Sample records for accreting first-ascent giant

  1. A sample of potential disk hosting first ascent red giants

    NASA Astrophysics Data System (ADS)

    Steele, Amy; Debes, John

    2018-01-01

    Observations of (sub)giants with planets and disks provide the first set of proof that disks can survive the first stages of post-main-sequence evolution, even though the disks are expected to dissipate by this time. The infrared (IR) excesses present around a number of post-main-sequence (PMS) stars could be due to a traditional debris disk with planets (e.g. kappa CrB), some remnant of enhanced mass loss (e.g. the shell-like structure of R Sculptoris), and/or background contamination. We present a sample of potential disk hosting first ascent red giants. These stars all have infrared excesses at 22 microns, and possibly host circumstellar debris. We summarize the characteristics of the sample to better inform the incidence rates of thermally emitting material around giant stars. A thorough follow-up study of these candidates would serve as the first step in probing the composition of the dust in these systems that have left the main sequence, providing clues to the degree of disk processing that occurs beyond the main-sequence.

  2. Migration of accreting giant planets

    NASA Astrophysics Data System (ADS)

    Robert, C.; Crida, A.; Lega, E.; Méheut, H.

    2017-09-01

    Giant planets forming in protoplanetary disks migrate relative to their host star. By repelling the gas in their vicinity, they form gaps in the disk's structure. If they are effectively locked in their gap, it follows that their migration rate is governed by the accretion of the disk itself onto the star, in a so-called type II fashion. Recent results showed however that a locking mechanism was still lacking, and was required to understand how giant planets may survive their disk. We propose that planetary accretion may play this part, and help reach this slow migration regime.

  3. Migration of accreting giant planets

    NASA Astrophysics Data System (ADS)

    Crida, A.; Bitsch, B.; Raibaldi, A.

    2016-12-01

    We present the results of 2D hydro simulations of giant planets in proto-planetary discs, which accrete gas at a more or less high rate. First, starting from a solid core of 20 Earth masses, we show that as soon as the runaway accretion of gas turns on, the planet is saved from type I migration : the gap opening mass is reached before the planet is lost into its host star. Furthermore, gas accretion helps opening the gap in low mass discs. Consequently, if the accretion rate is limited to the disc supply, then the planet is already inside a gap and in type II migration. We further show that the type II migration of a Jupiter mass planet actually depends on its accretion rate. Only when the accretion is high do we retrieve the classical picture where no gas crosses the gap and the planet follows the disc spreading. These results impact our understanding of planet migration and planet population synthesis models. The e-poster presenting these results in French can be found here: L'e-poster présentant ces résultats en français est disponible à cette adresse: http://sf2a.eu/semaine-sf2a/2016/posterpdfs/156_179_49.pdf.

  4. X-rays from accretion of red giant winds

    NASA Technical Reports Server (NTRS)

    Jura, M.; Helfand, D. J.

    1984-01-01

    X-ray observations of the late-type red giants Mira and R Aqr obtained with the Einstein Observatory are presented, and the general problems of white dwarf accretion from late-type giant winds is considered. The extremely low measured luminosities obtained for the two systems leads to the conclusion that the companions of Mira and R Aqr are most likely low-mass main sequence objects rather than white dwarfs as is usually assumed. The expected X-ray luminosities of true red giant/white dwarf systems are considered, and it is concluded that far too few have been detected if the canonical accretion scenario is adopted. A possible explanation of this situation in terms of grain-dominated Eddington-limited accretion is proposed.

  5. The MagAO Giant Accreting Protoplanet Survey (GAPlanetS): Recent Results

    NASA Astrophysics Data System (ADS)

    Follette, Katherine; Close, Laird; Males, Jared; Morzinski, Katie; Leonard, Clare; MagAO

    2018-01-01

    I will summarize recent results of the MagAO Giant Accreting Protoplant Survey (GAPlanetS), a search for accreting protoplanets at H-alpha inside of transitional disk gaps. These young, centrally-cleared circumstellar disks are often hosted by stars that are still actively accreting, making it likely that any planets that lie in their central cavities will also be actively accreting. Through differential imaging at Hydrogen-alpha using Magellan's visible light adaptive optics system, we have completed the first systematic search for H-alpha emission from accreting protoplanets in fifteen bright Southern hemisphere transitional disks. I will present results from this survey, including a second epoch on the LkCa 15 system that shows several accreting protoplanet candidates.

  6. Formation Of the Giant Planets By Concurrent Accretion Of Solids And Gas

    NASA Technical Reports Server (NTRS)

    Pollack, James B.; Hubickyj, Olenka; Bodenheimer, Peter; Lissauer, Jack J.; Podolak, Morris; Greenzweig, Yuval; Cuzzi, Jeffery N. (Technical Monitor)

    1995-01-01

    New numerical simulations of the formation of the giant planets are presented, in which for the first time both the gas and planetesimal accretion rates are calculated in a self-consistent, interactive fashion. The simulations combine three elements: 1) three-body accretion cross-sections of solids onto an isolated planetary embryo, 2) a stellar evolution code for the planet's gaseous envelope, and 3) a planetesimal dissolution code within the envelope, used to evaluate the planet's effective capture radius and the energy deposition profile of accreted material. Major assumptions include: The planet is embedded in a disk of gas and small planetesimals with locally uniform initial surface mass density, and planetesimals are not allowed to migrate into or out of the planet's feeding zone. All simulations are characterized by three major phases. During the first phase, the planet's mass consists primarily of solid material. The planetesimal accretion rate, which dominates that of gas, rapidly increases owing to runaway accretion, then decreases as the planet's feeding zone is depleted. During the second phase, both solid and gas accretion rates are small and nearly independent of time. The third phase, marked by runaway gas accretion, starts when the solid and gas masses are about equal. It is engendered by a strong positive feedback on the gas accretion rates, driven by the rapid contraction of the gaseous envelope and the rapid expansion of the outer boundary, which depends on the planet's total mass. The overall evolutionary time scale is generally determined by the length of the second phase. The actual rates at which the giant planets accreted small planetesimals is probably intermediate between the constant rates assumed in most previous studies and the highly variable rates that we have used. Within the context, of the adopted model of planetesimal accretion, the joint constraints of the time scale for dissipation of the solar nebula and the current high

  7. The Evolution of Gas Giant Entropy During Formation by Runaway Accretion

    NASA Astrophysics Data System (ADS)

    Berardo, David; Cumming, Andrew; Marleau, Gabriel-Dominique

    2017-01-01

    We calculate the evolution of gas giant planets during the runaway gas accretion phase of formation, to understand how the luminosity of young giant planets depends on the accretion conditions. We construct steady-state envelope models, and run time-dependent simulations of accreting planets with the code Modules for Experiments in Stellar Astrophysics. We show that the evolution of the internal entropy depends on the contrast between the internal adiabat and the entropy of the accreted material, parametrized by the shock temperature T 0 and pressure P 0. At low temperatures ({T}0≲ 300-1000 {{K}}, depending on model parameters), the accreted material has a lower entropy than the interior. The convection zone extends to the surface and can drive a high luminosity, leading to rapid cooling and cold starts. For higher temperatures, the accreted material has a higher entropy than the interior, giving a radiative zone that stalls cooling. For {T}0≳ 2000 {{K}}, the surface-interior entropy contrast cannot be accommodated by the radiative envelope, and the accreted matter accumulates with high entropy, forming a hot start. The final state of the planet depends on the shock temperature, accretion rate, and starting entropy at the onset of runaway accretion. Cold starts with L≲ 5× {10}-6 {L}⊙ require low accretion rates and starting entropy, and the temperature of the accreting material needs to be maintained close to the nebula temperature. If instead the temperature is near the value required to radiate the accretion luminosity, 4π {R}2σ {T}04˜ ({GM}\\dot{M}/R), as suggested by previous work on radiative shocks in the context of star formation, gas giant planets form in a hot start with L˜ {10}-4 {L}⊙ .

  8. THE SUPER LITHIUM-RICH RED GIANT RAPID ROTATOR G0928+73.2600: A CASE FOR PLANET ACCRETION?

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

    Carlberg, Joleen K.; Majewski, Steven R.; Rood, Robert T.

    2010-11-01

    We present the discovery of a super lithium-rich K giant star, G0928+73.2600. This red giant (T {sub eff} = 4885 K and log g = 2.65) is a fast rotator with a projected rotational velocity of 8.4 km s{sup -1} and an unusually high lithium abundance of A(Li) = 3.30 dex. Although the lack of a measured parallax precludes knowing the exact evolutionary phase, an isochrone-derived estimate of its luminosity places the star on the Hertzsprung-Russell diagram in a location that is not consistent with either the red bump on the first ascent of the red giant branch or withmore » the second ascent on the asymptotic giant branch, the two evolutionary stages where lithium-rich giant stars tend to cluster. Thus, even among the already unusual group of lithium-rich giant stars, G0928+73.2600 is peculiar. Using {sup 12}C/{sup 13}C as a tracer for mixing-more mixing leads to lower {sup 12}C/{sup 13}C-we find {sup 12}C/{sup 13}C = 28, which is near the expected value for standard first dredge-up mixing. We can therefore conclude that 'extra' deep mixing has not occurred. Regardless of the ambiguity of the evolutionary stage, the extremely large lithium abundance and the rotational velocity of this star are unusual, and we speculate that G0928+73.2600 has been enriched in both lithium and angular momentum from a sub-stellar companion.« less

  9. Changes in the metallicity of gas giant planets due to pebble accretion

    NASA Astrophysics Data System (ADS)

    Humphries, R. J.; Nayakshin, S.

    2018-06-01

    We run numerical simulations to study the accretion of gas and dust grains on to gas giant planets embedded into massive protoplanetary discs. The outcome is found to depend on the disc cooling rate, planet mass, grain size, and irradiative feedback from the planet. If radiative cooling is efficient, planets accrete both gas and pebbles rapidly, open a gap, and usually become massive brown dwarfs. In the inefficient cooling case, gas is too hot to accrete on to the planet but pebble accretion continues and the planets migrate inward rapidly. Radiative feedback from the planet tends to suppress gas accretion. Our simulations predict that metal enrichment of planets by dust grain accretion inversely correlates with the final planet mass, in accordance with the observed trend in the inferred bulk composition of Solar system and exosolar giant planets. To account for observations, however, as many as ˜30-50 per cent of the dust mass should be in the form of large grains.

  10. How Turbulence Can Set the Radial Distribution of Gas Giants Formed by Pebble Accretion

    NASA Astrophysics Data System (ADS)

    Morley Rosenthal, Mickey; Murray-Clay, Ruth

    2018-04-01

    I discuss how turbulence impacts the orbital separation at which the cores of gas giants can form via pebble accretion. While pebble accretion is extremely rapid for massive planets, I demonstrate that pebble accretion is inhibited at protoplanet masses, an effect which is strongly enhanced in a turbulent disk. Using these considerations I derive a “minimum” mass, past which pebble accretion proceeds on timescales less than the disk lifetime. By considering core formation where early growth to this minimum mass proceeds by gravitational focusing of planetesimals, I demonstrate that the the semi-major axes where gas giants can form are more restricted as the strength of the nebular turbulence increases — e.g. formation can only occur at distances < 30 AU for α > 10^-2. I also examine the implications of turbulence on the mass gas giants can reach before opening a substantial gap and halting growth. I find that while weak turbulence allows gas giants to form far out in the disk, the masses of these planets are substantially lower (< 1 Jupiter mass), which would preclude them from having been detected by the current generation of direct imaging surveys.

  11. Sustained Accretion on Gas Giants Surrounded by Low-Turbulence Circumplanetary Disks

    NASA Astrophysics Data System (ADS)

    D'Angelo, Gennaro; Marzari, Francesco

    2015-11-01

    Gas giants more massive than Saturn acquire most of their envelope while surrounded by a circumplanetary disk (CPD), which extends over a fraction of the planet’s Hill radius. Akin to circumstellar disks, CPDs may be subject to MRI-driven turbulence and contain low-turbulence regions, i.e., dead zones. It was suggested that CPDs may inhibit sustained gas accretion, thus limiting planet growth, because gas transport through a CPD may be severely reduced by a dead zone, a consequence at odds with the presence of Jupiter-mass (and larger) planets. We studied how an extended dead zone influences gas accretion on a Jupiter-mass planet, using global 3D hydrodynamics calculations with mesh refinements. The accretion flow from the circumstellar disk to the CPD is resolved locally at the length scale Rj, Jupiter's radius. The gas kinematic viscosity is assumed to be constant and the dead zone around the planet is modeled as a region of much lower viscosity, extending from ~Rj out to ~60Rj and off the mid-plane for a few CPD scale heights. We obtain accretion rates only marginally smaller than those reported by, e.g., D'Angelo et al. (2003), Bate et al. (2003), Bodenheimer et al. (2013), who applied the same constant kinematic viscosity everywhere, including in the CPD. As found by several previous studies (e.g., D’Angelo et al. 2003; Bate et al. 2003; Tanigawa et al. 2012; Ayliffe and Bate 2012; Gressel et al. 2013; Szulágyi et al. 2014), the accretion flow does not proceed through the CPD mid-plane but rather at and above the CPD surface, hence involving MRI-active regions (Turner et al. 2014). We conclude that the presence of a dead zone in a CPD does not inhibit gas accretion on a giant planet. Sustained accretion in the presence of a CPD is consistent not only with the formation of Jupiter but also with observed extrasolar planets more massive than Jupiter. We place these results in the context of the growth and migration of a pair of giant planets locked in the 2

  12. Fast accretion of the earth with a late moon-forming giant impact.

    PubMed

    Yu, Gang; Jacobsen, Stein B

    2011-10-25

    Constraints on the formation history of the Earth are critical for understanding of planet formation processes. (182)Hf-(182)W chronometry of terrestrial rocks points to accretion of Earth in approximately 30 Myr after the formation of the solar system, immediately followed by the Moon-forming giant impact (MGI). Nevertheless, some N-body simulations and (182)Hf-(182)W and (87)Rb-(87)Sr chronology of some lunar rocks have been used to argue for a later formation of the Moon at 52 to > 100 Myr. This discrepancy is often explained by metal-silicate disequilibrium during giant impacts. Here we describe a model of the (182)W isotopic evolution of the accreting Earth, including constraints from partitioning of refractory siderophile elements (Ni, Co, W, V, and Nb) during core formation, which can explain the discrepancy. Our modeling shows that the concentrations of the siderophile elements of the mantle are consistent with high-pressure metal-silicate equilibration in a terrestrial magma ocean. Our analysis shows that the timing of the MGI is inversely correlated with the time scale of the main accretion stage of the Earth. Specifically, the earliest time the MGI could have taken place right at approximately 30 Myr, corresponds to the end of main-stage accretion at approximately 30 Myr. A late MGI (> 52 Myr) requires the main stage of the Earth's accretion to be completed rapidly in < 10.7 ± 2.5 Myr. These are the two end member solutions and a continuum of solutions exists in between these extremes.

  13. The Fate of Exoplanets and the Red Giant Rapid Rotator Connection

    NASA Astrophysics Data System (ADS)

    Carlberg, Joleen K.; Majewski, Steven R.; Arras, Phil; Smith, Verne V.; Cunha, Katia; Bizyaev, Dmitry

    2011-03-01

    We have computed the fate of exoplanet companions around main sequence stars to explore the frequency of planet ingestion by their host stars during the red giant branch evolution. Using published properties of exoplanetary systems combined with stellar evolution models and Zahn's theory of tidal friction, we modeled the tidal decay of the planets' orbits as their host stars evolve. Most planets currently orbiting within 2 AU of their star are expected to be ingested by the end of their stars' red giant branch ascent. Our models confirm that many transiting planets are sufficiently close to their parent star that they will be accreted during the main sequence lifetime of the star. We also find that planet accretion may play an important role in explaining the mysterious red giant rapid rotators, although appropriate planetary systems do not seem to be plentiful enough to account for all such rapid rotators. We compare our modeled rapid rotators and surviving planetary systems to their real-life counterparts and discuss the implications of this work to the broader field of exoplanets.

  14. Fast accretion of the Earth with a late Moon-forming giant impact

    PubMed Central

    Yu, Gang; Jacobsen, Stein B.

    2011-01-01

    Constraints on the formation history of the Earth are critical for understanding of planet formation processes. 182Hf-182W chronometry of terrestrial rocks points to accretion of Earth in approximately 30 Myr after the formation of the solar system, immediately followed by the Moon-forming giant impact (MGI). Nevertheless, some N-body simulations and 182Hf-182W and 87Rb-87Sr chronology of some lunar rocks have been used to argue for a later formation of the Moon at 52 to > 100 Myr. This discrepancy is often explained by metal-silicate disequilibrium during giant impacts. Here we describe a model of the 182W isotopic evolution of the accreting Earth, including constraints from partitioning of refractory siderophile elements (Ni, Co, W, V, and Nb) during core formation, which can explain the discrepancy. Our modeling shows that the concentrations of the siderophile elements of the mantle are consistent with high-pressure metal-silicate equilibration in a terrestrial magma ocean. Our analysis shows that the timing of the MGI is inversely correlated with the time scale of the main accretion stage of the Earth. Specifically, the earliest time the MGI could have taken place right at approximately 30 Myr, corresponds to the end of main-stage accretion at approximately 30 Myr. A late MGI (> 52 Myr) requires the main stage of the Earth’s accretion to be completed rapidly in < 10.7 ± 2.5 Myr. These are the two end member solutions and a continuum of solutions exists in between these extremes. PMID:22006299

  15. Reduced gas accretion on super-Earths and ice giants

    NASA Astrophysics Data System (ADS)

    Lambrechts, M.; Lega, E.

    2017-10-01

    A large fraction of giant planets have gaseous envelopes that are limited to about 10% of their total mass budget. Such planets are present in the solar system (Uranus, Neptune) and are frequently observed in short periods around other stars (the so-called super-Earths). In contrast to these observations, theoretical calculations based on the evolution of hydrostatic envelopes argue that such low-mass envelopes cannot be maintained around cores exceeding five Earth masses. Instead, under nominal disk conditions, these planets would acquire massive envelopes through runaway gas accretion within the lifetime of the protoplanetary disk. In this work we show that planetary envelopes are not in hydrostatic balance, which slows down envelope growth. A series of 3D global, radiative hydrodynamical simulations reveal a steady-state gas flow, which enters through the poles and exits in the disk midplane. Gas is pushed through the outer envelope in about ten orbital timescales. In regions of the disk that are not significantly dust-depleted, envelope accretion onto cores of about five Earth masses can get stalled as the gas flow enters the deep interior. Accreted solids sublimate deep in the convective interior, but small opacity-providing grains are trapped in the flow and do not settle, which further prevents rapid envelope accretion. The transition to runaway gas accretion can however be reached when cores grow larger than typical super-Earths, beyond 15 Earth masses, and preferably when disk opacities are below κ = 1 cm2/g. These findings offer an explanation for the typical low-mass envelopes around the cores of super-Earths.

  16. Migration of giant planets in a time-dependent planetesimal accretion disc

    NASA Astrophysics Data System (ADS)

    Del Popolo, A.; Ekşi, K. Y.

    2002-05-01

    In this paper we develop further the model for the migration of planets introduced in Del Popolo et al. We first model the protoplanetary nebula as a time-dependent accretion disc, and find self-similar solutions to the equations of the accretion disc that give us explicit formulae for the spatial structure and the temporal evolution of the nebula. These equations are then used to obtain the migration rate of the planet in the planetesimal disc, and to study how the migration rate depends on the disc mass, on its time evolution and on some values of the dimensionless viscosity parameter α . We find that planets that are embedded in planetesimal discs, having total mass of 10-4 -0.1Msolar , can migrate inward a large distance for low values of α (e.g., α ~=10-3 -10-2 ) and/or large disc mass, and can survive only if the inner disc is truncated or because of tidal interaction with the star. Orbits with larger a are obtained for smaller values of the disc mass and/or for larger values of α . This model may explain several orbital features of the recently discovered giant planets orbiting nearby stars.

  17. Circumplanetary discs around young giant planets: a comparison between core-accretion and disc instability

    NASA Astrophysics Data System (ADS)

    Szulágyi, J.; Mayer, L.; Quinn, T.

    2017-01-01

    Circumplanetary discs can be found around forming giant planets, regardless of whether core accretion or gravitational instability built the planet. We carried out state-of-the-art hydrodynamical simulations of the circumplanetary discs for both formation scenarios, using as similar initial conditions as possible to unveil possible intrinsic differences in the circumplanetary disc mass and temperature between the two formation mechanisms. We found that the circumplanetary discs' mass linearly scales with the circumstellar disc mass. Therefore, in an equally massive protoplanetary disc, the circumplanetary discs formed in the disc instability model can be only a factor of 8 more massive than their core-accretion counterparts. On the other hand, the bulk circumplanetary disc temperature differs by more than an order of magnitude between the two cases. The subdiscs around planets formed by gravitational instability have a characteristic temperature below 100 K, while the core-accretion circumplanetary discs are hot, with temperatures even greater than 1000 K when embedded in massive, optically thick protoplanetary discs. We explain how this difference can be understood as the natural result of the different formation mechanisms. We argue that the different temperatures should persist up to the point when a full-fledged gas giant forms via disc instability; hence, our result provides a convenient criterion for observations to distinguish between the two main formation scenarios by measuring the bulk temperature in the planet vicinity.

  18. Forming Giant Planet Cores by Pebble Accretion -- Why Slow and Steady wins the Race

    NASA Astrophysics Data System (ADS)

    Kretke, Katherine A.; Levison, Harold F.

    2014-05-01

    In recent years there has been a radical new solution proposed to solve the problem of giant planet core formation. "Pebbles", particles ranging from centimeters to meters in size, have been shown to accrete extremely efficiently due to aerodynamic drag. Large capture cross-sections combined with fast pebble drift rates can allow a single planetesimal to grow from Ceres size to 10s of Earth masses well within the lifetime of gaseous circumstellar disks. However, at large sizes, the the capture-cross section of pebbles goes with the Hill sphere, forcing pebble accretion to becomes a fundamentally "oligarchic-like" process. This makes it difficult to form a few giant planet cores; instead a more generic result is many 10s to 100s of competing oligarchs. In this work, we present a way to get around this oligarchic dilemma If pebbles are assumed to form slowly over a long period of time, then the planetesimal growth rates are slow enough for the planetesimals to dynamically excite each other. As the larger planetisimals/proto-planets stir their smaller companions, these smaller bodies are excited to such a degree that they spend only a small fraction of their orbits embedded in the cooler pebble disk. This allows the larger bodies to starve their neighbors and maintain a relative runaway growth rate to high mass, effectively forming the cores of giant planets.

  19. Elemental Fractionation During Rapid Accretion of the Moon Triggered by a Giant Impact

    NASA Technical Reports Server (NTRS)

    Abe, Y.; Zahnle, K. J.; Hashimoto, A.

    1998-01-01

    Recently, Ida et al. made an N-body simulation of lunar accretion from a protolunar disk formed by a giant impact. One of their important conclusions is that the accretion time of the Moon is as short as one month. Such rapid accretion is a necessary consequence of the high surface density of a lunar mass disk accreting just beyond the Roche limit (about 3Re); the Safronov accretion time (a few days) is even shorter. The energy of accretion always exceeds the gravitational binding energy of newly arriving matter. Hence, without an energy sink, the accreting body is thermally unstable. For the Earth and other planets, radiation acts as the sink. However, in such a short accretion time, the Moon cannot radiate the accretional energy. Even radiating at a silicate cloudtop temperature of roughly 2000 K, it would take more than 100 yr to radiatively cool the Moon. The plausible alternative heat sinks are heat capacity, latent heat of vaporization, and thermal escape of the gas to space (i.e., hydrodynamic blowoff). The latter becomes plausible for the Moon because the scale height at 2000 K (about 300 km) is a significant fraction of the lunar radius. The early stages of lunar (or "lunatesimal") growth release relatively little energy and can occur simply by heating the material, especially if the accreting material is originally cold. However, the material is unlikely to be cold, because the disk itself is hot and cooling time is long, while the lunar accretion time iss very short. Therefore, the moon is likely to accrete condensed material just after it condenses. Accordingly, the newly accreted material will be on the verge of vaporization and will have very little heat capacity to spare. The immediate heat sink is the latent heat of vaporization. Most of the vapor will escape from the moon, because the thermal energy in the gas can be used to drive escape. However, vaporization is generally incomplete. the latent heat of vaporization exceeds the energy of accretion

  20. Fallback accretion on to a newborn magnetar: long GRBs with giant X-ray flares

    NASA Astrophysics Data System (ADS)

    Gibson, S. L.; Wynn, G. A.; Gompertz, B. P.; O'Brien, P. T.

    2018-05-01

    Flares in the X-ray afterglow of gamma-ray bursts (GRBs) share more characteristics with the prompt emission than the afterglow, such as pulse profile and contained fluence. As a result, they are believed to originate from late-time activity of the central engine and can be used to constrain the overall energy budget. In this paper, we collect a sample of 19 long GRBs observed by Swift-XRT that contain giant flares in their X-ray afterglows. We fit this sample with a version of the magnetar propeller model, modified to include fallback accretion. This model has already successfully reproduced extended emission in short GRBs. Our best fits provide a reasonable morphological match to the light curves. However, 16 out of 19 of the fits require efficiencies for the propeller mechanism that approach 100%. The high efficiency parameters are a direct result of the high energy contained in the flares and the extreme duration of the dipole component, which forces either slow spin periods or low magnetic fields. We find that even with the inclusion of significant fallback accretion, in all but a few cases it is energetically challenging to produce prompt emission, afterglow and giant flares within the constraints of the rotational energy budget of a magnetar.

  1. ASCENT Program

    NASA Technical Reports Server (NTRS)

    Brown, Richard; Collier, Gary; Heckenlaible, Richard; Dougherty, Edward; Dolenz, James; Ross, Iain

    2012-01-01

    The ASCENT program solves the three-dimensional motion and attendant structural loading on a flexible vehicle incorporating, optionally, an active analog thrust control system, aerodynamic effects, and staging of multiple bodies. ASCENT solves the technical problems of loads, accelerations, and displacements of a flexible vehicle; staging of the upper stage from the lower stage; effects of thrust oscillations on the vehicle; a payload's relative motion; the effect of fluid sloshing on vehicle; and the effect of winds and gusts on the vehicle (on the ground or aloft) in a continuous analysis. The ATTACH ASCENT Loads program reads output from the ASCENT flexible body loads program, and calculates the approximate load indicators for the time interval under consideration. It calculates the load indicator values from pre-launch to the end of the first stage.

  2. Guidance Concept for a Mars Ascent Vehicle First Stage

    NASA Technical Reports Server (NTRS)

    Queen, Eric M.

    2000-01-01

    This paper presents a guidance concept for use on the first stage of a Mars Ascent Vehicle (MAV). The guidance is based on a calculus of variations approach similar to that used for the final phase of the Apollo Earth return guidance. A three degree-of-freedom (3DOF) Monte Carlo simulation is used to evaluate performance and robustness of the algorithm.

  3. Formation of Large Regular Satellites of Giant Planets in an Extended Gaseous Nebula: Subnebula Model and Accretion of Satellites

    NASA Technical Reports Server (NTRS)

    Mosqueira, I.; Estrada, P. R.

    2000-01-01

    We model the subnebulae of Jupiter and Saturn wherein satellite accretion took place. We expect a giant planet subnebula to be composed of an optically thick (given gaseous opacity) inner region inside of the planet's centrifugal radius (located at r(sub c, sup J) = l5R(sub J) for Jupiter and r(sub c, sup S) = 22R(sub S) for Saturn), and an optically thin, extended outer disk out to a fraction of the planet's Roche lobe, which we choose to be R(sub roche)/5 (located at approximately 150R(sub J) near the inner irregular satellites for Jupiter, and approximately 200R(sub S) near Phoebe for Saturn). This places Titan and Ganymede in the inner disk, Callisto and Iapetus in the outer disk, and Hyperion in the transition region. The inner disk is the leftover of the gas accreted by the protoplanet. The outer disk results from the solar torque on nebula gas flowing into the protoplanet during the time of giant planet gap opening. For the sake of specificity, we use a cosmic mixture 'minimum mass' model to constrain the gas densities of the inner disks of Jupiter and Saturn (and also Uranus). For the total mass of the outer disk we use the simple scaling M(sub disk) = M(sub P)tau(sub gap)/tau(sub acc), where M(sub P) is the mass of the giant planet, tau(sub gap) is the gap opening timescale, and tau(sub acc) is the giant planet accretion time. This gives a total outer disk mass of approximately 100M(sub Callisto) for Jupiter and possibly approximately 200M(sub Iapetus) for Saturn (which contain enough condensables to form Callisto and Iapetus respectively). Our model has Ganymede at a subnebula temperature of approximately 250 K and Titan at approximately 100 K. The outer disks of Jupiter and Saturn have constant temperatures of 130 K and 90 K respectively.

  4. Spherical accretion in giant elliptical galaxies: multi-transonicity, shocks, and implications on AGN feedback

    NASA Astrophysics Data System (ADS)

    Raychaudhuri, Sananda; Ghosh, Shubhrangshu; Joarder, Partha S.

    2018-06-01

    Isolated massive elliptical galaxies, or that are present at the center of cool-core clusters, are believed to be powered by hot gas accretion directly from their surrounding hot X-ray emitting gaseous medium. This leads to a giant Bondi-type spherical/quasi-spherical accretion flow onto their host SMBHs, with the accretion flow region extending well beyond the Bondi radius. In this work, we present a detailed study of Bondi-type spherical flow in the context of these massive ellipticals by incorporating the effect of entire gravitational potential of the host galaxy in the presence of cosmological constant Λ, considering a five-component galactic system (SMBH + stellar + dark matter + hot gas + Λ). The current work is an extension of Ghosh & Banik (2015), who studied only the cosmological aspect of the problem. The galactic contribution to the potential renders the (adiabatic) spherical flow to become multi-transonic in nature, with the flow topology and flow structure significantly deviating from that of classical Bondi solution. More notably, corresponding to moderate to higher values of galactic mass-to-light ratios, we obtain Rankine-Hugoniot shocks in spherical wind flows. Galactic potential enhances the Bondi accretion rate. Our study reveals that there is a strict lower limit of ambient temperature below which no Bondi accretion can be triggered; which is as high as ˜9 × 106 K for flows from hot ISM-phase, indicating that the hot phase tightly regulates the fueling of host nucleus. Our findings may have wider implications, particularly in the context of outflow/jet dynamics, and radio-AGN feedback, associated with these massive galaxies in the contemporary Universe.

  5. The accretion of migrating giant planets

    NASA Astrophysics Data System (ADS)

    Dürmann, Christoph; Kley, Wilhelm

    2017-02-01

    Aims: Most studies concerning the growth and evolution of massive planets focus either on their accretion or their migration only. In this work we study both processes concurrently to investigate how they might mutually affect one another. Methods: We modeled a two-dimensional disk with a steady accretion flow onto the central star and embedded a Jupiter mass planet at 5.2 au. The disk is locally isothermal and viscosity is modeled using a constant α. The planet is held on a fixed orbit for a few hundred orbits to allow the disk to adapt and carve a gap. After this period, the planet is released and free to move according to the gravitational interaction with the gas disk. The mass accretion onto the planet is modeled by removing a fraction of gas from the inner Hill sphere, and the removed mass and momentum can be added to the planet. Results: Our results show that a fast migrating planet is able to accrete more gas than a slower migrating planet. Utilizing a tracer fluid we analyzed the origin of the accreted gas originating predominantly from the inner disk for a fast migrating planet. In the case of slower migration, the fraction of gas from the outer disk increases. We also found that even for very high accretion rates, in some cases gas crosses the planetary gap from the inner to the outer disk. Our simulations show that the crossing of gas changes during the migration process as the migration rate slows down. Therefore, classical type II migration where the planet migrates with the viscous drift rate and no gas crosses the gap is no general process but may only occur for special parameters and at a certain time during the orbital evolution of the planet.

  6. DEUTERIUM BURNING IN MASSIVE GIANT PLANETS AND LOW-MASS BROWN DWARFS FORMED BY CORE-NUCLEATED ACCRETION

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

    Bodenheimer, Peter; D'Angelo, Gennaro; Lissauer, Jack J.

    Using detailed numerical simulations, we study the formation of bodies near the deuterium-burning limit according to the core-nucleated giant planet accretion scenario. The objects, with heavy-element cores in the range 5-30 M{sub Circled-Plus }, are assumed to accrete gas up to final masses of 10-15 Jupiter masses (M{sub Jup}). After the formation process, which lasts 1-5 Myr and which ends with a ''cold-start'', low-entropy configuration, the bodies evolve at constant mass up to an age of several Gyr. Deuterium burning via proton capture is included in the calculation, and we determined the mass, M{sub 50}, above which more than 50%more » of the initial deuterium is burned. This often-quoted borderline between giant planets and brown dwarfs is found to depend only slightly on parameters, such as core mass, stellar mass, formation location, solid surface density in the protoplanetary disk, disk viscosity, and dust opacity. The values for M{sub 50} fall in the range 11.6-13.6 M{sub Jup}, in agreement with previous determinations that do not take the formation process into account. For a given opacity law during the formation process, objects with higher core masses form more quickly. The result is higher entropy in the envelope at the completion of accretion, yielding lower values of M{sub 50}. For masses above M{sub 50}, during the deuterium-burning phase, objects expand and increase in luminosity by one to three orders of magnitude. Evolutionary tracks in the luminosity versus time diagram are compared with the observed position of the companion to Beta Pictoris.« less

  7. CNO isotopes in red giant stars

    NASA Technical Reports Server (NTRS)

    Wannier, P. G.

    1985-01-01

    The production and distribution of the CNO nuclides is discussed in light of observed abundance ratios in red giants and in the interstellar medium. Isotope abundances have been measured in the atmospheres and in the recent ejecta of cool giants, including carbon stars, S-type stars and red supergiants as well as in oxygen-rich giants making their first ascent of the giant branch. Several of the observations suggest revision of currently accepted nuclear cross-sections and of the mixing processes operating in giant envelopes. By comparing red giant abundances with high-quality observations of the interstellar medium, conclusions are reached about the contribution of intermediate-mass stars to galactic nuclear evolution. The three oxygen isotopes, O-16, -17 and -18, are particularly valuable for such comparison because they reflect three different stages of stellar nucleosynthesis. One remarkable result comes from observations of O-17/O-18 in several classes of red giant stars. The observed range of values for red giants excludes the entire range of values seen in interstellar molecular clouds. Furthermore, both the observations of stars and interstellar clouds exclude the isotopic ratio found in the solar system.

  8. ORIGIN OF LITHIUM ENRICHMENT IN K GIANTS

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

    Kumar, Yerra Bharat; Reddy, Bacham E.; Lambert, David L.

    In this Letter, we report on a low-resolution spectroscopic survey for Li-rich K giants among 2000 low-mass (M {<=} 3 M{sub sun}) giants spanning the luminosity range from below to above the luminosity of the clump. Fifteen new Li-rich giants including four super Li-rich K giants (log {epsilon}(Li) {>=}3.2) were discovered. A significant finding is that there is a concentration of Li-rich K giants at the luminosity of the clump or red horizontal branch. This new finding is partly a consequence of the fact that our low-resolution survey is the first large survey to include giants well below and abovemore » the red giant branch (RGB) bump and clump locations in the H-R diagram. Origin of the lithium enrichment may be plausibly attributed to the conversion of {sup 3}He via {sup 7}Be to {sup 7}Li by the Cameron-Fowler mechanism but the location for the onset of the conversion is uncertain. Two possible opportunities to effect this conversion are discussed: the bump in the first ascent of the RGB and the He-core flash at the tip of the RGB. The finite luminosity spread of the Li-rich giants serves to reject the idea that Li enhancement is, in general, a consequence of a giant swallowing a large planet.« less

  9. Planet population synthesis driven by pebble accretion in cluster environments

    NASA Astrophysics Data System (ADS)

    Ndugu, N.; Bitsch, B.; Jurua, E.

    2018-02-01

    The evolution of protoplanetary discs embedded in stellar clusters depends on the age and the stellar density in which they are embedded. Stellar clusters of young age and high stellar surface density destroy protoplanetary discs by external photoevaporation and stellar encounters. Here, we consider the effect of background heating from newly formed stellar clusters on the structure of protoplanetary discs and how it affects the formation of planets in these discs. Our planet formation model is built on the core accretion scenario, where we take the reduction of the core growth time-scale due to pebble accretion into account. We synthesize planet populations that we compare to observations obtained by radial velocity measurements. The giant planets in our simulations migrate over large distances due to the fast type-II migration regime induced by a high disc viscosity (α = 5.4 × 10-3). Cold Jupiters (rp > 1 au) originate preferably from the outer disc, due to the large-scale planetary migration, while hot Jupiters (rp < 0.1 au) preferably form in the inner disc. We find that the formation of gas giants via pebble accretion is in agreement with the metallicity correlation, meaning that more gas giants are formed at larger metallicity. However, our synthetic population of isolated stars host a significant amount of giant planets even at low metallicity, in contradiction to observations where giant planets are preferably found around high metallicity stars, indicating that pebble accretion is very efficient in the standard pebble accretion framework. On the other hand, discs around stars embedded in cluster environments hardly form any giant planets at low metallicity in agreement with observations, where these changes originate from the increased temperature in the outer parts of the disc, which prolongs the core accretion time-scale of the planet. We therefore conclude that the outer disc structure and the planet's formation location determines the giant planet

  10. Oxygen isotopic evidence for accretion of Earth's water before a high-energy Moon-forming giant impact.

    PubMed

    Greenwood, Richard C; Barrat, Jean-Alix; Miller, Martin F; Anand, Mahesh; Dauphas, Nicolas; Franchi, Ian A; Sillard, Patrick; Starkey, Natalie A

    2018-03-01

    The Earth-Moon system likely formed as a result of a collision between two large planetary objects. Debate about their relative masses, the impact energy involved, and the extent of isotopic homogenization continues. We present the results of a high-precision oxygen isotope study of an extensive suite of lunar and terrestrial samples. We demonstrate that lunar rocks and terrestrial basalts show a 3 to 4 ppm (parts per million), statistically resolvable, difference in Δ 17 O. Taking aubrite meteorites as a candidate impactor material, we show that the giant impact scenario involved nearly complete mixing between the target and impactor. Alternatively, the degree of similarity between the Δ 17 O values of the impactor and the proto-Earth must have been significantly closer than that between Earth and aubrites. If the Earth-Moon system evolved from an initially highly vaporized and isotopically homogenized state, as indicated by recent dynamical models, then the terrestrial basalt-lunar oxygen isotope difference detected by our study may be a reflection of post-giant impact additions to Earth. On the basis of this assumption, our data indicate that post-giant impact additions to Earth could have contributed between 5 and 30% of Earth's water, depending on global water estimates. Consequently, our data indicate that the bulk of Earth's water was accreted before the giant impact and not later, as often proposed.

