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Sample records for 3d stellar atmospheres

  1. 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

  2. Micro- and macroturbulence predictions from CO5BOLD 3D stellar atmospheres .

    NASA Astrophysics Data System (ADS)

    Steffen, M.; Caffau, E.; Ludwig, H.-G.

    We present an overview of the current status of our efforts to derive the microturbulence and macroturbulence parameters (xi_mic and xi_mac) from the CIFIST grid of CO5BOLD 3D model atmospheres as a function of the basic stellar parameters T_{eff}, log g, and [M/H]. The latest results for the Sun and Procyon show that the derived microturbulence parameter depends significantly on the numerical resolution of the underlying 3D simulation, confirming that `low-resolution' models tend to underestimate the true value of xi_mic . Extending the investigation to 12 further simulations with different T_{eff}, log g, and [M/H], we obtain a first impression of the predicted trend of xi_mic over the Hertzsprung-Russell diagram: in agreement with empirical evidence, microturbulence increases towards higher effective temperature and lower gravity. The metallicity dependence of xi_mic must be interpreted with care, since it also reflects the deviation between the 1D and 3D photospheric temperature stratifications that increases systematically towards lower [M/H].

  3. On line contribution functions and examining spectral line formation in 3D model stellar atmospheres

    NASA Astrophysics Data System (ADS)

    Amarsi, A. M.

    2015-09-01

    Line contribution functions are useful diagnostics for studying spectral line formation in stellar atmospheres. I derive an expression for the contribution function to the absolute flux depression that emerges from three-dimensional `box-in-a-star' model stellar atmospheres. I illustrate the result by comparing the local thermodynamic equilibrium (LTE) spectral line formation of the high-excitation permitted OI 777 nm lines with the non-LTE case.

  4. The Stagger-grid: A grid of 3D stellar atmosphere models. I. Methods and general properties

    NASA Astrophysics Data System (ADS)

    Magic, Z.; Collet, R.; Asplund, M.; Trampedach, R.; Hayek, W.; Chiavassa, A.; Stein, R. F.; Nordlund, Å.

    2013-09-01

    Aims: We present the Stagger-grid, a comprehensive grid of time-dependent, three-dimensional (3D), hydrodynamic model atmospheres for late-type stars with realistic treatment of radiative transfer, covering a wide range in stellar parameters. This grid of 3D models is intended for various applications besides studies of stellar convection and atmospheres per se, including stellar parameter determination, stellar spectroscopy and abundance analysis, asteroseismology, calibration of stellar evolution models, interferometry, and extrasolar planet search. In this introductory paper, we describe the methods we applied for the computation of the grid and discuss the general properties of the 3D models as well as of their temporal and spatial averages (here denoted ⟨3D⟩ models). Methods: All our models were generated with the Stagger-code, using realistic input physics for the equation of state (EOS) and for continuous and line opacities. Our ~ 220 grid models range in effective temperature, Teff, from 4000 to 7000 K in steps of 500 K, in surface gravity, log g, from 1.5 to 5.0 in steps of 0.5 dex, and metallicity, [Fe/H], from - 4.0 to + 0.5 in steps of 0.5 and 1.0 dex. Results: We find a tight scaling relation between the vertical velocity and the surface entropy jump, which itself correlates with the constant entropy value of the adiabatic convection zone. The range in intensity contrast is enhanced at lower metallicity. The granule size correlates closely with the pressure scale height sampled at the depth of maximum velocity. We compare the ⟨3D⟩ models with currently widely applied one-dimensional (1D) atmosphere models, as well as with theoretical 1D hydrostatic models generated with the same EOS and opacity tables as the 3D models, in order to isolate the effects of using self-consistent and hydrodynamic modeling of convection, rather than the classical mixing length theory approach. For the first time, we are able to quantify systematically over a broad

  5. Non-LTE oxygen line formation in 3D hydrodynamic model stellar atmospheres

    NASA Astrophysics Data System (ADS)

    Amarsi, A. M.; Asplund, M.; Collet, R.; Leenaarts, J.

    2016-02-01

    The O I 777 nm lines are among the most commonly used diagnostics for the oxygen abundances in the atmospheres of FGK-type stars. However, they form in conditions that are far from local thermodynamic equilibrium (LTE). We explore the departures from LTE of atomic oxygen, and their impact on O I lines, across the STAGGER-grid of three-dimensional hydrodynamic model atmospheres. For the O I 777 nm triplet, we find significant departures from LTE. These departures are larger in stars with larger effective temperatures, smaller surface gravities, and larger oxygen abundances. We present grids of predicted 3D non-LTE based equivalent widths for the O I 616 nm, [O I] 630 nm, [O I] 636 nm, and O I 777 nm lines, as well as abundance corrections to 1D LTE based results.

  6. The Stagger-grid: A grid of 3D stellar atmosphere models. III. The relation to mixing length convection theory

    NASA Astrophysics Data System (ADS)

    Magic, Z.; Weiss, A.; Asplund, M.

    2015-01-01

    Aims: We investigate the relation between 1D atmosphere models that rely on the mixing length theory and models based on full 3D radiative hydrodynamic (RHD) calculations to describe convection in the envelopes of late-type stars. Methods: The adiabatic entropy value of the deep convection zone, sbot, and the entropy jump, Δs, determined from the 3D RHD models, were matched with the mixing length parameter, αMLT, from 1D hydrostatic atmosphere models with identical microphysics (opacities and equation-of-state). We also derived the mass mixing length parameter, αm, and the vertical correlation length of the vertical velocity, C[vz,vz], directly from the 3D hydrodynamical simulations of stellar subsurface convection. Results: The calibrated mixing length parameter for the Sun is α๏MLT (Sbot) = 1.98. . For different stellar parameters, αMLT varies systematically in the range of 1.7 - 2.4. In particular, αMLT decreases towards higher effective temperature, lower surface gravity and higher metallicity. We find equivalent results for α๏MLT (ΔS). In addition, we find a tight correlation between the mixing length parameter and the inverse entropy jump. We derive an analytical expression from the hydrodynamic mean-field equations that motivates the relation to the mass mixing length parameter, αm, and find that it qualitatively shows a similar variation with stellar parameter (between 1.6 and 2.4) with the solar value of α๏m = 1.83.. The vertical correlation length scaled with the pressure scale height yields 1.71 for the Sun, but only displays a small systematic variation with stellar parameters, the correlation length slightly increases with Teff. Conclusions: We derive mixing length parameters for various stellar parameters that can be used to replace a constant value. Within any convective envelope, αm and related quantities vary strongly. Our results will help to replace a constant αMLT. Appendices are available in electronic form at http

  7. 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.

  8. 3D acoustic atmospheric tomography

    NASA Astrophysics Data System (ADS)

    Rogers, Kevin; Finn, Anthony

    2014-10-01

    This paper presents a method for tomographically reconstructing spatially varying 3D atmospheric temperature profiles and wind velocity fields based. Measurements of the acoustic signature measured onboard a small Unmanned Aerial Vehicle (UAV) are compared to ground-based observations of the same signals. The frequency-shifted signal variations are then used to estimate the acoustic propagation delay between the UAV and the ground microphones, which are also affected by atmospheric temperature and wind speed vectors along each sound ray path. The wind and temperature profiles are modelled as the weighted sum of Radial Basis Functions (RBFs), which also allow local meteorological measurements made at the UAV and ground receivers to supplement any acoustic observations. Tomography is used to provide a full 3D reconstruction/visualisation of the observed atmosphere. The technique offers observational mobility under direct user control and the capacity to monitor hazardous atmospheric environments, otherwise not justifiable on the basis of cost or risk. This paper summarises the tomographic technique and reports on the results of simulations and initial field trials. The technique has practical applications for atmospheric research, sound propagation studies, boundary layer meteorology, air pollution measurements, analysis of wind shear, and wind farm surveys.

  9. Seeing a Stellar Explosion in 3D

    NASA Astrophysics Data System (ADS)

    2010-08-01

    Astronomers using ESO's Very Large Telescope have for the first time obtained a three-dimensional view of the distribution of the innermost material expelled by a recently exploded star. The original blast was not only powerful, according to the new results. It was also more concentrated in one particular direction. This is a strong indication that the supernova must have been very turbulent, supporting the most recent computer models. Unlike the Sun, which will die rather quietly, massive stars arriving at the end of their brief life explode as supernovae, hurling out a vast quantity of material. In this class, Supernova 1987A (SN 1987A) in the rather nearby Large Magellanic Cloud occupies a very special place. Seen in 1987, it was the first naked-eye supernova to be observed for 383 years (eso8704), and because of its relative closeness, it has made it possible for astronomers to study the explosion of a massive star and its aftermath in more detail than ever before. It is thus no surprise that few events in modern astronomy have been met with such an enthusiastic response by scientists. SN 1987A has been a bonanza for astrophysicists (eso8711 and eso0708). It provided several notable observational 'firsts', like the detection of neutrinos from the collapsing inner stellar core triggering the explosion, the localisation on archival photographic plates of the star before it exploded, the signs of an asymmetric explosion, the direct observation of the radioactive elements produced during the blast, observation of the formation of dust in the supernova, as well as the detection of circumstellar and interstellar material (eso0708). New observations making use of a unique instrument, SINFONI [1], on ESO's Very Large Telescope (VLT) have provided even deeper knowledge of this amazing event, as astronomers have now been able to obtain the first-ever 3D reconstruction of the central parts of the exploding material. This view shows that the explosion was stronger and

  10. Seeing a Stellar Explosion in 3D

    NASA Astrophysics Data System (ADS)

    2010-08-01

    Astronomers using ESO's Very Large Telescope have for the first time obtained a three-dimensional view of the distribution of the innermost material expelled by a recently exploded star. The original blast was not only powerful, according to the new results. It was also more concentrated in one particular direction. This is a strong indication that the supernova must have been very turbulent, supporting the most recent computer models. Unlike the Sun, which will die rather quietly, massive stars arriving at the end of their brief life explode as supernovae, hurling out a vast quantity of material. In this class, Supernova 1987A (SN 1987A) in the rather nearby Large Magellanic Cloud occupies a very special place. Seen in 1987, it was the first naked-eye supernova to be observed for 383 years (eso8704), and because of its relative closeness, it has made it possible for astronomers to study the explosion of a massive star and its aftermath in more detail than ever before. It is thus no surprise that few events in modern astronomy have been met with such an enthusiastic response by scientists. SN 1987A has been a bonanza for astrophysicists (eso8711 and eso0708). It provided several notable observational 'firsts', like the detection of neutrinos from the collapsing inner stellar core triggering the explosion, the localisation on archival photographic plates of the star before it exploded, the signs of an asymmetric explosion, the direct observation of the radioactive elements produced during the blast, observation of the formation of dust in the supernova, as well as the detection of circumstellar and interstellar material (eso0708). New observations making use of a unique instrument, SINFONI [1], on ESO's Very Large Telescope (VLT) have provided even deeper knowledge of this amazing event, as astronomers have now been able to obtain the first-ever 3D reconstruction of the central parts of the exploding material. This view shows that the explosion was stronger and

  11. 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.

  12. 3-D simulations of solar and stellar convection and magnetoconvection

    NASA Astrophysics Data System (ADS)

    Nordlund, Å.; Stein, R. F.

    1990-05-01

    We present the key components of a 3-D code designed for simulating the hydrodynamics and magnetohydrodynamics of stellar atmospheres and envelopes. Some particular properties of the code are: (1) the ability to handle strong stratification (extensive simulations with bottom/top pressure ratios of 3×104 have been performed, and simulations with pressure ratios of 5×106 are being initiated); (2) a detailed treatment of the radiating surface; (3) a functional form of the subgrid-scale diffusion designed to minimize the influence on resolved motions; (4) boundary conditions open to flows. The top boundary allows the transmission of short period waves, while the bottom boundary condition was designed to enforce a displacement node for radial pressure modes.

  13. 3D Models of Stellar Interactions

    NASA Astrophysics Data System (ADS)

    Mohamed, S.; Podsiadlowski, Ph.; Booth, R.; Maercker, M.; Ramstedt, S.; Vlemmings, W.; Harries, T.; Mackey, J.; Langer, N.; Corradi, R.

    2014-04-01

    Symbiotic binaries consist of a cool, evolved mass-losing giant and an accreting compact companion. As symbiotic nebulae show similar morphologies to those in planetary nebulae (so much so that it is often difficult to distinguish between the two), they are ideal laboratories for understanding the role a binary companion plays in shaping the circumstellar envelopes in these evolved systems. We will present 3D Smoothed Particle Hydrodynamics (SPH) models of interacting binaries, e.g. R Aquarii and Mira, and discuss the formation of spiral outflows, arcs, shells and equatorial density enhancements.We will also discuss the implications of the former for planetary nebulae, e.g. the Egg Nebula and Cat's Eye, and the latter for the formation of bipolar geometries, e.g. M2-9. We also investigate accretion and angular momentum evolution in symbiotic binaries which may be important to understand the formation of jets and more episodic mass-loss features we see in circumstellar envelopes and the orbital characteristics of binary central stars of planetary nebulae.

  14. Solar abundances and 3D model atmospheres

    NASA Astrophysics Data System (ADS)

    Ludwig, Hans-Günter; Caffau, Elisabetta; Steffen, Matthias; Bonifacio, Piercarlo; Freytag, Bernd; Cayrel, Roger

    2010-03-01

    We present solar photospheric abundances for 12 elements from optical and near-infrared spectroscopy. The abundance analysis was conducted employing 3D hydrodynamical (CO5BOLD) as well as standard 1D hydrostatic model atmospheres. We compare our results to others with emphasis on discrepancies and still lingering problems, in particular exemplified by the pivotal abundance of oxygen. We argue that the thermal structure of the lower solar photosphere is very well represented by our 3D model. We obtain an excellent match of the observed center-to-limb variation of the line-blanketed continuum intensity, also at wavelengths shortward of the Balmer jump.

  15. 3D geometry applied to atmospheric layers

    NASA Astrophysics Data System (ADS)

    Nadjib Kouahla, Mohamed; Moreels, Guy; Faivre, Michael

    Epipolar geometry is an efficient method for generating 3D representations of objects. Here we present an original application of this method to the case of atmospheric layers. Two synchronized simultaneous images of the same scene are taken in two sites at a distance D. The 36*36 fields of view are oriented face to face along the same line of sight, but in opposite directions. The elevation angle of the optical axis above the horizon is 17. The observed objects are airglow emissions or cirrus clouds or aircraft trails. In the case of clouds, the shape of the objects is diffuse. To obtain a superposition of the common observed zone, it is necessary to calculate a normalized cross-correlation coefficient (NCC) to identify pairs of matching points in both images. The perspective effect in the rectangular images is inverted to produce a satellite-type view of the atmospheric layer as could be seen from an overlying satellite. We developed a triangulation algorithm to retrieve the 3D surface of the observed layer. The stereoscopic method was used to retrieve the wavy structure of the OH emissive layer at the altitude of 87 km. The distance between the observing sites was 600 km. Results obtained in Peru from the sites of Cerro Cosmos and Cerro Verde will be presented. We are currently extending the stereoscopic procedure to the study of troposphere cirruses, of natural origin or induced by aircraft engines. In this case, the distance between observation sites is D 60 km.

  16. VizieR Online Data Catalog: STAGGER-grid of 3D stellar models. IV. (Magic+, 2015)

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    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. 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 7000K, logg from 1.5 to 5.0, and [Fe/H], from -4.0 to +0.5. From the resulting intensities at different wavelength, 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. (1 data file).

  17. 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.

  18. Optimizing Stellarators for Energetic Particle Confinement using BEAMS3D

    NASA Astrophysics Data System (ADS)

    Bolgert, Peter; Drevlak, Michael; Lazerson, Sam; Gates, David; White, Roscoe

    2015-11-01

    Energetic particle (EP) loss has been called the ``Achilles heel of stellarators,'' (Helander, Rep. Prog. Phys. 77 087001 (2014)) and there is a great need for magnetic configurations with improved EP confinement. In this study we utilize a newly developed capability of the stellarator optimization code STELLOPT: the ability to optimize EP confinement via an interface with guiding center code BEAMS3D (McMillan et al., Plasma Phys. Control. Fusion 56, 095019 (2014)). Using this new tool, optimizations of the W7-X experiment and ARIES-CS reactor are performed where the EP loss fraction is one of many target functions to be minimized. In W7-X, we simulate the experimental NBI system using realistic beam geometry and beam deposition physics. The goal is to find configurations with improved neutral beam deposition and energetic particle confinement. These calculations are compared to previous studies of W7-X NBI deposition. In ARIES-CS, we launch 3.5 MeV alpha particles from a near-axis flux surface using a uniform grid in toroidal and poloidal angle. As these particles are born from D-T reactions, we consider an isotropic distribution in velocity space. This research is supported by DoE Contract Number DE-AC02-09CH11466.

  19. 3D Radiative Transfer in Cloudy Atmospheres

    NASA Astrophysics Data System (ADS)

    Marshak, Alexander; Davis, Anthony

    Developments in three-dimensional cloud radiation over the past few decades are assessed and distilled into this contributed volume. Chapters are authored by subject-matter experts who address a broad audience of graduate students, researchers, and anyone interested in cloud-radiation processes in the solar and infrared spectral regions. After two introductory chapters and a section on the fundamental physics and computational techniques, the volume extensively treats two main application areas: the impact of clouds on the Earth's radiation budget, which is an essential aspect of climate modeling; and remote observation of clouds, especially with the advanced sensors on current and future satellite missions. http://www.springeronline.com/alert/article?a=3D1_1fva7w_1j826l_41z_6

  20. Measuring the Stellar Halo Velocity Anisotropy With 3D Kinematics

    NASA Astrophysics Data System (ADS)

    Cunningham, Emily C.; Deason, Alis J.; Guhathakurta, Puragra; Rockosi, Constance M.; van der Marel, Roeland P.; Sohn, S. Tony

    2016-08-01

    We present the first measurement of the anisotropy parameter β using 3D kinematic information outside of the solar neighborhood. Our sample consists of 13 Milky Way halo stars with measured proper motions and radial velocities in the line of sight of M31. Proper motions were measured using deep, multi-epoch HST imaging, and radial velocities were measured from Keck II/DEIMOS spectra. We measure β = -0.3-0.9 +0.4, which is consistent with isotropy, and inconsistent with measurements in the solar neighborhood. We suggest that this may be the kinematic signature of a relatively early, massive accretion event, or perhaps several such events.

  1. Stellar Ablation of Planetary Atmospheres

    NASA Technical Reports Server (NTRS)

    Moore, Thomas E.; Horwitz, J. L.

    2007-01-01

    We review observations and theories of the solar ablation of planetary atmospheres, focusing on the terrestrial case where a large magnetosphere holds off the solar wind, so that there is little direct atmospheric impact, but also couples the solar wind electromagnetically to the auroral zones. We consider the photothermal escape flows known as the polar wind or refilling flows, the enhanced mass flux escape flows that result from localized solar wind energy dissipation in the auroral zones, and the resultant enhanced neutral atom escape flows. We term these latter two escape flows the "auroral wind." We review observations and theories of the heating and acceleration of auroral winds, including energy inputs from precipitating particles, electromagnetic energy flux at magnetohydrodynamic and plasma wave frequencies, and acceleration by parallel electric fields and by convection pickup processes also known as "centrifugal acceleration." We consider also the global circulation of ionospheric plasmas within the magnetosphere, their participation in magnetospheric disturbances as absorbers of momentum and energy, and their ultimate loss from the magnetosphere into the downstream solar wind, loading reconnection processes that occur at high altitudes near the magnetospheric boundaries. We consider the role of planetary magnetization and the accumulating evidence of stellar ablation of extrasolar planetary atmospheres. Finally, we suggest and discuss future needs for both the theory and observation of the planetary ionospheres and their role in solar wind interactions, to achieve the generality required for a predictive science of the coupling of stellar and planetary atmospheres over the full range of possible conditions.

  2. Resolving stellar populations with crowded field 3D spectroscopy

    NASA Astrophysics Data System (ADS)

    Kamann, S.; Wisotzki, L.; Roth, M. M.

    2013-01-01

    We describe a new method of extracting the spectra of stars from observations of crowded stellar fields with integral field spectroscopy (IFS). Our approach extends the well-established concept of crowded field photometry in images into the domain of 3-dimensional spectroscopic datacubes. The main features of our algorithm follow. (1) We assume that a high-fidelity input source catalogue already exists, e.g. from HST data, and that it is not needed to perform sophisticated source detection in the IFS data. (2) Source positions and properties of the point spread function (PSF) vary smoothly between spectral layers of the datacube, and these variations can be described by simple fitting functions. (3) The shape of the PSF can be adequately described by an analytical function. Even without isolated PSF calibrator stars we can therefore estimate the PSF by a model fit to the full ensemble of stars visible within the field of view. (4) By using sparse matrices to describe the sources, the problem of extracting the spectra of many stars simultaneously becomes computationally tractable. We present extensive performance and validation tests of our algorithm using realistic simulated datacubes that closely reproduce actual IFS observations of the central regions of Galactic globular clusters. We investigate the quality of the extracted spectra under the effects of crowding with respect to the resulting signal-to-noise ratios (S/N) and any possible changes in the continuum level, as well as with respect to absorption line spectral parameters, radial velocities, and equivalent widths. The main effect of blending between two nearby stars is a decrease in the S/N in their spectra. The effect increases with the crowding in the field in a way that the maximum number of stars with useful spectra is always ~0.2 per spatial resolution element. This balance breaks down when exceeding a total source density of one significantly detected star per resolution element. We also explore the

  3. Oxygen spectral line synthesis: 3D non-LTE with CO5BOLD hydrodynamical model atmospheres.

    NASA Astrophysics Data System (ADS)

    Prakapavičius, D.; Steffen, M.; Kučinskas, A.; Ludwig, H.-G.; Freytag, B.; Caffau, E.; Cayrel, R.

    In this work we present first results of our current project aimed at combining the 3D hydrodynamical stellar atmosphere approach with non-LTE (NLTE) spectral line synthesis for a number of key chemical species. We carried out a full 3D-NLTE spectrum synthesis of the oxygen IR 777 nm triplet, using a modified and improved version of our NLTE3D package to calculate departure coefficients for the atomic levels of oxygen in a CO5BOLD 3D hydrodynamical solar model atmosphere. Spectral line synthesis was subsequently performed with the Linfor3D code. In agreement with previous studies, we find that the lines of the oxygen triplet produce deeper cores under NLTE conditions, due to the diminished line source function in the line forming region. This means that the solar oxygen IR 777 nm lines should be stronger in NLTE, leading to negative 3D NLTE-LTE abundance corrections. Qualitatively this result would support previous claims for a relatively low solar oxygen abundance. Finally, we outline several further steps that need to be taken in order to improve the physical realism and numerical accuracy of our current 3D-NLTE calculations.

  4. 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.

  5. 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.

  6. Construction concepts and validation of the 3D printed UST_2 modular stellarator

    NASA Astrophysics Data System (ADS)

    Queral, V.

    2015-03-01

    High accuracy, geometric complexity and thus high cost of stellarators tend to hinder the advance of stellarator research. Nowadays, new manufacturing methods might be developed for the production of small and middle-size stellarators. The methods should demonstrate advantages with respect common fabrication methods, like casting, cutting, forging and welding, for the construction of advanced highly convoluted modular stellarators. UST2 is a small modular three period quasi-isodynamic stellarator of major radius 0.26 m and plasma volume 10 litres being currently built to validate additive manufacturing (3D printing) for stellarator construction. The modular coils are wound in grooves defined on six 3D printed half period frames designed as light truss structures filled by a strong filler. A geometrically simple assembling configuration has been concocted for UST2 so as to try to lower the cost of the device while keeping the positioning accuracy of the different elements. The paper summarizes the construction and assembling concepts developed, the devised positioning methodology, the design of the coil frames and positioning elements and, an initial validation of the assembling of the components.

  7. Code System to Simulate 3D Tracer Dispersion in Atmosphere.

    Energy Science and Technology Software Center (ESTSC)

    2002-01-25

    Version 00 SHREDI is a shielding code system which executes removal-diffusion computations for bi-dimensional shields in r-z or x-y geometries. It may also deal with monodimensional problems (infinitely high cylinders or slabs). MESYST can simulate 3D tracer dispersion in the atmosphere. Three programs are part of this system: CRE_TOPO prepares the terrain data for MESYST. NOABL calculates three-dimensional free divergence windfields over complex terrain. PAS computes tracer concentrations and depositions on a given domain. Themore » purpose of this work is to develop a reliable simulation tool for pollutant atmospheric dispersion, which gives a realistic approach and allows one to compute the pollutant concentrations over complex terrains with good accuracy. The factional brownian model, which furnishes more accurate concentration values, is introduced to calculate pollutant atmospheric dispersion. The model was validated on SIESTA international experiments.« less

  8. 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.

  9. 3D Simulations of methane convective storms on Titan's atmosphere

    NASA Astrophysics Data System (ADS)

    Hueso, R.; Sánchez-Lavega, A.

    2005-08-01

    The arrival of the Cassini/Huygens mission to Titan has opened an unprecedented opportunity to study the atmosphere of this satellite. Under the pressure-temperature conditions on Titan, methane, a large atmospheric component amounting perhaps to a 3-5% of the atmosphere, is close to its triple point, potentially playing a similar role as water on Earth. The Huygens probe has shown a terrain shaped by erosion of probably liquid origin, suggestive of past rain. On the other hand, Voyager IRIS spectroscopic observations of Titan imply a saturated atmosphere of methane (amounting perhaps to 150 covered by methane clouds, if we think on Earth meteorology. However, observations from Earth and Cassini have shown that clouds are localized, transient and fast evolving, in particular in the South Pole (currently in its summer season). This might imply a lack of widespread presence on Titan of nuclei where methane could initiate condensation and particle growth with subsequent precipitation. We investigate different scenarios of moist convective storms on Titan using a complete 3D atmospheric model that incorporates a full microphysics treatment required to study cloud formation processes under a saturated atmosphere with low concentration of condensation nuclei. We study local convective development under a variety of atmospheric conditions: sub-saturation, super-saturation, abundances of condensation nuclei fall, condensation nuclei lifted from the ground or gently falling from the stratosphere. We show that under the appropriate circumstances, precipitation rates comparable to typical tropical storms on Earth can be found. Acknowledgements: This work has been funded by Spanish MCYT PNAYA2003-03216, fondos FEDER and Grupos UPV 15946/2004. R. Hueso acknowledges a post-doc fellowship from Gobierno Vasco.

  10. 3D modeling of clouds in GJ1214b's atmosphere

    NASA Astrophysics Data System (ADS)

    Charnay, Benjamin; Meadows, Victoria; leconte, Jérémy; Misra, Amit; Arnay, Giada

    2015-12-01

    GJ1214b is a warm mini-Neptune/waterworld and one of the few low-mass exoplanets whose atmosphere is characterizable by current telescopes. Recent observations indicated a flat transit spectrum in near-infrared which has been interpreted as the presence of high and thick condensate clouds of KCl or ZnS or photochemical hazes [1]. However, the formation of such high clouds/hazes would require a strong vertical mixing linked to the atmospheric circulation [2]. In order to understand the transport, distribution and observational implications of such clouds/haze, we studied the atmospheric circulation and cloud formation on GJ1214b for H-dominated and water-dominated atmospheres using the Generic LMDZ GCM.Firstly, we analyzed cloud-free atmospheres [3]. We showed that the zonal mean meridional circulation corresponds to an anti-Hadley circulation in most of the atmosphere with upwelling at midlatitude and downwelling at the equator. This circulation should strongly impact cloud formation and distribution, leading to a minimum of cloud at the equator. We also derived 1D equivalent eddy diffusion coefficients. The corresponding values should favor an efficient formation of photochemical haze in the upper atmosphere of GJ1214b.Secondly, we simulated cloudy atmospheres including latent heat release and radiative effects for KCl and ZnS clouds [4]. We analyzed their distribution and their impacts on the thermal structure. In particular, a stratospheric thermal inversion should likely be formed by absorption of stellar radiation by ZnS clouds. We showed that flat transit spectra consistent with HST observations are possible for cloud particle radii around 0.5 microns. Using the outputs of our GCM, we also generated emission and reflection spectra and phases curves.Finally, our results suggest that primary and secondary eclipses and phase curves observed by JWST should provide strong constraints on the nature of GJ1214b's atmosphere and clouds.references:[1] Kreidberg et al

  11. Edge Transport Modeling using the 3D EMC3-Eirene code on Tokamaks and Stellarators

    NASA Astrophysics Data System (ADS)

    Lore, J. D.; Ahn, J. W.; Briesemeister, A.; Ferraro, N.; Labombard, B.; McLean, A.; Reinke, M.; Shafer, M.; Terry, J.

    2015-11-01

    The fluid plasma edge transport code EMC3-Eirene has been applied to aid data interpretation and understanding the results of experiments with 3D effects on several tokamaks. These include applied and intrinsic 3D magnetic fields, 3D plasma facing components, and toroidally and poloidally localized heat and particle sources. On Alcator C-Mod, a series of experiments explored the impact of toroidally and poloidally localized impurity gas injection on core confinement and asymmetries in the divertor fluxes, with the differences between the asymmetry in L-mode and H-mode qualitatively reproduced in the simulations due to changes in the impurity ionization in the private flux region. Modeling of NSTX experiments on the effect of 3D fields on detachment matched the trend of a higher density at which the detachment occurs when 3D fields are applied. On DIII-D, different magnetic field models were used in the simulation and compared against the 2D Thomson scattering diagnostic. In simulating each device different aspects of the code model are tested pointing to areas where the model must be further developed. The application to stellarator experiments will also be discussed. Work supported by U.S. DOE: DE-AC05-00OR22725, DE AC02-09CH11466, DE-FC02-99ER54512, and DE-FC02-04ER54698.

  12. Stellar models with mixing length and T(τ) relations calibrated on 3D convection simulations

    NASA Astrophysics Data System (ADS)

    Salaris, Maurizio; Cassisi, Santi

    2015-05-01

    The calculation of the thermal stratification in the superadiabatic layers of stellar models with convective envelopes is a long-standing problem of stellar astrophysics, and has a major impact on predicted observational properties such as radius and effective temperature. The mixing length theory, almost universally used to model the superadiabatic convective layers, contains one free parameter to be calibrated (αml) whose value controls the resulting effective temperature. Here we present the first self-consistent stellar evolution models calculated by employing the atmospheric temperature stratification, Rosseland opacities, and calibrated variable αml (dependent on effective temperature and surface gravity) from a recently published large suite of three-dimensional radiation hydrodynamics simulations of stellar convective envelopes and atmospheres for solar stellar composition. From our calculations (with the same composition of the radiation hydrodynamics simulations), we find that the effective temperatures of models with the hydro-calibrated variable αml (that ranges between ~1.6 and ~2.0 in the parameter space covered by the simulations) present only minor differences, by at most ~30-50 K, compared to models calculated at constant solar αml (equal to 1.76, as obtained from the same simulations). The depth of the convective regions is essentially the same in both cases. We also analyzed the role played by the hydro-calibrated T(τ) relationships in determining the evolution of the model effective temperatures, when compared to alternative T(τ) relationships often used in stellar model computations. The choice of the T(τ) can have a larger impact than the use of a variable αml compared to a constant solar value. We found that the solar semi-empirical T(τ) by Vernazza et al. (1981, ApJS, 45, 635) provides stellar model effective temperatures that agree quite well with the results with the hydro-calibrated relationships.

  13. 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.

  14. 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.

  15. 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

    new research results with spectral synthesis codes developed for cool stars, while the second day focused on codes applied for modeling the spectra of hot stars. The workshop addressed five major topics in stellar atmospheres research: Spectrum synthesis codes Radiation hydrodynamics codes Atmospheric parameters, abundance, metallicity, and chemical tagging studies Large spectroscopic surveys New atomic database The workshop presentations discussed various important scientific issues by comparing detailed model spectra to identify differences that can influence and bias the resulting atmospheric parameters. Theoretical line-blanketed model spectra were compared in detail to high-resolution spectroscopic observations. Stellar spectra computed (i.e., in the Gaia Radial Velocity Spectrometer wavelength range) with 1-D model atmosphere structures were mutually compared, but also to 3-D models from advanced radiation hydrodynamics codes. Atmospheric parameters derived from spectrum synthesis calculations assuming Local Thermodynamic Equilibrium (LTE) were evaluated against more sophisticated non-LTE models of metal-poor stars and the extended atmospheres of giants and supergiants. The workshop presented an overview of high-resolution synthetic spectral libraries of model spectra computed with the synthesis codes. The spectral model grids will be utilized to derive stellar parameters with the Discrete Source Classifier Algorithms currently under development in the Gaia DPAC consortium (http://www.rssd.esa.int/index.php?project=GAIA&page=DPAC_Introduction). They are implemented for training Gaia data analysis algorithms for the classification of a wide variety of hot and cool star types; FGK and M stars, OB stars, white dwarfs, red supergiants, peculiar A and B stars, carbon stars, ultra cool dwarfs, various types of emission line stars, Be stars, Wolf-Rayet stars, etc. A substantial number of oral and poster presentations discussed different techniques for measuring the

  16. 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).

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

    NASA Astrophysics Data System (ADS)

    Collet, Remo

    2015-08-01

    Classical spectroscopic analyses of late-type stars generally rely on the use of synthetic spectra computed with stationary, one-dimensional (1D), hydrostatic model stellar atmospheres to quantitatively interpret observations. Recent years, however, have seen a rapid development in the field of three-dimensional (3D) hydrodynamical modelling of stellar atmospheres and stellar spectra.In this contribution, I will present results from realistic, time-dependent, hydrodynamical 3D simulations of stellar atmospheres of solar- and late-type stars, covering a wide range of stellar parameters and compositions, from main sequence to red giant branch and with metallicities from [Fe/H]=+0.5 down to [Fe/H]=-4. These 3D model atmospheres have been generated using a custom version of the radiation-magnetohydrodynamics Stagger-Code which implements state-of-the-art input micro-physics, equation of state and opacity data, and a realistic treatment of non-grey radiative transfer.I will describe the main properties of the simulations and discuss the application of 3D model atmospheres to spectral line-formation calculations and high-precision spectroscopy of late-type stars. I will illustrate the main effects of 3D modelling of stellar atmospheres and stellar spectra on the predicted strengths and shapes of spectral lines, highlighting the systematic differences with respect to calculations based on classical, 1D, hydrostatic models.In particular, I will present the results of spectroscopic carbon, nitrogen and oxygen abundance determinations based on the analysis of CH, NH, CN and OH molecular bands with 3D model stellar atmospheres. I will show that the differences with respect to classical analyses based on 1D models can be significant and of the order of 0.5 to 1 dex in terms of logarithmic abundances of these important elements.Finally, I will also discuss the application of 3D models to the analysis and interpretation of data from large-scale space-born and ground

  18. On the construction of a new 3d atlas of stellar spectral energy distributions

    NASA Astrophysics Data System (ADS)

    Mironov, A. V.; Zakharov, A. I.; Moshkalev, V. G.; Malkov, O. Yu.; Kilpio, E. Yu.

    Modern spectrophotometric atlases are burdened with significant systematic errors. In particular, the problems of spectrum calibration in the ultraviolet region are not solved; different parts of the spectrum are not thoroughly fit to each other; spectra of (even bright) stars, obtained by different authors, display large discrepancies. Here we discuss a possibility to construct a new atlas of spectral energy distributions (SEDs) for a large set of stars by comparison of empirical stellar spectra in dozens of modern spectrophotometric atlases, as well as the comparison of synthetic and observed color indices in different multicolor photometric systems. In this way we suppose to exclude most of systematic errors and construct a new three-dimensional (spectral class, luminosity class, metallicity) atlas of empirical stellar spectra for several thousand stars. After exclusion of interstellar reddenings, a semi-empirical atlas of average SEDs can be constructed for about 150--200 spectral subtypes. This would allow us to make calibrations of spectrophotometric and photometric parameters in terms of spectral types and physical parameters (Teff, log g, [m/H]) and to verify the accuracy of model stellar atmospheres.

  19. 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

  20. Radiative 3D MHD simulations of the spontaneous small-scale eruptions in the solar atmosphere

    NASA Astrophysics Data System (ADS)

    Kitiashvili, Irina N.

    2015-08-01

    Studying non-linear turbulent dynamics of the solar atmosphere is important for understanding mechanism of the solar and stellar brightness variations. High-resolution observations of the quiet Sun reveal ubiquitous distributions of high-speed jets, which are transport mass and energy into the solar corona and feeding the solar wind. However, the origin of these eruption events is still unknown. Using 3D realistic MHD numerical simulations we find that small-scale eruptions are produced by ubiquitous magnetized vortex tubes generated by the Sun's turbulent convection in subsurface layers. The swirling vortex tubes (resembling tornadoes) penetrate into the solar atmosphere, capture and stretch background magnetic field, and push the surrounding material up, generating shocks. Our simulations reveal complicated high-speed flow patterns and thermodynamic and magnetic structure in the erupting vortex tubes and shows that the eruptions are initiated in the subsurface layers and are driven by high-pressure gradients in the subphotosphere and photosphere and by the Lorentz force in the higher atmosphere layers. I will discuss about properties of these eruptions, their effects on brightness and spectral variations and comparison with observations.

  1. Stellar Occultation Probe of Triton's Atmosphere

    NASA Technical Reports Server (NTRS)

    Elliot, James L.

