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The red-giant branch bump provides valuable information for the investigation of the internal structure of low-mass stars. Because current models are unable to accurately predict the occurrence and efficiency of mixing processes beyond convective boundaries, one can use the luminosity of the bump --- a diagnostic of the maximum extension of the convective envelope during the first-dredge up --- as a calibrator for such processes. By combining asteroseismic and spectroscopic constraints, we expand the analysis of the bump to masses and metallicities beyond those previously accessible using globular clusters. Our dataset comprises nearly 3000 red-giant stars observed by {\it Kepler} and with APOGEE spectra. Using statistical mixture models, we are able to detect the bump in the average seismic parameters $\nu_{\rm max}$ and $\langle \Delta \nu \rangle$, and show that its observed position reveals general trends with mass and metallicity in line with expectations from models. Moreover, our analysis indicates that standard stellar models underestimate the depth of efficiently mixed envelopes. The inclusion of significant overshooting from the base of the convective envelope, with an efficiency that increases with decreasing metallicity, allows to reproduce the observed location of the bump. Interestingly, this trend was also reported in previous studies of globular clusters., Comment: 9 pages, 5 figures, Accepted for publication in ApJ

In this study we present photometric predictions for C-type Asymptotic Giant Branch Stars (AGB) stars from Eriks- son et al. (2014) for the James Webb Space Telescope (JWST) and the Wide- eld Infrared Survey Explorer (WISE) instruments. The photometric predictions we have done are for JWST’s general purpose wide-band lters on NIR- Cam and MIRI covering wavelengths of 0.7 — 21 microns. AGB stars contribute substantially to the integrated light of intermediate-age stellar popula- tions and is a substantial source of the metals (especially carbon) in galaxies. Studies of AGB stars are (among other reasons) important for the understanding of the chemical evolution and dust cycle of galaxies. Since the JWST is scheduled for launch in 2018 it should be a high priority to prepare observing strategies. With these predictions we hope it will be possible to optimize observing strategies of AGB stars and max- imize the science return of JWST. By testing our method on Whitelock et al. (2006) objects from the WISE catalog and comparing them with our photometric results based on Eriksson et al. (2014) we have been able to fit 20 objects with models. The photometric data set can be accessed at: http://www.astro.uu.se/AGBmodels/ABmags/

We study the eccentricity distribution of a thick disc sample of stars observed in the Radial Velocity Experiment (RAVE) and compare it to that expected in four simulations of thick disc formation in the literature (accretion of satellites, heating of a primordial thin disc during a merger, radial migration, and gas-rich mergers), as compiled by Sales et al. (2009). We find that the distribution of our sample is peaked at low eccentricities and falls off smoothly and rather steeply to high eccentricities. This distribution is fairly robust to changes in distances, thin disc contamination, and the particular thick disc sample used. Our results are inconsistent with what is expected for the pure accretion simulation, since we find that the dynamics of local thick disc stars implies that the majority must have formed "in situ". Of the remaining models explored, the eccentricity distribution of our stars appears to be most consistent with the gas-rich merger case., Comment: 8 pages, 7 figures, submitted to MNRAS

We study the eccentricity distribution of a thick-disc sample of stars (defined as those with V-y > 50 km s-1 and 1

Numerous experiments and observations have confirmed the existence of a dynamical 3-space, detectable directly by light-speed anisotropy experiments, and indirectly by means of novel gravitational effects, such as bore hole g-anomalies, predictable black hole masses, flat spiral-galaxy rotation curves, and the expansion of the universe, all without dark matter and dark energy. The dynamics for this 3-space follows from a unique generalisation of Newtonian gravity, once that is cast into a velocity formalism. This new theory of gravity is applied to the solar model of the sun to compute new density, pressure and temperature profiles, using polytrope modelling of the equation of state for the matter. These results should be applied to a re-analysis of solar neutrino production, and to stellar evolution in general.

