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Sample records for accurate stellar parameters

  1. Precise and accurate assessment of uncertainties in model parameters from stellar interferometry. Application to stellar diameters

    NASA Astrophysics Data System (ADS)

    Lachaume, Regis; Rabus, Markus; Jordan, Andres

    2015-08-01

    In stellar interferometry, the assumption that the observables can be seen as Gaussian, independent variables is the norm. In particular, neither the optical interferometry FITS (OIFITS) format nor the most popular fitting software in the field, LITpro, offer means to specify a covariance matrix or non-Gaussian uncertainties. Interferometric observables are correlated by construct, though. Also, the calibration by an instrumental transfer function ensures that the resulting observables are not Gaussian, even if uncalibrated ones happened to be so.While analytic frameworks have been published in the past, they are cumbersome and there is no generic implementation available. We propose here a relatively simple way of dealing with correlated errors without the need to extend the OIFITS specification or making some Gaussian assumptions. By repeatedly picking at random which interferograms, which calibrator stars, and which are the errors on their diameters, and performing the data processing on the bootstrapped data, we derive a sampling of p(O), the multivariate probability density function (PDF) of the observables O. The results can be stored in a normal OIFITS file. Then, given a model m with parameters P predicting observables O = m(P), we can estimate the PDF of the model parameters f(P) = p(m(P)) by using a density estimation of the observables' PDF p.With observations repeated over different baselines, on nights several days apart, and with a significant set of calibrators systematic errors are de facto taken into account. We apply the technique to a precise and accurate assessment of stellar diameters obtained at the Very Large Telescope Interferometer with PIONIER.

  2. Accurate characterization of the stellar and orbital parameters of the exoplanetary system WASP-33 b from orbital dynamics

    NASA Astrophysics Data System (ADS)

    Iorio, L.

    2016-01-01

    By using the most recently published Doppler tomography measurements and accurate theoretical modelling of the oblateness-driven orbital precessions, we tightly constrain some of the physical and orbital parameters of the planetary system hosted by the fast rotating star WASP-33. In particular, the measurements of the orbital inclination ip to the plane of the sky and of the sky-projected spin-orbit misalignment λ at two epochs about six years apart allowed for the determination of the longitude of the ascending node Ω and of the orbital inclination I to the apparent equatorial plane at the same epochs. As a consequence, average rates of change dot{Ω }_exp, dot{I}_exp of this two orbital elements, accurate to a ≈10-2 deg yr-1 level, were calculated as well. By comparing them to general theoretical expressions dot{Ω }_{J_2}, dot{I}_{J_2} for their precessions induced by an oblate star whose symmetry axis is arbitrarily oriented, we were able to determine the angle i⋆ between the line of sight the star's spin {S}^{star } and its first even zonal harmonic J_2^{star } obtaining i^{star } = {142}^{+10}_{-11} deg, J_2^{star } = 2.1^{+0.8}_{-0.5}times; 10^{-4}. As a by-product, the angle between {S}^{star } and the orbital angular momentum L is as large as about ψ ≈ 100 ° psi; ^{2008} = 99^{+5}_{-4} deg, ψ ^{{2014}} = 103^{+5}_{-4} deg and changes at a rate dot{ψ }= 0.{7}^{+1.5}_{-1.6} deg {yr}^{-1}. The predicted general relativistic Lense-Thirring precessions, of the order of ≈10-3deg yr-1, are, at present, about one order of magnitude below the measurability threshold.

  3. Model atmospheres and fundamental stellar parameters

    NASA Astrophysics Data System (ADS)

    Plez, B.

    2013-11-01

    I start by illustrating the need for precise and accurate fundamental stellar parameters through there examples: lithium abundances in metal-poor stars, the derivation of stellar ages from isochrones, and the chemical composition of planet-hosting stars. I present widely used methods (infrared flux method, spectroscopy) in the determination of T_{eff}, and log g. I comment upon difficulties encountered with the determination of stellar parameters of red supergiant stars, and I discuss the impact of non-LTE and 3D hydrodynamical effects.

  4. 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

    stellar parameters and the physics of the interior. I examine how the acoustic signature of the location of the base of stellar convective envelopes can be used as an absolute abundance indicator, and describe a novel 3He-burning instability in low mass stars along with the observational signatures of such a process. Finally, I examine the manner in which stellar rotation, observed in a population of objects, can be used as a means to distinguish between different evolutionary states, masses, and ages. I emphasize that rotation periods can be used as age indicators (as often discussed in the literature), but that the interpretation of rotation periods must be made within the context of the full stellar population to arrive at accurate results.

  5. GALA: Stellar atmospheric parameters and chemical abundances

    NASA Astrophysics Data System (ADS)

    Mucciarelli, A.; Pancino, E.; Lovisi, L.; Ferraro, F. R.; Lapenna, E.

    2013-02-01

    GALA is a freely distributed Fortran code to derive the atmospheric parameters (temperature, gravity, microturbulent velocity and overall metallicity) and abundances for individual species of stellar spectra using the classical method based on the equivalent widths of metallic lines. The abundances of individual spectral lines are derived by using the WIDTH9 code developed by R. L. Kurucz. GALA is designed to obtain the best model atmosphere, by optimizing temperature, surface gravity, microturbulent velocity and metallicity, after rejecting the discrepant lines. Finally, it computes accurate internal errors for each atmospheric parameter and abundance. The code obtains chemical abundances and atmospheric parameters for large stellar samples quickly, thus making GALA an useful tool in the epoch of the multi-object spectrographs and large surveys.

  6. The Araucaria Project: accurate stellar parameters and distance to evolved eclipsing binary ASAS J180057-2333.8 in Sagittarius Arm

    NASA Astrophysics Data System (ADS)

    Suchomska, K.; Graczyk, D.; Smolec, R.; Pietrzyński, G.; Gieren, W.; Stȩpień, K.; Konorski, P.; Pilecki, B.; Villanova, S.; Thompson, I. B.; Górski, M.; Karczmarek, P.; Wielgórski, P.; Anderson, R. I.

    2015-07-01

    We have analyzed the double-lined eclipsing binary system ASAS J180057-2333.8 from the All Sky Automated Survey (ASAS) catalogue. We measure absolute physical and orbital parameters for this system based on archival V-band and I-band ASAS photometry, as well as on high-resolution spectroscopic data obtained with ESO 3.6 m/HARPS and CORALIE spectrographs. The physical and orbital parameters of the system were derived with an accuracy of about 0.5-3 per cent. The system is a very rare configuration of two bright well-detached giants of spectral types K1 and K4 and luminosity class II. The radii of the stars are R1 = 52.12 ± 1.38 and R2 = 67.63 ± 1.40 R⊙ and their masses are M1 = 4.914 ± 0.021 and M2 = 4.875 ± 0.021 M⊙. The exquisite accuracy of 0.5 per cent obtained for the masses of the components is one of the best mass determinations for giants. We derived a precise distance to the system of 2.14 ± 0.06 kpc (stat.) ± 0.05 (syst.) which places the star in the Sagittarius-Carina arm. The Galactic rotational velocity of the star is Θs = 258 ± 26 km s-1 assuming Θ0 = 238 km s-1. A comparison with PARSEC isochrones places the system at the early phase of core helium burning with an age of slightly larger than 100 million years. The effect of overshooting on stellar evolutionary tracks was explored using the MESA star code.

  7. [Automatic Measurement of the Stellar Atmospheric Parameters Based Mass Estimation].

    PubMed

    Tu, Liang-ping; Wei, Hui-ming; Luo, A-li; Zhao, Yong-heng

    2015-11-01

    We have collected massive stellar spectral data in recent years, which leads to the research on the automatic measurement of stellar atmospheric physical parameters (effective temperature Teff, surface gravity log g and metallic abundance [Fe/ H]) become an important issue. To study the automatic measurement of these three parameters has important significance for some scientific problems, such as the evolution of the universe and so on. But the research of this problem is not very widely, some of the current methods are not able to estimate the values of the stellar atmospheric physical parameters completely and accurately. So in this paper, an automatic method to predict stellar atmospheric parameters based on mass estimation was presented, which can achieve the prediction of stellar effective temperature Teff, surface gravity log g and metallic abundance [Fe/H]. This method has small amount of computation and fast training speed. The main idea of this method is that firstly it need us to build some mass distributions, secondly the original spectral data was mapped into the mass space and then to predict the stellar parameter with the support vector regression (SVR) in the mass space. we choose the stellar spectral data from the United States SDSS-DR8 for the training and testing. We also compared the predicted results of this method with the SSPP and achieve higher accuracy. The predicted results are more stable and the experimental results show that the method is feasible and can predict the stellar atmospheric physical parameters effectively. PMID:26978937

  8. Stellar Parameter Determination Using Bayesian Techniques.

    NASA Astrophysics Data System (ADS)

    Ekanayake, Gemunu B.; Wilhelm, Ronald J.

    2015-01-01

    Spectral energy distributions of stars covering the wavelength range from far UV to far IR can be used to derive stellar atmospheric parameters (effective temperature, surface gravity and iron abundance) with a high reliability. For this purpose we are using a method based on Bayesian statistics, which make use of all available photometric data for a given star to construct stellar parameter probability distribution function (PDF) in order to determine the expectation values and their uncertainties in stellar parameters. The marginalized probabilities allow us to characterize the constraint for each parameter and estimate the influence of the quantity and quality of the photometric data on the resulting parameter values. We have obtained low resolution spectroscopy of blue horizontal branch, blue straggler and normal main sequence A, B, G and F stellar parameter standard stars using the McDonald observatory, 2.1m telescope to constrain both synthetic and empirical stellar libraries like Atlas9, MARCS, MILES and Pickles across a wide range in parameter space. This calibration process helps to evaluate the correlations between different stellar libraries and observed data especially in the UV part of the spectrum. When the calibration is complete the Bayesian analysis can be applied to large samples of data from GALEX, SDSS, 2MASS,WISE etc. We expect significant improvements to luminosity classification, distances and interstellar extinction using this technique.

  9. Estimating stellar effective temperatures and detected angular parameters using stochastic particle swarm optimization

    NASA Astrophysics Data System (ADS)

    Zhang, Chuan-Xin; Yuan, Yuan; Zhang, Hao-Wei; Shuai, Yong; Tan, He-Ping

    2016-09-01

    Considering features of stellar spectral radiation and sky surveys, we established a computational model for stellar effective temperatures, detected angular parameters and gray rates. Using known stellar flux data in some bands, we estimated stellar effective temperatures and detected angular parameters using stochastic particle swarm optimization (SPSO). We first verified the reliability of SPSO, and then determined reasonable parameters that produced highly accurate estimates under certain gray deviation levels. Finally, we calculated 177 860 stellar effective temperatures and detected angular parameters using data from the Midcourse Space Experiment (MSX) catalog. These derived stellar effective temperatures were accurate when we compared them to known values from literatures. This research makes full use of catalog data and presents an original technique for studying stellar characteristics. It proposes a novel method for calculating stellar effective temperatures and detecting angular parameters, and provides theoretical and practical data for finding information about radiation in any band.

  10. ZASPE: Zonal Atmospheric Stellar Parameters Estimator

    NASA Astrophysics Data System (ADS)

    Brahm, Rafael; Jordan, Andres; Hartman, Joel; Bakos, Gaspar

    2016-07-01

    ZASPE (Zonal Atmospheric Stellar Parameters Estimator) computes the atmospheric stellar parameters (Teff, log(g), [Fe/H] and vsin(i)) from echelle spectra via least squares minimization with a pre-computed library of synthetic spectra. The minimization is performed only in the most sensitive spectral zones to changes in the atmospheric parameters. The uncertainities and covariances computed by ZASPE assume that the principal source of error is the systematic missmatch between the observed spectrum and the sythetic one that produces the best fit. ZASPE requires a grid of synthetic spectra and can use any pre-computed library minor modifications.

  11. Theory of stellar convection: removing the mixing-length parameter

    NASA Astrophysics Data System (ADS)

    Pasetto, S.; Chiosi, C.; Cropper, M.; Grebel, E. K.

    2014-12-01

    Stellar convection is customarily described by Mixing-Length Theory, which makes use of the mixing length-scale to express the convective flux, velocity, and temperature gradients of the convective elements and stellar medium. The mixing length-scale is taken to be proportional to the local pressure scaleheight, and the proportionality factor (the mixing-length parameter) must be determined by comparing the stellar models to some calibrator, usually the Sun. No strong arguments exist to suggest that the mixing-length parameter is the same in all stars and at all evolutionary phases. The aim of this study is to present a new theory of stellar convection that does not require the mixing-length parameter. We present a self-consistent analytical formulation of stellar convection that determines the properties of stellar convection as a function of the physical behaviour of the convective elements themselves and of the surrounding medium. This new theory is formulated starting from a conventional solution of the Navier-Stokes/Euler equations, i.e. the Bernoulli equation for a perfect fluid, but expressed in a non-inertial reference frame comoving with the convective elements. In our formalism, the motion of stellar convective cells inside convectively unstable layers is fully determined by a new system of equations for convection in a non-local and time-dependent formalism. We obtain an analytical, non-local, time-dependent subsonic solution for the convective energy transport that does not depend on any free parameter. The theory is suitable for the outer convective zones of solar type stars and stars of all mass on the main-sequence band. The predictions of the new theory are compared with those from the standard mixing-length paradigm for the most accurate calibrator, the Sun, with very satisfactory results.

  12. Stellar atmospheric parameter estimation using Gaussian process regression

    NASA Astrophysics Data System (ADS)

    Bu, Yude; Pan, Jingchang

    2015-02-01

    As is well known, it is necessary to derive stellar parameters from massive amounts of spectral data automatically and efficiently. However, in traditional automatic methods such as artificial neural networks (ANNs) and kernel regression (KR), it is often difficult to optimize the algorithm structure and determine the optimal algorithm parameters. Gaussian process regression (GPR) is a recently developed method that has been proven to be capable of overcoming these difficulties. Here we apply GPR to derive stellar atmospheric parameters from spectra. Through evaluating the performance of GPR on Sloan Digital Sky Survey (SDSS) spectra, Medium resolution Isaac Newton Telescope Library of Empirical Spectra (MILES) spectra, ELODIE spectra and the spectra of member stars of galactic globular clusters, we conclude that GPR can derive stellar parameters accurately and precisely, especially when we use data preprocessed with principal component analysis (PCA). We then compare the performance of GPR with that of several widely used regression methods (ANNs, support-vector regression and KR) and find that with GPR it is easier to optimize structures and parameters and more efficient and accurate to extract atmospheric parameters.

  13. Stellar parameters and seismological analysis of the star 18 Scorpii

    NASA Astrophysics Data System (ADS)

    Li, T. D.; Bi, S. L.; Liu, K.; Tian, Z. J.; Shuai, G. Z.

    2012-10-01

    Aims: We constructed models of the structure and evolution of the stars including diffusion and extra-mixing caused by rotation to estimate stellar parameters of the solar twin 18 Scorpii. Methods: Based on the classical observed features, we considered three additional constraints, i.e., lithium abundance log N(Li), rotational period Proteq, and average large frequency separation ⟨△ν⟩, by combing stellar models with observations to determine stellar parameters and the possible evolutionary status of 18 Scorpii. Results: More accurate results of mass and age were found by our model than in previous studies. We estimate that the mass and age of 18 Scorpii are 1.030 ± 0.010 M⊙ and 3.66-0.50+0.44 Gyr, respectively. Moreover, the model gave better constraints of atmospheric features due to the accurate age estimation. Conclusions: The consideration of lithium, rotational period, and the average large frequency separation may help us in obtaining more accurate parameters of the star. Our results indicate that 18 Scorpii is a solar twin slightly more massive and younger than the Sun.

  14. EFFECT OF UNCERTAINTIES IN STELLAR MODEL PARAMETERS ON ESTIMATED MASSES AND RADII OF SINGLE STARS

    SciTech Connect

    Basu, Sarbani; Verner, Graham A.; Chaplin, William J.; Elsworth, Yvonne E-mail: gav@bison.ph.bham.ac.uk E-mail: y.p.elsworth@bham.ac.uk

    2012-02-10

    Accurate and precise values of radii and masses of stars are needed to correctly estimate properties of extrasolar planets. We examine the effect of uncertainties in stellar model parameters on estimates of the masses, radii, and average densities of solar-type stars. We find that in the absence of seismic data on solar-like oscillations, stellar masses can be determined to a greater accuracy than either stellar radii or densities; but to get reasonably accurate results the effective temperature, log g, and metallicity must be measured to high precision. When seismic data are available, stellar density is the most well-determined property, followed by radius, with mass the least well-determined property. Uncertainties in stellar convection, quantified in terms of uncertainties in the value of the mixing length parameter, cause the most significant errors in the estimates of stellar properties.

  15. Habitable zone dependence on stellar parameter uncertainties

    SciTech Connect

    Kane, Stephen R.

    2014-02-20

    An important property of exoplanetary systems is the extent of the Habitable Zone (HZ), defined as that region where water can exist in a liquid state on the surface of a planet with sufficient atmospheric pressure. Both ground- and space-based observations have revealed a plethora of confirmed exoplanets and exoplanetary candidates, most notably from the Kepler mission using the transit detection technique. Many of these detected planets lie within the predicted HZ of their host star. However, as is the case with the derived properties of the planets themselves, the HZ boundaries depend on how well we understand the host star. Here we quantify the uncertainties of HZ boundaries on the parameter uncertainties of the host star. We examine the distribution of stellar parameter uncertainties from confirmed exoplanet hosts and Kepler candidate hosts and translate these into HZ boundary uncertainties. We apply this to several known systems with an HZ planet to determine the uncertainty in their HZ status.

  16. Atmospheric Stellar Parameters using Numerical CCFs

    NASA Astrophysics Data System (ADS)

    Malavolta, L.

    2013-09-01

    We present a new technique for the determination of atmospheric stellar parameters for low signal-to-noise spectra, based on the determination of several numerical Cross Correlation Functions (CCFs). From a qualitative point of view it is well know that the shape of the CCF depends somehow by the characteristics of the spectrum under analysis, but the interplay between temperature, metallicity and gravity in line formation affects a direct determination from a single CCF. Taking inspiration by the wellexperimented approach in temperature determination with equivalent widths, we use several CCFs to break the temperature-metallicity degeneracy by including lines selected according to their excitation potential. The use of neutral Iron lines ensures a reduced effected from gravity, which is in turn determined using ionized species. Atmosphere parameters as function of the CCFs properties are calibrated using a set of stars with equivalent width (EW)-derived parameters from high signal-to-noise spectra (Adibekyan et al. 2012). First preliminary results are shown in 1, where the difference between the atmosphere parameters determined with our technique on individual observations are compared with the EW-based ones (on co-added spectra) as functions of the signal-to-noise for 1111 FGK stars. The aim of this technique is to provide a quick and reliable atmosphere parameters determination right after the first spectrum acquisition. In particular the project has started after the installation of HARPS-N at the Telescopio Nazionale Galileo (Cosentino et al. 2012) for confirmation and follow-up of Kepler super- Earth and hot-Neptunes candidates. The expected radial velocity semi-amplitude K induced by the transiting planet and the precision of the radial-velocity measurements depend strongly on the atmospheric parameters of the host stars. An underestimated expected K would cause the exclusion from the target list of a star with a detectable planet, while in the opposite

  17. SPADES: a Stellar PArameters DEtermination Software

    NASA Astrophysics Data System (ADS)

    Posbic, H.; Katz, D.; Caffau, E.; Bonifacio, P.; Sbordone, L.; Gomez, A.; Arenou, F.

    2011-12-01

    With the large amounts of spectroscopic data available today and the very large surveys to come (e.g. Gaia), the need for automatic data analysis software is unquestionable. We thus developed an automatic spectra analysis program for the determination of stellar parameters: radial velocity, effective temperature, surface gravity, micro-turbulence, metallicity and the elemental abundances of the elements present in the spectral range. Target stars for this software should include all types of stars. The analysis method relies on a line by line comparison of the spectrum of a target star to a library of synthetic spectra. The idea is built on the experience acquired in developing the TGMET (Katz et al. 1998, Soubiran et al. 2003), ETOILE (Katz 2001) and Abbo (Bonifacio & Caffau 2003) software.The method is presented and the performances are illustrated with GIRAFFE-like simulated spectra with high resolution (R = 25000), with high and low signal to noise ratios (down to SNR = 30). These spectra should be close to what could be targeted by the Gaia-ESO Survey (GCDS).

  18. Estimation of stellar atmospheric parameters from SDSS/SEGUE spectra

    NASA Astrophysics Data System (ADS)

    Re Fiorentin, P.; Bailer-Jones, C. A. L.; Lee, Y. S.; Beers, T. C.; Sivarani, T.; Wilhelm, R.; Allende Prieto, C.; Norris, J. E.

    2007-06-01

    We present techniques for the estimation of stellar atmospheric parameters (T_eff, log~g, [Fe/H]) for stars from the SDSS/SEGUE survey. The atmospheric parameters are derived from the observed medium-resolution (R = 2000) stellar spectra using non-linear regression models trained either on (1) pre-classified observed data or (2) synthetic stellar spectra. In the first case we use our models to automate and generalize parametrization produced by a preliminary version of the SDSS/SEGUE Spectroscopic Parameter Pipeline (SSPP). In the second case we directly model the mapping between synthetic spectra (derived from Kurucz model atmospheres) and the atmospheric parameters, independently of any intermediate estimates. After training, we apply our models to various samples of SDSS spectra to derive atmospheric parameters, and compare our results with those obtained previously by the SSPP for the same samples. We obtain consistency between the two approaches, with RMS deviations on the order of 150 K in T_eff, 0.35 dex in log~g, and 0.22 dex in [Fe/H]. The models are applied to pre-processed spectra, either via Principal Component Analysis (PCA) or a Wavelength Range Selection (WRS) method, which employs a subset of the full 3850-9000Å spectral range. This is both for computational reasons (robustness and speed), and because it delivers higher accuracy (better generalization of what the models have learned). Broadly speaking, the PCA is demonstrated to deliver more accurate atmospheric parameters when the training data are the actual SDSS spectra with previously estimated parameters, whereas WRS appears superior for the estimation of log~g via synthetic templates, especially for lower signal-to-noise spectra. From a subsample of some 19 000 stars with previous determinations of the atmospheric parameters, the accuracies of our predictions (mean absolute errors) for each parameter are T_eff to 170/170 K, log~g to 0.36/0.45 dex, and [Fe/H] to 0.19/0.26 dex, for methods (1

  19. New Theory of Stellar Convection without the mixing-length parameter: new stellar atmosphere models

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

    Stellar convection is customarily described by the mixing-length theory, which makes use of the mixing-length scale to express the convective flux, velocity, and temperature gradients of the convective elements and stellar medium. The mixing-length scale is taken to be proportional to the local pressure scale height, and the proportionality factor (the mixing-length parameter) must be determined by comparing the stellar models to some calibrator, usually the Sun.No strong arguments exist to claim that the mixing-length parameter is the same in all stars and all evolutionary phases. Because of this, all stellar models in literature are hampered by this basic uncertainty.In a recent paper (Pasetto et al 2014) we presented a new theory of stellar convection that does not require the mixing length parameter. Our self-consistent analytical formulation of stellar convection determines all the properties of stellar convection as a function of the physical behaviour of the convective elements themselves and the surrounding medium. The new theory of stellar convection is formulated starting from a conventional solution of the Navier-Stokes/Euler equations, i.e. the Bernoulli equation for a perfect fluid, but expressed in a non-inertial reference frame co-moving with the convective elements. In our formalism, the motion of stellar convective cells inside convective-unstable layers is fully determined by a new system of equations for convection in a non-local and time dependent formalism.We obtained an analytical, non-local, time-dependent solution for the convective energy transport that does not depend on any free parameter. The predictions of the new theory are now compared with those from the standard mixing-length paradigm with very satisfactory results for atmosphere models of the Sun and all the stars around the Hertzsprung-Russell diagram.

  20. Theory of Stellar Convection: Removing the Mixing-Length parameter

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

    Stellar convection is customarily described by the mixing-length theory, which makes use of the mixing-length scale to express the convective flux, velocity, and temperature gradients of the convective elements and stellar medium. The mixing-length scale is taken to be proportional to the local pressure scale height, and the proportionality factor (the mixing-length parameter) must be determined by comparing the stellar models to some calibrator, usually the Sun.No strong arguments exist to claim that the mixing-length parameter is the same in all stars and all evolutionary phases. Because of this, all stellar models in literature are hampered by this basic uncertainty.In a recent paper (Pasetto et al 2014) we presented a new theory of stellar convection that does not require the mixing length parameter. Our self-consistent analytical formulation of stellar convection determines all the properties of stellar convection as a function of the physical behaviour of the convective elements themselves and the surrounding medium. The new theory of stellar convection is formulated starting from a conventional solution of the Navier-Stokes/Euler equations, i.e. the Bernoulli equation for a perfect fluid, but expressed in a non-inertial reference frame co-moving with the convective elements. In our formalism, the motion of stellar convective cells inside convective-unstable layers is fully determined by a new system of equations for convection in a non-local and time dependent formalism.We obtained an analytical, non-local, time-dependent solution for the convective energy transport that does not depend on any free parameter. The predictions of the new theory are compared with those from the standard mixing-length paradigm with exceptional results for atmosphere models of the Sun and all the stars in the Hertzsprung-Russell diagram.

  1. The true stellar parameters of the Kepler target list

    NASA Astrophysics Data System (ADS)

    Farmer, R.; Kolb, U.; Norton, A. J.

    2013-09-01

    We present results of a population synthesis study of the Kepler field. We adapted BiSEPS, a code that includes a fully self-consistent treatment of single and binary star evolution, to generate a sample of synthetic stars that represents the Kepler Input Catalogue (KIC). By subjecting this synthetic sample to the same target selection criteria that defined the actual Kepler target list we obtain a synthetic target list. We analysed the synthetic target list in turn with the methods of the Kepler Stellar Classification Project (SCP), to obtain SCP-derived stellar parameters. From this we find significant differences between the actual physical stellar parameters and those derived by the SCP of the stars in the synthetic sample. For a main sequence (MS) star, we find on average a ˜ 3% increase in stellar radius and a consequent ˜3% overestimate of the radius for any transiting exoplanet, when considered over the whole target list.

  2. Investigation of physical parameters in stellar flares observed by GINGA

    NASA Technical Reports Server (NTRS)

    Stern, Robert A.

    1994-01-01

    This program involves analysis and interpretation of results from GINGA Large Area Counter (LAC) observations from a group of large stellar x-ray flares. All LAC data are re-extracted using the standard Hayashida method of LAC background subtraction and analyzed using various models available with the XSPEC spectral fitting program. Temperature-emission measure histories are available for a total of 5 flares observed by GINGA. These will be used to compare physical parameters of these flares with solar and stellar flare models.

  3. Investigation of physical parameters in stellar flares observed by GINGA

    NASA Technical Reports Server (NTRS)

    Stern, Robert A.

    1994-01-01

    This program involves analysis and interpretation of results from GINGA Large Area Counter (LAC) observations from a group of large stellar X-ray flares. All LAC data are re-extracted using the standard Hayashida method of LAC background subtraction and analyzed using various models available with the XSPEC spectral fitting program.Temperature-emission measure histories are available for a total of 5 flares observed by GINGA. These will be used to compare physical parameters of these flares with solar and stellar flare models.

  4. Determination of stellar parameters using binary system models

    NASA Astrophysics Data System (ADS)

    Blay, Georgina; Lovekin, Catherine

    2015-12-01

    Stellar parameters can be constrained more tightly with binary systems than can typically be done with single stars. We used a freely available binary fitting code to determine the best fitting parameters of a collection of potential eclipsing binary systems observed with the Kepler satellite. These model fits constrain the mass ratio, radii ratio, surface brightness ratio, and the orbital inclination of both stars in the binary system. The frequencies of these pulsations can then be determined and used to constrain asteroseismic models.

  5. Validation of LAMOST stellar parameters with the PASTEL catalog

    NASA Astrophysics Data System (ADS)

    Gao, Hua; Zhang, Hua-Wei; Xiang, Mao-Sheng; Huang, Yang; Liu, Xiao-Wei; Luo, A.-Li; Zhang, Hao-Tong; Wu, Yue; Zhang, Yong; Li, Guang-Wei; Du, Bing

    2015-12-01

    The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) published its first data release (DR1) in 2013, which is currently the largest dataset of stellar spectra in the world. We combine the PASTEL catalog and SIMBAD radial velocities as a testing standard to validate stellar parameters (effective temperature Teff, surface gravity log g, metallicity [Fe/H] and radial velocity Vr) derived from DR1. Through cross-identification of the DR1 catalogs and the PASTEL catalog, we obtain a preliminary sample of 422 stars. After removal of stellar parameter measurements from problematic spectra and applying effective temperature constraints to the sample, we compare the stellar parameters from DR1 with those from PASTEL and SIMBAD to demonstrate that the DR1 results are reliable in restricted ranges of Teff. We derive standard deviations of 110 K, 0.19 dex and 0.11 dex for Teff, log g and [Fe/H] respectively when Teff < 8000 K, and 4.91 km s-1 for Vr when Teff < 10 000 K. Systematic errors are negligible except for those of Vr. In addition, metallicities in DR1 are systematically higher than those in PASTEL, in the range of PASTEL [Fe/H] < -1.5.

  6. Estimating stellar atmospheric parameters based on Lasso features

    NASA Astrophysics Data System (ADS)

    Liu, Chuan-Xing; Zhang, Pei-Ai; Lu, Yu

    2014-04-01

    With the rapid development of large scale sky surveys like the Sloan Digital Sky Survey (SDSS), GAIA and LAMOST (Guoshoujing telescope), stellar spectra can be obtained on an ever-increasing scale. Therefore, it is necessary to estimate stellar atmospheric parameters such as Teff, log g and [Fe/H] automatically to achieve the scientific goals and make full use of the potential value of these observations. Feature selection plays a key role in the automatic measurement of atmospheric parameters. We propose to use the least absolute shrinkage selection operator (Lasso) algorithm to select features from stellar spectra. Feature selection can reduce redundancy in spectra, alleviate the influence of noise, improve calculation speed and enhance the robustness of the estimation system. Based on the extracted features, stellar atmospheric parameters are estimated by the support vector regression model. Three typical schemes are evaluated on spectral data from both the ELODIE library and SDSS. Experimental results show the potential performance to a certain degree. In addition, results show that our method is stable when applied to different spectra.

  7. Parameter and cost optimizations for a modular stellarator reactor

    NASA Astrophysics Data System (ADS)

    Hitchon, W. N. G.; Johnson, P. C.; Watson, C. J. H.

    1983-02-01

    The physical scaling and cost scaling of a modular stellarator reactor are described. It is shown that configurations based on l=2 are best able to support adequate beta, and physical relationships are derived which enable the geometry and parameters of an l=2 modular stellarator to be defined. A cost scaling for the components of the nuclear island is developed using Starfire (tokamak reactor study) engineering as a basis. It is shown that for minimum cost the stellarator should be of small aspect ratio. For a 4000 MWth plant, as Starfire, the optimum configuration is a 15 coil, 3 field period, l=2 device with a major radius of 16 m and a plasma minor radius of 2 m; and with a conservative wall loading of 2 MW/m2 and an average beta of 3.9%; the estimated cost per kilowatt (electrical) is marginally (7%) greater than Starfire.

  8. Stellar & Planetary Parameters for K2's M dwarf Systems

    NASA Astrophysics Data System (ADS)

    Martinez, Arturo Omar; Crossfield, Ian; Schlieder, Joshua E.; Petigura, Erik; Aller, Kimberly Mei; Lepine, Sebastien; Beichman, Charles A.; Howard, Andrew; Werner, Michael W.

    2016-01-01

    The ongoing K2 mission uses photometry in order to find planets around stars of various types. M dwarfs are of high interests since they have been shown to host more planets than any other main sequence stars and transiting planets around M dwarfs are easier to find. In this poster, we present stellar parameters from M dwarfs hosting transiting planet candidates discovered by our team. Spectra of various bright M dwarfs and K2 objects were obtained in the J, H, and K bands (0.95 microns to 2.52 microns) at R ~ 1000. We measure equivalent widths of spectra features to obtain stellar radii and effective temperatures. Since planet radii and equilibrium temperatures depend on calculating the parameters of its host stars, understanding the nature of the hosts stars improves the precision with which we can measure these K2 objects of interest.

  9. Atmosphere models and the determination of stellar parameters

    NASA Astrophysics Data System (ADS)

    Martins, F.

    2014-11-01

    We present the basic concepts necessary to build atmosphere models for any type of star. We then illustrate how atmosphere models can be used to determine stellar parameters. We focus on the effects of line-blanketing for hot stars, and on non-LTE and three dimensional effects for cool stars. We illustrate the impact of these effects on the determination of the ages of stars from the HR diagram.

  10. Predicting Fundamental Stellar Parameters From Photometric Light Curves

    NASA Astrophysics Data System (ADS)

    Miller, Adam; Richards, J.; Bloom, J. S.; a larger Team

    2014-01-01

    We present a new machine-learning-based framework for the prediction of the fundamental stellar parameters, Teff, log g, and [Fe/H], based on the photometric light curves of variable stellar sources. The method was developed following a systematic spectroscopic survey of stellar variability. Variable sources were selected from repeated Sloan Digital Sky Survey (SDSS) observations of Stripe 82, and spectroscopic observations were obtained with Hectospec on the 6.5-m Multi-Mirror Telescope. In sum, spectra were obtained for ~9000 stellar variables (including ~3000 from the SDSS archive), for which we measured Teff, log g, and [Fe/H] using the Segue Stellar Parameters Pipeline (SSPP). Examining the full sample of ~67k variables in Stripe 82, we show that the vast majority of photometric variables are consistent with main-sequence stars, even after restricting the search to high galactic latitudes. From the spectroscopic sample we confirm that most of these stellar variables are G and K dwarfs, though there is a bias in the output of the SSPP that prevents the identification of M type variables. We are unable to identify the dominant source of variability for these stars, but eclipsing systems and/or star spots are the most likely explanation. We develop a machine-learning model that can determine Teff, log g, and [Fe/H] without obtaining a spectrum. Instead, the random-forest-regression model uses SDSS color information and light-curve features to infer stellar properties. We detail how the feature set is pruned and the model is optimized to produce final predictions of Teff, log g, and [Fe/H] with a typical scatter of 165 K, 0.42 dex, and 0.33 dex, respectively. We further show that for the subset of variables with at least 50 observations in the g band the typical scatter reduces to 75 K, 0.19 dex, and 0.16 dex, respectively. We consider these results an important step on the path to the efficient and optimal extraction of information from future time

  11. Predicting Fundamental Stellar Parameters from Photometric Light Curves

    NASA Astrophysics Data System (ADS)

    Miller, A.

    We present a new machine learning based framework for the prediction of the fun- damental stellar parameters, Teff, logg, and [Fe/H], based on the photometric light curves of variable stellar sources. The method was developed following a systematic spectroscopic survey of stellar variability. Variable sources were selected from re- peated Sloan Digital Sky Survey (SDSS) observations of Stripe 82, and spectroscopic observations were obtained with Hectospec on the 6.5-m Multi-Mirror Telescope. In sum, spectra were obtained for ˜9,000 stellar variables (including ˜3,000 from the SDSS archive), for which we measured Teff, log g, and [Fe/H] using the Segue Stellar Parameters Pipeline (SSPP). Examining the full sample of ˜67,000 variables in Stripe 82, we show that the vast majority of photometric variables are consistent with main-sequence stars, even after restricting the search to high galactic latitudes. From the spectroscopic sample we confirm that most of these stellar variables are G and K dwarfs, though there is a bias in the output of the SSPP that prevents the identification of M type variables. We are unable to identify the dominant source of variability for these stars, but eclipsing systems and/or star spots are the most likely explanation. We develop a machine learning model that can determine Teff , log g, and [Fe/H] without obtaining a spectrum. Instead, the random forest regression model uses SDSS color information and light curve features to infer stellar properties. We detail how the feature set is pruned and the model is optimized to produce final predictions of Teff, log g, and [Fe/H] with a typical scatter of 165 K, 0.42 dex, and 0.33 dex, respectively. We further show that for the subset of variables with at least 50 observations in the g band the typical scatter reduces to 75 K, 0.19 dex, and 0.16 dex, respectively. We consider these results an important step on the path to the efficient and optimal extraction of information from future time

  12. The true stellar parameters of the Kepler target list

    NASA Astrophysics Data System (ADS)

    Farmer, R.; Kolb, U.; Norton, A. J.

    2013-08-01

    Using population synthesis tools we create a synthetic Kepler Input Catalogue (KIC) and subject it to the Kepler Stellar Classification Program (SCP) method for determining stellar parameters such as the effective temperature Teff and surface gravity g. We achieve a satisfactory match between the synthetic KIC and the real KIC in the log g versus log Teff diagram, while there is a significant difference between the actual physical stellar parameters and those derived by the SCP of the stars in the synthetic sample. We find a median difference ΔTeff = +500 K and ˜Δlog g = -0.2 dex for main-sequence (MS) stars, and ˜ΔTeff = +50 K and Δlog g = -0.5 dex for giants, although there is a large variation across parameter space. For a MS star the median difference in g would equate to a ˜3 per cent increase in stellar radius and a consequent ˜3 per cent overestimate of the radius for any transiting exoplanet. We find no significant difference between ΔTeff and Δlog g for single stars and the primary star in a binary system. We also re-created the Kepler target selection method and found that the binary fraction is unchanged by the target selection. Binaries are selected in similar proportions to single star systems; the fraction of MS dwarfs in the sample increases from about 75 to 80 per cent, and the giant star fraction decreases from 25 to 20 per cent.

  13. 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.

  14. Probabilistic Inference of Basic Stellar Parameters: Application to Flickering Stars

    NASA Astrophysics Data System (ADS)

    Angus, Ruth; Kipping, David. M.

    2016-05-01

    The relations between observable stellar parameters are usually assumed to be deterministic. That is, given an infinitely precise measurement of independent variable, “x”, and some model, the value of dependent variable, “y” can be known exactly. In practice this assumption is rarely valid and intrinsic stochasticity means that two stars with exactly the same “x” will have slightly different “y”s. The relation between short-timescale brightness fluctuations (flicker) of stars and both surface gravity and stellar density are two such stochastic relations that have until now been treated as deterministic ones. We recalibrate these relations in a probabilistic framework, using hierarchical Bayesian modeling to constrain the instrinsic scatter in the relations. We find evidence for additional scatter in the relationship, that cannot be accounted for by the observational uncertainties alone. The scatter in surface gravity and stellar density does not depend on flicker, suggesting that using flicker as a proxy for {log}g and ρ ⋆ is equally valid for dwarf and giant stars, despite the fact that the observational uncertainties tend to be larger for dwarfs. Based on archival data of the Kepler telescope.

  15. ASPCAP: The APOGEE Stellar Parameter and Chemical Abundances Pipeline

    NASA Astrophysics Data System (ADS)

    García Pérez, Ana E.; Allende Prieto, Carlos; Holtzman, Jon A.; Shetrone, Matthew; Mészáros, Szabolcs; Bizyaev, Dmitry; Carrera, Ricardo; Cunha, Katia; García-Hernández, D. A.; Johnson, Jennifer A.; Majewski, Steven R.; Nidever, David L.; Schiavon, Ricardo P.; Shane, Neville; Smith, Verne V.; Sobeck, Jennifer; Troup, Nicholas; Zamora, Olga; Weinberg, David H.; Bovy, Jo; Eisenstein, Daniel J.; Feuillet, Diane; Frinchaboy, Peter M.; Hayden, Michael R.; Hearty, Fred R.; Nguyen, Duy C.; O’Connell, Robert W.; Pinsonneault, Marc H.; Wilson, John C.; Zasowski, Gail

    2016-06-01

    The Apache Point Observatory Galactic Evolution Experiment (APOGEE) has built the largest moderately high-resolution (R ≈ 22,500) spectroscopic map of the stars across the Milky Way, and including dust-obscured areas. The APOGEE Stellar Parameter and Chemical Abundances Pipeline (ASPCAP) is the software developed for the automated analysis of these spectra. ASPCAP determines atmospheric parameters and chemical abundances from observed spectra by comparing observed spectra to libraries of theoretical spectra, using χ2 minimization in a multidimensional parameter space. The package consists of a fortran90 code that does the actual minimization and a wrapper IDL code for book-keeping and data handling. This paper explains in detail the ASPCAP components and functionality, and presents results from a number of tests designed to check its performance. ASPCAP provides stellar effective temperatures, surface gravities, and metallicities precise to 2%, 0.1 dex, and 0.05 dex, respectively, for most APOGEE stars, which are predominantly giants. It also provides abundances for up to 15 chemical elements with various levels of precision, typically under 0.1 dex. The final data release (DR12) of the Sloan Digital Sky Survey III contains an APOGEE database of more than 150,000 stars. ASPCAP development continues in the SDSS-IV APOGEE-2 survey.

  16. FAMA: An automatic code for stellar parameter and abundance determination

    NASA Astrophysics Data System (ADS)

    Magrini, Laura; Randich, Sofia; Friel, Eileen; Spina, Lorenzo; Jacobson, Heather; Cantat-Gaudin, Tristan; Donati, Paolo; Baglioni, Roberto; Maiorca, Enrico; Bragaglia, Angela; Sordo, Rosanna; Vallenari, Antonella

    2013-10-01

    Context. The large amount of spectra obtained during the epoch of extensive spectroscopic surveys of Galactic stars needs the development of automatic procedures to derive their atmospheric parameters and individual element abundances. Aims: Starting from the widely-used code MOOG by C. Sneden, we have developed a new procedure to determine atmospheric parameters and abundances in a fully automatic way. The code FAMA (Fast Automatic MOOG Analysis) is presented describing its approach to derive atmospheric stellar parameters and element abundances. The code, freely distributed, is written in Perl and can be used on different platforms. Methods: The aim of FAMA is to render the computation of the atmospheric parameters and abundances of a large number of stars using measurements of equivalent widths (EWs) as automatic and as independent of any subjective approach as possible. It is based on the simultaneous search for three equilibria: excitation equilibrium, ionization balance, and the relationship between log n(Fe i) and the reduced EWs. FAMA also evaluates the statistical errors on individual element abundances and errors due to the uncertainties in the stellar parameters. The convergence criteria are not fixed "a priori" but are based on the quality of the spectra. Results: In this paper we present tests performed on the solar spectrum EWs that assess the method's dependency on the initial parameters and we analyze a sample of stars observed in Galactic open and globular clusters. The current version of FAMA is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/558/A38

  17. Accurate parameter estimation for unbalanced three-phase system.

    PubMed

    Chen, Yuan; So, Hing Cheung

    2014-01-01

    Smart grid is an intelligent power generation and control console in modern electricity networks, where the unbalanced three-phase power system is the commonly used model. Here, parameter estimation for this system is addressed. After converting the three-phase waveforms into a pair of orthogonal signals via the α β-transformation, the nonlinear least squares (NLS) estimator is developed for accurately finding the frequency, phase, and voltage parameters. The estimator is realized by the Newton-Raphson scheme, whose global convergence is studied in this paper. Computer simulations show that the mean square error performance of NLS method can attain the Cramér-Rao lower bound. Moreover, our proposal provides more accurate frequency estimation when compared with the complex least mean square (CLMS) and augmented CLMS. PMID:25162056

  18. A Novel Tool for the Spectroscopic Inference of Fundamental Stellar Parameters

    NASA Astrophysics Data System (ADS)

    Czekala, Ian; Andrews, Sean M.; Latham, David W.; Torres, Guillermo

    2014-06-01

    We present a novel approach for making accurate and unbiased inferences of fundamental stellar parameters (e.g., effective temperature, surface gravity, metallicity) from spectroscopic observations, with reference to a library of synthetic spectra. The forward-modeling formalism we have developed is generic (easily adaptable to data from any instrument or covering any wavelength range) and modular, in that it can incorporate external prior knowledge or additional data (e.g., broadband photometry) and account for instrumental and non-stellar effects on the spectrum (e.g., parametric treatments of extinction, spots, etc.). An approach that employs adaptive correlated noise is used to account for systematic discrepancies between the observations and the synthetic spectral library, ensuring that issues like uncertainties in atomic or molecular constants do not strongly bias the parameter inferences. In addition to extracting a set of unbiased inferences of the (posterior) probability distributions for basic stellar parameters, our modeling approach also "maps" out problematic spectral regions in the synthetic libraries that could be used as a basis for improving the models. As a demonstration, we present some preliminary results from modeling optical spectra of well-characterized exoplanet host stars and nearby pre-main sequence stars. A basic set of adaptable software that performs this modeling approach will be released publicly.

  19. Stellar parameters and accretion rate of the transition disk star HD 142527 from X-shooter

    SciTech Connect

    Mendigutía, I.; Fairlamb, J.; Oudmaijer, R. D.; Montesinos, B.; Najita, J. R.; Brittain, S. D.; Van den Ancker, M. E.

    2014-07-20

    HD 142527 is a young pre-main-sequence star with properties indicative of the presence of a giant planet and/or a low-mass stellar companion. We have analyzed an X-Shooter/Very Large Telescope spectrum to provide accurate stellar parameters and accretion rate. The analysis of the spectrum, together with constraints provided by the spectral energy distribution fitting, the distance to the star (140 ± 20 pc), and the use of evolutionary tracks and isochrones, led to the following set of parameters: T{sub eff} = 6550 ± 100 K, log g = 3.75 ± 0.10, L{sub *}/L{sub ☉} = 16.3 ± 4.5, M{sub *}/M{sub ☉} = 2.0 ± 0.3, and an age of 5.0 ± 1.5 Myr. This stellar age provides further constraints to the mass of the possible companion estimated by Biller et al., being between 0.20 and 0.35 M{sub ☉}. Stellar accretion rates obtained from UV Balmer excess modeling and optical photospheric line veiling, and from the correlations with several emission lines spanning from the UV to the near-IR, are consistent with each other. The mean value from all previous tracers is 2 (±1) × 10{sup –7} M{sub ☉} yr{sup –1}, which is within the upper limit gas flow rate from the outer to the inner disk recently provided by Cassasus et al.. This suggests that almost all gas transferred between both components of the disk is not trapped by the possible planet(s) in between but fall onto the central star, although it is discussed how the gap flow rate could be larger than previously suggested. In addition, we provide evidence showing that the stellar accretion rate of HD 142527 has increased by a factor ∼7 on a timescale of 2 to 5 yr.

  20. Stellar Parameters and Accretion Rate of the Transition Disk Star HD 142527 from X-Shooter

    NASA Astrophysics Data System (ADS)

    Mendigutía, I.; Fairlamb, J.; Montesinos, B.; Oudmaijer, R. D.; Najita, J. R.; Brittain, S. D.; van den Ancker, M. E.

    2014-07-01

    HD 142527 is a young pre-main-sequence star with properties indicative of the presence of a giant planet and/or a low-mass stellar companion. We have analyzed an X-Shooter/Very Large Telescope spectrum to provide accurate stellar parameters and accretion rate. The analysis of the spectrum, together with constraints provided by the spectral energy distribution fitting, the distance to the star (140 ± 20 pc), and the use of evolutionary tracks and isochrones, led to the following set of parameters: T eff = 6550 ± 100 K, log g = 3.75 ± 0.10, L */L ⊙ = 16.3 ± 4.5, M */M ⊙ = 2.0 ± 0.3, and an age of 5.0 ± 1.5 Myr. This stellar age provides further constraints to the mass of the possible companion estimated by Biller et al., being between 0.20 and 0.35 M ⊙. Stellar accretion rates obtained from UV Balmer excess modeling and optical photospheric line veiling, and from the correlations with several emission lines spanning from the UV to the near-IR, are consistent with each other. The mean value from all previous tracers is 2 (±1) × 10-7 M ⊙ yr-1, which is within the upper limit gas flow rate from the outer to the inner disk recently provided by Cassasus et al.. This suggests that almost all gas transferred between both components of the disk is not trapped by the possible planet(s) in between but fall onto the central star, although it is discussed how the gap flow rate could be larger than previously suggested. In addition, we provide evidence showing that the stellar accretion rate of HD 142527 has increased by a factor ~7 on a timescale of 2 to 5 yr.

  1. STELLAR MASS-TO-LIGHT RATIOS FROM GALAXY SPECTRA: HOW ACCURATE CAN THEY BE?

    SciTech Connect

    Gallazzi, Anna; Bell, Eric F. E-mail: ericbell@umich.edu

    2009-12-01

    Stellar masses play a crucial role in the exploration of galaxy properties and the evolution of the galaxy population. In this paper, we explore the minimum possible uncertainties in stellar mass-to-light ratios (M {sub *}/L) from the assumed star formation history (SFH) and metallicity distribution, with the goals of providing a minimum set of requirements for observational studies. We use a large Monte Carlo library of SFHs to study as a function of galaxy spectral type and signal-to-noise ratio (S/N) the statistical uncertainties of M {sub *}/L values using either absorption-line data or broadband colors. The accuracy of M {sub *}/L estimates can be significantly improved by using metal-sensitive indices in combination with age-sensitive indices, in particular for galaxies with intermediate-age or young stellar populations. While M {sub *}/L accuracy clearly depends on the spectral S/N, there is no significant gain in improving the S/N much above 50 pixel{sup -1} and limiting uncertainties of {approx}0.03 dex are reached. Assuming that dust is accurately corrected or absent and that the redshift is known, color-based M {sub *}/L estimates are only slightly more uncertain than spectroscopic estimates (at comparable spectroscopic and photometric quality), but are more easily affected by systematic biases. This is the case in particular for galaxies with bursty SFHs (high H{delta} {sub A} at fixed D4000 {sub n}), the M {sub *}/L of which cannot be constrained any better than {approx}0.15 dex with any indicators explored here. Finally, we explore the effects of the assumed prior distribution in SFHs and metallicity, finding them to be higher for color-based estimates.

  2. ACCURATE STELLAR KINEMATICS AT FAINT MAGNITUDES: APPLICATION TO THE BOOeTES I DWARF SPHEROIDAL GALAXY

    SciTech Connect

    Koposov, Sergey E.; Gilmore, G.; Walker, M. G.; Belokurov, V.; Evans, N. Wyn; Okamoto, S.; Penarrubia, J.; Fellhauer, M.; Gieren, W.; Geisler, D.; Monaco, L.; Norris, J. E.; Wilkinson, M.; Wyse, R. F. G.; Zucker, D. B.

    2011-08-01

    We develop, implement, and characterize an enhanced data reduction approach which delivers precise, accurate, radial velocities from moderate resolution spectroscopy with the fiber-fed VLT/FLAMES+GIRAFFE facility. This facility, with appropriate care, delivers radial velocities adequate to resolve the intrinsic velocity dispersions of the very faint dwarf spheroidal (dSph) galaxies. Importantly, repeated measurements let us reliably calibrate our individual velocity errors (0.2 kms{sup -1} {<=} {delta}{sub V} {<=} 5 km s{sup -1}) and directly detect stars with variable radial velocities. We show, by application to the Booetes I dSph, that the intrinsic velocity dispersion of this system is significantly below 6.5 km s{sup -1} reported by previous studies. Our data favor a two-population model of Booetes I, consisting of a majority 'cold' stellar component, with velocity dispersion 2.4{sup +0.9}{sub -0.5} km s{sup -1}, and a minority 'hot' stellar component, with velocity dispersion {approx}9 km s{sup -1}, although we cannot completely rule out a single component distribution with velocity dispersion 4.6{sup 0.8}{sub -0.6} km s{sup -1}. We speculate that this complex velocity distribution actually reflects the distribution of velocity anisotropy in Booetes I, which is a measure of its formation processes.

  3. Photometric ``Flicker:'' Tracer of Granulation and an Accurate Measure of Stellar Surface Gravity

    NASA Astrophysics Data System (ADS)

    Bastien, Fabienne

    2015-04-01

    As a result of the high precision and cadence of surveys like NASA's Kepler, we may now directly observe the very low-level light variations in Sun-like stars. In my dissertation, I found that some of these variations unexpectedly arise from granulation, a result that enables us to more accurately determine the physical properties of Sun-like stars, permits us to understand the nature of surface convection and its connection to activity, and allows us to better determine the properties of planets around Sun-like stars. I find that granulation manifests through light ``flicker,'' thereby yielding a simple measurement of stellar surface gravity with a precision of 0.1 dex. I use this, together and solely with two other simple ways of characterizing the stellar photometric variations in a high quality light curve, to construct an evolutionary diagram for Sun-like stars from the main-sequence on towards the red giant branch. I use flicker to re-determine the fundamental properties of Kepler planet host stars, finding that the stars - and hence the planets orbiting them - are 20-30% larger than previous estimates. Finally, I show that high precision light curves can yield remarkably clean predictors of radial velocity (RV) jitter in magnetically inactive stars, allowing the exoplanet community to prioritize RV follow-up campaigns with discovery light curves and providing insight into the primary physical drivers of RV jitter in such stars.

  4. Accurate and robust estimation of camera parameters using RANSAC

    NASA Astrophysics Data System (ADS)

    Zhou, Fuqiang; Cui, Yi; Wang, Yexin; Liu, Liu; Gao, He

    2013-03-01

    Camera calibration plays an important role in the field of machine vision applications. The popularly used calibration approach based on 2D planar target sometimes fails to give reliable and accurate results due to the inaccurate or incorrect localization of feature points. To solve this problem, an accurate and robust estimation method for camera parameters based on RANSAC algorithm is proposed to detect the unreliability and provide the corresponding solutions. Through this method, most of the outliers are removed and the calibration errors that are the main factors influencing measurement accuracy are reduced. Both simulative and real experiments have been carried out to evaluate the performance of the proposed method and the results show that the proposed method is robust under large noise condition and quite efficient to improve the calibration accuracy compared with the original state.

  5. Machine learning of parameters for accurate semiempirical quantum chemical calculations

    DOE PAGESBeta

    Dral, Pavlo O.; von Lilienfeld, O. Anatole; Thiel, Walter

    2015-04-14

    We investigate possible improvements in the accuracy of semiempirical quantum chemistry (SQC) methods through the use of machine learning (ML) models for the parameters. For a given class of compounds, ML techniques require sufficiently large training sets to develop ML models that can be used for adapting SQC parameters to reflect changes in molecular composition and geometry. The ML-SQC approach allows the automatic tuning of SQC parameters for individual molecules, thereby improving the accuracy without deteriorating transferability to molecules with molecular descriptors very different from those in the training set. The performance of this approach is demonstrated for the semiempiricalmore » OM2 method using a set of 6095 constitutional isomers C7H10O2, for which accurate ab initio atomization enthalpies are available. The ML-OM2 results show improved average accuracy and a much reduced error range compared with those of standard OM2 results, with mean absolute errors in atomization enthalpies dropping from 6.3 to 1.7 kcal/mol. They are also found to be superior to the results from specific OM2 reparameterizations (rOM2) for the same set of isomers. The ML-SQC approach thus holds promise for fast and reasonably accurate high-throughput screening of materials and molecules.« less

  6. Machine learning of parameters for accurate semiempirical quantum chemical calculations

    SciTech Connect

    Dral, Pavlo O.; von Lilienfeld, O. Anatole; Thiel, Walter

    2015-04-14

    We investigate possible improvements in the accuracy of semiempirical quantum chemistry (SQC) methods through the use of machine learning (ML) models for the parameters. For a given class of compounds, ML techniques require sufficiently large training sets to develop ML models that can be used for adapting SQC parameters to reflect changes in molecular composition and geometry. The ML-SQC approach allows the automatic tuning of SQC parameters for individual molecules, thereby improving the accuracy without deteriorating transferability to molecules with molecular descriptors very different from those in the training set. The performance of this approach is demonstrated for the semiempirical OM2 method using a set of 6095 constitutional isomers C7H10O2, for which accurate ab initio atomization enthalpies are available. The ML-OM2 results show improved average accuracy and a much reduced error range compared with those of standard OM2 results, with mean absolute errors in atomization enthalpies dropping from 6.3 to 1.7 kcal/mol. They are also found to be superior to the results from specific OM2 reparameterizations (rOM2) for the same set of isomers. The ML-SQC approach thus holds promise for fast and reasonably accurate high-throughput screening of materials and molecules.

  7. Accurate parameters for HD 209458 and its planet from HST spectrophotometry

    NASA Astrophysics Data System (ADS)

    del Burgo, C.; Allende Prieto, C.

    2016-08-01

    We present updated parameters for the star HD 209458 and its transiting giant planet. The stellar angular diameter θ=0.2254±0.0017 mas is obtained from the average ratio between the absolute flux observed with the Hubble Space Telescope and that of the best-fitting Kurucz model atmosphere. This angular diameter represents an improvement in precision of more than four times compared to available interferometric determinations. The stellar radius R⋆=1.20±0.05 R⊙ is ascertained by combining the angular diameter with the Hipparcos trigonometric parallax, which is the main contributor to its uncertainty, and therefore the radius accuracy should be significantly improved with Gaia's measurements. The radius of the exoplanet Rp=1.41±0.06 RJ is derived from the corresponding transit depth in the light curve and our stellar radius. From the model fitting, we accurately determine the effective temperature, Teff=6071±20 K, which is in perfect agreement with the value of 6070±24 K calculated from the angular diameter and the integrated spectral energy distribution. We also find precise values from recent Padova Isochrones, such as R⋆=1.20±0.06 R⊙ and Teff=6099±41 K. We arrive at a consistent picture from these methods and compare the results with those from the literature.

  8. Grid search in stellar parameters: a software for spectrum analysis of single stars and binary systems

    NASA Astrophysics Data System (ADS)

    Tkachenko, A.

    2015-09-01

    Context. The currently operating space missions, as well as those that will be launched in the near future, will deliver high-quality data for millions of stellar objects. Since the majority of stellar astrophysical applications still (at least partly) rely on spectroscopic data, an efficient tool for the analysis of medium- to high-resolution spectroscopy is needed. Aims: We aim at developing an efficient software package for the analysis of medium- to high-resolution spectroscopy of single stars and those in binary systems. The major requirements are that the code should have a high performance, represent the state-of-the-art analysis tool, and provide accurate determinations of atmospheric parameters and chemical compositions for different types of stars. Methods: We use the method of atmosphere models and spectrum synthesis, which is one of the most commonly used approaches for the analysis of stellar spectra. Our Grid Search in Stellar Parameters (gssp) code makes use of the Message Passing Interface (OpenMPI) implementation, which makes it possible to run in parallel mode. The method is first tested on the simulated data and is then applied to the spectra of real stellar objects. Results: The majority of test runs on the simulated data were successful in that we were able to recover the initially assumed sets of atmospheric parameters. We experimentally find the limits in signal-to-noise ratios of the input spectra, below which the final set of parameters is significantly affected by the noise. Application of the gssp package to the spectra of three Kepler stars, KIC 11285625, KIC 6352430, and KIC 4931738, was also largely successful. We found an overall agreement of the final sets of the fundamental parameters with the original studies. For KIC 6352430, we found that dependence of the light dilution factor on wavelength cannot be ignored, as it has a significant impact on the determination of the atmospheric parameters of this binary system. Conclusions: The

  9. Direct computation of parameters for accurate polarizable force fields

    SciTech Connect

    Verstraelen, Toon Vandenbrande, Steven; Ayers, Paul W.

    2014-11-21

    We present an improved electronic linear response model to incorporate polarization and charge-transfer effects in polarizable force fields. This model is a generalization of the Atom-Condensed Kohn-Sham Density Functional Theory (DFT), approximated to second order (ACKS2): it can now be defined with any underlying variational theory (next to KS-DFT) and it can include atomic multipoles and off-center basis functions. Parameters in this model are computed efficiently as expectation values of an electronic wavefunction, obviating the need for their calibration, regularization, and manual tuning. In the limit of a complete density and potential basis set in the ACKS2 model, the linear response properties of the underlying theory for a given molecular geometry are reproduced exactly. A numerical validation with a test set of 110 molecules shows that very accurate models can already be obtained with fluctuating charges and dipoles. These features greatly facilitate the development of polarizable force fields.

  10. Accurate 3D quantification of the bronchial parameters in MDCT

    NASA Astrophysics Data System (ADS)

    Saragaglia, A.; Fetita, C.; Preteux, F.; Brillet, P. Y.; Grenier, P. A.

    2005-08-01

    The assessment of bronchial reactivity and wall remodeling in asthma plays a crucial role in better understanding such a disease and evaluating therapeutic responses. Today, multi-detector computed tomography (MDCT) makes it possible to perform an accurate estimation of bronchial parameters (lumen and wall areas) by allowing a quantitative analysis in a cross-section plane orthogonal to the bronchus axis. This paper provides the tools for such an analysis by developing a 3D investigation method which relies on 3D reconstruction of bronchial lumen and central axis computation. Cross-section images at bronchial locations interactively selected along the central axis are generated at appropriate spatial resolution. An automated approach is then developed for accurately segmenting the inner and outer bronchi contours on the cross-section images. It combines mathematical morphology operators, such as "connection cost", and energy-controlled propagation in order to overcome the difficulties raised by vessel adjacencies and wall irregularities. The segmentation accuracy was validated with respect to a 3D mathematically-modeled phantom of a pair bronchus-vessel which mimics the characteristics of real data in terms of gray-level distribution, caliber and orientation. When applying the developed quantification approach to such a model with calibers ranging from 3 to 10 mm diameter, the lumen area relative errors varied from 3.7% to 0.15%, while the bronchus area was estimated with a relative error less than 5.1%.

  11. Estimating Stellar Fundamental Parameters Using PCA: Application to Early Type Stars of GES Data

    NASA Astrophysics Data System (ADS)

    Farah, W.; Gebran, M.; Paletou, F.; Blomme, R.

    2015-12-01

    This work addresses a procedure to estimate fundamental stellar parameters such as T_{eff}, log g, [Fe/H], and v sin i using a dimensionality reduction technique called principal component analysis (PCA), applied to a large database of synthetic spectra. This technique shows promising results for inverting stellar parameters of observed targets from Gaia Eso Survey.

  12. VizieR Online Data Catalog: Stellar physical parameters for young stars (Monguio+, 2014)

    NASA Astrophysics Data System (ADS)

    Monguio, M.; Figueras, F.; Grosbol, P.

    2014-08-01

    A uvbyHβ Stromgren photometric survey covering 16 square degrees in the anticenter direction was carried out using the Wide Field Camera at the Isaac Newton Telescope. Physical parameters like stellar distances and extinctions for the young stars of our survey are presented here. We developed a new method for deriving physical parameters from Stromgren photometry and also implemented and tested it. This is a model-based method that uses the most recent available stellar atmospheric models and evolutionary tracks to interpolate in a 3D grid of the unreddened indexes [m1], [c1] and Hβ. Distances derived from both this method and the classical pre-Hipparcos calibrations were tested against Hipparcos parallaxes and found to be accurate. Furthermore, a shift in the atmospheric grids in the range Teff=[7000,9000]K was detected and a correction is proposed. The two methods were used to compute distances and reddening for around 12000 OBA-type stars in our Stromgren anticenter survey. Data from the IPHAS and 2MASS catalogs were used to complement the detection of emission line stars and to break the degeneracy between early and late photometric regions. We note that photometric distances can differ by more than 20%, those derived from the empirical calibrations being smaller than those derived with the new method, which agree better with the Hipparcos data. (1 data file).

  13. Stellar parameters of early-M dwarfs from ratios of spectral features at optical wavelengths

    NASA Astrophysics Data System (ADS)

    Maldonado, J.; Affer, L.; Micela, G.; Scandariato, G.; Damasso, M.; Stelzer, B.; Barbieri, M.; Bedin, L. R.; Biazzo, K.; Bignamini, A.; Borsa, F.; Claudi, R. U.; Covino, E.; Desidera, S.; Esposito, M.; Gratton, R.; González Hernández, J. I.; Lanza, A. F.; Maggio, A.; Molinari, E.; Pagano, I.; Perger, M.; Pillitteri, I.; Piotto, G.; Poretti, E.; Prisinzano, L.; Rebolo, R.; Ribas, I.; Shkolnik, E.; Southworth, J.; Sozzetti, A.; Suárez Mascareño, A.

    2015-05-01

    Context. Low-mass stars have been recognised as promising targets in the search for rocky, small planets with the potential of supporting life. As a consequence, Doppler search programmes using high-resolution spectrographs like HARPS or HARPS-N are providing huge quantities of optical spectra of M dwarfs. However, determining the stellar parameters of M dwarfs using optical spectra has proven to be challenging. Aims: We aim to calibrate empirical relationships to determine accurate stellar parameters for early-M dwarfs (spectral types M0-M4.5) using the same spectra as those that are used for radial velocity determinations, without the necessity of acquiring IR spectra or relying on atmospheric models and/or photometric calibrations. Methods: Our methodology consists of using ratios of pseudo-equivalent widths of spectral features as a temperature diagnostic, a technique frequently used in solar-type stars. Stars with effective temperatures obtained from interferometric estimates of their radii are used as calibrators. Empirical calibrations for the spectral type are also provided. Combinations of features and ratios of features are used to derive calibrations for the stellar metallicity. Our methods are then applied to a large sample of M dwarfs that are currently being observed in the framework of the HARPS GTO search for extrasolar planets. The derived temperatures and metallicities are used together with photometric estimates of mass, radius, and surface gravity to calibrate empirical relationships for these parameters. Results: A long list of spectral features in the optical spectra of early-M dwarfs was identified. This list shows that the pseudo-equivalent width of roughly 43% of the features is strongly anticorrelated with the effective temperature. The correlation with the stellar metallicity is weaker. A total of 112 temperature sensitive ratios were identified and calibrated over the range 3100-3950 K, providing effective temperatures with typical

  14. A method for determining stellar parameters from multicolor photometry

    NASA Astrophysics Data System (ADS)

    Sichevskij, S. G.

    2012-09-01

    Amethod for determining the most probable spectral types, color excesses E B- V , and distances of stars from multicolor photometry is described. The main idea of the method is modeling the photometric data using various models for the stellar spectra and the interstellar extinction law, and applying the maximum likelihood method. The reliability of the method is estimated using stars with known spectral types and WBVR photometry, based on the empirical library of stellar spectra of Pickles and the model for the interstellar extinction law developed by Fluks et al.

