time of disruption and the type of star disrupted, because the rising emission was not observed. Recently, two 'relativistic' candidate tidal disruption events were discovered, each of whose extreme X-ray luminosity and synchrotron radio emission were interpreted as the onset of emission from a relativistic jet. Here we report a luminous ultraviolet-optical flare from the nuclear region of an inactive galaxy at a redshift of 0.1696. The observed continuum is cooler than expected for a simple accreting debris disk, but the well-sampled rise and decay of the light curve follow the predicted mass accretion rate and can be modelled to determine the time of disruption to an accuracy of two days. The black hole has a mass of about two million solar masses, modulo a factor dependent on the mass and radius of the star disrupted. On the basis of the spectroscopic signature of ionized helium from the unbound debris, we determine that the disrupted star was a helium-rich stellar core. PMID:22575962

  5. Neutronization of matter in a stellar core and convection during gravitational collapse

    NASA Astrophysics Data System (ADS)

    Aksenov, A. G.; Chechetkin, V. M.

    2016-07-01

    The roles of neutrinos and convective instability in collapsing supernovae are considered. Spherically symmetrical computations of the collapse using the Boltzmann equation for the neutrinos lead to the formation of the condition of convective instability, {( {{partial P}/{partial s}} )_{ρ {Y_l}}}{ds}/{dr} + {( {{partial P}/{partial {Y_L}}} )_{ρ s}}{d{Y_L}}/{dr} < 0, in a narrow region of matter accretion above the neutrinosphere. If instability arises in this region, the three-dimensional solution will represent a correction to the spherically symmetrical solution for the gravitational collapse. The mean neutrino energies change only negligibly in the narrow region of accretion. Nuclear statistical equilibrium is usually assumed in the hot proto-neutron stellar core, to simplify the computations of the collapse. Neutronization with the participation of free neutrons is most efficient. However, the decay of nuclei into nucleons is hindered during the collapse, because the density grows too rapidly compared to the growth in the temperature, and an appreciable fraction of the energy is carried away by neutrinos. The entropy of the matter per nucleon is modest at the stellar center. All the energy is in degenerate electrons during the collapse. If the large energy of these degenerate electrons is taken into account, neutrons are efficiently formed, even in cool matter with reduced Y e (the difference between the numbers of electrons and positrons per nucleon). This process brings about an increase in the optical depth to neutrinos, the appearance of free neutrons, and an increase in the entropy per nucleon at the center. The convectively unstable region at the center increases. The development of large-scale convection is illustrated using a multi-dimensional gas-dynamical model for the evolution of a stationary, unstable state (without taking into account neutrino transport). The time for the development of convective instability (several milliseconds) does not

  6. Water in high-mass pre- and proto-stellar cores from Hi-GAL

    NASA Astrophysics Data System (ADS)

    Persson, Carina M.; Olmi, Luca; Codella, Claudio

    2015-08-01

    As a part of our on-going investigation of the earliest phases of massive star formation, we present Herschel-HIFI data of H2O, NH3 and N2H+ towards a sample of high-mass starless cores and proto-stellar objects in two galactic fields, each containing objects in different evolutionary stages. We observed 17 sources in the l = 30° galactic field, and 35 sources in the l = 59° field. The clumps in the l = 59°region have lower luminosity and mass than the l = 30° objects. We find that the sources with detections have much higher mean luminosities than compared to the sources with no detection of any line, but the mean masses are similar. Most sources with detections are proto-stellar, and at least two of the detected sources in the l = 59° region are in a more advanced stage of evolution. For the l = 30° sources no preferential evolutionary phase is evident. None of these sources, however, appear to belong to the late phase of envelope dispersal.The detections show complex line shapes from the protostellar envelopes, molecular outflows and infall. All detections in the l = 59° field show similar water line profiles with broad outflows, whereas towards l = 30° no outflows are detected and all sources display very different line shapes. Both water and ammonia are also often self-absorbed, sometimes saturated, and some sources show an inverse or a regular P-Cygni line profile. N2H+ do not exhibit line asymmetries or absorption. The integrated intensities of the three lines are correlated, and we also find correlations between the water line luminosity and continuum temperature. The typical water luminosity towards the l = 30° sources is lower than compared to l = 59° sources, but their continuum temperature is higher, which may suggest a later evolutionary stage.In the sight-lines towards 11 sources in the l = 30° field, among which four have no detections in the star-forming regions, we also detect H2O and NH3 in absorption from interstellar gas. Since

  7. 3D collapse of rotating stellar iron cores in general relativity including deleptonization and a nuclear equation of state.

    PubMed

    Ott, C D; Dimmelmeier, H; Marek, A; Janka, H-T; Hawke, I; Zink, B; Schnetter, E

    2007-06-29

    We present 2D and 3D simulations of the collapse of rotating stellar iron cores in general relativity employing a nuclear equation of state and an approximate treatment of deleptonization. We compare fully general relativistic and conformally flat evolutions and find that the latter treatment is sufficiently accurate for the core-collapse supernova problem. We focus on gravitational wave (GW) emission from rotating collapse, bounce, and early postbounce phases. Our results indicate that the GW signature of these phases is much more generic than previously estimated. We also track the growth of a nonaxisymmetric instability in one model, leading to strong narrow-band GW emission. PMID:17678077

  8. Magnetorotational collapse of massive stellar cores to neutron stars: Simulations in full general relativity

    NASA Astrophysics Data System (ADS)

    Shibata, Masaru; Liu, Yuk Tung; Shapiro, Stuart L.; Stephens, Branson C.

    2006-11-01

    We study magnetohydrodynamic (MHD) effects arising in the collapse of magnetized, rotating, massive stellar cores to proto-neutron stars (PNSs). We perform axisymmetric numerical simulations in full general relativity with a hybrid equation of state. The formation and early evolution of a PNS are followed with a grid of 2500×2500 zones, which provides better resolution than in previous (Newtonian) studies. We confirm that significant differential rotation results even when the rotation of the progenitor is initially uniform. Consequently, the magnetic field is amplified both by magnetic winding and the magnetorotational instability (MRI). Even if the magnetic energy EEM is much smaller than the rotational kinetic energy Trot at the time of PNS formation, the ratio EEM/Trot increases to 0.1 0.2 by the magnetic winding. Following PNS formation, MHD outflows lead to losses of rest mass, energy, and angular momentum from the system. The earliest outflow is produced primarily by the increasing magnetic stress caused by magnetic winding. The MRI amplifies the poloidal field and increases the magnetic stress, causing further angular momentum transport and helping to drive the outflow. After the magnetic field saturates, a nearly stationary, collimated magnetic field forms near the rotation axis and a Blandford-Payne type outflow develops along the field lines. These outflows remove angular momentum from the PNS at a rate given by J˙˜ηEEMCB, where η is a constant of order ˜0.1 and CB is a typical ratio of poloidal to toroidal field strength. As a result, the rotation period quickly increases for a strongly magnetized PNS until the degree of differential rotation decreases. Our simulations suggest that rapidly rotating, magnetized PNSs may not give rise to rapidly rotating neutron stars.

  9. New Era in 3-D Modeling of Convection and Magnetic Dynamos in Stellar Envelopes and Cores

    NASA Astrophysics Data System (ADS)

    Toomre, J.; Augustson, K. C.; Brown, B. P.; Browning, M. K.; Brun, A. S.; Featherstone, N. A.; Miesch, M. S.

    2012-09-01

    consider dynamo action within the cores of rotating A-type stars, finding that striking super-equipartition magnetic fields can be built there. These families of 3-D simulations are showing that a new era of detailed stellar modeling is becoming feasible through rapid advances in supercomputing, and these have the potential to help interpret and possibly even guide some of the observational efforts now under way.

  10. STELLAR AGES AND CONVECTIVE CORES IN FIELD MAIN-SEQUENCE STARS: FIRST ASTEROSEISMIC APPLICATION TO TWO KEPLER TARGETS

    SciTech Connect

    Silva Aguirre, V.; Christensen-Dalsgaard, J.; Chaplin, W. J.; Basu, S.; Deheuvels, S.; Brandao, I. M.; Cunha, M. S.; Sousa, S. G.; Dogan, G.; Metcalfe, T. S.; Serenelli, A. M.; Garcia, R. A.; Ballot, J.; Weiss, A.; Appourchaux, T.; Casagrande, L.; Cassisi, S.; Creevey, O. L.; Lebreton, Y.; Noels, A.; and others

    2013-06-01

    Using asteroseismic data and stellar evolution models we obtain the first detection of a convective core in a Kepler field main-sequence star, putting a stringent constraint on the total size of the mixed zone and showing that extra mixing beyond the formal convective boundary exists. In a slightly less massive target the presence of a convective core cannot be conclusively discarded, and thus its remaining main-sequence lifetime is uncertain. Our results reveal that best-fit models found solely by matching individual frequencies of oscillations corrected for surface effects do not always properly reproduce frequency combinations. Moreover, slightly different criteria to define what the best-fit model is can lead to solutions with similar global properties but very different interior structures. We argue that the use of frequency ratios is a more reliable way to obtain accurate stellar parameters, and show that our analysis in field main-sequence stars can yield an overall precision of 1.5%, 4%, and 10% in radius, mass, and age, respectively. We compare our results with those obtained from global oscillation properties, and discuss the possible sources of uncertainties in asteroseismic stellar modeling where further studies are still needed.

  11. A Combined Spectral/Godunov Code for the Simulation of Gravitational Waves from Stellar Supernova Core Collapse

    NASA Astrophysics Data System (ADS)

    Novak, J.; Dimmelmeier, H.; Font, J. A.

    2008-04-01

    Supernovae represent powerful sources of gravitational radiation. Their numerical simulation, even of simplified core collapse models, requires numerical techniques that are able to handle strong hydrodynamic shocks and a general-relativistic gravitational field. Such hydrodynamics can be modeled with high-resolution shock-capturing (HRSC) schemes, also known as Godunov schemes, in general relativity, while the Einstein equations for the gravitational field may require much computer power, if solved in the same way. It is therefore interesting to use spectral methods to model the gravitational field, which is always regular enough to avoid any Gibbs phenomenon, in conjunction with HRSC schemes for the hydrodynamics equations. We present such a code combining both methods to model stellar core collapse simulations and the resulting gravitational waves, with the most recent equations of state and a simplified neutrino treatment. Some additional results on neutron star oscillations are also shown.

  12. Structural Glitches near the Cores of Red Giants Revealed by Oscillations in g-mode Period Spacings from Stellar Models

    NASA Astrophysics Data System (ADS)

    Cunha, M. S.; Stello, D.; Avelino, P. P.; Christensen-Dalsgaard, J.; Townsend, R. H. D.

    2015-06-01

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

  13. Stellar neutrino energy loss rates due to {sup 24}Mg suitable for O+Ne+Mg core simulations

    SciTech Connect

    Nabi, Jameel-Un

    2008-10-15

    Neutrino losses from proto-neutron stars play a pivotal role to decide if these stars would be crushed into black holes or explode as supernovae. Recent observations of subluminous Type II-P supernovae (e.g., 2005cs, 2003gd, 1999br, 1997D) were able to rejuvenate the interest in 8-10 M{sub {center_dot}} stars that develop O+Ne+Mg cores. Simulation results of O+Ne+Mg cores show varying results in converting the collapse into an explosion. The neutrino energy loss rates are important input parameters in core collapse simulations. Proton-neutron quasiparticle random-phase approximation (pn-QRPA) theory has been used for calculation of neutrino energy loss rates due to {sup 24}Mg in stellar matter. The rates are presented on a detailed density-temperature grid suitable for simulation purposes. The calculated neutrino energy loss rates are enhanced up to more than one order of magnitude compared to the shell-model calculations and favor a lower entropy for the core of these massive stars.

  14. THE SUPERMASSIVE BLACK HOLE MASS-SPHEROID STELLAR MASS RELATION FOR SERSIC AND CORE-SERSIC GALAXIES

    SciTech Connect

    Scott, Nicholas; Graham, Alister W; Schombert, James

    2013-05-01

    We have examined the relationship between supermassive black hole mass (M{sub BH}) and the stellar mass of the host spheroid (M{sub sph,*}) for a sample of 75 nearby galaxies. To derive the spheroid stellar masses we used improved Two Micron All Sky Survey K{sub s}-band photometry from the ARCHANGEL photometry pipeline. Dividing our sample into core-Sersic and Sersic galaxies, we find that they are described by very different M{sub BH}-M{sub sph,*} relations. For core-Sersic galaxies-which are typically massive and luminous, with M{sub BH} {approx}> 2 Multiplication-Sign 10{sup 8} M{sub Sun }-we find M{sub BH}{proportional_to} M{sub sph,*}{sup 0.97{+-}0.14}, consistent with other literature relations. However, for the Sersic galaxies-with typically lower masses, M{sub sph,*} {approx}< 3 Multiplication-Sign 10{sup 10} M{sub Sun }-we find M{sub BH}{proportional_to}M{sub sph,*}{sup 2.22{+-}0.58}, a dramatically steeper slope that differs by more than 2 standard deviations. This relation confirms that, for Sersic galaxies, M{sub BH} is not a constant fraction of M{sub sph,*}. Sersic galaxies can grow via the accretion of gas which fuels both star formation and the central black hole, as well as through merging. Their black hole grows significantly more rapidly than their host spheroid, prior to growth by dry merging events that produce core-Sersic galaxies, where the black hole and spheroid grow in lockstep. We have additionally compared our Sersic M{sub BH}-M{sub sph,*} relation with the corresponding relation for nuclear star clusters, confirming that the two classes of central massive object follow significantly different scaling relations.

  15. The Hydra I cluster core. I. Stellar populations in the cD galaxy NGC 3311

    NASA Astrophysics Data System (ADS)

    Barbosa, C. E.; Arnaboldi, M.; Coccato, L.; Hilker, M.; Mendes de Oliveira, C.; Richtler, T.

    2016-05-01

    Context. The history of the mass assembly of brightest cluster galaxies may be studied by mapping the stellar populations at large radial distances from the galaxy centre, where the dynamical times are long and preserve the chemodynamical signatures of the accretion events. Aims: We provide extended and robust measurements of the stellar population parameters in NGC 3311, the cD galaxy at the centre of the Hydra I cluster, and out to three effective radii. We wish to characterize the processes that drove the build-up of the stellar light at all these radii. Methods: We obtained the spectra from several regions in NGC 3311 covering an area of ~3 arcmin2 in the wavelength range 4800 ≲ λ(Å) ≲ 5800, using the FORS2 spectrograph at the Very Large Telescope in the MXU mode. We measured the equivalent widths of seven absorption-features defined in the Lick/IDS system, which were modelled by single stellar populations, to provide luminosity-weighted ages, metallicities, and alpha element abundances. Results: The trends in the Lick indices and the distribution of the stellar population parameters indicate that the stars of NGC 3311 may be divided in two radial regimes, one within and the another beyond one effective radius, Re = 8.4 kpc, similar to the distinction between the inner galaxy and the external halo derived from the NGC 3311 velocity dispersion profile. The inner galaxy (R ≤ Re) is old (age ~14 Gyr), has negative metallicity gradients and positive alpha element gradients. The external halo is also very old, but has a negative age gradient. The metal and element abundances of the external halo both have a large scatter, indicating that stars from a variety of satellites with different masses have been accreted. The region in the extended halo associated with the off-centred envelope at 0°< PA < 90° has higher metallicity with respect to the symmetric external halo. Conclusions: The different stellar populations in the inner galaxy and extended halo

  16. The effect of neutrino transport on the collapse of iron stellar cores

    NASA Technical Reports Server (NTRS)

    Myra, E. S.; Bludman, S. A.; Hoffman, Y.; Lichtenstadt, I.; Sack, N.

    1987-01-01

    A multigroup flux-limited diffusion approximation to neutrino transport, correct to first order in material velocities, is described. The role of neutrino-electron scattering in determining core deleptonization is studied using a modified Fokker-Planck approximation in which adjacent neutrino energy groups are coupled. The moderate deleptonizaton obtained during infall restricts homologous core masses to less than 0.8 solar mass. With 0.6-0.8 solar mass of outer core to traverse, nuclear dissociation alone stalls the shock waves produced at core bounce. In addition, neutrino energy losses remove at least another 4 x 10 to the 51st ergs. In no case is matter ejected promptly as a direct result of the initial shock wave.

  17. 3D representation of the non-rotating origin

    NASA Astrophysics Data System (ADS)

    de Viron, O.; Dehant, V.

    2005-09-01

    In the frame of the IAU working group of Nomenclature in Fundamental Astronomy (of which one of the objectives is to make educational efforts for addressing the implementation of the IAU 2000 Resolutions for a large community of scientists), we have developed a set of didactic animation in order to give a physical understanding to the concept of non-rotating origin (NRO). In this paper, we give a short explanation on the existing animations, in order to encourage their use. A complete zip file with all the material is available on : http://danof.obspm.fr/iauWGnfa/Educational.html.

  18. Absolute properties of the eclipsing binary system AQ Serpentis: A stringent test of convective core overshooting in stellar evolution models

    SciTech Connect

    Torres, Guillermo; Vaz, Luiz Paulo R.; Sandberg Lacy, Claud H.; Claret, Antonio E-mail: lpv@fisica.ufmg.br E-mail: claret@iaa.es

    2014-02-01

    We report differential photometric observations and radial-velocity measurements of the detached, 1.69 day period, double-lined eclipsing binary AQ Ser. Accurate masses and radii for the components are determined to better than 1.8% and 1.1%, respectively, and are M {sub 1} = 1.417 ± 0.021 M {sub ☉}, M {sub 2} = 1.346 ± 0.024 M {sub ☉}, R {sub 1} = 2.451 ± 0.027 R {sub ☉}, and R {sub 2} = 2.281 ± 0.014 R {sub ☉}. The temperatures are 6340 ± 100 K (spectral type F6) and 6430 ± 100 K (F5), respectively. Both stars are considerably evolved, such that predictions from stellar evolution theory are particularly sensitive to the degree of extra mixing above the convective core (overshoot). The component masses are different enough to exclude a location in the H-R diagram past the point of central hydrogen exhaustion, which implies the need for extra mixing. Moreover, we find that current main-sequence models are unable to match the observed properties at a single age even when allowing the unknown metallicity, mixing length parameter, and convective overshooting parameter to vary freely and independently for the two components. The age of the more massive star appears systematically younger. AQ Ser and other similarly evolved eclipsing binaries showing the same discrepancy highlight an outstanding and largely overlooked problem with the description of overshooting in current stellar theory.

  19. Stellar chromospheres

    NASA Technical Reports Server (NTRS)

    Linsky, J. L.

    1980-01-01

    Developments in the understanding and use of chromospheric diagnostics are discussed with emphasis on the following aspects: (1) trends emerging from semiempirical models of single stars; (2) the validity of claims that theoretical models of chromospheres are becoming realistic; (3) the correlation between the widths of Ca 2 H and K line emission cores and stellar absolute luminosity extending over 15 magnitudes (Wilson-Bappu relation); and (4) the existence of systematic flow patterns in stellar chromospheres.

  20. The initial conditions of isolated star formation - IX. Akari mapping of an externally heated pre-stellar core

    NASA Astrophysics Data System (ADS)

    Nutter, D.; Stamatellos, D.; Ward-Thompson, D.

    2009-07-01

    We present observations of L1155 and L1148 in the Cepheus molecular cloud, taken using the Far Infrared Surveyor (FIS) instrument on the Akari satellite. We compare these data to submillimetre data taken using the Submillimetre Common-User Bolometer Array (SCUBA) camera on the James Clerk Maxwell Telescope, and far-infrared data taken with the imaging photo-polarimeter (ISOPHOT) camera on board the Infrared Space Observatory (ISO) satellite. The Akari data cover a similar spectral window and are consistent with the ISO data. All of the data show a relation between the position of the peak of emission and the wavelength for the core of L1155. We interpret this as a temperature gradient. We fit modified blackbody curves to the spectral energy distributions at two positions in the core and see that the central core in L1155 (L1155C) is approximately 2° warmer at one edge than it is in the centre. We consider a number of possible heating sources and conclude that the A6V star BD+67 1263 is the most likely candidate. This star is at a distance of 0.7pc from the front of L1155C in the plane of the sky. We carry out radiative transfer modelling of the L1155C core including the effects from the nearby star. We find that we can generate a good fit to the observed data at all wavelengths, and demonstrate that the different morphologies of the core at different wavelengths can be explained by the observed 2° temperature gradient. The L1148 core exhibits a similar morphology to that of L1155C, and the data are also consistent with a temperature gradient across the core. In this case, the most likely heating source is the star BD197053. Our findings illustrate very clearly that the apparent observed morphology of a pre-stellar core can be highly dependent on the wavelength of the observation, and that temperature gradients must be taken into account before converting images into column density distributions. This is important to note when interpreting Akari and Spitzer data

  1. [Surgical significance of intestinal non-rotation in adults].

    PubMed

    von Flüe, M; Herzog, U; Vogt, B; Tondelli, P; Harder, F

    1991-06-15

    Intestinal non-rotation has been recognized as a cause of obstruction in neonates and children. It is very rarely seen in the adult and assumes surgical significance owing to the potential risk of midgut or ileocecal volvulus. However, it can also cause significant intermittent abdominal pain in the adult. We describe six personally observed patients with this malformation and analyze 38 case reports published in the English and German literature since 1923. We establish that in the acute symptomatic form only emergency laparotomy can provide the correct diagnosis and decrease the risk of bowel disturbance. In the chronic forms, barium studies of the whole intestinal tract reveal varying degrees of midgut malrotation and the non-rotation is confirmed in each case. Also in these forms, exploratory laparotomy with a consequent staging of the abdominal situs is to be recommended. In the operation described by Ladd the ascending colon is sutured at the colon descendens and sigmoideum. After this procedure the mesenterial pedicle is fixed and the risk of midgut torsion remains minimal. All reported cases after surgery are symptom-free. PMID:1857952

  2. On the Shape of Core Overshooting in Stellar Model Computations, and Asteroseismic Tests

    NASA Astrophysics Data System (ADS)

    Moravveji, E.

    2015-12-01

    Slowly pulsating B stars (SPB) and γ Dor stars pulsate in high-order gravity (g-) modes. The frequencies of g-modes are sensitive to the detailed structure and evolution history of stars having convective cores. Receding convective cores in OB-type stars leave behind a chemically inhomogenous ∇μ > 0 radiative zone. Once a g-mode has radial nodes near the boundaries of these layers, the mode gets trapped and its period deviates from asymptotic period spacing. Careful study of such trapped modes allows constraining the extent of such layers by fitting individual pulsation frequencies. We employ 19 consecuitve dipole g-modes of a very rich Kepler SPB pulsator, KIC 10526294, to demonstrate the power of mode trapping in B-stars in studying the thermal and chemical stratification in the overshooting layer.

  3. The core mass-radius relation for giants - A new test of stellar evolution theory

    NASA Technical Reports Server (NTRS)

    Joss, P. C.; Rappaport, S.; Lewis, W.

    1987-01-01

    It is demonstrated here that the measurable properties of systems containing degenerate dwarfs can be used as a direct test of the core mass-radius relation for moderate-mass giants if the final stages of the loss of the envelope of the progenitor giant occurred via stable critical lobe overflow. This relation directly probes the internal structure of stars at a relatively advanced evolutionary state and is only modestly influenced by adjustable parameters. The measured properties of six binary systems, including such diverse systems as Sirius and Procyon and two millisecond pulsars, are utilized to derive constraints on the empirical core mass-radius relation, and the constraints are compared to the theoretical relation. The possibility that the final stages of envelope ejection of the giant progenitor of Sirius B occurred via critical lobe overflow in historical times is considered.

  4. Looking for high-mass young stellar objects: H2O and OH masers in ammonia cores

    NASA Astrophysics Data System (ADS)

    Codella, C.; Cesaroni, R.; López-Sepulcre, A.; Beltrán, M. T.; Furuya, R.; Testi, L.

    2010-02-01

    Context. The earliest stages of high-mass star formation have yet to be characterised well, because high-angular resolution observations are required to infer the properties of the molecular gas hosting the newly formed stars. Aims: We search for high-mass molecular cores in a large sample of 15 high-mass star-forming regions that are observed at high-angular resolution, extending a pilot survey based on a smaller number of objects. Methods: The sample was chosen from surveys of H2O and OH masers to favour the earliest phases of high-mass star formation. Each source was first observed with the 32-m single-dish Medicina antenna in the (1, 1) and (2, 2) inversion transitions at 1.3 cm of ammonia, which is an excellent tracer of dense gas. High-resolution maps in the NH3(2, 2) and (3, 3) lines and the 1.3 cm continuum were obtained successively with the VLA interferometer. Results: We detect continuum emission in almost all the observed star-forming regions, which corresponds to extended and UCHii regions created by young stellar objects with typical luminosities of ˜10^4~L⊙. However, only in three cases do we find a projected overlap between Hii regions and H2O and OH maser spots. On the other hand, the VLA images detect eight ammonia cores closely associated with the maser sources. The ammonia cores have sizes of ˜10^4 AU, and high masses (up to 104M⊙), and are very dense (from ˜10^6 to a few ×10^9 cm-3). The typical relative NH3 abundance is ≤10-7, in agreement with previous measurements in high-mass star-forming regions. Conclusions: The statistical analysis of the distribution between H2O and OH masers, NH3 cores, and Hii regions confirms that the earliest stages of high-mass star formation are characterised by high-density molecular cores with temperatures of on average ≥30 K, either without a detectable ionised region or associated with a hypercompact Hii region.

  5. Masgomas-4: Physical characterization of a double-core obscured cluster with a massive and very young stellar population

    NASA Astrophysics Data System (ADS)

    Ramírez Alegría, S.; Marín-Franch, A.; Herrero, A.

    2014-07-01

    Context. The discovery of new, obscured massive star clusters has changed our understanding of the Milky Way star-forming activity from a passive to a very active star-forming machine. The search for these obscured clusters is strongly supported by the use of all-sky, near-IR surveys. Aims: The main goal of the MASGOMAS project is to search for and study unknown, young, and massive star clusters in the Milky Way, using near-IR data. Here we try to determine the main physical parameters (distance, size, total mass, and age) of Masgomas-4, a new double-core obscured cluster. Methods: Using near-IR photometry (J, H, and KS) we selected a total of 21 stars as OB-type star candidates. Multi-object, near-IR follow-up spectroscopy allowed us to carry out the spectral classification of the OB-type candidates. Results: Of the 21 spectroscopically observed stars, ten are classified as OB-type stars, eight as F- to early G-type dwarf stars, and three as late-type giant stars. Spectroscopically estimated distances indicate that the OB-type stars belong to the same cluster, located at a distance of 1.90+1.28-0.90 kpc. Our spectrophotometric data confirm a very young and massive stellar population, with a clear concentration of pre-main-sequence massive candidates (Herbig Ae/Be) around one of the cluster cores. The presence of a surrounding H II cloud and the Herbig Ae/Be candidates indicate an upper age limit of 5 Myr.

  6. Non-rotating and rotating radiative-convective equilibrium

    NASA Astrophysics Data System (ADS)

    Zhou, Wenyu

    Radiative-convective equilibrium (RCE), in which the radiative cooling in the atmosphere is balanced by the convective heating in a horizontally homogeneous environment, is a good starting point for studying tropical convection. It also provides an idealized framework to compare analogous simulations by global climate models (GCMs) which rely on convective parameterizations, and cloud-resolving models (CRMs) which aim to explicitly resolve moist convection. In this work, we seek to further our understanding of tropical cyclones and convective aggregation in the idealized framework of non-rotating and rotating RCE with both types of models. First, we achieve rotating RCE by coupling the resolution and physics of a GCM to rotating hydrostatic dynamics. A large doubly-periodic f-plane is used to allow multiple tropical cyclones (TCs) to coexist. Both cases with fixed and coupled sea surface temperature (SST) are considered. For fixed SST, the sensitivity to environmental parameters is investigated. Particularly, we find that the intensity, radius of maximum wind and size of TCs increase with SST. For coupled SST, SST is predicted using a simple slab ocean model. The effect of the eyewall cooling on TC intensity is studied. We show that Potential-Intensity theory overestimates the impact of the eyewall cooling on TC intensity, as its key assumption that entropy is well-mixed along angular-momentum surfaces within the atmospheric boundary layer no longer holds in cases with substantial eyewall cooling. We then study TC genesis with a small doubly-periodic f-plane. Through cloud-resolving simulations, we show that vertical shear plays an important role on regulating the sensitivity of tropical cyclogenesis to both the environmental rotation and thermodynamic state. As indicated by analogous simulations with the resolution and physics of GCMs, such effects of wind shear might not be fully represented in GCMs. Finally, we investigate convective self-aggregation from non-rotating

  7. Theoretical study of diffusion processes around a non-rotating neutron star

    NASA Astrophysics Data System (ADS)

    Andra, D.; Rosyid, M. F.