Aim: Our purpose is to provide reliable stellar parameters for a significant sample of eclipsing binaries, which are representative of a whole dwarf and metal-poor galaxy. We also aim at providing a new estimate of the mean distance to the SMC and of its depth along the line of sight for the observed field of view. Method: We use radial velocity curves obtained with the ESO FLAMES facility at the VLT and light curves from the OGLE-II photometric survey. The radial velocities were obtained by least-squares fits of the observed spectra to synthetic ones, excluding the hydrogen Balmer lines. Results: Our sample contains 23 detached, 9 semi-detached and 1 overcontact systems. Most detached systems have properties consistent with stellar evolution calculations from single-star models at the standard SMC metallicity Z = 0.004, though they tend to be slightly overluminous. The few exceptions are probably due to third light contribution or insufficient signal-to-noise ratio. The mass ratios are consistent with a flat distribution, both for detached and semi-detached/contact binaries. A mass-luminosity relation valid from ~4 to ~18 Msol is derived. The uncertainties are in the +-2 to +-11% range for the masses, in the +-2 to +-5% range for the radii and in the +-1 to +-6% range for the effective temperatures. The average distance modulus is 19.11+-0.03 (66.4+-0.9 kpc). The moduli derived from the V and from the I data are consistent within 0.01 mag. The 2-sigma depth of the SMC is, for our field, of 0.25 mag or 7.6 kpc under the assumption of a gaussian distribution of stars along the line of sight. Three systems show significant apsidal motion, one of them with an apsidal period of 7.6 years, the shortest known to date for a detached system with main sequence stars., Comment: 61 pages, 41 figures; accepted for publication in Astronomy & Astrophysics

Rigorous statistical methods for estimating thermonuclear reaction rates and nucleosynthesis are becoming increasingly established in nuclear astrophysics. The main challenge being faced is that experimental reaction rates are highly complex quantities derived from a multitude of different measured nuclear parameters (e.g., astrophysical S-factors, resonance energies and strengths, particle and gamma-ray partial widths). We discuss the application of the Monte Carlo method to two distinct, but related, questions. First, given a set of measured nuclear parameters, how can one best estimate the resulting thermonuclear reaction rates and associated uncertainties? Second, given a set of appropriate reaction rates, how can one best estimate the abundances from nucleosynthesis (i.e., reaction network) calculations? The techniques described here provide probability density functions that can be used to derive statistically meaningful reaction rates and final abundances for any desired coverage probability. Examples are given for applications to s-process neutron sources, core-collapse supernovae, classical novae, and big bang nucleosynthesis., Comment: Accepted for publication in J. Phys. G Focus issue "Enhancing the interaction between nuclear experiment and theory through information and statistics"

We present CCD photometry of two southern open clusters. As part of the Bologna Open Cluster Chemical Evolution project we obtained BVI and UBVI imaging for NGC 2849 and NGC 6134, respectively. By means of the synthetic colour-magnitude diagram method and using various evolutionary sets of stellar evolution tracks with various metallicities, we determined at the same time age, distance and reddening. We also determined an approximate metallicity for NGC 2849, for which the information is not available from sounder methods like high-resolution spectroscopy. NGC 2849 turned to be 0.85-1.0 Gyr old with a solar metallicity. The foreground reddening is E(B - V) = 0.28 - 0.32, and the true distance modulus (m - M) 0 = 13.8-13.9. For NGC 6134 we did not obtain fully consistent answers from the V, B - V and V, V - I photometry, an unexpected problem, since both the metallicity and the reddening are known (from high-resolution spectroscopy and the U - B, B - V two colours diagram, respectively). This may either indicate a difficulty of current models (evolutionary tracks and/or models of atmosphere) to accurately reproduce colours, or be related to differences in the metal mixture assumed by the models and those of the clusters. Assuming the spectroscopic abundance and the colour excess [E(B - V) = 0.35] from the U - B, B - V plot, we derived a best age between 0.82 and 0.95 Gyr and a distance modulus 10.5. In agreement with previous studies, the NGC 6134 colour-magnitude diagram shows also a clear main sequence gap at V ˜ 15 and B-V ˜ 0.9-1.0 that is unexplained by canonical stellar evolution models. Fil: Ahumada, Andrea Veronica. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba. Departamento de Astrofisica Estelar; Argentina Fil: Cignoni, M.. Universitá di Bologna. Dipartimento di Astronomia; Italia; Fil: Bragaglia, A.. INAF-Osservatorio Astronomico di Bologna; Italia; Fil: Donati, P.. Universitá di Bologna. Dipartimento di Astronomia; Italia; Fil: Tosi, M.. INAF-Osservatorio Astronomico di Bologna; Italia; Fil: Marconi, G.. European Southern Observatory (ESO); Chile