    1998-01-01

    The goals of this research were (i) to better characterize Triton's atmospheric structure by probing a region not well investigated by Voyager and (ii) to begin acquiring baseline data for an investigation of the time evolution of the atmosphere which will set limits on the thermal conductivity of the surface and the total mass of N2 in the atmosphere. Our approach was to use observations (with the Kuiper Airborne Observatory) of a stellar occultation by Triton that was predicted to occur on 1993 July 10. As described in the attached reprint, we achieved these objectives through observation of this occultation and a subsequent one with the KAO in 1995. We found new results about Triton's atmospheric structure from the analysis of the two occultations observed with the KAO and ground-based data. These stellar occultation observations made both in the visible and infrared, have good spatial coverage of Triton including the first Triton central-flash observations, and are the first data to probe the 20-100 km altitude level on Triton. The small-planet light curve model of Elliot and Young (AJ 103, 991-1015) was generalized to include stellar flux refracted by the far limb, and then fitted to the data. Values of the pressure, derived from separate immersion and emersion chords, show no significant trends with latitude indicating that Triton's atmosphere is spherically symmetric at approximately 50 km altitude to within the error of the measurements. However, asymmetry observed in the central flash indicates the atmosphere is not homogeneous at the lowest levels probed (approximately 20 km altitude). From the average of the 1995 occultation data, the equivalent-isothermal temperature of the atmosphere is 47 +/- 1 K and the atmospheric pressure at 1400 km radius (approximately 50 km altitude) is 1.4 +/- 0.1 microbar. Both of these are not consistent with a model based on Voyager UVS and RSS observations in 1989 (Strobel et al, Icarus 120, 266-289). The atmospheric

  2. 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.

  3. 3D modeling of clouds in GJ1214b's atmosphere

    NASA Astrophysics Data System (ADS)

    Charnay, Benjamin; Meadows, Victoria; leconte, Jérémy; Misra, Amit; Arney, Giada

    2015-11-01

    GJ1214b is a warm mini-Neptune/waterworld and one of the few low-mass exoplanets whose atmosphere is characterizable by current telescopes. Recent observations indicated a flat transit spectrum in near-infrared which has been interpreted as the presence of high and thick condensate clouds of KCl or ZnS or photochemical hazes. However, the formation of such high clouds/hazes would require a strong vertical mixing linked to the atmospheric circulation. In order to understand the transport, distribution and observational implications of such clouds/haze, we studied the atmospheric circulation and cloud formation on GJ1214b for H-dominated and water-dominated atmospheres using the Generic LMDZ GCM.Firstly, we analyzed cloud-free atmospheres. We showed that the zonal mean meridional circulation corresponds to an anti-Hadley circulation in most of the atmosphere with upwelling at midlatitude and downwelling at the equator. This circulation should strongly impact cloud formation and distribution, leading to a minimum of cloud at the equator. We also derived 1D equivalent eddy diffusion coefficients. The corresponding values should favor an efficient formation of photochemical haze in the upper atmosphere of GJ1214b.Secondly, we simulated cloudy atmospheres including latent heat release and radiative effects for KCl and ZnS clouds. We analyzed their impacts on the thermal structure. In particular, we fund that ZnS clouds may lead to the formation of a stratospheric thermal inversion. We showed that flat transit spectra consistent with HST observations are possible for cloud particle radii around 0.5 microns. Using the outputs of our GCM, we also generated emission and reflection spectra and phases curves.Finally, our results suggest that primary and secondary eclipses and phase curves observed by JWST should provide strong constraints on the nature of GJ1214b's atmosphere and clouds.

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

    NASA Astrophysics Data System (ADS)

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

    2012-09-01

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

  5. Formation of molecular lines in stellar atmospheres

    NASA Technical Reports Server (NTRS)

    Hinkle, K. H.; Lambert, D. L.

    1975-01-01

    Statistical equilibrium of electronic states of diatomic molecules in stellar atmospheres is examined. Atmospheres discussed are representative of the sun, Arcturus (K-giant) and Betelgeuse (M-supergiant). A comparison of the relative collisional and radiative contributions to the equilibrium of the ground electronic state shows that this state is collisionally controlled and that the line source function for vibration-rotation transitions within this state is equivalent to the Planck function. Examination of the equilibrium for excited electronic states demonstrates that the exchange between these states and the ground electronic state is most probably determined by radiative excitation. This result implies that scattering rather than pure absorption is the appropriate mechanism for the formation of lines belonging to these electronic transitions. The scattering hypothesis is given a preliminary check against solar observations. Areas for future investigations are outlined.

  6. 3D-HST WFC3-SELECTED PHOTOMETRIC CATALOGS IN THE FIVE CANDELS/3D-HST FIELDS: PHOTOMETRY, PHOTOMETRIC REDSHIFTS, AND STELLAR MASSES

    SciTech Connect

    Skelton, Rosalind E.; Whitaker, Katherine E.; Momcheva, Ivelina G.; Van Dokkum, Pieter G.; Bezanson, Rachel; Leja, Joel; Nelson, Erica J.; Oesch, Pascal; Brammer, Gabriel B.; Labbé, Ivo; Franx, Marijn; Fumagalli, Mattia; Van der Wel, Arjen; Da Cunha, Elisabete; Maseda, Michael V.; Förster Schreiber, Natascha; Kriek, Mariska; Lundgren, Britt F.; Magee, Daniel; Marchesini, Danilo; and others

    2014-10-01

    The 3D-HST and CANDELS programs have provided WFC3 and ACS spectroscopy and photometry over ≈900 arcmin{sup 2} in five fields: AEGIS, COSMOS, GOODS-North, GOODS-South, and the UKIDSS UDS field. All these fields have a wealth of publicly available imaging data sets in addition to the Hubble Space Telescope (HST) data, which makes it possible to construct the spectral energy distributions (SEDs) of objects over a wide wavelength range. In this paper we describe a photometric analysis of the CANDELS and 3D-HST HST imaging and the ancillary imaging data at wavelengths 0.3-8 μm. Objects were selected in the WFC3 near-IR bands, and their SEDs were determined by carefully taking the effects of the point-spread function in each observation into account. A total of 147 distinct imaging data sets were used in the analysis. The photometry is made available in the form of six catalogs: one for each field, as well as a master catalog containing all objects in the entire survey. We also provide derived data products: photometric redshifts, determined with the EAZY code, and stellar population parameters determined with the FAST code. We make all the imaging data that were used in the analysis available, including our reductions of the WFC3 imaging in all five fields. 3D-HST is a spectroscopic survey with the WFC3 and ACS grisms, and the photometric catalogs presented here constitute a necessary first step in the analysis of these grism data. All the data presented in this paper are available through the 3D-HST Web site (http://3dhst.research.yale.edu)

  7. Stellar occultation studies of Saturn's upper atmosphere

    NASA Astrophysics Data System (ADS)

    Foust, Jeffrey Alan

    1999-10-01

    The properties of Saturn's upper atmosphere are not well- known despite several spacecraft flybys. However, the region of 1-100 μbar can be studied in detail by observing stellar occultations-when the planet passes in front of a star-from groundbased or Earth-orbiting telescopes. We use data from five such occultations: three observed in 1995 by the Faint Object Spectrograph (FOS) on the Hubble Space Telescope (HST), one observed in 1996 at the NASA Infrared Telescope Facility (IRTF) and one in 1989 observed by a different instrument at the IRTF. The data span latitudes from 52° south to 75° north. We fit isothermal models to each data set and also perform numerical inversions. These analyses show that temperatures in the 1-10 μbar range can vary significantly as a function of season and latitude, ranging from 121 to 160 K, in accordance with radiative transfer models for the atmosphere. We also search for evidence of gravity wave saturation in Saturn's upper atmosphere, as seen in other planetary atmospheres, by analyzing the power spectra of temperature and density data and by studying the temperature lapse rate in the atmosphere. Our analysis is consistent with saturated gravity waves for all data sets, although gravity wave saturation is not the sole explanation for the spectra. We take advantage of the wavelength-resolved HST FOS data to study the composition of Saturn's upper atmosphere. We measured the difference in feature times for data taken at two wavelengths, and use the different refractivities of hydrogen and helium, as a function of wavelength to compute the relative amounts of the two elements in the planet's atmosphere. We find that the helium mass fraction is 0.26 +/- 0.10, higher than that found using Voyager data, but marginally consistent with theoretical models for the evolution of Saturn's atmosphere, although the large error bars on the results make a definitive conclusion problematic. (Copies available exclusively from MIT Libraries, Rm

  8. 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

  9. 3D Model Atmospheres for Extremely Low-mass White Dwarfs

    NASA Astrophysics Data System (ADS)

    Tremblay, P.-E.; Gianninas, A.; Kilic, M.; Ludwig, H.-G.; Steffen, M.; Freytag, B.; Hermes, J. J.

    2015-08-01

    We present an extended grid of mean three-dimensional (3D) spectra for low-mass, pure-hydrogen atmosphere DA white dwarfs (WDs). We use CO5BOLD radiation-hydrodynamics 3D simulations covering Teff = 6000–11,500 K and log g = 5–6.5 (g in cm s‑2) to derive analytical functions to convert spectroscopically determined 1D temperatures and surface gravities to 3D atmospheric parameters. Along with the previously published 3D models, the 1D to 3D corrections are now available for essentially all known convective DA WDs (i.e., log g = 5–9). For low-mass WDs, the correction in temperature is relatively small (a few percent at the most), but the surface gravities measured from the 3D models are lower by as much as 0.35 dex. We revisit the spectroscopic analysis of the extremely low-mass (ELM) WDs, and demonstrate that the 3D models largely resolve the discrepancies seen in the radius and mass measurements for relatively cool ELM WDs in eclipsing double WD and WD + millisecond pulsar binary systems. We also use the 3D corrections to revise the boundaries of the ZZ Ceti instability strip, including the recently found ELM pulsators.

  10. Rapidly convergent algorithms for 3-D tandem and stellarator equilibria in the paraxial approximation

    SciTech Connect

    McNamara, B.

    1984-04-01

    Tandem and stellarator equilibria at high ..beta.. have proved hard to compute and the relaxation methods of Bauer et al., Chodura and Schluter, Hirshman, Strauss, and Pearlstein et al. have been slow to converge. This paper reports an extension of the low-..beta.. analytic method of Pearlstein, Kaiser, and Newcomb to arbitrary ..beta.. for tandem mirrors which converges in 10 to 20 iterations. Extensions of the method to stellarator equilibria are proposed and are very close to the analytic method of Johnson and Greene - the stellarator expansion. Most of the results of all these calculations can be adequately described by low-..beta.. approximations since the MHD stability limits occur at low ..beta... The tandem mirror, having weak curvature and a long central cell, allows finite Larmor radius effects to eliminate most ballooning modes and offers the possibility of really high average ..beta... This is the interest in developing such three-dimensional numerical algorithms.

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

  12. Assessing the habitability of planets with Earth-like atmospheres with 1D and 3D climate modeling

    NASA Astrophysics Data System (ADS)

    Godolt, M.; Grenfell, J. L.; Kitzmann, D.; Kunze, M.; Langematz, U.; Patzer, A. B. C.; Rauer, H.; Stracke, B.

    2016-07-01

    Context. The habitable zone (HZ) describes the range of orbital distances around a star where the existence of liquid water on the surface of an Earth-like planet is in principle possible. The applicability of one-dimensional (1D) climate models for the estimation of the HZ boundaries has been questioned by recent three-dimensional (3D) climate studies. While 3D studies can calculate the water vapor, ice albedo, and cloud feedback self-consistently and therefore allow for a deeper understanding and the identification of relevant climate processes, 1D model studies rely on fewer model assumptions and can be more easily applied to the large parameter space possible for extrasolar planets. Aims: We evaluate the applicability of 1D climate models to estimate the potential habitability of Earth-like extrasolar planets by comparing our 1D model results to those of 3D climate studies in the literature. We vary the two important planetary properties, surface albedo and relative humidity, in the 1D model. These depend on climate feedbacks that are not treated self-consistently in most 1D models. Methods: We applied a cloud-free 1D radiative-convective climate model to calculate the climate of Earth-like planets around different types of main-sequence stars with varying surface albedo and relative humidity profile. We compared the results to those of 3D model calculations available in the literature and investigated to what extent the 1D model can approximate the surface temperatures calculated by the 3D models. Results: The 1D parameter study results in a large range of climates possible for an Earth-sized planet with an Earth-like atmosphere and water reservoir at a certain stellar insolation. At some stellar insolations the full spectrum of climate states could be realized, i.e., uninhabitable conditions due to surface temperatures that are too high or too low as well as habitable surface conditions, depending only on the relative humidity and surface albedo assumed. When

  13. Time-dependent diffusion in stellar atmospheres

    NASA Astrophysics Data System (ADS)

    Alecian, G.; Stift, M. J.; Dorfi, E. A.

    2011-12-01

    The chemical peculiarities of Ap stars are due to abundance stratifications produced by atomic diffusion in their outer layers. Theoretical models can predict such stratifications, but so far only provide equilibrium solutions which correspond to the maximum depth-dependent abundances for each element that can be supported by the radiation field. However, these stratifications are actually built up through a non-linear, time-dependent process which has never been modelled for realistic stellar atmospheres. Here, we present the first numerical simulations of time-dependent diffusion. We solve the continuity equation after having computed, as accurately as possible, atomic diffusion velocities (with and without a magnetic field) for a simplified fictitious - but still realistic - chemical element: cloudium. The direct comparison with existing observations is not the immediate aim of this work but rather a general understanding of how the stratification build-up proceeds in time and space. Our results raise serious questions as to the relevance of equilibrium solutions and reinforce the suspicion that certain accumulations of chemical elements might prove unstable.

  14. The ATLAS3D Project - XXX. Star formation histories and stellar population scaling relations of early-type galaxies

    NASA Astrophysics Data System (ADS)

    McDermid, Richard M.; Alatalo, Katherine; Blitz, Leo; Bournaud, Frédéric; Bureau, Martin; Cappellari, Michele; 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.

    2015-04-01

    We present the stellar population content of early-type galaxies from the ATLAS3D survey. Using spectra integrated within apertures covering up to one effective radius, we apply two methods: one based on measuring line-strength indices and applying single stellar population (SSP) models to derive SSP-equivalent values of stellar age, metallicity, and alpha enhancement; and one based on spectral fitting to derive non-parametric star formation histories, mass-weighted average values of age, metallicity, and half-mass formation time-scales. Using homogeneously derived effective radii and dynamically determined galaxy masses, we present the distribution of stellar population parameters on the Mass Plane (MJAM, σe, R^maj_e), showing that at fixed mass, compact early-type galaxies are on average older, more metal-rich, and more alpha-enhanced than their larger counterparts. From non-parametric star formation histories, we find that the duration of star formation is systematically more extended in lower mass objects. Assuming that our sample represents most of the stellar content of today's local Universe, approximately 50 per cent of all stars formed within the first 2 Gyr following the big bang. Most of these stars reside today in the most massive galaxies (>1010.5 M⊙), which themselves formed 90 per cent of their stars by z ˜ 2. The lower mass objects, in contrast, have formed barely half their stars in this time interval. Stellar population properties are independent of environment over two orders of magnitude in local density, varying only with galaxy mass. In the highest density regions of our volume (dominated by the Virgo cluster), galaxies are older, alpha-enhanced, and have shorter star formation histories with respect to lower density regions.

  15. Division G Commission 36: Theory of Stellar Atmospheres

    NASA Astrophysics Data System (ADS)

    Puls, Joachim; Hubeny, Ivan; Asplund, Martin; Allard, France; Prieto, Carlos Allende; Ayres, Thomas R.; Carlsson, Mats; Gustafsson, Bengt; Kudritzki, Rolf-Peter; Ryabchikova, Tatiana A.

    2016-04-01

    Different from previous triennial reports, this report covers the activities of IAU Commission 36 `Theory of Stellar Atmospheres' over the past six years†, and will be the last report from the `old' Commission 36. After the General Assembly in Honolulu (August 2015), a new Commission `Stellar and Planetary Atmospheres' (C.G5, under Division G, `Stars and Stellar Physics') has come into life, and will continue our work devoted to the outer envelopes of stars, as well as extend it to the atmospheres of planets (see Sect. 4).

  16. 3D collapse of rotating stellar iron cores in general relativity including deleptonization and a nuclear equation of state.

    PubMed

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

    2007-06-29

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

  17. 3D mapping of stellar populations in galaxies as a function of environment

    NASA Astrophysics Data System (ADS)

    Thomas, Daniel

    2015-08-01

    MaNGA (Mapping Nearby Galaxies at Apache Point Observatory) is a6-year SDSS-IV survey that will obtain resolved spectroscopy from 3600A to 10300 A for a representative sample of 10,000 nearby galaxies. MaNGA will allow the internal kinematics and spatially-resolved properties of stellar populations and gas inside galaxies to be studied as a function of local environment and halo mass for the very first time. I will present results from our analysis of the first year MaNGA data. The main focus is on the 3-dimensional distribution of stellar population properties in galaxies - formation age, element abundance, IMF slope - studying how these vary spatially in galaxies as a function of galaxy environment and dark matter halo mass.

  18. Development of Scientific Simulation 3D Full Wave ICRF Code for Stellarators and Heating/CD Scenarios Development

    SciTech Connect

    Vdovin V.L.

    2005-08-15

    In this report we describe theory and 3D full wave code description for the wave excitation, propagation and absorption in 3-dimensional (3D) stellarator equilibrium high beta plasma in ion cyclotron frequency range (ICRF). This theory forms a basis for a 3D code creation, urgently needed for the ICRF heating scenarios development for the operated LHD, constructed W7-X, NCSX and projected CSX3 stellarators, as well for re evaluation of ICRF scenarios in operated tokamaks and in the ITER . The theory solves the 3D Maxwell-Vlasov antenna-plasma-conducting shell boundary value problem in the non-orthogonal flux coordinates ({Psi}, {theta}, {var_phi}), {Psi} being magnetic flux function, {theta} and {var_phi} being the poloidal and toroidal angles, respectively. All basic physics, like wave refraction, reflection and diffraction are self consistently included, along with the fundamental ion and ion minority cyclotron resonances, two ion hybrid resonance, electron Landau and TTMP absorption. Antenna reactive impedance and loading resistance are also calculated and urgently needed for an antenna -generator matching. This is accomplished in a real confining magnetic field being varying in a plasma major radius direction, in toroidal and poloidal directions, through making use of the hot dense plasma wave induced currents with account to the finite Larmor radius effects. We expand the solution in Fourier series over the toroidal ({var_phi}) and poloidal ({theta}) angles and solve resulting ordinary differential equations in a radial like {Psi}-coordinate by finite difference method. The constructed discretization scheme is divergent-free one, thus retaining the basic properties of original equations. The Fourier expansion over the angle coordinates has given to us the possibility to correctly construct the ''parallel'' wave number k{sub //}, and thereby to correctly describe the ICRF waves absorption by a hot plasma. The toroidal harmonics are tightly coupled with each

  19. [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

  20. Inferring the 3D gravitational field of the Milky Way with stellar streams

    NASA Astrophysics Data System (ADS)

    Price-Whelan, Adrian Michael

    2016-06-01

    We develop two new methods to measure the structure of matter around the Milky Way using stellar tidal streams from disrupting dwarf galaxies and globular clusters. The dark matter halo of the Milky Way is expected to be triaxial and filled with substructure, but measurements of the shape and profile of dark matter around the Galaxy are highly uncertain and often contradictory. We demonstrate that kinematic data from near-future surveys for stellar streams or shells produced by tidal disruption of stellar systems around the Milky Way will provide precise measures of the gravitational potential to test these predictions. We develop a probabilistic method for inferring the Galactic potential with tidal streams based on the idea that the stream stars were once close in phase space and test this method on synthetic datasets generated from N-body simulations of satellite disruption with observational uncertainties chosen to mimic current and near-future surveys of various stars. We find that with just four well-measured stream stars, we can infer properties of a triaxial potential with precisions of order 5--7 percent. We then demonstrate that, if the Milky Way's dark matter halo is triaxial and is not fully integrable (as is expected), an appreciable fraction of orbits will be chaotic. We examine the influence of chaos on the phase-space morphology of cold tidal streams and show that streams even in weakly chaotic regions look very different from those in regular regions. We discuss the implications of this fact given that we see several long, thin streams in the Galactic halo; our results suggest that long, cold streams around our Galaxy must exist only on regular (or very nearly regular) orbits and potentially provide a map of the regular regions of the Milky Way potential. We then apply this understanding of stream formation along chaotic orbits to the interpretation of a newly-discovered, puzzling stellar stream near the Galactic bulge. We conclude that the

  1. TLUSTY: Stellar Atmospheres, Accretion Disks, and Spectroscopic Diagnostics

    NASA Astrophysics Data System (ADS)

    Hubeny, Ivan; Lanz, Thierry

    2011-09-01

    TLUSTY is a user-oriented package written in FORTRAN77 for modeling stellar atmospheres and accretion disks and wide range of spectroscopic diagnostics. In the program's maximum configuration, the user may start from scratch and calculate a model atmosphere of a chosen degree of complexity, and end with a synthetic spectrum in a wavelength region of interest for an arbitrary stellar rotation and an arbitrary instrumental profile. The user may also model the vertical structure of annuli of an accretion disk.

  2. Global 3-d weather models for the atmospheric correction of gravity time series

    NASA Astrophysics Data System (ADS)

    Klügel, Thomas; Wziontek, Hartmut

    2016-04-01

    The use of 3-dimensional weather models allows for an effective reduction of atmospheric effects in gravity time series. In the past the BKG service Atmacs (Atmospheric Attraction Computation Service) provided 3-d atmospheric correction time series only for European stations of the International Geodynamics and Earth Tide Service (IGETS, formerly Global Geodynamics Project, GGP), which are based on the high resolution regional model COSMO-EU of the German Weather Service (DWD). The provision of 3-d density data from the global weather models GME (20 km resolution) and most recently ICON (13 km resolution) by the DWD now allows the computation of 3-d atmospheric correction time series for all IGETS stations worldwide. Due to the triangular grid structure, a different procedure for mass elements close to the computation point is necessary. By increasing the spatial resolution towards the computation point by linear interpolation of the grid values, the use of a point mass approach became possible with an approximation error below 0.3 nm/s2. This approach also allows to consider horizontal density gradients and a tilted model surface of the innermost cells. By means of a variance reduction at different frequency bands a significant improvement of the atmospheric correction can be demonstrated at many IGETS stations. The limited temporal resolution of recently 3 hours can be improved by the user by including local air pressure records using a remove-restore technique. Atmospheric correction time series are online available at http://atmacs.bkg.bund.de.

  3. 3D Modeling of GJ1214b’s Atmosphere: Formation of Inhomogeneous High Clouds and Observational Implications

    NASA Astrophysics Data System (ADS)

    Charnay, B.; Meadows, V.; Misra, A.; Leconte, J.; Arney, G.

    2015-11-01

    The warm sub-Neptune GJ1214b has a featureless transit spectrum that may be due to the presence of high and thick clouds or haze. Here, we simulate the atmosphere of GJ1214b with a 3D General Circulation Model for cloudy hydrogen-dominated atmospheres, including cloud radiative effects. We show that the atmospheric circulation is strong enough to transport micrometric cloud particles to the upper atmosphere and generally leads to a minimum of cloud at the equator. By scattering stellar light, clouds increase the planetary albedo to 0.4-0.6 and cool the atmosphere below 1 mbar. However, the heating by ZnS clouds leads to the formation of a stratospheric thermal inversion above 10 mbar, with temperatures potentially high enough on the dayside to evaporate KCl clouds. We show that flat transit spectra consistent with Hubble Space Telescope observations are possible if cloud particle radii are around 0.5 μm, and that such clouds should be optically thin at wavelengths >3 μm. Using simulated cloudy atmospheres that fit the observed spectra we generate transit, emission, and reflection spectra and phase curves for GJ1214b. We show that a stratospheric thermal inversion would be readily accessible in near- and mid-infrared atmospheric spectral windows. We find that the amplitude of the thermal phase curves is strongly dependent on metallicity, but only slightly impacted by clouds. Our results suggest that primary and secondary eclipses and phase curves observed by the James Webb Space Telescope in the near- to mid-infrared should provide strong constraints on the nature of GJ1214b's atmosphere and clouds.

  4. Virgo cluster and field dwarf ellipticals in 3D - III. Spatially and temporally resolved stellar populations

    NASA Astrophysics Data System (ADS)

    Ryś, Agnieszka; Koleva, Mina; Falcón-Barroso, Jesús; Vazdekis, Alexandre; Lisker, Thorsten; Peletier, Reynier; van de Ven, Glenn

    2015-09-01

    We present the stellar population analysis of a sample of 12 dwarf elliptical galaxies, observed with the SAURON integral field unit, using the full-spectrum fitting method. We show that star formation histories (SFHs) resolved into two populations can be recovered even within a limited wavelength range, provided that high signal-to-noise ratio (S/N) data are used. We confirm that dEs have had complex SFHs, with star formation extending to (more) recent epochs: for the majority of our galaxies star formation activity was either still strong a few (≲5) Gyr ago or they experienced a secondary burst of star formation roughly at that time. This latter possibility is in agreement with the proposed dE formation scenario where tidal harassment drives the gas remaining in their progenitors inwards and induces a star formation episode. For one of our field galaxies, ID 0918, we find a correlation between its stellar population and kinematic properties, pointing to a possible merger origin of its kinematically decoupled core. One of our cluster objects, VCC 1431, appears to be composed exclusively of an old population (≳10-12 Gyr). Combining this with our earlier dynamical results, we conclude that the galaxy was either ram-pressure stripped early on in its evolution in a group environment and subsequently tidally heated, or that it evolved in situ in the cluster's central parts, compact enough to avoid tidal disruption. These are only two of the examples illustrating the SFH richness of these objects confirmed with our data.

  5. Lithium in Stellar Atmospheres: Observations and Theory

    NASA Astrophysics Data System (ADS)

    Lyubimkov, L. S.

    2016-09-01

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

  6. Atomic Oscillator Strengths for Stellar Atmosphere Modeling

    NASA Astrophysics Data System (ADS)

    Ruffoni, Matthew; Pickering, Juliet C.

    2015-08-01

    In order to correctly model stellar atmospheres, fundamental atomic data must be available to describe atomic lines observed in their spectra. Accurate, laboratory-measured oscillator strengths (f-values) for Fe peak elements in neutral or low-ionisation states are particularly important for determining chemical abundances.However, advances in astronomical spectroscopy in recent decades have outpaced those in laboratory astrophysics, with the latter frequently being overlooked at the planning stages of new projects. As a result, numerous big-budget astronomy projects have been, and continue to be hindered by a lack of suitable, accurately-measured reference data to permit the analysis of expensive astronomical spectra; a problem only likely to worsen in the coming decades as spectrographs at new facilities increasingly move to infrared wavelengths.At Imperial College London - and in collaboration with NIST, Wisconsin University and Lund University - we have been working with the astronomy community in an effort to provide new accurately-measured f-values for a range of projects. In particular, we have been working closely with the Gaia-ESO (GES) and SDSS-III/APOGEE surveys, both of which have discovered that many lines that would make ideal candidates for inclusion in their analyses have poorly defined f-values, or are simply absent from the database. Using high-resolution Fourier transform spectroscopy (R ~ 2,000,000) to provide atomic branching fractions, and combining these with level lifetimes measured with laser induced fluorescence, we have provided new laboratory-measured f-values for a range of Fe-peak elements, most recently including Fe I, Fe II, and V I. For strong, unblended lines, uncertainties are as low as ±0.02 dex.In this presentation, I will describe how experimental f-values are obtained in the laboratory and present our recent work for GES and APOGEE. In particular, I will also discuss the strengths and limitations of current laboratory

  7. Dwarf ellipticals in the eye of SAURON: dynamical & stellar population analysis in 3D

    NASA Astrophysics Data System (ADS)

    Ryś, Agnieszka; Falcón-Barroso, Jesús; van de Ven, Glenn; Koleva, Mina

    2015-02-01

    We present the dynamical and stellar population analysis of 12 dwarf elliptical galaxies (dEs) observed using the SAURON IFU (WHT, La Palma). We demonstrate that dEs have lower angular momenta than their presumed late-type progenitors and we show that dE circular velocity curves are steeper than the rotation curves of galaxies with equal and up to an order of magnitude higher luminosity. Transformation due to tidal harassment is able to explain all of the above, unless the dE progenitors were already compact and had lower angular momenta at higher redshifts. We then look at the star formation histories (SFHs) of our galaxies and find that for the majority of them star formation activity was either still strong at a few Gyr of age or they experienced a secondary burst of star formation roughly at that time. This latter possibility would be in agreement with the scenario where tidal harassment drives the remaining gas inwards and induces a secondary star formation episode. Finally, one of our galaxies appears to be composed exclusively of an old population (>~12 Gyr). Combining this with our earlier dynamical results, we conclude that it either was ram-pressure stripped early on in its evolution in a group environment and subsequently tidally heated (which lowered its angular momentum and increased compactness), or that it evolved in situ in the cluster's central parts, compact enough to avoid tidal disruption.

  8. New Methods in Modeling of Hot Stellar Atmospheres

    NASA Astrophysics Data System (ADS)

    Sapar, A.; Poolamäe, R.; Sapar, L.

    In the present study we had three main aims. First to study the possibility of reducing the initial model atmosphere data to short analytical polynomials. The second was to use as the depth variable the logarithm of the local gas pressure instead the Rosseland mean. The third aim was to check the applicability of the derived formulae and proposed computation methods to obtain high precision self-consistent results in modeling hot plane-parallel stellar atmospheres. Introducing the dimensionless (reduced) local quantities θ =T/Teff β =P/P(T eff) it has been shown that for hot convection-free stellar atmospheres the curves log θ versus log β reduce an initial grid of models to simple polynomials and bring forth some general features of the model stellar atmospheres. Even for stellar atmospheres having the convective zones in the deeper atmospheric layers, the outer part of the atmosphere (up to T=Teff and for Teff> 5000 K) can be described in the same manner by curves log θ versus log β as for the hotter stars. Iterative modeling of any hot stellar atmosphere can be started from these formulae (obtained for solar abundances), using rational polynomial ratios for P(Teff), obtaining from these data the needed T versus P dependence. To check suitability of the formulae, the iterative correction of the model stellar atmospheres has been carried out by the traditional Unsöld-Lucy method and by the novel least squares optimization based on Levenberg-Marquardt method, followed by Broyden correction loop. It has been shown that the flux constancy obtained by it is almost 2 dex higher than obtained by the Unsöld-Lucy method. The precision estimators as criteria of the modeling algorithms self-consistency and of the computational precision level have been proposed and used.

  9. EISCAT 3D: A European three-dimensional imaging radar for atmospheric and geospace research

    NASA Astrophysics Data System (ADS)

    McCrea, Ian; Turunen, Esa

    2010-05-01

    (This talk is given on behalf of the EISCAT Scientific Association and the EISCAT_3D Design Team) EISCAT_3D is a new kind of three-dimensional imaging radar for high-latitude atmosphere and geospace studies, located in northern Scandinavia. The facility will consist of multiple large phased-array antenna transmitters/receivers in three countries, comprising some 100 000 individual antenna elements. The new radars will measure from the upper stratosphere to the magnetosphere and beyond, contributing to the basic, environmental and applied science that underpins the use of space by contemporary society. EISCAT_3D's capabilities go beyond anything currently available to the international research community, and will form a significant enhancement to the European Research area. Located in the auroral zone, at the edge of the northern polar vortex, EISCAT_3D will provide long-term continuous data for scientists studying global change, measuring the effects of man-made and natural variability on the middle and upper atmosphere. Its observations will underpin space weather prediction and monitoring, essential for operation and improved service of European space assets. In addition, EISCAT_3D will facilitate studies of solar system influences, such as solar wind, meteors, dust, energetic particles and cosmic rays. This will be done in collaboration with other research infrastructures, including the upper atmosphere programme of the SIOS proposal, focusing on observations made from Svalbard. The importance of EISCAT_3D has been recognised by its place on the ESFRI roadmap of future European Research facilities. The project has already gone through a four-year design study, funded by the European Union under the 6th Framework, and has recently applied for Preparatory Phase funding under the EU 7th Framework. The Preparatory Phase activities will facilitate the resolution of the remaining legal, financial and technical questions which must be addressed before EISCAT_3D can be

  10. Solar Chemical Abundances Determined with a CO5BOLD 3D Model Atmosphere

    NASA Astrophysics Data System (ADS)

    Caffau, E.; Ludwig, H.-G.; Steffen, M.; Freytag, B.; Bonifacio, P.

    2011-02-01

    In the last decade, the photospheric solar metallicity as determined from spectroscopy experienced a remarkable downward revision. Part of this effect can be attributed to an improvement of atomic data and the inclusion of NLTE computations, but also the use of hydrodynamical model atmospheres seemed to play a role. This "decrease" with time of the metallicity of the solar photosphere increased the disagreement with the results from helioseismology. With a CO 5 BOLD 3D model of the solar atmosphere, the CIFIST team at the Paris Observatory re-determined the photospheric solar abundances of several elements, among them C, N, and O. The spectroscopic abundances are obtained by fitting the equivalent width and/or the profile of observed spectral lines with synthetic spectra computed from the 3D model atmosphere. We conclude that the effects of granular fluctuations depend on the characteristics of the individual lines, but are found to be relevant only in a few particular cases. 3D effects are not responsible for the systematic lowering of the solar abundances in recent years. The solar metallicity resulting from this analysis is Z=0.0153, Z/ X=0.0209.

  11. Scaling of the asymptotic entropy jump in the superadiabatic layers of stellar atmospheres

    NASA Astrophysics Data System (ADS)

    Magic, Z.

    2016-02-01

    Context. Stellar structure calculations are able to predict precisely the properties of stars during their evolution. However, convection is still modelled by the mixing length theory; therefore, the upper boundary conditions near the optical surface do not agree with asteroseismic observations. Aims: We want to improve how the outer boundary conditions are determined in stellar structure calculations. Methods: We study realistic 3D stellar atmosphere models to find alternative properties. Results: We find that the asymptotic entropy run of the superadiabatic convective surface layers exhibit a distinct universal stratification when normalized by the entropy minimum and jump. Conclusions: The normalized entropy can be represented by a 5th order polynomial very accurately, and a 3rd order polynomial also yields accurate coefficients. This generic entropy stratification or the solar stratification, when scaled by the entropy jump and minimum, can be used to improve the modelling of superadiabatic surface layers in stellar structure calculations. Furthermore, this finding indicates that surface convection operates in the same way for all cool stars, but requires further scrutiny in order to improve our understanding of stellar atmospheres.

  12. 3D-radiative transfer in terrestrial atmosphere: An efficient parallel numerical procedure

    NASA Astrophysics Data System (ADS)

    Bass, L. P.; Germogenova, T. A.; Nikolaeva, O. V.; Kokhanovsky, A. A.; Kuznetsov, V. S.

    2003-04-01

    Light propagation and scattering in terrestrial atmosphere is usually studied in the framework of the 1D radiative transfer theory [1]. However, in reality particles (e.g., ice crystals, solid and liquid aerosols, cloud droplets) are randomly distributed in 3D space. In particular, their concentrations vary both in vertical and horizontal directions. Therefore, 3D effects influence modern cloud and aerosol retrieval procedures, which are currently based on the 1D radiative transfer theory. It should be pointed out that the standard radiative transfer equation allows to study these more complex situations as well [2]. In recent year the parallel version of the 2D and 3D RADUGA code has been developed. This version is successfully used in gammas and neutrons transport problems [3]. Applications of this code to radiative transfer in atmosphere problems are contained in [4]. Possibilities of code RADUGA are presented in [5]. The RADUGA code system is an universal solver of radiative transfer problems for complicated models, including 2D and 3D aerosol and cloud fields with arbitrary scattering anisotropy, light absorption, inhomogeneous underlying surface and topography. Both delta type and distributed light sources can be accounted for in the framework of the algorithm developed. The accurate numerical procedure is based on the new discrete ordinate SWDD scheme [6]. The algorithm is specifically designed for parallel supercomputers. The version RADUGA 5.1(P) can run on MBC1000M [7] (768 processors with 10 Gb of hard disc memory for each processor). The peak productivity is equal 1 Tfl. Corresponding scalar version RADUGA 5.1 is working on PC. As a first example of application of the algorithm developed, we have studied the shadowing effects of clouds on neighboring cloudless atmosphere, depending on the cloud optical thickness, surface albedo, and illumination conditions. This is of importance for modern satellite aerosol retrieval algorithms development. [1] Sobolev

  13. Deviations from LTE in a stellar atmosphere

    NASA Technical Reports Server (NTRS)

    Kalkofen, W.; Klein, R. I.; Stein, R. F.

    1979-01-01

    Deviations for LTE are investigated in an atmosphere of hydrogen atoms with one bound level, satisfying the equations of radiative, hydrostatic, and statistical equilibrium. The departure coefficient and the kinetic temperature as functions of the frequency dependence of the radiative cross section are studied analytically and numerically. Near the outer boundary of the atmosphere, the departure coefficient is smaller than unity when the radiative cross section grows with frequency faster than with the square of frequency; it exceeds unity otherwise. Far from the boundary the departure coefficient tends to exceed unity for any frequency dependence of the radiative cross section. Overpopulation always implies that the kinetic temperature in the statistical-equilibrium atmosphere is higher than the temperature in the corresponding LTE atmosphere. Upper and lower bounds on the kinetic temperature are given for an atmosphere with deviations from LTE only in the optically shallow layers when the emergent intensity can be described by a radiation temperature.

  14. Solar Radiation Transport in the Cloudy Atmosphere: A 3D Perspective on Observations and Climate Impacts

    NASA Technical Reports Server (NTRS)

    Davis, Anthony B.; Marshak, Alexander

    2010-01-01

    The interplay of sunlight with clouds is a ubiquitous and often pleasant visual experience, but it conjures up major challenges for weather, climate, environmental science and beyond. Those engaged in the characterization of clouds (and the clear air nearby) by remote sensing methods are even more confronted. The problem comes, on the one hand, from the spatial complexity of real clouds and, on the other hand, from the dominance of multiple scattering in the radiation transport. The former ingredient contrasts sharply with the still popular representation of clouds as homogeneous plane-parallel slabs for the purposes of radiative transfer computations. In typical cloud scenes the opposite asymptotic transport regimes of diffusion and ballistic propagation coexist. We survey the three-dimensional (3D) atmospheric radiative transfer literature over the past 50 years and identify three concurrent and intertwining thrusts: first, how to assess the damage (bias) caused by 3D effects in the operational 1D radiative transfer models? Second, how to mitigate this damage? Finally, can we exploit 3D radiative transfer phenomena to innovate observation methods and technologies? We quickly realize that the smallest scale resolved computationally or observationally may be artificial but is nonetheless a key quantity that separates the 3D radiative transfer solutions into two broad and complementary classes: stochastic and deterministic. Both approaches draw on classic and contemporary statistical, mathematical and computational physics.