    2014-10-01

    The general relativistic diffusion process on curved space-time manifold around a non-rotating neutron star has been analyzed. The general relativistic diffusion equation of diffusive particles around non-rotating neutron star is derived by constructing phase space in the parametrization of observer time in the hyperbolic coordinate system. This diffusion equation describes the stochastic dynamic of particles around non-rotating neutron stars. In this work we also have studied the diffusion processes around a non-rotating neutron star for asymptotic case.

  8. A unified N-body and statistical treatment of stellar dynamics. I - The hybrid code. II - Applications to globular cluster cores

    NASA Technical Reports Server (NTRS)

    Mcmillan, S. L. W.; Lightman, A. P.

    1984-01-01

    A unified N-body and statistical treatment of stellar dynamics is developed and applied to the late stages of core collapse and early stages of post collapse evolution in globular clusters. A 'hybrid' computer code is joined to a direct N-body code which is used to calculate exactly the behavior of particles in the inner spatial region, and the combination is used to follow particles statistically in the outer spatial region. A transition zone allows the exchange of particles and energy between the two regions. The main application results include: formation of a hard central binary system, reversal of core collapse and expansion due to the heat input from this binary, ejection of the binary from the core, and recollapse of the core; density profiles that form a one-parameter sequence during the core oscillations; and indications that these oscillations will eventually cease.

  9. ULTRAVIOLET-BRIGHT STELLAR POPULATIONS AND THEIR EVOLUTIONARY IMPLICATIONS IN THE COLLAPSED-CORE CLUSTER M15

    SciTech Connect

    Haurberg, Nathalie C.; Lubell, Gabriel M. G.; Cohn, Haldan N.; Lugger, Phyllis M.; Anderson, Jay; Cool, Adrienne M.; Serenelli, Aldo M. E-mail: glubell@astro.indiana.ed E-mail: lugger@astro.indiana.ed E-mail: cool@stars.sfsu.ed

    2010-10-10

    We performed deep photometry of the central region of the Galactic globular cluster M15 from archival Hubble Space Telescope data taken on the High Resolution Channel and Solar Blind Channel of the Advanced Camera for Surveys. Our data set consists of images in far-UV (FUV{sub 140}; F140LP), near-UV (NUV{sub 220}; F220W), and blue (B{sub 435}; F435W) filters. The addition of an optical filter complements previous UV work on M15 by providing an additional constraint on the UV-bright stellar populations. Using color-magnitude diagrams (CMDs), we identified several populations that arise from non-canonical evolution including candidate blue stragglers, extreme horizontal branch (HB) stars, blue hook (BHk) stars, cataclysmic variables (CVs), and helium-core white dwarfs (He WDs). Due to preliminary identification of several He WD and BHk candidates, we add M15 as a cluster containing an He WD sequence and suggest it be included among clusters with a BHk population. We also investigated a subset of CV candidates that appear in the gap between the main sequence (MS) and WDs in FUV{sub 140}-NUV{sub 220} but lie securely on the MS in NUV{sub 220}-B{sub 435}. These stars may represent a magnetic CV or detached WD-MS binary population. Additionally, we analyze our candidate He WDs using model cooling sequences to estimate their masses and ages and investigate the plausibility of thin versus thick hydrogen envelopes. Finally, we identify a class of UV-bright stars that lie between the HB and WD cooling sequences, a location not usually populated on cluster CMDs. We conclude these stars may be young, low-mass He WDs.

  10. Stellar Winds

    NASA Astrophysics Data System (ADS)

    Owocki, Stan

    A "stellar wind" is the continuous, supersonic outflow of matter from the surface layers of a star. Our sun has a solar wind, driven by the gas-pressure expansion of the hot (T > 106 K) solar corona. It can be studied through direct in situ measurement by interplanetary spacecraft; but analogous coronal winds in more distant solar-type stars are so tenuous and transparent that that they are difficult to detect directly. Many more luminous stars have winds that are dense enough to be opaque at certain wavelengths of the star's radiation, making it possible to study their wind outflows remotely through careful interpretation of the observed stellar spectra. Red giant stars show slow, dense winds that may be driven by the pressure from magnetohydrodyanmic waves. As stars with initial mass up to 8 M ⊙ evolve toward the Asymptotic Giant Branch (AGB), a combination of stellar pulsations and radiative scattering off dust can culminate in "superwinds" that strip away the entire stellar envelope, leaving behind a hot white dwarf stellar core with less than the Chandrasekhar mass of ˜ ​​ 1. 4M ⊙. The winds of hot, luminous, massive stars are driven by line-scattering of stellar radiation, but such massive stars can also exhibit superwind episodes, either as Red Supergiants or Luminous Blue Variable stars. The combined wind and superwind mass loss can strip the star's hydrogen envelope, leaving behind a Wolf-Rayet star composed of the products of earlier nuclear burning via the CNO cycle. In addition to such direct effects on a star's own evolution, stellar winds can be a substantial source of mass, momentum, and energy to the interstellar medium, blowing open large cavities or "bubbles" in this ISM, seeding it with nuclear processed material, and even helping trigger the formation of new stars, and influencing their eventual fate as white dwarves or core-collapse supernovae. This chapter reviews the properties of such stellar winds, with an emphasis on the various

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

    NASA Technical Reports Server (NTRS)

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

    1976-01-01

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

  12. Stellarator hybrids

    SciTech Connect

    Furth, H.P.; Ludescher, C.

    1984-08-01

    The present paper briefly reviews the subject of tokamak-stellarator and pinch-stellarator hybrids, and points to two interesting new possibilities: compact-torus-stellarators and mirror-stellarators.

  13. Electron-capture and β-decay Rates for sd-Shell Nuclei in Stellar Environments Relevant to High-density O-Ne-Mg Cores

    NASA Astrophysics Data System (ADS)

    Suzuki, Toshio; Toki, Hiroshi; Nomoto, Ken'ichi

    2016-02-01

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

  14. Wandering spleen with gastric volvulus and intestinal non-rotation in an adult male patient.

    PubMed

    Ooka, Minako; Kohda, Eiichi; Iizuka, Yuo; Nagamoto, Masashi; Ishii, Tomotaka; Saida, Yoshihisa; Shimizu, Norikazu; Gomi, Tatsuya

    2013-01-01

    We report an extremely rare case of wandering spleen (WS) complicated with gastric volvulus and intestinal non-rotation in a male adult. A 22-year-old man who had been previously treated for Wilson disease was admitted with severe abdominal pain. Radiological findings showed WS in the midline of the pelvic area. The stomach was mesenteroaxially twisted and intestinal non-rotation was observed. Radiology results did not show any evidence of splenic or gastrointestinal (GI) infarction. Elective emergency laparoscopy confirmed WS and intestinal non-rotation; however, gastric volvulus was not observed. It was suspected that the stomach had untwisted when gastric and laparoscopic tubes were inserted. Surgery is strongly recommended for WS because of the high risk of serious complications; however, some asymptomatic adult patients are still treated conservatively, such as the patient in this study. The present case is reported with reference to the literature. PMID:24349711

  15. Wandering spleen with gastric volvulus and intestinal non-rotation in an adult male patient

    PubMed Central

    Kohda, Eiichi; Iizuka, Yuo; Nagamoto, Masashi; Ishii, Tomotaka; Saida, Yoshihisa; Shimizu, Norikazu; Gomi, Tatsuya

    2013-01-01

    We report an extremely rare case of wandering spleen (WS) complicated with gastric volvulus and intestinal non-rotation in a male adult. A 22-year-old man who had been previously treated for Wilson disease was admitted with severe abdominal pain. Radiological findings showed WS in the midline of the pelvic area. The stomach was mesenteroaxially twisted and intestinal non-rotation was observed. Radiology results did not show any evidence of splenic or gastrointestinal (GI) infarction. Elective emergency laparoscopy confirmed WS and intestinal non-rotation; however, gastric volvulus was not observed. It was suspected that the stomach had untwisted when gastric and laparoscopic tubes were inserted. Surgery is strongly recommended for WS because of the high risk of serious complications; however, some asymptomatic adult patients are still treated conservatively, such as the patient in this study. The present case is reported with reference to the literature. PMID:24349711

  16. Stellar kinematics and structural properties of virgo cluster dwarf early-type galaxies from the SMAKCED project. I. Kinematically decoupled cores and implications for infallen groups in clusters

    SciTech Connect

    Toloba, E.; Guhathakurta, P.; Boissier, S.; Boselli, A.; Den Brok, M.; Falcón-Barroso, J.; Ryś, A.; Janz, J.; Lisker, T.; Laurikainen, E.; Salo, H.; Paudel, S.

    2014-03-10

    We present evidence for kinematically decoupled cores (KDCs) in two dwarf early-type (dE) galaxies in the Virgo cluster, VCC 1183 and VCC 1453, studied as part of the SMAKCED stellar absorption-line spectroscopy and imaging survey. These KDCs have radii of 1.''8 (0.14 kpc) and 4.''2 (0.33 kpc), respectively. Each of these KDCs is distinct from the main body of its host galaxy in two ways: (1) inverted sense of rotation and (2) younger (and possibly more metal-rich) stellar population. The observed stellar population differences are probably associated with the KDC, although we cannot rule out the possibility of intrinsic radial gradients in the host galaxy. We describe a statistical analysis method to detect, quantify the significance of, and characterize KDCs in long-slit rotation curve data. We apply this method to the two dE galaxies presented in this paper and to five other dEs for which KDCs have been reported in the literature. Among these seven dEs, there are four significant KDC detections, two marginal KDC detections, and one dE with an unusual central kinematic anomaly that may be an asymmetric KDC. The frequency of occurrence of KDCs and their properties provide important constraints on the formation history of their host galaxies. We discuss different formation scenarios for these KDCs in cluster environments and find that dwarf-dwarf wet mergers or gas accretion can explain the properties of these KDCs. Both of these mechanisms require that the progenitor had a close companion with a low relative velocity. This suggests that KDCs were formed in galaxy pairs residing in a poor group environment or in isolation whose subsequent infall into the cluster quenched star formation.

  17. Stellar Kinematics and Structural Properties of Virgo Cluster Dwarf Early-type Galaxies from the SMAKCED Project. I. Kinematically Decoupled Cores and Implications for Infallen Groups in Clusters

    NASA Astrophysics Data System (ADS)

    Toloba, E.; Guhathakurta, P.; van de Ven, G.; Boissier, S.; Boselli, A.; den Brok, M.; Falcón-Barroso, J.; Hensler, G.; Janz, J.; Laurikainen, E.; Lisker, T.; Paudel, S.; Peletier, R. F.; Ryś, A.; Salo, H.

    2014-03-01

    We present evidence for kinematically decoupled cores (KDCs) in two dwarf early-type (dE) galaxies in the Virgo cluster, VCC 1183 and VCC 1453, studied as part of the SMAKCED stellar absorption-line spectroscopy and imaging survey. These KDCs have radii of 1.''8 (0.14 kpc) and 4.''2 (0.33 kpc), respectively. Each of these KDCs is distinct from the main body of its host galaxy in two ways: (1) inverted sense of rotation and (2) younger (and possibly more metal-rich) stellar population. The observed stellar population differences are probably associated with the KDC, although we cannot rule out the possibility of intrinsic radial gradients in the host galaxy. We describe a statistical analysis method to detect, quantify the significance of, and characterize KDCs in long-slit rotation curve data. We apply this method to the two dE galaxies presented in this paper and to five other dEs for which KDCs have been reported in the literature. Among these seven dEs, there are four significant KDC detections, two marginal KDC detections, and one dE with an unusual central kinematic anomaly that may be an asymmetric KDC. The frequency of occurrence of KDCs and their properties provide important constraints on the formation history of their host galaxies. We discuss different formation scenarios for these KDCs in cluster environments and find that dwarf-dwarf wet mergers or gas accretion can explain the properties of these KDCs. Both of these mechanisms require that the progenitor had a close companion with a low relative velocity. This suggests that KDCs were formed in galaxy pairs residing in a poor group environment or in isolation whose subsequent infall into the cluster quenched star formation.

  18. Axisymmetric collapse simulations of rotating massive stellar cores in full general relativity: Numerical study for prompt black hole formation

    SciTech Connect

    Sekiguchi, Yu-ichirou; Shibata, Masaru

    2005-04-15

    We perform axisymmetric simulations for gravitational collapse of a massive iron core to a black hole in full general relativity. The iron cores are modeled by {gamma}=4/3 equilibrium polytrope for simplicity. The hydrodynamic equations are solved using a high-resolution shock-capturing scheme with a parametric equation of state. The Cartoon method is adopted for solving the Einstein equations. Simulations are performed for a wide variety of initial conditions changing the mass ({approx_equal}2.0-3.0M{sub {center_dot}}), the angular momentum, the rotational velocity profile of the core, and the parameters of the equations of state which are chosen so that the maximum mass of the cold spherical polytrope is {approx_equal}1.6M{sub {center_dot}}. Then, the criterion for the prompt black hole formation is clarified in terms of the mass and the angular momentum for several rotational velocity profile of the core and equations of state. It is found that (i) with the increase of the thermal energy generated by shocks, the threshold mass for the prompt black hole formation is increased by 20-40%, (ii) the rotational centrifugal force increases the threshold mass by < or approx. 25%, (iii) with the increase of the degree of differential rotation, the threshold mass is also increased, and (iv) the amplification factors shown in the results (i)-(iii) depend sensitively on the equation of state. We also find that the collapse dynamics and the structure of the shock formed at the bounce depend strongly on the stiffness of the adopted equation of state. In particular, as a new feature, a strong bipolar explosion is observed for the collapse of rapidly rotating iron cores with an equation of state which is stiff in subnuclear density and soft in supranuclear density. Gravitational waves are computed in terms of a quadrupole formula. It is also found that the waveform depends sensitively on the equations of state.

  19. Acute appendicitis with intestinal non-rotation presenting with partial small bowel obstruction diagnosed on CT.

    PubMed

    Zissin, R; Kots, E; Shpindel, T; Shapiro-Feinberg, M

    2000-05-01

    The findings of acute appendicitis on CT have been extensively described in the literature. This is a report of a case of acute appendicitis in a patient with intestinal non-rotation presenting with partial small bowel obstruction. Analysis of the CT findings allowed a correct diagnosis. PMID:10884757

  20. Vlasov formalism for extended relativistic mean field models: The crust-core transition and the stellar matter equation of state

    NASA Astrophysics Data System (ADS)

    Pais, Helena; Providência, Constança

    2016-07-01

    The Vlasov formalism is extended to relativistic mean field hadron models with nonlinear terms up to fourth order and applied to the calculation of the crust-core transition density. The effect of the nonlinear ω ρ and σ ρ coupling terms on the crust-core transition density and pressure and on the macroscopic properties of some families of hadronic stars is investigated. For that purpose, six families of relativistic mean field models are considered. Within each family, the members differ in the symmetry energy behavior. For all the models, the dynamical spinodals are calculated, and the crust-core transition density and pressure and the neutron star mass-radius relations are obtained. The effect on the star radius of the inclusion of a pasta calculation in the inner crust is discussed. The set of six models that best satisfy terrestrial and observational constraints predicts a radius of 13.6 ±0.3 km and a crust thickness of 1.36 ±0.06 km for a 1.4 M⊙ star.

  1. A Mid-Infrared Imaging Survey of Embedded Young Stellar Objects in the (rho) Ophiuchi Cloud Core

    NASA Technical Reports Server (NTRS)

    Barsony, Mary; Ressler, Michael E.; Marsh, Kenneth A.

    2005-01-01

    Results of a comprehensive, new, ground-based mid-infrared imaging survey of the young stellar population of the (rho) Ophiuchi cloud are presented. Data were acquired at the Palomar 5m and at the Keck 10m telescopes with the MIRLIN and LWS instruments, at 0'.5 and 0'.25 resolutions, respectively. Of 172 survey objects, 85 were detected. Among the 22 multiple systems observed, 15 were resolved and their individual component fluxes determined. A plot of the frequency distribution of the detected objects with SED spectral slope shows that YSOs spend approx.4 x 10(exp 5) yr in the flat-spectrum phase, clearing out their remnant infall envelopes. Mid-infrared variability is found among a significant fraction of the surveyed objects and is found to occur for all SED classes with optically thick disks. Large-amplitude near-infrared variability, also found for all SED classes with optically thick disks, seems to occur with somewhat higher frequency at the earlier evolutionary stages. Although a general trend of mid-infrared excess and near-infrared veiling exists progressing through SED classes, with Class I objects generally exhibiting r(sub K) >= 1, flat-spectrum objects with r(sub K) >= 0.58, and Class III objects with r(sub K) =0, Class II objects exhibit the widest range of r(sub K) values, ranging from 0 <= r(sub K) <= 4.5. However, the highly variable value of veiling that a single source can exhibit in any of the SED classes in which active disk accretion can take place is striking and is direct observational evidence for highly time-variable accretion activity in disks. Finally, by comparing mid-infrared versus near-infrared excesses in a subsample with well-determined effective temperatures and extinction values, disk-clearing mechanisms are explored. The results are consistent with disk clearing proceeding from the inside out.

  2. Modification of magicity toward the dripline and its impact on electron-capture rates for stellar core collapse

    NASA Astrophysics Data System (ADS)

    Raduta, Ad. R.; Gulminelli, F.; Oertel, M.

    2016-02-01

    The importance of microphysical inputs from laboratory nuclear experiments and theoretical nuclear structure calculations in the understanding of core-collapse dynamics and the subsequent supernova explosion is largely recognized in the recent literature. In this work, we analyze the impact of the masses of very neutron-rich nuclei on the matter composition during collapse and the corresponding electron-capture rate. To this end, we introduce an empirical modification of the popular Duflo-Zuker mass model to account for possible shell quenching far from stability. We study the effect of this quenching on the average electron-capture rate. We show that the pre-eminence of the closed shells with N =50 and N =82 in the collapse dynamics is considerably decreased if the shell gaps are reduced in the region of 78Ni and beyond. As a consequence, local modifications of the overall electron-capture rate of up to 30% can be expected, depending on the strength of magicity quenching. This finding has potentially important consequences on the entropy generation, the neutrino emissivity, and the mass of the core at bounce. Our work underlines the importance of new experimental measurements in this region of the nuclear chart, the most crucial information being the nuclear mass and the Gamow-Teller strength. Reliable microscopic calculations of the associated elementary rate, in a wide range of temperatures and electron densities, optimized on these new empirical information, will be additionally needed to get quantitative predictions of the collapse dynamics.

  3. The evolution of massive stars and their spectra. I. A non-rotating 60 M⊙ star from the zero-age main sequence to the pre-supernova stage

    NASA Astrophysics Data System (ADS)

    Groh, Jose H.; Meynet, Georges; Ekström, Sylvia; Georgy, Cyril

    2014-04-01

    For the first time, the interior and spectroscopic evolution of a massive star is analyzed from the zero-age main sequence (ZAMS) to the pre-supernova (SN) stage. For this purpose, we combined stellar evolution models using the Geneva code and stellar atmospheric/wind models using CMFGEN. With our approach, we were able to produce observables, such as a synthetic high-resolution spectrum and photometry, thereby aiding the comparison between evolution models and observed data. Here we analyze the evolution of a non-rotating 60 M⊙ star and its spectrum throughout its lifetime. Interestingly, the star has a supergiant appearance (luminosity class I) even at the ZAMS. We find the following evolutionary sequence of spectral types: O3 I (at the ZAMS), O4 I (middle of the H-core burning phase), B supergiant (BSG), B hypergiant (BHG), hot luminous blue variable (LBV; end of H-core burning), cool LBV (H-shell burning through the beginning of the He-core burning phase), rapid evolution through late WN and early WN, early WC (middle of He-core burning), and WO (end of He-core burning until core collapse). We find the following spectroscopic phase lifetimes: 3.22 × 106 yr for the O-type, 0.34 × 105 yr (BSG), 0.79 × 105 yr (BHG), 2.35 × 105 yr (LBV), 1.05 × 105 yr (WN), 2.57 × 105 yr (WC), and 3.80 × 104 yr (WO). Compared to previous studies, we find a much longer (shorter) duration for the early WN (late WN) phase, as well as a long-lived LBV phase. We show that LBVs arise naturally in single-star evolution models at the end of the MS when the mass-loss rate increases as a consequence of crossing the bistability limit. We discuss the evolution of the spectra, magnitudes, colors, and ionizing flux across the star's lifetime, and the way they are related to the evolution of the interior. We find that the absolute magnitude of the star typically changes by ~6 mag in optical filters across the evolution, with the star becoming significantly fainter in optical filters at

  4. Stellar evolution.

    NASA Technical Reports Server (NTRS)

    Chiu, H.-Y. (Editor); Muriel, A.

    1972-01-01

    Aspects of normal stellar evolution are discussed together with evolution near the main sequence, stellar evolution from main sequence to white dwarf or carbon ignition, the structure of massive main-sequence stars, and problems of stellar stability and stellar pulsation. Other subjects considered include variable stars, white dwarfs, close binaries, novae, early supernova luminosity, neutron stars, the photometry of field horizontal-branch stars, and stellar opacity. Transport mechanisms in stars are examined together with thermonuclear reactions and nucleosynthesis, the instability problem in nuclear burning shells, stellar coalescence, and intense magnetic fields in astrophysics. Individual items are announced in this issue.

  5. THE SPITZER c2d SURVEY OF NEARBY DENSE CORES: JET AND MOLECULAR OUTFLOW ASSOCIATED WITH A YOUNG STELLAR OBJECT IN CORE A OF L1251

    SciTech Connect

    Lee, Jeong-Eun; Kim, Il-Suk; Choi, Yunhee; Lee, Ho-Gyu; Shinn, Jong-Ho; Dunham, Michael M.; Evans, Neal J.; Kim, Chang Hee; Bourke, Tyler L. E-mail: tohogyu@gmail.com E-mail: nje@astro.as.utexas.edu

    2010-01-20

    A long infrared jet has been discovered by the Spitzer c2d Legacy Program in core A of L1251. It is associated with a very embedded Class 0 object with an accretion luminosity of about 0.9 L {sub sun} derived by radiative transfer model fitting to the observed spectral energy distribution. Comparing the observed Infrared Array Camera colors along the infrared jet with those calculated from a model of an admixture of gas with a power-law temperature distribution indicates that the jet is possibly created by a paraboloidal bow shock propagating into the ambient medium of n(H{sub 2}) = 10{sup 5} cm{sup -3}. In addition, the variation of the power-law index along the jet suggests that the portion of hot gas decreases with distance from the jet engine. The molecular outflow in this region has been mapped for the first time using CO data. From the calculated outflow momentum flux, a very strong lower limit to the average accretion luminosity is 3.6 sin i/cos{sup 3} i L {sub sun}, indicative of a decrease in the accretion rate with time.

  6. Volvulus of the ascending colon: an unusual complication of non-rotation of the midgut.

    PubMed

    Berger, R B; Hillemeier, A C; Stahl, R S; Markowitz, R I

    1982-01-01

    A case of non-rotation of the bowel is presented wherein volvulus of the colon occurred causing acute obstruction. Spontaneous reduction following a barium enema as well as the patient's history leads us to suspect that volvulus had occurred in the past and was responsible for the intermittent nature of the patient's symptoms. This type of volvulus is distinctly different from midgut volvulus and is a rare complication of the anomaly of intestinal rotation and fixation known as non-rotation of the bowel. Efforts should be made to study patients with malrotation anomalies at a time when they are acutely symptomatic so that intermittent volvulus such as shown here is not overlooked. PMID:7162881

  7. Fluid/gravity correspondence for general non-rotating black holes

    NASA Astrophysics Data System (ADS)

    Wu, Xiaoning; Ling, Yi; Tian, Yu; Zhang, Chengyong

    2013-07-01

    In this paper, we investigate the fluid/gravity correspondence in spacetime with general non-rotating weakly isolated horizon. With the help of a Petrov-like boundary condition and large mean curvature limit, we show that the dual hydrodynamical system is described by a generalized forced incompressible Navier-Stokes equation. Specially, for stationary black holes or those spacetime with some asymptotically stationary conditions, such a system reduces to a standard forced Navier-Stokes system.

  8. [An adult with mechanical ileus in association with non-rotation of the intestine].

    PubMed

    Andriessen, M J G; Koop, K A; Consten, E C J

    2005-05-01

    A mechanical ileus was considered in the differential diagnosis of a 28-year-old man who presented to the Emergency Clinic with acute, severe, painful cramps in the lower abdomen of 2 hours' duration, without radiation and with an urge to move constantly. An emergency laparotomy was then performed, revealing non-rotation of the intestine; the last segment ofthe small intestine was pinched off by a strangulation. Several strangulations were cleaved, after which the symptoms disappeared. Non-rotation, a form of malrotation, is a congenital anomaly of intestinal rotation. In adults, non-rotation is a rare diagnosis with a variable presentation. Surgical intervention is necessary in both the acute and the more chronic presentation. The chronic presentation is usually discovered by chance in patients who have had aspecific recurrent abdominal complaints for a long time; if malrotation is suspected, additional investigation, for example by means of a gastrointestinal contrast study, is necessary before resorting to surgery. In the acute situation, immediate surgery is the only proper decision. Surgical intervention comprises reduction of the volvulus, inspection of the mesenteric bands (Ladd's bands) that run from the coecum to the lateral peritoneum and compress the duodenum, and an appendectomy: the Ladd procedure. PMID:15909395

  9. Planetary Nebulae and their parent stellar populations. Tracing the mass assembly of M87 and Intracluster light in the Virgo cluster core

    NASA Astrophysics Data System (ADS)

    Arnaboldi, Magda; Longobardi, Alessia; Gerhard, Ortwin

    2016-08-01

    The diffuse extended outer regions of galaxies are hard to study because they are faint, with typical surface brightness of 1% of the dark night sky. We can tackle this problem by using resolved star tracers which remain visible at large distances from the galaxy centers. This article describes the use of Planetary Nebulae as tracers and the calibration of their properties as indicators of the star formation history, mean age and metallicity of the parent stars in the Milky Way and Local Group galaxies. We then report on the results from a deep, extended, planetary nebulae survey in a 0.5 deg2 region centered on the brightest cluster galaxy NGC 4486 (M87) in the Virgo cluster core, carried out with SuprimeCam@Subaru and FLAMES-GIRAFFE@VLT. Two planetary nebulae populations are identified out to 150 kpc distance from the center of M87. One population is associated with the M87 halo and the second one with the intracluster light in the Virgo cluster core. They have different line-of-sight velocity and spatial distributions, as well as different planetary nebulae specific frequencies and luminosity functions. The intracluster planetary nebulae in the surveyed region correspond to a luminosity of four times the luminosity of the Large Magellanic Cloud. The M87 halo planetary nebulae trace an older, more metal-rich, parent stellar population. A substructure detected in the projected phase-space of the line-of-sight velocity vs. major axis distance for the M87 halo planetary nebulae provides evidence for the recent accretion event of a satellite galaxy with luminosity twice that of M33. The satellite stars were tidally stripped about 1 Gyr ago, and reached apocenter at a major axis distance of 60-90 kpc from the center of M87. The M87 halo is still growing significantly at the distances where the substructure is detected.

  10. High-resolution imaging and crowded-field photometry of the stellar populations in the cores of the Globular Clusters M15 and M4

    NASA Astrophysics Data System (ADS)

    Butler, R. F.