The X-ray spectrum of Tycho's remant was observed in the energy range from 2 to 20 keV with Ginga in December, 1989. Fits of standard model spectra to the measured continuum above 4.5 keV showed that the spectrum of the remnant cannot satisfactorily be described by a single Bremsstrahlung component plus a Gaussian line for the Fe K-line blend. Such an approach was previously chosen to characterize Tycho's continuum measured with EXOSAT and Tenma up to 10 keV yielding divergent spectral parameters. Although the two-component modeling of the continuum yielded formally acceptable fits, the spectral parameters of the high energy component remained uncertain according to the very shallow chi2-valleys of the corresponding significance contours. The centroid of the Gaussian line is at 6.5 keV possibly indicating Fe line emssion from a hot plasma. A physical meaningful representation of Tycho's continuum is achieved by a multi-temperature spectrum provided by a numerical model. The 1-D model describes the hydrodynamical evolution of the remnant taking non-equilibrium ionization into account. The remarkable agreement between the model, and the measured continuum confirms the basic model assumption that a local temperature equilibrium between electrons and ions is almost instantaneously established in the remnant's X-ray emitting shell. From the model emissivity and the measured flux density a distance of Tycho of nearly 3 kpc is derived.

We performed a spectroscopic survey of nearly 700 stars probing the galactic thick disc far from the solar neighbourhood towards the galactic coordinates (l~277, b~47). The derived effective temperatures, surface gravities and overall metallicities were then combined with stellar evolution isochrones, radial velocities and proper motions to derive the distances, kinematics and orbital parameters of the sample stars. The targets belonging to each galactic component (thin disc, thick disc, halo) were selected either on their kinematics or according to their position above the galactic plane, and the vertical gradients were also estimated. We present here atmospheric parameters, distances and kinematics for this sample, and a comparison of our kinematic and metallicity distributions with the Besancon model of the Milky Way. The thick disc far from the solar neighbourhood is found to differ only slightly from the thick disc properties as derived in the solar vicinity. For regions where the thick disc dominates, we measured vertical velocity and metallicity trends of d(V_phi)/dZ = 19 +/- 8 km/s/kpc and d[M/H]/dZ = -0.14 +/- 0.05 dex/kpc, respectively. These trends can be explained as a smooth transition between the different galactic components, although intrinsic gradients could not be excluded. In addition, a correlation d(V_phi)/d[M/H] = -45 +/- 12 km/s/dex between the orbital velocity and the metallicity of the thick disc is detected. This gradient is inconsistent with the SDSS photometric survey analysis, which did not detect any such trend, and challenges radial migration models of thick disc formation. Estimations of the scale heights and scale lengths for different metallicity bins of the thick disc result in consistent values, with hR~3.4 \pm 0.7 kpc, and hZ~694 \pm 45 pc, showing no evidence of relics of destroyed massive satellites., 19 pages, 15 figures, accepted for publication in A&A

A unified X-ray spectral model which can be fitted to any of the spectra observed with Ginga is presented. The model consists of three components: an absorbed power-law component modified with an exponential cutoff at high energy, an absorbed blackbody component, and an iron emission line. The best-fitting values of parameters obtained using the model are given, and the interpretation of the physical meaning of these parameters is described.

We present a brief review on the atomic kinetics, modeling and interpretation of astrophysical observations, and laboratory astrophysics experiments. The emphasis is on benchmarking of opacity calculations relevant for solar structure models, photoionized plasmas research, the magnetohydrodynamic numerical simulation of accretion disk dynamics, and a connection between radiation transport effects and plasma source geometry details. Specific cases of application are discussed with relevance to recent and proposed laboratory astrophysics experiments as well as Chandra and X-ray Multi-Mirror Mission Newton observations.