  11. The Optical Gravitational Lensing Experiment. Small Amplitude Variable Red Giants in the Magellanic Clouds

    NASA Astrophysics Data System (ADS)

    Soszynski, I.; Udalski, A.; Kubiak, M.; Szymanski, M.; Pietrzynski, G.; Zebrun, K.; Szewczyk, O.; Wyrzykowski, L.

    2004-06-01

    We present analysis of the large sample of variable red giants from the Large and Small Magellanic Clouds detected during the second phase of the Optical Gravitational Lensing Experiment (OGLE-II) and supplemented with OGLE-III photometry. Comparing pulsation properties of detected objects we find that they constitute two groups with clearly distinct features. In this paper we analyze in detail small amplitude variable red giants (about 15400 and 3000 objects in the LMC and SMC, respectively). The vast majority of these objects are multi-periodic. At least 30% of them exhibit two modes closely spaced in the power spectrum, what likely indicates non-radial oscillations. About 50% exhibit additional so called Long Secondary Period. To distinguish between AGB and RGB red giants we compare PL diagrams of multi-periodic red giants located above and below the tip of the Red Giant Branch (TRGB). The giants above the TRGB form four parallel ridges in the PL diagram. Among much more numerous sample of giants below the TRGB we find objects located on the low luminosity extensions of these ridges, but most of the stars are located on the ridges slightly shifted in log P. We interpret the former as the second ascent AGB red giants and the latter as the first ascent RGB objects. Thus, we empirically show that the pulsating red giants fainter than the TRGB are a mixture of RGB and AGB giants. Finally, we compare the Petersen diagrams of the LMC, SMC and Galactic bulge variable red giants and find that they are basically identical indicating that the variable red giants in all these different stellar environments share similar pulsation properties.

  12. Oxygen isotopic evidence for accretion of Earth’s water before a high-energy Moon-forming giant impact

    PubMed Central

    Barrat, Jean-Alix; Sillard, Patrick; Starkey, Natalie A.

    2018-01-01

    The Earth-Moon system likely formed as a result of a collision between two large planetary objects. Debate about their relative masses, the impact energy involved, and the extent of isotopic homogenization continues. We present the results of a high-precision oxygen isotope study of an extensive suite of lunar and terrestrial samples. We demonstrate that lunar rocks and terrestrial basalts show a 3 to 4 ppm (parts per million), statistically resolvable, difference in Δ17O. Taking aubrite meteorites as a candidate impactor material, we show that the giant impact scenario involved nearly complete mixing between the target and impactor. Alternatively, the degree of similarity between the Δ17O values of the impactor and the proto-Earth must have been significantly closer than that between Earth and aubrites. If the Earth-Moon system evolved from an initially highly vaporized and isotopically homogenized state, as indicated by recent dynamical models, then the terrestrial basalt-lunar oxygen isotope difference detected by our study may be a reflection of post–giant impact additions to Earth. On the basis of this assumption, our data indicate that post–giant impact additions to Earth could have contributed between 5 and 30% of Earth’s water, depending on global water estimates. Consequently, our data indicate that the bulk of Earth’s water was accreted before the giant impact and not later, as often proposed. PMID:29600271

  13. CNO isotopes in red giant stars

    NASA Technical Reports Server (NTRS)

    Wannier, P. G.

    1985-01-01

    Observational data on CNO abundance ratios in red giants and the interstellar medium (ISM) are analyzed for the implications for the production and distribution of CNO nuclides. The data included isotope abundance measurements for the atmospheres and recent ejecta of cool giants, e.g., carbon stars, S-type stars, red supergiants and oxygen-rich giants beginning an ascent of the giant branch. The contribution of intermediate-mass stars to galactic nuclear evolution is discussed after comparing red giant abundances with ISM abundances, particularly the isotopes O-16, -17 and -18. The O-12/O-18 ratios of red giants are distinctly different from those in interstellar molecular clouds. The CNO values also vary widely from the values found in the solar system.

  14. Accretion rates of protoplanets

    NASA Astrophysics Data System (ADS)

    Greenzweig, Yuval

    The giant planets' solid cores must have formed prior to the dispersal of the primordial solar nebula, to allow the capture of their massive, gaseous envelopes from the nebula. Recent observations of disks of dust surrounding nearby solar-like stars lead to estimates of nebula lifetimes at 106 to 107 years. Thus, theories of solid particle accretion must explain how the solid cores of the giant planets may have formed within comparable timescales. Calculations are presented which support the sole currently hypothesized mechanism of planetary accretion in which the duration of the stage of growth from planetesimals (1 to 10 km size bodies) to moon- or planet-size bodies lies within the widely accepted time constraint mentioned above. It has been shown that under certain conditions a growth advantage is given to the larger bodies of a swarm of Sun-orbiting planetesimals, resulting in runaway growth of the largest body (or bodies) in the swarm. The gravitational cross section of the protoplanet (the largest body in the swarm) increases with its size, eventually requiring the inclusion of the effect of the solar tidal force on the interaction between it and a passing planetesimal. Thus, numerical integrations of the three-body problem (Sun, protoplanet and planetesimal) are needed to determine the accretion rates of protoplanets. Existing analytical formulas are refined for the two-body (no solar tidal force) accretion rates of planetesimals or small protoplanets, and numerically derives the three-body accretion rates of large protoplanets. The three-body accretion rates calculated span a wide range of protoplanetary orbital radii, masses, and densities, and a wide range of planetesimal orbital eccentricities and inclinations. The most useful numerical results are approximated by algebraic expressions, to facilitate their use in accretion calculations, particularly by numerical codes. Since planetary accretion rates depend strongly on planetesimal random velocities

  15. Radiative Hydrodynamics and the Formation of Gas Giant Planets

    NASA Astrophysics Data System (ADS)

    Durisen, Richard H.

    2009-05-01

    Gas giant planets undoubtedly form from the orbiting gas and dust disks commonly observed around young stars, and there are two principal mechanisms proposed for how this may occur. The core accretion plus gas capture model argues that a solid core forms first and then accretes gas from the surrounding disk once the core becomes massive enough (about 10 Earth masses). The gas accumulation process is comparatively slow but becomes hydrodynamic at later times. The disk instability model alternatively suggests that gas giant planet formation is initiated by gas-phase gravitational instabilities (GIs) that fragment protoplanetary disks into bound gaseous protoplanets rapidly, on disk orbit period time scales. Solid cores then form more slowly by accretion of solid planetesimals and settling. The overall formation time scales for these two mechanisms can differ by orders of magnitude. Both involve multidimensional hydrodynamic flows at some phase, late in the process for core accretion and early on for disk instability. The ability of cores to accrete gas and the ability of GIs to produce bound clumps depend on how rapidly gas can lose energy by radiation. This regulatory process, while important for controlling the time scale for core accretion plus gas capture, turns out to be absolutely critical for disk instability to work at all. For this reason, I will focus in my talk on the use of radiation hydrodynamics simulations to determine whether and where disk instability can actually form gas giant planets in disks. Results remain controversial, but simulations by several different research groups support analytic arguments that disk instability leading to fragmentation probably cannot occur in disks around Sun-like stars at orbit radii of 10's of Earth-Sun distances or less. On the other hand, very recent simulations suggest that very young, rapidly accreting disks with much larger radii (100's of times the Sun-Earth distance) can indeed readily fragment by disk

  16. Ejection of iron-bearing giant-impact fragments and the dynamical and geochemical influence of the fragment re-accretion

    NASA Astrophysics Data System (ADS)

    Genda, Hidenori; Iizuka, Tsuyoshi; Sasaki, Takanori; Ueno, Yuichiro; Ikoma, Masahiro

    2017-07-01

    The Earth was born in violence. Many giant collisions of protoplanets are thought to have occurred during the terrestrial planet formation. Here we investigated the giant impact stage by using a hybrid code that consistently deals with the orbital evolution of protoplanets around the Sun and the details of processes during giant impacts between two protoplanets. A significant amount of materials (up to several tens of percent of the total mass of the protoplanets) is ejected by giant impacts. We call these ejected fragments the giant-impact fragments (GIFs). In some of the erosive hit-and-run and high-velocity collisions, metallic iron is also ejected, which comes from the colliding protoplanets' cores. From ten numerical simulations for the giant impact stage, we found that the mass fraction of metallic iron in GIFs ranges from ∼1 wt% to ∼25 wt%. We also discussed the effects of the GIFs on the dynamical and geochemical characteristics of formed terrestrial planets. We found that the GIFs have the potential to solve the following dynamical and geochemical conflicts: (1) The Earth, currently in a near circular orbit, is likely to have had a highly eccentric orbit during the giant impact stage. The GIFs are large enough in total mass to lower the eccentricity of the Earth to its current value via their dynamical friction. (2) The concentrations of highly siderophile elements (HSEs) in the Earth's mantle are greater than what was predicted experimentally. Re-accretion of the iron-bearing GIFs onto the Earth can contribute to the excess of HSEs. In addition, Iron-bearing GIFs provide significant reducing agent that could transform primitive CO2-H2O atmosphere and ocean into more reducing H2-bearing atmosphere. Thus, GIFs are important for the origin of Earth's life and its early evolution.

  17. Evolution of Pre-Main Sequence Accretion Disks

    NASA Technical Reports Server (NTRS)

    Hartmann, Lee W.

    2002-01-01

    The aim of this project is to develop a comprehensive global picture of the physical conditions in, and evolutionary timescales of, pre-main sequence accretion disks. The results of this work will help constrain the initial conditions for planet formation. To this end we plan to: (1) Develop much larger samples of 3-10 Myr-old stars to provide better empirical constraints on protoplanetary disk evolution; (2) Study the dusty emission and accretion rates in these systems, with ages closer to the expected epoch of (giant) planet formation at 3-10 Myr; and (3) Develop detailed model disk structures consistent with observations to infer physical conditions in protoplanetary disks and to constrain possible grain growth as the first stage of planetesimal formation.

  18. Giant Planets around FGK Stars Probably Form through Core Accretion

    NASA Astrophysics Data System (ADS)

    Wang, Wei; Wang, Liang; Li, Xiang; Chen, Yuqin; Zhao, Gang

    2018-06-01

    We present a statistical study of the planet–metallicity (P–M) correlation by comparing the 744 stars with candidate planets (SWPs) in the Kepler field that have been observed with LAMOST, and a sample of distance-independent, fake “twin” stars in the Kepler field with no planet reported (CKSNPs) yet. With well-defined and carefully selected large samples, we find for the first time a turnoff P–M correlation of Δ[Fe/H]SWPs–SNPs, which on average increases from ∼0.00 ± 0.03 dex to 0.06 ± 0.03 dex, and to 0.12 ± 0.03 for stars with Earth-, Neptune-, and Jupiter-sized planets successively, and then declines to ∼‑0.01 ± 0.03 dex for more massive planets or brown dwarfs. Moreover, the percentage of those systems with positive Δ[Fe/H] has the same turnoff pattern. We also find that FG-type stars follow this general trend, but K-type stars are different. Moderate metal enhancement (∼0.1–0.2 dex) for K-type stars with planets of radii between 2 and 4 R ⊕, compared to CKSNPs is observed, which indicates much higher metallicities are required for Super-Earths and Neptune-sized planets to form around K-type stars. We point out that the P–M correlation is actually metallicity-dependent, i.e., the correlation is positive at solar and supersolar metallicities, and negative at subsolar metallicities. No steady increase of Δ[Fe/H] against planet sizes is observed for rocky planets, excluding the pollution scenario as a major mechanism for the P–M correlation. All these clues suggest that giant planets probably form differently from rocky planets or more massive planets/brown dwarfs, and the core accretion scenario is highly favored, and high metallicity is a prerequisite for massive planets to form.

  19. Giant Planet Formation

    NASA Astrophysics Data System (ADS)

    D'Angelo, G.; Durisen, R. H.; Lissauer, J. J.

    2010-12-01

    Gas giant planets play a fundamental role in shaping the orbital architecture of planetary systems and in affecting the delivery of volatile materials to terrestrial planets in the habitable zones. Current theories of gas giant planet formation rely on either of two mechanisms: the core accretion model and the disk instability model. In this chapter, we describe the essential principles upon which these models are built and discuss the successes and limitations of each model in explaining observational data of giant planets orbiting the Sun and other stars.

  20. The tip of the Red Giant Branch as a Distance Indicator for Resolved Galaxies: II. Computer Simulations

    NASA Technical Reports Server (NTRS)

    Madore, B. F.; Freedman, W. L.

    1994-01-01

    Based on both empirical data for nearby galaxies, and on computer simulations, we show that measuring the position of the tip of the first-ascent red-giant branch (TRGB) provides a means of obtaining the distances to nearby galaxies with a precision and accuracy comparable to using Cepheids and/or RR Lyrae variables.

  1. Gap opening by gas accretion and influence on planet populations

    NASA Astrophysics Data System (ADS)

    Crida, A.; Bitsch, B.; Ndugu, N.; Morbidelli, A.

    2017-09-01

    Giant planets grow and migrate in protoplanetary disks. Because they accrete gas from their horseshoe region until the latter is depleted, we find that giant planets can open a gap before being lost into their central star by type I migration. A reduced type II migration is then enough and necessary to limit the total amount of migration that a giant planet suffers during its formation.

  2. Ascent/Descent Software

    NASA Technical Reports Server (NTRS)

    Brown, Charles; Andrew, Robert; Roe, Scott; Frye, Ronald; Harvey, Michael; Vu, Tuan; Balachandran, Krishnaiyer; Bly, Ben

    2012-01-01

    The Ascent/Descent Software Suite has been used to support a variety of NASA Shuttle Program mission planning and analysis activities, such as range safety, on the Integrated Planning System (IPS) platform. The Ascent/Descent Software Suite, containing Ascent Flight Design (ASC)/Descent Flight Design (DESC) Configuration items (Cis), lifecycle documents, and data files used for shuttle ascent and entry modeling analysis and mission design, resides on IPS/Linux workstations. A list of tools in Navigation (NAV)/Prop Software Suite represents tool versions established during or after the IPS Equipment Rehost-3 project.

  3. Magnetic fields in giant planet formation and protoplanetary discs

    NASA Astrophysics Data System (ADS)

    Keith, Sarah Louise

    2015-12-01

    Protoplanetary discs channel accretion onto their host star. How this is achieved is critical to the growth of giant planets which capture their massive gaseous atmosphere from the surrounding flow. Theoretical studies find that an embedded magnetic field could power accretion by hydromagnetic turbulence or torques from a large-scale field. This thesis presents a study of the inuence of magnetic fields in three key aspects of this process: circumplanetary disc accretion, gas flow across gaps in protoplanetary discs, and magnetic-braking in accretion discs. The first study examines the conditions needed for self-consistent accretion driven by magnetic fields or gravitational instability. Models of these discs typically rely on hydromagnetic turbulence as the source of effective viscosity. However, magnetically coupled,accreting regions may be so limited that the disc may not support sufficient inflow. An improved Shakura-Sunyaev ? disc is used to calculate the ionisation fraction and strength of non-ideal effects. Steady magnetically-driven accretion is limited to the thermally ionised, inner disc so that accretion in the remainder of the disc is time-dependent. The second study addresses magnetic flux transport in an accretion gap evacuated by a giant planet. Assuming the field is passively drawn along with the gas, the hydrodynamical simulation of Tanigawa, Ohtsuki & Machida (2012) is used for an a posteriori analysis of the gap field structure. This is used to post-calculate magnetohydrodynamical quantities. This assumption is self-consistent as magnetic forces are found to be weak, and good magnetic coupling ensures the field is frozen into the gas. Hall drift dominates across much of the gap, with the potential to facilitate turbulence and modify the toroidal field according to the global field orientation. The third study considers the structure and stability of magnetically-braked accretion discs. Strong evidence for MRI dead-zones has renewed interest in

  4. GIANT X-RAY BUMP IN GRB 121027A: EVIDENCE FOR FALL-BACK DISK ACCRETION

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

    Wu Xuefeng; Hou Shujin; Lei Weihua, E-mail: xfwu@pmo.ac.cn, E-mail: leiwh@hust.edu.cn

    2013-04-20

    A particularly interesting discovery in observations of GRB 121027A is that of a giant X-ray bump detected by the Swift/X-Ray Telescope. The X-ray afterglow re-brightens sharply at {approx}10{sup 3} s after the trigger by more than two orders of magnitude in less than 200 s. This X-ray bump lasts for more than 10{sup 4} s. It is quite different from typical X-ray flares. In this Letter we propose a fall-back accretion model to interpret this X-ray bump within the context of the collapse of a massive star for a long-duration gamma-ray burst. The required fall-back radius of {approx}3.5 Multiplication-Sign 10{supmore » 10} cm and mass of {approx}0.9-2.6 M{sub Sun} imply that a significant part of the helium envelope should survive through the mass loss during the last stage of the massive progenitor of GRB 121027A.« less

  5. Mass loss in M67 giants - Evidence from isochrone fitting

    NASA Technical Reports Server (NTRS)

    Tripicco, Michael J.; Dorman, Ben; Bell, R. A.

    1993-01-01

    A comparison between the color-magnitude diagram of M67 and a new set of theoretical evolutionary models which include all phases from the unevolved main-sequence through core-helium burning and onto the AGB is presented. The present 5-Gyr solar abundance isochrone is found to yield an excellent fit to the whole of the M67 color-magnitude diagram. A differential technique that compares the gap in color between clump giants and normal red giants, on one hand, with the temperature gap between core He-burning tracks and first-ascent RGB tracks, on the other, strongly indicates that the clump giants in M67 have masses of 0.70 solar mass or less. The extremely large amount of mass loss that is deduced is well in excess of that found for globular cluster stars. Possible resolutions of this problem are that degree of mass loss increases with total stellar mass, or with metallicity.

  6. Planetesimal dissolution in the envelopes of the forming, giant planets

    NASA Technical Reports Server (NTRS)

    Pollack, J. B.; Podolak, M.; Bodenheimer, P.; Christofferson, B.

    1986-01-01

    An evaluation is made of the capacity of planetesimals to penetrate the envelopes of giant planets during their growth phase, by means of a core instability mechanism in which the growing core becomes gradually more adept in the gravitational concentration of gas from its solar nebula environment, until a runaway gas accretion occurs. If most of the accreted mass is contained in planetesimals larger that about 1 km, the critical core mass for runaway accretion will not significantly change when planetesimal dissolution is taken into account; it is accordingly suggested that giant planet envelopes should contain above-solar proportions of virtually all elements, relative to hydrogen.

  7. Disk tides and accretion runaway

    NASA Technical Reports Server (NTRS)

    Ward, William R.; Hahn, Joseph M.

    1995-01-01

    It is suggested that tidal interaction of an accreting planetary embryo with the gaseous preplanetary disk may provide a mechanism to breach the so-called runaway limit during the formation of the giant planet cores. The disk tidal torque converts a would-be shepherding object into a 'predator,' which can continue to cannibalize the planetesimal disk. This is more likely to occur in the giant planet region than in the terrestrial zone, providing a natural cause for Jupiter to predate the inner planets and form within the O(10(exp 7) yr) lifetime of the nebula.

  8. KEPLER RAPIDLY ROTATING GIANT STARS

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

    Costa, A. D.; Martins, B. L. Canto; Bravo, J. P.

    2015-07-10

    Rapidly rotating giant stars are relatively rare and may represent important stages of stellar evolution, resulting from stellar coalescence of close binary systems or accretion of substellar companions by their hosting stars. In the present Letter, we report 17 giant stars observed in the scope of the Kepler space mission exhibiting rapid rotation behavior. For the first time, the abnormal rotational behavior for this puzzling family of stars is revealed by direct measurements of rotation, namely from photometric rotation period, exhibiting a very short rotation period with values ranging from 13 to 55 days. This finding points to remarkable surfacemore » rotation rates, up to 18 times the rotation of the Sun. These giants are combined with six others recently listed in the literature for mid-infrared (IR) diagnostics based on Wide-field Infrared Survey Explorer information, from which a trend for an IR excess is revealed for at least one-half of the stars, but at a level far lower than the dust excess emission shown by planet-bearing main-sequence stars.« less

  9. New Directions in Giant Planet Formation

    NASA Astrophysics Data System (ADS)

    Youdin, Andrew

    The proposed research will explore the limits of the core accretion mechanism for forming giant planets, both in terms of timescale and orbital distance. This theoretical research will be useful in interpreting the results of ongoing exoplanet searches. The effects of radiogenic heating and aerodynamic accretion of pebbles and boulders will be included in time-dependent models of atmospheric structure and growth. To investigate these issues, we will develop and publicly share a protoplanet atmospheric evolution code as an extension of the MESA stellar evolution code. By focusing on relevant processes in the early stages of giant planet formation, we can refine model predictions for exoplanet searches at a wide range of stellar ages and distances from the host star.

  10. Dynamical Upheaval in Ice Giant Formation: A Solution to the Fine-tuning Problem in the Formation Story

    NASA Astrophysics Data System (ADS)

    Frelikh, Renata; Murray-Clay, Ruth

    2018-04-01

    We report on our recent theoretical work, where we suggest that a protoplanetary disk dynamical instability may have played a crucial role in determining the atmospheric size of the solar system’s ice giants. In contrast to the gas giants, the intermediate-size ice giants never underwent runaway gas accretion in a full gas disk. However, as their substantial core masses are comparable to those of the gas giants, they would have gone runaway, given enough time. In the standard scenario, the ice giants stay at roughly their current size for most of the disk lifetime, undergoing period of slow gas accretion onto ~full-sized cores that formed early-on. The gas disk dissipates before the ice giants accumulate too much gas, but we believe this is fine tuned. A considerable amount of solids is observed in outer disks in mm-to-cm sized particles (pebbles). Assisted by gas drag, these pebbles rapidly accrete onto cores. This would cause the growing ice giants to exceed their current core masses, and quickly turn into gas giants. To resolve this problem, we propose that Uranus and Neptune stayed small for the bulk of the disk lifetime. They only finished their core and atmospheric growth in a short timeframe just as the disk gas dissipated, accreting most of their gas from a disk depleted to ~1% of its original mass. The ice giants have atmospheric mass fractions comparable to the disk gas-to-solid ratio of this depleted disk. This coincides with a disk dynamical upheaval onset by the depletion of gas. We propose that the cores started growing closer-in, where they were kept small by proximity to Jupiter and Saturn. As the gas cleared, the cores were kicked out by the gas giants. Then, they finished their core growth and accreted their atmospheres from the remaining, sparse gas at their current locations. We predict that the gas giants may play a key role in forming intermediate-size atmospheres in the outer disk.

  11. DISCOVERY OF SUPER-Li-RICH RED GIANTS IN DWARF SPHEROIDAL GALAXIES

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

    Kirby, Evan N.; Fu, Xiaoting; Deng, Licai

    2012-06-10

    Stars destroy lithium (Li) in their normal evolution. The convective envelopes of evolved red giants reach temperatures of millions of kelvin, hot enough for the {sup 7}Li(p, {alpha}){sup 4}He reaction to burn Li efficiently. Only about 1% of first-ascent red giants more luminous than the luminosity function bump in the red giant branch exhibit A(Li) > 1.5. Nonetheless, Li-rich red giants do exist. We present 15 Li-rich red giants-14 of which are new discoveries-among a sample of 2054 red giants in Milky Way dwarf satellite galaxies. Our sample more than doubles the number of low-mass, metal-poor ([Fe/H] {approx}< -0.7) Li-richmore » red giants, and it includes the most-metal-poor Li-enhanced star known ([Fe/H] = -2.82, A(Li){sub NLTE} = 3.15). Because most of the stars have Li abundances larger than the universe's primordial value, the Li in these stars must have been created rather than saved from destruction. These Li-rich stars appear like other stars in the same galaxies in every measurable regard other than Li abundance. We consider the possibility that Li enrichment is a universal phase of evolution that affects all stars, and it seems rare only because it is brief.« less

  12. Implications of pebble accretion on the composition of hot and cold Jupiters

    NASA Astrophysics Data System (ADS)

    Bitsch, Bertram; Johansen, Anders; Madhusudhan, Nikku

    2016-10-01

    The formation of the planetary cores of gas giants via the accretion of planetesimals takes very long and is not compatible with the lifetime of protoplanetary discs (Levison et al. 2010). This time-scale problem can be solved through the accretion of pebbles onto a planetary seed. Contrary to planetesimals, pebbles feel the headwind from the gas which robs them of angular momentum allowing an efficient growth from the entire Hill sphere, which reduces the growth time-scale by several orders of magnitude (Lambrechts & Johansen, 2012; 2014). However, pebble accretion self-terminates when the planets start to open a partial gap in the disc, which accelerates the gas outside of the planets orbit to super-Keplerian speeds and thus stops the flow of pebbles onto the planetary core (Lambrechts et al. 2014). Typically this mass is of the order of 10-20 Earth masses, depending on the local disc properties. The planet can then start to accrete a gaseous envelope without a pollution of pebbles. During its growth, the planet migrates through the disc, which evolves in time (Bitsch et al. 2015a,b).Different volatile species like CO2 or H2O have different condensation temperatures and are thus present in either solid or gaseous form at different locations in the disc. A pebble accreting planet can thus only accrete volatiles that are in solid form, while a gas accreting planet will only accrete volatiles which are in gaseous form. Therefore the final chemical composition of the planetary atmosphere of a giant planet is strongly influenced by the formation location of the initial planetary seed and its subsequent migration path through the disc. Additionally, the envelope can be enriched through the erosion of the planetary core.I will discuss the implications of the formation of planets via pebble accretion and their subsequent migration through the disc on the composition of gas giants. In particular I will focus on the carbon to oxygen ratio of hot Jupiters around other stars

  13. A hybrid scenario for gas giant planet formation in rings

    NASA Astrophysics Data System (ADS)

    Durisen, Richard H.; Cai, Kai; Mejía, Annie C.; Pickett, Megan K.

    2005-02-01

    The core-accretion mechanism for gas giant formation may be too slow to create all observed gas giant planets during reasonable gas disk lifetimes, but it has yet to be firmly established that the disk instability model can produce permanent bound gaseous protoplanets under realistic conditions. Based on our recent simulations of gravitational instabilities in disks around young stars, we suggest that, even if instabilities due to disk self-gravity do not produce gaseous protoplanets directly, they may create persistent dense rings that are conducive to accelerated growth of gas giants through core accretion. The rings occur at and near the boundary between stable and unstable regions of the disk and appear to be produced by resonances with discrete spiral modes on the unstable side.

  14. Formation of the giant planets

    NASA Technical Reports Server (NTRS)

    Lissauer, Jack J.

    2006-01-01

    The observed properties of giant planets, models of their evolution and observations of protoplanetary disks provide constraints on the formation of gas giant planets. The four largest planets in our Solar System contain considerable quantities of hydrogen and helium, which could not have condensed into solid planetesimals within the protoplanetary disk. All three (transiting) extrasolar giant planets with well determined masses and radii also must contain substantial amounts of these light gases. Jupiter and Saturn are mostly hydrogen and helium, but have larger abundances of heavier elements than does the Sun. Neptune and Uranus are primarily composed of heavier elements. HD 149026 b, which is slightly more massive than is Saturn, appears to have comparable quantities of light gases and heavy elements. HD 209458 b and TrES-1 are primarily hydrogen and helium, but may contain supersolar abundances of heavy elements. Spacecraft flybys and observations of satellite orbits provide estimates of the gravitational moments of the giant planets in our Solar System, which in turn provide information on the internal distribution of matter within Jupiter, Saturn, Uranus and Neptune. Atmospheric thermal structure and heat flow measurements constrain the interior temperatures of planets. Internal processes may cause giant planets to become more compositionally differentiated or alternatively more homogeneous; high-pressure laboratory .experiments provide data useful for modeling these processes. The preponderance of evidence supports the core nucleated gas accretion model. According to this model, giant planets begin their growth by the accumulation of small solid bodies, as do terrestrial planets. However, unlike terrestrial planets, the growing giant planet cores become massive enough that they are able to accumulate substantial amounts of gas before the protoplanetary disk dissipates. The primary questions regarding the core nucleated growth model is under what conditions

  15. The Planetary Accretion Shock. I. Framework for Radiation-hydrodynamical Simulations and First Results

    NASA Astrophysics Data System (ADS)

    Marleau, Gabriel-Dominique; Klahr, Hubert; Kuiper, Rolf; Mordasini, Christoph

    2017-02-01

    The key aspect determining the postformation luminosity of gas giants has long been considered to be the energetics of the accretion shock at the surface of the planet. We use one-dimensional radiation-hydrodynamical simulations to study the radiative loss efficiency and to obtain postshock temperatures and pressures and thus entropies. The efficiency is defined as the fraction of the total incoming energy flux that escapes the system (roughly the Hill sphere), taking into account the energy recycling that occurs ahead of the shock in a radiative precursor. We focus in this paper on a constant equation of state (EOS) to isolate the shock physics but use constant and tabulated opacities. While robust quantitative results will have to await a self-consistent treatment including hydrogen dissociation and ionization, the results presented here show the correct qualitative behavior and can be understood from semianalytical calculations. The shock is found to be isothermal and supercritical for a range of conditions relevant to the core accretion formation scenario (CA), with Mach numbers { M }≳ 3. Across the shock, the entropy decreases significantly by a few times {k}{{B}}/{{baryon}}. While nearly 100% of the incoming kinetic energy is converted to radiation locally, the efficiencies are found to be as low as roughly 40%, implying that a significant fraction of the total accretion energy is brought into the planet. However, for realistic parameter combinations in the CA scenario, we find that a nonzero fraction of the luminosity always escapes the Hill sphere. This luminosity could explain, at least in part, recent observations in the young LkCa 15 and HD 100546 systems.

  16. Focused Wind Mass Accretion in Mira AB

    NASA Astrophysics Data System (ADS)

    Karovska, Margarita; de Val-Borro, M.; Hack, W.; Raymond, J.; Sasselov, D.; Lee, N. P.

    2011-05-01

    At a distance of about only 100pc, Mira AB is the nearest symbiotic system containing an Asymptotic Giant Branch (AGB) star (Mira A), and a compact accreting companion (Mira B) at about 0.5" from Mira A. Symbiotic systems are interacting binaries with a key evolutionary importance as potential progenitors of a fraction of asymmetric Planetary Nebulae, and SN type Ia, cosmological distance indicators. The region of interaction has been studied using high-angular resolution, multiwavelength observations ranging from radio to X-ray wavelengths. Our results, including high-angular resolution Chandra imaging, show a "bridge" between Mira A and Mira B, indicating gravitational focusing of the Mira A wind, whereby components exchange matter directly in addition to the wind accretion. We carried out a study using 2-D hydrodynamical models of focused wind mass accretion to determine the region of wind acceleration and the characteristics of the accretion in Mira AB. We highlight some of our results and discuss the impact on our understanding of accretion processes in symbiotic systems and other detached and semidetached interacting systems.

  17. Aerodynamic Analyses and Database Development for Lift-Off/Transition and First Stage Ascent of the Ares I A106 Vehicle

    NASA Technical Reports Server (NTRS)

    Pamadi, Bandu N.; Pei, Jing; Covell, Peter F.; Favaregh, Noah M.; Gumbert, Clyde R.; Hanke, Jeremy L.

    2011-01-01

    NASA Langley Research Center, in partnership with NASA Marshall Space Flight Center and NASA Ames Research Center, was involved in the aerodynamic analyses, testing, and database development for the Ares I A106 crew launch vehicle in support of the Ares Design and Analysis Cycle. This paper discusses the development of lift-off/transition and ascent databases. The lift-off/transition database was developed using data from tests on a 1.75% scale model of the A106 configuration in the NASA Langley 14x22 Subsonic Wind Tunnel. The power-off ascent database was developed using test data on a 1% A106 scale model from two different facilities, the Boeing Polysonic Wind Tunnel and the NASA Langley Unitary Plan Wind Tunnel. The ascent database was adjusted for differences in wind tunnel and flight Reynolds numbers using USM3D CFD code. The aerodynamic jet interaction effects due to first stage roll control system were modeled using USM3D and OVERFLOW CFD codes.

  18. Late accretion to the terrestrial planets

    NASA Astrophysics Data System (ADS)

    Brasser, Ramon; Mojzsis, Stephen; Werner, Stephanie; Matsumura, Soko; Ida, Shigeru

    2017-10-01

    IntroductionIt is generally accepted that silicate-metal (`rocky') planet formation relies on coagulation from a mixture of sub-Mars sized planetary embryos and (smaller) planetesimals that dynamically emerge from the evolving circum-solar disc in the first few million years of our Solar System. Once the planets have, for the most part, assembled after a giant impact phase, they continue to be bombarded by a multitude of planetesimals left over from accretion. Here we place limits on the mass and evolution of these planetesimals based on constraints from the highly siderophile element (HSE) budget of the Moon. The terrestrial and lunar HSE budgets indicate that Earth’s and Moon’s additions through late accretion were 0.7 wt% and 0.02 wt% respectively. The disproportionate high accretion between the Earth and Moon could be explained by stochastic accretion of a few remaining Ceres-sized bodies that preferentially targeted the Earth.ResultsFrom a combination of N-body and Monte Carlo simulations of planet formation we conclude:1) matching the terrestrial to lunar HSE ratio requires that late accretion on Earth mostly consisted of a single lunar-size impactor striking the Earth before 4.45 Ga2) the flux of terrestrial impactors must have been low avoid wholesale melting of Earth's crust after 4.4 Ga[6], and to simultaneously match the number of observed lunar basins3) after the terrestrial planets have fully formed, the mass in remnant planetesimals was ~0.001 Earth mass, lower than most previous models suggest.4) Mars' HSE budget also requires a colossal impact with a Ceres-sized object before 4.43 Ga, whose visible remnant could be the hemispherical dichotomy.These conclusions lead to an Hadean eon which is more clement than assumed previously. In addition, our dynamically and geochemically self-consistent scenario requires that future N-body simulations of rocky planet formation either directly incorporate collisional grinding or rely on pebble accretion.

  19. Thermodynamics of giant planet formation: shocking hot surfaces on circumplanetary discs

    NASA Astrophysics Data System (ADS)

    Szulágyi, J.; Mordasini, C.

    2017-02-01

    The luminosity of young giant planets can inform about their formation and accretion history. The directly imaged planets detected so far are consistent with the `hot-start' scenario of high entropy and luminosity. If nebular gas passes through a shock front before being accreted into a protoplanet, the entropy can be substantially altered. To investigate this, we present high-resolution, three-dimensional radiative hydrodynamic simulations of accreting giant planets. The accreted gas is found to fall with supersonic speed in the gap from the circumstellar disc's upper layers on to the surface of the circumplanetary disc and polar region of the protoplanet. There it shocks, creating an extended hot supercritical shock surface. This shock front is optically thick; therefore, it can conceal the planet's intrinsic luminosity beneath. The gas in the vertical influx has high entropy which when passing through the shock front decreases significantly while the gas becomes part of the disc and protoplanet. This shows that circumplanetary discs play a key role in regulating a planet's thermodynamic state. Our simulations furthermore indicate that around the shock surface extended regions of atomic - sometimes ionized - hydrogen develop. Therefore, circumplanetary disc shock surfaces could influence significantly the observational appearance of forming gas giants.

  20. Hot-start Giant Planets Form with Radiative Interiors

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

    Berardo, David; Cumming, Andrew, E-mail: david.berardo@mcgill.ca, E-mail: andrew.cumming@mcgill.ca

    In the hot-start core accretion formation model for gas giants, the interior of a planet is usually assumed to be fully convective. By calculating the detailed internal evolution of a planet assuming hot-start outer boundary conditions, we show that such a planet will in fact form with a radially increasing internal entropy profile, so that its interior will be radiative instead of convective. For a hot outer boundary, there is a minimum value for the entropy of the internal adiabat S {sub min} below which the accreting envelope does not match smoothly onto the interior, but instead deposits high entropymore » material onto the growing interior. One implication of this would be to at least temporarily halt the mixing of heavy elements within the planet, which are deposited by planetesimals accreted during formation. The compositional gradient this would impose could subsequently disrupt convection during post-accretion cooling, which would alter the observed cooling curve of the planet. However, even with a homogeneous composition, for which convection develops as the planet cools, the difference in cooling timescale will change the inferred mass of directly imaged gas giants.« less

  1. Formation of the Giant Planets by Concurrent Accretion of Solids and Gas

    NASA Technical Reports Server (NTRS)

    Hubickyj, Olenka

    1997-01-01

    Models were developed to simulate planet formation. Three major phases are characterized in the simulations: (1) planetesimal accretion rate, which dominates that of gas, rapidly increases owing to runaway accretion, then decreases as the planet's feeding zone is depleted; (2) occurs when both solid and gas accretion rates are small and nearly independent of time; and (3) starts when the solid and gas masses are about equal and is marked by runaway gas accretion. The models applicability to planets in our Solar System are judged using two basic "yardsticks". The results suggest that the solar nebula dissipated while Uranus and Neptune were in the second phase, during which, for a relatively long time, the masses of their gaseous envelopes were small but not negligible compared to the total masses. Background information, results and a published article are included in the report.

  2. Pebble Accretion in Turbulent Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Xu, Ziyan; Bai, Xue-Ning; Murray-Clay, Ruth A.