  15. Solar radiation transport in the cloudy atmosphere: a 3D perspective on observations and climate impacts

    NASA Astrophysics Data System (ADS)

    Davis, Anthony B.; Marshak, Alexander

    2010-02-01

    The interplay of sunlight with clouds is a ubiquitous and often pleasant visual experience, but it conjures up major challenges for weather, climate, environmental science and beyond. Those engaged in the characterization of clouds (and the clear air nearby) by remote sensing methods are even more confronted. The problem comes, on the one hand, from the spatial complexity of real clouds and, on the other hand, from the dominance of multiple scattering in the radiation transport. The former ingredient contrasts sharply with the still popular representation of clouds as homogeneous plane-parallel slabs for the purposes of radiative transfer computations. In typical cloud scenes the opposite asymptotic transport regimes of diffusion and ballistic propagation coexist. We survey the three-dimensional (3D) atmospheric radiative transfer literature over the past 50 years and identify three concurrent and intertwining thrusts: first, how to assess the damage (bias) caused by 3D effects in the operational 1D radiative transfer models? Second, how to mitigate this damage? Finally, can we exploit 3D radiative transfer phenomena to innovate observation methods and technologies? We quickly realize that the smallest scale resolved computationally or observationally may be artificial but is nonetheless a key quantity that separates the 3D radiative transfer solutions into two broad and complementary classes: stochastic and deterministic. Both approaches draw on classic and contemporary statistical, mathematical and computational physics.

  16. 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.

  17. A study of the 3D radiative transfer effect in cloudy atmospheres

    NASA Astrophysics Data System (ADS)

    Okata, M.; Teruyuki, N.; Suzuki, K.

    2015-12-01

    Evaluation of the effect of clouds in the atmosphere is a significant problem in the Earth's radiation budget study with their large uncertainties of microphysics and the optical properties. In this situation, we still need more investigations of 3D cloud radiative transer problems using not only models but also satellite observational data.For this purpose, we have developed a 3D-Monte-Carlo radiative transfer code that is implemented with various functions compatible with the OpenCLASTR R-Star radiation code for radiance and flux computation, i.e. forward and backward tracing routines, non-linear k-distribution parameterization (Sekiguchi and Nakajima, 2008) for broad band solar flux calculation, and DM-method for flux and TMS-method for upward radiance (Nakajima and Tnaka 1998). We also developed a Minimum cloud Information Deviation Profiling Method (MIDPM) as a method for a construction of 3D cloud field with MODIS/AQUA and CPR/CloudSat data. We then selected a best-matched radar reflectivity factor profile from the library for each of off-nadir pixels of MODIS where CPR profile is not available, by minimizing the deviation between library MODIS parameters and those at the pixel. In this study, we have used three cloud microphysical parameters as key parameters for the MIDPM, i.e. effective particle radius, cloud optical thickness and top of cloud temperature, and estimated 3D cloud radiation budget. We examined the discrepancies between satellite observed and mode-simulated radiances and three cloud microphysical parameter's pattern for studying the effects of cloud optical and microphysical properties on the radiation budget of the cloud-laden atmospheres.

  18. Validation of INSAT-3D atmospheric motion vectors for monsoon 2015

    NASA Astrophysics Data System (ADS)

    Sharma, Priti; Rani, S. Indira; Das Gupta, M.

    2016-05-01

    Atmospheric Motion Vector (AMV) over Indian Ocean and surrounding region is one of the most important sources of tropospheric wind information assimilated in numerical weather prediction (NWP) system. Earlier studies showed that the quality of Indian geo-stationary satellite Kalpana-1 AMVs was not comparable to that of other geostationary satellites over this region and hence not used in NWP system. Indian satellite INSAT-3D was successfully launched on July 26, 2013 with upgraded imaging system as compared to that of previous Indian satellite Kalpana-1. INSAT-3D has middle infrared band (3.80 - 4.00 μm) which is capable of night time pictures of low clouds and fog. Three consecutive images of 30-minutes interval are used to derive the AMVs. New height assignment scheme (using NWP first guess and replacing old empirical GA method) along with modified quality control scheme were implemented for deriving INSAT-3D AMVs. In this paper an attempt has been made to validate these AMVs against in-situ observations as well as against NCMRWF's NWP first guess for monsoon 2015. AMVs are subdivided into three different pressure levels in the vertical viz. low (1000 - 700 hPa), middle (700 - 400 hPa) and high (400 - 100 hPa) for validation purpose. Several statistics viz. normalized root mean square vector difference; biases etc. have been computed over different latitudinal belt. Result shows that the general mean monsoon circulations along with all the transient monsoon systems are well captured by INSAT-3D AMVs, as well as the error statistics viz., RMSE etc of INSAT-3D AMVs is now comparable to other geostationary satellites.

  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. 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.

  1. <3D> NLTE line formation in the atmospheres of red supergiants

    NASA Astrophysics Data System (ADS)

    Bergemann, M.; Kudritzki, R. P.; Davies, B.; Plez, B.; Gazak, Z.; Chiavassa, A.

    2013-05-01

    Red supergiants with their enormous brightness at J-band are ideal probes of cosmic chemical composition. It is therefore crucial to have realistic models of radiative transfer in their atmospheres, which will permit determination of abundances accurate to 0.15 dex, the precision attainable with future telescope facilities in galaxies as distant as tens of Mpc. Here, we study the effects of non-local thermodynamic equilibrium (NLTE) on the formation of iron, titanium, and silicon lines, which dominate J-band spectra of red supergiants. It is shown that the NLTE radiative transfer models enable accurate derivation of metallicity and effective temperature in the J-band. We also discuss consequences for RSG spectrum synthesis in different spectral windows, including the heavily TiO-blanketed optical region, and atmospheric structure. We then touch upon challenges of NLTE integration with new generation of 3D hydrodynamical RSG models and present the first calculations of NLTE spectra with the mean 3D model of Betelgeuse.

  2. 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.

  3. Sulfur in the early martian atmosphere revisited: Experiments with a 3-D Global Climate Model

    NASA Astrophysics Data System (ADS)

    Kerber, Laura; Forget, François; Wordsworth, Robin

    2015-11-01

    Volcanic SO2 in the martian atmosphere has been invoked as a way to create a sustained or transient greenhouse during early martian history. Many modeling studies have been performed to test the feasibility of this hypothesis, resulting in a range of conclusions, from highly feasible to highly improbable. In this study we perform a wide range of simulations using the 3-D Laboratoire de Météorologie Dynamique Generic Global Climate Model (GCM) in order to place earlier results into context and to explore the sensitivity of model outcomes to parameters such as SO2 mixing ratio, atmospheric H2O content, background atmospheric pressure, and aerosol size, abundance, and composition. We conclude that SO2 is incapable of creating a sustained greenhouse on early Mars, and that even in the absence of aerosols, local and daily temperatures rise above 273 K for only for limited periods with favorable background CO2 pressures. In the presence of even small amounts of aerosols, the surface is dramatically cooled for realistic aerosol sizes. Brief, mildly warm conditions require the co-occurrence of many improbable factors, while cooling is achieved for a wide range of model parameters. Instead of causing warming, sulfur in the martian atmosphere may have caused substantial cooling, leading to the end of clement climate conditions on early Mars.

  4. A new 3D numerical model of cosmogenic nuclide 10Be production in the atmosphere

    NASA Astrophysics Data System (ADS)

    Kovaltsov, Gennady A.; Usoskin, Ilya G.

    2010-03-01

    A new quantitative model of production of the cosmogenic isotope 10Be by cosmic rays in the Earth's atmosphere is presented. The CRAC:10Be (Cosmic Ray induced Atmospheric Cascade for 10Be) model is based on a full numerical Monte-Carlo simulation of the nucleonic-electromagnetic-muon cascade induced by cosmic rays in the atmosphere and is able to compute the isotope's production rate at any given 3D location (geographical and altitude) and time, for all possible parameters including solar energetic particle events. The model was tested against the results of direct measurements of the 10Be production in a number of dedicated experiments to confirm its quantitative correctness. A set of tabulated values for the yield function is provided along with a detailed numerical recipe forming a "do-it-yourself" kit, which allows anyone interested to apply the model for any given conditions. This provides a useful tool for applying the cosmogenic isotope method in direct integration with other models, e.g., dynamical atmospheric transport.

  5. Oscillatory phenomena in solar and stellar atmospheres

    NASA Astrophysics Data System (ADS)

    Bloomfield, David Shaun

    This thesis presents varying studies into the nature of intensity oscillations observed both on the Sun and two active cool stars. The first part concentrates on the detection of correlated oscillations occuring between differing heights in the solar atmosphere above quiet-Sun magnetic network bright points (NBPs), interpreted as signatures of energy propagation. This is achieved through correlating in time the wavelet power spectra of lightcurves from images obtained in several optical wavelengths. In four of the eleven NBPs studied, evidence is found for upwardly-propagating, low-frequency waves (1.4 mHz, 2.1 mHz) in the lower chromosphere, decreasing in oscillatory power with the onset, or increase in power, of higher-frequency waves (2.9 mHz, 4.0 mHz) within the upper chromosphere. Moving higher into the atmosphere two of the four cases of higher frequency waves also show a decrease in power. These observational detections are interpreted as transverse-mode magnetohydrodynamic (MHD) waves undergoing non-linear mode coupling to longitudinal-modes at double the frequency, which shock or otherwise dissipate in the high chromosphere. Evidence is also found for additional upward- and downward- directed waves within all the NBPs studied. The extension of wavelet power techniques into the analysis of phase difference and phase coherence is also presented, utilising UV intensities obtained from above a weak solar network element. The problems associated with the quantification of phase coherence values are outlined and a comparison of two differing methods is carried out. Changes observed in the evolution of phase difference between oscillations detected in the UV emission of the temperature minimum and low transition region are shown to be due to the alteration of the underlying magnetic topology, occuring when same polarity flux emerges nearby. The final part of this thesis concerns the differing situation of intensity variations during energetic flare phenomena on

  6. The Solar Photospheric Oxygen Abundance and the Role of 3D Model Atmospheres

    NASA Astrophysics Data System (ADS)

    Caffau, E.; Steffen, M.; Ludwig, H.-G.

    2008-09-01

    The solar oxygen abundance has undergone a major downward revision in the last decade, reputedly as a result of employing 3D hydrodynamical simulations to model the inhomogeneous structure of the solar photosphere. The very low oxygen abundance advocated by Asplund et al. 2004, A(O)=8.66, together with the downward revision of the abundances of other key elements, has created serious problems for solar models to explain the helioseismic measurements. In an effort to contribute to the dispute of whether the Sun has "solar" or "sub-solar" abundances, we have re-derived its photospheric abundance of oxygen, nitrogen, and other elements, independently of previous analyses. We applied a state-of-the art 3D (CO5BOLD) hydrodynamical simulation of the solar granulation as well as different 1D model atmospheres for the line by line spectroscopic abundance determinations. The analysis is based on both standard disk-center and full-disk spectral atlases; for oxygen we acquired in addition spectra at different heliocentric angles. The derived abundances are the result of equivalent width and/or line profile fitting of the available atomic lines. Our recommended oxygen abundance is A(O)=8.76+- 0.07, 0.1 dex higher than the value of Asplund et al. (2004). Our current estimate of the overall solar metallicity is 0.014< Z<0.016. Questions we discuss include: (i) Is the general downward revision of the solar abundances a 3D effect? (ii) How large are the abundance corrections due to horizontal inhomogeneities? (iii) What is the main reason for the differences between the abundances obtained in our study and those derived by Apslund and coworkers? (iv) How large are the uncertainties in the observed solar spectra? (v) What is the reason why the two forbidden oxygen lines, [OI] lambda 630 nm and [OI] lambda 636.3 nm, give significantly different answers for the solar oxygen abundance?

  7. Plasma penetration depth and mechanical properties of atmospheric plasma-treated 3D aramid woven composites

    NASA Astrophysics Data System (ADS)

    Chen, X.; Yao, L.; Xue, J.; Zhao, D.; Lan, Y.; Qian, X.; Wang, C. X.; Qiu, Y.

    2008-12-01

    Three-dimensional aramid woven fabrics were treated with atmospheric pressure plasmas, on one side or both sides to determine the plasma penetration depth in the 3D fabrics and the influences on final composite mechanical properties. The properties of the fibers from different layers of the single side treated fabrics, including surface morphology, chemical composition, wettability and adhesion properties were investigated using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), contact angle measurement and microbond tests. Meanwhile, flexural properties of the composites reinforced with the fabrics untreated and treated on both sides were compared using three-point bending tests. The results showed that the fibers from the outer most surface layer of the fabric had a significant improvement in their surface roughness, chemical bonding, wettability and adhesion properties after plasma treatment; the treatment effect gradually diminished for the fibers in the inner layers. In the third layer, the fiber properties remained approximately the same to those of the control. In addition, three-point bending tests indicated that the 3D aramid composite had an increase of 11% in flexural strength and 12% in flexural modulus after the plasma treatment. These results indicate that composite mechanical properties can be improved by the direct fabric treatment instead of fiber treatment with plasmas if the fabric is less than four layers thick.

  8. 3-D water vapor field in the atmospheric boundary layer observed with scanning differential absorption lidar

    NASA Astrophysics Data System (ADS)

    Späth, Florian; Behrendt, Andreas; Muppa, Shravan Kumar; Metzendorf, Simon; Riede, Andrea; Wulfmeyer, Volker

    2016-04-01

    High-resolution three-dimensional (3-D) water vapor data of the atmospheric boundary layer (ABL) are required to improve our understanding of land-atmosphere exchange processes. For this purpose, the scanning differential absorption lidar (DIAL) of the University of Hohenheim (UHOH) was developed as well as new analysis tools and visualization methods. The instrument determines 3-D fields of the atmospheric water vapor number density with a temporal resolution of a few seconds and a spatial resolution of up to a few tens of meters. We present three case studies from two field campaigns. In spring 2013, the UHOH DIAL was operated within the scope of the HD(CP)2 Observational Prototype Experiment (HOPE) in western Germany. HD(CP)2 stands for High Definition of Clouds and Precipitation for advancing Climate Prediction and is a German research initiative. Range-height indicator (RHI) scans of the UHOH DIAL show the water vapor heterogeneity within a range of a few kilometers up to an altitude of 2 km and its impact on the formation of clouds at the top of the ABL. The uncertainty of the measured data was assessed for the first time by extending a technique to scanning data, which was formerly applied to vertical time series. Typically, the accuracy of the DIAL measurements is between 0.5 and 0.8 g m-3 (or < 6 %) within the ABL even during daytime. This allows for performing a RHI scan from the surface to an elevation angle of 90° within 10 min. In summer 2014, the UHOH DIAL participated in the Surface Atmosphere Boundary Layer Exchange (SABLE) campaign in southwestern Germany. Conical volume scans were made which reveal multiple water vapor layers in three dimensions. Differences in their heights in different directions can be attributed to different surface elevation. With low-elevation scans in the surface layer, the humidity profiles and gradients can be related to different land cover such as maize, grassland, and forest as well as different surface layer

  9. Granulation properties of giants, dwarfs, and white dwarfs from the CIFIST 3D model atmosphere grid

    NASA Astrophysics Data System (ADS)

    Tremblay, P.-E.; Ludwig, H.-G.; Freytag, B.; Steffen, M.; Caffau, E.

    2013-09-01

    Three-dimensional model atmospheres for giants, dwarfs, and white dwarfs, computed with the CO5BOLD code and part of the CIFIST grid, have been used for spectroscopic and asteroseismic studies. Unlike existing plane-parallel 1D structures, these simulations predict the spatially and temporally resolved emergent intensity so that granulation can be analysed, which provides insights on how convective energy transfer operates in stars. The wide range of atmospheric parameters of the CIFIST 3D simulations (3600 < Teff (K) < 13 000 and 1 < log g < 9) allows the comparison of convective processes in significantly different environments. We show that the relative intensity contrast is correlated with both the Mach and Péclet numbers in the photosphere. The horizontal size of granules varies between 3 and 10 times the local pressure scale height, with a tight correlation between the factor and the Mach number of the flow. Given that convective giants, dwarfs, and white dwarfs cover the same range of Mach and Péclet numbers, we conclude that photospheric convection operates in a very similar way in those objects. Table 1 and Appendix A are available in electronic form at http://www.aanda.org

  10. Characterization and evolution of distant planetary atmospheres using stellar occultations

    NASA Astrophysics Data System (ADS)

    Young, L. A.

    2008-09-01

    Ground-based or near-Earth (e.g., HST) stellar occultations of every atmosphere in our solar system has been observed: Venus, Mars, Jupiter, Saturn, Titan, Uranus, Neptune, Triton, and Pluto [1]. These observations probe the atmospheres at roughly 0.1 to 100 microbar. I will talk about three aspects of stellar occultations: one-dimensional vertical profiles of the atmosphere, two- or three-dimensional atmospheric states, and the time evolution of atmosphere. In all three, I will draw on recent observations, with an emphasis on Pluto. Occultations are particularly important for the study of Pluto's atmosphere, which is impossible to study with imaging, and extremely difficult to study with spectroscopy. It was discovered by stellar occultation in 1988 [2]. No subsequent Pluto occultations were observed until two events in 2002 [3]. Pluto is now crossing the galactic plane, and there have been several additional occultations observed since 2006. These include a high signal-to-noise observation from the Anglo Australian Observatory in 2006 [4] (Fig 1), densely spaced visible and infrared observations of Pluto's upper atmosphere from telescopes in the US and Mexico in March, 2007 [5] (Fig. 2), and a dualwavelength central flash observation from Mt. John in July, 2007 [6] (Fig 3). The flux from a star occulted by an atmosphere diminishes primarily due to the increase in refraction with depth in the atmosphere, defocusing the starlight, although absorption and tangential focusing can also contribute. Because the atmospheric density, to first order, follows an exponential, it is feasible to derive a characteristic pressure and temperature from isothermal fits to even low-quality occultation light curves. Higher quality light curves allow fits with more flexible models, or light curve inversions that derive temperatures limited by the resolution of the data. These allow the derivation of one-dimensional profiles of temperature and pressure vs. altitude, which are critical

  11. 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.

  12. The Rossiter-McLaughlin effect reloaded: Probing the 3D spin-orbit geometry, differential stellar rotation, and the spatially-resolved stellar spectrum of star-planet systems

    NASA Astrophysics Data System (ADS)

    Cegla, H. M.; Lovis, C.; Bourrier, V.; Beeck, B.; Watson, C. A.; Pepe, F.

    2016-04-01

    When a planet transits its host star, it blocks regions of the stellar surface from view; this causes a distortion of the spectral lines and a change in the line-of-sight (LOS) velocities, known as the Rossiter-McLaughlin (RM) effect. Since the LOS velocities depend, in part, on the stellar rotation, the RM waveform is sensitive to the star-planet alignment (which provides information on the system's dynamical history). We present a new RM modelling technique that directly measures the spatially-resolved stellar spectrum behind the planet. This is done by scaling the continuum flux of the (HARPS) spectra by the transit light curve, and then subtracting the in- from the out-of-transit spectra to isolate the starlight behind the planet. This technique does not assume any shape for the intrinsic local profiles. In it, we also allow for differential stellar rotation and centre-to-limb variations in the convective blueshift. We apply this technique to HD 189733 and compare to 3D magnetohydrodynamic (MHD) simulations. We reject rigid body rotation with high confidence (>99% probability), which allows us to determine the occulted stellar latitudes and measure the stellar inclination. In turn, we determine both the sky-projected (λ ≈ -0.4 ± 0.2°) and true 3D obliquity (ψ ≈ 7+12-4°). We also find good agreement with the MHD simulations, with no significant centre-to-limb variations detectable in the local profiles. Hence, this technique provides a new powerful tool that can probe stellar photospheres, differential rotation, determine 3D obliquities, and remove sky-projection biases in planet migration theories. This technique can be implemented with existing instrumentation, but will become even more powerful with the next generation of high-precision radial velocity spectrographs.

  13. 3D atmospheric structure of the prototypical roAp star HD 24712 (HR1217)

    NASA Astrophysics Data System (ADS)

    Lüftinger, T.; Kochukhov, O.; Ryabchikova, T.; Piskunov, N.; Weiss, W. W.; Ilyin, I.

    2008-04-01

    The first analysis of the structure of the surface magnetic field of a rapidly oscillating Ap (roAp) star is presented. We obtain information about abundance distributions of a number of chemical elements on the surface of the prototypical roAp star HD 24712 and about magnetic field geometry. Inverting rotationally modulated spectra in Stokes parameters I and V obtained with the SOFIN spectropolarimeter attached to the NOT, we recover surface abundance structures of sixteen different chemical elements, including Mg, Ca, Sc, Ti, Cr, Fe, Co, Ni, Y, La, Ce, Pr, Nd, Gd, Tb, and Dy. Our analysis reveal a pure dipolar structure of the stellar magnetic field and surprising and unexpected correlations of the various elemental surface abundance structures to this field geometry. Stratification analysis at phases of both magnetic extrema enable us to obtain the vertical dimension in the atmosphere of HD 24712. High time resolved spectroscopic data and observations obtained with the MOST space photometer give us the possibility to compare (Lüftinger, 2007) our results to detailed pulsational analysis.

  14. Dislocations in magnetohydrodynamic waves in a stellar atmosphere.

    PubMed

    López Ariste, A; Collados, M; Khomenko, E

    2013-08-23

    We describe the presence of wave front dislocations in magnetohydrodynamic waves in stratified stellar atmospheres. Scalar dislocations such as edges and vortices can appear in Alfvén waves, as well as in general magnetoacoustic waves. We detect those dislocations in observations of magnetohydrodynamic waves in sunspots in the solar chromosphere. Through the measured charge of all the dislocations observed, we can give for the first time estimates of the modal contribution in the waves propagating along magnetic fields in solar sunspots. PMID:24010425

  15. 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

  16. Variability of the hydrogen in the martian upper atmosphere as simulated by a 3D atmosphere-exosphere coupling

    NASA Astrophysics Data System (ADS)

    Chaufray, J.-Y.; Gonzalez-Galindo, F.; Forget, F.; Lopez-Valverde, M. A.; Leblanc, F.; Modolo, R.; Hess, S.

    2015-01-01

    We present the temporal variability of the atomic and molecular hydrogen density derived from a 3D General Circulation Model describing the martian atmosphere from the surface to the exobase. A kinetic exospheric model is used to compute the hydrogen density above the exobase. We use these models to study the diurnal and seasonal variations of the hydrogen density and the Jeans escape rate as well as their variations with solar activity, assuming a classic dust scenario. We find that the diurnal variations of the hydrogen density are important with a peak in the dawn region during equinoxes and a peak on the nightside during solstices. These features result from the dynamics of the martian upper atmosphere. The variations of the atomic hydrogen Jeans escape with seasons and solar activity are in the range 1.3 × 1025 s-1-4.4 × 1026 s-1. A factor ∼8 is due to the seasonal variations with a maximum during the winter solstice in the northern hemisphere and a minimum during the summer solstice in the northern hemisphere that we attribute to the variation of the Mars-Sun distance. A factor ∼5 is due to the solar cycle with a maximum escape rate at high solar activity. The variations of the molecular hydrogen Jeans escape with seasons and solar activity are in the range 3 × 1022 s-1-6 × 1024 s-1. A factor ∼10 is due to the seasonal variations with a maximum during the winter solstice in the northern hemisphere and a minimum during the summer solstice in the northern hemisphere. A factor ∼20 is due to the solar cycle with a maximum escape rate at high solar activity. If Jeans escape is the major escape channel for hydrogen, the hydrogen escape is never limited by diffusion. The hydrogen density above 10,000 km presents seasonal and solar cycle variations similar to the Jeans escape rate at all latitudes and local times. This 3D temporal model of the hydrogen thermosphere/exosphere will be useful to interpret future MAVEN observations and the consequences of the

  17. Sulfur in the Early Martian Atmosphere Revisited: Experiments with a 3-D Global Climate Model

    NASA Astrophysics Data System (ADS)

    Kerber, L.; Forget, F.; Wordsworth, R.

    2013-09-01

    [8]. A successful working model for the early Martian atmosphere and hydrosphere must be able not only to produce conditions suitable for liquid water at the surface, but also to explain how the nature of this aqueous activity changed over time and eventually diminished. There are two major end-member hypotheses: first, that early Mars was wet and warm, with a sustained greenhouse that made it possible for liquid water to be stable on the surface for extended periods [e.g., 2, 12-14], and second, that early Mars was generally cold, and that most of the aqueous alteration took place underground [3,5] or during transient warm periods tied to impact cratering [15], or volcanism [16]. In both of these scenarios it is generally agreed that in order to make valley networks and sulfate deposits, a hydrological cycle is needed which is able to recycle water from the lowlands back to the highlands (i.e., the one-time emptying of a regional aquifer would not be sufficient to create the observed features) [4,17]. This would require some precipitation to fall on the southern highlands, either flowing overland or filtering into groundwater aquifers. In both cases, volcanic gases (especially SO2) have been suggested as a possible way of creating either a sustained or transient greenhouse. Several researchers have tested the addition of SO2 to climate models in order to assess whether it would provide an adequate amount of greenhouse warming to allow liquid water to flow across the surface [18-21], with differing results. Postawko and Kuhn [18] found a warming effect of 14 K in a 0.1 bar atmosphere with an SO2 abundance of 1000 ppm. Johnson et al. [20] used a 3-D global circulation model and found a warming of 15-25 K for 245 ppm of SO2 in a dry 0.5 bar atmosphere. Tian et al. [21] used a 1-D model to explore a wide range of SO2 mixing values and CO2 partial pressures, finding a warming of around ~25 K for 100 ppm in a 0.5 bar atmosphere with a fully saturated troposphere (~40 K

  18. Estimation of Atmospheric Methane Surface Fluxes Using a Global 3-D Chemical Transport Model

    NASA Astrophysics Data System (ADS)

    Chen, Y.; Prinn, R.

    2003-12-01

    Accurate determination of atmospheric methane surface fluxes is an important and challenging problem in global biogeochemical cycles. We use inverse modeling to estimate annual, seasonal, and interannual CH4 fluxes between 1996 and 2001. The fluxes include 7 time-varying seasonal (3 wetland, rice, and 3 biomass burning) and 3 steady aseasonal (animals/waste, coal, and gas) global processes. To simulate atmospheric methane, we use the 3-D chemical transport model MATCH driven by NCEP reanalyzed observed winds at a resolution of T42 ( ˜2.8° x 2.8° ) in the horizontal and 28 levels (1000 - 3 mb) in the vertical. By combining existing datasets of individual processes, we construct a reference emissions field that represents our prior guess of the total CH4 surface flux. For the methane sink, we use a prescribed, annually-repeating OH field scaled to fit methyl chloroform observations. MATCH is used to produce both the reference run from the reference emissions, and the time-dependent sensitivities that relate individual emission processes to observations. The observational data include CH4 time-series from ˜15 high-frequency (in-situ) and ˜50 low-frequency (flask) observing sites. Most of the high-frequency data, at a time resolution of 40-60 minutes, have not previously been used in global scale inversions. In the inversion, the high-frequency data generally have greater weight than the weekly flask data because they better define the observational monthly means. The Kalman Filter is used as the optimal inversion technique to solve for emissions between 1996-2001. At each step in the inversion, new monthly observations are utilized and new emissions estimates are produced. The optimized emissions represent deviations from the reference emissions that lead to a better fit to the observations. The seasonal processes are optimized for each month, and contain the methane seasonality and interannual variability. The aseasonal processes, which are less variable, are

  19. 3D Atmospheric Radiative Transfer for Cloud System-Resolving Models: Forward Modelling and Observations

    SciTech Connect

    Howard Barker; Jason Cole

    2012-05-17

    Utilization of cloud-resolving models and multi-dimensional radiative transfer models to investigate the importance of 3D radiation effects on the numerical simulation of cloud fields and their properties.

  20. 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.

  1. The calculation and publication of a grid of line-blanketed model stellar atmospheres

    NASA Technical Reports Server (NTRS)

    Avrett, E. H.

    1972-01-01

    The luminosity, mass, and elemental abundances, as well as other properties of each star are studied in order to locate them in an evolutionary pattern. A method for determining the flux, gravity, and abundances at the stellar surface is the construction of theoretical stellar atmospheric models that predict the observed energy distribution and detailed stellar spectrum.

  2. 13CH3D kinetic isotope effects for methane oxidation by OH - predicting the "clumped" isotopic signature of atmospheric methane

    NASA Astrophysics Data System (ADS)

    Whitehill, A. R.; Joelsson, L. M. T.; Wang, D. T.; Johnson, M. S.; Ono, S.

    2015-12-01

    Methane is a significant long-lived greenhouse gas, but the tropospheric methane budget is not entirely constrained. "Clumped" isotopologues of methane, including 13CH3D, can provide additional constraints on the atmospheric methane cycle. Interpretation of these novel isotope tracers requires an understanding of the "clumped" isotopic signature of various methane sources, as well as the kinetic isotope effects of the methane sink reactions. We performed a series of photochemical experiments to measure the isotopic fractionation during the CH4+OH reaction. Experiments were carried out in a 100 L quartz photochemical reactor. Photolysis of ozone (O3) in the presence of water (H2O) was used to produce OH radicals. Experiments were performed in a helium bath gas. Fourier transform infrared spectroscopy (FTIR) was used to monitor reaction progress. At various intervals during the reaction, methane was sampled from the cell and analyzed for isotope ratios by tunable infrared laser direct absorption spectroscopy (TILDAS). By simultaneously measuring four different isotopologues of methane (12CH4,12CH3D, 13CH4, 13CH3D), we were able to constrain the kinetic isotope effects for 12CH3D, 13CH4, and the doubly-substitued isotopologue 13CH3D. These results are combined with published clumped isotope data from different methane sources to model the Δ13CH3D (i.e. deviation from "stochastic" distribution of isotopes) of tropospheric methane and its sensitivity to different sources. The Δ13CH3D value of tropospheric methane does not strongly depend upon isotope fractionation during the OH sink reaction. Rather, the Δ13CH3D value of tropospheric methane reflects a mixing of different source signatures. Due to nonlinearity in mixing of Δ13CH3D, the Δ13CH3D value of tropospheric methane will be larger than the weighted average of the Δ13CH3D value of the sources. A first order interpretation of variations in the Δ13CH3D value of tropospheric methane is that it reflects changes

  3. Atmospheric Motion Vectors from INSAT-3D: Initial quality assessment and its impact on track forecast of cyclonic storm NANAUK

    NASA Astrophysics Data System (ADS)

    Deb, S. K.; Kishtawal, C. M.; Kumar, Prashant; Kiran Kumar, A. S.; Pal, P. K.; Kaushik, Nitesh; Sangar, Ghansham

    2016-03-01

    The advanced Indian meteorological geostationary satellite INSAT-3D was launched on 26 July 2013 with an improved imager and an infrared sounder and is placed at 82°E over the Indian Ocean region. With the advancement in retrieval techniques of different atmospheric parameters and with improved imager data have enhanced the scope for better understanding of the different tropical atmospheric processes over this region. The retrieval techniques and accuracy of one such parameter, Atmospheric Motion Vectors (AMV) has improved significantly with the availability of improved spatial resolution data along with more options of spectral channels in the INSAT-3D imager. The present work is mainly focused on providing brief descriptions of INSAT-3D data and AMV derivation processes using these data. It also discussed the initial quality assessment of INSAT-3D AMVs for a period of six months starting from 01 February 2014 to 31 July 2014 with other independent observations: i) Meteosat-7 AMVs available over this region, ii) in-situ radiosonde wind measurements, iii) cloud tracked winds from Multi-angle Imaging Spectro-Radiometer (MISR) and iv) numerical model analysis. It is observed from this study that the qualities of newly derived INSAT-3D AMVs are comparable with existing two versions of Meteosat-7 AMVs over this region. To demonstrate its initial application, INSAT-3D AMVs are assimilated in the Weather Research and Forecasting (WRF) model and it is found that the assimilation of newly derived AMVs has helped in reduction of track forecast errors of the recent cyclonic storm NANAUK over the Arabian Sea. Though, the present study is limited to its application to one case study, however, it will provide some guidance to the operational agencies for implementation of this new AMV dataset for future applications in the Numerical Weather Prediction (NWP) over the south Asia region.

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

    SciTech Connect

    Zemskova, Varvara; Garaud, Pascale; Deal, Morgan; Vauclair, Sylvie

    2014-11-10

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

  5. Gravitational damping of Alfven waves in stellar atmospheres and winds

    NASA Technical Reports Server (NTRS)

    Khabibrakhmanov, I. K.; Mullan, D. J.

    1994-01-01

    We consider how gravity affects the propagation of Alfven waves in a stellar atmosphere. We show that when the ion gyrofrequency exceeds the collision rate, the waves are absorbed at a rate proportional to the gravitational acceleration g. Estimates show that this mechanism can readily account for the observed energy losses in the solar chromosphere. The mechanism predicts that the pressure at the top of the chromosphere P(sub Tc) should scale with g as P(sub Tc) proportional to g(exp delta), where delta approximately equals 2/3; this is close to empirical results which suggest delta approximately equals 0.6. Gravitational damping leads to deposition of energy at a rate proportional to the mass of the particles. Hence, heavier ion are heated more effectively than protons. This is consistent with the observed proportionality between ion temperature and mass in the solar wind. Gravitational damping causes the local g to be effectively decreased by an amount proportional to the wave energy. This feature affects the acceleration of the solar wind. Gravitational damping may also lead to self-regulation of the damping of Alfven waves in stellar winds: this is relevant in the context of slow massive winds in cool giants.

  6. Probing the Martian atmosphere with MAVEN/IUVS stellar occultations

    NASA Astrophysics Data System (ADS)

    Gröller, H.; Yelle, R. V.; Koskinen, T. T.; Montmessin, F.; Lacombe, G.; Schneider, N. M.; Deighan, J.; Stewart, A. I. F.; Jain, S. K.; Chaffin, M. S.; Crismani, M. M. J.; Stiepen, A.; Lefèvre, F.; McClintock, W. E.; Clarke, J. T.; Holsclaw, G. M.; Mahaffy, P. R.; Bougher, S. W.; Jakosky, B. M.

    2015-11-01

    The first campaign of stellar occultations with the Imaging Ultraviolet Spectrograph (IUVS) instrument on board of Mars Atmosphere and Volatile EvolutioN (MAVEN) mission was executed between 24 and 26 March 2015. From this campaign 13 occultations are used to retrieve CO2 and O2 number densities in the altitude range between 100 and 150 km. Observations probe primarily the low-latitude regions on the nightside of the planet, just past the dawn and dusk terminator. Calculation of temperature from the CO2 density profiles reveals that the lower thermosphere is significantly cooler than predicted by the models in the Mars Climate Database. A systematically cold layer with temperatures of 105-120 K is seen in the occultations at a pressure level around 7 × 10-6 Pa.

  7. Data Needs for Stellar Atmosphere and Spectrum Modeling

    NASA Technical Reports Server (NTRS)

    Short, C. I.

    2006-01-01

    The main data need for stellar atmosphere and spectrum modeling remains atomic and molecular transition data, particularly energy levels and transition cross-sections. We emphasize that data is needed for bound-free (b - f) as well as bound-bound (b - b), and collisional as well as radiative transitions. Data is now needed for polyatomic molecules as well as atoms, ions, and diatomic molecules. In addition, data for the formation of, and extinction due to, liquid and solid phase dust grains is needed. A prioritization of species and data types is presented, and gives emphasis to Fe group elements, and elements important for the investigation of nucleosynthesis and Galactic chemical evolution, such as the -elements and n-capture elements. Special data needs for topical problems in the modeling of cool stars and brown dwarfs are described.

  8. Pluto's Atmosphere from the July 2010 Stellar Occultation

    NASA Astrophysics Data System (ADS)

    Person, Michael J.; Elliot, J. L.; Bosh, A. S.; Gulbis, A. A. S.; Jensen-Clem, R.; Lockhart, M. F.; Zangari, A. M.; Zuluaga, C. A.; Levine, S. E.; Pasachoff, J. M.; Souza, S. P.; Lu, M.; Malamut, C.; Rojo, P.; Bailyn, C. D.; MacDonald, R. K. D.; Ivarsen, K. M.; Reichart, D. E.; LaCluyze, A. P.; Nysewander, M. C.; Haislip, J. B.

    2010-10-01

    We have observed the 4 July 2010 stellar occultation by Pluto as part of our program of monitoring Pluto's atmospheric changes over the last decade. Successful observations were obtained from three sites: Cerro Calan and Cerro Tololo, Chile, as well as the HESS-project site (High Energy Stereoscopic System) in southwestern Namibia. Successful telescope apertures ranged from 0.45 m to 1.0 m and resulted in seven occultation light curves for the event from among the three sites. Simultaneous analysis of the seven light curves indicates that Pluto's atmosphere continues to be stable, as the calculated atmospheric radii are consistent with those detected in 2006 (Elliot et al., AJ 134, 1, 2007) and 2007 (Person et al., AJ 136, 1510, 2008), continuing the stability that followed the large pressure increase detected between 1988 (Millis et al., Icarus 105, 282, 1993) and 2002 (Elliot et al., Nature 424, 165, 2003). We will present the overall astrometric solution as well as current profiles for Pluto's upper atmospheric temperature and pressure obtained from inversion of the light curves (Elliot, Person, and Qu, AJ 126, 1041, 2003). This work was supported, in part, by grants NNX10AB27G to MIT, NNX08AO50G to Williams College, and NNH08AI17I to the USNO from NASA's Planetary Astronomy Division. The 0.75-m ATOM (Automatic Telescope for Optical Monitoring) light curve was obtained with the generous assistance of the HESS-project staff, arranged by Stefan Wagner and Marcus Hauser of the University of Heidelberg. The 0.45-m Goto telescope at Cerro Calán National Astronomical Observatory, Universidad de Chile, was donated by the Government of Japan. PROMPT (Panchromatic Robotic Optical Monitoring and Polarimetry Telescopes) observations at Cerro Tololo were made possible by the Robert Martin Ayers Science Fund. Student participation was supported in part by NSF's REU program and NASA's Massachusetts Space Grant.