  15. Fundamental Parameters of Nearby Red Dwarfs: Stellar Radius as an Indicator of Age

    NASA Astrophysics Data System (ADS)

    Silverstein, Michele L.; Henry, Todd J.; Winters, Jennifer G.; Jao, Wei-Chun; Riedel, Adric R.; Dieterich, Sergio; RECONS Team

    2016-01-01

    Red dwarfs dominate the Galactic population, yet determining one of their most fundamental characteristics --- age --- has proven difficult. The characterization of red dwarfs in terms of their age is fundamental to mapping the history of star and, ultimately, planet formation in the Milky Way. Here we report on a compelling technique to evaluate the radii of red dwarfs, which can be used to provide leverage in estimating their ages. These radii are also particularly valuable in the cases of transiting exoplanet hosts because accurate stellar radii are required to determine accurate planetary radii.In this work, we use the BT-Settl models in combination with Johnson-Kron-Cousins VRI, 2MASS JHK, and WISE All-Sky Release photometry to produce spectral energy distributions (SEDs) to determine the temperatures and bolometric fluxes for 500 red dwarfs, most of which are in the southern sky. The full suites of our photometric and astrometric data (including hundreds of accurate new parallaxes from the RECONS team at the CTIO/SMARTS 0.9m) allow us to also determine the bolometric luminosities and radii. This method of radius determination is validated by a comparison of our measurements to those found using the CHARA Array (Boyajian et al. 2012), which match within a few percent.In addition to a compilation of red dwarf fundamental parameters, our findings provide a snapshot of relative stellar ages in the solar neighborhood. Of particular interest are the cohorts of very young and very old stars identified within 50 pc. These outliers exemplify the demographic extremes of the nearest stars.This effort has been supported by the NSF through grants AST-0908402, AST-1109445, and AST-1412026, and via observations made possible by the SMARTS Consortium.

  16. VERIFYING ASTEROSEISMICALLY DETERMINED PARAMETERS OF KEPLER STARS USING HIPPARCOS PARALLAXES: SELF-CONSISTENT STELLAR PROPERTIES AND DISTANCES

    SciTech Connect

    Silva Aguirre, V.; Chaplin, W. J.; Bedding, T. R.; Christensen-Dalsgaard, J.; Kjeldsen, H.; Casagrande, L.; Basu, S.; Campante, T. L.; Monteiro, M. J. P. F. G.; Huber, D.; Miglio, A.; Elsworth, Y.; Hekker, S.; Serenelli, A. M.; Garcia, R. A.; Mathur, S.; Ballot, J.; Creevey, O. L.; Gilliland, R. L.; Metcalfe, T. S.; and others

    2012-09-20

    Accurately determining the properties of stars is of prime importance for characterizing stellar populations in our Galaxy. The field of asteroseismology has been thought to be particularly successful in such an endeavor for stars in different evolutionary stages. However, to fully exploit its potential, robust methods for estimating stellar parameters are required and independent verification of the results is mandatory. With this purpose, we present a new technique to obtain stellar properties by coupling asteroseismic analysis with the InfraRed Flux Method. By using two global seismic observables and multi-band photometry, the technique allows us to obtain masses, radii, effective temperatures, bolometric fluxes, and hence distances for field stars in a self-consistent manner. We apply our method to 22 solar-like oscillators in the Kepler short-cadence sample, that have accurate Hipparcos parallaxes. Our distance determinations agree to better than 5%, while measurements of spectroscopic effective temperatures and interferometric radii also validate our results. We briefly discuss the potential of our technique for stellar population analysis and models of Galactic Chemical Evolution.

  17. Verifying Asteroseismically Determined Parameters of Kepler Stars Using Hipparcos Parallaxes: Self-consistent Stellar Properties and Distances

    NASA Astrophysics Data System (ADS)

    Silva Aguirre, V.; Casagrande, L.; Basu, S.; Campante, T. L.; Chaplin, W. J.; Huber, D.; Miglio, A.; Serenelli, A. M.; Ballot, J.; Bedding, T. R.; Christensen-Dalsgaard, J.; Creevey, O. L.; Elsworth, Y.; García, R. A.; Gilliland, R. L.; Hekker, S.; Kjeldsen, H.; Mathur, S.; Metcalfe, T. S.; Monteiro, M. J. P. F. G.; Mosser, B.; Pinsonneault, M. H.; Stello, D.; Weiss, A.; Tenenbaum, P.; Twicken, J. D.; Uddin, K.

    2012-09-01

    Accurately determining the properties of stars is of prime importance for characterizing stellar populations in our Galaxy. The field of asteroseismology has been thought to be particularly successful in such an endeavor for stars in different evolutionary stages. However, to fully exploit its potential, robust methods for estimating stellar parameters are required and independent verification of the results is mandatory. With this purpose, we present a new technique to obtain stellar properties by coupling asteroseismic analysis with the InfraRed Flux Method. By using two global seismic observables and multi-band photometry, the technique allows us to obtain masses, radii, effective temperatures, bolometric fluxes, and hence distances for field stars in a self-consistent manner. We apply our method to 22 solar-like oscillators in the Kepler short-cadence sample, that have accurate Hipparcos parallaxes. Our distance determinations agree to better than 5%, while measurements of spectroscopic effective temperatures and interferometric radii also validate our results. We briefly discuss the potential of our technique for stellar population analysis and models of Galactic Chemical Evolution.

  18. Open cluster Dolidze 25: Stellar parameters and the metallicity in the Galactic anticentre

    NASA Astrophysics Data System (ADS)

    Negueruela, I.; Simón-Díaz, S.; Lorenzo, J.; Castro, N.; Herrero, A.

    2015-12-01

    Context. The young open cluster Dolidze 25, in the direction of the Galactic anticentre, has been attributed a very low metallicity, with typical abundances between -0.5 and -0.7 dex below solar. Aims: We intend to derive accurate cluster parameters and accurate stellar abundances for some of its members. Methods: We have obtained a large sample of intermediate- and high-resolution spectra for stars in and around Dolidze 25. We used the fastwind code to generate stellar atmosphere models to fit the observed spectra. We derive stellar parameters for a large number of OB stars in the area, and abundances of oxygen and silicon for a number of stars with spectral types around B0. Results: We measure low abundances in stars of Dolidze 25. For the three stars with spectral types around B0, we find 0.3 dex (Si) and 0.5 dex (O) below the values typical in the solar neighbourhood. These values, even though not as low as those given previously, confirm Dolidze 25 and the surrounding H ii region Sh2-284 as the most metal-poor star-forming environment known in the Milky Way. We derive a distance 4.5 ± 0.3 kpc to the cluster (rG ≈ 12.3 kpc). The cluster cannot be older than ~3 Myr, and likely is not much younger. One star in its immediate vicinity, sharing the same distance, has Si and O abundances at most 0.15 dex below solar. Conclusions: The low abundances measured in Dolidze 25 are compatible with currently accepted values for the slope of the Galactic metallicity gradient, if we take into account that variations of at least ±0.15 dex are observed at a given radius. The area traditionally identified as Dolidze 25 is only a small part of a much larger star-forming region that comprises the whole dust shell associated with Sh2-284 and very likely several other smaller H ii regions in its vicinity. Based on observations made with the Nordic Optical Telescope, the Mercator Telescope, and the telescopes of the Isaac Newton Group.

  19. Accurate lattice parameter measurements of stoichiometric uranium dioxide

    NASA Astrophysics Data System (ADS)

    Leinders, Gregory; Cardinaels, Thomas; Binnemans, Koen; Verwerft, Marc

    2015-04-01

    The paper presents and discusses lattice parameter analyses of pure, stoichiometric UO2. Attention was paid to prepare stoichiometric samples and to maintain stoichiometry throughout the analyses. The lattice parameter of UO2.000±0.001 was evaluated as being 547.127 ± 0.008 pm at 20 °C, which is substantially higher than many published values for the UO2 lattice constant and has an improved precision by about one order of magnitude. The higher value of the lattice constant is mainly attributed to the avoidance of hyperstoichiometry in the present study and to a minor extent to the use of the currently accepted Cu Kα1 X-ray wavelength value. Many of the early studies used Cu Kα1 wavelength values that differ from the currently accepted value, which also contributed to an underestimation of the true lattice parameter.

  20. Empirical calibration of the near-infrared Ca ii triplet - II. The stellar atmospheric parameters

    NASA Astrophysics Data System (ADS)

    Cenarro, A. J.; Gorgas, J.; Cardiel, N.; Pedraz, S.; Peletier, R. F.; Vazdekis, A.

    2001-09-01

    We present a homogeneous set of stellar atmospheric parameters (Teff, logg, [Fe/H]) for a sample of about 700 field and cluster stars which constitute a new stellar library in the near-IR developed for stellar population synthesis in this spectral region (λ8350-9020). Having compiled the available atmospheric data in the literature for field stars, we have found systematic deviations between the atmospheric parameters from different bibliographic references. The Soubiran, Katz & Cayrel sample of stars with very well determined fundamental parameters has been taken as our standard reference system, and other papers have been calibrated and bootstrapped against it. The obtained transformations are provided in this paper. Once most of the data sets were on the same system, final parameters were derived by performing error weighted means. Atmospheric parameters for cluster stars have also been revised and updated according to recent metallicity scales and colour-temperature relations.

  1. Linearly Supporting Feature Extraction for Automated Estimation of Stellar Atmospheric Parameters

    NASA Astrophysics Data System (ADS)

    Li, Xiangru; Lu, Yu; Comte, Georges; Luo, Ali; Zhao, Yongheng; Wang, Yongjun

    2015-05-01

    We describe a scheme to extract linearly supporting (LSU) features from stellar spectra to automatically estimate the atmospheric parameters {{T}{\\tt{eff} }}, log g, and [Fe/H]. “Linearly supporting” means that the atmospheric parameters can be accurately estimated from the extracted features through a linear model. The successive steps of the process are as follow: first, decompose the spectrum using a wavelet packet (WP) and represent it by the derived decomposition coefficients; second, detect representative spectral features from the decomposition coefficients using the proposed method Least Absolute Shrinkage and Selection Operator (LARS)bs; third, estimate the atmospheric parameters {{T}{\\tt{eff} }}, log g, and [Fe/H] from the detected features using a linear regression method. One prominent characteristic of this scheme is its ability to evaluate quantitatively the contribution of each detected feature to the atmospheric parameter estimate and also to trace back the physical significance of that feature. This work also shows that the usefulness of a component depends on both the wavelength and frequency. The proposed scheme has been evaluated on both real spectra from the Sloan Digital Sky Survey (SDSS)/SEGUE and synthetic spectra calculated from Kurucz's NEWODF models. On real spectra, we extracted 23 features to estimate {{T}{\\tt{eff} }}, 62 features for log g, and 68 features for [Fe/H]. Test consistencies between our estimates and those provided by the Spectroscopic Parameter Pipeline of SDSS show that the mean absolute errors (MAEs) are 0.0062 dex for log {{T}{\\tt{eff} }} (83 K for {{T}{\\tt{eff} }}), 0.2345 dex for log g, and 0.1564 dex for [Fe/H]. For the synthetic spectra, the MAE test accuracies are 0.0022 dex for log {{T}{\\tt{eff} }} (32 K for {{T}{\\tt{eff} }}), 0.0337 dex for log g, and 0.0268 dex for [Fe/H].

  2. Clinically accurate fetal ECG parameters acquired from maternal abdominal sensors

    PubMed Central

    CLIFFORD, Gari; SAMENI, Reza; WARD, Mr. Jay; ROBINSON, Julian; WOLFBERG, Adam J.

    2011-01-01

    OBJECTIVE To evaluate the accuracy of a novel system for measuring fetal heart rate and ST-segment changes using non-invasive electrodes on the maternal abdomen. STUDY DESIGN Fetal ECGs were recorded using abdominal sensors from 32 term laboring women who had a fetal scalp electrode (FSE) placed for a clinical indication. RESULTS Good quality data for FHR estimation was available in 91.2% of the FSE segments, and 89.9% of the abdominal electrode segments. The root mean square (RMS) error between the FHR data calculated by both methods over all processed segments was 0.36 beats per minute. ST deviation from the isoelectric point ranged from 0 to 14.2% of R-wave amplitude. The RMS error between the ST change calculated by both methods averaged over all processed segments was 3.2%. CONCLUSION FHR and ST change acquired from the maternal abdomen is highly accurate and on average is clinically indistinguishable from FHR and ST change calculated using FSE data. PMID:21514560

  3. SP_Ace: a new code to derive stellar parameters and elemental abundances

    NASA Astrophysics Data System (ADS)

    Boeche, C.; Grebel, E. K.

    2016-03-01

    Context. Ongoing and future massive spectroscopic surveys will collect large numbers (106-107) of stellar spectra that need to be analyzed. Highly automated software is needed to derive stellar parameters and chemical abundances from these spectra. Aims: We developed a new method of estimating the stellar parameters Teff, log g, [M/H], and elemental abundances. This method was implemented in a new code, SP_Ace (Stellar Parameters And Chemical abundances Estimator). This is a highly automated code suitable for analyzing the spectra of large spectroscopic surveys with low or medium spectral resolution (R = 2000-20 000). Methods: After the astrophysical calibration of the oscillator strengths of 4643 absorption lines covering the wavelength ranges 5212-6860 Å and 8400-8924 Å, we constructed a library that contains the equivalent widths (EW) of these lines for a grid of stellar parameters. The EWs of each line are fit by a polynomial function that describes the EW of the line as a function of the stellar parameters. The coefficients of these polynomial functions are stored in a library called the "GCOG library". SP_Ace, a code written in FORTRAN95, uses the GCOG library to compute the EWs of the lines, constructs models of spectra as a function of the stellar parameters and abundances, and searches for the model that minimizes the χ2 deviation when compared to the observed spectrum. The code has been tested on synthetic and real spectra for a wide range of signal-to-noise and spectral resolutions. Results: SP_Ace derives stellar parameters such as Teff, log g, [M/H], and chemical abundances of up to ten elements for low to medium resolution spectra of FGK-type stars with precision comparable to the one usually obtained with spectra of higher resolution. Systematic errors in stellar parameters and chemical abundances are presented and identified with tests on synthetic and real spectra. Stochastic errors are automatically estimated by the code for all the parameters

  4. THE AGE AND STELLAR PARAMETERS OF THE PROCYON BINARY SYSTEM

    SciTech Connect

    Liebert, James; Arnett, David; Fontaine, Gilles; Young, Patrick A.; Williams, Kurtis A. E-mail: darnett@as.arizona.edu E-mail: pyoung.3@asu.edu

    2013-05-20

    The Procyon AB binary system (orbital period 40.838 yr, a newly refined determination) is near and bright enough that the component radii, effective temperatures, and luminosities are very well determined, although more than one possible solution to the masses has limited the claimed accuracy. Preliminary mass determinations for each component are available from Hubble Space Telescope imaging, supported by ground-based astrometry and an excellent Hipparcos parallax; we use these for our preferred solution for the binary system. Other values for the masses are also considered. We have employed the TYCHO stellar evolution code to match the radius and luminosity of the F5 IV-V primary star to determine the system's most likely age as 1.87 {+-} 0.13 Gyr. Since prior studies of Procyon A found its abundance indistinguishable from solar, the solar composition of Asplund, Grevesse, and Sauval (Z = 0.014) is assumed for the Hertzsprung-Russell diagram fitting. An unsuccessful attempt to fit using the older solar abundance scale of Grevesse and Sauval (Z = 0.019) is also reported. For Procyon B, 11 new sequences for the cooling of non-DA white dwarfs have been calculated to investigate the dependences of the cooling age on (1) the mass, (2) core composition, (3) helium layer mass, and (4) heavy-element opacities in the helium envelope. Our calculations indicate a cooling age of 1.19 {+-} 0.11 Gyr, which implies that the progenitor mass of Procyon B was 2.59{sub -0.26}{sup +0.44} M{sub Sun }. In a plot of initial versus final mass of white dwarfs in astrometric binaries or star clusters (all with age determinations), the Procyon B final mass lies several {sigma} below a straight line fit.

  5. Predicting accurate line shape parameters for CO2 transitions

    NASA Astrophysics Data System (ADS)

    Gamache, Robert R.; Lamouroux, Julien

    2013-11-01

    The vibrational dependence of CO2 half-widths and line shifts are given by a modification of the model proposed by Gamache and Hartmann [Gamache R, Hartmann J-M. J Quant Spectrosc Radiat Transfer 2004;83:119]. This model allows the half-widths and line shifts for a ro-vibrational transition to be expressed in terms of the number of vibrational quanta exchanged in the transition raised to a power and a reference ro-vibrational transition. Calculations were made for 24 bands for lower rotational quantum numbers from 0 to 160 for N2-, O2-, air-, and self-collisions with CO2. These data were extrapolated to J″=200 to accommodate several databases. Comparison of the CRB calculations with measurement gives very high confidence in the data. In the model a Quantum Coordinate is defined by (c1 |Δν1|+c2 |Δν2|+c3|Δν3|)p. The power p is adjusted and a linear least-squares fit to the data by the model expression is made. The procedure is iterated on the correlation coefficient, R, until [|R|-1] is less than a threshold. The results demonstrate the appropriateness of the model. The model allows the determination of the slope and intercept as a function of rotational transition, broadening gas, and temperature. From the data of the fits, the half-width, line shift, and the temperature dependence of the half-width can be estimated for any ro-vibrational transition, allowing spectroscopic CO2 databases to have complete information for the line shape parameters.

  6. An autoencoder of stellar spectra and its application in automatically estimating atmospheric parameters

    NASA Astrophysics Data System (ADS)

    Yang, Tan; Li, Xiangru

    2015-09-01

    This article investigates the problem of estimating stellar atmospheric parameters from spectra. Feature extraction is a key procedure in estimating stellar parameters automatically. We propose a scheme for spectral feature extraction and atmospheric parameter estimation using the following three procedures: firstly, learn a set of basic structure elements (BSEs) from stellar spectra using an autoencoder; secondly, extract representative features from stellar spectra based on the learned BSEs through some procedures of convolution and pooling; thirdly, estimate stellar parameters (Teff, log g, [Fe/H]) using a back-propagation (BP) network. The proposed scheme has been evaluated on both real spectra from Sloan Digital Sky Survey (SDSS)/Sloan Extension for Galactic Understanding and Exploration (SEGUE) and synthetic spectra calculated from Kurucz's new opacity distribution function (NEWODF) models. The best mean absolute errors (MAEs) are 0.0060 dex for log Teff, 0.1978 dex for log g and 0.1770 dex for [Fe/H] for the real spectra and 0.0004 dex for log Teff, 0.0145 dex for log g and 0.0070 dex for [Fe/H] for the synthetic spectra.

  7. The SEGUE Stellar Parameter Pipeline. II. Validation with Galactic Globular and Open Clusters

    SciTech Connect

    Lee, Y.S.; Beers, T.C.; Sivarani, T.; Johnson, J.A.; An, D.; Wilhelm, R.; Prieto, C.Allende; Koesterke, L.; Re Fiorentin, P.; Bailer-Jones, C.A.L.; Norris, J.E.

    2007-10-01

    The authors validate the performance and accuracy of the current SEGUE (Sloan Extension for Galactic Understanding and Exploration) Stellar Parameter Pipeline (SSPP), which determines stellar atmospheric parameters (effective temperature, surface gravity, and metallicity) by comparing derived overall metallicities and radial velocities from selected likely members of three globular clusters (M 13, M 15, and M 2) and two open clusters (NGC 2420 and M 67) to the literature values. Spectroscopic and photometric data obtained during the course of the original Sloan Digital Sky Survey (SDSS-1) and its first extension (SDSS-II/SEGUE) are used to determine stellar radial velocities and atmospheric parameter estimates for stars in these clusters. Based on the scatter in the metallicities derived for the members of each cluster, they quantify the typical uncertainty of the SSPP values, {sigma}([Fe/H]) = 0.13 dex for stars in the range of 4500 K {le} T{sub eff} {le} 7500 K and 2.0 {le} log g {le} 5.0, at least over the metallicity interval spanned by the clusters studied (-2.3 {le} [Fe/H] < 0). The surface gravities and effective temperatures derived by the SSPP are also compared with those estimated from the comparison of the color-magnitude diagrams with stellar evolution models; they find satisfactory agreement. At present, the SSPP underestimates [Fe/H] for near-solar-metallicity stars, represented by members of M 67 in this study, by {approx} 0.3 dex.

  8. STELLAR PARAMETERS AND METALLICITIES OF STARS HOSTING JOVIAN AND NEPTUNIAN MASS PLANETS: A POSSIBLE DEPENDENCE OF PLANETARY MASS ON METALLICITY

    SciTech Connect

    Ghezzi, L.; Cunha, K.; De Araujo, F. X.; De la Reza, R.; Smith, V. V.; Schuler, S. C.

    2010-09-10

    The metal content of planet-hosting stars is an important ingredient that may affect the formation and evolution of planetary systems. Accurate stellar abundances require the determinations of reliable physical parameters, namely, the effective temperature, surface gravity, microturbulent velocity, and metallicity. This work presents the homogeneous derivation of such parameters for a large sample of stars hosting planets (N = 117), as well as a control sample of disk stars not known to harbor giant, closely orbiting planets (N = 145). Stellar parameters and iron abundances are derived from an automated analysis technique developed for this work. As previously found in the literature, the results in this study indicate that the metallicity distribution of planet-hosting stars is more metal rich by {approx}0.15 dex when compared to the control sample stars. A segregation of the sample according to planet mass indicates that the metallicity distribution of stars hosting only Neptunian-mass planets (with no Jovian-mass planets) tends to be more metal poor in comparison with that obtained for stars hosting a closely orbiting Jovian planet. The significance of this difference in metallicity arises from a homogeneous analysis of samples of FGK dwarfs which do not include the cooler and more problematic M dwarfs. This result would indicate that there is a possible link between planet mass and metallicity such that metallicity plays a role in setting the mass of the most massive planet. Further confirmation, however, must await larger samples.

  9. CONNECTION BETWEEN DYNAMICALLY DERIVED INITIAL MASS FUNCTION NORMALIZATION AND STELLAR POPULATION PARAMETERS

    SciTech Connect

    McDermid, Richard M.; Cappellari, Michele; Bayet, Estelle; Bureau, Martin; Davies, Roger L.; Alatalo, Katherine; Blitz, Leo; Bois, Maxime; Bournaud, Frédéric; Duc, Pierre-Alain; Davis, Timothy A.; De Zeeuw, P. T.; Emsellem, Eric; Kuntschner, Harald; Khochfar, Sadegh; Krajnović, Davor; Morganti, Raffaella; Oosterloo, Tom; Naab, Thorsten; and others

    2014-09-10

    We report on empirical trends between the dynamically determined stellar initial mass function (IMF) and stellar population properties for a complete, volume-limited sample of 260 early-type galaxies from the ATLAS{sup 3D} project. We study trends between our dynamically derived IMF normalization α{sub dyn} ≡ (M/L){sub stars}/(M/L){sub Salp} and absorption line strengths, and interpret these via single stellar population-equivalent ages, abundance ratios (measured as [α/Fe]), and total metallicity, [Z/H]. We find that old and alpha-enhanced galaxies tend to have on average heavier (Salpeter-like) mass normalization of the IMF, but stellar population does not appear to be a good predictor of the IMF, with a large range of α{sub dyn} at a given population parameter. As a result, we find weak α{sub dyn}-[α/Fe] and α{sub dyn} –Age correlations and no significant α{sub dyn} –[Z/H] correlation. The observed trends appear significantly weaker than those reported in studies that measure the IMF normalization via the low-mass star demographics inferred through stellar spectral analysis.

  10. Connection between Dynamically Derived Initial Mass Function Normalization and Stellar Population Parameters

    NASA Astrophysics Data System (ADS)

    McDermid, Richard M.; Cappellari, Michele; Alatalo, Katherine; Bayet, Estelle; Blitz, Leo; Bois, Maxime; Bournaud, Frédéric; Bureau, Martin; Crocker, Alison F.; Davies, Roger L.; Davis, Timothy A.; de Zeeuw, P. T.; Duc, Pierre-Alain; Emsellem, Eric; Khochfar, Sadegh; Krajnović, Davor; Kuntschner, Harald; Morganti, Raffaella; Naab, Thorsten; Oosterloo, Tom; Sarzi, Marc; Scott, Nicholas; Serra, Paolo; Weijmans, Anne-Marie; Young, Lisa M.

    2014-09-01

    We report on empirical trends between the dynamically determined stellar initial mass function (IMF) and stellar population properties for a complete, volume-limited sample of 260 early-type galaxies from the ATLAS3D project. We study trends between our dynamically derived IMF normalization αdyn ≡ (M/L)stars/(M/L)Salp and absorption line strengths, and interpret these via single stellar population-equivalent ages, abundance ratios (measured as [α/Fe]), and total metallicity, [Z/H]. We find that old and alpha-enhanced galaxies tend to have on average heavier (Salpeter-like) mass normalization of the IMF, but stellar population does not appear to be a good predictor of the IMF, with a large range of αdyn at a given population parameter. As a result, we find weak αdyn-[α/Fe] and αdyn -Age correlations and no significant αdyn -[Z/H] correlation. The observed trends appear significantly weaker than those reported in studies that measure the IMF normalization via the low-mass star demographics inferred through stellar spectral analysis.

  11. IN-SYNC I: Homogeneous stellar parameters from high-resolution apogee spectra for thousands of pre-main sequence stars

    SciTech Connect

    Cottaar, Michiel; Meyer, Michael R.; Covey, Kevin R.; Nidever, David L.; Stassun, Keivan G.; Foster, Jonathan B.; Tan, Jonathan C.; Da Rio, Nicola; Chojnowski, S. Drew; Skrutskie, Michael; Majewski, Steven R.; Wilson, John C.; Zasowski, Gail; Flaherty, Kevin M.; Frinchaboy, Peter M.

    2014-10-20

    Over two years, 8859 high-resolution H-band spectra of 3493 young (1-10 Myr) stars were gathered by the multi-object spectrograph of the APOGEE project as part of the IN-SYNC ancillary program of the SDSS-III survey. Here we present the forward modeling approach used to derive effective temperatures, surface gravities, radial velocities, rotational velocities, and H-band veiling from these near-infrared spectra. We discuss in detail the statistical and systematic uncertainties in these stellar parameters. In addition, we present accurate extinctions by measuring the E(J – H) of these young stars with respect to the single-star photometric locus in the Pleiades. Finally, we identify an intrinsic stellar radius spread of about 25% for late-type stars in IC 348 using three (nearly) independent measures of stellar radius, namely, the extinction-corrected J-band magnitude, the surface gravity, and the Rsin i from the rotational velocities and literature rotation periods. We exclude that this spread is caused by uncertainties in the stellar parameters by showing that the three estimators of stellar radius are correlated, so that brighter stars tend to have lower surface gravities and larger Rsin i than fainter stars at the same effective temperature. Tables providing the spectral and photometric parameters for the Pleiades and IC 348 have been provided online.

  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. Accurate Atmospheric Parameters at Moderate Resolution Using Spectral Indices: Preliminary Application to the MARVELS Survey

    NASA Astrophysics Data System (ADS)

    Ghezzi, Luan; Dutra-Ferreira, Letícia; Lorenzo-Oliveira, Diego; Porto de Mello, Gustavo F.; Santiago, Basílio X.; De Lee, Nathan; Lee, Brian L.; da Costa, Luiz N.; Maia, Marcio A. G.; Ogando, Ricardo L. C.; Wisniewski, John P.; González Hernández, Jonay I.; Stassun, Keivan G.; Fleming, Scott W.; Schneider, Donald P.; Mahadevan, Suvrath; Cargile, Phillip; Ge, Jian; Pepper, Joshua; Wang, Ji; Paegert, Martin

    2014-12-01

    Studies of Galactic chemical, and dynamical evolution in the solar neighborhood depend on the availability of precise atmospheric parameters (effective temperature T eff, metallicity [Fe/H], and surface gravity log g) for solar-type stars. Many large-scale spectroscopic surveys operate at low to moderate spectral resolution for efficiency in observing large samples, which makes the stellar characterization difficult due to the high degree of blending of spectral features. Therefore, most surveys employ spectral synthesis, which is a powerful technique, but relies heavily on the completeness and accuracy of atomic line databases and can yield possibly correlated atmospheric parameters. In this work, we use an alternative method based on spectral indices to determine the atmospheric parameters of a sample of nearby FGK dwarfs and subgiants observed by the MARVELS survey at moderate resolving power (R ~ 12,000). To avoid a time-consuming manual analysis, we have developed three codes to automatically normalize the observed spectra, measure the equivalent widths of the indices, and, through a comparison of those with values calculated with predetermined calibrations, estimate the atmospheric parameters of the stars. The calibrations were derived using a sample of 309 stars with precise stellar parameters obtained from the analysis of high-resolution FEROS spectra, permitting the low-resolution equivalent widths to be directly related to the stellar parameters. A validation test of the method was conducted with a sample of 30 MARVELS targets that also have reliable atmospheric parameters derived from the high-resolution spectra and spectroscopic analysis based on the excitation and ionization equilibria method. Our approach was able to recover the parameters within 80 K for T eff, 0.05 dex for [Fe/H], and 0.15 dex for log g, values that are lower than or equal to the typical external uncertainties found between different high-resolution analyses. An additional test was

  14. Accurate atmospheric parameters at moderate resolution using spectral indices: Preliminary application to the marvels survey

    SciTech Connect

    Ghezzi, Luan; Da Costa, Luiz N.; Maia, Marcio A. G.; Ogando, Ricardo L. C.; Dutra-Ferreira, Letícia; Lorenzo-Oliveira, Diego; Porto de Mello, Gustavo F.; Santiago, Basílio X.; De Lee, Nathan; Lee, Brian L.; Ge, Jian; Wisniewski, John P.; González Hernández, Jonay I.; Stassun, Keivan G.; Cargile, Phillip; Pepper, Joshua; Fleming, Scott W.; Schneider, Donald P.; Mahadevan, Suvrath; Wang, Ji; and others

    2014-12-01

    Studies of Galactic chemical, and dynamical evolution in the solar neighborhood depend on the availability of precise atmospheric parameters (effective temperature T {sub eff}, metallicity [Fe/H], and surface gravity log g) for solar-type stars. Many large-scale spectroscopic surveys operate at low to moderate spectral resolution for efficiency in observing large samples, which makes the stellar characterization difficult due to the high degree of blending of spectral features. Therefore, most surveys employ spectral synthesis, which is a powerful technique, but relies heavily on the completeness and accuracy of atomic line databases and can yield possibly correlated atmospheric parameters. In this work, we use an alternative method based on spectral indices to determine the atmospheric parameters of a sample of nearby FGK dwarfs and subgiants observed by the MARVELS survey at moderate resolving power (R ∼ 12,000). To avoid a time-consuming manual analysis, we have developed three codes to automatically normalize the observed spectra, measure the equivalent widths of the indices, and, through a comparison of those with values calculated with predetermined calibrations, estimate the atmospheric parameters of the stars. The calibrations were derived using a sample of 309 stars with precise stellar parameters obtained from the analysis of high-resolution FEROS spectra, permitting the low-resolution equivalent widths to be directly related to the stellar parameters. A validation test of the method was conducted with a sample of 30 MARVELS targets that also have reliable atmospheric parameters derived from the high-resolution spectra and spectroscopic analysis based on the excitation and ionization equilibria method. Our approach was able to recover the parameters within 80 K for T {sub eff}, 0.05 dex for [Fe/H], and 0.15 dex for log g, values that are lower than or equal to the typical external uncertainties found between different high-resolution analyses. An

  15. Catching the fish - Constraining stellar parameters for TX Piscium using spectro-interferometric observations

    NASA Astrophysics Data System (ADS)

    Klotz, D.; Paladini, C.; Hron, J.; Aringer, B.; Sacuto, S.; Marigo, P.; Verhoelst, T.

    2013-02-01

    Context. Stellar parameter determination is a challenging task when dealing with galactic giant stars. The combination of different investigation techniques has proven to be a promising approach. Aims: We analyse archive spectra obtained with the Short Wavelength Spectrometer (SWS) onboard ISO, and new interferometric observations from the Very Large Telescope MID-infrared Interferometric instrument (VLTI/MIDI) of a very well studied carbon-rich giant: TX Psc. The aim of this work is to determine stellar parameters using spectroscopy and interferometry. Methods: The observations are used to constrain the model atmosphere, and eventually the stellar evolutionary model in the region where the tracks map the beginning of the carbon star sequence. Two different approaches are used to determine stellar parameters: (i) the "classic" interferometric approach where the effective temperature is fixed by using the angular diameter in the N-band (from interferometry) and the apparent bolometric magnitude; (ii) parameters are obtained by fitting a grid of state-of-the-art hydrostatic models to spectroscopic and interferometric observations. Results: We find good agreement between the parameters of the two methods. The effective temperature and luminosity clearly place TX Psc in the carbon-rich AGB star domain in the H-R-diagram. Current evolutionary tracks suggest that TX Psc became a C-star just recently, which means that the star is still in a "quiet" phase compared to the subsequent strong-wind regime. This agrees with the C/O ratio being only slightly greater than one. Based on observations made with ESO telescopes at Paranal Observatory under program IDs 74.D-0601, 60.A-9224, 77.C-0440, 60.A-9006, 78.D-0112, 84.D-0805.

  16. Are Patient-Specific Joint and Inertial Parameters Necessary for Accurate Inverse Dynamics Analyses of Gait?

    PubMed Central

    Reinbolt, Jeffrey A.; Haftka, Raphael T.; Chmielewski, Terese L.; Fregly, Benjamin J.

    2013-01-01

    Variations in joint parameter values (axis positions and orientations in body segments) and inertial parameter values (segment masses, mass centers, and moments of inertia) as well as kinematic noise alter the results of inverse dynamics analyses of gait. Three-dimensional linkage models with joint constraints have been proposed as one way to minimize the effects of noisy kinematic data. Such models can also be used to perform gait optimizations to predict post-treatment function given pre-treatment gait data. This study evaluates whether accurate patient-specific joint and inertial parameter values are needed in three-dimensional linkage models to produce accurate inverse dynamics results for gait. The study was performed in two stages. First, we used optimization analyses to evaluate whether patient-specific joint and inertial parameter values can be calibrated accurately from noisy kinematic data, and second, we used Monte Carlo analyses to evaluate how errors in joint and inertial parameter values affect inverse dynamics calculations. Both stages were performed using a dynamic, 27 degree-of-freedom, full-body linkage model and synthetic (i.e., computer generated) gait data corresponding to a nominal experimental gait motion. In general, joint but not inertial parameter values could be found accurately from noisy kinematic data. Root-mean-square (RMS) errors were 3° and 4 mm for joint parameter values and 1 kg, 22 mm, and 74,500 kg*mm2 for inertial parameter values. Furthermore, errors in joint but not inertial parameter values had a significant effect on calculated lower-extremity inverse dynamics joint torques. The worst RMS torque error averaged 4% bodyweight*height (BW*H) due to joint parameter variations but less than 0.25% BW*H due to inertial parameter variations. These results suggest that inverse dynamics analyses of gait utilizing linkage models with joint constraints should calibrate the model’s joint parameter values to obtain accurate joint

  17. A MACHINE-LEARNING METHOD TO INFER FUNDAMENTAL STELLAR PARAMETERS FROM PHOTOMETRIC LIGHT CURVES

    SciTech Connect

    Miller, A. A.; Bloom, J. S.; Richards, J. W.; Starr, D. L.; Lee, Y. S.; Butler, N. R.; Tokarz, S.; Smith, N.; Eisner, J. A.

    2015-01-10

    A fundamental challenge for wide-field imaging surveys is obtaining follow-up spectroscopic observations: there are >10{sup 9} photometrically cataloged sources, yet modern spectroscopic surveys are limited to ∼few× 10{sup 6} targets. As we approach the Large Synoptic Survey Telescope era, new algorithmic solutions are required to cope with the data deluge. Here we report the development of a machine-learning framework capable of inferring fundamental stellar parameters (T {sub eff}, log g, and [Fe/H]) using photometric-brightness variations and color alone. A training set is constructed from a systematic spectroscopic survey of variables with Hectospec/Multi-Mirror Telescope. In sum, the training set includes ∼9000 spectra, for which stellar parameters are measured using the SEGUE Stellar Parameters Pipeline (SSPP). We employed the random forest algorithm to perform a non-parametric regression that predicts T {sub eff}, log g, and [Fe/H] from photometric time-domain observations. Our final optimized model produces a cross-validated rms error (RMSE) of 165 K, 0.39 dex, and 0.33 dex for T {sub eff}, log g, and [Fe/H], respectively. Examining the subset of sources for which the SSPP measurements are most reliable, the RMSE reduces to 125 K, 0.37 dex, and 0.27 dex, respectively, comparable to what is achievable via low-resolution spectroscopy. For variable stars this represents a ≈12%-20% improvement in RMSE relative to models trained with single-epoch photometric colors. As an application of our method, we estimate stellar parameters for ∼54,000 known variables. We argue that this method may convert photometric time-domain surveys into pseudo-spectrographic engines, enabling the construction of extremely detailed maps of the Milky Way, its structure, and history.

  18. A Machine-learning Method to Infer Fundamental Stellar Parameters from Photometric Light Curves

    NASA Astrophysics Data System (ADS)

    Miller, A. A.; Bloom, J. S.; Richards, J. W.; Lee, Y. S.; Starr, D. L.; Butler, N. R.; Tokarz, S.; Smith, N.; Eisner, J. A.

    2015-01-01

    A fundamental challenge for wide-field imaging surveys is obtaining follow-up spectroscopic observations: there are >109 photometrically cataloged sources, yet modern spectroscopic surveys are limited to ~few× 106 targets. As we approach the Large Synoptic Survey Telescope era, new algorithmic solutions are required to cope with the data deluge. Here we report the development of a machine-learning framework capable of inferring fundamental stellar parameters (T eff, log g, and [Fe/H]) using photometric-brightness variations and color alone. A training set is constructed from a systematic spectroscopic survey of variables with Hectospec/Multi-Mirror Telescope. In sum, the training set includes ~9000 spectra, for which stellar parameters are measured using the SEGUE Stellar Parameters Pipeline (SSPP). We employed the random forest algorithm to perform a non-parametric regression that predicts T eff, log g, and [Fe/H] from photometric time-domain observations. Our final optimized model produces a cross-validated rms error (RMSE) of 165 K, 0.39 dex, and 0.33 dex for T eff, log g, and [Fe/H], respectively. Examining the subset of sources for which the SSPP measurements are most reliable, the RMSE reduces to 125 K, 0.37 dex, and 0.27 dex, respectively, comparable to what is achievable via low-resolution spectroscopy. For variable stars this represents a ≈12%-20% improvement in RMSE relative to models trained with single-epoch photometric colors. As an application of our method, we estimate stellar parameters for ~54,000 known variables. We argue that this method may convert photometric time-domain surveys into pseudo-spectrographic engines, enabling the construction of extremely detailed maps of the Milky Way, its structure, and history.

  19. VizieR Online Data Catalog: Abundances and stellar parameters of LAMOST stars (Lee+, 2015)

    NASA Astrophysics Data System (ADS)

    Lee, Y. S.; Beers, T. C.; Carlin, J. L.; Newberg, H. J.; Hou, Y.; Li, G.; Luo, A.-L.; Wu, Y.; Yang, M.; Zhang, H.; Zhang, W.; Zhang, Y.

    2016-04-01

    By performing a coordinate match with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST; see DR1 in Luo et al. 2015, cat. V/146) stellar database, we selected stars with LAMOST spectra in common with stars having available spectroscopy from the Apache Point Observatory Galactic Evolution Experiment (APOGEE; Majewski et al. 2015, submitted), the RAdial Velocity Experiment (RAVE; see Kordopatis et al. 2013, cat. III/272), and the Sloan Extension for Galactic Understanding and Exploration (SEGUE; see Yanny et al. 2009, cat. J/AJ/137/4377). The LAMOST Experiment for Galactic Understanding and Exploration (LEGUE) survey is an ongoing spectroscopic survey being conducted with the Guoshoujing telescope in northeast China. This telescope employs a fixed 4-m Schmidt-type reflector with 4000 optical fibers in the focal plane to obtain spectra of astronomical objects in a 5° field of view. The LEGUE and SEGUE surveys have very similar spectral coverage and resolving power (R~1800). The LAMOST stellar targets mostly comprise stars brighter than r< 17, whereas the SEGUE stars range from r=14 to r=21. SEGUE-1 was executed during the second phase of the Sloan Digital Sky Survey (SDSS-II). This effort was continued as SEGUE-2 during the third phase of SDSS (SDSS-III). APOGEE was designed to obtain high-resolution near-infrared spectra (in the H-band between 1.51 and 1.70μm). The spectra obtained by APOGEE have a resolving power R~22500 and high S/N (>100). APOGEE-1 was a sub-survey of SDSS-III, and is now completed. Its extension, APOGEE-2, is presently underway as part of SDSS-IV. The RAVE survey was designed to observe about a million stars in the southern hemisphere, and obtain optical spectra over the wavelength range 8410-8795Å, the region of the CaII triplet, at a resolving power R~7500. SEGUE-1 and SEGUE-2 have employed the SEGUE Stellar Parameter Pipeline (SSPP; Lee et al. 2008, cat. J/AJ/136/2050; Allende Prieto et al. 2008, cat. J/AJ/136

  20. VizieR Online Data Catalog: Stellar atmospheric parameters in MILES library (Cenarro+, 2007)

    NASA Astrophysics Data System (ADS)

    Cenarro, A. J.; Peletier, R. F.; Sanchez-Blazquez, P.; Selam, S. O.; Toloba, E.; Cardiel, N.; Falcon-Barroso, J.; Gorgas, J.; Jimenez-Vicente, J.; Vazdekis, A.

    2007-09-01

    We present a homogeneous set of stellar atmospheric parameters (Teff, logg, [Fe/H]) for MILES, a new spectral stellar library covering the range {lambda}{lambda}3525-7500{AA} at 2.3{AA} (FWHM) spectral resolution. The library consists of 985 stars spanning a large range in atmospheric parameters, from super-metal-rich, cool stars to hot, metal-poor stars. The spectral resolution, spectral type coverage and number of stars represent a substantial improvement over previous libraries used in population synthesis models. The atmospheric parameters that we present here are the result of a previous, extensive compilation from the literature. In order to construct a homogeneous data set of atmospheric parameters we have taken the sample of stars of Soubiran, Katz & Cayrel (1998, Cat. , which has very well determined fundamental parameters, as the standard reference system for our field stars, and have calibrated and bootstrapped the data from other papers against it. The atmospheric parameters for our cluster stars have also been revised and updated according to recent metallicity scales, colour-temperature relations and improved set of isochrones. (2 data files).

  1. VizieR Online Data Catalog: Stellar atmospheric parameters in MILES library (Cenarro+, 2007)

    NASA Astrophysics Data System (ADS)

    Cenarro, A. J.; Peletier, R. F.; Sanchez-Blazquez, P.; Selam, S. O.; Toloba, E.; Cardiel, N.; Falcon-Barroso, J.; Gorgas, J.; Jimenez-Vicente, J.; Vazdekis, A.

    2007-09-01

    We present a homogeneous set of stellar atmospheric parameters (Teff, logg, [Fe/H]) for MILES, a new spectral stellar library covering the range λλ3525-7500Å at 2.3Å (FWHM) spectral resolution. The library consists of 985 stars spanning a large range in atmospheric parameters, from super-metal-rich, cool stars to hot, metal-poor stars. The spectral resolution, spectral type coverage and number of stars represent a substantial improvement over previous libraries used in population synthesis models. The atmospheric parameters that we present here are the result of a previous, extensive compilation from the literature. In order to construct a homogeneous data set of atmospheric parameters we have taken the sample of stars of Soubiran, Katz & Cayrel (1998, Cat. , which has very well determined fundamental parameters, as the standard reference system for our field stars, and have calibrated and bootstrapped the data from other papers against it. The atmospheric parameters for our cluster stars have also been revised and updated according to recent metallicity scales, colour-temperature relations and improved set of isochrones. (2 data files).

  2. Medium-resolution Isaac Newton Telescope library of empirical spectra - II. The stellar atmospheric parameters

    NASA Astrophysics Data System (ADS)

    Cenarro, A. J.; Peletier, R. F.; Sánchez-Blázquez, P.; Selam, S. O.; Toloba, E.; Cardiel, N.; Falcón-Barroso, J.; Gorgas, J.; Jiménez-Vicente, J.; Vazdekis, A.

    2007-01-01

    We present a homogeneous set of stellar atmospheric parameters (Teff, logg, [Fe/H]) for MILES, a new spectral stellar library covering the range λλ 3525-7500Å at 2.3Å (FWHM) spectral resolution. The library consists of 985 stars spanning a large range in atmospheric parameters, from super-metal-rich, cool stars to hot, metal-poor stars. The spectral resolution, spectral type coverage and number of stars represent a substantial improvement over previous libraries used in population synthesis models. The atmospheric parameters that we present here are the result of a previous, extensive compilation from the literature. In order to construct a homogeneous data set of atmospheric parameters we have taken the sample of stars of Soubiran, Katz & Cayrel, which has very well determined fundamental parameters, as the standard reference system for our field stars, and have calibrated and bootstrapped the data from other papers against it. The atmospheric parameters for our cluster stars have also been revised and updated according to recent metallicity scales, colour-temperature relations and improved set of isochrones.

  3. A simple and accurate resist parameter extraction method for sub-80-nm DRAM patterns

    NASA Astrophysics Data System (ADS)

    Lee, Sook; Hwang, Chan; Park, Dong-Woon; Kim, In-Sung; Kim, Ho-Chul; Woo, Sang-Gyun; Cho, Han-Ku; Moon, Joo-Tae

    2004-05-01

    Due to the polarization effect of high NA lithography, the consideration of resist effect in lithography simulation becomes increasingly important. In spite of the importance of resist simulation, many process engineers are reluctant to consider resist effect in lithography simulation due to time-consuming procedure to extract required resist parameters and the uncertainty of measurement of some parameters. Weiss suggested simplified development model, and this model does not require the complex kinetic parameters. For the device fabrication engineers, there is a simple and accurate parameter extraction and optimizing method using Weiss model. This method needs refractive index, Dill"s parameters and development rate monitoring (DRM) data in parameter extraction. The parameters extracted using referred sequence is not accurate, so that we have to optimize the parameters to fit the critical dimension scanning electron microscopy (CD SEM) data of line and space patterns. Hence, the FiRM of Sigma-C is utilized as a resist parameter-optimizing program. According to our study, the illumination shape, the aberration and the pupil mesh point have a large effect on the accuracy of resist parameter in optimization. To obtain the optimum parameters, we need to find the saturated mesh points in terms of normalized intensity log slope (NILS) prior to an optimization. The simulation results using the optimized parameters by this method shows good agreement with experiments for iso-dense bias, Focus-Exposure Matrix data and sub 80nm device pattern simulation.

  4. APOSTLE OBSERVATIONS OF GJ 1214b: SYSTEM PARAMETERS AND EVIDENCE FOR STELLAR ACTIVITY

    SciTech Connect

    Kundurthy, P.; Agol, E.; Becker, A. C.; Williams, B.; Mukadam, A.; Barnes, R.

    2011-04-20

    We present three transits of GJ 1214b, observed as part of the Apache Point Observatory Survey of Transit Light Curves of Exoplanets. By applying Markov Chain Monte Carlo techniques to a multi-wavelength data set which included our r-band light curves and previously gathered data of GJ 1214b, we confirm earlier estimates of system parameters. Using spectral energy distribution fitting, mass-luminosity relations, and light curve data, we derived absolute parameters for the star and planet, improving uncertainties by a factor of two for the stellar mass (M{sub *} = 0.153{sup +0.010}{sub -0.009} M{sub sun}), stellar radius (R{sub *} = 0.210{sup +0.005}{sub -0.004} R{sub sun}), planetary radius (R{sub p} = 2.74{sup +0.06}{sub -0.05} R{sub +}), and planetary density ({rho}{sub p} = 1.68 {+-} 0.23 g cm{sup -3}). Transit times derived from our study show no evidence for strong transit timing variations. We also report the detection of two features in our light curves which we believe are evidence for a low-energy stellar flare and a spot-crossing event.

  5. RESEARCH PAPER: Automated estimation of stellar fundamental parameters from low resolution spectra: the PLS method

    NASA Astrophysics Data System (ADS)

    Zhang, Jian-Nan; Luo, A.-Li; Zhao, Yong-Heng

    2009-06-01

    PLS (Partial Least Squares regression) is introduced into an automatic estimation of fundamental stellar spectral parameters. It extracts the most correlative spectral component to the parameters (Teff, log g and [Fe/H]), and sets up a linear regression function from spectra to the corresponding parameters. Considering the properties of stellar spectra and the PLS algorithm, we present a piecewise PLS regression method for estimation of stellar parameters, which is composed of one PLS model for Teff, and seven PLS models for log g and [Fe/H] estimation. Its performance is investigated by large experiments on flux calibrated spectra and continuum normalized spectra at different signal-to-noise ratios (SNRs) and resolutions. The results show that the piecewise PLS method is robust for spectra at the medium resolution of 0.23 nm. For low resolution 0.5 nm and 1 nm spectra, it achieves competitive results at higher SNR. Experiments using ELODIE spectra of 0.23 nm resolution illustrate that our piecewise PLS models trained with MILES spectra are efficient for O ~ G stars: for flux calibrated spectra, the systematic offsets are 3.8%, 0.14 dex, and -0.09 dex for Teff, log g and [Fe/H], with error scatters of 5.2%, 0.44 dex and 0.38 dex, respectively; for continuum normalized spectra, the systematic offsets are 3.8%, 0.12dex, and -0.13dex for Teff, log g and [Fe/H], with error scatters of 5.2%, 0.49 dex and 0.41 dex, respectively. The PLS method is rapid, easy to use and does not rely as strongly on the tightness of a parameter grid of templates to reach high precision as Artificial Neural Networks or minimum distance methods do.

  6. VizieR Online Data Catalog: Fundamental stellar parameters from PolarBase (Paletou+, 2015)

    NASA Astrophysics Data System (ADS)

    Paletou, F.; Boehm, T.; Watson, V.; Trouilhet, J.-F.

    2015-02-01

    Our reference spectra are taken from the Elodie stellar library (Prugniel et al. 2007, astro-ph/0703658, Cat. III/251; Prugniel & Soubiran 2001A&A...369.1048P, Cat. III/218). Our main purpose is inverting of stellar parameters from high-resolution spectra coming from Narval and ESPaDOnS spectropolarimeters. These data are now available from the public database PolarBase (Petit et al., 2014PASP..126..469P, Cat. J/PASP/126/469). Narval is a modern spectropolarimeter operating in the 380-1000nm spectral domain, with a spectral resolution of 65000 in its polarimetric mode. It is an improved copy, adapted to the 2m TBL telescope, of the ESPaDOnS spectropolarimeter, which is in operations since 2004 at the 3.6m aperture CFHT telescope. (1 data file).

  7. Measuring accurate body parameters of dressed humans with large-scale motion using a Kinect sensor.

    PubMed

    Xu, Huanghao; Yu, Yao; Zhou, Yu; Li, Yang; Du, Sidan

    2013-01-01

    Non-contact human body measurement plays an important role in surveillance, physical healthcare, on-line business and virtual fitting. Current methods for measuring the human body without physical contact usually cannot handle humans wearing clothes, which limits their applicability in public environments. In this paper, we propose an effective solution that can measure accurate parameters of the human body with large-scale motion from a Kinect sensor, assuming that the people are wearing clothes. Because motion can drive clothes attached to the human body loosely or tightly, we adopt a space-time analysis to mine the information across the posture variations. Using this information, we recover the human body, regardless of the effect of clothes, and measure the human body parameters accurately. Experimental results show that our system can perform more accurate parameter estimation on the human body than state-of-the-art methods. PMID:24064597

  8. Analytical Expressions for the Envelope Binding Energy of Giants as a Function of Basic Stellar Parameters

    NASA Astrophysics Data System (ADS)

    Loveridge, A. J.; van der Sluys, M. V.; Kalogera, V.

    2011-12-01

    The common-envelope (CE) phase is an important stage in the evolution of binary stellar populations. The most common way to compute the change in orbital period during a CE is to relate the binding energy of the envelope of the Roche-lobe filling giant to the change in orbital energy. Especially in population-synthesis codes, where the evolution of millions of stars must be computed and detailed evolutionary models are too expensive computationally, simple approximations are made for the envelope binding energy. In this study, we present accurate analytic prescriptions based on detailed stellar-evolution models that provide the envelope binding energy for giants with metallicities between Z = 10-4 and Z = 0.03 and masses between 0.8 M ⊙ and 100 M ⊙, as a function of the metallicity, mass, radius, and evolutionary phase of the star. Our results are also presented in the form of electronic data tables and Fortran routines that use them. We find that the accuracy of our fits is better than 15% for 90% of our model data points in all cases, and better than 10% for 90% of our data points in all cases except the asymptotic giant branches for three of the six metallicities we consider. For very massive stars (M >~ 50 M ⊙), when stars lose more than ~20% of their initial mass due to stellar winds, our fits do not describe the models as accurately. Our results are more widely applicable—covering wider ranges of metallicity and mass—and are of higher accuracy than those of previous studies.

  9. ANALYTICAL EXPRESSIONS FOR THE ENVELOPE BINDING ENERGY OF GIANTS AS A FUNCTION OF BASIC STELLAR PARAMETERS

    SciTech Connect

    Loveridge, A. J.; Van der Sluys, M. V.; Kalogera, V.

    2011-12-10

    The common-envelope (CE) phase is an important stage in the evolution of binary stellar populations. The most common way to compute the change in orbital period during a CE is to relate the binding energy of the envelope of the Roche-lobe filling giant to the change in orbital energy. Especially in population-synthesis codes, where the evolution of millions of stars must be computed and detailed evolutionary models are too expensive computationally, simple approximations are made for the envelope binding energy. In this study, we present accurate analytic prescriptions based on detailed stellar-evolution models that provide the envelope binding energy for giants with metallicities between Z = 10{sup -4} and Z = 0.03 and masses between 0.8 M{sub Sun} and 100 M{sub Sun }, as a function of the metallicity, mass, radius, and evolutionary phase of the star. Our results are also presented in the form of electronic data tables and Fortran routines that use them. We find that the accuracy of our fits is better than 15% for 90% of our model data points in all cases, and better than 10% for 90% of our data points in all cases except the asymptotic giant branches for three of the six metallicities we consider. For very massive stars (M {approx}> 50 M{sub Sun }), when stars lose more than {approx}20% of their initial mass due to stellar winds, our fits do not describe the models as accurately. Our results are more widely applicable-covering wider ranges of metallicity and mass-and are of higher accuracy than those of previous studies.

  10. Fundamental stellar parameters and metallicities from Bayesian spectroscopy: application to low- and high-resolution spectra

    NASA Astrophysics Data System (ADS)

    Schönrich, Ralph; Bergemann, Maria

    2014-09-01

    We present a unified framework to derive fundamental stellar parameters by combining all available observational and theoretical information for a star. The algorithm relies on the method of Bayesian inference, which for the first time directly integrates the spectroscopic analysis pipeline based on the global spectrum synthesis and allows for comprehensive and objective error calculations given the priors. Arbitrary input data sets can be included into our analysis and other stellar quantities, in addition to stellar age, effective temperature, surface gravity, and metallicity, can be computed on demand. We lay out the mathematical framework of the method and apply it to several observational data sets, including high- and low-resolution spectra (UVES, NARVAL, HARPS, SDSS/SEGUE). We find that simpler approximations for the spectroscopic probability distribution function, which are inherent to past Bayesian approaches, lead to deviations of several standard deviations and unreliable errors on the same data. By its flexibility and the simultaneous analysis of multiple independent measurements for a star, it will be ideal to analyse and cross-calibrate the large ongoing and forthcoming surveys, like Gaia-European Southern Observatory (ESO), SDSS, Gaia and LSST.

  11. The Lyman-Continuum Fluxes and Stellar Parameters of O and Early B-Type Stars

    NASA Technical Reports Server (NTRS)

    Vacca, William D.; Garmany, Catherine D.; Shull, J. Michael

    1996-01-01

    Using the results of the most recent stellar atmosphere models applied to a sample of hot stars, we construct calibrations of effective temperature (T(sub eff)), and gravity (log(sub g)) with a spectral type and luminosity class for Galactic 0-type and early B-type stars. From the model results we also derive an empirical relation between the bolometric correction and T(sub eff) and log g. Using a sample of stars with known distances located in OB associations in the Galaxy and the Large Magellanic Cloud, we derive a new calibration of M(sub v) with spectral class. With these new calibrations and the stellar atmosphere models of Kurucz, we calculate the physical parameters and ionizing photon luminosities in the H(0) and He(0) continua for O and early B-type stars. We find substantial differences between our values of the Lyman- continuum luminosity and those reported in the literature. We also discuss the systematic discrepancy between O-type stellar masses derived from spectroscopic models and those derived from evolutionary tracks. Most likely, the cause of this 'mass discrepancy' lies primarily in the atmospheric models, which are plane parallel and hydrostatic and therefore do not account for an extended atmosphere and the velocity fields in a stellar wind. Finally, we present a new computation of the Lyman-continuum luminosity from 429 known O stars located within 2.5 kpc of the Sun. We find the total ionizing luminosity from this population ((Q(sub 0)(sup T(sub ot))) = 7.0 x 10(exp 51) photons/s) to be 47% larger than that determined using the Lyman continuum values tabulated by Panagia.

  12. Determining stellar atmospheric parameters and chemical abundances of FGK stars with iSpec

    NASA Astrophysics Data System (ADS)

    Blanco-Cuaresma, S.; Soubiran, C.; Heiter, U.; Jofré, P.

    2014-09-01

    Context. An increasing number of high-resolution stellar spectra is available today thanks to many past and ongoing extensive spectroscopic surveys. Consequently, the scientific community needs automatic procedures to derive atmospheric parameters and individual element abundances. Aims: Based on the widely known SPECTRUM code by R.O. Gray, we developed an integrated spectroscopic software framework suitable for the determination of atmospheric parameters (i.e., effective temperature, surface gravity, metallicity) and individual chemical abundances. The code, named iSpec and freely distributed, is written mainly in Python and can be used on different platforms. Methods: iSpec can derive atmospheric parameters by using the synthetic spectral fitting technique and the equivalent width method. We validated the performance of both approaches by developing two different pipelines and analyzing the Gaia FGK benchmark stars spectral library. The analysis was complemented with several tests designed to assess other aspects, such as the interpolation of model atmospheres and the performance with lower quality spectra. Results: We provide a code ready to perform automatic stellar spectral analysis. We successfully assessed the results obtained for FGK stars with high-resolution and high signal-to-noise spectra. The code is available via http://www.blancocuaresma.com/s/

  13. The SEGUE Stellar Parameter Pipeline. 1. Description and Initial Validation Tests

    SciTech Connect

    Lee, Young Sun; Beers, Timothy C.; Sivarani, Thirupathi; Allende Prieto, Carlos; Koesterke, Lars; Wilhelm, Ronald; Norris, John e.; Bailer-Jones, Coryn A.L.; Re Fiorentin, Paola; Rockosi, Constance M.; Yanny, Brian; /Fermilab /Rensselaer Poly. /Harvard-Smithsonian Ctr. Astrophys.

    2007-10-01

    The authors describe the development and implementation of the SEGUE (Sloan Extension for Galactic Exploration and Understanding) Stellar Parameter Pipeline (SSPP). The SSPP derives, using multiple techniques, radial velocities and the fundamental stellar atmospheric parameters (effective temperature, surface gravity, and metallicity) for AFGK-type stars, based on medium-resolution spectroscopy and ugriz photometry obtained during the course of the original Sloan Digital Sky Survey (SDSS-I) and its Galactic extension (SDSS-II/SEGUE). the SSPP also provides spectral classification for a much wider range of stars, including stars with temperatures outside of the window where atmospheric parameters can be estimated with the current approaches. This is Paper I in a series of papers on the SSPP; it provides an overview of the SSPP, and initial tests of its performance using multiple data sets. Random and systematic errors are critically examined for the current version of the SSPP, which has been used for the sixth public data release of the SDSS (DR-6).

  14. Accurate and transferable extended Hückel-type tight-binding parameters

    NASA Astrophysics Data System (ADS)

    Cerdá, J.; Soria, F.

    2000-03-01

    We show how the simple extended Hückel theory can be easily parametrized in order to yield accurate band structures for bulk materials, while the resulting optimized atomic orbital basis sets present good transferability properties. The number of parameters involved is exceedingly small, typically ten or eleven per structural phase. We apply the method to almost fifty elemental and compound bulk phases.

  15. VizieR Online Data Catalog: IN-SYNC. I. APOGEE stellar parameters (Cottaar+, 2014)

    NASA Astrophysics Data System (ADS)

    Cottaar, M.; Covey, K. R.; Meyer, M. R.; Nidever, D. L.; Stassun, K. G.; Foster, J. B.; Tan, J. C.; Chojnowski, S. D.; da Rio, N.; Flaherty, K. M.; Frinchaboy, P. M.; Skrutskie, M.; Majewski, S. R.; Wilson, J. C.; Zasowski, G.

    2015-06-01

    The spectra were collected with APOGEE's multi-object, high-resolution (R~22500) spectrograph with a spectral range covering much of the H band from 1.51 to 1.69um, which is fiber-fed from the Sloan 2.5m telescope. We provide two companion tables to this paper, which contain the derived stellar parameters for the stars in IC 348 and the Pleiades. The first table contains one row per star with the mean spectral and photometric parameters. The second table contains one row per epoch with the spectral parameters measured at that epoch. In both tables we provide the uncertainties computed by Equation (5). (2 data files).

  16. Stellar parameters for stars of the CoRoT exoplanet field

    NASA Astrophysics Data System (ADS)

    Cortés, C.; Maciel, S. C.; Vieira, S.; Ferreira Lopes, C. E.; Leão, I. C.; de Oliveira, G. P.; Correia, C.; Canto Martins, B. L.; Catelan, M.; De Medeiros, J. R.

    2015-09-01

    Context. Spectroscopic observations represent a fundamental step in the physical characterization of stars and, in particular, in the precise location of stars in the HR diagram. Rotation is also a key parameter, impacting stellar properties and evolution, which modulates the interior and manifests itself on the surface of stars. To date, the lack of analysis based on large samples has prevented our understanding of the real impact of stellar parameters and rotation on the stellar evolution as well as on the behavior of surface abundances. The space missions, CoRoT and Kepler, are providing us with rotation periods for thousands of stars, thus enabling a robust assessment of the behavior of rotation for different populations and evolutionary stages. For these reasons, the follow-up programs are fundamental to increasing the returns of these space missions. An analysis that combines spectroscopic data and rotation/modulation periods obtained from these space missions provides the basis for establishing the evolutionary behavior of the angular momentum of solar-like stars at different evolutionary stages, and the relation of rotation with other relevant physical and chemical parameters. Aims: To support the computation and evolutionary interpretation of periods associated with the rotational modulation, oscillations, and variability of stars located in the CoRoT fields, we are conducting a spectroscopic survey for stars located in the fields already observed by the satellite. These observations allow us to compute physical and chemical parameters for our stellar sample. Methods: Using spectroscopic observations obtained with UVES/VLT and Hydra/Blanco, and based on standard analysis techniques, we computed physical and chemical parameters (Teff, log (g), [Fe/H], vmic, vrad, vsin (i), and A(Li)) for a large sample of CoRoT targets. Results: We provide physical and chemical parameters for a sample comprised of 138 CoRoT targets. Our analysis shows the stars in our

  17. Fundamental stellar and accretion disc parameters of the eclipsing binary DQ Velorum

    NASA Astrophysics Data System (ADS)

    Barría, D.; Mennickent, R. E.; Schmidtobreick, L.; Djurašević, G.; Kołaczkowski, Z.; Michalska, G.; Vučković, M.; Niemczura, E.

    2013-04-01

    Context. To add to the growing collection of well-studied double periodic variables (DPVs) we have carried out the first spectroscopic and photometric analysis of the eclipsing binary DQ Velorum to obtain its main physical stellar and orbital parameters. Aims: Combining spectroscopic and photometric observations that cover several orbital cycles allows us to estimate the stellar properties of the binary components and the orbital parameters. We also searched for circumstellar material around the more massive star. Methods: We separated DQ Velorum composite spectra and measured radial velocities with an iterative method for double spectroscopic binaries. We obtained the radial velocity curves and calculated the spectroscopic mass ratio. We compared our single-lined spectra with a grid of synthetic spectra and estimated the temperature of the stars. We modeled the V-band light curve with a fitting method based on the simplex algorithm, which includes an accretion disc. To constrain the main stellar parameters we fixed the mass ratio and donor temperature to the values obtained by our spectroscopic analysis. Results: We obtain a spectroscopic mass ratio q = 0.31 ± 0.03 together with donor and gainer masses Md = 2.2 ± 0.2 M⊙, Mg = 7.3 ± 0.3 M⊙, the radii Rd = 8.4 ± 0.2 R⊙, Rg = 3.6 ± 0.2 R⊙ and temperatures Td = 9400 ± 100 K, Tg = 18 500 ± 500 K for the stellar components. We find that DQ Vel is a semi-detached system consisting of a B3V gainer and an A1III donor star plus an extended accretion disc around the gainer. The disc is filling 89% of the gainer Roche lobe with a temperature of 6580 ± 300 K at the outer radius. It has a concave shape that is thicker at its edge (de = 0.6 ± 0.1 R⊙) than at its centre (dc = 0.3 ± 0.1 R⊙). We find a significant sub-orbital frequency of 0.19 d-1 in the residuals of the V-band light curve, which we interpret as a pulsation of an slowly pulsating B-type (SPB) of a gainer star. We also estimate the distance to

  18. Accurate parameters of the oldest known rocky-exoplanet hosting system: Kepler-10 revisited

    SciTech Connect

    Fogtmann-Schulz, Alexandra; Hinrup, Brian; Van Eylen, Vincent; Christensen-Dalsgaard, Jørgen; Kjeldsen, Hans; Silva Aguirre, Víctor; Tingley, Brandon

    2014-02-01

    Since the discovery of Kepler-10, the system has received considerable interest because it contains a small, rocky planet which orbits the star in less than a day. The system's parameters, announced by the Kepler team and subsequently used in further research, were based on only five months of data. We have reanalyzed this system using the full span of 29 months of Kepler photometric data, and obtained improved information about its star and the planets. A detailed asteroseismic analysis of the extended time series provides a significant improvement on the stellar parameters: not only can we state that Kepler-10 is the oldest known rocky-planet-harboring system at 10.41 ± 1.36 Gyr, but these parameters combined with improved planetary parameters from new transit fits gives us the radius of Kepler-10b to within just 125 km. A new analysis of the full planetary phase curve leads to new estimates on the planetary temperature and albedo, which remain degenerate in the Kepler band. Our modeling suggests that the flux level during the occultation is slightly lower than at the transit wings, which would imply that the nightside of this planet has a non-negligible temperature.

  19. Accurate procedure for deriving UTI at a submilliarcsecond accuracy from Greenwich Sidereal Time or from the stellar angle

    NASA Astrophysics Data System (ADS)

    Capitaine, N.; Gontier, A.-M.