    2017-09-01

    It has been realized in recent years that the accretion of pebble-sized dust particles onto planetary cores is an important mode of core growth, which enables the formation of giant planets at large distances and assists planet formation in general. The pebble accretion theory is built upon the orbit theory of dust particles in a laminar protoplanetary disk (PPD). For sufficiently large core mass (in the “Hill regime”), essentially all particles of appropriate sizes entering the Hill sphere can be captured. However, the outer regions of PPDs are expected to be weakly turbulent due to the magnetorotational instability (MRI), where turbulent stirring of particle orbits may affect the efficiency of pebble accretion. We conduct shearing-box simulations of pebble accretion with different levels of MRI turbulence (strongly turbulent assuming ideal magnetohydrodynamics, weakly turbulent in the presence of ambipolar diffusion, and laminar) and different core masses to test the efficiency of pebble accretion at a microphysical level. We find that accretion remains efficient for marginally coupled particles (dimensionless stopping time {τ }s˜ 0.1{--}1) even in the presence of strong MRI turbulence. Though more dust particles are brought toward the core by the turbulence, this effect is largely canceled by a reduction in accretion probability. As a result, the overall effect of turbulence on the accretion rate is mainly reflected in the changes in the thickness of the dust layer. On the other hand, we find that the efficiency of pebble accretion for strongly coupled particles (down to {τ }s˜ 0.01) can be modestly reduced by strong turbulence for low-mass cores.

  3. Timing of the formation and migration of giant planets as constrained by CB chondrites

    PubMed Central

    Johnson, Brandon C.; Walsh, Kevin J.; Minton, David A.; Krot, Alexander N.; Levison, Harold F.

    2016-01-01

    The presence, formation, and migration of giant planets fundamentally shape planetary systems. However, the timing of the formation and migration of giant planets in our solar system remains largely unconstrained. Simulating planetary accretion, we find that giant planet migration produces a relatively short-lived spike in impact velocities lasting ~0.5 My. These high-impact velocities are required to vaporize a significant fraction of Fe,Ni metal and silicates and produce the CB (Bencubbin-like) metal-rich carbonaceous chondrites, a unique class of meteorites that were created in an impact vapor-melt plume ~5 My after the first solar system solids. This indicates that the region where the CB chondrites formed was dynamically excited at this early time by the direct interference of the giant planets. Furthermore, this suggests that the formation of the giant planet cores was protracted and the solar nebula persisted until ~5 My. PMID:27957541

  4. Timing of the formation and migration of giant planets as constrained by CB chondrites.

    PubMed

    Johnson, Brandon C; Walsh, Kevin J; Minton, David A; Krot, Alexander N; Levison, Harold F

    2016-12-01

    The presence, formation, and migration of giant planets fundamentally shape planetary systems. However, the timing of the formation and migration of giant planets in our solar system remains largely unconstrained. Simulating planetary accretion, we find that giant planet migration produces a relatively short-lived spike in impact velocities lasting ~0.5 My. These high-impact velocities are required to vaporize a significant fraction of Fe,Ni metal and silicates and produce the CB (Bencubbin-like) metal-rich carbonaceous chondrites, a unique class of meteorites that were created in an impact vapor-melt plume ~5 My after the first solar system solids. This indicates that the region where the CB chondrites formed was dynamically excited at this early time by the direct interference of the giant planets. Furthermore, this suggests that the formation of the giant planet cores was protracted and the solar nebula persisted until ~5 My.

  5. The Fuzziness of Giant Planets’ Cores

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

    Helled, Ravit; Stevenson, David

    2017-05-01

    Giant planets are thought to have cores in their deep interiors, and the division into a heavy-element core and hydrogen–helium envelope is applied in both formation and structure models. We show that the primordial internal structure depends on the planetary growth rate, in particular, the ratio of heavy elements accretion to gas accretion. For a wide range of likely conditions, this ratio is in one-to-one correspondence with the resulting post-accretion profile of heavy elements within the planet. This flux ratio depends sensitively on the assumed solid-surface density in the surrounding nebula. We suggest that giant planets’ cores might not bemore » distinct from the envelope and includes some hydrogen and helium, and the deep interior can have a gradual heavy-element structure. Accordingly, Jupiter’s core may not be well defined. Accurate measurements of Jupiter’s gravitational field by Juno could put constraints on Jupiter’s core mass. However, as we suggest here, the definition of Jupiter’s core is complex, and the core’s physical properties (mass, density) depend on the actual definition of the core and on the planet’s growth history.« less

  6. Evidence of an Upper Bound on the Masses of Planets and Its Implications for Giant Planet Formation

    NASA Astrophysics Data System (ADS)

    Schlaufman, Kevin C.

    2018-01-01

    Celestial bodies with a mass of M≈ 10 {M}{Jup} have been found orbiting nearby stars. It is unknown whether these objects formed like gas-giant planets through core accretion or like stars through gravitational instability. I show that objects with M≲ 4 {M}{Jup} orbit metal-rich solar-type dwarf stars, a property associated with core accretion. Objects with M≳ 10 {M}{Jup} do not share this property. This transition is coincident with a minimum in the occurrence rate of such objects, suggesting that the maximum mass of a celestial body formed through core accretion like a planet is less than 10 {M}{Jup}. Consequently, objects with M≳ 10 {M}{Jup} orbiting solar-type dwarf stars likely formed through gravitational instability and should not be thought of as planets. Theoretical models of giant planet formation in scaled minimum-mass solar nebula Shakura–Sunyaev disks with standard parameters tuned to produce giant planets predict a maximum mass nearly an order of magnitude larger. To prevent newly formed giant planets from growing larger than 10 {M}{Jup}, protoplanetary disks must therefore be significantly less viscous or of lower mass than typically assumed during the runaway gas accretion stage of giant planet formation. Either effect would act to slow the Type I/II migration of planetary embryos/giant planets and promote their survival. These inferences are insensitive to the host star mass, planet formation location, or characteristic disk dissipation time.

  7. Growing the gas-giant planets by the gradual accumulation of pebbles

    NASA Astrophysics Data System (ADS)

    Levison, Harold F.; Kretke, Katherine A.; Duncan, Martin J.

    2015-08-01

    It is widely held that the first step in forming gas-giant planets, such as Jupiter and Saturn, was the production of solid `cores' each with a mass roughly ten times that of the Earth. Getting the cores to form before the solar nebula dissipates (in about one to ten million years; ref. 3) has been a major challenge for planet formation models. Recently models have emerged in which `pebbles' (centimetre-to-metre-sized objects) are first concentrated by aerodynamic drag and then gravitationally collapse to form objects 100 to 1,000 kilometres in size. These `planetesimals' can then efficiently accrete left-over pebbles and directly form the cores of giant planets. This model is known as `pebble accretion' theoretically, it can produce cores of ten Earth masses in only a few thousand years. Unfortunately, full simulations of this process show that, rather than creating a few such cores, it produces a population of hundreds of Earth-mass objects that are inconsistent with the structure of the Solar System. Here we report that this difficulty can be overcome if pebbles form slowly enough to allow the planetesimals to gravitationally interact with one another. In this situation, the largest planetesimals have time to scatter their smaller siblings out of the disk of pebbles, thereby stifling their growth. Our models show that, for a large and physically reasonable region of parameter space, this typically leads to the formation of one to four gas giants between 5 and 15 astronomical units from the Sun, in agreement with the observed structure of the Solar System.

  8. Accretion of Cometary Nuclei in the Solar Nebula: Boulders, Not Pebbles

    NASA Astrophysics Data System (ADS)

    Weissman, Paul R.; A'Hearn, Michael

    2015-11-01

    Comets are the most primitive bodies in the solar system. They retain a largely unprocessed record of conditions in the primordial solar nebula 4.56 Gyr ago, including the initial accretion of dust and ice particles into macroscopic bodies. Current accretion theory suggests that ice and dust aggregates grew to pebble (cm) sizes before streaming instabilities and gravitational collapse brought these pebble swarms together as km-sized (or larger) bodies. Recent imaging of the nucleus of comet 67P/Churyumov-Gerasimenko by the Rosetta OSIRIS camera team has revealed the existence of “goose bump” terrain on the nucleus surface and lining the interior walls of large, ~200 m diameter and 180 m deep cylindrical pits. These pits are believed to be sinkholes, formed when near-surface materials collapse into voids within the nucleus, revealing the fresh comet interior on the walls of the pits. The goose bump terrain consists of 3-4 m diameter “boulders” randomly stacked one on top of another. We propose that these boulders, likely with an icy-conglomerate composition, are the basic building blocks of cometary nuclei. This is the first observational confirmation of current accretion theories, with the caveat that rather than pebbles, the preferred size range is 3-4 m boulders for objects formed in the giant planets region of the solar system. The presence of icy grains beyond the solar nebula snow-line and the large heliocentric range of the giant planets region likely contribute to the formation of these larger boulders, before they are incorporated into cometary nuclei. This work was supported by NASA through the U.S. Rosetta Project.

  9. Evolution of Pre-Main Sequence Accretion Disks

    NASA Technical Reports Server (NTRS)

    Hartmann, Lee W.

    2000-01-01

    The aim of this project was to develop a comprehensive global picture of the physical conditions in, and evolutionary timescales of, pre-main sequence accretion disks. The results of this work will help constrain the initial conditions for planet formation. To this end we: (1) Developed detailed calculations of disk structure to study physical conditions and investigate the observational effects of grain growth in T Tauri disks; (2) Studied the dusty emission and accretion rates in older disk systems, with ages closer to the expected epoch of (giant) planet formation at 3-10 Myr, and (3) Began a project to develop much larger samples of 3-10 Myr-old stars to provide better empirical constraints on protoplanetary disk evolution.

  10. SEISMIC DIAGNOSTICS OF RED GIANTS: FIRST COMPARISON WITH STELLAR MODELS

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

    Montalban, J.; Miglio, A.; Noels, A.

    2010-10-01

    The clear detection with CoRoT and KEPLER of radial and non-radial solar-like oscillations in many red giants paves the way for seismic inferences on the structure of such stars. We present an overview of the properties of the adiabatic frequencies and frequency separations of radial and non-radial oscillation modes for an extended grid of models. We highlight how their detection allows a deeper insight into the internal structure and evolutionary state of red giants. In particular, we find that the properties of dipole modes constitute a promising seismic diagnostic tool of the evolutionary state of red giant stars. We comparemore » our theoretical predictions with the first 34 days of KEPLER data and predict the frequency diagram expected for red giants in the CoRoT exofield in the galactic center direction.« less

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

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

  12. Inner Super-Earths, Outer Gas Giants: How Pebble Isolation and Migration Feedback Keep Jupiters Cold

    NASA Astrophysics Data System (ADS)

    Fung, Jeffrey; Lee, Eve J.

    2018-06-01

    The majority of gas giants (planets of masses ≳102 M ⊕) are found to reside at distances beyond ∼1 au from their host stars. Within 1 au, the planetary population is dominated by super-Earths of 2–20 M ⊕. We show that this dichotomy between inner super-Earths and outer gas giants can be naturally explained should they form in nearly inviscid disks. In laminar disks, a planet can more easily repel disk gas away from its orbit. The feedback torque from the pile-up of gas inside the planet’s orbit slows down and eventually halts migration. A pressure bump outside the planet’s orbit traps pebbles and solids, starving the core. Gas giants are born cold and stay cold: more massive cores are preferentially formed at larger distances, and they barely migrate under disk feedback. We demonstrate this using two-dimensional hydrodynamical simulations of disk–planet interaction lasting up to 105 years: we track planet migration and pebble accretion until both come to an end by disk feedback. Whether cores undergo runaway gas accretion to become gas giants or not is determined by computing one-dimensional gas accretion models. Our simulations show that in an inviscid minimum mass solar nebula, gas giants do not form inside ∼0.5 au, nor can they migrate there while the disk is present. We also explore the dependence on disk mass and find that gas giants form further out in less massive disks.

  13. Possible Rapid Gas Giant Planet Formation in the Solar Nebula and Other Protoplanetary Disks.

    PubMed

    Boss

    2000-06-20

    Gas giant planets have been detected in orbit around an increasing number of nearby stars. Two theories have been advanced for the formation of such planets: core accretion and disk instability. Core accretion, the generally accepted mechanism, requires several million years or more to form a gas giant planet in a protoplanetary disk like the solar nebula. Disk instability, on the other hand, can form a gas giant protoplanet in a few hundred years. However, disk instability has previously been thought to be important only in relatively massive disks. New three-dimensional, "locally isothermal," hydrodynamical models without velocity damping show that a disk instability can form Jupiter-mass clumps, even in a disk with a mass (0.091 M middle dot in circle within 20 AU) low enough to be in the range inferred for the solar nebula. The clumps form with initially eccentric orbits, and their survival will depend on their ability to contract to higher densities before they can be tidally disrupted at successive periastrons. Because the disk mass in these models is comparable to that apparently required for the core accretion mechanism to operate, the models imply that disk instability could obviate the core accretion mechanism in the solar nebula and elsewhere.

  14. Theories of Giant Planet Formation

    NASA Technical Reports Server (NTRS)

    Lissauer, Jack J.; Young, Richard E. (Technical Monitor)

    1998-01-01

    An overview of current theories of planetary formation, with emphasis on giant planets, is presented. The most detailed models are based upon observations of our own Solar System and of young stars and their environments. While these models predict that rocky planets should form around most single stars, the frequency of formation of gas giant planets is more difficult to predict theoretically. Terrestrial planets are believed to grow via pairwise accretion until the spacing of planetary orbits becomes large enough that the configuration is stable for the age of the system. Giant planets begin their growth as do terrestrial planets, but they become massive enough that they are able to accumulate substantial amounts of gas before the protoplanetary disk dissipates. Most models for extrasolar giant planets suggest that they formed as did Jupiter and Saturn (in nearly circular orbits, far enough from the star that ice could), and subsequently migrated to their current positions, although some models suggest in situ formation.

  15. Water Delivery and Giant Impacts in the 'Grand Tack' Scenario

    NASA Technical Reports Server (NTRS)

    O'Brien, David P.; Walsh, Kevin J.; Morbidelli, Alessandro; Raymond, Sean N.; Mandell, Avi M.

    2014-01-01

    A new model for terrestrial planet formation has explored accretion in a truncated protoplanetary disk, and found that such a configuration is able to reproduce the distribution of mass among the planets in the Solar System, especially the Earth/Mars mass ratio, which earlier simulations have generally not been able to match. Walsh et al. tested a possible mechanism to truncate the disk-a two-stage, inward-then-outward migration of Jupiter and Saturn, as found in numerous hydrodynamical simulations of giant planet formation. In addition to truncating the disk and producing a more realistic Earth/Mars mass ratio, the migration of the giant planets also populates the asteroid belt with two distinct populations of bodies-the inner belt is filled by bodies originating inside of 3 AU, and the outer belt is filled with bodies originating from between and beyond the giant planets (which are hereafter referred to as 'primitive' bodies). One implication of the truncation mechanism proposed in Walsh et al. is the scattering of primitive planetesimals onto planet-crossing orbits during the formation of the planets. We find here that the planets will accrete on order 1-2% of their total mass from these bodies. For an assumed value of 10% for the water mass fraction of the primitive planetesimals, this model delivers a total amount of water comparable to that estimated to be on the Earth today. The radial distribution of the planetary masses and the dynamical excitation of their orbits are a good match to the observed system. However, we find that a truncated disk leads to formation timescales more rapid than suggested by radiometric chronometers. In particular, the last giant impact is typically earlier than 20 Myr, and a substantial amount of mass is accreted after that event. This is at odds with the dating of the Moon-forming impact and the estimated amount of mass accreted by Earth following that event. However, 5 of the 27 planets larger than half an Earth mass formed in

  16. Lunar Ascent and Rendezvous Trajectory Design

    NASA Technical Reports Server (NTRS)

    Sostaric, Ronald R.; Merriam, Robert S.

    2008-01-01

    The Lunar Lander Ascent Module (LLAM) will leave the lunar surface and actively rendezvous in lunar orbit with the Crew Exploration Vehicle (CEV). For initial LLAM vehicle sizing efforts, a nominal trajectory, along with required delta-V and a few key sensitivities, is very useful. A nominal lunar ascent and rendezvous trajectory is shown, along with rationale and discussion of the trajectory shaping. Also included are ascent delta-V sensitivities to changes in target orbit and design thrust-to-weight of the vehicle. A sample launch window for a particular launch site has been completed and is included. The launch window shows that budgeting enough delta-V for two missed launch opportunities may be reasonable. A comparison between yaw steering and on-orbit plane change maneuvers is included. The comparison shows that for large plane changes, which are potentially necessary for an anytime return from mid-latitude locations, an on-orbit maneuver is much more efficient than ascent yaw steering. For a planned return, small amounts of yaw steering may be necessary during ascent and must be accounted for in the ascent delta-V budget. The delta-V cost of ascent yaw steering is shown, along with sensitivity to launch site latitude. Some discussion of off-nominal scenarios is also included. In particular, in the case of a failed Powered Descent Initiation burn, the requirements for subsequent rendezvous with the Orion vehicle are outlined.

  17. Massive star formation by accretion. I. Disc accretion

    NASA Astrophysics Data System (ADS)

    Haemmerlé, L.; Eggenberger, P.; Meynet, G.; Maeder, A.; Charbonnel, C.

    2016-01-01

    Context. Massive stars likely form by accretion and the evolutionary track of an accreting forming star corresponds to what is called the birthline in the Hertzsprung-Russell (HR) diagram. The shape of this birthline is quite sensitive to the evolution of the entropy in the accreting star. Aims: We first study the reasons why some birthlines published in past years present different behaviours for a given accretion rate. We then revisit the question of the accretion rate, which allows us to understand the distribution of the observed pre-main-sequence (pre-MS) stars in the HR diagram. Finally, we identify the conditions needed to obtain a large inflation of the star along its pre-MS evolution that may push the birthline towards the Hayashi line in the upper part of the HR diagram. Methods: We present new pre-MS models including accretion at various rates and for different initial structures of the accreting core. We compare them with previously published equivalent models. From the observed upper envelope of pre-MS stars in the HR diagram, we deduce the accretion law that best matches the accretion history of most of the intermediate-mass stars. Results: In the numerical computation of the time derivative of the entropy, some treatment leads to an artificial loss of entropy and thus reduces the inflation that the accreting star undergoes along the birthline. In the case of cold disc accretion, the existence of a significant swelling during the accretion phase, which leads to radii ≳ 100 R⊙ and brings the star back to the red part of the HR diagram, depends sensitively on the initial conditions. For an accretion rate of 10-3M⊙ yr-1, only models starting from a core with a significant radiative region evolve back to the red part of the HR diagram. We also obtain that, in order to reproduce the observed upper envelope of pre-MS stars in the HR diagram with an accretion law deduced from the observed mass outflows in ultra-compact HII regions, the fraction of the

  18. Tidal Barrier and the Asymptotic Mass of Proto-Gas Giant Planets

    NASA Astrophysics Data System (ADS)

    Dobbs-Dixon, Ian; Li, Shu Lin; Lin, D. N. C.

    2007-05-01

    According to the conventional sequential accretion scenario, observed extrasolar planets acquired their current masses via efficient gas accretion onto super-Earth cores with accretion timescales that rapidly increase with mass. Gas accretion in weak-line T Tauri disks may be quenched by global depletion of gas, but such a mechanism is unlikely to have stalled the growth in planetary systems that contain relatively low-mass, close-in planets together with more massive, longer period companions. Here, we suggest a potential solution for this conundrum. In general, supersonic infall of surrounding gas onto a protoplanet is only possible interior to both its Bondi and Roche radii. Above the critical mass where the Roche and Bondi radii are equal to the disk thickness, the protoplanet's tidal perturbation induces the formation of a gap. However, despite continued diffusion into the gap, the azimuthal flux across the protoplanet's Roche lobe will be quenched. Using two different schemes, we present the results of numerical simulations and analysis to show that the accretion rate increases rapidly with the ratio of the protoplanet's Roche to Bondi radii or equivalently to the disk thickness. Gas accretion is quenched, yielding relatively low protoplanetary masses, in regions with low aspect ratios. This becomes important for determining the gas giant planet's mass function, the distribution of their masses within multiple-planet systems, and for suppressing the emergence of gas giants around low-mass stars. Finally, we find that accretion rates onto protoplanets declines gradually on a characteristic timescale of a few Myr, during which the protracted accretion timescale onto circumplanetary disks may allow for the formation and retention of regular satellites.

  19. DASCH ON KU Cyg: A {approx} 5 YEAR DUST ACCRETION EVENT IN {approx} 1900

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

    Tang Sumin; Grindlay, Jonathan; Los, Edward

    2011-09-01

    KU Cyg is an eclipsing binary consisting of an F-type star accreting through a large accretion disk from a K5III red giant. Here we present the discovery of a 5 year dip around 1900 found from its 100 year DASCH light curve. It showed a {approx}0.5 mag slow fading from 1899 to 1903 and brightened back around 1904 on a relatively shorter timescale. The light curve shape of the 1899-1904 fading-brightening event differs from the dust production and dispersion process observed in R Coronae Borealis stars, which usually has a faster fading and slower recovery, and for KU Cyg ismore » probably related to the accretion disk surrounding the F star. The slow fading in KU Cyg is probably caused by increases in dust extinction in the disk, and the subsequent quick brightening may be due to the evaporation of dust transported inward through the disk. The extinction excess which caused the fading may arise from increased mass transfer rate in the system or from dust clump ejections from the K giant.« less

  20. Formation of terrestrial planets in eccentric and inclined giant planet systems

    NASA Astrophysics Data System (ADS)

    Sotiriadis, Sotiris; Libert, Anne-Sophie; Raymond, Sean N.

    2018-06-01

    Aims: Evidence of mutually inclined planetary orbits has been reported for giant planets in recent years. Here we aim to study the impact of eccentric and inclined massive giant planets on the terrestrial planet formation process, and investigate whether it can possibly lead to the formation of inclined terrestrial planets. Methods: We performed 126 simulations of the late-stage planetary accretion in eccentric and inclined giant planet systems. The physical and orbital parameters of the giant planet systems result from n-body simulations of three giant planets in the late stage of the gas disc, under the combined action of Type II migration and planet-planet scattering. Fourteen two- and three-planet configurations were selected, with diversified masses, semi-major axes (resonant configurations or not), eccentricities, and inclinations (including coplanar systems) at the dispersal of the gas disc. We then followed the gravitational interactions of these systems with an inner disc of planetesimals and embryos (nine runs per system), studying in detail the final configurations of the formed terrestrial planets. Results: In addition to the well-known secular and resonant interactions between the giant planets and the outer part of the disc, giant planets on inclined orbits also strongly excite the planetesimals and embryos in the inner part of the disc through the combined action of nodal resonance and the Lidov-Kozai mechanism. This has deep consequences on the formation of terrestrial planets. While coplanar giant systems harbour several terrestrial planets, generally as massive as the Earth and mainly on low-eccentric and low-inclined orbits, terrestrial planets formed in systems with mutually inclined giant planets are usually fewer, less massive (<0.5 M⊕), and with higher eccentricities and inclinations. This work shows that terrestrial planets can form on stable inclined orbits through the classical accretion theory, even in coplanar giant planet systems

  1. Runaway gas accretion and gap opening versus type I migration

    NASA Astrophysics Data System (ADS)

    Crida, A.; Bitsch, B.

    2017-03-01

    Growing planets interact with their natal protoplanetary disc, which exerts a torque onto them allowing them to migrate in the disc. Small mass planets do not affect the gas profile and migrate in the fast type-I migration. Although type-I migration can be directed outwards for planets smaller than 20 - 30M⊕ in some regions of the disc, planets above this mass should be lost into the central star long before the disc disperses. Massive planets push away material from their orbit and open a gap. They subsequently migrate in the slower, type II migration, which could save them from migrating all the way to the star. Hence, growing giant planets can be saved if and only if they can reach the gap opening mass, because this extends their migration timescale, allowing them to eventually survive at large orbits until the disc itself disperses. However, most of the previous studies only measured the torques on planets with fixed masses and orbits to determine the migration rate. Additionally, the transition between type-I and type-II migration itself is not well studied, especially when taking the growth mechanism of rapid gas accretion from the surrounding disc into account. Here we use isothermal 2D disc simulations with FARGO-2D1D to study the migration behaviour of gas accreting protoplanets in discs. We find that migrating giant planets always open gaps in the disc. We further show analytically and numerically that in the runaway gas accretion regime, the growth time-scale is comparable to the type-I migration time-scale, indicating that growing planets will reach gap opening masses before migrating all the way to the central star in type-I migration if the disc is not extremely viscous and/or thick. An accretion rate limited to the radial gas flow in the disc, in contrast, is not fast enough. When gas accretion by the planet is taken into account, the gap opening process is accelerated because the planet accretes material originating from its horseshoe region. This

  2. Efficiency of planetesimal ablation in giant planetary envelopes

    NASA Astrophysics Data System (ADS)

    Pinhas, Arazi; Madhusudhan, Nikku; Clarke, Cathie

    2016-12-01

    Observations of exoplanetary spectra are leading to unprecedented constraints on their atmospheric elemental abundances, particularly O/H, C/H, and C/O ratios. Recent studies suggest that elemental ratios could provide important constraints on formation and migration mechanisms of giant exoplanets. A fundamental assumption in such studies is that the chemical composition of the planetary envelope represents the sum-total of compositions of the accreted gas and solids during the formation history of the planet. We investigate the efficiency with which accreted planetesimals ablate in a giant planetary envelope thereby contributing to its composition rather than sinking to the core. From considerations of aerodynamic drag causing `frictional ablation' and the envelope temperature structure causing `thermal ablation', we compute mass ablations for impacting planetesimals of radii 30 m to 1 km for different compositions (ice to iron) and a wide range of velocities and impact angles, assuming spherical symmetry. Icy impactors are fully ablated in the outer envelope for a wide range of parameters. Even for Fe impactors substantial ablation occurs in the envelope for a wide range of sizes and velocities. For example, iron impactors of sizes below ˜0.5 km and velocities above ˜30 km s-1 are found to ablate by ˜60-80 per cent within the outer envelope at pressures below 103 bar due to frictional ablation alone. For deeper pressures (˜107 bar), substantial ablation happens over a wider range of parameters. Therefore, our exploratory study suggests that atmospheric abundances of volatile elements in giant planets reflect their accretion history during formation.

  3. Steamworlds: Atmospheric Structure and Critical Mass of Planets Accreting Icy Pebbles

    NASA Astrophysics Data System (ADS)

    Chambers, John

    2017-11-01

    In the core accretion model, gas-giant planets first form a solid core, which then accretes gas from a protoplanetary disk when the core exceeds a critical mass. Here, we model the atmosphere of a core that grows by accreting ice-rich pebbles. The ice fraction of pebbles evaporates in warm regions of the atmosphere, saturating it with water vapor. Excess water precipitates to lower altitudes. Beneath an outer radiative region, the atmosphere is convective, following a moist adiabat in saturated regions due to water condensation and precipitation. Atmospheric mass, density, and temperature increase with core mass. For nominal model parameters, planets with core masses (ice + rock) between 0.08 and 0.16 Earth masses have surface temperatures between 273 and 647 K and form an ocean. In more massive planets, water exists as a supercritical convecting fluid mixed with gas from the disk. Typically, the core mass reaches a maximum (the critical mass) as a function of the total mass when the core is 2-5 Earth masses. The critical mass depends in a complicated way on pebble size, mass flux, and dust opacity due to the occasional appearance of multiple core-mass maxima. The core mass for an atmosphere of 50% hydrogen and helium may be a more robust indicator of the onset of gas accretion. This mass is typically 1-3 Earth masses for pebbles that are 50% ice by mass, increasing with opacity and pebble flux and decreasing with pebble ice/rock ratio.

  4. On the Minimum Core Mass for Giant Planet Formation

    NASA Astrophysics Data System (ADS)

    Piso, Ana-Maria; Youdin, Andrew; Murray-Clay, Ruth

    2013-07-01

    The core accretion model proposes that giant planets form by the accretion of gas onto a solid protoplanetary core. Previous studies have found that there exists a "critical core mass" past which hydrostatic solutions can no longer be found and unstable atmosphere collapse occurs. This core mass is typically quoted to be around 10Me. In standard calculations of the critical core mass, planetesimal accretion deposits enough heat to alter the luminosity of the atmosphere, increasing the core mass required for the atmosphere to collapse. In this study we consider the limiting case in which planetesimal accretion is negligible and Kelvin-Helmholtz contraction dominates the luminosity evolution of the planet. We develop a two-layer atmosphere model with an inner convective region and an outer radiative zone that matches onto the protoplanetary disk, and we determine the minimum core mass for a giant planet to form within the typical disk lifetime for a variety of disk conditions. We denote this mass as critical core mass. The absolute minimum core mass required to nucleate atmosphere collapse is ˜ 8Me at 5 AU and steadily decreases to ˜ 3.5Me at 100 AU, for an ideal diatomic gas with a solar composition and a standard ISM opacity law. Lower opacity and disk temperature significantly reduce the critical core mass, while a decrease in the mean molecular weight of the nebular gas results in a larger critical core mass. Our results yield lower mass cores than corresponding studies for large planetesimal accretion rates.

  5. Modeling Hf-W Evolution for Earth, Moon and Mars in Grand Tack Accretion Simulations: The Isotopic Consequences of Rapid Accretion

    NASA Astrophysics Data System (ADS)

    Zube, N.; Nimmo, F.; Jacobson, S. A.; Fischer, R. A.

    2017-12-01

    Short-lived isotopes, such as the decay of lithophile 182Hf into siderophile 182W with a half-life of 9 My, can provide constraints on the timescales of planetary core formation and accretion. Classical accretion scenarios have produced Hf-W isotopic outcomes like those measured presently on the Earth [2,3]. We examine Grand Tack accretion simulations [4,5] and determine the mantle equilibration conditions necessary to produce the observed tungsten isotopic anomaly. Additionally, we follow Hf-W evolution for pairs of bodies that experience a last giant impact fitting the conditions of Earth's Moon-forming collision. In this way, we determine the likelihood of producing the observed almost indistinguishable W isotope anomalies of the Earth and Moon mantles [6]. We model Hf-W evolution for growing planets in 141 N-body simulations during late accretion in the Grand Tack scenario. For each case, we vary the equilibration factor during collisions—the fraction of impactor core that experiences re-equilibration with the entire target mantle—in steps ranging from none (cores merging) to complete equilibration. For Earth-like and Mars-like surviving planets, we find that cases with a high equilibration factor (k > 0.8) and an intermediate (2:1 - 4:1) ratio of initial embryo mass to planetesimal mass were most frequently able to approximate the observed W measurements for Earth and Mars. The equilibration factor required is more restrictive than the one found for classical accretion scenarios [2,3] and may not be consistent with fluid-dynamical predictions [7]. Moons made of impactor material from Earth's last giant impact are only able to result in an Earth-Moon pair having sufficiently similar W anomalies with a likelihood of 8% or less across all simulations. This indicates that a scenario where the Moon isotopically equilibrated with the Earth's mantle after the impact [8] may be required to explain the measured values. [1] Kleine et al. 2009 [2] Nimmo et al. 2010

  6. Growth of asteroids, planetary embryos, and Kuiper belt objects by chondrule accretion

    PubMed Central

    Johansen, Anders; Low, Mordecai-Mark Mac; Lacerda, Pedro; Bizzarro, Martin

    2015-01-01

    Chondrules are millimeter-sized spherules that dominate primitive meteorites (chondrites) originating from the asteroid belt. The incorporation of chondrules into asteroidal bodies must be an important step in planet formation, but the mechanism is not understood. We show that the main growth of asteroids can result from gas drag–assisted accretion of chondrules. The largest planetesimals of a population with a characteristic radius of 100 km undergo runaway accretion of chondrules within ~3 My, forming planetary embryos up to Mars’s size along with smaller asteroids whose size distribution matches that of main belt asteroids. The aerodynamical accretion leads to size sorting of chondrules consistent with chondrites. Accretion of millimeter-sized chondrules and ice particles drives the growth of planetesimals beyond the ice line as well, but the growth time increases above the disc lifetime outside of 25 AU. The contribution of direct planetesimal accretion to the growth of both asteroids and Kuiper belt objects is minor. In contrast, planetesimal accretion and chondrule accretion play more equal roles in the formation of Moon-sized embryos in the terrestrial planet formation region. These embryos are isolated from each other and accrete planetesimals only at a low rate. However, the continued accretion of chondrules destabilizes the oligarchic configuration and leads to the formation of Mars-sized embryos and terrestrial planets by a combination of direct chondrule accretion and giant impacts. PMID:26601169

  7. Growth of asteroids, planetary embryos, and Kuiper belt objects by chondrule accretion

    NASA Astrophysics Data System (ADS)

    Johansen, Anders; Mac Low, Mordecai-Mark; Lacerda, Pedro; Bizzarro, Martin

    2015-04-01

    Chondrules are millimeter-sized spherules that dominate primitive meteorites (chondrites) originating from the asteroid belt. The incorporation of chondrules into asteroidal bodies must be an important step in planet formation, but the mechanism is not understood. We show that the main growth of asteroids can result from gas drag-assisted accretion of chondrules. The largest planetesimals of a population with a characteristic radius of 100 km undergo runaway accretion of chondrules within ~3 My, forming planetary embryos up to Mars's size along with smaller asteroids whose size distribution matches that of main belt asteroids. The aerodynamical accretion leads to size sorting of chondrules consistent with chondrites. Accretion of millimeter-sized chondrules and ice particles drives the growth of planetesimals beyond the ice line as well, but the growth time increases above the disc lifetime outside of 25 AU. The contribution of direct planetesimal accretion to the growth of both asteroids and Kuiper belt objects is minor. In contrast, planetesimal accretion and chondrule accretion play more equal roles in the formation of Moon-sized embryos in the terrestrial planet formation region. These embryos are isolated from each other and accrete planetesimals only at a low rate. However, the continued accretion of chondrules destabilizes the oligarchic configuration and leads to the formation of Mars-sized embryos and terrestrial planets by a combination of direct chondrule accretion and giant impacts.

  8. Growth of asteroids, planetary embryos, and Kuiper belt objects by chondrule accretion.

    PubMed

    Johansen, Anders; Low, Mordecai-Mark Mac; Lacerda, Pedro; Bizzarro, Martin

    2015-04-01

    Chondrules are millimeter-sized spherules that dominate primitive meteorites (chondrites) originating from the asteroid belt. The incorporation of chondrules into asteroidal bodies must be an important step in planet formation, but the mechanism is not understood. We show that the main growth of asteroids can result from gas drag-assisted accretion of chondrules. The largest planetesimals of a population with a characteristic radius of 100 km undergo runaway accretion of chondrules within ~3 My, forming planetary embryos up to Mars's size along with smaller asteroids whose size distribution matches that of main belt asteroids. The aerodynamical accretion leads to size sorting of chondrules consistent with chondrites. Accretion of millimeter-sized chondrules and ice particles drives the growth of planetesimals beyond the ice line as well, but the growth time increases above the disc lifetime outside of 25 AU. The contribution of direct planetesimal accretion to the growth of both asteroids and Kuiper belt objects is minor. In contrast, planetesimal accretion and chondrule accretion play more equal roles in the formation of Moon-sized embryos in the terrestrial planet formation region. These embryos are isolated from each other and accrete planetesimals only at a low rate. However, the continued accretion of chondrules destabilizes the oligarchic configuration and leads to the formation of Mars-sized embryos and terrestrial planets by a combination of direct chondrule accretion and giant impacts.

  9. Accreting transition discs with large cavities created by X-ray photoevaporation in C and O depleted discs

    NASA Astrophysics Data System (ADS)

    Ercolano, Barbara; Weber, Michael L.; Owen, James E.

    2018-01-01

    Circumstellar discs with large dust depleted cavities and vigorous accretion on to the central star are often considered signposts for (multiple) giant planet formation. In this Letter, we show that X-ray photoevaporation operating in discs with modest (factors 3-10) gas-phase depletion of carbon and oxygen at large radii ( > 15 au) yields the inner radius and accretion rates for most of the observed discs, without the need to invoke giant planet formation. We present one-dimensional viscous evolution models of discs affected by X-ray photoevaporation assuming moderate gas-phase depletion of carbon and oxygen, well within the range reported by recent observations. Our models use a simplified prescription for scaling the X-ray photoevaporation rates and profiles at different metallicity, and our quantitative result depends on this scaling. While more rigorous hydrodynamical modelling of mass-loss profiles at low metallicities is required to constrain the observational parameter space that can be explained by our models, the general conclusion that metal sequestering at large radii may be responsible for the observed diversity of transition discs is shown to be robust. Gap opening by giant planet formation may still be responsible for a number of observed transition discs with large cavities and very high accretion rate.

  10. Episodic accretion: the interplay of infall and disc instabilities

    NASA Astrophysics Data System (ADS)

    Kuffmeier, Michael; Frimann, Søren; Jensen, Sigurd S.; Haugbølle, Troels

    2018-04-01

    Using zoom-simulations carried out with the adaptive mesh-refinement code RAMSES with a dynamic range of up to 227 ≈ 1.34 × 108 we investigate the accretion profiles around six stars embedded in different environments inside a (40 pc)3 giant molecular cloud, the role of mass infall and disc instabilities on the accretion profile, and thus on the luminosity of the forming protostar. Our results show that the environment in which the protostar is embedded determines the overall accretion profile of the protostar. Infall on to the circumstellar disc may trigger gravitational disc instabilities in the disc at distances of around ˜10 to ˜50 au leading to rapid transport of angular momentum and strong accretion bursts. These bursts typically last for about ˜10 to a ˜100 yr, consistent with typical orbital times at the location of the instability, and enhance the luminosity of the protostar. Calculations with the stellar evolution code MESA show that the accretion bursts induce significant changes in the protostellar properties, such as the stellar temperature and radius. We apply the obtained protostellar properties to produce synthetic observables with RADMC3D and predict that accretion bursts lead to observable enhancements around 20 to 200 μm in the spectral energy distribution of Class 0 type young stellar objects.

  11. Wind models for the NSTS ascent trajectory biasing for wind load alleviation

    NASA Technical Reports Server (NTRS)

    Smith, O. E.; Adelfang, S. I.; Batts, G. W.; Hill, C. K.