  9. Constructing an Atmospheric Methane Budget Using 13CH3D and CH2D2 in Sources and Sinks

    NASA Astrophysics Data System (ADS)

    Haghnegahdar, M. A.; Schauble, E. A.; Young, E. D.

    2015-12-01

    We develop a theoretical model using relative abundances and fractionations of 13CH3D and CH2D2, the doubly substituted mass-18 isotopologues of methane, to quantitatively track the sources and the sinks of atmospheric methane. The goal is a better determination of the methane budget in the atmosphere. Different methane sources have different isotope ratios because of variations in substrates, formation reactions, and temperatures. Isotope ratio measurements will provide useful constraints on source components and sink processes. However, bulk isotope ratios alone are unlikely to be diagnostic because of mixing of sources. Using recently published budgets (Whiticar and Schaefer 2007) and estimates of equilibration temperatures of various methane sources (Stolper et al., 2014; Wang et al., 2015), including an assumption that biogenic methane sources are near-stochastic (Wang et al., 2015), we estimated the abundances in air of singly- and doubly-substituted isotopologues in terms of both bulk ratios and deviations from the stochastic distributions of multiply-substituted species. δ13CH3D and δCH2D2 for the total atmospheric sources are predicted to be -493‰ and -330‰, whereas Δ13CH3D, and ΔCH2D2, enrichments relative to stochastic, are predicted to be +4.7‰ and +21.5‰. The composition of atmospheric methane will also be influenced by sink reactions. The main sink reactions with OH• and Cl• have been modeled with first-principles transition state theory, using simplified corrections for tunneling (Wigner 1932). Our model predicts that the main sink reactions in the atmosphere generate distinct signatures of lower Δ13CH3D and ΔCH2D2 relative to the source composition, while at the same time increasing δ13CH3D and δCH2D2. Measurements of both Δ13CH3D and ΔCH2D2 are now possible with the new large-geometry gas-source mass spectrometer at UCLA permitting testing of these predictions.

  10. 3D Mapping of plasma effective areas via detection of cancer cell damage induced by atmospheric pressure plasma jets

    NASA Astrophysics Data System (ADS)

    Han, Xu; Liu, Yueing; Stack, M. Sharon; Ptasinska, Sylwia

    2014-12-01

    In the present study, a nitrogen atmospheric pressure plasma jet (APPJ) was used for irradiation of oral cancer cells. Since cancer cells are very susceptible to plasma treatment, they can be used as a tool for detection of APPJ-effective areas, which extended much further than the visible part of the APPJ. An immunofluorescence assay was used for DNA damage identification, visualization and quantification. Thus, the effective damage area and damage level were determined and plotted as 3D images.

  11. Atmospheric Nitrogen Trifluoride: Optimized emission estimates using 2-D and 3-D Chemical Transport Models from 1973-2008

    NASA Astrophysics Data System (ADS)

    Ivy, D. J.; Rigby, M. L.; Prinn, R. G.; Muhle, J.; Weiss, R. F.

    2009-12-01

    We present optimized annual global emissions from 1973-2008 of nitrogen trifluoride (NF3), a powerful greenhouse gas which is not currently regulated by the Kyoto Protocol. In the past few decades, NF3 production has dramatically increased due to its usage in the semiconductor industry. Emissions were estimated through the 'pulse-method' discrete Kalman filter using both a simple, flexible 2-D 12-box model used in the Advanced Global Atmospheric Gases Experiment (AGAGE) network and the Model for Ozone and Related Tracers (MOZART v4.5), a full 3-D atmospheric chemistry model. No official audited reports of industrial NF3 emissions are available, and with limited information on production, a priori emissions were estimated using both a bottom-up and top-down approach with two different spatial patterns based on semiconductor perfluorocarbon (PFC) emissions from the Emission Database for Global Atmospheric Research (EDGAR v3.2) and Semiconductor Industry Association sales information. Both spatial patterns used in the models gave consistent results, showing the robustness of the estimated global emissions. Differences between estimates using the 2-D and 3-D models can be attributed to transport rates and resolution differences. Additionally, new NF3 industry production and market information is presented. Emission estimates from both the 2-D and 3-D models suggest that either the assumed industry release rate of NF3 or industry production information is still underestimated.

  12. Atmospheric nonequilibrium mini-plasma jet created by a 3D printer

    SciTech Connect

    Takamatsu, Toshihiro; Kawano, Hiroaki; Miyahara, Hidekazu; Okino, Akitoshi; Azuma, Takeshi

    2015-07-15

    In this study, a small-sized plasma jet source with a 3.7 mm head diameter was created via a 3D printer. The jet’s emission properties and OH radical concentrations (generated by argon, helium, and nitrogen plasmas) were investigated using optical emission spectrometry (OES) and electron spin resonance (ESR). As such, for OES, each individual gas plasma propagates emission lines that derive from gases and ambient air inserted into the measurement system. For the case of ESR, a spin adduct of the OH radical is typically observed for all gas plasma treatment scenarios with a 10 s treatment by helium plasma generating the largest amount of OH radicals at 110 μM. Therefore, it was confirmed that a plasma jet source made by a 3D printer can generate stable plasmas using each of the aforementioned three gases.

  13. Quiescent Galaxies in the 3D-HST Survey: Spectroscopic Confirmation of a Large Number of Galaxies With Relatively Old Stellar Populations at z Approx. 2

    NASA Technical Reports Server (NTRS)

    Tease, Katherine Whitaker; vanDokkum, Pieter G.; Brammer, Gabriel; Momcheva, Ivelina; Skelton, Rosalind; Franx, Marijin; Kriek, Mariska; Labbe, Ivo; Fumagalli, Mattia; Lundgren, Britt F.; Nelson, Erica J.; Patel, Shannon G.; Rix, Hans-Walter

    2013-01-01

    Quiescent galaxies at z approx. 2 have been identified in large numbers based on rest-frame colors, but only a small number of these galaxies have been spectroscopically confirmed to show that their rest-frame optical spectra show either strong Balmer or metal absorption lines. Here, we median stack the rest-frame optical spectra for 171 photometrically quiescent galaxies at 1.4 < z < 2.2 from the 3D-HST grism survey. In addition to H (4861 ),we unambiguously identify metal absorption lines in the stacked spectrum, including the G band (4304 ),Mgi (5175 ), and Na i (5894 ). This finding demonstrates that galaxies with relatively old stellar populations already existed when the universe was approx. 3 Gyr old, and that rest-frame color selection techniques can efficiently select them. We find an average age of 1.3+0.10.3 Gyr when fitting a simple stellar population to the entire stack. We confirm our previous result from medium-band photometry that the stellar age varies with the colors of quiescent galaxies: the reddest 80 of galaxies are dominated by metal lines and have a relatively old mean age of 1.6+0.50.4 Gyr, whereas the bluest (and brightest) galaxies have strong Balmer lines and a spectroscopic age of 0.9+0.20.1 Gyr. Although the spectrum is dominated by an evolved stellar population, we also find [O iii] and H emission. Interestingly, this emission is more centrally concentrated than the continuum with LOiii = 1.7+/- 0.3 x 10(exp 40) erg/s, indicating residual central star formation or nuclear activity.

  14. Quiescent Galaxies in the 3D-HST Survey: Spectroscopic Confirmation of a Large Number of Galaxies with Relatively Old Stellar Populations at Z approx. 2

    NASA Technical Reports Server (NTRS)

    Tease, Katherine Whitaker; VanDokkum, Pieter G.; Brammer, Gabriel; Momcheva, Ivelina G.; Skelton, Rosalind; Franx, Marijn; Kriek, Mariska; Labbe, Ivo; Fumagalli, Mattia; Lundgren, Britt F.; Nelson, Erica J.; Patel, Shannon G.; Rix, Hans-Walter

    2013-01-01

    Quiescent galaxies at zeta approximately 2 have been identified in large numbers based on rest-frame colors, but only a small number of these galaxies have been spectroscopically confirmed to show that their rest-frame optical spectra show either strong Balmer or metal absorption lines. Here, we median stack the rest-frame optical spectra for 171 photometrically quiescent galaxies at 1.4 less than z less than 2.2 from the 3D-HST grism survey. In addition to H(Beta) (lambda 4861 Angstroms), we unambiguously identify metal absorption lines in the stacked spectrum, including the G band (lambda 4304 Angstroms), Mg I (lambda 5175 Angstroms), and Na i (lambda 5894 Angstroms). This finding demonstrates that galaxies with relatively old stellar populations already existed when the universe was approximately 3 Gyr old, and that rest-frame color selection techniques can efficiently select them. We find an average age of 1.3(+0.1/-0.3) Gyr when fitting a simple stellar population to the entire stack. We confirm our previous result from medium-band photometry that the stellar age varies with the colors of quiescent galaxies: the reddest 80% of galaxies are dominated by metal lines and have a relatively old mean age of 1.6(+0.5/-0.4) Gyr, whereas the bluest (and brightest) galaxies have strong Balmer lines and a spectroscopic age of 0.9(+0.2/-0.1) Gyr. Although the spectrum is dominated by an evolved stellar population, we also find [O III] and Hß emission. Interestingly, this emission is more centrally concentrated than the continuum with L(sub OIII) = 1.7 +/- 0.3 × 10(exp 40 erg s-1, indicating residual central star formation or nuclear activity.

  15. QUIESCENT GALAXIES IN THE 3D-HST SURVEY: SPECTROSCOPIC CONFIRMATION OF A LARGE NUMBER OF GALAXIES WITH RELATIVELY OLD STELLAR POPULATIONS AT z {approx} 2

    SciTech Connect

    Whitaker, Katherine E.; Van Dokkum, Pieter G.; Momcheva, Ivelina G.; Skelton, Rosalind; Nelson, Erica J.; Brammer, Gabriel; Franx, Marijn; Labbe, Ivo; Fumagalli, Mattia; Patel, Shannon G.; Kriek, Mariska; Lundgren, Britt F.; Rix, Hans-Walter

    2013-06-20

    Quiescent galaxies at z {approx} 2 have been identified in large numbers based on rest-frame colors, but only a small number of these galaxies have been spectroscopically confirmed to show that their rest-frame optical spectra show either strong Balmer or metal absorption lines. Here, we median stack the rest-frame optical spectra for 171 photometrically quiescent galaxies at 1.4 < z < 2.2 from the 3D-HST grism survey. In addition to H{beta} ({lambda}4861 A), we unambiguously identify metal absorption lines in the stacked spectrum, including the G band ({lambda}4304 A), Mg I ({lambda}5175 A), and Na I ({lambda}5894 A). This finding demonstrates that galaxies with relatively old stellar populations already existed when the universe was {approx}3 Gyr old, and that rest-frame color selection techniques can efficiently select them. We find an average age of 1.3{sup +0.1}{sub -0.3} Gyr when fitting a simple stellar population to the entire stack. We confirm our previous result from medium-band photometry that the stellar age varies with the colors of quiescent galaxies: the reddest 80% of galaxies are dominated by metal lines and have a relatively old mean age of 1.6{sup +0.5}{sub -0.4} Gyr, whereas the bluest (and brightest) galaxies have strong Balmer lines and a spectroscopic age of 0.9{sup +0.2}{sub -0.1} Gyr. Although the spectrum is dominated by an evolved stellar population, we also find [O III] and H{beta} emission. Interestingly, this emission is more centrally concentrated than the continuum with L{sub OIII}=1.7{+-}0.3 Multiplication-Sign 10{sup 40} erg s{sup -1}, indicating residual central star formation or nuclear activity.

  16. Pluto's atmosphere from stellar occultations in 2012 and 2013

    NASA Astrophysics Data System (ADS)

    Dias-Oliveira, Alex; Sicardy, Bruno; Lellouch, Emmanuel; Vieira-Martins, Roberto; Assafin, Marcelo; Ignácio Bueno Camargo, Júlio; Braga-Ribas, Felipe; Gomes-Júnior, Altair; Bendetti-Rossi, Gustavo; Colas, François; Decock, Alice; Doressoundiram, Alain; Dumas, Christophe; Emílio, Marcelo; Fabrega Polleri, Joaquin; Gil-Hutton, Ricardo; Gillon, Michael; Girard, Julien; Hau, George; Ivanov, Valentin; Jehin, Emmanuel; Lecacheux, Jean; Leiva, Rodrigo; Lopez-Sisterna, Cecília; Mancini, Luigi; Manfroid, Jean; Maury, Alain; Meza, Erick; Morales, Nicolas; Nagy, Leslie; Opitom, Cyrielle; Ortiz, José Luiz; Pollock, Joe; Roques, Françoise; Snodgrass, Colin; François Soulier, Jean; Thirouin, Audrey; Vanzi, Leonardo; Widemann, Thomas; Reichart, Daniel; LaCluyze, Aaron; Haislip, Joshua B.; Ivarsen, Kevin; Dominik, Martin; Jørgensen, Uffe; Skottfelt, Jesper

    2015-11-01

    We present results from two Pluto stellar occultations observed on 18 July 2012 and 04 May 2013, and monitored respectively from five and six sites in South America. Both campaigns involved large telescopes (including the 8.2-m VLT at ESO/Paranal). The high SNR ratios and multi-chord coverage provide amoung the best Pluto atmospheric profiles ever obtained from the ground.We show that a spherically symmetric, clear (no-haze) and pure N2 atmosphere with a unique temperature profile satisfactorily fits the twelve lightcurves provided by the two events. We find, however, a small but significant increase of pressure of 6% (6-sigma level) between the two dates, with values of 2.16 ± 0.2 and 2.30 ± 0.01 μbar at the reference radius 1275 km, respectively.We provide atmospheric constrains between 1190 km and 1450 km from Pluto's center, and we determine the temperature profile with accuracy of a few km in vertical scale. Our model shows a stratosphere with strong positive gradient between 1190 km (at 36 K, 11 μbar) and r =1215 km (6.0 μbar), where a temperature maximum of 110 K is reached. Above it is a mesosphere with negative thermal gradient of -0.2 K/km up to 1,390 km (0.25 μbar), at which point, the mesosphere connects itself to a more isothermal upper branch at 81 K. This profile provides (assuming no troposphere) a Pluto surface radius of 1190 ± 5 km, consistent with preliminary values obtained by New Horizons. Currently measured CO abundances are too low to explain the negative mesospheric thermal gradient. We explore the possibility of an HCN (recently detected by ALMA) cooling. This model, however, requires largely supersaturated HCN. Zonal winds and vertical compositional variations of the atmosphere are also unable to explain the observed mesospheric trend.These events are the last useful ground-based occultations recorded before the 29 June 2015 occultation observed from Australia and New Zealand, and before the NASA's New Horizons flyby of July 2015

  17. Characterizing and Understanding Large-Scale Wave Propagation in the Atmosphere through Graphs of 3D Information Flow

    NASA Astrophysics Data System (ADS)

    Deng, Y.; Ebert-Uphoff, I.; Chen, J.

    2015-12-01

    Causal discovery seeks to discover potential cause-effect relationships from observational data. Here we adopt the idea of interpreting large-scale atmospheric dynamical processes, particularly those tied to propagation of large-scale waves, as information flow around the globe, which can then be calculated using causal discovery methods. We apply a well-established causal discovery algorithm - based on constraint-based structure learning of probabilistic graphical models - toward 51 years of 6-hourly, atmospheric isobaric-level geopotential height data to construct the first-ever graphs of 3D information flow in the atmosphere. These graphs are created globally for different seasons and their connection to phase/energy propagation of atmospheric waves are investigated. Specifically, we examine the information flows 1) in the topical region that represent horizontal and vertical propagations of Kelvin and Rossby-gravity waves whose associated momentum transfer are known to play a key role in the Quasi-Biennial Oscillation (QBO), and 2) in the northern extratropics that represent propagations of planetary-scale waves whose heat/momentum fluxes are responsible for vacillations in the polar stratospheric vortex and occurrences of extreme events such as the stratospheric sudden warming. The sensitivity of the constructed graphs of 3D information flow to data resolution and pre-processing methods (e.g., spatial and temporal filtering) will be discussed.

  18. Non-LTE modeling of cold stellar atmospheres

    NASA Astrophysics Data System (ADS)

    Feautrier, N.; Spielfiedel, A.; Guitou, M.; Belyaev, A. K.

    2014-12-01

    Non-LTE modelisation of stellar atmospheres requires an accurate knowledge of collisional rate coefficients (mainly with H atoms) that compete with radiative rates to populate the atomic levels. In the framework of the SAM-GAIA project we carry out an interdisciplinary work combining quantum chemistry and collision physics. Present studies concern collisional excitation of MgI, CaI and OI by H-atoms. Considering the Mg-H case, the resulting cross sections and rate coefficients point out the sensitivity of the results with the quantum chemistry data. The calculations show that the usual approximate Drawin formula leads to errors by factors up to 10^5. As was already found in Li+H and Na+H collisions, excitation processes were found of the same order of magnitude as charge transfer processes. However, unlike Li and Na, Mg has different spin terms, singlet and triplet, leading both to doublet molecular MgH electronic states. Collisional rates between spin-allowed and optically spin-forbidden atomic states are found to be of the same order of magnitude although optically spin-forbidden states are only collisionally coupled. Thus, we may expect consequences on non-LTE calculations.

  19. Capturing atmospheric effects on 3D millimeter wave radar propagation patterns

    NASA Astrophysics Data System (ADS)

    Cook, Richard D.; Fiorino, Steven T.; Keefer, Kevin J.; Stringer, Jeremy

    2016-05-01

    Traditional radar propagation modeling is done using a path transmittance with little to no input for weather and atmospheric conditions. As radar advances into the millimeter wave (MMW) regime, atmospheric effects such as attenuation and refraction become more pronounced than at traditional radar wavelengths. The DoD High Energy Laser Joint Technology Offices High Energy Laser End-to-End Operational Simulation (HELEEOS) in combination with the Laser Environmental Effects Definition and Reference (LEEDR) code have shown great promise simulating atmospheric effects on laser propagation. Indeed, the LEEDR radiative transfer code has been validated in the UV through RF. Our research attempts to apply these models to characterize the far field radar pattern in three dimensions as a signal propagates from an antenna towards a point in space. Furthermore, we do so using realistic three dimensional atmospheric profiles. The results from these simulations are compared to those from traditional radar propagation software packages. In summary, a fast running method has been investigated which can be incorporated into computational models to enhance understanding and prediction of MMW propagation through various atmospheric and weather conditions.

  20. Revolutionising incoherent scatter science with EISCAT_3D: A European three-dimensional imaging radar for atmospheric and geospace research

    NASA Astrophysics Data System (ADS)

    Turunen, Esa; McCrea, Ian; Kosch, Mike

    2010-05-01

    EISCAT_3D will be Europe's next-generation radar for the study of the high-latitude atmosphere and geospace, located in northern Fenno-Scandinavia, with capabilities going well beyond anything currently available to the international research community. The facility will consist of several very large active phased-array antenna transmitters/receivers, and multiple passive sites located in three countries. Depending on the available funding, EISCAT_3D will be comprised of tens of thousands, up to more than 100 000, individual antenna elements. EISCAT_3D combines several key attributes which have never before been available together in a single radar, such as volumetric imaging and tracking, aperture synthesis imaging, multistatic configuration, improved sensitivity and transmitter flexibility. The use of advanced beam-forming technology allows the beam direction to be switched in milliseconds, rather than the minutes which it can take to re-position dish-based radars. This allows very wide spatial coverage to be obtained, by interleaving multiple beam directions to carry out quasi-simultaneous volumetric imaging. It also allows objects such as satellites and space debris to be tracked across the sky. At the passive sites, the design allows for at least five simultaneous beams at full bandwidth, rising to over twenty beams if the bandwidth is limited to the ion line, allowing the whole range of the transmitted beam to be imaged from each passive site, using holographic radar techniques. EISCAT_3D has a modular configuration, which allows an active array to be split into smaller elements to be used for aperture synthesis imaging. The result will be an entirely new data product, consisting of range-dependent images of small sub-beamwidth scale structures, with sizes down to 20 m. EISCAT_3D will be the first phased array incoherent scatter radar to use a multistatic configuration. A minimum of five radar sites, consisting of two pairs located around 120 km and 250 km

  1. Identification and characterisation of small-scale heating events in the solar atmosphere from 3D MHD simulations

    NASA Astrophysics Data System (ADS)

    Guerreiro, Nuno; Haberreiter, Margit; Hansteen, Viggo; Schmutz, Werner

    2015-04-01

    We study the properties of the small-scale heating events in the solar atmosphere in the nano flare and micro flare energy scale using 3D MHD simulations. We put forward a method to identify and track the heating events in time to study their life times, frequency distributions and spectral signatures. These results aim to better understand the observations from future space missions such as the EUI and SPICE instruments onboard Solar Orbiter and improve our knowledge of the role of small-scale heating events in the heating of the corona.

  2. Soil-plant-atmosphere water balance via time-lapse 3D Electrical Resistivity Tomography and Eddy covariance measurements

    NASA Astrophysics Data System (ADS)

    Boaga, J.; Consoli, S.; Papa, R.; Cassiani, G.

    2013-12-01

    The understanding of mass and energy exchanges between soil, plants and atmosphere (SPA) is a key component for the characterization of the critical zone, housing a number of important mechanisms controlling hydrology, biota and climate. This understanding requires reliable methods for the quantification of these mass and energy exchanges encompassing possibly all three major components, i.e. soil, plants and atmosphere. In this work we present an attempt to characterize jointly the soil state changes and the energy and mass fluxes above a heterogeneous canopy, both mediated by the plant activity from roots to foliage. The experiments have been conducted within an orange orchard located in Eastern Sicily (Italy), characterized by the typical Mediterranean semi-arid climate. The subsoil dynamics, particularly influenced by irrigation and root uptake, has been characterized using a time-lapse non-invasive 3D micro-electrical tomography (ERT) setup. We designed, built and installed a 3D electrical tomography apparatus consisting of 48 buried electrodes on 4 instrumented micro boreholes plus 24 mini-electrodes on the surface spaced 0.1 m on a square grid. During the monitoring, we collected repeated ERT and TDR soil moisture measurements, as well as laboratory characterization of the soil electrical properties as a function of moisture content and pore water electrical conductivity. The results demonstrate that 3D micro-ERT is capable of characterizing subsoil conditions and monitoring root zone activities, especially in terms of root zone suction regions. In terms of energy and mass fluxes, we used the Eddy Covariance (EC) technique to directly measure both the sensible and latent heat fluxes exchanged between the plant-atmosphere continuum. The EC method was integrated with the surface energy balance of the SPA system. The joint availability of state changes and fluxes allows for a quantitative analysis of mass balance in the soil-plant-atmosphere system. The

  3. "SMART": A Compact and Handy FORTRAN Code for the Physics of Stellar Atmospheres

    NASA Astrophysics Data System (ADS)

    Sapar, A.; Poolamäe, R.

    2003-01-01

    a special case, using duly chosen pixels on the stellar disk, the spectrum of rotating star can be computed. No instrumental broadening has been incorporated in the code of SMART. To facilitate study of stellar spectra, a GUI (Graphical User Interface) with selection of labels by ions has been compiled to study the spectral lines of different elements and ions in the computed emergent flux. An amazing feature of SMART is that its code is very short: it occupies only 4 two-sided two-column A4 sheets in landscape format. In addition, if well commented, it is quite easily readable and understandable. We have used the tactics of writing the comments on the right-side margin (columns starting from 73). Such short code has been composed widely using the unified input physics (for example the ionisation cross-sections for bound-free transitions and the electron and ion collision rates). As current restriction to the application area of the present version of the SMART is that molecules are since ignored. Thus, it can be used only for luke and hot stellar atmospheres. In the computer code we have tried to avoid bulky often over-optimised methods, primarily meant to spare the time of computations. For instance, we compute the continuous absorption coefficient at every wavelength. Nevertheless, during an hour by the personal computer in our disposal AMD Athlon XP 1700+, 512MB DDRAM) a stellar spectrum with spectral step resolution λ / dλ = 3D100,000 for spectral interval 700 -- 30,000 Å is computed. The model input data and the line data used by us are both the ones computed and compiled by R. Kurucz. In order to follow presence and representability of quantum states and to enumerate them for NLTE studies a C++ code, transforming the needed data to the LATEX version, has been compiled. Thus we have composed a quantum state list for all neutrals and ions in the Kurucz file 'gfhyperall.dat'. The list enables more adequately to compose the concept of super-states, including

  4. A 3-D RBF-FD elliptic solver for irregular boundaries: modeling the atmospheric global electric circuit with topography

    NASA Astrophysics Data System (ADS)

    Bayona, V.; Flyer, N.; Lucas, G. M.; Baumgaertner, A. J. G.

    2015-04-01

    A numerical model based on Radial Basis Function-generated Finite Differences (RBF-FD) is developed for simulating the Global Electric Circuit (GEC) within the Earth's atmosphere, represented by a 3-D variable coefficient linear elliptic PDE in a spherically-shaped volume with the lower boundary being the Earth's topography and the upper boundary a sphere at 60 km. To our knowledge, this is (1) the first numerical model of the GEC to combine the Earth's topography with directly approximating the differential operators in 3-D space, and related to this (2) the first RBF-FD method to use irregular 3-D stencils for discretization to handle the topography. It benefits from the mesh-free nature of RBF-FD, which is especially suitable for modeling high-dimensional problems with irregular boundaries. The RBF-FD elliptic solver proposed here makes no limiting assumptions on the spatial variability of the coefficients in the PDE (i.e. the conductivity profile), the right hand side forcing term of the PDE (i.e. distribution of current sources) or the geometry of the lower boundary.

  5. The ATLAS3D project - XXI. Correlations between gradients of local escape velocity and stellar populations in early-type galaxies

    NASA Astrophysics Data System (ADS)

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

    2013-07-01

    We explore the connection between the local escape velocity, Vesc, and the stellar population properties in the ATLAS3D survey, a complete, volume-limited sample of nearby early-type galaxies. We make use of ugriz photometry to construct Multi-Gaussian Expansion models of the surface brightnesses of our galaxies. We are able to fit the full range of surface brightness profiles found in our sample, and in addition we reproduce the results of state-of-the-art photometry in the literature with residuals of 0.04 mag. We utilize these photometric models and SAURON integral-field spectroscopy, combined with Jeans dynamical modelling, to determine the local Vesc derived from the surface brightness. We find that the local Vesc is tightly correlated with the Mg b and Fe5015 line strengths and optical colours, and anti-correlated with the Hβ line strength. In the case of the Mg b and colour-Vesc relations we find that the relation within individual galaxies follows the global relation between different galaxies. We intentionally ignored any uncertain contribution due to dark matter since we are seeking an empirical description of stellar population gradients in early-type galaxies that is ideal for quantitative comparison with model predictions. We also make use of single stellar population (SSP) modelling to transform our line strength index measurements into the SSP-equivalent parameters age (t), metallicity ([Z/H]) and α-enhancement [α/Fe]. The residuals from the relation are correlated with age, [α/Fe], molecular gas mass and local environmental density. We identify a population of galaxies that occur only at low Vesc that exhibit negative gradients in the Mg b- and Colour-Vesc relations. These galaxies typically have young central stellar populations and contain significant amounts of molecular gas and dust. Combining these results with N-body simulations of binary mergers we use the Mg b-Vesc relation to constrain the possible number of dry mergers experienced by

  6. COOP 3D ARPA Experiment 109 National Center for Atmospheric Research

    NASA Technical Reports Server (NTRS)

    1998-01-01

    Coupled atmospheric and hydrodynamic forecast models were executed on the supercomputing resources of the National Center for Atmospheric Research (NCAR) in Boulder, Colorado and the Ohio Supercomputing Center (OSC)in Columbus, Ohio. respectively. The interoperation of the forecast models on these geographically diverse, high performance Cray platforms required the transfer of large three dimensional data sets at very high information rates. High capacity, terrestrial fiber optic transmission system technologies were integrated with those of an experimental high speed communications satellite in Geosynchronous Earth Orbit (GEO) to test the integration of the two systems. Operation over a spacecraft in GEO orbit required modification of the standard configuration of legacy data communications protocols to facilitate their ability to perform efficiently in the changing environment characteristic of a hybrid network. The success of this performance tuning enabled the use of such an architecture to facilitate high data rate, fiber optic quality data communications between high performance systems not accessible to standard terrestrial fiber transmission systems. Thus obviating the performance degradation often found in contemporary earth/satellite hybrids.

  7. 3D magnetic field configuration of small-scale reconnection events in the solar plasma atmosphere

    SciTech Connect

    Shimizu, T.

    2015-10-15

    The outer solar atmosphere, i.e., the corona and the chromosphere, is replete with small energy-release events, which are accompanied by transient brightening and jet-like ejections. These events are considered to be magnetic reconnection events in the solar plasma, and their dynamics have been studied using recent advanced observations from the Hinode spacecraft and other observatories in space and on the ground. These events occur at different locations in the solar atmosphere and vary in their morphology and amount of the released energy. The magnetic field configurations of these reconnection events are inferred based on observations of magnetic fields at the photospheric level. Observations suggest that these magnetic configurations can be classified into two groups. In the first group, two anti-parallel magnetic fields reconnect to each other, yielding a 2D emerging flux configuration. In the second group, helical or twisted magnetic flux tubes are parallel or at a relative angle to each other. Reconnection can occur only between anti-parallel components of the magnetic flux tubes and may be referred to as component reconnection. The latter configuration type may be more important for the larger class of small-scale reconnection events. The two types of magnetic configurations can be compared to counter-helicity and co-helicity configurations, respectively, in laboratory plasma collision experiments.

  8. Vertical Scan (V-SCAN) for 3-D Grid Adaptive Mesh Refinement for an atmospheric Model Dynamical Core

    NASA Astrophysics Data System (ADS)

    Andronova, N. G.; Vandenberg, D.; Oehmke, R.; Stout, Q. F.; Penner, J. E.

    2009-12-01

    One of the major building blocks of a rigorous representation of cloud evolution in global atmospheric models is a parallel adaptive grid MPI-based communication library (an Adaptive Blocks for Locally Cartesian Topologies library -- ABLCarT), which manages the block-structured data layout, handles ghost cell updates among neighboring blocks and splits a block as refinements occur. The library has several modules that provide a layer of abstraction for adaptive refinement: blocks, which contain individual cells of user data; shells - the global geometry for the problem, including a sphere, reduced sphere, and now a 3D sphere; a load balancer for placement of blocks onto processors; and a communication support layer which encapsulates all data movement. A major performance concern with adaptive mesh refinement is how to represent calculations that have need to be sequenced in a particular order in a direction, such as calculating integrals along a specific path (e.g. atmospheric pressure or geopotential in the vertical dimension). This concern is compounded if the blocks have varying levels of refinement, or are scattered across different processors, as can be the case in parallel computing. In this paper we describe an implementation in ABLCarT of a vertical scan operation, which allows computing along vertical paths in the correct order across blocks transparent to their resolution and processor location. We test this functionality on a 2D and a 3D advection problem, which tests the performance of the model’s dynamics (transport) and physics (sources and sinks) for different model resolutions needed for inclusion of cloud formation.

  9. 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.

  10. 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.

  11. 3D modelling of the early martian climate under a denser CO2 atmosphere: Temperatures and CO2 ice clouds

    NASA Astrophysics Data System (ADS)

    Forget, F.; Wordsworth, R.; Millour, E.; Madeleine, J.-B.; Kerber, L.; Leconte, J.; Marcq, E.; Haberle, R. M.

    2013-01-01

    On the basis of geological evidence, it is often stated that the early martian climate was warm enough for liquid water to flow on the surface thanks to the greenhouse effect of a thick atmosphere. We present 3D global climate simulations of the early martian climate performed assuming a faint young Sun and a CO2 atmosphere with surface pressure between 0.1 and 7 bars. The model includes a detailed radiative transfer model using revised CO2 gas collision induced absorption properties, and a parameterisation of the CO2 ice cloud microphysical and radiative properties. A wide range of possible climates is explored using various values of obliquities, orbital parameters, cloud microphysic parameters, atmospheric dust loading, and surface properties. Unlike on present day Mars, for pressures higher than a fraction of a bar, surface temperatures vary with altitude because of the adiabatic cooling and warming of the atmosphere when it moves vertically. In most simulations, CO2 ice clouds cover a major part of the planet. Previous studies had suggested that they could have warmed the planet thanks to their scattering greenhouse effect. However, even assuming parameters that maximize this effect, it does not exceed +15 K. Combined with the revised CO2 spectroscopy and the impact of surface CO2 ice on the planetary albedo, we find that a CO2 atmosphere could not have raised the annual mean temperature above 0 °C anywhere on the planet. The collapse of the atmosphere into permanent CO2 ice caps is predicted for pressures higher than 3 bar, or conversely at pressure lower than 1 bar if the obliquity is low enough. Summertime diurnal mean surface temperatures above 0 °C (a condition which could have allowed rivers and lakes to form) are predicted for obliquity larger than 40° at high latitudes but not in locations where most valley networks or layered sedimentary units are observed. In the absence of other warming mechanisms, our climate model results are thus consistent

  12. The Intercomparison of 3D Radiation Codes (I3RC): Showcasing Mathematical and Computational Physics in a Critical Atmospheric Application

    NASA Astrophysics Data System (ADS)

    Davis, A. B.; Cahalan, R. F.

    2001-05-01

    The Intercomparison of 3D Radiation Codes (I3RC) is an on-going initiative involving an international group of over 30 researchers engaged in the numerical modeling of three-dimensional radiative transfer as applied to clouds. Because of their strong variability and extreme opacity, clouds are indeed a major source of uncertainty in the Earth's local radiation budget (at GCM grid scales). Also 3D effects (at satellite pixel scales) invalidate the standard plane-parallel assumption made in the routine of cloud-property remote sensing at NASA and NOAA. Accordingly, the test-cases used in I3RC are based on inputs and outputs which relate to cloud effects in atmospheric heating rates and in real-world remote sensing geometries. The main objectives of I3RC are to (1) enable participants to improve their models, (2) publish results as a community, (3) archive source code, and (4) educate. We will survey the status of I3RC and its plans for the near future with a special emphasis on the mathematical models and computational approaches. We will also describe some of the prime applications of I3RC's efforts in climate models, cloud-resolving models, and remote-sensing observations of clouds, or that of the surface in their presence. In all these application areas, computational efficiency is the main concern and not accuracy. One of I3RC's main goals is to document the performance of as wide a variety as possible of three-dimensional radiative transfer models for a small but representative number of ``cases.'' However, it is dominated by modelers working at the level of linear transport theory (i.e., they solve the radiative transfer equation) and an overwhelming majority of these participants use slow-but-robust Monte Carlo techniques. This means that only a small portion of the efficiency vs. accuracy vs. flexibility domain is currently populated by I3RC participants. To balance this natural clustering the present authors have organized a systematic outreach towards

  13. Temperature distribution in a stellar atmosphere diagnostic basis

    NASA Technical Reports Server (NTRS)

    Jefferies, J. T.; Morrison, N. D.

    1973-01-01

    A stellar chromosphere is considered a region where the temperature increases outward and where the temperature structure of the gas controls the shape of the spectral lines. It is shown that lines which have collision-dominated source sink terms, like the Ca(+) and Mg(+) H and K lines, can be used to obtain the distribution of temperature with height from observed line profiles. Intrinsic emission lines and geometrical emission lines are found in spectral regions where the continuum is depressed. In visual regions, where the continuum is not depressed, emission core in absorption lines are attributed to reflections of intrinsic emission lines.

  14. Implementation of a 3D-Var system for atmospheric profiling data assimilation into the RAMS model: initial results

    NASA Astrophysics Data System (ADS)

    Federico, S.

    2013-12-01

    This paper presents the current status of development of a three-dimensional variational data assimilation system (3D-Var). The system can be used with different numerical weather prediction models, but it is mainly designed to be coupled with the Regional Atmospheric Modelling System (RAMS). Analyses are given for the following parameters: zonal and meridional wind components, temperature, relative humidity, and geopotential height. Important features of the data assimilation system are the use of incremental formulation of the cost function, and the representation of the background error by recursive filters and the eigenmodes of the vertical component of the background error covariance matrix. This matrix is estimated by the National Meteorological Center (NMC) method. The data assimilation and forecasting system is applied to the real context of atmospheric profiling data assimilation, and in particular to the short-term wind prediction. The analyses are produced at 20 km horizontal resolution over central Europe and extend over the whole troposphere. Assimilated data are vertical soundings of wind, temperature, and relative humidity from radiosondes, and wind measurements of the European wind profiler network. Results show the validity of the analyses because they are closer to the observations (lower root mean square error (RMSE)) compared to the background (higher RMSE), and the differences of the RMSEs are in agreement with the data assimilation settings. To quantify the impact of improved initial conditions on the short-term forecast, the analyses are used as initial conditions of three-hours forecasts of the RAMS model. In particular two sets of forecasts are produced: (a) the first uses the ECMWF analysis/forecast cycle as initial and boundary conditions; (b) the second uses the analyses produced by the 3D-Var as initial conditions, then it is driven by the ECMWF forecast. The improvement is quantified by considering the horizontal components of the wind

  15. On the parameterization of 1D vertical mixing in planetary atmospheres: insights from 2D and 3D simulations

    NASA Astrophysics Data System (ADS)

    Zhang, Xi; Showman, Adam P.