    1993-08-01

    Present observations using modern astrometric techniques are supposed to provide the Earth orientation parameters, and therefore UT1, with an accuracy better than ±1 mas. In practice, UT1 is determined through the intermediary of Greenwich Sidereal Time (GST), using both the conventional relationship between Greenwich Mean Sidereal Time (GMST) and UTl (Aoki et al. 1982) and the so-called "equation of the equinoxes" limited to the first order terms with respect to the nutation quantities. This highly complex relation between sidereal time and UT1 is not accurate at the milliaresecond level which gives rise to spurious terms of milliaresecond amplitude in the derived UTl. A more complete relationship between GST and UT1 has been recommended by Aoki & Kinoshita (1983) and Aoki (1991) taking into account the second order terms in the difference between GST and GM ST, the largest one having an amplitude of 2.64 mas and a 18.6 yr-period. This paper explains how this complete expansion of GST implicitly uses the concept of "nonrotating origin" (NRO) as proposed by Guinot in 1979 and would, therefore, provide a more accurate value of UTl and consequently of the Earth's angular velocity. This paper shows, moreover, that such a procedure would be simplified and conceptually clarified by the explicit use of the NRO as previously proposed (Guinot 1979; Capitaine et al. 1986). The two corresponding options (implicit or explicit use of the NRO) are shown to be equivalent for defining the specific Earth's angle of rotation and then UT1. The of the use of such an accurate procedure which has been proposed in the new IERS standards (McCarthy 1992a) instead of the usual one are estimated for the practical derivation of UT1.

  20. Identification of accurate nonlinear rainfall-runoff models with unique parameters

    NASA Astrophysics Data System (ADS)

    Schoups, G.; Vrugt, J. A.; Fenicia, F.; van de Giesen, N.

    2009-04-01

    We propose a strategy to identify models with unique parameters that yield accurate streamflow predictions, given a time-series of rainfall inputs. The procedure consists of five general steps. First, an a priori range of model structures is specified based on prior general and site-specific hydrologic knowledge. To this end, we rely on a flexible model code that allows a specification of a wide range of model structures, from simple to complex. Second, using global optimization each model structure is calibrated to a record of rainfall-runoff data, yielding optimal parameter values for each model structure. Third, accuracy of each model structure is determined by estimating model prediction errors using independent validation and statistical theory. Fourth, parameter identifiability of each calibrated model structure is estimated by means of Monte Carlo Markov Chain simulation. Finally, an assessment is made about each model structure in terms of its accuracy of mimicking rainfall-runoff processes (step 3), and the uniqueness of its parameters (step 4). The procedure results in the identification of the most complex and accurate model supported by the data, without causing parameter equifinality. As such, it provides insight into the information content of the data for identifying nonlinear rainfall-runoff models. We illustrate the method using rainfall-runoff data records from several MOPEX basins in the US.

  1. Abundances, Stellar Parameters, and Spectra from the SDSS-III/APOGEE Survey

    NASA Astrophysics Data System (ADS)

    Holtzman, Jon A.; Shetrone, Matthew; Johnson, Jennifer A.; Allende Prieto, Carlos; Anders, Friedrich; Andrews, Brett; Beers, Timothy C.; Bizyaev, Dmitry; Blanton, Michael R.; Bovy, Jo; Carrera, Ricardo; Chojnowski, S. Drew; Cunha, Katia; Eisenstein, Daniel J.; Feuillet, Diane; Frinchaboy, Peter M.; Galbraith-Frew, Jessica; García Pérez, Ana E.; García-Hernández, D. A.; Hasselquist, Sten; Hayden, Michael R.; Hearty, Fred R.; Ivans, Inese; Majewski, Steven R.; Martell, Sarah; Meszaros, Szabolcs; Muna, Demitri; Nidever, David; Nguyen, Duy Cuong; O'Connell, Robert W.; Pan, Kaike; Pinsonneault, Marc; Robin, Annie C.; Schiavon, Ricardo P.; Shane, Neville; Sobeck, Jennifer; Smith, Verne V.; Troup, Nicholas; Weinberg, David H.; Wilson, John C.; Wood-Vasey, W. M.; Zamora, Olga; Zasowski, Gail

    2015-11-01

    The SDSS-III/Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey operated from 2011-2014 using the APOGEE spectrograph, which collects high-resolution (R ˜ 22,500), near-IR (1.51-1.70 μm) spectra with a multiplexing (300 fiber-fed objects) capability. We describe the survey data products that are publicly available, which include catalogs with radial velocity, stellar parameters, and 15 elemental abundances for over 150,000 stars, as well as the more than 500,000 spectra from which these quantities are derived. Calibration relations for the stellar parameters ({T}{eff}, {log} g, [M/H], [α/M]) and abundances (C, N, O, Na, Mg, Al, Si, S, K, Ca, Ti, V, Mn, Fe, Ni) are presented and discussed. The internal scatter of the abundances within clusters indicates that abundance precision is generally between 0.05 and 0.09 dex across a broad temperature range; it is smaller for some elemental abundances within more limited ranges and at high signal-to-noise ratio. We assess the accuracy of the abundances using comparison of mean cluster metallicities with literature values, APOGEE observations of the solar spectrum and of Arcturus, comparison of individual star abundances with other measurements, and consideration of the locus of derived parameters and abundances of the entire sample, and find that it is challenging to determine the absolute abundance scale; external accuracy may be good to 0.1-0.2 dex. Uncertainties may be larger at cooler temperatures ({T}{eff} \\lt 4000 {{K}}). Access to the public data release and data products is described, and some guidance for using the data products is provided.

  2. Morphological parameters of a Spitzer survey of stellar structure in galaxies

    SciTech Connect

    Holwerda, B. W.; Muñoz-Mateos, J.-C.; Sheth, K.; Kim, T.; Meidt, S.; Mizusawa, T.; Hinz, J. L.; Zaritsky, D.; Regan, M. W.; Gil de Paz, A.; Menéndez-Delmestre, K.; Seibert, M.; Ho, L. C.; Gadotti, D. A.; Erroz-Ferrer, S. E-mail: benne.holwerda@gmail.com [Instituto de Astrofísica de Canarias, Vía Láctea s and others

    2014-01-20

    The morphology of galaxies can be quantified to some degree using a set of scale-invariant parameters. Concentration (C), asymmetry (A), smoothness (S), the Gini index (G), the relative contribution of the brightest pixels to the second-order moment of the flux (M {sub 20}), ellipticity (E), and the Gini index of the second-order moment (G{sub M} ) have all been applied to morphologically classify galaxies at various wavelengths. Here, we present a catalog of these parameters for the Spitzer Survey of stellar structure in Galaxies, a volume-limited, near-infrared (NIR) imaging survey of nearby galaxies using the 3.6 and 4.5 μm channels of the Infrared Array Camera on board the Spitzer Space Telescope. Our goal is to provide a reference catalog of NIR quantified morphology for high-redshift studies and galaxy evolution models with enough detail to resolve stellar mass morphology. We explore where normal, non-interacting galaxies—those typically found on the Hubble tuning fork—lie in this parameter space and show that there is a tight relation between concentration (C {sub 82}) and M {sub 20} for normal galaxies. M {sub 20} can be used to classify galaxies into earlier and later types (i.e., to separate spirals from irregulars). Several criteria using these parameters exist to select systems with a disturbed morphology, i.e., those that appear to be undergoing a tidal interaction. We examine the applicability of these criteria to Spitzer NIR imaging. We find that four relations, based on the parameters A and S, G and M {sub 20}, G{sub M} , C, and M {sub 20}, respectively, select outliers in morphological parameter space, but each selects different subsets of galaxies. Two criteria (G{sub M} > 0.6, G > –0.115 × M {sub 20} + 0.384) seem most appropriate to identify possible mergers and the merger fraction in NIR surveys. We find no strong relation between lopsidedness and most of these morphological parameters, except for a weak dependence of lopsidedness on

  3. Inversion of stellar fundamental parameters from ESPaDOnS and Narval high-resolution spectra

    NASA Astrophysics Data System (ADS)

    Paletou, F.; Böhm, T.; Watson, V.; Trouilhet, J.-F.

    2015-01-01

    The general context of this study is the inversion of stellar fundamental parameters from high-resolution Echelle spectra. We aim at developing a fast and reliable tool for the post-processing of spectra produced by ESPaDOnS and Narval spectropolarimeters. Our inversion tool relies on principal component analysis. It allows reducing dimensionality and defining a specific metric for the search of nearest neighbours between an observed spectrum and a set of observed spectra taken from the Elodie stellar library. Effective temperature, surface gravity, total metallicity, and projected rotational velocity are derived. Various tests presented in this study that were based solely on information coming from a spectral band centred on the Mg i b-triplet and had spectra from FGK stars are very promising. Based on observations obtained at the Télescope Bernard Lyot (TBL, Pic du Midi, France), which is operated by the Observatoire Midi-Pyrénées, Université de Toulouse, Centre National de la Recherche Scientifique (France) and the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council of Canada, CNRS/INSU and the University of Hawaii (USA).

  4. The SEGUE Stellar Parameter Pipeline and the alpha elements of stars in the Milky Way

    NASA Astrophysics Data System (ADS)

    Lee, Young Sun

    I describe the development and implementation of the SEGUE (Sloan Extension for Galactic Exploration and Understanding) Stellar Parameter Pipeline (SSPP). The SSPP derives, using multiple techniques, radial velocities and stellar atmospheric parameters (effective temperature, T eff , surface gravity, log g, and metallicity, [Fe/H]) for AFGK type stars, based on medium-resolution spectroscopy and ugriz photometry obtained during the original Sloan Digital Sky Survey (SDSS-I) and its Galactic extension (SDSS-II/SEGUE). The SSPP also provides spectral classification for a wider range of stars, including stars with temperatures outside of the window where stellar parameters can not be estimated with the current approaches. Adding the average internal scatter rom the multiple methods and the external uncertainty from the comparisons withthe high-resolution analysis, quadratically, the typical uncertainties in the stellar parameters delivered by the SSPP are s( T eff ) = 157 K, s(log g ) = 0.29 dex, and s([Fe/H]) = 0.24 dex, over the range 4500 K < T eff < 7500 K. Tests of the accuracy and precision of the SSPP, by comparing the stellar parameters for selected members of three globular clusters (M 13, M 15, and M 2) and two open clusters (NGC 2420 and M 67) to the literature values, are also presented. Spectroscopic and photometric data obtained during the SDSS-I and SDSS-II/SEGUE are used to determine atmospheric parameter and radial velocity estimates for stars in these clusters. Based on the scatter in the metallicities derived for the members of each cluster, I quantify the typical uncertainty of the SSPP values, s([Fe/H]) = 0.13 dex for stars in the range of -0.3 <= g - r <= 1.3 and 2.0 <= log g <= 5.0, at least over the metallicity interval spanned by the clusters studied (-2.3 <= [Fe/H] <= 0), and with signal-to-noise ratios greater than ~ 10/1. The surface gravities and effective temperatures derived by the SSPP are also compared with those estimated from the

  5. Limb darkening and exoplanets: testing stellar model atmospheres and identifying biases in transit parameters

    NASA Astrophysics Data System (ADS)

    Espinoza, Néstor; Jordán, Andrés

    2015-06-01

    Limb darkening is fundamental in determining transit light-curve shapes, and is typically modelled by a variety of laws that parametrize the intensity profile of the star that is being transited. Confronted with a transit light curve, some authors fix the parameters of these laws, the so-called limb darkening coefficients (LDCs), while others prefer to let them float in the light-curve fitting procedure. Which of these is the best strategy, however, is still unclear, as well as how and by how much each of these can bias the retrieved transit parameters. In this work we attempt to clarify those points by first recalculating these LDCs, comparing them to measured values from Kepler transit light curves using an algorithm that takes into account uncertainties in both the geometry of the transit and the parameters of the stellar host. We show there are significant departures from predicted model values, suggesting that our understanding of limb darkening still needs to improve. Then, we show through simulations that if one uses the quadratic limb darkening law to parametrize limb darkening, fixing and fitting the LDCs can lead to significant biases - up to ˜3 and ˜1 per cent in Rp/R*, respectively - which are important for several confirmed and candidate exoplanets. We conclude that, in this case, the best approach is to let the LDCs be free in the fitting procedure. Strategies to avoid biases in data from present and future missions involving high precision measurements of transit parameters are described.

  6. VizieR Online Data Catalog: FAMA code for stellar parameters and abundances (Magrini+, 2013)

    NASA Astrophysics Data System (ADS)

    Magrini, L.; Randich, S.; Friel, E.; Spina, L.; Jacobson, H.; Cantat-Gaudin, T.; Donati, P.; Baglioni, R.; Maiorca, E.; Bragaglia, A.; Sordo, R.; Vallenari, A.

    2013-07-01

    FAMA v.1, July 2013, distributed with MOOGv2013 and Kurucz models. Perl Codes: read_out2.pl read_final.pl driver.pl sclipping_26.0.pl sclipping_final.pl sclipping_26.1.pl confronta.pl fama.pl Model atmopheres and interpolator (Kurucz models): MODEL_ATMO MOOG_files: files to compile MOOG (the most recent version of MOOG can be obtained from http://www.as.utexas.edu/~chris/moog.html) FAMAmoogfiles: files to update when compiling MOOG OUTPUT: directory in which the results will be stored, contains a sm macro to produce final plots automoog.par: files with parameters for FAMA 1) OUTPUTdir 2) MOOGdir 3) modelsdir 4) 1.0 (default) percentage of the dispersion of FeI abundances to be considered to compute the errors on the stellar parameters, 1.0 means 100%, thus to compute e.g., the error on Teff we allow to code to find the Teff corresponding to a slope given by σ(FeI)/range(EP). 5) 1.2 (default) σ clipping for FeI lines 6) 1.0 (default) σ clipping for FeII lines 7) 1.0 (default) σ clipping for the other elements 8) 1.0 (default) value of the QP parameter, higher values mean less strong convergence criteria. star.iron: EWs in the correct format to test the code sun.par: initial parameters for the test (1 data file).

  7. Wavelet analysis of the parameters of edge plasma fluctuations in the L-2M stellarator

    NASA Astrophysics Data System (ADS)

    Maslov, S. A.; Vasilkov, D. G.; Kholnov, Yu V.; Skvortsova, N. N.

    2016-01-01

    Wavelet analysis results are presented for evolution of the spectral fluctuation characteristics of the edge plasma density and potential in the L-2M stellarator for fast and slow transport transitions. The fast transition comes out as a sharp increase of the energy and electron density within ∼0.1ms and the slow one as a weak parameter change during a 0.5 to 1 ms time interval. It is shown that the use of the “Mexican hat” and Morlet wavelets allows one to detect the moment of the fast transition, whereas applying the Haar wavelet adds to this also an estimate of its duration, conforming to the analytical calculations, and reveals the temporal structure of the slow transition.

  8. Cool stars: spectral library of high-resolution echelle spectra and database of stellar parameters

    NASA Astrophysics Data System (ADS)

    Montes, D.

    2013-05-01

    During the last years our group have undertake several high resolution spectroscopic surveys of nearby FGKM stars with different spectrographs (FOCES, SARG, SOFIN, FIES, HERMES). A large number of stars have been already observed and we have already determined spectral types, rotational velocities as well as radial velocities, Lithium abundance and several chromospheric activity indicators. We are working now in a homogeneous determination of the fundamental stellar parameters (T_{eff}, log{g}, ξ and [Fe/H]) and chemical abundances of many elements of all these stars. Some fully reduced spectra in FITS format have been available via ftp and in the {http://www.ucm.es/info/Astrof/invest/actividad/spectra.html}{Worl Wide Web} (Montes et al. 1997, A&AS, 123, 473; Montes et al. 1998, A&AS, 128, 485; and Montes et al. 1999, ApJS, 123, 283) and some particular spectral regions of the echelle spectra are available at VizieR by López-Santiago et al. 2010, A&A, 514, A97. We are now working in made accessible all the spectra of our different surveys in a Virtual Observatory ({http://svo.cab.inta-csic.es/}{VO}) compliant library and database accessible using a common web interface following the standards of the International Virtual Observatory Alliance ({http://www.ivoa.net/}{IVOA}). The spectral library includes F, G, K and M field stars, from dwarfs to giants. The spectral coverage is from 3800 to 10000 Å, with spectral resolution ranging from 40000 to 80000. The database will provide in addition the stellar parameters determined for these spectra using {http://cdsads.u-strasbg.fr/abs/2012arXiv1205.4879T}{StePar} (Tabernero et al. 2012, A&A, 547, A13).

  9. Parameter Estimation of Ion Current Formulations Requires Hybrid Optimization Approach to Be Both Accurate and Reliable

    PubMed Central

    Loewe, Axel; Wilhelms, Mathias; Schmid, Jochen; Krause, Mathias J.; Fischer, Fathima; Thomas, Dierk; Scholz, Eberhard P.; Dössel, Olaf; Seemann, Gunnar

    2016-01-01

    Computational models of cardiac electrophysiology provided insights into arrhythmogenesis and paved the way toward tailored therapies in the last years. To fully leverage in silico models in future research, these models need to be adapted to reflect pathologies, genetic alterations, or pharmacological effects, however. A common approach is to leave the structure of established models unaltered and estimate the values of a set of parameters. Today’s high-throughput patch clamp data acquisition methods require robust, unsupervised algorithms that estimate parameters both accurately and reliably. In this work, two classes of optimization approaches are evaluated: gradient-based trust-region-reflective and derivative-free particle swarm algorithms. Using synthetic input data and different ion current formulations from the Courtemanche et al. electrophysiological model of human atrial myocytes, we show that neither of the two schemes alone succeeds to meet all requirements. Sequential combination of the two algorithms did improve the performance to some extent but not satisfactorily. Thus, we propose a novel hybrid approach coupling the two algorithms in each iteration. This hybrid approach yielded very accurate estimates with minimal dependency on the initial guess using synthetic input data for which a ground truth parameter set exists. When applied to measured data, the hybrid approach yielded the best fit, again with minimal variation. Using the proposed algorithm, a single run is sufficient to estimate the parameters. The degree of superiority over the other investigated algorithms in terms of accuracy and robustness depended on the type of current. In contrast to the non-hybrid approaches, the proposed method proved to be optimal for data of arbitrary signal to noise ratio. The hybrid algorithm proposed in this work provides an important tool to integrate experimental data into computational models both accurately and robustly allowing to assess the often non

  10. An accurate Fortran code for computing hydrogenic continuum wave functions at a wide range of parameters

    NASA Astrophysics Data System (ADS)

    Peng, Liang-You; Gong, Qihuang

    2010-12-01

    The accurate computations of hydrogenic continuum wave functions are very important in many branches of physics such as electron-atom collisions, cold atom physics, and atomic ionization in strong laser fields, etc. Although there already exist various algorithms and codes, most of them are only reliable in a certain ranges of parameters. In some practical applications, accurate continuum wave functions need to be calculated at extremely low energies, large radial distances and/or large angular momentum number. Here we provide such a code, which can generate accurate hydrogenic continuum wave functions and corresponding Coulomb phase shifts at a wide range of parameters. Without any essential restrict to angular momentum number, the present code is able to give reliable results at the electron energy range [10,10] eV for radial distances of [10,10] a.u. We also find the present code is very efficient, which should find numerous applications in many fields such as strong field physics. Program summaryProgram title: HContinuumGautchi Catalogue identifier: AEHD_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEHD_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 1233 No. of bytes in distributed program, including test data, etc.: 7405 Distribution format: tar.gz Programming language: Fortran90 in fixed format Computer: AMD Processors Operating system: Linux RAM: 20 MBytes Classification: 2.7, 4.5 Nature of problem: The accurate computation of atomic continuum wave functions is very important in many research fields such as strong field physics and cold atom physics. Although there have already existed various algorithms and codes, most of them can only be applicable and reliable in a certain range of parameters. We present here an accurate FORTRAN program for

  11. Estimating stellar atmospheric parameters based on LASSO and support-vector regression

    NASA Astrophysics Data System (ADS)

    Lu, Yu; Li, Xiangru

    2015-09-01

    A scheme for estimating atmospheric parameters Teff, log g and [Fe/H] is proposed on the basis of the Least Absolute Shrinkage and Selection Operator (LASSO) algorithm and Haar wavelet. The proposed scheme consists of three processes. A spectrum is decomposed using the Haar wavelet transform and low-frequency components at the fourth level are considered as candidate features. Then, spectral features from the candidate features are detected using the LASSO algorithm to estimate the atmospheric parameters. Finally, atmospheric parameters are estimated from the extracted spectral features using the support-vector regression (SVR) method. The proposed scheme was evaluated using three sets of stellar spectra from the Sloan Digital Sky Survey (SDSS), Large Sky Area Multi-object Fibre Spectroscopic Telescope (LAMOST) and Kurucz's model, respectively. The mean absolute errors are as follows: for the 40 000 SDSS spectra, 0.0062 dex for log Teff (85.83 K for Teff), 0.2035 dex for log g and 0.1512 dex for [Fe/H]; for the 23 963 LAMOST spectra, 0.0074 dex for log Teff (95.37 K for Teff), 0.1528 dex for log g and 0.1146 dex for [Fe/H]; for the 10 469 synthetic spectra, 0.0010 dex for log Teff (14.42K for Teff), 0.0123 dex for log g and 0.0125 dex for [Fe/H].

  12. BINARY CONTAMINATION IN THE SEGUE SAMPLE: EFFECTS ON SSPP DETERMINATIONS OF STELLAR ATMOSPHERIC PARAMETERS

    SciTech Connect

    Schlesinger, Katharine J.; Johnson, Jennifer A.; Masseron, Thomas; Gaudi, B. Scott; Lee, Young Sun; Beers, Timothy C.; Yanny, Brian; Rockosi, Constance M.

    2010-08-20

    We examine the effects that unresolved binaries have on the determination of various stellar atmospheric parameters for targets from the Sloan Extension for Galactic Understanding and Exploration (SEGUE) using numerical modeling, a grid of synthetic spectra, and the SEGUE Stellar Parameter Pipeline (SSPP). The SEGUE survey, a component of the Sloan Digital Sky Survey-II (SDSS-II) project focusing on Galactic structure, provides medium resolution spectroscopy for over 200,000 stars of various spectral types over a large area on the sky. To model undetected binaries that may be in this sample, we use a variety of mass distributions for the primary and secondary stars in conjunction with empirically determined relationships for orbital parameters to determine the fraction of G - K dwarf stars, defined by SDSS color cuts as having 0.48 {<=} (g - r){sub 0} {<=} 0.75, that will be blended with a secondary companion. We focus on the G-K dwarf sample in SEGUE as it records the history of chemical enrichment in our galaxy. To determine the effect of the secondary on the spectroscopic parameters, specifically effective temperature, surface gravity, metallicity, and [{alpha}/Fe], we synthesize a grid of model spectra from 3275 to 7850 K and [Fe/H] = -0.5 to -2.5 from MARCS model atmospheres using TurboSpectrum. These temperature and metallicity ranges roughly correspond to a stellar mass range of 0.1-1.0 M{sub sun}. We assume that both stars in the pair have the same metallicity. We analyze both 'infinite' signal-to-noise ratio (S/N) models and degraded versions of the spectra, at median S/N of 50, 25, and 10. By running individual and combined spectra (representing the binaries) through the SSPP, we determine that {approx}10% of the blended G - K dwarf pairs with S/N {>=} 25 will have their atmospheric parameter determinations, in particular temperature and metallicity, noticeably affected by the presence of an undetected secondary; namely, they will be shifted beyond the

  13. Data reduction, radial velocities and stellar parameters from spectra in the very low signal-to-noise domain

    NASA Astrophysics Data System (ADS)

    Malavolta, Luca

    2013-10-01

    different approach with respect to the ESO pipeline. We then analyze deeply the best way to perform sky sub- traction and continuum normalization, the most important sources respectively of noise and systematics in radial velocity determination and chemical analysis of spectra. The huge number of spectra of our dataset requires an automatic but robust approach, which we do not fail to provide. We finally determine radial velocities for the stars in the sample with unprecedented precision with respect to previous works with similar data and we recover the same stellar atmosphere parameters of other studies performed on the same cluster but on brighter stars, with higher spectral resolution and wavelength range ten times larger than our data. In the final chapter of the thesis we face a similar problem but from a completely different perspective. High resolution, high SNR data from the High Accuracy Radial Velocity Planet Searcher spectro- graph (HARPS) in La Silla (Chile) have been used to calibrate the at- mospheric stellar parameters as functions of the main characteristics of Cross-Correlation Functions, specifically built by including spec- tral lines with different sensitivity to stellar atmosphere parameters. These tools has been designed to be quick and to be easy to imple- ment in a instrument pipeline for a real-time determination, neverthe- less they provide accurate parameters even for lower SNR spectra.

  14. Accurate optical parameter extraction procedure for broadband near-infrared spectroscopy of brain matter

    PubMed Central

    Najafizadeh, Laleh; Gandjbakhche, Amir H.; Pourrezaei, Kambiz; Daryoush, Afshin

    2013-01-01

    Abstract. Modeling behavior of broadband (30 to 1000 MHz) frequency modulated near-infrared (NIR) photons through a phantom is the basis for accurate extraction of optical absorption and scattering parameters of biological turbid media. Photon dynamics in a phantom are predicted using both analytical and numerical simulation and are related to the measured insertion loss (IL) and insertion phase (IP) for a given geometry based on phantom optical parameters. Accuracy of the extracted optical parameters using finite element method (FEM) simulation is compared to baseline analytical calculations from the diffusion equation (DE) for homogenous brain phantoms. NIR spectroscopy is performed using custom-designed, broadband, free-space optical transmitter (Tx) and receiver (Rx) modules that are developed for photon migration at wavelengths of 680, 780, and 820 nm. Differential detection between two optical Rx locations separated by 0.3 cm is employed to eliminate systemic artifacts associated with interfaces of the optical Tx and Rx with the phantoms. Optical parameter extraction is achieved for four solid phantom samples using the least-square-error method in MATLAB (for DE) and COMSOL (for FEM) simulation by fitting data to measured results over broadband and narrowband frequency modulation. Confidence in numerical modeling of the photonic behavior using FEM has been established here by comparing the transmission mode’s experimental results with the predictions made by DE and FEM for known commercial solid brain phantoms. PMID:23322361

  15. Accurate estimation of motion blur parameters in noisy remote sensing image

    NASA Astrophysics Data System (ADS)

    Shi, Xueyan; Wang, Lin; Shao, Xiaopeng; Wang, Huilin; Tao, Zhong

    2015-05-01

    The relative motion between remote sensing satellite sensor and objects is one of the most common reasons for remote sensing image degradation. It seriously weakens image data interpretation and information extraction. In practice, point spread function (PSF) should be estimated firstly for image restoration. Identifying motion blur direction and length accurately is very crucial for PSF and restoring image with precision. In general, the regular light-and-dark stripes in the spectrum can be employed to obtain the parameters by using Radon transform. However, serious noise existing in actual remote sensing images often causes the stripes unobvious. The parameters would be difficult to calculate and the error of the result relatively big. In this paper, an improved motion blur parameter identification method to noisy remote sensing image is proposed to solve this problem. The spectrum characteristic of noisy remote sensing image is analyzed firstly. An interactive image segmentation method based on graph theory called GrabCut is adopted to effectively extract the edge of the light center in the spectrum. Motion blur direction is estimated by applying Radon transform on the segmentation result. In order to reduce random error, a method based on whole column statistics is used during calculating blur length. Finally, Lucy-Richardson algorithm is applied to restore the remote sensing images of the moon after estimating blur parameters. The experimental results verify the effectiveness and robustness of our algorithm.

  16. Tidally Enhanced Stellar Wind in Binaries as a Second Parameter for the Horizontal Branch Morphology of Globular Clusters

    NASA Astrophysics Data System (ADS)

    Han, Z.; Lei, Z.

    2014-04-01

    Metallicity is the first parameter to influence the horizontal branch morphology of globular clusters. It has been found, however, that some other parameters may also play an important role in affecting the morphology. While the nature of these other important parameters remains unclear, they are believed to be correlated with the mass loss during the red giant stages, from which the horizontal branch stars have descended. Unfortunately, the mass loss during the red giant stages of stellar evolution are poorly understood at present. In this talk, we investigate the physical consequences of tidally-enhanced stellar winds during the evolution of binary stars on enhancing the mass loss of red giant primaries, with accompanying effects for the horizontal branch morphology of globular clusters. In a binary system, the stellar wind of the red giant primary star may be largely enhanced by its companion star. Different separation of the binary system, however, will lead to a different mass loss rate of the primary star. We found that red, blue, and extreme horizontal branch stars are all produced under the effects of tidally-enhanced stellar wind without any additional assumptions on the mass loss dispersion. Furthermore, the horizontal branch morphology is found to be insensitive to the tidal enhancement parameter, B.

  17. Derivation of stellar parameters from Gaia RVS spectra with prediction uncertainty using Generative Artificial Neural Networks (GANNs)

    NASA Astrophysics Data System (ADS)

    Manteiga, Minia; Dafonte, Jose Carlos; Ulla, Ana; Alvarez, Marco Antonio; Garabato, Daniel; Fustes, Diego

    2015-08-01

    The main purpose of Gaia Radial Velocity Spectrograph (RVS) is to measure the radial velocity of stars in the near infrared CaII spectral region. However, RVS will be used also for estimating the main stellar astrophysical parameters: effective temperature (Teff), logarithm of surface gravity (logg), abundance of metal elements with respect to hydrogen ([Fe/H]) and abundance of alpha elements with respect to iron ([α/Fe]). The software package being developed by Gaia DPAC (Data Processing and Analysis Consorcium) is composed by a bunch of modules which address the problem of parameterization from different perspectives This work focuses on developments carried out in the framework of one of these modules, called ANN, that is based on the application of Artificial Neural Networks.ANNs are a great tool that offers non-linear regression capabilities to any degree of complexity. Furthermore, they can provide accurate predictions when new data is presented to them, since they can generalize their solutions. However, in principle, ANNs are not able to give a measure of uncertainty over their predictions. Giving a measure of uncertainty over predictions is desirable in application domains where posterior inferences need to assess the quality of the predictions, especially when the behaviour of the system is not completely known. This is the case of data analysis coming from complex scientific missions like Gaia. This work presents a new architecture for ANNs, Generative ANNs (GANNs), that models the forward function instead of the inverse one. The advantage of forward modelling is that it estimates the actual observation, so that the fit between the estimated observation and the actual observation can be assessed, which allows for novelty detection, model evaluation and active learning. Furthermore, GANNs can be integrated in a Bayesian framework, which allows to estimate the full posterior distribution over the parameters of interest, to perform model comparisons, etc.

  18. Fundamental Parameters and Spectral Energy Distributions of Young and Field Age Objects with Masses Spanning the Stellar to Planetary Regime

    NASA Astrophysics Data System (ADS)

    Filippazzo, Joe; Rice, Emily L.; Faherty, Jacqueline K.; Cruz, Kelle L.; Godfrey, Paige A.; BDNYC

    2016-01-01

    The physical and atmospheric properties of ultracool dwarfs are deeply entangled due to the degenerate effects of mass, age, metallicity, clouds and dust, activity, rotation, and possibly even formation mechanism on observed spectra. Accurate determination of fundamental parameters for a wide diversity of objects at the low end of the IMF is thus crucial to testing stellar and planetary formation theories. To determine these quantities, we constructed and flux calibrated nearly-complete spectral energy distributions (SEDs) for 221 M, L, T, and Y dwarfs using published parallaxes and 0.3-40 μm spectra and photometry. From these homogeneous SEDs, we calculated bolometric luminosity (Lbol), effective temperature (Teff), mass, surface gravity, radius, spectral indexes, synthetic photometry, and bolometric corrections (BCs) for each object. We used these results to derive Lbol, Teff, and BC polynomial relations across the entire very-low-mass star/brown dwarf/planetary mass regime. We use a subsample of objects with age constraints based on nearby young moving group membership, companionship with a young star, or spectral signatures of low surface gravity to define new age-sensitive diagnostics and characterize the reddening of young substellar atmospheres as a redistribution of flux from the near-infrared into the mid-infrared. Consequently we find the SED flux pivots at Ks band, making BCKs as a function of spectral type a tight and age independent relationship. We find that young L dwarfs are systematically 300 K cooler than field age objects of the same spectral type and up to 600 K cooler than field age objects of the same absolute H magnitude. Finally, we present preliminary comparisons of these empirical results to best fit parameters from four different model atmosphere grids via Markov-Chain Monte Carlo analysis in order to create prescriptions for the reliable and efficient characterization of new ultracool dwarfs.

  19. Radio pulsations from AD Leo: diagnostics of electric currents and plasma parameters in stellar flares

    NASA Astrophysics Data System (ADS)

    Kouprianova, E. G.; Stepanov, A. V.; Zaitsev, V. V.

    2006-08-01

    Using pulsations characteristics from AD Leo radio flares observed with Arecibo (Bastian et al., 1990) and Effelsberg (Stepanov et al. , 2001) radio telescopes, the values of electric currents (7-40)×10 ^11 A and plasma parameters in stellar flares are determined. It was shown that radio pulsations can be due to both sausage oscillations of as well as current RLC-oscillations in a flare loop (Zaitsev et al ., 1988, 2004). Explanation of very intense radio bursts (T[b ]≥ 10^15 K) in terms of coherent plasma emission gives the magnetic field value (100-300 G) and the electron number density (10^10^ - 10^11 cm^-3) in the flares. The energy of electric current stored in flares was estimated as (1-50) ×10^25 J. It is shown that <10% of stored energy was released in the flares. References Bastian, T., Bookbinder, J., Dulk, G.A., Davis, M. 1990, ApJ, 353, 265 Stepanov, A.V., Kliem, B., Zaitsev, V.V. et al. 2001, A&A, 374, 1072 Zaitsev, V.V., Stepanov, A.V., Urpo, S., Pohjolainen, S., 1998, A& A, 337, 887. Zaitsev, V.V., Kislyakov, A.G., Stepanov, A.V., Kliem, B., Fuerst, E. 2004, Astron. Lett. 30, 319

  20. New Insights into Stellar Magnetism from the Spectropolarimetry in All Four Stokes Parameters

    NASA Astrophysics Data System (ADS)

    Kochukhov, O.; Snik, F.; Piskunov, N.; Jeffers, S. V.; Keller, C. U.; Makaganiuk, V.; Valenti, J. A.; Johns-Krull, C. M.; Rodenhuis, M.; Stempels, H. C.

    2011-12-01

    Development of high-resolution spectropolarimetry has stimulated a major progress in our understanding of the magnetism and activity of late-type stars. During the last decade magnetic fields were discovered and mapped for various types of active stars using spectropolarimetric methods. However, these observations and modeling attempts are inherently incomplete since they are based on the interpretation of the stellar circular polarization alone. Taking advantage of the recently commissioned HARPS polarimeter, we obtained the first systematic observations of cool active stars in all four Stokes parameters. Here we report detection of the magnetically induced linear polarization in the RS CVn binary HR 1099 and phase-resolved full Stokes vector observations of varepsilon Eri. For the latter star we measured the field strength with the precision of ˜0.1 G over a complete rotation cycle and reconstructed the global field topology with the help of magnetic Doppler imaging. Our observations of the inactive solar-like star α Cen A indicate the absence of the global field stronger than 0.2 G.

  1. Hot and Cool: Stellar Parameters of the Prototype LBV AG Carinae across the HR Diagram

    NASA Astrophysics Data System (ADS)

    Groh, J. H.

    2010-06-01

    I discuss the temporal evolution of the stellar parameters of the prototype LBV AG Carinae, which has been the most variable object among the Galactic LBVs during the last 20 years. Based on a detailed spectroscopic analysis using the radiative transfercode CMFGEN, we found that AG Car was at different sides of the bi-stability limit in different epochs, as predicted by Vink & de Koter (2002). Contrary to the common assumption by the community, we found that the bolometric luminosity of AG Car decreases from 1.5×106 Lsun to 1.0×106 Lsun as the star moves towards maximum flux in the V band. To explain such decrease, the expansion of about 0.6-2 Msun is needed, which is comparable to the nebular mass found around lower-luminosity LBVs and to that of the Little Homunculus of η Car. We speculate that the S/,Dor-type instability could be a failed Giant Eruption, with several solar masses never becoming unbound from the star.

  2. Stellar abundances and ages for metal-rich Milky Way globular clusters. Stellar parameters and elemental abundances for 9 HB stars in NGC 6352

    NASA Astrophysics Data System (ADS)

    Feltzing, S.; Primas, F.; Johnson, R. A.

    2009-01-01

    Context: Metal-rich globular clusters provide important tracers of the formation of our Galaxy. Moreover, and not less important, they are very important calibrators for the derivation of properties of extra-galactic metal-rich stellar populations. Nonetheless, only a few of the metal-rich globular clusters in the Milky Way have been studied using high-resolution stellar spectra to derive elemental abundances. Additionally, Rosenberg et al. identified a small group of metal-rich globular clusters that appeared to be about 2 billion years younger than the bulk of the Milky Way globular clusters. However, it is unclear if like is compared with like in this dataset as we do not know the enhancement of α-elements in the clusters and the amount of α-elements is well known to influence the derivation of ages for globular clusters. Aims: We derive elemental abundances for the metal-rich globular cluster NGC 6352 and we present our methods to be used in up-coming studies of other metal-rich globular clusters. Methods: We present a study of elemental abundances for α- and iron-peak elements for nine HB stars in the metal-rich globular cluster NGC 6352. The elemental abundances are based on high-resolution, high signal-to-noise spectra obtained with the UVES spectrograph on VLT. The elemental abundances have been derived using standard LTE calculations and stellar parameters have been derived from the spectra themselves by requiring ionizational as well as excitational equilibrium. Results: We find that NGC 6352 has [Fe/H] = -0.55, is enhanced in the α-elements to about +0.2 dex for Ca, Si, and Ti relative to Fe. For the iron-peak elements we find solar values. Based on the spectroscopically derived stellar parameters we find that an E(B-V) = 0.24 and (m-M) ≃ 14.05 better fits the data than the nominal values. An investigation of log gf-values for suitable Fe i lines lead us to the conclusion that the commonly used correction to the May et al. (1974) data should not be

  3. The catalog of edge-on disk galaxies from SDSS. I. The catalog and the structural parameters of stellar disks

    SciTech Connect

    Bizyaev, D. V.; Kautsch, S. J.; Mosenkov, A. V.; Reshetnikov, V. P.; Sotnikova, N. Ya.; Yablokova, N. V.; Hillyer, R. W.

    2014-05-20

    We present a catalog of true edge-on disk galaxies automatically selected from the Seventh Data Release of the Sloan Digital Sky Survey (SDSS). A visual inspection of the g, r, and i images of about 15,000 galaxies allowed us to split the initial sample of edge-on galaxy candidates into 4768 (31.8% of the initial sample) genuine edge-on galaxies, 8350 (55.7%) non-edge-on galaxies, and 1865 (12.5%) edge-on galaxies not suitable for simple automatic analysis because these objects either show signs of interaction and warps, or nearby bright stars project on it. We added more candidate galaxies from RFGC, EFIGI, RC3, and Galaxy Zoo catalogs found in the SDSS footprints. Our final sample consists of 5747 genuine edge-on galaxies. We estimate the structural parameters of the stellar disks (the stellar disk thickness, radial scale length, and central surface brightness) in the galaxies by analyzing photometric profiles in each of the g, r, and i images. We also perform simplified three-dimensional modeling of the light distribution in the stellar disks of edge-on galaxies from our sample. Our large sample is intended to be used for studying scaling relations in the stellar disks and bulges and for estimating parameters of the thick disks in different types of galaxies via the image stacking. In this paper, we present the sample selection procedure and general description of the sample.

  4. Expand MILES spectral library for LAMOST stellar parameter determination using Chinese 2.4 and 2.16 metereter telescopes

    NASA Astrophysics Data System (ADS)

    Wang, Chun; Liu, Xiaowei; Huang, Yang; Zuo, Fang; Yuan, Haibo; Ren, Juanjuan; Chen, Bingqiu; Xiang, Maosheng; Zhang, Huawei; Luo, Ali; Shi, Jianrong

    2015-08-01

    We present a new medium resolution (full width at half-maximum FWHM ~ 2.4 Å) spectral library containing 1903 stellar spectra with a wavelength coverage of 3800-9000 Å based on MILES spectral library which contains 985 blue arm spectra with wavelength coverage of 3500-7500 Å at a spectral resolution of 2.5 Å (FWHM). The spectra are observed with Chinese Xinglong 2.16 meter telescope of blue arm spectra (with wavelength coverage 3800-5180 Å ) and Gaomeigu 2.4 meter telescope of red arm spectra (with wavelength coverage 5150-9000 Å ), respectively. This new library aims to improve the stellar atmospheric parameters determination accuracy of LAMOST Stellar Parameter Pipeline at Peking University (LSP3) and minimize the limitation of LSP3 . It also could be used in the spectral synthesis of stellar populations of galaxies and many other astronomical fields. Now 560 blue arm and 496 red arm spectra have been observed and reduced. The accuracy of wavelength-calibration and flux-calibration are better than ~ 0.3 Å and ~ 5 per cent, respectively. The mean signal to noise ratios of all spectra are almost larger than 100 per Å.

  5. Transit confirmation and improved stellar and planet parameters for the super-Earth HD 97658 b and its host star

    SciTech Connect

    Van Grootel, V.; Gillon, M.; Scuflaire, R.; Valencia, D.; Madhusudhan, N.; Demory, B.-O.; Queloz, D.; Dragomir, D.; Howe, A. R.; Burrows, A. S.; Deming, D.; Ehrenreich, D.; Lovis, C.; Mayor, M.; Pepe, F.; Segransan, D.; Udry, S.; Seager, S.

    2014-05-01

    Super-Earths transiting nearby bright stars are key objects that simultaneously allow for accurate measurements of both their mass and radius, providing essential constraints on their internal composition. We present here the confirmation, based on Spitzer transit observations, that the super-Earth HD 97658 b transits its host star. HD 97658 is a low-mass (M {sub *} = 0.77 ± 0.05 M {sub ☉}) K1 dwarf, as determined from the Hipparcos parallax and stellar evolution modeling. To constrain the planet parameters, we carry out Bayesian global analyses of Keck-High Resolution Echelle Spectrometer (Keck-HIRES) radial velocities and Microvariability and Oscillations of STars (MOST) and Spitzer photometry. HD 97658 b is a massive (M{sub P}=7.55{sub −0.79}{sup +0.83} M{sub ⊕}) and large (R{sub P}=2.247{sub −0.095}{sup +0.098}R{sub ⊕} at 4.5 μm) super-Earth. We investigate the possible internal compositions for HD 97658 b. Our results indicate a large rocky component, of at least 60% by mass, and very little H-He components, at most 2% by mass. We also discuss how future asteroseismic observations can improve the knowledge of the HD 97658 system, in particular by constraining its age. Orbiting a bright host star, HD 97658 b will be a key target for upcoming space missions such as the Transiting Exoplanet Survey Satellite (TESS), the Characterizing Exoplanet Satellite (CHEOPS), the Planetary Transits and Oscillations of stars (PLATO), and the James Webb Space Telescope to characterize thoroughly its structure and atmosphere.

  6. Stellar parameters and chemical abundances of 223 evolved stars with and without planets

    NASA Astrophysics Data System (ADS)

    Jofré, E.; Petrucci, R.; Saffe, C.; Saker, L.; de la Villarmois, E. Artur; Chavero, C.; Gómez, M.; Mauas, P. J. D.

    2015-02-01

    Aims: We present fundamental stellar parameters, chemical abundances, and rotational velocities for a sample of 86 evolved stars with planets (56 giants; 30 subgiants), and for a control sample of 137 stars (101 giants; 36 subgiants) without planets. The analysis was based on both high signal-to-noise and resolution echelle spectra. The main goals of this work are i) to investigate chemical differences between evolved stars that host planets and those of the control sample without planets; ii) to explore potential differences between the properties of the planets around giants and subgiants; and iii) to search for possible correlations between these properties and the chemical abundances of their host stars. Implications for the scenarios of planet formation and evolution are also discussed. Methods: The fundamental stellar parameters (Teff, log g, [Fe/H], ξt) were computed homogeneously using the FUNDPAR code. The chemical abundances of 14 elements (Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Zn, and Ba) were obtained using the MOOG code. Rotational velocities were derived from the full width at half maximum of iron isolated lines. Results: In agreement with previous studies, we find that subgiants with planets are, on average, more metal-rich than subgiants without planets by ~0.16 dex. The [Fe/H] distribution of giants with planets is centered at slightly subsolar metallicities and there is no metallicity enhancement relative to the [Fe/H] distribution of giants without planets. Furthermore, contrary to recent results, we do not find any clear difference between the metallicity distributions of stars with and without planets for giants with M⋆> 1.5 M⊙. With regard to the other chemical elements, the analysis of the [X/Fe] distributions shows differences between giants with and without planets for some elements, particularly V, Co, and Ba. Subgiants with and without planets exhibit similar behavior for most of the elements. On the other hand, we find no

  7. Ages and metallicities for quiescent galaxies in the Shapley supercluster: driving parameters of the stellar populations

    NASA Astrophysics Data System (ADS)

    Smith, Russell J.; Lucey, John R.; Hudson, Michael J.

    2009-12-01

    We use high signal-to-noise spectroscopy for a sample of 232 quiescent galaxies in the Shapley supercluster, to investigate how their stellar populations depend on velocity dispersion (σ), luminosity and stellar mass. The sample spans a large range in velocity dispersion (30-300kms-1) and in luminosity (MR from -18.7 to -23.2). Estimates of age, total metallicity (Z/H) and α-element abundance ratio (α/Fe) were derived from absorption-line analysis, using single-burst models of Thomas and collaborators. Using the Rose CaII index, we conclude that recent star formation (frosting) events are not responsible for the intermediate ages observed in some of the galaxies. Age, Z/H and α/Fe are correlated positively with velocity dispersion, but we also find significant residual trends with luminosity: at given σ, the brighter galaxies are younger, less α-enriched and have higher Z/H. At face value, these results might suggest that the stellar populations depend on stellar mass as well as on velocity dispersion. However, we show that the observed trends can be reproduced by models in which the stellar populations depend systematically only on σ, and are independent of stellar mass M*. For age, the observed luminosity correlation arises because young galaxies are brighter, at fixed M*. For metallicity, the observed luminosity dependence arises because metal-rich galaxies, at fixed mass, tend also to be younger, and hence brighter. We find a good match to the observed luminosity correlations with age ~σ+0.40, Z/H~σ+0.35,α/Fe ~σ+0.20, where the slopes are close to those found when fitting traditional scaling relations. We conclude that the star formation and enrichment histories of galaxies are determined primarily by the depth of their gravitational potential wells. The observed residual correlations with luminosity do not imply a corresponding dependence on stellar mass.

  8. Significance of accurate diffraction corrections for the second harmonic wave in determining the acoustic nonlinearity parameter

    SciTech Connect

    Jeong, Hyunjo; Zhang, Shuzeng; Li, Xiongbing; Barnard, Dan

    2015-09-15

    The accurate measurement of acoustic nonlinearity parameter β for fluids or solids generally requires making corrections for diffraction effects due to finite size geometry of transmitter and receiver. These effects are well known in linear acoustics, while those for second harmonic waves have not been well addressed and therefore not properly considered in previous studies. In this work, we explicitly define the attenuation and diffraction corrections using the multi-Gaussian beam (MGB) equations which were developed from the quasilinear solutions of the KZK equation. The effects of making these corrections are examined through the simulation of β determination in water. Diffraction corrections are found to have more significant effects than attenuation corrections, and the β values of water can be estimated experimentally with less than 5% errors when the exact second harmonic diffraction corrections are used together with the negligible attenuation correction effects on the basis of linear frequency dependence between attenuation coefficients, α{sub 2} ≃ 2α{sub 1}.

  9. Homogeneous spectroscopic parameters for bright planet host stars from the northern hemisphere . The impact on stellar and planetary mass

    NASA Astrophysics Data System (ADS)

    Sousa, S. G.; Santos, N. C.; Mortier, A.; Tsantaki, M.; Adibekyan, V.; Delgado Mena, E.; Israelian, G.; Rojas-Ayala, B.; Neves, V.

    2015-04-01

    Aims: In this work we derive new precise and homogeneous parameters for 37 stars with planets. For this purpose, we analyze high resolution spectra obtained by the NARVAL spectrograph for a sample composed of bright planet host stars in the northern hemisphere. The new parameters are included in the SWEET-Cat online catalogue. Methods: To ensure that the catalogue is homogeneous, we use our standard spectroscopic analysis procedure, ARES+MOOG, to derive effective temperatures, surface gravities, and metallicities. These spectroscopic stellar parameters are then used as input to compute the stellar mass and radius, which are fundamental for the derivation of the planetary mass and radius. Results: We show that the spectroscopic parameters, masses, and radii are generally in good agreement with the values available in online databases of exoplanets. There are some exceptions, especially for the evolved stars. These are analyzed in detail focusing on the effect of the stellar mass on the derived planetary mass. Conclusions: We conclude that the stellar mass estimations for giant stars should be managed with extreme caution when using them to compute the planetary masses. We report examples within this sample where the differences in planetary mass can be as high as 100% in the most extreme cases. Based on observations obtained at the Telescope Bernard Lyot (USR5026) operated by the Observatoire Midi-Pyrénées and the Institut National des Science de l'Univers of the Centre National de la Recherche Scientifique of France (Run ID L131N11 - OPTICON_2013A_027).

  10. Fundamental stellar parameters and age-metallicity relation of Kepler red giants in comparison with theoretical evolutionary tracks

    NASA Astrophysics Data System (ADS)

    Takeda, Y.; Tajitsu, A.; Sato, B.; Liu, Y.-J.; Chen, Y.-Q.; Zhao, G.

    2016-04-01

    Spectroscopic parameters (effective temperature, metallicity, etc) were determined for a large sample of ˜100 red giants in the Kepler field, for which mass, radius, and evolutionary status had already been asteroseismologically established. These two kinds of spectroscopic and seismic information suffice to define the position on the `luminosity versus effective temperature' diagram and to assign an appropriate theoretical evolutionary track to each star. Making use of this advantage, we examined whether the stellar location on this diagram really matches the assigned track, which would make an interesting consistency check between theory and observation. It turned out that satisfactory agreement was confirmed in most cases (˜90 per cent, though appreciable discrepancies were seen for some stars such as higher mass red-clump giants), suggesting that recent stellar evolution calculations are practically reliable. Since the relevant stellar age could also be obtained by this comparison, we derived the age-metallicity relation for these Kepler giants and found the following characteristics: (1) the resulting distribution is quite similar to what was previously concluded for F-, G-, and K-type stars dwarfs; (2) the dispersion of metallicity progressively increases as the age becomes older; (3) nevertheless, the maximum metallicity at any stellar age remains almost flat, which means the existence of super/near-solar metallicity stars in a considerably wide age range from ˜(2-3) × 108 to ˜1010 yr.

  11. Consistency of VDJ Rearrangement and Substitution Parameters Enables Accurate B Cell Receptor Sequence Annotation

    PubMed Central

    Ralph, Duncan K.; Matsen, Frederick A.

    2016-01-01

    VDJ rearrangement and somatic hypermutation work together to produce antibody-coding B cell receptor (BCR) sequences for a remarkable diversity of antigens. It is now possible to sequence these BCRs in high throughput; analysis of these sequences is bringing new insight into how antibodies develop, in particular for broadly-neutralizing antibodies against HIV and influenza. A fundamental step in such sequence analysis is to annotate each base as coming from a specific one of the V, D, or J genes, or from an N-addition (a.k.a. non-templated insertion). Previous work has used simple parametric distributions to model transitions from state to state in a hidden Markov model (HMM) of VDJ recombination, and assumed that mutations occur via the same process across sites. However, codon frame and other effects have been observed to violate these parametric assumptions for such coding sequences, suggesting that a non-parametric approach to modeling the recombination process could be useful. In our paper, we find that indeed large modern data sets suggest a model using parameter-rich per-allele categorical distributions for HMM transition probabilities and per-allele-per-position mutation probabilities, and that using such a model for inference leads to significantly improved results. We present an accurate and efficient BCR sequence annotation software package using a novel HMM “factorization” strategy. This package, called partis (https://github.com/psathyrella/partis/), is built on a new general-purpose HMM compiler that can perform efficient inference given a simple text description of an HMM. PMID:26751373

  12. Consistency of VDJ Rearrangement and Substitution Parameters Enables Accurate B Cell Receptor Sequence Annotation.

    PubMed

    Ralph, Duncan K; Matsen, Frederick A

    2016-01-01

    VDJ rearrangement and somatic hypermutation work together to produce antibody-coding B cell receptor (BCR) sequences for a remarkable diversity of antigens. It is now possible to sequence these BCRs in high throughput; analysis of these sequences is bringing new insight into how antibodies develop, in particular for broadly-neutralizing antibodies against HIV and influenza. A fundamental step in such sequence analysis is to annotate each base as coming from a specific one of the V, D, or J genes, or from an N-addition (a.k.a. non-templated insertion). Previous work has used simple parametric distributions to model transitions from state to state in a hidden Markov model (HMM) of VDJ recombination, and assumed that mutations occur via the same process across sites. However, codon frame and other effects have been observed to violate these parametric assumptions for such coding sequences, suggesting that a non-parametric approach to modeling the recombination process could be useful. In our paper, we find that indeed large modern data sets suggest a model using parameter-rich per-allele categorical distributions for HMM transition probabilities and per-allele-per-position mutation probabilities, and that using such a model for inference leads to significantly improved results. We present an accurate and efficient BCR sequence annotation software package using a novel HMM "factorization" strategy. This package, called partis (https://github.com/psathyrella/partis/), is built on a new general-purpose HMM compiler that can perform efficient inference given a simple text description of an HMM. PMID:26751373

  13. LAMOST Observations in the Kepler Field. Analysis of the Stellar Parameters Measured with LASP Based on Low-resolution Spectra

    NASA Astrophysics Data System (ADS)

    Ren, Anbing; Fu, Jianning; De Cat, Peter; Wu, Yue; Yang, Xiaohu; Shi, Jianrong; Luo, Ali; Zhang, Haotong; Dong, Subo; Zhang, Ruyuan; Zhang, Yong; Hou, Yonghui; Wang, Yuefei; Cao, Zihuang; Du, Bing

    2016-08-01

    All 14 subfields of the Kepler field were observed at least once with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (lamost, Xinglong Observatory, China) during the 2012–2014 observation seasons. There are 88,628 reduced spectra with a signal-to-noise ratio in the g band (S/N g ) ≥ 6 after the first round (2012–2014) of observations of the lamost– Kepler project (LK-project). By adopting the upgraded version of the lamost Stellar Parameter pipeline (lasp), we have determined the atmospheric parameters ({T}{eff}, {log}g, and [Fe/H]) and heliocentric radial velocity v rad for 51,406 stars with 61,226 spectra. Compared with the atmospheric parameters derived from both high-resolution spectroscopy and asteroseismology for common stars in Huber et al., an external calibration of lasp atmospheric parameters was made, leading to the determination of the external errors for giants and dwarfs. Multiple spectroscopic observations of the same objects in the LK-project were used to estimate the internal uncertainties of the atmospheric parameters as a function of S/N g with the unbiased estimation method. The lasp atmospheric parameters were calibrated based on both the external and internal uncertainties for the giants and dwarfs. A general statistical analysis of the stellar parameters leads to the discovery of 106 candidate metal-poor stars, 9 candidate very metal-poor stars, and 18 candidate high-velocity stars. Fitting formulae were obtained segmentally for both the calibrated atmospheric parameters of the LK-project and the Kepler Input Catalog (KIC) parameters with common stars. The calibrated atmospheric parameters and radial velocities of the LK-project will be useful for studying stars in the Kepler field. ) located at the Xinglong Observatory, China.

  14. New determination of abundances and stellar parameters for a set of weak G-band stars

    NASA Astrophysics Data System (ADS)

    Palacios, A.; Jasniewicz, G.; Masseron, T.; Thévenin, F.; Itam-Pasquet, J.; Parthasarathy, M.

    2016-03-01

    Context. Weak G-band (wGb) stars are a very peculiar class of red giants; they are almost devoided of carbon and often present mild lithium enrichment. Despite their very puzzling abundance patterns, very few detailed spectroscopic studies existed up to a few years ago, which prevented any clear understanding of the wGb phenomenon. We recently proposed the first consistent analysis of published data for a sample of 28 wGb stars and were able to identify them as descendants of early A-type to late B-type stars, although we were not able to conclude on their evolutionary status or the origin of their peculiar abundance pattern. Aims: Using new high-resolution spectra, we present the study of a new sample of wGb stars with the aim of homogeneously deriving their fundamental parameters and surface abundances for a selected set of chemical species that we use to improve our insight on this peculiar class of objects. Methods: We obtained high-resolution and high signal-to-noise spectra for 19 wGb stars in the southern and northern hemisphere that we used to perform consistent spectral synthesis to derive their fundamental parameters and metallicities, as well as the spectroscopic abundances for Li, C, 12C/13C, N, O, Na, Sr, and Ba. We also computed dedicated stellar evolution models that we used to determine the masses and to investigate the evolutionary status and chemical history of the stars in our sample. Results: We confirm that the wGb stars are stars with initial masses in the range 3.2 to 4.2 M⊙. We suggest that a large fraction could be mildly evolved stars on the subgiant branch currently undergoing the first dredge-up, while a smaller number of stars are more probably in the core He burning phase at the clump. After analysing their abundance pattern, we confirm their strong nitrogen enrichment anti-correlated with large carbon depletion, characteristic of material fully processed through the CNO cycle to an extent not known in evolved intermediate-mass stars

  15. Accurate analytical method for the extraction of solar cell model parameters

    NASA Astrophysics Data System (ADS)

    Phang, J. C. H.; Chan, D. S. H.; Phillips, J. R.

    1984-05-01

    Single diode solar cell model parameters are rapidly extracted from experimental data by means of the presently derived analytical expressions. The parameter values obtained have a less than 5 percent error for most solar cells, in light of the extraction of model parameters for two cells of differing quality which were compared with parameters extracted by means of the iterative method.

  16. 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.

  17. Environmental dependence of the stellar velocity dispersion at fixed parameters or for different galaxy families in the main galaxy sample of SDSS DR10

    NASA Astrophysics Data System (ADS)

    Deng, Xinfa; Jiang, Peng; Zhong, Shuangying; Ding, Yingping

    2015-01-01

    Using the apparent magnitude-limited Main Galaxy Sample of Sloan Digital Sky Survey Data Release 10 (SDSS DR10), we examine the environmental dependence of the stellar velocity dispersion at fixed parameters or for different galaxy families. Limiting or fixing certain parameters exerts substantial influence on the environmental dependence of the stellar velocity dispersion of the galaxies which suggests that much of the stellar velocity dispersion-density relation is likely attributable to the relations between other galaxy parameters and density. The environmental dependence of the stellar velocity dispersion for red galaxies is very strong in certain redshift bins. This dependence can still be observed in some redshift bins for late-type galaxies, HSM galaxies, and LSM galaxies but is fairly weak in all redshift bins for early-type galaxies and blue galaxies.

  18. Stochastic stellar cluster initial mass functions: Models and impact on integrated cluster parameter determination

    SciTech Connect

    Anders, P.; Kotulla, R.; De Grijs, R.; Wicker, J.

    2013-12-01

    Stellar clusters are regularly used to study the evolution of their host galaxy. Except for a few nearby galaxies, these studies rely on the interpretation of integrated cluster properties, especially integrated photometry observed using multiple filters (i.e., the spectral energy distribution, SED). To allow interpretation of such observations, we present a large set of GALEV cluster models using the realistic approach of adopting stochastically sampled stellar initial mass functions. We provide models for a wide range of cluster masses (10{sup 3}-2 × 10{sup 5} M {sub ☉}), metallicities (–2.3 ≤ [Fe/H] ≤ +0.18 dex), foreground extinction, and 184 regularly used filters. We analyze various sets of stochastic cluster SEDs by fitting them with non-stochastic models, which is the procedure commonly used in this field. We identify caveats and quantify the fitting uncertainties associated with this standard procedure. We show that this can yield highly unreliable fitting results, especially for low-mass clusters.

  19. Polynomial Fitting of DT-MRI Fiber Tracts Allows Accurate Estimation of Muscle Architectural Parameters

    PubMed Central

    Damon, Bruce M.; Heemskerk, Anneriet M.; Ding, Zhaohua

    2012-01-01

    Fiber curvature is a functionally significant muscle structural property, but its estimation from diffusion-tensor MRI fiber tracking data may be confounded by noise. The purpose of this study was to investigate the use of polynomial fitting of fiber tracts for improving the accuracy and precision of fiber curvature (κ) measurements. Simulated image datasets were created in order to provide data with known values for κ and pennation angle (θ). Simulations were designed to test the effects of increasing inherent fiber curvature (3.8, 7.9, 11.8, and 15.3 m−1), signal-to-noise ratio (50, 75, 100, and 150), and voxel geometry (13.8 and 27.0 mm3 voxel volume with isotropic resolution; 13.5 mm3 volume with an aspect ratio of 4.0) on κ and θ measurements. In the originally reconstructed tracts, θ was estimated accurately under most curvature and all imaging conditions studied; however, the estimates of κ were imprecise and inaccurate. Fitting the tracts to 2nd order polynomial functions provided accurate and precise estimates of κ for all conditions except very high curvature (κ=15.3 m−1), while preserving the accuracy of the θ estimates. Similarly, polynomial fitting of in vivo fiber tracking data reduced the κ values of fitted tracts from those of unfitted tracts and did not change the θ values. Polynomial fitting of fiber tracts allows accurate estimation of physiologically reasonable values of κ, while preserving the accuracy of θ estimation. PMID:22503094

  20. FAST TRACK COMMUNICATION Accurate estimate of α variation and isotope shift parameters in Na and Mg+

    NASA Astrophysics Data System (ADS)

    Sahoo, B. K.

    2010-12-01

    We present accurate calculations of fine-structure constant variation coefficients and isotope shifts in Na and Mg+ using the relativistic coupled-cluster method. In our approach, we are able to discover the roles of various correlation effects explicitly to all orders in these calculations. Most of the results, especially for the excited states, are reported for the first time. It is possible to ascertain suitable anchor and probe lines for the studies of possible variation in the fine-structure constant by using the above results in the considered systems.

  1. Accurate nuclear masses from a three parameter Kohn-Sham DFT approach (BCPM)

    SciTech Connect

    Baldo, M.; Robledo, L. M.; Schuck, P.; Vinas, X.

    2012-10-20

    Given the promising features of the recently proposed Barcelona-Catania-Paris (BCP) functional [1], it is the purpose of this work to still improve on it. It is, for instance, shown that the number of open parameters can be reduced from 4-5 to 2-3, i.e. by practically a factor of two without deteriorating the results.

  2. THE SEGUE STELLAR PARAMETER PIPELINE. V. ESTIMATION OF ALPHA-ELEMENT ABUNDANCE RATIOS FROM LOW-RESOLUTION SDSS/SEGUE STELLAR SPECTRA

    SciTech Connect

    Lee, Young Sun; Beers, Timothy C.; Prieto, Carlos Allende; Lai, David K.; Rockosi, Constance M.; Johnson, Jennifer A.; An, Deokkeun; Sivarani, Thirupathi; Yanny, Brian E-mail: beers@pa.msu.edu E-mail: david@ucolick.org E-mail: heather@vegemite.case.edu E-mail: deokkeun@ewha.ac.kr E-mail: yanny@fnal.gov

    2011-03-15

    We present a method for the determination of [{alpha}/Fe] ratios from low-resolution (R = 2000) SDSS/SEGUE stellar spectra. By means of a star-by-star comparison with degraded spectra from the ELODIE spectral library and with a set of moderately high-resolution (R = 15, 000) and medium-resolution (R = 6000) spectra of SDSS/SEGUE stars, we demonstrate that we are able to measure [{alpha}/Fe] from SDSS/SEGUE spectra (with S/N>20/1) to a precision of better than 0.1 dex, for stars with atmospheric parameters in the range T{sub eff} = [4500, 7000] K, log g = [1.5, 5.0], and [Fe/H] = [-1.4, +0.3], over the range [{alpha}/Fe] = [-0.1, +0.6]. For stars with [Fe/H] <-1.4, our method requires spectra with slightly higher signal-to-noise to achieve this precision (S/N>25/1). Over the full temperature range considered, the lowest metallicity star for which a confident estimate of [{alpha}/Fe] can be obtained from our approach is [Fe/H] {approx}-2.5; preliminary tests indicate that a metallicity limit as low as [Fe/H] {approx}-3.0 may apply to cooler stars. As a further validation of this approach, weighted averages of [{alpha}/Fe] obtained for SEGUE spectra of likely member stars of Galactic globular clusters (M15, M13, and M71) and open clusters (NGC 2420, M67, and NGC 6791) exhibit good agreement with the values of [{alpha}/Fe] from previous studies. The results of the comparison with NGC 6791 imply that the metallicity range for the method may extend to {approx}+0.5.

  3. Towards the computations of accurate spectroscopic parameters and vibrational spectra for organic compounds

    NASA Astrophysics Data System (ADS)

    Hochlaf, M.; Puzzarini, C.; Senent, M. L.

    2015-07-01

    We present multi-component computations for rotational constants, vibrational and torsional levels of medium-sized molecules. Through the treatment of two organic sulphur molecules, ethyl mercaptan and dimethyl sulphide, which are relevant for atmospheric and astrophysical media, we point out the outstanding capabilities of explicitly correlated coupled clusters (CCSD(T)-F12) method in conjunction with the cc-pVTZ-F12 basis set for the accurate predictions of such quantities. Indeed, we show that the CCSD(T)-F12/cc-pVTZ-F12 equilibrium rotational constants are in good agreement with those obtained by means of a composite scheme based on CCSD(T) calculations that accounts for the extrapolation to the complete basis set (CBS) limit and core-correlation effects [CCSD(T)/CBS+CV], thus leading to values of ground-state rotational constants rather close to the corresponding experimental data. For vibrational and torsional levels, our analysis reveals that the anharmonic frequencies derived from CCSD(T)-F12/cc-pVTZ-F12 harmonic frequencies and anharmonic corrections (Δν = ω - ν) at the CCSD/cc-pVTZ level closely agree with experimental results. The pattern of the torsional transitions and the shape of the potential energy surfaces along the torsional modes are also well reproduced using the CCSD(T)-F12/cc-pVTZ-F12 energies. Interestingly, this good accuracy is accompanied with a strong reduction of the computational costs. This makes the procedures proposed here as schemes of choice for effective and accurate prediction of spectroscopic properties of organic compounds. Finally, popular density functional approaches are compared with the coupled cluster (CC) methodologies in torsional studies. The long-range CAM-B3LYP functional of Handy and co-workers is recommended for large systems.

  4. Lower bound on reliability for Weibull distribution when shape parameter is not estimated accurately

    NASA Technical Reports Server (NTRS)

    Huang, Zhaofeng; Porter, Albert A.

    1991-01-01

    The mathematical relationships between the shape parameter Beta and estimates of reliability and a life limit lower bound for the two parameter Weibull distribution are investigated. It is shown that under rather general conditions, both the reliability lower bound and the allowable life limit lower bound (often called a tolerance limit) have unique global minimums over a range of Beta. Hence lower bound solutions can be obtained without assuming or estimating Beta. The existence and uniqueness of these lower bounds are proven. Some real data examples are given to show how these lower bounds can be easily established and to demonstrate their practicality. The method developed here has proven to be extremely useful when using the Weibull distribution in analysis of no-failure or few-failures data. The results are applicable not only in the aerospace industry but anywhere that system reliabilities are high.