    1989-01-01

    New concepts are presented for aerospace vehicle ascent wind profile biasing. The purpose for wind biasing the ascent trajectory is to provide ascent wind loads relief and thus decrease the probability for launch delays due to wind loads exceeding critical limits. Wind biasing trajectories to the profile of monthly mean winds have been widely used for this purpose. The wind profile models presented give additional alternatives for wind biased trajectories. They are derived from the properties of the bivariate normal probability function using the available wind statistical parameters for the launch site. The analytical expressions are presented to permit generalizations. Specific examples are given to illustrate the procedures. The wind profile models can be used to establish the ascent trajectory steering commands to guide the vehicle through the first stage. For the National Space Transportation System (NSTS) program these steering commands are called I-loads.

  12. The Thermal States of Accreting Planets: From Mars-like Embryos to a MAD Earth

    NASA Astrophysics Data System (ADS)

    Stewart, S. T.; Lock, S. J.

    2015-12-01

    The thermal states of rocky planets can vary widely during the process of accretion. The thermal structure affects several major processes on the growing planet, including the mechanics of core formation, pressure-temperature conditions for metal-silicate equilibration, mixing, and atmospheric erosion. Because impact energy is distributed heterogeneously, accretional energy is preferentially deposited in the gravitationally re-equilibrated outer layers of the planet for both small and giant impacts. The resulting stably stratified structure inhibits complete mixing within the mantle. Initially, the specific energy of giant impacts between Mars-mass embryos leads to melting of the mantle. However, as planet formation progresses, the specific energies of giant impacts increase and can drive the mantle into a transient supercritical state. In the hottest regions of the planet, metal and silicates are miscible, and metal exsolution occurs as the structure cools. The cooling time of the supercritical structure is typically longer than the timescale for metal segregation to the core. Thus, these high temperature excursions during planet formation are significant for understanding metal-silicate equilibration. Furthermore, when a supercritical planet is also rapidly rotating, the mantle, atmosphere and disk (MAD) form a continuous dynamic and thermodynamic structure. Lunar origin by condensation from a MAD Earth can explain the major characteristics of the Moon (Lock et al., this meeting). One of the greatest uncertainties in understanding the thermal states of planets during accretion is the changing composition and mass of the atmosphere. After the dispersal of the solar nebula, the thermal boundary condition imposed by the atmosphere can vary between silicate vapor and condensed ices. The coupled problem of atmospheric origin and planetary accretion can be used to constrain the many uncertainties in the growth and divergence of the terrestrial planets in our solar

  13. The first skull of the earliest giant panda

    PubMed Central

    Jin, Changzhu; Ciochon, Russell L.; Dong, Wei; Hunt, Robert M.; Liu, Jinyi; Jaeger, Marc; Zhu, Qizhi

    2007-01-01

    Fossils of the giant panda Ailuropoda (Order Carnivora, Family Ursidae) are largely isolated teeth, mandibles, and a few rare skulls, known from the late Pliocene to late Pleistocene in China and Southeast Asia. Much of this material represents a Pleistocene chronospecies, Ailuropoda baconi, an animal larger than the living giant panda, Ailuropoda melanoleuca. The earliest certain record of Ailuropoda is the late Pliocene chronospecies, Ailuropoda microta, smaller than either A. baconi or A. melanoleuca, and previously known only from teeth and a few mandibles from karst caves in south China. Here, we report the discovery of the first skull of A. microta, establishing its cranial anatomy and demonstrating that the specialized cranial and dental adaptations of Ailuropoda for durophagous feeding behavior centered on bamboo were already evident in this late Pliocene species. The skull from Jinyin cave (Guangxi) and dental remains from other karst localities in southeastern China show that Ailuropoda microta occupied south China from ≈2 to 2.4 Myr ago after a marked global climatic deterioration. Dental and basicranial anatomy indicate a less specialized morphology early in the history of the lineage and support derivation of the giant panda from the Miocene Asian ursid Ailurarctos PMID:17578912

  14. Winds and accretion in delta Sagittae

    NASA Technical Reports Server (NTRS)

    Eaton, Joel A.; Hartkopf, William I.; Mcalister, Harold A.; Mason, Brian D.

    1995-01-01

    The ten-year binary delta Sge (M2 Ib-II+B9.5 V) is a zeta Aur binary containing an abnormally cool component. Combining our analysis of the system as a visual binary with Batten's radial-velocity solution leads to the following properties: i = 40 deg, a = 51 mas = 8.83 A.U. = 1893 solar radius, hence d = 173 pc; M(sub B) = 2.9 solar mass and M(sub M) = 3.8 solar mass; and R(sub B) = 2.6 solar radius and R(sub M) = 152 solar radius. This interpretation of the orbit places the M supergiant on the asymptotic giant branch. We have collected ultraviolet spectra throughout the star's 1980-90 orbit, concentrated around the conjuction of 1990. The wind of the M giant appears in these as narrow shell lines of singly ionized metals, chiefly Fe II, with P-Cyg profiles at many phases, which show the slow variation in strength expected for the orbit but no pronounced atmospheric eclipse. The terminal velocity of the wind is 16-18 km/s, and its excitation temperature is approximately 10,000 K. Most of the broadening of the wind lines is caused by differential expansion of the atmosphere, with (unmeasurably) low turbulent velocities. Nontheless, the mass loss rate (1.1 +/- 0.4 X 10 (exp -8) solar mas/yr) is almost the same as found previously by Reimers and Schroder for very different assumptions about the velocity structure. Also seen in the spectrum throughout the orbit are the effects of a variable, high-speed wind as well as evidence for accretion onto the B9.5 star. This high-speed wind absorbs in species of all ionization stages observed, e. g., C II, Mg II, Al III, SI IV, C IV, and has a terminaal velocity in the range 200-450 km/s. We presume this wind originates at the B dwarf, not the M supergiant, and speculate that it comes from an accretion disk, as suggested by recent models of magnetically moderated accretion. Evidence for accretion is redshifted absorption in the same transitions formed in the high-speed wind, as well as broad emission lines of singly ionized

  15. Crew Exploration Vehicle Ascent Abort Overview

    NASA Technical Reports Server (NTRS)

    Davidson, John B., Jr.; Madsen, Jennifer M.; Proud, Ryan W.; Merritt, Deborah S.; Sparks, Dean W., Jr.; Kenyon, Paul R.; Burt, Richard; McFarland, Mike

    2007-01-01

    One of the primary design drivers for NASA's Crew Exploration Vehicle (CEV) is to ensure crew safety. Aborts during the critical ascent flight phase require the design and operation of CEV systems to escape from the Crew Launch Vehicle and return the crew safely to the Earth. To accomplish this requirement of continuous abort coverage, CEV ascent abort modes are being designed and analyzed to accommodate the velocity, altitude, atmospheric, and vehicle configuration changes that occur during ascent. The analysis involves an evaluation of the feasibility and survivability of each abort mode and an assessment of the abort mode coverage. These studies and design trades are being conducted so that more informed decisions can be made regarding the vehicle abort requirements, design, and operation. This paper presents an overview of the CEV, driving requirements for abort scenarios, and an overview of current ascent abort modes. Example analysis results are then discussed. Finally, future areas for abort analysis are addressed.

  16. Steamworlds: Atmospheric Structure and Critical Mass of Planets Accreting Icy Pebbles

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

    Chambers, John, E-mail: jchambers@carnegiescience.edu

    In the core accretion model, gas-giant planets first form a solid core, which then accretes gas from a protoplanetary disk when the core exceeds a critical mass. Here, we model the atmosphere of a core that grows by accreting ice-rich pebbles. The ice fraction of pebbles evaporates in warm regions of the atmosphere, saturating it with water vapor. Excess water precipitates to lower altitudes. Beneath an outer radiative region, the atmosphere is convective, following a moist adiabat in saturated regions due to water condensation and precipitation. Atmospheric mass, density, and temperature increase with core mass. For nominal model parameters, planetsmore » with core masses (ice + rock) between 0.08 and 0.16 Earth masses have surface temperatures between 273 and 647 K and form an ocean. In more massive planets, water exists as a supercritical convecting fluid mixed with gas from the disk. Typically, the core mass reaches a maximum (the critical mass) as a function of the total mass when the core is 2–5 Earth masses. The critical mass depends in a complicated way on pebble size, mass flux, and dust opacity due to the occasional appearance of multiple core-mass maxima. The core mass for an atmosphere of 50% hydrogen and helium may be a more robust indicator of the onset of gas accretion. This mass is typically 1–3 Earth masses for pebbles that are 50% ice by mass, increasing with opacity and pebble flux and decreasing with pebble ice/rock ratio.« less

  17. Numerical Simulations of Wind Accretion in Symbiotic Binaries

    NASA Astrophysics Data System (ADS)

    de Val-Borro, M.; Karovska, M.; Sasselov, D.

    2009-08-01

    About half of the binary systems are close enough to each other for mass to be exchanged between them at some point in their evolution, yet the accretion mechanism in wind accreting binaries is not well understood. We study the dynamical effects of gravitational focusing by a binary companion on winds from late-type stars. In particular, we investigate the mass transfer and formation of accretion disks around the secondary in detached systems consisting of an asymptotic giant branch (AGB) mass-losing star and an accreting companion. The presence of mass outflows is studied as a function of mass-loss rate, wind temperature, and binary orbital parameters. A two-dimensional hydrodynamical model is used to study the stability of mass transfer in wind accreting symbiotic binary systems. In our simulations we use an adiabatic equation of state and a modified version of the isothermal approximation, where the temperature depends on the distance from the mass losing star and its companion. The code uses a block-structured adaptive mesh refinement method that allows us to have high resolution at the position of the secondary and resolve the formation of bow shocks and accretion disks. We explore the accretion flow between the components and formation of accretion disks for a range of orbital separations and wind parameters. Our results show the formation of stream flow between the stars and accretion disks of various sizes for certain orbital configurations. For a typical slow and massive wind from an AGB star the flow pattern is similar to a Roche lobe overflow with accretion rates of 10% of the mass loss from the primary. Stable disks with exponentially decreasing density profiles and masses of the order 10-4 solar masses are formed when wind acceleration occurs at several stellar radii. The disks are geometrically thin with eccentric streamlines and close to Keplerian velocity profiles. The formation of tidal streams and accretion disks is found to be weakly dependent on

  18. Giant Impacts on Earth-Like Worlds

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-05-01

    Earth has experienced a large number of impacts, from the cratering events that may have caused mass extinctions to the enormous impact believed to have formed the Moon. A new study examines whether our planets impact history is typical for Earth-like worlds.N-Body ChallengesTimeline placing the authors simulations in context of the history of our solar system (click for a closer look). [Quintana et al. 2016]The final stages of terrestrial planet formation are thought to be dominated by giant impacts of bodies in the protoplanetary disk. During this stage, protoplanets smash into one another and accrete, greatly influencing the growth, composition, and habitability of the final planets.There are two major challenges when simulating this N-body planet formation. The first is fragmentation: since computational time scales as N^2, simulating lots of bodies that split into many more bodies is very computationally intensive. For this reason, fragmentation is usually ignored; simulations instead assume perfect accretion during collisions.Total number of bodies remaining within the authors simulations over time, with fragmentation included (grey) and ignored (red). Both simulations result in the same final number of bodies, but the ones that include fragmentation take more time to reach that final number. [Quintana et al. 2016]The second challengeis that many-body systems are chaotic, which means its necessary to do a large number of simulations to make statistical statements about outcomes.Adding FragmentationA team of scientists led by Elisa Quintana (NASA NPP Senior Fellow at the Ames Research Center) has recently pushed at these challenges by modeling inner-planet formation using a code that does include fragmentation. The team ran 140 simulations with and 140 without the effects of fragmentation using similar initial conditions to understand how including fragmentation affects the outcome.Quintana and collaborators then used the fragmentation-inclusive simulations to

  19. Challenging dyke ascent models using novel laboratory experiments: Implications for reinterpreting evidence of magma ascent and volcanism

    NASA Astrophysics Data System (ADS)

    Kavanagh, Janine L.; Burns, Alec J.; Hilmi Hazim, Suraya; Wood, Elliot P.; Martin, Simon A.; Hignett, Sam; Dennis, David J. C.

    2018-04-01

    Volcanic eruptions are fed by plumbing systems that transport magma from its source to the surface, mostly fed by dykes. Here we present laboratory experiments that model dyke ascent to eruption using a tank filled with a crust analogue (gelatine, which is transparent and elastic) that is injected from below by a magma analogue (dyed water). This novel experimental setup allows, for the first time, the simultaneous measurement of fluid flow, sub-surface and surface deformation during dyke ascent. During injection, a penny-shaped fluid-filled crack is formed, intrudes, and traverses the gelatine slab vertically to then erupt at the surface. Polarised light shows the internal stress evolution as the dyke ascends, and an overhead laser scanner measures the surface elevation change in the lead-up to dyke eruption. Fluorescent passive-tracer particles that are illuminated by a laser sheet are monitored, and the intruding fluid's flow dynamics and gelatine's sub-surface strain evolution is measured using particle image velocimetry and digital image correlation, respectively. We identify 4 previously undescribed stages of dyke ascent. Stage 1, early dyke growth: the initial dyke grows from the source, and two fluid jets circulate as the penny-shaped crack is formed. Stage 2, pseudo-steady dyke growth: characterised by the development of a rapidly uprising, central, single pseudo-steady fluid jet, as the dyke grows equally in length and width, and the fluid down-wells at the dyke margin. Sub-surface host strain is localised at the head region and the tail of the dyke is largely static. Stage 3, pre-eruption unsteady dyke growth: an instability in the fluid flow appears as the central fluid jet meanders, the dyke tip accelerates towards the surface and the tail thins. Surface deformation is only detected in the immediate lead-up to eruption and is characterised by an overall topographic increase, with axis-symmetric topographic highs developed above the dyke tip. Stage 4 is

  20. Comparison of a discrete steepest ascent method with the continuous steepest ascent method for optimal programing

    NASA Technical Reports Server (NTRS)

    Childs, A. G.

    1971-01-01

    A discrete steepest ascent method which allows controls which are not piecewise constant (for example, it allows all continuous piecewise linear controls) was derived for the solution of optimal programming problems. This method is based on the continuous steepest ascent method of Bryson and Denham and new concepts introduced by Kelley and Denham in their development of compatible adjoints for taking into account the effects of numerical integration. The method is a generalization of the algorithm suggested by Canon, Cullum, and Polak with the details of the gradient computation given. The discrete method was compared with the continuous method for an aerodynamics problem for which an analytic solution is given by Pontryagin's maximum principle, and numerical results are presented. The discrete method converges more rapidly than the continuous method at first, but then for some undetermined reason, loses its exponential convergence rate. A comparsion was also made for the algorithm of Canon, Cullum, and Polak using piecewise constant controls. This algorithm is very competitive with the continuous algorithm.

  1. The formation of giant planets in wide orbits by photoevaporation-synchronized migration

    NASA Astrophysics Data System (ADS)

    Guilera, O. M.; Miller Bertolami, M. M.; Ronco, M. P.

    2017-10-01

    The discovery of giant planets in wide orbits represents a major challenge for planet formation theory. In the standard core accretion paradigm, planets are expected to form at radial distances ≲20 au in order to form massive cores (with masses ≳10 M⊕) able to trigger the gaseous runaway growth before the dissipation of the disc. This has encouraged authors to find modifications of the standard scenario as well as alternative theories like the formation of planets by gravitational instabilities in the disc to explain the existence of giant planets in wide orbits. However, there is not yet consensus on how these systems are formed. In this Letter, we present a new natural mechanism for the formation of giant planets in wide orbits within the core accretion paradigm. If photoevaporation is considered, after a few Myr of viscous evolution a gap in the gaseous disc is opened. We found that, under particular circumstances planet migration becomes synchronized with the evolution of the gap, which results in an efficient outward planet migration. This mechanism is found to allow the formation of giant planets with masses Mp ≲ 1MJup in wide stable orbits as large as ∼130 au from the central star.

  2. First INTEGRAL and Swift Observations of a Giant Outburst of A 0535+26

    NASA Technical Reports Server (NTRS)

    Caballero, I.; Mueller, S.; Bordas, P.; Ferrigno, C.; Kuehnel, M.; Pottschmodt, K.; Kretschmar, P.; Wilms, J.; Kreykenbohm, I.; Santangelo, A.; hide

    2012-01-01

    The Be/X-ray binary A 0535+26 has shown three giant outbursts since 2005, after a long period of quiescence. The giant outbursts in 2005 (approx.5.2 Crab, 15-50 keY range) and 2009 (approx.5.6 Crab) could not be observed by most X-ray observatories due to Sun observing constraints. Finally, a giant outburst in February 2011, that reached a flux of approx.3.8 Crab, was monitored with INTEGRAL and Swift TOO observations. We present first results these observations, with a special focus on the cyclotron lines present in the X-ray spectrum of the source.

  3. On 7Li Enrichment by Low-Mass Metal-Poor Red Giant Branch Stars.

    PubMed

    de La Reza R; da Silva L; Drake; Terra

    2000-06-01

    First-ascent red giants with strong and very strong Li lines have just been discovered in globular clusters. Using the stellar internal prompt (7)Li enrichment-mass-loss scenario, we explore the possibility of (7)Li enrichment in the interstellar matter of the globular cluster M3 produced by these Li-rich giants. We found that enrichment as large as 70% or more compared to the initial (7)Li content of M3 can be obtained during the entire life of this cluster. However, because M3 will cross into the Galactic plane several times, the new (7)Li will be very probably removed by ram pressure into the disk. Globular clusters appear then as possible new sources of (7)Li in the Galactic disk. It is also suggested that the known Na/Al variations in stars of globular clusters could be somehow related to the (7)Li variations and that the cool bottom process mixing mechanism acting in the case of (7)Li could also play a role in the case of Na and Al surface enrichments.

  4. Theories of the origin and evolution of the giant planets

    NASA Technical Reports Server (NTRS)

    Pollack, J. B.; Bodenheimer, P.

    1989-01-01

    Following the accretion of solids and gases in the solar nebula, the giant planets contracted to their present sizes over the age of the solar system. It is presently hypothesized that this contraction was rapid, but not hydrodynamic; at a later stage, a nebular disk out of which the regular satellites formed may have been spun out of the outer envelope of the contracting giant planets due to a combination of total angular momentum conservation and the outward transfer of specific angular momentum in the envelope. If these hypotheses are true, the composition of the irregular satellites directly reflects the composition of planetesimals from which the giant planets formed, while the composition of the regular satellites is indicative of the composition of the less volatile components of the outer envelopes of the giant planets.

  5. The Formation of Terrestrial Planets from the Direct Accretion of Pebbles

    NASA Astrophysics Data System (ADS)

    Levison, Harold F.; Kretke, Katherine; Walsh, Kevin

    2014-11-01

    A radical new scenario has recently been suggested for the formation of giant planet cores that reports to solve this long-standing problem. This scenario, known as pebble accretion, envisions: 1) Planetesimals form directly from millimeter- to meter-sized objects (the pebbles) that are concentrated by turbulent eddies and then gravitationally collapse to form 100 — 1000 km objects (Cuzzi+ 2008, AJ 687, 1432; Johansen+ 2007, Nature 448, 1022). 2) These planetesimals quickly sweep up the remaining pebbles because their capture cross sections are significantly enhanced by aerodynamic drag (Lambrechts & Johansen 2012, A&A 544, A32; Ormel & Klahr (2010) A&A Volume 520, id.A43). Calculations show that a single 1000 km object embedded in a swarm of pebbles can grow to ~10 Earth-masses in less than 10,000 years. These short timescales present a problem in the terrestrial planet region because it took many tens of millions of years for the Earth to form (Touboul+ 2007, Nature 450, 1206). However, recent full-scale simulations of core formation have shown that the only way to grow a small number of giant planets in the Solar System is for the pebbles to form over a long period of time (Kretke & Levison 2014, AJ, submitted; Levison & Kretke in prep.) in a process we call 'Slow Pebble Accretion'. Thus, here we will present preliminary results of a study of slow pebble accretion in the terrestrial planet zone.

  6. Ascent/descent ancillary data production user's guide

    NASA Technical Reports Server (NTRS)

    Brans, H. R.; Seacord, A. W., II; Ulmer, J. W.

    1986-01-01

    The Ascent/Descent Ancillary Data Product, also called the A/D BET because it contains a Best Estimate of the Trajectory (BET), is a collection of trajectory, attitude, and atmospheric related parameters computed for the ascent and descent phases of each Shuttle Mission. These computations are executed shortly after the event in a post-flight environment. A collection of several routines including some stand-alone routines constitute what is called the Ascent/Descent Ancillary Data Production Program. A User's Guide for that program is given. It is intended to provide the reader with all the information necessary to generate an Ascent or a Descent Ancillary Data Product. It includes descriptions of the input data and output data for each routine, and contains explicit instructions on how to run each routine. A description of the final output product is given.

  7. Three-dimensional hydrodynamical models of wind and outburst-related accretion in symbiotic systems

    NASA Astrophysics Data System (ADS)

    de Val-Borro, M.; Karovska, M.; Sasselov, D. D.; Stone, J. M.

    2017-07-01

    Gravitationally focused wind accretion in binary systems consisting of an evolved star with a gaseous envelope and a compact accreting companion is a possible mechanism to explain mass transfer in symbiotic binaries. We study the mass accretion around the secondary caused by the strong wind from the primary late-type component using global three-dimensional hydrodynamic numerical simulations during quiescence and outburst stages. In particular, the dependence of the mass accretion rate on the mass-loss rate, wind parameters and phases of wind outburst development is considered. For a typical wind from an asymptotic giant branch star with a mass-loss rate of 10-6 M⊙ yr-1 and wind speeds of 20-50 km s-1, the mass transfer through a focused wind results in efficient infall on to the secondary. Accretion rates on to the secondary of 5-20 per cent of the mass-loss from the primary are obtained during quiescence and outburst periods where the wind velocity and mass-loss rates are varied, about 20-50 per cent larger than in the standard Bondi-Hoyle-Lyttleton approximation. This mechanism could be an important method for explaining observed accretion luminosities and periodic modulations in the accretion rates for a broad range of interacting binary systems.

  8. MIGRATION AND GROWTH OF PROTOPLANETARY EMBRYOS. II. EMERGENCE OF PROTO-GAS-GIANT CORES VERSUS SUPER EARTH PROGENITORS

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

    Liu, Beibei; Zhang, Xiaojia; Lin, Douglas N. C.

    2015-01-01

    Nearly 15%-20% of solar type stars contain one or more gas giant planets. According to the core-accretion scenario, the acquisition of their gaseous envelope must be preceded by the formation of super-critical cores with masses 10 times or larger than that of the Earth. It is natural to link the formation probability of gas giant planets with the supply of gases and solids in their natal disks. However, a much richer population of super Earths suggests that (1) there is no shortage of planetary building block material, (2) a gas giant's growth barrier is probably associated with whether it can mergemore » into super-critical cores, and (3) super Earths are probably failed cores that did not attain sufficient mass to initiate efficient accretion of gas before it is severely depleted. Here we construct a model based on the hypothesis that protoplanetary embryos migrated extensively before they were assembled into bona fide planets. We construct a Hermite-Embryo code based on a unified viscous-irradiation disk model and a prescription for the embryo-disk tidal interaction. This code is used to simulate the convergent migration of embryos, and their close encounters and coagulation. Around the progenitors of solar-type stars, the progenitor super-critical-mass cores of gas giant planets primarily form in protostellar disks with relatively high (≳ 10{sup –7} M {sub ☉} yr{sup –1}) mass accretion rates, whereas systems of super Earths (failed cores) are more likely to emerge out of natal disks with modest mass accretion rates, due to the mean motion resonance barrier and retention efficiency.« less

  9. Kimberlite ascent by assimilation-fuelled buoyancy.

    PubMed

    Russell, James K; Porritt, Lucy A; Lavallée, Yan; Dingwell, Donald B

    2012-01-18

    Kimberlite magmas have the deepest origin of all terrestrial magmas and are exclusively associated with cratons. During ascent, they travel through about 150 kilometres of cratonic mantle lithosphere and entrain seemingly prohibitive loads (more than 25 per cent by volume) of mantle-derived xenoliths and xenocrysts (including diamond). Kimberlite magmas also reputedly have higher ascent rates than other xenolith-bearing magmas. Exsolution of dissolved volatiles (carbon dioxide and water) is thought to be essential to provide sufficient buoyancy for the rapid ascent of these dense, crystal-rich magmas. The cause and nature of such exsolution, however, remains elusive and is rarely specified. Here we use a series of high-temperature experiments to demonstrate a mechanism for the spontaneous, efficient and continuous production of this volatile phase. This mechanism requires parental melts of kimberlite to originate as carbonatite-like melts. In transit through the mantle lithosphere, these silica-undersaturated melts assimilate mantle minerals, especially orthopyroxene, driving the melt to more silicic compositions, and causing a marked drop in carbon dioxide solubility. The solubility drop manifests itself immediately in a continuous and vigorous exsolution of a fluid phase, thereby reducing magma density, increasing buoyancy, and driving the rapid and accelerating ascent of the increasingly kimberlitic magma. Our model provides an explanation for continuous ascent of magmas laden with high volumes of dense mantle cargo, an explanation for the chemical diversity of kimberlite, and a connection between kimberlites and cratons.

  10. Global hydromagnetic simulations of a planet embedded in a dead zone: Gap opening, gas accretion, and formation of a protoplanetary jet

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

    Gressel, O.; Nelson, R. P.; Turner, N. J.

    We present global hydrodynamic (HD) and magnetohydrodynamic (MHD) simulations with mesh refinement of accreting planets embedded in protoplanetary disks (PPDs). The magnetized disk includes Ohmic resistivity that depends on the overlying mass column, leading to turbulent surface layers and a dead zone near the midplane. The main results are: (1) the accretion flow in the Hill sphere is intrinsically three-dimensional for HD and MHD models. Net inflow toward the planet is dominated by high-latitude flows. A circumplanetary disk (CPD) forms. Its midplane flows outward in a pattern whose details differ between models. (2) The opening of a gap magnetically couplesmore » and ignites the dead zone near the planet, leading to stochastic accretion, a quasi-turbulent flow in the Hill sphere, and a CPD whose structure displays high levels of variability. (3) Advection of magnetized gas onto the rotating CPD generates helical fields that launch magnetocentrifugally driven outflows. During one specific epoch, a highly collimated, one-sided jet is observed. (4) The CPD's surface density is ∼30 g cm{sup −2}, small enough for significant ionization and turbulence to develop. (5) The accretion rate onto the planet in the MHD simulation reaches a steady value 8 × 10{sup –3} M {sub ⊕} yr{sup –1} and is similar in the viscous HD runs. Our results suggest that gas accretion onto a forming giant planet within a magnetized PPD with a dead zone allows rapid growth from Saturnian to Jovian masses. As well as being relevant for giant planet formation, these results have important implications for the formation of regular satellites around gas giant planets.« less

  11. Accretion of Jupiter-mass planets in the limit of vanishing viscosity

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

    Szulágyi, J.; Morbidelli, A.; Crida, A.

    In the core-accretion model, the nominal runaway gas-accretion phase brings most planets to multiple Jupiter masses. However, known giant planets are predominantly Jupiter mass bodies. Obtaining longer timescales for gas accretion may require using realistic equations of states, or accounting for the dynamics of the circumplanetary disk (CPD) in the low-viscosity regime, or both. Here we explore the second way by using global, three-dimensional isothermal hydrodynamical simulations with eight levels of nested grids around the planet. In our simulations, the vertical inflow from the circumstellar disk (CSD) to the CPD determines the shape of the CPD and its accretion rate.more » Even without a prescribed viscosity, Jupiter's mass-doubling time is ∼10{sup 4} yr, assuming the planet at 5.2 AU and a Minimum Mass Solar Nebula. However, we show that this high accretion rate is due to resolution-dependent numerical viscosity. Furthermore, we consider the scenario of a layered CSD, viscous only in its surface layer, and an inviscid CPD. We identify two planet-accretion mechanisms that are independent of the viscosity in the CPD: (1) the polar inflow—defined as a part of the vertical inflow with a centrifugal radius smaller than two Jupiter radii and (2) the torque exerted by the star on the CPD. In the limit of zero effective viscosity, these two mechanisms would produce an accretion rate 40 times smaller than in the simulation.« less

  12. Volatile accretion history of the terrestrial planets and dynamic implications.

    PubMed

    Albarède, Francis

    2009-10-29

    Accretion left the terrestrial planets depleted in volatile components. Here I examine evidence for the hypothesis that the Moon and the Earth were essentially dry immediately after the formation of the Moon-by a giant impact on the proto-Earth-and only much later gained volatiles through accretion of wet material delivered from beyond the asteroid belt. This view is supported by U-Pb and I-Xe chronologies, which show that water delivery peaked approximately 100 million years after the isolation of the Solar System. Introduction of water into the terrestrial mantle triggered plate tectonics, which may have been crucial for the emergence of life. This mechanism may also have worked for the young Venus, but seems to have failed for Mars.

  13. Rocketdyne - Lunar Ascent Engine. Chapter 7, Appendix I

    NASA Technical Reports Server (NTRS)

    Harmon, Tim

    2009-01-01

    The ascent engine was the last one from the moon, and I want to focus on the idea of redundancy and teams in regard to the engine. By teams, I mean teamwork - not just within Rocketdyne. It was teamwork within Rocketdyne; it was teamwork within Grumman; it was teamwork within NASA. These were all important elements leading to the successful development of the lunar excursion module (LEM) engine. Communication, rapid response, and cooperation were all important. Another aspect that went into the development of the ascent engine was the integration of technology and of lessons learned. We pushed all the above, plus technology and lessons learned, into a program, and that led to a successful result. One of the things that I like to think about - again in retrospect - is how it is very "in" now to have integrated product and process teams. These are buzzwords for teamwork in all program phases. That s where you combine a lot of groups into a single organization to get a job done. The ascent engine program epitomized that kind of integration and focus, and because this was the mid- to late-1960s; this was new ground for Rocketdyne, Grumman, and NASA. Redundancy was really a major hallmark of the Apollo Program. Everything was redundant. Once you got the rocket going, you could even lose one of the big F-1 engines, and it would still make it to orbit. And once the first stage separated from the rest of the vehicle, the second stage could do without an engine and still make a mission. This redundancy was demonstrated when an early Apollo launch shut down a J-2 second-stage engine. Actually, they shut down two J-2 engines on that flight. Even the third stage, with its single J-2 engine, was backed up because the first two stages could toss it into a recoverable orbit. If the third stage didn't work, you were circling the earth, and you had time to recover the command module and crew. Remember how on the Apollo 13 flight, there was sufficient system redundancy even when we

  14. Simulations of SSLV Ascent and Debris Transport

    NASA Technical Reports Server (NTRS)

    Rogers, Stuart; Aftosmis, Michael; Murman, Scott; Chan, William; Gomez, Ray; Gomez, Ray; Vicker, Darby; Stuart, Phil

    2006-01-01

    A viewgraph presentation on Computational Fluid Dynamic (CFD) Simulation of Space Shuttle Launch Vehicle (SSLV) ascent and debris transport analysis is shown. The topics include: 1) CFD simulations of the Space Shuttle Launch Vehicle ascent; 2) Debris transport analysis; 3) Debris aerodynamic modeling; and 4) Other applications.

  15. Are Giant Planet Satellites Mini-solar Systems?

    NASA Astrophysics Data System (ADS)

    Mosqueira, I.; Estrada, P. R.

    2003-12-01

    The regular satellites of Jupiter and Saturn exhibit a number of characteristics strongly suggestive of formation in a thin (aspect ratio H/r ˜ 0.1) circumplanetary gas disk (Mosqueira and Estrada 2003a). Also, the mass ratio of the largest satellites to the primary μ ˜ 10-4 lead one to think of these satellite systems as scaled-down solar systems. Yet, the larger mass ratio for the giant planets to the primary μ ˜ 10-3 appears to limit the usefulness of the planet-satellite analogy. If gap-opening determines the final size of at least Jupiter (Lin and Papaloizou 1993), then significantly smaller objects would be unable to truncate the disk. There are, however, at least two significant difficulties with this point of view. First, the non-linear or thermal gap-opening criterion (Lin and Papaloizou 1993) does not yield a Jupiter mass. Second, the migration timescale due to planet-disk interactions (Ward 1997) is too fast for the formation of giant planets through the core accretion process (Pollack et. al 1996) despite recent work which has lengthened it by up to an order of magnitude (Tanaka et al. 2002, D'Angelo et al. 2002, Bate et al. 2003). An alternative viewpoint has accretion taking place in a weakly turbulent disk, and the survival of both planets and satellites a direct consequence of gap-opening. In this view at least the largest satellites (Mosqueira and Estrada 2003b) and planetary cores ( ˜ 10 M⊕ ; Rafikov 2002) were able to open gaps in the disk. However, because the waves launched by such pertubers do not become non-linear immediately, the gap begins to form a distance away from the perturber given by the shocking length of acoustic waves (Goodman and Rafikov 2001; Rafikov 2002). Estrada and Mosqueira (2003) have suggested that the annulus of material adjacent to the proto-planet that immediately precedes the runaway gas accretion phase (Pollack et al. 1996) can be used to provide the mass needed to lead to the formation of a giant planet. If

  16. Radio Observations as a Tool to Investigate Shocks and Asymmetries in Accreting White Dwarf Binaries

    NASA Astrophysics Data System (ADS)

    Weston, Jennifer Helen Seng; E-Nova Project

    2017-01-01

    In this dissertation, I use radio observations with the Karl G. Jansky Very Large Array (VLA) to reveal that colliding flows within the ejecta from nova explosions can lead to shocks that accelerate particles and produce radio synchrotron emission. In both novae V1723 Aql and V5589 Sgr, radio emission within the first one to two months deviated strongly from the classic thermal model for radio emission from novae. Three years of radio observations of V1723 Aql show that multiple outflows from the system collided to create non-thermal shocks with a brightness temperature of >106 K. After these shocks faded, the radio light curve became roughly consistent with an expanding thermal shell. However, resolved images of V1723 Aql show elongated material that apparently rotates its major axis over the course of 15 months. In the case of nova V5589 Sgr, I show that the early radio emission is dominated by a shock-powered non-thermal flare that produces strong (kTx > 33 keV) X-rays. These findings have important implications for understanding how normal novae generate GeV gamma-rays.Additionally, I present VLA observations of the symbiotic star CH Cyg and two small surveys of symbiotic binaries. Radio observations of CH Cyg tie the ejection of a collimated jet to a change of state in the accretion disk, strengthening the link between bipolar outflows from accreting white dwarfs and other types of accreting compact objects. Next, I use a survey of eleven accretion-driven symbiotic binaries to determine that the radio brightness of a symbiotic system could potentially be used as an indicator of whether it is powered predominantly by shell burning on the surface of the white dwarf or by accretion. This survey also produces the first radio detections of seven of the target systems. In the second survey of seventeen symbiotic binaries, I spatially resolve extended radio emission in several systems for the first time. The results from these surveys provide some support for the

  17. Constraints on Jet Formation Mechanisms with the Most Energetic Giant Outbursts in MS 0735+7421

    NASA Astrophysics Data System (ADS)

    Li, Shuang-Liang; Cao, Xinwu

    2012-07-01

    Giant X-ray cavities lie in some active galactic nuclei (AGNs) locating in central galaxies of clusters, which are estimated to have stored 1055-1062 erg of energy. Most of these cavities are thought to be inflated by jets of AGNs on a timescale of >~ 107 years. The jets can be either powered by rotating black holes or the accretion disks surrounding black holes, or both. The observations of giant X-ray cavities can therefore be used to constrain jet formation mechanisms. In this work, we choose the most energetic cavity, MS 0735+7421, with stored energy ~1062 erg, to constrain the jet formation mechanisms and the evolution of the central massive black hole in this source. The bolometric luminosity of the AGN in this cavity is ~10-5 L Edd, however, the mean power of the jet required to inflate the cavity is estimated as ~0.02L Edd, which implies that the source has previously experienced strong outbursts. During outbursts, the jet power and the mass accretion rate should be significantly higher than its present values. We construct an accretion disk model in which the angular momentum and energy carried away by jets are properly included to calculate the spin and mass evolution of the massive black hole. In our calculations, different jet formation mechanisms are employed, and we find that the jets generated with the Blandford-Znajek (BZ) mechanism are unable to produce the giant cavity with ~1062 erg in this source. Only the jets accelerated with a combination of the Blandford-Payne and BZ mechanisms can successfully inflate such a giant cavity if the magnetic pressure is close to equipartition with the total (radiation+gas) pressure of the accretion disk. For a dynamo-generated magnetic field in the disk, such an energetic giant cavity can be inflated by the magnetically driven jets only if the initial black hole spin parameter a 0 >~ 0.95. Our calculations show that the final spin parameter a of the black hole is always ~0.9-0.998 for all the computational

  18. Gentlest ascent dynamics for calculating first excited state and exploring energy landscape of Kohn-Sham density functionals.

    PubMed

    Li, Chen; Lu, Jianfeng; Yang, Weitao

    2015-12-14

    We develop the gentlest ascent dynamics for Kohn-Sham density functional theory to search for the index-1 saddle points on the energy landscape of the Kohn-Sham density functionals. These stationary solutions correspond to excited states in the ground state functionals. As shown by various examples, the first excited states of many chemical systems are given by these index-1 saddle points. Our novel approach provides an alternative, more robust way to obtain these excited states, compared with the widely used ΔSCF approach. The method can be easily generalized to target higher index saddle points. Our results also reveal the physical interest and relevance of studying the Kohn-Sham energy landscape.

  19. Giant Impacts and Earth's Primordial Atmosphere

    NASA Astrophysics Data System (ADS)

    Agnor, C.; Asphaug, E.