    1999-02-01

    This thesis presents work performed at the Department of Physics, University College Galway from 1992 to 1997. It is concerned with ground- and space-based high-resolution optical imaging of globular cluster cores, and the subsequent application of image-restoration and crowded-field photometry techniques; thus we may gain an improved understanding of the nature of their stellar populations, by either monitoring their temporal behaviour over moderate periods for the first time, or by obtaining a more precise "static" picture than was hitherto possible. These goals can be achieved by the development of innovative instrumentation and data analysis techniques. The particularly unique aspect of this work is that it deals with the first application of two-dimensional photon-counting detectors (2D-PCDs) and post-exposure image sharpening (PEIS) for crowded-field photometry. The thesis starts by introducing some basic concepts and characteristics of globular clusters and the diverse stellar species which they contain, in particular those predicted to have formed as a result of dynamical processes in the cluster cores, and those which exhibit variability in emission over time. It then reviews the fields of high-resolution imaging through the turbulent atmosphere & image deconvolution, optical stellar photometry, and Hubble Space Telescope observing and data reduction, each concluded with a description of the systems used in the work reported here (for the HST chapter this involves photometry of WFPC2 (Wide Field & Planetary Camera 2) observations of M15 (NGC 7078) released into the archives in 1995). The core of the thesis begins with a review of the observations to date of the objects with which this thesis is chiefly concerned, M15 and M4 (NGC 6121). In the following sections we describe the observations of these clusters which were made using the TRIFFID camera between 1992 and 1995, the image sharpening and calibration steps performed, and the photometric techniques

  11. Jet Engine Bird Ingestion Simulations: Comparison of Rotating to Non-Rotating Fan Blades

    NASA Technical Reports Server (NTRS)

    Howard, Samuel A.; Hammer, Jeremiah T.; Carney, Kelly S.; Pereira, J. Michael

    2013-01-01

    Bird strike events in commercial airliners are a fairly common occurrence. According to data collected by the US Department of Agriculture, over 80,000 bird strikes were reported in the period 1990 to 2007 in the US alone (Ref. 1). As a result, bird ingestion is an important factor in aero engine design and FAA certification. When it comes to bird impacts on engine fan blades, the FAA requires full-scale bird ingestion tests on an engine running at full speed to pass certification requirements. These rotating tests are complex and very expensive. To reduce development costs associated with new materials for fan blades, it is desirable to develop more cost effective testing procedures than full-scale rotating engine tests for material evaluation. An impact test on a nonrotating single blade that captures most of the salient physics of the rotating test would go a long way towards enabling large numbers of evaluative material screening tests. NASA Glenn Research Center has been working to identify a static blade test procedure that would be effective at reproducing similar results as seen in rotating tests. The current effort compares analytical simulations of a bird strike on various non-rotating blades to a bird strike simulation on a rotating blade as a baseline case. Several different concepts for simulating the rotating loads on a non-rotating blade were analyzed with little success in duplicating the deformation results seen in the rotating case. The rotating blade behaves as if it were stiffer than the non-rotating blade resulting in less plastic deformation from a given bird impact. The key factor limiting the success of the non-rotating blade simulations is thought to be the effect of gyroscopics. Prior to this effort, it was anticipated the difficulty would be in matching the prestress in the blade due to centrifugal forces Additional work is needed to verify this assertion, and to determine if a static test procedure can simulate the gyroscopic effects in

  12. Jet Engine Bird Ingestion Simulations: Comparison of Rotating to Non-Rotating Fan Blades

    NASA Technical Reports Server (NTRS)

    Howard, Samuel A.; Hammer, Jeremiah; Carney, Kelly S.; Pereira, J. Michael

    2013-01-01

    Bird strike events in commercial airliners are a fairly common occurrence. According to data collected by the US Department of Agriculture, over 80,000 bird strikes were reported in the period 1990-2007 in the US alone [1]. As a result, bird ingestion is an important factor in aero engine design and FAA certification. When it comes to bird impacts on engine fan blades, the FAA requires full-scale bird ingestion tests on an engine running at full speed to pass certification requirements. These rotating tests are complex and very expensive. To reduce development costs associated with new materials for fan blades, it is desirable to develop more cost effective testing procedures than full-scale rotating engine tests for material evaluation. An impact test on a non-rotating single blade that captures most of the salient physics of the rotating test would go a long way towards enabling large numbers of evaluative material screening tests. NASA Glenn Research Center has been working to identify a static blade test procedure that would be effective at reproducing similar results as seen in rotating tests. The current effort compares analytical simulations of a bird strike on various nonrotating blades to a bird strike simulation on a rotating blade as a baseline case. Several different concepts for simulating the rotating loads on a non-rotating blade were analyzed with little success in duplicating the deformation results seen in the rotating case. The rotating blade behaves as if it were stiffer than the non-rotating blade resulting in less plastic deformation from a given bird impact. The key factor limiting the success of the non-rotating blade simulations is thought to be the effect of gyroscopics. Prior to this effort, it was anticipated the difficulty would be in matching the pre-stress in the blade due to centrifugal forces Additional work is needed to verify this assertion, and to determine if a static test procedure can simulate the gyroscopic effects in a

  13. High-resolution imaging and crowded-field photometry of the stellar populations in the cores of the Globular Clusters M15 and M4

    NASA Astrophysics Data System (ADS)

    Butler, R. F.

    1999-02-01

    This thesis presents work performed at the Department of Physics, University College Galway from 1992 to 1997. It is concerned with ground- and space-based high-resolution optical imaging of globular cluster cores, and the subsequent application of image-restoration and crowded-field photometry techniques; thus we may gain an improved understanding of the nature of their stellar populations, by either monitoring their temporal behaviour over moderate periods for the first time, or by obtaining a more precise "static" picture than was hitherto possible. These goals can be achieved by the development of innovative instrumentation and data analysis techniques. The particularly unique aspect of this work is that it deals with the first application of two-dimensional photon-counting detectors (2D-PCDs) and post-exposure image sharpening (PEIS) for crowded-field photometry. The thesis starts by introducing some basic concepts and characteristics of globular clusters and the diverse stellar species which they contain, in particular those predicted to have formed as a result of dynamical processes in the cluster cores, and those which exhibit variability in emission over time. It then reviews the fields of high-resolution imaging through the turbulent atmosphere & image deconvolution, optical stellar photometry, and Hubble Space Telescope observing and data reduction, each concluded with a description of the systems used in the work reported here (for the HST chapter this involves photometry of WFPC2 (Wide Field & Planetary Camera 2) observations of M15 (NGC 7078) released into the archives in 1995). The core of the thesis begins with a review of the observations to date of the objects with which this thesis is chiefly concerned, M15 and M4 (NGC 6121). In the following sections we describe the observations of these clusters which were made using the TRIFFID camera between 1992 and 1995, the image sharpening and calibration steps performed, and the photometric techniques

  14. Stellar Dynamos

    NASA Astrophysics Data System (ADS)

    Charbonneau, Paul

    This chapter steps finally away from the sun and towards the stars, the idea being to apply the physical insight gained so far to see how much of stellar magnetism can be understood in terms of dynamo action. Dynamo action in the convective core of massive main-sequence stars is first considered and shown viable. For intermediate-mass main-sequence stars the fossil field hypothesis will carry the day, although possible dynamo alternatives are also briefly discussed. The extension of the solar dynamo models investigated in Chap. 3 (10.1007/978-3-642-32093-4_3) to other solar-type stars will first take us through an important detour in first having to understand rotational evolution in response to angular momentum loss in a magnetized wind. Dynamo action in fully convective stars comes next, and the chapter closes with an overview of the situation for pre- and post-main-sequence stars and compact objects, leading finally to the magnetic fields of galaxies and beyond.

  15. Fast axis servo for the fast and precise machining of non-rotational symmetric optics

    NASA Astrophysics Data System (ADS)

    Tian, Fujing; Yin, Ziqiang; Li, Shengyi

    2014-08-01

    A new long range tool servo-fast axis servo is developed, which is used for fabricating the non-rotational symmetric optics surface with millimeters' sag. The mechanism design, motion modeling and development of FAS device were studied. The FAS consists of a linear motor, aerostatic bearings, high-resolution encoder and a motion controller. A control strategy consists of a proportional, integral and derivative (PID) feedback controller and velocity/acceleration feedforward controller is implemented to accommodate the system control performance. Experimental tests have been carried out to verify the performance of the FAS system.

  16. [INTESTINAL NON-ROTATION AS CAUSE OF RECURRENT ABDOMINAL PAIN:REPORT OF A CASE AND LITERATURE REVIEW

    PubMed

    García Barrionuevo, Alcides; Castro De La Mata Guerra, Rodrigo; García; Rodríguez Castro, Manuel; Ganoza Arenas, Carmela

    2000-01-01

    A 32 years old male patient with recurrent abdominal pain was admitted to the hospital with the clinical picture of intestinal obstruction. An emergency laparotomy was performed and the diagnosis of intestinal non-rotation and cecum volvulus was done. Right hemicolectomy and terminoterminal ileocolic anastomosis was performed. Pathology showed ischemia and necrosis in the resected segment. Clinical presentation, diagnosis methods and therapeutic options of intestinal malrotation and non-rotation are discussed. PMID:12140578

  17. Computations of the collapse of a stellar iron core allowing for the absorption, emission, and scattering of electron neutrinos and anti-neutrinos

    NASA Astrophysics Data System (ADS)

    Aksenov, A. G.; Chechetkin, V. M.

    2012-03-01

    The collapse of the iron core of a star with mass 1.4 M ⊙ is computed. The initial model was chosen to be polytropic, P ∝ ρ 1+1/ n , with n = 3. The equation of state takes into account the equilibrium radiation of photons, a mixture of Fermi gases comprised of free nucleons and ideal gases comprised of nuclei (Fe, He) in equilibrium with respect to nuclear reactions, and electron-positron gas. The transport equation for electron neutrinos and anti-neutrinos is also included. The absorption and emission of neutrinos and anti-neutrinos with the participation of free nucleons and nuclei is taken into account, as well as scattering on electrons. The main goal of this study is to develop a numerical method for the joint solution of the gas-dynamical equations formatter and the Boltzmann kinetic equations for the distribution functions of various types of neutrinos in both optically thin and optically thick regions. The spherically symmetrical case is considered, but the dependences of the distribution functions on all the phase-space variables—the mass coordinate, particle energy, cosine of the angle between the radius vector and the particle momentum, and time, ( m, ɛ, µ, t)—are retained in the description of the neutrino transport. When computing reaction rates, the exact quantum-mechanical expressions for the probabilities of processes are used, with integration over the entire momentum phase space. The gas-dynamical variables depend on the mass coordinate and time, ( m, t). The solution yields neutrino light curves, which have narrow maximum with characteristic widths ≈10 ms. This makes it possible to place constraints on the mass of the electron neutrino based on the detection of short bursts of radiation, ≲4 eV. Part of the neutrino energy is absorbed in the envelope of the stellar core (˜1050 erg). This is associated with the higher mean neutrino energies in this model, which is more exact than models with neutrino thermal conductivity. This

  18. 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.

  19. Ray Tracing Through Non-Rotationally Symmetrical Systems With A Desktop Computer

    NASA Astrophysics Data System (ADS)

    Mackay, R. M.; Busse lle, F. J.

    1986-10-01

    A general ray-trace program has been developed for use on a desktop computer which traces finite rays through any non-rotationally symmetrical system. In particular any combination of decentred, tilted and rotated surface has been considered. Surface types such as Conic sections with and without Aspherics, Toric surfaces, surfaces of S and T Cylindrical sections, and Axicons, may be ray-traced. Each surface is defined in terms of a local rectangular co-ordinate system and has a particular aperture shape attributed to it. Aperture shapes may be defined as circular, elliptical, rectangular or quadrilateral. Also the centre of any aperture shape may be displaced from its local coordinate origin to facilitate the tracing of off-axis paraboloids. Before transferring to the next surface, the local coordinates are referred back to an initial reference coordinate system. Finally a means of assessing aberrations has been included. The main task here was to get a mathematical model of a non-rotationally symmetrical finite ray-trace running on an inexpensive desk top computer. The program was written for the BBC MICRO in order to investigate devices such as scanning systems for modern Thermal Imagers etc.

  20. EXPLOSIVE NUCLEOSYNTHESIS IN THE NEUTRINO-DRIVEN ASPHERICAL SUPERNOVA EXPLOSION OF A NON-ROTATING 15 M{sub sun} STAR WITH SOLAR METALLICITY

    SciTech Connect

    Fujimoto, Shin-ichiro; Kotake, Kei; Hashimoto, Masa-aki; Ono, Masaomi; Ohnishi, Naofumi

    2011-09-01

    We investigate explosive nucleosynthesis in a non-rotating 15 M{sub sun} star with solar metallicity that explodes by a neutrino-heating supernova (SN) mechanism aided by both standing accretion shock instability (SASI) and convection. To trigger explosions in our two-dimensional hydrodynamic simulations, we approximate the neutrino transport with a simple light-bulb scheme and systematically change the neutrino fluxes emitted from the protoneutron star. By a post-processing calculation, we evaluate abundances and masses of the SN ejecta for nuclei with a mass number {<=}70, employing a large nuclear reaction network. Aspherical abundance distributions, which are observed in nearby core-collapse SN remnants, are obtained for the non-rotating spherically symmetric progenitor, due to the growth of a low-mode SASI. The abundance pattern of the SN ejecta is similar to that of the solar system for models whose masses range between (0.4-0.5) M{sub sun} of the ejecta from the inner region ({<=}10, 000 km) of the precollapse core. For the models, the explosion energies and the {sup 56}Ni masses are {approx_equal} 10{sup 51}erg and (0.05-0.06) M{sub sun}, respectively; their estimated baryonic masses of the neutron star are comparable to the ones observed in neutron-star binaries. These findings may have little uncertainty because most of the ejecta is composed of matter that is heated via the shock wave and has relatively definite abundances. The abundance ratios for Ne, Mg, Si, and Fe observed in the Cygnus loop are reproduced well with the SN ejecta from an inner region of the 15 M{sub sun} progenitor.

  1. Stellar Populations

    NASA Astrophysics Data System (ADS)

    Peletier, Reynier F.

    2013-10-01

    This is a summary of my lectures during the 2011 Canary Islands Winter School in Puerto de la Cruz. I give an introduction to the field of stellar populations in galaxies, and highlight some new results. Since the title of the Winter School is Secular Evolution in Galaxies I mostly concentrate on nearby galaxies, which are best suited to study this theme. Of course, the understanding of stellar populations is intimately connected to understanding the formation and evolution of galaxies, one of the great outstanding problems of astronomy. We are currently in a situation where very large observational advances have been made in recent years. Galaxies have been detected up to a redshift of ten. A huge effort has to be made so that stellar population theory can catch up with observations. Since most galaxies are far away, information about them has to come from stellar population synthesis of integrated light. Here I will discuss how stellar evolution theory, together with observations in our Milky Way and Local Group, are used as building blocks to analyse these integrated stellar populations.

  2. Stellar Imager

    NASA Technical Reports Server (NTRS)

    Carpenter, Kenneth

    2007-01-01

    The Stellar Imager (SI) is one of NASA's "Vision Missions" - concepts for future, space-based, strategic missions that could enormously increase our capabilities for observing the Cosmos. SI is designed as a UV/Optical Interferometer which will enable 0.1 milli-arcsecond (mas) spectral imaging of stellar surfaces and, via asteroseismology, stellar interiors and of the Universe in general. The ultra-sharp images of the Stellar Imager will revolutionize our view of many dynamic astrophysical processes by transforming point sources into extended sources, and snapshots into evolving views. SI, with a characteristic angular resolution of 0.1 milli-arcseconds at 2000 Angstroms, represents an advance in image detail of several hundred times over that provided by the Hubble Space Telescope. The Stellar Imager will zoom in on what today-with few exceptions - we only know as point sources, revealing processes never before seen, thus providing a tool as fundamental to astrophysics as the microscope is to the study of life on Earth. SI's science focuses on the role of magnetism in the Universe, particularly on magnetic activity on the surfaces of stars like the Sun. It's prime goal is to enable long-term forecasting of solar activity and the space weather that it drives, in support of the Living With a Star program in the Exploration Era. SI will also revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically controlled processes in the Universe. Stellar Imager is included as a "Flagship and Landmark Discovery Mission" in the 2005 Sun Solar System Connection (SSSC) Roadmap and as a candidate for a "Pathways to Life Observatory" in the Exploration of the Universe Division (EUD) Roadmap (May, 2005) and as such is a candidate mission for the 2025-2030 timeframe. An artist's drawing of the current "baseline" concept for SI is presented.

  3. [Clinical aspects and therapy of intestinal non-rotation in adults].

    PubMed

    von Flüe, M; Bailleux, A; Stähelin, F; Vogt, B

    1990-06-01

    The intestinal non-rotation is a rare fetal disorder of the gut torsion. Its manifestation is very rarely seen in the adult, either in form of a volvulus of the midgut or ileocecal with an acute onset, or as chronic recurrent abdominal pain. Each diagnostic or therapeutic delay increases the risk of strangulation and may end as an abdominal disaster. We describe three own cases and we try to elucidate the diagnostic and therapeutic problems. Our proceeding: In the acute symptomatic form the explorative laparotomy with a consequent staging of the abdominal situs is the safest way to get an exact diagnosis. Therapeutically the procedure described by LADD is the best torsion prophylaxis; the ascending colon is sawn to the descending colon. Due to a paratopia, the appendectomy is recommended. In the chronic forms the contrast enema and the gastrointestinal barium study are the main diagnostic procedures. In the operation described by Fitzgerald and the ascending colon and the mesentery of the small bowel are--after incision of the common mesentery--fixed at their anatomical site. PMID:2228684

  4. Volvulus of the ascending colon in a non-rotated midgut: Plain film and MDCT findings

    PubMed Central

    Camera, Luigi; Calabrese, Milena; Mainenti, Pier Paolo; Masone, Stefania; Vecchio, Walter Del; Persico, Giovanni; Salvatore, Marco

    2012-01-01

    Colonic volvulus is a relatively uncommon cause of large bowel obstruction usually involving mobile, intra-peritoneal, colonic segments. Congenital or acquired anatomic variation may be associated with an increased risk of colonic volvulus which can occasionally involve retro-peritoneal segments. We report a case of 54-year-old female who presented to our Institution to perform a plain abdominal film series for acute onset of cramping abdominal pain. Both the upright and supine films showed signs of acute colonic obstruction which was thought to be due to an internal hernia of the transverse colon into the lesser sac. The patient was therefore submitted to a multi-detector contrast-enhanced computed tomography (CT). CT findings were initially thought to be consistent with the presumed diagnosis of internal hernia but further evaluation and coronal reformatting clearly depicted the presence of a colonic volvulus possibly resulting from a retro-gastric colon. At surgery, a volvulus of the ascending colon was found and a right hemi-colectomy had to be performed. However, a non rotated midgut with a right-sided duodeno-jejunal flexure and a left sided colon was also found at laparotomy and overlooked in the pre-operative CT. Retrospective evaluation of CT images was therefore performed and a number of CT signs of intestinal malrotation could be identified. PMID:23150768

  5. Intestinal non-rotation and pseudoobstruction in myotonic dystrophy: case report and review of the literature.

    PubMed

    Sartoretti, C; Sartoretti, S; DeLorenzi, D; Buchmann, P

    1996-01-01

    Myotonic dystrophy is an autosomal dominant inherited disease of the skeletal and cardiac musculature that involves the pharyngeal and gastrointestinal smooth and striated muscles, resulting in velopharyngeal insufficiency, Swallowing difficulties, gastrointestinal motility disorders and anal incontinence. Gastrointestinal symptoms are found in a large proportion of patients suffering from this disease and may herald the onset of muscular disorders, in rare cases they are even the predominant feature of the disorder. We report on a 31-years-old patient with formerly undiagnosed myotonic dystrophy in combination with a non-rotation of the intestinal tract, an association of disorders that to our knowledge never has been reported before. Our patient was admitted as an emergency with signs of an acute abdomen with ileus, associated with acute aspiration pneumonia. Surgical intervention was avoided once the diagnosis of myotonic dystrophy had been confirmed and the patient was treated successfully by conservative therapy. A review of the literature indicates that conservative treatment of motility disorders of the bowel in patients with myotonic dystrophy is to be recommended. PMID:8919334

  6. GRAVITATIONAL WAVES FROM STELLAR COLLAPSE

    SciTech Connect

    C. L. FRYER

    2001-01-01

    Stellar core-collapse plays an important role in nearly all facets of astronomy: cosmology (as standard candles), formation of compact objects, nucleosynthesis and energy deposition in galaxies. In addition, they release energy in powerful explosions of light over a range of energies, neutrinos, and the subject of this meeting, gravitational waves. Because of this broad range of importance, astronomers have discovered a number of constraints which can be used to help them understand the importance of stellar core-collapse as gravitational wave sources.

  7. Cold testing of quasi-optical mode converters using a generator for non-rotating high-order gyrotron modes.

    PubMed

    Kim, S G; Kim, D S; Choe, M S; Lee, W; So, J; Choi, E M

    2014-10-01

    In this paper, we test the performance of a quasi-optical, internal-gyrotron mode converter. When cold testing mode converters, a rotating higher-order mode is commonly used. However, this requires a nontrivial design and precise alignment. We thus propose a new technique for testing gyrotron mode converters by using a simple, non-rotating, higher-order mode generator. We demonstrate the feasibility of this technique for a W-band gyrotron quasi-optical mode converter by examining the excitation of a TE6,2 mode from a non-rotating mode generator. Our results demonstrate that this new cold-test scheme is an easy and efficient method for verifying the performance of quasi-optical mode converters. PMID:25362436

  8. Physics of Stellar Convection

    NASA Astrophysics Data System (ADS)

    Arnett, W. David

    2009-05-01

    We review recent progress using numerical simulations as a testbed for development of a theory of stellar convection, much as envisaged by John von Newmann. Necessary features of the theory, non-locality and fluctuations, are illustrated by computer movies. It is found that the common approximation of convection as a diffusive process presents the wrong physical picture, and improvements are suggested. New observational results discussed at the conference are gratifying in their validation of some of our theoretical ideas, especially the idea that SNIb and SNIc events are related to the explosion of massive star cores which have been stripped by mass loss and binary interactions [1

  9. STELLARATOR INJECTOR

    DOEpatents

    Post, R.F.

    1962-09-01

    A method and means are described for injecting energetic neutral atoms or molecular ions into dense magnetically collimated plasma columns of stellarators and the like in such a manner that the atoms or ions are able to significantly penetrate the column before being ionized by collision with the plasma constituent particles. Penetration of the plasma column by the neutral atoms or molecular ions is facilitated by superposition of two closely spaced magnetic mirrors on the plasma confinement field. The mirrors are moved apart to magnetically sweep plasma from a region between the mirrors and establish a relatively low plasma density therein. By virture of the low density, neutral atoms or molecular ions injected into the region significantly penetrate the plasma column before being ionized. Thereafter, the mirrors are diminished to permit the injected material to admix with the plasma in the remainder of the column. (AEC)

  10. Introduction to stellar evolution

    NASA Astrophysics Data System (ADS)

    Scilla, Degl’Innocenti

    2016-04-01

    This contribution is meant as a first brief introduction to stellar physics. First I shortly describe the main physical processes active in stellar structures then I summarize the most important features during the stellar life-cycle.

  11. Gravitational Waves from Core-collapse Supernovae and Long GRBsLong GRBs and massive stellar explosions from frame dragging around black holes

    NASA Astrophysics Data System (ADS)

    van Putten, M. H. P. M.

    2014-08-01

    The most energetic long GRBs and core-collapse supernovae may be powered by black hole inner engines. Normalized light curves of the BATSE catalogue of long GRBs are remarkably consistent with energizing an inner disk in the process of black hole spindown. A broad band chirp spectrum observed in a recent analysis of BeppoSax light curves of long GRBs may reflect the induced turbulence. Nearby CC-SNe are therefore potential sources of gravitational wave emissions with durations of tens of seconds commensurate with long GRBs.

  12. Stellar evolution in blue populous clusters of the Small Magellanic Cloud and the problems of envelope semiconvection and convective core overshooting

    NASA Technical Reports Server (NTRS)

    Stothers, Richard B.; Chin, Chao-Wen

    1992-01-01

    New theoretical evolutionary sequences of models for stars with low metallicities, appropriate to the Small Magellanic Cloud, are derived with both standard Cox-Stewart opacities and the new Rogers-Iglesias opacities. Only those sequences with little or no convective core overshooting are found to be capable of reproducing the two most critical observations: the maximum effective temperature displayed by the hot evolved stars and the difference between the average bolometric magnitudes of the hot and cool evolved stars. An upper limit to the ratio of the mean overshoot distance beyond the classical Schwarzschild core boundary to the local pressure scale height is set at 0.2. It is inferred from the frequency of cool supergiants in NGC 330 that the Ledoux criterion, rather than the Schwarzschild criterion, for convection and semiconvection in the envelopes of massive stars is strongly favored. Residuals from the fitting for NGC 330 suggest the possibility of fast interior rotation in the stars of this cluster. NGC 330 and NGC 458 have ages of about 3 x 10 exp 7 and about 1 x 10 exp 8 yr, respectively.

  13. Far-infrared/submillimetre properties of pre-stellar cores L1521E, L1521F and L1689B as revealed by the Herschel SPIRE instrument - I. Central positions

    NASA Astrophysics Data System (ADS)

    Makiwa, G.; Naylor, D. A.; van der Wiel, M. H. D.; Ward-Thompson, D.; Kirk, J. M.; Eyres, S.; Abergel, A.; Köhler, M.

    2016-05-01

    Dust grains play a key role in the physics of star-forming regions, even though they constitute only ˜1 per cent of the mass of the interstellar medium. The derivation of accurate dust parameters such as temperature (Td), emissivity spectral index (β) and column density requires broad-band continuum observations at far-infrared wavelengths. We present Herschel-Spectral and Photometric Imaging Receiver Array (SPIRE) Fourier Transform Spectrometer (FTS) measurements of three starless cores: L1521E, L1521F and L1689B, covering wavelengths between 194 and 671 μm. This paper is the first to use our recently updated SPIRE-FTS intensity calibration, yielding a direct match with SPIRE photometer measurements of extended sources. In addition, we carefully assess the validity of calibration schemes depending on-source extent and on the strength of background emission. The broad-band far-infrared spectra for all three sources peak near 250 μm. Our observations therefore provide much tighter constraints on the spectral energy distribution (SED) shape than measurements that do not probe the SED peak. The spectra are fitted using modified blackbody functions, allowing both Td and β to vary as free parameters. This yields Td of 9.8±0.2, 15.6±0.5 and 10.9±0.2 K and corresponding β of 2.6∓0.9, 0.8∓0.1 and 2.4∓0.8 for L1521E, L1521F and L1689B, respectively. The derived core masses are 1.0±0.1, 0.10±0.01 and 0.49±0.05 M⊙, respectively. The core mass/Jeans mass ratios for L1521E and L1689B exceed unity indicating that they are unstable to gravitational collapse, and thus pre-stellar cores. By comparison, the elevated temperature and gravitational stability of L1521F support previous arguments that this source is more evolved and likely a protostar.

  14. Stellar Vampires Unmasked

    NASA Astrophysics Data System (ADS)

    2006-10-01

    result in anomalous abundances. ESO PR Photo 37/06 ESO PR Photo 37/06 Abundances in Blue Straggler Stars In the core of a globular cluster, stars are packed extremely close to each other: more than 4000 stars are found in the innermost light-year-sized cube of 47 Tucanae. Thus, stellar collisions are thought to be very frequent and the collision channel for the formation of blue stragglers should be extremely efficient. The chemical signature detected by these observations demonstrates that also the binary mass-transfer scenario is fully active even in a high-density cluster like 47 Tuc. "Our discovery is therefore a fundamental step toward the solution of the long-standing mystery of blue straggler formation in globular clusters," said Ferraro. Measurements of so many faint stars are only possible since the advent of 8-m class telescopes equipped with multiplexing capability spectrographs. In this case, the astronomers used the FLAMES/Giraffe instrument that allows the simultaneous observation of up to 130 targets at a time, making it ideally suited for surveying individual stars in closely populated fields.