  5. Lower bound on reliability for Weibull distribution when shape parameter is not estimated accurately

    NASA Technical Reports Server (NTRS)

    Huang, Zhaofeng; Porter, Albert A.

    1990-01-01

    The mathematical relationships between the shape parameter Beta and estimates of reliability and a life limit lower bound for the two parameter Weibull distribution are investigated. It is shown that under rather general conditions, both the reliability lower bound and the allowable life limit lower bound (often called a tolerance limit) have unique global minimums over a range of Beta. Hence lower bound solutions can be obtained without assuming or estimating Beta. The existence and uniqueness of these lower bounds are proven. Some real data examples are given to show how these lower bounds can be easily established and to demonstrate their practicality. The method developed here has proven to be extremely useful when using the Weibull distribution in analysis of no-failure or few-failures data. The results are applicable not only in the aerospace industry but anywhere that system reliabilities are high.

  6. THE SEGUE STELLAR PARAMETER PIPELINE. IV. VALIDATION WITH AN EXTENDED SAMPLE OF GALACTIC GLOBULAR AND OPEN CLUSTERS

    SciTech Connect

    Smolinski, Jason P.; Lee, Young Sun; Beers, Timothy C.; An, Deokkeun; Bickerton, Steven J.; Loomis, Craig P.; Johnson, Jennifer A.; Rockosi, Constance M.; Yanny, Brian E-mail: lee@pa.msu.edu E-mail: deokkeun@ewha.ac.kr E-mail: cloomis@astro.princeton.edu E-mail: crockosi@ucolick.org E-mail: yanny@fnal.gov

    2011-03-15

    Spectroscopic and photometric data for likely member stars of five Galactic globular clusters (M3, M53, M71, M92, and NGC 5053) and three open clusters (M35, NGC 2158, and NGC 6791) are processed by the current version of the SEGUE Stellar Parameter Pipeline (SSPP), in order to determine estimates of metallicities and radial velocities (RVs) for the clusters. These results are then compared to values from the literature. We find that the mean metallicity (([Fe/H])) and mean radial velocity ((RV)) estimates for each cluster are almost all within 2{sigma} of the adopted literature values; most are within 1{sigma}. We also demonstrate that the new version of the SSPP achieves small, but noteworthy, improvements in ([Fe/H]) estimates at the extrema of the cluster metallicity range, as compared to a previous version of the pipeline software. These results provide additional confidence in the application of the SSPP for studies of the abundances and kinematics of stellar populations in the Galaxy.

  7. The SEGUE Stellar Parameter Pipeline. IV. Validation with an Extended Sample of Galactic Globular and Open Clusters

    SciTech Connect

    Smolinski, Jason P.; Beers, Timothy C.; Lee, Young Sun; An, Deokkeun; Bickerton, Steven J.; Johnson, Jennifer A.; Loomis, Craig P.; Rockosi, Constance M.; Sivarani, Thirupathi; Yanny, Brian; /Fermilab

    2010-08-01

    Spectroscopic and photometric data for likely member stars of five Galactic globular clusters (M 3, M 53, M 71, M 92, and NGC 5053) and three open clusters (M 35, NGC 2158, and NGC 6791) are processed by the current version of the SEGUE Stellar Parameter Pipeline (SSPP), in order to determine estimates of metallicities and radial velocities for the clusters. These results are then compared to values from the literature. We find that the mean metallicity (<[Fe/H]>) and mean radial velocity (hRVi) estimates for each cluster are almost all within 2{sigma} of the adopted literature values; most are within 1{sigma}. We also demonstrate that the new version of the SSPP achieves small, but noteworthy, improvements in <[Fe/H]> estimates at the extrema of the cluster metallicity range, as compared to a previous version of the pipeline software. These results provide additional confidence in the application of the SSPP for studies of the abundances and kinematics of stellar populations in the Galaxy.

  8. A PUBLIC K{sub s} -SELECTED CATALOG IN THE COSMOS/ULTRAVISTA FIELD: PHOTOMETRY, PHOTOMETRIC REDSHIFTS, AND STELLAR POPULATION PARAMETERS {sup ,}

    SciTech Connect

    Muzzin, Adam; Franx, Marijn; Labbe, Ivo; Marchesini, Danilo; Stefanon, Mauro; Milvang-Jensen, Bo; Fynbo, J. P. U.; Dunlop, James S.; Brammer, Gabriel; Van Dokkum, Pieter

    2013-05-01

    We present a catalog covering 1.62 deg{sup 2} of the COSMOS/UltraVISTA field with point-spread function (PSF) matched photometry in 30 photometric bands. The catalog covers the wavelength range 0.15-24 {mu}m including the available GALEX, Subaru, Canada-France-Hawaii Telescope, VISTA, and Spitzer data. Catalog sources have been selected from the DR1 UltraVISTA K{sub s} band imaging that reaches a depth of K {sub s,tot} = 23.4 AB (90% completeness). The PSF-matched catalog is generated using position-dependent PSFs ensuring accurate colors across the entire field. Also included is a catalog of photometric redshifts (z {sub phot}) for all galaxies computed with the EAZY code. Comparison with spectroscopy from the zCOSMOS 10k bright sample shows that up to z {approx} 1.5 the z {sub phot} are accurate to {Delta}z/(1 + z) = 0.013, with a catastrophic outlier fraction of only 1.6%. The z {sub phot} also show good agreement with the z {sub phot} from the NEWFIRM Medium Band Survey out to z {approx} 3. A catalog of stellar masses and stellar population parameters for galaxies determined using the FAST spectral energy distribution fitting code is provided for all galaxies. Also included are rest-frame U - V and V - J colors, L {sub 2800} and L {sub IR}. The UVJ color-color diagram confirms that the galaxy bi-modality is well-established out to z {approx} 2. Star-forming galaxies also obey a star-forming 'main sequence' out to z {approx} 2.5, and this sequence evolves in a manner consistent with previous measurements. The COSMOS/UltraVISTA K{sub s} -selected catalog covers a unique parameter space in both depth, area, and multi-wavelength coverage and promises to be a useful tool for studying the growth of the galaxy population out to z {approx} 3-4.

  9. Accurate Prediction of Severe Allergic Reactions by a Small Set of Environmental Parameters (NDVI, Temperature)

    PubMed Central

    Andrianaki, Maria; Azariadis, Kalliopi; Kampouri, Errika; Theodoropoulou, Katerina; Lavrentaki, Katerina; Kastrinakis, Stelios; Kampa, Marilena; Agouridakis, Panagiotis; Pirintsos, Stergios; Castanas, Elias

    2015-01-01

    Severe allergic reactions of unknown etiology,necessitating a hospital visit, have an important impact in the life of affected individuals and impose a major economic burden to societies. The prediction of clinically severe allergic reactions would be of great importance, but current attempts have been limited by the lack of a well-founded applicable methodology and the wide spatiotemporal distribution of allergic reactions. The valid prediction of severe allergies (and especially those needing hospital treatment) in a region, could alert health authorities and implicated individuals to take appropriate preemptive measures. In the present report we have collecterd visits for serious allergic reactions of unknown etiology from two major hospitals in the island of Crete, for two distinct time periods (validation and test sets). We have used the Normalized Difference Vegetation Index (NDVI), a satellite-based, freely available measurement, which is an indicator of live green vegetation at a given geographic area, and a set of meteorological data to develop a model capable of describing and predicting severe allergic reaction frequency. Our analysis has retained NDVI and temperature as accurate identifiers and predictors of increased hospital severe allergic reactions visits. Our approach may contribute towards the development of satellite-based modules, for the prediction of severe allergic reactions in specific, well-defined geographical areas. It could also probably be used for the prediction of other environment related diseases and conditions. PMID:25794106

  10. An Accurate and Generic Testing Approach to Vehicle Stability Parameters Based on GPS and INS

    PubMed Central

    Miao, Zhibin; Zhang, Hongtian; Zhang, Jinzhu

    2015-01-01

    With the development of the vehicle industry, controlling stability has become more and more important. Techniques of evaluating vehicle stability are in high demand. As a common method, usually GPS sensors and INS sensors are applied to measure vehicle stability parameters by fusing data from the two system sensors. Although prior model parameters should be recognized in a Kalman filter, it is usually used to fuse data from multi-sensors. In this paper, a robust, intelligent and precise method to the measurement of vehicle stability is proposed. First, a fuzzy interpolation method is proposed, along with a four-wheel vehicle dynamic model. Second, a two-stage Kalman filter, which fuses the data from GPS and INS, is established. Next, this approach is applied to a case study vehicle to measure yaw rate and sideslip angle. The results show the advantages of the approach. Finally, a simulation and real experiment is made to verify the advantages of this approach. The experimental results showed the merits of this method for measuring vehicle stability, and the approach can meet the design requirements of a vehicle stability controller. PMID:26690154

  11. An Accurate and Generic Testing Approach to Vehicle Stability Parameters Based on GPS and INS.

    PubMed

    Miao, Zhibin; Zhang, Hongtian; Zhang, Jinzhu

    2015-01-01

    With the development of the vehicle industry, controlling stability has become more and more important. Techniques of evaluating vehicle stability are in high demand. As a common method, usually GPS sensors and INS sensors are applied to measure vehicle stability parameters by fusing data from the two system sensors. Although prior model parameters should be recognized in a Kalman filter, it is usually used to fuse data from multi-sensors. In this paper, a robust, intelligent and precise method to the measurement of vehicle stability is proposed. First, a fuzzy interpolation method is proposed, along with a four-wheel vehicle dynamic model. Second, a two-stage Kalman filter, which fuses the data from GPS and INS, is established. Next, this approach is applied to a case study vehicle to measure yaw rate and sideslip angle. The results show the advantages of the approach. Finally, a simulation and real experiment is made to verify the advantages of this approach. The experimental results showed the merits of this method for measuring vehicle stability, and the approach can meet the design requirements of a vehicle stability controller. PMID:26690154

  12. Accurate motion parameter estimation for colonoscopy tracking using a regression method

    NASA Astrophysics Data System (ADS)

    Liu, Jianfei; Subramanian, Kalpathi R.; Yoo, Terry S.

    2010-03-01

    Co-located optical and virtual colonoscopy images have the potential to provide important clinical information during routine colonoscopy procedures. In our earlier work, we presented an optical flow based algorithm to compute egomotion from live colonoscopy video, permitting navigation and visualization of the corresponding patient anatomy. In the original algorithm, motion parameters were estimated using the traditional Least Sum of squares(LS) procedure which can be unstable in the context of optical flow vectors with large errors. In the improved algorithm, we use the Least Median of Squares (LMS) method, a robust regression method for motion parameter estimation. Using the LMS method, we iteratively analyze and converge toward the main distribution of the flow vectors, while disregarding outliers. We show through three experiments the improvement in tracking results obtained using the LMS method, in comparison to the LS estimator. The first experiment demonstrates better spatial accuracy in positioning the virtual camera in the sigmoid colon. The second and third experiments demonstrate the robustness of this estimator, resulting in longer tracked sequences: from 300 to 1310 in the ascending colon, and 410 to 1316 in the transverse colon.

  13. Accurate solutions, parameter studies and comparisons for the Euler and potential flow equations

    NASA Technical Reports Server (NTRS)

    Anderson, W. Kyle; Batina, John T.

    1988-01-01

    Parameter studies are conducted using the Euler and potential flow equation models for steady and unsteady flows in both two and three dimensions. The Euler code is an implicit, upwind, finite volume code which uses the Van Leer method of flux vector splitting which has been recently extended for use on dynamic meshes and maintain all the properties of the original splitting. The potential flow code is an implicit, finite difference method for solving the transonic small disturbance equations and incorporates both entropy and vorticity corrections into the solution procedures thereby extending its applicability into regimes where shock strength normally precludes its use. Parameter studies resulting in benchmark type calculations include the effects of spatial and temporal refinement, spatial order of accuracy, far field boundary conditions for steady flow, frequency of oscillation, and the use of subiterations at each time step to reduce linearization and factorization errors. Comparisons between Euler and potential flow results are made, as well as with experimental data where available.

  14. Accurate solutions, parameter studies and comparisons for the Euler and potential flow equations

    NASA Technical Reports Server (NTRS)

    Anderson, W. Kyle; Batina, John T.

    1988-01-01

    Parameter studies are conducted using the Euler and potential flow equation models for unsteady and steady flows in both two and three dimensions. The Euler code is an implicit, upwind, finite volume code which uses the Van Leer method of flux-vector-splitting which has been recently extended for use on dynamic meshes and maintain all the properties of the original splitting. The potential flow code is an implicit, finite difference method for solving the transonic small disturbance equations and incorporates both entropy and vorticity corrections into the solution procedures thereby extending its applicability into regimes where shock strength normally precludes its use. Parameter studies resulting in benchmark type calculations include the effects of spatial and temporal refinement, spatial order of accuracy, far field boundary conditions for steady flow, frequency of oscillation, and the use of subiterations at each time step to reduce linearization and factorization errors. Comparisons between Euler and potential flows results are made as well as with experimental data where available.

  15. Can a combination of ultrasonographic parameters accurately evaluate concussion and guide return-to-play decisions?

    PubMed

    Cartwright, Michael S; Dupuis, Janae E; Bargoil, Jessica M; Foster, Dana C

    2015-09-01

    Mild traumatic brain injury, often referred to as concussion, is a common, potentially debilitating, and costly condition. One of the main challenges in diagnosing and managing concussion is that there is not currently an objective test to determine the presence of a concussion and to guide return-to-play decisions for athletes. Traditional neuroimaging tests, such as brain magnetic resonance imaging, are normal in concussion, and therefore diagnosis and management are guided by reported symptoms. Some athletes will under-report symptoms to accelerate their return-to-play and others will over-report symptoms out of fear of further injury or misinterpretation of underlying conditions, such as migraine headache. Therefore, an objective measure is needed to assist in several facets of concussion management. Limited data in animal and human testing indicates that intracranial pressure increases slightly and cerebrovascular reactivity (the ability of the cerebral arteries to auto-regulate in response to changes in carbon dioxide) decreases slightly following mild traumatic brain injury. We hypothesize that a combination of ultrasonographic measurements (optic nerve sheath diameter and transcranial Doppler assessment of cerebrovascular reactivity) into a single index will allow for an accurate and non-invasive measurement of intracranial pressure and cerebrovascular reactivity, and this index will be clinically relevant and useful for guiding concussion diagnosis and management. Ultrasound is an ideal modality for the evaluation of concussion because it is portable (allowing for evaluation in many settings, such as on the playing field or in a combat zone), radiation-free (making repeat scans safe), and relatively inexpensive (resulting in nearly universal availability). This paper reviews the literature supporting our hypothesis that an ultrasonographic index can assist in the diagnosis and management of concussion, and it also presents limited data regarding the

  16. Accurate Structure and Dynamics of the Metal-Site of Paramagnetic Metalloproteins from NMR Parameters Using Natural Bond Orbitals

    PubMed Central

    2012-01-01

    A natural bond orbital (NBO) analysis of unpaired electron spin density in metalloproteins is presented, which allows a fast and robust calculation of paramagnetic NMR parameters. Approximately 90% of the unpaired electron spin density occupies metal–ligand NBOs, allowing the majority of the density to be modeled by only a few NBOs that reflect the chemical bonding environment. We show that the paramagnetic relaxation rate of protons can be calculated accurately using only the metal–ligand NBOs and that these rates are in good agreement with corresponding rates measured experimentally. This holds, in particular, for protons of ligand residues where the point-dipole approximation breaks down. To describe the paramagnetic relaxation of heavy nuclei, also the electron spin density in the local orbitals must be taken into account. Geometric distance restraints for 15N can be derived from the paramagnetic relaxation enhancement and the Fermi contact shift when local NBOs are included in the analysis. Thus, the NBO approach allows us to include experimental paramagnetic NMR parameters of 15N nuclei as restraints in a structure optimization protocol. We performed a molecular dynamics simulation and structure determination of oxidized rubredoxin using the experimentally obtained paramagnetic NMR parameters of 15N. The corresponding structures obtained are in good agreement with the crystal structure of rubredoxin. Thus, the NBO approach allows an accurate description of the geometric structure and the dynamics of metalloproteins, when NMR parameters are available of nuclei in the immediate vicinity of the metal-site. PMID:22329704

  17. The Stellar Parameters and Evolutionary State of the Primary in the d' Symbiotic System StHα 190

    NASA Astrophysics Data System (ADS)

    Smith, Verne V.; Pereira, Claudio B.; Cunha, Katia

    2001-07-01

    We report on a high-resolution spectroscopic stellar parameter and abundance analysis of a d' symbiotic star: the yellow component of StHα190. This star has recently been discovered, and confirmed here, to be a rapidly rotating (vsini=100+/-10 km s-1) subgiant, or giant, that exhibits radial velocity variations of probably at least 40 km s-1, indicating the presence of a companion (as in many symbiotic systems, the companion is a hot white dwarf star). An analysis of the red spectrum reveals the cool stellar component to have an effective temperature of Teff=5300+/-150 K and a surface gravity of logg=3.0+/-0.5 (this corresponds to an approximate spectral type of G4 III/IV). These parameters result in an estimated primary luminosity of 45 Lsolar, implying a distance of about 780 pc (within a factor of 2). The iron and calcium abundances are found to be close to solar; however, barium is overabundant, relative to Fe and Ca, by about 0.5 dex. The Ba enhancement reflects mass transfer of s-process-enriched material when the current white dwarf was an asymptotic giant branch star, of large physical dimension (>=1 AU). The past and future evolution of this binary system depends critically on its current orbital period, which is not yet known. Concerted and frequent radial velocity measurements are needed to provide crucial physical constraints to this d' symbiotic system. Based on observations made with the 2.1 m telescope of McDonald Observatory, University of Texas.

  18. GUIDANCE2: accurate detection of unreliable alignment regions accounting for the uncertainty of multiple parameters

    PubMed Central

    Sela, Itamar; Ashkenazy, Haim; Katoh, Kazutaka; Pupko, Tal

    2015-01-01

    Inference of multiple sequence alignments (MSAs) is a critical part of phylogenetic and comparative genomics studies. However, from the same set of sequences different MSAs are often inferred, depending on the methodologies used and the assumed parameters. Much effort has recently been devoted to improving the ability to identify unreliable alignment regions. Detecting such unreliable regions was previously shown to be important for downstream analyses relying on MSAs, such as the detection of positive selection. Here we developed GUIDANCE2, a new integrative methodology that accounts for: (i) uncertainty in the process of indel formation, (ii) uncertainty in the assumed guide tree and (iii) co-optimal solutions in the pairwise alignments, used as building blocks in progressive alignment algorithms. We compared GUIDANCE2 with seven methodologies to detect unreliable MSA regions using extensive simulations and empirical benchmarks. We show that GUIDANCE2 outperforms all previously developed methodologies. Furthermore, GUIDANCE2 also provides a set of alternative MSAs which can be useful for downstream analyses. The novel algorithm is implemented as a web-server, available at: http://guidance.tau.ac.il. PMID:25883146

  19. Accurate Analytical and Statistical Approaches to Reduce O-C Discrepancies in the Precessional Parameters

    NASA Astrophysics Data System (ADS)

    Martínez, M. J.; Marco, F. J.; López, J. A.

    2009-02-01

    The Hipparcos catalog provides a reference frame at optical wavelengths for the new International Celestial Reference System (ICRS). This new reference system was adopted following the resolution agreed at the 23rd IAU General Assembly held in Kyoto in 1997. Differences in the Hipparcos system of proper motions and the previous materialization of the reference frame, the FK5, are expected to be caused only by the combined effects of the motion of the equinox of the FK5 and the precession of the equator and the ecliptic. Several authors have pointed out an inconsistency between the differences in proper motion of the Hipparcos-FK5 and the correction of the precessional values derived from VLBI and lunar laser ranging (LLR) observations. Most of them have claimed that these discrepancies are due to slightly biased proper motions in the FK5 catalog. The different mathematical models that have been employed to explain these errors have not fully accounted for the discrepancies in the correction of the precessional parameters. Our goal here is to offer an explanation for this fact. We propose the use of independent parametric and nonparametric models. The introduction of a nonparametric model, combined with the inner product in the square integrable functions over the unitary sphere, would give us values which do not depend on the possible interdependencies existing in the data set. The evidence shows that zonal studies are needed. This would lead us to introduce a local nonparametric model. All these models will provide independent corrections to the precessional values, which could then be compared in order to study the reliability in each case. Finally, we obtain values for the precession corrections that are very consistent with those that are currently adopted.

  20. VizieR Online Data Catalog: RGB stars in Galactic GC stellar parameters (Dias+, 2016)

    NASA Astrophysics Data System (ADS)

    Dias, B.; Barbuy, B.; Saviane, I.; Held, E.; da Costa, G.; Ortolani, S.; Gullieuszik, M.; Vasquez, S.

    2016-03-01

    Spectroscopic parameters for 758 red giant branch stars in 51 Milky Way globular clusters. For each star star ID, cluster name, equatorial coordinates, magnitude, colour, heliocentric velocities, membership classification member, effective temperature, surface gravity, metallicity, Mg and alpha-element abundance. We note that magnitude and colours are not calibrated. (2 data files).

  1. The long-period RS Canum Venaticorum binary IM Pegasi. I. Orbital and stellar parameters

    NASA Astrophysics Data System (ADS)

    Berdyugina, S. V.; Ilyin, I.; Tuominen, I.

    1999-07-01

    New high-resolution and high signal-to-noise ratio spectroscopic observations carried out in 1996-1997 are analysed. A total of 85 new high quality radial velocity measurements are used for determining the new orbital parameters: T_conj=HJD2450342.883+24.64880E, e=0.0, gamma =-14.09 {km s(-1) }, K1=34.39 {km s(-1) }. A model atmosphere analysis of the averaged spectrum of the star has yielded a self-consistent set of fundamental parameters of the primary component: {T_eff}=4450 K, {log g=2.4, [M/H]=0.0, {xi_t }=1.6 {km s(-1) }, {v sini=26.5 {km s(-1) }. The primary is found to be a typical K2 III giant with the mass of about 1.5 M_⊙ which has undergone the first convective mixing on the Red Giant Branch ([C/H]=-0.32, [N/H]=0.30, C/N=1.15). The unspotted V magnitude of the star of 5fm 55 is estimated from the observed variations of the TiO band and quasi-simultaneous photometry. Combining all parameters, the radius and inclination of the primary as well as a probable spectral class of the secondary are estimated. based on observations collected at the 2.6\\,m telescope of the Crimean Astrophysical Observatory, Ukraine and the Nordic Optical Telescope (NOT), La Palma, Spain

  2. The active RS Canum Venaticorum binary II Pegasi. I. Stellar and orbital parameters

    NASA Astrophysics Data System (ADS)

    Berdyugina, S. V.; Jankov, S.; Ilyin, I.; Tuominen, I.; Fekel, F. C.

    1998-06-01

    A detailed model atmosphere analysis of high-resolution and high S/N CCD spectra of II Peg has yielded for the first time a self-consistent set of fundamental parameters of the primary component: {T_eff}=4600 K, {log g=3.2, [M/H]=-0.4, {xi_t }=2.0 {km s(-1) }. In addition, 121 new high quality radial velocity measurements allowed us to determine improved orbital parameters, resulting in a new orbital ephemeris of T_conj=2449582.9268+6.724333E. The position of the primary of II Peg in the HR diagram with the new parameters corresponds to a K2 IV star with mass ~0.8 M_⊙. The evolved character of the star is confirmed by the C/N ratio, which is reduced significantly relative to the solar value. The unspotted V magnitude of the star of 6fm 9 is estimated from the observed variations of the TiO bands and quasi-simultaneous photometry. The blend of Li{ i 6707 Angstroms is suspected to vary in equivalent width due to spot modulation. The lithium abundance for the unspotted star, Li/H=1.0±m0.1, is found to be consistent with other post-main sequence chromospherically active stars. Combining all parameters, the radius R ~ 3.4 R_⊙ and the inclination i ~ 60° of the primary are estimated with the assumption that its rotational axis is perpendicular to the orbital plane. The secondary is probably a M0-M3 V star with a mass of about 0.4 M_⊙. Based on observations collected at the Nordic Optical Telescope (NOT), La Palma, Spain; the 2.6 m telescope of the Crimean Astrophysical Observatory, Ukraine; the 2.7 m and 2.1 m telescopes of the McDonald Observatory, USA; the coudé feed telescope of the Kitt Peak National Observatory, USA Table 2 is also available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html.

  3. The SEGUE Stellar Parameter Pipeline. III. Comparison with High-Resolution Spectroscopy of SDSS/SEGUE Field Stars

    SciTech Connect

    Allende Prieto, C.; Sivarani, T.; Beers, T.C.; Lee, Y.S.; Koesterke, L.; Shetrone, M.; Sneden, C.; Lambert, D.L.; Wilhelm, R.; Rockosi, C.M.; Lai, D.

    2007-10-01

    The authors report high-resolution spectroscopy of 125 field stars previously observed as part of the Sloan Digital Sky Survey and its program for Galactic studies, the Sloan Extension for Galactic Understanding and Exploration (SEGUE). These spectra are used to measure radial velocities and to derive atmospheric parameters, which they compare with those reported by the SEGUE Stellar Parameter Pipeline (SSPP). The SSPP obtains estimates of these quantities based on SDSS ugriz photometry and low-resolution (R {approx} 2000) spectroscopy. For F- and G-type stars observed with high signal-to-noise ratios (S/N), they empirically determine the typical random uncertainties in the radial velocities, effective temperatures, surface gravities, and metallicities delivered by the SSPP to be 2.4 km s{sup -1}, 130 K (2.2%), 0.21 dex, and 0.11 dex, respectively, with systematic uncertainties of a similar magnitude in the effective temperatures and metallicities. They estimate random errors for lower S/N spectra based on numerical simulations.

  4. Kinematics and Velocity Ellipsoid Parameters of Stellar Groups and Open Star Clusters: II Cool Stars

    NASA Astrophysics Data System (ADS)

    Elsanhoury, W. H.

    2016-06-01

    Based on the galactic space velocity components (U, V, W) and with aid of the vector and matrix analyses, we computed the velocity ellipsoid parameters for 790 late-type stars from CoRoT (Convection, Rotation and Transits) observations and 290 L dwarf stars. We ran the calculations for spectral types F, G, and K for late-type stars and L0, L1, L2, and L3 for L dwarf stars. We found that the ratio of the middle to the major axis in the galaxy ranged from 0.35 to 0.73. The vertex deviation from the galactic center was very small for the samples under investigation, which agrees well with earlier calculations.

  5. VizieR Online Data Catalog: SWEETCat I. Stellar parameters for host stars (Santos+, 2013)

    NASA Astrophysics Data System (ADS)

    Santos, N. C.; Sousa, S. G.; Mortier, A.; Neves, V.; Adibekyan, V.; Tsantaki, M.; Delgado Mena, E.; Bonfils, X.; Israelian, G.; Mayor, M.; Udry; S.

    2013-07-01

    The file sweetcat.dat contains the spectroscopic parameters for all the planet hosts compiled for this work (data as of July 2013). Up to date tables can be found at http://www.astro.up.pt/resources/sweet-cat . The spectra were gathered through observations, made by our team, and by the use of the ESO archive. In total, six different spectrographs were used: FEROS (2.2m ESO/MPI telescope, La Silla, Chile), FIES (Nordic Optical Telescope, La Palma, Spain), HARPS (3.6m ESO telescope, La Silla, Chile), SARG (TNG Telescope, La Palma, Spain), SOPHIE (1.93m telescope, OHP, France), and UVES (VLT Kueyen telescope, Paranal, Chile). (2 data files).

  6. A Weibull statistics-based lignocellulose saccharification model and a built-in parameter accurately predict lignocellulose hydrolysis performance.

    PubMed

    Wang, Mingyu; Han, Lijuan; Liu, Shasha; Zhao, Xuebing; Yang, Jinghua; Loh, Soh Kheang; Sun, Xiaomin; Zhang, Chenxi; Fang, Xu

    2015-09-01

    Renewable energy from lignocellulosic biomass has been deemed an alternative to depleting fossil fuels. In order to improve this technology, we aim to develop robust mathematical models for the enzymatic lignocellulose degradation process. By analyzing 96 groups of previously published and newly obtained lignocellulose saccharification results and fitting them to Weibull distribution, we discovered Weibull statistics can accurately predict lignocellulose saccharification data, regardless of the type of substrates, enzymes and saccharification conditions. A mathematical model for enzymatic lignocellulose degradation was subsequently constructed based on Weibull statistics. Further analysis of the mathematical structure of the model and experimental saccharification data showed the significance of the two parameters in this model. In particular, the λ value, defined the characteristic time, represents the overall performance of the saccharification system. This suggestion was further supported by statistical analysis of experimental saccharification data and analysis of the glucose production levels when λ and n values change. In conclusion, the constructed Weibull statistics-based model can accurately predict lignocellulose hydrolysis behavior and we can use the λ parameter to assess the overall performance of enzymatic lignocellulose degradation. Advantages and potential applications of the model and the λ value in saccharification performance assessment were discussed. PMID:26121186

  7. Evaluating Gaia performances on eclipsing binaries. IV. Orbits and stellar parameters for SV Cam, BS Dra and HP Dra

    NASA Astrophysics Data System (ADS)

    Milone, E. F.; Munari, U.; Marrese, P. M.; Williams, M. D.; Zwitter, T.; Kallrath, J.; Tomov, T.

    2005-10-01

    This is the fourth in a series of papers that aim both to provide reasonable orbits for a number of eclipsing binaries and to evaluate the expected performance of Gaia of these objects and the accuracy that is achievable in the determination of such fundamental stellar parameters as mass and radius. In this paper, we attempt to derive the orbits and physical parameters for three eclipsing binaries in the mid-F to mid-G spectral range. As for previous papers, only the H_P, V_T, BT photometry from the Hipparcos/Tycho mission and ground-based radial velocities from spectroscopy in the region 8480-8740 Å are used in the analyses. These data sets simulate the photometric and spectroscopic data that are expected to be obtained by Gaia, the approved ESA Cornerstone mission to be launched in 2011. The systems targeted in this paper are SV Cam, BS Dra and HP Dra. SV Cam and BS Dra have been studied previously, allowing comparisons of the derived parameters with those from full scale and devoted ground-based investigations. HP Dra has no published orbital solution. SV Cam has a β Lyrae type light curve and the others have Algol-like light curves. SV Cam has the complication of light curve anomalies, usually attributed to spots; BS Dra has non-solar metallicity, and HP Dra appears to have a small eccentricity and a sizeable time derivative in the argument of the periastron. Thus all three provide interesting and different test cases.

  8. Optimization of tissue physical parameters for accurate temperature estimation from finite-element simulation of radiofrequency ablation.

    PubMed

    Subramanian, Swetha; Mast, T Douglas

    2015-10-01

    Computational finite element models are commonly used for the simulation of radiofrequency ablation (RFA) treatments. However, the accuracy of these simulations is limited by the lack of precise knowledge of tissue parameters. In this technical note, an inverse solver based on the unscented Kalman filter (UKF) is proposed to optimize values for specific heat, thermal conductivity, and electrical conductivity resulting in accurately simulated temperature elevations. A total of 15 RFA treatments were performed on ex vivo bovine liver tissue. For each RFA treatment, 15 finite-element simulations were performed using a set of deterministically chosen tissue parameters to estimate the mean and variance of the resulting tissue ablation. The UKF was implemented as an inverse solver to recover the specific heat, thermal conductivity, and electrical conductivity corresponding to the measured area of the ablated tissue region, as determined from gross tissue histology. These tissue parameters were then employed in the finite element model to simulate the position- and time-dependent tissue temperature. Results show good agreement between simulated and measured temperature. PMID:26352462

  9. Optimization of tissue physical parameters for accurate temperature estimation from finite-element simulation of radiofrequency ablation

    NASA Astrophysics Data System (ADS)

    Subramanian, Swetha; Mast, T. Douglas

    2015-09-01

    Computational finite element models are commonly used for the simulation of radiofrequency ablation (RFA) treatments. However, the accuracy of these simulations is limited by the lack of precise knowledge of tissue parameters. In this technical note, an inverse solver based on the unscented Kalman filter (UKF) is proposed to optimize values for specific heat, thermal conductivity, and electrical conductivity resulting in accurately simulated temperature elevations. A total of 15 RFA treatments were performed on ex vivo bovine liver tissue. For each RFA treatment, 15 finite-element simulations were performed using a set of deterministically chosen tissue parameters to estimate the mean and variance of the resulting tissue ablation. The UKF was implemented as an inverse solver to recover the specific heat, thermal conductivity, and electrical conductivity corresponding to the measured area of the ablated tissue region, as determined from gross tissue histology. These tissue parameters were then employed in the finite element model to simulate the position- and time-dependent tissue temperature. Results show good agreement between simulated and measured temperature.

  10. 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.

  11. A New Synthetic Library of the Near-infrared Ca II Triplet Indices. I. Index Definition, Calibration, and Relations with Stellar Atmospheric Parameters

    NASA Astrophysics Data System (ADS)

    Du, W.; Luo, A. L.; Zhao, Y. H.

    2012-02-01

    Adopting the SPECTRUM package, which is a stellar spectral synthesis program, we have synthesized a comprehensive set of 2890 near-infrared (NIR) synthetic spectra with a resolution and wavelength sampling similar to the Sloan Digital Sky Survey (SDSS) and the forthcoming Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) spectra. During the synthesis, we applied the "New grids of ATLAS9 Model Atmosphere" to develop a grid of local thermodynamic equilibrium model atmospheres for effective temperatures (T eff) ranging from 3500 to 7500 K, for surface gravities (log g) from 0.5 to 5.0 dex, for metallicities ([Fe/H]) from -4.0 to 0.5 dex, and for solar ([α/Fe] = 0.0 dex) and non-solar ([α/Fe] = +0.4 dex) abundances. This synthetic stellar library is composed of 1350 solar scaled abundance (SSA) and 1530 non-solar scaled abundance (NSSA) spectra, grounding on which we have defined a new set of NIR Ca II triplet indices and an index CaT as the sum of the three. These defined indices were automatically measured on every spectrum of the synthetic stellar library and calibrated with the indices computed on the observational spectra from the INDO-U.S. stellar library. In order to check the effect of α-element enhancement on the so-defined Ca II indices, we compared indices measured on the SSA spectra with those on the NSSA ones at the same trine of stellar parameters (T eff, log g, [Fe/H]); luckily, little influences of α-element enhancement were found. Furthermore, comparisons of our synthetic indices with the observational ones from measurements on the INDO-U.S. stellar library, the SDSS-DR7 and SDSS-DR8 spectroscopic survey are presented, respectively, for dwarfs and giants in specific. For dwarfs, our synthetic indices could well reproduce the behaviors of the observational indices versus stellar parameters, which verifies the validity of our index definitions for dwarfs. For giants, the consistency between our synthetic indices and the observational

  12. A NEW SYNTHETIC LIBRARY OF THE NEAR-INFRARED Ca II TRIPLET INDICES. I. INDEX DEFINITION, CALIBRATION, AND RELATIONS WITH STELLAR ATMOSPHERIC PARAMETERS

    SciTech Connect

    Du, W.; Luo, A. L.; Zhao, Y. H. E-mail: lal@nao.cas.cn

    2012-02-15

    Adopting the SPECTRUM package, which is a stellar spectral synthesis program, we have synthesized a comprehensive set of 2890 near-infrared (NIR) synthetic spectra with a resolution and wavelength sampling similar to the Sloan Digital Sky Survey (SDSS) and the forthcoming Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) spectra. During the synthesis, we applied the 'New grids of ATLAS9 Model Atmosphere' to develop a grid of local thermodynamic equilibrium model atmospheres for effective temperatures (T{sub eff}) ranging from 3500 to 7500 K, for surface gravities (log g) from 0.5 to 5.0 dex, for metallicities ([Fe/H]) from -4.0 to 0.5 dex, and for solar ([{alpha}/Fe] = 0.0 dex) and non-solar ([{alpha}/Fe] = +0.4 dex) abundances. This synthetic stellar library is composed of 1350 solar scaled abundance (SSA) and 1530 non-solar scaled abundance (NSSA) spectra, grounding on which we have defined a new set of NIR Ca II triplet indices and an index CaT as the sum of the three. These defined indices were automatically measured on every spectrum of the synthetic stellar library and calibrated with the indices computed on the observational spectra from the INDO-U.S. stellar library. In order to check the effect of {alpha}-element enhancement on the so-defined Ca II indices, we compared indices measured on the SSA spectra with those on the NSSA ones at the same trine of stellar parameters (T{sub eff}, log g, [Fe/H]); luckily, little influences of {alpha}-element enhancement were found. Furthermore, comparisons of our synthetic indices with the observational ones from measurements on the INDO-U.S. stellar library, the SDSS-DR7 and SDSS-DR8 spectroscopic survey are presented, respectively, for dwarfs and giants in specific. For dwarfs, our synthetic indices could well reproduce the behaviors of the observational indices versus stellar parameters, which verifies the validity of our index definitions for dwarfs. For giants, the consistency between our synthetic

  13. 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

  14. Beyond the diffraction limit of optical/IR interferometers. II. Stellar parameters of rotating stars from differential phases

    NASA Astrophysics Data System (ADS)

    Hadjara, M.; Domiciano de Souza, A.; Vakili, F.; Jankov, S.; Millour, F.; Meilland, A.; Khorrami, Z.; Chelli, A.; Baffa, C.; Hofmann, K.-H.; Lagarde, S.; Robbe-Dubois, S.

    2014-09-01

    Context. As previously demonstrated on Achernar, one can derive the angular radius, rotational velocity, axis tilt, and orientation of a fast-rotating star from the differential phases obtained by spectrally resolved long baseline interferometry using earth-rotation synthesis. Aims: We applied this method on a small sample of stars for different spectral types and classes, in order to generalize the technique to other rotating stars across the H-R diagram and determine their fundamental parameters. Methods: We used differential phase data from the AMBER/VLTI instrument obtained prior to refurbishing its spectrometer in 2010. With the exception of Fomalhaut, which has been observed in the medium-resolution mode of AMBER (λ/δλ ≈ 1500), our three other targets, Achernar, Altair, and δ Aquilae offered high-resolution (λ/δλ ≈ 12 000) spectro-interferometric data around the Brγ absorption line in K band. These data were used to constrain the input parameters of an analytical, still realistic model to interpret the observations with a systematic approach for the error budget analysis in order to robustly conclude on the physics of our 4 targets. We applied the super resolution provided by differential phases φdiff to measure the size (equatorial radius Req and angular diameter ⌀eq), the equatorial rotation velocity (Veq), the inclination angle (i), and the rotation axis position angle (PArot) of 4 fast-rotating stars: Achernar, Altair, δ Aquilae, and Fomalhaut. The stellar parameters of the targets were constrained using a semi-analytical algorithm dedicated to fast rotators SCIROCCO. Results: The derived parameters for each star were Req = 11.2 ± 0.5 R⊙, Veqsini = 290 ± 17 km s-1, PArot = 35.4° ± 1.4°, for Achernar; Req = 2.0 ± 0.2 R⊙, Veqsini = 226 ± 34 km s-1, PArot = -65.5° ± 5.5°, for Altair; Req = 2.2 ± 0.3 R⊙, Veqsini = 74 ± 35 km s-1, PArot = -101.2° ± 14°, for δ Aquilae; and Req = 1.8 ± 0.2 R⊙, Veqsini = 93 ± 16 km s-1

  15. VizieR Online Data Catalog: Stellar parameters for CoRoT exoplanet field stars (Cortes+, 2015)

    NASA Astrophysics Data System (ADS)

    Cortes, C.; Maciel, S. C.; Vieira, S.; Ferreira Lopes, C. E.; Leao, I. C.; de Oliveira, G. P.; Correia, C.; Canto Martins, B. L.; Catelan, M.; de Medeiros, J. R.

    2016-08-01

    The present stellar sample is composed of 138 stars of spectral types F, G, and K, with visual magnitudes V between 10 to 14, located in two exoplanet fields observed by CoRoT, namely the Galactic center (LRc01: Long Run Center 01) and the Galactic anticenter (LRa01: Long Run Anticenter 01) fields. (4 data files).

  16. Improved centroid moment tensor analyses in the NIED AQUA (Accurate and QUick Analysis system for source parameters)

    NASA Astrophysics Data System (ADS)

    Kimura, H.; Asano, Y.; Matsumoto, T.

    2012-12-01

    The rapid determination of hypocentral parameters and their transmission to the public are valuable components of disaster mitigation. We have operated an automatic system for this purpose—termed the Accurate and QUick Analysis system for source parameters (AQUA)—since 2005 (Matsumura et al., 2006). In this system, the initial hypocenter, the moment tensor (MT), and the centroid moment tensor (CMT) solutions are automatically determined and posted on the NIED Hi-net Web site (www.hinet.bosai.go.jp). This paper describes improvements made to the AQUA to overcome limitations that became apparent after the 2011 Tohoku Earthquake (05:46:17, March 11, 2011 in UTC). The improvements included the processing of NIED F-net velocity-type strong motion records, because NIED F-net broadband seismographs are saturated for great earthquakes such as the 2011 Tohoku Earthquake. These velocity-type strong motion seismographs provide unsaturated records not only for the 2011 Tohoku Earthquake, but also for recording stations located close to the epicenters of M>7 earthquakes. We used 0.005-0.020 Hz records for M>7.5 earthquakes, in contrast to the 0.01-0.05 Hz records employed in the original system. The initial hypocenters determined based on arrival times picked by using seismograms recorded by NIED Hi-net stations can have large errors in terms of magnitude and hypocenter location, especially for great earthquakes or earthquakes located far from the onland Hi-net network. The size of the 2011 Tohoku Earthquake was initially underestimated in the AQUA to be around M5 at the initial stage of rupture. Numerous aftershocks occurred at the outer rise east of the Japan trench, where a great earthquake is anticipated to occur. Hence, we modified the system to repeat the MT analyses assuming a larger size, for all earthquakes for which the magnitude was initially underestimated. We also broadened the search range of centroid depth for earthquakes located far from the onland Hi

  17. 55 CANCRI: STELLAR ASTROPHYSICAL PARAMETERS, A PLANET IN THE HABITABLE ZONE, AND IMPLICATIONS FOR THE RADIUS OF A TRANSITING SUPER-EARTH

    SciTech Connect

    Von Braun, Kaspar; Kane, Stephen R.; Ciardi, David R.; Tabetha, S. Boyajian; McAlister, Harold A.; White, Russel; Ten Brummelaar, Theo A.; Schaefer, Gail; Sturmann, Laszlo; Sturmann, Judit; Turner, Nils H.; Farrington, Chris; Goldfinger, P. J.; Van Belle, Gerard T.; Raymond, Sean N.; Lopez-Morales, Mercedes; Ridgway, Stephen T.

    2011-10-10

    The bright star 55 Cancri is known to host five planets, including a transiting super-Earth. The study presented here yields directly determined values for 55 Cnc's stellar astrophysical parameters based on improved interferometry: R = 0.943 {+-} 0.010 R{sub sun}, T{sub EFF} = 5196 {+-} 24 K. We use isochrone fitting to determine 55 Cnc's age to be 10.2 {+-} 2.5 Gyr, implying a stellar mass of 0.905 {+-} 0.015 M{sub sun}. Our analysis of the location and extent of the system's habitable zone (HZ; 0.67-1.32 AU) shows that planet f, with period {approx}260 days and Msin i = 0.155 M{sub Jupiter}, spends the majority of the duration of its elliptical orbit in the circumstellar HZ. Though planet f is too massive to harbor liquid water on any planetary surface, we elaborate on the potential of alternative low-mass objects in planet f's vicinity: a large moon and a low-mass planet on a dynamically stable orbit within the HZ. Finally, our direct value for 55 Cancri's stellar radius allows for a model-independent calculation of the physical diameter of the transiting super-Earth 55 Cnc e ({approx}2.05 {+-} 0.15 R{sub +}), which, depending on the planetary mass assumed, implies a bulk density of 0.76 {rho}{sub +} or 1.07 {rho}{sub +}.

  18. A Comparison of Stellar Elemental Abundance Techniques and Measurements

    NASA Astrophysics Data System (ADS)

    Hinkel, Natalie R.; Young, Patrick A.; Pagano, Michael D.; Desch, Steven J.; Anbar, Ariel D.; Adibekyan, Vardan; Blanco-Cuaresma, Sergi; Carlberg, Joleen K.; Delgado Mena, Elisa; Liu, Fan; Nordlander, Thomas; Sousa, Sergio G.; Korn, Andreas; Gruyters, Pieter; Heiter, Ulrike; Jofré, Paula; Santos, Nuno C.; Soubiran, Caroline

    2016-09-01

    Stellar elemental abundances are important for understanding the fundamental properties of a star or stellar group, such as age and evolutionary history, as well as the composition of an orbiting planet. However, as abundance measurement techniques have progressed, there has been little standardization between individual methods and their comparisons. As a result, different stellar abundance procedures determine measurements that vary beyond the quoted error for the same elements within the same stars. The purpose of this paper is to better understand the systematic variations between methods and offer recommendations for producing more accurate results in the future. We invited a number of participants from around the world (Australia, Portugal, Sweden, Switzerland, and the United States) to calculate 10 element abundances (C, O, Na, Mg, Al, Si, Fe, Ni, Ba, and Eu) using the same stellar spectra for four stars (HD 361, HD 10700, HD 121504, and HD 202206). Each group produced measurements for each star using (1) their own autonomous techniques, (2) standardized stellar parameters, (3) a standardized line list, and (4) both standardized parameters and a line list. We present the resulting stellar parameters, absolute abundances, and a metric of data similarity that quantifies the homogeneity of the data. We conclude that standardization of some kind, particularly stellar parameters, improves the consistency between methods. However, because results did not converge as more free parameters were standardized, it is clear there are inherent issues within the techniques that need to be reconciled. Therefore, we encourage more conversation and transparency within the community such that stellar abundance determinations can be reproducible as well as accurate and precise.

  19. GGOS and the EOP - the key role of SLR for a stable estimation of highly accurate Earth orientation parameters

    NASA Astrophysics Data System (ADS)

    Bloßfeld, Mathis; Panzetta, Francesca; Müller, Horst; Gerstl, Michael

    2016-04-01

    The GGOS vision is to integrate geometric and gravimetric observation techniques to estimate consistent geodetic-geophysical parameters. In order to reach this goal, the common estimation of station coordinates, Stokes coefficients and Earth Orientation Parameters (EOP) is necessary. Satellite Laser Ranging (SLR) provides the ability to study correlations between the different parameter groups since the observed satellite orbit dynamics are sensitive to the above mentioned geodetic parameters. To decrease the correlations, SLR observations to multiple satellites have to be combined. In this paper, we compare the estimated EOP of (i) single satellite SLR solutions and (ii) multi-satellite SLR solutions. Therefore, we jointly estimate station coordinates, EOP, Stokes coefficients and orbit parameters using different satellite constellations. A special focus in this investigation is put on the de-correlation of different geodetic parameter groups due to the combination of SLR observations. Besides SLR observations to spherical satellites (commonly used), we discuss the impact of SLR observations to non-spherical satellites such as, e.g., the JASON-2 satellite. The goal of this study is to discuss the existing parameter interactions and to present a strategy how to obtain reliable estimates of station coordinates, EOP, orbit parameter and Stokes coefficients in one common adjustment. Thereby, the benefits of a multi-satellite SLR solution are evaluated.

  20. Accurate fundamental parameters of CoRoT asteroseismic targets. The solar-like stars HD 49933, HD 175726, HD 181420, and HD 181906

    NASA Astrophysics Data System (ADS)

    Bruntt, H.

    2009-10-01

    Context: The CoRoT satellite has provided high-quality light curves of several solar-like stars. Analysis of these light curves provides oscillation frequencies that make it possible to probe the interior of the stars. However, additional constraints on the fundamental parameters of the stars are important for the theoretical modelling to be successful. Aims: We estimate the fundamental parameters (mass, radius, and luminosity) of the first four solar-like targets to be observed in the asteroseismic field. In addition, we determine their effective temperature, metallicity, and detailed abundance patterns. Methods: To constrain the stellar mass, radius and age we used the shotgun software, which compares the location of the stars in the Hertzsprung-Russell diagram with theoretical evolution models. This method takes the uncertainties of the observed parameters into account, including the large separation determined from the solar-like oscillations. We determined the effective temperatures and abundance patterns in the stars from the analysis of high-resolution spectra obtained with the HARPS, NARVAL, ELODIE and FEROS spectrographs. Results: We determined the mass, radius, and luminosity of the four CoRoT targets to within 5{-}10%, 2{-}4% and 5{-}13%, respectively. The quality of the stellar spectra determines how well we can constrain the effective temperature. For the two best spectra we get 1-σ uncertainties below 60 K and 100{-}150 K for the other two. The uncertainty on the surface gravity is less than 0.08 dex for three stars, while it is 0.15 dex for HD 181906. The reason for the larger uncertainty is that the spectrum has two components with a luminosity ratio of L_p/Ls = 0.50±0.15. While Hipparcos astrometric data strongly suggest it is a binary star, we find evidence that the fainter star may be a background star, since it is less luminous but hotter.

  1. Numerical parameter constraints for accurate PIC-DSMC simulation of breakdown from arc initiation to stable arcs

    NASA Astrophysics Data System (ADS)

    Moore, Christopher; Hopkins, Matthew; Moore, Stan; Boerner, Jeremiah; Cartwright, Keith

    2015-09-01

    Simulation of breakdown is important for understanding and designing a variety of applications such as mitigating undesirable discharge events. Such simulations need to be accurate through early time arc initiation to late time stable arc behavior. Here we examine constraints on the timestep and mesh size required for arc simulations using the particle-in-cell (PIC) method with direct simulation Monte Carlo (DMSC) collisions. Accurate simulation of electron avalanche across a fixed voltage drop and constant neutral density (reduced field of 1000 Td) was found to require a timestep ~ 1/100 of the mean time between collisions and a mesh size ~ 1/25 the mean free path. These constraints are much smaller than the typical PIC-DSMC requirements for timestep and mesh size. Both constraints are related to the fact that charged particles are accelerated by the external field. Thus gradients in the electron energy distribution function can exist at scales smaller than the mean free path and these must be resolved by the mesh size for accurate collision rates. Additionally, the timestep must be small enough that the particle energy change due to the fields be small in order to capture gradients in the cross sections versus energy. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. DOE's National Nuclear Security Administration under Contract DE-AC04-94AL85000.

  2. Kea: A New Tool to Obtain Stellar Parameters from Low to Moderate Signal-to-noise and High-resolution Echelle Spectra

    NASA Astrophysics Data System (ADS)

    Endl, Michael; Cochran, William D.

    2016-09-01

    In this paper, we describe Kea a new spectroscopic fitting method to derive stellar parameters from moderate to low signal-to-noise, high-resolution spectra. We developed this new tool to analyze the massive data set of the Kepler mission reconnaissance spectra that we have obtained at McDonald Observatory. We use Kea to determine effective temperatures (T eff), metallicity ([Fe/H]), surface gravity (log g), and projected rotational velocity (v{sin}i). Kea compares the observations to a large library of synthetic spectra that covers a wide range of different T eff, [Fe/H], and log g values. We calibrated Kea on observations of well-characterized standard stars (the Kepler field “platinum” sample) that range in T eff from 5000 to 6500 K, in [Fe/H] from ‑0.5 to +0.4 dex, and in log g from 3.2 to 4.6 dex. We then compared the Kea results from reconnaissance spectra of 45 Kepler objects of interest (KOIs) to stellar parameters derived from higher signal-to-noise spectra obtained with Keck/HIRES. We find typical uncertainties of 100 K in T eff, 0.12 dex in [Fe/H], and 0.18 dex in log g. Named after Nestor notabilis an alpine parrot native to New Zealand.

  3. Stellar Parameters for HD 69830, a Nearby Star with Three Neptune Mass Planets and an Asteroid Belt

    NASA Astrophysics Data System (ADS)

    Tanner, Angelle; Boyajian, Tabetha S.; von Braun, Kaspar; Kane, Stephen; Brewer, John M.; Farrington, Chris; van Belle, Gerard T.; Beichman, Charles A.; Fischer, Debra; ten Brummelaar, Theo A.; McAlister, Harold A.; Schaefer, Gail

    2015-02-01

    We used the CHARA Array to directly measure the angular diameter of HD 69830, home to three Neptune mass planets and an asteroid belt. Our measurement of 0.674 ± 0.014 mas for the limb-darkened angular diameter of this star leads to a physical radius of R * = 0.9058 ± 0.0190 R ⊙ and luminosity of L * = 0.622 ± 0.014 L ⊙ when combined with a fit to the spectral energy distribution of the star. Placing these observed values on an Hertzsprung-Russel diagram along with stellar evolution isochrones produces an age of 10.6 ± 4 Gyr and mass of 0.863 ± 0.043 M ⊙. We use archival optical echelle spectra of HD 69830 along with an iterative spectral fitting technique to measure the iron abundance ([Fe/H] = -0.04 ± 0.03), effective temperature (5385 ± 44 K), and surface gravity (log g = 4.49 ± 0.06). We use these new values for the temperature and luminosity to calculate a more precise age of 7.5 ± 3 Gyr. Applying the values of stellar luminosity and radius to recent models on the optimistic location of the habitable zone produces a range of 0.61-1.44 AU partially outside the orbit of the furthest known planet (d) around HD 69830. Finally, we estimate the snow line at a distance of 1.95 ± 0.19 AU, which is outside the orbit of all three planets and its asteroid belt.

  4. Fundamental stellar parameters for selected T-Tauri stars in the Chamaeleon and Rho Ophiuchus star-forming regions

    NASA Astrophysics Data System (ADS)

    James, D. J.; Aarnio, A. N.; Richert, A. J. W.; Cargile, P. A.; Santos, N. C.; Melo, C. H. F.; Bouvier, J.

    2016-06-01

    We present the results of an optical photometry and high-resolution spectroscopy campaign for a modest sample of X-ray selected stars in the Chamaeleon and Rho Ophiuchus star-forming regions. With R˜ 50 000 optical spectra, we establish kinematic membership of the parent association and confirm stellar youth for each star in our sample. With the acquisition of new standardized BVIc photometry, in concert with near-infrared data from the literature, we derive age and mass from stellar positions in model-dependent Hertzsprung-Russell diagrams. We compare isochronal ages derived using colour-dependent extinction values finding that, within error bars, ages are the same irrespective of whether E(B - V), E(V - Ic), E(J - H) or E(H - K) is used to establish extinction, although model ages tend to be marginally younger for redder Ecolour values. For Cham I and η Cham members, we derive ages of ≲5-6 Myr, whereas our three η Cha candidates are more consistent with a ≳25 Myr post-T Tauri star population. In Rho Ophiuchus, most stars in our sample have isochronal ages <10 Myr. Five objects show evidence of strong infrared excess (Av > 5) in the Two Micron All Sky Survey colour-colour diagram, however in terms of Hα emission, all stars except RXJ1625.6-2613 are consistent with being weak-lined T-Tauri stars. Spectral energy distributions (SEDs) over the range ≃4000 Å <λ < 1000 μm, show that only one Chamaeleon star (RXJ1112.7 -7637) and three Rho Ophiuchus stars (ROXR1 13, RXJ1625.6-2613 & RXJ1627.1-2419) reveal substantial departures from a bare photosphere.

  5. 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.

  6. A non-empirical, parameter-free, hybrid functional for accurate calculations of optoelectronic properties of finite systems

    NASA Astrophysics Data System (ADS)

    Brawand, Nicholas; Vörös, Márton; Govoni, Marco; Galli, Giulia

    The accurate prediction of optoelectronic properties of molecules and solids is a persisting challenge for current density functional theory (DFT) based methods. We propose a hybrid functional where the mixing fraction of exact and local exchange is determined by a non-empirical, system dependent function. This functional yields ionization potentials, fundamental and optical gaps of many, diverse systems in excellent agreement with experiments, including organic and inorganic molecules and nanocrystals. We further demonstrate that the newly defined hybrid functional gives the correct alignment between the energy level of the exemplary TTF-TCNQ donor-acceptor system. DOE-BES: DE-FG02-06ER46262.

  7. Towards an accurate specific reaction parameter density functional for water dissociation on Ni(111): RPBE versus PW91.

    PubMed

    Jiang, Bin; Guo, Hua

    2016-08-01

    In search for an accurate description of the dissociative chemisorption of water on the Ni(111) surface, we report a new nine-dimensional potential energy surface (PES) based on a large number of density functional theory points using the RPBE functional. Seven-dimensional quantum dynamical calculations have been carried out on the RPBE PES, followed by site averaging and lattice effect corrections, yielding sticking probabilities that are compared with both the previous theoretical results based on a PW91 PES and experiment. It is shown that the RPBE functional increases the reaction barrier, but has otherwise a minor impact on the PES topography. Better agreement with experimental results is obtained with the new PES, but the agreement is still not quantitative. Possible sources of the remaining discrepancies are discussed. PMID:27436348

  8. An accurate and simple technique of determination of the maximum power point and measurement of some solar cell parameters

    NASA Astrophysics Data System (ADS)

    Deb, S.; Maitra, K.; Roychoudhuri, A.

    1985-06-01

    In the wake of the energy crisis, attempts are being made to develop a variety of energy conversion devices, such as solar cells. The single most important operational characteristic for a conversion element generating electricity is the V against I curve. Three points on this characteristic curve are of paramount importance, including the short-circuit, the open-circuit, and the maximum power point. The present paper has the objective to propose a new simple and accurate method of determining the maximum power point (Vm, Im) of the V against I characteristics, based on a geometrical interpretation. The method is general enough to be applicable to any energy conversion device having a nonlinear V against I characteristic. The paper provides also a method for determining the fill factor (FF), the series resistance (Rs), and the diode ideality factor (A) from a single set of connected observations.

  9. 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

  10. Accurate determination of interface trap state parameters by admittance spectroscopy in the presence of a Schottky barrier contact: Application to ZnO-based solar cells

    NASA Astrophysics Data System (ADS)

    Marin, Andrew T.; Musselman, Kevin P.; MacManus-Driscoll, Judith L.

    2013-04-01

    This work shows that when a Schottky barrier is present in a photovoltaic device, such as in a device with an ITO/ZnO contact, equivalent circuit analysis must be performed with admittance spectroscopy to accurately determine the pn junction interface recombination parameters (i.e., capture cross section and density of trap states). Without equivalent circuit analysis, a Schottky barrier can produce an error of ˜4-orders of magnitude in the capture cross section and ˜50% error in the measured density of trap states. Using a solution processed ZnO/Cu2O photovoltaic test system, we apply our analysis to clearly separate the contributions of interface states at the pn junction from the Schottky barrier at the ITO/ZnO contact so that the interface state recombination parameters can be accurately characterized. This work is widely applicable to the multitude of photovoltaic devices, which use ZnO adjacent to ITO.

  11. Stellar parameters of M dwarfs from low and high-resolution spectra together with new model atmospheres

    NASA Astrophysics Data System (ADS)

    Rajpurohit, A. S.; Reylé, C.; Schultheis, M.; Allard, F.; Scholz, R.; Homeier, D.

    2012-12-01

    We present an optical spectral atlas of stars covering the whole M-dwarf sequence. It consists of 95 M dwarfs at solar metallicity observed at low-resolution with EMMI@NTT and 21 M-subdwarfs, extreme-subdwarfs and ultra-subdwarfs observed at high resolution with UVES@VLT. Using the most recent PHOENIX BT-Settl stellar model atmospheres we perform a detailed comparison with our observed spectra using χ^2 minimization technique. We confront the models with low-resolution spectra of M dwarfs at solar metallicity and we assign effective temperatures to the M dwarfs. We present temperature versus spectral type and colour relations and their comparison with others found in the literature. We also present our high-resolution spectra of the subdwarfs (sdM, esdM, usdM) and compare them to the newest grid of the BT Settl models which uses the revised solar abundances of Caffau et al (2011). This comparison allows us to study the spectral details of cool atmospheres, to determine precise [Fe/H] values for our objects, and to investigate the effect of metallicity on cool dwarf atmospheres. This study also helps to validate the atmosphere models and improve them by determining new constants on molecular opacities, dust cloud formation etc.

  12. A two-parameter kinetic model based on a time-dependent activity coefficient accurately describes enzymatic cellulose digestion

    PubMed Central

    Kostylev, Maxim; Wilson, David

    2014-01-01

    Lignocellulosic biomass is a potential source of renewable, low-carbon-footprint liquid fuels. Biomass recalcitrance and enzyme cost are key challenges associated with the large-scale production of cellulosic fuel. Kinetic modeling of enzymatic cellulose digestion has been complicated by the heterogeneous nature of the substrate and by the fact that a true steady state cannot be attained. We present a two-parameter kinetic model based on the Michaelis-Menten scheme (Michaelis L and Menten ML. (1913) Biochem Z 49:333–369), but with a time-dependent activity coefficient analogous to fractal-like kinetics formulated by Kopelman (Kopelman R. (1988) Science 241:1620–1626). We provide a mathematical derivation and experimental support to show that one of the parameters is a total activity coefficient and the other is an intrinsic constant that reflects the ability of the cellulases to overcome substrate recalcitrance. The model is applicable to individual cellulases and their mixtures at low-to-medium enzyme loads. Using biomass degrading enzymes from a cellulolytic bacterium Thermobifida fusca we show that the model can be used for mechanistic studies of enzymatic cellulose digestion. We also demonstrate that it applies to the crude supernatant of the widely studied cellulolytic fungus Trichoderma reesei and can thus be used to compare cellulases from different organisms. The two parameters may serve a similar role to Vmax, KM, and kcat in classical kinetics. A similar approach may be applicable to other enzymes with heterogeneous substrates and where a steady state is not achievable. PMID:23837567

  13. Petermann I and II spot size: Accurate semi analytical description involving Nelder-Mead method of nonlinear unconstrained optimization and three parameter fundamental modal field

    NASA Astrophysics Data System (ADS)

    Roy Choudhury, Raja; Roy Choudhury, Arundhati; Kanti Ghose, Mrinal

    2013-01-01

    A semi-analytical model with three optimizing parameters and a novel non-Gaussian function as the fundamental modal field solution has been proposed to arrive at an accurate solution to predict various propagation parameters of graded-index fibers with less computational burden than numerical methods. In our semi analytical formulation the optimization of core parameter U which is usually uncertain, noisy or even discontinuous, is being calculated by Nelder-Mead method of nonlinear unconstrained minimizations as it is an efficient and compact direct search method and does not need any derivative information. Three optimizing parameters are included in the formulation of fundamental modal field of an optical fiber to make it more flexible and accurate than other available approximations. Employing variational technique, Petermann I and II spot sizes have been evaluated for triangular and trapezoidal-index fibers with the proposed fundamental modal field. It has been demonstrated that, the results of the proposed solution identically match with the numerical results over a wide range of normalized frequencies. This approximation can also be used in the study of doped and nonlinear fiber amplifier.

  14. Coupling 1D Navier Stokes equation with autoregulation lumped parameter networks for accurate cerebral blood flow modeling

    NASA Astrophysics Data System (ADS)

    Ryu, Jaiyoung; Hu, Xiao; Shadden, Shawn C.

    2014-11-01

    The cerebral circulation is unique in its ability to maintain blood flow to the brain under widely varying physiologic conditions. Incorporating this autoregulatory response is critical to cerebral blood flow modeling, as well as investigations into pathological conditions. We discuss a one-dimensional nonlinear model of blood flow in the cerebral arteries that includes coupling of autoregulatory lumped parameter networks. The model is tested to reproduce a common clinical test to assess autoregulatory function - the carotid artery compression test. The change in the flow velocity at the middle cerebral artery (MCA) during carotid compression and release demonstrated strong agreement with published measurements. The model is then used to investigate vasospasm of the MCA, a common clinical concern following subarachnoid hemorrhage. Vasospasm was modeled by prescribing vessel area reduction in the middle portion of the MCA. Our model showed similar increases in velocity for moderate vasospasms, however, for serious vasospasm (~ 90% area reduction), the blood flow velocity demonstrated decrease due to blood flow rerouting. This demonstrates a potentially important phenomenon, which otherwise would lead to false-negative decisions on clinical vasospasm if not properly anticipated.

  15. ON THE ROLE OF DISKS IN THE FORMATION OF STELLAR SYSTEMS: A NUMERICAL PARAMETER STUDY OF RAPID ACCRETION

    SciTech Connect

    Kratter, Kaitlin M.; Matzner, Christopher D.; Krumholz, Mark R.; Klein, Richard I.

    2010-01-10

    We study rapidly accreting, gravitationally unstable disks with a series of idealized global, numerical experiments using the code ORION. Our numerical parameter study focuses on protostellar disks, showing that one can predict disk behavior and the multiplicity of the accreting star system as a function of two dimensionless parameters which compare the infall rate to the disk sound speed and orbital period. Although gravitational instabilities become strong, we find that fragmentation into binary or multiple systems occurs only when material falls in several times more rapidly than the canonical isothermal limit. The disk-to-star accretion rate is proportional to the infall rate and governed by gravitational torques generated by low-m spiral modes. We also confirm the existence of a maximum stable disk mass: disks that exceed approx50% of the total system mass are subject to fragmentation and the subsequent formation of binary companions.

  16. Accurate Calculation of Hydration Free Energies using Pair-Specific Lennard-Jones Parameters in the CHARMM Drude Polarizable Force Field

    PubMed Central

    Baker, Christopher M.; Lopes, Pedro E. M.; Zhu, Xiao; Roux, Benoît; MacKerell, Alexander D.

    2010-01-01

    Lennard-Jones (LJ) parameters for a variety of model compounds have previously been optimized within the CHARMM Drude polarizable force field to reproduce accurately pure liquid phase thermodynamic properties as well as additional target data. While the polarizable force field resulting from this optimization procedure has been shown to satisfactorily reproduce a wide range of experimental reference data across numerous series of small molecules, a slight but systematic overestimate of the hydration free energies has also been noted. Here, the reproduction of experimental hydration free energies is greatly improved by the introduction of pair-specific LJ parameters between solute heavy atoms and water oxygen atoms that override the standard LJ parameters obtained from combining rules. The changes are small and a systematic protocol is developed for the optimization of pair-specific LJ parameters and applied to the development of pair-specific LJ parameters for alkanes, alcohols and ethers. The resulting parameters not only yield hydration free energies in good agreement with experimental values, but also provide a framework upon which other pair-specific LJ parameters can be added as new compounds are parametrized within the CHARMM Drude polarizable force field. Detailed analysis of the contributions to the hydration free energies reveals that the dispersion interaction is the main source of the systematic errors in the hydration free energies. This information suggests that the systematic error may result from problems with the LJ combining rules and is combined with analysis of the pair-specific LJ parameters obtained in this work to identify a preliminary improved combining rule. PMID:20401166

  17. The stellar populations of massive galaxies in the local Universe

    NASA Astrophysics Data System (ADS)

    McDermid, Richard M.