    2002-09-01

    Estimates of Earth's accretion timescale based on modeling (e.g. Wetherill 1990) and isotopic evidence (Halliday and Porcelli 2000) indicate that the Earth formed in 25-100 Myr. At least a portion of this accretion took place in the presence of the solar nebula. While the problem of nailing down the nebular lifetime remains open, observations of dust disks surrounding young stars and meteoritic evidence suggest that the gas disk existed and was involved in making planetary material for 10 Myr (e.g. Podosek & Cassen 1994, Trilling et al. 2001). The persistence of a remnant of the nebula's original gas disk during terrestrial planet accretion is certainly plausible. The existence of this remnant nebula has dynamical (Agnor & Ward 2002, Kominami & Ida 2002) and geochemical (Porcelli & Pepin 2000) implications for terrestrial planet formation. Nakazawa et al. (1985) explored the structure of Earth's primordial atmosphere as the solar nebula was dissipating. They found that even for low surface densities of nebular gas ( σ gas ~ 1 g cm-2 or ~0.1% of the minimum mass nebula), Earth can capture a significant primordial atmosphere directly from the nebula (i.e. total mass up to a few lunar masses, or ~ 105 times the current atmosphere). Such a massive primordial atmosphere may have played a dynamical role in the formation of the Moon (e.g. models of lunar capture have employed aerodynamic drag in Earth's atmosphere as the primary mechanism for reducing the Moon's orbital energy, Nakazawa et al. 1983). Conversely, the formation of the Moon may have played a role in removing Earth's primordial atmosphere. Giant impacts have been suggested as one possible mechanism that could accomplish global atmospheric removal (Ahrens 1993). We are using smooth particle hydrodynamics (SPH) to model the removal of Earth's primordial atmosphere via giant impact. We employ initial conditions similar to recent works on lunar formation (e.g. Canup & Asphaug 2001) but also include ideal gas

  20. Design and Analysis of Optimal Ascent Trajectories for Stratospheric Airships

    NASA Astrophysics Data System (ADS)

    Mueller, Joseph Bernard

    Stratospheric airships are lighter-than-air vehicles that have the potential to provide a long-duration airborne presence at altitudes of 18-22 km. Designed to operate on solar power in the calm portion of the lower stratosphere and above all regulated air traffic and cloud cover, these vehicles represent an emerging platform that resides between conventional aircraft and satellites. A particular challenge for airship operation is the planning of ascent trajectories, as the slow moving vehicle must traverse the high wind region of the jet stream. Due to large changes in wind speed and direction across altitude and the susceptibility of airship motion to wind, the trajectory must be carefully planned, preferably optimized, in order to ensure that the desired station be reached within acceptable performance bounds of flight time and energy consumption. This thesis develops optimal ascent trajectories for stratospheric airships, examines the structure and sensitivity of these solutions, and presents a strategy for onboard guidance. Optimal ascent trajectories are developed that utilize wind energy to achieve minimum-time and minimum-energy flights. The airship is represented by a three-dimensional point mass model, and the equations of motion include aerodynamic lift and drag, vectored thrust, added mass effects, and accelerations due to mass flow rate, wind rates, and Earth rotation. A representative wind profile is developed based on historical meteorological data and measurements. Trajectory optimization is performed by first defining an optimal control problem with both terminal and path constraints, then using direct transcription to develop an approximate nonlinear parameter optimization problem of finite dimension. Optimal ascent trajectories are determined using SNOPT for a variety of upwind, downwind, and crosswind launch locations. Results of extensive optimization solutions illustrate definitive patterns in the ascent path for minimum time flights across

  1. I-process Nucleosynthesis and Mass Retention Efficiency in He-shell Flash Evolution of Rapidly Accreting White Dwarfs

    NASA Astrophysics Data System (ADS)

    Denissenkov, Pavel A.; Herwig, Falk; Battino, Umberto; Ritter, Christian; Pignatari, Marco; Jones, Samuel; Paxton, Bill

    2017-01-01

    Based on stellar evolution simulations, we demonstrate that rapidly accreting white dwarfs (WDs) in close binary systems are an astrophysical site for the intermediate neutron-capture process. During recurrent and very strong He-shell flashes in the stable H-burning accretion regime H-rich material enters the He-shell flash convection zone. {}12{{C}}(p,γ ){}13{{N}} reactions release enough energy to potentially impact convection, and I process is activated through the {}13{{C}}{(α ,{{n}})}16{{O}} reaction. The H-ingestion flash may not cause a split of the convection zone as it was seen in simulations of He-shell flashes in post-AGB and low-Z asymptotic giant branch (AGB) stars. We estimate that for the production of first-peak heavy elements this site can be of similar importance for galactic chemical evolution as the s-process production by low-mass AGB stars. The He-shell flashes result in the expansion and, ultimately, ejection of the accreted and then I-process enriched material, via super-Eddington-luminosity winds or Roche-lobe overflow. The WD models do not retain any significant amount of the accreted mass, with a He retention efficiency of ≲ 10 % depending on mass and convective boundary mixing assumptions. This makes the evolutionary path of such systems to supernova Ia explosion highly unlikely.

  2. Evolution of migrating protoplanets heated by pebble accretion

    NASA Astrophysics Data System (ADS)

    Chrenko, Ondrej; Broz, Miroslav; Lambrechts, Michiel

    2017-10-01

    We study the interactions in a protoplanetary system consisting of a gas disk, a pebble disk and embedded low-mass protoplanets. The hydrodynamic simulations are performed using a new code based on 2D FARGO (Masset 2000) which we call FARGO_THORIN (http://sirrah.troja.mff.cuni.cz/~chrenko/). The code treats the hydrodynamics of gas and pebbles within a two-fluid approximation, accounts for the heating and cooling processes in the gaseous component (including heating due to pebble accretion) and propagates the planets in 3D using a high-order integration scheme (IAS15; Rein & Spiegel 2015). Our aim is to investigate how pebble accretion alters the orbital evolution of protoplanets undergoing Type-I migration.First, we demonstrate that pebble accretion can heat the protoplanets so that their luminosity induces the heating torque (Benítez-Llambay et al. 2015) and the hot-trail effect (Chrenko et al. 2017; Eklund & Masset 2017). The heating torque is always positive and alters the migration rates and directions profoundly, thus changing the position of planet traps and deserts. The hot-trail effect, on the other hand, pumps the eccentricity of initially circular orbits up to e ~ h. After becoming eccentric, the protoplanets exhibit reduced probability of resonant locking during the migration and moreover, their close encounters become more frequent and provide more opportunities for scattering or merger events. The mergers can be massive enough to become giant planet cores. We discuss the importance of the excited eccentricities and violent orbital evolution for the extrasolar planet population synthesis. Finally, we present an extended model with flux-mean opacities caused by a coupled disk of coagulating dust grains with a realistic size distribution. The aim of this model is to constrain possible pathways of migrating planets towards the inner rim of the protoplanetary disk.

  3. On the Terminal Rotation Rates of Giant Planets

    NASA Astrophysics Data System (ADS)

    Batygin, Konstantin

    2018-04-01

    Within the general framework of the core-nucleated accretion theory of giant planet formation, the conglomeration of massive gaseous envelopes is facilitated by a transient period of rapid accumulation of nebular material. While the concurrent build-up of angular momentum is expected to leave newly formed planets spinning at near-breakup velocities, Jupiter and Saturn, as well as super-Jovian long-period extrasolar planets, are observed to rotate well below criticality. In this work, we demonstrate that the large luminosity of a young giant planet simultaneously leads to the generation of a strong planetary magnetic field, as well as thermal ionization of the circumplanetary disk. The ensuing magnetic coupling between the planetary interior and the quasi-Keplerian motion of the disk results in efficient braking of planetary rotation, with hydrodynamic circulation of gas within the Hill sphere playing the key role of expelling spin angular momentum to the circumstellar nebula. Our results place early-stage giant planet and stellar rotation within the same evolutionary framework, and motivate further exploration of magnetohydrodynamic phenomena in the context of the final stages of giant planet formation.

  4. Star Formation in Massive Clusters via Bondi Accretion

    NASA Astrophysics Data System (ADS)

    Murray, Norman; Chang, Philip

    2012-02-01

    Essentially all stars form in giant molecular clouds (GMCs). However, inside GMCs, most of the gas does not participate in star formation; rather, denser gas accumulates in clumps in the GMC, with the bulk of the stars in a given GMC forming in a few of the most massive clumps. In the Milky Way, these clumps have masses M cl <~ 5 × 10-2 of the GMC, radii r cl ~ 1 pc, and free-fall times τcl ~ 2 × 105 yr. We show that clumps inside GMCs should accrete at a modified Bondi accretion rate, which depends on clump mass as \\dot{M}_{cl}\\sim M_{cl}^{5/4}. This rate is initially rather slow, usually slower than the initial star formation rate inside the clump (we adopt the common assumption that inside the clump, \\dot{M}_*=\\epsilon _ffM_{cl}/\\tau _{cl}, with epsilonff ≈ 0.017). However, after ~2 GMC free-fall times τGMC, the clump accretion rate accelerates rapidly; formally, the clump can accrete the entire GMC in ~3τGMC. At the same time, the star formation rate accelerates, tracking the Bondi accretion rate. If the GMC is disrupted by feedback from the largest clump, half the stars in that clump form in the final τGMC before the GMC is disrupted. The theory predicts that the distribution of effective star formation rates, measured per GMC free-fall time, is broad, ranging from ~0.001 up to 0.1 or larger and that the mass spectrum of star clusters is flatter than that of clumps, consistent with observations.

  5. Paraspinal arteriovenous malformation Onyx embolization via an Ascent balloon.

    PubMed

    Martínez-Galdámez, Mario; Rodriguez-Arias, Carlos A; Utiel, Elena; Arreba, Emilio; Gonzalo, Miguel; Arenillas, Juan F

    2013-03-22

    Purely extradural lumbar spinal arteriovenous malformations (AVMs) are rare lesions that have diverse presentations and imaging features. The treatment of a symptomatic high flow paraspinal AVM with multiple feeders remains a challenge. We report the first use of an Ascent balloon (dual lumen balloon catheter) to deliver Onyx with excellent penetration to a paraspinal AVM.

  6. Paraspinal arteriovenous malformation Onyx embolization via an Ascent balloon.

    PubMed

    Martínez-Galdámez, Mario; Rodriguez-Arias, Carlos A; Utiel, Elena; Arreba, Emilio; Gonzalo, Miguel; Arenillas, Juan F

    2014-04-01

    Purely extradural lumbar spinal arteriovenous malformations (AVMs) are rare lesions that have diverse presentations and imaging features. The treatment of a symptomatic high flow paraspinal AVM with multiple feeders remains a challenge. We report the first use of an Ascent balloon (dual lumen balloon catheter) to deliver Onyx with excellent penetration to a paraspinal AVM.

  7. The ascent of water

    Treesearch

    Melvin T. Tyree

    2003-01-01

    The transport system that drives sap ascent from soil to leaves is extraordinary and controversial. Like their animal counterparts, large multicellular plants need to supply all their cells with fuel and water.

  8. Human Mars Ascent Vehicle Performance Sensitivities

    NASA Technical Reports Server (NTRS)

    Polsgrove, Tara P.; Thomas, Herbert D.

    2016-01-01

    Human Mars mission architecture studies have shown that the ascent vehicle mass drives performance requirements for the descent and in-space transportation elements. Understanding the sensitivity of Mars ascent vehicle (MAV) mass to various mission and vehicle design choices enables overall transportation system optimization. This paper presents the results of a variety of sensitivity trades affecting MAV performance including: landing site latitude, target orbit, initial thrust to weight ratio, staging options, specific impulse, propellant type and engine design.

  9. Ascent Guidance for a Winged Boost Vehicle. M.S. Thesis

    NASA Technical Reports Server (NTRS)

    Corvin, Michael Alexander

    1988-01-01

    The objective of the advanced ascent guidance study was to investigate guidance concepts which could contribute to increased autonomy during ascent operations in a winged boost vehicle such as the proposed Shuttle II. The guidance scheme was required to yield near a full-optimal ascent in the presence of vehicle system and environmental dispersions. The study included consideration of trajectory shaping issues, trajectory design, closed loop and predictive adaptive guidance techniques and control of dynamic pressure by throttling. An extensive ascent vehicle simulation capability was developed for use in the study.

  10. Coordinated observations of interacting peculiar red giant binaries, 2

    NASA Technical Reports Server (NTRS)

    Ake, T.

    1995-01-01

    IUE and H alpha observations continued on a two-year program to monitor the UV variability of three interacting peculiar red giant (PRG) binaries, HD 59643 (C6,s), HD 35155 (S3/2), and HR 1105 (S3.5/2.5). All of these systems were suspected to involve accretion of material from the PRG to a white-dwarf secondary, based mainly on previous IUE investigations. They were primary candidates from earlier surveys of PRG's to test the hypothesis that the Tc-poor PRG's are formed as a result of mass transfer from a secondary component rather than from internal thermal pulsing while on the asymptotic red giant branch.

  11. Coordinated observations of interacting peculiar red giant binaries, 1

    NASA Technical Reports Server (NTRS)

    Ake, T.

    1995-01-01

    IUE Observations were begun for a two-year program to monitor the UV variability of three interacting peculiar red giant (PRG) binaries, HD 59643 (C6,s) HD 35155 (S3/2), and HR 1105 (S3.5/2.5). All of these systems were suspected to involve accretion of material from the PRG to a white-dwarf secondary, based mainly on previous IUE investigations. From our earlier surveys of PRG's, they were primary candidates to test the hypothesis that Tc-poor PRG's are formed as a result of mass transfer from a secondary component rather than from internal thermal pulsing while on the asymptotic red giant branch.

  12. Cold, clumpy accretion onto an active supermassive black hole

    NASA Astrophysics Data System (ADS)

    Tremblay, Grant R.; Oonk, J. B. Raymond; Combes, Françoise; Salomé, Philippe; O'Dea, Christopher P.; Baum, Stefi A.; Voit, G. Mark; Donahue, Megan; McNamara, Brian R.; Davis, Timothy A.; McDonald, Michael A.; Edge, Alastair C.; Clarke, Tracy E.; Galván-Madrid, Roberto; Bremer, Malcolm N.; Edwards, Louise O. V.; Fabian, Andrew C.; Hamer, Stephen; Li, Yuan; Maury, Anaëlle; Russell, Helen R.; Quillen, Alice C.; Urry, C. Megan; Sanders, Jeremy S.; Wise, Michael W.

    2016-06-01

    Supermassive black holes in galaxy centres can grow by the accretion of gas, liberating energy that might regulate star formation on galaxy-wide scales. The nature of the gaseous fuel reservoirs that power black hole growth is nevertheless largely unconstrained by observations, and is instead routinely simplified as a smooth, spherical inflow of very hot gas. Recent theory and simulations instead predict that accretion can be dominated by a stochastic, clumpy distribution of very cold molecular clouds—a departure from the ‘hot mode’ accretion model—although unambiguous observational support for this prediction remains elusive. Here we report observations that reveal a cold, clumpy accretion flow towards a supermassive black hole fuel reservoir in the nucleus of the Abell 2597 Brightest Cluster Galaxy (BCG), a nearby (redshift z = 0.0821) giant elliptical galaxy surrounded by a dense halo of hot plasma. Under the right conditions, thermal instabilities produce a rain of cold clouds that fall towards the galaxy’s centre, sustaining star formation amid a kiloparsec-scale molecular nebula that is found at its core. The observations show that these cold clouds also fuel black hole accretion, revealing ‘shadows’ cast by the molecular clouds as they move inward at about 300 kilometres per second towards the active supermassive black hole, which serves as a bright backlight. Corroborating evidence from prior observations of warmer atomic gas at extremely high spatial resolution, along with simple arguments based on geometry and probability, indicate that these clouds are within the innermost hundred parsecs of the black hole, and falling closer towards it.

  13. Cold, clumpy accretion onto an active supermassive black hole.

    PubMed

    Tremblay, Grant R; Oonk, J B Raymond; Combes, Françoise; Salomé, Philippe; O'Dea, Christopher P; Baum, Stefi A; Voit, G Mark; Donahue, Megan; McNamara, Brian R; Davis, Timothy A; McDonald, Michael A; Edge, Alastair C; Clarke, Tracy E; Galván-Madrid, Roberto; Bremer, Malcolm N; Edwards, Louise O V; Fabian, Andrew C; Hamer, Stephen; Li, Yuan; Maury, Anaëlle; Russell, Helen R; Quillen, Alice C; Urry, C Megan; Sanders, Jeremy S; Wise, Michael W

    2016-06-09

    Supermassive black holes in galaxy centres can grow by the accretion of gas, liberating energy that might regulate star formation on galaxy-wide scales. The nature of the gaseous fuel reservoirs that power black hole growth is nevertheless largely unconstrained by observations, and is instead routinely simplified as a smooth, spherical inflow of very hot gas. Recent theory and simulations instead predict that accretion can be dominated by a stochastic, clumpy distribution of very cold molecular clouds--a departure from the 'hot mode' accretion model--although unambiguous observational support for this prediction remains elusive. Here we report observations that reveal a cold, clumpy accretion flow towards a supermassive black hole fuel reservoir in the nucleus of the Abell 2597 Brightest Cluster Galaxy (BCG), a nearby (redshift z = 0.0821) giant elliptical galaxy surrounded by a dense halo of hot plasma. Under the right conditions, thermal instabilities produce a rain of cold clouds that fall towards the galaxy's centre, sustaining star formation amid a kiloparsec-scale molecular nebula that is found at its core. The observations show that these cold clouds also fuel black hole accretion, revealing 'shadows' cast by the molecular clouds as they move inward at about 300 kilometres per second towards the active supermassive black hole, which serves as a bright backlight. Corroborating evidence from prior observations of warmer atomic gas at extremely high spatial resolution, along with simple arguments based on geometry and probability, indicate that these clouds are within the innermost hundred parsecs of the black hole, and falling closer towards it.

  14. WIYN Open Cluster Study. LXXVI. Li Evolution Among Stars of Low/Intermediate Mass: The Metal-deficient Open Cluster NGC 2506

    NASA Astrophysics Data System (ADS)

    Anthony-Twarog, Barbara J.; Lee-Brown, Donald B.; Deliyannis, Constantine P.; Twarog, Bruce A.

    2018-03-01

    HYDRA spectra of 287 stars in the field of NGC 2506 from the turnoff through the giant branch are analyzed. With previous data, 22 are identified as probable binaries; 90 more are classified as potential non-members. Spectroscopic analyses of ∼60 red giants and slowly rotating turnoff stars using line equivalent widths and a neural network approach lead to [Fe/H] = ‑0.27 ± 0.07 (s.d.) and [Fe/H] = ‑0.27 ± 0.06 (s.d.), respectively. Li abundances are derived for 145 probable single-star members, 44 being upper limits. Among turnoff stars outside the Li-dip, A(Li) = 3.04 ± 0.16 (s.d.), with no trend with color, luminosity, or rotation speed. Evolving from the turnoff across the subgiant branch, there is a well-delineated decline to A(Li) ∼1.25 at the giant branch base, coupled with the rotational spindown from between ∼20 and 70 km s‑1 to less than 20 km s‑1 for stars entering the subgiant branch and beyond. A(Li) remains effectively constant from the giant branch base to the red giant clump level. A new member above the clump redefines the path of the first-ascent red giant branch; its Li is 0.6 dex below the first-ascent red giants. With one exception, all post-He-flash stars have upper limits to A(Li), at or below the level of the brightest first-ascent red giant. The patterns are in excellent qualitative agreement with the model predictions for low/intermediate-mass stars which undergo rotation-induced mixing at the turnoff and subgiant branch, first dredge-up, and thermohaline mixing beyond the red giant bump.

  15. Paraspinal arteriovenous malformation Onyx embolization via an Ascent balloon

    PubMed Central

    Martínez-Galdámez, Mario; Rodriguez-Arias, Carlos A; Utiel, Elena; Arreba, Emilio; Gonzalo, Miguel; Arenillas, Juan F

    2013-01-01

    Purely extradural lumbar spinal arteriovenous malformations (AVMs) are rare lesions that have diverse presentations and imaging features. The treatment of a symptomatic high flow paraspinal AVM with multiple feeders remains a challenge. We report the first use of an Ascent balloon (dual lumen balloon catheter) to deliver Onyx with excellent penetration to a paraspinal AVM. PMID:23524491

  16. On Small Disturbance Ascent Vent Behavior

    NASA Technical Reports Server (NTRS)

    Woronowicz, Michael

    2015-01-01

    As a spacecraft undergoes ascent in a launch vehicle, its ambient pressure environment transitions from one atmosphere to high vacuum in a matter of a few minutes. Venting of internal cavities is necessary to prevent the buildup of pressure differentials across cavity walls. These pressure differentials are often restricted to low levels to prevent violation of container integrity. Such vents usually consist of fixed orifices, ducts, or combinations of both. Duct conductance behavior is fundamentally different from that for orifices in pressure driven flows governing the launch vehicle ascent depressurization environment. Duct conductance is governed by the average pressure across its length, while orifice conductance is dictated by a pressure ratio. Hence, one cannot define a valid equivalent orifice for a given duct across a range of pressure levels. This presentation discusses development of expressions for these two types of vent elements in the limit of small pressure differentials, explores conditions for their validity, and compares their features regarding ascent depressurization performance.

  17. Accretion onto stellar mass black holes

    NASA Astrophysics Data System (ADS)

    Deegan, Patrick

    2009-12-01

    I present work on the accretion onto stellar mass black holes in several scenarios. Due to dynamical friction stellar mass black holes are expected to form high density cusps in the inner parsec of our Galaxy. These compact remnants may be accreting cold dense gas present there, and give rise to potentially observable X-ray emission. I build a simple but detailed time-dependent model of such emission. Future observations of the distribution and orbits of the gas in the inner parsec of Sgr A* will put tighter constraints on the cusp of compact remnants. GRS 1915+105 is an LMXB, whose large orbital period implies a very large accretion disc and explains the extraordinary duration of its current outburst. I present smoothed particle hydrodynamic simulations of the accretion disc. The models includes the thermo-viscous instability, irradiation from the central object and wind loss. I find that the outburst of GRS 1915+105 should last a minimum of 20 years and up to ˜ 100 years if the irradiation is playing a significant role in this system. The predicted recurrence times are of the order of 104 years, making the duty cycle of GRS 1915+105 to be a few 0.1%. I present a simple analytical method to describe the observable behaviour of long period black hole LMXBs, similar to GRS 1915+105. Constructing two simple models for the surface density in the disc, outburst and quiescence times are calculated as a function of orbital period. LMXBs are an important constituent of the X-ray light function (XLF) of giant elliptical galaxies. I find that the duty cycle can vary considerably with orbital period, with implications for modelling the XLF.

  18. The ascent of kimberlite: Insights from olivine

    NASA Astrophysics Data System (ADS)

    Brett, R. C.; Russell, J. K.; Andrews, G. D. M.; Jones, T. J.

    2015-08-01

    Olivine xenocrysts are ubiquitous in kimberlite deposits worldwide and derive from the disaggregation of mantle-derived peridotitic xenoliths. Here, we provide descriptions of textural features in xenocrystic olivine from kimberlite deposits at the Diavik Diamond Mine, Canada and at Igwisi Hills volcano, Tanzania. We establish a relative sequence of textural events recorded by olivine during magma ascent through the cratonic mantle lithosphere, including: xenolith disaggregation, decompression fracturing expressed as mineral- and fluid-inclusion-rich sealed and healed cracks, grain size and shape modification by chemical dissolution and abrasion, late-stage crystallization of overgrowths on olivine xenocrysts, and lastly, mechanical milling and rounding of the olivine cargo prior to emplacement. Ascent through the lithosphere operates as a "kimberlite factory" wherein progressive upward dyke propagation of the initial carbonatitic melt fractures the overlying mantle to entrain and disaggregate mantle xenoliths. Preferential assimilation of orthopyroxene (Opx) xenocrysts by the silica-undersaturated carbonatitic melt leads to deep-seated exsolution of CO2-rich fluid generating buoyancy and supporting rapid ascent. Concomitant dissolution of olivine produces irregular-shaped relict grains preserved as cores to most kimberlitic olivine. Multiple generations of decompression cracks in olivine provide evidence for a progression in ambient fluid compositions (e.g., from carbonatitic to silicic) during ascent. Numerical modelling predicts tensile failure of xenoliths (disaggregation) and olivine (cracks) over ascent distances of 2-7 km and 15-25 km, respectively, at velocities of 0.1 to >4 m s-1. Efficient assimilation of Opx during ascent results in a silica-enriched, olivine-saturated kimberlitic melt (i.e. SiO2 >20 wt.%) that crystallizes overgrowths on partially digested and abraded olivine xenocrysts. Olivine saturation is constrained to occur at pressures <1 GPa; an

  19. Cryomagma Ascent on Europa

    NASA Astrophysics Data System (ADS)

    Lesage, E.; Massol, H.; Schmidt, F.

    2018-06-01

    This study aims at modeling the cryomagma ascent from a liquid reservoir to Europa's surface. We obtain the eruption duration and emitted cryomagma volume at the surface for different chamber depths and volumes and different cryomagma compositions.

  20. Blinded by the light: on the relationship between CO first overtone emission and mass accretion rate in massive young stellar objects

    NASA Astrophysics Data System (ADS)

    Ilee, J. D.; Oudmaijer, R. D.; Wheelwright, H. E.; Pomohaci, R.

    2018-07-01

    To date, there is no explanation as to why disc-tracing CO first overtone (or `bandhead') emission is not a ubiquitous feature in low- to medium-resolution spectra of massive young stellar objects (MYSOs), but instead is only detected towards approximately 25 per cent of their spectra. In this paper, we investigate the hypothesis that only certain mass accretion rates result in detectable bandhead emission in the near-infrared spectra of MYSOs. Using an analytic disc model combined with an LTE model of the CO emission, we find that high accretion rates (≳10-4 M⊙ yr-1) result in large dust sublimation radii, a larger contribution to the K-band continuum from hot dust at the dust sublimation radius, and therefore correspondingly lower CO emission with respect to the continuum. On the other hand, low accretion rates (≲10-6 M⊙ yr-1) result in smaller dust sublimation radii, a correspondingly smaller emitting area of CO, and thus also lower CO emission with respect to the continuum. In general, moderate accretion rates produce the most prominent, and therefore detectable, CO first overtone emission. We compare our findings to a recent near-infrared spectroscopic survey of MYSOs, finding results consistent with our hypothesis. We conclude that the detection rate of CO bandhead emission in the spectra of MYSOs could be the result of MYSOs exhibiting a range of mass accretion rates, perhaps due to the variable accretion suggested by recent multi-epoch observations of these objects.

  1. Blinded by the light: on the relationship between CO first overtone emission and mass accretion rate in massive young stellar objects

    NASA Astrophysics Data System (ADS)

    Ilee, J. D.; Oudmaijer, R. D.; Wheelwright, H. E.; Pomohaci, R.

    2018-04-01

    To date, there is no explanation as to why disc-tracing CO first overtone (or `bandhead') emission is not a ubiquitous feature in low- to medium-resolution spectra of massive young stellar objects, but instead is only detected toward approximately 25 per cent of their spectra. In this paper, we investigate the hypothesis that only certain mass accretion rates result in detectable bandhead emission in the near infrared spectra of MYSOs. Using an analytic disc model combined with an LTE model of the CO emission, we find that high accretion rates (≳ 10-4 M⊙yr-1) result in large dust sublimation radii, a larger contribution to the K-band continuum from hot dust at the dust sublimation radius, and therefore correspondingly lower CO emission with respect to the continuum. On the other hand, low accretion rates (≲ 10-6 M⊙yr-1) result in smaller dust sublimation radii, a correspondingly smaller emitting area of CO, and thus also lower CO emission with respect to the continuum. In general, moderate accretion rates produce the most prominent, and therefore detectable, CO first overtone emission. We compare our findings to a recent near-infrared spectroscopic survey of MYSOs, finding results consistent with our hypothesis. We conclude that the detection rate of CO bandhead emission in the spectra of MYSOs could be the result of MYSOs exhibiting a range of mass accretion rates, perhaps due to the variable accretion suggested by recent multi-epoch observations of these objects.

  2. Combining ascent loads

    NASA Technical Reports Server (NTRS)

    Houbolt, J. C.

    1972-01-01

    Criteria and guidelines are presented for combining loads that develop during the ascent phase of a space flight. The primary load-caring structure is discussed including the basic tank and interconnecting members, engine support mounts and connections to tank structure, transition structures between stages, payload shrouds, and the basic support points at separation planes.

  3. Evaluating the Controls on Magma Ascent Rates Through Numerical Modelling

    NASA Astrophysics Data System (ADS)

    Thomas, M. E.; Neuberg, J. W.

    2015-12-01

    The estimation of the magma ascent rate is a key factor in predicting styles of volcanic activity and relies on the understanding of how strongly the ascent rate is controlled by different magmatic parameters. The ability to link potential changes in such parameters to monitoring data is an essential step to be able to use these data as a predictive tool. We present the results of a suite of conduit flow models that assess the influence of individual model parameters such as the magmatic water content, temperature or bulk magma composition on the magma flow in the conduit during an extrusive dome eruption. By systematically varying these parameters we assess their relative importance to changes in ascent rate. The results indicate that potential changes to conduit geometry and excess pressure in the magma chamber are amongst the dominant controlling variables that effect ascent rate, but the single most important parameter is the volatile content (assumed in this case as only water). Modelling this parameter across a range of reported values causes changes in the calculated ascent velocities of up to 800%, triggering fluctuations in ascent rates that span the potential threshold between effusive and explosive eruptions.

  4. Examining shear processes during magma ascent

    NASA Astrophysics Data System (ADS)

    Kendrick, J. E.; Wallace, P. A.; Coats, R.; Lamur, A.; Lavallée, Y.

    2017-12-01

    Lava dome eruptions are prone to rapid shifts from effusive to explosive behaviour which reflects the rheology of magma. Magma rheology is governed by composition, porosity and crystal content, which during ascent evolves to yield a rock-like, viscous suspension in the upper conduit. Geophysical monitoring, laboratory experiments and detailed field studies offer the opportunity to explore the complexities associated with the ascent and eruption of such magmas, which rest at a pivotal position with regard to the glass transition, allowing them to either flow or fracture. Crystal interaction during flow results in strain-partitioning and shear-thinning behaviour of the suspension. In a conduit, such characteristics favour the formation of localised shear zones as strain is concentrated along conduit margins, where magma can rupture and heal in repetitive cycles. Sheared magmas often record a history of deformation in the form of: grain size reduction; anisotropic permeable fluid pathways; mineral reactions; injection features; recrystallisation; and magnetic anomalies, providing a signature of the repetitive earthquakes often observed during lava dome eruptions. The repetitive fracture of magma at ( fixed) depth in the conduit and the fault-like products exhumed at spine surfaces indicate that the last hundreds of meters of ascent may be controlled by frictional slip. Experiments on a low-to-high velocity rotary shear apparatus indicate that shear stress on a slip plane is highly velocity dependent, and here we examine how this influences magma ascent and its characteristic geophysical signals.

  5. Role for syn-eruptive plagioclase disequilibrium crystallisation in basaltic magma ascent dynamics

    NASA Astrophysics Data System (ADS)

    La Spina, Giuseppe; Burton, Mike; de'Michieli Vitturi, Mattia; Arzilli, Fabio

    2017-04-01

    Magma ascent dynamics in volcanic conduits play a key role in determining the eruptive style of a volcano. The lack of direct observations inside the conduit means that numerical conduit models, constrained with observational data, provide invaluable tools for quantitative insights into complex magma ascent dynamics. The highly nonlinear, interdependent processes involved in magma ascent dynamics require several simplifications when modelling their ascent. For example, timescales of magma ascent in conduit models are typically assumed to be much longer than crystallisation and gas exsolution for basaltic eruptions. However, it is now recognized that basaltic magmas may rise fast enough for disequilibrium processes to play a key role on the ascent dynamics. The quantification of the characteristic times for crystallisation and exsolution processes are fundamental to our understanding of such disequilibria and ascent dynamics. Using observations from Mount Etna's 2001 eruption and a magma ascent model we are able to constrain timescales for crystallisation and exsolution processes. Our results show that plagioclase reaches equilibrium in 1-2 h, whereas ascent times were 1 h. Furthermore, we have related the amount of plagioclase in erupted products with the ascent dynamics of basaltic eruptions. We find that relatively high plagioclase content requires crystallisation in a shallow reservoir, whilst a low plagioclase content reflects a disequilibrium crystallisation occurring during a fast ascent from depth to the surface. Using these new constraints on disequilibrium plagioclase crystallisation we also reproduce observed crystal abundances for different basaltic eruptions: Etna 2002/2003, Stromboli 2007 (effusive eruption) and 1930 (paroxysm) and different Pu'u' O'o eruptions at Kilauea (episodes 49-53). Therefore, our results show that disequilibrium processes play a key role on the ascent dynamics of basaltic magmas and cannot be neglected when describing basaltic

  6. Isotopic ratios D/H and 15N/14N in giant planets

    NASA Astrophysics Data System (ADS)

    Marboeuf, Ulysse; Thiabaud, Amaury; Alibert, Yann; Benz, Willy

    2018-04-01

    The determination of isotopic ratios in planets is important since it allows us to investigate the origins and initial composition of materials. The present work aims to determine the possible range of values for isotopic ratios D/H and 15N/14N in giant planets. The main objective is to provide valuable theoretical assumptions on the isotopic composition of giant planets, their internal structure, and the main reservoirs of species. We use models of ice formation and planet formation that compute the composition of ices and gas accreted in the core and the envelope of planets. Assuming a single initial value for isotopic ratios in volatile species, and disruption of planetesimals in the envelope of gaseous planets, we obtain a wide variety of D/H and 15N/14N ratios in low-mass planets (≤100 Mearth) due to the migration pathway of planets, the accretion time of gas species whose relative abundance evolves with time, and isotope exchanges among species. If giant planets with mass greater than 100 Mearth have solar isotopic ratios such as Jupiter and Saturn due to their higher envelope mass, Neptune-type planets present values ranging between one and three times the solar value. It seems therefore difficult to use isotopic ratios in the envelope of these planets to get information about their formation in the disc. For giant planets, the ratios allow us to constrain the mass fraction of volatile species in the envelope needed to reproduce the observational data by assuming initial values for isotopic ratios in volatile species.

  7. Migration of accreting planets in radiative discs from dynamical torques

    NASA Astrophysics Data System (ADS)

    Pierens, A.; Raymond, S. N.

    2016-11-01

    We present the results of hydrodynamical simulations of the orbital evolution of planets undergoing runaway gas accretion in radiative discs. We consider accreting disc models with constant mass flux through the disc, and where radiative cooling balances the effect of viscous heating and stellar irradiation. We assume that 20-30 M⊕ giant planet cores are formed in the region where viscous heating dominates and migrate outward under the action of a strong entropy-related corotation torque. In the case where gas accretion is neglected and for an α viscous stress parameter α = 2 × 10-3, we find evidence for strong dynamical torques in accreting discs with accretion rates {dot{M}}≳ 7× 10^{-8} M_{⊙} yr{}^{-1}. Their main effect is to increase outward migration rates by a factor of ˜2 typically. In the presence of gas accretion, however, runaway outward migration is observed with the planet passing through the zero-torque radius and the transition between the viscous heating and stellar heating dominated regimes. The ability for an accreting planet to enter a fast migration regime is found to depend strongly on the planet growth rate, but can occur for values of the mass flux through the disc of {dot{M}}≳ 5× 10^{-8} M_{⊙} yr{}^{-1}. We find that an episode of runaway outward migration can cause an accreting planet formed in the 5-10 au region to temporarily orbit at star-planet separations as large as ˜60-70 au. However, increase in the amplitude of the Lindblad torque associated with planet growth plus change in the streamline topology near the planet systematically cause the direction of migration to be reversed. Subsequent evolution corresponds to the planet migrating inward rapidly until it becomes massive enough to open a gap in the disc and migrate in the type II regime. Our results indicate that a planet can reach large orbital distances under the combined effect of dynamical torques and gas accretion, but an alternative mechanism is required to

  8. Formation of Giant Planets and Brown Dwarves

    NASA Technical Reports Server (NTRS)

    Lissauer, Jack J.

    2003-01-01

    According to the prevailing core instability model, giant planets begin their growth by the accumulation of small solid bodies, as do terrestrial planets. However, unlike terrestrial planets, the growing giant planet cores become massive enough that they are able to accumulate substantial amounts of gas before the protoplanetary disk dissipates. Models predict that rocky planets should form in orbit about most stars. It is uncertain whether or not gas giant planet formation is common, because most protoplanetary disks may dissipate before solid planetary cores can grow large enough to gravitationally trap substantial quantities of gas. Ongoing theoretical modeling of accretion of giant planet atmospheres, as well as observations of protoplanetary disks, will help decide this issue. Observations of extrasolar planets around main sequence stars can only provide a lower limit on giant planet formation frequency . This is because after giant planets form, gravitational interactions with material within the protoplanetary disk may cause them to migrat inwards and be lost to the central star. The core instability model can only produce planets greater than a few jovian masses within protoplanetary disks that are more viscous than most such disks are believed to be. Thus, few brown dwarves (objects massive enough to undergo substantial deuterium fusion, estimated to occur above approximately 13 jovian masses) are likely to be formed in this manner. Most brown dwarves, as well as an unknown number of free-floating objects of planetary mass, are probably formed as are stars, by the collapse of extended gas/dust clouds into more compact objects.

  9. Performance analysis of the ascent propulsion system of the Apollo spacecraft

    NASA Technical Reports Server (NTRS)

    Hooper, J. C., III

    1973-01-01

    Activities involved in the performance analysis of the Apollo lunar module ascent propulsion system are discussed. A description of the ascent propulsion system, including hardware, instrumentation, and system characteristics, is included. The methods used to predict the inflight performance and to establish performance uncertainties of the ascent propulsion system are discussed. The techniques of processing the telemetered flight data and performing postflight performance reconstruction to determine actual inflight performance are discussed. Problems that have been encountered and results from the analysis of the ascent propulsion system performance during the Apollo 9, 10, and 11 missions are presented.

  10. Mass Accretion Rate of Very Low Luminosity Objects

    NASA Astrophysics Data System (ADS)

    Sung, Ren-Shiang; Lai, Shih-Ping; Hsieh, Tien-Hao

    2013-08-01

    We propose to measure the mass accretion rate of six Very Low Luminosity Objects (VeLLOs) using Near-infrared Integral Spectrometer (NIFS). The extremely low luminosity of VeLLOs, L_int ≤ 0.1 L_⊙, was previously thought not existing in the nature because the typical accretion rate gives much larger accretion luminosity even for the lowest mass star (``Luminosity Problem''). The commonly accepted solution is that the accretion rate is not constant but episodic. Thus, VeLLOs could be interpreted as protostars being in the quiescent phase of accretion activities. However, there is no observational data directly measuring the mass accretion rate of VeLLOs. The main goal of this proposal is to examine such theory and directly measure the mass accretion rate of VeLLOs for the first time. We propose to measure the blue continuum excess (veiling) of the stellar spectrum, which is the most reliable method for measuring the accretion rate. The measurements have to be made in infrared due to the very high extinction for highly embedded protostars. Our proposal provide a first opportunity to explain the long time ``Luminosity Problem'' through the observational aspects, and Gemini is the only instrument that can provide accurate and high sensitivity infrared spectroscopy measurements within reasonably short time scale.