    2015-11-01

    Most of the current atmospheric chemistry models for planets (e.g., Krasnopolsky & Parshev 1981; Yung & Demore 1982; Yung, Allen & Pinto 1984; Lavvas et al. 2008; Zhang et al. 2012) and exoplanets (e.g., Line, Liang & Yung 2010; Moses et al. 2011; Hu & Seager 2014) adopt a one-dimensional (1D) chemical-diffusion approach in the vertical coordinate. Although only a crude approximation, these 1D models have succeeded in explaining the global-averaged vertical profiles of many chemical species in observations. One of the important assumptions of these models is that all chemical species are transported via the same eddy diffusion profile--that is, the assumption is made that the eddy diffusivity is a fundamental property of the dynamics alone, and does not depend on the chemistry. Here we show that, as also noticed in the Earth community (e.g., Holton 1986), this “homogenous eddy diffusion” assumption generally breaks down. We first show analytically why the 1D eddy diffusivity must generally depend both on the horizontal eddy mixing and the chemical lifetime of the species. This implies that the long-lived species and short-lived chemical species will generally exhibit different eddy diffusion profiles, even in a given atmosphere with identical dynamics. Next, we present tracer-transport simulations in a 2D chemical-diffusion-advection model (Shia et al. 1989; Zhang, Shia & Yung 2013) and a 3D general circulation model (MITgcm, e.g., Liu & Showman 2013), for both rapid-rotating planets and tidally-locked exoplanets, to further explore the effect of chemical timescales on the eddy diffusivity. From the 2D and 3D simulation outputs, we derive effective 1D eddy diffusivity profiles for chemical tracers exhibiting a range of chemical timescales. We show that the derived eddy diffusivity can depend strongly on the horizontal eddy mixing and chemistry, although the dependences are more complex than the analytic model predicts. Overall, these results suggest that

  16. Model estimates of inelastic calcium-hydrogen collision data for non-LTE stellar atmospheres modeling

    NASA Astrophysics Data System (ADS)

    Belyaev, A. K.; Yakovleva, S. A.; Guitou, M.; Mitrushchenkov, A. O.; Spielfiedel, A.; Feautrier, N.

    2016-03-01

    Aims: Inelastic processes in low-energy Ca + H and Ca+ + H- collisions are treated for the states from the ground state up to the ionic state with the aim to provide rate coefficients needed for non-LTE modeling of Ca in cool stellar atmospheres. Methods: The electronic molecular structure was determined using a recently proposed model approach that is based on an asymptotic method. Nonadiabatic nuclear dynamics were treated by means of multichannel formulas, based on the Landau-Zener model for nonadiabatic transition probabilities. Results: The cross sections and rate coefficients for inelastic processes in Ca + H and Ca+ + H- collisions were calculated for all transitions between 17 low-lying covalent states plus the ionic state. It is shown that the highest rate coefficient values correspond to the excitation, de-excitation, ion-pair formation, and mutual neutralization processes involving the Ca(4s5s 1,3S) and the ionic Ca+ + H- states. The next group with the second highest rate coefficients includes the processes involving the Ca(4s5p 1,3P), Ca(4s4d 1,3D), and Ca(4s4p 1P) states. The processes from these two groups are likely to be important for non-LTE modeling. Tables 2-11 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/587/A114

  17. 3-D laser confocal microscopy study of the oxidation of NdFeB magnets in atmospheric conditions

    NASA Astrophysics Data System (ADS)

    Meakin, J. P.; Speight, J. D.; Sheridan, R. S.; Bradshaw, A.; Harris, I. R.; Williams, A. J.; Walton, A.

    2016-08-01

    Neodymium iron boron (NdFeB) magnets are used in a number of important applications, such as generators in gearless wind turbines, motors in electric vehicles and electronic goods (e.g.- computer hard disk drives, HDD). Hydrogen can be used as a processing gas to separate and recycle scrap sintered Nd-Fe-B magnets from end-of-life products to form a powder suitable for recycling. However, the magnets are likely to have been exposed to atmospheric conditions prior to processing, and any oxidation could lead to activation problems for the hydrogen decrepitation reaction. Many previous studies on the oxidation of NdFeB magnets have been performed at elevated temperatures; however, few studies have been formed under atmospheric conditions. In this paper a combination of 3-D laser confocal microscopy and Raman spectroscopy have been used to assess the composition, morphology and rate of oxidation/corrosion on scrap sintered NdFeB magnets. Confocal microscopy has been employed to measure the growth of surface reaction products at room temperature, immediately after exposure to air. The results showed that there was a significant height increase at the triple junctions of the Nd-rich grain boundaries. Using Raman spectroscopy, the product was shown to consist of Nd2O3 and formed only on the Nd-rich triple junctions. The diffusion coefficient of the triple junction reaction product growth at 20 °C was determined to be approximately 4 × 10-13 cm2/sec. This value is several orders of magnitude larger than values derived from the diffusion controlled oxide growth observations at elevated temperatures in the literature. This indicates that the growth of the room temperature oxidation products are likely defect enhanced processes at the NdFeB triple junctions.

  18. Development of a 3D Soil-Plant-Atmosphere Continuum (SPAC) coupled to a Land Surface Model

    NASA Astrophysics Data System (ADS)

    Bisht, G.; Riley, W. J.; Lorenzetti, D.; Tang, J.

    2015-12-01

    Exchange of water between the atmosphere and biosphere via evapotranspiration (ET) influences global hydrological, energy, and biogeochemical cycles. Isotopic analysis has shown that evapotranspiration over the continents is largely dominated by transpiration. Water is taken up from soil by plant roots, transported through the plant's vascular system, and evaporated from the leaves. Yet current Land Surface Models (LSMs) integrated into Earth System Models (ESMs) treat plant roots as passive components. These models distribute the ET sink vertically over the soil column, neglect the vertical pressure distribution along the plant vascular system, and assume that leaves can directly access water from any soil layer within the root zone. Numerous studies have suggested that increased warming due to climate change will lead drought and heat-induced tree mortality. A more mechanistic treatment of water dynamics in the soil-plant-atmosphere continuum (SPAC) is essential for investigating the fate of ecosystems under a warmer climate. In this work, we describe a 3D SPAC model that can be coupled to a LSM. The SPAC model uses the variably saturated Richards equations to simulate water transport. The model uses individual governing equations and constitutive relationships for the various SPAC components (i.e., soil, root, and xylem). Finite volume spatial discretization and backward Euler temporal discretization is used to solve the SPAC model. The Portable, Extensible Toolkit for Scientific Computation (PETSc) is used to numerically integrate the discretized system of equations. Furthermore, PETSc's multi-physics coupling capability (DMComposite) is used to solve the tightly coupled system of equations of the SPAC model. Numerical results are presented for multiple test problems.

  19. Giant Impacts on Terrestrial Planets: A High-Resolution 3D Study of Magma Ocean Formation and Atmospheric Blowoff

    NASA Astrophysics Data System (ADS)

    Stewart-Mukhopadhyay, Sarah

    The end stages of terrestrial planet formation are dominated by giant impact events, which may significantly affect the final composition of a planet. The physical changes from giant impacts include formation of magma oceans and atmospheric blowoff. We propose to conduct unique numerical experiments to investigate the physics of giant impacts in order to determine their effect on the thermal state and volatile budget of terrestrial planets (0.1 to 10 Earth masses). Proposed work: High-resolution 3D giant impacts between differentiated silicate-iron and ice-silicate planets will be modeled with both the widely-used CTH shock physics code and a new second-order Godunov finite-volume hydrocode called AREPO. AREPO's powerful arbitrary Lagrangian-Eulerian grid and computational efficiency allows for unprecedented resolution of planetary structure (e.g., crust and ocean). Expected results: (1) We will calculate the amount of melt generated and fraction of atmosphere lost during different classes of giant impacts (merging, graze and merge, hit and run, and erosion/disruption). (2) We will derive general scaling laws to describe these complicated phenomena. (3) We will consider the effect of re-accretion of ejected material at late times on the total thermal input of giant impact events. (4) And we will test the giant impact hypothesis for the high bulk density of Mercury by conducting orbital integrations of ejected debris to determine the amount of re-accreted mantle material for different impact orientations. The science team has an established collaborative body of work in giant impact simulations and hydrocode development. As in previous studies, the simulation results will be generalized into sets of simple equations describing collision outcomes that are suitable for N-body planet formation models. The proposed work supports the goals of the Origins of Solar Systems program by conducting a fundamental theoretical investigation of a key stage of planet formation

  20. Stellar Winds and High-Energy Radiation: Evolution and influences on planetary atmospheres

    NASA Astrophysics Data System (ADS)

    Johnstone, C.; Tu, L.; Güdel, M.; Lüftinger, T.; Lammer, H.; Kislyakova, K.; Fichtinger, B.

    2015-10-01

    As part of the Austrian research network "Pathways to Habitability: From Disks to Active Stars, Planets and Life" (path.univie.ac.at), we study the evolution of stellar output (e.g. winds, high-energy radiation) over the lifetimes of solar-like stars and the influence of stellar output on the development of habitable planetary environments. We have developed a coupled stellar rotation-wind-radiation model that describes the long term evolution of stellar output over the course of a star's life. We show that the initial rotation rate of a star can significantly influence the evolution of winds and high-energy radiation and therefore the development of planetary atmospheres.

  1. A Fourier Optics Method for Calculating Stellar Occultation Light Curves by Objects with Thin Atmospheres

    NASA Astrophysics Data System (ADS)

    Young, E. F.

    2012-08-01

    A stellar occultation occurs when a solar system object passes in front of a distant star. The light curves resulting from stellar occultations can reveal many aspects of the obscuring object. For airless bodies, the diffraction light curve specifies the object's size, distance and, if several chords are observed, shape. Occultation light curves are especially sensitive to the presence of atmospheres; the refraction light curve is a function of the atmosphere's density, pressure, and temperature profiles. The goal of this paper is to develop a practical algorithm to model the simultaneous effects of diffraction and refraction for objects in which both phenomena are observable. The algorithm we present is flexible: it can be used to calculate light curves by objects with arbitrary shapes and arbitrary atmospheres (including the presence of opacity sources such as hazes), provided that the atmosphere can be represented by a thin screen with a phase delay and an opacity defined at each location in the screen. Because the algorithm is limited at present to thin atmospheres (in which rays from a star are bent but undergo virtually no translation as they pass through an atmosphere), the gas giants, Earth, Mars, and Venus are not treated. Examples of stellar occultations are presented for round or irregularly shaped objects having thin atmospheres of various column densities.

  2. A FOURIER OPTICS METHOD FOR CALCULATING STELLAR OCCULTATION LIGHT CURVES BY OBJECTS WITH THIN ATMOSPHERES

    SciTech Connect

    Young, E. F.

    2012-08-15

    A stellar occultation occurs when a solar system object passes in front of a distant star. The light curves resulting from stellar occultations can reveal many aspects of the obscuring object. For airless bodies, the diffraction light curve specifies the object's size, distance and, if several chords are observed, shape. Occultation light curves are especially sensitive to the presence of atmospheres; the refraction light curve is a function of the atmosphere's density, pressure, and temperature profiles. The goal of this paper is to develop a practical algorithm to model the simultaneous effects of diffraction and refraction for objects in which both phenomena are observable. The algorithm we present is flexible: it can be used to calculate light curves by objects with arbitrary shapes and arbitrary atmospheres (including the presence of opacity sources such as hazes), provided that the atmosphere can be represented by a thin screen with a phase delay and an opacity defined at each location in the screen. Because the algorithm is limited at present to thin atmospheres (in which rays from a star are bent but undergo virtually no translation as they pass through an atmosphere), the gas giants, Earth, Mars, and Venus are not treated. Examples of stellar occultations are presented for round or irregularly shaped objects having thin atmospheres of various column densities.

  3. Computation of Solar Radiative Fluxes by 1D and 3D Methods Using Cloudy Atmospheres Inferred from A-train Satellite Data

    NASA Technical Reports Server (NTRS)

    Barker, Howard W.; Kato, Serji; Wehr, T.

    2012-01-01

    The main point of this study was to use realistic representations of cloudy atmospheres to assess errors in solar flux estimates associated with 1D radiative transfer models. A scene construction algorithm, developed for the EarthCARE satellite mission, was applied to CloudSat, CALIPSO, and MODIS satellite data thus producing 3D cloudy atmospheres measuring 60 km wide by 13,000 km long at 1 km grid-spacing. Broadband solar fluxes and radiances for each (1 km)2 column where then produced by a Monte Carlo photon transfer model run in both full 3D and independent column approximation mode (i.e., a 1D model).

  4. NON-EQUILIBRIUM IONIZATION IN THE BIFROST STELLAR ATMOSPHERE CODE

    SciTech Connect

    Olluri, K.; Gudiksen, B. V.; Hansteen, V. H.

    2013-03-15

    The chromosphere and transition region have for the last 20 years been known to be quite dynamic layers of the solar atmosphere, characterized by timescales shorter than the ionization equilibrium timescales of many of the ions dominating emission in these regions. Due to the fast changes in the properties of the atmosphere, long ionization and recombination times can lead these ions to being found far from their equilibrium temperatures. A number of the spectral lines that we observe can therefore not be expected a priori to reflect information about local quantities such as the density or temperature, and interpreting observations requires numerical modeling. Modeling the ionization balance is computationally expensive and has earlier only been done in one dimension. However, one-dimensional models can primarily be used to investigate the possible importance of a physical effect, but cannot verify or disprove the importance of that effect in the fully three-dimensional solar atmosphere. Here, using the atomic database package DIPER, we extend one-dimensional methods and implement a solver for the rate equations of the full three-dimensional problem, using the numerical code Bifrost. We present our implementation and report on a few test cases. We also report on studies of the important C IV and Fe XII ions in a semi-realistic two-dimensional solar atmosphere model, focusing on differences between statistical equilibrium and non-equilibrium ionization results.

  5. The important role of stellar atmosphere spectra for a consistent spectrophotometric calibration from the optical to the infrared wavelengths

    NASA Astrophysics Data System (ADS)

    Decin, L.

    2008-12-01

    We discuss the role of stellar atmosphere models in the spectrophotometric calibration pedigree. It is shown that stellar atmosphere spectra form an essential ingredient for spectrophotometric calibration. Compared with other (infrared) calibration networks currently available, the marcs grid is shown to provide the calibration community with spectral reference energy distributions of higher accuracy improving the spectrophotometric calibration of infrared spectrometers by more than 3%.

  6. Application of AVHRR vegetation index to study atmosphere-biosphere exchange of CO2: Results from a 3-D tracer transport model

    NASA Technical Reports Server (NTRS)

    Fung, Inez Y.; Tucker, C. J.; Prentice, Katharine C.

    1985-01-01

    The 'normalized difference vegetation indices' (NVI) derived from AVHRR radiances are combined with field data of soil respiration and a global map of net primary productivity to prescribe, for the globe, the seasonal exchange of CO2 between the atmosphere and the terrestrial biosphere. The monthly fluxes of CO2 thus obtained are used as inputs to a 3-D tracer transport model which uses winds generated by a 3-D atmospheric general circulation model to advect CO2 as an inert constituent. Analysis of the 3-D model results shows reasonable agreement between the simulated and observed annual cycles of atmospheric CO2 at the locations of the remote monitoring stations. The application is shown of atmospheric CO2 distributions to calibrate the NVI in terms of carbon fluxes. The approach suggests that the NVI may be used to provide quantitative information about long term and global scale variations of photosynthetic activity and of atmospheric CO2 concentrations provided that variations in the atmospheric circulation and in atmospheric composition are known.

  7. Implementation of a 3-D-Var system for atmospheric profiling data assimilation into the RAMS model: initial results

    NASA Astrophysics Data System (ADS)

    Federico, S.

    2013-04-01

    This paper presents the current status of development of a three-dimensional variational data assimilation system. The system can be used with different numerical weather prediction models, but it is mainly designed to be coupled with the Regional Atmospheric Modelling System (RAMS). Analyses are given for the following parameters: zonal and meridional wind components, temperature, relative humidity, and geopotential height. Important features of the data assimilation system are the use of incremental formulation of the cost-function, and the use of an analysis space represented by recursive filters and eigenmodes of the vertical background error matrix. This matrix and the length-scale of the recursive filters are estimated by the National Meteorological Center (NMC) method. The data assimilation and forecasting system is applied to the real context of atmospheric profiling data assimilation, and in particular to the short-term wind prediction. The analyses are produced at 20 km horizontal resolution over central Europe and extend over the whole troposphere. Assimilated data are vertical soundings of wind, temperature, and relative humidity from radiosondes, and wind measurements of the European wind profiler network. Results show the validity of the analysis solutions because they are closer to the observations (lower RMSE) compared to the background (higher RMSE), and the differences of the RMSEs are consistent with the data assimilation settings. To quantify the impact of improved initial conditions on the short-term forecast, the analyses are used as initial conditions of a three-hours forecast of the RAMS model. In particular two sets of forecasts are produced: (a) the first uses the ECMWF analysis/forecast cycle as initial and boundary conditions; (b) the second uses the analyses produced by the 3-D-Var scheme as initial conditions, then is driven by the ECMWF forecast. The improvement is quantified by considering the horizontal components of the wind, which

  8. 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.

  9. Probing the Martian Atmosphere with MAVEN/IUVS Stellar Occultations

    NASA Astrophysics Data System (ADS)

    Gröller, H.; Yelle, R. V.; Koskinen, T.; Montmessin, F.; Lacombe, G.; Schneider, N. M.; Deighan, J.; Stewart, I. F.; Jain, S.; Chaffin, M.; Crismani, M. M. J.; Stiepen, A.; Lefèvre, F.; McClintock, B.; Clarke, J. T.; Holsclaw, G.; Mahaffy, P. R.; Bougher, S. W.; Jakosky, B. M.

    2015-12-01

    We present the first results of FUV and MUV stellar occultations taken with the Imaging UltraViolet Spectrometer (IUVS) onboard MAVEN. The FUV and MUV channels of the IUVS together cover the spectral range from 115 to 330 nm. The first two campaigns were executed during March 24 and March 26, 2015, and during May 17 and May 18, 2015, respectively. So far 13 occultations could be used to retrieve CO2 and O2 number densities in the altitude range between 100 and 150 km from the first occultation campaign. From the second occultation campaign number densities for CO2, O3, and aerosols were obtained between 20 and 100 km altitude. Temperature profiles for the same altitude ranges were calculated by applying the constraint of hydrostatic equilibrium to the CO2 densities. With a cadence of 2.6 s, including a 2.0 s integration time, the altitude resolution of the density and temperature profiles is between 1.5 and 4.5 km, depending on the geometry of the particular occultation. The retrieved density profiles of CO2 and O2 agree with previous measurements obtained by the Mars Express SPICAM instrument and by Viking 1 and 2. The corresponding O2 mixing ratios range from 1 to 5 x 10-3, also in agreement with previous observations. The temperatures that we retrieved agree with the models in the Mars Climate Database (MCD) between 10-2 and 10-4 Pa. At lower pressures, however, the measured temperatures are on average 70 K to 100 K cooler than the temperatures predicted by the MCD. This is because the model temperatures increase steadily with altitude above the mesopause whereas the observed temperatures decrease at pressures less than 3.5 x 10-5 Pa, reaching a minimum near 7 x 10-6 Pa. The large differences between the MCD and our results indicate that global models of thermal structure around the mesopause need to be revised.

  10. The Evolution of Stellar Rotation and the Hydrogen Atmospheres of Habitable-zone Terrestrial Planets

    NASA Astrophysics Data System (ADS)

    Johnstone, C. P.; Güdel, M.; Stökl, A.; Lammer, H.; Tu, L.; Kislyakova, K. G.; Lüftinger, T.; Odert, P.; Erkaev, N. V.; Dorfi, E. A.

    2015-12-01

    Terrestrial planets formed within gaseous protoplanetary disks can accumulate significant hydrogen envelopes. The evolution of such an atmosphere due to XUV driven evaporation depends on the activity evolution of the host star, which itself depends sensitively on its rotational evolution, and therefore on its initial rotation rate. In this Letter, we derive an easily applicable method for calculating planetary atmosphere evaporation that combines models for a hydrostatic lower atmosphere and a hydrodynamic upper atmosphere. We show that the initial rotation rate of the central star is of critical importance for the evolution of planetary atmospheres and can determine if a planet keeps or loses its primordial hydrogen envelope. Our results highlight the need for a detailed treatment of stellar activity evolution when studying the evolution of planetary atmospheres.

  11. A Three Dimensional Picture of RS CVN Stellar Atmospheres

    NASA Astrophysics Data System (ADS)

    Linsky, Jeffrey L.

    The ROSAT all-sky survey provides a unique opportunity to study an RS CVn system simultaneously at x-ray, EUV, UV, optical, and radio wavelengths at many phases throughout an orbital period. ROSAT can detect the x-ray flux of each candidate system during each 30 second viewing 16 times per day for at least 2 days. We request a block of 7 IUE shifts to obtain NEAR SIMULTANEOUS emission line fluxes (SWP-LO) and Mg IT line profiles (LWP-HI), and we will obtain contemporaneous optical photometry and spectroscopy and VLA radio fluxes (3.6, 6, and 20 cm). one objective of this PROPOSAL is to obtain the FIRST 3-D MODEL OF THE INHOMOGENEOUS PHOTOSPHERE, CHROMOSPHERE, AND CORONA OF A STAR OTHER THAN THE SUN. We will use optical photometry and spectroscopy to map the spotted photospheres of each star, and the Mg II line profiles to DOPPLERIMAGE their chromospheres, to determine the location, size, and surface flux of the active regions. We will then use the time variation of the UV emission line and x-ray fluxes to determine what fluxes are due to the quiet and active regions separately. These data will provide SURFACE FLUXES for the quiet and active regions separately. We will then will model BOTH REGIONS independently using an emission measure analysis. We will also model any flares observed. The second part of the program will be a simultaneous UV/X-ray SURVEY with the objective of DETERMINING THE RANGE OF PHYSICAL MODELS APPLICABLE TO THE CHROMOSPHERES AND CORONAE OF RS CVN SYSTEMS. We propose to obtain emission line fluxes (SWP-LO) and Mg II line profiles (LWP-HI) of all bright RS CVns observed by ROSAT from mid-July through September 1990 that meet the IUE observing constraints. About 17 systems in the Strassmeier catalog will likely be observed during this period. While many RS CVn systems have been observed separately by IUE and x-ray satellites, SIMULTANEOUS UV and x-ray observations are required to model these spatially inhomogenous and timevariable systems. This

  12. Stellar occultations by turbulent planetary atmospheres. I - A heuristic scattering model. II - The Beta Scorpii events

    NASA Technical Reports Server (NTRS)

    Hubbard, W. B.; Jokipii, J. R.

    1977-01-01

    Effects of atmospheric turbulence on stellar-occultation inversion procedures are investigated using a heuristic scattering model that is believed to reproduce the essential features of turbulence. A quantitative estimate is made of the size of the error in deducing the mean refractivity profile of a planetary atmosphere, taking into account constant as well as exponential scattering. It is shown that ordinary turbulence has no important effect on the average intensity profile in a stellar occultation but could have an important instantaneous effect. A critical examination of possible manifestations of turbulent scattering during occultations of Beta Sco by Jupiter indicates that all observed phenomena during these events can be understood in terms of scintillations produced by turbulence.

  13. Line-blanketed model stellar atmospheres applied to Sirius. Ph.D. Thesis - Maryland Univ.

    NASA Technical Reports Server (NTRS)

    Fowler, J. W.

    1972-01-01

    The primary goal of this analysis is to determine whether the effects of atomic bound-bound transitions on stellar atmospheric structure can be represented well in models. The investigation is based on an approach which is called the method of artificial absorption edges. The method is described, developed, tested, and applied to the problem of fitting a model stellar atmosphere to Sirius. It is shown that the main features of the entire observed spectrum of Sirius can be reproduced to within the observational uncertainty by a blanketed flux-constant model with T sub eff = 9700 K and Log g = 4.26. The profile of H sub gamma is reproduced completely within the standard deviations of the measurements except near line center, where non-LTE effects are expected to be significant. The equivalent width of H sub gamma, the Paschen slope, the Balmer jump, and the absolute flux at 5550 A all agree with the observed values.

  14. Buoyancy waves in Pluto’s high atmosphere: Implications for stellar occultations

    NASA Astrophysics Data System (ADS)

    Hubbard, W. B.; McCarthy, D. W.; Kulesa, C. A.; Benecchi, S. D.; Person, M. J.; Elliot, J. L.; Gulbis, A. A. S.

    2009-11-01

    We apply scintillation theory to stellar signal fluctuations in the high-resolution, high signal/noise, dual-wavelength data from the MMT observation of the 2007 March 18 occultation of P445.3 by Pluto. A well-defined high wavenumber cutoff in the fluctuations is consistent with viscous-thermal dissipation of buoyancy waves (internal gravity waves) in Pluto's high atmosphere, and provides strong evidence that the underlying density fluctuations are governed by the gravity-wave dispersion relation.

  15. A Numerical Method for Calculating Stellar Occultation Light Curves from an Arbitrary Atmospheric Model

    NASA Technical Reports Server (NTRS)

    Chamberlain, D. M.; Elliot, J. L.

    1997-01-01

    We present a method for speeding up numerical calculations of a light curve for a stellar occultation by a planetary atmosphere with an arbitrary atmospheric model that has spherical symmetry. This improved speed makes least-squares fitting for model parameters practical. Our method takes as input several sets of values for the first two radial derivatives of the refractivity at different values of model parameters, and interpolates to obtain the light curve at intermediate values of one or more model parameters. It was developed for small occulting bodies such as Pluto and Triton, but is applicable to planets of all sizes. We also present the results of a series of tests showing that our method calculates light curves that are correct to an accuracy of 10(exp -4) of the unocculted stellar flux. The test benchmarks are (i) an atmosphere with a l/r dependence of temperature, which yields an analytic solution for the light curve, (ii) an atmosphere that produces an exponential refraction angle, and (iii) a small-planet isothermal model. With our method, least-squares fits to noiseless data also converge to values of parameters with fractional errors of no more than 10(exp -4), with the largest errors occurring in small planets. These errors are well below the precision of the best stellar occultation data available. Fits to noisy data had formal errors consistent with the level of synthetic noise added to the light curve. We conclude: (i) one should interpolate refractivity derivatives and then form light curves from the interpolated values, rather than interpolating the light curves themselves; (ii) for the most accuracy, one must specify the atmospheric model for radii many scale heights above half light; and (iii) for atmospheres with smoothly varying refractivity with altitude, light curves can be sampled as coarsely as two points per scale height.

  16. Metal Hydride and Alkali Halide Opacities in Extrasolar Giant Planets and Cool Stellar Atmospheres

    NASA Technical Reports Server (NTRS)

    Weck, Philippe F.; Stancil, Phillip C.; Kirby, Kate; Schweitzer, Andreas; Hauschildt, Peter H.

    2006-01-01

    The lack of accurate and complete molecular line and continuum opacity data has been a serious limitation to developing atmospheric models of cool stars and Extrasolar Giant Planets (EGPs). We report our recent calculations of molecular opacities resulting from the presence of metal hydrides and alkali halides. The resulting data have been included in the PHOENIX stellar atmosphere code (Hauschildt & Baron 1999). The new models, calculated using spherical geometry for all gravities considered, also incorporate our latest database of nearly 670 million molecular lines, and updated equations of state.

  17. Limits on the radius and a possible atmosphere of Charon from its 1980 stellar occultation

    NASA Technical Reports Server (NTRS)

    Elliot, J. L.; Young, L. A.

    1991-01-01

    Walker's (1980) stellar occultation data for Charon are presently fit by a model which encompasses the possibility of differential refraction by an atmosphere, followed by a sudden occultation behind Charon's limb. The 601.5-km Charon radius lower limit thus obtained may serve as a constraint in models of the mutual event data; while the model fits considered support a Charonian atmosphere of indeterminate composition, time resolution is insufficient for certainty and the data may be interpretable as indications of either a slight extinction near Charon or an entirely unidentified and unassociated effect.

  18. An effective calculation method in theory of non-LTE stellar atmospheres - linearization separation technique.

    NASA Astrophysics Data System (ADS)

    Wu, G. Q.; Huang, R. Q.

    1994-06-01

    This paper introduces a new calculation method of non-LTE stellar atmospheres. This method is based on the combination of the advantages of the complete linearization method by Auer and Mihalas (1969) and the separated-iteration technique. First, the equation of radiative transfer and constraints are linearized respectively, then the linearized equation of the radiative transfer and the linearized constraints are solved, separately. It overcomes the disadvantages of requiring the simultaneous solution of the corresponding equations by the complete linearization. The applicability of this method by calculating a small sample of H-He atmospheres and H line formations is demonstrated.

  19. 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.

  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. Near-infrared spectro-interferometry of Mira variables and comparisons to 1D dynamic model atmospheres and 3D convection simulations

    NASA Astrophysics Data System (ADS)

    Wittkowski, M.; Chiavassa, A.; Freytag, B.; Scholz, M.; Höfner, S.; Karovicova, I.; Whitelock, P. A.

    2016-03-01

    Aims: We aim at comparing spectro-interferometric observations of Mira variable asymptotic giant branch (AGB) stars with the latest 1D dynamic model atmospheres based on self-excited pulsation models (CODEX models) and with 3D dynamic model atmospheres including pulsation and convection (CO5BOLD models) to better understand the processes that extend the molecular atmosphere to radii where dust can form. Methods: We obtained a total of 20 near-infrared K-band spectro-interferometric snapshot observations of the Mira variables o Cet, R Leo, R Aqr, X Hya, W Vel, and R Cnc with a spectral resolution of about 1500. We compared observed flux and visibility spectra with predictions by CODEX 1D dynamic model atmospheres and with azimuthally averaged intensities based on CO5BOLD 3D dynamic model atmospheres. Results: Our visibility data confirm the presence of spatially extended molecular atmospheres located above the continuum radii with large-scale inhomogeneities or clumps that contribute a few percent of the total flux. The detailed structure of the inhomogeneities or clumps show a variability on time scales of 3 months and above. Both modeling attempts provided satisfactory fits to our data. In particular, they are both consistent with the observed decrease in the visibility function at molecular bands of water vapor and CO, indicating a spatially extended molecular atmosphere. Observational variability phases are mostly consistent with those of the best-fit CODEX models, except for near-maximum phases, where data are better described by near-minimum models. Rosseland angular diameters derived from the model fits are broadly consistent between those based on the 1D and the 3D models and with earlier observations. We derived fundamental parameters including absolute radii, effective temperatures, and luminosities for our sources. Conclusions: Our results provide a first observational support for theoretical results that shocks induced by convection and pulsation in the

  4. Virgo cluster and field dwarf ellipticals in 3D - I. On the variety of stellar kinematic and line-strength properties

    NASA Astrophysics Data System (ADS)

    Ryś, Agnieszka; Falcón-Barroso, Jesús; van de Ven, Glenn

    2013-02-01

    We present the first large-scale stellar kinematic and line-strength maps for dwarf elliptical galaxies (nine in the Virgo cluster and three in the field environment) obtained with the SAURON (Spectrographic Areal Unit for Research on Optical Nebulae) integral-field unit. No two galaxies in our sample are alike: we see that the level of rotation is not tied to flattening (we have, e.g., round rotators and flattened non-rotators); we observe kinematic twists in one Virgo and one field object; we discover large-scale kinematically decoupled components in two field galaxies; we see varying gradients in line-strength maps, from nearly flat to strongly peaked in the centre. The great variety of morphological, kinematic and stellar population parameters seen in our data points to a formation scenario in which properties are shaped stochastically. A combined effect of ram-pressure stripping and galaxy harassment is the most probable explanation. We show the need for a comprehensive analysis of kinematic, dynamical and stellar population properties which will enable us to place dwarf ellipticals and processes that govern their evolution in the wider context of galaxy formation.

  5. The ATLAS3D project - III. A census of the stellar angular momentum within the effective radius of early-type galaxies: unveiling the distribution of fast and slow rotators

    NASA Astrophysics Data System (ADS)

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

    2011-06-01

    We provide a census of the apparent stellar angular momentum within one effective radius of a volume-limited sample of 260 early-type galaxies (ETGs) in the nearby Universe, using the integral-field spectroscopy obtained in the course of the ATLAS3D project. We exploit the λR parameter (previously used via a constant threshold value of 0.1) to characterize the existence of two families of ETGs: slow rotators which exhibit complex stellar velocity fields and often include stellar kinematically distinct cores, and fast rotators which have regular velocity fields. Our complete sample of 260 ETGs leads to a new criterion to disentangle fast and slow rotators which now includes a dependency on the apparent ellipticity ɛ. It separates the two classes significantly better than the previous prescription and better than a criterion based on V/σ: slow rotators and fast rotators have λR lower and larger than ?, respectively, where kFS= 0.31 for measurements made within an effective radius Re. We show that the vast majority of ETGs are fast rotators: these have the regular stellar rotation, with aligned photometric and kinematic axes (Paper II of this series), include discs and often bars and represent 86 ± 2 per cent (224/260) of all ETGs in the volume-limited ATLAS3D sample. Fast rotators span the full range of apparent ellipticities from ɛ= 0 to 0.85, and we suggest that they cover intrinsic ellipticities from about 0.35 to 0.85, the most flattened having morphologies consistent with spiral galaxies. Only a small fraction of ETGs are slow rotators representing 14 ± 2 per cent (36/260) of the ATLAS3D sample of ETGs. Of all slow rotators, 11 per cent (4/36) exhibit two counter-rotating stellar disc-like components and are rather low-mass objects (Mdyn < 1010.5 M⊙). All other slow rotators (32/36) appear relatively round on the sky (ɛe < 0.4), tend to be massive (Mdyn > 1010.5 M⊙), and often (17/32) exhibit kinematically distinct cores. Slow rotators dominate the

  6. 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/

  7. Impact of assimilation of INSAT-3D retrieved atmospheric motion vectors on short-range forecast of summer monsoon 2014 over the South Asian region

    NASA Astrophysics Data System (ADS)

    Kumar, Prashant; Deb, Sanjib K.; Kishtawal, C. M.; Pal, P. K.

    2016-01-01

    The Weather Research and Forecasting (WRF) model and its three-dimensional variational data assimilation system are used in this study to assimilate the INSAT-3D, a recently launched Indian geostationary meteorological satellite derived from atmospheric motion vectors (AMVs) over the South Asian region during peak Indian summer monsoon month (i.e., July 2014). A total of four experiments were performed daily with and without assimilation of INSAT-3D-derived AMVs and the other AMVs available through Global Telecommunication System (GTS) for the entire month of July 2014. Before assimilating these newly derived INSAT-3D AMVs in the numerical model, a preliminary evaluation of these AMVs is performed with National Centers for Environmental Prediction (NCEP) final model analyses. The preliminary validation results show that root-mean-square vector difference (RMSVD) for INSAT-3D AMVs is ˜3.95, 6.66, and 5.65 ms-1 at low, mid, and high levels, respectively, and slightly more RMSVDs are noticed in GTS AMVs (˜4.0, 8.01, and 6.43 ms-1 at low, mid, and high levels, respectively). The assimilation of AMVs has improved the WRF model of produced wind speed, temperature, and moisture analyses as well as subsequent model forecasts over the Indian Ocean, Arabian Sea, Australia, and South Africa. Slightly more improvements are noticed in the experiment where only the INSAT-3D AMVs are assimilated compared to the experiment where only GTS AMVs are assimilated. The results also show improvement in rainfall predictions over the Indian region after AMV assimilation. Overall, the assimilation of INSAT-3D AMVs improved the WRF model short-range predictions over the South Asian region as compared to control experiments.

  8. Monitoring the Stellar Activity of Transit-Hosting Stars II: supporting HST exoplanet atmosphere observations

    NASA Astrophysics Data System (ADS)

    Wilson, Paul Anthony; Evans, Tom; Sing, David K.; Aigrain, Suzanne

    2012-02-01

    We propose to use the CTIO 1.3m telescope with ANDICAM to monitor 5 bright stars that host transiting exoplanets in an effort to characterise their activity. These observations will provide critical ground-based support for our large HST program that has been granted 124 orbits to perform a survey of UV-optical atmospheric transmission spectra for 8 hot Jupiters using the STIS instrument (Cycle 19, Prog 12473, PI D Sing). They are required because active stellar regions inevitably contaminate measured planetary light curves by causing the apparent planet-to-star radius to vary in a wavelength dependent manner. Regular ground-based photometric monitoring performed using the CTIO 1.3m telescope will allow us to determine the spot activity at the time of the HST observations, so that the stellar baseline flux can be accurately normalised for every transit observed, enabling transmission spectra from multiple visits to be combined.

  9. Examination of Pluto's Atmospheric Figure with the P131.1 Stellar Occultation

    NASA Astrophysics Data System (ADS)

    Person, M. J.; Elliot, J. L.; Clancy, K. B.; Tholen, D. J.; Rayner, J. T.; Pasachoff, J. M.; Babcock, B. A.; Ticehurst, D. R.; Hall, D.; Roberts, L. C., Jr.; Bosh, A. S.; Eikenberry, S. S.; Moon, D. S.; Buie, M. W.; Dunham, E. W.; Olkin, C. B.; Taylor, B.; Kern, S. D.; Osip, D. J.; Qu, S.; Salyk, C. V.; Leggett, S. K.; Levine, S. E.; Stone, R. C.

    2002-12-01

    From the 1988 stellar occultation by Pluto, Millis (et al., Icarus, 105, 282) did not report any deviation from sphericity in Pluto's atmospheric figure. However, stellar occultation measurements of Triton throughout the late 1990's revealed a significant deviation from a spherical figure in Triton's atmospheric shape (Elliot et al., Icarus, 148, 347, and Person 2001, S.M. Thesis, Dept. of Earth Atmos. and Plan. Sci., Mass. Inst. Of Tech., Cambridge MA). This deviation is unexpected since Triton's rotation period is slow (5.88 days), but the resulting non-spherical shape could be due to high winds. The Triton results have prompted us to examine Pluto's atmospheric figure with more recent data. The stellar occultation by Pluto of the 15th magnitude star designated P131.1 (McDonald and Elliot, AJ, 119, 1999) on 2002 August 21 (UT) provided the first significant chance since the Triton results to measure such non-sphericity in Pluto's atmosphere. The occultation was observed from numerous stations in Hawaii and the western United States (see Elliot et al., Pasachoff et al., Clancy et al., this conference). We present the results of our analysis of these datasets in searching for non-spherical deviations in Pluto's atmospheric figure. The light curves from the observations were analyzed together in the occultation coordinate system of Elliot et al., (AJ, 106, 2544). The datasets from the various Mauna Kea telescopes are redundant with each other in figure space, but provide valuable cross checks among their timing systems. The Mauna Kea and Lick datasets straddle the center of Pluto's figure, providing strong constraints on model fits to cross sections of the atmospheric shape. As a second measure of possible non-sphericity, the individual light curves can be individually fit with atmospheric models in the manner of Elliot and Young (AJ, 103, 991), to search for asymmetry indicative of a non-circular atmospheric cross section around the limb of the planet. This work

  10. Analysis of stellar occultation data for planetary atmospheres. I - Model fitting, with application to Pluto

    NASA Technical Reports Server (NTRS)

    Elliot, J. L.; Young, L. A.