From a pulse-timing analysis of Ginga observations of the binary X-ray pulsar Her X-1 obtained during the interval 1989 April-June local orbital parameters are determined for a short high state. An orbital epoch is also determined in the adjacent main high state. By comparing these orbital solutions with previously published results, a decrease is detected in the orbital period for Her X-1 over the interval 1971-1989. The value is substantially larger than the value predicted from current estimates of the mass-transfer rate, and motivates consideration of other mechanisms of mass transfer and/or mass loss. A second result from these observations is a close agreement between orbital parameters determined separately in main high and short high states. This agreement places strong constraints on the obliquity of the stellar companion, HZ Her, if undergoing forced precession with a 35-day period. As a consequence further doubt is placed on the slaved-disk model as the underlying cause of the 35-day cycle in Her X-1.

Balıkesir Üniversitesi, Fen Bilimleri Enstitüsü, Fizik Anabilim Dalı, Paczynski'nin GOB programı [1] yardımı ile düşük kütleli yıldız zarflarının yüzey ısı akışındaki konveksiyon rolünü çalıştık. 0.4 ve 1.1 M◎ kütle aralığında değen veya değmeye yakın olan çift yıldızların bileşenleri için atmosferik modelleri dikkate aldık. Lucy 'nin önerdiği yöntem [2] takip edilerek, soğuk yıldızların oldukça geniş kütle, ışıtma ve etkin sıcaklık aralıkları için benzer ß (~0.06-0.1) değerleri elde edildi. Aynı zamanda Paczynski 'nin programları [1] yardımıyla donukluğun yıldızların yarıçapları üzerine etkisini inceledik. Kurucz donukluklarından [3] yeni donukluk tabloları oluşturmak için Lagrange interpolasyon metodunu [4] kullandık. Kurucz donukluklarının sonuçlarını, Huebner donuklukları [5]' nın, Iglesias ve Rogers donuklukları [6,7] 'nın sonuçları ile karşılaştırdık. Schwarzschild 'ın [8] dikkate aldığı kütle aralıklarının aynısı için hesaplamaları kontrol ettik. Bu çalışmada, eski donuklukların yeni olanları ile değiştirilmesi hesaplanan yarıçapları % 5-10 kadar değiştirmiştir. Yıldız modellerindeki nükleer enerji oluşum oranlarını açıklamaları ile birlikte verdik. Gözlemsel kontroller için, genç çoklu yıldız sistemi U Oph (ADS 10428)'nin analiz sonuçlarını kullandık. U Oph 'nin yapısal ve evrimsel durumunu kontrol etmek için Paczynski 'nin HB8 programını [1] kullandık. Çoklu sistemin yaşını yaklaşık 38 Milyon yıl olarak tahmin ettik., We study the role of convection in the surface heat flow of low mass stellar envelopes with the aid of Paczynski 's domain program GOB [1]. We have considered atmospheric models for a range of masses similar to the components of contact or near - contact binaries between 0.4 and 1.1 M◎. If the procedure proposed by Lucy [2] is followed, similar values of the index β (~0.06-0.1) are obtained for a fairly wide range of masses, luminosities and effective temperature of cool stars. We have also examined the effect of opacity on stellar radii with the aid of Paczynski 's programs [1]. We used Lagrange interpolation method [4] to prepare new opacity tables from Kurucz opacities [3]. We have compared the results of Kuruz opacities with those of Huebner opacities [5], Iglesias and Rogers opacities [6,7]. We have checked calculations for the same ranges of masses considered by Schwarzschild [8]. In this study, changes of old opacities with new ones have changed the calculated radii by up to ~ 5-10 %. We have presented nuclear energy generation rates in stellar models with explanations. We have used results of analysis of the young, multiple star U Oph (ADS 10428) for observational checks. We have used the HB8 program of Paczynski [1] to check our results for the structure and evolutionary condition of U Oph. We have estimate an age of the multiple system at around 38 My.