  11. Control and Evaluation of a Powered Transfemoral Prosthesis for Stair Ascent.

    PubMed

    Ledoux, Elissa D; Goldfarb, Michael

    2017-07-01

    This paper assesses the metabolic effort exerted by three transfemoral amputees, when using a powered knee and ankle prosthesis for stair ascent, relative to ascending stairs with passive knee and ankle prostheses. The paper describes a controller that provides step-over stair ascent behavior reflective of healthy stair ascent biomechanics, and describes its implementation in a powered prosthesis prototype. Stair ascent experiments were performed with three unilateral transfemoral amputee subjects, comparing the oxygen consumption required to ascend stairs using the powered prosthesis (with a step-over gait), relative to using their daily-use energetically passive prostheses (with a step-to gait). Results indicate on average a 24% reduction in oxygen consumption and a 30% reduction in stair ascent timewhen using the powered prosthesis, relative to when using the passive prostheses. All subjects expressed a strong preference for ascending stairs using the powered prosthesis.

  12. Wind-accelerated orbital evolution in binary systems with giant stars

    NASA Astrophysics Data System (ADS)

    Chen, Zhuo; Blackman, Eric G.; Nordhaus, Jason; Frank, Adam; Carroll-Nellenback, Jonathan

    2018-01-01

    Using 3D radiation-hydrodynamic simulations and analytic theory, we study the orbital evolution of asymptotic giant branch (AGB) binary systems for various initial orbital separations and mass ratios, and thus different initial accretion modes. The time evolution of binary separations and orbital periods are calculated directly from the averaged mass-loss rate, accretion rate and angular momentum loss rate. We separately consider spin-orbit synchronized and zero-spin AGB cases. We find that the angular momentum carried away by the mass loss together with the mass transfer can effectively shrink the orbit when accretion occurs via wind-Roche lobe overflow. In contrast, the larger fraction of mass lost in Bondi-Hoyle-Lyttleton accreting systems acts to enlarge the orbit. Synchronized binaries tend to experience stronger orbital period decay in close binaries. We also find that orbital period decay is faster when we account for the non-linear evolution of the accretion mode as the binary starts to tighten. This can increase the fraction of binaries that result in common envelope, luminous red novae, Type Ia supernovae and planetary nebulae with tight central binaries. The results also imply that planets in the habitable zone around white dwarfs are unlikely to be found.

  13. General-relativistic Simulations of Four States of Accretion onto Millisecond Pulsars

    NASA Astrophysics Data System (ADS)

    Parfrey, Kyle; Tchekhovskoy, Alexander

    2017-12-01

    Accreting neutron stars can power a wide range of astrophysical phenomena including short- and long-duration gamma-ray bursts, ultra-luminous X-ray sources, and X-ray binaries. Numerical simulations are a valuable tool for studying the accretion-disk–magnetosphere interaction that is central to these problems, most clearly for the recently discovered transitional millisecond pulsars. However, magnetohydrodynamic (MHD) methods, widely used for simulating accretion, have difficulty in highly magnetized stellar magnetospheres, while force-free methods, suitable for such regions, cannot include the accreting gas. We present an MHD method that can stably evolve essentially force-free, highly magnetized regions, and describe the first time-dependent relativistic simulations of magnetized accretion onto millisecond pulsars. Our axisymmetric general-relativistic MHD simulations for the first time demonstrate how the interaction of a turbulent accretion flow with a pulsar’s electromagnetic wind can lead to the transition of an isolated pulsar to the accreting state. This transition naturally leads to the formation of relativistic jets, whose power can greatly exceed the power of the isolated pulsar’s wind. If the accretion rate is below a critical value, the pulsar instead expels the accretion stream. More generally, our simulations produce for the first time the four possible accretion regimes, in order of decreasing mass accretion rate: (a) crushed magnetosphere and direct accretion; (b) magnetically channeled accretion onto the stellar poles; (c) the propeller state, where material enters through the light cylinder but is prevented from accreting by the centrifugal barrier; (d) almost perfect exclusion of the accretion flow from the light cylinder by the pulsar wind.

  14. Role of syn-eruptive plagioclase disequilibrium crystallization in basaltic magma ascent dynamics.

    PubMed

    La Spina, G; Burton, M; De' Michieli Vitturi, M; Arzilli, F

    2016-12-12

    Timescales of magma ascent in conduit models are typically assumed to be much longer than crystallization and gas exsolution for basaltic eruptions. However, it is now recognized that basaltic magmas may rise fast enough for disequilibrium processes to play a key role on the ascent dynamics. The quantification of the characteristic times for crystallization and exsolution processes are fundamental to our understanding of such disequilibria and ascent dynamics. Here we use observations from Mount Etna's 2001 eruption and a magma ascent model to constrain timescales for crystallization and exsolution processes. Our results show that plagioclase reaches equilibrium in 1-2 h, whereas ascent times were <1 h. Using these new constraints on disequilibrium plagioclase crystallization we also reproduce observed crystal abundances for different basaltic eruptions. The strong relation between magma ascent rate and disequilibrium crystallization and exsolution plays a key role in controlling eruption dynamics in basaltic volcanism.

  15. Role of syn-eruptive plagioclase disequilibrium crystallization in basaltic magma ascent dynamics

    PubMed Central

    La Spina, G.; Burton, M.; de' Michieli Vitturi, M.; Arzilli, F.

    2016-01-01

    Timescales of magma ascent in conduit models are typically assumed to be much longer than crystallization and gas exsolution for basaltic eruptions. However, it is now recognized that basaltic magmas may rise fast enough for disequilibrium processes to play a key role on the ascent dynamics. The quantification of the characteristic times for crystallization and exsolution processes are fundamental to our understanding of such disequilibria and ascent dynamics. Here we use observations from Mount Etna's 2001 eruption and a magma ascent model to constrain timescales for crystallization and exsolution processes. Our results show that plagioclase reaches equilibrium in 1–2 h, whereas ascent times were <1 h. Using these new constraints on disequilibrium plagioclase crystallization we also reproduce observed crystal abundances for different basaltic eruptions. The strong relation between magma ascent rate and disequilibrium crystallization and exsolution plays a key role in controlling eruption dynamics in basaltic volcanism. PMID:27941750

  16. Foundations of Black Hole Accretion Disk Theory.

    PubMed

    Abramowicz, Marek A; Fragile, P Chris

    2013-01-01

    This review covers the main aspects of black hole accretion disk theory. We begin with the view that one of the main goals of the theory is to better understand the nature of black holes themselves. In this light we discuss how accretion disks might reveal some of the unique signatures of strong gravity: the event horizon, the innermost stable circular orbit, and the ergosphere. We then review, from a first-principles perspective, the physical processes at play in accretion disks. This leads us to the four primary accretion disk models that we review: Polish doughnuts (thick disks), Shakura-Sunyaev (thin) disks, slim disks, and advection-dominated accretion flows (ADAFs). After presenting the models we discuss issues of stability, oscillations, and jets. Following our review of the analytic work, we take a parallel approach in reviewing numerical studies of black hole accretion disks. We finish with a few select applications that highlight particular astrophysical applications: measurements of black hole mass and spin, black hole vs. neutron star accretion disks, black hole accretion disk spectral states, and quasi-periodic oscillations (QPOs).

  17. Frontal joint dynamics when initiating stair ascent from a walk versus a stand.

    PubMed

    Vallabhajosula, Srikant; Yentes, Jennifer M; Stergiou, Nicholas

    2012-02-02

    Ascending stairs is a challenging activity of daily living for many populations. Frontal plane joint dynamics are critical to understand the mechanisms involved in stair ascension as they contribute to both propulsion and medio-lateral stability. However, previous research is limited to understanding these dynamics while initiating stair ascent from a stand. We investigated if initiating stair ascent from a walk with a comfortable self-selected speed could affect the frontal plane lower-extremity joint moments and powers as compared to initiating stair ascent from a stand and if this difference would exist at consecutive ipsilateral steps on the stairs. Kinematics data using a 3-D motion capture system and kinetics data using two force platforms on the first and third stair treads were recorded simultaneously as ten healthy young adults ascended a custom-built staircase. Data were collected from two starting conditions of stair ascent, from a walk (speed: 1.42 ± 0.21 m/s) and from a stand. Results showed that subjects generated greater peak knee abductor moment and greater peak hip abductor moment when initiating stair ascent from a walk. Greater peak joint moments and powers at all joints were also seen while ascending the second ipsilateral step. Particularly, greater peak hip abductor moment was needed to avoid contact of the contralateral limb with the intermediate step by counteracting the pelvic drop on the contralateral side. This could be important for therapists using stair climbing as a testing/training tool to evaluate hip strength in individuals with documented frontal plane abnormalities (i.e. knee and hip osteoarthritis, ACL injury). Copyright © 2011 Elsevier Ltd. All rights reserved.

  18. Frontal Joint Dynamics when Initiating Stair Ascent from a Walk versus a Stand

    PubMed Central

    Vallabhajosula, Srikant; Yentes, Jennifer M.; Stergiou, Nicholas

    2011-01-01

    Ascending stairs is a challenging activity of daily living for many populations. Frontal plane joint dynamics are critical to understand the mechanisms involved in stair ascension as they contribute to both propulsion and medio-lateral stability. However, previous research is limited to understanding these dynamics while initiating stair ascent from a stand. We investigated if initiating stair ascent from a walk with a comfortable self-selected speed could affect the frontal plane lower-extremity joint moments and powers as compared to initiating stair ascent from a stand and if this difference would exist at consecutive ipsilateral steps on the stairs. Kinematics data using a 3-D motion capture system and kinetics data using two force platforms on the first and third stair treads were recorded simultaneously as ten healthy young adults ascended a custom-built staircase. Data were collected from two starting conditions of stair ascent, from a walk (speed: 1.42±0.21m/s) and from a stand. Results showed that subjects generated greater peak knee abductor moment and greater peak hip abductor moment when initiating stair ascent from a walk. Greater peak joint moments and powers at all joints were also seen while ascending the second ipsilateral step. Particularly, greater peak hip abductor moment was needed to avoid contact of the contralateral limb with the intermediate step by counteracting the pelvic drop on the contralateral side. This could be important for therapists using stair climbing as a testing/training tool to evaluate hip strength in individuals with documented frontal plane abnormalities (i.e. knee and hip osteoarthritis, ACL injury). PMID:22172606

  19. STS-97 ascent team in WFCR

    NASA Image and Video Library

    2000-11-20

    JSC2000-07294 (20 November 2000) --- The 40-odd flight controllers assigned to the STS-97 ascent team and some special guests pose for a group portrait in the shuttle flight control room in Houston's Mission Control Center (JSC). The five guests attired in the blue and white shirts are the flight crew members for the STS-97 crew, scheduled to be launched from Florida on the last day of this month. The astronauts are, from the left, Joseph R. Tanner, Carlos I. Noriega, Brent W. Jett, Jr., Michael J. Bloomfield and Marc Garneau, who represents the Canadian Space Agency (CSA). Ascent shift flight director Wayne Hale stands next to Tanner.

  20. SOLAR-LIKE OSCILLATIONS IN LOW-LUMINOSITY RED GIANTS: FIRST RESULTS FROM KEPLER

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

    Bedding, T. R.; Huber, D.; Stello, D.

    2010-04-20

    We have measured solar-like oscillations in red giants using time-series photometry from the first 34 days of science operations of the Kepler Mission. The light curves, obtained with 30 minute sampling, reveal clear oscillations in a large sample of G and K giants, extending in luminosity from the red clump down to the bottom of the giant branch. We confirm a strong correlation between the large separation of the oscillations ({delta}{nu}) and the frequency of maximum power ({nu}{sub max}). We focus on a sample of 50 low-luminosity stars ({nu}{sub max} > 100 {mu}Hz, L {approx}< 30 L {sub sun}) havingmore » high signal-to-noise ratios and showing the unambiguous signature of solar-like oscillations. These are H-shell-burning stars, whose oscillations should be valuable for testing models of stellar evolution and for constraining the star formation rate in the local disk. We use a new technique to compare stars on a single echelle diagram by scaling their frequencies and find well-defined ridges corresponding to radial and non-radial oscillations, including clear evidence for modes with angular degree l = 3. Measuring the small separation between l = 0 and l = 2 allows us to plot the so-called C-D diagram of {delta}{nu}{sub 02} versus {delta}{nu}. The small separation {delta}{nu}{sub 01} of l = 1 from the midpoint of adjacent l = 0 modes is negative, contrary to the Sun and solar-type stars. The ridge for l = 1 is notably broadened, which we attribute to mixed modes, confirming theoretical predictions for low-luminosity giants. Overall, the results demonstrate the tremendous potential of Kepler data for asteroseismology of red giants.« less

  1. Tungsten isotope evidence for post-giant impact equilibration of the Earth and Moon

    NASA Astrophysics Data System (ADS)

    Kruijer, T.; Kleine, T.; Fischer-Gödde, M.

    2015-12-01

    The Moon is thought to have formed by re-accretion of material ejected by a giant impact on Earth [e.g., 1]. This model, at least in its classical form, predicts an isotopic difference between the Earth and Moon, because the Moon would largely consist of impactor material. Yet Earth and Moon show an unexpected isotopic similarity for many elements [e.g., 2]. Here we use variations in 182W—the decay-product of short-lived 182Hf (t1/2~9 Myr)—between the Moon and the bulk silicate Earth (BSE) to shed new light on this issue. We precisely determined the lunar 182W value by analysing KREEP-rich samples with MC-ICPMS and a new approach for quantifying cosmogenic 182W variations using Hf isotopes [6]. We find that the Moon shows a 27±4 ppm 182W excess over the modern BSE, in excellent agreement with [7]. This excess agrees with the predicted 182W change resulting from disproportional late accretion to the Earth and Moon after Earth's core had fully formed [6,7]. Thus, the pre-late-veneer BSE and the Moon were indistinguishable in 182W. However, the giant impact itself should have caused a notable Earth-Moon 182W difference by (1) changing the ɛ182W of the proto-Earth mantle by adding impactor mantle and core material, both carrying distinct 182W anomalies, and (2) by supplying W-rich but 182W-depleted impactor core material into the lunar accretion disk [6]. Thus, the Earth-Moon 182W homogeneity is an unexpected outcome of the giant impact. Unlike for Ti and O isotopes, the 182W homogeneity cannot be explained by accretion of impactor and proto-Earth from a homogeneous inner disk reservoir [3] or by making the Moon fully from proto-Earth mantle [4,5]. Thus, the 182W results require an efficient post-impact isotopic equilibration of the BSE and the Moon, but the mechanism for this has yet to be explored. One option is that Earth's mantle and its vapour atmosphere remained connected with the lunar accretion disk just after the giant impact [8]. [1] Canup R

  2. Planet traps and first planets: The critical metallicity for gas giant formation

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

    Hasegawa, Yasuhiro; Hirashita, Hiroyuki, E-mail: yasu@asiaa.sinica.edu.tw, E-mail: hirashita@asiaa.sinica.edu.tw

    2014-06-10

    The ubiquity of planets poses an interesting question: when are first planets formed in galaxies? We investigate this by adopting a theoretical model where planet traps are combined with the standard core accretion scenario in which the efficiency of forming planetary cores directly relates to the metallicity ([Fe/H]) in disks. Three characteristic exoplanetary populations are examined: hot Jupiters, exo-Jupiters around 1 AU, and low-mass planets in tight orbits, such as super-Earths. We statistically compute planet formation frequencies (PFFs), as well as the orbital radius (〈R{sub rapid}〉) within which gas accretion becomes efficient enough to form Jovian planets, as a functionmore » of metallicity (–2 ≤ [Fe/H] ≤–0.6). We show that the total PFFs for these three populations increase steadily with metallicity. This is the direct outcome of the core accretion picture. For the metallicity range considered here, the population of low-mass planets dominates Jovian planets. The Jovian planets contribute to the PFFs above [Fe/H] ≅ –1. We find that the hot Jupiters form more efficiently than the exo-Jupiters at [Fe/H] ≲ –0.7. This arises from the slower growth of planetary cores and their more efficient radial inward transport by the host traps in lower metallicity disks. We show that the critical metallicity for forming Jovian planets is [Fe/H] ≅ –1.2 by comparing 〈R{sub rapid}〉 of hot Jupiters and low-mass planets. The comparison intrinsically links to the different gas accretion efficiency between these two types of planets. Therefore, this study implies that important physical processes in planet formation may be tested by exoplanet observations around metal-poor stars.« less

  3. Accretion signatures in the X-shooter spectrum of the substellar companion to SR12

    NASA Astrophysics Data System (ADS)

    Santamaría-Miranda, Alejandro; Cáceres, Claudio; Schreiber, Matthias R.; Hardy, Adam; Bayo, Amelia; Parsons, Steven G.; Gromadzki, Mariusz; Aguayo Villegas, Aurora Belén

    2018-04-01

    About a dozen substellar companions orbiting young stellar objects or pre-main sequence stars at several hundred au have been identified in the last decade. These objects are interesting both due to the uncertainties surrounding their formation, and because their large separation from the host star offers the potential to study the atmospheres of young giant planets and brown dwarfs. Here, we present X-shooter spectroscopy of SR 12 C, a ˜2 Myr young brown dwarf orbiting SR 12 at an orbital separation of 1083 au. We determine the spectral type, gravity, and effective temperature via comparison with models and observational templates of young brown dwarfs. In addition, we detect and characterize accretion using several accretion tracers. We find SR 12 C to be a brown dwarf of spectral type L0 ± 1, log g = 4 ± 0.5, an effective temperature of 2600 ± 100 K. Our spectra provide clear evidence for accretion at a rate of ˜10-10 M⊙ yr-1. This makes SR 12 one of the few sub-stellar companions with a reliable estimate for its accretion rate. A comparison of the ages and accretion rates of sub-stellar companions with young isolated brown dwarfs does not reveal any significant differences. If further accretion rate measurements of a large number of substellar companions can confirm this trend, this would hint towards a similar formation mechanism for substellar companions at large separations and isolated brown dwarfs.

  4. SRB ascent aerodynamic heating design criteria reduction study, volume 1

    NASA Technical Reports Server (NTRS)

    Crain, W. K.; Frost, C. L.; Engel, C. D.

    1989-01-01

    An independent set of solid rocket booster (SRB) convective ascent design environments were produced which would serve as a check on the Rockwell IVBC-3 environments used to design the ascent phase of flight. In addition, support was provided for lowering the design environments such that Thermal Protection System (TPS), based on conservative estimates, could be removed leading to a reduction in SRB refurbishment time and cost. Ascent convective heating rates and loads were generated at locations in the SRB where lowering the thermal environment would impact the TPS design. The ascent thermal environments are documented along with the wind tunnel/flight test data base used as well as the trajectory and environment generation methodology. Methodology, as well as, environment summaries compared to the 1980 Design and Rockwell IVBC-3 Design Environment are presented in this volume, 1.

  5. The Delivery of Water to the Lunar Mantle by Late Planetesimal Accretion (Invited)

    NASA Astrophysics Data System (ADS)

    Bottke, W. F.; Walker, R. J.; Day, J.; Nesvorny, D.; Elkins-Tanton, L. T.

    2010-12-01

    The final stages of planet formation in the inner Solar System are thought to have culminated in enormous planetary collisions, such as the hypothesized ‘giant impact’ origin for the Earth and Moon that occurred ~50-100 My after the formation of the first Solar System solids. The giant impact event probably triggered a final phase of core formation on these worlds, with global magma oceans effectively stripping the terrestrial and lunar mantles of highly siderophile elements (HSE; Re, Os, Ir, Ru, Pt, Rh, Pd, Au), which have extremely high metal-silicate partition coefficients. Studies of mantle-derived terrestrial peridotites and derivative lunar mantle melts, however, show that the terrestrial and lunar mantles have elevated absolute, and approximately chondritic relative abundances of highly siderophile elements (HSE). We argue this material was most likely delivered by continued planetesimal accretion via HSE-rich impactors within tens of My of core formation termination, with subsequently-accreted materials mixed into each mantle by convection. This process, often called the “late veneer” but here termed late accretion, delivered > 0.4% Earth masses to the terrestrial mantle and produced an Earth/Moon mass input ratio of ~1,000. Using Monte Carlo models, we found that this high ratio most likely came from planetesimal populations dominated by massive impactors. Specifically, if the late accretion population had the form dN ∝ D-q dD (i.e., dN is the number of planetesimals of diameter D within bin dD), the power law index of the projectiles was q < 2 for 200 < D < 4000 km. Interestingly, q ~ 2 populations are also found in planetesimal size distributions derived from evidence taken near 1 AU (e.g., D > 250 km asteroids in the inner/central main belt with semimajor axis < 2.8 AU, the population of non-saturated ancient martian impact basins with 700 < D < 2000 km) as well as from new planetary accretion models that allow planetesimals to be “born big

  6. Rapid and slow: Varying magma ascent rates as a mechanism for Vulcanian explosions

    NASA Astrophysics Data System (ADS)

    Cassidy, Mike; Cole, Paul. D.; Hicks, Kelby E.; Varley, Nick R.; Peters, Nial; Lerner, Allan H.

    2015-06-01

    Vulcanian explosions are one of the most common types of volcanic activity observed at silicic volcanoes. Magma ascent rates are often invoked as being the fundamental control on their explosivity, yet this factor is poorly constrained for low magnitude end-member Vulcanian explosions, which are particularly poorly understood, partly due to the rarity of ash samples and low gas fluxes. We describe ash generated by small Vulcanian explosions at Volcán de Colima in 2013, where we document for the first time marked differences in the vesicularity, crystal characteristics (volume fraction, size and shape) and glass compositions in juvenile material from discrete events. We interpret these variations as representing differing ascent styles and speeds of magma pulses within the conduit. Heterogeneous degassing during ascent leads to fast ascending, gas-rich magma pulses together with slow ascending gas-poor magma pulses within the same conduit. This inferred heterogeneity is complemented by SO2 flux data, which show transient episodes of both open and closed system degassing, indicating efficient shallow fracture sealing mechanisms, which allows for gas overpressure to generate small Vulcanian explosions.

  7. An Accreting Protoplanet: Confirmation and Characterization of LkCa15b

    NASA Astrophysics Data System (ADS)

    Follette, Katherine; Close, Laird; Males, Jared; Macintosh, Bruce; Sallum, Stephanie; Eisner, Josh; Kratter, Kaitlin M.; Morzinski, Katie; Hinz, Phil; Weinberger, Alycia; Rodigas, Timothy J.; Skemer, Andrew; Bailey, Vanessa; Vaz, Amali; Defrere, Denis; spalding, eckhart; Tuthill, Peter

    2015-12-01

    We present a visible light adaptive optics direct imaging detection of a faint point source separated by just 93 milliarcseconds (~15 AU) from the young star LkCa 15. Using Magellan AO's visible light camera in Simultaneous Differential Imaging (SDI) mode, we imaged the star at Hydrogen alpha and in the neighboring continuum as part of the Giant Accreting Protoplanet Survey (GAPplanetS) in November 2015. The continuum images provide a sensitive and simultaneous probe of PSF residuals and instrumental artifacts, allowing us to isolate H-alpha accretion luminosity from the LkCa 15b protoplanet, which lies well inside of the LkCa15 transition disk gap. This detection, combined with a nearly simultaneous near-infrared detection with the Large Binocular Telescope, provides an unprecedented glimpse at a planetary system during epoch of planet formation. [Nature result in press. Please embargo until released

  8. Super-Eddington Accretion in Tidal Disruption Events: the Impact of Realistic Fallback Rates on Accretion Rates

    NASA Astrophysics Data System (ADS)

    Wu, Samantha; Coughlin, Eric R.; Nixon, Chris

    2018-04-01

    After the tidal disruption of a star by a massive black hole, disrupted stellar debris can fall back to the hole at a rate significantly exceeding its Eddington limit. To understand how black hole mass affects the duration of super-Eddington accretion in tidal disruption events, we first run a suite of simulations of the disruption of a Solar-like star by a supermassive black hole of varying mass to directly measure the fallback rate onto the hole, and we compare these fallback rates to the analytic predictions of the "frozen-in" model. Then, adopting a Zero-Bernoulli Accretion flow as an analytic prescription for the accretion flow around the hole, we investigate how the accretion rate onto the black hole evolves with the more accurate fallback rates calculated from the simulations. We find that numerically-simulated fallback rates yield accretion rates onto the hole that can, depending on the black hole mass, be nearly an order of magnitude larger than those predicted by the frozen-in approximation. Our results place new limits on the maximum black hole mass for which super-Eddington accretion occurs in tidal disruption events.

  9. Enabling Parametric Optimal Ascent Trajectory Modeling During Early Phases of Design

    NASA Technical Reports Server (NTRS)

    Holt, James B.; Dees, Patrick D.; Diaz, Manuel J.

    2015-01-01

    -modal due to the interaction of various constraints. Additionally, when these obstacles are coupled with The Program to Optimize Simulated Trajectories [1] (POST), an industry standard program to optimize ascent trajectories that is difficult to use, it requires expert trajectory analysts to effectively optimize a vehicle's ascent trajectory. As it has been pointed out, the paradigm of trajectory optimization is still a very manual one because using modern computational resources on POST is still a challenging problem. The nuances and difficulties involved in correctly utilizing, and therefore automating, the program presents a large problem. In order to address these issues, the authors will discuss a methodology that has been developed. The methodology is two-fold: first, a set of heuristics will be introduced and discussed that were captured while working with expert analysts to replicate the current state-of-the-art; secondly, leveraging the power of modern computing to evaluate multiple trajectories simultaneously, and therefore, enable the exploration of the trajectory's design space early during the pre-conceptual and conceptual phases of design. When this methodology is coupled with design of experiments in order to train surrogate models, the authors were able to visualize the trajectory design space, enabling parametric optimal ascent trajectory information to be introduced with other pre-conceptual and conceptual design tools. The potential impact of this methodology's success would be a fully automated POST evaluation suite for the purpose of conceptual and preliminary design trade studies. This will enable engineers to characterize the ascent trajectory's sensitivity to design changes in an arbitrary number of dimensions and for finding settings for trajectory specific variables, which result in optimal performance for a "dialed-in" launch vehicle design. The effort described in this paper was developed for the Advanced Concepts Office [2] at NASA Marshall

  10. Planetary Formation: From the Earth and Moon to Extrasolar Giant Planets

    NASA Technical Reports Server (NTRS)

    Lissauer, Jack; DeVincenzi, Donald (Technical Monitor)

    1999-01-01

    An overview of current theories of star and planet formation is presented. These models are based upon observations of the Solar System and of young stars and their environments. They predict that rocky planets should form around most single stars, although it is possible that in some cases such planets are lost to orbital decay within the protoplanetary disk. The frequency of formation of gas giant planets is more difficult to predict theoretically. Terrestrial planets are believed to grow via pairwise accretion until the spacing of planetary orbits becomes large enough that the configuration is stable for the age of the system. Giant planets begin their growth like terrestrial planets, but they become massive enough that they are able to accumulate substantial amounts of gas before the protoplanetary disk dissipates. Specific issues to be discussed include: (1) how large a solid core is needed to initiate rapid accumulation of gas? (2) can giant planets form very close to stars? (3) could a giant impact leading to lunar formation have occurred approximately 100 million years after the condensation of the oldest meteorites?

  11. Planetary Formation: From the Earth and Moon to Extrasolar Giant Planets

    NASA Technical Reports Server (NTRS)

    Lissauer, Jack J.; DeVincenzi, Donald (Technical Monitor)

    1999-01-01

    An overview of current theories of star and planet formation is presented. These models are based upon observations of the Solar System and of young stars and their environments. They predict that rocky planets should form around most single stars, although it is possible that in some cases-such planets are lost to orbital decay within the protoplanetary disk. The frequency of formation of gas giant planets is more difficult to predict theoretically. Terrestrial planets are believed to grow via pairwise accretion until the spacing of planetary orbits becomes large enough that the configuration is stable for the age of the system. Giant planets begin their growth like terrestrial planets, but they become massive enough that they are able to accumulate substantial amounts of gas before the protoplanetary disk dissipates. Specific issues to be discussed include: (1) how large a solid core is needed to initiate rapid accumulation of gas? (2) can giant planets form very close to stars? (3) could a giant impact leading to lunar formation have occurred approx. 100 million years after the condensation of the oldest meteorites?

  12. Late veneer and late accretion to the terrestrial planets

    NASA Astrophysics Data System (ADS)

    Brasser, R.; Mojzsis, S. J.; Werner, S. C.; Matsumura, S.; Ida, S.

    2016-12-01

    It is generally accepted that silicate-metal ('rocky') planet formation relies on coagulation from a mixture of sub-Mars sized planetary embryos and (smaller) planetesimals that dynamically emerge from the evolving circum-solar disc in the first few million years of our Solar System. Once the planets have, for the most part, assembled after a giant impact phase, they continue to be bombarded by a multitude of planetesimals left over from accretion. Here we place limits on the mass and evolution of these planetesimals based on constraints from the highly siderophile element (HSE) budget of the Moon. Outcomes from a combination of N-body and Monte Carlo simulations of planet formation lead us to four key conclusions about the nature of this early epoch. First, matching the terrestrial to lunar HSE ratio requires either that the late veneer on Earth consisted of a single lunar-size impactor striking the Earth before 4.45 Ga, or that it originated from the impact that created the Moon. An added complication is that analysis of lunar samples indicates the Moon does not preserve convincing evidence for a late veneer like Earth. Second, the expected chondritic veneer component on Mars is 0.06 weight percent. Third, the flux of terrestrial impactors must have been low (≲10-6 M⊕ Myr-1) to avoid wholesale melting of Earth's crust after 4.4 Ga, and to simultaneously match the number of observed lunar basins. This conclusion leads to an Hadean eon which is more clement than assumed previously. Last, after the terrestrial planets had fully formed, the mass in remnant planetesimals was ∼10-3 M⊕, lower by at least an order of magnitude than most previous models suggest. Our dynamically and geochemically self-consistent scenario requires that future N-body simulations of rocky planet formation either directly incorporate collisional grinding or rely on pebble accretion.

  13. Controlled Ascent From the Surface of an Asteroid

    NASA Technical Reports Server (NTRS)

    Shen, Haijun; Roithmayr, Carlos M.; Cornelius, David M.

    2014-01-01

    The National Aeronautics and Space Administration (NASA) is currently investigating a conceptual robotic mission to collect a small boulder up to 4 m in diameter resting on the surface of a large Near Earth Asteroid (NEA). Because most NEAs are not well characterized, a great range of uncertainties in boulder mass properties and NEA surface characteristics must be considered in the design of this mission. These uncertainties are especially significant when the spacecraft ascends with the boulder in tow. The most important requirement during ascent is to keep the spacecraft in an upright posture to maintain healthy ground clearances for the two large solar arrays. This paper focuses on the initial stage (the first 50 m) of ascent from the surface. Specifically, it presents a sensitivity study of the solar array ground clearance, control authority, and accelerations at the array tips in the presence of a variety of uncertainties including various boulder sizes, densities, shapes and orientations, locations of the true center of mass, and push-off force distributions. Results are presented, and appropriate operations are recommended in the event some of the off-nominal cases occur.

  14. Early Results from NICER Observations of Accreting Neutron Stars

    NASA Astrophysics Data System (ADS)

    Chakrabarty, Deepto; Ozel, Feryal; Arzoumanian, Zaven; Gendreau, Keith C.; Bult, Peter; Cackett, Ed; Chenevez, Jerome; Fabian, Andy; Guillot, Sebastien; Guver, Tolga; Homan, Jeroen; Keek, Laurens; Lamb, Frederick; Ludlam, Renee; Mahmoodifar, Simin; Markwardt, Craig B.; Miller, Jon M.; Psaltis, Dimitrios; Strohmayer, Tod E.; Wilson-Hodge, Colleen A.; Wolff, Michael T.

    2018-01-01

    The Neutron Star Interior Composition Explorer (NICER) offers significant new capabilities for the study of accreting neuton stars relative to previous X-ray missions including large effective area, low background, and greatly improved low-energy response. The NICER Burst and Accretion Working Group has designed a 2 Ms observation program to study a number of phenomena in accreting neutron stars including type-I X-ray bursts, superbursts, accretion-powered pulsations, quasi-periodic oscillations, and accretion disk reflection spectra. We present some early results from the first six months of the NICER mission.

  15. The Rise and Fall of μ Velorum: A Remarkable Flare on a Yellow Giant Star Observed with the Extreme Ultraviolet Explorer

    NASA Astrophysics Data System (ADS)

    Ayres, Thomas R.; Osten, Rachel A.; Brown, Alexander

    1999-11-01

    The close visual double μ Velorum (HD 93497; G6 III+dF) consists of a yellow giant and a fainter companion currently 2" apart. Recently μ Vel was the source of a large flare recorded by the Extreme Ultraviolet Explorer. The long 1.5 day decay phase was like the extremes seen on hyperactive RS CVn-type binaries. The primary, μ Vel A is a 3 Msolar star, in the ``rapid braking zone'' redward of G0 III. Yellow giants are not commonly reported as flare stars, perhaps because the first-crossers are relatively rare and not well represented in the observational samples. The secondary star is classified G2 V, but the 1700 Å energy distribution places it earlier on the main sequence, probably F4 or F5 V, in a class also not usually known for coronal variability. The long duration of the μ Vel event suggests that it occurred in a significantly elongated structure of moderate density, ne<~109 cm-3. If it was a magnetic plasmoid, like a coronal mass ejection on the Sun, then such events might play a role in shedding angular momentum from active evolved stars. The associated spin-down could control the activity survival time of red giants (in later stages of evolution than the first-crosser μ Vel) whose dynamos were rejunvenated by dredge-up of angular momentum from the interior, or more exotic sources, such as cannibalism of close-in substellar companions during the first or second ascent.

  16. Closed-loop endo-atmospheric ascent guidance for reusable launch vehicle

    NASA Astrophysics Data System (ADS)

    Sun, Hongsheng

    This dissertation focuses on the development of a closed-loop endo-atmospheric ascent guidance algorithm for the 2nd generation reusable launch vehicle. Special attention has been given to the issues that impact on viability, complexity and reliability in on-board implementation. The algorithm is called once every guidance update cycle to recalculate the optimal solution based on the current flight condition, taking into account atmospheric effects and path constraints. This is different from traditional ascent guidance algorithms which operate in a simple open-loop mode inside atmosphere, and later switch to a closed-loop vacuum ascent guidance scheme. The classical finite difference method is shown to be well suited for fast solution of the constrained optimal three-dimensional ascent problem. The initial guesses for the solutions are generated using an analytical vacuum optimal ascent guidance algorithm. Homotopy method is employed to gradually introduce the aerodynamic forces to generate the optimal solution from the optimal vacuum solution. The vehicle chosen for this study is the Lockheed Martin X-33 lifting-body reusable launch vehicle. To verify the algorithm presented in this dissertation, a series of open-loop and closed-loop tests are performed for three different missions. Wind effects are also studied in the closed-loop simulations. For comparison, the solutions for the same missions are also obtained by two independent optimization softwares. The results clearly establish the feasibility of closed-loop endo-atmospheric ascent guidance of rocket-powered launch vehicles. ATO cases are also tested to assess the adaptability of the algorithm to autonomously incorporate the abort modes.

  17. Super-Earths: Atmospheric Accretion, Thermal Evolution and Envelope Loss

    NASA Astrophysics Data System (ADS)

    Ginzburg, Sivan; Inamdar, Niraj K.; Schlichting, Hilke E.

    Combined mass and radius observations have recently revealed many short-period planets a few times the size of Earth but with significantly lower densities. A natural explanation for the low density of these super Earths super-Earth is a voluminous gas atmosphere that engulfs more compact rocky cores. Planets with such substantial gas atmospheres may be a missing link between smaller planets, that did not manage to obtain or keep an atmosphere, and larger planets, that accreted gas too quickly and became gas giants gas- . In this chapter we review recent advancements in the understanding of low-density low- super-Earth formation and evolution. Specifically, we present a consistent picture of the various stages in the lives of these planets: gas accretion from the protoplanetary disk, possible atmosphere heating and evaporation mechanisms, collisions between planets, and finally, evolution up to the age at which the planets are observed.

  18. Origin of water in the inner Solar System: Planetesimals scattered inward during Jupiter and Saturn's rapid gas accretion

    NASA Astrophysics Data System (ADS)

    Raymond, Sean N.; Izidoro, Andre

    2017-11-01

    There is a long-standing debate regarding the origin of the terrestrial planets' water as well as the hydrated C-type asteroids. Here we show that the inner Solar System's water is a simple byproduct of the giant planets' formation. Giant planet cores accrete gas slowly until the conditions are met for a rapid phase of runaway growth. As a gas giant's mass rapidly increases, the orbits of nearby planetesimals are destabilized and gravitationally scattered in all directions. Under the action of aerodynamic gas drag, a fraction of scattered planetesimals are deposited onto stable orbits interior to Jupiter's. This process is effective in populating the outer main belt with C-type asteroids that originated from a broad (5-20 AU-wide) region of the disk. As the disk starts to dissipate, scattered planetesimals reach sufficiently eccentric orbits to cross the terrestrial planet region and deliver water to the growing Earth. This mechanism does not depend strongly on the giant planets' orbital migration history and is generic: whenever a giant planet forms it invariably pollutes its inner planetary system with water-rich bodies.

  19. Understanding which parameters control shallow ascent of silicic effusive magma

    NASA Astrophysics Data System (ADS)

    Thomas, Mark E.; Neuberg, Jurgen W.