  15. NEW TWO-DIMENSIONAL MODELS OF SUPERNOVA EXPLOSIONS BY THE NEUTRINO-HEATING MECHANISM: EVIDENCE FOR DIFFERENT INSTABILITY REGIMES IN COLLAPSING STELLAR CORES

    SciTech Connect

    Mueller, Bernhard; Janka, Hans-Thomas; Heger, Alexander E-mail: thj@mpa-garching.mpg.de

    2012-12-10

    The neutrino-driven explosion mechanism for core-collapse supernovae in its modern flavor relies on the additional support of hydrodynamical instabilities in achieving shock revival. Two possible candidates, convection and the so-called standing accretion shock instability (SASI), have been proposed for this role. In this paper, we discuss new successful simulations of supernova explosions that shed light on the relative importance of these two instabilities. While convection has so far been observed to grow first in self-consistent hydrodynamical models with multi-group neutrino transport, we here present the first such simulation in which the SASI grows faster while the development of convection is initially inhibited. We illustrate the features of this SASI-dominated regime using an explosion model of a 27 M{sub Sun} progenitor, which is contrasted with a convectively dominated model of an 8.1 M{sub Sun} progenitor with subsolar metallicity, whose early post-bounce behavior is more in line with previous 11.2 M{sub Sun} and 15 M{sub Sun} explosion models. We analyze the conditions discriminating between the two different regimes, showing that a high mass-accretion rate and a short advection timescale are conducive for strong SASI activity. We also briefly discuss some important factors for capturing the SASI-driven regime, such as general relativity, the progenitor structure, a nuclear equation of state leading to a compact proto-neutron star, and the neutrino treatment. Finally, we evaluate possible implications of our findings for two-dimensional and three-dimensional supernova simulations.

  16. New Two-dimensional Models of Supernova Explosions by the Neutrino-heating Mechanism: Evidence for Different Instability Regimes in Collapsing Stellar Cores

    NASA Astrophysics Data System (ADS)

    Müller, Bernhard; Janka, Hans-Thomas; Heger, Alexander

    2012-12-01

    The neutrino-driven explosion mechanism for core-collapse supernovae in its modern flavor relies on the additional support of hydrodynamical instabilities in achieving shock revival. Two possible candidates, convection and the so-called standing accretion shock instability (SASI), have been proposed for this role. In this paper, we discuss new successful simulations of supernova explosions that shed light on the relative importance of these two instabilities. While convection has so far been observed to grow first in self-consistent hydrodynamical models with multi-group neutrino transport, we here present the first such simulation in which the SASI grows faster while the development of convection is initially inhibited. We illustrate the features of this SASI-dominated regime using an explosion model of a 27 M ⊙ progenitor, which is contrasted with a convectively dominated model of an 8.1 M ⊙ progenitor with subsolar metallicity, whose early post-bounce behavior is more in line with previous 11.2 M ⊙ and 15 M ⊙ explosion models. We analyze the conditions discriminating between the two different regimes, showing that a high mass-accretion rate and a short advection timescale are conducive for strong SASI activity. We also briefly discuss some important factors for capturing the SASI-driven regime, such as general relativity, the progenitor structure, a nuclear equation of state leading to a compact proto-neutron star, and the neutrino treatment. Finally, we evaluate possible implications of our findings for two-dimensional and three-dimensional supernova simulations.

  17. Hydrodynamic stellar interactions in dense star clusters

    NASA Technical Reports Server (NTRS)

    Rasio, Frederic A.

    1993-01-01

    Highly detailed HST observations of globular-cluster cores and galactic nuclei motivate new theoretical studies of the violent dynamical processes which govern the evolution of these very dense stellar systems. These processes include close stellar encounters and direct physical collisions between stars. Such hydrodynamic stellar interactions are thought to explain the large populations of blue stragglers, millisecond pulsars, X-ray binaries, and other peculiar sources observed in globular clusters. Three-dimensional hydrodynamics techniques now make it possible to perform realistic numerical simulations of these interactions. The results, when combined with those of N-body simulations of stellar dynamics, should provide for the first time a realistic description of dense star clusters. Here I review briefly current theoretical work on hydrodynamic stellar interactions, emphasizing its relevance to recent observations.

  18. Stellar Metamorphosis:

    NASA Technical Reports Server (NTRS)

    2002-01-01

    [TOP LEFT AND RIGHT] The Hubble Space Telescope's Wide Field and Planetary Camera 2 has captured images of the birth of two planetary nebulae as they emerge from wrappings of gas and dust, like butterflies breaking out of their cocoons. These images highlight a fleeting phase in the stellar burnout process, occurring just before dying stars are transformed into planetary nebulae. The left-hand image is the Cotton Candy nebula, IRAS 17150-3224; the right-hand image, the Silkworm nebula, IRAS 17441-2411. Called proto-planetary nebulae, these dying stars have been caught in a transition phase between a red giant and a planetary nebula. This phase is only about 1,000 years long, very short in comparison to the 1 billion-year lifetime of a star. These images provide the earliest snapshots of the transition process. Studying images of proto-planetary nebulae is important to understanding the process of star death. A star begins to die when it has exhausted its thermonuclear fuel - hydrogen and helium. The star then becomes bright and cool (red giant phase) and swells to several tens of times its normal size. It begins puffing thin shells of gas off into space. These shells become the star's cocoon. In the Hubble images, the shells are the concentric rings seen around each nebula. But the images also reveal the nebulae breaking out from those shells. The butterfly-like wings of gas and dust are a common shape of planetary nebulae. Such butterfly shapes are created by the 'interacting winds' process, in which a more recent 'fast wind' - material propelled by radiation from the hot central star - punches a hole in the cocoon, allowing the nebula to emerge. (This 'interacting wind' theory was first proposed by Dr. Sun Kwok to explain the origin of planetary nebulae, and has been subsequently proven successful in explaining their shapes.) The nebulae are being illuminated by light from the invisible central star, which is then reflected toward us. We are viewing the nebulae

  19. Granular ripples under rotating flow: a new experimental technique for studying ripples in non-rotating, geophysical applications?

    PubMed

    Thomas, P J; Zoueshtiagh, F

    2005-07-15

    A review of our research investigating a new pattern formation process in granular material underlying a rotating fluid is given. The purpose of this summary is to introduce the phenomenon to the geophysical research community and to draw attention to the potential practical benefits of our new experimental method. To this end, the applied and scientific advantages of the technique over traditional studies employing, for instance, water channels, are discussed for the first time. It is shown here that the system rotation in our new technique does not appear to affect the scaling law expressing the dependence of the ripple-pattern wavelength on the governing independent experimental parameters. This suggests that it may become possible to extrapolate appropriate results from rotating to non-rotating systems and, hence, to geophysical environments. Consequently, our new technique may find applications in the context of geophysical research on the formation of sedimentary granular ripple structures. PMID:16011938

  20. Fano-Agarwal couplings and non-rotating wave approximation in single-photon timed Dicke subradiance

    NASA Astrophysics Data System (ADS)

    Mirza, Imran M.; Begzjav, Tuguldur

    2016-04-01

    Recently a new class of single-photon timed Dicke (TD) subradiant states has been introduced with possible applications in single-photon–based quantum information storage and on demand ultrafast retrieval (Scully M. O., Phys. Rev. Lett., 115 (2015) 243602). However, the influence of any kind of virtual processes on the decay of these new kind of subradiant states has been left as an open question. In the present paper, we focus on this problem in detail. In particular, we investigate how pure Fano-Agarwal couplings and other virtual processes arising from non-rotating wave approximation impact the decay of otherwise sub- and superradiant states. In addition to the overall virtual couplings among all TD states, we also focus on the dominant role played by the couplings between specific TD states.

  1. History of Stellar Interferometry

    NASA Technical Reports Server (NTRS)

    Lawson, Peter R.

    2004-01-01

    This viewgraph presentation reviews the history of stellar interferometry from the suggestion of Fizeau that stellar interferometry was possible,to the use of the Mark I, II and III for astrometry. Photographs, and parts of original articles are presented.

  2. Initiating solar system formation through stellar shock waves

    NASA Technical Reports Server (NTRS)

    Boss, A. P.; Myhill, E. A.

    1993-01-01

    Isotopic anomalies in presolar grains and other meteoritical components require nucleosynthesis in stellar interiors, condensation into dust grains in stellar envelopes, transport of the grains through the interstellar medium by stellar outflows, and finally injection of the grains into the presolar nebula. The proximity of the presolar cloud to these energetic stellar events suggests that a shock wave from a stellar outflow might have initiated the collapse of an otherwise stable presolar cloud. We have begun to study the interactions of stellar shock waves with thermally supported, dense molecular cloud cores, using a three spatial dimension (3D) radiative hydrodynamics code. Supernova shock waves have been shown by others to destroy quiescent clouds, so we are trying to determine if the much smaller shock speeds found in, e.g., asymptotic giant branch (AGB) star winds, are strong enough to initiate collapse in an otherwise stable, rotating, solar-mass cloud core, without leading to destruction of the cloud.

  3. Comparison of CFD simulations to non-rotating MEXICO blades experiment in the LTT wind tunnel of TUDelft

    NASA Astrophysics Data System (ADS)

    Zhang, Ye; van Zuijlen, Alexander; van Bussel, Gerard

    2014-06-01

    In this paper, three dimensional flow over non-rotating MEXICO blades is simulated by CFD methods. The numerical results are compared with the latest MEXICO wind turbine blades measurements obtained in the low speed low turbulence (LTT) wind tunnel of Delft University of Technology. This study aims to validate CFD codes by using these experimental data measured in well controlled conditions. In order to avoid use of wind tunnel corrections, both the blades and the wind tunnel test section are modelled in the simulations. The ability of Menter's k - ω shear stress transport (SST) turbulence model is investigated at both attached flow and massively separated flow cases. Steady state Reynolds averaged Navier Stokes (RANS) equations are solved in these computations. The pressure distribution at three measured sections are compared under the conditions of different inflow velocities and a range of angles of attack. The comparison shows that at attached flow condition, good agreement can be obtained for all three airfoil sections. Even with massively separated flow, still fairly good pressure distribution comparison can be found for the DU and NACA airfoil sections, although the RISØ section shows poor comparison. At the near stall case, considerable deviations exists on the forward half part of the upper surface for all three sections.

  4. The Solar-Stellar Connection

    NASA Astrophysics Data System (ADS)

    Schunker, Hannah

    2015-08-01

    The influence of rotation on stellar magnetism, and the importance of the shear layer between a radiative core and the convective envelope for the generation of magnetic fields are key to understanding solar-like dynamos. Despite having an abundance of observational constraints, the answer to the solar dynamo problem remains tantalisingly out of reach. With the advent of space-based instrumentation for asteroseismology including Kepler, CoRoT, and in the future PLATO, we can exploit the sheer number of observations, and complementary techniques to constrain the rotation of Sun-like stars.

  5. Stellar Presentations (Abstract)

    NASA Astrophysics Data System (ADS)

    Young, D.

    2015-12-01

    (Abstract only) The AAVSO is in the process of expanding its education, outreach and speakers bureau program. powerpoint presentations prepared for specific target audiences such as AAVSO members, educators, students, the general public, and Science Olympiad teams, coaches, event supervisors, and state directors will be available online for members to use. The presentations range from specific and general content relating to stellar evolution and variable stars to specific activities for a workshop environment. A presentation—even with a general topic—that works for high school students will not work for educators, Science Olympiad teams, or the general public. Each audience is unique and requires a different approach. The current environment necessitates presentations that are captivating for a younger generation that is embedded in a highly visual and sound-bite world of social media, twitter and U-Tube, and mobile devices. For educators, presentations and workshops for themselves and their students must support the Next Generation Science Standards (NGSS), the Common Core Content Standards, and the Science Technology, Engineering and Mathematics (STEM) initiative. Current best practices for developing relevant and engaging powerpoint presentations to deliver information to a variety of targeted audiences will be presented along with several examples.

  6. Models of cuspy triaxial stellar systems - IV. Rotating systems

    NASA Astrophysics Data System (ADS)

    Carpintero, D. D.; Muzzio, J. C.

    2016-06-01

    We built two self-consistent models of triaxial, cuspy, rotating stellar systems adding rotation to non-rotating models presented in previous papers of this series. The final angular velocity of the material is not constant and varies with the distance to the centre and with the height over the equator of the systems, but the figure rotation is very uniform in both cases. Even though the addition of rotation to the models modifies their original semi-axes ratios, the final rotating models are considerably flattened and triaxial. An analysis of the orbital content of the models shows that about two-thirds of their orbits are chaotic yet the models are very stable over intervals of the order of one Hubble time. The bulk of regular orbits are short-axis tubes, while long-axis tubes are replaced by tubes whose axes lie on the short-long axes plane, but do not coincide with the major axis. Other types of regular orbits that do not appear in non-rotating systems, like horseshoes and orbits that cross themselves, are also found in the present models. Finally, our frequency maps show empty regions where studies of orbits on fixed potentials found orbits, a likely consequence of the self-consistency of our models that excludes them.

  7. Stellar evolution as seen by mixed modes

    NASA Astrophysics Data System (ADS)

    Mosser, Benoît

    2015-09-01

    The detection of mixed modes in subgiants and red giants allows us to monitor stellar evolution from the main sequence to the asymptotic giant branch and draw seismic evolutionary tracks. Quantified asteroseismic definitions that characterize the change in the evolutionary stages have been defined. This seismic information can now be used for stellar modelling, especially for studying the energy transport in the helium burning core or for specifying the inner properties of stars all along their evolution. Modelling will also allow us to study stars identified in the helium subflash stage, high-mass stars either arriving or quitting the secondary clump, or stars that could be in the blue-loop stage.

  8. Stellar yields of rotating first stars

    SciTech Connect

    Takahashi, Koh; Umeda, Hideyuki; Yoshida, Takashi

    2014-05-02

    First stars, also called population III stars, are born in the earliest universe without any heavy elements. These stars are the first nuclear reactor in the universe and affect their circumstances emitting synthesized materials. Not only the stellar evolution, but also their chemical yields have many distinctive characteristics. We have modeled evolution of population III stars including effect of stellar rotation. Internal mixing induced by rotation naturally results in primary nitrogen production. Evolution of rotating massive stars is followed until the core collapse phase. The new Pop III yield model will consistently explain the observed abundances of metal-poor systems.

  9. Magnetorotational iron core collapse

    NASA Technical Reports Server (NTRS)

    Symbalisty, E. M. D.

    1984-01-01

    During its final evolutionary stages, a massive star, as considered in current astrophysical theory, undergoes rapid collapse, thereby triggering a sequence of a catastrophic event which results in a Type II supernova explosion. A remnant neutron star or a black hole is left after the explosion. Stellar collapse occurs, when thermonuclear fusion has consumed the lighter elements present. At this stage, the core consists of iron. Difficulties arise regarding an appropriate model with respect to the core collapse. The present investigation is concerned with the evolution of a Type II supernova core including the effects of rotation and magnetic fields. A simple neutrino model is developed which reproduced the spherically symmetric results of Bowers and Wilson (1982). Several two-dimensional computational models of stellar collapse are studied, taking into account a case in which a 15 solar masses iron core was artificially given rotational and magnetic energy.

  10. Stellar feedback efficiencies: supernovae versus stellar winds

    NASA Astrophysics Data System (ADS)

    Fierlinger, Katharina M.; Burkert, Andreas; Ntormousi, Evangelia; Fierlinger, Peter; Schartmann, Marc; Ballone, Alessandro; Krause, Martin G. H.; Diehl, Roland

    2016-02-01

    Stellar winds and supernova (SN) explosions of massive stars (`stellar feedback') create bubbles in the interstellar medium (ISM) and insert newly produced heavy elements and kinetic energy into their surroundings, possibly driving turbulence. Most of this energy is thermalized and immediately removed from the ISM by radiative cooling. The rest is available for driving ISM dynamics. In this work we estimate the amount of feedback energy retained as kinetic energy when the bubble walls have decelerated to the sound speed of the ambient medium. We show that the feedback of the most massive star outweighs the feedback from less massive stars. For a giant molecular cloud (GMC) mass of 105 M⊙ (as e.g. found in the Orion GMCs) and a star formation efficiency of 8 per cent the initial mass function predicts a most massive star of approximately 60 M⊙. For this stellar evolution model we test the dependence of the retained kinetic energy of the cold GMC gas on the inclusion of stellar winds. In our model winds insert 2.34 times the energy of an SN and create stellar wind bubbles serving as pressure reservoirs. We find that during the pressure-driven phases of the bubble evolution radiative losses peak near the contact discontinuity (CD), and thus the retained energy depends critically on the scales of the mixing processes across the CD. Taking into account the winds of massive stars increases the amount of kinetic energy deposited in the cold ISM from 0.1 per cent to a few per cent of the feedback energy.

  11. 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.

  12. Double-helix stellarator

    SciTech Connect

    Moroz, P.E.

    1997-09-01

    A new stellarator configuration, the Double-Helix Stellarator (DHS), is introduced. This novel configuration features a double-helix center post as the only helical element of the stellarator coil system. The DHS configuration has many unique characteristics. One of them is the extreme low plasma aspect ratio, A {approx} 1--1.2. Other advantages include a high enclosed volume, appreciable rotational transform, and a possibility of extreme-high-{beta} MHD equilibria. Moreover, the DHS features improved transport characteristics caused by the absence of the magnetic field ripple on the outboard of the torus. Compactness, simplicity and modularity of the coil system add to the DHS advantages for fusion applications.

  13. Stellarator-Spheromak

    SciTech Connect

    Moroz, P.E.

    1997-03-01

    A novel concept for magnetic plasma confinement, Stellarator-Spheromak (SSP), is proposed. Numerical analysis with the classical-stellarator-type outboard stellarator windings demonstrates a number of potential advantages of SSP for controlled nuclear fusion. Among the main ones are: simple and compact magnet coil configuration, absence of material structures (e.g. magnet coils or conducting walls) in the center of the torus, high rotational transform, and a possibility of MHD equilibria with very high {beta} (pressure/magnetic pressure) of the confined plasma.

  14. Stellar atmospheric structural patterns

    NASA Technical Reports Server (NTRS)

    Thomas, R. N.

    1983-01-01

    The thermodynamics of stellar atmospheres is discussed. Particular attention is given to the relation between theoretical modeling and empirical evidence. The characteristics of distinctive atmospheric regions and their radical structures are discussed.

  15. Evolution of stellar entropy

    NASA Astrophysics Data System (ADS)

    de Souza, R. A.; de Avellar, M. G. B.; Horvath, J. E.

    2015-11-01

    An appraisal of the behavior of stellar entropy along stellar evolution is made. It is shown that the entropy per baryon of a star of a fixed baryon number decreases monotonically with increasing compactness of the star. The same entropy per baryon increases only whenever an irreversible collapse of the star happens. The recent proposals for a gravitational entropy related to curvature may justify the huge increase of the entropy in the ultimate collapse to a black hole.

  16. Stellar population synthesis

    NASA Astrophysics Data System (ADS)

    Zhang, Feng-Hui; Li, Li-Fang; Han, Zhan-Wen

    In this paper we review the study of stellar population synthesis. So far there exist three methods in the study of the integrated light of stellar population-trail-and error, automated, and evolutionary population synthesis (EPS). We have discussed advantages and disadvantages for these methods. Among the three methods the EPS is the most direct approach to model galaxies. In this scheme, the model builder starts with knowledge of stellar evolution and attempts to build a model galaxy with physical input parameters such as star formation rate (SFR) and the initial mass function (IMF) slope. Therefore we have discussed emphatically the EPS method. First we have described and given the often used grids of several key ingredients in the EPS studies: (1) the library of evolutionary tracks used to calculate isochrones in the color-magnitude diagram (CMD), (2) the libraries of spectra adopted, which include empirical and theoretical stellar spectral libraries, star cluster library, active galactic nuclear (AGN) library and galaxy library, to derive the integrated spectral energy distributions (ISED) or magnitudes and colors in the suitable passbands, (3) the IMF used to evaluate the relative proportions of stars in the various evolutionary phases, and (4) the assumption for the underlying star formation rate (SFR) and chemical enrichment. Then we have listed several population synthesis criterions, i.e. broadband color indices, the integrated spectral energy distribution (ISED) and narrow band color indices, given the basic method of calculating broadband colors and flux-distribution for a simple stellar population (SSP). At last we have discussed simply the existed limitations, which are caused by some uncertainties in its two principal building blocks: stellar evolution models and spectral libraries in the studies of the EPS. Stellar evolution models are often subject to limitations in the following areas: the atomic data (radiative opacities, heavy element mixture

  17. PREFACE: A Stellar Journey A Stellar Journey

    NASA Astrophysics Data System (ADS)

    Asplund, M.

    2008-10-01

    The conference A Stellar Journey was held in Uppsala, Sweden, 23 27June 2008, in honour of Professor Bengt Gustafsson's 65th birthday. The choice of Uppsala as the location for this event was obvious given Bengt's long-standing association with the city stemming back to his school days. With the exception of a two-year postdoc stint in Copenhagen, five years as professor at Stockholm University and two years as director of the Sigtuna foundation, Bengt has forged his illustrious professional career at Uppsala University. The symposium venue was Museum Gustavianum, once the main building of the oldest university in Scandinavia. The title of the symposium is a paraphrasing of Bengt's popular astronomy book Kosmisk Resa (in English: Cosmic Journey) written in the early eighties. I think this aptly symbolizes his career that has been an astronomical voyage from near to far, from the distant past to the present. The original book title was modified slightly to reflect that most of his work to date has dealt with stars in one way or another. In addition it also gives credit to Bengt's important role as a guiding light for a very large number of students, colleagues and collaborators, indeed for several generations of astronomers. For me personally, the book Kosmisk Resa bears particular significance as it has shaped my life rather profoundly. Although I had already decided to become an astronomer, when I first read the book as a 14-year-old I made up my mind then and there that I would study under Bengt Gustafsson and work on stars. Indeed I have remained true to this somewhat audacious resolution. I suspect that a great number of us have similar stories how Bengt has had a major influence on our lives, whether on the professional or personal level. Perhaps Bengt's most outstanding characteristic is his enthralling enthusiasm. This is equally true whether he is pondering some scientific conundrum, supervising students or performing in front of an audience, be it an

  18. Las Campanas Stellar Library

    NASA Astrophysics Data System (ADS)

    Chilingarian, Igor; Zolotukhin, Ivan; Beletsky, Yuri; Worthey, Guy

    2015-08-01

    Stellar libraries are fundamental tools required to understand stellar populations in star clusters and galaxies as well as properties of individual stars. Comprehensive libraries exist in the optical domain, but the near-infrared (NIR) domain stays a couple of decades behind. Here we present the Las Campanas Stellar Library project aiming at obtaining high signal-to-noise intermediate-resolution (R=8000) NIR spectra (0.83<λ<2.5μm) for a sample of 1200 stars in the Southern sky using the Folded-port InfraRed Echelette spectrograph at the 6.5-m Magellan Baade telescope. We developed a dedicated observing strategy and customized the telescope control software in order to achieve the highest possible level of data homogeniety. As of 2015, we observed about 600 stars of all spectral types and luminosity classes making our library the largest homogeneous collection of stellar spectra covering the entire NIR domain. We also re-calibrated in flux and wavelength the two existing optical stellar libraries, INDO-US and UVES-POP and followed up about 400 non-variable stars in the NIR in order to get complete optical-NIR coverage. Worth mentioning that our current sample includes about 80 AGB stars and a few dozens of bulge/LMC/SMC stars.

  19. Stellar population in LLAGN

    NASA Astrophysics Data System (ADS)

    González Delgado, Rosa M.

    2004-11-01

    LLAGN that include low-ionization nuclear emission-line regions (LINERs), and transition-type objects (TOs) represent the most common type of nuclear activity. Here, a study of the central stellar population of LLAGN is presented. Our goal is to search for spectroscopic signatures of young and intermediate age stars, and to investigate their relationship with the ionization mechanism in LLAGN. The method used is based on the stellar population synthesis of the UV-optical continuum of the innermost (20-100 pc) regions in these galaxies. Half of the LINERs and TOs of the Palomar catalogue are analysed. It is found that weak-[OI] ([OI]/Hα≤0.25) LLAGN have an intermediate age stellar population that dominates the optical light. But young stellar clusters dominate the UV continuum in these objects. These clusters can co-exist with a black-hole in spatial scales of a few pc. Most of the strong-[OI] LLAGN have a predominantly old stellar population. These results suggest that young and intermediate age stars do not play a significant role in the ionization of LLAGN with strong [OI].

  20. 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

  1. Stellar Populations. A User Guide from Low to High Redshift

    NASA Astrophysics Data System (ADS)

    Greggio, Laura; Renzini, Alvio

    2011-09-01

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

  2. Stellar Astrophysical Fluid Dynamics

    NASA Astrophysics Data System (ADS)

    Thompson, Michael J.; Christensen-Dalsgaard, Jørgen

    2003-05-01

    Preface; 1. A selective overview Jørgen Christensen-Dalsgaard and Michael J. Thompson; Part I. Stellar Convection and Oscillations: 2. On the diversity of stellar pulsations Wojciech A. Dziembowski; 3. Acoustic radiation and mode excitation by turbulent convection Günter Houdek; 4. Understanding roAp stars Margarida S. Cunha; 5. Waves in the magnetised solar atmosphere Colin S. Rosenthal; Part II. Stellar Rotation and Magnetic Fields: 6. Stellar rotation: a historical survey Leon Mestel; 7. The oscillations of rapidly rotating stars Michel Rieutord; 8. Solar tachocline dynamics: eddy viscosity, anti-friction, or something in between? Michael E. McIntyre; 9. Dynamics of the solar tachocline Pascale Garaud; 10. Dynamo processes: the interaction of turbulence and magnetic fields Michael Proctor; 11. Dynamos in planets Chris Jones; Part III. Physics and Structure of Stellar Interiors: 12. Solar constraints on the equation of state Werner Däppen; 13. 3He transport and the solar neutrino problem Chris Jordinson; 14. Mixing in stellar radiation zones Jean-Paul Zahn; 15. Element settling and rotation-induced mixing in slowly rotating stars Sylvie Vauclair; Part IV. Helio- and Asteroseismology: 16. Solar structure and the neutrino problem Hiromoto Shibahashi; 17. Helioseismic data analysis Jesper Schou; 18. Seismology of solar rotation Takashi Sekii; 19. Telechronohelioseismology Alexander Kosovichev; Part V. Large-Scale Numerical Experiments: 20. Bridges between helioseismology and models of convection zone dynamics Juri Toomre; 21. Numerical simulations of the solar convection zone Julian R. Elliott; 22. Modelling solar and stellar magnetoconvection Nigel Weiss; 23. Nonlinear magnetoconvection in the presence of a strong oblique field Keith Julien, Edgar Knobloch and Steven M. Tobias; 24. Simulations of astrophysical fluids Marcus Brüggen; Part VI. Dynamics: 25. A magic electromagnetic field Donald Lynden-Bell; 26. Continuum equations for stellar dynamics Edward A

  3. Stellar Astrophysical Fluid Dynamics

    NASA Astrophysics Data System (ADS)

    Thompson, Michael J.; Christensen-Dalsgaard, Jørgen

    2008-02-01

    Preface; 1. A selective overview Jørgen Christensen-Dalsgaard and Michael J. Thompson; Part I. Stellar Convection and Oscillations: 2. On the diversity of stellar pulsations Wojciech A. Dziembowski; 3. Acoustic radiation and mode excitation by turbulent convection Günter Houdek; 4. Understanding roAp stars Margarida S. Cunha; 5. Waves in the magnetised solar atmosphere Colin S. Rosenthal; Part II. Stellar Rotation and Magnetic Fields: 6. Stellar rotation: a historical survey Leon Mestel; 7. The oscillations of rapidly rotating stars Michel Rieutord; 8. Solar tachocline dynamics: eddy viscosity, anti-friction, or something in between? Michael E. McIntyre; 9. Dynamics of the solar tachocline Pascale Garaud; 10. Dynamo processes: the interaction of turbulence and magnetic fields Michael Proctor; 11. Dynamos in planets Chris Jones; Part III. Physics and Structure of Stellar Interiors: 12. Solar constraints on the equation of state Werner Däppen; 13. 3He transport and the solar neutrino problem Chris Jordinson; 14. Mixing in stellar radiation zones Jean-Paul Zahn; 15. Element settling and rotation-induced mixing in slowly rotating stars Sylvie Vauclair; Part IV. Helio- and Asteroseismology: 16. Solar structure and the neutrino problem Hiromoto Shibahashi; 17. Helioseismic data analysis Jesper Schou; 18. Seismology of solar rotation Takashi Sekii; 19. Telechronohelioseismology Alexander Kosovichev; Part V. Large-Scale Numerical Experiments: 20. Bridges between helioseismology and models of convection zone dynamics Juri Toomre; 21. Numerical simulations of the solar convection zone Julian R. Elliott; 22. Modelling solar and stellar magnetoconvection Nigel Weiss; 23. Nonlinear magnetoconvection in the presence of a strong oblique field Keith Julien, Edgar Knobloch and Steven M. Tobias; 24. Simulations of astrophysical fluids Marcus Brüggen; Part VI. Dynamics: 25. A magic electromagnetic field Donald Lynden-Bell; 26. Continuum equations for stellar dynamics Edward A

  4. PREFACE: A Stellar Journey A Stellar Journey

    NASA Astrophysics Data System (ADS)

    Asplund, M.