    2013-07-01

    I present a brief review of the stellar population properties of massive galaxies, focusing on early-type galaxies in particular, with emphasis on recent results from the ATLAS3D Survey. I discuss the occurence of young stellar ages, cold gas, and ongoing star formation in early-type galaxies, the presence of which gives important clues to the evolutionary path of these galaxies. Consideration of empirical star formation histories gives a meaningful picture of galaxy stellar population properties, and allows accurate comparison of mass estimates from populations and dynamics. This has recently provided strong evidence of a non-universal IMF, as supported by other recent evidences. Spatially-resolved studies of stellar populations are also crucial to connect distinct components within galaxies to spatial structures seen in other wavelengths or parameters. Stellar populations in the faint outer envelopes of early-type galaxies are a formidable frontier for observers, but promise to put constraints on the ratio of accreted stellar mass versus that formed `in situ' - a key feature of recent galaxy formation models. Galaxy environment appears to play a key role in controlling the stellar population properties of low mass galaxies. Simulations remind us, however, that current day galaxies are the product of a complex assembly and environment history, which gives rise to the trends we see. This has strong implications for our interpretation of environmental trends.

  18. Fundamental Parameters and Spectral Energy Distributions of Young and Field Age Objects with Masses Spanning the Stellar to Planetary Regime

    NASA Astrophysics Data System (ADS)

    Filippazzo, Joseph C.; Rice, Emily L.; Faherty, Jacqueline; Cruz, Kelle L.; Van Gordon, Mollie M.; Looper, Dagny L.

    2015-09-01

    We combine optical, near-infrared, and mid-infrared spectra and photometry to construct expanded spectral energy distributions for 145 field age (>500 Myr) and 53 young (lower age estimate <500 Myr) ultracool dwarfs (M6-T9). This range of spectral types includes very low mass stars, brown dwarfs, and planetary mass objects, providing fundamental parameters across both the hydrogen and deuterium burning minimum masses for the largest sample assembled to date. A subsample of 29 objects have well constrained ages as probable members of a nearby young moving group. We use 182 parallaxes and 16 kinematic distances to determine precise bolometric luminosities (Lbol) and radius estimates from evolutionary models give semi-empirical effective temperatures (Teff) for the full range of young and field age late-M, L, and T dwarfs. We construct age-sensitive relationships of luminosity, temperature, and absolute magnitude as functions of spectral type and absolute magnitude to disentangle the effects of degenerate physical parameters such as Teff, surface gravity, and clouds on spectral morphology. We report bolometric corrections in J for both field age and young objects and find differences of up to a magnitude for late-L dwarfs. Our correction in Ks shows a larger dispersion but not necessarily a different relationship for young and field age sequences. We also characterize the NIR-MIR reddening of low gravity L dwarfs and identify a systematically cooler Teff of up to 300 K from field age objects of the same spectral type and 400 K cooler from field age objects of the same MH magnitude.

  19. Model Atmospheres of Irradiated Exoplanets: The Influence of Stellar Parameters, Metallicity, and the C/O Ratio

    NASA Astrophysics Data System (ADS)

    Mollière, P.; van Boekel, R.; Dullemond, C.; Henning, Th.; Mordasini, C.

    2015-11-01

    Many parameters constraining the spectral appearance of exoplanets are still poorly understood. We therefore study the properties of irradiated exoplanet atmospheres over a wide parameter range including metallicity, C/O ratio, and host spectral type. We calculate a grid of 1D radiative-convective atmospheres and emission spectra. We perform the calculations with our new Pressure-Temperature Iterator and Spectral Emission Calculator for Planetary Atmospheres (PETIT) code, assuming chemical equilibrium. The atmospheric structures and spectra are made available online. We find that atmospheres of planets with C/O ratios ˜1 and {T}{{eff}} ≳ 1500 K can exhibit inversions due to heating by the alkalis because the main coolants CH4, H2O, and HCN are depleted. Therefore, temperature inversions possibly occur without the presence of additional absorbers like TiO and VO. At low temperatures we find that the pressure level of the photosphere strongly influences whether the atmospheric opacity is dominated by either water (for low C/O) or methane (for high C/O), or both (regardless of the C/O). For hot, carbon-rich objects this pressure level governs whether the atmosphere is dominated by methane or HCN. Further we find that host stars of late spectral type lead to planetary atmospheres which have shallower, more isothermal temperature profiles. In agreement with prior work we find that for planets with {T}{{eff}}\\lt 1750 K the transition between water or methane dominated spectra occurs at C/O ˜ 0.7, instead of ˜1, because condensation preferentially removes oxygen.

  20. Absolute Stellar Parameters of KIC 09246715: A Double-giant Eclipsing System with a Solar-like Oscillator

    NASA Astrophysics Data System (ADS)

    Hełminiak, K. G.; Ukita, N.; Kambe, E.; Konacki, M.

    2015-11-01

    We present our results of a combined analysis of radial velocity and light curves (LCs) of a double-lined spectroscopic and eclipsing binary KIC 09246715, observed photometrically by the Kepler satellite and spectroscopically with the OAO-1.88 m telescope with the HIgh-Dispersion Echelle Spectrograph. The target was claimed to be composed of two red giants, one of which is showing solar-like oscillations. We have found that the mass and radius of the primary are {M}1=2.169+/- 0.024 {M}⊙ and {R}1=8.47+/- 0.13 {R}⊙ , and of the secondary are {M}2=2.143+/- 0.025 {M}⊙ and {R}2=8.18+/- 0.09 {R}⊙ , which confirms their double-giant status. Our secondary is the star to which the oscillations were attributed. Results of its previous asteroseismic analysis are in agreement with ours, only significantly less precise, but the subsequent LC-based study failed to derive the correct mass and radius of our primary. KIC 09246715 is one of the rare cases where asteroseismic parameters of a solar-like oscillator were confirmed by an independent method and only the third example of a Galactic double-giant eclipsing binary with masses and radii measured with precision below 2%.

  1. DETERMINATION OF STELLAR RADII FROM ASTEROSEISMIC DATA

    SciTech Connect

    Basu, Sarbani; Chaplin, William J.; Elsworth, Yvonne E-mail: w.j.chaplin@bham.ac.u

    2010-02-20

    The NASA Kepler mission is designed to find planets through transits. Accurate and precise radii of the detected planets depend on knowing the radius of the host star accurately, which is difficult unless the temperature and luminosity of the star are known precisely. Kepler, however, has an asteroseismology program that will provide seismic variables that can characterize stellar radii easily, accurately, and extremely precisely. In this paper, we describe the Yale-Birmingham (YB) method to determine stellar radii using a combination of seismic and conventional variables and analyze the effect of these variables on the result. We find that for main-sequence stars, a knowledge of the parallax is not important to get accurate radii using the YB method: we can get results to an accuracy and precision of better than a few percent if we know the effective temperature and the seismic parameters for these stars. Metallicity does not make much difference either. However, good estimates of the effective temperature and metallicity, along with those of the seismic parameters, are essential to determine radii of subgiants properly. On the other hand, for red giants we find that determining radii properly is not possible without a good estimate of the parallax. We find that the so-called 'surface term' in the seismic data has minimal effect on the inferred radii. Uncertainties in the convective mixing length can matter under some circumstances and can cause a systematic shift in the inferred radii. Blind tests with data simulated to match those expected from the asteroseismic survey phase of Kepler show that it will be possible to infer stellar radii successfully using our method.

  2. 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.

  3. 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.

  4. 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

  5. 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.

  6. Measuring the stellar wind parameters in IGR J17544-2619 and Vela X-1 constrains the accretion physics in supergiant fast X-ray transient and classical supergiant X-ray binaries

    NASA Astrophysics Data System (ADS)

    Giménez-García, A.; Shenar, T.; Torrejón, J. M.; Oskinova, L.; Martínez-Núñez, S.; Hamann, W.-R.; Rodes-Roca, J. J.; González-Galán, A.; Alonso-Santiago, J.; González-Fernández, C.; Bernabeu, G.; Sander, A.

    2016-06-01

    Context. Classical supergiant X-ray binaries (SGXBs) and supergiant fast X-ray transients (SFXTs) are two types of high-mass X-ray binaries (HMXBs) that present similar donors but, at the same time, show very different behavior in the X-rays. The reason for this dichotomy of wind-fed HMXBs is still a matter of debate. Among the several explanations that have been proposed, some of them invoke specific stellar wind properties of the donor stars. Only dedicated empiric analysis of the donors' stellar wind can provide the required information to accomplish an adequate test of these theories. However, such analyses are scarce. Aims: To close this gap, we perform a comparative analysis of the optical companion in two important systems: IGR J17544-2619 (SFXT) and Vela X-1 (SGXB). We analyze the spectra of each star in detail and derive their stellar and wind properties. As a next step, we compare the wind parameters, giving us an excellent chance of recognizing key differences between donor winds in SFXTs and SGXBs. Methods: We use archival infrared, optical and ultraviolet observations, and analyze them with the non-local thermodynamic equilibrium (NLTE) Potsdam Wolf-Rayet model atmosphere code. We derive the physical properties of the stars and their stellar winds, accounting for the influence of X-rays on the stellar winds. Results: We find that the stellar parameters derived from the analysis generally agree well with the spectral types of the two donors: O9I (IGR J17544-2619) and B0.5Iae (Vela X-1). The distance to the sources have been revised and also agree well with the estimations already available in the literature. In IGR J17544-2619 we are able to narrow the uncertainty to d = 3.0 ± 0.2 kpc. From the stellar radius of the donor and its X-ray behavior, the eccentricity of IGR J17544-2619 is constrained to e< 0.25. The derived chemical abundances point to certain mixing during the lifetime of the donors. An important difference between the stellar winds of the

  7. On the utility of spectroscopic imaging as a tool for generating geometrically accurate MR images and parameter maps in the presence of field inhomogeneities and chemical shift effects.

    PubMed

    Bakker, Chris J G; de Leeuw, Hendrik; van de Maat, Gerrit H; van Gorp, Jetse S; Bouwman, Job G; Seevinck, Peter R

    2013-01-01

    Lack of spatial accuracy is a recognized problem in magnetic resonance imaging (MRI) which severely detracts from its value as a stand-alone modality for applications that put high demands on geometric fidelity, such as radiotherapy treatment planning and stereotactic neurosurgery. In this paper, we illustrate the potential and discuss the limitations of spectroscopic imaging as a tool for generating purely phase-encoded MR images and parameter maps that preserve the geometry of an object and allow localization of object features in world coordinates. Experiments were done on a clinical system with standard facilities for imaging and spectroscopy. Images were acquired with a regular spin echo sequence and a corresponding spectroscopic imaging sequence. In the latter, successive samples of the acquired echo were used for the reconstruction of a series of evenly spaced images in the time and frequency domain. Experiments were done with a spatial linearity phantom and a series of test objects representing a wide range of susceptibility- and chemical-shift-induced off-resonance conditions. In contrast to regular spin echo imaging, spectroscopic imaging was shown to be immune to off-resonance effects, such as those caused by field inhomogeneity, susceptibility, chemical shift, f(0) offset and field drift, and to yield geometrically accurate images and parameter maps that allowed object structures to be localized in world coordinates. From these illustrative examples and a discussion of the limitations of purely phase-encoded imaging techniques, it is concluded that spectroscopic imaging offers a fundamental solution to the geometric deficiencies of MRI which may evolve toward a practical solution when full advantage will be taken of current developments with regard to scan time reduction. This perspective is backed up by a demonstration of the significant scan time reduction that may be achieved by the use of compressed sensing for a simple phantom. PMID:22898694

  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. Rotation–Activity Correlations in K and M Dwarfs. I. Stellar Parameters and Compilations of v sin i and P/sin i for a Large Sample of Late-K and M Dwarfs

    NASA Astrophysics Data System (ADS)

    Houdebine, E. R.; Mullan, D. J.; Paletou, F.; Gebran, M.

    2016-05-01

    The reliable determination of rotation–activity correlations (RACs) depends on precise measurements of the following stellar parameters: T eff, parallax, radius, metallicity, and rotational speed v sin i. In this paper, our goal is to focus on the determination of these parameters for a sample of K and M dwarfs. In a future paper (Paper II), we will combine our rotational data with activity data in order to construct RACs. Here, we report on a determination of effective temperatures based on the (R–I) C color from the calibrations of Mann et al. and Kenyon & Hartmann for four samples of late-K, dM2, dM3, and dM4 stars. We also determine stellar parameters (T eff, log(g), and [M/H]) using the principal component analysis–based inversion technique for a sample of 105 late-K dwarfs. We compile all effective temperatures from the literature for this sample. We determine empirical radius–[M/H] correlations in our stellar samples. This allows us to propose new effective temperatures, stellar radii, and metallicities for a large sample of 612 late-K and M dwarfs. Our mean radii agree well with those of Boyajian et al. We analyze HARPS and SOPHIE spectra of 105 late-K dwarfs, and we have detected v sin i in 92 stars. In combination with our previous v sin i measurements in M and K dwarfs, we now derive P/sin i measures for a sample of 418 K and M dwarfs. We investigate the distributions of P/sin i, and we show that they are different from one spectral subtype to another at a 99.9% confidence level. Based on observations available at Observatoire de Haute Provence and the European Southern Observatory databases and on Hipparcos parallax measurements.

  10. 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.

  11. Observational Constraints on Stellar Flares and Prominences

    NASA Astrophysics Data System (ADS)

    Aarnio, Alicia

    2016-07-01

    Multi-wavelength surveys have catalogued a wealth of stellar flare data for stars representing a broad range of masses and ages. Young solar analogs inform our understanding of the Sun's evolution and the influence of its activity on early solar system formation, while field star observations allow us to place its current activity into context within a statistical ensemble of main-sequence G-type stars. At the same time, stellar observations probe a variety of interior and coronal conditions, providing constraints on models of equilibrium (and loss thereof!) for magnetic structures. In this review, I will focus on our current understanding of stellar flares, prominences, and coronal mass ejections as a function of stellar parameters. As our interpretation of stellar data relies heavily on solar-stellar analogy, I will explore how far into extreme stellar parameter spaces this comparison can be invoked.

  12. Calibration of DFT Functionals for the Prediction of 57Fe Mössbauer Spectral Parameters in Iron-Nitrosyl and Iron-Sulfur Complexes: Accurate Geometries Prove Essential

    PubMed Central

    Sandala, Gregory M.; Hopmann, Kathrin H.; Ghosh, Abhik

    2011-01-01

    structure. Significant improvements to the isomer shift calibrations are obtained for B3LYP and B3LYP* when geometries obtained with the OLYP functional are used. In addition, greatly improved performance of these functionals is found if the complete test set is grouped separately into Fe–NO and Fe–S complexes. Calibration fits including only Fe–NO complexes are found to be excellent, while those containing the non-nitrosyl Fe–S complexes alone are found to demonstrate less accurate correlations. Similar trends are also found with OLYP, OPBE, PW91, and BP86. Correlations between experimental and calculated QSs were also investigated. Generally, universal and separate Fe–NO and Fe–S fit parameters obtained to determine QSs are found to be of good to excellent quality for every density functional examined, especially if [Fe4(NO)4(μ3-S)4]− is removed from the test set. PMID:22039359

  13. Systematic Non-LTE Study of the -2.6 < [Fe/H] < 0.2 F and G dwarfs in the Solar Neighborhood. I. Stellar Atmosphere Parameters

    NASA Astrophysics Data System (ADS)

    Sitnova, T.; Zhao, G.; Mashonkina, L.; Chen, Y.; Liu, F.; Pakhomov, Yu.; Tan, K.; Bolte, M.; Alexeeva, S.; Grupp, F.; Shi, J.-R.; Zhang, H.-W.

    2015-08-01

    We present atmospheric parameters for 51 nearby F and G dwarf and subgiant stars uniformly distributed over the -2.60< [{Fe}/{{H}}]< +0.20 metallicity range that is suitable for the Galactic chemical evolution research. Lines of iron in the two ionization stages, Fe I and Fe II, were used to derive a homogeneous set of effective temperatures, surface gravities, iron abundances, and microturbulence velocities. Our spectroscopic analyses took advantage of employing high-resolution (R ≥ 60,000) Shane/Hamilton and Canada-France-Hawaii Telescope/ESPaDOnS observed spectra and non-LTE (NLTE) line formation for Fe I and Fe II in the classical one-dimensional model atmospheres. The spectroscopic method was tested in advance with the 20 benchmark stars, for which there are multiple measurements of the infrared flux method effective temperature and their Hipparcos parallax error is less than 10%. We found NLTE abundances from lines of Fe I and Fe II to be consistent within 0.06 dex for every benchmark star, when applying a scaling factor of {S}{{H}} = 0.5 to the Drawinian rates of inelastic Fe+H collisions. The obtained atmospheric parameters were checked for each program star by comparing its position in the log g-{T}{eff} plane with the theoretical evolutionary track of given metallicity and α-enhancement in the Yi et al. grid. Our final effective temperatures lie exactly in between the {T}{IRFM} scales of Alonso et al. and Casagrande et al., with a mean difference of +46 and -51 K, respectively. NLTE leads to higher surface gravity compared with that for LTE. The shift in log g is smaller than 0.1 dex for stars with [Fe/H] ≥slant -0.75, {T}{eff} ≤ 5750 K, or log g ≥ 4.20. NLTE analysis is crucial for the very metal-poor turnoff and subgiant stars, for which the shift in log g between NLTE and LTE can be up to 0.5 dex. The obtained accurate atmospheric parameters will be used in the forthcoming papers to determine NLTE abundances of important astrophysical elements

  14. Research of autonomous celestial navigation based on new measurement model of stellar refraction

    NASA Astrophysics Data System (ADS)

    Yu, Cong; Tian, Hong; Zhang, Hui; Xu, Bo

    2014-09-01

    Autonomous celestial navigation based on stellar refraction has attracted widespread attention for its high accuracy and full autonomy.In this navigation method, establishment of accurate stellar refraction measurement model is the fundament and key issue to achieve high accuracy navigation. However, the existing measurement models are limited due to the uncertainty of atmospheric parameters. Temperature, pressure and other factors which affect the stellar refraction within the height of earth's stratosphere are researched, and the varying model of atmosphere with altitude is derived on the basis of standard atmospheric data. Furthermore, a novel measurement model of stellar refraction in a continuous range of altitudes from 20 km to 50 km is produced by modifying the fixed altitude (25 km) measurement model, and equation of state with the orbit perturbations is established, then a simulation is performed using the improved Extended Kalman Filter. The results show that the new model improves the navigation accuracy, which has a certain practical application value.

  15. [A Method to Estimate Metal Abundance from Stellar Spectra Using Ca Line Index].

    PubMed

    Pan, Jing-chang; Luo, A-li; Li, Xiang-ru; Wei, Peng

    2015-09-01

    This paper presents a method to estimate stellar metallicity based on BP neural network and Ca line index. This method trains a BP ANN model from SDSS/SEGUE stellar spectra and parameters provided by SSPP. The values of Teff and the line index of Ca lines are the input of network while the [Fe/H] values are the oputput of the network. A set of samples are resampled from the set of all and then a network model is trained. The network can be used to predict the stellar metallicity from low-resolution spsectra. The experiment shows that the proposed method can accurately and effectively measure the [Fe/H] from the stellar spectra. PMID:26669184

  16. 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.

  17. PREFACE: Stellar Atmospheres in the Gaia Era - Preface

    NASA Astrophysics Data System (ADS)

    Lobel, Alex; De Greve, Jean-Pierre; Van Rensbergen, Walter

    2011-12-01

    Volume 328 (2011) of the Journal of Physics: Conference Series provides a record of the invited and contributed talks, and of the posters presented at the GREAT-ESF workshop entitled `Stellar Atmospheres in the Gaia Era: Quantitative Spectroscopy and Comparative Spectrum Modelling' (http://great-esf.oma.be and mirrored at http://spectri.freeshell.org/great-esf). The conference was held on 23-24 June 2011 at the Vrije Universiteit Brussel, Belgium. 47 scientists from 11 countries around the world attended the workshop. The ESA-Gaia satellite (launch mid 2013) will observe a billion stellar objects in the Galaxy and provide spectrophotometric and high-resolution spectra of an unprecedented number of stars observed with a space-based instrument. The confrontation of these data with theoretical models will significantly advance our understanding of the physics of stellar atmospheres. New stellar populations such as previously unknown emission line stars will be discovered, and fundamental questions such as the basic scenarios of stellar evolution will be addressed with Gaia data. The 33 presentations and 4 main discussion sessions at the workshop addressed important topics in spectrum synthesis methods and detailed line profile calculations urgently needed for accurate modelling of stellar spectra. It brought together leading scientists and students of the stellar physics communities investigating hot and cool star spectra. The scientific programme of the workshop consisted of 23 oral (6 invited) and 10 poster presentations about cool stars (first day; Comparative Spectrum Modelling and Quantitative Spectroscopy of Cool Stars), and hot stars (second day; Quantitative Spectroscopy of Hot Stars). The hot and cool stars communities use different spectrum modelling codes for determining basic parameters such as the effective temperature, surface gravity, iron abundance, and the chemical composition of stellar atmospheres. The chaired sessions of the first day highlighted

  18. Construct a new method accurately extracting parameters associate with absorption and scattering coefficients of epithelium and stroma: using perpendicular and oblique fiber bundle probes

    NASA Astrophysics Data System (ADS)

    Hsieh, H. P.; Sung, K. B.; Hsu, F. W.

    2014-05-01

    Diffuse reflectance spectroscopy has been applied as a non-invasive method to measure tissue optical properties, which are associate with anatomical information. The algorithm widely used to extract, optical parameters from reflectance spectra is the regression method, which is time-consuming and frequently converge to local maxima. In this study, the effects of parameters changes on spectra are analyzed in different fiber geometries, source-detector separations and wavelengths. In the end of this paper, a new fitting algorithm is proposed base on parameters features found. The new algorithm is expected to enhance the accuracy of parameters extracted and save 75% of the process time.

  19. Results of Compact Stellarator Eengineering Trade Studies

    SciTech Connect

    T. Brown, L. Bromberg, and M. Cole

    2009-09-25

    A number of technical requirements and performance criteria can drive stellarator costs, e.g., tight tolerances, accurate coil positioning, low aspect ratio (compactness), choice of assembly strategy, metrology, and complexity of the stellarator coil geometry. With the completion of a seven-year design and construction effort of the National Compact Stellarator Experiment (NCSX) it is useful to interject the NCSX experience along with the collective experiences of the NCSX stellarator community to improving the stellarator configuration. Can improvements in maintenance be achieved by altering the stellarator magnet configuration with changes in the coil shape or with the combination of trim coils? Can a mechanical configuration be identified that incorporates a partial set of shaped fixed stellarator coils along with some removable coil set to enhance the overall machine maintenance? Are there other approaches that will simplify the concepts, improve access for maintenance, reduce overall cost and improve the reliability of a stellarator based power plant? Using ARIES-CS and NCSX as reference cases, alternative approaches have been studied and developed to show how these modifications would favorably impact the stellarator power plant and experimental projects. The current status of the alternate stellarator configurations being developed will be described and a comparison made to the recently designed and partially built NCSX device and the ARIES-CS reactor design study.

  20. Results of Compact Stellarator Engineering Trade Studies

    SciTech Connect

    Tom Brown, L. Bromberg, M. Cole

    2009-05-27

    number of technical requirements and performance criteria can drive stellarator costs, e.g., tight tolerances, accurate coil positioning, low aspect ratio (compactness), choice of assembly strategy, metrology, and complexity of the stellarator coil geometry. With the completion of a seven-year design and construction effort of the National Compact Stellarator Experiment (NCSX) it is useful to interject the NCSX experience along with the collective experiences of the NCSX stellarator community to improving the stellarator configuration. Can improvements in maintenance be achieved by altering the stellarator magnet configuration with changes in the coil shape or with the combination of trim coils? Can a mechanical configuration be identified that incorporates a partial set of shaped fixed stellarator coils along with some removable coil set to enhance the overall machine maintenance? Are there other approaches that will simplify the concepts, improve access for maintenance, reduce overall cost and improve the reliability of a stellarator based power plant? Using ARIES-CS and NCSX as reference cases, alternative approaches have been studied and developed to show how these modifications would favorably impact the stellarator power plant and experimental projects. The current status of the alternate stellarator configurations being developed will be described and a comparison made to the recently designed and partially built NCSX device and the ARIES-CS reactor design study.

  1. 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)

  2. 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.

  3. Exploring Stellar Populations and Asteroseismology with APOGEE and Kepler

    NASA Astrophysics Data System (ADS)

    Epstein, Courtney R.; Elsworth, Y. P.; Shetrone, M. D.; Mosser, B.; Tayar, J.; Harding, P.; Pinsonneault, M. H.; Silva Aguirre, V.; Basu, S.; Bizyaev, D.; Bedding, T.; Chaplin, W. J.; Garcia, R.; Garcia Perez, A.; Hearty, F.; Hekker, S.; Huber, D.; Ivans, I. I.; Majewski, S.; Mathur, S.; Serenelli, A.; Schiavon, R. P.; Schoenrich, R.; Sobeck, J.; Zasowski, G.

    2014-01-01

    Accurate measurements of fundamental stellar properties are vital for improving our understanding of stellar populations and galactic evolution. Asteroseismology makes possible precise measurements of stellar mass, radius, and surface gravity. Combining these asteroseismic measurements with spectroscopic temperatures and abundances enables the derivation of precise ages for field stars. To achieve that goal, two complementary surveys, the Apache Point Observatory Galactic Evolution Experiment (APOGEE) and the Kepler Asteroseismic Science Consortium (KASC), are working together to characterize the fundamental properties thousands of red giants in the Kepler field. As a first step toward deriving ages, asteroseismic masses need to be calibrated with independent mass constraints. I will describe how we use a sample of halo stars to test asteroseismic results in the metal-poor regime. The age of halo stars is well constrained by many lines of evidence, including isochrones fits to globular clusters, white dwarf cooling sequence, and the radioactive decay of uranium and thorium. These age constraints translate to a strict prior on halo star masses. I show that the seismic masses are sensitive to the method used to derive seismic parameters and to published, theoretically motivated corrections. The implications of this work for stellar populations are discussed.

  4. PREFACE: A Stellar Journey A Stellar Journey

    NASA Astrophysics Data System (ADS)

    Asplund, M.

    2008-10-01

    astronomical talk, student lecture, musical concert or theatre play. Another attribute of Bengt is his boundless optimism, which not the least has helped many of his students overcome the unavoidable moments of despair (this is only true as long as one is aware of the well-known BG factor: multiply any of Bengt's estimates for the time required to complete a task by at least a factor of three). His personal traits make working with Bengt always very enjoyable as well as highly educating. Bengt's work also extends well beyond the domain of astronomy, including music, literature, theatre, religion, research ethics, science policy and science popularization. Bengt is an excellent role model for a successful scientist with a rich and rewarding life outside of academia. The symposium A Stellar Journey was divided into five sessions covering basically the main research areas Bengt has worked on: Stellar atmospheres, Solar/stellar spectroscopy, Stellar parameters, Stellar evolution and nucleosynthesis and Stellar populations. In addition, one afternoon was devoted to a session entitled Anything but astronomy (see the symposium program), which tried to showcase Bengt's diverse interests outside of astronomy with talks ranging from religion and history of science over science popularization and future studies to literature and music. My task, as chair of the Scientific Organizing Committee, to put together an exciting scientific program of invited reviews and talks was made considerably easier thanks to the excellent suggestions by the other SOC members: Ann Boesgaard, Sofia Feltzing, John Lattanzio, Andre Maeder, Bertrand Plez and Monique Spite. I believe in the end we were successful in achieving our charge, an impression corroborated by the many encouraging comments from various participants during and after the conference. I am particularly grateful to Nils Bergvall, Bengt Edvardsson and Bertrand Plez for their time-consuming efforts in arranging the extraordinary and greatly

  5. PROBABILISTIC CATALOGS FOR CROWDED STELLAR FIELDS

    SciTech Connect

    Brewer, Brendon J.; Foreman-Mackey, Daniel; Hogg, David W.

    2013-07-01

    We present and implement a probabilistic (Bayesian) method for producing catalogs from images of stellar fields. The method is capable of inferring the number of sources N in the image and can also handle the challenges introduced by noise, overlapping sources, and an unknown point-spread function. The luminosity function of the stars can also be inferred, even when the precise luminosity of each star is uncertain, via the use of a hierarchical Bayesian model. The computational feasibility of the method is demonstrated on two simulated images with different numbers of stars. We find that our method successfully recovers the input parameter values along with principled uncertainties even when the field is crowded. We also compare our results with those obtained from the SExtractor software. While the two approaches largely agree about the fluxes of the bright stars, the Bayesian approach provides more accurate inferences about the faint stars and the number of stars, particularly in the crowded case.

  6. Probabilistic Catalogs for Crowded Stellar Fields

    NASA Astrophysics Data System (ADS)

    Brewer, Brendon J.; Foreman-Mackey, Daniel; Hogg, David W.

    2013-07-01

    We present and implement a probabilistic (Bayesian) method for producing catalogs from images of stellar fields. The method is capable of inferring the number of sources N in the image and can also handle the challenges introduced by noise, overlapping sources, and an unknown point-spread function. The luminosity function of the stars can also be inferred, even when the precise luminosity of each star is uncertain, via the use of a hierarchical Bayesian model. The computational feasibility of the method is demonstrated on two simulated images with different numbers of stars. We find that our method successfully recovers the input parameter values along with principled uncertainties even when the field is crowded. We also compare our results with those obtained from the SExtractor software. While the two approaches largely agree about the fluxes of the bright stars, the Bayesian approach provides more accurate inferences about the faint stars and the number of stars, particularly in the crowded case.

  7. 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.

  8. GJ 1214 reviewed. Trigonometric parallax, stellar parameters, new orbital solution, and bulk properties for the super-Earth GJ 1214b

    NASA Astrophysics Data System (ADS)

    Anglada-Escudé, G.; Rojas-Ayala, B.; Boss, A. P.; Weinberger, A. J.; Lloyd, J. P.

    2013-03-01

    Context. GJ 1214 is orbited by a transiting super-Earth-mass planet. It is a primary target for ongoing efforts to understand the emerging population of super-Earth-mass planets around M dwarfs, some of which are detected within the liquid water (habitable) zone of their host stars. Aims: We present new precision astrometric measurements, a re-analysis of HARPS radial velocity measurements, and new medium-resolution infrared spectroscopy of GJ 1214. We combine these measurements with recent transit follow-up observations and new catalog photometry to provide a comprehensive update of the star-planet properties. Methods: The distance is obtained with 0.6% relative uncertainty using CAPScam astrometry. The new value increases the nominal distance to the star by ~10% and is significantly more precise than previous measurements. Improved radial velocity measurements have been obtained analyzing public HARPS spectra of GJ 1214 using the HARPS-TERRA software and are 25% more precise than the original ones. The Doppler measurements combined with recently published transit observations significantly refine the constraints on the orbital solution, especially on the planet's eccentricity. The analysis of the infrared spectrum and photometry confirm that the star is enriched in metals compared to the Sun. Results: Using all this new fundamental information, combined with empirical mass-luminosity relations for low mass stars, we derive updated values for the bulk properties of the star-planet system. We also use infrared absolute fluxes to estimate the stellar radius and to re-derive the star-planet properties. Both approaches provide very consistent values for the system. Our analysis shows that the updated expected value for the planet mean density is 1.6 ± 0.6 g cm-3, and that a density comparable to the Earth (~5.5 g cm-3) is now ruled out with very high confidence. Conclusions: This study illustrates how the fundamental properties of M dwarfs are of paramount importance

  9. Stark broadening data for stellar plasma research.

    NASA Astrophysics Data System (ADS)

    Dimitrijević, M. S.

    Results of an effort to provide to astrophysicists and physicists an as much as possible complete set of Stark broadening parameters needed for stellar opacity calculations, stellar atmosphere modelling, abundance determinations and diagnostics of different plasmas in astrophysics, physics and plasma technology, are presented. Stark broadening has been considered within the semiclassical perturbation, and the modified semiempirical approaches.

  10. Testing the accuracy of synthetic stellar libraries

    NASA Astrophysics Data System (ADS)

    Martins, Lucimara P.; Coelho, Paula

    2007-11-01

    One of the main ingredients of stellar population synthesis models is a library of stellar spectra. Both empirical and theoretical libraries are used for this purpose, and the question about which one is preferable is still debated in the literature. Empirical and theoretical libraries are being improved significantly over the years, and many libraries have become available lately. However, it is not clear in the literature what are the advantages of using each of these new libraries, and how far behind models are compared to observations. Here we compare in detail some of the major theoretical libraries available in the literature with observations, aiming at detecting weaknesses and strengths from the stellar population modelling point of view. Our test is twofold: we compared model predictions and observations for broad-band colours and for high-resolution spectral features. Concerning the broad-band colours, we measured the stellar colour given by three recent sets of model atmospheres and flux distributions, and compared them with a recent UBVRIJHK calibration which is mostly based on empirical data. We found that the models can reproduce with reasonable accuracy the stellar colours for a fair interval in effective temperatures and gravities. The exceptions are (1) the U - B colour, where the models are typically redder than the observations, and (2) the very cool stars in general (V - K >~ 3). Castelli & Kurucz is the set of models that best reproduce the bluest colours (U - B, B - V) while Gustafsson et al. and Brott & Hauschildt more accurately predict the visual colours. The three sets of models perform in a similar way for the infrared colours. Concerning the high-resolution spectral features, we measured 35 spectral indices defined in the literature on three high-resolution synthetic libraries, and compared them with the observed measurements given by three empirical libraries. The measured indices cover the wavelength range from ~3500 to ~8700Å. We

  11. MODELING MULTI-WAVELENGTH STELLAR ASTROMETRY. II. DETERMINING ABSOLUTE INCLINATIONS, GRAVITY-DARKENING COEFFICIENTS, AND SPOT PARAMETERS OF SINGLE STARS WITH SIM LITE

    SciTech Connect

    Coughlin, Jeffrey L.; Harrison, Thomas E.; Gelino, Dawn M.

    2010-11-10

    We present a novel technique to determine the absolute inclination of single stars using multi-wavelength submilliarcsecond astrometry. The technique exploits the effect of gravity darkening, which causes a wavelength-dependent astrometric displacement parallel to a star's projected rotation axis. We find that this effect is clearly detectable using SIM Lite for various giant stars and rapid rotators, and present detailed models for multiple systems using the REFLUX code. We also explore the multi-wavelength astrometric reflex motion induced by spots on single stars. We find that it should be possible to determine spot size, relative temperature, and some positional information for both giant and nearby main-sequence stars utilizing multi-wavelength SIM Lite data. These data will be extremely useful in stellar and exoplanet astrophysics, as well as supporting the primary SIM Lite mission through proper multi-wavelength calibration of the giant star astrometric reference frame, and reduction of noise introduced by starspots when searching for extrasolar planets.

  12. Empirical calibrations of optical absorption-line indices based on the stellar library MILES

    NASA Astrophysics Data System (ADS)

    Johansson, Jonas; Thomas, Daniel; Maraston, Claudia

    2010-07-01

    Stellar population models of absorption-line indices are an important tool for the analysis of stellar population spectra. They are most accurately modelled through empirical calibrations of absorption-line indices with the stellar parameters such as effective temperature, metallicity and surface gravity, which are the so-called fitting functions. Here we present new empirical fitting functions for the 25 optical Lick absorption-line indices based on the new stellar library Medium resolution INT Library of Empirical Spectra (MILES). The major improvements with respect to the Lick/IDS library are the better sampling of stellar parameter space, a generally higher signal-to-noise ratio and a careful flux calibration. In fact, we find that errors on individual index measurements in MILES are considerably smaller than in Lick/IDS. Instead, we find the rms of the residuals between the final fitting functions and the data to be dominated by errors in the stellar parameters. We provide fitting functions for both Lick/IDS and MILES spectral resolutions and compare our results with other fitting functions in the literature. A FORTRAN 90 code is available online in order to simplify the implementation in stellar population models. We further calculate the offsets in index measurements between the Lick/IDS system to a flux-calibrated system. For this purpose, we use the three libraries MILES, ELODIE and STELIB. We find that offsets are negligible in some cases, most notably for the widely used indices Hβ, Mgb, Fe5270 and Fe5335. In a number of cases, however, the difference between the flux-calibrated library and Lick/IDS is significant with the offsets depending on index strengths. Interestingly, there is no general agreement between the three libraries for a large number of indices, which hampers the derivation of a universal offset between the Lick/IDS and flux-calibrated systems.

  13. Chaotic pulsations in stellar models

    SciTech Connect

    Buchler, J.R. )

    1990-12-01

    The irregular behavior of large-amplitude pulsating stars undergoing radial oscillations is examined theoretically, with a focus on hydrodynamic simulations of the W Virginis population II Cepheids (stars which show both regular and RV Tau characteristics). Sequences of models are constructed as one-parameter families (with luminosity, mass, and composition fixed and Teff as the control parameter) and analyzed to derive a systematic map of the bifurcation set; i.e., of the possible types of pulsations. The results are presented graphically, and it is shown that both cascades of period doubling (via destabilization of an overtone through a half-integer-type resonance) and tangent bifurcation are possible routes to chaos in these systems, depending on the stellar parameters. The general robustness of the chaotic behavior and the existence of a 'chaotic blue edge' in stellar-parameter space are demonstrated. 55 refs.

  14. 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

  15. Accurate calculations on 12 Λ-S and 28 Ω states of BN+ cation: potential energy curves, spectroscopic parameters and spin-orbit coupling.

    PubMed

    Shi, Deheng; Liu, Qionglan; Sun, Jinfeng; Zhu, Zunlue

    2014-03-25

    The potential energy curves (PECs) of 28 Ω states generated from the 12 states (X(4)Σ(-), 1(2)Π, 1(2)Σ(-), 1(2)Δ, 1(2)Σ(+), 2(2)Π, A(4)Π, B(4)Σ(-), 3(2)Π, 1(6)Σ(-), 2(2)Σ(-) and 1(6)Π) of the BN(+) cation are studied for the first time for internuclear separations from about 0.1 to 1.0 nm using an ab initio quantum chemical method. All the Λ-S states correlate to the first four dissociation channels. The 1(6)Σ(-), 3(2)Π and A(4)Π states are found to be the inverted ones. The 1(2)Σ(+), 2(2)Π, 3(2)Π and 2(2)Σ(-) states are found to possess the double well. The PECs are calculated by the complete active space self-consistent field method, which is followed by the internally contracted multireference configuration interaction approach with the Davidson correction. Core-valence correlation correction is included by a cc-pCV5Z basis set. Scalar relativistic correction is calculated by the third-order Douglas-Kroll Hamiltonian approximation at the level of a cc-pV5Z basis set. The convergent behavior of present calculations is discussed with respect to the basis set and level of theory. The spin-orbit coupling is accounted for by the state interaction approach with the Breit-Pauli Hamiltonian using the all-electron cc-pCV5Z basis set. All the PECs are extrapolated to the complete basis set limit. The spectroscopic parameters are obtained, and the vibrational properties of 1(2)Σ(+), 2(2)Π, 3(2)Π and 2(2)Σ(-) states are evaluated. Analyses demonstrate that the spectroscopic parameters reported here can be expected to be reliably predicted ones. The conclusion is gained that the effect of spin-orbit coupling on the spectroscopic parameters are not obvious almost for all the Λ-S states involved in the present paper. PMID:24334021

  16. Accurate calculations on 9 Λ-S and 28 Ω states of NSe radical in the gas phase: potential energy curves, spectroscopic parameters and spin-orbit couplings.

    PubMed

    Shi, Deheng; Li, Peiling; Sun, Jinfeng; Zhu, Zunlue

    2014-01-01

    The potential energy curves (PECs) of 28 Ω states generated from 9 Λ-S states (X(2)Π, 1(4)Π, 1(6)Π, 1(2)Σ(+), 1(4)Σ(+), 1(6)Σ(+), 1(4)Σ(-), 2(4)Π and 1(4)Δ) are studied for the first time using an ab initio quantum chemical method. All the 9 Λ-S states correlate to the first two dissociation limits, N((4)Su)+Se((3)Pg) and N((4)Su)+Se((3)Dg), of NSe radical. Of these Λ-S states, the 1(6)Σ(+), 1(4)Σ(+), 1(6)Π, 2(4)Π and 1(4)Δ are found to be rather weakly bound states. The 1(2)Σ(+) is found to be unstable and has double wells. And the 1(6)Σ(+), 1(4)Σ(+), 1(4)Π and 1(6)Π are found to be the inverted ones with the SO coupling included. The PEC calculations are made by the complete active space self-consistent field method, which is followed by the internally contracted multireference configuration interaction approach with the Davidson modification. The spin-orbit coupling is accounted for by the state interaction approach with the Breit-Pauli Hamiltonian. The convergence of the present calculations is discussed with respect to the basis set and the level of theory. Core-valence correlation corrections are included with a cc-pCVTZ basis set. Scalar relativistic corrections are calculated by the third-order Douglas-Kroll Hamiltonian approximation at the level of a cc-pV5Z basis set. All the PECs are extrapolated to the complete basis set limit. The variation with internuclear separation of spin-orbit coupling constants is discussed in brief for some Λ-S states with one shallow well on each PEC. The spectroscopic parameters of 9 Λ-S and 28 Ω states are determined by fitting the first ten vibrational levels whenever available, which are calculated by solving the rovibrational Schrödinger equation with Numerov's method. The splitting energy in the X(2)Π Λ-S state is determined to be about 864.92 cm(-1), which agrees favorably with the measurements of 891.80 cm(-1). Moreover, other spectroscopic parameters of Λ-S and Ω states involved here are

  17. PRINCIPAL COMPONENT ANALYSIS OF SLOAN DIGITAL SKY SURVEY STELLAR SPECTRA

    SciTech Connect

    McGurk, Rosalie C.; Kimball, Amy E.; Ivezic, Zeljko

    2010-03-15

    We apply Principal Component Analysis (PCA) to {approx}100,000 stellar spectra obtained by the Sloan Digital Sky Survey (SDSS). In order to avoid strong nonlinear variation of spectra with effective temperature, the sample is binned into 0.02 mag wide intervals of the g - r color (-0.20 < g - r < 0.90, roughly corresponding to MK spectral types A3-K3), and PCA is applied independently for each bin. In each color bin, the first four eigenspectra are sufficient to describe the observed spectra within the measurement noise. We discuss correlations of eigencoefficients with metallicity and gravity estimated by the Sloan Extension for Galactic Understanding and Exploration Stellar Parameters Pipeline. The resulting high signal-to-noise mean spectra and the other three eigenspectra are made publicly available. These data can be used to generate high-quality spectra for an arbitrary combination of effective temperature, metallicity, and gravity within the parameter space probed by the SDSS. The SDSS stellar spectroscopic database and the PCA results presented here offer a convenient method to classify new spectra, to search for unusual spectra, to train various spectral classification methods, and to synthesize accurate colors in arbitrary optical bandpasses.

  18. Is scoring system of computed tomography based metric parameters can accurately predicts shock wave lithotripsy stone-free rates and aid in the development of treatment strategies?

    PubMed Central

    Badran, Yasser Ali; Abdelaziz, Alsayed Saad; Shehab, Mohamed Ahmed; Mohamed, Hazem Abdelsabour Dief; Emara, Absel-Aziz Ali; Elnabtity, Ali Mohamed Ali; Ghanem, Maged Mohammed; ELHelaly, Hesham Abdel Azim

    2016-01-01

    Objective: The objective was to determine the predicting success of shock wave lithotripsy (SWL) using a combination of computed tomography based metric parameters to improve the treatment plan. Patients and Methods: Consecutive 180 patients with symptomatic upper urinary tract calculi 20 mm or less were enrolled in our study underwent extracorporeal SWL were divided into two main groups, according to the stone size, Group A (92 patients with stone ≤10 mm) and Group B (88 patients with stone >10 mm). Both groups were evaluated, according to the skin to stone distance (SSD) and Hounsfield units (≤500, 500–1000 and >1000 HU). Results: Both groups were comparable in baseline data and stone characteristics. About 92.3% of Group A rendered stone-free, whereas 77.2% were stone-free in Group B (P = 0.001). Furthermore, in both group SWL success rates was a significantly higher for stones with lower attenuation <830 HU than with stones >830 HU (P < 0.034). SSD were statistically differences in SWL outcome (P < 0.02). Simultaneous consideration of three parameters stone size, stone attenuation value, and SSD; we found that stone-free rate (SFR) was 100% for stone attenuation value <830 HU for stone <10 mm or >10 mm but total number SWL sessions and shock waves required for the larger stone group were higher than in the smaller group (P < 0.01). Furthermore, SFR was 83.3% and 37.5% for stone <10 mm, mean HU >830, SSD 90 mm and SSD >120 mm, respectively. On the other hand, SFR was 52.6% and 28.57% for stone >10 mm, mean HU >830, SSD <90 mm and SSD >120 mm, respectively. Conclusion: Stone size, stone density (HU), and SSD is simple to calculate and can be reported by radiologists to applying combined score help to augment predictive power of SWL, reduce cost, and improving of treatment strategies. PMID:27141192

  19. PREFACE: A Stellar Journey A Stellar Journey

    NASA Astrophysics Data System (ADS)

    Asplund, M.

    2008-10-01

    astronomical talk, student lecture, musical concert or theatre play. Another attribute of Bengt is his boundless optimism, which not the least has helped many of his students overcome the unavoidable moments of despair (this is only true as long as one is aware of the well-known BG factor: multiply any of Bengt's estimates for the time required to complete a task by at least a factor of three). His personal traits make working with Bengt always very enjoyable as well as highly educating. Bengt's work also extends well beyond the domain of astronomy, including music, literature, theatre, religion, research ethics, science policy and science popularization. Bengt is an excellent role model for a successful scientist with a rich and rewarding life outside of academia. The symposium A Stellar Journey was divided into five sessions covering basically the main research areas Bengt has worked on: Stellar atmospheres, Solar/stellar spectroscopy, Stellar parameters, Stellar evolution and nucleosynthesis and Stellar populations. In addition, one afternoon was devoted to a session entitled Anything but astronomy (see the symposium program), which tried to showcase Bengt's diverse interests outside of astronomy with talks ranging from religion and history of science over science popularization and future studies to literature and music. My task, as chair of the Scientific Organizing Committee, to put together an exciting scientific program of invited reviews and talks was made considerably easier thanks to the excellent suggestions by the other SOC members: Ann Boesgaard, Sofia Feltzing, John Lattanzio, Andre Maeder, Bertrand Plez and Monique Spite. I believe in the end we were successful in achieving our charge, an impression corroborated by the many encouraging comments from various participants during and after the conference. I am particularly grateful to Nils Bergvall, Bengt Edvardsson and Bertrand Plez for their time-consuming efforts in arranging the extraordinary and greatly

  20. Yonsei Evolutionary Population Synthesis (YEPS) Model. I. Spectroscopic Evolution of Simple Stellar Populations

    NASA Astrophysics Data System (ADS)

    Chung, Chul; Yoon, Suk-Jin; Lee, Sang-Yoon; Lee, Young-Wook

    2013-01-01

    We present a series of papers on the 2012 version of the Yonsei Evolutionary Population Synthesis (YEPS) model, which was constructed based on over 20 years of research. This first paper delineates the spectroscopic aspect of integrated light from stellar populations older than 1 Gyr. The standard YEPS is based on the most up-to-date Yonsei-Yale stellar evolutionary tracks and BaSel 3.1 flux libraries, and provides absorption line indices of the Lick/IDS system and high-order Balmer lines for simple stellar populations as functions of stellar parameters, such as metallicity, age, and α-element mixture. Special care has been taken to incorporate a systematic contribution from horizontal-branch (HB) stars, which alters the temperature-sensitive Balmer lines significantly, resulting in up to a 5 Gyr difference in the age estimation of old, metal-poor stellar populations. We also find that HBs exert an appreciable effect not only on the Balmer lines but also on the metallicity-sensitive lines, including the magnesium index. This is critical in explaining the intriguing bimodality found in index distributions of globular clusters in massive galaxies and to accurately derive spectroscopic metallicities from various indices. A full set of the spectroscopic and photometric YEPS model data of the entire parameter space is currently downloadable at http://web.yonsei.ac.kr/cosmic/data/YEPS.htm.

  1. YONSEI EVOLUTIONARY POPULATION SYNTHESIS (YEPS) MODEL. I. SPECTROSCOPIC EVOLUTION OF SIMPLE STELLAR POPULATIONS

    SciTech Connect

    Chung, Chul; Yoon, Suk-Jin; Lee, Sang-Yoon; Lee, Young-Wook

    2013-01-15

    We present a series of papers on the 2012 version of the Yonsei Evolutionary Population Synthesis (YEPS) model, which was constructed based on over 20 years of research. This first paper delineates the spectroscopic aspect of integrated light from stellar populations older than 1 Gyr. The standard YEPS is based on the most up-to-date Yonsei-Yale stellar evolutionary tracks and BaSel 3.1 flux libraries, and provides absorption line indices of the Lick/IDS system and high-order Balmer lines for simple stellar populations as functions of stellar parameters, such as metallicity, age, and {alpha}-element mixture. Special care has been taken to incorporate a systematic contribution from horizontal-branch (HB) stars, which alters the temperature-sensitive Balmer lines significantly, resulting in up to a 5 Gyr difference in the age estimation of old, metal-poor stellar populations. We also find that HBs exert an appreciable effect not only on the Balmer lines but also on the metallicity-sensitive lines, including the magnesium index. This is critical in explaining the intriguing bimodality found in index distributions of globular clusters in massive galaxies and to accurately derive spectroscopic metallicities from various indices. A full set of the spectroscopic and photometric YEPS model data of the entire parameter space is currently downloadable at http://web.yonsei.ac.kr/cosmic/data/YEPS.htm.

  2. Photochemical parameters of atmospheric source gases: accurate determination of OH reaction rate constants over atmospheric temperatures, UV and IR absorption spectra

    NASA Astrophysics Data System (ADS)

    Orkin, V. L.; Khamaganov, V. G.; Martynova, L. E.; Kurylo, M. J.

    2012-12-01

    The emissions of halogenated (Cl, Br containing) organics of both natural and anthropogenic origin contribute to the balance of and changes in the stratospheric ozone concentration. The associated chemical cycles are initiated by the photochemical decomposition of the portion of source gases that reaches the stratosphere. Reactions with hydroxyl radicals and photolysis are the main processes dictating the compound lifetime in the troposphere and release of active halogen in the stratosphere for a majority of halogen source gases. Therefore, the accuracy of photochemical data is of primary importance for the purpose of comprehensive atmospheric modeling and for simplified kinetic estimations of global impacts on the atmosphere, such as in ozone depletion (i.e., the Ozone Depletion Potential, ODP) and climate change (i.e., the Global Warming Potential, GWP). The sources of critically evaluated photochemical data for atmospheric modeling, NASA/JPL Publications and IUPAC Publications, recommend uncertainties within 10%-60% for the majority of OH reaction rate constants with only a few cases where uncertainties lie at the low end of this range. These uncertainties can be somewhat conservative because evaluations are based on the data from various laboratories obtained during the last few decades. Nevertheless, even the authors of the original experimental works rarely estimate the total combined uncertainties of the published OH reaction rate constants to be less than ca. 10%. Thus, uncertainties in the photochemical properties of potential and current atmospheric trace gases obtained under controlled laboratory conditions still may constitute a major source of uncertainty in estimating the compound's environmental impact. One of the purposes of the presentation is to illustrate the potential for obtaining accurate laboratory measurements of the OH reaction rate constant over the temperature range of atmospheric interest. A detailed inventory of accountable sources of

  3. Accurate calculations on the 22 electronic states and 54 spin-orbit states of the O2 molecule: potential energy curves, spectroscopic parameters and spin-orbit coupling.

    PubMed

    Liu, Hui; Shi, Deheng; Sun, Jinfeng; Zhu, Zunlue; Shulin, Zhang

    2014-04-24

    The potential energy curves (PECs) of 54 spin-orbit states generated from the 22 electronic states of O2 molecule are investigated for the first time for internuclear separations from about 0.1 to 1.0nm. Of the 22 electronic states, the X(3)Σg(-), A(')(3)Δu, A(3)Σu(+), B(3)Σu(-), C(3)Πg, a(1)Δg, b(1)Σg(+), c(1)Σu(-), d(1)Πg, f(1)Σu(+), 1(5)Πg, 1(3)Πu, 2(3)Σg(-), 1(5)Σu(-), 2(1)Σu(-) and 2(1)Δg are found to be bound, whereas the 1(5)Σg(+), 2(5)Σg(+), 1(1)Πu, 1(5)Δg, 1(5)Πu and 2(1)Πu are found to be repulsive ones. The B(3)Σu(-) and d(1)Πg states possess the double well. And the 1(3)Πu, C(3)Πg, A'(3)Δu, 1(5)Δg and 2(5)Σg(+) states are the inverted ones when the spin-orbit coupling is included. The PEC calculations are done by the complete active space self-consistent field (CASSCF) method, which is followed by the internally contracted multireference configuration interaction (icMRCI) approach with the Davidson correction. Core-valence correlation and scalar relativistic corrections are taken into account. The convergence of present calculations is evaluated with respect to the basis set and level of theory. The vibrational properties are discussed for the 1(5)Πg, 1(3)Πu, d(1)Πg and 1(5)Σu(-) states and for the second well of the B(3)Σu(-) state. The spin-orbit coupling effect is accounted for by the state interaction method with the Breit-Pauli Hamiltonian. The PECs of all the electronic states and spin-orbit states are extrapolated to the complete basis set limit. The spectroscopic parameters are obtained, and compared with available experimental and other theoretical results. Analyses demonstrate that the spectroscopic parameters reported here can be expected to be reliably predicted ones. The conclusion is obtained that the effect of spin-orbit coupling on the spectroscopic parameters are small almost for all the electronic states involved in this paper except for the 1(5)Σu(-), 1(5)Πg and 1(3)Πu. PMID:24486866

  4. 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

  5. Accurate calculations on the 12 electronic states and 23 Ω states of the SiBr+ cation: potential energy curves, spectroscopic parameters and spin-orbit coupling

    NASA Astrophysics Data System (ADS)

    Shi, De-Heng; Liu, Qionglan; Yu, Wei; Sun, Jinfeng; Zhu, Zunlue

    2014-05-01

    The potential energy curves (PECs) of 23 Ω states generated from the 12 electronic states (X1 Σ +, 21 Σ +, 11 Σ -, 11 Π, 21 Π, 11 Δ, 13 Σ +, 23 Σ +, 13 Σ -, a3 Π, 23 Π and 13 Δ) are studied for the first time. All the states correlate to the first dissociation channel of the SiBr+ cation. Of these electronic states, the 23 Σ + is the repulsive one without the spin-orbit coupling, whereas it becomes the bound one with the spin-orbit coupling added. On the one hand, without the spin-orbit coupling, the 11 Π, 21 Π and 23 Π are the rather weakly bound states, and only the 11 Π state possesses the double well; on the other hand, with the spin-orbit coupling included, the a3 Π and 11 Π states possess the double well, and the 13 Σ + and 13 Σ - are the inverted states. The PECs are calculated by the CASSCF method, which is followed by the internally contracted MRCI approach with the Davidson modification. Scalar relativistic correction is calculated by the third-order Douglas-Kroll Hamiltonian approximation with a cc-pVTZ-DK basis set. Core-valence correlation correction is included with a cc-pCVTZ basis set. The spin-orbit coupling is accounted for by the state interaction method with the Breit-Pauli Hamiltonian using the all-electron aug-cc-pCVTZ basis set. All the PECs are extrapolated to the complete basis set limit. The variation with internuclear separation of the spin-orbit coupling constant is discussed in brief. The spectroscopic parameters are evaluated for the 11 bound electronic states and the 23 bound Ω states, and are compared with available measurements. Excellent agreement has been found between the present results and the experimental data. It demonstrates that the spectroscopic parameters reported here can be expected to be reliably predicted ones. The Franck-Condon factors and radiative lifetimes of the transitions from the a3 Π 0 + and a3 Π 1 states to the X1 Σ + 0+ state are calculated for several low vibrational levels, and

  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. Photodynamical modeling of hierarchical stellar system KOI-126

    NASA Astrophysics Data System (ADS)

    Earl, Nicholas Michael

    The power and precision of the Kepler space telescope has provided the astrophysical field with a valuable insight into the dynamics of extra-solar systems. KOI-126 represents the first eclipsing hierarchical triple stellar system identified in the Kepler mission's photometry. The dynamics of the system are such that ascertaining the parameters of each body accurately (better than a few percent) is possible from the photometry alone. This allows determination of the characteristics while avoiding biases inherent in traditional studies of low-mass eclipsing systems. The parameter set for KOI-126 was originally reported on by Carter et al. and is uniquely composed of a low-mass binary, KOI-126 B and KOI-126 C. This pair orbits a third, more massive star KOI-126 A. The original analysis employed a full dynamical-photometric model, utilizing a Levenberg-Marquardt algorithm and least-squares minimization, to fit the short-cadence (i.e. successive 58.84 second cadence exposures) photometric data from the Kepler spacecraft captured over a period of 247 days. The updated catalog of short-cadence data now covers a span of 1,300 days. In light of the new data, and the valuable contribution accurately sampled fully-convective stars offer to theoretical stellar models, it is therefore relevant to refine the parameters of this system. Furthermore, with the ubiquity of multi-stellar systems, a well documented, portable, scalable computer modeling code for N-body systems is introduced. Thus, a new analysis is done on KOI-126 using this parallelized dynamical-photometric modeling package written in Python, based on Carter et al.'s original code, titled Pynamic. Pynamic allows the use of several fitting algorithms, but in this analysis utilizes the affine-invariant Markov chain Monte Carlo ensemble.

  8. 146 Kepler-Lamost targets fundamental parameters

    NASA Astrophysics Data System (ADS)

    Wu, Yaqian

    2015-08-01

    Accurate stellar fundamental parameters with high precision are important for distinguishing stellar populationand star study.Turn-off stars are in the relatively vital stellar evolution state. Studying turn-off stars can help us to have a more comprehensive understand of the stellar physics.With the help of observation provided by Lamost project, we obtain atmospheric parameters of 146 turn-off stars from LSP3 pipeline. Combined with stellar pulsation data from Kepler, we can get asteroseismic characteristic of stars,such as Δν and νmax.In this paper,we constructed a grid of evolutionary models, with the mass range from 0.8 to 2.5 M⊙ and metallicities Zini = 0.0085, 0.0105, 0.0130, 0.0165, 0.0200, 0.0250, 0.0300, 0.0400 (i.e.[Fe/H] from -0.3 to 0.4dex).All evolutionary tracks were started in the pre-main sequence birth line and ended at the base of Red Giant Branch.Based on the stellar model grid we constructed,as well as Kepler-Lamost observations, we obtained fundamental parameters of 146 around turn-off stars, and found that 112 targets lied in turn-off state or in the Main Sequence,15 targets are subgiant stars and 7 targets have evolved to the red giants stage.Then we use pulsation code(JIG) of Guenther to extract theorical individual frequencies and calculate theorical Δν.Meanwhile we obtained more precise fundamental parameters of these stars.

  9. 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.

  10. BANYAN. IV. Fundamental parameters of low-mass star candidates in nearby young stellar kinematic groups—isochronal age determination using magnetic evolutionary models

    SciTech Connect

    Malo, Lison; Doyon, René; Albert, Loïc; Lafrenière, David; Artigau, Étienne; Gagné, Jonathan; Feiden, Gregory A.; Riedel, Adric E-mail: doyon@astro.umontreal.ca

    2014-09-01

    Based on high-resolution optical spectra obtained with ESPaDOnS at Canada-France-Hawaii Telescope, we determine fundamental parameters (T {sub eff}, R, L {sub bol}, log g, and metallicity) for 59 candidate members of nearby young kinematic groups. The candidates were identified through the BANYAN Bayesian inference method of Malo et al., which takes into account the position, proper motion, magnitude, color, radial velocity, and parallax (when available) to establish a membership probability. The derived parameters are compared to Dartmouth magnetic evolutionary models and field stars with the goal of constraining the age of our candidates. We find that, in general, low-mass stars in our sample are more luminous and have inflated radii compared to older stars, a trend expected for pre-main-sequence stars. The Dartmouth magnetic evolutionary models show a good fit to observations of field K and M stars, assuming a magnetic field strength of a few kG, as typically observed for cool stars. Using the low-mass members of the β Pictoris moving group, we have re-examined the age inconsistency problem between lithium depletion age and isochronal age (Hertzspring-Russell diagram). We find that the inclusion of the magnetic field in evolutionary models increases the isochronal age estimates for the K5V-M5V stars. Using these models and field strengths, we derive an average isochronal age between 15 and 28 Myr and we confirm a clear lithium depletion boundary from which an age of 26 ± 3 Myr is derived, consistent with previous age estimates based on this method.

  11. ASteCA: Automated Stellar Cluster Analysis

    NASA Astrophysics Data System (ADS)

    Perren, G. I.; Vázquez, R. A.; Piatti, A. E.

    2015-04-01

    We present the Automated Stellar Cluster Analysis package (ASteCA), a suit of tools designed to fully automate the standard tests applied on stellar clusters to determine their basic parameters. The set of functions included in the code make use of positional and photometric data to obtain precise and objective values for a given cluster's center coordinates, radius, luminosity function and integrated color magnitude, as well as characterizing through a statistical estimator its probability of being a true physical cluster rather than a random overdensity of field stars. ASteCA incorporates a Bayesian field star decontamination algorithm capable of assigning membership probabilities using photometric data alone. An isochrone fitting process based on the generation of synthetic clusters from theoretical isochrones and selection of the best fit through a genetic algorithm is also present, which allows ASteCA to provide accurate estimates for a cluster's metallicity, age, extinction and distance values along with its uncertainties. To validate the code we applied it on a large set of over 400 synthetic MASSCLEAN clusters with varying degrees of field star contamination as well as a smaller set of 20 observed Milky Way open clusters (Berkeley 7, Bochum 11, Czernik 26, Czernik 30, Haffner 11, Haffner 19, NGC 133, NGC 2236, NGC 2264, NGC 2324, NGC 2421, NGC 2627, NGC 6231, NGC 6383, NGC 6705, Ruprecht 1, Tombaugh 1, Trumpler 1, Trumpler 5 and Trumpler 14) studied in the literature. The results show that ASteCA is able to recover cluster parameters with an acceptable precision even for those clusters affected by substantial field star contamination. ASteCA is written in Python and is made available as an open source code which can be downloaded ready to be used from its official site.

  12. Theory and modeling of stellar atmospheres

    NASA Astrophysics Data System (ADS)

    Hubeny, Ivan

    2010-08-01

    I will briefly outline basic concepts of the stellar atmospheres theory. After summarizing basic structural equations describing a stellar atmospheres, an emphasis is given to describing efficient numerical methods developed to deal with the stellar atmosphere problem, namely the method of complete linearization ant its recent variants, and the whole class of methods known by name Accelerated Lambda Iteration. In the next part of the lectures I will briefly summarize existing computer codes, with an emphasis on our code TLUSTY, and list some of the most useful grids of model atmospheres that are publicly available. Next, I will show how the model atmospheres and synthetic spectra are used in quantitative stellar spectroscopy in order to determine basic stellar parameters and chemical abundances. Finally, I will briefly describe an application of model atmosphere theory and models to related objects, such as accretion disks around various accretors, and atmospheres of substellar-mass objects-extrasolar giant planets and brown dwarfs.

  13. High-precision spectroscopy of late-type stars with three-dimensional model stellar atmospheres

    NASA Astrophysics Data System (ADS)

    Collet, Remo

    2015-08-01

    -based stellar surveys (e.g Gaia and Gaia-ESO) for the determination of accurate stellar parameters, elemental abundances, and radial velocities.

  14. Stellar parametrization from Gaia RVS spectra

    NASA Astrophysics Data System (ADS)

    Recio-Blanco, A.; de Laverny, P.; Allende Prieto, C.; Fustes, D.; Manteiga, M.; Arcay, B.; Bijaoui, A.; Dafonte, C.; Ordenovic, C.; Ordoñez Blanco, D.

    2016-01-01

    found for A-type stars, while the log(g) derivation is more accurate (errors of 0.07 and 0.12 dex at GRVS = 12.6 and 13.4, respectively). For the faintest stars, with GRVS≳ 13-14, a Teff input from the spectrophotometric-derived parameters will allow the final GSP-Spec parametrization to be improved. Conclusions: The reported results, while neglecting possible mismatches between synthetic and real spectra, show that the contribution of the RVS-based stellar parameters will be unique in the brighter part of the Gaia survey, which allows for crucial age estimations and accurate chemical abundances. This will constitute a unique and precious sample, providing many pieces of the Milky Way history puzzle with unprecedented precision and statistical relevance.

  15. 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).

  16. 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}.

  17. Parasitic analysis and π-type Butterworth-Van Dyke model for complementary-metal-oxide-semiconductor Lamb wave resonator with accurate two-port Y-parameter characterizations.

    PubMed

    Wang, Yong; Goh, Wang Ling; Chai, Kevin T-C; Mu, Xiaojing; Hong, Yan; Kropelnicki, Piotr; Je, Minkyu

    2016-04-01

    The parasitic effects from electromechanical resonance, coupling, and substrate losses were collected to derive a new two-port equivalent-circuit model for Lamb wave resonators, especially for those fabricated on silicon technology. The proposed model is a hybrid π-type Butterworth-Van Dyke (PiBVD) model that accounts for the above mentioned parasitic effects which are commonly observed in Lamb-wave resonators. It is a combination of interdigital capacitor of both plate capacitance and fringe capacitance, interdigital resistance, Ohmic losses in substrate, and the acoustic motional behavior of typical Modified Butterworth-Van Dyke (MBVD) model. In the case studies presented in this paper using two-port Y-parameters, the PiBVD model fitted significantly better than the typical MBVD model, strengthening the capability on characterizing both magnitude and phase of either Y11 or Y21. The accurate modelling on two-port Y-parameters makes the PiBVD model beneficial in the characterization of Lamb-wave resonators, providing accurate simulation to Lamb-wave resonators and oscillators. PMID:27131699

  18. Parasitic analysis and π-type Butterworth-Van Dyke model for complementary-metal-oxide-semiconductor Lamb wave resonator with accurate two-port Y-parameter characterizations

    NASA Astrophysics Data System (ADS)

    Wang, Yong; Goh, Wang Ling; Chai, Kevin T.-C.; Mu, Xiaojing; Hong, Yan; Kropelnicki, Piotr; Je, Minkyu

    2016-04-01

    The parasitic effects from electromechanical resonance, coupling, and substrate losses were collected to derive a new two-port equivalent-circuit model for Lamb wave resonators, especially for those fabricated on silicon technology. The proposed model is a hybrid π-type Butterworth-Van Dyke (PiBVD) model that accounts for the above mentioned parasitic effects which are commonly observed in Lamb-wave resonators. It is a combination of interdigital capacitor of both plate capacitance and fringe capacitance, interdigital resistance, Ohmic losses in substrate, and the acoustic motional behavior of typical Modified Butterworth-Van Dyke (MBVD) model. In the case studies presented in this paper using two-port Y-parameters, the PiBVD model fitted significantly better than the typical MBVD model, strengthening the capability on characterizing both magnitude and phase of either Y11 or Y21. The accurate modelling on two-port Y-parameters makes the PiBVD model beneficial in the characterization of Lamb-wave resonators, providing accurate simulation to Lamb-wave resonators and oscillators.