    1992-01-01

    Consideration is given to an analytic model for a stellar-occultation light curve developed for a small, spherically symmetric planetary atmosphere that includes thermal and molecular weight gradients in a region that overlies an extinction layer. The model incorporates two equivalent sets of parameters. One set specifies the occultation light curve in terms of signal levels, times, and time intervals. The other set specifies physical parameters of the planetary atmosphere. Equations are given for the transforming between the sets of parameters, including their errors and correlation coefficients. Detailed numerical calculations are presented for a benchmark case. The results obtained are consistent with the isothermal prediction of the 'methane-thermostat' model of Pluto's atmosphere.

  11. Parametric 3D Atmospheric Reconstruction in Highly Variable Terrain with Recycled Monte Carlo Paths and an Adapted Bayesian Inference Engine

    NASA Technical Reports Server (NTRS)

    Langmore, Ian; Davis, Anthony B.; Bal, Guillaume; Marzouk, Youssef M.

    2012-01-01

    We describe a method for accelerating a 3D Monte Carlo forward radiative transfer model to the point where it can be used in a new kind of Bayesian retrieval framework. The remote sensing challenge is to detect and quantify a chemical effluent of a known absorbing gas produced by an industrial facility in a deep valley. The available data is a single low resolution noisy image of the scene in the near IR at an absorbing wavelength for the gas of interest. The detected sunlight has been multiply reflected by the variable terrain and/or scattered by an aerosol that is assumed partially known and partially unknown. We thus introduce a new class of remote sensing algorithms best described as "multi-pixel" techniques that call necessarily for a 3D radaitive transfer model (but demonstrated here in 2D); they can be added to conventional ones that exploit typically multi- or hyper-spectral data, sometimes with multi-angle capability, with or without information about polarization. The novel Bayesian inference methodology uses adaptively, with efficiency in mind, the fact that a Monte Carlo forward model has a known and controllable uncertainty depending on the number of sun-to-detector paths used.

  12. A Stellar Occultation Sensor Using Absorption and Refraction of Starlight for Atmospheric Profile Measurements

    NASA Astrophysics Data System (ADS)

    Morgan, F.; Yee, J.; Murphy, G.; Swartz, W.; Demajistre, R.; Vervack, R.; Morrison, D.

    2008-12-01

    The Self-Calibrating H2O and O3 Nighttime Environmental Remote Sensor (SCHOONERS) is a compact, integrated UV-IR imaging spectrograph and imager for spaceborne stellar occultation measurements, developed under the NASA Instrument Incubator Program and based on the measurement technique and retrieval demonstrated by the MSX/UVISI instrument. The imaging spectrograph, covering a spectral range between 300 and 900 nm, measures the varying absorption of starlight as a star sets through the Earth's atmosphere to determine vertical profiles of atmospheric constituents. The relative star position measured by the co-aligned imager not only provides position feedback to the active-tracking loop but also measures the star refraction angle for determining the atmospheric density and temperature profiles. The instrument has a 25-cm-diameter aperture and employs a two-axis gimbaled telescope to provide acquisition and tracking of the star. It also uses a two-axis high-precision vernier mirror to correct for spacecraft jitter and maintain the star within the field-of-view. SCHOONERS' hardware and accompanying software have been demonstrated in end-to-end laboratory tests. SCHOONERS' built-in image tracking and motion compensation mechanism, coupled with its small size and limited spacecraft resource requirements, makes it suitable for deployment on existing and future spacecraft platforms as an instrument-of-opportunity. In this paper, stellar occultation sensing technique, experiment requirements, and SCHOONERS design and expected performance will be presented.

  13. Ion-Atom and Atom-Atom Collisional Processes and Modeling of Stellar Atmospheres

    NASA Astrophysics Data System (ADS)

    Mihajlov, A. A.; Ignjatovic, Lj. M.; Sreckovic, V. A.; Dimitrijevic, M. S.; Dimitrijevic, M. S.

    2015-09-01

    We report the results obtained in our previous works on the influence of two groups of collisional processes (ion--atom and atom--atom) on the optical and kinetic properties of weakly ionised plasma. The first group includes radiative processes of the photodissociation/association type and radiative charge exchange, the second one -- chemi-ionisation/recombination processes. The effect of the radiative processed is assessed by comparing their intensities with those of the known competing processed in application to the solar photosphere and to the photospheres of DB white dwarfs. The studied chemi-ionisation/recombination processes are considered from the viewpoint of their influence on the populations of the excited states of the hydrogen atom (the Sun and an M-type red dwarf with an effective temperature of 3800~K) and helium atom (DB white dwarfs). The effect of these processes on the populations of the excited states of the hydrogen atom has been studied using the PHOENIX code, which generates the model of the considered atmosphere. The reported results demonstrate the unquestionable influence of the considered radiative and chemi- ionisation/recombination processes on the optical properties and on the kinetics of the weakly ionised layers in stellar atmospheres. It can be expected that the reported results will be a sufficient reason for including these processes in the models of stellar atmospheres.

  14. A possible deuterium anomaly: Implications of the CH3D/CH4 mixing ratios in the atmospheres of Jupiter, Saturn, and Uranus

    NASA Technical Reports Server (NTRS)

    Lutz, Barry L.; Debergh, Catherine; Owen, Tobias

    1986-01-01

    Observations of CH3D in the atmospheres of the outer planets provide a test of the theory of deuterium fractionation equilibrium in the formation and evolution of these planets. Recent measurements of the CH3D/CH4 mixing ratios made for Saturn and Uranus are presented and intercompared with current values of Jupiter, illustrating large differences between the planets. Their implied D/H ratios are compared to D/H ratios derived from measurements of HD/H2; and, in the cases of Jupiter and Saturn, they may be incompatible. Implications of these comparisons are discussed in terms of the deuterium fractionation chemistry and possible enrichments of deuterium in the core ices of the planets.

  15. Atmospheric effects of stellar cosmic rays on Earth-like exoplanets orbiting M-dwarfs

    NASA Astrophysics Data System (ADS)

    Tabataba-Vakili, F.; Grenfell, J. L.; Grießmeier, J.-M.; Rauer, H.

    2016-01-01

    M-dwarf stars are generally considered favourable for rocky planet detection. However, such planets may be subject to extreme conditions due to possible high stellar activity. The goal of this work is to determine the potential effect of stellar cosmic rays on key atmospheric species of Earth-like planets orbiting in the habitable zone of M-dwarf stars and show corresponding changes in the planetary spectra. We build upon the cosmic rays model scheme of previous works, who considered cosmic ray induced NOx production, by adding further cosmic ray induced production mechanisms (e.g. for HOx) and introducing primary protons of a wider energy range (16 MeV-0.5 TeV). Previous studies suggested that planets in the habitable zone that are subject to strong flaring conditions have high atmospheric methane concentrations, while their ozone biosignature is completely destroyed. Our current study shows, however, that adding cosmic ray induced HOx production can cause a decrease in atmospheric methane abundance of up to 80%. Furthermore, the cosmic ray induced HOx molecules react with NOx to produce HNO3, which produces strong HNO3 signals in the theoretical spectra and reduces NOx-induced catalytic destruction of ozone so that more than 25% of the ozone column remains. Hence, an ozone signal remains visible in the theoretical spectrum (albeit with a weaker intensity) when incorporating the new cosmic ray induced NOx and HOx schemes, even for a constantly flaring M-star case. We also find that HNO3 levels may be high enough to be potentially detectable. Since ozone concentrations, which act as the key shield against harmful UV radiation, are affected by cosmic rays via NOx-induced catalytic destruction of ozone, the impact of stellar cosmic rays on surface UV fluxes is also studied.

  16. 3D Monte Carlo simulation of solar radiance in the clear-sky and low-cloud atmosphere for retrieval of aerosol and cloud characteristics

    NASA Astrophysics Data System (ADS)

    Zhuravleva, Tatiana; Bedareva, Tatiana; Nasrtdinov, Ilmir

    As is well known, the spectral measurements of direct and diffuse solar radiation can be used to retrieve the optical and microphysical characteristics of atmospheric aerosol and clouds. Most methods of radiation calculations, which are used to solve the inverse problems, are implemented under the assumption of horizontal homogeneity of the atmosphere (clear-sky and overcast conditions). However, it is recognized that the 3D effects of clouds have a significant impact on the transfer of solar radiation in the atmosphere which can be the cause of errors in retrieval of aerosol and cloud properties. In this work, we present the algorithms of the Monte Carlo method for calculating the angular structure of diffuse radiation in the molecular-aerosol atmosphere and the appearance of isolated cloud. The simulation of radiative characteristics with specified spectral resolution is performed in spherical model of the atmosphere for the conditions of observations at the Earth’s surface and at the top of the atmosphere. Cloud is approximated by inverted paraboloid. The molecular absorption is accounted for on the basis of approximation of transmission function by short exponential series (k-distribution method). The specific features of the radiative transfer, caused by the 3D effects of clouds, are considered depending on cloud location in space and its sizes, sensing scheme, and illumination conditions. The simulation results of the brightness fields in the clear sky and in the appearance of isolated cloud are compared. This work was supported in part by the Russian Fund for Basic Research (through the grant no. 12-05-00169).

  17. A New High-precision Correction Method of Temperature Distribution in Model Stellar Atmospheres

    NASA Astrophysics Data System (ADS)

    Sapar, A.; Poolamäe, R.; Sapar, L.

    The main features of the temperature correction methods, suggested and used in modeling of plane-parallel stellar atmospheres, are discussed. The main features of the new method are described. Derivation of the formulae for a version of the Unsöld-Lucy method, used by us in the SMART (Stellar Model Atmospheres and Radiative Transport) software for modeling stellar atmospheres, is presented. The method is based on a correction of the model temperature distribution based on minimizing differences of flux from its accepted constant value and on the requirement of the lack of its gradient, meaning that local source and sink terms of radiation must be equal. The final relative flux constancy obtainable by the method with the SMART code turned out to have the precision of the order of 0.5 %. Some of the rapidly converging iteration steps can be useful before starting the high-precision model correction. The corrections of both the flux value and of its gradient, like in Unsöld-Lucy method, are unavoidably needed to obtain high-precision flux constancy. A new temperature correction method to obtain high-precision flux constancy for plane-parallel LTE model stellar atmospheres is proposed and studied. The non-linear optimization is carried out by the least squares, in which the Levenberg-Marquardt correction method and thereafter additional correction by the Broyden iteration loop were applied. Small finite differences of temperature (δ T/T=10-3) are used in the computations. A single Jacobian step appears to be mostly sufficient to get flux constancy of the order 10-2 %. The dual numbers and their generalization -- the dual complex numbers (the duplex numbers) -- enable automatically to get the derivatives in the nilpotent part of the dual numbers. A version of the SMART software is in the stage of refactorization to dual and duplex numbers, what enables to get rid of the finite differences, as an additional source of lowering precision of the computed results.

  18. Model Stellar Atmospheres and Real Stellar Atmospheres and Status of the ATLAS12 Opacity Sampling Program and of New Programs for Rosseland and for Distribution Function Opacity

    NASA Technical Reports Server (NTRS)

    Kurucz, Robert L.

    1996-01-01

    I discuss errors in theory and in interpreting observations that are produced by the failure to consider resolution in space, time, and energy. I discuss convection in stellar model atmospheres and in stars. Large errors in abundances are possible such as the factor of ten error in the Li abundance for extreme Population II stars. Finally I discuss the variation of microturbulent velocity with depth, effective temperature, gravity, and abundance. These variations must be dealt with in computing models and grids and in any type of photometric calibration. I have also developed a new opacity-sampling version of my model atmosphere program called ATLAS12. It recognizes more than 1000 atomic and molecular species, each in up to 10 isotopic forms. It can treat all ions of the elements up through Zn and the first 5 ions of heavier elements up through Es. The elemental and isotopic abundances are treated as variables with depth. The fluxes predicted by ATLAS12 are not accurate in intermediate or narrow bandpass intervals because the sample size is too small. A special stripped version of the spectrum synthesis program SYNTHE is used to generate the surface flux for the converged model using the line data on CD-ROMs 1 and 15. ATLAS12 can be used to produce improved models for Am and Ap stars. It should be very useful for investigating diffusion effects in atmospheres. It can be used to model exciting stars for H II regions with abundances consistent with those of the H II region. These programs and line files will be distributed on CD-ROMs.

  19. Time Resolved 3-D Mapping of Atmospheric Aerosols and Clouds During the Recent ARM Water Vapor IOP

    NASA Technical Reports Server (NTRS)

    Schwemmer, Geary; Miller, David; Wilkerson, Thomas; Andrus, Ionio; Starr, David OC. (Technical Monitor)

    2001-01-01

    The HARLIE lidar was deployed at the ARM SGP site in north central Oklahoma and recorded over 100 hours of data on 16 days between 17 September and 6 October 2000 during the recent Water Vapor Intensive Operating Period (IOP). Placed in a ground-based trailer for upward looking scanning measurements of clouds and aerosols, HARLIE provided a unique record of time-resolved atmospheric backscatter at 1 micron wavelength. The conical scanning lidar images atmospheric backscatter along the surface of an inverted 90 degree (full angle) cone up to an altitude of 20 km. 360 degree scans having spatial resolutions of 20 meters in the vertical and 1 degree in azimuth were obtained every 36 seconds. Various boundary layer and cloud parameters are derived from the lidar data, as well as atmospheric wind vectors where there is Sufficiently resolved structure that can be traced moving through the surface described by the scanning laser beam. Comparison of HARLIE measured winds with radiosonde measured winds validates the accuracy of this new technique for remotely measuring atmospheric winds without Doppler information.

  20. Pluto’s Atmosphere from the 23 June 2011 Stellar Occultation: Airborne and Ground Observations

    NASA Astrophysics Data System (ADS)

    Person, Michael J.; Bosh, A. S.; Levine, S. E.; Gulbis, A. A. S.; Zangari, A. M.; Zuluaga, C. A.; Dunham, E. W.; Pasachoff, J. M.; Babcock, B. A.; Pandey, S.; Armhein, D.; Sallum, S.; Tholen, D. J.; Collins, P.; Bida, T.; Taylor, B.; Wolf, J.; Meyer, A.; Pfueller, E.; Wiedermann, M.; Roesser, H.; Lucas, R.; Kakkala, M.; Ciotti, J.; Plunkett, S.; Hiraoka, N.; Best, W.; Pilger, E. L.; Miceli, M.; Springmann, A.; Hicks, M.; Thackeray, B.; Emery, J.; Rapoport, S.; Ritchie, I.

    2012-10-01

    The double stellar occultation by Pluto and Charon of 2011 June 23 was observed from numerous ground stations as well as the Stratospheric Observatory for Infrared Astronomy (SOFIA). This first airborne occultation observation since 1995 resulted in the best occultation chords recorded for the event, in three optical wavelength bands. The data obtained from SOFIA were combined with chords obtained from the ground at the IRTF (including a full spectral light curve), the USNO--Flagstaff Station, and Leeward Community College to give a detailed profile of Pluto’s atmosphere. The data show a return to the distinct upper and lower atmospheric regions with a knee, or kink in the light curves separating them as was observed in 1988 (Millis et al. 1993), rather than the smoothly transitioning bowl-shaped light curves of recent years (Elliot et al. 2007). We analyze the upper atmosphere by fitting a model to all of the light curves obtained, resulting in a half-light radius of 1288 ± 1 km. We analyze the lower atmosphere with two different methods to provide results under the separate assumptions of particulate haze and a strong thermal gradient. Results indicate that the lower atmosphere evolves on short seasonal timescales, changing between 1988 and 2006, and then returning to approximately the 1988 state in 2011, though at significantly higher pressures. Throughout these changes, the upper atmosphere remains remarkably stable in structure, again excepting the overall pressure changes. No evidence of the onset of atmospheric collapse predicted by frost migration models is yet seen, and the atmosphere appears to be remaining at a stable pressure level. This work was supported in part by NASA Planetary Astronomy grants to MIT (NNX10AB27G) and Williams College (NNX08AO50G, NNH11ZDA001N), as well as grants from USRA (#8500-98-003) and Ames Research (#NAS2-97-01) to Lowell Observatory.

  1. A 3-D RBF-FD solver for modeling the atmospheric global electric circuit with topography (GEC-RBFFD v1.0)

    NASA Astrophysics Data System (ADS)

    Bayona, V.; Flyer, N.; Lucas, G. M.; Baumgaertner, A. J. G.

    2015-10-01

    A numerical model based on radial basis function-generated finite differences (RBF-FD) is developed for simulating the global electric circuit (GEC) within the Earth's atmosphere, represented by a 3-D variable coefficient linear elliptic partial differential equation (PDE) in a spherically shaped volume with the lower boundary being the Earth's topography and the upper boundary a sphere at 60 km. To our knowledge, this is (1) the first numerical model of the GEC to combine the Earth's topography with directly approximating the differential operators in 3-D space and, related to this, (2) the first RBF-FD method to use irregular 3-D stencils for discretization to handle the topography. It benefits from the mesh-free nature of RBF-FD, which is especially suitable for modeling high-dimensional problems with irregular boundaries. The RBF-FD elliptic solver proposed here makes no limiting assumptions on the spatial variability of the coefficients in the PDE (i.e., the conductivity profile), the right hand side forcing term of the PDE (i.e., distribution of current sources) or the geometry of the lower boundary.

  2. Implementation of the Blade Element Momentum Method into a High-Resolution 3-D Atmospheric Model: Evaluating a Parameterization for Wind Turbines

    NASA Astrophysics Data System (ADS)

    Sta. Maria, M.; Ketefian, G. S.; Jacobson, M. Z.

    2010-12-01

    In order to simulate better the effects of wind turbines on meteorology and climate, a parameterization based on the Blade Element Momentum (BEM) theory was developed and integrated into a high-resolution 3-D non-hydrostatic atmospheric model that conserves several domain-integrated quantities. The BEM model calculates the forces the blade exerts on the atmosphere and feeds it back as body forces in the momentum equations of the atmospheric model. Since the BEM method calculates these forces along a turbine blade, the parameterization allows for model spatial resolutions on the order of a few to tens of meters. This study examines the advantages and limitations of such a parameterization. The BEM calculates the rotational force that the blades exert on the air, and this study investigates whether this parameterization is able to capture rotation in the wake. The dependency on model resolution is also studied to determine the optimum model resolution for simulating wind turbine-atmosphere interactions. The atmospheric model is also used to estimate the distance downwind of a turbine at which wind speeds recover. This is an important parameter for determining optimal wind farm spacing. Model results will be compared with previous parameterizations and wake data gathered in the field and from wind tunnel studies.

  3. A new 3D numerical model for production of cosmogenic spallation products (7) Be, (10) Be, (22) Na in the atmosphere

    NASA Astrophysics Data System (ADS)

    Usoskin, Ilya; Kovaltsov, Gennady

    A new quantitative model of production of the cosmogenic isotopes, produced by spallation of atmospheric constitutes by the nucleonic component of cosmic rays induced cascade in the Earth's atmosphere is presented. We presents the results for three cosmogenic isotopes: 7 Be, 10 Be and 22 Na, using the CRAC (Cosmic Ray induced Atmospheric Cascade) model is based on a full numerical Monte-Carlo simulation of the nucleonic-electromagnetic-muon cascade induced by cosmic rays in the atmosphere and is able to compute the isotope's production rate at any given 3D location (geographical and altitude) and time, for all possible parameters including solar energetic particle events. The model was tested against the results of direct measurements of production of 10 Be and 7 Be in a number of dedicated experiments to confirm its quantitative correctness. A set of tabulated values for the yield function is provided along with a detailed numerical recipe forming a `do-it-yourself' kit, which allows anyone interested to apply the model for any given conditions. This provides a useful tool for applying the cosmogenic isotope method in direct integration with other models, e.g., dynamical atmospheric transport.

  4. Numerical study of atmospheric particulate matters: source apportionment to characterize 3D transport and transformation of precursors and secondary pollutants

    NASA Astrophysics Data System (ADS)

    Wu, Dongwei

    In recent years, Mainland China, and in particular the industrial hotbed of the Pearl River Delta (PRD) has experienced an increasingly serious problem of high concentrations of airborne particulate matter. Following the tightening-up of China's air quality policies in recent years, and with especially fine particles now added to a new air quality objective, the identification of major source regions and major types of pollutants has become critically important. In this study, a source-oriented method (Particulate Source Apportionment Technology: PSAT) implemented in 3-D Comprehensive Air Quality Model (CAMx), has been applied to analyze how different emission activities impact fine particle concentration in the PRD region. By using this method, a detailed source region and emission category contribution matrix is derived for all regions within the Hong Kong/PRD region. Source appointment results shows that, in summer and spring time, emissions inside PRD region are the major fine particle sources, contribution 70.7% (11.2 mug/m3) and 52.5% (13.1 mug/m3) to the total figure. Super-regional transports are found to be significant in autumn and winter, contribution 58.5% (20.2 mug/m3) and 64.6% (27.8 mug/m3) of the total fine particles in PRD and Hong Kong region. Another important cause of high PM levels has been the transport of fine particles between cities within the PRD region, with three different regions selected for detailed analysis. Results show that mobile vehicle and industry emission are the two major sources for fine particles. Meanwhile, over the same period in Hong Kong, marine proved to be another very significant source of particle pollutant in addition to the significant impact from motor vehicle. Results show that for the Hong Kong/PRD region local reduction of mobile sources and collaboration between different areas could have succeeded in alleviating the air pollution problem.

  5. Novel 3D Tissue Engineered Bone Model, Biomimetic Nanomaterials, and Cold Atmospheric Plasma Technique for Biomedical Applications

    NASA Astrophysics Data System (ADS)

    Wang, Mian

    This thesis research is consist of four chapters, including biomimetic three-dimensional tissue engineered nanostructured bone model for breast cancer bone metastasis study (Chapter one), cold atmospheric plasma for selectively ablating metastatic breast cancer (Chapter two), design of biomimetic and bioactive cold plasma modified nanostructured scaffolds for enhanced osteogenic differentiation of bone marrow derived mesenchymal stem cells (Chapter three), and enhanced osteoblast and mesenchymal stem cell functions on titanium with hydrothermally treated nanocrystalline hydroxyapatite/magnetically treated carbon nanotubes for orthopedic applications (Chapter four). All the thesis research is focused on nanomaterials and the use of cold plasma technique for various biomedical applications.

  6. Detection and characterization of small-scale heating events in the solar atmosphere from 3D-MHD simulations and their potential role in coronal heating

    NASA Astrophysics Data System (ADS)

    Guerreiro, Nuno; Haberreiter, Margit; Schmutz, Werner; Hansteen, Viggo

    2016-07-01

    Aiming at better understanding the mechanism(s) responsible for the coronal heating we focus on analyzing the properties of the magnetically generated small-scale heating events (SSHEs) in the solar atmosphere. We present a comprehensive method to detect and follow SSHEs over time in 3D-MHD simulations of the solar atmosphere. Applying the method we are able to better understand the properties of the SSHEs and how the plasma in their vicinity respond to them. We study the lifetime, energy and spectral signatures and show that the energy flux dissipated by them is enough to heat the corona. Ultimately, these results will be important for the coordinated scientific exploration of SPICE and EUI along with other instruments on board solar orbiter.

  7. Characterization of small-scale heating events in the solar atmosphere from 3D-MHD simulations and their potential role in coronal heating

    NASA Astrophysics Data System (ADS)

    Guerreiro, Nuno; Haberreiter, Margit; Hansteen, Viggo; Schmutz, Werner

    2016-04-01

    Aiming at better understanding the mechanism(s) responsible for the coronal heating and the ubiquitous redshifts observed in the lower transition region we focus on analyzing the properties of small-scale heating events (SSHEs) in the solar atmosphere. We present a comprehensive method to follow SSHEs over time in 3D-MHD simulations of the solar atmosphere. Applying the method we are able to better understand the properties of the SSHEs and how the plasma in their vicinity respond to them. We present results for the lifetime, energy and spectral signatures of the SSHEs. Ultimately, these results will be important for the coordinated scientific exploration of SPICE and EUI along with other interments on board solar orbiter. ​

  8. An Investigation of the Seasonal Changes of Neptune's Atmosphere via a July 2008 Stellar Occultation Event

    NASA Astrophysics Data System (ADS)

    Uckert, Kyle; Chanover, N.; Miller, C.; Olkin, C.; Young, L.; Hammel, H.; Bauer, J.

    2012-10-01

    We extract physical atmospheric parameters from a July 23, 2008 single-chord stellar occultation of the star USNO-B1.0 0759-0739128 by Neptune using both light curve model fitting and numerical inversion techniques. We observed the occultation event using the Agile CCD camera mounted on the Astrophysical Research Consortium 3.5m telescope at Apache Point Observatory. We acquired a series of 13,340 0.5 second images from approximately 07:14 to 09:05 UT. Neptune was observed through an airmass ranging from 1.57 to 1.46, with atmospheric seeing of approximately 0.6" throughout the event. We used the Johnson I-band filter, which was chosen to reduce the contribution of scattered light from Neptune. Methane absorption at 0.89 μm in Neptune’s upper stratosphere causes Neptune to appear darker at this bandpass, reducing the amount of scattered light in the image. A 0.5 second integration time with negligible frame-transfer provides an atmospheric sampling at the microbar pressure level of approximately 4 samples per scale height. Stellar occultations of Neptune were observed extensively in the 1980's to search for evidence of a ring system around the planet prior to the arrival of Voyager 2. No new occultations of Neptune have been published since 1990, due in part to the diffuse star field the planet has been traveling though. We compare the stratospheric temperature derived from the 2008 occultation to published temperatures of Neptune at similar atmospheric pressures derived from previous stellar occultations and from mid-IR spectral data collected within the last decade. The two leading hypotheses for explaining the observed temperature variations of Neptune are seasonal variability and variations in the Lyman-alpha flux received at Neptune due to the 11-year solar cycle. We investigate the effect each of these mechanisms may have on the gradual changes of Neptune’s average stratospheric temperature. This work is supported by funds from NASA grant NAG5-1247.

  9. Multi-wavelength simulations of atmospheric radiation from Io with a 3-D spherical-shell backward Monte Carlo radiative transfer model

    NASA Astrophysics Data System (ADS)

    Gratiy, Sergey L.; Walker, Andrew C.; Levin, Deborah A.; Goldstein, David B.; Varghese, Philip L.; Trafton, Laurence M.; Moore, Chris H.

    2010-05-01

    Conflicting observations regarding the dominance of either sublimation or volcanism as the source of the atmosphere on Io and disparate reports on the extent of its spatial distribution and the absolute column abundance invite the development of detailed computational models capable of improving our understanding of Io's unique atmospheric structure and origin. Improving upon previous models, Walker et al. (Walker, A.C., Gratiy, S.L., Levin, D.A., Goldstein, D.B., Varghese, P.L., Trafton, L.M., Moore, C.H., Stewart, B. [2009]. Icarus) developed a fully 3-D global rarefied gas dynamics model of Io's atmosphere including both sublimation and volcanic sources of SO 2 gas. The fidelity of the model is tested by simulating remote observations at selected wavelength bands and comparing them to the corresponding astronomical observations of Io's atmosphere. The simulations are performed with a new 3-D spherical-shell radiative transfer code utilizing a backward Monte Carlo method. We present: (1) simulations of the mid-infrared disk-integrated spectra of Io's sunlit hemisphere at 19 μm, obtained with TEXES during 2001-2004; (2) simulations of disk-resolved images at Lyman- α obtained with the Hubble Space Telescope (HST), Space Telescope Imaging Spectrograph (STIS) during 1997-2001; and (3) disk-integrated simulations of emission line profiles in the millimeter wavelength range obtained with the IRAM-30 m telescope in October-November 1999. We found that the atmospheric model generally reproduces the longitudinal variation in band depth from the mid-infrared data; however, the best match is obtained when our simulation results are shifted ˜30° toward lower orbital longitudes. The simulations of Lyman- α images do not reproduce the mid-to-high latitude bright patches seen in the observations, suggesting that the model atmosphere sustains columns that are too high at those latitudes. The simulations of emission line profiles in the millimeter spectral region support

  10. Albedo and atmospheric constraints of dwarf planet Makemake from a stellar occultation.

    PubMed

    Ortiz, J L; Sicardy, B; Braga-Ribas, F; Alvarez-Candal, A; Lellouch, E; Duffard, R; Pinilla-Alonso, N; Ivanov, V D; Littlefair, S P; Camargo, J I B; Assafin, M; Unda-Sanzana, E; Jehin, E; Morales, N; Tancredi, G; Gil-Hutton, R; de la Cueva, I; Colque, J P; Da Silva Neto, D N; Manfroid, J; Thirouin, A; Gutiérrez, P J; Lecacheux, J; Gillon, M; Maury, A; Colas, F; Licandro, J; Mueller, T; Jacques, C; Weaver, D; Milone, A; Salvo, R; Bruzzone, S; Organero, F; Behrend, R; Roland, S; Vieira-Martins, R; Widemann, T; Roques, F; Santos-Sanz, P; Hestroffer, D; Dhillon, V S; Marsh, T R; Harlingten, C; Bagatin, A Campo; Alonso, M L; Ortiz, M; Colazo, C; Lima, H J F; Oliveira, A S; Kerber, L O; Smiljanic, R; Pimentel, E; Giacchini, B; Cacella, P; Emilio, M

    2012-11-22

    Pluto and Eris are icy dwarf planets with nearly identical sizes, comparable densities and similar surface compositions as revealed by spectroscopic studies. Pluto possesses an atmosphere whereas Eris does not; the difference probably arises from their differing distances from the Sun, and explains their different albedos. Makemake is another icy dwarf planet with a spectrum similar to Eris and Pluto, and is currently at a distance to the Sun intermediate between the two. Although Makemake's size (1,420 ± 60 km) and albedo are roughly known, there has been no constraint on its density and there were expectations that it could have a Pluto-like atmosphere. Here we report the results from a stellar occultation by Makemake on 2011 April 23. Our preferred solution that fits the occultation chords corresponds to a body with projected axes of 1,430 ± 9 km (1σ) and 1,502 ± 45 km, implying a V-band geometric albedo p(V) = 0.77 ± 0.03. This albedo is larger than that of Pluto, but smaller than that of Eris. The disappearances and reappearances of the star were abrupt, showing that Makemake has no global Pluto-like atmosphere at an upper limit of 4-12 nanobar (1σ) for the surface pressure, although a localized atmosphere is possible. A density of 1.7 ± 0.3 g cm(-3) is inferred from the data. PMID:23172214

  11. Albedo and atmospheric constraints of dwarf planet Makemake from a stellar occultation

    NASA Astrophysics Data System (ADS)

    Ortiz, J. L.; Sicardy, B.; Braga-Ribas, F.; Alvarez-Candal, A.; Lellouch, E.; Duffard, R.; Pinilla-Alonso, N.; Ivanov, V. D.; Littlefair, S. P.; Camargo, J. I. B.; Assafin, M.; Unda-Sanzana, E.; Jehin, E.; Morales, N.; Tancredi, G.; Gil-Hutton, R.; de La Cueva, I.; Colque, J. P.; da Silva Neto, D. N.; Manfroid, J.; Thirouin, A.; Gutiérrez, P. J.; Lecacheux, J.; Gillon, M.; Maury, A.; Colas, F.; Licandro, J.; Mueller, T.; Jacques, C.; Weaver, D.; Milone, A.; Salvo, R.; Bruzzone, S.; Organero, F.; Behrend, R.; Roland, S.; Vieira-Martins, R.; Widemann, T.; Roques, F.; Santos-Sanz, P.; Hestroffer, D.; Dhillon, V. S.; Marsh, T. R.; Harlingten, C.; Campo Bagatin, A.; Alonso, M. L.; Ortiz, M.; Colazo, C.; Lima, H. J. F.; Oliveira, A. S.; Kerber, L. O.; Smiljanic, R.; Pimentel, E.; Giacchini, B.; Cacella, P.; Emilio, M.

    2012-11-01

    Pluto and Eris are icy dwarf planets with nearly identical sizes, comparable densities and similar surface compositions as revealed by spectroscopic studies. Pluto possesses an atmosphere whereas Eris does not; the difference probably arises from their differing distances from the Sun, and explains their different albedos. Makemake is another icy dwarf planet with a spectrum similar to Eris and Pluto, and is currently at a distance to the Sun intermediate between the two. Although Makemake's size (1,420 +/- 60 km) and albedo are roughly known, there has been no constraint on its density and there were expectations that it could have a Pluto-like atmosphere. Here we report the results from a stellar occultation by Makemake on 2011 April 23. Our preferred solution that fits the occultation chords corresponds to a body with projected axes of 1,430 +/- 9 km (1σ) and 1,502 +/- 45 km, implying a V-band geometric albedo pV = 0.77 +/- 0.03. This albedo is larger than that of Pluto, but smaller than that of Eris. The disappearances and reappearances of the star were abrupt, showing that Makemake has no global Pluto-like atmosphere at an upper limit of 4-12 nanobar (1σ) for the surface pressure, although a localized atmosphere is possible. A density of 1.7 +/- 0.3 g cm-3 is inferred from the data.

  12. Single stars in the Hyades open cluster. Fiducial sequence for testing stellar and atmospheric models

    NASA Astrophysics Data System (ADS)

    Kopytova, Taisiya G.; Brandner, Wolfgang; Tognelli, Emanuele; Prada Moroni, Pier Giorgio; Da Rio, Nicola; Röser, Siegfried; Schilbach, Elena

    2016-01-01

    Context. Age and mass determinations for isolated stellar objects remain model-dependent. While stellar interior and atmospheric theoretical models are rapidly evolving, we need a powerful tool to test them. Open clusters are good candidates for this role. Aims: We aim to create a fiducial sequence of stellar objects for testing stellar and atmospheric models. Methods: We complement previous studies on the Hyades multiplicity by Lucky Imaging observations with the AstraLux Norte camera. This allows us to exclude possible binary and multiple systems with companions outside a 2-7 AU separation and to create a single-star sequence for the Hyades. The sequence encompasses 250 main-sequence stars ranging from A5V to M6V. Using the Tool for Astrophysical Data Analysis (TA-DA), we create various theoretical isochrones applying different combinations of interior and atmospheric models. We compare the isochrones with the observed Hyades single-star sequence on J vs. J-Ks, J vs. J-H, and Ks vs. H-Ks color-magnitude diagrams. As a reference we also compute absolute fluxes and magnitudes for all stars from X-ray to mid-infrared based on photometric measurements available in the literature(ROSAT X-ray, GALEX UV, APASS gri, 2MASS JHKs, and WISE W1 to W4). Results: We find that combinations of both PISA and DARTMOUTH stellar interior models with BT-Settl 2010 atmospheric models describe the observed sequence well. We use PISA in combination with BT-Settl 2010 models to derive theoretical predictions for physical parameters (Teff, mass, log g) of 250 single stars in the Hyades. The full sequence covers the mass range of 0.13-2.30 M⊙, and effective temperatures between 3060 K and 8200 K. Conclusions: Within the measurement uncertainties, the current generation of models agree well with the single-star sequence. The primary limitations are the uncertainties in the measurement of the distances to individual Hyades members, and uncertainties in the photometry. Gaia parallaxes

  13. Radiative Transfer Methods: new exact results for testing the accuracy of the ALI numerical method for a stellar atmosphere

    NASA Astrophysics Data System (ADS)

    Chevallier, L.

    2010-11-01

    Tests are presented of the 1D Accelerated Lambda Iteration method, which is widely used for solving the radiative transfer equation for a stellar atmosphere. We use our ARTY code as a reference solution and tables for these tests are provided. We model a static idealized stellar atmosphere, which is illuminated on its inner face and where internal sources are distributed with weak or strong gradients. This is an extension of published tests for a slab without incident radiation and gradients. Typical physical conditions for the continuum radiation and spectral lines are used, as well as typical values for the numerical parameters in order to reach a 1% accuracy. It is shown that the method is able to reach such an accuracy for most cases but the spatial discretization has to be refined for strong gradients and spectral lines, beyond the scope of realistic stellar atmospheres models. Discussion is provided on faster methods.

  14. Alkali Halide Opacity in Brown Dwarf and Cool Stellar Atmospheres: A Study of Lithium Chloride

    NASA Astrophysics Data System (ADS)

    Kirby, K.; Weck, P. F.; Schweitzer, A.; Stancil, P. C.; Hauschildt, P. H.

    2003-12-01

    Recent thermochemical equilibrium calculations have revealed the important role played by lithium chloride in the lithium chemistry of cool dwarf atmospheres (K. Lodders 1999, ApJ 519, 793). Indeed, LiCl appears to be the dominant Li-bearing gas over an extended domain of the (P,T) diagram, typically for temperatures below 1500 K. LiCl has a large dipole moment in its ground electronic state which can give rise to intense rovibrational line spectra. In addition, LiCl can make dipole transitions to several low-lying unbound excited states, causing dissociation of the molecule. For these reasons, LiCl may be a significant source of line and continuum opacity in brown dwarf and cool stellar atmospheres. In this work, we report calculations of complete lists of line oscillator strengths and photodissociation cross sections for the low-lying electronic states of LiCl. We have performed single- and double-excitation configuration interaction calculations using the ALCHEMY ab initio package (Mc Lean et al. 1991, MOTECC 91, Elsevier, Leiden) and obtained the potential curves and the corresponding dipole transition moment functions between the X 1Σ ^+ ground state and the B 1Σ ^+ and A 1Π excited states. The resulting line oscillator strengths and molecular photodissociation cross sections have been included in the PHOENIX stellar atmosphere code (Hauschildt & Baron 1999, J. Comput. App. Math. 102, 41). The new models, calculated using spherical geometry for all gravities considered, also incorporate our latest database of nearly 670 million molecular lines, and updated equations of state (EOS). This work was supported in part by NSF grants AST-9720704 and AST-0086246, NASA grants NAG5-8425, NAG5-9222, and NAG5-10551 as well as NASA/JPL grant 961582.