    2008-10-01

    The conference A Stellar Journey was held in Uppsala, Sweden, 23 27June 2008, in honour of Professor Bengt Gustafsson's 65th birthday. The choice of Uppsala as the location for this event was obvious given Bengt's long-standing association with the city stemming back to his school days. With the exception of a two-year postdoc stint in Copenhagen, five years as professor at Stockholm University and two years as director of the Sigtuna foundation, Bengt has forged his illustrious professional career at Uppsala University. The symposium venue was Museum Gustavianum, once the main building of the oldest university in Scandinavia. The title of the symposium is a paraphrasing of Bengt's popular astronomy book Kosmisk Resa (in English: Cosmic Journey) written in the early eighties. I think this aptly symbolizes his career that has been an astronomical voyage from near to far, from the distant past to the present. The original book title was modified slightly to reflect that most of his work to date has dealt with stars in one way or another. In addition it also gives credit to Bengt's important role as a guiding light for a very large number of students, colleagues and collaborators, indeed for several generations of astronomers. For me personally, the book Kosmisk Resa bears particular significance as it has shaped my life rather profoundly. Although I had already decided to become an astronomer, when I first read the book as a 14-year-old I made up my mind then and there that I would study under Bengt Gustafsson and work on stars. Indeed I have remained true to this somewhat audacious resolution. I suspect that a great number of us have similar stories how Bengt has had a major influence on our lives, whether on the professional or personal level. Perhaps Bengt's most outstanding characteristic is his enthralling enthusiasm. This is equally true whether he is pondering some scientific conundrum, supervising students or performing in front of an audience, be it an

  5. Fred's Contributions to Stellar Evolution

    NASA Astrophysics Data System (ADS)

    Mestel, L.

    2003-07-01

    Fred began work on stellar structure after Hans Bethe and Carl-Friedrich von Weizsäcker had independently established that the thermonuclear fusion of hydrogen into helium is the primary source of the energy radiated by the Sun and other main sequence stars. A joint paper with Ray Lyttleton included this temperature-sensitive process explicitly in the energy equation, effectively vindicating the essentials of the theory of homogeneous gaseous stars presented in Sir Arthur Eddington's celebrated monograph `The Internal Constitution of the Stars'. Agreement with the solar luminosity can be obtained with two alternative values for the hydrogen content. In a subsequent paper, Fred argued convincingly in favour of the case with a very high rather than a moderate fraction of hydrogen. An epoch-making joint paper with Martin Schwarzschild followed the evolution of a low mass star through nuclear processing, from the main sequence into the giant domain in the Hertzsprung-Russell diagram. The slowly growing, burnt-out core becomes degenerate and nearly isothermal, while the photospheric boundary condition forces the expanding envelope to become largely convective. At the top of the giant branch, the degenerate core becomes hot enough for the fusion of helium into carbon; the consequent secular instability, noted first in studies of white dwarfs, brings the star down to the `horizontal branch', the location of the short-period globular cluster Cepheids. Two subsequent papers with Brian Haselgrove studied in further detail the structure of both main sequence and giant stars.

  6. Stellar Feedback of the First Binaries

    NASA Astrophysics Data System (ADS)

    Chen, Ke-Jung; Bromm, Volker; Heger, Alexander

    2015-08-01

    We present the results from our cosmological simulations of impacts of the first binaries. Recent results of the Pop III star formation suggest that those stars tend to form into binaries or multiple stellar systems, so the Pop III stars could be less massive than we originally thought. It implies most Pop III stars would die as core-collapse supernovae (CCSNe) instead of pair-instability supernovae (PSNe). CCSNe and PSNe have very different nucleosynthesis products and explosion energies that could significantly affect the chemical enrichment in the IGM. Besides, the results from stellar archeology also suggested the Pop III CCSN models could produce abundance patterns in good accord with the observation of metal poor stars. We use the recent results of Pop III stellar models and their nucleosynthesis products as initial inputs for our cosmological simulations and trace the transport of ejected metals to study their chemical impacts to the early universe. We will discusses how stellar feedback from the first binaries affects the primordial IGM, the major building block of the first galaxies.

  7. Anisotropic charged core envelope star

    NASA Astrophysics Data System (ADS)

    Mafa Takisa, P.; Maharaj, S. D.

    2016-08-01

    We study a charged compact object with anisotropic pressures in a core envelope setting. The equation of state is quadratic in the core and linear in the envelope. There is smooth matching between the three regions: the core, envelope and the Reissner-Nordström exterior. We show that the presence of the electric field affects the masses, radii and compactification factors of stellar objects with values which are in agreement with previous studies. We investigate in particular the effect of electric field on the physical features of the pulsar PSR J1614-2230 in the core envelope model. The gravitational potentials and the matter variables are well behaved within the stellar object. We demonstrate that the radius of the core and the envelope can vary by changing the parameters in the speed of sound.

  8. Progress Toward Attractive Stellarators

    SciTech Connect

    Neilson, G H; Brown, T G; Gates, D A; Lu, K P; Zarnstorff, M C; Boozer, A H; Harris, J H; Meneghini, O; Mynick, H E; Pomphrey, N; Reiman, A H; Xanthopoulos, P

    2011-01-05

    The quasi-axisymmetric stellarator (QAS) concept offers a promising path to a more compact stellarator reactor, closer in linear dimensions to tokamak reactors than previous stellarator designs. Concept improvements are needed, however, to make it more maintainable and more compatible with high plant availability. Using the ARIES-CS design as a starting point, compact stellarator designs with improved maintenance characteristics have been developed. While the ARIES-CS features a through-the-port maintenance scheme, we have investigated configuration changes to enable a sector-maintenance approach, as envisioned for example in ARIES AT. Three approaches are reported. The first is to make tradeoffs within the QAS design space, giving greater emphasis to maintainability criteria. The second approach is to improve the optimization tools to more accurately and efficiently target the physics properties of importance. The third is to employ a hybrid coil topology, so that the plasma shaping functions of the main coils are shared more optimally, either with passive conductors made of high-temperature superconductor or with local compensation coils, allowing the main coils to become simpler. Optimization tools are being improved to test these approaches.

  9. A Stellar Demonstrator

    ERIC Educational Resources Information Center

    Ros, Rosa M.

    2009-01-01

    The main purpose of the stellar demonstrator is to help explain the movement of stars. In particular, students have difficulties understanding why, if they are living in the Northern Hemisphere, they may observe starts in the Southern Hemisphere, or why circumpolar stars are not the same in different parts of Europe. Using the demonstrator, these…

  10. Opacity of stellar matter

    SciTech Connect

    Rogers, F J

    1998-09-17

    New efforts to calculate opacity have produced significant improvements in the quality of stellar models. The most dramatic effect has been large opacity enhancements for stars subject to large amplitude pulsations. Significant improvement in helioseismic modeling has also been obtained. A description and comparisons of the new opacity efforts are give

  11. Stellar Ontogeny: From Dust...

    ERIC Educational Resources Information Center

    MOSAIC, 1978

    1978-01-01

    Discusses the process of star formation. Infrared and radio astronomy, particularly microwave astronomy is used to provide information on different stages of stellar formation. The role of dust and gas which swirl through the interstellar regions of a galaxy and the collapse of a cloud in star formation are also presented. (HM)

  12. Trends of stellar entropy along stellar evolution

    NASA Astrophysics Data System (ADS)

    de Avellar, Guilherme Bronzato, Marcio; Alvares de Souza, Rodrigo; Horvath, Jorge Ernesto

    2016-02-01

    This paper is devoted to discussing the difference in the thermodynamic entropy budget per baryon in each type of stellar object found in the Universe. We track and discuss the actual decrease of the stored baryonic thermodynamic entropy from the most primitive molecular cloud up to the final fate of matter in black holes, passing through evolved states of matter as found in white dwarfs and neutron stars. We then discuss the case of actual stars with different masses throughout their evolution, clarifying the role of the virial equilibrium condition for the decrease in entropy and related issues. Finally, we discuss the role of gravity in driving the composition and the structural changes of stars with different Main Sequence masses during their evolution up to the final product. Particularly, we discuss the entropy of a black hole in this context arguing that the dramatic increase in its entropy, differently from the other cases, is due to the gravitational field itself.

  13. Stellar dynamic spectroscopy

    NASA Astrophysics Data System (ADS)

    Bastian, T. S.; Dulk, G. A.; Bookbinder, J. A.

    The dynamic spectrum, a three dimensional record of the radio intensity as a function both of time and frequency, has long been used as a probe of plasma processes in the solar corona. Beginning with the work of Wild and McCready (1950) dynamic spectroscopy has been used to distinguish between the multitude of radio wave emitting phenomena which occur in the solar corona and to infer the physical mechanisms responsible. Stellar dynamic spectroscopy has always been a tantalizing prospect. The vast body of experience with solar dynamic spectroscopy would prove invaluable in interpreting stellar dynamic spectra. Further, the new parameter regimes presented by stellar coronas would allow further insight to be gained in the physical processes at work in stellar coronas. Recently, Bastian and Bookbinder (1987) used the Very Large Array The National Radio Astronomy Observatory is operated by Associated Universities, Inc. under contract with the National Science Foundation. in spectral line mode at 1.4 GHz with a bandwidth of 50 MHz to obtain the first dynamic spectra of nearby flare stars. The spectral resolution was 3.125 MHz and the temporal resolution was 5 s. While the relative bandwidth was less than ideal (δν/ν ˜ 5%), the spectra so obtained were sufficient to show the presence of narrowband structure in a radio outburst from the well-known dMe flare star UV Ceti. Several efforts are now underway to obtain stellar dynamic spectra, of both RS CVn binaries and dMe flare stars, with higher degrees of spectral and temporal resolution. Among these are use of a 1024 channel correlator with the 1000' telescope at Arecibo and use of the Berkeley Fast Pulsar Search Machine (Kulkarni et al. 1984) with the Green Bank 140' telescope.

  14. Stellar Pulsations and Stellar Evolution: Conflict, Cohabitation, or Symbiosis?

    NASA Astrophysics Data System (ADS)

    Weiss, Achim

    While the analysis of stellar pulsations allows the determination of current properties of a star, stellar evolution models connect it with its previous history. In many cases results from both methods do not agree. In this review some classical and current cases of disagreement are presented. In some cases these conflicts led to an improvement of the theory of stellar evolution, while in others they still remain unsolved. Some well-known problems of stellar physics are pointed out as well, for which it is hoped that seismology—or in general the analysis of stellar pulsations—will help to resolve them. The limits of this symbiosis will be discussed as well.

  15. Stellar feedback in dwarf galaxy formation.

    PubMed

    Mashchenko, Sergey; Wadsley, James; Couchman, H M P

    2008-01-11

    Dwarf galaxies pose substantial challenges for cosmological models. In particular, current models predict a dark-matter density that is divergent at the center, which is in sharp contrast with observations that indicate a core of roughly constant density. Energy feedback, from supernova explosions and stellar winds, has been proposed as a major factor shaping the evolution of dwarf galaxies. We present detailed cosmological simulations with sufficient resolution both to model the relevant physical processes and to directly assess the impact of stellar feedback on observable properties of dwarf galaxies. We show that feedback drives large-scale, bulk motions of the interstellar gas, resulting in substantial gravitational potential fluctuations and a consequent reduction in the central matter density, bringing the theoretical predictions in agreement with observations. PMID:18048653

  16. Stellar activity: Astrophysics relevant to global change

    NASA Technical Reports Server (NTRS)

    Haisch, Bernhard M.

    1994-01-01

    FRESIP will obtain a great deal of data on stellar activity and flares on F, G and K dwarfs. Rotation periods, flare distributions and possibly stellar cycles will emerge. This apparently curiosity-driven research actually has implications for our understanding of global climate change. Significant climate change during the seventeenth-century Maunder Minimum is thought to be related to a change in the solar condition. Recently acquired data from the Greenland Ice-core Project suggest that far greater climate changes on decade time scales may have occurred during the previous interglacial. It is possible that a yet more drastic change in state of the Sun was responsible. We have no relevant solar data, but can begin to explore this possibility by observing an ensemble of solar-like stars.

  17. The Stellar Observations Network Group - first results

    NASA Astrophysics Data System (ADS)

    Antoci, Victoria; Grundahl, Frank; Christensen-Dalsgaard, Joergen; Kjeldsen, Hans

    2015-08-01

    SONG - the Stellar Observations Network Group is a Danish-led project set to design and build a global network of 1-m telescopes to carry out detailed studies of solar-like stars using asteroseismology and to discover and characterise exo-planets and their star system. Here we present more than 100 nights of high-precision radial velocity measurements from 2014 of the subgiant mu Herculis. Preliminary analyses of the largest ground-based data set ever obtained for such as star clearly show the detection of stochastically excited pressure modes. The high quality of our data allows unique extraction of individual modes over many orders in the frequency spectrum, leading to studies of rotation, convection, near-surface effects, core structure using mixed modes and stellar activity.

  18. Involvement of membrane proteins and ion channels on the self-rotation of human cells in a non-rotating AC electric field.

    PubMed

    Vaillier, Clarisse; Honegger, Thibault; Kermarrec, Frédérique; Gidrol, Xavier; Peyrade, David

    2015-05-01

    Dielectrophoresis is a force that has been exploited in microsystems for label-free characterization and separation of cells, when their electrical signature is known. However, the polarization effect of cells at the transmembrane protein level is not well established. In this work, we have use the self-rotation effect of cells in a non-rotating field, known as the "Quincke effect," in order to measure the maximum rotation frequency (frotmax ) of different cell populations when modifying the composition of their membrane. We investigated the influence of active ionic transportation of membrane protein concentration on frotmax of HEK cells. Our results show that ionic transportation is responsible for the reduction of conductivity within the cytoplasm, which results in higher frotmax . However, the influence of the concentration of proteins in the membrane, achieved by silencing gene expression in cancer cells, changes significantly frotmax , which is not explained by the changes of ionic conductivity within the cell. PMID:25808576

  19. Absolute stellar photometry on moderate-resolution FPA images

    USGS Publications Warehouse

    Stone, T.C.

    2009-01-01

    An extensive database of star (and Moon) images has been collected by the ground-based RObotic Lunar Observatory (ROLO) as part of the US Geological Survey program for lunar calibration. The stellar data are used to derive nightly atmospheric corrections for the observations from extinction measurements, and absolute calibration of the ROLO sensors is based on observations of Vega and published reference flux and spectrum data. The ROLO telescopes were designed for imaging the Moon at moderate resolution, thus imposing some limitations for the stellar photometry. Attaining accurate stellar photometry with the ROLO image data has required development of specialized processing techniques. A key consideration is consistency in discriminating the star core signal from the off-axis point spread function. The analysis and processing methods applied to the ROLO stellar image database are described. ?? 2009 BIPM and IOP Publishing Ltd.

  20. Stellar Dynamics around a Massive Black Hole I: Secular Collisionless Theory

    NASA Astrophysics Data System (ADS)

    Sridhar, S.; Touma, Jihad R.

    2016-03-01

    We present a theory in three parts, of the secular dynamics of a (Keplerian) stellar system of mass M orbiting a black hole of mass M• ≫ M. Here we describe the collisionless dynamics; Papers II and III are on the (collisional) theory of Resonant Relaxation. The mass ratio, ε = M/M• ≪ 1, is a natural small parameter implying a separation of time scales between the short Kepler orbital periods and the longer orbital precessional periods. The collisionless Boltzmann equation (CBE) for the stellar distribution function (DF) is averaged over the fast Kepler orbital phase using the method of multiple scales. The orbit-averaged system is described by a secular DF, F, in a reduced phase space. F obeys a secular CBE that includes stellar self-gravity, general relativistic corrections up to 1.5 post-Newtonian order, and external sources varying over secular times. Secular dynamics, even with general time dependence, conserves the semi-major axis of every star. This additional integral of motion promotes extra regularity of the stellar orbits, and enables the construction of equilibria, F0, through a secular Jeans theorem. A linearized secular CBE determines the response and stability of F0. Spherical, non-rotating equilibria may support long-lived, warp-like distortions. We also prove that an axisymmetric, zero-thickness, flat disc is secularly stable to all in-plane perturbations, when its DF, F0, is a monotonic function of the angular momentum at fixed energy.

  1. Stellar dynamics around a massive black hole - I. Secular collisionless theory

    NASA Astrophysics Data System (ADS)

    Sridhar, S.; Touma, Jihad R.

    2016-06-01

    We present a theory in three parts, of the secular dynamics of a (Keplerian) stellar system of mass M orbiting a black hole of mass M• ≫ M. Here we describe the collisionless dynamics; Papers II and III are on the (collisional) theory of resonant relaxation. The mass ratio, ε = M/M• ≪ 1, is a natural small parameter implying a separation of time-scales between the short Kepler orbital periods and the longer orbital precessional periods. The collisionless Boltzmann equation (CBE) for the stellar distribution function (DF) is averaged over the fast Kepler orbital phase using the method of multiple scales. The orbit-averaged system is described by a secular DF, F, in a reduced phase space. F obeys a secular CBE that includes stellar self-gravity, general relativistic corrections up to 1.5 post-Newtonian order, and external sources varying over secular times. Secular dynamics, even with general time dependence, conserves the semimajor axis of every star. This additional integral of motion promotes extra regularity of the stellar orbits, and enables the construction of equilibria, F0, through a secular Jeans theorem. A linearized secular CBE determines the response and stability of F0. Spherical, non-rotating equilibria may support long-lived, warp-like distortions. We also prove that an axisymmetric, zero-thickness, flat disc is secularly stable to all in-plane perturbations, when its DF, F0, is a monotonic function of the angular momentum at fixed energy.

  2. Constraints on stellar evolution from white dwarf asteroseismology

    NASA Astrophysics Data System (ADS)

    Bischoff-Kim, Agnès

    2015-01-01

    High mass and low mass stars follow a similar evolution until the inert core phase that follows the end of the core helium burning stage. In particular, one common phase of stellar evolution is the alpha capture reaction that turns carbon into oxygen in the core. We can obtain constraints on this reaction rate by studying the remnants of low mass stars, as this is the ultimate reaction that occurs in their core. We also present results that allow us to test the time dependent calculations of diffusion in dense interiors.

  3. Stellar radio emission (Review)

    NASA Astrophysics Data System (ADS)

    Zhelezniakov, V. V.

    The current understanding of the radio-emission characteristics of 'ordinary' main sequence stars as well as giants and supergiants is examined. Particular consideration is given to radio emission from supergiants, Young T Tauri stars, magnetic Ap stars, flare stars of UV Ceti type, Alpha Sco, and RS CVn objects. It is noted that the study of stellar radio emission is in its initial stage. Further progress in this area depends on successes in finding new radio sources, associated, for example, with magnetic stars, and on an intensified investigation of the frequency spectra and polarization of already-discovered radio stars. It is also noted that, although the current knowledge of solar physics can help in understanding stellar radio emission, models and ideas developed for solar conditions should not be mechanically transferred to other stars by a simple change in scale.

  4. Stellar Inertial Navigation Workstation

    NASA Technical Reports Server (NTRS)

    Johnson, W.; Johnson, B.; Swaminathan, N.

    1989-01-01

    Software and hardware assembled to support specific engineering activities. Stellar Inertial Navigation Workstation (SINW) is integrated computer workstation providing systems and engineering support functions for Space Shuttle guidance and navigation-system logistics, repair, and procurement activities. Consists of personal-computer hardware, packaged software, and custom software integrated together into user-friendly, menu-driven system. Designed to operate on IBM PC XT. Applied in business and industry to develop similar workstations.

  5. Chaos and stellar streams

    NASA Astrophysics Data System (ADS)

    Price-Whelan, Adrian M.; Johnston, Kathryn V.; Valluri, Monica; Pearson, Sarah; Kupper, Andreas Hans Wilhelm; Hogg, David W.

    2016-01-01

    Cosmological simulations predict that dark matter halos around galaxies should be triaxial in shape with universal density profiles. A significant number of orbits in such systems are chaotic, though it is commonly assumed that chaos is not dynamically relevant for galaxy halos because the timescales over which chaos is computed to be important are generally long relative to the dynamical time. In recent work, we showed that even when chaos is not important for restructuring the global structure of a galaxy, chaos can greatly enhance the density evolution and alter the morphologies of stellar streams over just a few orbital times by causing streams to 'fan out.' This occurs because the orbits of the stars in stellar streams have small distributions of fundamental frequencies and are therefore sensitive to mild chaos that modulates the frequencies on small-scales over much faster timescales. This suggests that the morphology of tidal streams alone can be used to estimate the significance of chaos along the orbits of the progenitor systems, thereby placing constraints on the global properties of the gravitational potential. I will explain our theoretical understanding of this phenomenon and discuss implications for a recently discovered stellar stream (the Ophiuchus stream) that may be on a chaotic orbit in the inner Milky Way due to the influence of the time-dependent, triaxial potential of the Galactic bar.

  6. Massive Stars: Stellar Populations

    NASA Astrophysics Data System (ADS)

    Bianchi, Luciana

    2007-07-01

    Massive stars dominate the chemical and dynamical evolution of the ISM, and ultimately of their parent galaxy and the universe, because of their fast evolution and intense supersonic winds. Four decades ago, the first rocket UV spectra of massive stars revealed the importance of mass loss and began to change our understanding of their evolution. Recently, advances in stellar modeling, and the observation of crucial ions in the far-UV spectral range, led to the resolution of long-standing issues in our understanding of massive star atmospheres. A revised (downwards) calibration of Teff for early spectral types is emerging as a result. Meanwhile, HST imaging, and large ground-based telescopes with multislit spectroscopic capabilities, had opened the possibility of resolved studies of stellar populations in Local Group galaxies, which sample a variety of metallicity and environment conditions. More recently, GALEX is providing a global, deep view of the young stellar populations for hundreds of nearby galaxies, revealing their recent star-formation history and modalities. The wide-field coverage and sensitivity of the GALEX UV imaging, easily detecting extremely low levels of star formation, is again changing some of our views on massive star formation in galaxies.

  7. Convective Overshoot in Stellar Interior

    NASA Astrophysics Data System (ADS)

    Zhang, Q. S.

    2015-07-01

    clusters Hyades, Praesepe, NGC6633, NGC752, NGC3680, and M67, using the model and parameter same to the solar case to deal with the convective envelope overshoot mixing, the lithium abundances on the surface of the stellar models were consistent with the observations. In the case of the binary HY Vir, the same model and parameter also make the radii and effective temperatures of HY Vir stars with convective cores be consistent with the observations. Based on the implications of the above results, we found that the simple overshoot mixing model may need to be improved significantly. Motivated by those implications, we established a new model of the overshoot mixing based on the fluid dynamic equations, and worked out the diffusion coefficient of convective mixing. The diffusion coefficient shows different behaviors in convection zone and overshoot region. In the overshoot region, the buoyancy does negative works on flows, thus the fluid flows around the equilibrium location, which leads to a small scale and low efficiency of overshoot mixing. The physical properties are significantly different from the classical NMLT, and consistent with the helioseismic studies and numerical simulations. The new model was tested in stellar evolution, and its parameter was calibrated.

  8. The impact of stellar evolution on planetary system development

    NASA Technical Reports Server (NTRS)

    Bodenheimer, Peter

    1989-01-01

    The connection between stellar evolution and planet formation is investigated. Particular attention is given to the problem posed by the fact that the formation of Jupiter occurred before the formation of Mars and that the formation of the solid core of Saturn was completed before the dissipation of the gas in the nebula. Several possible solutions to this problem are suggested.

  9. Stellar Spectroscopy during Exoplanet Transits: Revealing structures across stellar surfaces

    NASA Astrophysics Data System (ADS)

    Dravins, Dainis; Ludwig, Hans-Günter; Dahlén, Erik

    2015-08-01

    Exoplanet transits permit to study stellar surface portions that successively become hidden behind the planet. Differential spectroscopy between various transit phases reveals spectra of those stellar surface segments that were hidden. The deduced center-to-limb behavior of stellar spectral line shapes, asymmetries and wavelength shifts enables detailed tests of 3-dimensional hydrodynamic models of stellar atmospheres, such that are required for any precise determination of abundances or seismic properties. Such models can now be computed for widely different classes of stars (including metal-poor ones and white dwarfs), but have been feasible to test and verify only for the Sun with its resolved surface structure. Exoplanet transits may also occur across features such as starspots, whose magnetic signatures will be retrieved from spectra of sufficient fidelity.Knowing the precise background stellar spectra, also properties of exoplanet atmospheres are better constrained: e.g., the Rossiter-McLaughlin effect becomes resolved as not only a simple change of stellar wavelength, but as a variation of the full line profiles and their asymmetries.Such studies are challenging since exoplanets cover only a tiny fraction of the stellar disk. Current work, analyzing sequences of high-fidelity ESO UVES spectra, demonstrate that such spatially resolved stellar spectra can already be (marginally) retrieved in a few cases with the brightest host stars. Already in a near future, ongoing exoplanet surveys are likely to find further bright hosts that will enable such studies for various stellar types. http://arxiv.org/abs/1408.1402

  10. Using modern stellar observables to constrain stellar parameters and the physics of the stellar interior

    NASA Astrophysics Data System (ADS)

    van Saders, Jennifer L.

    2014-05-01

    The current state and future evolution of a star is, in principle, specified by a only a few physical quantities: the mass, age, hydrogen, helium, and metal abundance. These same fundamental quantities are crucial for reconstructing the history of stellar systems ranging in scale from planetary systems to galaxies. However, the fundamental parameters are rarely directly observable, and we are forced to use proxies that are not always sensitive or unique functions of the stellar parameters we wish to determine. Imprecise or inaccurate determinations of the fundamental parameters often limit our ability to draw inferences about a given system. As new technologies, instruments, and observing techniques become available, the list of viable stellar observables increases, and we can explore new links between the observables and fundamental quantities in an effort to better characterize stellar systems. In the era of missions such as Kepler, time-domain observables such as the stellar rotation period and stellar oscillations are now available for an unprecedented number of stars, and future missions promise to further expand the sample. Furthermore, despite the successes of stellar evolution models, the processes and detailed structure of the deep stellar interior remains uncertain. Even in the case of well-measured, well understood stellar observables, the link to the underlying parameters contains uncertainties due to our imperfect understanding of stellar interiors. Model uncertainties arise from sources such as the treatment of turbulent convection, transport of angular momentum and mixing, and assumptions about the physical conditions of stellar matter. By carefully examining the sensitivity of stellar observables to physical processes operating within the star and model assumptions, we can design observational tests for the theory of stellar interiors. I propose a series of tools based on new or revisited stellar observables that can be used both to constrain

  11. Stellar structure of magnetars

    NASA Astrophysics Data System (ADS)

    Dong, JianMin; Zuo, Wei; Gu, JianZhong; Shang, XinLe

    2016-04-01

    Magnetars are strong magnetized neutron stars which could emit quiescent X-ray, repeating burst of soft gamma ray, and even the giant flares. We investigate the effects of magnetic fields on the structure of isolated magnetars. The stellar structure together with the magnetic field configuration can be obtained at the same time within a self-consistent procedure. The magnetar mass and radius are found to be weakly enhanced by the strong magnetic fields. Unlike other previous investigations, the magnetic field is unable to violate the mass limit of the neutron stars.

  12. Stellar figure sensor

    NASA Technical Reports Server (NTRS)

    Peters, W. N.