  19. Automatic stellar spectra parameterisation in the IR Ca ii triplet region

    NASA Astrophysics Data System (ADS)

    Kordopatis, G.; Recio-Blanco, A.; de Laverny, P.; Bijaoui, A.; Hill, V.; Gilmore, G.; Wyse, R. F. G.; Ordenovic, C.

    2011-11-01

    minimum in the fit and the algorithm must avoid being trapped in false local minima. The second algorithm, DEGAS, uses a pattern-recognition approach and consequently has a more global vision of the parameter space. The best-fit synthetic spectrum is derived through a series of comparisons between the observed and synthetic spectra, summed over wavelength pixels, with additional refinements in the set of synthetic spectra after each stage, i.e. a decision tree. Results: We identified physical degeneracies in different regions of the H - R diagram: hot dwarf and giant stars share the same spectral signatures. Furthermore, it is very difficult to determine an accurate value for the surface gravity of cooler dwarfs. These effects are intensified when the lack of information increases, which happens for low-metallicity stars or spectra with low signal-to-noise ratios (SNRs). Our results demonstrate that the local projection method is preferred for spectra with high SNR, whereas the decision-tree method is preferred for spectra of lower SNR. We therefore propose a hybrid approach, combining these methods, and demonstrate that sufficiently accurate results for the purposes of galactic archaeology studies are retrieved down to SNR ~ 20 for typical parameter values of stars belonging to the local thin or thick disc, and for SNR down to ~50 for the more metal-poor giant stars of the halo. Conclusions: If unappreciated, degeneracies in stellar parameters can introduce biases and systematic errors in derived quantities for target stars such as distances and full space motions. These can be minimised using the knowledge gained by thorough testing of the proposed stellar classification algorithm, which in turn lead to robust automated methods for the coming extensive spectroscopic surveys of stars in the Local Group.

  20. 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.

  1. The Cannon: A Data-driven Approach to Stellar Label Determination

    NASA Astrophysics Data System (ADS)

    Ness, M.; Hogg, David W.; Rix, H.-W.; Ho, Anna. Y. Q.; Zasowski, G.

    2015-07-01

    New spectroscopic surveys offer the promise of stellar parameters and abundances (“stellar labels”) for hundreds of thousands of stars; this poses a formidable spectral modeling challenge. In many cases, there is a subset of reference objects for which the stellar labels are known with high(er) fidelity. We take advantage of this with The Cannon, a new data-driven approach for determining stellar labels from spectroscopic data. The Cannon learns from the “known” labels of reference stars how the continuum-normalized spectra depend on these labels by fitting a flexible model at each wavelength; then, The Cannon uses this model to derive labels for the remaining survey stars. We illustrate The Cannon by training the model on only 542 stars in 19 clusters as reference objects, with {T}{eff}, {log} g, and [{Fe}/{{H}}] as the labels, and then applying it to the spectra of 55,000 stars from APOGEE DR10. The Cannon is very accurate. Its stellar labels compare well to the stars for which APOGEE pipeline (ASPCAP) labels are provided in DR10, with rms differences that are basically identical to the stated ASPCAP uncertainties. Beyond the reference labels, The Cannon makes no use of stellar models nor any line-list, but needs a set of reference objects that span label-space. The Cannon performs well at lower signal-to-noise, as it delivers comparably good labels even at one-ninth the APOGEE observing time. We discuss the limitations of The Cannon and its future potential, particularly, to bring different spectroscopic surveys onto a consistent scale of stellar labels.

  2. Using MASSCLEAN to Describe Stellar Clusters Found in the Vista Variables in the Via Lactea (VVV) Survey

    NASA Astrophysics Data System (ADS)

    Popescu, B.; Hanson, M. M.; Borissova, J.; Kurtev, R.; Ivanov, V. D.; Catelan, M.; Larsen, S. S.; Minniti, D.; Lucas, P.

    2014-10-01

    The important parameters: age, mass and distance of resolved or partially resolved stellar clusters are better accurately determined by using color-magnitude diagrams (CMD). However, when the main sequence turnoff is not available or clearly identifiable, large errors in all parameters result when using simple isochrone fitting, particularly when observations are limited to near-infrared bands. We used the MASSCLEAN package to perform 5 million Monte Carlo simulations of stochastically sampled stellar clusters in order to generate CMD templates for a variety of cluster masses and ages and which mimic the observational photometric errors. This results in the creation of tens of thousands of n-dimensional stellar density maps (templates) in numerous color planes as a function of age and mass. We use these MASSCLEAN CMD templates to refine and sharpen traditional isochrone fitting to analyze the newly discovered stellar clusters/cluster candidates from the Vista Variables in the Via Lactea (VVV) Survey. Our MASSCLEAN templates are also being used to design and optimize search algorithms for stellar clusters in broad-band surveys.

  3. The Non-Stellar Infrared Continuum of Seyfert Galaxies

    NASA Technical Reports Server (NTRS)

    Alonso-Herrero, Almudena; Quillen, Alice C.; Simpson, Chris; Efstathiou, Andreas; Ward, Martin J.

    2000-01-01

    JHKL'M (1 - 5 micrometers) imaging of a sample of Seyfert 2 galaxies is presented. We have performed an accurate estimate of the near-infrared non-stellar nuclear fluxes. We confirm that the near-infrared nuclear continuum between 1 and 2.2microns of some Seyfert 2s is dominated by stellar emission, whereas the continuum emission at longer wavelengths (lambda = 3 - 5 micrometers) is almost entirely non-stellar in origin. The non-stellar spectral energy distributions (SED) in the infrared (up to 15 micrometers) of Seyfert galaxies show a variety of shapes, and they are well reproduced with the tapered disk models of Efstathiou & Rowan-Robinson (1995). We have used two models, one including an optically thin cone component found to fit the SED of NGC 1068, and a coneless model. Although our modelling of the SEDs does not allow us to favor either model to account for all the observed SEDs, we find that the viewing angle towards the central source is well constrained by both models. The galaxies in our sample have fitted values of the viewing angle in the range Theta(sub V) = 0 deg - 64 deg, for the assumed model parameters. We have also investigated non-stellar color-color diagrams (L' - M vs. H - M and L' - M vs. H - L'). The colors of the Seyfert galaxies with viewing angles Theta(sub v) less than 30 deg are better reproduced with the cone model. These diagrams provide a good means to separate Seyfert 2s with moderate obscuration (A(sub V) approx. less than 20 mag from hard X-ray observations) from those with high obscuration. The ground-based 4.8 microns and ISO 9.6 microns luminosities are well correlated with the hard X-ray luminosities of Seyfert ls and 2s. These continuum emissions appear as a good indicator of the AGN luminosity, at least in the cases of hard X-ray Compton-thin Seyfert galaxies (N(sub H) less than or = 10(exp 24)/sq cm). We finally stress the finding that some Compton thick galaxies show bright non-stellar emission at 5 microns This suggests

  4. KEPLER MISSION STELLAR AND INSTRUMENT NOISE PROPERTIES

    SciTech Connect

    Gilliland, Ronald L.; Chaplin, William J.; Elsworth, Yvonne P.; Miglio, Andrea; Dunham, Edward W.; Argabright, Vic S.; Borucki, William J.; Bryson, Stephen T.; Koch, David G.; Walkowicz, Lucianne M.; Basri, Gibor; Buzasi, Derek L.; Caldwell, Douglas A.; Jenkins, Jon M.; Van Cleve, Jeffrey; Welsh, William F.

    2011-11-01

    Kepler mission results are rapidly contributing to fundamentally new discoveries in both the exoplanet and asteroseismology fields. The data returned from Kepler are unique in terms of the number of stars observed, precision of photometry for time series observations, and the temporal extent of high duty cycle observations. As the first mission to provide extensive time series measurements on thousands of stars over months to years at a level hitherto possible only for the Sun, the results from Kepler will vastly increase our knowledge of stellar variability for quiet solar-type stars. Here, we report on the stellar noise inferred on the timescale of a few hours of most interest for detection of exoplanets via transits. By design the data from moderately bright Kepler stars are expected to have roughly comparable levels of noise intrinsic to the stars and arising from a combination of fundamental limitations such as Poisson statistics and any instrument noise. The noise levels attained by Kepler on-orbit exceed by some 50% the target levels for solar-type, quiet stars. We provide a decomposition of observed noise for an ensemble of 12th magnitude stars arising from fundamental terms (Poisson and readout noise), added noise due to the instrument and that intrinsic to the stars. The largest factor in the modestly higher than anticipated noise follows from intrinsic stellar noise. We show that using stellar parameters from galactic stellar synthesis models, and projections to stellar rotation, activity, and hence noise levels reproduce the primary intrinsic stellar noise features.

  5. Magnetohydrostatic modelling of stellar coronae

    NASA Astrophysics Data System (ADS)

    MacTaggart, D.; Gregory, S. G.; Neukirch, T.; Donati, J.-F.

    2016-02-01

    We introduce to the stellar physics community a method of modelling stellar coronae that can be considered to be an extension of the potential field. In this approach, the magnetic field is coupled to the background atmosphere. The model is magnetohydrostatic and is a balance between the Lorentz force, the pressure gradient and gravity. Analytical solutions are possible and we consider a particular class of equilibria in this paper. The model contains two free parameters and the effects of these on both the geometry and topology of the coronal magnetic field are investigated. A demonstration of the approach is given using a magnetogram derived from Zeeman-Doppler imaging of the 0.75 M⊙ M-dwarf star GJ 182.

  6. 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.

  7. 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.

  8. Probabilistic Description of Stellar Ensembles

    NASA Astrophysics Data System (ADS)

    Cerviño, Miguel

    I describe the modeling of stellar ensembles in terms of probability distributions. This modeling is primary characterized by the number of stars included in the considered resolution element, whatever its physical (stellar cluster) or artificial (pixel/IFU) nature. It provides a solution of the direct problem of characterizing probabilistically the observables of stellar ensembles as a function of their physical properties. In addition, this characterization implies that intensive properties (like color indices) are intrinsically biased observables, although the bias decreases when the number of stars in the resolution element increases. In the case of a low number of stars in the resolution element (N<105), the distributions of intensive and extensive observables follow nontrivial probability distributions. Such a situation ​​​ can be computed by means of Monte Carlo simulations where data mining techniques would be applied. Regarding the inverse problem of obtaining physical parameters from observational data, I show how some of the scatter in the data provides valuable physical information since it is related to the system size (and the number of stars in the resolution element). However, making use of such ​​​ information requires following iterative procedures in the data analysis.

  9. Accelerated Fitting of Stellar Spectra

    NASA Astrophysics Data System (ADS)

    Ting, Yuan-Sen; Conroy, Charlie; Rix, Hans-Walter

    2016-07-01

    Stellar spectra are often modeled and fitted by interpolating within a rectilinear grid of synthetic spectra to derive the stars’ labels: stellar parameters and elemental abundances. However, the number of synthetic spectra needed for a rectilinear grid grows exponentially with the label space dimensions, precluding the simultaneous and self-consistent fitting of more than a few elemental abundances. Shortcuts such as fitting subsets of labels separately can introduce unknown systematics and do not produce correct error covariances in the derived labels. In this paper we present a new approach—Convex Hull Adaptive Tessellation (chat)—which includes several new ideas for inexpensively generating a sufficient stellar synthetic library, using linear algebra and the concept of an adaptive, data-driven grid. A convex hull approximates the region where the data lie in the label space. A variety of tests with mock data sets demonstrate that chat can reduce the number of required synthetic model calculations by three orders of magnitude in an eight-dimensional label space. The reduction will be even larger for higher dimensional label spaces. In chat the computational effort increases only linearly with the number of labels that are fit simultaneously. Around each of these grid points in the label space an approximate synthetic spectrum can be generated through linear expansion using a set of “gradient spectra” that represent flux derivatives at every wavelength point with respect to all labels. These techniques provide new opportunities to fit the full stellar spectra from large surveys with 15–30 labels simultaneously.

  10. Comprehensive stellar population models and the disentanglement of age and metallicity effects

    NASA Technical Reports Server (NTRS)

    Worthey, Guy

    1994-01-01

    applied in a differential sense have smaller uncertainties. (4) In the present models the dominant error for colors is probably the transformation from stellar atmospheric parameters to stellar colors. (5) Stellar B - V is difficult to model, and current spreads among different authors can reach 0.2 mag. (6) If known defects in the stellar flux library are corrected, the population model colors of this work in passbands redder than U would be accurate to roughly 0.03 mag in an absolute sense. These corrections are not made in the tables of model output.

  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. Investigation of the empirical stellar library

    NASA Astrophysics Data System (ADS)

    Guo, Y. X.; Luo, A. L.

    During the large sample survey of LAMOST, mass spectrum of stars was obtained. The analysis of physical parameters, chemical composition and motion track can help us understand more about the structure and evolution of the Milky Way. Based on the investigation and research done on libraries of stellar spectra issued(such as in CDS), here I give an overview of the current status of empirical stellar libraries. I classify the valuable data according to specific criterion, such as spectral coverage/domain and resolution. After the integration of these spectrum, we will finally construct our own library of observed stellar spectra for LAMOST, which will serve as reference for the classification and automatic parameter analysis of stars, as well as for study of the galaxies evolution.

  15. The structure and Stellar Populations of Nuclear Star Clusters in Late-type Spiral Galaxies From HST/WFC3 Imaging

    NASA Astrophysics Data System (ADS)

    Carson, Daniel

    2016-06-01

    Luminous, compact stellar systems known as nuclear clusters (NCs) are commonly found in the centers of galaxies across the entire Hubble sequence. I present an analysis of the structure and stellar populations of a sample of ten of the nearest and brightest NCs residing in late-type spiral galaxies, using imaging data from Hubble Space Telescope Wide Field Camera 3 in seven bands that span the near-ultraviolet to the near-infrared. The intrinsic shapes and sizes of the NCs, disentangled from the effects of point spread function (PSF) blurring, were measured using GALFIT. For six of the ten NCs in our sample, we find changes in the effective radius with wavelength, which suggests that many NCs contain radially varying stellar populations. There is also a general trend of increasing roundness of the NCs at longer wavelengths, suggesting that the youngest stars in NCs typically form in disks. I developed a Monte Carlo code to fit linear combinations of simple stellar population models to the observed spectral energy distribution (SED) of each NC and assess the uncertainties in the fit parameters. Tests using mock SEDs with known input parameters demonstrate that although the method is susceptible to degeneracies between model SEDs, the code is robust and accurately recovers the total stellar mass for a wide range of NC colors and ages. I present global star formation histories and stellar mass estimates for each cluster, which are in good agreement with previous dynamical studies. The clusters are generally dominated by an old (> 1 Gyr) population, but are best described by multi-age models. The spatially resolved properties of the stellar populations of each NC were also studied by performing SED fits on a pixel-by-pixel basis. These fits reveal radial age gradients in the same NCs that exhibited variation in the effective radius with wavelength. Finally, I present deprojected density profiles and estimates of the central stellar density of each cluster.

  16. 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.

  17. 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.

  18. Deriving stellar inclination of slow rotators using stellar activity signal

    NASA Astrophysics Data System (ADS)

    Dumusque, Xavier

    2015-01-01

    Stellar inclination is an important parameter for many astrophysical studies. In the context of exoplanets, this allows us to derive the true obliquity of a system if the projected stellar spin-planetary orbit angle can measured via the Rossiter-Mclaughlin effect. 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 that can reproduce the photometric and spectroscopic variations induced by stellar activity, we are able to fit the activity variation of solar-type stars and derive their inclination. The case of the equator-on star HD189733 will be presented, as well as the case of Alpha Centauri B, which present an inclination of 45+9-19 degrees, implying that the earth-mass orbiting planet is not transiting if aligned with its host star. Other exemples will also demonstrate the power of the technique, that can infer a stellar inclination, even for slow rotators like Alpha Centauri B, that present a projected rotational velocity smaller than 1.15 km.s-1. In addition, the SOAP 2.0 simulation can be used to correct for the effect of activity when one major active region is dominating the RV signal. This could enhance the detection of small mass exoplanets orbiting slightly active stars.This project is funded by ETAEARTH (European Union Seventh Framework Programme (FP7/2007-2013) under Grant Agreement n. 313014), a transnational collaboration between European countries and the US (the Swiss Space Office, the Harvard Origin of Life Initiative, the Scottish Universities Physics Alliance, the University of Geneva, the Smithsonian Astrophysical Observatory, the Italian National Astrophysical Institute, the University of St. Andrews, Queens University Belfast, and the University of Edinburgh) setup to optimize the synergy between space-and ground-based data whose scientific potential for the characterization of

  19. Treatment of atomic and molecular line blanketing by opacity sampling. [atmospheric optics - stellar atmospheres

    NASA Technical Reports Server (NTRS)

    Johnson, H. R.; Krupp, B. M.

    1975-01-01

    An opacity sampling (OS) technique for treating the radiative opacity of large numbers of atomic and molecular lines in cool stellar atmospheres is presented. Tests were conducted and results show that the structure of atmospheric models is accurately fixed by the use of 1000 frequency points, and 500 frequency points is often adequate. The effects of atomic and molecular lines are separately studied. A test model computed by using the OS method agrees very well with a model having identical atmospheric parameters computed by the giant line (opacity distribution function) method.

  20. Stellar activity and coronal heating: an overview of recent results.

    PubMed

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

    2015-05-28

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

  1. Stellar activity and coronal heating: an overview of recent results

    PubMed Central

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

    2015-01-01

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

  2. Ripple transport in Helical-Axis Advanced Stellarators: A comparison with classical stellarator/torsatrons

    SciTech Connect

    Beidler, C.D.; Hitchon, W.N.G.

    1995-07-01

    Calculations of the neoclassical transport rates due to particles trapped in the helical ripples of a stellarator`s magnetic field are carried out, based on solutions of the bounceaveraged kinetic equation. These calculations employ a model for the magnetic field strength, B, which is an accurate approximation to the actual B for a wide variety of stellarator-type devices, among which are Helical-Axis Advanced Stellarators (Helias) as well as conventional stellarators and torsatrons. Comparisons are carried out in which it is shown that the Helias concept leads to significant reductions in neoclassical transport rates throughout the entire long-mean-free-path regime, with the reduction being particularly dramatic in the {nu}{sup {minus}1} regime. These findings are confirmed by numerical simulations. Further, it is shown that the behavior of deeply trapped particles in Helias can be fundamentally different from that in classical stellarator/torsatrons; as a consequence, the beneficial effects of a radial electric field on the transport make themselves felt at lower collision frequency than is usual.

  3. Prediction of stellar occultations by satellite of asteroids

    NASA Astrophysics Data System (ADS)

    Berthier, J.; Marchis, F.; Descamps, P.; Hestroffer, D.

    2004-11-01

    Our group is working on the orbit determination of asteroid satellites on the last four years gathering data recorded with several AO systems. Based upon our observations, we focused specifically on models for (22) Kalliope, (121) Hermione, (45) Eugenia and (90) Antiope systems characterizing accurately their dynamical and physical properties (Marchis et al., 2003, 2004a, 2004b). These models will be regularly improved with new observations. This work allow us to predict the position of the secondary during stellar occultations. A successful observation will give us direct measurements of the size and shape of the moonlet which is usually too small to be resolved by any available AO systems. These parameters are important to better constrain the mass of the system, its density, and consequently the internal structure of the primary. We will predict the Earth track path of the secondary and primary events for the next years stellar occultations happening under good observing conditions and involving the satellites of (22) Kalliope, (121) Hermione, (45) Eugenia and the same-size binary asteroid (90) Antiope. A regularly updated web page http://stellarocc.imcce.fr/ contains the list of the events. This work is supported by the National Science Foundation Science and Technology Center for Adaptive Optics, and is based partly on observations collected at the European Southern Observatory, Chile.

  4. WFPC2 Stellar Photometry with HSTphot

    NASA Technical Reports Server (NTRS)

    Dolphin, Andrew E.

    2000-01-01

    HSTphot, a photometry package designed to handle the undersampled PSFs found in WFPC2 images, is introduced and described, as well as some of the considerations that have to be made in order to obtain accurate PSF-fitting stellar photometry with WFPC2 data. Tests of HSTphot's internal reliability are made using multiple observations of the same field, and tests of external reliability are made by comparing with DoPHOT reductions of the same data. Subject headz'ngs: techniques: photometric

  5. Radiation-driven winds of hot luminous stars. XVIII. The unreliability of stellar and wind parameter determinations from optical vs. UV spectral analysis of selected central stars of planetary nebulae and the possibility of some CSPNs as single-star supernova Ia progenitors

    NASA Astrophysics Data System (ADS)

    Hoffmann, T. L.; Pauldrach, A. W. A.; Kaschinski, C. B.

    2016-08-01

    Context. The uncertainty in the degree to which radiation-driven winds of hot stars might be affected by small inhomogeneities in the density leads to a corresponding uncertainty in the determination of the atmospheric mass loss rates from the strength of optical recombination lines and - since the mass loss rate is not a free parameter but a function of the stellar parameters mass, radius, luminosity, and abundances - in principle also in the determination of these stellar parameters. Furthermore, the optical recombination lines also react sensitively to even small changes in the density structure resulting from the (often assumed instead of computed) velocity law of the outflow. This raises the question of how reliable the parameter determinations from such lines are. Aims: The currently existing severe discrepancy between central stars of planetary nebulae (CSPN) stellar and wind parameters derived from model fits to the optical spectra and those derived using hydrodynamically consistent model fits to the UV spectra is to be reassessed via a simultaneous optical/UV analysis using a state-of-the-art model atmosphere code. Methods: We have modified our hydrodynamically consistent model atmosphere code with an implementation of the usual ad hoc treatment of clumping (small inhomogeneities in the density) in the wind. This allows us to re-evaluate, with respect to their influence on the appearance of the UV spectra and their compatibility with the observations, the parameters determined in an earlier study that had employed clumping in its models to achieve a fit to the observed optical spectra. Results: The discrepancy between the optical and the UV analyses is confirmed to be the result of a missing consistency between stellar and wind parameters in the optical analysis. While clumping in the wind does significantly increase the emission in the optical hydrogen and helium recombination lines, the influence of the density (velocity field) is of the same order as

  6. 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.

  7. 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].

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

    NASA Technical Reports Server (NTRS)

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

    1981-01-01

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

  9. 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

  10. THE RESOLVED STELLAR HALO OF NGC 253

    SciTech Connect

    Bailin, Jeremy; Bell, Eric F.; Chappell, Samantha N.; Radburn-Smith, David J.; De Jong, Roelof S.

    2011-07-20

    We have obtained Magellan/IMACS and Hubble Space Telescope (HST)/Advanced Camera for Surveys imaging data that resolve red giant branch stars in the stellar halo of the starburst galaxy NGC 253. The HST data cover a small area, and allow us to accurately interpret the ground-based data, which cover 30% of the halo to a distance of 30 kpc, allowing us to make detailed quantitative measurements of the global properties and structure of a stellar halo outside of the Local Group. The geometry of the halo is significantly flattened in the same sense as the disk, with a projected axis ratio of b/a {approx} 0.35 {+-} 0.1. The total stellar mass of the halo is estimated to be M{sub halo} {approx} (2.5 {+-} 1.5) x 10{sup 9} M{sub sun}, or 6% of the total stellar mass of the galaxy, and has a projected radial dependence that follows a power law of index -2.8 {+-} 0.6, corresponding to a three-dimensional power-law index of {approx} - 4. The total luminosity and profile shape that we measure for NGC 253 are somewhat larger and steeper than the equivalent values for the Milky Way and M31, but are well within the scatter of model predictions for the properties of stellar halos built up in a cosmological context. Structure within the halo is seen at a variety of scales: there is small kpc-scale density variation and a large shelf-like feature near the middle of the field. The techniques that have been developed will be essential for quantitatively comparing our upcoming larger sample of observed stellar halos to models of halo formation.

  11. On stellar limb darkening and exoplanetary transits

    NASA Astrophysics Data System (ADS)

    Howarth, Ian D.

    2011-12-01

    This paper examines how to compare stellar limb-darkening coefficients evaluated from model atmospheres with those derived from photometry. Different characterizations of a given model atmosphere can give quite different numerical results (even for a given limb-darkening 'law'), while light-curve analyses yield limb-darkening coefficients that are dependent on system geometry, and that are not directly comparable to any model-atmosphere representation. These issues are examined in the context of exoplanetary transits, which offer significant advantages over traditional binary-star eclipsing systems in the study of stellar limb darkening. 'Like for like' comparisons between light-curve analyses and new model-atmosphere results, mediated by synthetic photometry, are conducted for a small sample of stars. Agreement between the resulting synthetic-photometry/atmosphere-model (SPAM) limb-darkening coefficients and empirical values ranges from very good to quite poor, even though the targets investigated show only a small dispersion in fundamental stellar parameters.

  12. 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

  13. 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

  14. Catalyzed D-D stellarator reactor

    DOE PAGESBeta

    Sheffield, John; Spong, Donald A.

    2016-05-12

    The advantages of using the catalyzed deuterium-deuterium (D-D) approach for a fusion reactor—lower and less energetic neutron flux and no need for a tritium breeding blanket—have been evaluated in previous papers, giving examples of both tokamak and stellarator reactors. This paper presents an update for the stellarator example, taking account of more recent empirical transport scaling results and design studies of lower-aspect-ratio stellarators. We use a modified version of the Generic Magnetic Fusion Reactor model to cost a stellarator-type reactor. Recently, this model has been updated to reflect the improved science and technology base and costs in the magnetic fusionmore » program. Furthermore, it is shown that an interesting catalyzed D-D, stellarator power plant might be possible if the following parameters could be achieved: R/ ≈ 4, required improvement factor to ISS04 scaling, FR = 0.9 to 1.15, <β> ≈ 8.0% to 11.5%, Zeff ≈ 1.45 plus a relativistic temperature correction, fraction of fast ions lost ≈ 0.07, Bm ≈ 14 to 16 T, and R ≈ 18 to 24 m.« less

  15. CH in stellar atmospheres: an extensive linelist

    NASA Astrophysics Data System (ADS)

    Masseron, T.; Plez, B.; Van Eck, S.; Colin, R.; Daoutidis, I.; Godefroid, M.; Coheur, P.-F.; Bernath, P.; Jorissen, A.; Christlieb, N.

    2014-11-01

    The advent of high-resolution spectrographs and detailed stellar atmosphere modelling has strengthened the need for accurate molecular data. Carbon-enhanced metal-poor (CEMP) stars spectra are interesting objects with which to study transitions from the CH molecule. We combine programs for spectral analysis of molecules and stellar-radiative transfer codes to build an extensive CH linelist, including predissociation broadening as well as newly identified levels. We show examples of strong predissociation CH lines in CEMP stars, and we stress the important role played by the CH features in the Bond-Neff feature depressing the spectra of barium stars by as much as 0.2 mag in the λ = 3000-5500 Å range. Because of the extreme thermodynamic conditions prevailing in stellar atmospheres (compared to the laboratory), molecular transitions with high energy levels can be observed. Stellar spectra can thus be used to constrain and improve molecular data. Full Table 14 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/571/A47

  16. 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

  17. 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…

  18. 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)

  19. 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.

  20. Convective Overshoot in Stellar Interior

    NASA Astrophysics Data System (ADS)

    Zhang, Q. S.

    2015-07-01

    In stellar interiors, the turbulent thermal convection transports matters and energy, and dominates the structure and evolution of stars. The convective overshoot, which results from the non-local convective transport from the convection zone to the radiative zone, is one of the most uncertain and difficult factors in stellar physics at present. The classical method for studying the convective overshoot is the non-local mixing-length theory (NMLT). However, the NMLT bases on phenomenological assumptions, and leads to contradictions, thus the NMLT was criticized in literature. At present, the helioseismic studies have shown that the NMLT cannot satisfy the helioseismic requirements, and have pointed out that only the turbulent convection models (TCMs) can be accepted. In the first part of this thesis, models and derivations of both the NMLT and the TCM were introduced. In the second part, i.e., the work part, the studies on the TCM (theoretical analysis and applications), and the development of a new model of the convective overshoot mixing were described in detail. In the work of theoretical analysis on the TCM, the approximate solution and the asymptotic solution were obtained based on some assumptions. The structure of the overshoot region was discussed. In a large space of the free parameters, the approximate/asymptotic solutions are in good agreement with the numerical results. We found an important result that the scale of the overshoot region in which the thermal energy transport is effective is 1 HK (HK is the scale height of turbulence kinetic energy), which does not depend on the free parameters of the TCM. We applied the TCM and a simple overshoot mixing model in three cases. In the solar case, it was found that the temperature gradient in the overshoot region is in agreement with the helioseismic requirements, and the profiles of the solar lithium abundance, sound speed, and density of the solar models are also improved. In the low-mass stars of open

  1. Calculation of the geometrical three-point parameter constant appearing in the second order accurate effective medium theory expression for the B-term diffusion coefficient in fully porous and porous-shell random sphere packings.

    PubMed

    Deridder, Sander; Desmet, Gert

    2012-02-01

    Using computational fluid dynamics (CFD), the effective B-term diffusion constant γ(eff) has been calculated for four different random sphere packings with different particle size distributions and packing geometries. Both fully porous and porous-shell sphere packings are considered. The obtained γ(eff)-values have subsequently been used to determine the value of the three-point geometrical constant (ζ₂) appearing in the 2nd-order accurate effective medium theory expression for γ(eff). It was found that, whereas the 1st-order accurate effective medium theory expression is accurate to within 5% over most part of the retention factor range, the 2nd-order accurate expression is accurate to within 1% when calculated with the best-fit ζ₂-value. Depending on the exact microscopic geometry, the best-fit ζ₂-values typically lie in the range of 0.20-0.30, holding over the entire range of intra-particle diffusion coefficients typically encountered for small molecules (0.1 ≤ D(pz)/D(m) ≤ 0.5). These values are in agreement with the ζ₂-value proposed by Thovert et al. for the random packing they considered. PMID:22236565

  2. 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.

  3. Stellar encounter driven red-giant star mass loss in globular clusters

    SciTech Connect

    Pasquato, Mario; Moraghan, Anthony; Chung, Chul; Lee, Young-Wook; De Luca, Andrea; Raimondo, Gabriella; Carini, Roberta; Brocato, Enzo

    2014-07-01

    Globular cluster (GC) color-magnitude diagrams (CMDs) are reasonably well understood in terms of standard stellar evolution. However, there are still some open issues, such as fully accounting for the horizontal branch (HB) morphology in terms of chemical and dynamical parameters. Mass loss on the red giant branch (RGB) shapes the mass distribution of the HB stars, and the color distribution in turn. The physical mechanisms driving mass loss are still unclear, as direct observations fail to reveal a clear correlation between mass-loss rate and stellar properties. The HB mass distribution is further complicated by helium-enhanced multiple stellar populations due to differences in the evolving mass along the HB. We present a simple analytical mass-loss model based on tidal stripping through Roche-Lobe overflow during stellar encounters. Our model naturally results in a non-Gaussian mass-loss distribution with high skewness and contains only two free parameters. We fit it to the HB mass distribution of four Galactic GCs, as obtained from fitting the CMD with zero age HB models. The best-fit model accurately reproduces the observed mass distribution. If confirmed on a wider sample of GCs, our results would account for the effects of dynamics in RGB mass-loss processes and provide a physically motivated procedure for synthetic CMDs of GCs. Our physical modeling of mass loss may result in the ability to disentangle the effects of dynamics and helium-enhanced multiple populations on the HB morphology and is instrumental in making HB morphology a probe of the dynamical state of GCs, leading to an improved understanding of their evolution.

  4. Connection between dynamically derived IMF normalisation and stellar populations

    NASA Astrophysics Data System (ADS)

    McDermid, Richard M.

    2015-04-01

    In this contributed talk I present recent results on the connection between stellar population properties and the normalisation of the stellar initial mass function (IMF) measured using stellar dynamics, based on a large sample of 260 early-type galaxies observed as part of the ATLAS3D project. This measure of the IMF normalisation is found to vary non-uniformly with age- and metallicity-sensitive absorption line strengths. Applying single stellar population models, there are weak but measurable trends of the IMF with age and abundance ratio. Accounting for the dependence of stellar population parameters on velocity dispersion effectively removes these trends, but subsequently introduces a trend with metallicity, such that `heavy' IMFs favour lower metallicities. The correlations are weaker than those found from previous studies directly detecting low-mass stars, suggesting some degree of tension between the different approaches of measuring the IMF. Resolving these discrepancies will be the focus of future work.

  5. 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.

  6. 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.

  7. A new correction of stellar oscillation frequencies for near-surface effects

    NASA Astrophysics Data System (ADS)

    Ball, W. H.; Gizon, L.

    2014-08-01

    Context. Space-based observations of solar-like oscillations present an opportunity to constrain stellar models using individual mode frequencies. However, current stellar models are inaccurate near the surface, which introduces a systematic difference that must be corrected. Aims: We introduce and evaluate two parametrizations of the surface corrections based on formulae given by Gough (1990, LNP, 367, 283). The first we call a cubic term proportional to ν3/ ℐ and the second has an additional inverse term proportional to ν-1/ ℐ, where ν and ℐ are the frequency and inertia of an oscillation mode. Methods: We first show that these formulae accurately correct model frequencies of two different solar models (Model S and a calibrated MESA model) when compared to observed BiSON frequencies. In particular, even the cubic form alone fits significantly better than a power law. We then incorporate the parametrizations into a modelling pipeline that simultaneously fits the surface effects and the underlying stellar model parameters. We apply this pipeline to synthetic observations of a Sun-like stellar model, solar observations degraded to typical asteroseismic uncertainties, and observations of the well-studied CoRoT target HD 52265. For comparison, we also run the pipeline with the scaled power-law correction proposed by Kjeldsen et al. (2008, ApJ, 683, L175). Results: The fits to synthetic and degraded solar data show that the method is unbiased and produces best-fit parameters that are consistent with the input models and known parameters of the Sun. Our results for HD 52265 are consistent with previous modelling efforts and the magnitude of the surface correction is similar to that of the Sun. The fit using a scaled power-law correction is significantly worse but yields consistent parameters, suggesting that HD 52265 is sufficiently Sun-like for the same power-law to be applicable. Conclusions: We find that the cubic term alone is suitable for asteroseismic

  8. 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.

  9. 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.

  10. 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.

  11. Oppositely directed waves of stellar activity in simple dynamo models

    NASA Astrophysics Data System (ADS)

    Tarbeeva, S. M.; Sokoloff, D. D.

    2016-07-01

    Excitations of two oppositely directed waves of stellar activity generated by two dynamo-active layers located in a single stellar hemisphere are examined using simple dynamo models. The domains of model parameters corresponding to various types and directions of the activity waves are found. It is shown that oppositely directed waves of activity are generated if the dynamo numbers have the same order of magnitude, ~105-106, but opposite signs. How frequently this case can be observed among real stars remains open to question. The report of oppositely directed waves of stellar activity in the literature is especially valuable in this connection.

  12. Binary stellar winds. [flow and magnetic field interactions

    NASA Technical Reports Server (NTRS)

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

    1974-01-01

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

  13. Binary stellar winds. [flow and magnetic field geometry

    NASA Technical Reports Server (NTRS)

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

    1974-01-01

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

  14. Stellar Vampires Unmasked

    NASA Astrophysics Data System (ADS)

    2006-10-01

    Astronomers have found possible proofs of stellar vampirism in the globular cluster 47 Tucanae. Using ESO's Very Large Telescope, they found that some hot, bright, and apparently young stars in the cluster present less carbon and oxygen than the majority of their sisters. This indicates that these few stars likely formed by taking their material from another star. "This is the first detection of a chemical signature clearly pointing to a specific scenario to form so-called 'Blue straggler stars' in a globular cluster", said Francesco Ferraro, from the Astronomy Department of Bologna University (Italy) and lead-author of the paper presenting the results. Blue stragglers are unexpectedly young-looking stars found in stellar aggregates, such as globular clusters, which are known to be made up of old stars. These enigmatic objects are thought to be created in either direct stellar collisions or through the evolution and coalescence of a binary star system in which one star 'sucks' material off the other, rejuvenating itself. As such, they provide interesting constraints on both binary stellar evolution and star cluster dynamics. To date, the unambiguous signatures of either stellar traffic accidents or stellar vampirism have not been observed, and the formation mechanisms of Blue stragglers are still a mystery. The astronomers used ESO's Very Large Telescope to measure the abundance of chemical elements at the surface of 43 Blue straggler stars in the globular cluster 47 Tucanae [1]. They discovered that six of these Blue straggler stars contain less carbon and oxygen than the majority of these peculiar objects. Such an anomaly indicates that the material at the surface of the blue stragglers comes from the deep interiors of a parent star [2]. Such deep material can reach the surface of the blue straggler only during the mass transfer process occurring between two stars in a binary system. Numerical simulations indeed show that the coalescence of stars should not

  15. Black holes in young stellar clusters

    SciTech Connect

    Goswami, Sanghamitra; Kiel, Paul; Rasio, Frederic A.

    2014-02-01

    We present theoretical models for stellar black hole (BH) properties in young, massive star clusters. Using a Monte Carlo code for stellar dynamics, we model realistic star clusters with N ≅ 5 × 10{sup 5} stars and significant binary fractions (up to 50%) with self-consistent treatments of stellar dynamics and stellar evolution. We compute the formation rates and characteristic properties of single and binary BHs for various representative ages, cluster parameters, and metallicities. Because of dynamical interactions and supernova (SN) kicks, more single BHs end up retained in clusters compared to BHs in binaries. We also find that the ejection of BHs from a cluster is a strong function of initial density. In low-density clusters (where dynamical effects are negligible), it is mainly SN kicks that eject BHs from the cluster, whereas in high-density clusters (initial central density ρ {sub c}(0) ∼ 10{sup 5} M {sub ☉} pc{sup –3} in our models) the BH ejection rate is enhanced significantly by dynamics. Dynamical interactions of binary systems in dense clusters also modify the orbital period and eccentricity distributions while increasing the probability of a BH having a more massive companion.

  16. ATLAS3D Stellar Population Gradients

    NASA Astrophysics Data System (ADS)

    Kuntschner, Harald

    2015-04-01

    We present stellar population gradients of early-type galaxies from the ATLAS3D survey: a complete, volume-limited multi-wavelength survey of 260 early-type galaxies in the local 42 Mpc volume. Using emission-corrected spectra integrated within elliptical annuli we measure line-strength indices and apply single stellar population (SSP) models to derive SSP-equivalent values of stellar age, metallicity, and alpha enhancement as function of radius. For all galaxies we derive basic linear stellar population gradients versus radius logR/Re). These gradients are examined on their own and versus three mass-sensitive parameters: K-band luminosity MK, velocity dispersion within one effective radius log σe, and our dynamical mass MJAM. We find a correlation between positive age gradients (younger centre) and steeper negative metallicity gradients with a Spearman rank correlation coefficient of -0.46 and a significance of 7.65 × 10-15. Furthermore, we find a robustly estimated mean metallicity gradient of Δ[Z/H] = -0.37 +/- 0.01 for the sample with a significant trend for more massive galaxies to have shallower profiles. While there is no clear distinction between fast and slow rotators or signs of environmental influence, we do detect a significantly larger range of [Z/H]-gradients towards low mass galaxies.

  17. GALA: An Automatic Tool for the Abundance Analysis of Stellar Spectra

    NASA Astrophysics Data System (ADS)

    Mucciarelli, Alessio; Pancino, Elena; Lovisi, Loredana; Ferraro, Francesco R.; Lapenna, Emilio

    2013-04-01

    GALA is a freely distributed Fortran code for automatically deriving the atmospheric parameters (temperature, gravity, microturbulent velocity, and overall metallicity) and abundances for individual species of stellar spectra using the classical method based on the equivalent widths of metallic lines. The abundances of individual spectral lines are derived by using the WIDTH9 code developed by R. L. Kurucz. GALA is designed to obtain the best model atmosphere by optimizing temperature, surface gravity, microturbulent velocity, and metallicity after rejecting the discrepant lines. Finally, it computes accurate internal errors for each atmospheric parameter and abundance. GALA is suitable for analyzing both early- and late-type stars, under the assumption of local thermodynamical equilibrium. The code permits us to obtain chemical abundances and atmospheric parameters for large stellar samples in a very short time, thus making GALA a useful tool in the epoch of multi-object spectrographs and large surveys. An extensive set of tests with both synthetic and observed spectra is performed and discussed to explore the capabilities and robustness of the code. Based on observations collected at the ESO-VLT under programs 65.L-0165, 165.L-0263, 073.D-0211, 080.D-0368, 083.D-0208, and 266.D-5655 and on data available in the ELODIE archive. This research has also made use of the SIMBAD database, operated at CDS, Strasbourg, France.

  18. GALA: AN AUTOMATIC TOOL FOR THE ABUNDANCE ANALYSIS OF STELLAR SPECTRA

    SciTech Connect

    Mucciarelli, Alessio; Lovisi, Loredana; Ferraro, Francesco R.; Lapenna, Emilio

    2013-04-01

    GALA is a freely distributed Fortran code for automatically deriving the atmospheric parameters (temperature, gravity, microturbulent velocity, and overall metallicity) and abundances for individual species of stellar spectra using the classical method based on the equivalent widths of metallic lines. The abundances of individual spectral lines are derived by using the WIDTH9 code developed by R. L. Kurucz. GALA is designed to obtain the best model atmosphere by optimizing temperature, surface gravity, microturbulent velocity, and metallicity after rejecting the discrepant lines. Finally, it computes accurate internal errors for each atmospheric parameter and abundance. GALA is suitable for analyzing both early- and late-type stars, under the assumption of local thermodynamical equilibrium. The code permits us to obtain chemical abundances and atmospheric parameters for large stellar samples in a very short time, thus making GALA a useful tool in the epoch of multi-object spectrographs and large surveys. An extensive set of tests with both synthetic and observed spectra is performed and discussed to explore the capabilities and robustness of the code.

  19. Stellar Properties of Pulsating B Star Candidates in the Kepler Field

    NASA Astrophysics Data System (ADS)

    Waskie, Steven; McSwain, M. Virginia

    2016-01-01

    We measure physical properties of 31 candidate β Cephei, slowly pulsating B stars (SPB), and hybrid pulsating B stars in the Kepler field. We employ LTE Kurucz ATLAS9 model atmospheres and the TLUSTY BSTAR2006 non-LTE grid to measure the projected rotational velocity, v sin i, effective temperature, Teff, and surface gravity, log g, from blue optical spectra for our stars. Results are plotted against the evolutionary tracks of Ekström et al. for determination of stellar masses, radii, and ages. Accurate determination of these parameters is crucial for asteroseismic analysis as it has been shown by Balona et al. that the predicted parameters in the Kepler Input Catalog (KIC) for these hot stars are unreliable.We would like to thank Lehigh University for supporting this research. This work has been funded by NSF grants AST-1109247 and PHY-11359195.

  20. 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

  1. Stellar Angular Diameter Relations for Microlensing Surveys

    NASA Astrophysics Data System (ADS)

    Adams, Arthur; Boyajian, Tabetha S.; von Braun, Kaspar

    2016-01-01

    Determining the physical properties of microlensing events depends on having accurate angular radii of the source star. Using long-baseline optical interferometry we are able to determine the angular sizes of nearby stars with uncertainties less than 2 percent. We present empirical estimates of angular diameters for both dwarfs/subgiants and giant stars as functions of five color indices which are relevant to planned microlensing surveys. We find in all considered colors that metallicity does not play a statistically significant role in predicting stellar size for the samples of stars considered.

  2. HLINOP: Hydrogen LINe OPacity in stellar atmospheres

    NASA Astrophysics Data System (ADS)

    Barklem, P. S.; Piskunov, N.

    2015-07-01

    HLINOP is a collection of codes for computing hydrogen line profiles and opacities in the conditions typical of stellar atmospheres. It includes HLINOP for approximate quick calculation of any line of neutral hydrogen (suitable for model atmosphere calculations), based on the Fortran code of Kurucz and Peterson found in ATLAS9. It also includes HLINPROF, for detailed, accurate calculation of lower Balmer line profiles (suitable for detailed analysis of Balmer lines) and HBOP, to implement the occupation probability formalism of Daeppen, Anderson and Milhalas (1987) and thus account for the merging of bound-bound and bound-free opacity (used often as a wrapper to HLINOP for model atmosphere calculations).

  3. MHD stability of the MHH2 stellarator

    SciTech Connect

    Garabedian, P.R.

    1998-12-31

    The NSTAB code provides a computer implementation of the variational principle of magnetohydrodynamics. Excellent resolution is obtained by combining a spectral representation in the toroidal and poloidal angles with a low order, but exceptionally accurate, finite difference scheme in the radial direction. Conservation form of the magnetostatics equations is used to capture islands and current sheets effectively on crude grids. This method enables one to discuss global stability by analyzing bifurcated solutions of the equilibrium problem. The author applies it to investigate the physics of the MHH2 stellarator, whose magnetic structure has a remarkable property of quasi-axial symmetry.

  4. Grading More Accurately

    ERIC Educational Resources Information Center

    Rom, Mark Carl

    2011-01-01

    Grades matter. College grading systems, however, are often ad hoc and prone to mistakes. This essay focuses on one factor that contributes to high-quality grading systems: grading accuracy (or "efficiency"). I proceed in several steps. First, I discuss the elements of "efficient" (i.e., accurate) grading. Next, I present analytical results…

  5. 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.

  6. 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.

  7. 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.

  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. Polarized Continuum Radiation from Stellar Atmospheres

    NASA Astrophysics Data System (ADS)

    Harrington, J. Patrick

    2015-10-01

    Continuum scattering by free electrons can be significant in early type stars, while in late type stars Rayleigh scattering by hydrogen atoms or molecules may be important. Computer programs used to construct models of stellar atmospheres generally treat the scattering of the continuum radiation as isotropic and unpolarized, but this scattering has a dipole angular dependence and will produce polarization. We review an accurate method for evaluating the polarization and limb darkening of the radiation from model stellar atmospheres. We use this method to obtain results for: (i) Late type stars, based on the MARCS code models (Gustafsson et al. 2008), and (ii) Early type stars, based on the NLTE code TLUSTY (Lanz and Hubeny 2003). These results are tabulated at http://www.astro.umd.edu/~jph/Stellar_Polarization.html. While the net polarization vanishes for an unresolved spherical star, this symmetry is broken by rapid rotation or by the masking of part of the star by a binary companion or during the transit of an exoplanet. We give some numerical results for these last cases.

  10. New Stellar Science with Astro-H

    NASA Astrophysics Data System (ADS)

    Tsuboi, Yohko; Ishibashi, Kazunori; Audard, Marc; Hamaguchi, Kenji; Leutenegger, Maurice A.; Maeda, Yoshitomo; Mori, Koji; Murakami, Hiroshi; Sugawara, Yasuharu; Tsujimoto, Masahiro; ASTRO-H Team

    2015-01-01

    The upcoming X-ray mission ASTRO-H has the unprecedented high energy resolution and highly accurate energy determination (i.e., stable gain) of Soft X-ray Spectrometer (SXS). Combined with the broad-band capability of Soft and Hard X-ray Imagers (SXI and HXI), we will be able to explore a new horizon to extend our understanding of stars and related phenomena. We here highlight the stellar science topics that the ASTRO-H team considers of high priority. (1) Formation of a central star in protostars will be shed light on, for the first time, with the detection of the Doppler shifts of Fe K lines, (2) Dynamical movement of materials during flares will be captured as the Doppler shifts of Fe K lines, (3) Evidence for accreting plasma will be examined in T Tauri star with a diagnostic of the density-sensitive lines, (4) The fluorescent Fe emission line will be commonly observed in massive stellar binary, and then the geometry of the hot gas, which illuminates the stellar surface, would be diagnosed, (5) Hot plasma have been found to fill cavities in star forming regions with unidentified lines. The diagnostics of the lines will determine whether they originate from Non-Equilibrium Ionization conditions or charge exchange.

  11. MASSCLEAN: MASSive CLuster Evolution and ANalysis package -- A new tool for stellar clusters

    NASA Astrophysics Data System (ADS)

    Popescu, Bogdan

    2010-11-01

    Stellar clusters are laboratories for stellar evolution. Their stellar content have an uniform age and chemical composition, but span a large mass interval. The majority of stars are born in clusters and end up in the general field population. An accurate characterization of stellar clusters could be used to built better models, from stellar evolution to the evolution of an entire galaxy. Regardless of the fact that they are so close, for many Milky Way clusters it is difficult to be observed because they are obscured by the dust in the disk of our Galaxy. The clusters from the Local Group and beyond are too distant, so only their integrated properties could be used most of the time. There is one way to analyze the observational data, to search for clusters, and to describe them: simulations. MASSCLEAN (MASSive CLuster Evolution and ANalysis) package was developed to provide a better characterization of Galactic clusters, to derive selection effects of current surveys, and to provide information about the extra-galactic clusters. Simulations of known Galactic clusters are used to get better constraints on their parameters, like mass, age, extinction, chemical composition and distance. This is the traditional way to describe the Galactic clusters, fitting the data using the available models. The difference is that MASSCLEAN simulations provide a consistent set of parameters. The majority of extra-galactic clusters are known only from their integrated properties, integrated magnitudes and colors. The current models for stellar populations are available only in the infinite mass limit. But the real clusters have a finite mass, and their integrated colors show a large dispersion (stochastic fluctuations). The description of the variation of integrated colors as a function of mass and age lead to the creation of MASSCLEANcolors database, based on 70 million Monte Carlo simulations. Since the entries in the database form a consistent set of integrated colors, integrated

  12. Stellar population models at high spectral resolution

    NASA Astrophysics Data System (ADS)

    Maraston, C.; Strömbäck, G.

    2011-12-01

    We present new, high-to-intermediate spectral resolution stellar population models, based on four popular libraries of empirical stellar spectra, namely Pickles, ELODIE, STELIB and MILES. These new models are the same as our previous models, but with higher resolution and based on empirical stellar spectra, while keeping other ingredients the same including the stellar energetics, the atmospheric parameters and the treatment of the thermally pulsating asymptotic giant branch and the horizontal branch morphology. We further compute very high resolution (R= 20 000) models based on the theoretical stellar library MARCS which extends to the near-infrared. We therefore provide merged high-resolution stellar population models, extending from ˜1000 to 25 000 Å, using our previously published high-resolution theoretical models which extended to the ultraviolet. We compare how these libraries perform in stellar population models and highlight spectral regions where discrepancies are found. We confirm our previous findings that the flux around the V band is lower (in a normalized sense) in models based on empirical libraries than in those based on the BaSeL-Kurucz library, which results in a bluer B-V colour. Most noticeably the theoretical library MARCS gives results fully consistent with the empirical libraries. This same effect is also found in other models using MILES, namely Vazdekis et al. and Conroy & Gunn, even though the latter authors reach the opposite conclusion. The bluer predicted B-V colour (by 0.05 mag in our models) is in better agreement with both the colours of luminous red galaxies and globular cluster data. We test the models on their ability to reproduce, through full spectral fitting, the ages and metallicities of Galactic globular clusters as derived from colour-magnitude diagram (CMD) fitting and find overall good agreement. We also discuss extensively the Lick indices calculated directly on the integrated MILES-based spectral energy distributions

  13. The physics of the accretion process in the formation and evolution of Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    Manara, C. F.

    2014-07-01

    The formation of planets is thought to happen in protoplanetary disks surrounding young stars during the first few Myrs of their pre-main-sequence evolution. In order to understand planet formation a detailed knowledge of the disk evolution process is needed. By studying the interaction of the disk with the central star, which includes accretion of matter due to viscous processes in the disk, we can constrain the physical conditions of the inner gaseous disk in which planet formation takes place. With the recent advent of the X-Shooter spectrograph, a second generation instrument of the ESO/VLT, the excess emission due to accretion in the ultraviolet can be studied simultaneously with the accretion signatures in the visible and in the near-infrared, finally giving a complete view of this phenomenon. In this Thesis I have studied various X-Shooter datasets of young stars to determine the intensity and the properties of the accretion process at various phases of disk evolution and as a function of the central star mass and age. To fully exploit the potential of the X-Shooter spectra, I have developed an innovative method of analysis to derive accretion and stellar parameters with an automatic algorithm. This is based on a set of models, composed of a set of photospheric templates of young stars that I gathered and characterized, a set of slab models, that I have coded, to reproduce the emission due to the accretion shock, and a reddening law to take into account extinction effects. This method allows to accurately determine for the first time the stellar and accretion parameters of the targets self-consistently and with no prior assumptions, a significant improvement with respect to previous studies. I have applied this methodology to determine the correct stellar parameters of two objects in the Orion Nebula Cluster that were reported in the literature to have an anomalous old age. My analysis has shown why previous investigations could not resolve the degeneracy

  14. Averaged equilibrium and stability in low-aspect-ratio stellarators

    SciTech Connect

    Garcia, L.; Carreras, B.A.; Dominguez, N.

    1989-01-01

    The MHD equilibrium and stability calculations or stellarators are complex because of the intrinsic three-dimensional (3-D) character of these configurations. The stellarators expansion simplifies the equilibrium calculation by reducing it to a two-dimensional (2-D) problem. The classical stellarator expansion includes terms up to order epsilon/sup 2/, and the vacuum magnetic field is also included up to this order. For large-aspect-ratio configurations, the results of the stellarator expansion agree well with 3-D numerical equilibrium results. But for low-aspect-ratio configurations, these are significant discrepancies with 3-D equilibrium calculations. The main reason for these discrepancies is the approximation in the vacuum field contributions. This problem can be avoided by applying the average method in a vacuum flux coordinate system. In this way, the exact vacuum magnetic field contribution is included and the results agree well with 3-D equilibrium calculations even for low-aspect-ratio configurations. Using the average method in a vacuum flux coordinate system also permit the accurate calculation of local stability properties with the Mercier criterion. The main improvement is in the accurate calculation of the geodesic curvature term. In this paper, we discuss the application of the average method in flux coordinates to the calculation of the Mercier criterion for low-aspect-ratio stellarator configurations. 12 refs., 3 figs.

  15. 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.

  16. Accurate monotone cubic interpolation

    NASA Technical Reports Server (NTRS)

    Huynh, Hung T.

    1991-01-01

    Monotone piecewise cubic interpolants are simple and effective. They are generally third-order accurate, except near strict local extrema where accuracy degenerates to second-order due to the monotonicity constraint. Algorithms for piecewise cubic interpolants, which preserve monotonicity as well as uniform third and fourth-order accuracy are presented. The gain of accuracy is obtained by relaxing the monotonicity constraint in a geometric framework in which the median function plays a crucial role.

  17. Accurate Finite Difference Algorithms

    NASA Technical Reports Server (NTRS)

    Goodrich, John W.

    1996-01-01

    Two families of finite difference algorithms for computational aeroacoustics are presented and compared. All of the algorithms are single step explicit methods, they have the same order of accuracy in both space and time, with examples up to eleventh order, and they have multidimensional extensions. One of the algorithm families has spectral like high resolution. Propagation with high order and high resolution algorithms can produce accurate results after O(10(exp 6)) periods of propagation with eight grid points per wavelength.

  18. CALIBRATIONS OF ATMOSPHERIC PARAMETERS OBTAINED FROM THE FIRST YEAR OF SDSS-III APOGEE OBSERVATIONS

    SciTech Connect

    Mészáros, Sz.; Allende Prieto, C.; Holtzman, J.; García Pérez, A. E.; Chojnowski, S. D.; Hearty, F. R.; Majewski, S. R.; Schiavon, R. P.; Basu, S.; Bizyaev, D.; Chaplin, W. J.; Elsworth, Y.; Cunha, K.; Epstein, C.; Johnson, J. A.; Frinchaboy, P. M.; García, R. A.; Kallinger, T.; Koesterke, L.; and others

    2013-11-01

    The Sloan Digital Sky Survey III (SDSS-III) Apache Point Observatory Galactic Evolution Experiment (APOGEE) is a three-year survey that is collecting 10{sup 5} high-resolution spectra in the near-IR across multiple Galactic populations. To derive stellar parameters and chemical compositions from this massive data set, the APOGEE Stellar Parameters and Chemical Abundances Pipeline (ASPCAP) has been developed. Here, we describe empirical calibrations of stellar parameters presented in the first SDSS-III APOGEE data release (DR10). These calibrations were enabled by observations of 559 stars in 20 globular and open clusters. The cluster observations were supplemented by observations of stars in NASA's Kepler field that have well determined surface gravities from asteroseismic analysis. We discuss the accuracy and precision of the derived stellar parameters, considering especially effective temperature, surface gravity, and metallicity; we also briefly discuss the derived results for the abundances of the α-elements, carbon, and nitrogen. Overall, we find that ASPCAP achieves reasonably accurate results for temperature and metallicity, but suffers from systematic errors in surface gravity. We derive calibration relations that bring the raw ASPCAP results into better agreement with independently determined stellar parameters. The internal scatter of ASPCAP parameters within clusters suggests that metallicities are measured with a precision better than 0.1 dex, effective temperatures better than 150 K, and surface gravities better than 0.2 dex. The understanding provided by the clusters and Kepler giants on the current accuracy and precision will be invaluable for future improvements of the pipeline.

  19. Stellar Rotation Effects in Polarimetric Microlensing

    NASA Astrophysics Data System (ADS)

    Sajadian, Sedighe

    2016-07-01

    It is well known that the polarization signal in microlensing events of hot stars is larger than that of main-sequence stars. Most hot stars rotate rapidly around their stellar axes. The stellar rotation creates ellipticity and gravity-darkening effects that break the spherical symmetry of the source's shape and the circular symmetry of the source's surface brightness respectively. Hence, it causes a net polarization signal for the source star. This polarization signal should be considered in polarimetric microlensing of fast rotating stars. For moderately rotating stars, lensing can magnify or even characterize small polarization signals due to the stellar rotation through polarimetric observations. The gravity-darkening effect due to a rotating source star creates asymmetric perturbations in polarimetric and photometric microlensing curves whose maximum occurs when the lens trajectory crosses the projected position of the rotation pole on the sky plane. The stellar ellipticity creates a time shift (i) in the position of the second peak of the polarimetric curves in transit microlensing events and (ii) in the peak position of the polarimetric curves with respect to the photometric peak position in bypass microlensing events. By measuring this time shift via polarimetric observations of microlensing events, we can evaluate the ellipticity of the projected source surface on the sky plane. Given the characterizations of the FOcal Reducer and low dispersion Spectrograph (FORS2) polarimeter at the Very Large Telescope, the probability of observing this time shift is very small. The more accurate polarimeters of the next generation may well measure these time shifts and evaluate the ellipticity of microlensing source stars.

  20. Stellar Populations with APOGEE and Kepler

    NASA Astrophysics Data System (ADS)

    Johnson, Jennifer; Pinsonneault, Marc H.; Elsworth, Yvonne P.; Epstein, Courtney R.; Hekker, Saskia; Meszaros, Szabolcs; Chaplin, William J.; Garcia, Rafael; Holtzman, Jon A.; Mathur, Savita; García Pérez, Ana; Basu, Sarbani; Girardi, Leo; Silva Aguirre, Víctor; Shetrone, Matthew D.; Stello, Dennis; Rodrigues, Thaise; Allende-Prieto, Carlos; An, Deokkeun; Beck, Paul; Bizyaev, Dmitry; Bovy, Jo; Cunha, Katia M. L.; De Ridder, Joris; Garcia-Hernandez, D.

    2015-01-01

    The history of the Milky Way is recorded in its stars, but dissecting stellar populations is not a straighforward process. Key information is gained by analyzing the absorption lines from high-resolution spectroscopy of stellar atmospheres by the APOGEE survey and analyzing the frequencies in power spectra of photometric lightcurves by Kepler Asteroseismic Science Consortium, in particular the large frequency separation and the frequency of maximum power. From spectroscopy, we measure effective temperature, rotation, metallicity and abundance ratios, while seismology provides gravities, rotation,and evolutionary state. Combined, these two techniques yield other fundamental parameters such as mass and radius. I will discuss revolutionary insights into Galactic evolution gained by this extensive dataset.

  1. Preferred longitudes in solar and stellar activity

    NASA Astrophysics Data System (ADS)

    Berdyugina, S. V.

    An analysis of the distribution of starspots on the surfaces of very active stars, such as RS CVn- FK Com-type stars as well as young solar analogs, reveals preferred longitudes of spot formation and their quasi-periodic oscillations, i.e. flip-flop cycles. A non-linear migration of the preferred longitudes suggests the presence of the differential rotation and variations of mean spot latitudes. It enables recovering stellar butterfly diagrams. Such phenomena are found to persist in the sunspot activity as well. A comparison of the observed properties of preferred longitudes on the Sun with those detected on more active stars leads to the conclusion that we can learn fine details of the stellar dynamo by studying the Sun, while its global parameters on the evolutionary time scale are provided by a sample of active stars.

  2. Accurate stopping power measurements for (0.21-2.68) MeV/u 1H+ and 4He+ ions crossing thin Al foils; extraction of the (I, b) parameters

    NASA Astrophysics Data System (ADS)

    Moussa, D.; Damache, S.; Ouichaoui, S.

    2015-01-01

    The stopping powers of thin Al foils for H+ and 4He+ ions have been measured over the energy range E = (206.03- 2680.05) keV/amu with an overall relative uncertainty better than 1% using the transmission method. The derived S (E) experimental data are compared to previous ones from the literature, to values derived by the SRIM-2008 code or compiled in the ICRU-49 report, and to the predictions of Sigmund-Schinner binary collision stopping theory. Besides, the S (E) data for H+ ions together with those for He2+ ions reported by Andersen et al. (1977) have been analyzed over the energy interval E > 1.0 MeV using the modified Bethe-Bloch stopping theory. The following sets of values have been inferred for the mean excitation potential, I, and the Barkas-Andersen parameter, b, for H+ and He+ projectiles, respectively: { (I = 164 ± 3) eV, b = 1.40 } and { (I = 163 ± 2.5) eV, b = 1.38 } . As expected, the I parameter is found to be independent of the projectile electronic structure presumably indicating that the contribution of charge exchange effects becomes negligible as the projectile velocity increases. Therefore, the I parameter must be determined from precise stopping power measurements performed at high projectile energies where the Bethe stopping theory is fully valid.

  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. Fundamental Parameters of Eclipsing Binaries in the Kepler Field of View

    NASA Astrophysics Data System (ADS)

    Matson, Rachel A.

    2016-01-01

    Accurate knowledge of stellar parameters such as mass, radius, composition, and age inform our understanding of stellar evolution and constrain theoretical models. Binaries and, in particular, eclipsing binaries make it possible to directly measure these parameters without reliance on models or scaling relations. In my dissertation I derive fundamental parameters of stars in close binary systems with and without (detected) tertiary companions and obtain accurate masses and radii of the components to compare with evolutionary models. Radial velocities and spectroscopic orbits are derived from optical spectra, while Doppler tomography is used to determine effective temperatures, projected rotational velocities, and metallicities for each component of the binary. These parameters are then combined with Kepler photometry to obtain accurate masses and radii through light curve and radial velocity fitting with the binary modeling software ELC. Here, I present spectroscopic orbits, atmospheric parameters, and estimated masses for 41 eclipsing binaries (including seven with tertiary companions) that were observed with Kepler and have periods less then six days. Further analysis, including binary modeling and comparison with evolutionary models is shown for a sub-sample of these stars.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. Inference on gravitational waves from coalescences of stellar-mass compact objects and intermediate-mass black holes

    NASA Astrophysics Data System (ADS)

    Haster, Carl-Johan; Wang, Zhilu; Berry, Christopher P. L.; Stevenson, Simon; Veitch, John; Mandel, Ilya

    2016-04-01

    Gravitational waves from coalescences of neutron stars or stellar-mass black holes into intermediate-mass black holes (IMBHs) of ≳100 solar masses represent one of the exciting possible sources for advanced gravitational-wave detectors. These sources can provide definitive evidence for the existence of IMBHs, probe globular-cluster dynamics, and potentially serve as tests of general relativity. We analyse the accuracy with which we can measure the masses and spins of the IMBH and its companion in intermediate-mass-ratio coalescences. We find that we can identify an IMBH with a mass above 100 M⊙ with 95 per cent confidence provided the massive body exceeds 130 M⊙. For source masses above ˜200 M⊙, the best measured parameter is the frequency of the quasi-normal ringdown. Consequently, the total mass is measured better than the chirp mass for massive binaries, but the total mass is still partly degenerate with spin, which cannot be accurately measured. Low-frequency detector sensitivity is particularly important for massive sources, since sensitivity to the inspiral phase is critical for measuring the mass of the stellar-mass companion. We show that we can accurately infer source parameters for cosmologically redshifted signals by applying appropriate corrections. We investigate the impact of uncertainty in the model gravitational waveforms and conclude that our main results are likely robust to systematics.

  13. Planetary transits and stellar variability

    NASA Astrophysics Data System (ADS)

    Aigrain, Suzanne

    2005-01-01

    This thesis focuses on the detection of extrasolar planets via the transit method, and more specifically addresses issues relevant to the preparation of upcoming space missions such as CoRoT, Kepler, Eddington, aiming to detect terrestrial planets. The automated detection of transits in tens of thousands of noisy light curves is a challenging task because of the brief, shallow and rare nature of the sought-after signal. I developed a Bayesian transit detection algorithm and tested it through Monte Carlo simulations. This led to a number of improvements to the algorithm, resulting in a maximum likelihood box-fitting approach that is simpler and, for detection purposes, more effective. I also developed an empirical model of the intrinsic micro-variability of the parent stars, which constitutes one of the main performance limitations for space-based transit searches, and used this model to optimise variability filters. These tools were used to identify optimal regions of the stellar parameter space to be targeted by missions such as CoRoT and Eddington, through Monte Carlo simulations and participation in the first CoRoT blind transit detection exercise. Recently, the same tools have been used to analyse ground-based data from the University of New South Wales planet search project, leading to the identification of several potential transiting planet candidates.

  14. The Stagger-grid: A grid of 3D stellar atmosphere models. IV. Limb darkening coefficients

    NASA Astrophysics Data System (ADS)

    Magic, Z.; Chiavassa, A.; Collet, R.; Asplund, M.