    2014-11-01

    The estimation of the magma ascent rate is key to predicting volcanic activity and relies on the understanding of how strongly the ascent rate is controlled by different magmatic parameters. Linking potential changes of such parameters to monitoring data is an essential step to be able to use these data as a predictive tool. We present the results of a suite of conduit flow models Soufrière that assess the influence of individual model parameters such as the magmatic water content, temperature or bulk magma composition on the magma flow in the conduit during an extrusive dome eruption. By systematically varying these parameters we assess their relative importance to changes in ascent rate. We show that variability in the rate of low frequency seismicity, assumed to correlate directly with the rate of magma movement, can be used as an indicator for changes in ascent rate and, therefore, eruptive activity. The results indicate that conduit diameter and excess pressure in the magma chamber are amongst the dominant controlling variables, but the single most important parameter is the volatile content (assumed as only water). Modeling this parameter in the range of reported values causes changes in the calculated ascent velocities of up to 800%.

  20. Design Considerations for a Crewed Mars Ascent Vehicle

    NASA Technical Reports Server (NTRS)

    Rucker, Michelle A.

    2015-01-01

    Exploration architecture studies identified the Mars Ascent Vehicle (MAV) as one of the largest "gear ratio" items in a crewed Mars mission. Because every kilogram of mass ascended from the Martian surface requires seven kilograms or more of ascent propellant, it is desirable for the MAV to be as small and lightweight as possible. Analysis identified four key factors that drive MAV sizing: 1) Number of crew: more crew members require more equipment-and a larger cabin diameter to hold that equipment-with direct implications to structural, thermal, propulsion, and power subsystem mass. 2) Which suit is worn during ascent: Extravehicular Activity (EVA) type suits are physically larger and heavier than Intravehicular Activity (IVA) type suits and because they are less flexible, EVA suits require more elbow-room to maneuver in and out of. An empty EVA suit takes up about as much cabin volume as a crew member. 3) How much time crew spends in the MAV: less than about 12 hours and the MAV can be considered a "taxi" with few provisions for crew comfort. However, if the crew spends more than 12 consecutive hours in the MAV, it begins to look like a Habitat requiring more crew comfort items. 4) How crew get into/out of the MAV: ingress/egress method drives structural mass (for example, EVA hatch vs. pressurized tunnel vs. suit port) as well as consumables mass for lost cabin atmosphere, and has profound impacts on surface element architecture. To minimize MAV cabin mass, the following is recommended: Limit MAV usage to 24 consecutive hours or less; discard EVA suits on the surface and ascend wearing IVA suits; Limit MAV functionality to ascent only, rather than dual-use ascent/habitat functions; and ingress/egress the MAV via a detachable tunnel to another pressurized surface asset.

  1. Evaluation of the Shuttle GN&C during powered ascent flight phase. [Guidance Navigation and Control equipment system design and flight tests

    NASA Technical Reports Server (NTRS)

    Olson, L.; Sunkel, J. W.

    1982-01-01

    An overview of the ascent trajectory and GN&C (guidance, navigation, and control) system design is followed by a summary of flight test results for the ascent phase of STS-1. The most notable variance from nominal pre-flight predictions was the lofted trajectory observed in first stage due to an unanticipated shift in pitch aerodynamic characteristics from those predicted by wind tunnel tests. The GN&C systems performed as expected on STS-1 throughout powered flight. Following a discussion of the software constants changed for Flight 2 to provide adequate performance margin, a summary of test results from STS-2 and STS-3 is presented. Vehicle trajectory response and GN&C system behavior were very similar to STS-1. Ascent aerodynamic characteristics extracted from the first two test flights were included in the data base used to design the first stage steering and pitch trim profiles for STS-3.

  2. Ascent guidance algorithm using lidar wind measurements

    NASA Technical Reports Server (NTRS)

    Cramer, Evin J.; Bradt, Jerre E.; Hardtla, John W.

    1990-01-01

    The formulation of a general nonlinear programming guidance algorithm that incorporates wind measurements in the computation of ascent guidance steering commands is discussed. A nonlinear programming (NLP) algorithm that is designed to solve a very general problem has the potential to address the diversity demanded by future launch systems. Using B-splines for the command functional form allows the NLP algorithm to adjust the shape of the command profile to achieve optimal performance. The algorithm flexibility is demonstrated by simulation of ascent with dynamic loading constraints through a set of random wind profiles with and without wind sensing capability.

  3. The Spiral Wave Instability Induced by a Giant Planet. I. Particle Stirring in the Inner Regions of Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Bae, Jaehan; Nelson, Richard P.; Hartmann, Lee

    2016-12-01

    We have recently shown that spiral density waves propagating in accretion disks can undergo a parametric instability by resonantly coupling with and transferring energy into pairs of inertial waves (or inertial-gravity waves when buoyancy is important). In this paper, we perform inviscid three-dimensional global hydrodynamic simulations to examine the growth and consequence of this instability operating on the spiral waves driven by a Jupiter-mass planet in a protoplanetary disk. We find that the spiral waves are destabilized via the spiral wave instability (SWI), generating hydrodynamic turbulence and sustained radially alternating vertical flows that appear to be associated with long wavelength inertial modes. In the interval 0.3 {R}{{p}}≤slant R≤slant 0.7{R}{{p}}, where R p denotes the semimajor axis of the planetary orbit (assumed to be 5 au), the estimated vertical diffusion rate associated with the turbulence is characterized by {α }{diff}∼ (0.2{--}1.2)× {10}-2. For the disk model considered here, the diffusion rate is such that particles with sizes up to several centimeters are vertically mixed within the first pressure scale height. This suggests that the instability of spiral waves launched by a giant planet can significantly disperse solid particles and trace chemical species from the midplane. In planet formation models where the continuous local production of chondrules/pebbles occurs over Myr timescales to provide a feedstock for pebble accretion onto these bodies, this stirring of solid particles may add a time constraint: planetary embryos and large asteroids have to form before a gas giant forms in the outer disk, otherwise the SWI will significantly decrease the chondrule/pebble accretion efficiency.

  4. The Correlation between Mixing Length and Metallicity on the Giant Branch: Implications for Ages in the Gaia Era

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

    Tayar, Jamie; Somers, Garrett; Pinsonneault, Marc H.

    2017-05-01

    In the updated APOGEE- Kepler catalog, we have asteroseismic and spectroscopic data for over 3000 first ascent red giants. Given the size and accuracy of this sample, these data offer an unprecedented test of the accuracy of stellar models on the post-main-sequence. When we compare these data to theoretical predictions, we find a metallicity dependent temperature offset with a slope of around 100 K per dex in metallicity. We find that this effect is present in all model grids tested, and that theoretical uncertainties in the models, correlated spectroscopic errors, and shifts in the asteroseismic mass scale are insufficient tomore » explain this effect. Stellar models can be brought into agreement with the data if a metallicity-dependent convective mixing length is used, with Δ α {sub ML,YREC} ∼ 0.2 per dex in metallicity, a trend inconsistent with the predictions of three-dimensional stellar convection simulations. If this effect is not taken into account, isochrone ages for red giants from the Gaia data will be off by as much as a factor of two even at modest deviations from solar metallicity ([Fe/H] = −0.5).« less

  5. Whole-body angular momentum during stair ascent and descent.

    PubMed

    Silverman, Anne K; Neptune, Richard R; Sinitski, Emily H; Wilken, Jason M

    2014-04-01

    The generation of whole-body angular momentum is essential in many locomotor tasks and must be regulated in order to maintain dynamic balance. However, angular momentum has not been investigated during stair walking, which is an activity that presents a biomechanical challenge for balance-impaired populations. We investigated three-dimensional whole-body angular momentum during stair ascent and descent and compared it to level walking. Three-dimensional body-segment kinematic and ground reaction force (GRF) data were collected from 30 healthy subjects. Angular momentum was calculated using a 13-segment whole-body model. GRFs, external moment arms and net joint moments were used to interpret the angular momentum results. The range of frontal plane angular momentum was greater for stair ascent relative to level walking. In the transverse and sagittal planes, the range of angular momentum was smaller in stair ascent and descent relative to level walking. Significant differences were also found in the ground reaction forces, external moment arms and net joint moments. The sagittal plane angular momentum results suggest that individuals alter angular momentum to effectively counteract potential trips during stair ascent, and reduce the range of angular momentum to avoid falling forward during stair descent. Further, significant differences in joint moments suggest potential neuromuscular mechanisms that account for the differences in angular momentum between walking conditions. These results provide a baseline for comparison to impaired populations that have difficulty maintaining dynamic balance, particularly during stair ascent and descent. Copyright © 2014 Elsevier B.V. All rights reserved.

  6. Prototype automated post-MECO ascent I-load Verification Data Table

    NASA Technical Reports Server (NTRS)

    Lardas, George D.

    1990-01-01

    A prototype automated processor for quality assurance of Space Shuttle post-Main Engine Cut Off (MECO) ascent initialization parameters (I-loads) is described. The processor incorporates Clips rules adapted from the quality assurance criteria for the post-MECO ascent I-loads. Specifically, the criteria are implemented for nominal and abort targets, as given in the 'I-load Verification Data Table, Part 3, Post-MECO Ascent, Version 2.1, December 1989.' This processor, ivdt, compares a given l-load set with the stated mission design and quality assurance criteria. It determines which I-loads violate the stated criteria, and presents a summary of I-loads that pass or fail the tests.

  7. Tharsis Formation by Chemical Plume Due to Giant Impact Event

    NASA Astrophysics Data System (ADS)

    Fleck, J.; Weeraratne, D. S.; Olson, P.

    2014-12-01

    Tharsis formed early in the history of Mars, likely during the Noachian but later than the hemispheric crustal dichotomy that it partially overprints (Johnson and Phillips, 2005; Solomon et al., 2005; Wenzel et al., 2004). It has been suggested that the crustal dichotomy may have been formed by a giant impact (Andrews-Hanna et al., 2008; Marinova et al., 2008; Nimmo et al., 2008). Several models have been proposed to explain a localized orogeny, but predict multiple, evenly-spaced plumes or have instability growth and rise times which are longer than Tharsis formation. We use fluid dynamic experiments to model the differentiation process during Mars accretion using low viscosity glucose syrup solutions and an emulsion of liquid gallium for the metal-rich magma ocean and a high viscosity glucose syrup for the mantle. Our experiments demonstrate the formation of metal-silicate diapirs from metal emulsion drops that form a pond at the base of the magma ocean. The diapirs descend through the underlying mantle with trailing conduit of low viscosity silicate material. The silicate material is buoyant and eventually ascends back through the conduit. Remaining emulsion drops that do not adhere with the diapir fall through the conduit, forcing the buoyant molten silicate material to exit the conduit laterally and ascend along a new trajectory. The time elapsed between diapir formation and ascent of the chemical plume in experiments scales with the time between the formation of the crustal dichotomy on Mars and the formation of Tharsis. Our model offers an explanation for the rapid formation of Tharsis on the edge of the crustal dichotomy via a single large upwelling event followed by smaller upwellings producing and the late stages of effusive volcanism observed in the Tharsis region.

  8. How do accretion discs break?

    NASA Astrophysics Data System (ADS)

    Dogan, Suzan

    2016-07-01

    Accretion discs are common in binary systems, and they are often found to be misaligned with respect to the binary orbit. The gravitational torque from a companion induces nodal precession in misaligned disc orbits. In this study, we first calculate whether this precession is strong enough to overcome the internal disc torques communicating angular momentum. We compare the disc precession torque with the disc viscous torque to determine whether the disc should warp or break. For typical parameters precession wins: the disc breaks into distinct planes that precess effectively independently. To check our analytical findings, we perform 3D hydrodynamical numerical simulations using the PHANTOM smoothed particle hydrodynamics code, and confirm that disc breaking is widespread and enhances accretion on to the central object. For some inclinations, the disc goes through strong Kozai cycles. Disc breaking promotes markedly enhanced and variable accretion and potentially produces high-energy particles or radiation through shocks. This would have significant implications for all binary systems: e.g. accretion outbursts in X-ray binaries and fuelling supermassive black hole (SMBH) binaries. The behaviour we have discussed in this work is relevant to a variety of astrophysical systems, for example X-ray binaries, where the disc plane may be tilted by radiation warping, SMBH binaries, where accretion of misaligned gas can create effectively random inclinations and protostellar binaries, where a disc may be misaligned by a variety of effects such as binary capture/exchange, accretion after binary formation.

  9. The tip of the red giant branch as a distance indicator for resolved galaxies. 2: Computer simulations

    NASA Technical Reports Server (NTRS)

    Madore, Barry F.; Freedman, Wendy L.

    1995-01-01

    Based on both empirical data for the nearby galaxies, and on computer simulations, we show that measuring the position of the tip of the first-ascent red-giant branch provides a means of obtaining the distances to nearby galaxies with a precision and accuracy comparable to using Cepheids and/or RR Lyrae variables. We present an analysis of synthetic I vs (V-I) color magnitude diagrams of Population 2 systems to investigate the use of the observed discontinuity in the I-band luminosity function as a primary distance indicator. In the simulations we quantify the effects (1) signal to noise, (2) crowding, (3) population size, and (4) non-giant-branch-star contamination, on the method adopted for detecting the discontinuity,, measuring its luminosity, and estimating its uncertainity. We discuss sources of systematic error in the context of observable parameters, such as the signal-to-noise ratio and/or surface brightness. The simulations are then scaled to observed color-magnitude diagrams. It is concluded, that from the ground the tip of the red-giant-branch method can be sucessfully used to determine distances accurate to +/- 10% for galaxies out to 3 Mpc (mu approximately 27.5 mag); and from space a factor of four further in distance (mu approximately 30.6 mag) can be reached using HST. This method can be applied whereever a metal-poor population (-2.0 less than Z less than -0.7) of red-giant stars is detected (whose age is in the range 7-17 Gyr), whether that population resides in the halo of a spiral galaxy, the extended outer disk of a dwarf irregular, or in the outer periphery of an elliptical galaxy.

  10. Observationally Constraining Gas Giant Composition via Their Host Star Abundances

    NASA Astrophysics Data System (ADS)

    Teske, Johanna; Thorngren, Daniel; Fortney, Jonathan

    2018-01-01

    While the photospheric abundances of the Sun match many rock-forming elemental abundances in the Earth to within 10 mol%, as well as in Mars, the Moon, and meteorites, the Solar System giant planets are of distinctly non-stellar composition — Jupiter's bulk metallicity (inferred from its bulk density, measured from spacecraft data) is ∼ x5-10 solar, and Saturn is ∼ x10-20 solar. This knowledge has led to dramatic advances in understanding models of core accretion, which now match the heavy element enrichment of each of the Solar System's giant planets. However, we have thus far lacked similar data for exoplanets to use as a check for formation and composition models over a much larger parameter space. Here we present a study of the host stars of a sample of cool transiting gas giants with measured bulk metal fractions (as in Thorngren et al. 2016) to better constrain the relation Zplanet/Zstar — giant exoplanet metal enrichment relative to the host star. We add a new dimension of chemical variation, measuring C, O, Mg, Si, Ni, and well as Fe (on which previous Zplanet/Zstar calculations were based). Our analysis provides the best constraints to date on giant exoplanet interior composition and how this relates to formation environment, and make testable predictions for JWST observations of exoplanet atmospheres.

  11. Black Hole Disk Accretion in Supernovae

    NASA Astrophysics Data System (ADS)

    Nomura, H.; Mineshige, S.; Hirose, M.; Nomoto, K.; Suzuki, T.

    Hydrodynamical disk accretion flow onto a new-born black hole in a supernova is studied using the SPH (Smoothed Particle Hydrodynamics) method. It has been suggested that a mass of ~0.1Modot falls back to a black hole by a reverse shock. If the progenitor was rotating before the explosion, the accreting material should have a certain amount of angular momentum, thus forming an accretion disk. Disk material will eventually accrete towards the central object via viscosity with a supercritical accretion rate, dotM / dotMc > 106, for first several tens of days. (Here, dotMc is the Eddington luminosity divided by c2.) We then expect that such an accretion disk is optically thick and advection-dominated; that is, the disk is so hot that produced energy and photons are advected inward rather than being radiated away. Thus, the disk luminosity is much less than the Eddington luminosity (~1038erg s-1). The disk becomes hot and dense; for dotM / dotMc ~106 and the viscosity parameter alphavis ~0.01, for example, T ~109K and rho ~103gcm-3 in the vicinity of the central object. Efficient nucleosynthesis is hence expected even for reasonable viscosity magnitudes, although produced elements may be swallowed by the black hole.

  12. Ablative overlays for Space Shuttle leading edge ascent heat protection

    NASA Technical Reports Server (NTRS)

    Strauss, E. L.

    1975-01-01

    Ablative overlays were evaluated via a plasma-arc simulation of the ascent pulse on the leading edge of the Space Shuttle Orbiter. Overlay concepts included corkboard, polyisocyanurate foam, low-density Teflon, epoxy, and subliming salts. Their densities ranged from 4.9 to 81 lb per cu ft, and the thicknesses varied from 0.107 to 0.330 in. Swept-leading-edge models were fabricated from 30-lb per cu ft silicone-based ablators. The overlays were bonded to maintain the surface temperature of the base ablator below 500 F during ascent. Foams provided minimum-weight overlays, and subliming salts provided minimum-thickness overlays. Teflon left the most uniform surface after ascent heating.

  13. Evolutionary sequences of very hot, low-mass, accreting white dwarfs with application to symbiotic variables and ultrasoft/supersoft low-luminosity x-ray sources

    NASA Technical Reports Server (NTRS)

    Sion, Edward M.; Starrfield, Sumner G.

    1994-01-01

    We present the first detailed model results of quasi-static evolutionary sequences of very hot low-mass white dwarfs accreting hydrogen-rich material at rates between 1 x 10(exp -7) and 1 x 10(exp -9) solar mass/yr. Most of the sequences were generated from starting models whose core thermal structures were not thermally relaxed in the thermal pulse cycle-averaged sense of an asymptotic giant branch stellar core. Hence, the evolution at constant accretion rate was not invariably characterized by series of identical shell flashes. Sequences exhibiting stable steady state nuclear burning at the accretion supply rate as well as sequences exhibiting recurrent thermonuclear shell flashes are presented and discussed. In some cases, the white dwarf accretors remain small (less than 10(exp 11) cm) and very hot even during the shell flash episode. They then experience continued but reduced hydrogen shell burning during the longer quiescent intervals while their surface temperatures increase both because of compressional heating and envelope structure readjustment in response to accretion over thousands of years. Both accretion and continued hydrogen burning power these models with luminosities of a few times 10(exp 37) ergs/s. We suggest that the physical properties of these model sequences are of considerable relevance to the observed outburst and quiescent behavior of those symbiotic variables and symbiotic novae containing low-mass white dwarfs. We also suggest that our models are relevant to the observational characteristics of the growing class of low-luminosity, supersoft/ultrasoft X-ray sources in globular clusters, and the Magellanic Clouds.

  14. On the possibility of enrichment and differentiation in gas giants during birth by disk instability

    NASA Astrophysics Data System (ADS)

    Boley, Aaron C.; Durisen, Richard H.

    2011-11-01

    We investigate the coupling between solids and gas during the formation of gas giant planets by disk fragmentation in the outer regions of massive disks. We find that fragments can become differentiated at birth. Even if an entire clump does not survive, differentiation could create solids cores that survive to accrete gaseous envelopes later.

  15. IMPLICATIONS OF RAPID CORE ROTATION IN RED GIANTS FOR INTERNAL ANGULAR MOMENTUM TRANSPORT IN STARS

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

    Tayar, Jamie; Pinsonneault, Marc H., E-mail: tayar.1@osu.edu

    2013-09-20

    Core rotation rates have been measured for red giant stars using asteroseismology. These data, along with helioseismic measurements and open cluster spin-down studies, provide powerful clues about the nature and timescale for internal angular momentum transport in stars. We focus on two cases: the metal-poor red giant KIC 7341231 ({sup O}tto{sup )} and intermediate-mass core helium burning stars. For both, we examine limiting case studies for angular momentum coupling between cores and envelopes under the assumption of rigid rotation on the main sequence. We discuss the expected pattern of core rotation as a function of mass and radius. In themore » case of Otto, strong post-main-sequence coupling is ruled out and the measured core rotation rate is in the range of 23-33 times the surface value expected from standard spin-down models. The minimum coupling timescale (0.17-0.45 Gyr) is significantly longer than that inferred for young open cluster stars. This implies ineffective internal angular momentum transport in early first ascent giants. By contrast, the core rotation rates of evolved secondary clump stars are found to be consistent with strong coupling given their rapid main-sequence rotation. An extrapolation to the white dwarf regime predicts rotation periods between 330 and 0.0052 days, depending on mass and decoupling time. We identify two key ingredients that explain these features: the presence of a convective core and inefficient angular momentum transport in the presence of larger mean molecular weight gradients. Observational tests that can disentangle these effects are discussed.« less

  16. JUPITER WILL BECOME A HOT JUPITER: CONSEQUENCES OF POST-MAIN-SEQUENCE STELLAR EVOLUTION ON GAS GIANT PLANETS

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

    Spiegel, David S.; Madhusudhan, Nikku, E-mail: dave@ias.edu, E-mail: Nikku.Madhusudhan@yale.edu

    When the Sun ascends the red giant branch (RGB), its luminosity will increase and all the planets will receive much greater irradiation than they do now. Jupiter, in particular, might end up more highly irradiated than the hot Neptune GJ 436b and, hence, could appropriately be termed a 'hot Jupiter'. When their stars go through the RGB or asymptotic giant branch stages, many of the currently known Jupiter-mass planets in several-AU orbits will receive levels of irradiation comparable to the hot Jupiters, which will transiently increase their atmospheric temperatures to {approx}1000 K or more. Furthermore, massive planets around post-main-sequence starsmore » could accrete a non-negligible amount of material from the enhanced stellar winds, thereby significantly altering their atmospheric chemistry as well as causing a significant accretion luminosity during the epochs of most intense stellar mass loss. Future generations of infrared observatories might be able to probe the thermal and chemical structure of such hot Jupiters' atmospheres. Finally, we argue that, unlike their main-sequence analogs (whose zonal winds are thought to be organized in only a few broad, planetary-scale jets), red-giant hot Jupiters should have multiple, narrow jets of zonal winds and efficient day-night redistribution.« less

  17. Magnetically gated accretion in an accreting 'non-magnetic' white dwarf.

    PubMed

    Scaringi, S; Maccarone, T J; D'Angelo, C; Knigge, C; Groot, P J

    2017-12-13

    White dwarfs are often found in binary systems with orbital periods ranging from tens of minutes to hours in which they can accrete gas from their companion stars. In about 15 per cent of these binaries, the magnetic field of the white dwarf is strong enough (at 10 6 gauss or more) to channel the accreted matter along field lines onto the magnetic poles. The remaining systems are referred to as 'non-magnetic', because until now there has been no evidence that they have a magnetic field that is strong enough to affect the accretion dynamics. Here we report an analysis of archival optical observations of the 'non-magnetic' accreting white dwarf in the binary system MV Lyrae, whose light curve displays quasi-periodic bursts of about 30 minutes duration roughly every 2 hours. The timescale and amplitude of these bursts indicate the presence of an unstable, magnetically regulated accretion mode, which in turn implies the existence of magnetically gated accretion, in which disk material builds up around the magnetospheric boundary (at the co-rotation radius) and then accretes onto the white dwarf, producing bursts powered by the release of gravitational potential energy. We infer a surface magnetic field strength for the white dwarf in MV Lyrae of between 2 × 10 4 gauss and 1 × 10 5 gauss, too low to be detectable by other current methods. Our discovery provides a new way of studying the strength and evolution of magnetic fields in accreting white dwarfs and extends the connections between accretion onto white dwarfs, young stellar objects and neutron stars, for which similar magnetically gated accretion cycles have been identified.

  18. SPH Simulations of Spherical Bondi Accretion: First Step of Implementing AGN Feedback in Galaxy Formation

    NASA Astrophysics Data System (ADS)

    Barai, Paramita; Proga, D.; Nagamine, K.

    2011-01-01

    Our motivation is to numerically test the assumption of Black Hole (BH) accretion (that the central massive BH of a galaxy accretes mass at the Bondi-Hoyle accretion rate, with ad-hoc choice of parameters), made in many previous galaxy formation studies including AGN feedback. We perform simulations of a spherical distribution of gas, within the radius range 0.1 - 200 pc, accreting onto a central supermassive black hole (the Bondi problem), using the 3D Smoothed Particle Hydrodynamics code Gadget. In our simulations we study the radial distribution of various gas properties (density, velocity, temperature, Mach number). We compute the central mass inflow rate at the inner boundary (0.1 pc), and investigate how different gas properties (initial density and velocity profiles) and computational parameters (simulation outer boundary, particle number) affect the central inflow. Radiative processes (namely heating by a central X-ray corona and gas cooling) have been included in our simulations. We study the thermal history of accreting gas, and identify the contribution of radiative and adiabatic terms in shaping the gas properties. We find that the current implementation of artificial viscosity in the Gadget code causes unwanted extra heating near the inner radius.

  19. Simulating X-ray bursts during a transient accretion event

    NASA Astrophysics Data System (ADS)

    Johnston, Zac; Heger, Alexander; Galloway, Duncan K.

    2018-06-01

    Modelling of thermonuclear X-ray bursts on accreting neutron stars has to date focused on stable accretion rates. However, bursts are also observed during episodes of transient accretion. During such events, the accretion rate can evolve significantly between bursts, and this regime provides a unique test for burst models. The accretion-powered millisecond pulsar SAX J1808.4-3658 exhibits accretion outbursts every 2-3 yr. During the well-sampled month-long outburst of 2002 October, four helium-rich X-ray bursts were observed. Using this event as a test case, we present the first multizone simulations of X-ray bursts under a time-dependent accretion rate. We investigate the effect of using a time-dependent accretion rate in comparison to constant, averaged rates. Initial results suggest that using a constant, average accretion rate between bursts may underestimate the recurrence time when the accretion rate is decreasing, and overestimate it when the accretion rate is increasing. Our model, with an accreted hydrogen fraction of X = 0.44 and a CNO metallicity of ZCNO = 0.02, reproduces the observed burst arrival times and fluences with root mean square (rms) errors of 2.8 h, and 0.11× 10^{-6} erg cm^{-2}, respectively. Our results support previous modelling that predicted two unobserved bursts and indicate that additional bursts were also missed by observations.

  20. Hybrid adaptive ascent flight control for a flexible launch vehicle

    NASA Astrophysics Data System (ADS)

    Lefevre, Brian D.

    hybrid adaptive flight controller, development of a Newton's method based online parameter update that is modified to include a step size which regulates the rate of change in the parameter estimates, comparison of the modified Newton's method and recursive least squares online parameter update algorithms, modification of the neural network's input structure to accommodate for the nature of the nonlinearities present in a launch vehicle's ascent flight, examination of both tracking error based and modeling error based neural network weight update laws, and integration of feedback filters for the purpose of preventing harmful interaction between the flight control system and flexible structural modes. To validate the hybrid adaptive controller, a high-fidelity Ares I ascent flight simulator and a classical gain-scheduled proportional-integral-derivative (PID) ascent flight controller were obtained from the NASA Marshall Space Flight Center. The classical PID flight controller is used as a benchmark when analyzing the performance of the hybrid adaptive flight controller. Simulations are conducted which model both nominal and off-nominal flight conditions with structural flexibility of the vehicle either enabled or disabled. First, rigid body ascent simulations are performed with the hybrid adaptive controller under nominal flight conditions for the purpose of selecting the update laws which drive the indirect and direct adaptive components. With the neural network disabled, the results revealed that the recursive least squares online parameter update caused high frequency oscillations to appear in the engine gimbal commands. This is highly undesirable for long and slender launch vehicles, such as the Ares I, because such oscillation of the rocket nozzle could excite unstable structural flex modes. In contrast, the modified Newton's method online parameter update produced smooth control signals and was thus selected for use in the hybrid adaptive launch vehicle flight

  1. Erythrocytes retain hypoxic adenosine response for faster acclimatization upon re-ascent

    PubMed Central

    Song, Anren; Zhang, Yujin; Han, Leng; Yegutkin, Gennady G.; Liu, Hong; Sun, Kaiqi; D'Alessandro, Angelo; Li, Jessica; Karmouty-Quintana, Harry; Iriyama, Takayuki; Weng, Tingting; Zhao, Shushan; Wang, Wei; Wu, Hongyu; Nemkov, Travis; Subudhi, Andrew W.; Jameson-Van Houten, Sonja; Julian, Colleen G.; Lovering, Andrew T.; Hansen, Kirk C.; Zhang, Hong; Bogdanov, Mikhail; Dowhan, William; Jin, Jianping; Kellems, Rodney E.; Eltzschig, Holger K.; Blackburn, Michael; Roach, Robert C.; Xia, Yang

    2017-01-01

    Faster acclimatization to high altitude upon re-ascent is seen in humans; however, the molecular basis for this enhanced adaptive response is unknown. We report that in healthy lowlanders, plasma adenosine levels are rapidly induced by initial ascent to high altitude and achieved even higher levels upon re-ascent, a feature that is positively associated with quicker acclimatization. Erythrocyte equilibrative nucleoside transporter 1 (eENT1) levels are reduced in humans at high altitude and in mice under hypoxia. eENT1 deletion allows rapid accumulation of plasma adenosine to counteract hypoxic tissue damage in mice. Adenosine signalling via erythrocyte ADORA2B induces PKA phosphorylation, ubiquitination and proteasomal degradation of eENT1. Reduced eENT1 resulting from initial hypoxia is maintained upon re-ascent in humans or re-exposure to hypoxia in mice and accounts for erythrocyte hypoxic memory and faster acclimatization. Our findings suggest that targeting identified purinergic-signalling network would enhance the hypoxia adenosine response to counteract hypoxia-induced maladaptation. PMID:28169986

  2. Crew Exploration Vehicle Ascent Abort Coverage Analysis

    NASA Technical Reports Server (NTRS)

    Abadie, Marc J.; Berndt, Jon S.; Burke, Laura M.; Falck, Robert D.; Gowan, John W., Jr.; Madsen, Jennifer M.

    2007-01-01

    An important element in the design of NASA's Crew Exploration Vehicle (CEV) is the consideration given to crew safety during various ascent phase failure scenarios. To help ensure crew safety during this critical and dynamic flight phase, the CEV requirements specify that an abort capability must be continuously available from lift-off through orbit insertion. To address this requirement, various CEV ascent abort modes are analyzed using 3-DOF (Degree Of Freedom) and 6-DOF simulations. The analysis involves an evaluation of the feasibility and survivability of each abort mode and an assessment of the abort mode coverage using the current baseline vehicle design. Factors such as abort system performance, crew load limits, thermal environments, crew recovery, and vehicle element disposal are investigated to determine if the current vehicle requirements are appropriate and achievable. Sensitivity studies and design trades are also completed so that more informed decisions can be made regarding the vehicle design. An overview of the CEV ascent abort modes is presented along with the driving requirements for abort scenarios. The results of the analysis completed as part of the requirements validation process are then discussed. Finally, the conclusions of the study are presented, and future analysis tasks are recommended.

  3. Apollo experience report: Mission planning for lunar module descent and ascent

    NASA Technical Reports Server (NTRS)

    Bennett, F. V.

    1972-01-01

    The premission planning, the real-time situation, and the postflight analysis for the Apollo 11 lunar descent and ascent are described. A comparison between premission planning and actual results is included. A navigation correction capability, developed from Apollo 11 postflight analysis was used successfully on Apollo 12 to provide the first pinpoint landing. An experience summary, which illustrates typical problems encountered by the mission planners, is also included.

  4. Mars Ascent Vehicle Gross Lift-off Mass Sensitivities for Robotic Mars Sample Return

    NASA Technical Reports Server (NTRS)

    Dux, Ian J.; Huwaldt, Joseph A.; McKamey, R. Steve; Dankanich, John W.

    2011-01-01

    The Mars ascent vehicle is a critical element of the robotic Mars Sample Return (MSR) mission. The Mars ascent vehicle must be developed to survive a variety of conditions including the trans-Mars journey, descent through the Martian atmosphere and the harsh Martian surface environments while maintaining the ability to deliver its payload to a low Mars orbit. The primary technology challenge of developing the Mars ascent vehicle system is designing for all conditions while ensuring the mass limitations of the entry descent and landing system are not exceeded. The NASA In-Space Propulsion technology project has initiated the development of Mars ascent vehicle technologies with propulsion system performance and launch environments yet to be defined. To support the project s evaluation and development of various technology options the sensitivity of the Mars ascent vehicle gross lift-off mass to engine performance, inert mass, target orbits, and launch conditions has been completed with the results presented herein.

  5. Analyzing the Spectra of Accreting X-Ray Pulsars

    NASA Astrophysics Data System (ADS)

    Wolff, Michael

    This proposal seeks funding for the analysis of accretion-powered X-ray pulsar spectra from NASA/ HEASARC archived X-ray data. Spectral modeling of accreting X-ray pulsars can tell us a great deal about the physical conditions in and near high mass X-ray binary systems. Such systems have accretion flows where plasma is initially channeled from an accretion disk by the strong neutron star magnetic field, eventually falling onto the magnetic polar cap of the neutron star compact object. Many of these accreting X-ray pulsars have X-ray spectra that consist of broad power-law continua with superposed cyclotron resonant scattering features indicating magnetic field strengths above 10^12 G. The energies of these cyclotron line features have recently been shown to vary with X-ray luminosity in a number of sources such as Her X-1 and V 0332+53, a phenomenon not well understood. Another recent development is the relatively new analytic model for the spectral continuum formation in accretion-powered pulsar systems developed by Becker & Wolff. In their formalism the accretion flows are assumed to go through radiation- dominated radiative shocks and settle onto the neutron star surface. The radiation field consists of strongly Comptonized bremsstrahlung emission from the entire plasma, Comptonized cyclotron emission from the de-excitations of Landau-excited electrons in the neutron star magnetic field, and Comptonized black-body emission from a thermal mound near the neutron star surface. We seek to develop the data analysis tools to apply this model framework to the X-ray data from a wide set of sources to make progress characterizing the basic accretion properties (e.g., magnetic field strength, plasma temperatures, polar cap size, accretion rate per unit area, dominance of bulk vs. thermal Comptonization) as well as understanding the variations of the cyclotron line energies with X-ray luminosity. The three major goals of our proposed work are as follows: In the first year

  6. THE PROPERTIES OF HEAVY ELEMENTS IN GIANT PLANET ENVELOPES

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

    Soubiran, François; Militzer, Burkhard

    The core-accretion model for giant planet formation suggests a two-layer picture for the initial structure of Jovian planets, with heavy elements in a dense core and a thick H–He envelope. Late planetesimal accretion and core erosion could potentially enrich the H–He envelope in heavy elements, which is supported by the threefold solar metallicity that was measured in Jupiter’s atmosphere by the Galileo entry probe. In order to reproduce the observed gravitational moments of Jupiter and Saturn, models for their interiors include heavy elements, Z , in various proportions. However, their effect on the equation of state of the hydrogen–helium mixturesmore » has not been investigated beyond the ideal mixing approximation. In this article, we report results from ab initio simulations of fully interacting H–He– Z mixtures in order to characterize their equation of state and to analyze possible consequences for the interior structure and evolution of giant planets. Considering C, N, O, Si, Fe, MgO, and SiO{sub 2}, we show that the behavior of heavy elements in H–He mixtures may still be represented by an ideal mixture if the effective volumes and internal energies are chosen appropriately. In the case of oxygen, we also compute the effect on the entropy. We find the resulting changes in the temperature–pressure profile to be small. A homogeneous distribution of 2% oxygen by mass changes the temperature in Jupiter’s interior by only 80 K.« less

  7. Survey Says...! Women rising above challenges in atmospheric science through ASCENT

    NASA Astrophysics Data System (ADS)

    Edwards, L. M.; Thiry, H.; Hallar, A. G.; Avallone, L. M.

    2011-12-01

    The Atmospheric Sciences Collaborations and Enriching NeTworks (ASCENT) project is in its third year of connecting early career atmospheric scientists with female senior scientists in related fields. The annual workshops have demonstrated the range of career and personal decisions that current successful senior scientists have made, presented tools and resources, created new networks of collaboration, and provided a forum for informal and formal discussions of issues that face early career female atmospheric scientists. A formal assessment has been ongoing, with participants responding to questions relating to the workshops themselves, in addition to a longitudinal study that asks participants about the impact of ASCENT months or years after their workshop experience. Through this evaluation, the workshop organizers have been able to tailor the workshop schedule, reunion events, and communication, to fit the needs of the participants and manage the project better to achieve their desired outcomes. The results so far have shown that participants felt they enhanced their professional networks, and over 90% had maintained contact with other ASCENT participants six months after the workshop. Participants also reported to have gained knowledge and resources for women scientists and had fewer career obstacles six months after ASCENT. ASCENT organizers will share lessons learned throughout the process and some examples of best practices they have discovered. The assessment design, and most recent results from all three workshop cohorts will also be presented.

  8. The effect of accretion environment at large radius on hot accretion flows

    NASA Astrophysics Data System (ADS)

    Yang, Xiao-Hong; Bu, De-Fu

    2018-05-01

    We study the effects of accretion environment (gas density, temperature, and angular momentum) at large radii (˜10 pc) on luminosity of hot accretion flows. The radiative feedback effects from the accretion flow on the accretion environment are also self-consistently taken into account. We find that the slowly rotating flows at large radii can significantly deviate from Bondi accretion when radiation heating and cooling are considered. We further find that when the temperature of environment gas is low (e.g. T = 2 × 107 K), the luminosity of hot accretion flows is high. When the temperature of gas is high (e.g. T ≥ 4 × 107 K), the luminosity of hot accretion flow significantly deceases. The environment gas density can also significantly influence the luminosity of accretion flows. When density is higher than ˜4 × 10-22 g cm-3 and temperature is lower than 2 × 107 K, hot accretion flow with luminosity lower than 2 per cent LEdd is not present. Therefore, the parsec-scale environment density and temperature are two important parameters to determine the luminosity. The results are also useful for the subgrid models adopted by the cosmological simulations.