  15. A 3D Global Climate Model of the Pluto atmosphere coupled to a volatile transport model to interpret New Horizons observations, including the N2, CH4 and CO cycles and the formation of organic hazes

    NASA Astrophysics Data System (ADS)

    Bertrand, Tanguy; Forget, Francois

    2016-04-01

    To interpret New Horizons observations and simulate the Pluto climate system, we have developed a Global Climate Model (GCM) of Pluto's atmosphere. In addition to a 3D "dynamical core" which solves the equation of meteorology, the model takes into account the N2 condensation and sublimation and its thermal and dynamical effects, the vertical turbulent mixing, the radiative transfer through methane and carbon monoxide, molecular thermal conduction, and a detailed surface thermal model with different thermal inertia for various timescales (diurnal, seasonal). The GCM also includes a detailed model of the CH4 and CO cycles, taking into account their transport by the atmospheric circulation and turbulence, as well as their condensation and sublimation on the surface and in the atmosphere, possibly forming methane ice clouds. The GCM consistently predicts the 3D methane abundance in the atmosphere, which is used as an input for our radiative transfer calculation. In a second phase, we also developed a volatile transport model, derived from the GCM, which can be run over thousands of years in order to reach consistent initial states for the GCM runs and better explore the seasonal processes on Pluto. Results obtained with the volatile transport model show that the distribution of N2, CH4 and CO ices primarily depends on the seasonal thermal inertia used for the different ices, and is affected by the assumed topography as well. As observed, it is possible to form a large and permanent nitrogen glacier with CO and CH4 ice deposits in an equatorial basin corresponding to Sputnik Planum, while having a surface pressure evolution consistent with stellar occultations and New Horizons data. In addition, most of the methane ice is sequestered with N2 ice in the basin but seasonal polar caps of CH4 frosts also form explaining the bright polar caps observed with Hubble in the 1980s and in line with New Horizons observations. Using such balanced combination of surface and

  16. Dynamics of local isolated magnetic flux tubes in a fast-rotating stellar atmosphere

    SciTech Connect

    Chou, W.; Tajima, C.T.; Matsumoto, R. |; Shibata, K.

    1998-01-01

    Dynamics of magnetic flux tubes in the fast rotating stellar atmosphere is studied. We focus on the effects and signatures of the instability of the flux tube emergence influenced by the Coriolis force. We present the result from a linear stability analysis and discuss its possible signatures in the course of the evolution of G-type and M-type stars. We present a three dimensional magnetohydrodynamical simulation of local isolated magnetic flux tubes under a magnetic buoyancy instability in co-rotating Cartesian coordinates. We find that the combination of the buoyancy instability and the Coriolis effect gives rise to a mechanism, to twist the emerging magnetic flux tube into a helical structure. The tilt angle, east-west asymmetry and magnetic helicity of the Twisted flux tubes in the simulations are studied in detail. The linear and nonlinear analyses provide hints as to what kind of pattern of large spots in young M-type main-sequence stars might be observed. We find that young and old G-type stars may have different distributions of spots while M-type stars may always have low latitudes spots. The size of stellar spots may decrease when a star becomes older, due to the decreasing of magnetic field. A qualitative comparison with solar observations is also presented.

  17. 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].

  18. An Iterative Phase-Space Explicit Discontinuous Galerkin Method for Stellar Radiative Transfer in Extended Atmospheres

    SciTech Connect

    de Almeida, V.F.

    2004-01-28

    A phase-space discontinuous Galerkin (PSDG) method is presented for the solution of stellar radiative transfer problems. It allows for greater adaptivity than competing methods without sacrificing generality. The method is extensively tested on a spherically symmetric, static, inverse-power-law scattering atmosphere. Results for different sizes of atmospheres and intensities of scattering agreed with asymptotic values. The exponentially decaying behavior of the radiative field in the diffusive-transparent transition region and the forward peaking behavior at the surface of extended atmospheres were accurately captured. The integrodifferential equation of radiation transfer is solved iteratively by alternating between the radiative pressure equation and the original equation with the integral term treated as an energy density source term. In each iteration, the equations are solved via an explicit, flux-conserving, discontinuous Galerkin method. Finite elements are ordered in wave fronts perpendicularly to the characteristic curves so that elemental linear algebraic systems are solved quickly by sweeping the phase space element by element. Two implementations of a diffusive boundary condition at the origin are demonstrated wherein the finite discontinuity in the radiative intensity is accurately captured by the proposed method. This allows for a consistent mechanism to preserve photon luminosity. The method was proved to be robust and fast, and a case is made for the adequacy of parallel processing. In addition to classical two-dimensional plots, results of normalized radiative intensity were mapped onto a log-polar surface exhibiting all distinguishing features of the problem studied.

  19. Stellar scintillation in the short exposure regime and atmospheric coherence time evaluation

    NASA Astrophysics Data System (ADS)

    Kornilov, V.

    2011-06-01

    Aims: Accurately measuring the atmospheric coherence time is still a significant problem despite a variety of applicable methods. The Multi-Aperture Scintillation Sensor (MASS) designed for the vertical profiling of optical turbulence also provides a measurements of coherence time, but its results were found to be biased. Hence there is a need for a more robust method to determine τ0. Methods: The effect of smoothing the stellar scintillation by a finite exposure of the detector is considered. The short exposure regime is described and its limits are defined. The re-analysis of previous measurements with the MASS is performed to test the applicability of this approach in real data processing. It is shown that most of the actual measurements satisfy the criteria of short exposures. Results: The expressions for the mean wind speeds bar V_2 in the free atmosphere from the measurement of the scintillation indices are derived for this regime. These values provide an estimate of the atmospheric coherence time τ0 without the need of empirical calibration. The verification of the method based on real measurements of the resulting τ0 agree well with independent methods.

  20. Solar/Stellar Irradiance Comparison Experiment (SOLSTICE) on the Upper Atmosphere Research Satellite (UARS)

    NASA Technical Reports Server (NTRS)

    Rottman, Gary J.; Woods, Thomas N.; London, Julius; Ayres, Thomas R.

    2003-01-01

    A final report on the operational activities related to the UARS Solar Stellar irradiance Comparison Experiment (SOLSTICE) is presented. Scientific activities of SOLSTICE has also been supported. The UARS SOLSTICE originated at the University of Colorado in 1981. One year after the UARS launch in 1991, the operations and research support activities for SOLSTICE were moved to the High Altitude Observatory (HAO) of the National Center for Atmospheric Research (NCAR). The SOLSTICE program continued at HAO with the National Science Foundation, and after four years, it was moved once again back to the University of Colorado. At the University after 1997 this subject grant was issued to further extend the operations activities from July 2001 through September 2002. Although this is a final report for one particular activity, in fact the SOLSTICE operations activity -first at the University, then at HAO, and now again at the University -has continued in a seamless fashion.

  1. Size, density, albedo and atmosphere limit of dwarf planet Eris from a stellar occultation

    NASA Astrophysics Data System (ADS)

    Sicardy, B.; Ortiz, J. L.; Assafin, M.; Jehin, E.; Maury, A.; Lellouch, E.; Gil-Hutton, R.; Braga-Ribas, F.; Colas, F.; Lecacheux, J.; Roques, F.; Santos-Sanz, P.; Morales, N.; Thirouin, A.; Camargo, J. I. B.; Vieira-Martins, R.; Gillon, M.; Manfroid, J.; Behrend, R.; Widemann, T.

    2011-10-01

    We report the observation of a multi-chord stellar occultation by the dwarf planet (136199) Eris. The event was observed on November 6, 2010 UT, from two sites in Chile. Our observation is consistent with a spherical Eris with radius RE=1163±6 km, density ?=2.52±0.05 g cm-3, and visible geometric albedo pV=0.96+0.09 -0.04. Besides being remarkably similar in size to Pluto, Eris appears as one of the intrinsically brightest objects of the solar system, with a density suggesting a mainly rocky interior. Upper limits of about 1 nbar are derived for the surface pressure of possible nitrogen, argon or methane atmospheres of the dwarf planet.

  2. Characterisation of small-scale heating events in the solar atmosphere from 3D MHD simulations and their potential role in coronal heating

    NASA Astrophysics Data System (ADS)

    Haberreiter, M.; Guerreiro, N.; Hansteen, V. H.; Schmutz, W. K.

    2015-12-01

    The physical mechanism that heats the solar corona is one of the still open science questions in solar physics. One of the proposed mechanism for coronal heating are nanoflares. To investigate their role in coronal heating we study the properties of the small-scale heating events in the solar atmosphere using 3D MHD simulations. We present a method to identify and track these heating events in time which allows us to study their life time, energy, and spectral signatures. These spectal signatures will be compared with available spectrosopic observations obtained with IRIS and SUMER. Ultimately, these results will be important for the coordinated scientific exploitation of SPICE and EUI along with other instruments onboard Solar Orbiter to address the coronal heating problem.

  3. New weather depiction technology for night vision goggle (NVG) training: 3D virtual/augmented reality scene-weather-atmosphere-target simulation

    NASA Astrophysics Data System (ADS)

    Folaron, Michelle; Deacutis, Martin; Hegarty, Jennifer; Vollmerhausen, Richard; Schroeder, John; Colby, Frank P.

    2007-04-01

    US Navy and Marine Corps pilots receive Night Vision Goggle (NVG) training as part of their overall training to maintain the superiority of our forces. This training must incorporate realistic targets; backgrounds; and representative atmospheric and weather effects they may encounter under operational conditions. An approach for pilot NVG training is to use the Night Imaging and Threat Evaluation Laboratory (NITE Lab) concept. The NITE Labs utilize a 10' by 10' static terrain model equipped with both natural and cultural lighting that are used to demonstrate various illumination conditions, and visual phenomena which might be experienced when utilizing night vision goggles. With this technology, the military can safely, systematically, and reliably expose pilots to the large number of potentially dangerous environmental conditions that will be experienced in their NVG training flights. A previous SPIE presentation described our work for NAVAIR to add realistic atmospheric and weather effects to the NVG NITE Lab training facility using the NVG - WDT(Weather Depiction Technology) system (Colby, et al.). NVG -WDT consist of a high end multiprocessor server with weather simulation software, and several fixed and goggle mounted Heads Up Displays (HUDs). Atmospheric and weather effects are simulated using state-of-the-art computer codes such as the WRF (Weather Research μ Forecasting) model; and the US Air Force Research Laboratory MODTRAN radiative transport model. Imagery for a variety of natural and man-made obscurations (e.g. rain, clouds, snow, dust, smoke, chemical releases) are being calculated and injected into the scene observed through the NVG via the fixed and goggle mounted HUDs. This paper expands on the work described in the previous presentation and will describe the 3D Virtual/Augmented Reality Scene - Weather - Atmosphere - Target Simulation part of the NVG - WDT. The 3D virtual reality software is a complete simulation system to generate realistic

  4. SCATTERING POLARIZATION AND HANLE EFFECT IN STELLAR ATMOSPHERES WITH HORIZONTAL INHOMOGENEITIES

    SciTech Connect

    Manso Sainz, Rafael; Trujillo Bueno, Javier E-mail: jtb@iac.es

    2011-12-10

    Scattering of light from an anisotropic source produces linear polarization in spectral lines and in the continuum. In the outer layers of a stellar atmosphere the anisotropy of the radiation field is typically dominated by the radiation escaping away, but local horizontal fluctuations of the physical conditions may also contribute, distorting the illumination and, hence, the polarization pattern. Additionally, a magnetic field may perturb and modify the line scattering polarization signals through the Hanle effect. Here, we study such symmetry-breaking effects. We develop a method to solve the transfer of polarized radiation in a scattering atmosphere with weak horizontal fluctuations of the opacity and source functions. It comprises linearization (small opacity and Planck function fluctuations are assumed), reduction to a quasi-plane-parallel problem through harmonic analysis, and the problem's numerical solution by generalized standard techniques. We apply this method to study scattering polarization in atmospheres with horizontal fluctuations in the Planck function and opacity. We derive several very general results and constraints from considerations on the symmetries and dimensionality of the problem, and we give explicit solutions of a few illustrative problems of special interest. For example, we show (1) how the amplitudes of the fractional linear polarization signals change when considering increasingly smaller horizontal atmospheric inhomogeneities, (2) that in the presence of such inhomogeneities even a vertical magnetic field may modify the scattering line polarization, and (3) that forward scattering polarization may be produced without the need for an inclined magnetic field. These results are important for understanding the physics of the problem and as benchmarks for multidimensional radiative transfer codes.

  5. 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].

  6. Pluto Atmospheric Activity, Ephemeris Offset and Charon Orbital Radius Constrained by Stellar Occultations

    NASA Astrophysics Data System (ADS)

    Sicardy, Bruno; Boissel, Y.; Colas, F.; Roques, F.; Widemann, T.; Assafin, M.; Camargo, J. I. B.; da Silva Neto, D. N.; Ribas, F. B.; Vieira Martins, R.; Andrei, A. H.; Behrend, R.; Beisker, W.; Herald, D.; Bolt, G.; Broughton, J.; Dobosz, T.; Gault, D.; Groom, R.; Kerr, S.; Anderson, P.; Batista, V.; Blair, L.; Greenhill, J.; Frappa, E.; Benard, F.; Teng, J. P.; Gruhn, C.; Blanchard, G.; Castets, M.

    2008-09-01

    We have pursued in 2008 our observing program of stellar occultations by Pluto and its satellites. This program started in 2002, and revealed a two-fold increase of Pluto atmospheric pressure between 1988 and 2002. Various occultations observed in 2006 and 2007 did not reveal any further increase in pressure. Also, a measure of Charon's radius was made using an occultation observed on 11 July 2005. At the moment of writing this abstract, two Pluto occultations have been successfully observed, one on 22 June 2008 (with five positive detections from Australia) and one on 24 June 2008 (with one positive detection from CFHT/Mauna Kea, Hawaii). Furthermore, one positive observation of a Charon occultation has been achieved on 22 June 2008 from La Reunion Island. Data are still being analyzed, and three different results will be presented: (1) The evolution of Pluto's atmospheric pressure since 2002, (2) the evolution of Pluto's positional offset with respect to the DE413 barycentric ephemeris since 2005, showing in particular a linear trend and an offset in declination of more than +0.1 arcsec in 2008, and (3) a new, independent measure of the distance Pluto-Charon using the 22 June 2008 occultation, taking advantage that Pluto and Charon occulted the same target star. Note that since only one occultation chord is available for that event, it is not possible to update Charon's radius using this data.

  7. A statistical method for treating molecular line opacities. [in cool stellar atmospheres

    NASA Technical Reports Server (NTRS)

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

    1976-01-01

    A method for treating atomic and molecular line opacities in cool stellar atmospheres by a statistical opacity sampling is investigated. Under the usual assumptions of plane-parallel geometry, radiative equilibrium, hydrostatic equilibrium, and LTE, each radiative quantity is computed monochromatically at each chosen frequency and depth without any averaging of the opacity. The number of frequencies needed to allow an accurate integration of the energy flux over a given spectral interval is investigated as a function of depth, including opacity for both CN and C2. This method is extended to the calculation of a model atmosphere of a star, and the effect of the number and placement of frequency points is studied. The method is applied to treating molecular lines of CO, C2, and CN in a cool carbon star. Significant advantages of the opacity sampling method are its flexibility, which permits computation of models having arbitrary variations of chemical composition and of opacity with wavelength and depth, and generalizability to include departures from LTE.

  8. One Year of atmospheric stellar Occultation Measurements with GOMOS on ENVISAT

    NASA Astrophysics Data System (ADS)

    Bertaux, J.-L.; Hauchecorne, A.; Dalaudier, F.; Cot, C.; Kyrölä, E.; Tamminen, J.; Fussen, D.

    2003-04-01

    GOMOS is the first space instrument dedicated to the study of the atmosphere of the Earth with the technique of stellar occultations (Global Ozone Monitoring by Occultation of Stars), allowing to measure the atmospheric transmission as a function of wavelength. This ESA funded instrument is placed on ENVISAT platform, which polar orbit allows to have a good latitude coverage. Because it is self-calibrated, it is particularly well adapted to the long time trend monitoring of stratospheric species. With 4 spectrometers the wavelength coverage of 245 nm to 942 nm allows to monitor ozone, H2O, NO2, NO3, air, aerosols, O2 and the temperature profiles. Two additional fast photometers (1 kHz sampling rate) allows for the correction of scintillations, as well as a study of the turbulence regime. A high vertical resolution profile of the temperature may also be obtained from the time shift between the red and the blue photometer. ENVISAT was launched on March 1st, 2002. During the first year of operation, approximately 300 occultations per day were recorded,mainly on the night side. Altitude range covers from 120 km down to 15 km, and sometimes as low as 6 km. The validation of ozone vertical profiles with lidars and other external sources show no noticeable bias. Scintillations are more severe than anticipated in the altitude range 25-35 km, requiring a new algorithm for the retrieval of NO2 and NO3 line densities from atmospheric transmission spectra. Individual and global results on O3, NO2, NO3, H2O, and O2 will be presented and discussed, as well as preliminary assimilation exercises with a Chemistry Transport Model.

  9. 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

  10. 3D mapping of water in oolithic limestone at atmospheric and vacuum saturation using X-ray micro-CT differential imaging

    SciTech Connect

    Boone, M.A.; De Kock, T.; Bultreys, T.; De Schutter, G.; Vontobel, P.; Van Hoorebeke, L.; Cnudde, V.

    2014-11-15

    Determining the distribution of fluids in porous sedimentary rocks is of great importance in many geological fields. However, this is not straightforward, especially in the case of complex sedimentary rocks like limestone, where a multidisciplinary approach is often needed to capture its broad, multimodal pore size distribution and complex pore geometries. This paper focuses on the porosity and fluid distribution in two varieties of Massangis limestone, a widely used natural building stone from the southeast part of the Paris basin (France). The Massangis limestone shows locally varying post-depositional alterations, resulting in different types of pore networks and very different water distributions within the limestone. Traditional techniques for characterizing the porosity and pore size distribution are compared with state-of-the-art neutron radiography and X-ray computed microtomography to visualize the distribution of water inside the limestone at different imbibition conditions. X-ray computed microtomography images have the great advantage to non-destructively visualize and analyze the pore space inside of a rock, but are often limited to the larger macropores in the rock due to resolution limitations. In this paper, differential imaging is successfully applied to the X-ray computed microtomography images to obtain sub-resolution information about fluid occupancy and to map the fluid distribution in three dimensions inside the scanned limestone samples. The detailed study of the pore space with differential imaging allows understanding the difference in the water uptake behavior of the limestone, a primary factor that affects the weathering of the rock. - Highlights: • The water distribution in a limestone was visualized in 3D with micro-CT. • Differential imaging allowed to map both macro and microporous zones in the rock. • The 3D study of the pore space clarified the difference in water uptake behavior. • Trapped air is visualized in the moldic

  11. Simulated Photoevaporative Mass Loss from Hot Jupiters in 3D

    NASA Astrophysics Data System (ADS)

    Tripathi, Anjali; Kratter, Kaitlin M.; Murray-Clay, Ruth A.; Krumholz, Mark R.

    2015-08-01

    Ionizing stellar photons heat the upper regions of planetary atmospheres, driving atmospheric mass loss. Gas escaping from several hot, hydrogen-rich planets has been detected using UV and X-ray transmission spectroscopy. Because these planets are tidally locked, and thus asymmetrically irradiated, escaping gas is unlikely to be spherically symmetric. In this paper, we focus on the effects of asymmetric heating on local outflow structure. We use the Athena code for hydrodynamics to produce 3D simulations of hot Jupiter mass loss that jointly model wind launching and stellar heating via photoionization. Our fiducial planet is an inflated, hot Jupiter with radius {R}{{p}}=2.14{R}{Jup} and mass {M}{{p}}=0.53{M}{Jup}. We irradiate the initially neutral, atomic hydrogen atmosphere with 13.6 eV photons and compute the outflow’s ionization structure. There are clear asymmetries in the atmospheric outflow, including a neutral shadow on the planet’s nightside. Given an incident ionizing UV flux comparable to that of the Sun, we find a steady-state mass loss rate of ˜ 2× {10}10 g s-1. The total mass loss rate and the outflow substructure along the substellar ray show good agreement with earlier 1D models, for two different fluxes. Our 3D data cube can be used to generate the outflow’s extinction spectrum during transit. As a proof of concept, we find absorption of stellar Lyα at Doppler-shifted velocities of up to ±50 km s-1. Our work provides a starting point for further 3D models that can be used to predict observable signatures of hot Jupiter mass loss.

  12. The new code of spectrum synthesis in magnetic stellar atmospheres with stratification of abundances

    NASA Astrophysics Data System (ADS)

    Khan, S.

    2004-10-01

    Here we present a new spectrum synthesis code SynthM for magnetic stars. SynthM works under the assumption of LTE in a plane-parallel atmosphere and is based on the non-magnetic spectrum synthesis code SynthVa of prof. V.Tsymbal. The SynthM code includes anomalous Zeeman pattern calculation, computation of local IQUV Stokes and disk integration algorithm. The transfer equation is solved by DELO method with quadratic approximation for the source function. The code allows use of two built-in analytical models of stellar magnetic field configuration (one of which identical to Piskunov's SynthMag model and the other is based on conception of "virtual" magnetic charges). Also, it is possible to use an arbitrary model of magnetic field configuration by setting the modulus and direction of field for each integrating node of a surface grid. Two integration methods are included in the code. SynthM allows one to calculate synthetic spectrum with preset stratification of abundances. SynthM is written in Fortran 95. The comparison of calculated IQUV Stokes shows good agreement between the SynthM and SynthMag (Piskunov 1999) codes. The practical application of the designed code is illustrated by the example of synthetic spectrum test calculation for the region 6146-6150 Å of the observed spectrum of β CrB.

  13. Pluto’s Atmosphere from Stellar Occultations in 2012 and 2013

    NASA Astrophysics Data System (ADS)

    Dias-Oliveira, A.; Sicardy, B.; Lellouch, E.; Vieira-Martins, R.; Assafin, M.; Camargo, J. I. B.; Braga-Ribas, F.; Gomes-Júnior, A. R.; Benedetti-Rossi, G.; Colas, F.; Decock, A.; Doressoundiram, A.; Dumas, C.; Emilio, M.; Fabrega Polleri, J.; Gil-Hutton, R.; Gillon, M.; Girard, J. H.; Hau, G. K. T.; Ivanov, V. D.; Jehin, E.; Lecacheux, J.; Leiva, R.; Lopez-Sisterna, C.; Mancini, L.; Manfroid, J.; Maury, A.; Meza, E.; Morales, N.; Nagy, L.; Opitom, C.; Ortiz, J. L.; Pollock, J.; Roques, F.; Snodgrass, C.; Soulier, J. F.; Thirouin, A.; Vanzi, L.; Widemann, T.; Reichart, D. E.; LaCluyze, A. P.; Haislip, J. B.; Ivarsen, K. M.; Dominik, M.; Jørgensen, U.; Skottfelt, J.

    2015-09-01

    We analyze two multi-chord stellar occultations by Pluto that were observed on 2012 July 18th and 2013 May 4th, and respectively monitored from five and six sites. They provide a total of fifteen light curves, 12 of which were used for a simultaneous fit that uses a unique temperature profile, assuming a clear (no haze) and pure N2 atmosphere, but allowing for a possible pressure variation between the two dates. We find a solution that satisfactorily fits (i.e., within the noise level) all of the 12 light curves, providing atmospheric constraints between ˜1190 km (pressure ˜11 μbar) and ˜1450 km (pressure ˜0.1 μbar) from Pluto’s center. Our main results are: (1) the best-fitting temperature profile shows a stratosphere with a strong positive gradient between 1190 km (at 36 K, 11 μbar) and r = 1215 km (6.0 μbar), where a temperature maximum of 110 K is reached; above it is a mesosphere with a negative thermal gradient of -0.2 K km-1 up to ˜1390 km (0.25 μbar), where the mesosphere connects itself to a more isothermal upper branch around 81 K; (2) the pressure shows a small (6%) but significant increase (6σ level) between the two dates; (3) without a troposphere, Pluto’s radius is found to be {R}{{P}}=1190\\+/- 5 km. Allowing for a troposphere, RP is constrained to lie between 1168 and 1195 km; and (4) the currently measured CO abundance is too small to explain the mesospheric negative thermal gradient. Cooling by HCN is possible, but only if this species is largely saturated. Alternative explanations like zonal winds or vertical compositional variations of the atmosphere are unable to explain the observed mesospheric negative thermal gradient. Partly based on observations made with the ESO camera NACO at the Very Large Telescope (Paranal), under program IDs 089.C-0314(C) and 291.C-5016. The prediction uses observations made with the WFI camera at the 2.2 m Telescope, under program ID 079.A-9202(A).

  14. The ATLAS3D project - XX. Mass-size and mass-σ distributions of early-type galaxies: bulge fraction drives kinematics, mass-to-light ratio, molecular gas fraction and stellar initial mass function

    NASA Astrophysics Data System (ADS)

    Cappellari, Michele; McDermid, Richard M.; Alatalo, Katherine; Blitz, Leo; Bois, Maxime; Bournaud, Frédéric; Bureau, M.; 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.

    2013-07-01

    In the companion Paper XV of this series, we derive accurate total mass-to-light ratios (M/L)_JAM≈ (M/L)({r}= {R_e}) within a sphere of radius r= {R_e} centred on the galaxy, as well as stellar (M/L)stars (with the dark matter removed) for the volume-limited and nearly mass-selected (stellar mass M_star ≳ 6× 10^9 { M_{⊙}}) ATLAS3D sample of 260 early-type galaxies (ETGs, ellipticals Es and lenticulars S0s). Here, we use those parameters to study the two orthogonal projections ({M_JAM}, {σ _e}) and ({M_JAM}, {R_e^maj}) of the thin Mass Plane (MP) ({M_JAM}, {σ _e}, {R_e^maj}) which describes the distribution of the galaxy population, where {M_JAM}≡ L× (M/L)_JAM≈ M_star. The distribution of galaxy properties on both projections of the MP is characterized by: (i) the same zone of exclusion (ZOE), which can be transformed from one projection to the other using the scalar virial equation. The ZOE is roughly described by two power laws, joined by a break at a characteristic mass {M_JAM}≈ 3× 10^{10} { M_{⊙}}, which corresponds to the minimum Re and maximum stellar density. This results in a break in the mean {M_JAM}-{σ _e} relation with trends {M_JAM}∝ σ _e^{2.3} and {M_JAM}∝ σ _e^{4.7} at small and large σe, respectively; (ii) a characteristic mass {M_JAM}≈ 2× 10^{11} { M_{⊙}} which separates a population dominated by flat fast rotator with discs and spiral galaxies at lower masses, from one dominated by quite round slow rotators at larger masses; (iii) below that mass the distribution of ETGs' properties on the two projections of the MP tends to be constant along lines of roughly constant σe, or equivalently along lines with {R_e^maj}∝ {M_JAM}, respectively (or even better parallel to the ZOE: {R_e^maj}∝ M_JAM^{0.75}); (iv) it forms a continuous and parallel sequence with the distribution of spiral galaxies; (v) at even lower masses, the distribution of fast-rotator ETGs and late spirals naturally extends to that of dwarf ETGs (Sph

  15. Tropospheric Airborne Meteorological Data Reporting (TAMDAR) Sensor Validation and Verification on National Oceanographic and Atmospheric Administration (NOAA) Lockheed WP-3D Aircraft

    NASA Technical Reports Server (NTRS)

    Tsoucalas, George; Daniels, Taumi S.; Zysko, Jan; Anderson, Mark V.; Mulally, Daniel J.

    2010-01-01

    As part of the National Aeronautics and Space Administration's Aviation Safety and Security Program, the Tropospheric Airborne Meteorological Data Reporting project (TAMDAR) developed a low-cost sensor for aircraft flying in the lower troposphere. This activity was a joint effort with support from Federal Aviation Administration, National Oceanic and Atmospheric Administration, and industry. This paper reports the TAMDAR sensor performance validation and verification, as flown on board NOAA Lockheed WP-3D aircraft. These flight tests were conducted to assess the performance of the TAMDAR sensor for measurements of temperature, relative humidity, and wind parameters. The ultimate goal was to develop a small low-cost sensor, collect useful meteorological data, downlink the data in near real time, and use the data to improve weather forecasts. The envisioned system will initially be used on regional and package carrier aircraft. The ultimate users of the data are National Centers for Environmental Prediction forecast modelers. Other users include air traffic controllers, flight service stations, and airline weather centers. NASA worked with an industry partner to develop the sensor. Prototype sensors were subjected to numerous tests in ground and flight facilities. As a result of these earlier tests, many design improvements were made to the sensor. The results of tests on a final version of the sensor are the subject of this report. The sensor is capable of measuring temperature, relative humidity, pressure, and icing. It can compute pressure altitude, indicated air speed, true air speed, ice presence, wind speed and direction, and eddy dissipation rate. Summary results from the flight test are presented along with corroborative data from aircraft instruments.

  16. Europeana and 3D

    NASA Astrophysics Data System (ADS)

    Pletinckx, D.

    2011-09-01

    The current 3D hype creates a lot of interest in 3D. People go to 3D movies, but are we ready to use 3D in our homes, in our offices, in our communication? Are we ready to deliver real 3D to a general public and use interactive 3D in a meaningful way to enjoy, learn, communicate? The CARARE project is realising this for the moment in the domain of monuments and archaeology, so that real 3D of archaeological sites and European monuments will be available to the general public by 2012. There are several aspects to this endeavour. First of all is the technical aspect of flawlessly delivering 3D content over all platforms and operating systems, without installing software. We have currently a working solution in PDF, but HTML5 will probably be the future. Secondly, there is still little knowledge on how to create 3D learning objects, 3D tourist information or 3D scholarly communication. We are still in a prototype phase when it comes to integrate 3D objects in physical or virtual museums. Nevertheless, Europeana has a tremendous potential as a multi-facetted virtual museum. Finally, 3D has a large potential to act as a hub of information, linking to related 2D imagery, texts, video, sound. We describe how to create such rich, explorable 3D objects that can be used intuitively by the generic Europeana user and what metadata is needed to support the semantic linking.

  17. Charon's Radius and Atmospheric Constraints from the 2005 July 11 Stellar Occultation

    NASA Astrophysics Data System (ADS)

    Gulbis, A. A. S.; Elliot, J. L.; Person, M. J.; Adams, E. R.; Kern, S. D.; Kramer, E. A.; Babcock, B. A.; Gangestad, J. W.; Pasachoff, J. M.; Souza, S. P.; Osip, D. J.; Emililo, M.; Tuvikene, T.

    2005-12-01

    On 2005 July 11 (UT), Charon occulted the star ``C313.2" (originally identified as a Pluto occultation star [McDonald & Elliot, Astron. J. 120, 1599, 2000]; UCAC2 26257135; R = 14.8). We arranged to observe this event using five telescopes at four sites: the 0.6-m at Pico dos Dias Obs. (Brazil), the 0.84-m at Obs. Cerro Armazones, the 2.5-m du Pont and 6.5-m Clay at Las Campanas Obs., and the 8-m Gemini South at Cerro Pacha (Chile). The observations were successful at all stations excluding Pico dos Dias, which was clouded out. The Acquisition Camera was employed at Gemini South, while the remaining sites used POETS (Portable Occultation, Eclipse, and Transit Systems). Each system utilized a high-speed camera, a control computer, and a GPS to establish accurate timing. The cameras contain back-illuminated CCDs, with > 90% quantum efficiency, ˜ 6 electrons read noise, and 1.74 ms deadtime during frame transfer. For this event, data rates were 2 - 10 Hz and signal-to-noise ratios were 28 - 273 (normalized to 1 s). The Clay telescope light curve had high enough time resolution and signal-to-noise to detect the first diffraction fringe. This dataset marks significant improvement over the only previously viewed stellar occultation by Charon (Walker, MNRAS 192, 47, 1980; Elliot & Young, Icarus 89, 244, 1991). By fitting the light curves with models derived from French and Gierasch (Astron. J. 81, 445, 1976), we have calculated Charon's radius and placed strong constraints on an atmosphere. These results seem consistent with a collisional origin of the Pluto-Charon system in which either of the precursor bodies may have been differentiated (McKinnon, Astrophys. J. Lett. 344, L41, 1989). Support provided, in part, by NASA Planetary Astronomy grants NNG04GE48G, NNG04GF25G, and NNH04ZSS001N, IAP P5/36 of the Belgian Federal Office, and BIL 01/3 of the Flemish Ministry.

  18. Combined stellar structure and atmosphere models for massive stars. Wolf-Rayet models with spherically outflowing envelopes.

    NASA Astrophysics Data System (ADS)

    Schaerer, D.

    1996-05-01

    We present a simple analytical method to describe the structure of a spherically expanding envelope with strong mass outflow. The structure is consistently connected to the hydrostatic stellar interior and provides an adequate description of the outer boundary conditions for stellar models with large mass loss rates. We apply our treatment to evolutionary models of Wolf-Rayet (WR) stars in order to study the possible influence of the stellar winds on the interior, and to determine more reliable radii of WR stars. Independently of the wind parameters (wind density, opacity, velocity law) the interior structure and evolution of WR stars is found to be unaffected by the outer layers. On the other hand, the stellar parameters (radii, effective temperatures) may well depend on the wind structure. For hydrogen rich WR stars (WNL) we find the existence of a temperature domain in the HR-diagram, where a transient concentration of stars on their blueward track is predicted in case of a strong backwarming from the wind. For WNE and WC/WO stars with strong mass loss rates we also derive subphotospheric radii corresponding to Rosseland optical depths of τ~10-20. The dependence of the subphotospheric radii on the adopted envelope structure is discussed. With respect to wind-free stellar models the subphotospheric radii are increased by up to a factor of ~4 for the most luminous WNE or WC stars. These radii and the corresponding effective temperatures should roughly be comparable with the stellar parameters (``core'' radii and temperatures) of non-LTE atmosphere models of WR stars. Comparisons using the newly derived subphotospheric radii yields a better agreement with observations. The stellar parameters obtained with the new treatment allow a better assignment of theoretical spectra to evolutionary tracks of evolved WR stars (WNE, WC). This also provides the base for future studies of the spectral evolution of post main-sequence massive stars and their descendants. We also

  19. 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

  20. 3d-3d correspondence revisited

    NASA Astrophysics Data System (ADS)

    Chung, Hee-Joong; Dimofte, Tudor; Gukov, Sergei; Sułkowski, Piotr

    2016-04-01

    In fivebrane compactifications on 3-manifolds, we point out the importance of all flat connections in the proper definition of the effective 3d {N}=2 theory. The Lagrangians of some theories with the desired properties can be constructed with the help of homological knot invariants that categorify colored Jones polynomials. Higgsing the full 3d theories constructed this way recovers theories found previously by Dimofte-Gaiotto-Gukov. We also consider the cutting and gluing of 3-manifolds along smooth boundaries and the role played by all flat connections in this operation.

  1. 3D and Education

    NASA Astrophysics Data System (ADS)

    Meulien Ohlmann, Odile

    2013-02-01

    Today the industry offers a chain of 3D products. Learning to "read" and to "create in 3D" becomes an issue of education of primary importance. 25 years professional experience in France, the United States and Germany, Odile Meulien set up a personal method of initiation to 3D creation that entails the spatial/temporal experience of the holographic visual. She will present some different tools and techniques used for this learning, their advantages and disadvantages, programs and issues of educational policies, constraints and expectations related to the development of new techniques for 3D imaging. Although the creation of display holograms is very much reduced compared to the creation of the 90ies, the holographic concept is spreading in all scientific, social, and artistic activities of our present time. She will also raise many questions: What means 3D? Is it communication? Is it perception? How the seeing and none seeing is interferes? What else has to be taken in consideration to communicate in 3D? How to handle the non visible relations of moving objects with subjects? Does this transform our model of exchange with others? What kind of interaction this has with our everyday life? Then come more practical questions: How to learn creating 3D visualization, to learn 3D grammar, 3D language, 3D thinking? What for? At what level? In which matter? for whom?

  2. BEAMS3D Neutral Beam Injection Model

    SciTech Connect

    Lazerson, Samuel

    2014-04-14

    With the advent of applied 3D fi elds in Tokamaks and modern high performance stellarators, a need has arisen to address non-axisymmetric effects on neutral beam heating and fueling. We report on the development of a fully 3D neutral beam injection (NBI) model, BEAMS3D, which addresses this need by coupling 3D equilibria to a guiding center code capable of modeling neutral and charged particle trajectories across the separatrix and into the plasma core. Ionization, neutralization, charge-exchange, viscous velocity reduction, and pitch angle scattering are modeled with the ADAS atomic physics database [1]. Benchmark calculations are presented to validate the collisionless particle orbits, neutral beam injection model, frictional drag, and pitch angle scattering effects. A calculation of neutral beam heating in the NCSX device is performed, highlighting the capability of the code to handle 3D magnetic fields.

  3. 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.