    1973-01-01

    A compilation of analytical and experimental data is presented concerning the stellar figure sensor. The sensor is an interferometric device which is located in the focal plane of an orbiting large space telescope (LST). The device was designed to perform interferometry on the optical wavefront of a single star after it has propagated through the LST. An analytical model of the device was developed and its accuracy was verified by an operating laboratory breadboard. A series of linear independent control equations were derived which define the operations required for utilizing a focal plane figure sensor in the control loop for the secondary mirror position and for active control of the primary mirror.

  13. A Stellar Highway

    NASA Astrophysics Data System (ADS)

    Rijsdijk, Case

    2015-10-01

    Thomas Henderson, at the Royal Observatory of the Cape, was the first person to measure the distance to a star in 1834. Robert Innes, at the Union Observatory in Johannesburg, discovered that Proxima Centauri was the nearest star to the Sun in 1915. The idea of marking the 100th anniversary of the discovery of Proxima Centauri in 2015 led to the development of a Stellar Highway, similar to the well-known scale models of the Solar System or Planetary Highways, but showing the scaled distance between stars.

  14. Period change and stellar evolution of β Cephei stars

    NASA Astrophysics Data System (ADS)

    Neilson, Hilding R.; Ignace, Richard

    2015-12-01

    The β Cephei stars represent an important class of massive star pulsators that probe the evolution of B-type stars and the transition from main sequence to hydrogen-shell burning evolution. By understanding β Cep stars, we gain insights into the detailed physics of massive star evolution, including rotational mixing, convective core overshooting, magnetic fields, and stellar winds, all of which play important roles. Similarly, modeling their pulsation provides additional information into their interior structures. Furthermore, measurements of the rate of change of pulsation period offer a direct measure of β Cephei stellar evolution. In this work, we compute state-of-the-art stellar evolution models assuming different amounts of initial rotation and convective core overshoot and measure the theoretical rates of period change, that we compare to rates previously measured for a sample of β Cephei stars. The results of this comparison are mixed. For three stars, the rates are too low to infer any information from stellar evolution models, whereas for three other stars the rates are too high. We infer stellar parameters, such as mass and age, for two β Cephei stars: ξ1 CMa and δ Cet, which agree well with independent measurements. We explore ideas for why models may not predict the higher rates of period change. In particular, period drifts in β Cep stars can artificially lead to overestimated rates of secular period change.

  15. Distinctive translational and self-rotational motion of lymphoma cells in an optically induced non-rotational alternating current electric field

    PubMed Central

    Zhang, Ke; Yang, Xieliu; Liu, Lianqing; Yu, Haibo; Zhang, Weijing

    2015-01-01

    In this paper, the translational motion and self-rotational behaviors of the Raji cells, a type of B-cell lymphoma cell, in an optically induced, non-rotational, electric field have been characterized by utilizing a digitally programmable and optically activated microfluidics chip with the assistance of an externally applied AC bias potential. The crossover frequency spectrum of the Raji cells was studied by observing the different linear translation responses of these cells to the positive and negative optically induced dielectrophoresis force generated by a projected light pattern. This digitally projected spot served as the virtual electrode to generate an axisymmetric and non-uniform electric field. Then, the membrane capacitance of the Raji cells could be directly measured. Furthermore, Raji cells under this condition also exhibited a self-rotation behavior. The repeatable and controlled self-rotation speeds of the Raji cells to the externally applied frequency and voltage were systematically investigated and characterized via computer-vision algorithms. The self-rotational speed of the Raji cells reached a maximum value at 60 kHz and demonstrated a quadratic relationship with respect to the applied voltage. Furthermore, optically projected patterns of four orthogonal electrodes were also employed as the virtual electrodes to manipulate the Raji cells. These results demonstrated that Raji cells located at the center of the four electrode pattern could not be self-rotated. Instead any Raji cells that deviated from this center area would also self-rotate. Most importantly, the Raji cells did not exhibit the self-rotational behavior after translating and rotating with respect to the center of any two adjacent electrodes. The spatial distributions of the electric field generated by the optically projected spot and the pattern of four electrodes were also modeled using a finite element numerical simulation. These simulations validated that the electric field

  16. Distinctive translational and self-rotational motion of lymphoma cells in an optically induced non-rotational alternating current electric field.

    PubMed

    Liang, Wenfeng; Zhang, Ke; Yang, Xieliu; Liu, Lianqing; Yu, Haibo; Zhang, Weijing

    2015-01-01

    In this paper, the translational motion and self-rotational behaviors of the Raji cells, a type of B-cell lymphoma cell, in an optically induced, non-rotational, electric field have been characterized by utilizing a digitally programmable and optically activated microfluidics chip with the assistance of an externally applied AC bias potential. The crossover frequency spectrum of the Raji cells was studied by observing the different linear translation responses of these cells to the positive and negative optically induced dielectrophoresis force generated by a projected light pattern. This digitally projected spot served as the virtual electrode to generate an axisymmetric and non-uniform electric field. Then, the membrane capacitance of the Raji cells could be directly measured. Furthermore, Raji cells under this condition also exhibited a self-rotation behavior. The repeatable and controlled self-rotation speeds of the Raji cells to the externally applied frequency and voltage were systematically investigated and characterized via computer-vision algorithms. The self-rotational speed of the Raji cells reached a maximum value at 60 kHz and demonstrated a quadratic relationship with respect to the applied voltage. Furthermore, optically projected patterns of four orthogonal electrodes were also employed as the virtual electrodes to manipulate the Raji cells. These results demonstrated that Raji cells located at the center of the four electrode pattern could not be self-rotated. Instead any Raji cells that deviated from this center area would also self-rotate. Most importantly, the Raji cells did not exhibit the self-rotational behavior after translating and rotating with respect to the center of any two adjacent electrodes. The spatial distributions of the electric field generated by the optically projected spot and the pattern of four electrodes were also modeled using a finite element numerical simulation. These simulations validated that the electric field

  17. Stellar activity cycles and asteroseismology

    NASA Astrophysics Data System (ADS)

    Salabert, D.

    2011-12-01

    The success of helioseismology is due to its capability to accurately measure the p-mode parameters of the solar eigenmode spectrum, which allow us to infer unique information about the internal structure and dynamics of the Sun from its surface all the way down to the core. It has contributed greatly to a clearer understanding of the Sun and provided insights into the complex solar magnetism, by means for instance of the variability of the characteristics of the p-mode spectrum. Indeed, variations in the mean strength of the solar magnetic field lead to significant shifts in the frequencies of even the lowest-degree p modes with high levels of correlation with solar surface activity proxies. These frequency shifts are explained to arise from structural changes in the outer layers of the Sun during the 11-year activity cycle, which is understood to be driven by a dynamo process. However, clear differences between p-mode frequencies and solar surface activity during the unusually extended minimum of cycle 23 were observed. The origin of the p-mode variability is thus far from being properly understood and a better comprehension of its relationship with solar and stellar activity cycles will help us in our understanding of the dynamo processes. Spectroscopic measurements of Ca H and K emission lines revealed magnetic activity variations in a large sample of solar-type stars with timescales ranging from 2.5 and 25 years. This broad range of cycle periods is thought to reflect differences in the rotational properties and the depths of the surface convection zones with various masses and ages. However, spectroscopic measurements are only good proxies of surface magnetic fields. The recent discovery of variations with magnetic activity in the p-mode oscillation frequencies of the solar-like star HD 49933 observed by CoRoT, with a frequency dependence comparable in shape to the one observed in the Sun, opens a new era in the study of the physical phenomena involved in the

  18. Stellar Evolution Physics 2 Volume Hardback Set

    NASA Astrophysics Data System (ADS)

    Iben, Icko

    2012-12-01

    Volume 1: Part I. Introduction and Overview: 1. Qualitative description of single and binary star evolution; 2. Quantitative foundations of stellar evolution theory; Part II. Basic Physical Processes in Stellar Interiors: 3. Properties of and physical processes in the interiors of main sequence stars - order of magnitude estimates; 4. Statistical physics, thermodynamics, and equations of state; 5. Polytropes and single zone models: elementary tools for understanding some aspects of stellar structure and evolution; 6. Hydrogen-burning nuclear reactions and energy-generation rates; 7. Photon-matter interactions and opacity; 8. Equations of stellar evolution and methods of solution; Part III. Pre-Main Sequence, Main Sequence, and Shell Hydrogen Burning Evolution of Single Stars: 9. Star formation and evolution to the main-sequence; 10. Solar structure and neutrino physics; 11. Evolution during core hydrogen-burning phases up to the onset of helium burning; Volume 2: Part IV. Transport Processes, Weak Interaction Processes and Helium-Burning Reactions: 12. Diffusion and gravitational settling; 13. Heat conduction by electrons; 14. Beta decay and electron capture at high densities in stars; 15. The current-current weak interaction and the production of neutrino-antineutrino pairs; 16. Helium-burning nuclear reactions and energy-generation rates; Part V. Evolution during Helium-Burning Phases: 17. Evolution of a low mass model burning helium and hydrogen; 18. Evolution of an intermediate mass model burning helium and hydrogen; 19. Neutron production and neutron capture in a thermally pulsing asymptotic giant branch star of intermediate mass; 20. Evolution of a massive population I model during helium- and carbon-burning stages; Part VI. Terminal Evolution of Low and Intermediate Mass Stars: 21. Wind mass loss on the AGB and formation of a circumstellar envelope, evolution of the remnant as the central star of a planetary nebula, and white dwarf evolution; Index.

  19. New Insights into Stellar Astrophysics from High-Precision Photometry

    NASA Astrophysics Data System (ADS)

    Soderblom, David R.

    2013-01-01

    The rich harvest of information on the occurrence and nature of planets around solar-type stars is why Kepler was built, but equally profound from this mission are the insights and quantitative physical studies of stars. The Kepler sample is dominated by the ~100,000 stars that are like the Sun, yet the Kepler field includes examples of nearly every stellar type. Kepler's exquisite photometry - continuously over an extended time - has enabled the detection of new phenomena and has provided critical tests of stellar models. In this brief review I will summarize some of the exciting new findings that Kepler has made possible, including: Stellar surface granulation in late-type stars; Evidence for rapid rotation of the cores of some evolved stars; Flares on G, K and M stars; Precise ages for older solar-type stars; Evidence for "mixed" modes in evolved stars that couple p-modes to interior g-modes; Stellar differential rotation; Detection of stellar activity cycles from asteroseismology; Mixing processes in stars; Detailed studies of eclipsing binaries; A comparison of the Sun to similar stars; Pulsating stars; Stellar surface features revealed by planet transits.

  20. Starspots and Stellar Rotation: Stellar Activity with Kepler

    NASA Astrophysics Data System (ADS)

    Walkowicz, L. M.; Basri, G. S.

    2011-12-01

    While the telescopic study of starspots dates back to Galileos observations of our own Sun, recent space-borne photometric missions (such as MOST, CoRoT, and Kepler) are opening a new window into understanding these ubiquitous manifestations of stellar activity. Because of the intimate link between stellar rotation and the generation of the magnetic field, starspots cause a modulation in the lightcurve at the rate of stellar rotation. To complicate matters, stars rotate differentially, so the stellar rotation rate is not really best characterized by a single value but rather by a range of rotation rates. Through high-precision, long-term photometric monitoring of stars of different spectral types and activity strengths, it is possible to determine stellar rotation rates and differential rotation measures. In addition, modeling these lightcurves can tell us about the properties of stellar spots, such as location, areal coverage, and lifetime. New observations provide precision photometry for a large cohort of stars, ranging from Sun-like to rather different stellar properties, at a spread of ages, making these lightcurves a powerful tool for understanding magnetic activity for stars of all activity levels. Here, I will discuss how Kepler can provide new insight into the continuum of stellar activity and our own Suns place amongst the stars.

  1. Confronting uncertainties in stellar physics. II. Exploring differences in main-sequence stellar evolution tracks

    NASA Astrophysics Data System (ADS)

    Stancliffe, R. J.; Fossati, L.; Passy, J.-C.; Schneider, F. R. N.

    2016-02-01

    We assess the systematic uncertainties in stellar evolutionary calculations for low- to intermediate-mass, main-sequence stars. We compare published stellar tracks from several different evolution codes with our own tracks computed using the stellar codes stars and mesa. In particular, we focus on tracks of 1 and 3 M⊙ at solar metallicity. We find that the spread in the available 1 M⊙ tracks (computed before the recent solar composition revision) can be covered by tracks between 0.97-1.01 M⊙ computed with the stars code. We assess some possible causes of the origin of this uncertainty, including how the choice of input physics and the solar constraints used to perform the solar calibration affect the tracks. We find that for a 1 M⊙ track, uncertainties of around 10% in the initial hydrogen abundance and initial metallicity produce around a 2% error in mass. For the 3 M⊙ tracks, there is very little difference between the tracks from the various different stellar codes. The main difference comes in the extent of the main sequence, which we believe results from the different choices of the implementation of convective overshooting in the core. Uncertainties in the initial abundances lead to a 1-2% error in the mass determination. These uncertainties cover only part of the total error budget, which should also include uncertainties in the input physics (e.g., reaction rates, opacities, convective models) and any missing physics (e.g., radiative levitation, rotation, magnetic fields). Uncertainties in stellar surface properties such as luminosity and effective temperature will further reduce the accuracy of any potential mass determinations.

  2. [Megaduodenum with non-rotation].

    PubMed

    Lambrecht, W; Gürtler, K F

    1983-06-01

    In a 16-year-old girl who suffered from non-characteristic upper abdominal complaints, the gastrointestinal passage revealed an extreme megaduodenum associated with nonrotation. Intraoperatively, congenital adhesions were found as cause which had stenosed the duodenojejunal transition and had become fixed in the right upper abdomen. After separating the adhesions, resecting the stenosis and narrowing the duodenum, intestinal continuity was restored by means of an end-to side duodenojejunostomy. The causes, signs, diagnosis and therapy of the megaduodenum are discussed. PMID:6637118

  3. Chromospheric activity and stellar evolution

    NASA Technical Reports Server (NTRS)

    Kippenhahn, R.

    1973-01-01

    A study of stellar chromospheres based on the internal structure of particular stars is presented. Used are complex flow diagrams of the linkage paths between mass loss, angular momentum loss, magnetic field from the turbulent dynamo and its relations to differential rotations and the convection zone, and stellar evolution.

  4. Three-dimensional stellarator codes

    PubMed Central

    Garabedian, P. R.

    2002-01-01

    Three-dimensional computer codes have been used to develop quasisymmetric stellarators with modular coils that are promising candidates for a magnetic fusion reactor. The mathematics of plasma confinement raises serious questions about the numerical calculations. Convergence studies have been performed to assess the best configurations. Comparisons with recent data from large stellarator experiments serve to validate the theory. PMID:12140367

  5. Radioactive elements in stellar atmospheres

    SciTech Connect

    Gopka, Vira; Yushchenko, Alexander; Goriely, Stephane; Shavrina, Angelina; Kang, Young Woon

    2006-07-12

    The identification of lines of radioactive elements (Tc, Pm and elements with 83stellar atmospheres, contamination of stellar atmosphere by recent SN explosion, and spallation reactions.

  6. SUPER-CRITICAL GROWTH OF MASSIVE BLACK HOLES FROM STELLAR-MASS SEEDS

    SciTech Connect

    Madau, Piero; Haardt, Francesco; Dotti, Massimo

    2014-04-01

    We consider super-critical accretion with angular momentum onto stellar-mass black holes as a possible mechanism for growing billion-solar-mass black holes from light seeds at early times. We use the radiatively inefficient ''slim disk'' solution—advective, optically thick flows that generalize the standard geometrically thin disk model—to show how mildly super-Eddington intermittent accretion may significantly ease the problem of assembling the first massive black holes when the universe was less than 0.8 Gyr old. Because of the low radiative efficiencies of slim disks around non-rotating as well as rapidly rotating black holes, the mass e-folding timescale in this regime is nearly independent of the spin parameter. The conditions that may lead to super-critical growth in the early universe are briefly discussed.

  7. The Solar-Stellar Connection

    NASA Astrophysics Data System (ADS)

    Brun, A. S.; García, R. A.; Houdek, G.; Nandy, D.; Pinsonneault, M.

    2015-12-01

    We discuss how recent advances in observations, theory and numerical simulations have allowed the stellar community to progress in its understanding of stellar convection, rotation and magnetism and to assess the degree to which the Sun and other stars share similar dynamical properties. Ensemble asteroseismology has become a reality with the advent of large time domain studies, especially from space missions. This new capability has provided improved constraints on stellar rotation and activity, over and above that obtained via traditional techniques such as spectropolarimetry or CaII H&K observations. New data and surveys covering large mass and age ranges have provided a wide parameter space to confront theories of stellar magnetism. These new empirical databases are complemented by theoretical advances and improved multi-D simulations of stellar dynamos. We trace these pathways through which a lucid and more detailed picture of magnetohydrodynamics of solar-like stars is beginning to emerge and discuss future prospects.

  8. The stellar opacities

    NASA Astrophysics Data System (ADS)

    Turck-Chièze, S.; Gilles, D.; Gilleron, F.; Pain, J. C.

    2013-11-01

    Opacities are fundamental ingredients of stellar physics. Helioseismology and asteroseismology have put in evidence anomalies that could be attributed to an insufficient knowledge of the photon-plasma interactions. We work on a revision of this plasma physics in the conditions where the anomalies have been found: the region of the iron opacity peak near log T= 5.2 and the inner radiative region of Sun and solar-like stars. The international OPAC consortium performs new calculations, compares them and looks for the origin of their differences. In parallel, experimental campaigns are realized, others are in preparation to validate some conclusions on the reliability of the new proposed calculations. New tables for astrophysics will be performed in the framework of the ANR OPACITY and their influence on seismic observables will be studied. We explicit here the difficulty of the computations together with some computation resources.

  9. Early stellar evolution

    NASA Technical Reports Server (NTRS)

    Stahler, Steven W.

    1994-01-01

    Research into the formation and early evolution of stars is currently an area of great interest and activity. The theoretical and observational foundations for this development are reviewed in this paper. By now, the basic physics governing cloud collapse is well understood, as is the structure of the resulting protostars. However, the theory predicts protostellar luminosities that are greater than those of most infrared sources. Observationally, it is thought that protostars emit powerful winds that push away remnant cloud gas, but both the origin of these winds and the nature of their interaction with ambient gas are controversial. Finally, the theory of pre-main-sequence stars has been modified to incorporate more realistic initial conditions. This improvement helps to explain the distribution of such stars in the H-R diagram. Many important issues, such as the origin of binary stars and stellar clusters, remain as challenges for future research.

  10. Stellar radio emission

    NASA Technical Reports Server (NTRS)

    Bookbinder, Jay A.

    1988-01-01

    This paper presents an overview of the various radiation mechanisms believed to play a role in stellar radio emission. The radio emission from most stars is nonthermal and is generally due to mildly relativistic electrons with energies from a few keV to over 10 MeV. Magnetic fields play a crucial role both in accelerating the electrons to the requisite energies and in mediating the emission mechanism. They also play a fundamental role in creating the velocity anisotropies that are necessary for the operation of some of the coherent emission mechanisms. Coherent emission is seen most commonly on the M dwarfs, rarely on the RS CVns, and has yet to be detected for any other class of star. These coherent processes are best studied by means of their dynamic spectra; such studies are now just getting underway.

  11. Asteroseismic stellar activity relations

    NASA Astrophysics Data System (ADS)

    Bonanno, A.; Corsaro, E.; Karoff, C.

    2014-11-01

    Context. In asteroseismology an important diagnostic of the evolutionary status of a star is the small frequency separation which is sensitive to the gradient of the mean molecular weight in the stellar interior. It is thus interesting to discuss the classical age-activity relations in terms of this quantity. Moreover, as the photospheric magnetic field tends to suppress the amplitudes of acoustic oscillations, it is important to quantify the importance of this effect by considering various activity indicators. Aims: We propose a new class of age-activity relations that connects the Mt. Wilson S index and the average scatter in the light curve with the small frequency separation and the amplitude of the p-mode oscillations. Methods: We used a Bayesian inference to compute the posterior probability of various empirical laws for a sample of 19 solar-like active stars observed by the Kepler telescope. Results: We demonstrate the presence of a clear correlation between the Mt. Wilson S index and the relative age of the stars as indicated by the small frequency separation, as well as an anti-correlation between the S index and the oscillation amplitudes. We argue that the average activity level of the stars shows a stronger correlation with the small frequency separation than with the absolute age that is often considered in the literature. Conclusions: The phenomenological laws discovered in this paper have the potential to become new important diagnostics to link stellar evolution theory with the dynamics of global magnetic fields. In particular we argue that the relation between the Mt. Wilson S index and the oscillation amplitudes is in good agreement with the findings of direct numerical simulations of magneto-convection.

  12. Alaska Athabascan stellar astronomy

    NASA Astrophysics Data System (ADS)

    Cannon, Christopher M.

    Stellar astronomy is a fundamental component of Alaska Athabascan cultures that facilitates time-reckoning, navigation, weather forecasting, and cosmology. Evidence from the linguistic record suggests that a group of stars corresponding to the Big Dipper is the only widely attested constellation across the Northern Athabascan languages. However, instruction from expert Athabascan consultants shows that the correlation of these names with the Big Dipper is only partial. In Alaska Gwich'in, Ahtna, and Upper Tanana languages the Big Dipper is identified as one part of a much larger circumpolar humanoid constellation that spans more than 133 degrees across the sky. The Big Dipper is identified as a tail, while the other remaining asterisms within the humanoid constellation are named using other body part terms. The concept of a whole-sky humanoid constellation provides a single unifying system for mapping the night sky, and the reliance on body-part metaphors renders the system highly mnemonic. By recognizing one part of the constellation the stargazer is immediately able to identify the remaining parts based on an existing mental map of the human body. The circumpolar position of a whole-sky constellation yields a highly functional system that facilitates both navigation and time-reckoning in the subarctic. Northern Athabascan astronomy is not only much richer than previously described; it also provides evidence for a completely novel and previously undocumented way of conceptualizing the sky---one that is unique to the subarctic and uniquely adapted to northern cultures. The concept of a large humanoid constellation may be widespread across the entire subarctic and have great antiquity. In addition, the use of cognate body part terms describing asterisms within humanoid constellations is similarly found in Navajo, suggesting a common ancestor from which Northern and Southern Athabascan stellar naming strategies derived.

  13. Stellar 'Incubators' Seen Cooking up Stars

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site] Figure 1

    [figure removed for brevity, see original site] [figure removed for brevity, see original site] Figure 2Figure 3Figure 4Figure 5

    This image composite compares visible-light and infrared views from NASA's Spitzer Space Telescope of the glowing Trifid Nebula, a giant star-forming cloud of gas and dust located 5,400 light-years away in the constellation Sagittarius.

    Visible-light images of the Trifid taken with NASA's Hubble Space Telescope, Baltimore, Md. (inside left, figure 1) and the National Optical Astronomy Observatory, Tucson, Ariz., (outside left, figure 1) show a murky cloud lined with dark trails of dust. Data of this same region from the Institute for Radioastronomy millimeter telescope in Spain revealed four dense knots, or cores, of dust (outlined by yellow circles), which are 'incubators' for embryonic stars. Astronomers thought these cores were not yet ripe for stars, until Spitzer spotted the warmth of rapidly growing massive embryos tucked inside.

    These embryos are indicated with arrows in the false-color Spitzer picture (right, figure 1), taken by the telescope's infrared array camera. The same embryos cannot be seen in the visible-light pictures (left, figure 1). Spitzer found clusters of embryos in two of the cores and only single embryos in the other two. This is one of the first times that multiple embryos have been observed in individual cores at this early stage of stellar development.

  14. Observational techniques to measure solar and stellar oscillations

    NASA Astrophysics Data System (ADS)

    García, R. A.

    2015-02-01

    As said by Sir A. Eddington in 1925: "Our telescopes may probe farther and farther into the depths of space. At first sight it would seem that the deep interior of the sun and stars is less accessible to scientific investigation than any other region of the universe. What appliance can pierce through the outer layers of a star and test the conditions within?" Eddington ([89]). Nowadays, asteroseismology has proven its ability to pierce below stellar photospheres and allow us to "see" inside the interior of thousands of stars down to the stellar cores, answering the question asked by Eddington ninety years ago. In this chapter we review the general properties of the spectral analysis which is the base of any asteroseismic investigation. After describing the stellar power spectrum, we will describe in details the characterization of the modal spectrum. This chapter will end by a brief description of the instrumentation in both helio and asteroseismology.

  15. Astrospheres and Stellar Bow shocks

    NASA Astrophysics Data System (ADS)

    Van Marle, Allard Jan

    2016-07-01

    As stars evolve, they deliver feedback to the surrounding medium in the form of stellar wind and radiation. These shape the surrounding matter, forming what is called an astrosphere, a sphere of influence in which the star dominates the morphology and composition of the surrounding medium. Astrospheres are fascinating objects. Because they are formed through the interaction between the stellar feedback and the interstellar gas, they can tell us a great deal about both. Furthermore, because they are shaped over time they provide us with a window into the past. This is of particular interest for the study of stellar evolution, because the astrosphere reflects changes in the properties of the stellar wind, which relate directly to the properties of the star. A special sub-class of astrospheres, the stellar bow shocks, occur when the progenitor star moves through the surrounding medium at supersonic speed. Because the properties of the bow shock relate directly to both the stellar wind and the interstellar medium, the shape and size of the bow shock can be used to determine these properties. Using state-of-the-art numerical codes, it is possible to simulate the interaction between the stellar wind and radiation and the interstellar medium. These results can then be compared to observations. They can also be used to predict the type of observations that are best suited to study these objects. In this fashion computational and observational astronomy can support each other in their efforts to gain a better understanding of stars and their environment.

  16. Extreme Low Aspect Ratio Stellarators

    NASA Astrophysics Data System (ADS)

    Moroz, Paul

    1997-11-01

    Recently proposed Spherical Stellarator (SS) concept [1] includes the devices with stellarator features and low aspect ratio, A <= 3.5, which is very unusual for stellarators (typical stellarators have A ≈ 7-10 or above). Strong bootstrap current and high-β equilibria are two distinguished elements of the SS concept leading to compact, steady-state, and efficient fusion reactor. Different coil configurations advantageous for the SS have been identified and analyzed [1-6]. In this report, we will present results on novel stellarator configurations which are unusual even for the SS approach. These are the extreme-low-aspect-ratio-stellarators (ELARS), with the aspect ratio A ≈ 1. We succeeded in finding ELARS configurations with extremely compact, modular, and simple design compatible with significant rotational transform (ι ≈ 0.1 - 0.15), large plasma volume, and good particle transport characteristics. [1] P.E. Moroz, Phys. Rev. Lett. 77, 651 (1996); [2] P.E. Moroz, Phys. Plasmas 3, 3055 (1996); [3] P.E. Moroz, D.B. Batchelor et al., Fusion Tech. 30, 1347 (1996); [4] P.E. Moroz, Stellarator News 48, 2 (1996); [5] P.E. Moroz, Plasma Phys. Reports 23, 502 (1997); [6] P.E. Moroz, Nucl. Fusion 37, No. 8 (1997). *Supported by DOE Grant No. DE-FG02-97ER54395.

  17. Stellar Snowflake Cluster

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site] Figure 1 Stellar Snowflake Cluster Combined Image [figure removed for brevity, see original site] Figure 2 Infrared Array CameraFigure 3 Multiband Imaging Photometer

    Newborn stars, hidden behind thick dust, are revealed in this image of a section of the Christmas Tree cluster from NASA's Spitzer Space Telescope, created in joint effort between Spitzer's infrared array camera and multiband imaging photometer instruments.

    The newly revealed infant stars appear as pink and red specks toward the center of the combined image (fig. 1). The stars appear to have formed in regularly spaced intervals along linear structures in a configuration that resembles the spokes of a wheel or the pattern of a snowflake. Hence, astronomers have nicknamed this the 'Snowflake' cluster.

    Star-forming clouds like this one are dynamic and evolving structures. Since the stars trace the straight line pattern of spokes of a wheel, scientists believe that these are newborn stars, or 'protostars.' At a mere 100,000 years old, these infant structures have yet to 'crawl' away from their location of birth. Over time, the natural drifting motions of each star will break this order, and the snowflake design will be no more.