    2015-01-01

    Aims: We compute the emergent stellar spectra from the UV to far infrared for different viewing angles using realistic 3D model atmospheres for a large range in stellar parameters to predict the stellar limb darkening. Methods: We have computed full 3D LTE synthetic spectra based on 3D radiative hydrodynamic atmosphere models from the Stagger-grid in the ranges: Teff from 4000 to 7000 K, log g from 1.5 to 5.0, and [Fe/H], from -4.0 to +0.5. From the resulting intensities, we derived coefficients for the standard limb darkening laws considering a number of often-used photometric filters. Furthermore, we calculated theoretical transit light curves, in order to quantify the differences between predictions by the widely used 1D model atmosphere and our 3D models. Results: The 3D models are often found to predict steeper darkening towards the limb compared to the 1D models, mainly due to the temperature stratifications and temperature gradients being different in the 3D models compared to those predicted with 1D models based on the mixing length theory description of convective energy transport. The resulting differences in the transit light curves are rather small; however, these can be significant for high-precision observations of extrasolar transits, and are able to lower the residuals from the fits with 1D limb darkening profiles. Conclusions: We advocate the use of the new limb darkening coefficients provided for the standard four-parameter non-linear power law, which can fit the limb darkening more accurately than other choices. Full Table A.1 and the grid of spectra are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/573/A90, as well as at http://www.stagger-stars.net

  15. Accurate determination of optical bandgap and lattice parameters of Zn{sub 1-x}Mg{sub x}O epitaxial films (0{<=}x{<=}0.3) grown by plasma-assisted molecular beam epitaxy on a-plane sapphire

    SciTech Connect

    Laumer, Bernhard; Schuster, Fabian; Stutzmann, Martin; Bergmaier, Andreas; Dollinger, Guenther; Eickhoff, Martin

    2013-06-21

    Zn{sub 1-x}Mg{sub x}O epitaxial films with Mg concentrations 0{<=}x{<=}0.3 were grown by plasma-assisted molecular beam epitaxy on a-plane sapphire substrates. Precise determination of the Mg concentration x was performed by elastic recoil detection analysis. The bandgap energy was extracted from absorption measurements with high accuracy taking electron-hole interaction and exciton-phonon complexes into account. From these results a linear relationship between bandgap energy and Mg concentration is established for x{<=}0.3. Due to alloy disorder, the increase of the photoluminescence emission energy with Mg concentration is less pronounced. An analysis of the lattice parameters reveals that the epitaxial films grow biaxially strained on a-plane sapphire.

  16. The Local Stellar Velocity Field via Vector Spherical Harmonics

    NASA Technical Reports Server (NTRS)

    Makarov, V. V.; Murphy, D. W.

    2007-01-01

    We analyze the local field of stellar tangential velocities for a sample of 42,339 nonbinary Hipparcos stars with accurate parallaxes, using a vector spherical harmonic formalism.We derive simple relations between the parameters of the classical linear model (Ogorodnikov-Milne) of the local systemic field and low-degree terms of the general vector harmonic decomposition. Taking advantage of these relationships, we determine the solar velocity with respect to the local stars of (V(sub X), V(sub Y), V(sub Z)) = (10.5, 18.5, 7.3) +/- 0.1 km s(exp -1) not for the asymmetric drift with respect to the local standard of rest. If only stars more distant than 100 pc are considered, the peculiar solar motion is (V(sub X), V(sub Y), V(sub Z)) = (9.9, 15.6, 6.9) +/- 0.2 km s(exp -1). The adverse effects of harmonic leakage, which occurs between the reflex solar motion represented by the three electric vector harmonics in the velocity space and higher degree harmonics in the proper-motion space, are eliminated in our analysis by direct subtraction of the reflex solar velocity in its tangential components for each star...

  17. Accurate measurement of time

    NASA Astrophysics Data System (ADS)

    Itano, Wayne M.; Ramsey, Norman F.

    1993-07-01

    The paper discusses current methods for accurate measurements of time by conventional atomic clocks, with particular attention given to the principles of operation of atomic-beam frequency standards, atomic hydrogen masers, and atomic fountain and to the potential use of strings of trapped mercury ions as a time device more stable than conventional atomic clocks. The areas of application of the ultraprecise and ultrastable time-measuring devices that tax the capacity of modern atomic clocks include radio astronomy and tests of relativity. The paper also discusses practical applications of ultraprecise clocks, such as navigation of space vehicles and pinpointing the exact position of ships and other objects on earth using the GPS.

  18. 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.

  19. 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.

  20. Accurate quantum chemical calculations

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.; Taylor, Peter R.

    1989-01-01

    An important goal of quantum chemical calculations is to provide an understanding of chemical bonding and molecular electronic structure. A second goal, the prediction of energy differences to chemical accuracy, has been much harder to attain. First, the computational resources required to achieve such accuracy are very large, and second, it is not straightforward to demonstrate that an apparently accurate result, in terms of agreement with experiment, does not result from a cancellation of errors. Recent advances in electronic structure methodology, coupled with the power of vector supercomputers, have made it possible to solve a number of electronic structure problems exactly using the full configuration interaction (FCI) method within a subspace of the complete Hilbert space. These exact results can be used to benchmark approximate techniques that are applicable to a wider range of chemical and physical problems. The methodology of many-electron quantum chemistry is reviewed. Methods are considered in detail for performing FCI calculations. The application of FCI methods to several three-electron problems in molecular physics are discussed. A number of benchmark applications of FCI wave functions are described. Atomic basis sets and the development of improved methods for handling very large basis sets are discussed: these are then applied to a number of chemical and spectroscopic problems; to transition metals; and to problems involving potential energy surfaces. Although the experiences described give considerable grounds for optimism about the general ability to perform accurate calculations, there are several problems that have proved less tractable, at least with current computer resources, and these and possible solutions are discussed.

  1. 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

  2. Clinical application of a novel automatic algorithm for actigraphy-based activity and rest period identification to accurately determine awake and asleep ambulatory blood pressure parameters and cardiovascular risk.

    PubMed

    Crespo, Cristina; Fernández, José R; Aboy, Mateo; Mojón, Artemio

    2013-03-01

    This paper reports the results of a study designed to determine whether there are statistically significant differences between the values of ambulatory blood pressure monitoring (ABPM) parameters obtained using different methods-fixed schedule, diary, and automatic algorithm based on actigraphy-of defining the main activity and rest periods, and to determine the clinical relevance of such differences. We studied 233 patients (98 men/135 women), 61.29 ± .83 yrs of age (mean ± SD). Statistical methods were used to measure agreement in the diagnosis and classification of subjects within the context of ABPM and cardiovascular disease risk assessment. The results show that there are statistically significant differences both at the group and individual levels. Those at the individual level have clinically significant implications, as they can result in a different classification, and, therefore, different diagnosis and treatment for individual subjects. The use of an automatic algorithm based on actigraphy can lead to better individual treatment by correcting the accuracy problems associated with the fixed schedule on patients whose actual activity/rest routine differs from the fixed schedule assumed, and it also overcomes the limitations and reliability issues associated with the use of diaries. PMID:23130607

  3. 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

  4. Abundances, planetary nebulae, and stellar evolution

    NASA Technical Reports Server (NTRS)

    Aller, Lawrence H.

    1994-01-01

    Among Henry Norris Russell's many achievements were his contributions to solar and stellar spectroscopy, in particular, to an analysis of the chemical composition of the solar atmosphere. The question of composition differences between stars was hotly debated; some distinguished astronomers argued that all stars had the solar composition. Some early challenges to this doctrine are described. Determinations of chemical compositions of gaseous nebulae were much more difficult. If we observe the lines of a given chemical element in one ionization stage in a stellar spectrum, we can deduce readily the abundance of that element. No such luxury is available for a planetary or diffuse gaseous nebula. We must measure lines of as many ionization stages as we can. Furthermore, a nebula is an extended object. Often detailed spectroscopy is at hand only for narrow pencil columns taken through the image. Different observers use a variety of apertures. Fortunately it is possible to calculate theoretical spectra for any arbitrary cross section taken through a symmetrical model, so UV, optical, and IR observations all can be compared properly with a prediction. The value of high-resolution spectra obtained with instruments such as the Hamilton Echelle Spectrograph at Lick Observatory is emphasized. Improved fluxes for weak but important transitions are found. Close blends of lines of different ions can be resolved, and checks can be made on predictions of atomic parameters such as Einstein A-values and collision strengths. High spectral resolution data have been obtained and reduced for 22 planetary nebulae of varying size, structure, stellar population membership, dustiness, level of excitation, evolutionary status, and chemical compositions. The promise seems justified that with such extensive, high quality data, additional insights on nebular genesis and late states of stellar evolution can be found. The present survey is confined to nebulae of high surface brightness, but

  5. Abundances, planetary nebulae, and stellar evolution

    NASA Astrophysics Data System (ADS)

    Aller, Lawrence H.

    1994-09-01

    Among Henry Norris Russell's many achievements were his contributions to solar and stellar spectroscopy, in particular, to an analysis of the chemical composition of the solar atmosphere. The question of composition differences between stars was hotly debated; some distinguished astronomers argued that all stars had the solar composition. Some early challenges to this doctrine are described. Determinations of chemical compositions of gaseous nebulae were much more difficult. If we observe the lines of a given chemical element in one ionization stage in a stellar spectrum, we can deduce readily the abundance of that element. No such luxury is available for a planetary or diffuse gaseous nebula. We must measure lines of as many ionization stages as we can. Furthermore, a nebula is an extended object. Often detailed spectroscopy is at hand only for narrow pencil columns taken through the image. Different observers use a variety of apertures. Fortunately it is possible to calculate theoretical spectra for any arbitrary cross section taken through a symmetrical model, so UV, optical, and IR observations all can be compared properly with a prediction. The value of high-resolution spectra obtained with instruments such as the Hamilton Echelle Spectrograph at Lick Observatory is emphasized. Improved fluxes for weak but important transitions are found. Close blends of lines of different ions can be resolved, and checks can be made on predictions of atomic parameters such as Einstein A-values and collision strengths. High spectral resolution data have been obtained and reduced for 22 planetary nebulae of varying size, structure, stellar population membership, dustiness, level of excitation, evolutionary status, and chemical compositions. The promise seems justified that with such extensive, high quality data, additional insights on nebular genesis and late states of stellar evolution can be found. The present survey is confined to nebulae of high surface brightness, but

  6. Spectroscopic parameters for solar-type stars with moderate-to-high rotation. New parameters for ten planet hosts

    NASA Astrophysics Data System (ADS)

    Tsantaki, M.; Sousa, S. G.; Santos, N. C.; Montalto, M.; Delgado-Mena, E.; Mortier, A.; Adibekyan, V.; Israelian, G.

    2014-10-01

    Context. Planetary studies demand precise and accurate stellar parameters as input for inferring the planetary properties. Different methods often provide different results that could lead to biases in the planetary parameters. Aims: In this work, we present a refinement of the spectral synthesis technique designed to treat fast rotating stars better. This method is used to derive precise stellar parameters, namely effective temperature, surface gravity, metallicity, and rotational velocity. The procedure is tested for FGK stars with low and moderate-to-high rotation rates. Methods: The spectroscopic analysis is based on the spectral synthesis package Spectroscopy Made Easy (SME), which assumes Kurucz model atmospheres in LTE. The line list where the synthesis is conducted is comprised of iron lines, and the atomic data are derived after solar calibration. Results: The comparison of our stellar parameters shows good agreement with literature values, both for slowly and for fast rotating stars. In addition, our results are on the same scale as the parameters derived from the iron ionization and excitation method presented in our previous works. We present new atmospheric parameters for 10 transiting planet hosts as an update to the SWEET-Cat catalog. We also re-analyze their transit light curves to derive new updated planetary properties. Based on observations collected at the La Silla Observatory, ESO (Chile) with the FEROS spectrograph at the 2.2 m telescope (ESO runs ID 089.C-0444(A), 088.C-0892(A)) and with the HARPS spectrograph at the 3.6 m telescope (ESO runs ID 072.C-0488(E), 079.C-0127(A)); at the Observatoire de Haute-Provence (OHP, CNRS/OAMP), France, with the SOPHIE spectrograph at the 1.93 m telescope and at the Observatoire Midi-Pyrénées (CNRS), France, with the NARVAL spectrograph at the 2 m Bernard Lyot Telescope (Run ID L131N11).Appendix A is available in electronic form at http://www.aanda.org

  7. 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.

  8. 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.

  9. Axisymmetric Simulations of Hot Jupiter-Stellar Wind Hydrodynamic Interaction

    NASA Astrophysics Data System (ADS)

    Christie, Duncan; Arras, Phil; Li, Zhi-Yun

    2016-03-01

    Gas giant exoplanets orbiting at close distances to the parent star are subjected to large radiation and stellar wind fluxes. In this paper, hydrodynamic simulations of the planetary upper atmosphere and its interaction with the stellar wind are carried out to understand the possible flow regimes and how they affect the Lyα transmission spectrum. Following Tremblin and Chiang, charge exchange reactions are included to explore the role of energetic atoms as compared to thermal particles. In order to understand the role of the tail as compared to the leading edge of the planetary gas, the simulations were carried out under axisymmetry, and photoionization and stellar wind electron impact ionization reactions were included to limit the extent of the neutrals away from the planet. By varying the planetary gas temperature, two regimes are found. At high temperature, a supersonic planetary wind is found, which is turned around by the stellar wind and forms a tail behind the planet. At lower temperatures, the planetary wind is shut off when the stellar wind penetrates inside where the sonic point would have been. In this regime mass is lost by viscous interaction at the boundary between planetary and stellar wind gases. Absorption by cold hydrogen atoms is large near the planetary surface, and decreases away from the planet as expected. The hot hydrogen absorption is in an annulus and typically dominated by the tail, at large impact parameter, rather than by the thin leading edge of the mixing layer near the substellar point.

  10. Can stellar activity make a planet seem misaligned?

    NASA Astrophysics Data System (ADS)

    Oshagh, M.; Dreizler, S.; Santos, N. C.; Figueira, P.; Reiners, A.

    2016-08-01

    Several studies have shown that the occultation of stellar active regions by the transiting planet can generate anomalies in the high-precision transit light curves, and these anomalies may lead to an inaccurate estimate of the planetary parameters (e.g., the planet radius). Since the physics and geometry behind the transit light curve and the Rossiter-McLaughlin effect (spectroscopic transit) are the same, the Rossiter-McLaughlin observations are expected to be affected by the occultation of stellar active regions in a similar way. In this paper we perform a fundamental test on the spin-orbit angles as derived by Rossiter-McLaughlin measurements, and we examine the impact of the occultation of stellar active regions by the transiting planet on the spin-orbit angle estimations. Our results show that the inaccurate estimation on the spin-orbit angle due to stellar activity can be quite significant (up to ~30 deg), particularly for the edge-on, aligned, and small transiting planets. Therefore, our results suggest that the aligned transiting planets are the ones that can be easily misinterpreted as misaligned owing to the stellar activity. In other words, the biases introduced by ignoring stellar activity are unlikely to be the culprit for the highly misaligned systems.

  11. An eclipsing-binary distance to the Large Magellanic Cloud accurate to two per cent.

    PubMed

    Pietrzyński, G; Graczyk, D; Gieren, W; Thompson, I B; Pilecki, B; Udalski, A; Soszyński, I; Kozłowski, S; Konorski, P; Suchomska, K; Bono, G; Moroni, P G Prada; Villanova, S; Nardetto, N; Bresolin, F; Kudritzki, R P; Storm, J; Gallenne, A; Smolec, R; Minniti, D; Kubiak, M; Szymański, M K; Poleski, R; Wyrzykowski, L; Ulaczyk, K; Pietrukowicz, P; Górski, M; Karczmarek, P

    2013-03-01

    In the era of precision cosmology, it is essential to determine the Hubble constant to an accuracy of three per cent or better. At present, its uncertainty is dominated by the uncertainty in the distance to the Large Magellanic Cloud (LMC), which, being our second-closest galaxy, serves as the best anchor point for the cosmic distance scale. Observations of eclipsing binaries offer a unique opportunity to measure stellar parameters and distances precisely and accurately. The eclipsing-binary method was previously applied to the LMC, but the accuracy of the distance results was lessened by the need to model the bright, early-type systems used in those studies. Here we report determinations of the distances to eight long-period, late-type eclipsing systems in the LMC, composed of cool, giant stars. For these systems, we can accurately measure both the linear and the angular sizes of their components and avoid the most important problems related to the hot, early-type systems. The LMC distance that we derive from these systems (49.97 ± 0.19 (statistical) ± 1.11 (systematic) kiloparsecs) is accurate to 2.2 per cent and provides a firm base for a 3-per-cent determination of the Hubble constant, with prospects for improvement to 2 per cent in the future. PMID:23467166

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. BASE-9: Bayesian Analysis for Stellar Evolution with nine variables

    NASA Astrophysics Data System (ADS)

    Robinson, Elliot; von Hippel, Ted; Stein, Nathan; Stenning, David; Wagner-Kaiser, Rachel; Si, Shijing; van Dyk, David

    2016-08-01

    The BASE-9 (Bayesian Analysis for Stellar Evolution with nine variables) software suite recovers star cluster and stellar parameters from photometry and is useful for analyzing single-age, single-metallicity star clusters, binaries, or single stars, and for simulating such systems. BASE-9 uses a Markov chain Monte Carlo (MCMC) technique along with brute force numerical integration to estimate the posterior probability distribution for the age, metallicity, helium abundance, distance modulus, line-of-sight absorption, and parameters of the initial-final mass relation (IFMR) for a cluster, and for the primary mass, secondary mass (if a binary), and cluster probability for every potential cluster member. The MCMC technique is used for the cluster quantities (the first six items listed above) and numerical integration is used for the stellar quantities (the last three items in the above list).

  18. Bonnsai: a Bayesian tool for comparing stars with stellar evolution models

    NASA Astrophysics Data System (ADS)

    Schneider, F. R. N.; Langer, N.; de Koter, A.; Brott, I.; Izzard, R. G.; Lau, H. H. B.

    2014-10-01

    Powerful telescopes equipped with multi-fibre or integral field spectrographs combined with detailed models of stellar atmospheres and automated fitting techniques allow for the analysis of large number of stars. These datasets contain a wealth of information that require new analysis techniques to bridge the gap between observations and stellar evolution models. To that end, we develop Bonnsai (BONN Stellar Astrophysics Interface), a Bayesian statistical method, that is capable of comparing all available observables simultaneously to stellar models while taking observed uncertainties and prior knowledge such as initial mass functions and distributions of stellar rotational velocities into account. Bonnsai can be used to (1) determine probability distributions of fundamental stellar parameters such as initial masses and stellar ages from complex datasets; (2) predict stellar parameters that were not yet observationally determined; and (3) test stellar models to further advance our understanding of stellar evolution. An important aspect of Bonnsai is that it singles out stars that cannot be reproduced by stellar models through χ2 hypothesis tests and posterior predictive checks. Bonnsai can be used with any set of stellar models and currently supports massive main-sequence single star models of Milky Way and Large and Small Magellanic Cloud composition. We apply our new method to mock stars to demonstrate its functionality and capabilities. In a first application, we use Bonnsai to test the stellar models of Brott et al. (2011, A&A, 530, A115) by comparing the stellar ages inferred for the primary and secondary stars of eclipsing Milky Way binaries of which the components range in mass between 4.5 and 28 M⊙. Ages are determined from dynamical masses and radii that are known to better than 3%. We show that the stellar models must include rotation because stellar radii can be increased by several percent via centrifugal forces. We find that the average age

  19. The Spitzer Survey of Stellar Structure in Galaxies (S4G): Stellar Masses, Sizes, and Radial Profiles for 2352 Nearby Galaxies

    NASA Astrophysics Data System (ADS)

    Muñoz-Mateos, Juan Carlos; Sheth, Kartik; Regan, Michael; Kim, Taehyun; Laine, Jarkko; Erroz-Ferrer, Santiago; Gil de Paz, Armando; Comeron, Sebastien; Hinz, Joannah; Laurikainen, Eija; Salo, Heikki; Athanassoula, E.; Bosma, Albert; Bouquin, Alexandre Y. K.; Schinnerer, Eva; Ho, Luis; Zaritsky, Dennis; Gadotti, Dimitri A.; Madore, Barry; Holwerda, Benne; Menéndez-Delmestre, Karín; Knapen, Johan H.; Meidt, Sharon; Querejeta, Miguel; Mizusawa, Trisha; Seibert, Mark; Laine, Seppo; Courtois, Helene

    2015-07-01

    The Spitzer Survey of Stellar Structure in Galaxies is a volume, magnitude, and size-limited survey of 2352 nearby galaxies with deep imaging at 3.6 and 4.5 μm. In this paper, we describe our surface photometry pipeline and showcase the associated data products that we have released to the community. We also identify the physical mechanisms leading to different levels of central stellar mass concentration for galaxies with the same total stellar mass. Finally, we derive the local stellar mass-size relation at 3.6 μm for galaxies of different morphologies. Our radial profiles reach stellar mass surface densities below ˜ 1 {M}⊙ {{pc}}-2. Given the negligible impact of dust and the almost constant mass-to-light ratio at these wavelengths, these profiles constitute an accurate inventory of the radial distribution of stellar mass in nearby galaxies. From these profiles we have also derived global properties such as asymptotic magnitudes (and the corresponding stellar masses), isophotal sizes and shapes, and concentration indices. These and other data products from our various pipelines (science-ready mosaics, object masks, 2D image decompositions, and stellar mass maps) can be publicly accessed at IRSA (http://irsa.ipac.caltech.edu/data/SPITZER/S4G/).

  20. 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.

  1. 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.

  2. SUB-STELLAR COMPANIONS AND STELLAR MULTIPLICITY IN THE TAURUS STAR-FORMING REGION

    SciTech Connect

    Daemgen, Sebastian; Bonavita, Mariangela; Jayawardhana, Ray; Lafrenière, David; Janson, Markus

    2015-02-01

    We present results from a large, high-spatial-resolution near-infrared imaging search for stellar and sub-stellar companions in the Taurus-Auriga star-forming region. The sample covers 64 stars with masses between those of the most massive Taurus members at ∼3 M {sub ☉} and low-mass stars at ∼0.2 M {sub ☉}. We detected 74 companion candidates, 34 of these reported for the first time. Twenty-five companions are likely physically bound, partly confirmed by follow-up observations. Four candidate companions are likely unrelated field stars. Assuming physical association with their host star, estimated companion masses are as low as ∼2 M {sub Jup}. The inferred multiplicity frequency within our sensitivity limits between ∼10-1500 AU is 26.3{sub −4.9}{sup +6.6}%. Applying a completeness correction, 62% ± 14% of all Taurus stars between 0.7 and 1.4 M {sub ☉} appear to be multiple. Higher order multiples were found in 1.8{sub −1.5}{sup +4.2}% of the cases, in agreement with previous observations of the field. We estimate a sub-stellar companion frequency of ∼3.5%-8.8% within our sensitivity limits from the discovery of two likely bound and three other tentative very low-mass companions. This frequency appears to be in agreement with what is expected from the tail of the stellar companion mass ratio distribution, suggesting that stellar and brown dwarf companions share the same dominant formation mechanism. Further, we find evidence for possible evolution of binary parameters between two identified sub-populations in Taurus with ages of ∼2 Myr and ∼20 Myr, respectively.

  3. 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.

  4. 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.

  5. Innovations in Quasi-Poloidal Stellarator Design

    NASA Astrophysics Data System (ADS)

    Nelson, B. E.; Lyon, J. F.; Freudenberg, K. D.; Fogarty, P. J.; Benson, R. D.; Madhukar, M.

    2006-10-01

    The Quasi-Poloidal Stellarator (QPS) is being developed with very low plasma aspect ratio, 1/2-1/4 that of existing stellarators. Design innovation is driven by both the complex 3-D geometry and the need for reduced cost and risk in fabrication, so QPS differs significantly in design and construction from other toroidal devices. An internally cooled, compacted cable conductor consisting of stranded copper filaments wound around an internal copper cooling tube was developed that can be wound into complex 3-D shapes. This conductor is wound directly onto the complex, highly accurate, stainless steel coil winding forms. Simplified coil winding procedures lead to faster fabrication and reduced technical risk. A full-size prototype of the largest and most complex of the winding forms has been cast using a patternless process (machined sand molds) and a high-temperature pour, which resulted in <1/10 the major weld repairs of similar sand castings using conventional patterns, and machined to high precision. A vacuum-tight cover is welded over each coil pack and a high-temperature cyanate ester resin is used for vacuum pressure impregnation of the coils because it has several important advantages over the usual epoxy. The completed coils are then installed in an external vacuum vessel.

  6. Energy balance of stellar coronae. III - Effect of stellar mass and radius

    NASA Technical Reports Server (NTRS)

    Hammer, R.

    1984-01-01

    A homologous transformation is derived which permits the application of the numerical coronal models of Hammer from a star with solar mass and radius to other stars. This scaling requires a few approximations concerning the lower boundary conditions and the temperature dependence of the conductivity and emissivity. These approximations are discussed and found to be surprisingly mild. Therefore, the scaling of the coronal models to other stars is rather accurate; it is found to be particularly accurate for main-sequence stars. The transformation is used to derive an equation that gives the maximum temperature of open coronal regions as a function of stellar mass and radius, the coronal heating flux, and the characteristic damping length over which the corona is heated.

  7. The Interaction Between Late-Stage Stellar Mass Loss and the Hot Interstellar Medium in Elliptical Galaxies

    NASA Astrophysics Data System (ADS)

    Parriott, Joel Richard

    Stellar mass loss is thought to be the dominant source of hot gas in elliptical galaxies, but calculations have yet to accurately treat the processes by which this mass loss enters the interstellar medium. The details of this interaction have direct implications for resolving several important disagreements between X-ray observations and the standard cooling flow model, and we suggest a mechanism for the interaction which could help to mitigate these disagreements. We test this new picture by conducting a series of highly accurate two dimensional numerical hydrodynamic simulations of the complex interaction between the stellar ejecta and the surrounding hot medium. We develop a distributed memory parallel processing version of the original Piecewise Parabolic Method (PPM) serial code using a portable message passing standard (MPI). Performance tests of this code on a Cray T3E and IBM SP2 show it to have a parallel efficiency of 80%-90% at N=32 processors despite its heavy data communication load. The results of our simulations, which sample a representative phase-space of the ambient gas density (n~10-3 cm-3) and the stellar velocity through this ambient medium (σ1D~200 km/s), show a reduction in the heating efficiency compared to the standard model. In this model, there is a 100% efficient and instantaneous thermalization of the stellar mass loss, to the local velocity dispersion temperature, by the contact discontinuity and bow shock established as the hot gas flows past the stellar outflow. We find that these shocks are not the primary heating mechanism; rather, the ambient flow imparts momentum to the stellar ejecta to push it into a wake behind the star, which is where the bulk of the heating is done by large amplitude Kelvin-Helmholtz instabilities in the flow that mix the cold (T<105 K) stellar material with the hotter (T=3×106 K) ambient gas. Although this mixing is sufficient to eventually heat and merge all of the ejecta in the adiabatic case, the

  8. Stellar Nucleosynthesis in the Hyades Open Cluster

    NASA Astrophysics Data System (ADS)

    Schuler, Simon C.; King, Jeremy R.; The, Lih-Sin

    2009-08-01

    We report a comprehensive light-element (Li, C, N, O, Na, Mg, and Al) abundance analysis of three solar-type main sequence (MS) dwarfs and three red giant branch (RGB) clump stars in the Hyades open cluster using high-resolution and high signal-to-noise spectroscopy. The abundances have been derived in a self-consistent fashion, and for each group (MS or RGB), the CNO abundances are found to be in excellent star-to-star agreement. Using the dwarfs to infer the initial composition of the giants, the combined abundance patterns confirm that the giants have undergone the first dredge-up and that material processed by the CN cycle has been mixed to the surface layers. The observed abundances are compared to predictions of a standard stellar model based on the Clemson-American University of Beirut (CAUB) stellar evolution code. The model reproduces the observed evolution of the N and O abundances, as well as the previously derived 12C/13C ratio, but it fails to predict by a factor of 1.5 the observed level of 12C depletion. A similar discord appears to exist in previously reported observed and modeled C abundances of giants in the Galactic disk. Random uncertainties in the mean abundances and uncertainties related to possible systematic errors in the Hyades dwarf and giant parameter scales cannot account for the discrepancy in the observed and modeled abundances. Li abundances are derived to determine if noncanonical extra mixing, like that seen in low-mass metal-poor giants, has occurred in the Hyades giants. The Li abundance of the giant γ Tau is in good accord with the predicted level of surface Li dilution, but a ~0.35 dex spread in the giant Li abundances is found and cannot be explained by the stellar model. Possible sources of the spread are discussed; however, it is apparent that the differential mechanism responsible for the Li dispersion must be unrelated to the uniformly low 12C abundances of the giants. Na, Mg, and Al abundances are derived as an additional

  9. Radii, masses, and ages of 18 bright stars using interferometry and new estimations of exoplanetary parameters

    NASA Astrophysics Data System (ADS)

    Ligi, R.; Creevey, O.; Mourard, D.; Crida, A.; Lagrange, A.-M.; Nardetto, N.; Perraut, K.; Schultheis, M.; Tallon-Bosc, I.; ten Brummelaar, T.

    2016-02-01

    Context. Accurate stellar parameters are needed in numerous domains of astrophysics. The position of stars on the Hertzsprung-Russell diagram is an important indication of their structure and evolution, and it helps improve stellar models. Furthermore, the age and mass of stars hosting planets are required elements for studying exoplanetary systems. Aims: We aim at determining accurate parameters of a set of 18 bright exoplanet host and potential host stars from interferometric measurements, photometry, and stellar models. Methods: Using the VEGA/CHARA interferometer operating in the visible domain, we measured the angular diameters of 18 stars, ten of which host exoplanets. We combined them with their distances to estimate their radii. We used photometry to derive their bolometric flux and, then, their effective temperature and luminosity to place them on the H-R diagram. We then used the PARSEC models to derive their best fit ages and masses, with error bars derived from Monte Carlo calculations. Results: Our interferometric measurements lead to an average of 1.9% uncertainty on angular diameters and 3% on stellar radii. There is good agreement between measured and indirect estimations of angular diameters (either from SED fitting or from surface brightness relations) for main sequence (MS) stars, but not as good for more evolved stars. For each star, we provide a likelihood map in the mass-age plane; typically, two distinct sets of solutions appear (an old and a young age). The errors on the ages and masses that we provide account for the metallicity uncertainties, which are often neglected by other works. From measurements of its radius and density, we also provide the mass of 55 Cnc independently of models. From the stellar masses, we provide new estimates of semi-major axes and minimum masses of exoplanets with reliable uncertainties. We also derive the radius, density, and mass of 55 Cnc e, a super-Earth that transits its stellar host. Our exoplanetary

  10. A Critical Assessment of Stellar Mass Measurement Methods

    NASA Astrophysics Data System (ADS)

    Mobasher, Bahram; Dahlen, Tomas; Ferguson, Henry C.; Acquaviva, Viviana; Barro, Guillermo; Finkelstein, Steven L.; Fontana, Adriano; Gruetzbauch, Ruth; Johnson, Seth; Lu, Yu; Papovich, Casey J.; Pforr, Janine; Salvato, Mara; Somerville, Rachel S.; Wiklind, Tommy; Wuyts, Stijn; Ashby, Matthew L. N.; Bell, Eric; Conselice, Christopher J.; Dickinson, Mark E.; Faber, Sandra M.; Fazio, Giovanni; Finlator, Kristian; Galametz, Audrey; Gawiser, Eric; Giavalisco, Mauro; Grazian, Andrea; Grogin, Norman A.; Guo, Yicheng; Hathi, Nimish; Kocevski, Dale; Koekemoer, Anton M.; Koo, David C.; Newman, Jeffrey A.; Reddy, Naveen; Santini, Paola; Wechsler, Risa H.

    2015-07-01

    This is the second paper in a series aimed at investigating the main sources of uncertainty in measuring the observable parameters in galaxies from their spectral energy distributions (SEDs). In the first paper we presented a detailed account of the photometric redshift measurements and an error analysis of this process. In this paper we perform a comprehensive study of the main sources of random and systematic error in stellar mass estimates for galaxies, and their relative contributions to the associated error budget. Since there is no prior knowledge of the stellar mass of galaxies (unlike their photometric redshifts), we use mock galaxy catalogs with simulated multi-waveband photometry and known redshift, stellar mass, age and extinction for individual galaxies. The multi-waveband photometry for the simulated galaxies were generated in 13 filters spanning from U-band to mid-infrared wavelengths. Given different parameters affecting stellar mass measurement (photometric signal-to-noise ratios (S/N), SED fitting errors and systematic effects), the inherent degeneracies and correlated errors, we formulated different simulated galaxy catalogs to quantify these effects individually. For comparison, we also generated catalogs based on observed photometric data of real galaxies in the Great Observatories Origins Deep Survey-South field, spanning the same passbands. The simulated and observed catalogs were provided to a number of teams within the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey collaboration to estimate the stellar masses for individual galaxies. A total of 11 teams participated, with different combinations of stellar mass measurement codes/methods, population synthesis models, star formation histories, extinction and age. For each simulated galaxy, the differences between the input stellar masses, Minput, and those estimated by each team, Mest, is defined as {{Δ }}{log}(M)\\equiv {log}({M}{estimated})-{log}({M}{input}), and used to

  11. 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.

  12. Accurate abundance determinations in S stars

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

    S-type stars are thought to be the first objects, during their evolution on the asymptotic giant branch (AGB), to experience s-process nucleosynthesis and third dredge-ups, and therefore to exhibit s-process signatures in their atmospheres. Until present, the modeling of these processes is subject to large uncertainties. Precise abundance determinations in S stars are of extreme importance for constraining e.g., the depth and the formation of the 13C pocket. In this paper a large grid of MARCS model atmospheres for S stars is used to derive precise abundances of key s-process elements and iron. A first estimation of the atmospheric parameters is obtained using a set of well-chosen photometric and spectroscopic indices for selecting the best model atmosphere of each S star. Abundances are derived from spectral line synthesis, using the selected model atmosphere. Special interest is paid to technetium, an element without stable isotopes. Its detection in stars is considered as the best possible signature that the star effectively populates the thermally-pulsing AGB (TP-AGB) phase of evolution. The derived Tc/Zr abundances are compared, as a function of the derived [Zr/Fe] overabundances, with AGB stellar model predictions. The computed [Zr/Fe] overabundances are in good agreement with the AGB stellar evolution model predictions, while the Tc/Zr abundances are slightly over-predicted. This discrepancy can help to set stronger constraints on nucleosynthesis and mixing mechanisms in AGB stars.

  13. Improved Diffusion Coefficients for Stellar Plasmas

    NASA Astrophysics Data System (ADS)

    Brassard, P.; Fontaine, G.

    2014-04-01

    We are currently working on the fourth generation of our codes for building evolutionary and static models of hot subdwarf and white dwarf stars. One of the improvements of these codes consists in an update of all the microphysics involved in the computations. As part of our efforts, we have taken a look at possible improvements for the diffusion coefficients. Since the publication of the widely used diffusion coefficients of Paquette et al. (1986), the number-crunching power of computers has immensely increased, allowing more accurate computations of the triple collision integrals. We have thus produced new tables of diffusion coefficients with higher accuracy and higher resolution than before, of general use in stellar astrophysics.

  14. Stellar radii from long-baseline interferometry

    NASA Astrophysics Data System (ADS)

    Kervella, Pierre

    2008-10-01

    Long baseline interferometers now measure the angular diameters of nearby stars with sub-percent accuracy. They can be translated in photospheric radii when the parallax is known, thus creating a novel and powerful constraint for stellar models. I present applications of interferometric radius measurements to the modeling of main sequence stars. Over the last few years, we obtained accurate measurements of the linear radius of many of the nearest stars: Procyon A, 61 Cyg A & B, α Cen A & B, Sirius A, Proxima. . . Firstly, I describe the example of our modeling of Procyon A (F5IV-V) with the CESAM code, constrained using spectrophotometry, the linear radius, and asteroseismic frequencies. I also present our recent results on the low-mass 61 Cyg system (K5V+K7V), for which asteroseismic frequencies have not been detected yet.

  15. Open Questions in Stellar Nuclear Physics: I

    SciTech Connect

    Gai, Moshe

    2004-09-13

    No doubt, among the most exciting discoveries of the third millennium thus far are oscillations of massive neutrinos and dark energy that leads to an accelerated expansion of the Universe. Accordingly, Nuclear Physics is presented with two extraordinary challenges: the need for precise (5% or better) prediction of solar neutrino fluxes within the Standard Solar Model, and the need for an accurate (5% or better) understanding of stellar evolution and in particular of Type Ia super nova that are used as cosmological standard candle. In contrast, much confusion is found in the field with contradicting data and strong statements of accuracy that can not be supported by current data. We discuss an experimental program to address these challenges and disagreements.

  16. Open Questions in Stellar Nuclear Physics: II

    SciTech Connect

    Gai, Moshe

    2004-09-13

    No doubt, among the most exciting discoveries of the third millennium thus far are oscillations of massive neutrinos and dark energy that leads to an accelerated expansion of the Universe. Accordingly, Nuclear Physics is presented with two extraordinary challenges: the need for precise (5% or better) prediction of solar neutrino fluxes within the Standard Solar Model, and the need for an accurate (5% or better) understanding of stellar evolution and in particular of Type Ia super nova that are used as cosmological standard candle. In contrast, much confusion is found in the field with contradicting data and strong statements of accuracy that can not be supported by current data. We discuss an experimental program to address these challenges and disagreements.

  17. The Milky Way Tomography with SDSS. 2. Stellar Metallicity

    SciTech Connect

    Ivezic, Zeljko; Sesar, Branimir; Juric, Mario; Bond, Nicholas; Dalcanton, Julianne; Rockosi, Constance M.; Yanny, Brian; Newberg, Heidi J.; Beers, Timothy C.; Prieto, Carlos Allende; Wilhelm, Ron; /Texas Tech. /Michigan State U.

    2008-04-01

    In addition to optical photometry of unprecedented quality, the Sloan Digital Sky Survey (SDSS) is producing a massive spectroscopic database which already contains over 280,000 stellar spectra. Using effective temperature and metallicity derived from SDSS spectra for {approx}60,000 F and G type main sequence stars (0.2 < g-r < 0.6), we develop polynomial models, reminiscent of traditional methods based on the UBV photometry, for estimating these parameters from the SDSS u-g and g-r colors. These estimators reproduce SDSS spectroscopic parameters with a root-mean-square scatter of 100 K for effective temperature, and 0.2 dex for metallicity (limited by photometric errors), which are similar to random and systematic uncertainties in spectroscopic determinations. We apply this method to a photometric catalog of coadded SDSS observations and study the photometric metallicity distribution of {approx}200,000 F and G type stars observed in 300 deg{sup 2} of high Galactic latitude sky. These deeper (g < 20.5) and photometrically precise ({approx}0.01 mag) coadded data enable an accurate measurement of the unbiased metallicity distribution for a complete volume-limited sample of stars at distances between 500 pc and 8 kpc. The metallicity distribution can be exquisitely modeled using two components with a spatially varying number ratio, that correspond to disk and halo. The best-fit number ratio of the two components is consistent with that implied by the decomposition of stellar counts profiles into exponential disk and power-law halo components by Juric et al. (2008). The two components also possess the kinematics expected for disk and halo stars. The metallicity of the halo component can be modeled as a spatially invariant Gaussian distribution with a mean of [Fe/H] = -1.46 and a standard deviation of {approx}0.3 dex. The disk metallicity distribution is non-Gaussian, with a remarkably small scatter (rms {approx}0.16 dex) and the median smoothly decreasing with distance

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

    SciTech Connect

    Trampedach, Regner; Asplund, Martin; Collet, Remo; Nordlund, Ake

    2013-05-20

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

  19. Precise spectroscopic parameters for solar-type stars with moderate-to-high rotation

    NASA Astrophysics Data System (ADS)

    Tsantaki, M.; Sousa, S.; Santos, N. C.; Montalto, M.

    2014-07-01

    One of the primary objectives of Gaia is to survey billions stars and build the most precise 3D map of the Milky Way. Automated techniques of spectral analysis are needed to perform a rapid and homogeneous processing of the data to provide precise and accurate stellar parameters, such as for the GAIA-ESO survey. In this context, our recent work is based on the spectral synthesis technique to derive parameters for both slowly and fast rotating stars (Tsantaki et al. 2014). The spectroscopic analysis was performed using the package Spectroscopy Made Easy (SME; Valenti & Piskunov 1996) and a specific methodology to deal with fast rotators (υsini up to 50 km/s). The spectral regions, including the atomic data of all the lines in our analysis are available online in SME readable format http://mariatsantaki.weebly.com;. A comparison between the parameters derived with our methodology and with the iron ionization and excitation method (e.g. Sousa et al. 2008; Tsantaki et al. 2013) shows that both results are on the same scale. Additionally, for fast rotating stars, our results are in good agreement with literature values when comparing to other methods. We are now able to provide parameters for a very wide group of stars: from giants to dwarfs and from slowly to fast rotating stars. Except for galactic studies, stellar parameters are important for the planetary characterization. We provided updated stellar and planetary properties for ten systems. The stellar parameters were compiled in the SWEET-Catalogue (https://www.astro.up.pt/resources/sweet-cat/).

  20. Stellar Populations in Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    MacArthur, L. A.; Courteau, S.; Bell, E. F.; Holtzman, J. A.

    2004-12-01

    We investigate optical and near-IR color gradients in a sample of 172 low-inclination galaxies spanning Hubble types S0--Irr. The colors are compared to stellar population synthesis models from which luminosity-weighted average ages and metallicities are determined. We explore the effects of different underlying star formation histories and additional bursts of star formation. Because the observed gradients show radial structure, we measure ``inner'' and ``outer'' disk age and metallicity gradients. Relative trends in age and metallicity and their gradients are explored as a function of Hubble type, rotational velocity, total near-IR galaxy magnitude, central surface brightness, and scale length. We find strong correlations in age and metallicity with Hubble type, rotational velocity, total magnitude, and central surface brightness in the sense that earlier-type, faster rotating, more luminous, and higher surface brightness galaxies are older and more metal-rich, suggesting an early and more rapid star formation history for these galaxies. The increasing trends level off for T ⪉ 4 (Sbc and earlier), V {rot} ⪆ 120 km s-1, MK ⪉ -23 mag, and μ 0 ⪉ 18.5 mag arcsec-2. Outer disk gradients are weaker than the inner gradients as expected for a slower variation of the potential and surface brightness in the outer parts. We find that stronger age gradients are associated with weaker metallicity gradients. Relative trends in gradients with galaxy parameters do not agree with predictions of semi-analytic models of hierarchical galaxy formation, possibly as a result of bar-induced radial flows. However, the observed trends are in agreement with chemo-spectro photometric models of spiral galaxy evolution based on CDM-motivated scaling laws but including none of the hierarchical merging characteristics. This implies a strong dependence of the star formation history of spiral galaxies on the galaxy potential and halo spin parameter. L.A.M. and S.C acknowledge support

  1. 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.

  2. 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

  3. Developing Accurate Spatial Maps of Cotton Fiber Quality Parameters

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Awareness of the importance of cotton fiber quality (Gossypium, L. sps.) has increased as advances in spinning technology require better quality cotton fiber. Recent advances in geospatial information sciences allow an improved ability to study the extent and causes of spatial variability in fiber p...

  4. 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.

  5. Stellar hydrodynamical modeling of dwarf galaxies: simulation methodology, tests, and first results

    NASA Astrophysics Data System (ADS)

    Vorobyov, Eduard I.; Recchi, Simone; Hensler, Gerhard

    2015-07-01

    Context. In spite of enormous progress and brilliant achievements in cosmological simulations, they still lack numerical resolution or physical processes to simulate dwarf galaxies in sufficient detail. Accurate numerical simulations of individual dwarf galaxies are thus still in demand. Aims: We aim to improve available numerical techniques to simulate individual dwarf galaxies. In particular, we aim to (i) study in detail the coupling between stars and gas in a galaxy, exploiting the so-called stellar hydrodynamical approach; and (ii) study for the first time the chemodynamical evolution of individual galaxies starting from self-consistently calculated initial gas distributions. Methods: We present a novel chemodynamical code for studying the evolution of individual dwarf galaxies. In this code, the dynamics of gas is computed using the usual hydrodynamics equations, while the dynamics of stars is described by the stellar hydrodynamics approach, which solves for the first three moments of the collisionless Boltzmann equation. The feedback from stellar winds and dying stars is followed in detail. In particular, a novel and detailed approach has been developed to trace the aging of various stellar populations, which facilitates an accurate calculation of the stellar feedback depending on the stellar age. The code has been accurately benchmarked, allowing us to provide a recipe for improving the code performance on the Sedov test problem. Results: We build initial equilibrium models of dwarf galaxies that take gas self-gravity into account and present different levels of rotational support. Models with high rotational support (and hence high degrees of flattening) develop prominent bipolar outflows; a newly-born stellar population in these models is preferentially concentrated to the galactic midplane. Models with little rotational support blow away a large fraction of the gas and the resulting stellar distribution is extended and diffuse. Models that start from non

  6. The Stellar Wind from the Central Star of NGC 7009

    NASA Technical Reports Server (NTRS)

    Sonneborn, George; Iping, Rosina; Chu, You-Hua; Gruendl, Robert

    2006-01-01

    Observations of NGC 7009, including its central star HD 200516, have been obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite, providing spectra covering 905-1187 A with spectral resolution of 15 km/sec. One observation was made with the 30x30 arcsec aperture and includes the star plus the entire nebula. A second observation used the 1.25x20arcsec slit significantly reducing the nebular 'contamination' of the stellar spectrum. This poster discusses the spectrum of the central star. A strong FUV continuum, as expected for Teff=82,000K, dominates the spectrum. The most prominent spectral feature is a very strong P-Cygni profile of O VI 1032-1038. This paper presents models of the stellar spectrum and the wind features to further refine the stellar parameters and mass loss rate.

  7. Hydrogen Atom Collision Processes in Cool Stellar Atmospheres: Effects on Spectral Line Strengths and Measured Chemical Abundances in Old Stars

    NASA Astrophysics Data System (ADS)

    Barklem, Paul S.

    2012-12-01

    The precise measurement of the chemical composition of stars is a fundamental problem relevant to many areas of astrophysics. State-of-the-art approaches attempt to unite accurate descriptions of microphysics, non-local thermodynamic equilibrium (non-LTE) line formation and 3D hydrodynamical model atmospheres. In this paper I review progress in understanding inelastic collisions of hydrogen atoms with other species and their influence on spectral line formation and derived abundances in stellar atmospheres. These collisions are a major source of uncertainty in non-LTE modelling of spectral lines and abundance determinations, especially for old, metal-poor stars, which are unique tracers of the early evolution of our galaxy. Full quantum scattering calculations of direct excitation processes X(nl) + H leftrightarrow X(n'l') + H and charge transfer processes X(nl) + H leftrightarrow X+ + H- have been done for Li, Na and Mg [1,2,3] based on detailed quantum chemical data, e.g. [4]. Rate coefficients have been calculated and applied to non-LTE modelling of spectral lines in stellar atmospheres [5,6,7,8,9]. In all cases we find that charge transfer processes from the first excited S-state are very important, and the processes affect measured abundances for Li, Na and Mg in some stars by as much as 60%. Effects vary with stellar parameters (e.g. temperature, luminosity, metal content) and so these processes are important not only for accurate absolute abundances, but also for relative abundances among dissimilar stars.

  8. 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.

  9. SME@XSEDE: An automated spectral synthesis tool for stellar characterization

    NASA Astrophysics Data System (ADS)

    Hebb, Leslie; Cargile, Phillip

    2015-01-01

    Over the last decade, large scale discovery surveys like Kepler have produced vast catalogs of newly discovered extrasolar planetary systems. Most of these systems require stellar characterization of the host stars in order to derive the host star masses and completely solve for the planetary properties. Currently, there is no widely accepted and standardized method to determine fundamental parameters from stellar spectra. Here, we present a new approach to automating stellar characterization of large datasets of high resolution spectra. Our software, called SME@XSEDE, is based on one of the most widely used spectral synthesis algorithms, Spectroscopy Made Easy (SME), originally described in Valenti and Piskanov (1996). Like SME, SME@XSEDE compares an observed spectrum to synthetic model spectra derived through radiative transfer calculations for a range of stellar parameters in order to find the global stellar properties (temperature, gravity, metallicity, vsini, and individual abundances) that result in a synthetic spectrum that best matches an observed spectrum. We use the XSEDE super computer cluster to run many sets of initial guesses of stellar parameters to determine robust SME-based solutions without extensive, hands-on work. In this paper, we describe our software in detail and compare results derived from the application of SME@XSEDE to several well-studied datasets of stellar parameters including Valenti and Fischer 2005, Torres et al. 2012, and Huber et al 2013.

  10. The universal stellar mass-stellar metallicity relation for dwarf galaxies

    SciTech Connect

    Kirby, Evan N.; Bullock, James S.; Cohen, Judith G.; Guhathakurta, Puragra; Gallazzi, Anna

    2013-12-20

    We present spectroscopic metallicities of individual stars in seven gas-rich dwarf irregular galaxies (dIrrs), and we show that dIrrs obey the same mass-metallicity relation as the dwarf spheroidal (dSph) satellites of both the Milky Way and M31: Z{sub ∗}∝M{sub ∗}{sup 0.30±0.02}. The uniformity of the relation is in contradiction to previous estimates of metallicity based on photometry. This relationship is roughly continuous with the stellar mass-stellar metallicity relation for galaxies as massive as M {sub *} = 10{sup 12} M {sub ☉}. Although the average metallicities of dwarf galaxies depend only on stellar mass, the shapes of their metallicity distributions depend on galaxy type. The metallicity distributions of dIrrs resemble simple, leaky box chemical evolution models, whereas dSphs require an additional parameter, such as gas accretion, to explain the shapes of their metallicity distributions. Furthermore, the metallicity distributions of the more luminous dSphs have sharp, metal-rich cut-offs that are consistent with the sudden truncation of star formation due to ram pressure stripping.

  11. The Universal Stellar Mass-Stellar Metallicity Relation for Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Kirby, Evan N.; Cohen, Judith G.; Guhathakurta, Puragra; Cheng, Lucy; Bullock, James S.; Gallazzi, Anna

    2013-12-01

    We present spectroscopic metallicities of individual stars in seven gas-rich dwarf irregular galaxies (dIrrs), and we show that dIrrs obey the same mass-metallicity relation as the dwarf spheroidal (dSph) satellites of both the Milky Way and M31: Z_* \\propto M_*^{0.30+/- 0.02}. The uniformity of the relation is in contradiction to previous estimates of metallicity based on photometry. This relationship is roughly continuous with the stellar mass-stellar metallicity relation for galaxies as massive as M * = 1012 M ⊙. Although the average metallicities of dwarf galaxies depend only on stellar mass, the shapes of their metallicity distributions depend on galaxy type. The metallicity distributions of dIrrs resemble simple, leaky box chemical evolution models, whereas dSphs require an additional parameter, such as gas accretion, to explain the shapes of their metallicity distributions. Furthermore, the metallicity distributions of the more luminous dSphs have sharp, metal-rich cut-offs that are consistent with the sudden truncation of star formation due to ram pressure stripping. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

  12. VizieR Online Data Catalog: SP_Ace derived data from stellar spectra (Boeche+, 2016)

    NASA Astrophysics Data System (ADS)

    Boeche, C.; Grebel, E. K.

    2015-11-01

    SP_Ace is a software designed to derive stellar parameters and elemental abundances from stellar spectra. In this tables we report the stellar parameters Teff, logg, [M/H], and chemical abundances [El/H] for ten elements derived with the software SP_Ace from spectra of the ELODIE spectral library (Prugniel et al., 2007, Cat. III/251), the benchmark stars (Jofre et al., 2014, Cat. J/A+A/564/A133), and the S4N library (Allende Prieto et al., 2004, Cat. J/A+A/420/183) degraded to spectral resolution R=12,000 and S/N=100. (3 data files).

  13. 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.

  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. Resolving polarized stellar features thanks to polarimetric interferometry

    NASA Astrophysics Data System (ADS)

    Rousselet-Perraut, Karine; Chesneau, Olivier; Vakili, Farrokh; Mourard, Denis; Janel, Sebastien; Lavaud, Laurent; Crocherie, Axel

    2003-02-01

    Polarimetry is a powerful means for detecting and constraining various physical phenomena, such as scattering processes or magnetic fields, occuring in a large panel of stellar objects: extended atmospheres of hot stars, CP stars, Young Stellar Objects, Active Galaxy Nuclei, ... However, the lack of angular resolution is generally a strong handicap to drastically constrain the physical parameters and the geometry of the polarizing phenomena because of the cancelling of the polarized signal. In fact, even if stellar features are strongly polarized, the (spectro-)polarimetric signal integrated over the stellar surface rarely exceeds few percents. Coupling polarimetric and interferometric devices allows to resolve these local polarized structures and thus to constrain complex patchy stellar surfaces and/or environments such as disk topology in T Tauri stars, hot stars radiative winds or oscillations in Be star envelopes. In this article, we explain how interfero-polarimetric observables, basically the contrast and the position of the interference fringe patterns versus polarization (and even versus wavelength) are powerful to address the above scientific drivers and we emphasize on the key point of instrumental and data calibrations: since interferometric measurements are differential ones between 2 or more beams, this strongly relaxes the calibration requirements for the fringe phase observable. Prospects induced by the operation of the optical aperture synthesis arrays are also discussed.

  16. Mapping the Stellar Content of the Milky Way with LSST

    NASA Astrophysics Data System (ADS)

    Bochanski, John J.; Thorman, P.; Covey, K.; Olsen, K.; Dhital, S.; Beers, T. C.; Boeshaar, P.; Cargile, P.; Catelan, M.; Digel, S.; Guhathakurta, P.; Henry, T.; Ivezic, Z.; Juric, M.; Kalirai, J.; Kirkpatrick, J.; McGehee, P. M.; Minniti, D.; Mukadam, A.; Pepper, J.; Prsa, A.; Roškar, R.; Smith, J.; Stassun, K.; Tyson, A.; LSST Stellar Populations Collaboration; Milky Way Collaboration; Local Volume Science Collaboration

    2012-01-01

    The Large Synoptic Survey Telescope (LSST) will map half of the sky in six filters down to r=27.5 (AB mag; 5-sigma), with typical precision of one percent (0.01 mag). The ten year baseline of the survey will provide about a thousand multi-epoch observations for objects brighter than r=24.5, yielding variability, proper motions and trigonometric parallax measurements for hundreds of millions of stars. The resulting photometric and astrometric catalogs will enable novel and unique investigations, detailing the formation and evolution of the Milky Way's stellar populations, as well as neighboring galaxies. We highlight some of the enabled science studies, including results from the output source catalog derived from simulated LSST images. A few examples of the stellar populations projects will be shown: sampling a census of the MLT population near the solar neighborhood; mapping the structure and stellar metallicity content of the Milky Way's disk and halo; assembling catalogs of eclipsing binaries, subdwarfs and white dwarfs, suitable for measuring fundamental stellar parameters; and measuring the Milky Way's star formation history using stellar ages determined from gyrochronology and rotation periods, as well as the white dwarf luminosity function. We also highlight the studies enabled by the "Deep Drilling" fields, patches within the LSST footprint that will be imaged at a higher cadence over the course of the survey.

  17. THE FIRST ACCURATE PARALLAX DISTANCE TO A BLACK HOLE

    SciTech Connect

    Miller-Jones, J. C. A.; Jonker, P. G.; Dhawan, V.; Brisken, W.; Rupen, M. P.; Nelemans, G.; Gallo, E.

    2009-12-01

    Using astrometric VLBI observations, we have determined the parallax of the black hole X-ray binary V404 Cyg to be 0.418 +- 0.024 mas, corresponding to a distance of 2.39 +- 0.14 kpc, significantly lower than the previously accepted value. This model-independent estimate is the most accurate distance to a Galactic stellar-mass black hole measured to date. With this new distance, we confirm that the source was not super-Eddington during its 1989 outburst. The fitted distance and proper motion imply that the black hole in this system likely formed in a supernova, with the peculiar velocity being consistent with a recoil (Blaauw) kick. The size of the quiescent jets inferred to exist in this system is <1.4 AU at 22 GHz. Astrometric observations of a larger sample of such systems would provide useful insights into the formation and properties of accreting stellar-mass black holes.

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

    NASA Astrophysics Data System (ADS)

    Morscher, Maggie

    Globular clusters are gravitationally bound systems containing up to millions of stars, and are found ubiquitously in massive galaxies, including the Milky Way. With densities as high as a million stars per cubic parsec, they are one of the few places in the Universe where stars interact with one another. They therefore provide us with a unique laboratory for studying how gravitational interactions can facilitate the formation of exotic systems, such as X-ray binaries containing black holes, and merging double black hole binaries, which are produced much less efficiently in isolation. While telescopes can provide us with a snapshot of what these dense clusters look like at present, we must rely on detailed numerical simulations to learn about their evolution. These simulations are quite challenging, however, since dense star clusters are described by a complicated set of physical processes occurring on many different length and time scales, including stellar and binary evolution, weak gravitational scattering encounters, strong resonant binary interactions, and tidal stripping by the host galaxy. Until very recently, it was not possible to model the evolution of systems with millions of stars, the actual number contained in the largest clusters, including all the relevant physics required describe these systems accurately. The Northwestern Group's Henon Monte Carlo code, CMC, which has been in development for over a decade, is a powerful tool that can be used to construct detailed evolutionary models of large star clusters. With its recent parallelization, CMC is now capable of addressing a particularly interesting unsolved problem in astrophysics: the dynamical evolution of stellar black holes in dense star clusters. Our current understanding of the stellar initial mass function and massive star evolution suggests that young globular clusters may have formed hundreds to thousands of stellar-mass black holes, the remnants of stars with initial masses from 20 - 100

  19. 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.

  20. Baroclinic instability in stellar radiation zones

    SciTech Connect

    Kitchatinov, L. L.

    2014-03-20

    Surfaces of constant pressure and constant density do not coincide in differentially rotating stars. Stellar radiation zones with baroclinic stratification can be unstable. Instabilities in radiation zones are of crucial importance for angular momentum transport, mixing of chemical species, and, possibly, for magnetic field generation. This paper performs linear analysis of baroclinic instability in differentially rotating stars. Linear stability equations are formulated for differential rotation of arbitrary shape and then solved numerically for rotation nonuniform in radius. As the differential rotation increases, r- and g-modes of initially stable global oscillations transform smoothly into growing modes of baroclinic instability. The instability can therefore be interpreted as stability loss to r- and g-modes excitation. Regions of stellar parameters where r- or g-modes are preferentially excited are defined. Baroclinic instability onsets at a very small differential rotation of below 1%. The characteristic time of instability growth is about 1000 rotation periods. Growing disturbances possess kinetic helicity. Magnetic field generation by the turbulence resulting from baroclinic instability in differentially rotating radiation zones is therefore possible.

  1. An atlas of selected calibrated stellar spectra

    NASA Technical Reports Server (NTRS)

    Walker, Russell G.; Cohen, Martin

    1992-01-01

    Five hundred and fifty six stars in the IRAS PSC-2 that are suitable for stellar radiometric standards and are brighter than 1 Jy at 25 microns were identified. In addition, 123 stars that meet all of our criteria for calibration standards, but which lack a luminosity class were identified. An approach to absolute stellar calibration of broadband infrared filters based upon new models of Vega and Sirius due to Kurucz (1992) is presented. A general technique used to assemble continuous wide-band calibrated infrared spectra is described and an absolutely calibrated 1-35 micron spectrum of alpha(Tau) is constructed and the method using new and carefully designed observations is independently validated. The absolute calibration of the IRAS Low Resolution Spectrometer (LRS) database is investigated by comparing the observed spectrum of alpha(Tau) with that assumed in the original LRS calibration scheme. Neglect of the SiO fundamental band in alpha(Tau) has led to the presence of a specious 'emission' feature in all LRS spectra near 8.5 microns, and to an incorrect spectral slope between 8 and 12 microns. Finally, some of the properties of asteroids that effect their utility as calibration objects for the middle and far infrared region are examined. A technique to determine, from IRAS multiwaveband observations, the basic physical parameters needed by various asteroid thermal models that minimize the number of assumptions required is developed.

  2. Application of self-organizing map to stellar spectral classifications

    NASA Astrophysics Data System (ADS)

    Bazarghan, Mahdi

    2012-01-01

    We present an automatic, fast, accurate and robust method of classifying astronomical objects. The Self Organizing Map (SOM) as an unsupervised Artificial Neural Network (ANN) algorithm is used for classification of stellar spectra of stars. The SOM is used to make clusters of different spectral classes of Jacoby, Hunter and Christian (JHC) library. This ANN technique needs no training examples and the stellar spectral data sets are directly fed to the network for the classification. The JHC library contains 161 spectra out of which, 158 spectra are selected for the classification. These 158 spectra are input vectors to the network and mapped into a two dimensional output grid. The input vectors close to each other are mapped into the same or neighboring neurons in the output space. So, the similar objects are making clusters in the output map and making it easy to analyze high dimensional data. After running the SOM algorithm on 158 stellar spectra, with 2799 data points each, the output map is analyzed and found that, there are 7 clusters in the output map corresponding to O to M stellar type. But, there are 12 misclassifications out of 158 and all of them are misclassified into the neighborhood of correct clusters which gives a success rate of about 92.4%.

  3. 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)

  4. 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.

  5. 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…

  6. The Local Stellar Velocity Field via Vector Spherical Harmonics

    NASA Astrophysics Data System (ADS)

    Makarov, V. V.; Murphy, D. W.

    2007-07-01

    We analyze the local field of stellar tangential velocities for a sample of 42,339 nonbinary Hipparcos stars with accurate parallaxes, using a vector spherical harmonic formalism. We derive simple relations between the parameters of the classical linear model (Ogorodnikov-Milne) of the local systemic field and low-degree terms of the general vector harmonic decomposition. Taking advantage of these relationships, we determine the solar velocity with respect to the local stars of (VX,VY,VZ)=(10.5,18.5,7.3)+/-0.1 km s-1 not corrected for the asymmetric drift with respect to the local standard of rest. If only stars more distant than 100 pc are considered, the peculiar solar motion is (VX,VY,VZ)=(9.9,15.6,6.9)+/-0.2 km s-1. The adverse effects of harmonic leakage, which occurs between the reflex solar motion represented by the three electric vector harmonics in the velocity space and higher degree harmonics in the proper-motion space, are eliminated in our analysis by direct subtraction of the reflex solar velocity in its tangential components for each star. The Oort parameters determined by a straightforward least-squares adjustment in vector spherical harmonics are A=14.0+/-1.4, B=-13.1+/-1.2, K=1.1+/-1.8, and C=-2.9+/-1.4 km s-1 kpc-1. The physical meaning and the implications of these parameters are discussed in the framework of a general linear model of the velocity field. We find a few statistically significant higher degree harmonic terms that do not correspond to any parameters in the classical linear model. One of them, a third-degree electric harmonic, is tentatively explained as the response to a negative linear gradient of rotation velocity with distance from the Galactic plane, which we estimate at ~-20 km s-1 kpc-1. A similar vertical gradient of rotation velocity has been detected for more distant stars representing the thick disk (z>1 kpc), but here we surmise its existence in the thin disk at z<200 pc. The most unexpected and unexplained term within

  7. The Local Stellar Velocity Field via Vector Spherical Harmonics

    NASA Technical Reports Server (NTRS)

    Markarov, V. V.; Murphy, D. W.

    2007-01-01

    We analyze the local field of stellar tangential velocities for a sample of 42,339 nonbinary Hipparcos stars with accurate parallaxes, using a vector spherical harmonic formalism. We derive simple relations between the parameters of the classical linear model (Ogorodnikov-Milne) of the local systemic field and low-degree terms of the general vector harmonic decomposition. Taking advantage of these relationships, we determine the solar velocity with respect to the local stars of (V(sub X), V(sub Y), V(sub Z)) (10.5, 18.5, 7.3) +/- 0.1 km s(exp -1) not corrected for the asymmetric drift with respect to the local standard of rest. If only stars more distant than 100 pc are considered, the peculiar solar motion is (V(sub X), V(sub Y), V(sub Z)) (9.9, 15.6, 6.9) +/- 0.2 km s(exp -1). The adverse effects of harmonic leakage, which occurs between the reflex solar motion represented by the three electric vector harmonics in the velocity space and higher degree harmonics in the proper-motion space, are eliminated in our analysis by direct subtraction of the reflex solar velocity in its tangential components for each star. The Oort parameters determined by a straightforward least-squares adjustment in vector spherical harmonics are A=14.0 +/- 1.4, B=13.1 +/- 1.2, K=1.1 +/- 1.8, and C=2.9 +/- 1.4 km s(exp -1) kpc(exp -1). The physical meaning and the implications of these parameters are discussed in the framework of a general linear model of the velocity field. We find a few statistically significant higher degree harmonic terms that do not correspond to any parameters in the classical linear model. One of them, a third-degree electric harmonic, is tentatively explained as the response to a negative linear gradient of rotation velocity with distance from the Galactic plane, which we estimate at approximately -20 km s(exp -1) kpc(exp -1). A similar vertical gradient of rotation velocity has been detected for more distant stars representing the thick disk (z greater than 1 kpc

  8. High Frequency QRS ECG Accurately Detects Cardiomyopathy

    NASA Technical Reports Server (NTRS)

    Schlegel, Todd T.; Arenare, Brian; Poulin, Gregory; Moser, Daniel R.; Delgado, Reynolds

    2005-01-01

    High frequency (HF, 150-250 Hz) analysis over the entire QRS interval of the ECG is more sensitive than conventional ECG for detecting myocardial ischemia. However, the accuracy of HF QRS ECG for detecting cardiomyopathy is unknown. We obtained simultaneous resting conventional and HF QRS 12-lead ECGs in 66 patients with cardiomyopathy (EF = 23.2 plus or minus 6.l%, mean plus or minus SD) and in 66 age- and gender-matched healthy controls using PC-based ECG software recently developed at NASA. The single most accurate ECG parameter for detecting cardiomyopathy was an HF QRS morphological score that takes into consideration the total number and severity of reduced amplitude zones (RAZs) present plus the clustering of RAZs together in contiguous leads. This RAZ score had an area under the receiver operator curve (ROC) of 0.91, and was 88% sensitive, 82% specific and 85% accurate for identifying cardiomyopathy at optimum score cut-off of 140 points. Although conventional ECG parameters such as the QRS and QTc intervals were also significantly longer in patients than controls (P less than 0.001, BBBs excluded), these conventional parameters were less accurate (area under the ROC = 0.77 and 0.77, respectively) than HF QRS morphological parameters for identifying underlying cardiomyopathy. The total amplitude of the HF QRS complexes, as measured by summed root mean square voltages (RMSVs), also differed between patients and controls (33.8 plus or minus 11.5 vs. 41.5 plus or minus 13.6 mV, respectively, P less than 0.003), but this parameter was even less accurate in distinguishing the two groups (area under ROC = 0.67) than the HF QRS morphologic and conventional ECG parameters. Diagnostic accuracy was optimal (86%) when the RAZ score from the HF QRS ECG and the QTc interval from the conventional ECG were used simultaneously with cut-offs of greater than or equal to 40 points and greater than or equal to 445 ms, respectively. In conclusion 12-lead HF QRS ECG employing

  9. Optimization of compact stellarator configuration as fusion devicesa)

    NASA Astrophysics Data System (ADS)

    Najmabadi, Farrokh; Rene Raffray, A.; Ku, Long-Poe; Lyon, James F.; Aries Team

    2006-05-01

    Optimization of the stellarator configuration requires tradeoffs among a large number of physics parameters and engineering constraints. An integrated study of compact stellarator power plants, ARIES-CS, aims at examining these tradeoffs and defining key R&D areas. Configurations with a plasma aspect ratio of A ⩽6 and excellent quasiaxisymmetry (QA) in both two and three field period versions were developed while reducing α-particle losses to <10%. Stability to linear ideal MHD modes was attained, but at the expense of reduced QA (and increased α-particle losses) and increased complexity of the plasma shape. Recent experimental results indicate, however, that linear MHD stability limits may not be applicable to stellarators. By utilizing a highly efficient shield-only region in strategic areas, the minimum standoff was reduced by ˜30%. This allows a comparable reduction in the machine size. The device configuration, assembly, and maintenance procedures appear to impose severe constraints: three distinct approaches were developed, each applicable to a certain blanket concept and/or stellarator configuration. Modular coils are designed to examine the geometric complexity and to understand the constraints imposed by the maximum allowable field, desirable coil-plasma separation, coil-coil spacing, and other coil parameters. A cost-optimization system code has also been developed and will be utilized to assess the tradeoff among physics and engineering constraints in a self-consistent manner in the final phase of the ARIES-CS study.