International audience; A recently developed treatment of partition functions in the equation of state (Mihalas, Hummer, Daeppen, MH&D) has led to a substantial improvement in the agreement between observed and theoretically predicted solar p-mode oscillation frequencies. The MH&D equation of state is a realization of the free-energy-minimization method, based on the so-called 'chemical picture', in which ionization and dissociation reactions are assumed to be those that maximize entropy, or equivalently, minimize the free energy. An alternative equation of state has recently been developed at Livermore. It realizes a virial expansion of pressure, and is based on the 'physical picture', in which explicitly only fundamental species (i.e., electrons and nuclei) appear. Results of a first comparison between thermodynamic quantities of the MH&D and Livermore equations of state are presented. For simplicity, a mixture with only hydrogen and helium (90 percent H and 10 percent He by number) is chosen. The comparison is made for a low-density and a high-density case. In the first case, the conditions are those of the hydrogen and helium ionization zones of the sun, in the second case those of the solar center. In both cases, the MH&D and Livermore results agree strikingly, despite the very different formalisms they are based on.

We have obtained CCD BVI imaging of the old open clusters Berkeley 32 and King 11. Using the synthetic colour-magnitude diagram method with three different sets of stellar evolution models of various metallicities, with and without overshooting, we have determined their age, distance, reddening, and indicative metallicity, as well as distance from the Galactic centre and height from the Galactic plane. The best parameters derived for Berkeley 32 are: subsolar metallicity (Z=0.008 represents the best choice, Z=0.006 or 0.01 are more marginally acceptable), age = 5.0-5.5 Gyr (models with overshooting; without overshooting the age is 4.2-4.4 Gyr with poorer agreement), (m-M)_0=12.4-12.6, E(B-V)=0.12-0.18 (with the lower value being more probable because it corresponds to the best metallicity), Rgc ~ 10.7-11 kpc, and |Z| ~ 231-254 pc. The best parameters for King 11 are: Z=0.01, age=3.5-4.75 Gyr, (m-M)_0=11.67-11.75, E(B-V)=1.03-1.06, Rgc ~ 9.2-10 kpc, and |Z| ~ 253-387 pc., Accepted for publication on MNRAS (figs. 6 and 10 shown at degraded resolution)

Radiating, slowly rotating bodies in general relativity (Melfo, Alejandra; Núñez, Luis; Patiño, Alberto; Herrera, Luis) Abstract We propose a method to obtain axisymmetric, dynamic solutions to the Einstein equations that can represent a radiating collapsing body in slow differential rotation. The method is a generalization of the semi-numeric approach developed but Herrera, Jimenez, & Ruggeri, in 1980, for the spherically symmetric case. Solutions are properly matched to the exterior Kerr-Vaidya metric, and the values of the physically relevant variables (density, pressure, fluid velocity, and energy flux) are obtained inside the matter distribution. As an example of the method, a model based on Schwarzschild interior homogeneous static solution is presented. melfo@ula.ve nunez@ula.ve patino@ula.ve lherrera@dino.conicit.ve Nivel monográfico

It is well known that a spherically symmetric constant density static star, modeled as a perfect fluid, possesses a bound on its mass m by its radial size R given by 2m/R \le 8/9 and that this bound continues to hold when the energy density decreases monotonically. The existence of such a bound is intriguing because it occurs well before the appearance of an apparent horizon at m = R/2. However, the assumptions made are extremely restrictive. They do not hold in a humble soap bubble and they certainly do not approximate any known topologically stable field configuration. We show that the 8/9 bound is robust by relaxing these assumptions. If the density is monotonically decreasing and the tangential stress is less than or equal to the radial stress we show that the 8/9 bound continues to hold through the entire bulk if m is replaced by the quasi-local mass. If the tangential stress exceeds the radial stress and/or the density is not monotonic we cannot recover the 8/9 bound. However, we can show that 2m/R remains strictly bounded away from unity by constructing an explicit upper bound which depends only on the ratio of the stresses and the variation of the density., 16 pages, Revtex