    While most of the visible-light stars that give the Christmas Tree cluster its name and triangular shape do not shine brightly in Spitzer's infrared eyes, all of the stars forming from this dusty cloud are considered part of the cluster.

    Like a dusty cosmic finger pointing up to the newborn clusters, Spitzer also illuminates the optically dark and dense Cone nebula, the tip of which can be seen towards the bottom left corner of each image.

    This combined image shows the presence of organic molecules mixed with dust as wisps of green, which have been illuminated by nearby star formation. The larger yellowish dots neighboring the baby red stars in the Snowflake Cluster are massive stellar infants forming

  18. The Hibernating Stellar Magnet

    NASA Astrophysics Data System (ADS)

    2008-09-01

    First Optically Active Magnetar-Candidate Discovered Astronomers have discovered a most bizarre celestial object that emitted 40 visible-light flashes before disappearing again. It is most likely to be a missing link in the family of neutron stars, the first case of an object with an amazingly powerful magnetic field that showed some brief, strong visible-light activity. Hibernating Stellar Magnet ESO PR Photo 31/08 The Hibernating Stellar Magnet This weird object initially misled its discoverers as it showed up as a gamma-ray burst, suggesting the death of a star in the distant Universe. But soon afterwards, it exhibited some unique behaviour that indicates its origin is much closer to us. After the initial gamma-ray pulse, there was a three-day period of activity during which 40 visible-light flares were observed, followed by a brief near-infrared flaring episode 11 days later, which was recorded by ESO's Very Large Telescope. Then the source became dormant again. "We are dealing with an object that has been hibernating for decades before entering a brief period of activity", explains Alberto J. Castro-Tirado, lead author of a paper in this week's issue of Nature. The most likely candidate for this mystery object is a 'magnetar' located in our own Milky Way galaxy, about 15 000 light-years away towards the constellation of Vulpecula, the Fox. Magnetars are young neutron stars with an ultra-strong magnetic field a billion billion times stronger than that of the Earth. "A magnetar would wipe the information from all credit cards on Earth from a distance halfway to the Moon," says co-author Antonio de Ugarte Postigo. "Magnetars remain quiescent for decades. It is likely that there is a considerable population in the Milky Way, although only about a dozen have been identified." Some scientists have noted that magnetars should be evolving towards a pleasant retirement as their magnetic fields decay, but no suitable source had been identified up to now as evidence for

  19. Stellar populations of stellar halos: Results from the Illustris simulation

    NASA Astrophysics Data System (ADS)

    Cook, B. A.; Conroy, C.; Pillepich, A.; Hernquist, L.

    2016-08-01

    The influence of both major and minor mergers is expected to significantly affect gradients of stellar ages and metallicities in the outskirts of galaxies. Measurements of observed gradients are beginning to reach large radii in galaxies, but a theoretical framework for connecting the findings to a picture of galactic build-up is still in its infancy. We analyze stellar populations of a statistically representative sample of quiescent galaxies over a wide mass range from the Illustris simulation. We measure metallicity and age profiles in the stellar halos of quiescent Illustris galaxies ranging in stellar mass from 1010 to 1012 M ⊙, accounting for observational projection and luminosity-weighting effects. We find wide variance in stellar population gradients between galaxies of similar mass, with typical gradients agreeing with observed galaxies. We show that, at fixed mass, the fraction of stars born in-situ within galaxies is correlated with the metallicity gradient in the halo, confirming that stellar halos contain unique information about the build-up and merger histories of galaxies.

  20. SI: The Stellar Imager

    NASA Technical Reports Server (NTRS)

    Carpenter, Kenneth G.; Schrijver, Carolus J.; Karovska, Margarita

    2006-01-01

    The ultra-sharp images of the Stellar Imager (SI) will revolutionize our view of many dynamic astrophysical processes: The 0.1 milliarcsec resolution of this deep-space telescope will transform point sources into extended sources, and simple snapshots into spellbinding evolving views. SI s science focuses on the role of magnetism in the Universe, particularly on magnetic activity on the surfaces of stars like the Sun. SI s prime goal is to enable long-term forecasting of solar activity and the space weather that it drives in support of the Living With a Star program in the Exploration Era by imaging a sample of magnetically active stars with enough resolution to map their evolving dynamo patterns and their internal flows. By exploring the Universe at ultra-high resolution, SI will also revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magnetohydrodynamically controlled structures and processes in the Universe.

  1. Stellar duplicity and nucleosynthesis

    NASA Astrophysics Data System (ADS)

    Izzard, Rob

    2014-09-01

    Half or more of all stars more massive than our Sun are orbited by one (or more) companion stars. Many companions are close enough that the evolution of both stars is greatly altered by the transfer of mass and angular momentum from one star to the other. Such mass transfer is highly likely during the late stages of evolution, such as on the giant branches, which are quite coincidentally also when stars undergo interesting nucleosynthesis. Direct mass transfer truncates the (A)GB prematurely compared to single stars and the ensuing stellar envelope is ejected perhaps to form a (chemically peculiar?) planetary nebula. In wider binaries, where one star has captured material from a long-dead companion, we can probe the nucleosynthesis that happened in ancient stars as well as fundamental astrophysical phenomena like wind accretion and circumbinary disc formation. I will focus on recent quantitative work on nucleosynthesis in mass-transfer systems, such as carbon-enhanced metal-poor and barium stars, and highlight some of the key open questions - and opportunities - that will dominate the next decade of duplicitous nucleosynthesis.

  2. Devastated Stellar Neighborhood

    NASA Technical Reports Server (NTRS)

    2008-01-01

    This image from NASA's Spitzer Space Telescope shows the nasty effects of living near a group of massive stars: radiation and winds from the massive stars (white spot in center) are blasting planet-making material away from stars like our sun. The planetary material can be seen as comet-like tails behind three stars near the center of the picture. The tails are pointing away from the massive stellar furnaces that are blowing them outward.

    The picture is the best example yet of multiple sun-like stars being stripped of their planet-making dust by massive stars.

    The sun-like stars are about two to three million years old, an age when planets are thought to be growing out of surrounding disks of dust and gas. Astronomers say the dust being blown from the stars is from their outer disks. This means that any Earth-like planets forming around the sun-like stars would be safe, while outer planets like Uranus might be nothing more than dust in the wind.

    This image shows a portion of the W5 star-forming region, located 6,500 light-years away in the constellation Cassiopeia. It is a composite of infrared data from Spitzer's infrared array camera and multiband imaging photometer. Light with a wavelength of 3.5 microns is blue, while light from the dust of 24 microns is orange-red.

  3. Ultraviolet stellar astronomy

    NASA Technical Reports Server (NTRS)

    Henize, K. G.; Wray, J. D.; Kondo, Y.; Ocallaghan, F. (Principal Investigator)

    1975-01-01

    The author has identified the following significant results. During all three Skylab missions, prism-on observations were obtained in 188 starfields and prism-off observations in 31 starfields. In general, the fields are concentrated in the Milky Way where the frequency of hot stars is highest. These fields cover an area approximately 3660 degrees and include roughly 24 percent of a band 30 deg wide centered on the plane of the Milky Way. A census of stars in the prism-on fields shows that nearly 6,000 stars have measurable flux data at a wavelength of 2600A, that 1,600 have measurable data at 2000A, and that 400 show useful data at 1500A. Obvious absorption or emission features shortward of 2000A are visible in approximately 120 stars. This represents a bonanza of data useful for statistical studies of stellar classification and of interstellar reddening as well as for studies of various types of peculiar stars.

  4. The Narrabri Stellar Intensity Interferometer: a 50th birthday tribute

    NASA Astrophysics Data System (ADS)

    Tuthill, Peter G.

    2014-07-01

    This year marks the 50th anniversary since the first scientific measurements were produced with the Narrabri Stellar Intensity Interferometer, which was constructed in the early 1960's by Robert Hanbury Brown and Richard Twiss. A collaboration between the Universities of Sydney and Manchester, the interferometer was the culmination of a series of experiments which pioneered the technique of intensity interferometry. The immediate controversy surrounding the quantum implications of the technique enveloped some of the most eminent physicists of the day, sparking a debate about nonlocal effects and optical coherence. A full explanation of the workings of the intensity interferometer in a quantum context was finally put forward by Roy Glauber, ultimately earning him the 2005 Nobel Prize in Physics. The intensity interferometer rekindled the field of high resolution stellar imaging, which had been extinguished for a half century (following the failure of Pease's 50-foot beam on Mt Wilson), while delivering the first ever measurements of the sizes of normal stars - establishing an effective temperature scaling relationship which has underpinned stellar astronomy for 50 years. This directly paved the way for the next generation of Michelson Stellar Interferometers. Intensity interferometry itself has found application in several fields (notably particle physics), and plans are in active development for modern reprises within stellar interferometry. However undoubtedly the greatest legacy lies in the Hanbury Brown Twiss (HBT) effect being the foundational experiment for what is now known as Quantum Optics - a field which underpins a huge sector of the technology which enables our modern world. This invited review discuses the development of the interferometer, including the controversy that its underlying principles generated within the contemporary physics community. The core scientific output generated by the instrument is presented, together with the impact of the

  5. Asteroseismic Signatures of Evolving Internal Stellar Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Cantiello, Matteo; Fuller, Jim; Bildsten, Lars

    2016-06-01

    Recent asteroseismic analyses indicate the presence of strong (B ≳ 105 G) magnetic fields in the cores of many red giant stars. Here, we examine the implications of these results for the evolution of stellar magnetic fields, and we make predictions for future observations. Those stars with suppressed dipole modes indicative of strong core fields should exhibit moderate but detectable quadrupole mode suppression. The long magnetic diffusion times within stellar cores ensure that dynamo-generated fields are confined to mass coordinates within the main-sequence (MS) convective core, and the observed sharp increase in dipole mode suppression rates above 1.5 M ⊙ is likely explained by the larger convective core masses and faster rotation of these more massive stars. In clump stars, core fields of ∼105 G can suppress dipole modes, whose visibility should be equal to or less than the visibility of suppressed modes in ascending red giants. High dipole mode suppression rates in low-mass (M ≲ 2 M ⊙) clump stars would indicate that magnetic fields generated during the MS can withstand subsequent convective phases and survive into the compact remnant phase. Finally, we discuss implications for observed magnetic fields in white dwarfs and neutron stars, as well as the effects of magnetic fields in various types of pulsating stars.

  6. UNIFYING THE ZOO OF JET-DRIVEN STELLAR EXPLOSIONS

    SciTech Connect

    Lazzati, Davide; Blackwell, Christopher H.; Morsony, Brian J.; Begelman, Mitchell C.

    2012-05-01

    We present a set of numerical simulations of stellar explosions induced by relativistic jets emanating from a central engine sitting at the center of compact, dying stars. We explore a wide range of durations of the central engine activity, two candidate stellar progenitors, and two possible values of the total energy release. We find that even if the jets are narrowly collimated, their interaction with the star unbinds the stellar material, producing a stellar explosion. We also find that the outcome of the explosion can be very different depending on the duration of the engine activity. Only the longest-lasting engines result in successful gamma-ray bursts. Engines that power jets only for a short time result in relativistic supernova (SN) explosions, akin to observed engine-driven SNe such as SN2009bb. Engines with intermediate durations produce weak gamma-ray bursts, with properties similar to nearby bursts such as GRB 980425. Finally, we find that the engines with the shortest durations, if they exist in nature, produce stellar explosions that lack sizable amounts of relativistic ejecta and are therefore dynamically indistinguishable from ordinary core-collapse SNe.

  7. Unifying the Zoo of Jet-driven Stellar Explosions

    NASA Astrophysics Data System (ADS)

    Lazzati, Davide; Morsony, Brian J.; Blackwell, Christopher H.; Begelman, Mitchell C.

    2012-05-01

    We present a set of numerical simulations of stellar explosions induced by relativistic jets emanating from a central engine sitting at the center of compact, dying stars. We explore a wide range of durations of the central engine activity, two candidate stellar progenitors, and two possible values of the total energy release. We find that even if the jets are narrowly collimated, their interaction with the star unbinds the stellar material, producing a stellar explosion. We also find that the outcome of the explosion can be very different depending on the duration of the engine activity. Only the longest-lasting engines result in successful gamma-ray bursts. Engines that power jets only for a short time result in relativistic supernova (SN) explosions, akin to observed engine-driven SNe such as SN2009bb. Engines with intermediate durations produce weak gamma-ray bursts, with properties similar to nearby bursts such as GRB 980425. Finally, we find that the engines with the shortest durations, if they exist in nature, produce stellar explosions that lack sizable amounts of relativistic ejecta and are therefore dynamically indistinguishable from ordinary core-collapse SNe.

  8. Optimizing Stellarators for Turbulent Transport

    SciTech Connect

    H.E. Mynick, N.Pomphrey, and P. Xanthopoulos

    2010-05-27

    Up to now, the term "transport-optimized" stellarators has meant optimized to minimize neoclassical transport, while the task of also mitigating turbulent transport, usually the dominant transport channel in such designs, has not been addressed, due to the complexity of plasma turbulence in stellarators. Here, we demonstrate that stellarators can also be designed to mitigate their turbulent transport, by making use of two powerful numerical tools not available until recently, namely gyrokinetic codes valid for 3D nonlinear simulations, and stellarator optimization codes. A first proof-of-principle configuration is obtained, reducing the level of ion temperature gradient turbulent transport from the NCSX baseline design by a factor of about 2.5.

  9. Inferred properties of stellar granulation

    SciTech Connect

    Gray, D.F.; Toner, C.G.

    1985-06-01

    Apparent characteristics of stellar granulation in F and G main-sequence stars are inferred directly from observed spectral-line asymmetries and from comparisons of numerical simulations with the observations: (1) the apparent granulation velocity increases with effective temperature, (2) the dispersion of granule velocities about their mean velocity of rise increases with the apparent granulation velocity, (3) the mean velocity of rise of granules must be less than the total line broadening, (4) the apparent velocity difference between granules and dark lanes corresponds to the granulation velocity deduced from stellar line bisectors, (5) the dark lanes show velocities of fall approximately twice as large as the granule rise velocities, (6) the light contributed to the stellar flux by the granules is four to ten times more than the light from the dark lanes. Stellar rotation is predicted to produce distortions in the line bisectors which may give information on the absolute velocity displacements of the line bisectors. 37 references.

  10. Comparison of Hyperonic Equations of State for Core Collapse Supernovae Simulations

    NASA Astrophysics Data System (ADS)

    Char, Prasanta; Banik, Sarmistha

    In this work, we study the dynamical collapse of a non rotating massive star to a black hole using relativistic supernova equations of state (EoS) incorporating Λ hyperons which would be populated, due to Pauli exclusion principle, in the dense matter region after the core collapse. We use 1D GR hydrodynamic code GR1D for our numerical simulations and compare the properties of the currently available hyperonic equations of state.

  11. Solar and stellar coronal plasmas

    NASA Technical Reports Server (NTRS)

    Golub, L.

    1985-01-01

    Progress made in describing and interpreting coronal plasma processes and the relationship between the solar corona and its stellar counterparts is reported. Topics covered include: stellar X-ray emission, HEAO 2 X-ray survey of the Pleiades, closed coronal structures, X-ray survey of main-sequence stars with shallow convection zones, implications of the 1400 MHz flare emission, and magnetic field stochasticity.

  12. STELLAR POPULATION VARIATIONS IN THE MILKY WAY's STELLAR HALO

    SciTech Connect

    Bell, Eric F.; Xue Xiangxiang; Rix, Hans-Walter; Ruhland, Christine; Hogg, David W.

    2010-12-15

    If the stellar halos of disk galaxies are built up from the disruption of dwarf galaxies, models predict highly structured variations in the stellar populations within these halos. We test this prediction by studying the ratio of blue horizontal branch stars (BHB stars; more abundant in old, metal-poor populations) to main-sequence turn-off stars (MSTO stars; a feature of all populations) in the stellar halo of the Milky Way using data from the Sloan Digital Sky Survey. We develop and apply an improved technique to select BHB stars using ugr color information alone, yielding a sample of {approx}9000 g < 18 candidates where {approx}70% of them are BHB stars. We map the BHB/MSTO ratio across {approx}1/4 of the sky at the distance resolution permitted by the absolute magnitude distribution of MSTO stars. We find large variations of the BHB/MSTO star ratio in the stellar halo. Previously identified, stream-like halo structures have distinctive BHB/MSTO ratios, indicating different ages/metallicities. Some halo features, e.g., the low-latitude structure, appear to be almost completely devoid of BHB stars, whereas other structures appear to be rich in BHB stars. The Sagittarius tidal stream shows an apparent variation in the BHB/MSTO ratio along its extent, which we interpret in terms of population gradients within the progenitor dwarf galaxy. Our detection of coherent stellar population variations between different stellar halo substructures provides yet more support to cosmologically motivated models for stellar halo growth.

  13. EARLY EVOLUTION OF PRESTELLAR CORES

    SciTech Connect

    Horedt, G. P.

    2013-08-20

    Prestellar cores are approximated by singular polytropic spheres. Their early evolution is studied analytically with a Bondi-like scheme. The considered approximation is meaningful for polytropic exponents {gamma} between 0 and 6/5, implying radial power-law density profiles between r {sup -1} and r {sup -2.5}. Gravitationally unstable Jeans and Bonnor-Ebert masses differ at most by a factor of 3.25. Tidally stable prestellar cores must have a mean density contrast {approx}> 8 with respect to the external parent cloud medium. The mass-accretion rate relates to the cube of equivalent sound speed, as in Shu's seminal paper. The prestellar masses accreted over 10{sup 5} years cover the whole stellar mass spectrum; they are derived in simple closed form, depending only on the polytropic equation of state. The stellar masses that can be formed via strict conservation of angular momentum are at most of the order of a brown dwarf.

  14. Physics and chemistry of the late stages of stellar evolution — an introduction

    NASA Astrophysics Data System (ADS)

    Kwok, Sun

    2016-07-01

    The stellar evolution from the asymptotic giant branch (AGB) to planetary nebulae (PN) contains some of the most interesting physical and chemical processes in the Universe. Within a time period of one million years starting from the nucleosynthesis of carbon in the core, we witness the chemical synthesis of molecules in the atmosphere, followed by the condensation of minerals and organics in the stellar outflow. Different phases of supersonic stellar winds, both spherical symmetric and highly collimated, and their interactions lead to a series of dynamical processes and morphological transformation of the stellar ejecta. Most interestingly, PN are now known to be major sources of complex organics in the Galaxy. Organic compounds of mixed aromatic and aliphatic structures have been observed to form in the post-AGB evolution over time scales as short as hundreds of years. There is likely that these stellar organics journeyed through the Galaxy and were embedded in early Solar System.

  15. Progress in the engineering design of the National Compact Stellarator Experiment (NCSX)

    SciTech Connect

    Reiersen, W.T.; Brooks, A.; Brown, T.

    2000-01-21

    The National Compact Stellarator Experiment (NCSX) is a proof-of-principle experiment whose objective is to demonstrate high beta operation in a quasi-axisymmetric stellarator. NCSX will be housed in the Princeton Beta Experiment (PBX-M) test cell. Many of the existing site assets including the test cell, TF and PF coils, power supplies, neutral beam heating systems, and site utilities can be re-used, minimizing the cost of the project. Saddle coils are used in the reference design. The stellarator core is pre-fabricated and dropped into place on the PBX-M platform. The existing TF and PF coils are then reassembled around the stellarator core. Alternate coil topologies are also being explored.

  16. Composite Cores

    NASA Technical Reports Server (NTRS)

    1990-01-01

    Spang & Company's new configuration of converter transformer cores is a composite of gapped and ungapped cores assembled together in concentric relationship. The net effect of the composite design is to combine the protection from saturation offered by the gapped core with the lower magnetizing requirement of the ungapped core. The uncut core functions under normal operating conditions and the cut core takes over during abnormal operation to prevent power surges and their potentially destructive effect on transistors. Principal customers are aerospace and defense manufacturers. Cores also have applicability in commercial products where precise power regulation is required, as in the power supplies for large mainframe computers.

  17. Nucleation of strange matter in dense stellar cores

    SciTech Connect

    Horvath, J.E. Sao Paulo, Sao Paulo ); Benvenuto, O.G. La Plata ); Vucetich, H. La Plata )

    1992-05-15

    We investigate the nucleation of strange quark matter inside hot, dense nuclear matter. Applying Zel'dovich's kinetic theory of nucleation we find a lower limit of the temperature {ital T} for strange-matter bubbles to appear, which happens to be satisfied inside the Kelvin-Helmholtz cooling era of a compact star life but not much after it. Our bounds thus suggest that a prompt conversion could be achieved, giving support to earlier expectations for nonstandard type-II supernova scenarios.

  18. Ring of Stellar Death

    NASA Technical Reports Server (NTRS)

    2004-01-01

    This false-color image from NASA's Spitzer Space Telescope shows a dying star (center) surrounded by a cloud of glowing gas and dust. Thanks to Spitzer's dust-piercing infrared eyes, the new image also highlights a never-before-seen feature -- a giant ring of material (red) slightly offset from the cloud's core. This clumpy ring consists of material that was expelled from the aging star.

    The star and its cloud halo constitute a 'planetary nebula' called NGC 246. When a star like our own Sun begins to run out of fuel, its core shrinks and heats up, boiling off the star's outer layers. Leftover material shoots outward, expanding in shells around the star. This ejected material is then bombarded with ultraviolet light from the central star's fiery surface, producing huge, glowing clouds -- planetary nebulas -- that look like giant jellyfish in space.

    In this image, the expelled gases appear green, and the ring of expelled material appears red. Astronomers believe the ring is likely made of hydrogen molecules that were ejected from the star in the form of atoms, then cooled to make hydrogen pairs. The new data will help explain how planetary nebulas take shape, and how they nourish future generations of stars.

    This image composite was taken on Dec. 6, 2003, by Spitzer's infrared array camera, and is composed of images obtained at four wavelengths: 3.6 microns (blue), 4.5 microns (green), 5.8 microns (orange) and 8 microns (red).

  19. Introduction to stellar astrophysics. Volume 1 - Basic stellar observations and data. Volume 2 - Stellar atmospheres

    NASA Astrophysics Data System (ADS)

    Boehm-Vitense, Erika

    Volume 1: The global properties of stars and the observational techniques used to determine them are examined in an introduction for undergraduate students. Chapters are devoted to stellar positions, proper motions, brightness, color-magnitude diagrams, luminosities, angular radii, and effective temperatures. Also considered are stellar masses and radii, spectral classification, population II stars, stellar rotation, magnetic fields, peculiar spectra, pulsating stars, explosive stars, the sun, and interstellar absorption. Diagrams, graphs, sample images and spectra, tables of numerical constants, and a set of problems are provided. Volume 2: The basic principles used in the study of the outer layers of a star are discussed. The subjects addressed include stellar magnitudes, colors, and spectra; temperature estimates for stars; radiative transfer; depth dependence of the source function; the continuous absorption coefficient; the influence of the nongreyness of the absorption coefficient; pressure stratification; theory of line formation; hydrogen lines; spectrum analysis; nonlocal thermodynamic equilibrium; the hydrogen convection zone; stellar chromospheres, transition layers, and coronae; and stellar winds.

  20. Stellar model chromospheres. VI - Empirical estimates of the chromospheric radiative losses of late-type stars

    NASA Technical Reports Server (NTRS)

    Linsky, J. L.; Ayres, T. R.

    1978-01-01

    A method is developed for estimating the nonradiative heating of stellar chromospheres by measuring the net radiative losses in strong Fraunhofer line cores. This method is applied to observations of the Mg II resonance lines in a sample of 32 stars including the sun. At most a small dependence of chromospheric nonradiative heating on stellar surface gravity is found, which is contrary to the large effect predicted by recent calculations based on acoustic-heating theories.

  1. Dynamics and evolution of dense stellar systems

    NASA Astrophysics Data System (ADS)

    Fregeau, John M.

    2004-10-01

    The research presented in this thesis comprises a theoretical study of several aspects relating to the dynamics and evolution of dense stellar systems such as globular clusters. First, I present the results of a study of mass segregation in two-component star clusters, based on a large number of numerical N-body simulations using our Monte-Carlo code. Heavy objects, which could represent stellar remnants such as neutron stars or black holes, exhibit behavior that is in quantitative agreement with simple analytical arguments. Light objects, which could represent free-floating planets or brown dwarfs, are predominantly lost from the cluster, as expected from simple analytical arguments, but may remain in the halo in larger numbers than expected. Using a recent null detection of planetary-mass microlensing events in M22, I find an upper limit of ˜25% at the 63% confidence level for the current mass fraction of M22 in the form of very low-mass objects. Turning to more realistic clusters, I present a study of the evolution of clusters containing primordial binaries, based on an enhanced version of the Monte-Carlo code that treats binary interactions via cross sections and analytical prescriptions. All models exhibit a long-lived “binary burning” phase lasting many tens of relaxation times. The structural parameters of the models during this phase match well those of most observed Galactic globular clusters. At the end of this phase, clusters that have survived tidal disruption undergo deep core collapse, followed by gravothermal oscillations. The results clearly show that the presence of even a small fraction of binaries in a cluster is sufficient to support the core against collapse significantly beyond the normal core collapse time predicted without the presence of binaries. For tidally truncated systems, collapse is delayed sufficiently that the cluster will undergo complete tidal disruption before core collapse. Moving a step beyond analytical prescriptions, I

  2. Stellar diameters and temperatures. IV. Predicting stellar angular diameters

    SciTech Connect

    Boyajian, Tabetha S.; Van Belle, Gerard; Von Braun, Kaspar

    2014-03-01

    The number of stellar angular diameter measurements has greatly increased over the past few years due to innovations and developments in the field of long baseline optical interferometry. We use a collection of high-precision angular diameter measurements for nearby, main-sequence stars to develop empirical relations that allow the prediction of stellar angular sizes as a function of observed photometric color. These relations are presented for a combination of 48 broadband color indices. We empirically show for the first time a dependence on metallicity of these relations using Johnson (B – V) and Sloan (g – r) colors. Our relations are capable of predicting diameters with a random error of less than 5% and represent the most robust and empirical determinations of stellar angular sizes to date.

  3. Stellar Oxygen Abundances

    NASA Astrophysics Data System (ADS)

    King, Jeremy

    1994-04-01

    This dissertation addresses several issues concerning stellar oxygen abundances. The 7774 {\\AA} O I triplet equivalent widths of Abia & Rebolo [1989, AJ, 347, 186] for metal-poor dwarfs are found to be systematically too high. I also argue that current effective temperatures used in halo star abundance studies may be ~150 K too low. New color-Teff relations are derived for metal-poor stars. Using the revised Teff values and improved equivalent widths for the 7774A O I triplet, the mean [O/Fe] ratio for a handful of halo stars is found to be +0.52 with no dependence on Teff or [Fe/H]. Possible cosmological implications of the hotter Teff scale are discussed along with additional evidence supporting the need for a higher temperature scale for metal-poor stars. Our Teff scale leads to a Spite Li plateau value of N(Li)=2.28 +/- 0.09. A conservative minimal primordial value of N(Li)=2.35 is inferred. If errors in the observations and models are considered, consistency with standard models of Big Bang nucleosynthesis is still achieved with this larger Li abundance. The revised Teff scale raises the observed B/Be ratio of HD 140283 from 10 to 12, making its value more comfortably consistent with the production of the observed B and Be by ordinary spallation. Our Teff values are found to be in good agreement with values predicted from both the Victoria and Yale isochrone color-Teff relations. Thus, it appears likely that no changes in globular cluster ages would result. Next, we examine the location of the break in the [O/Fe] versus [Fe/H] plane in a quantitative fashion. Analysis of a relatively homogeneous data set does not favor any unique break point in the range -1.7 /= -3), in agreement with the new results for halo dwarfs. We find that the gap in the observed [O/H] distribution, noted by Wheeler et al

  4. The Dynamical Evolution of Stellar Black Holes in Globular Clusters

    NASA Astrophysics Data System (ADS)

    Morscher, Meagan; Pattabiraman, Bharath; Rodriguez, Carl; Rasio, Frederic A.; Umbreit, Stefan

    2015-02-01

    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 ⊙. 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 × 106 stars. In almost all models we find that significant numbers of BHs (up to ~103) 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 "mass segregation instability") 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.