  10. A nonextensive view of the stellar braking indices

    NASA Astrophysics Data System (ADS)

    de Freitas, D. B.; Cavalcante, F. J.; Soares, B. B.; Silva, J. R. P.

    2015-08-01

    The present work is based on the effects of the magnetic braking for the angular-mometum loss evolution and, consequently, the relationship between stellar rotation and age. In general, this loss rate denoted by {d}J/{d}t depends on the angular velocity Ω in the form {d}J/ {d}t\\proptoΩq , where q is a parameter from nonextensive statistical mechanics. In the context of the stellar rotation, this parameter is directly related to the braking index. For q equal to unity, the scenario of the saturation of the magnetic field is recovered. Such an approach was proposed and investigated by de Freitas and De Medeiros for unsaturated field stars. We propose a new nonextensive approach for the stellar rotational evolution based on the Reiners and Mohanty model. We developed a nonextensive version of Reiners and Mohanty torque, and compare it with the model proposed in de Freitas and De Medeiros, by using a sample of velocity v\\sin i for ∼16000 field F- and G- stars. As a result, we show that the Kawaler and Reiners-Mohanty models exhibit strong discrepancies in relation to the domain of validity of the entropic index q. These discrepancies are mainly due to sensitivity on the stellar radius. Our results also showed that the modified Kawaler prescription is consistent in a wider mass ranges, while the Reiners and Mohanty model is restricted to masses less than from G6 stars.

  11. Revisiting the correlation between stellar activity and planetary surface gravity

    NASA Astrophysics Data System (ADS)

    Figueira, P.; Oshagh, M.; Adibekyan, V. Zh.; Santos, N. C.

    2014-12-01

    Aims: We re-evaluate the correlation between planetary surface gravity and stellar host activity as measured by the index log (R'HK). This correlation, previously identified by Hartman (2010, ApJ, 717, L138), is now analyzed in light of an extended measurement dataset, roughly three times larger than the original one. Methods: We calculated the Spearman rank correlation coefficient between the two quantities and its associated p-value. The correlation coefficient was calculated for both the full dataset and the star-planet pairs that follow the conditions proposed by Hartman (2010). To do so, we considered effective temperatures both as collected from the literature and from the SWEET-Cat catalog, which provides a more homogeneous and accurate effective temperature determination. Results: The analysis delivers significant correlation coefficients, but with a lower value than those obtained by Hartman (2010). The two datasets are compatible, and we show that a correlation coefficient as high as previously published can arise naturally from a small-number statistics analysis of the current dataset. The correlation is recovered for star-planet pairs selected using the different conditions proposed by Hartman (2010). Remarkably, the usage of SWEET-Cat temperatures led to higher correlation coefficient values. We highlight and discuss the role of the correlation betwen different parameters such as effective temperature and activity index. Several additional effects on top of those discussed previously were considered, but none fully explains the detected correlation. In light of the complex issue discussed here, we encourage the different follow-up teams to publish their activity index values in the form of a log (R'HK) index so that a comparison across stars and instruments can be pursued. Appendix A is available in electronic form at http://www.aanda.org

  12. STARS: the Stellar Absorption and Refraction Sensor

    NASA Astrophysics Data System (ADS)

    Yee, Jeng-Hwa; Morrison, Daniel; Murphy, Graham A.; Morgan, M. F.; Humm, David C.; Silverglate, Peter R.; Vervack, Ronald; Paxton, Larry J.

    2002-01-01

    The Stellar Absorption and Refraction Sensor (STARS) is a compact, large-aperture instrument that combines a UV-IR imaging spectrograph with a co-aligned visible-light imager to make simultaneous absorptive and refractive stellar occultation measurements. The absorption measurements provided by the spectrograph allow the determination of vertical profiles of atmospheric constituents. The coincident refraction observations made by the image yield high-precision measurements of atmospheric density, pressure, and temperature and provide independent knowledge of both the refracted light path and Rayleigh extinction, which are critical in reducing the uncertainty in the retrieved constituent profiles in the lower atmosphere. STARS employs a two-axis gimbaled telescope to acquire and track the star and a two-axis, high-precision, fast-steering mirror to correct for spacecraft jitter and maintain the star within the spectrograph field of view. The relative star position measured by the imager provides position feedback to the active tracking loop of the fast-steering mirror. With funding from NASA's Instrument Incubator Program, a laboratory facility has been developed to demonstrate the overall instrument performance and, in particular, its capability to acquire and track a setting, refracting, and scintillating star, to compensate for various degrees of platform jitter, and to provide the pointing knowledge required for accurate determination of the atmospheric quantities. The combination of built-in image tracking and motion compensation capabilities, small size, and limited spacecraft resource requirements makes STARS and its tracking mechanism suitable for deployment on existing and future commercial spacecraft platforms for applications that require high-precision pointing. In this paper, we present details of the instrument design and its expected performance based on our laboratory tests.

  13. IN-SYNC. IV. The Young Stellar Population in the Orion A Molecular Cloud

    NASA Astrophysics Data System (ADS)

    Da Rio, Nicola; Tan, Jonathan C.; Covey, Kevin R.; Cottaar, Michiel; Foster, Jonathan B.; Cullen, Nicholas C.; Tobin, John J.; Kim, Jinyoung S.; Meyer, Michael R.; Nidever, David L.; Stassun, Keivan G.; Chojnowski, S. Drew; Flaherty, Kevin M.; Majewski, Steve; Skrutskie, Michael F.; Zasowski, Gail; Pan, Kaike

    2016-02-01

    We present the results of the Sloan Digital Sky Survey APOGEE INfrared Spectroscopy of Young Nebulous Clusters program (IN-SYNC) survey of the Orion A molecular cloud. This survey obtained high-resolution near-infrared spectroscopy of about 2700 young pre-main-sequence stars on a ˜ 6^\\circ field of view. We have measured accurate stellar parameters ({T}{{eff}}, {log}g, v{sin}i) and extinctions and placed the sources in the Hertzsprung-Russel diagram (HRD). We have also extracted radial velocities for the kinematic characterization of the population. We compare our measurements with literature results to assess the performance and accuracy of the survey. Source extinction shows evidence for dust grains that are larger than those in the diffuse interstellar medium: we estimate an average RV = 5.5 in the region. Importantly, we find a clear correlation between HRD inferred ages and spectroscopic surface-gravity-inferred ages and between extinction and disk presence; this strongly suggests a real spread of ages larger than a few Myr. Focusing on the young population around NGC 1980/ι Ori, which has previously been suggested to be a separate, foreground, older cluster, we confirm its older (˜5 Myr) age and low AV, but considering that its radial velocity distribution is indistinguishable from Orion A’s population, we suggest that NGC 1980 is part of Orion A’s star formation activity. Based on their stellar parameters and kinematic properties, we identify 383 new candidate members of Orion A, most of which are diskless sources in areas of the region poorly studied by previous works.

  14. Metrics for Optimization of Large Synoptic Survey Telescope Observations of Stellar Variables and Transients

    NASA Astrophysics Data System (ADS)

    Lund, Michael B.; Siverd, Robert J.; Pepper, Joshua A.; Stassun, Keivan G.

    2016-02-01

    The Large Synoptic Survey Telescope (LSST) will be the largest time-domain photometric survey ever. In order to maximize the LSST science yield for a broad array of transient stellar phenomena, it is necessary to optimize the survey cadence, coverage, and depth via quantitative metrics that are specifically designed to characterize the time-domain behavior of various types of stellar transients. In this paper, we present three such metrics built on the LSST Metric Analysis Framework model. Two of the metrics quantify the ability of LSST to detect non-periodic and/or non-recurring transient events and the ability of LSST to reliably measure periodic signals of various timescales. The third metric provides a way to quantify the range of stellar parameters in the stellar populations that LSST will probe. We provide example uses of these metrics and discuss some implications based on these metrics for optimization of the LSST survey for observations of stellar variables and transients.

  15. The Cepheid in the eclipsing binary system OGLE-LMC-CEP1812 is a stellar merger

    NASA Astrophysics Data System (ADS)

    Neilson, Hilding; Ignace, Richard

    2014-06-01

    Classical Cepheids and eclipsing binary systems are powerful probes for measuring stellar fundamental parameters and constraining stellar astrophysics. A Cepheid in an eclipsing binary system is even more powerful, constraining stellar physics, the distance scale and the Cepheid mass discrepancy. However, these systems are rare, only three have been discovered. One of these, OGLE-LMC-CEP1812, presents a new mystery: where the Cepheid component appears to be younger than its red giant companion. In this work, we present stellar evolution models and show that the Cepheid is actually product of a stellar merger during main sequence evolution that causes the Cepheid to be a rejuvenated star. This result raises new questions into the evolution of Cepheids and their connections to smaller-mass anomalous Cepheids.

  16. On the stellar rotation-activity connection

    NASA Technical Reports Server (NTRS)

    Rosner, R.

    1983-01-01

    The relationship between rotation rates and surface activity in late-type dwarf stars is explored in a survey of recent theoretical and observational studies. Current theoretical models of stellar-magnetic-field production and coronal activity are examined, including linear kinematic dynamo theory, nonlinear dynamos using approximations, and full numerical simulations of the MHD equations; and some typical results are presented graphically. The limitations of the modeling procedures and the constraints imposed by the physics are indicated. The statistical techniques used in establishing correlations between various observational parameters are analyzed critically, and the methods developed for quasar luminosity functions by Avni et al. (1980) are used to evaluate the effects of upper detection bounds, incomplete samples, and missing data for the case of rotation and X-ray flux data.

  17. Generic Stellarator-like Magnetic Fusion Reactor

    NASA Astrophysics Data System (ADS)

    Sheffield, John; Spong, Donald

    2015-11-01

    The Generic Magnetic Fusion Reactor paper, published in 1985, has been updated, reflecting the improved science and technology base in the magnetic fusion program. Key changes beyond inflation are driven by important benchmark numbers for technologies and costs from ITER construction, and the use of a more conservative neutron wall flux and fluence in modern fusion reactor designs. In this paper the generic approach is applied to a catalyzed D-D stellarator-like reactor. It is shown that an interesting power plant might be possible if the following parameters could be achieved for a reference reactor: R/ < a > ~ 4 , confinement factor, fren = 0.9-1.15, < β > ~ 8 . 0 -11.5 %, Zeff ~ 1.45 plus a relativistic temperature correction, fraction of fast ions lost ~ 0.07, Bm ~ 14-16 T, and R ~ 18-24 m. J. Sheffield was supported under ORNL subcontract 4000088999 with the University of Tennessee.

  18. How Accurate are SuperCOSMOS Positions?

    NASA Astrophysics Data System (ADS)

    Schaefer, Adam; Hunstead, Richard; Johnston, Helen

    2014-02-01

    Optical positions from the SuperCOSMOS Sky Survey have been compared in detail with accurate radio positions that define the second realisation of the International Celestial Reference Frame (ICRF2). The comparison was limited to the IIIaJ plates from the UK/AAO and Oschin (Palomar) Schmidt telescopes. A total of 1 373 ICRF2 sources was used, with the sample restricted to stellar objects brighter than BJ = 20 and Galactic latitudes |b| > 10°. Position differences showed an rms scatter of 0.16 arcsec in right ascension and declination. While overall systematic offsets were < 0.1 arcsec in each hemisphere, both the systematics and scatter were greater in the north.

  19. A Stellar-mass-dependent Drop in Planet Occurrence Rates

    NASA Astrophysics Data System (ADS)

    Mulders, Gijs D.; Pascucci, Ilaria; Apai, Dániel

    2015-01-01

    The Kepler spacecraft has discovered a large number of planets with up to one-year periods and down to terrestrial sizes. While the majority of the target stars are main-sequence dwarfs of spectral type F, G, and K, Kepler covers stars with effective temperatures as low as 2500 K, which corresponds to M stars. These cooler stars allow characterization of small planets near the habitable zone, yet it is not clear if this population is representative of that around FGK stars. In this paper, we calculate the occurrence of planets around stars of different spectral types as a function of planet radius and distance from the star and show that they are significantly different from each other. We further identify two trends. First, the occurrence of Earth- to Neptune-sized planets (1-4 R ⊕) is successively higher toward later spectral types at all orbital periods probed by Kepler; planets around M stars occur twice as frequently as around G stars, and thrice as frequently as around F stars. Second, a drop in planet occurrence is evident at all spectral types inward of a ~10 day orbital period, with a plateau further out. By assigning to each spectral type a median stellar mass, we show that the distance from the star where this drop occurs is stellar mass dependent, and scales with semi-major axis as the cube root of stellar mass. By comparing different mechanisms of planet formation, trapping, and destruction, we find that this scaling best matches the location of the pre-main-sequence co-rotation radius, indicating efficient trapping of migrating planets or planetary building blocks close to the star. These results demonstrate the stellar-mass dependence of the planet population, both in terms of occurrence rate and of orbital distribution. The prominent stellar-mass dependence of the inner boundary of the planet population shows that the formation or migration of planets is sensitive to the stellar parameters.

  20. A STELLAR-MASS-DEPENDENT DROP IN PLANET OCCURRENCE RATES

    SciTech Connect

    Mulders, Gijs D.; Pascucci, Ilaria; Apai, Dániel

    2015-01-10

    The Kepler spacecraft has discovered a large number of planets with up to one-year periods and down to terrestrial sizes. While the majority of the target stars are main-sequence dwarfs of spectral type F, G, and K, Kepler covers stars with effective temperatures as low as 2500 K, which corresponds to M stars. These cooler stars allow characterization of small planets near the habitable zone, yet it is not clear if this population is representative of that around FGK stars. In this paper, we calculate the occurrence of planets around stars of different spectral types as a function of planet radius and distance from the star and show that they are significantly different from each other. We further identify two trends. First, the occurrence of Earth- to Neptune-sized planets (1-4 R {sub ⊕}) is successively higher toward later spectral types at all orbital periods probed by Kepler; planets around M stars occur twice as frequently as around G stars, and thrice as frequently as around F stars. Second, a drop in planet occurrence is evident at all spectral types inward of a ∼10 day orbital period, with a plateau further out. By assigning to each spectral type a median stellar mass, we show that the distance from the star where this drop occurs is stellar mass dependent, and scales with semi-major axis as the cube root of stellar mass. By comparing different mechanisms of planet formation, trapping, and destruction, we find that this scaling best matches the location of the pre-main-sequence co-rotation radius, indicating efficient trapping of migrating planets or planetary building blocks close to the star. These results demonstrate the stellar-mass dependence of the planet population, both in terms of occurrence rate and of orbital distribution. The prominent stellar-mass dependence of the inner boundary of the planet population shows that the formation or migration of planets is sensitive to the stellar parameters.

  1. Theory of stellar convection II: first stellar models

    NASA Astrophysics Data System (ADS)

    Pasetto, S.; Chiosi, C.; Chiosi, E.; Cropper, M.; Weiss, A.

    2016-04-01

    We present here the first stellar models on the Hertzsprung-Russell diagram (HRD), in which convection is treated according to the new scale-free convection theory (SFC theory) by Pasetto et al. (2014). The aim is to compare the results of the new theory with those from the classical, calibrated mixing-length (ML) theory to examine differences and similarities. We integrate the equations describing the structure of the atmosphere from the stellar surface down to a few percent of the stellar mass using both ML theory and SFC theory. The key temperature over pressure gradients, the energy fluxes, and the extension of the convective zones are compared in both theories. The analysis is first made for the Sun and then extended to other stars of different mass and evolutionary stage. The results are adequate: the SFC theory yields convective zones, temperature gradients ∇ and ∇e, and energy fluxes that are very similar to those derived from the "calibrated" MT theory for main sequence stars. We conclude that the old scale dependent ML theory can now be replaced with a self-consistent scale-free theory able to predict correct results, as it is more physically grounded than the ML theory. Fundamentally, the SFC theory offers a deeper insight of the underlying physics than numerical simulations.

  2. Theory of stellar convection - II. First stellar models

    NASA Astrophysics Data System (ADS)

    Pasetto, S.; Chiosi, C.; Chiosi, E.; Cropper, M.; Weiss, A.

    2016-07-01

    We present here the first stellar models on the Hertzsprung-Russell diagram, in which convection is treated according to the new scale-free convection theory (SFC theory) by Pasetto et al. The aim is to compare the results of the new theory with those from the classical, calibrated mixing-length (ML) theory to examine differences and similarities. We integrate the equations describing the structure of the atmosphere from the stellar surface down to a few per cent of the stellar mass using both ML theory and SFC theory. The key temperature over pressure gradients, the energy fluxes, and the extension of the convective zones are compared in both theories. The analysis is first made for the Sun and then extended to other stars of different mass and evolutionary stage. The results are adequate: the SFC theory yields convective zones, temperature gradients ∇ and ∇e, and energy fluxes that are very similar to those derived from the `calibrated' MT theory for main-sequence stars. We conclude that the old scale dependent ML theory can now be replaced with a self-consistent scale-free theory able to predict correct results, as it is more physically grounded than the ML theory. Fundamentally, the SFC theory offers a deeper insight of the underlying physics than numerical simulations.

  3. Three-dimensional analysis of tokamaks and stellarators

    PubMed Central

    Garabedian, Paul R.

    2008-01-01

    The NSTAB equilibrium and stability code and the TRAN Monte Carlo transport code furnish a simple but effective numerical simulation of essential features of present tokamak and stellarator experiments. When the mesh size is comparable to the island width, an accurate radial difference scheme in conservation form captures magnetic islands successfully despite a nested surface hypothesis imposed by the mathematics. Three-dimensional asymmetries in bifurcated numerical solutions of the axially symmetric tokamak problem are relevant to the observation of unstable neoclassical tearing modes and edge localized modes in experiments. Islands in compact stellarators with quasiaxial symmetry are easier to control, so these configurations will become good candidates for magnetic fusion if difficulties with safety and stability are encountered in the International Thermonuclear Experimental Reactor (ITER) project. PMID:18768807

  4. Three-dimensional analysis of tokamaks and stellarators.

    PubMed

    Garabedian, Paul R

    2008-09-16

    The NSTAB equilibrium and stability code and the TRAN Monte Carlo transport code furnish a simple but effective numerical simulation of essential features of present tokamak and stellarator experiments. When the mesh size is comparable to the island width, an accurate radial difference scheme in conservation form captures magnetic islands successfully despite a nested surface hypothesis imposed by the mathematics. Three-dimensional asymmetries in bifurcated numerical solutions of the axially symmetric tokamak problem are relevant to the observation of unstable neoclassical tearing modes and edge localized modes in experiments. Islands in compact stellarators with quasiaxial symmetry are easier to control, so these configurations will become good candidates for magnetic fusion if difficulties with safety and stability are encountered in the International Thermonuclear Experimental Reactor (ITER) project. PMID:18768807

  5. Quantifying the line-of-sight mass distributions for time-delay lenses with stellar masses

    NASA Astrophysics Data System (ADS)

    Rusu, Cristian; Fassnacht, Chris; Treu, Tommaso; Suyu, Sherry; Auger, Matt; Koopmans, Leon; Marshall, Phil; Wong, Kenneth; Collett, Thomas; Agnello, Adriano; Blandford, Roger; Courbin, Frederic; Hilbert, Stefan; Meylan, Georges; Sluse, Dominique

    2014-12-01

    Measuring cosmological parameters with a realistic account of systematic uncertainties is currently one of the principal challenges of physical cosmology. Building on our recent successes with two gravitationally lensed systems, we have started a program to achieve accurate cosmographic measurements from five gravitationally lensed quasars. We aim at measuring H_0 with an accuracy better than 4%, comparable to but independent from measurements by current BAO, SN or Cepheid programs. The largest current contributor to the error budget in our sample is uncertainty about the line-of-sight mass distribution and environment of the lens systems. In this proposal, we request wide-field u-band imaging of the only lens in our sample without already available Spitzer/IRCA observations, B1608+656. The proposed observations are critical for reducing these uncertainties by providing accurate redshifts and in particular stellar masses for galaxies in the light cones of the target lens system. This will establish lensing as a powerful and independent tool for determining cosmography, in preparation for the hundreds of time-delay lenses that will be discovered by future surveys.

  6. The relationship between the WR classification and stellar models. II. The WN stars without hydrogen

    NASA Astrophysics Data System (ADS)

    Smith, Lindsey F.; Maeder, A.

    1998-06-01

    We consider the relationships between the classification parameters of WN stars in the new 3-dimensional classification of Smith et al. (1996) and the corresponding and related parameters that define stellar atmosphere models. Specifically, we consider: FWHM of HeII 4686 vs. v_infty ; hydrogen content by direct inspection vs. hydrogen content by modelling and vs. colour (b-v)_0; ionisation subclass and M_v; vs. effective temperature. From these data we argue that the WN b and only the WN b stars (i.e. stars with EW 5411 > 40 Angstroms \\ or FWHM 4686 > 30 Angstroms) are entirely free of hydrogen. For the WN b stars, we consider the relationships of EW 5411 and FWHM 4686 to the derived temperature T_*; the mass loss rate; and the surface mass flux. It appears that, to first approximation, the stars are a one-parameter family and the spectral classification criteria are sufficient to give an indication of the intrinsic colour, absolute magnitude (not very accurately), effective temperature T_* and terminal velocity. Theoretical models suggest that the critical parameter defining most of the properties of a WN b star is its present mass. However, the behaviour of FWHM 4686 suggests the presence of a second parameter that affects the mass loss rate and terminal velocity of the wind. We suggest that the second parameter may be either (or a combination of) the internal mean molecular weight or the rotation rate of the star. We further compare the relationships predicted by evolutionary models with those found for observed stars (using atmosphere models), highlighting the present difficulties in these comparisons.

  7. NNLOPS accurate associated HW production

    NASA Astrophysics Data System (ADS)

    Astill, William; Bizon, Wojciech; Re, Emanuele; Zanderighi, Giulia

    2016-06-01

    We present a next-to-next-to-leading order accurate description of associated HW production consistently matched to a parton shower. The method is based on reweighting events obtained with the HW plus one jet NLO accurate calculation implemented in POWHEG, extended with the MiNLO procedure, to reproduce NNLO accurate Born distributions. Since the Born kinematics is more complex than the cases treated before, we use a parametrization of the Collins-Soper angles to reduce the number of variables required for the reweighting. We present phenomenological results at 13 TeV, with cuts suggested by the Higgs Cross section Working Group.

  8. MIUSCAT: extended MILES spectral coverage - I. Stellar population synthesis models

    NASA Astrophysics Data System (ADS)

    Vazdekis, A.; Ricciardelli, E.; Cenarro, A. J.; Rivero-González, J. G.; Díaz-García, L. A.; Falcón-Barroso, J.

    2012-07-01

    We extend the spectral range of our stellar population synthesis models based on the MILES and CaT empirical stellar spectral libraries. For this purpose, we combine these two libraries with the Indo-U.S. to construct composite stellar spectra to feed our models. The spectral energy distributions (SEDs) computed with these models and the originally published models are combined to construct composite SEDs for single-age, single-metallicity stellar populations (SSPs) covering the range λλ3465-9469 Å at moderately high and uniform resolution (full width at half-maximum = 2.51 Å). The colours derived from these SSP SEDs provide good fits to Galactic globular cluster data. We find that the colours involving redder filters are very sensitive to the initial mass function (IMF), as well as a number of features and molecular bands throughout the spectra. To illustrate the potential use of these models, we focus on the Na I doublet at 8200 Å and with the aid of the newly synthesized SSP model SEDs, we define a new IMF-sensitive index that is based on this feature, which overcomes various limitations from previous index definitions for low-velocity dispersion stellar systems. We propose an index-index diagram based on this feature and the neighbouring Ca II triplet at 8600 Å, to constrain the IMF if the age and [Na/Fe] abundance are known. Finally we also show a survey-oriented spectrophotometric application which evidences the accurate flux calibration of these models for carrying out reliable spectral fitting techniques. These models are available through our user-friendly website.

  9. The Properties of the local Interstellar Medium and the Interaction of the Stellar Winds of epsilon Indi and lambda Andromedae with the Interstellar Environment

    NASA Technical Reports Server (NTRS)

    Wood, Brian E.; Alexander, William R.; Linsky, Jeffrey L.

    1996-01-01

    We present new observations of the Ly alpha lines of Epsilon Indi (K5 5) and A Andromedae (G8 4-3 + ?) These data were obtained by the Goddard High Resolution Spectrograph (GHRS) on the Hubble Space Telescope. Analysis of the interstellar H 1 and D 1 absorption lines reveals that the velocities and temperatures inferred from the H 1 lines are inconsistent with the parameters inferred from the D 1 lines, unless the H 1 absorption is assumed to be produced by two absorption components. One absorption component is produced by interstellar material. For both lines of sight observed, the velocity of this component is consistent with the velocity predicted by the local flow vector. For the Epsilon Indi data, the large velocity separation between the stellar emission and the interstellar absorption allows us to measure the H 1 column density independent of the shape of the intrinsic stellar Ly alpha profile. This approach permits us to quote an accurate column density and to assess its uncertainty with far more confidence than in previous analyses, for which the errors were dominated by uncertainties in the assumed stellar profiles.

  10. Quasi-axially symmetric stellarators

    PubMed Central

    Garabedian, Paul R.

    1998-01-01

    Confinement of a plasma for controlled thermonuclear fusion is studied numerically. Toroidal equilibria are considered, with an emphasis on the Modular Helias-like Heliac 2 (MHH2), which is a stellarator of low aspect ratio with just two field periods surrounded by 16 modular coils. The geometry is fully three-dimensional, but there is an axial symmetry of the magnetic structure that is calculated to give confinement competitive with that in circular tokamaks. Additional vertical and toroidal field coils, together with a current drive, provide the flexibility and the control of rotational transform necessary for a successful experiment. An MHH3 device with three field periods and comparable quasi-axial symmetry is presented, too, and because of reversed shear, its physical properties may be better. Variational analysis of equilibrium and stability is shown to give a more reliable prediction of performance for these stellarators than linearized or local theories that suffer from a failure of differentiability and convergence. PMID:9707544

  11. Quasi-axially symmetric stellarators.

    PubMed

    Garabedian, P R

    1998-08-18

    Confinement of a plasma for controlled thermonuclear fusion is studied numerically. Toroidal equilibria are considered, with an emphasis on the Modular Helias-like Heliac 2 (MHH2), which is a stellarator of low aspect ratio with just two field periods surrounded by 16 modular coils. The geometry is fully three-dimensional, but there is an axial symmetry of the magnetic structure that is calculated to give confinement competitive with that in circular tokamaks. Additional vertical and toroidal field coils, together with a current drive, provide the flexibility and the control of rotational transform necessary for a successful experiment. An MHH3 device with three field periods and comparable quasi-axial symmetry is presented, too, and because of reversed shear, its physical properties may be better. Variational analysis of equilibrium and stability is shown to give a more reliable prediction of performance for these stellarators than linearized or local theories that suffer from a failure of differentiability and convergence. PMID:9707544

  12. The Solar/Stellar Connection

    NASA Astrophysics Data System (ADS)

    Brun, Allan Sacha

    2015-08-01

    The Sun is the archetype of magnetic star. Its proximity and the wealth of very high accuracy observations that this has allowed us to gather over many decades have greatly helped us understanding how solar-like stars (e.g with a convective envelope) redistribute angular momentum and generate a cyclic magnetic field. However most models have been so fine tuned that when they are straightforwardly extended to other solar-like stars and are compared with the ever growing stellar magnetism and differential rotation observations the agreement is not as good as one could hope. In this review I will discuss based on theoretical considerations and multi-D MHD stellar models what can be considered as robust properties of solar-like star dynamics and magnetism and what is still speculative.

  13. Stellar structures in Extended Gravity

    NASA Astrophysics Data System (ADS)

    Capozziello, S.; De Laurentis, M.

    2016-09-01

    Stellar structures are investigated by considering the modified Lané-Emden equation coming out from Extended Gravity. In particular, this equation is obtained in the Newtonian limit of f ( R) -gravity by introducing a polytropic relation between the pressure and the density into the modified Poisson equation. The result is an integro-differential equation, which, in the limit f ( R) → R , becomes the standard Lané-Emden equation usually adopted in the stellar theory. We find the radial profiles of gravitational potential by solving for some values of the polytropic index. The solutions are compatible with those coming from General Relativity and could be physically relevant in order to address peculiar and extremely massive objects.

  14. Modular Stellarator Fusion Reactor concept

    SciTech Connect

    Miller, R.L.; Krakowski, R.A.

    1981-08-01

    A preliminary conceptual study is made of the Modular Stellarator Reactor (MSR). A steady-state ignited, DT-fueled, magnetic fusion reactor is proposed for use as a central electric-power station. The MSR concept combines the physics of the classic stellarator confinement topology with an innovative, modular-coil design. Parametric tradeoff calculations are described, leading to the selection of an interim design point for a 4-GWt plant based on Alcator transport scaling and an average beta value of 0.04 in an l = 2 system with a plasma aspect ratio of 11. The physics basis of the design point is described together with supporting magnetics, coil-force, and stress computations. The approach and results presented herein will be modified in the course of ongoing work to form a firmer basis for a detailed conceptual design of the MSR.

  15. STELLAR WIND INFLUENCE ON PLANETARY DYNAMOS

    SciTech Connect

    Heyner, Daniel; Glassmeier, Karl-Heinz; Schmitt, Dieter

    2012-05-10

    We examine the possible influence of early stellar wind conditions on the evolution of planetary dynamo action. In our model, the dynamo operates within a significant ambient magnetospheric magnetic field generated by the interaction between the stellar wind and the planetary magnetic field. This provides a negative feedback mechanism which quenches the dynamo growth. The external magnetic field magnitude which the dynamo experiences, and thus the strength of the quenching, depends on the stellar wind dynamic pressure. As this pressure significantly changes during stellar evolution, we argue that under early stellar system conditions the coupling between the stellar wind and the interior dynamics of a planet is much more important than has been thought up to now. We demonstrate the effects of the feedback coupling in the course of stellar evolution with a planet at a similar distance to the central star as Mercury is to the Sun.

  16. Apparent Stellar Wobble by a Planet in a Circumstellar Disk: Limitations on Planet Detection by Astrometry

    NASA Technical Reports Server (NTRS)

    Takeuchi, Taku; Velusamy, T.; Lin, D. N. C.

    2005-01-01

    Astrometric detection of a stellar wobble on the plane of the sky will provide us the next breakthrough in searching for extrasolar planets. The Space Interferometry Mission (SIM) is expected to achieve high-precision astrometry as accurate as 1 (mu)as, which is precise enough to discover a newborn Jupiter mass planet around a pre-main-sequence (PMS) star in the Taurus-Auriga star-forming region. PMS stars, however, have circumstellar disks that may be obstacles to the precise measurement of the stellar position.We present results on disk influences on the stellar wobble. The density waves excited by a planet move both the disk's mass center and the photocenter. The motion of the disk mass center induces an additional wobble of the stellar position, and the motion of the disk photocenter causes a contamination in the measurement of the stellar position. We show that the additional stellar motion dynamically caused by the disk's gravity is always negligible but that the contamination by the disk light can interfere with the precise measurement of the stellar position if the planet's mass is smaller than approximately 10MJ. The motion of the disk photocenter is sensitive to a slight change in the wave pattern and the disk properties. Measurements by interferometers are generally insensitive to extended sources such as disks. Because of this property, SIM will not suffer significant contamination by the disk light, even if the planet's mass is as small as 1M(sub J).

  17. ACCURATE ESTIMATIONS OF STELLAR AND INTERSTELLAR TRANSITION LINES OF TRIPLY IONIZED GERMANIUM

    SciTech Connect

    Dutta, Narendra Nath; Majumder, Sonjoy E-mail: sonjoy@gmail.com

    2011-08-10

    In this paper, we report on weighted oscillator strengths of E1 transitions and transition probabilities of E2 transitions among different low-lying states of triply ionized germanium using highly correlated relativistic coupled cluster (RCC) method. Due to the abundance of Ge IV in the solar system, planetary nebulae, white dwarf stars, etc., the study of such transitions is important from an astrophysical point of view. The weighted oscillator strengths of E1 transitions are presented in length and velocity gauge forms to check the accuracy of the calculations. We find excellent agreement between calculated and experimental excitation energies. Oscillator strengths of few transitions, wherever studied in the literature via other theoretical and experimental approaches, are compared with our RCC calculations.

  18. Accurate stellar masses for SB2 components: Interferometric observations for Gaia validation

    NASA Astrophysics Data System (ADS)

    Halbwachs, J.-L.; Boffin, H. M. J.; Le Bouquin, J.-B.; Famaey, B.; Salomon, J.-B.; Arenou, F.; Pourbaix, D.; Anthonioz, F.; Grellmann, R.; Guieu, S.; Guillout, P.; Jorissen, A.; Kiefer, F.; Lebreton, Y.; Mazeh, T.; Nebot Gómez-Morán, A.; Sana, H.; Tal-Or, L.

    2015-12-01

    A sample of about 70 double-lined spectroscopic binaries (SB2) is followed with radial velocity (RV) measurements, in order to derive the masses of their components when the astrometric measurements of Gaia will be available. A subset of 6 SB2 was observed in interferometry with VLTI/PIONIER, and the components were separated for each binary. The RV measurements already obtained were combined with the interferometric observations and the masses of the components were derived. The accuracies of the 12 masses are presently between 0.4 and 7 %, but they will still be improved in the future. These masses will be used to validate the masses which will be obtained from Gaia. In addition, the parallaxes derived from the combined visual+spectroscopic orbits are compared to that of Hipparcos, and a mass-luminosity relation is derived in the infrared H band.

  19. Integrated inertial stellar attitude sensor

    NASA Technical Reports Server (NTRS)

    Brady, Tye M. (Inventor); Kourepenis, Anthony S. (Inventor); Wyman, Jr., William F. (Inventor)

    2007-01-01

    An integrated inertial stellar attitude sensor for an aerospace vehicle includes a star camera system, a gyroscope system, a controller system for synchronously integrating an output of said star camera system and an output of said gyroscope system into a stream of data, and a flight computer responsive to said stream of data for determining from the star camera system output and the gyroscope system output the attitude of the aerospace vehicle.

  20. Geometry Dependence of Stellarator Turbulence

    SciTech Connect

    H.E. Mynick, P. Xanthopoulos and A.H. Boozer

    2009-08-10

    Using the nonlinear gyrokinetic code package GENE/GIST, we study the turbulent transport in a broad family of stellarator designs, to understand the geometry-dependence of the microturbulence. By using a set of flux tubes on a given flux surface, we construct a picture of the 2D structure of the microturbulence over that surface, and relate this to relevant geometric quantities, such as the curvature, local shear, and effective potential in the Schrodinger-like equation governing linear drift modes.

  1. Solar and Stellar Eclipse Mapping

    NASA Astrophysics Data System (ADS)

    Budding, E.

    2007-05-01

    The special circumstance of solar eclipse affords an opportunity to review its background, particularly in the cultural context of western Anatolia. This links with a current project of çanakkale Onsekiz Mart University. Turning to the more general subject of stellar eclipses, topics of particular note concern: choice of fitting functions, disk eclipses, spot eclipses and the gravity-darkening effect. These topics arise within new era eclipsing binary studies and are relevant to active researches on remote binaries and extrasolar planets.

  2. The AMBRE Project: Stellar Parameterisation of ESO Archived Spectra

    NASA Astrophysics Data System (ADS)

    de Laverny, P.; Recio-Blanco, A.; Worley, C. C.; De Pascale, M.; Hill, V.; Bijaoui, A.

    2013-09-01

    AMBRE is a Galactic archaeology project set up by ESO and the Observatoire de la Côte d'Azur in order to determine the stellar atmospheric parameters for the archived spectra from the ESO spectrographs FEROS, HARPS, UVES and GIRAFFE. A total of about 230000 spectra have now been homogeneously analysed and, for most (i.e., the slow-rotating FGKM-type stars), parameterised by their effective temperatures, surface gravities, global metallicities, α-element to iron abundance ratios and radial velocities. The determination of the stellar parameters is carried out using a pipeline that has been specifically developed for AMBRE. This pipeline is based on the MATISSE algorithm initially developed for the analysis of the Gaia Radial Velocity Spectrometer data.

  3. The homunculus of Eta Carinae: An interacting stellar winds paradigm

    NASA Technical Reports Server (NTRS)

    Frank, Adam; Balick, Bruce; Davidson, Kris

    1995-01-01

    We simulate the origin and evolution of the bipolar nebula surrounding Eta Car using numerical two-dimensional gasdynamic models. The generalized interacting stellar winds scenario, wherein a stellar wind interacts with an aspherical circumstellar environment, is adopted. The eruption wind of 1840-1860, which is taken to be spherically symmetric, interacts with a preeruption toroidal density environment. Using reasonable assumptions of initial conditions and eruption parameters based on archival data, we have performed over 30 simulations in an effort to bracket the initial parameters which produce models that best match observations. We find that models with high pole-to-equator density contrasts (greater than 100) and toroidal density configurations nicely account for the observed morphology and kinematics of the homunculus.

  4. James Webb Space Telescope Observations of Stellar Occultations by Solar System Bodies and Rings

    NASA Astrophysics Data System (ADS)

    Santos-Sanz, P.; French, R. G.; Pinilla-Alonso, N.; Stansberry, J.; Lin, Z.-Y.; Zhang, Z.-W.; Vilenius, E.; Müller, Th.; Ortiz, J. L.; Braga-Ribas, F.; Bosh, A.; Duffard, R.; Lellouch, E.; Tancredi, G.; Young, L.; Milam, Stefanie N.; the JWST “Occultations” Focus Group

    2016-01-01

    In this paper, we investigate the opportunities provided by the James Webb Space Telescope (JWST) for significant scientific advances in the study of Solar System bodies and rings using stellar occultations. The strengths and weaknesses of the stellar occultation technique are evaluated in light of JWST's unique capabilities. We identify several possible JWST occultation events by minor bodies and rings and evaluate their potential scientific value. These predictions depend critically on accurate a priori knowledge of the orbit of JWST near the Sun-Earth Lagrange point 2 (L2). We also explore the possibility of serendipitous stellar occultations by very small minor bodies as a byproduct of other JWST observing programs. Finally, to optimize the potential scientific return of stellar occultation observations, we identify several characteristics of JWST's orbit and instrumentation that should be taken into account during JWST's development.

  5. How to accurately bypass damage

    PubMed Central

    Broyde, Suse; Patel, Dinshaw J.

    2016-01-01

    Ultraviolet radiation can cause cancer through DNA damage — specifically, by linking adjacent thymine bases. Crystal structures show how the enzyme DNA polymerase η accurately bypasses such lesions, offering protection. PMID:20577203

  6. Eddington's Stellar Models and Early Twentieth Century Astrophysics

    NASA Astrophysics Data System (ADS)

    Eisberg, Joann

    1991-06-01

    Between 1916 and 1926, Arthur Stanley Eddington developed models of the temperature, pressure and density in the interior of stars. The models generated a relationship between stellar mass and luminosity that agreed well with observation. Coupled with the evolutionary theory that astronomers then thought governed stars, the models explained the distribution of stars upon the Hertzsprung-Russell diagram. This thesis argues that Eddington's models were shaped by the cosmological concerns that had preoccupied the British astronomical community in the preceding decade. British astronomers participated in a program of statistical cosmology, spearheaded by the Dutch astronomer, J. C. Kapteyn, to map the universe by studying the distribution of stars in neighborhoods successively more distant from the sun. The parameters of chief concern in this program were proper motion, which was used to measure stellar distance, and luminosity, considered the most important inherent characteristic of a star. In 1913 Henry Norris Russell published an empirical diagram of stellar luminosity and spectral type, on which he based a new theory of the evolution of stars from bright, red giants to bright, blue giants, to faint red dwarfs. British astronomers recognized the theory and diagram as fruits of the statistical program, and they rapidly accepted its parameters as the ones a stellar model should generate. Prompted by his interest in cepheid variable stars to construct a model of stars in radiative equilibrium, Eddington's first concern was to reproduce the features of Russell's diagram. Russell's evolutionary theory played so large a role in Eddington's work that when his own mass -luminosity relationship threatened to overturn it, he tailored his theory of stellar energy generation to preserve it.

  7. Disk Galaxy Stellar Velocity Ellipsoids

    NASA Astrophysics Data System (ADS)

    Westfall, Kyle B.; Bershady, M. A.; Verheijen, M. A. W.; Andersen, D. R.; Swaters, R. A.

    2007-12-01

    We have measured the disk stellar velocity ellipsoids in a subset of spiral galaxies observed for the Disk-Mass Survey, which provide information on disk stability and secular heating mechanisms. Our methodology invokes our 2D ionized gas and stellar kinematics and a suite of dynamical assumptions based on the Jeans' equations. When combined with orthogonal axes from our 2D data, either the epicycle approximation (EA) or asymmetric drift (AD) equation may close the necessary equation set, individually. We have isolated large observational and inherent systematic effects via EA-only, AD-only, and EA+AD ellipsoid decomposition methodologies. In an attempt to minimize these effects and generate robust ellipsoid measurements we explore constraints provided by higher order expansions of the Jeans' equations and direct orbital integrations. We compare our best ellipsoid axial ratio estimates to similar measurements made by, e.g., van der Kruit & de Grijs (1999, A&A, 352, 129) and Shapiro et al. (2003, AJ, 126, 2707). Finally, we discuss possibilities for the measurement of vertical velocity dispersions in low-surface-brightness galaxies by applying the characterization of the stellar velocity ellipsoid in late-type galaxies. This work is supported by the National Science Foundation (AST-0607516).

  8. Heating of the stellar corona

    NASA Technical Reports Server (NTRS)

    Parker, E. N.

    1986-01-01

    The present state of development of the theory of coronal heating is summarized. Coronal heating is the general cause of stellar X-ray emission, and it is also the cause of stellar mass loss in most stars. Hence a quantitive theory of coronal heating is an essential part of X-ray astronomy, and the development of a correct theory of coronal heating should be a primary concern of X-ray astronomers. The magnetohydrodynamical effects involved in coronal heating are not without interest in their own right, representing phenomena largely unknown in the terrestrial laboratory. Until these effects can be evaluated and assembled into a comprehensive theory of coronal heating for at least one star, the interpretation of the X-ray emissions of all stars is a phenomenological study at best, based on arbitrary organization and display of X-ray luminosity against bolometric luminosity, rotation rate, etc. The sun provides the one opportunity to pursue the exotic physical effects that combine to heat a stellar corona.

  9. Stellar oscillations in modified gravity

    NASA Astrophysics Data System (ADS)

    Sakstein, Jeremy

    2013-12-01

    Starting from the equations of modified gravity hydrodynamics, we derive the equations of motion governing linear, adiabatic, radial perturbations of stars in scalar-tensor theories. There are two new features: first, the eigenvalue equation for the period of stellar oscillations is modified such that the eigenfrequencies are always larger than predicted by general relativity. Second, the general relativity condition for stellar instability is altered so that the adiabatic index can fall below 4/3 before unstable modes appear. Stars are more stable in modified gravity theories. Specializing to the case of chameleonlike theories, we investigate these effects numerically using both polytropic Lane-Emden stars and models coming from modified gravity stellar structure simulations. We find that the change in the oscillation period of Cepheid star models can be as large as 30% for order-one matter couplings and the change in the inferred distance using the period-luminosity relation can be up to three times larger than if one had only considered the modified equilibrium structure. We discuss the implications of these results for recent and upcoming astrophysical tests and estimate that previous methods can produce new constraints such that the modifications are screened in regions of Newtonian potential of O(10-8).

  10. A census of stellar mass in ten massive haloes at z ~ 1 from the GCLASS Survey

    NASA Astrophysics Data System (ADS)

    van der Burg, R. F. J.; Muzzin, A.; Hoekstra, H.; Wilson, G.; Lidman, C.; Yee, H. K. C.

    2014-01-01

    Aims: We study the stellar mass content of massive haloes in the redshift range 0.86 < z < 1.34, by measuring (1) the stellar mass in the central galaxy versus total dynamical halo mass; (2) the total stellar mass (including satellites) versus total halo mass; and (3) the radial stellar mass and number density profiles for the ensemble halo. Methods: We use a Ks-band selected catalogue for the 10 clusters in the Gemini Cluster Astrophysics Spectroscopic Survey (GCLASS), with photometric redshifts and stellar masses measured from 11-band SED fitting. Combining the photometric catalogues with the deep spectroscopic component of GCLASS, we correct the cluster galaxy sample for interlopers. We also perform a dynamical analysis of the cluster galaxies to estimate the halo mass M200 for each cluster based on a measurement of its velocity dispersion. Results: (1) We find that the central galaxy stellar mass fraction decreases with total halo mass and that this is in reasonable, quantitative agreement with measurements from abundance matching studies at z ~ 1. (2) The total stellar mass fractions of these systems decrease with halo mass, indicating that lower mass systems are more efficient at transforming baryons into stars. We find the total stellar mass to be a good proxy for total halo mass, with a small intrinsic scatter. When we compare these results from GCLASS with literature measurements, we find that the stellar mass fraction at fixed halo mass shows no significant evolution in the range 0 < z < 1. (3) We measure a relatively high NFW concentration parameter cg ~ 7 for the stellar mass distribution in these clusters, and debate a possible scenario for explaining the evolution of the stellar mass distribution from the GCLASS sample to their likely descendants at lower redshift. Conclusions: The stellar mass measurements in the z ~ 1 haloes provided by GCLASS puts constraints on the stellar mass assembly history of clusters observed in the local Universe. A simple

  11. Accurate Evaluation of Quantum Integrals

    NASA Technical Reports Server (NTRS)

    Galant, David C.; Goorvitch, D.

    1994-01-01

    Combining an appropriate finite difference method with Richardson's extrapolation results in a simple, highly accurate numerical method for solving a Schr\\"{o}dinger's equation. Important results are that error estimates are provided, and that one can extrapolate expectation values rather than the wavefunctions to obtain highly accurate expectation values. We discuss the eigenvalues, the error growth in repeated Richardson's extrapolation, and show that the expectation values calculated on a crude mesh can be extrapolated to obtain expectation values of high accuracy.

  12. Accurate wavelength calibration method for flat-field grating spectrometers.

    PubMed

    Du, Xuewei; Li, Chaoyang; Xu, Zhe; Wang, Qiuping

    2011-09-01

    A portable spectrometer prototype is built to study wavelength calibration for flat-field grating spectrometers. An accurate calibration method called parameter fitting is presented. Both optical and structural parameters of the spectrometer are included in the wavelength calibration model, which accurately describes the relationship between wavelength and pixel position. Along with higher calibration accuracy, the proposed calibration method can provide information about errors in the installation of the optical components, which will be helpful for spectrometer alignment. PMID:21929865

  13. Accurate Molecular Polarizabilities Based on Continuum Electrostatics

    PubMed Central

    Truchon, Jean-François; Nicholls, Anthony; Iftimie, Radu I.; Roux, Benoît; Bayly, Christopher I.

    2013-01-01

    A novel approach for representing the intramolecular polarizability as a continuum dielectric is introduced to account for molecular electronic polarization. It is shown, using a finite-difference solution to the Poisson equation, that the Electronic Polarization from Internal Continuum (EPIC) model yields accurate gas-phase molecular polarizability tensors for a test set of 98 challenging molecules composed of heteroaromatics, alkanes and diatomics. The electronic polarization originates from a high intramolecular dielectric that produces polarizabilities consistent with B3LYP/aug-cc-pVTZ and experimental values when surrounded by vacuum dielectric. In contrast to other approaches to model electronic polarization, this simple model avoids the polarizability catastrophe and accurately calculates molecular anisotropy with the use of very few fitted parameters and without resorting to auxiliary sites or anisotropic atomic centers. On average, the unsigned error in the average polarizability and anisotropy compared to B3LYP are 2% and 5%, respectively. The correlation between the polarizability components from B3LYP and this approach lead to a R2 of 0.990 and a slope of 0.999. Even the F2 anisotropy, shown to be a difficult case for existing polarizability models, can be reproduced within 2% error. In addition to providing new parameters for a rapid method directly applicable to the calculation of polarizabilities, this work extends the widely used Poisson equation to areas where accurate molecular polarizabilities matter. PMID:23646034

  14. Fundamental Parameters of Kepler Eclipsing Binaries. I. KIC 5738698

    NASA Astrophysics Data System (ADS)

    Matson, Rachel A.; Gies, Douglas R.; Guo, Zhao; Orosz, Jerome A.

    2016-06-01

    Eclipsing binaries serve as a valuable source of stellar masses and radii that inform stellar evolutionary models and provide insight into additional astrophysical processes. The exquisite light curves generated by space-based missions such as Kepler offer the most stringent tests to date. We use the Kepler light curve of the 4.8 day eclipsing binary KIC 5739896 with ground based optical spectra to derive fundamental parameters for the system. We reconstruct the component spectra to determine the individual atmospheric parameters, and model the Kepler photometry with the binary synthesis code Eclipsing Light Curve to obtain accurate masses and radii. The two components of KIC 5738698 are F-type stars with {M}1\\=\\1.39+/- 0.04 {M}ȯ , {M}2\\=\\1.34+/- 0.06 {M}ȯ , and {R}1\\=\\1.84+/- 0.03 {R}ȯ , {R}2\\=\\1.72+/- 0.03 {R}ȯ . We also report a small eccentricity (e≲ 0.0017) and unusual albedo values that are required to match the detailed shape of the Kepler light curve. Comparison with evolutionary models indicate an approximate age of 2.3 Gyr for the system.

  15. Astrostatistical Analysis in Solar and Stellar Physics

    NASA Astrophysics Data System (ADS)

    Stenning, David Craig

    the solar cycle that are missed when the model is fit using only the sunspot numbers. In Part II of this dissertation we focus on two related lines of research involving Bayesian analysis of stellar evolution. We first focus on modeling multiple stellar populations in star clusters. It has long been assumed that all star clusters are comprised of single stellar populations---stars that formed at roughly the same time from a common molecular cloud. However, recent studies have produced evidence that some clusters host multiple populations, which has far-reaching scientific implications. We develop a Bayesian hierarchical model for multiple-population star clusters, extending earlier statistical models of stellar evolution (e.g., van Dyk et al. 2009, Stein et al. 2013). We also devise an adaptive Markov chain Monte Carlo algorithm to explore the complex posterior distribution. We use numerical studies to demonstrate that our method can recover parameters of multiple-population clusters, and also show how model misspecification can be diagnosed. Our model and computational tools are incorporated into an open-source software suite known as BASE-9. We also explore statistical properties of the estimators and determine that the influence of the prior distribution does not diminish with larger sample sizes, leading to non-standard asymptotics. In a final line of research, we present the first-ever attempt to estimate the carbon fraction of white dwarfs. This quantity has important implications for both astrophysics and fundamental nuclear physics, but is currently unknown. We use a numerical study to demonstrate that assuming an incorrect value for the carbon fraction leads to incorrect white-dwarf ages of star clusters. Finally, we present our attempt to estimate the carbon fraction of the white dwarfs in the well-studied star cluster 47 Tucanae.

  16. Temperature-dependent nuclear partition functions and abundances in the stellar interior

    NASA Astrophysics Data System (ADS)

    Nabi, Jameel-Un; Nasser Tawfik, Abdel; Ezzelarab, Nada; Abas Khan, Ali

    2016-05-01

    We calculate the temperature-dependent nuclear partition functions (TDNPFs) and nuclear abundances for 728 nuclei, assuming nuclear statistical equilibrium (NSE). The theories of stellar evolution support NSE. Discrete nuclear energy levels have been calculated microscopically, using the pn-QRPA theory, up to an excitation energy of 10 MeV in the calculation of the TDNPFs. This feature of our paper distinguishes it from previous calculations. Experimental data is also incorporated wherever available to ensure the reliability of our results. Beyond 10 MeV, we employ a simple Fermi gas model and perform integration over the nuclear level densities to approximate the TDNPFs. We calculate nuclidic abundances, using the Saha equation, as a function of three parameters: stellar density, stellar temperature and the lepton-to-baryon content of stellar matter. All these physical parameters are considered to be extremely important in the stellar interior. The results obtained in this paper show that the equilibrium configuration of nuclei remains unaltered by increasing the stellar density (only the calculated nuclear abundances increase by roughly the same order of magnitude). Increasing the stellar temperature smoothes the equilibrium configuration showing peaks at the neutron-number magic nuclei.

  17. The use of stellar occultations to study the figures and atmospheres of small bodies in the outer solar system

    NASA Astrophysics Data System (ADS)

    Person, Michael James

    The methods of analyzing stellar occultations by small bodies in the outer solar system are discussed with examples from Triton, Pluto, and Charon. Simulations were performed characterizing the analysis of multi-chord occultations including: the effects of the direction of residual minimization in figure fits, the complications in measuring the reliability of fitted figure parameters when there are few degrees of freedom, and the proper treatment of grazing chords in model fitting. The 2005 July 11 C313.2 stellar occultation by Charon was analyzed. Occultation timings from the three published data sets were combined to accurately determine the mean radius of Charon: 606.0 ± 1.5 km. The analysis indicates that a slight oblateness in the body (0.006 ± 0.003) best matches the data, with a confidence level of 86%. Charon's mean radius corresponds to a bulk density of 1.63 ± 0.07 g/cm 3 , which is significantly less than Pluto's (1.92 ± 0.12 g/cm 3 ), consistent with an impact formation scenario in which at least one of the impactors was differentiated. The 2002 August 21 P131.1 and the 1988 June 9 P8 stellar occultations by Pluto were analyzed. The ellipticity of Pluto's atmosphere as measured by the P131.1 event is 0.066 ± 0.040, with a Gaussian confidence level of 63%, and the ellipticity as measured by the P8 occultations is 0.091 ± 0.041, with a Gaussian confidence level of 70%. If this nonsphericity is confirmed, its size and variation could possibly be attributed to superrotating winds driven by sources such as surface frost migration due to changing insolation patterns or albedo properties, gravity waves, and an asymmetric mass distribution in Pluto itself. The 2001 August 23 Tr231 stellar occultation by Triton was analyzed. The half- light radius of Triton's atmosphere was calculated from astrometrically calibrated model fits to the occultation light curve. The resulting half-light radius of 1479.01 km is larger than the value of 1456.3 km derived from

  18. VizieR Online Data Catalog: Stellar populations of NGC 3311 (Barbosa+, 2016)

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

    We have observe the stellar halo over NGC 3311, the central galaxy of the Hydra I cluster, using 118 small slits avoiding point sources. The data was obtained with FORS2 spectrograph at the Very Large Telescope using the spectroscopic mask mode (MXU). Equivalent width of absorption line features were measured in the Lick/IDS sytem, and stellar population parameters, ie. age, metallicity and alpha-element abundances, were calculated using single stellar populations with models from Thomas et al. (2011MNRAS.412.2183T). (1 data file).

  19. THE ARAUCARIA PROJECT: AN ACCURATE DISTANCE TO THE LATE-TYPE DOUBLE-LINED ECLIPSING BINARY OGLE SMC113.3 4007 IN THE SMALL MAGELLANIC CLOUD

    SciTech Connect

    Graczyk, Dariusz; Pietrzynski, Grzegorz; Gieren, Wolfgang; Pilecki, Bogumil; Mennickent, Ronald E-mail: wgieren@astro-udec.cl; and others

    2012-05-10

    We have analyzed the long-period, double-lined eclipsing binary system OGLE SMC113.3 4007 (SC10 137844) in the Small Magellanic Cloud. The binary lies in the northeastern part of the galaxy and consists of two evolved, well-detached, non-active G8 giants. The orbit is eccentric with e = 0.311, and the orbital period is 371.6 days. Using extensive high-resolution spectroscopic and multi-color photometric data, we have determined a true distance modulus of the system of m - M = 18.83 {+-} 0.02 (statistical) {+-} 0.05 (systematic) mag using a surface-brightness-color relation for giant stars. This method is insensitive to metallicity and reddening corrections and depends only very little on stellar atmosphere model assumptions. Additionally, we derived very accurate, at the level of 1%-2%, physical parameters of both giant stars, particularly their masses and radii, making our results important for comparison with stellar evolution models. Our analysis underlines the high potential of late-type, double-lined detached binary systems for accurate distance determinations to nearby galaxies.

  20. Properties and effects on stellar burning of fractionally charged nuclei

    SciTech Connect

    Boyd, R.N.; Turner, R.E.; Rybarcyk, L.; Joseph, C.

    1985-02-01

    The consequences of unconfined quarks which may have been left over from the big bang, especially as to how they might participate in nucleosynthesis, are examined. Possible properties of the fractionally charged nuclei (Q-nuclei) thus produced, including ..beta..-decay half-lives, binding energies, energy level densities, and thermonnuclear reaction rates, are studied. Stellar burning cycles are suggested by these considerations in which the Q-nuclei could contribute significantly to stellar nucleosynthesis, even at an extremely low abundance level, provided that they satisfy some constraints. A model is suggested which accommodates all the constraints thus imposed. Possible implications of the existence of Q-nuclei for stellar evolution are considered, adn the results of a calculation are presented which confirm that no obvious conflicts with the known parameters of the Sun are encountered. The significance of the possible existence of Q-nuclei for future searches for free fractionally charged entities is discussed. Finally, it is noted that any particle which, when added to a nucleus, increases the nucleon binding energy somewhat could perform stellar burning cycles similar to those described in this paper. Subject headings: elementary particles-neutrinos-nuclear reactions:nucleosynthesis-stars: interiors

  1. A Unified Computational Model for Solar and Stellar Flares

    NASA Astrophysics Data System (ADS)

    Allred, Joel C.; Kowalski, Adam F.; Carlsson, Mats

    2015-08-01

    We present a unified computational framework that can be used to describe impulsive flares on the Sun and on dMe stars. The models assume that the flare impulsive phase is caused by a beam of charged particles that is accelerated in the corona and propagates downward depositing energy and momentum along the way. This rapidly heats the lower stellar atmosphere causing it to explosively expand and dramatically brighten. Our models consist of flux tubes that extend from the sub-photosphere into the corona. We simulate how flare-accelerated charged particles propagate down one-dimensional flux tubes and heat the stellar atmosphere using the Fokker-Planck kinetic theory. Detailed radiative transfer is included so that model predictions can be directly compared with observations. The flux of flare-accelerated particles drives return currents which additionally heat the stellar atmosphere. These effects are also included in our models. We examine the impact of the flare-accelerated particle beams on model solar and dMe stellar atmospheres and perform parameter studies varying the injected particle energy spectra. We find the atmospheric response is strongly dependent on the accelerated particle cutoff energy and spectral index.

  2. A Unified Computational Model for Solar and Stellar Flares

    NASA Technical Reports Server (NTRS)

    Allred, Joel C.; Kowalski, Adam F.; Carlsson, Mats

    2015-01-01

    We present a unified computational framework that can be used to describe impulsive flares on the Sun and on dMe stars. The models assume that the flare impulsive phase is caused by a beam of charged particles that is accelerated in the corona and propagates downward depositing energy and momentum along the way. This rapidly heats the lower stellar atmosphere causing it to explosively expand and dramatically brighten. Our models consist of flux tubes that extend from the sub-photosphere into the corona. We simulate how flare-accelerated charged particles propagate down one-dimensional flux tubes and heat the stellar atmosphere using the Fokker-Planck kinetic theory. Detailed radiative transfer is included so that model predictions can be directly compared with observations. The flux of flare-accelerated particles drives return currents which additionally heat the stellar atmosphere. These effects are also included in our models. We examine the impact of the flare-accelerated particle beams on model solar and dMe stellar atmospheres and perform parameter studies varying the injected particle energy spectra. We find the atmospheric response is strongly dependent on the accelerated particle cutoff energy and spectral index.

  3. A Unified Computational Model for Solar and Stellar Flares

    NASA Astrophysics Data System (ADS)

    Allred, Joel; Kowalski, Adam; Carlsson, Mats

    2015-04-01

    We describe a unified computational framework which can be used to model impulsive flares on the Sun and on dMe stars. The models are constructed assuming that the flare impulsive phase is caused by a beam of charged particles (primarily electrons and protons) that is accelerated in the corona and propagates downward depositing energy and momentum along the way. This rapidly heats the lower stellar atmosphere causing it to explosively expand and emission to dramatically brighten. Our models consist of flux tubes that extend from the sub-photosphere into the corona. We simulate how these flare-accelerated particles propagate down one dimensional flux tubes and heat the stellar atmosphere using Fokker-Planck kinetic theory. Detailed radiative transfer is included so that model predictions can be directly compared with observations. The flux of flare-accelerated particles drives return currents which additionally heat the stellar atmosphere, and these effects are also included in our models. We examine the impact of the flare-accelerated particle beams on model solar and dMe stellar atmospheres and perform parameter studies varying the injected particle energy spectra. We find the atmospheric response is strongly dependent on the accelerated particle cutoff energy and spectral index.

  4. Evidences for Black Hole Formation by Complete Stellar Collapse

    NASA Astrophysics Data System (ADS)

    Mirabel, Igor Felix

    2016-07-01

    One of the most critical parameters that determines the formation of binary black holes is the range of masses of black holes that may form by direct collapse, namely, with no energetic supernova kicks that would unbound the stellar binary. Theoretical models set mass ranges and limits for black hole formation through the complete collapse of the stellar progenitor. However, observational constraints for those mass limits have been elusive. Since the velocity of a stellar black hole encodes the history of its formation and evolution, it may provide observational constraints on the strength of kicks by natal supernova explosions in the formation of the black hole. Based on the motion in three dimensions of five black hole binaries in our Galaxy it is found that the three black holes with < 10 solar masses are runaway black hole binaries due to kicks from natal supernovae, whereas the two black holes with 10 to 15 solar masses remained in their birth place and must have been form by complete or almost complete collapse of the progenitor star. These observations show that there may be binary black holes with components having masses as low as 10 solar masses, which suggests that a significant fraction of massive stellar binaries would end as black hole binaries that would produce a large stochastic gravitational-wave background.

  5. Stellar photometry including saturated images: Results on M67 with WFPC2

    NASA Technical Reports Server (NTRS)

    Gilliland, Ronald L.

    1994-01-01

    The Wide Field and Planetary Camera 2 (WFPC2) on Hubble Space Telescope (HST) is providing unsurpassed imaging capabilities and supporting accurate stellar photometry over large fields of view at high angular resolution. I discuss a feature of the WFPC2 CCD systems that nominally limits the dynamic range attainable with single exposures: a 12 bit analog to digital converter that does not allow sampling of the CCD full-well depth even at the low gain (14e(sup -)/DN) setting. I demonstrate that accurate stellar photometry can be performed on stellar images that are strongly saturated. Two 40 s exposures in V and I bands on the old open cluster M67 are analyzed to demonstrate photometric capabilities with a dynamic range of over 12 mag from single exposures. New photometric results for both bright and faint objects in M67 are derived from the WFPC2 data.

  6. Two highly accurate methods for pitch calibration

    NASA Astrophysics Data System (ADS)

    Kniel, K.; Härtig, F.; Osawa, S.; Sato, O.

    2009-11-01

    Among profiles, helix and tooth thickness pitch is one of the most important parameters of an involute gear measurement evaluation. In principle, coordinate measuring machines (CMM) and CNC-controlled gear measuring machines as a variant of a CMM are suited for these kinds of gear measurements. Now the Japan National Institute of Advanced Industrial Science and Technology (NMIJ/AIST) and the German national metrology institute the Physikalisch-Technische Bundesanstalt (PTB) have each developed independently highly accurate pitch calibration methods applicable to CMM or gear measuring machines. Both calibration methods are based on the so-called closure technique which allows the separation of the systematic errors of the measurement device and the errors of the gear. For the verification of both calibration methods, NMIJ/AIST and PTB performed measurements on a specially designed pitch artifact. The comparison of the results shows that both methods can be used for highly accurate calibrations of pitch standards.

  7. Modeling Small Stellar Populations Using Starburst99

    NASA Astrophysics Data System (ADS)

    Vazquez, Gerardo Arturo; Leitherer, Claus

    2015-08-01

    Stellar populations synthesis models have proven to be excellent tools to learn about galaxy evolution. However, modeling small stellar populations (lower than 105 M⊙) has been an intriguing and continuous to be a field of intensive research. In this work, we have developed a new approach to form stars from clusters first, where massive stars are formed from fractions of mass of small stellar clusters. This new approximation is based on the empirical power law (mc-2) for the mass function of clusters between 20-1100 M⊙ found in recent years and the maximum stellar mass that can be formed in a cluster. Incorporating this new approach to form clusters has made us upgrade the way we integrate the stellar properties and the way that the isochrone is produced with a new technique. To produce the new models we have used the most recent version of Starburst99 that incorporates the most recent stellar evolution models with rotation. On the verge of solving nearby stellar populations and observing small stellar populations across the universe, this new approach brings a new scope on trying to disentangle the nature of hyper and supermassive stars in small stellar populations. In this work we present this new approach and the results when these models are applied to very energetic stellar populations such as the cluster in NGC 3603. Our most important result is that we have modeled the ionizing power of this cluster and some others by forming enough supermassive stars in a cluster of ~104 M⊙.

  8. POLLUX: a database of synthetic stellar spectra

    NASA Astrophysics Data System (ADS)

    Palacios, A.; Gebran, M.; Josselin, E.; Martins, F.; Plez, B.; Belmas, M.; Lèbre, A.

    2010-06-01

    Aims: Synthetic spectra are needed to determine fundamental stellar and wind parameters of all types of stars. They are also used for the construction of theoretical spectral libraries helpful for stellar population synthesis. Therefore, a database of theoretical spectra is required to allow rapid and quantitative comparisons to spectroscopic data. We provide such a database offering an unprecedented coverage of the entire Hertzsprung-Russell diagram. Methods: We present the POLLUX database of synthetic stellar spectra. For objects with Teff ≤ 6000 K, MARCS atmosphere models are computed and the program TURBOSPECTRUM provides the synthetic spectra. ATLAS12 models are computed for stars