  4. Pluto's Atmosphere from the 2015 June 29 Ground-based Stellar Occultation at the Time of the New Horizons Flyby

    NASA Astrophysics Data System (ADS)

    Sicardy, B.; Talbot, J.; Meza, E.; Camargo, J. I. B.; Desmars, J.; Gault, D.; Herald, D.; Kerr, S.; Pavlov, H.; Braga-Ribas, F.; Assafin, M.; Benedetti-Rossi, G.; Dias-Oliveira, A.; Gomes-Júnior, A. R.; Vieira-Martins, R.; Bérard, D.; Kervella, P.; Lecacheux, J.; Lellouch, E.; Beisker, W.; Dunham, D.; Jelínek, M.; Duffard, R.; Ortiz, J. L.; Castro-Tirado, A. J.; Cunniffe, R.; Querel, R.; Yock, P. C.; Cole, A. A.; Giles, A. B.; Hill, K. M.; Beaulieu, J. P.; Harnisch, M.; Jansen, R.; Pennell, A.; Todd, S.; Allen, W. H.; Graham, P. B.; Loader, B.; McKay, G.; Milner, J.; Parker, S.; Barry, M. A.; Bradshaw, J.; Broughton, J.; Davis, L.; Devillepoix, H.; Drummond, J.; Field, L.; Forbes, M.; Giles, D.; Glassey, R.; Groom, R.; Hooper, D.; Horvat, R.; Hudson, G.; Idaczyk, R.; Jenke, D.; Lade, B.; Newman, J.; Nosworthy, P.; Purcell, P.; Skilton, P. F.; Streamer, M.; Unwin, M.; Watanabe, H.; White, G. L.; Watson, D.

    2016-03-01

    We present results from a multi-chord Pluto stellar occultation observed on 2015 June 29 from New Zealand and Australia. This occurred only two weeks before the NASA New Horizons flyby of the Pluto system and serves as a useful comparison between ground-based and space results. We find that Pluto's atmosphere is still expanding, with a significant pressure increase of 5 ± 2% since 2013 and a factor of almost three since 1988. This trend rules out, as of today, an atmospheric collapse associated with Pluto's recession from the Sun. A central flash, a rare occurrence, was observed from several sites in New Zealand. The flash shape and amplitude are compatible with a spherical and transparent atmospheric layer of roughly 3 km in thickness whose base lies at about 4 km above Pluto's surface, and where an average thermal gradient of about 5 K km-1 prevails. We discuss the possibility that small departures between the observed and modeled flash are caused by local topographic features (mountains) along Pluto's limb that block the stellar light. Finally, using two possible temperature profiles, and extrapolating our pressure profile from our deepest accessible level down to the surface, we obtain a possible range of 11.9-13.7 μbar for the surface pressure. Partly based on observations made with the ESO WFI camera at the 2.2 m Telescope (La Silla), under program ID 079.A-9202(A) within the agreement between the ON/MCTI and the Max Planck Society, with the ESO camera NACO at the Very Large Telescope (Paranal), under program ID 089.C-0314(C), and at the Pico dos Dias Observatory/LNA, Brazil.

  5. 3D Imaging.

    ERIC Educational Resources Information Center

    Hastings, S. K.

    2002-01-01

    Discusses 3 D imaging as it relates to digital representations in virtual library collections. Highlights include X-ray computed tomography (X-ray CT); the National Science Foundation (NSF) Digital Library Initiatives; output peripherals; image retrieval systems, including metadata; and applications of 3 D imaging for libraries and museums. (LRW)

  6. A laboratory study of the 8.65 micron fundamental of (C-12)H3D at temperatures relevant to Titan's atmosphere

    NASA Technical Reports Server (NTRS)

    Varanasi, P.; Giver, L. P.; Valero, F. P. J.

    1983-01-01

    Spectral transmittance measurements have been performed in the nu6-fundamental of (C-12)H3D at 153 K. Relevant to the studies of the emission spectra of Titan recorded by the IRIS instruments on board Voyagers 1 and 2, N2 has been used as the broadening gas. Excellent agreement between experimental and theoretical spectral transmittance has been the result of using N2-broadened line widths and their dependence upon temperature measured in the nu2-fundamental and S = 63.6 per(sq cm atm) for the absolute intensity of the nu6-fundamental.

  7. The composition of Saturn's atmosphere at northern temperate latitudes from Voyager IRIS spectra - NH3, PH3, C2H2, C2H6, CH3D, CH4, and the Saturnian D/H isotopic ratio

    NASA Technical Reports Server (NTRS)

    Courtin, R.; Gautier, D.; Marten, A.; Bezard, B.; Hanel, R.

    1984-01-01

    The vertical distributions and mixing ratios of minor constituents in the northern hemisphere of Saturn are investigated. Results are obtained for NH3, PH3, C2H2, C2H6, CH3D, and CH4; the D/H ratio is obtained from the CH4 and CH3D abundances. The NH3 mixing ratio in the upper atmosphere is found to be compatible with the saturated partial pressure. The inferred PH3/H2 ratio of 1.4 + or - 0.8 x 10 to the -6th is higher than the value derived from the solar P/H ratio. The stratospheric C2H2/H2 and C2H6/H2 ratios are, respectively, 2.1 + or - 1.4 x 10 to the -7th and 3.0 + or - 1.1 x 10 to the -6th; the latter decreases sharply below the 20-50 mbar level. The results for CH3D/H2 and CH4/H2 imply an enrichment of Saturn's upper atmosphere in carbon by a factor of at least three over the solar abundance. The interpretation of two NH3 lines in the five-micron window suggests a NH3/H2 ratio at the two bar level below the solar value.

  8. Atmosphere expansion and mass loss of close-orbit giant exoplanets heated by stellar XUV. I. Modeling of hydrodynamic escape of upper atmospheric material

    SciTech Connect

    Shaikhislamov, I. F.; Khodachenko, M. L.; Sasunov, Yu. L.; Lammer, H.; Kislyakova, K. G.; Erkaev, N. V.

    2014-11-10

    In the present series of papers we propose a consistent description of the mass loss process. To study in a comprehensive way the effects of the intrinsic magnetic field of a close-orbit giant exoplanet (a so-called hot Jupiter) on atmospheric material escape and the formation of a planetary inner magnetosphere, we start with a hydrodynamic model of an upper atmosphere expansion in this paper. While considering a simple hydrogen atmosphere model, we focus on the self-consistent inclusion of the effects of radiative heating and ionization of the atmospheric gas with its consequent expansion in the outer space. Primary attention is paid to an investigation of the role of the specific conditions at the inner and outer boundaries of the simulation domain, under which different regimes of material escape (free and restricted flow) are formed. A comparative study is performed of different processes, such as X-ray and ultraviolet (XUV) heating, material ionization and recombination, H{sub 3}{sup +} cooling, adiabatic and Lyα cooling, and Lyα reabsorption. We confirm the basic consistency of the outcomes of our modeling with the results of other hydrodynamic models of expanding planetary atmospheres. In particular, we determine that, under the typical conditions of an orbital distance of 0.05 AU around a Sun-type star, a hot Jupiter plasma envelope may reach maximum temperatures up to ∼9000 K with a hydrodynamic escape speed of ∼9 km s{sup –1}, resulting in mass loss rates of ∼(4-7) · 10{sup 10} g s{sup –1}. In the range of the considered stellar-planetary parameters and XUV fluxes, that is close to the mass loss in the energy-limited case. The inclusion of planetary intrinsic magnetic fields in the model is a subject of the follow-up paper (Paper II).

  9. OBSERVATIONAL CONSTRAINTS ON THE STELLAR RADIATION FIELD IMPINGING ON TRANSITIONAL DISK ATMOSPHERES

    SciTech Connect

    Szulagyi, Judit; Pascucci, Ilaria; Abraham, Peter; Moor, Attila; Apai, Daniel; Bouwman, Jeroen

    2012-11-01

    Mid-infrared atomic and ionic line ratios measured in spectra of pre-main-sequence stars are sensitive indicators of the hardness of the radiation field impinging on the disk surface. We present a low-resolution Spitzer IRS search for [Ar II] at 6.98 {mu}m, [Ne II] at 12.81 {mu}m, and [Ne III] 15.55 {mu}m lines in 56 transitional disks. These objects, characterized by reduced near-infrared but strong far-infrared excess emission, are ideal targets to set constraints on the stellar radiation field onto the disk, because their spectra are not contaminated by shock emission from jets/outflows or by molecular emission lines. After demonstrating that we can detect [Ne II] lines and recover their fluxes from the low-resolution spectra, here we report the first detections of [Ar II] lines toward protoplanetary disks. We did not detect [Ne III] emission in any of our sources. Our [Ne II]/[Ne III] line flux ratios combined with literature data suggest that a soft-EUV or X-ray spectrum produces these gas lines. Furthermore, the [Ar II]/[Ne II] line flux ratios point to a soft X-ray and/or soft-EUV stellar spectrum as the ionization source of the [Ar II] and [Ne II] emitting layer of the disk. If the soft X-ray component dominates over the EUV, then we would expect larger photoevaporation rates and, hence, a reduction of the time available to form planets.

  10. TRACE 3-D documentation

    SciTech Connect

    Crandall, K.R.

    1987-08-01

    TRACE 3-D is an interactive beam-dynamics program that calculates the envelopes of a bunched beam, including linear space-charge forces, through a user-defined transport system. TRACE 3-D provides an immediate graphics display of the envelopes and the phase-space ellipses and allows nine types of beam-matching options. This report describes the beam-dynamics calculations and gives detailed instruction for using the code. Several examples are described in detail.

  11. Improving the Ni I atomic model for solar and stellar atmospheric models

    SciTech Connect

    Vieytes, M. C.; Fontenla, J. M. E-mail: johnf@digidyna.com

    2013-06-01

    Neutral nickel (Ni I) is abundant in the solar atmosphere and is one of the important elements that contribute to the emission and absorption of radiation in the spectral range between 1900 and 3900 Å. Previously, the Solar Radiation Physical Modeling (SRPM) models of the solar atmosphere only considered a few levels of this species. Here, we improve the Ni I atomic model by taking into account 61 levels and 490 spectral lines. We compute the populations of these levels in full NLTE using the SRPM code and compare the resulting emerging spectrum with observations. The present atomic model significantly improves the calculation of the solar spectral irradiance at near-UV wavelengths, which is important for Earth atmospheric studies, and particularly for ozone chemistry.

  12. PORTA: A Massively Parallel Code for 3D Non-LTE Polarized Radiative Transfer

    NASA Astrophysics Data System (ADS)

    Štěpán, J.

    2014-10-01

    The interpretation of the Stokes profiles of the solar (stellar) spectral line radiation requires solving a non-LTE radiative transfer problem that can be very complex, especially when the main interest lies in modeling the linear polarization signals produced by scattering processes and their modification by the Hanle effect. One of the main difficulties is due to the fact that the plasma of a stellar atmosphere can be highly inhomogeneous and dynamic, which implies the need to solve the non-equilibrium problem of generation and transfer of polarized radiation in realistic three-dimensional stellar atmospheric models. Here we present PORTA, a computer program we have developed for solving, in three-dimensional (3D) models of stellar atmospheres, the problem of the generation and transfer of spectral line polarization taking into account anisotropic radiation pumping and the Hanle and Zeeman effects in multilevel atoms. The numerical method of solution is based on a highly convergent iterative algorithm, whose convergence rate is insensitive to the grid size, and on an accurate short-characteristics formal solver of the Stokes-vector transfer equation which uses monotonic Bezier interpolation. In addition to the iterative method and the 3D formal solver, another important feature of PORTA is a novel parallelization strategy suitable for taking advantage of massively parallel computers. Linear scaling of the solution with the number of processors allows to reduce the solution time by several orders of magnitude. We present useful benchmarks and a few illustrations of applications using a 3D model of the solar chromosphere resulting from MHD simulations. Finally, we present our conclusions with a view to future research. For more details see Štěpán & Trujillo Bueno (2013).

  13. High Altitude Structure in Pluto's Atmosphere from the 2007 March 18 Stellar Occultation

    NASA Astrophysics Data System (ADS)

    Person, Michael J.; Elliot, J. L.; Gulbis, A. A.; Zuluaga, C. A.; Babcock, B. A.; Pasachoff, J. M.; McKay, A. J.; Souza, S. P.; Hubbard, W. B.; Kulesa, C. A.; McCarthy, D. W.; Kern, S. D.; Levine, S. E.; Bosh, A. S.; Ryan, E. V.; Ryan, W. H.; Meyer, A.; Wolf, J.; Hill, J. M.

    2007-10-01

    Visible wavelength observations were made of the 2007 March 18 Pluto occultation of the star P445.3 (UCAC2 25823784; McDonald and Elliot, AJ 120, 1599) from five US sites by our consortium (Pasachoff, et al., 2007, this meeting). Simultaneous model fitting to all of our light curve data yielded 1207 ± 4 km as the half-light shadow radius of Pluto's atmosphere. This radius is consistent with the 1208 ± 9 km result measured in 2006 (Elliot, et al., AJ 134,1) and confirms that the large increase in atmospheric pressure measured between the 1988 and 2002 (Elliot, et al., Nature 424,165 Sicardy, et al., Nature 424, 168) observations has ceased. Inversion of the highest signal-to-noise visible light curve, obtained with the Portable Occultation Eclipse and Transit Systems (POETS; Souza, et al., PASP 118, 1550) at the 6.5-m MMT (MMTO, Fred Lawrence Whipple Observatory, Mt. Hopkins) resulted in number density, pressure, and temperature profiles for Pluto's atmosphere in the radius range of 1340 - 1460 km (assuming the dominant atmospheric component is N2). These inversions reveal oscillating deviations of the number density from a simple exponential profile in Pluto's upper atmosphere that are coherent across the 1000 km length of the grazing occultation and also in the 300 km line of sight. Here, we interpret this structure as vertically propagating waves in Pluto's upper atmosphere, and provide a feasible mechanism for the maintenance of this large-scale coherence in terms of Rossby planetary waves. This work was partially funded by NASA Planetary Astronomy grants NNG04GE48G, NNG04GF25G, NNH04ZSS001N, and NNG05GG75G. Partial funding for MMTO observations was also provided by Astronomy Camp. Some of the observations reported here were obtained at the MMT Observatory, a joint facility of the University of Arizona and the Smithsonian Institution.

  14. A joint data assimilation system (Tan-Tracker) to simultaneously estimate surface CO2 fluxes and 3-D atmospheric CO2 concentrations from observations

    NASA Astrophysics Data System (ADS)

    Tian, X.; Xie, Z.; Liu, Y.; Cai, Z.; Fu, Y.; Zhang, H.; Feng, L.

    2014-12-01

    We have developed a novel framework ("Tan-Tracker") for assimilating observations of atmospheric CO2 concentrations, based on the POD-based (proper orthogonal decomposition) ensemble four-dimensional variational data assimilation method (PODEn4DVar). The high flexibility and the high computational efficiency of the PODEn4DVar approach allow us to include both the atmospheric CO2 concentrations and the surface CO2 fluxes as part of the large state vector to be simultaneously estimated from assimilation of atmospheric CO2 observations. Compared to most modern top-down flux inversion approaches, where only surface fluxes are considered as control variables, one major advantage of our joint data assimilation system is that, in principle, no assumption on perfect transport models is needed. In addition, the possibility for Tan-Tracker to use a complete dynamic model to consistently describe the time evolution of CO2 surface fluxes (CFs) and the atmospheric CO2 concentrations represents a better use of observation information for recycling the analyses at each assimilation step in order to improve the forecasts for the following assimilations. An experimental Tan-Tracker system has been built based on a complete augmented dynamical model, where (1) the surface atmosphere CO2 exchanges are prescribed by using a persistent forecasting model for the scaling factors of the first-guess net CO2 surface fluxes and (2) the atmospheric CO2 transport is simulated by using the GEOS-Chem three-dimensional global chemistry transport model. Observing system simulation experiments (OSSEs) for assimilating synthetic in situ observations of surface CO2 concentrations are carefully designed to evaluate the effectiveness of the Tan-Tracker system. In particular, detailed comparisons are made with its simplified version (referred to as TT-S) with only CFs taken as the prognostic variables. It is found that our Tan-Tracker system is capable of outperforming TT-S with higher assimilation

  15. A 3D Global climate model of the Pluto atmosphere to interpret New Horizons observations, including the N2, CH4 and CO cycles and the formation of organic hazes

    NASA Astrophysics Data System (ADS)

    Forget, Francois; Bertrand, Tanguy; Vangvichith, Melanie; Leconte, Jeremy

    2015-11-01

    To interpret New Horizons observations and simulate the Pluto climate system, we have developed a Global Climate Model (GCM) of Pluto's atmosphere. In addition to a 3D "dynamical core" which solves the equations of meteorology, the model takes into account the N2 condensation and sublimation and its thermal and dynamical effects, the vertical turbulent mixing, the radiative transfer through methane and carbon monoxide, molecular thermal conduction, and a detailed surface thermal model with different thermal inertia for various timescales (diurnal, seasonal).The GCM also includes a detailed model of the CH4 and CO cycles, taking into account their transport by the atmospheric circulation and turbulence, as well as their condensation and sublimation on the surface and in the atmosphere, possibly forming methane ice clouds. The GCM consistently predicts the 3D methane abundance in the atmosphere, which is used as an input for our radiative transfer calculation.Because of the radiative timescales, the surface thermal inertia and the slow evolution of the methane cycle, the model takes more than 20 years to become insensitive to the assumed atmospheric initial states. We typically start our simulations in 1975 to simulate 2015, but remain sensitive to the assumed initial ices distribution and seasonal thermal inertia map. The simulated thermal structure and waves can be compared to the New Horizons occultations measurements. As observed, the longitudinal variability is very limited, for fundamental reasons.In addition, we have developed a 3D model of the formation of organic hazes within the GCM. It includes the different steps of aerosols formation as understood on Titan: photolysis of CH4 in the upper atmosphere by the Lyman-alpha radiation, production of various gaseous precursor species, conversion into solid particles through chemistry and aggregation processes, and gravitational sedimentation. Significant amount of haze particles are found to be present at all

  16. 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.

  17. THE SIZE, SHAPE, ALBEDO, DENSITY, AND ATMOSPHERIC LIMIT OF TRANSNEPTUNIAN OBJECT (50000) QUAOAR FROM MULTI-CHORD STELLAR OCCULTATIONS

    SciTech Connect

    Braga-Ribas, F.; Vieira-Martins, R.; Camargo, J. I. B.; Sicardy, B.; Lellouch, E.; Lecacheux, J.; Ortiz, J. L.; Morales, N.; Tancredi, G.; Roland, S.; Bruzzone, S.; Assafin, M.; Vachier, F.; Colas, F.; Maury, A.; Emilio, M.; Amorim, A.; Unda-Sanzana, E.; Almeida, L. A.; and others

    2013-08-10

    We present results derived from the first multi-chord stellar occultations by the transneptunian object (50000) Quaoar, observed on 2011 May 4 and 2012 February 17, and from a single-chord occultation observed on 2012 October 15. If the timing of the five chords obtained in 2011 were correct, then Quaoar would possess topographic features (crater or mountain) that would be too large for a body of this mass. An alternative model consists in applying time shifts to some chords to account for possible timing errors. Satisfactory elliptical fits to the chords are then possible, yielding an equivalent radius R{sub equiv} = 555 {+-} 2.5 km and geometric visual albedo p{sub V} = 0.109 {+-} 0.007. Assuming that Quaoar is a Maclaurin spheroid with an indeterminate polar aspect angle, we derive a true oblateness of {epsilon}= 0.087{sup +0.0268}{sub -0.0175}, an equatorial radius of 569{sup +24}{sub -17} km, and a density of 1.99 {+-} 0.46 g cm{sup -3}. The orientation of our preferred solution in the plane of the sky implies that Quaoar's satellite Weywot cannot have an equatorial orbit. Finally, we detect no global atmosphere around Quaoar, considering a pressure upper limit of about 20 nbar for a pure methane atmosphere.

  18. The Size, Shape, Albedo, Density, and Atmospheric Limit of Transneptunian Object (50000) Quaoar from Multi-chord Stellar Occultations

    NASA Astrophysics Data System (ADS)

    Braga-Ribas, F.; Sicardy, B.; Ortiz, J. L.; Lellouch, E.; Tancredi, G.; Lecacheux, J.; Vieira-Martins, R.; Camargo, J. I. B.; Assafin, M.; Behrend, R.; Vachier, F.; Colas, F.; Morales, N.; Maury, A.; Emilio, M.; Amorim, A.; Unda-Sanzana, E.; Roland, S.; Bruzzone, S.; Almeida, L. A.; Rodrigues, C. V.; Jacques, C.; Gil-Hutton, R.; Vanzi, L.; Milone, A. C.; Schoenell, W.; Salvo, R.; Almenares, L.; Jehin, E.; Manfroid, J.; Sposetti, S.; Tanga, P.; Klotz, A.; Frappa, E.; Cacella, P.; Colque, J. P.; Neves, C.; Alvarez, E. M.; Gillon, M.; Pimentel, E.; Giacchini, B.; Roques, F.; Widemann, T.; Magalhães, V. S.; Thirouin, A.; Duffard, R.; Leiva, R.; Toledo, I.; Capeche, J.; Beisker, W.; Pollock, J.; Cedeño Montaña, C. E.; Ivarsen, K.; Reichart, D.; Haislip, J.; Lacluyze, A.

    2013-08-01

    We present results derived from the first multi-chord stellar occultations by the transneptunian object (50000) Quaoar, observed on 2011 May 4 and 2012 February 17, and from a single-chord occultation observed on 2012 October 15. If the timing of the five chords obtained in 2011 were correct, then Quaoar would possess topographic features (crater or mountain) that would be too large for a body of this mass. An alternative model consists in applying time shifts to some chords to account for possible timing errors. Satisfactory elliptical fits to the chords are then possible, yielding an equivalent radius R equiv = 555 ± 2.5 km and geometric visual albedo pV = 0.109 ± 0.007. Assuming that Quaoar is a Maclaurin spheroid with an indeterminate polar aspect angle, we derive a true oblateness of \\epsilon = 0.087^{+0.0268}_{-0.0175}, an equatorial radius of 569^{+24}_{-17} km, and a density of 1.99 ± 0.46 g cm-3. The orientation of our preferred solution in the plane of the sky implies that Quaoar's satellite Weywot cannot have an equatorial orbit. Finally, we detect no global atmosphere around Quaoar, considering a pressure upper limit of about 20 nbar for a pure methane atmosphere.

  19. Inferring transit time distributions from atmospheric tracer data: Assessment of the predictive capacities of Lumped Parameter Models on a 3D crystalline aquifer model

    NASA Astrophysics Data System (ADS)

    Marçais, J.; de Dreuzy, J.-R.; Ginn, T. R.; Rousseau-Gueutin, P.; Leray, S.

    2015-06-01

    While central in groundwater resources and contaminant fate, Transit Time Distributions (TTDs) are never directly accessible from field measurements but always deduced from a combination of tracer data and more or less involved models. We evaluate the predictive capabilities of approximate distributions (Lumped Parameter Models abbreviated as LPMs) instead of fully developed aquifer models. We develop a generic assessment methodology based on synthetic aquifer models to establish references for observable quantities as tracer concentrations and prediction targets as groundwater renewal times. Candidate LPMs are calibrated on the observable tracer concentrations and used to infer renewal time predictions, which are compared with the reference ones. This methodology is applied to the produced crystalline aquifer of Plœmeur (Brittany, France) where flows leak through a micaschists aquitard to reach a sloping aquifer where they radially converge to the producing well, issuing broad rather than multi-modal TTDs. One, two and three parameters LPMs were calibrated to a corresponding number of simulated reference anthropogenic tracer concentrations (CFC-11, 85Kr and SF6). Extensive statistical analysis over the aquifer shows that a good fit of the anthropogenic tracer concentrations is neither a necessary nor a sufficient condition to reach acceptable predictive capability. Prediction accuracy is however strongly conditioned by the use of a priori relevant LPMs. Only adequate LPM shapes yield unbiased estimations. In the case of Plœmeur, relevant LPMs should have two parameters to capture the mean and the standard deviation of the residence times and cover the first few decades [0; 50 years]. Inverse Gaussian and shifted exponential performed equally well for the wide variety of the reference TTDs from strongly peaked in recharge zones where flows are diverging to broadly distributed in more converging zones. When using two sufficiently different atmospheric tracers like

  20. Three-Layered Atmospheric Structure in Accretion Disks Around Stellar-Mass Black Holes

    NASA Technical Reports Server (NTRS)

    Zhang, S. N.; Cui, Wei; Chen, Wan; Yao, Yangsen; Zhang, Xiaoling; Sun, Xuejun; Wu, Xue-Bing; Xu, Haiguang

    2000-01-01

    Modeling of the x-ray spectra of the Galactic superluminal jet sources GRS 1915+105 and GRO J1655-40 reveals a three-layered atmospheric structure in the inner region of the inner accretion disks. Above the cold and optically thick disk with a temperature of 0.2 to 0.5 kiloelectron volts, there is a warm layer with a temperature of 1.0 to 1.5 kiloelectron volts and an optical depth around 10. Sometimes there is also a much hotter, optically thin corona above the warm layer, with a temperature of 100 kiloelectron volts or higher and an optical depth around unity. The structural similarity between the accretion disks and the solar atmosphere suggests that similar physical processes may be operating in these different systems.

  1. MISTiC Winds, a Micro-Satellite Constellation Approach to High Resolution Observations of the Atmosphere using Infrared Sounding and 3D Winds Measurements

    NASA Astrophysics Data System (ADS)

    Maschhoff, K. R.; Polizotti, J. J.; Susskind, J.; Aumann, H. H.

    2015-12-01

    MISTiCTM Winds is an approach to improve short-term weather forecasting based on a miniature high resolution, wide field, thermal emission spectrometry instrument that will provide global tropospheric vertical profiles of atmospheric temperature and humidity at high (3-4 km) horizontal and vertical ( 1 km) spatial resolution. MISTiC's extraordinarily small size, payload mass of less than 15 kg, and minimal cooling requirements can be accommodated aboard a 27U-class CubeSat or an ESPA-Class micro-satellite. Low fabrication and launch costs enable a LEO sun-synchronous sounding constellation that would collectively provide frequent IR vertical profiles and vertically resolved atmospheric motion vector wind observations in the troposphere. These observations are highly complementary to present and emerging environmental observing systems, and would provide a combination of high vertical and horizontal resolution not provided by any other environmental observing system currently in operation. The spectral measurements that would be provided by MISTiC Winds are similar to those of NASA's Atmospheric Infrared Sounder that was built by BAE Systems and operates aboard the AQUA satellite. These new observations, when assimilated into high resolution numerical weather models, would revolutionize short-term and severe weather forecasting, save lives, and support key economic decisions in the energy, air transport, and agriculture arenas-at much lower cost than providing these observations from geostationary orbit. In addition, this observation capability would be a critical tool for the study of transport processes for water vapor, clouds, pollution, and aerosols. Key technical risks are being reduced through laboratory and airborne testing under NASA's Instrument Incubator Program.

  2. Radiochromic 3D Detectors

    NASA Astrophysics Data System (ADS)

    Oldham, Mark

    2015-01-01

    Radiochromic materials exhibit a colour change when exposed to ionising radiation. Radiochromic film has been used for clinical dosimetry for many years and increasingly so recently, as films of higher sensitivities have become available. The two principle advantages of radiochromic dosimetry include greater tissue equivalence (radiologically) and the lack of requirement for development of the colour change. In a radiochromic material, the colour change arises direct from ionising interactions affecting dye molecules, without requiring any latent chemical, optical or thermal development, with important implications for increased accuracy and convenience. It is only relatively recently however, that 3D radiochromic dosimetry has become possible. In this article we review recent developments and the current state-of-the-art of 3D radiochromic dosimetry, and the potential for a more comprehensive solution for the verification of complex radiation therapy treatments, and 3D dose measurement in general.

  3. Response of Atmospheric Biomarkers to NOx-Induced Photochemistry Generated by Stellar Cosmic Rays for Earth-like Planets in the Habitable Zone of M Dwarf Stars

    PubMed Central

    Grießmeier, Jean-Mathias; von Paris, Philip; Patzer, A. Beate C.; Lammer, Helmut; Stracke, Barbara; Gebauer, Stefanie; Schreier, Franz; Rauer, Heike

    2012-01-01

    Abstract Understanding whether M dwarf stars may host habitable planets with Earth-like atmospheres and biospheres is a major goal in exoplanet research. If such planets exist, the question remains as to whether they could be identified via spectral signatures of biomarkers. Such planets may be exposed to extreme intensities of cosmic rays that could perturb their atmospheric photochemistry. Here, we consider stellar activity of M dwarfs ranging from quiet up to strong flaring conditions and investigate one particular effect upon biomarkers, namely, the ability of secondary electrons caused by stellar cosmic rays to break up atmospheric molecular nitrogen (N2), which leads to production of nitrogen oxides (NOx) in the planetary atmosphere, hence affecting biomarkers such as ozone (O3). We apply a stationary model, that is, without a time dependence; hence we are calculating the limiting case where the atmospheric chemistry response time of the biomarkers is assumed to be slow and remains constant compared with rapid forcing by the impinging stellar flares. This point should be further explored in future work with time-dependent models. We estimate the NOx production using an air shower approach and evaluate the implications using a climate-chemical model of the planetary atmosphere. O3 formation proceeds via the reaction O+O2+M→O3+M. At high NOx abundances, the O atoms arise mainly from NO2 photolysis, whereas on Earth this occurs via the photolysis of molecular oxygen (O2). For the flaring case, O3 is mainly destroyed via direct titration, NO+O3→NO2+O2, and not via the familiar catalytic cycle photochemistry, which occurs on Earth. For scenarios with low O3, Rayleigh scattering by the main atmospheric gases (O2, N2, and CO2) became more important for shielding the planetary surface from UV radiation. A major result of this work is that the biomarker O3 survived all the stellar-activity scenarios considered except for the strong case, whereas the biomarker

  4. Bootstrapping 3D fermions

    NASA Astrophysics Data System (ADS)

    Iliesiu, Luca; Kos, Filip; Poland, David; Pufu, Silviu S.; Simmons-Duffin, David; Yacoby, Ran

    2016-03-01

    We study the conformal bootstrap for a 4-point function of fermions < ψψψψ> in 3D. We first introduce an embedding formalism for 3D spinors and compute the conformal blocks appearing in fermion 4-point functions. Using these results, we find general bounds on the dimensions of operators appearing in the ψ × ψ OPE, and also on the central charge C T . We observe features in our bounds that coincide with scaling dimensions in the GrossNeveu models at large N . We also speculate that other features could coincide with a fermionic CFT containing no relevant scalar operators.

  5. Molecular Line and Continuum Opacities for Modeling of Extrasolar Giant Planet and Cool Stellar Atmospheres

    NASA Technical Reports Server (NTRS)

    Weck, P. F.; Schweitzer, A.; Stancil, P. C.; Hauschildt, P. H.; Kirby, K.; Yamaguchi, Y.; Allen, W. D.

    2002-01-01

    The molecular line and continuum opacities are investigated in the atmospheres of cool stars and Extrasolar Giant Planets (EGPs). Using a combination of ab inito and experimentally derived potential curves and dipole transition moments, accurate data have been calculated for rovibrationally-resolved oscillator strengths and photodissociation cross sections in the B' (sup 2)Sigma+ (left arrow) X (sup 2)Sigma+ and A (sup 2)Pi (left arrow) X (sup 2)Sigma+ band systems in MgH. We also report our progress on the study of the electronic structure of LiCl and FeH.

  6. A spherical, non-LTE, blanketed model stellar atmosphere for Phi CAS (FOIa)

    NASA Astrophysics Data System (ADS)

    Rosenzweig, Patricia

    By constructing a model atmosphere, the theoretical energy distribution of the emergent radiation that best matches the observed energy distribution of the star Phi Cassiopeiae is calculated; its effective temperature and surface gravity are thus derived. In order to use the pair method to derive the extinction curve for NGC 457 of which Phi Cas is a member, a new method is developed for choosing a lightly reddened comparison star, which consists of matching the equivalent widths of spectral features that are particularly strong and sensitive to temperature and luminosity. The intrinsic energy distribution of Phi Cas was determined from 1500 to 5800 A. A detailed new spherical model atmosphere was constructed. The equation of transfer was solved with the constraints of hydrostatic and pure radiative equilibrium. The statistical equilibrium of 10 to the 6th transitions was treated. Several tests have demonstrated this model to be reliable. Results imply a mass of 6.3 + or - 3.6 solar masses, which agrees with the mass of the main-sequence turnoff of NGC 457.

  7. New Horizons Alice ultraviolet observations of a stellar occultation by Jupiter’s atmosphere

    NASA Astrophysics Data System (ADS)

    Greathouse, Thomas K.; Gladstone, G. R.; Moses, J. I.; Stern, S. A.; Retherford, K. D.; Vervack, R. J.; Slater, D. C.; Versteeg, M. H.; Davis, M. W.; Young, L. A.; Steffl, A. J.; Throop, H.; Parker, J. Wm.

    2010-07-01

    The Alice ultraviolet spectrograph onboard the New Horizons spacecraft observed two occultations of the bright star χ Ophiucus by Jupiter's atmosphere on February 22 and 23, 2007 during the approach phase of the Jupiter flyby. The ingress occultation probed the atmosphere at 32°N latitude near the dawn terminator, while egress probed 18°N latitude near the dusk terminator. A detailed analysis of both the ingress and egress occultations, including the effects of molecular hydrogen, methane, acetylene, ethylene, and ethane absorptions in the far ultraviolet (FUV), constrains the eddy diffusion coefficient at the homopause level to be 3.4-2.8+9.0×106 cm 2 s -1, consistent with Voyager measurements and other analyses (Festou, M.C., Atreya, S.K., Donahue, T.M., Sandel, B.R., Shemansky, D.E., Broadfoot, A.L. [1981]. J. Geophys. Res. 86, 5717-5725; Vervack Jr., R.J., Sandel, B.R., Gladstone, G.R., McConnell, J.C., Parkinson, C.D. [1995]. Icarus 114, 163-173; Yelle, R.V., Young, L.A., Vervack Jr., R.J., Young, R., Pfister, L., Sandel, B.R. [1996]. J. Geophys. Res. 101 (E1), 2149-2162). However, the actual derived pressure level of the methane homopause for both occultations differs from that derived by Festou et al. (1981) and Yelle et al. (1996) from the Voyager ultraviolet occultations, suggesting possible changes in the strength of atmospheric mixing with time. We find that at 32°N latitude, the methane concentration is 3.1-0.5+0.5×108 cm -3 at 70,397 km, the methane concentration is 1.2-0.3+0.3×109 cm -3 at 70,383 km, the acetylene concentration is 1.4-0.2+0.4×108 cm -3 at 70,364 km, and the ethane concentration is 6.8-0.8+1.1×108 cm -3 at 70,360 km. At 18°N latitude, the methane concentration is 3.2-0.7+0.7×108 cm -3 at 71,345 km, the methane concentration is 1.2-0.2+0.6×109 cm -3 at 71,332 km, the acetylene concentration is 1.6-0.6+0.3×108 cm -3 at 71,318 km, and the ethane concentration is 7.0-2.5+2.4×108 cm -3 at 71,315 km. We also find that the H 2

  8. Global 3-D modeling of atmospheric ozone in the free troposphere and the stratosphere with emphasis on midlatitude regions. Final report

    SciTech Connect

    Brasseur, G.; Tie, X.; Walters, S.

    1999-03-01

    The authors have used several global chemical/transport models (1) to study the contribution of various physical, chemical, and dynamical processes to the budget of mid-latitude ozone in the stratosphere and troposphere; (2) to analyze the potential mechanisms which are responsible for the observed ozone perturbations at mid-latitudes of the lower stratosphere and in the upper troposphere; (3) to calculate potential changes in atmospheric ozone response to anthropogenic changes (e.g., emission of industrially manufactured CFCs, CO, and NO{sub x}) and to natural perturbations (e.g., volcanic eruptions and biomass burning); and (4) to estimate the impact of these changes on the radiative forcing to the climate system and on the level of UV-B radiation at the surface.

  9. Atmospheric Limitations in Stellar Seismology: Should One Measure Radial Velocity or Brightness Fluctuations?

    NASA Technical Reports Server (NTRS)

    Fossat, E.

    1984-01-01

    Low degree p-modes of the Sun have been measured in spatially integrated sunlight (the Sun as a star) both in Doppler shift and in intensity fluctuations. These observations are a good starting point for the discussion of the best way to collect equivalent data on other stars. It is assumed that the Sun is removed far enough in space to become an ordinary star of magnitude zero to one. Evidently another star will oscillate with different frequencies and different amplitudes, but some reference must be made to start with. Using this scheme, a detailed investigation of the limitations of observational accuracy in the search for global p-modes is made. The sources of noise stand in the Sun itself, in the instrumentation, in the observing time duration, in the corpuscular nature of the light and mostly in the Earth atmosphere in the case of ground based observations.

  10. Statistical equilibrium calculations for silicon in early-type model stellar atmospheres

    NASA Technical Reports Server (NTRS)

    Kamp, L. W.

    1976-01-01

    Line profiles of 36 multiplets of silicon (Si) II, III, and IV were computed for a grid of model atmospheres covering the range from 15,000 to 35,000 K in effective temperature and 2.5 to 4.5 in log (gravity). The computations involved simultaneous solution of the steady-state statistical equilibrium equations for the populations and of the equation of radiative transfer in the lines. The variables were linearized, and successive corrections were computed until a minimal accuracy of 1/1000 in the line intensities was reached. The common assumption of local thermodynamic equilibrium (LTE) was dropped. The model atmospheres used also were computed by non-LTE methods. Some effects that were incorporated into the calculations were the depression of the continuum by free electrons, hydrogen and ionized helium line blocking, and auto-ionization and dielectronic recombination, which later were found to be insignificant. Use of radiation damping and detailed electron (quadratic Stark) damping constants had small but significant effects on the strong resonance lines of Si III and IV. For weak and intermediate-strength lines, large differences with respect to LTE computations, the results of which are also presented, were found in line shapes and strengths. For the strong lines the differences are generally small, except for the models at the hot, low-gravity extreme of our range. These computations should be useful in the interpretation of the spectra of stars in the spectral range B0-B5, luminosity classes III, IV, and V.