  5. THE DYNAMICAL EVOLUTION OF STELLAR BLACK HOLES IN GLOBULAR CLUSTERS

    SciTech Connect

    Morscher, Meagan; Pattabiraman, Bharath; Rodriguez, Carl; Rasio, Frederic A.; Umbreit, Stefan

    2015-02-10

    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{sup 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.

  6. Compact Stellarator Path to DEMO

    NASA Astrophysics Data System (ADS)

    Lyon, J. F.

    2007-11-01

    Issues for a DEMO reactor are sustaining an ignited/high-Q plasma in steady state, avoiding disruptions and large variations in power flux to the wall, adequate confinement of thermal plasma and alpha-particles, control of a burning plasma, particle and power handling, etc. Compact stellarators have key advantages -- steady-state high-plasma-density operation without external current drive or disruptions, stability without a close conducting wall or active feedback systems, and low recirculating power -- in addition to moderate plasma aspect ratio, good confinement, and high-beta potential. The ARIES-CS study established that compact stellarators can be competitive with tokamaks as reactors. Many of the issues for a compact stellarator DEMO can be answered using results from large tokamaks, ITER D-T experiments and fusion materials, technology and component development programs, in addition to stellarators in operation, under construction or in development. However, a large next-generation stellarator will be needed to address some physics issues: size scaling and confinement at higher parameters, burning plasma issues, and operation with a strongly radiative divertor. Technology issues include simpler coils, structure, and divertor fabrication, and better cost information.

  7. Inferences on Stellar Activity and Stellar Cycles from Asteroseismology

    NASA Astrophysics Data System (ADS)

    Chaplin, William J.; Basu, Sarbani

    2014-12-01

    The solar activity cycle can be studied using many different types of observations, such as counting sunspots, measuring emission in the Ca II H&K lines, magnetograms, radio emissions, etc. One of the more recent ways of studying solar activity is to use the changing properties of solar oscillations. Stellar activity cycles are generally studied using the Ca II lines, or sometimes using photometry. Asteroseismology is potentially an exciting means of studying these cycles. In this article we examine whether or not asteroseismic data can be used for this purpose, and what the asteroseismic signatures of stellar activity are. We also examine how asteroseismology may help in more indirect ways.

  8. DIRECT STELLAR RADIATION PRESSURE AT THE DUST SUBLIMATION FRONT IN MASSIVE STAR FORMATION: EFFECTS OF A DUST-FREE DISK

    SciTech Connect

    Tanaka, Kei E. I.; Nakamoto, Taishi

    2011-10-01

    In massive star formation ({approx}> 40 M{sub sun}) by core accretion, the direct stellar radiation pressure acting on the dust particles exceeds the gravitational force and interferes with mass accretion at the dust sublimation front, the first absorption site. Ram pressure generated by high accretion rates of 10{sup -3} M{sub sun} yr{sup -1} is thought to be required to overcome the direct stellar radiation pressure. We investigate the direct stellar irradiation on the dust sublimation front, including the inner accretion disk structure. We show that the ram pressure of the accretion disk is lower than the stellar radiation pressure at the dust sublimation front. Thus, another mechanism must overcome the direct stellar radiation pressure. We suggest that the inner hot dust-free region is optically thick, shielding the dust sublimation front from direct stellar irradiation. Thus, accretion would not halt at the dust sublimation front, even at lower accretion rates.

  9. Stellar Explosions: Hydrodynamics and Nucleosynthesis

    NASA Astrophysics Data System (ADS)

    José, Jordi

    2015-12-01

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

  10. Rotational signature of the Milky Way stellar halo

    NASA Astrophysics Data System (ADS)

    Fermani, Francesco; Schönrich, Ralph

    2013-07-01

    We measure the rotation of the Milky Way stellar halo on two samples of blue horizontal branch (BHB) field halo stars from the Sloan Digital Sky Survey (SDSS) with four different methods. The two samples comprise 1582 and 2563 stars, respectively, and reach out to ˜50 kpc in galactocentric distance. Two of the methods to measure rotation rely exclusively on line-of-sight (l.o.s.) velocities, namely the popular double power-law model and a direct estimate of the de-projected l.o.s. velocity. The other two techniques use the full 3D motions: the radial velocity based rotation estimator of Schönrich et al. and a simple 3D azimuthal velocity mean. In this context we (a) critique the popular model and (b) assess the reliability of the estimators. All four methods agree on a weakly prograde or non-rotating halo. Further, we observe no duality in the rotation of sub-samples with different metallicities or at different radii. We trace the rotation gradient across metallicity measured by Deason et al. on a similar sample of BHB stars back to the inclusion of regions in the apparent magnitude-surface gravity plane known to be contaminated. In the spectroscopically selected sample of Xue et al., we flag ˜500 hot metal-poor stars for their peculiar kinematics w.r.t. to both their cooler metal-poor counterparts and the metal-rich stars in the same sample. They show a seemingly retrograde behaviour in l.o.s. velocities, which is not confirmed by the 3D estimators. Their anomalous vertical motion hints at either a pipeline problem or a stream-like component rather than a smooth retrograde population.

  11. Atomic Data for Stellar Nucleosynthesis

    NASA Astrophysics Data System (ADS)

    Sneden, Christopher Alan; Lawler, James E.; Den Hartog, Elizabeth A.; Wood, Michael

    2015-08-01

    Stellar chemical composition analyses can only yield reliable abundances if the atomic transition parameters are accurately determined. During the last couple of decades a renewed emphasis on laboratory spectroscopy has produced large sets of useful atomic transition probabilities for species of interest to stellar spectroscopists. In many cases the transition data are of such high quality that they play little part in the abundance error budgets. In this talk we will review the current state of atomic parameters, highlighting the areas of satisfactory progress and noting places where further laboratoryprogress will be welcome.

  12. Nucleosynthesis and Stellar Evolution

    NASA Astrophysics Data System (ADS)

    Woosley, S. E.

    Preface I. Nuclear Astrophysics Nuclear cross sections Nuclear reaction rates Approximations to reaction rates for heavy nuclei Nuclear reaction networks II. Nuclear Reactions During Advanced Burning Stages of Massive Stars Carbon burning Neon burning Oxygen burning Silicon burning Nuclear statistical equilibrium (NSE) NSE network calculations Equilibrium at high densities III. Approximate Thermodynamic Conditions for Advanced Burning Stages in Massive Stars Burning in hydrostatic equilibrium Explosive burning conditions IV. Parametrized Network Calculations of Nucleosynthesis Helium Burning Carbon burning Neon burning Oxygen burning Silicon burning Summary V. Classical Novae and X-ray Bursts Classical novae Parametrized nucleosynthesis calculations Numerical calculations of a model nova Type I X-ray bursts VI. The Evolution of Massive Stars; M >= 8 Msun Stars that become type II supernovae Computer results Nucleosynthesis in pre-supernova stars The evolution to instability of more massive stars VII. Type II Supernovae Light curves and spectra of type II supernovae The type II explosion mechanism: core collapse and bounce "Delayed" explosions The role of rotation Nucleosynthesis in type II supernovae Unusual type II supernovae and "type III" supernovae VIII. Type I Supernovae General thermonuclear models The current standard model Nucleosynthesis in the standard model Spectral synthesis in type I supernovae Peculiar Type I's More on the physics of carbon ignition: flame propagation the conductive velocity the "turbulent" flame velocity Carbon detonation: The phase velocity and "spontaneous combustion" Initial conditions References

  13. Deriving Stellar Inclination of Slow Rotators Using Stellar Activity

    NASA Astrophysics Data System (ADS)

    Dumusque, X.

    2014-12-01

    Stellar inclination is an important parameter for many astrophysical studies. Although different techniques allow us to estimate stellar inclination for fast rotators, it becomes much more difficult when stars are rotating slower than ~2-2.5 km s-1. By using the new activity simulation SOAP 2.0 which can reproduce the photometric and spectroscopic variations induced by stellar activity, we are able to fit observations of solar-type stars and derive their inclination. For HD 189733, we estimate the stellar inclination to be i=84+6-20 deg, which implies a star-planet obliquity of \\psi =4+18-4 considering previous measurements of the spin-orbit angle. For α Cen B, we derive an inclination of i=45+9-19, which implies that the rotational spin of the star is not aligned with the orbital spin of the α Cen binary system. In addition, assuming that α Cen Bb is aligned with its host star, no transit would occur. The inclination of α Cen B can be measured using 40 radial-velocity measurements, which is remarkable given that the projected rotational velocity of the star is smaller than 1.15 km s-1. Based on observations made with the MOST satellite, the HARPS instrument on the ESO 3.6 m telescope at La Silla Observatory (Chile), and the SOPHIE instrument at the Observatoire de Haute Provence (France).

  14. Deriving stellar inclination of slow rotators using stellar activity

    SciTech Connect

    Dumusque, X.

    2014-12-01

    Stellar inclination is an important parameter for many astrophysical studies. Although different techniques allow us to estimate stellar inclination for fast rotators, it becomes much more difficult when stars are rotating slower than ∼2-2.5 km s{sup –1}. By using the new activity simulation SOAP 2.0 which can reproduce the photometric and spectroscopic variations induced by stellar activity, we are able to fit observations of solar-type stars and derive their inclination. For HD 189733, we estimate the stellar inclination to be i=84{sub −20}{sup +6} deg, which implies a star-planet obliquity of ψ=4{sub −4}{sup +18} considering previous measurements of the spin-orbit angle. For α Cen B, we derive an inclination of i=45{sub −19}{sup +9}, which implies that the rotational spin of the star is not aligned with the orbital spin of the α Cen binary system. In addition, assuming that α Cen Bb is aligned with its host star, no transit would occur. The inclination of α Cen B can be measured using 40 radial-velocity measurements, which is remarkable given that the projected rotational velocity of the star is smaller than 1.15 km s{sup –1}.

  15. MHD Simulations of Core Collapse Supernovae with Cosmos++

    NASA Astrophysics Data System (ADS)

    Akiyama, Shizuka; Salmonson, Jay

    2010-10-01

    We performed 2D, axisymmetric, MHD simulations with Cosmos++ in order to examine the growth of the magnetorotational instability (MRI) in core-collapse supernovae. We have initialized a non-rotating 15 Msolar progenitor, infused with differential rotation and poloidal magnetic fields. The collapse of the iron core is simulated with the Shen EOS, and the parametric Ye and entropy evolution. The wavelength of the unstable mode in the post-collapse environment is expected to be only ~200 m. In order to achieve the fine spatial resolution requirement, we employed remapping technique after the iron core has collapsed and bounced. The MRI unstable region appears near the equator and angular momentum and entropy are transported outward. Higher resolution remap run display more vigorous overturns and stronger transport of angular momentum and entropy. Our results are in agreement with the earlier work by Akiyama et al. [1] and Obergaulinger et al. [2].

  16. β-DECAY of Key Titanium Isotopes in Stellar Environment

    NASA Astrophysics Data System (ADS)

    Nabi, Jameel-Un; Bakhadir, Irgaziev

    Amongst iron regime nuclei, β-decay rates on titanium isotopes are considered to be important during the late phases of evolution of massive stars. The key β-decay isotopes during presupernova evolution were searched from available literature and a microscopic calculation of the decay rates were performed using the proton-neutron quasiparticle random phase approximation (pn-QRPA) theory. As per earlier simulation results, electron capture and β-decay on certain isotopes of titanium are considered to be important for the presupernova evolution of massive stars. Earlier the stellar electron capture rates and neutrino energy loss rates due to relevant titanium isotopes were presented. In this paper we finally present the β-decay rates of key titanium isotopes in stellar environment. The results are also compared against previous calculations. The pn-QRPA β-decay rates are bigger at high stellar temperatures and smaller at high stellar densities compared to the large scale shell model results. This study can prove useful for the core-collapse simulators.

  17. A Young Cluster With an Extended Main Sequence Turnoff: Confirmation of a Prediction of the Stellar Rotation Scenario

    NASA Astrophysics Data System (ADS)

    Bastian, N.; Niederhofer, F.; Kozhurina-Platais, V.; Salaris, M.; Larsen, S.; Cabrera-Ziri, I.; Cordero, M.; Ekström, S.; Geisler, D.; Georgy, C.; Hilker, M.; Kacharov, N.; Li, C.; Mackey, D.; Mucciarelli, A.; Platais, I.

    2016-04-01

    We present Hubble Space Telescope photometry of NGC 1850, a ˜100 Myr, ˜105 M⊙ cluster in the Large Magellanic Cloud. The colour magnitude diagram clearly shows the presence of an extended main sequence turnoff (eMSTO). The use of non-rotating stellar isochrones leads to an age spread of ˜40 Myr. This is in good agreement with the age range expected when the effects of rotation in MSTO stars are wrongly interpreted in terms of age spread. We also do not find evidence for multiple, isolated episodes of star-formation bursts within the cluster, in contradiction to scenarios that invoke actual age spreads to explain the eMSTO phenomenon. NGC 1850 therefore continues the trend of eMSTO clusters where the inferred age spread is proportional to the age of the cluster. While our results confirm a key prediction of the scenario where stellar rotation causes the eMSTO feature, direct measurements of the rotational rate of MSTO stars is required to definitively confirm or refute whether stellar rotation is the origin of the eMSTO phenomenon or if it is due to an as yet undiscovered effect.

  18. A young cluster with an extended main-sequence turnoff: confirmation of a prediction of the stellar rotation scenario

    NASA Astrophysics Data System (ADS)

    Bastian, N.; Niederhofer, F.; Kozhurina-Platais, V.; Salaris, M.; Larsen, S.; Cabrera-Ziri, I.; Cordero, M.; Ekström, S.; Geisler, D.; Georgy, C.; Hilker, M.; Kacharov, N.; Li, C.; Mackey, D.; Mucciarelli, A.; Platais, I.

    2016-07-01

    We present Hubble Space Telescope photometry of NGC 1850, a ˜100 Myr, ˜105 M⊙ cluster in the Large Magellanic Cloud. The colour-magnitude diagram clearly shows the presence of an extended main-sequence turnoff (eMSTO). The use of non-rotating stellar isochrones leads to an age spread of ˜40 Myr. This is in good agreement with the age range expected when the effects of rotation in the main-sequence turnoff (MSTO) stars are wrongly interpreted in terms of age spread. We also do not find evidence for multiple, isolated episodes of star formation bursts within the cluster, in contradiction to scenarios that invoke actual age spreads to explain the eMSTO phenomenon. NGC 1850 therefore continues the trend of eMSTO clusters, where the inferred age spread is proportional to the age of the cluster. While our results confirm a key prediction of the scenario where stellar rotation causes the eMSTO feature, direct measurements of the rotational rate of MSTO stars is required to definitively confirm or refute whether stellar rotation is the origin of the eMSTO phenomenon or if it is due to an as yet undiscovered effect.

  19. TEM turbulence optimisation in stellarators

    NASA Astrophysics Data System (ADS)

    Proll, J. H. E.; Mynick, H. E.; Xanthopoulos, P.; Lazerson, S. A.; Faber, B. J.

    2016-01-01

    With the advent of neoclassically optimised stellarators, optimising stellarators for turbulent transport is an important next step. The reduction of ion-temperature-gradient-driven turbulence has been achieved via shaping of the magnetic field, and the reduction of trapped-electron mode (TEM) turbulence is addressed in the present paper. Recent analytical and numerical findings suggest TEMs are stabilised when a large fraction of trapped particles experiences favourable bounce-averaged curvature. This is the case for example in Wendelstein 7-X (Beidler et al 1990 Fusion Technol. 17 148) and other Helias-type stellarators. Using this knowledge, a proxy function was designed to estimate the TEM dynamics, allowing optimal configurations for TEM stability to be determined with the STELLOPT (Spong et al 2001 Nucl. Fusion 41 711) code without extensive turbulence simulations. A first proof-of-principle optimised equilibrium stemming from the TEM-dominated stellarator experiment HSX (Anderson et al 1995 Fusion Technol. 27 273) is presented for which a reduction of the linear growth rates is achieved over a broad range of the operational parameter space. As an important consequence of this property, the turbulent heat flux levels are reduced compared with the initial configuration.

  20. The SOHO-Stellar Connection

    NASA Technical Reports Server (NTRS)

    Ayres, Thomas R.

    1999-01-01

    Objective was to conduct a variety of observing programs with the SUMER spectrometer on SOHO, in order to further the understanding of the solar-stellar connection. The program was a continuation of SOHO GO program NAG5-6124 of the previous year.

  1. 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…

  2. Integrated Circuit Stellar Magnitude Simulator

    ERIC Educational Resources Information Center

    Blackburn, James A.

    1978-01-01

    Describes an electronic circuit which can be used to demonstrate the stellar magnitude scale. Six rectangular light-emitting diodes with independently adjustable duty cycles represent stars of magnitudes 1 through 6. Experimentally verifies the logarithmic response of the eye. (Author/GA)

  3. RETENTION OF STELLAR-MASS BLACK HOLES IN GLOBULAR CLUSTERS

    SciTech Connect

    Morscher, Meagan; Umbreit, Stefan; Farr, Will M.; Rasio, Frederic A. E-mail: s-umbreit@northwestern.edu E-mail: rasio@northwestern.edu

    2013-01-20

    Globular clusters should be born with significant numbers of stellar-mass black holes (BHs). It has been thought for two decades that very few of these BHs could be retained through the cluster lifetime. With masses {approx}10 M{sub Sun }, BHs are {approx}20 times more massive than an average cluster star. They segregate into the cluster core, where they may eventually decouple from the remainder of the cluster. The small-N core then evaporates on a short timescale. This is the so-called Spitzer instability. Here we present the results of a full dynamical simulation of a globular cluster containing many stellar-mass BHs with a realistic mass spectrum. Our Monte Carlo simulation code includes detailed treatments of all relevant stellar evolution and dynamical processes. Our main finding is that old globular clusters could still contain many BHs at present. In our simulation, we find no evidence for the Spitzer instability. Instead, most of the BHs remain well mixed with the rest of the cluster, with only the innermost few tens of BHs segregating significantly. Over the 12 Gyr evolution, fewer than half of the BHs are dynamically ejected through strong binary interactions in the cluster core. The presence of BHs leads to long-term heating of the cluster, ultimately producing a core radius on the high end of the distribution for Milky Way globular clusters (and those of other galaxies). A crude extrapolation from our model suggests that the BH-BH merger rate from globular clusters could be comparable to the rate in the field.

  4. Early dynamical evolution of substructured stellar clusters

    NASA Astrophysics Data System (ADS)

    Dorval, Julien; Boily, Christian

    2015-08-01

    It is now widely accepted that stellar clusters form with a high level of substructure (Kuhn et al. 2014, Bate 2009), inherited from the molecular cloud and the star formation process. Evidence from observations and simulations also indicate the stars in such young clusters form a subvirial system (Kirk et al. 2007, Maschberger et al. 2010). The subsequent dynamical evolution can cause important mass loss, ejecting a large part of the birth population in the field. It can also imprint the stellar population and still be inferred from observations of evolved clusters. Nbody simulations allow a better understanding of these early twists and turns, given realistic initial conditions. Nowadays, substructured, clumpy young clusters are usually obtained through pseudo-fractal growth (Goodwin et al. 2004) and velocity inheritance. Such models are visually realistics and are very useful, they are however somewhat artificial in their velocity distribution. I introduce a new way to create clumpy initial conditions through a "Hubble expansion" which naturally produces self consistent clumps, velocity-wise. A velocity distribution analysis shows the new method produces realistic models, consistent with the dynamical state of the newly created cores in hydrodynamic simulation of cluster formation (Klessen & Burkert 2000). I use these initial conditions to investigate the dynamical evolution of young subvirial clusters, up to 80000 stars. I find an overall soft evolution, with hierarchical merging leading to a high level of mass segregation. I investigate the influence of the mass function on the fate of the cluster, specifically on the amount of mass loss induced by the early violent relaxation. Using a new binary detection algorithm, I also find a strong processing of the native binary population.

  5. The axisymmetric stellar wind of AG Carinae

    NASA Technical Reports Server (NTRS)

    Schulte-Ladbeck, Regina E.; Clayton, Geoffrey C.; Hillier, D. John; Harries, Tim J.; Howarth, Ian D.

    1994-01-01

    We present optical linear spectropolarimetry of the Luminous Blue Variable AG Carinae obtained after a recent visual brightness increase. The absence of He II lambda 4686 emission, together with the weakening of the He I spectrum and the appearance of Fe lines in the region around 5300 A, confirm that AG Car has started a new excursion across the HR diagram. The H alpha line profile exhibits very extended line wings that are polarized differently in both amount and position angle from either the continuum or the line core. The polarization changes across H alpha, together with variable continuum polarization, indicate the presence of intrinsic polarization. Coexistence of the line-wing polarization with extended flux-line wings evidences that both are formed by electron scattering in a dense wind. The position angle rotates across the line profiles, in a way that presently available models suggest is due to rotation and expansion of the scattering material. AG Car displays very large variations of its linear polarization with time, Delta P approximately 1.2%, indicating significant variations in envelope opacity. We find that the polarization varies along a preferred position angle of approximately 145 deg (with a scatter of +/- 10 deg) which we interpret as a symmetry axis of the stellar wind (with an ambiguity of 90 deg). This position angle is co-aligned with the major axis of the AG Car ring nebula and perpendicular to the AG Car jet. Our observations thus suggest that the axisymmetric geometry seen in the resolved circumstellar environment at various distances already exists within a few stellar radii of AG Car. From the H alpha polarization profile we deduce an interstellar polarization of Q = 0.31%, U = -1.15% at H alpha. The inferred interstellar polarization implies that the intrinsic polarization is not always of the same sign. This indicates either significant temporal changes in the envelope geometry, or it may arise from effects of multiple scattering

  6. Spectral evolution of young stellar objects

    NASA Technical Reports Server (NTRS)

    Adams, F. C.

    1986-01-01

    An evolutionary sequence, from protostars to pre-main-sequence stars, is suggested for the classification of young stellar objects. This sequence is derived by comparing the predictions of the theoretical models of Adams and Shu with the morphological classification scheme of Lada and Wilking. We first define the spectral index in the near- and mid-infrared, n is identical to d log(nu F sub nu)/d log nu, and then interpret the class of sources with negative spectral indices as protostars. The inferred mass infall rates for these objects are generally consistent with the measured gas temperatures of approx. 35 K in Ophiuchus, and of approx. 10 K in Taurus. Fitting the data requires us to adopt cloud rotation rates in Ophiuchus which are typically an order of magnitude greater than in Taurus, and we speculate on the mechanistic origin for this difference. Next, we consider a subclass of T Tauri stars with near- and mid-infrared excesses and positive or zero spectral indices. We find that the objects with the steeper indices can be understood as the post-infall products from the collapse of rotating cloud cores, where the infrared excesses arise from the simple reprocessing of visible stellar photons in optically thick but spatially thin disks. The sources with flatter spectra may require massive accretion disks. Given the existence of protostars and naked star/disk systems, there is a natural interpretation of another subclass of T Tauri stars, those with two peaks in their emergent spectral energy distributions. These are readily explained as intermediate cases in which dust envelopes still surround the stars and disks. Finally, we find that the theory can be extended to explain the spectral energy distribution of FU Orionis, a famous outburst source. Our model suggests that FU Orionis has a disk, but it offers no discrimination between the competing ideas that the outburst took place on the star or in the disk.

  7. Disk Accretion and the Stellar Birthline

    NASA Astrophysics Data System (ADS)

    Hartmann, Lee; Cassen, Patrick; Kenyon, Scott J.

    1997-02-01

    We present a simplified analysis of some effects of disk accretion on the early evolution of fully convective, low-mass pre-main-sequence stars. Our analysis builds on the previous seminal work of Stahler, but it differs in that the accretion of material occurs over a small area of the stellar surface, such as through a disk or magnetospheric accretion column, so that most of the stellar photosphere is free to radiate to space. This boundary condition is similar to the limiting case considered by Palla & Stahler for intermediate-mass stars. We argue that for a wide variety of disk mass accretion rates, material will be added to the star with relatively small amounts of thermal energy. Protostellar evolution calculated assuming this ``low-temperature'' limit of accretion generally follows the results of Stahler because of the thermostatic nature of deuterium fusion, which prevents protostars from contracting below a ``birthline'' in the H-R diagram. Our calculated protostellar radii tend to fall below Stahler's at higher masses; the additional energy loss from the stellar photosphere in the case of disk accretion tends to make the protostar contract. The low-temperature disk accretion evolutionary tracks never fall below the deuterium-fusion birthline until the internal deuterium is depleted, but protostellar tracks can lie above the birthline in the H-R diagram if the initial radius of the protostellar core is large enough or if rapid disk accretion (such as might occur during FU Ori outbursts) adds significant amounts of thermal energy to the star. These possibilities cannot be ruled out by either theoretical arguments or observational constraints at present, so that individual protostars might evolve along a multiplicity of birthlines with a modest range of luminosity at a given mass. Our results indicate that there are large uncertainties in assigning ages for the youngest stars from H-R diagram positions, given the uncertainty in birthline positions. Our

  8. Understanding the size growth of massive galaxies through stellar populations

    NASA Astrophysics Data System (ADS)

    Ferreras, Ignacio

    2015-08-01

    The growth of massive galaxies remains an open problem. The observational evidence seems to converge on a two-stage scenario, where a compact massive core is formed during an early, intense burst, followed by a more extended process of mass and size growth at intermediate redshift (z<2). This talk focuses on the latter, exploring the growth of massive galaxies through a detailed analysis of the stellar populations in close pairs, to study their formation history. Two surveys are explored (SHARDS and GAMA), probing the stellar populations of pre-merging systems out to z~1.3, and down to a mass ratio ~1:100. We will compare the results between medium band spectral fitting (SHARDS) and those from a more targeted analysis of line strengths in the GAMA data. The combination of the two datasets provide a unique insight of the growth channel of massive galaxies via mergers.

  9. Gravitational effects of condensate dark matter on compact stellar objects

    SciTech Connect

    Li, X.Y.; Wang, F.Y.; Cheng, K.S. E-mail: fayinwang@gmail.com

    2012-10-01

    We study the gravitational effect of non-self-annihilating dark matter on compact stellar objects. The self-interaction of condensate dark matter can give high accretion rate of dark matter onto stars. Phase transition to condensation state takes place when the dark matter density exceeds the critical value. A compact degenerate dark matter core is developed and alter the structure and stability of the stellar objects. Condensate dark matter admixed neutron stars is studied through the two-fluid TOV equation. The existence of condensate dark matter deforms the mass-radius relation of neutron stars and lower their maximum baryonic masses and radii. The possible effects on the Gamma-ray Burst rate in high redshift are discussed.

  10. Simulating Convection in Stellar Envelopes

    NASA Astrophysics Data System (ADS)

    Tanner, Joel

    Understanding convection in stellar envelopes, and providing a mathematical description of it, would represent a substantial advance in stellar astrophysics. As one of the largest sources of uncertainty in stellar models, existing treatments of convection fail to account for many of the dynamical effects of convection, such as turbulent pressure and asymmetry in the velocity field. To better understand stellar convection, we must be able to study and examine it in detail, and one of the best tools for doing so is numerical simulation. Near the stellar surface, both convective and radiative process play a critical role in determining the structure and gas dynamics. By following these processes from first principles, convection can be simulated self-consistently and accurately, even in regions of inefficient energy transport where existing descriptions of convection fail. Our simulation code includes two radiative transfer solvers that are based on different assumptions and approximations. By comparing simulations that differ only in their respective radiative transfer methods, we are able to isolate the effect that radiative efficiency has on the structure of the superadiabatic layer. We find the simulations to be in good general agreement, but they show distinct differences in the thermal structure in the superadiabatic layer and atmosphere. Using the code to construct a grid of three-dimensional radiation hydrodynamic simulations, we investigate the link between convection and various chemical compositions. The stellar parameters correspond to main-sequence stars at several surface gravities, and span a range in effective temperatures (4500 < Teff < 6400). Different chemical compositions include four metallicities (Z = 0.040, 0.020, 0.010, 0.001), three helium abundances (Y = 0.1, 0.2, 0.3) and several levels of alpha-element enhancement. Our grid of simulations shows that various convective properties, such as velocity and the degree of superadiabaticity, are