Only a small number of high mass stars (> 30 Mo) have fundamental parameters (i.e. masses and radii) measured with high enough accuracy from eclipsing binaries to constrain formation and evolutionary models of massive stars. This work aims to increase this limited sample, by studying the 4 massive eclipsing binary candidates discovered by Bonanos in the young massive cluster Westerlund 1. We present new follow-up echelle spectroscopy of these binaries and models of their light and radial velocity curves. We obtain fundamental parameters (i.e. masses, radii) for the 8 component stars, finding masses that span a range of 10-40 Mo, and contributing accurate fundamental parameters for 1 additional very massive star, the 33 Mo component of W13. WR77o is found to have a ~40 Mo companion, which provides a second dynamical constraint on the mass of the progenitor of the magnetar known in the cluster. We also use W13 to estimate the first, direct, eclipsing binary distance to Westerlund 1 and therefore the magnetar, and find it to be at 3.7 +/- 0.6 kpc. Our results confirm previous evidence for a high mass for the progenitor of the magnetar. In addition, the availability of eclipsing binaries with accurate parameters opens the way for direct, independent, high precision eclipsing binary distance measurements to Westerlund 1., 11 pages, 11 figures, 7 tables, accepted for publication in A&A

The s-process in massive stars is analyzed as a function of metallicity. The nucleosynthesis occurring in both core helium and shell carbon burning is investigated by numerically modeling nuclear reaction networks, subject to the conditions provided by stellar models. The efficiency of the neutron-capture mechanism depends on the amount of enhancement that is assumed for the α-rich nuclei, that are observed to be overabundant with respect to iron in stars of metallicity lower than solar

The location of the instability strip in the C-M diagram of Galactic Cepheids is discussed with the aid of the 1990 calculations of model Cepheids by Chiosi & Wood. It is found that the difficulty pointed out by Fernie (the slope of the empirical red boundary of the strip is different from that customarily assumed) has no reason to occur because it is entirely due to the use of strips having parallel blue and red edges, while in reality they have a different slope. The number-period distribution expected from different models for intermediate-mass stars is also examined

An overview is presented of calculations of stellar opacities in the transition region below the photosphere corresponding to temperatures of 3,500-11,600 K. Available opacity calculations in the temperature range of interest are reviewed showing significant differences. The differences for specific classes of stellar opacities are attributed to changes in composition, temperature variations, and density variations. The influence of CO and CO(+) are examined in detail to demonstrate the affect of molecular composition on the determination of opacity. CO and CO(+) are expected to affect the opacities in the 70,000/cm and 10,000-20,000/cm regions, and it is concluded that other species can affect the opacity calculation, if not as markedly. The significance of the molecular processes for opacities in this range demonstrates that opacity calculations should incorporate these data for precise estimates.

The study of old open clusters such as IC 4651 has brought into evidence that the age assigned to these clusters heavily depends on the type of stellar models in use, that is, standard models or models with a certain amount of convective overshoot from the core. While standard models lead to age estimates that reasonably agree among the various sources provided that the same physical assumptions (chemical composition, opacity, nuclear reaction rates, etc.) are adopted, models with convective overshoot give ages that are largely discrepant even if the same input physics is used (the efficiency of core overshoot in particular)

The interior properties of four solar models from the recent astrophysical literature are presented. The first three are standard solar models, each with somewhat different input physics. The fourth is an unconventional model designed to address the solar neutrino problem, with reduced central opacity to simulate the effects of weakly interacting massive particles.

The theory of spectral formation during the explosion and contraction stages of X-ray bursters, which include the effects of Computonization and free-free absorption and emission, is described. Analytical expressions are provided for color ratios, and the spectral shape is given as a function of input parameters, elemental abundance, neutron star mass and radius, and Eddington ratio. An Eulerian calculation is used to determine the photospheric evolution accurately during the Eddington luminosity phase. The developed analytical theory for hydrodynamics of the expansion takes into account the dependence of Compton scattering opacity on electron temperature. An analytical expression is derived from the sonic point position and the value of the sonic velcoity. Using this value as a boundary condition at the sonic point, the velocity, density, and temperature profile are calculated throughout the whole photosphere. It is shown that the atmopsphere radiates spectra having a low-energy power-law shape and blackbody-like hard tail. In the expansion stage the spectra depend strongly on the temperature of the helium-burning zone at the neutron star surface. The X-ray photosheric radius increases to approximately 100 km or more, depending on the condition of the nuclear burning on the surface of the neutron star in the course of the expansion.

In this paper, we present results from an investigation of the rotational properties of strange stars, using models with a canonical value of the bag constant. The changes in structure resulting from uniform rotation have been calculated within the slow rotation regime and the minimum rotation periods consistent with stability to nonaxisymmetric perturbations have also been calculated.