  9. Dynamic modeling and ascent flight control of Ares-I Crew Launch Vehicle

    NASA Astrophysics Data System (ADS)

    Du, Wei

    stability under mal-function of the roll control system. The roll motion of the Ares-I Crew Launch Vehicle under nominal flight conditions is actively stabilized by its roll control system employing thrusters. This dissertation describes the ascent flight control design problem of Ares-I in the event of disabled or failed roll control. A simple pitch/yaw control logic is developed for such a technically challenging problem by exploiting the inherent versatility of a quaternion-based attitude control system. The proposed scheme requires only the desired inertial attitude quaternion to be re-computed using the actual uncontrolled roll angle information to achieve an ascent flight trajectory identical to the nominal flight case with active roll control. Another approach that utilizes a simple adjustment of the proportional-derivative gains of the quaternion-based flight control system without active roll control is also presented. This approach doesn't require the re-computation of desired inertial attitude quaternion. A linear stability criterion is developed for proper adjustments of attitude and rate gains. The linear stability analysis results are validated by nonlinear simulations of the ascent flight phase. However, the first approach, requiring a simple modification of the desired attitude quaternion, is recommended for the Ares-I as well as other launch vehicles in the event of no active roll control. Finally, the method derived to stabilize a large flexible launch vehicle in the event of uncontrolled roll drift is generalized as a modified attitude quaternion feedback law. It is used to stabilize an axisymmetric rigid body by two independent control torques.

  10. To accrete or not accrete, that is the question

    USGS Publications Warehouse

    von Huene, Roland E.

    1986-01-01

    Along modern convergent margins tectonic processes span a spectrum from accretion to erosion. The process of accretion is generally recognized because it leaves a geologic record, whereas the process of erosion is generally hypothetical because it produces a geologic hiatus. Major conditions that determine the dominance of accretion or erosion at modern convergent margins are: 1) rate and direction of plate convergence, 2) sediment supply and type in the trench, and 3) topography of the subducting ocean floor. Most change in structure has been ascribed to plate motion, but both erosion and accretion are observed along the same convergence margin. Thus sediment supply and topography are probably of equivalent importance to plate motion because both erosion and accretion are observed under constant conditions of plate convergence. The dominance of accretion or erosion at a margin varies with the thickness of trench sediment. In a sediment flooded trench, the proportions of subducted and accreted sediment are commonly established by the position of a decollement along a weak horizon in the sediment section. Thus, the vertical variation of sediment strength and the distribution of horizontal stress are important factors. Once deformation begins, the original sediment strength is decreased by sediment remolding and where sediment thickens rapidly, increases in pore fluid pressure can be pronounced. In sediment-starved trenches, where the relief of the subducting ocean floor is not smoothed over, the front of the margin must respond to the topography subducted as well as that accreted. The hypothesized erosion by the drag of positive features against the underside of the upper plate (a high stress environment) may alternate with erosion due to the collapse of a margin front into voids such as graben (a low stress environment). ?? 1986 Ferdinand Enke Verlag Stuttgart.

  11. The effects of different rates of ascent on the incidence of altitude decompression sickness

    NASA Technical Reports Server (NTRS)

    Kumar, K. V.; Waligora, James M.

    1989-01-01

    The effect of different rates of ascent on the incidence of altitude decompression sickness (DCS) was analyzed by a retrospective study on 14,123 man-flights involving direct ascent up to 38,000 ft altitude. The data were classified on the basis of altitude attained, denitrogenation at ground level, duration of stay at altitude, rest or exercise while at altitude, frequency of exercise at altitude, and ascent rates. This database was further divided on the basis of ascent rates into different groups from 1000 ft/min up to 53,000 ft/min. The database was analyzed using multiple correlation and regression methods, and the results of the analysis reveal that ascent rates influence the incidence of DCS in combination with the various factors mentioned above. Rate of ascent was not a significant predictor of DCS and showed a low, but significant multiple correlation (R=0.31) with the above factors. Further, the effects of rates below 2500 ft/min are significantly different from that of rates above 2500 ft/min on the incidence of symptoms (P=0.03) and forced descent (P=0.01). At rates above 2500 ft/min and up to 53,000 ft/min, the effects of ascent rates are not significantly different (P greater than 0.05) in the population examined while the effects of rates below 2500 ft/min are not clear.

  12. Are Phobos and Deimos the result of a giant impact?

    NASA Astrophysics Data System (ADS)

    Craddock, Robert A.

    2011-02-01

    Despite many efforts an adequate theory describing the origin of Phobos and Deimos has not been realized. In recent years a number of separate observations suggest the possibility that the martian satellites may have been the result of giant impact. Similar to the Earth-Moon system, Mars has too much angular momentum. A planetesimal with 0.02 Mars masses must have collided with that planet early in its history in order for Mars to spin at its current rate (Dones, L., Tremaine, S. [1993]. Science 259, 350-354). Although subject to considerable error, current crater-scaling laws and an analysis of the largest known impact basins on the martian surface suggest that this planetesimal could have formed either the proposed 10,600 by 8500-km-diameter Borealis basin, the 4970-km-diameter Elysium basin, the 4500-km-diameter Daedalia basin or, alternatively, some other basin that is no longer identifiable. It is also probable that this object impacted Mars at a velocity great enough to vaporize rock (>7 km/s), which is necessary to place large amounts of material into orbit. If material vaporized from the collision with the Mars-spinning planetesimal were placed into orbit, an accretion disk would have resulted. It is possible that as material condensed and dissipated beyond the Roche limit forming small, low-mass satellites due to gravity instabilities within the disk. Once the accretion disk dissipated, tidal forces and libration would have pulled these satellites back down toward the martian surface. In this scenario, Phobos and Deimos would have been among the first two satellites to form, and Deimos the only satellite formed—and preserved—beyond synchronous rotation. The low mass of Phobos and Deimos is explained by the possibility that they are composed of loosely aggregated material from the accretion disk, which also implies that they do not contain any volatile elements. Their orbital eccentricity and inclination, which are the most difficult parameters to

  13. The Origin Of Phobos And Deimos By A Giant Impact

    NASA Astrophysics Data System (ADS)

    Craddock, R. A.

    2011-10-01

    Despite many efforts an adequate theory describing the origin of Phobos and Deimos has not been realized. In recent years a number of separate observations suggest the possibility that the Martian satellites may have been the result of giant impact [1]. Similar to the Earth-Moon system, Mars has too much angular momentum. A planetesimal with 0.02 Mars masses must have collided with that planet early in its history in order for Mars to spin at its current rate [2]. Although subject to considerable error, current crater scaling laws and an analysis of the largest known impact basins on the Martian surface suggest that this planetesimal could have formed either the proposed 10,600 by 8,500-kmdiameter Borealis basin, the 4,970-km-diameter Elysium basin, the 4,500-km-diameter Daedalia basin or, alternatively, some other basin that is no longer identifiable. It is also probable that this object impacted Mars at a velocity great enough to vaporize rock (>7 km/s), which is necessary to place large amounts of material into orbit. If material vaporized from the collision with the Mars-spinning planetesimal were placed into orbit, an accretion disk would have resulted. It is possible that as material condensed and dissipated beyond the Roche limit forming small, low-mass satellites due to gravity instabilities within the disk. Once the accretion disk dissipated, tidal forces and libration would have pulled these satellites back down toward the Martian surface. In this scenario, Phobos and Deimos would have been among the first two satellites to form, and Deimos the only satellite formed--and preserved-- beyond synchronous rotation. The low mass of Phobos and Deimos is explained by the possibility that they are composed of loosely aggregated material from the accretion disk, which also implies that they do not contain any volatile elements. Their orbital eccentricity and inclination, which are the most difficult parameters to explain easily with the various capture scenarios

  14. Magnetically gated accretion in an accreting ‘non-magnetic’ white dwarf

    NASA Astrophysics Data System (ADS)

    Scaringi, S.; Maccarone, T. J.; D’Angelo, C.; Knigge, C.; Groot, P. J.

    2017-12-01

    White dwarfs are often found in binary systems with orbital periods ranging from tens of minutes to hours in which they can accrete gas from their companion stars. In about 15 per cent of these binaries, the magnetic field of the white dwarf is strong enough (at 106 gauss or more) to channel the accreted matter along field lines onto the magnetic poles. The remaining systems are referred to as ‘non-magnetic’, because until now there has been no evidence that they have a magnetic field that is strong enough to affect the accretion dynamics. Here we report an analysis of archival optical observations of the ‘non-magnetic’ accreting white dwarf in the binary system MV Lyrae, whose light curve displays quasi-periodic bursts of about 30 minutes duration roughly every 2 hours. The timescale and amplitude of these bursts indicate the presence of an unstable, magnetically regulated accretion mode, which in turn implies the existence of magnetically gated accretion, in which disk material builds up around the magnetospheric boundary (at the co-rotation radius) and then accretes onto the white dwarf, producing bursts powered by the release of gravitational potential energy. We infer a surface magnetic field strength for the white dwarf in MV Lyrae of between 2 × 104 gauss and 1 × 105 gauss, too low to be detectable by other current methods. Our discovery provides a new way of studying the strength and evolution of magnetic fields in accreting white dwarfs and extends the connections between accretion onto white dwarfs, young stellar objects and neutron stars, for which similar magnetically gated accretion cycles have been identified.

  15. Accreting CO material onto ONe white dwarfs towards accretion-induced collapse

    NASA Astrophysics Data System (ADS)

    Wu, Cheng-Yuan; Wang, Bo

    2018-03-01

    The final outcomes of accreting ONe white dwarfs (ONe WDs) have been studied for several decades, but there are still some issues that are not resolved. Recently, some studies suggested that the deflagration of oxygen would occur for accreting ONe WDs with Chandrasekhar masses. In this paper, we aim to investigate whether ONe WDs can experience accretion-induced collapse (AIC) or explosions when their masses approach the Chandrasekhar limit. Employing the stellar evolution code Modules for Experiments in Stellar Astrophysics (MESA), we simulate the long-term evolution of ONe WDs with accreting CO material. The ONe WDs undergo weak multicycle carbon flashes during the mass-accretion process, leading to mass increase of the WDs. We found that different initial WD masses and mass-accretion rates influence the evolution of central density and temperature. However, the central temperature cannot reach the explosive oxygen ignition temperature due to neutrino cooling. This work implies that the final outcome of accreting ONe WDs is electron-capture induced collapse rather than thermonuclear explosion.

  16. Measuring the speed of magma ascent during explosive eruptions of Kilauea, Hawaii

    NASA Astrophysics Data System (ADS)

    Ferguson, D. J.; Ruprecht, P.; Plank, T. A.; Hauri, E. H.; Gonnermann, H. M.; Houghton, B. F.; Swanson, D. A.

    2014-12-01

    The size and intensity of volcanic eruptions is controlled by a combination of the physical properties of magmas and the conditions of magma ascent. At basaltic volcanoes, where relatively fluid magmas are erupted, sustained explosive eruptions vary widely in style, from Hawaiian fountains erupted 10s to 100s of meter high to large Plinian type events, involving >20 km high eruption plumes. Decompression of magmas leads to volatile saturation and bubble growth, however it remains disputed how the dynamics of shallow ascent and degassing might control this disparate eruptive behaviour, or whether factors such as the initial volatile content exert the primary control on eruption style. A key issue is that the physical conditions of magma ascent, which may significantly impact eruptive dynamics, remain largely unconstrained by observational data. Here we quantify two primary variables - decompression rates and volatile contents - for magmas from three contrasting eruptions of Kīlauea volcano, Hawaii, using microanalysis and modelling of volatile diffusion along small melt tubes or embayments found in olivine crystals carried by the ascending magmas. During ascent decreasing solubility causes dissolved volatiles to diffuse along the embayment towards growing bubbles at the crystal edge. By modelling the diffusion of H2O, CO2 and S we obtain decompression rates, and indirectly ascent velocities, for the rising magma. For Hawaiian style fountaining events we obtain ascent rates of 0.05-0.07 MPa s-1 (~1 m s-1), whereas for a more intense subplinian eruption we obtain a notably faster rate of 0.29 MPa s-1 (>10m s-1). The timescales of melt transport from the storage region during these eruptions varied from around 3 to 40 minutes. We find no link between pre-eruptive volatile contents and eruption intensity, rather our results suggest that the eventual size of sustained explosive basaltic eruptions is likely governed by factors affecting the ascent velocity of melts in

  17. Numerical simulation of plagioclase rim growth during magma ascent at Bezymianny Volcano, Kamchatka

    NASA Astrophysics Data System (ADS)

    Gorokhova, N. V.; Melnik, O. E.; Plechov, P. Yu.; Shcherbakov, V. D.

    2013-08-01

    Slow CaAl-NaSi interdiffusion in plagioclase crystals preserves chemical zoning of plagioclase in detail, which, along with strong dependence of anorthite content in plagioclase on melt composition, pressure, and temperature, make this mineral an important source of information on magma processes. A numerical model of zoned crystal growth is developed in the paper. The model is based on equations of multicomponent diffusion with diagonal cross-component diffusion terms and accounts for mass conservation on the melt-crystal interface and growth rate controlled by undercooling. The model is applied to the data of plagioclase rim zoning from several recent Bezymianny Volcano (Kamchatka) eruptions. We show that an equilibrium growth model cannot explain crystallization of naturally observed plagioclase during magma ascent. The developed non-equilibrium model reproduced natural plagioclase zoning and allowed magma ascent rates to be constrained. Matching of natural and simulated zoning suggests ascent from 100 to 50 MPa during 15-20 days. Magma ascent rate from 50 MPa to the surface varies from eruption to eruption: plagioclase zoning from the December 2006 eruption suggests ascent to the surface in less than 1 day, whereas plagioclase zoning from March 2000 and May 2007 eruptions are better explained by magma ascent over periods of more than 30 days). Based on comparison of diffusion coefficients for individual elements a mechanism of atomic diffusion during plagioclase crystallization is proposed.

  18. Magmatic Ascent and Eruption Processes on Mercury

    NASA Astrophysics Data System (ADS)

    Head, J. W.; Wilson, L.

    2018-05-01

    MESSENGER volcanic landform data and information on crustal composition allow us to model the generation, ascent, and eruption of magma; Mercury explosive and effusive eruption processes differ significantly from other terrestrial planetary bodies.

  19. Degassing during quiescence as a trigger of magma ascent and volcanic eruptions

    PubMed Central

    Girona, Társilo; Costa, Fidel; Schubert, Gerald

    2015-01-01

    Understanding the mechanisms that control the start-up of volcanic unrest is crucial to improve the forecasting of eruptions at active volcanoes. Among the most active volcanoes in the world are the so-called persistently degassing ones (e.g., Etna, Italy; Merapi, Indonesia), which emit massive amounts of gas during quiescence (several kilotonnes per day) and erupt every few months or years. The hyperactivity of these volcanoes results from frequent pressurizations of the shallow magma plumbing system, which in most cases are thought to occur by the ascent of magma from deep to shallow reservoirs. However, the driving force that causes magma ascent from depth remains unknown. Here we demonstrate that magma ascent can be triggered by the passive release of gas during quiescence, which induces the opening of pathways connecting deep and shallow magma reservoirs. This top-down mechanism for volcanic eruptions contrasts with the more common bottom-up mechanisms in which magma ascent is only driven by processes occurring at depth. A cause-effect relationship between passive degassing and magma ascent can explain the fact that repose times are typically much longer than unrest times preceding eruptions, and may account for the so frequent unrest episodes of persistently degassing volcanoes. PMID:26666396

  20. Degassing during quiescence as a trigger of magma ascent and volcanic eruptions.

    PubMed

    Girona, Társilo; Costa, Fidel; Schubert, Gerald

    2015-12-15

    Understanding the mechanisms that control the start-up of volcanic unrest is crucial to improve the forecasting of eruptions at active volcanoes. Among the most active volcanoes in the world are the so-called persistently degassing ones (e.g., Etna, Italy; Merapi, Indonesia), which emit massive amounts of gas during quiescence (several kilotonnes per day) and erupt every few months or years. The hyperactivity of these volcanoes results from frequent pressurizations of the shallow magma plumbing system, which in most cases are thought to occur by the ascent of magma from deep to shallow reservoirs. However, the driving force that causes magma ascent from depth remains unknown. Here we demonstrate that magma ascent can be triggered by the passive release of gas during quiescence, which induces the opening of pathways connecting deep and shallow magma reservoirs. This top-down mechanism for volcanic eruptions contrasts with the more common bottom-up mechanisms in which magma ascent is only driven by processes occurring at depth. A cause-effect relationship between passive degassing and magma ascent can explain the fact that repose times are typically much longer than unrest times preceding eruptions, and may account for the so frequent unrest episodes of persistently degassing volcanoes.

  1. Ascent Rates of Rhyolitic Magma During the Opening Stages of Explosive Caldera-Forming Eruptions

    NASA Astrophysics Data System (ADS)

    Myers, M.; Wallace, P. J.; Wilson, C. J. N.; Watkins, J. M.; Liu, Y.; Morgan, D. J.

    2016-12-01

    We investigate the timescales of rhyolitic magma ascent for three supereruptions that show contrasting eruptive behavior at eruption onset: (1) the Bishop Tuff, CA where early fallout graded directly into climactic eruption, (2) the Oruanui eruption, Taupo NZ, which experienced a significant time break between the initial fallout and subsequent activity and (3) the Huckleberry Ridge, Yellowstone where initial activity was episodic, with eruptive pauses totaling days to weeks. During ascent, decompression causes volatile exsolution from the host melt, creating H2O and CO2 gradients in reentrants (REs; unsealed inclusions) that can be modeled to estimate ascent timescales1,2,3. Using a code1 refined to include an error minimization function, we present modeled ascent rates for REs from Huckleberry Ridge (n=10), Bishop (n=14), and Oruanui (n=4), measured using FTIR (20 μm resolution, 4-15 points per RE). Best-fit profiles for the Bishop REs give ascent rates of 0.6-30 m/s, which overlap with those of the Huckleberry (0.3-5.5 m/s), but extend to higher values. Although ascent rate and initial eruptive behavior are somewhat decoupled, there is an increase in the number of faster ascent rates and greater starting depths with higher stratigraphic height in the Huckleberry Ridge and Bishop fall deposits. Preliminary work on Oruanui REs indicates rates of 0.15-2.0 m/s, which overlie the lower end of the Bishop and Huckleberry REs, in agreement with previous data1. Overall, there is significant overlap between the three datasets (average 4±7 m/s). Our calculated ascent rates fall towards the lower end of ascent rates that have been estimated (5-40 m/s4) using theoretical and numerical modeling of conduit flow for Plinian rhyolitic eruptions below the fragmentation depth. 1 Liu Y et al. 2007: J Geophys Res 112, B06204; 2 Humphreys MCS et al. 2008: Earth Planet Sci Lett 270, 25; 3 Lloyd et al., 2014: J Volcanol Geotherm Res 283, 1; 4Rutherford MJ 2008: Rev Mineral Geochem 69

  2. Evolution of the luminosity function of quasar accretion disks

    NASA Technical Reports Server (NTRS)

    Caditz, David M.; Petrosian, Vahe; Wandel, Amri

    1991-01-01

    Using an accretion-disk model, accretion disk luminosities are calculated for a grid of black hole masses and accretion rates. It is shown that, as the black-hole mass increases with time, the monochromatic luminosity at a given frequency first increases and then decreases rapidly as this frequency is crossed by the Wien cutoff. The upper limit on the monochromatic luminosity, which is characteristic for a given epoch, constrains the evolution of quasar luminosities and determines the evolultion of the quasar luminosity function.

  3. Independent Orbiter Assessment (IOA): Analysis of the ascent thrust vector control actuator subsystem

    NASA Technical Reports Server (NTRS)

    Wilson, R. E.; Riccio, J. R.

    1986-01-01

    The results of the Independent Orbiter Assessment (IOA) of the Failure Modes and Effects Analysis (FMEA) and Critical Items List (CIL) are presented. The IOA approach features a top-down analysis of the hardware to determine failure modes, criticality, and potential critical items. To preserve independence, this analysis was accomplished without reliance upon the results contained within the NASA FMEA/CIL documentation. The independent analysis results for the Ascent Thrust Vector Control (ATVC) Actuator hardware are documented. The function of the Ascent Thrust Vector Control Actuators (ATVC) is to gimbal the main engines to provide for attitude and flight path control during ascent. During first stage flight, the SRB nozzles provide nearly all the steering. After SRB separation, the Orbiter is steered by gimbaling of its main engines. There are six electrohydraulic servoactuators, one pitch and one yaw for each of the three main engines. Each servoactuator is composed of four electrohydraulic servovalve assemblies, one second stage power spool valve assembly, one primary piston assembly and a switching valve. Each level of hardware was evaluated and analyzed for possible failure modes and effects. Criticality was assigned based upon the severity of the effect for each failure mode. Critical failures resulting in loss of ATVC were mainly due to loss of hydraulic fluid, fluid contamination and mechanical failures.

  4. Chemistry in "The Ascent of Man."

    ERIC Educational Resources Information Center

    Hostettler, John D.; Brooks, Kenneth

    1980-01-01

    Describes "The Ascent of Man," a course emphasizing science and human values. Detailed are some chemical topics covered in the course, and how these topics are used in other traditional chemistry courses. Topics discussed include alchemy, the chemical revolution, steam engines, the Manhattan project, and several bioethical problems. (CS)

  5. Outward Migration of Giant Planets in Orbital Resonance

    NASA Astrophysics Data System (ADS)

    D'Angelo, G.; Marzari, F.

    2013-05-01

    A pair of giant planets interacting with a gaseous disk may be subject to convergent orbital migration and become locked into a mean motion resonance. If the orbits are close enough, the tidal gaps produced by the planets in the disk may overlap. This represents a necessary condition to activate the outward migration of the pair. However, a number of other conditions must also be realized in order for this mechanism to operate. We have studied how disk properties, such as turbulence viscosity, temperature, surface density gradient, mass, and age, may affect the outcome of the outward migration process. We have also investigated the implications on this mechanism of the planets' gas accretion. If the pair resembles Jupiter and Saturn, the 3:2 orbital resonance may drive them outward until they reach stalling radii for migration, which are within ~10 AU of the star for disks representative of the early proto-solar nebula. However, planet post-formation conditions in the disk indicate that such planets become typically locked in the 1:2 orbital resonance, which does not lead to outward migration. Planet growth via gas accretion tends to alter the planets' mass-ratio and/or the disk accretion rate toward the star, reducing or inhibiting outward migration. Support from NASA Outer Planets Research Program and NASA Origins of Solar Systems Program is gratefully acknowledged.

  6. A Gas-Poor Planetesimal Feeding Model for the Formation of Giant Planet Satellite Systems: Consequences for the Atmosphere of Titan

    NASA Technical Reports Server (NTRS)

    Estrada, P. R.; Mosqueira, I.

    2005-01-01

    Given our presently inadequate understanding of the turbulent state of the solar and planetary nebulae, we believe the way to make progress in satellite formation is to consider two end member models that avoid over-reliance on specific choices of the turbulence (alpha), which is essentially a free parameter. The first end member model postulates turbulence decay once giant planet accretion ends. If so, Keplerian disks must eventually pass through the quiescent phases, so that the survival of satellites (and planets) ultimately hinges on gap-opening. In this scenario, the criterion for gap-opening itself sets the value for the gas surface density of the satellite disk.

  7. Ascent trajectory optimization for stratospheric airship with thermal effects

    NASA Astrophysics Data System (ADS)

    Guo, Xiao; Zhu, Ming

    2013-09-01

    Ascent trajectory optimization with thermal effects is addressed for a stratospheric airship. Basic thermal characteristics of the stratospheric airship are introduced. Besides, the airship’s equations of motion are constructed by including the factors about aerodynamic force, added mass and wind profiles which are developed based on horizontal-wind model. For both minimum-time and minimum-energy flights during ascent, the trajectory optimization problem is described with the path and terminal constraints in different scenarios and then, is converted into a parameter optimization problem by a direct collocation method. Sparse Nonlinear OPTimizer(SNOPT) is employed as a nonlinear programming solver and two scenarios are adopted. The solutions obtained illustrate that the trajectories are greatly affected by the thermal behaviors which prolong the daytime minimum-time flights of about 20.8% compared with that of nighttime in scenario 1 and of about 10.5% in scenario 2. And there is the same trend for minimum-energy flights. For the energy consumption of minimum-time flights, 6% decrease is abstained in scenario 1 and 5% decrease in scenario 2. However, a few energy consumption reduction is achieved for minimum-energy flights. Solar radiation is the principal component and the natural wind also affects the thermal behaviors of stratospheric airship during ascent. The relationship between take-off time and performance of airship during ascent is discussed. it is found that the take-off time at dusk is best choice for stratospheric airship. And in addition, for saving energy, airship prefers to fly downwind.

  8. Novel knee joint mechanism of transfemoral prosthesis for stair ascent.

    PubMed

    Inoue, Koh; Wada, Takahiro; Harada, Ryuchi; Tachiwana, Shinichi

    2013-06-01

    The stability of a transfemoral prosthesis when walking on flat ground has been established by recent advances in knee joint mechanisms and their control methods. It is, however, difficult for users of a transfemoral prosthesis to ascend stairs. This difficulty is mainly due to insufficient generation of extension moment around the knee joint of the prosthesis to lift the body to the next step on the staircase and prevent any unexpected flexion of the knee joint in the stance phase. Only a prosthesis with an actuator has facilitated stair ascent using a step-over-step gait (1 foot is placed per step). However, its use has issues associated with the durability, cost, maintenance, and usage environment. Therefore, the purpose of this research is to develop a novel knee joint mechanism for a prosthesis that generates an extension moment around the knee joint in the stance phase during stair ascent, without the use of any actuators. The proposed mechanism is based on the knowledge that the ground reaction force increases during the stance phase when the knee flexion occurs. Stair ascent experiments with the prosthesis showed that the proposed prosthesis can realize stair ascent without any undesirable knee flexion. In addition, the prosthesis is able to generate a positive knee joint moment power in the stance phase even without any power source.

  9. Apollo 16, LM-11 ascent propulsion system final flight evaluation

    NASA Technical Reports Server (NTRS)

    Griffin, W. G.

    1974-01-01

    The duty cycle for the LM-11 APS consisted of two firings, an ascent stage liftoff from the lunar surface, and the terminal phase initiation (TPI) burn. APS performance for the first firing was evaluated and found to be satisfactory. No propulsion data were received from the second APS burn; however, all indications were that the burn was nominal. Engine ignition for the APS lunar liftoff burn occured at the Apollo elapsed time (AET) of 175:31:47.9 (hours:minutes:seconds). Burn duration was 427.7 seconds.

  10. ECCENTRICITY EVOLUTION THROUGH ACCRETION OF PROTOPLANETS

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

    Matsumoto, Yuji; Nagasawa, Makiko; Ida, Shigeru, E-mail: yuji.matsumoto@nao.ac.jp, E-mail: nagasawa.m.ad@m.titech.ac.jp, E-mail: ida@elsi.jp

    2015-09-10

    Most super-Earths detected by the radial velocity (RV) method have significantly smaller eccentricities than the eccentricities corresponding to velocity dispersion equal to their surface escape velocity (“escape eccentricities”). If orbital instability followed by giant impacts among protoplanets that have migrated from outer regions is considered, it is usually considered that eccentricities of the merged bodies become comparable to those of orbital crossing bodies, which are excited up to their escape eccentricities by close scattering. However, the eccentricity evolution in the in situ accretion model has not been studied in detail. Here, we investigate the eccentricity evolution through N-body simulations. Wemore » have found that the merged planets tend to have much smaller eccentricities than escape eccentricities due to very efficient collision damping. If the protoplanet orbits are initially well separated and their eccentricities are securely increased, an inner protoplanet collides at its apocenter with an outer protoplanet at its pericenter. The eccentricity of the merged body is the smallest for such configurations. Orbital inclinations are also damped by this mechanism and planets tend to share a same orbital plane, which is consistent with Kepler data. Such efficient collision damping is not found when we start calculations from densely packed orbits of the protoplanets. If the protoplanets are initially in the mean-motion resonances, which corresponds to well separated orbits, the in situ accretion model well reproduces the features of eccentricities and inclinations of multiple super-Earths/Earth systems discovered by RV and Kepler surveys.« less

  11. Seismometer reading from impact made by Lunar Module ascent stage

    NASA Technical Reports Server (NTRS)

    1969-01-01

    The seismometer reading from the impact made by the Lunar Module ascent stage when it struck the lunar surface. The impact was registered by the Passive Seismic Experiment Package (PSEP) which was deployed on the Moon by the Apollo 12 astronauts. The Lunar module's ascent stage was jettisoned and sent toward impact on the Moon after Astronauts Charles Conrad Jr. and Alan L. Bean returned to lunar orbit and rejoined Astronaut Richard F. Gordon Jr., in the Command/Service Modules.

  12. Sensitivity analysis of the space shuttle to ascent wind profiles

    NASA Technical Reports Server (NTRS)

    Smith, O. E.; Austin, L. D., Jr.

    1982-01-01

    A parametric sensitivity analysis of the space shuttle ascent flight to the wind profile is presented. Engineering systems parameters are obtained by flight simulations using wind profile models and samples of detailed (Jimsphere) wind profile measurements. The wind models used are the synthetic vector wind model, with and without the design gust, and a model of the vector wind change with respect to time. From these comparison analyses an insight is gained on the contribution of winds to ascent subsystems flight parameters.

  13. Accretion of Rocky Planets by Hot Jupiters

    NASA Astrophysics Data System (ADS)

    Ketchum, Jacob A.; Adams, Fred C.; Bloch, Anthony M.

    2011-11-01

    The observed population of Hot Jupiters displays a stunning variety of physical properties, including a wide range of densities and core sizes for a given planetary mass. Motivated by the observational sample, this Letter studies the accretion of rocky planets by Hot Jupiters, after the Jovian planets have finished their principal migration epoch and become parked in ~4 day orbits. In this scenario, rocky planets form later and then migrate inward due to torques from the remaining circumstellar disk, which also damps the orbital eccentricity. This mechanism thus represents one possible channel for increasing the core masses and metallicities of Hot Jupiters. This Letter determines probabilities for the possible end states for the rocky planet: collisions with the Jovian planets, accretion onto the star, ejection from the system, and long-term survival of both planets. These probabilities depend on the mass of the Jovian planet and its starting orbital eccentricity, as well as the eccentricity damping rate for the rocky planet. Since these systems are highly chaotic, a large ensemble (N ~ 103) of simulations with effectively equivalent starting conditions is required. Planetary collisions are common when the eccentricity damping rate is sufficiently low, but are rare otherwise. For systems that experience planetary collisions, this work determines the distributions of impact velocities—both speeds and impact parameters—for the collisions. These velocity distributions help determine the consequences of the impacts, e.g., where energy and heavy elements are deposited within the giant planets.

  14. 1FGL J1417.7-4407: A Likely Gamma-Ray Bright Binary with A Massive Neutron Star and A Giant Secondary

    NASA Technical Reports Server (NTRS)

    Strader, Jay; Chomiuk, Laura; Cheung, C. C.; Sand, David J.; Donato, Davide; Corbet, Robin H. D.; Koeppe, Dana; Edwards, Philip G.; Stevens, Jamie; Petrov, Leonid

    2015-01-01

    We present multiwavelength observations of the persistent Fermi-Large Area Telescope unidentified gamma-ray source 1FGL J1417.7-4407, showing it is likely to be associated with a newly discovered X-ray binary containing a massive neutron star (nearly 2 solar mass) and a approximately 0.35 solar mass giant secondary with a 5.4 day period. SOAR optical spectroscopy at a range of orbital phases reveals variable double-peaked H alpha emission, consistent with the presence of an accretion disk. The lack of radio emission and evidence for a disk suggests the gamma-ray emission is unlikely to originate in a pulsar magnetosphere, but could instead be associated with a pulsar wind, relativistic jet, or could be due to synchrotron self-Compton at the disk-magnetosphere boundary. Assuming a wind or jet, the high ratio of gamma- ray to X-ray luminosity (approximately 20) suggests efficient production of gamma-rays, perhaps due to the giant companion. The system appears to be a low-mass X-ray binary that has not yet completed the pulsar recycling process. This system is a good candidate to monitor for a future transition between accretion-powered and rotational-powered states, but in the context of a giant secondary.

  15. Rocky core solubility in Jupiter and giant exoplanets.

    PubMed

    Wilson, Hugh F; Militzer, Burkhard

    2012-03-16

    Gas giants are believed to form by the accretion of hydrogen-helium gas around an initial protocore of rock and ice. The question of whether the rocky parts of the core dissolve into the fluid H-He layers following formation has significant implications for planetary structure and evolution. Here we use ab initio calculations to study rock solubility in fluid hydrogen, choosing MgO as a representative example of planetary rocky materials, and find MgO to be highly soluble in H for temperatures in excess of approximately 10,000 K, implying the potential for significant redistribution of rocky core material in Jupiter and larger exoplanets.

  16. Magma ascent and lava flow emplacement rates during the 2011 Axial Seamount eruption based on CO2 degassing

    NASA Astrophysics Data System (ADS)

    Jones, M. R.; Soule, S. A.; Gonnermann, H. M.; Le Roux, V.; Clague, D. A.

    2018-07-01

    Quantitative metrics for eruption rates at mid-ocean ridges (MORs) would improve our understanding of the structure and formation of the uppermost oceanic crust and would provide a means to link volcanic processes with the conditions of the underlying magmatic system. However, these metrics remain elusive because no MOR eruptions have been directly observed. The possibility of disequilibrium degassing in mid-ocean ridge basalts (MORB), due to high eruptive depressurization rates, makes the analysis of volatile concentrations in MORB glass a promising method for evaluating eruption rates. In this study, we estimate magma ascent and lava flow emplacement rates during the 2011 eruption of Axial Seamount based on numerical modeling of diffusion-controlled bubble growth and new measurements of dissolved volatiles, vesicularity, and vesicle size distributions in erupted basalts. This dataset provides a unique view of the variability in magma ascent (∼0.02-1.2 m/s) and lava flow rates (∼0.1-0.7 m/s) during a submarine MOR eruption based on 50 samples collected from a >10 km long fissure system and three individual lava flow lobes. Samples from the 2011 eruption display an unprecedented range in dissolved CO2 concentrations, nearly spanning the full range observed on the global MOR system. The variable vesicularity and dissolved CO2 concentrations in these samples can be explained by differences in the extent of degassing, dictated by flow lengths and velocities during both vertical ascent and horizontal flow along the seafloor. Our results document, for the first time, the variability in magma ascent rates during a submarine eruption (∼0.02-1.2 m/s), which spans the global range previously proposed based on CO2 degassing. The slowest ascent rates are associated with hummocky flows while faster ascent rates produce channelized sheet flows. This study corroborates degassing-based models for eruption rates using comparisons with independent methods and documents the

  17. Space Launch System Ascent Static Aerodynamic Database Development

    NASA Technical Reports Server (NTRS)

    Pinier, Jeremy T.; Bennett, David W.; Blevins, John A.; Erickson, Gary E.; Favaregh, Noah M.; Houlden, Heather P.; Tomek, William G.

    2014-01-01

    This paper describes the wind tunnel testing work and data analysis required to characterize the static aerodynamic environment of NASA's Space Launch System (SLS) ascent portion of flight. Scaled models of the SLS have been tested in transonic and supersonic wind tunnels to gather the high fidelity data that is used to build aerodynamic databases. A detailed description of the wind tunnel test that was conducted to produce the latest version of the database is presented, and a representative set of aerodynamic data is shown. The wind tunnel data quality remains very high, however some concerns with wall interference effects through transonic Mach numbers are also discussed. Post-processing and analysis of the wind tunnel dataset are crucial for the development of a formal ascent aerodynamics database.

  18. Acceleration of Cooling of Ice Giants by Condensation in Early Atmospheres

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

    Kurosaki, Kenji; Ikoma, Masahiro, E-mail: kurosaki.k@nagoya-u.jp, E-mail: ikoma@eps.s.u-tokyo.ac.jp

    The present infrared brightness of a planet originates partly from the accretion energy that the planet gained during its formation and hence provides important constraints to the planet formation process. A planet cools down from a hot initial state to the present state by losing energy through radiative emission from its atmosphere. Thus, the atmospheric properties affect the planetary cooling rate. Previous theories of giant planet cooling assume that the atmospheric composition is unchanged throughout the evolution. Planet formation theories, however, suggest that the atmospheres especially of ice giants are rich in heavy elements in the early stages. These heavy elementsmore » include condensable species such as H{sub 2}O, NH{sub 3}, and CH{sub 4}, which are expected to have a great impact on atmospheric temperature and thus on radiative emission through latent heat release. In this study we investigate the effect of such condensation on the planetary emission flux and quantify the impact on the cooling timescale. We then demonstrate that the latent heat of these species keeps the atmosphere hot and thus the emission flux high for billions of years, resulting in an acceleration of the cooling of ice giants. This sheds light on the long-standing problem that Uranus is much less bright than theoretically predicted and is different in brightness from Neptune in spite of the similarity in mass and radius. We also find that young ice giants with highly enriched atmospheres are much brighter in the mid-infrared than ice giants with non-enriched atmospheres. This provides important implications for future direct imaging of extrasolar ice giants.« less

  19. NanoSIMS results from olivine-hosted melt embayments: Magma ascent rate during explosive basaltic eruptions

    NASA Astrophysics Data System (ADS)

    Lloyd, Alexander S.; Ruprecht, Philipp; Hauri, Erik H.; Rose, William; Gonnermann, Helge M.; Plank, Terry

    2014-08-01

    pressure (> 145 MPa), with similar decompression rates to the single-stage model for the shallower stage. The magma ascent rates reported here are among the first for explosive basaltic eruptions and demonstrate the potential of the embayment method for quantifying magmatic timescales associated with eruptions of different vigor.

  20. Pebble-isolation mass: Scaling law and implications for the formation of super-Earths and gas giants

    NASA Astrophysics Data System (ADS)

    Bitsch, Bertram; Morbidelli, Alessandro; Johansen, Anders; Lega, Elena; Lambrechts, Michiel; Crida, Aurélien

    2018-04-01

    The growth of a planetary core by pebble accretion stops at the so-called pebble isolation mass, when the core generates a pressure bump that traps drifting pebbles outside its orbit. The value of the pebble isolation mass is crucial in determining the final planet mass. If the isolation mass is very low, gas accretion is protracted and the planet remains at a few Earth masses with a mainly solid composition. For higher values of the pebble isolation mass, the planet might be able to accrete gas from the protoplanetary disc and grow into a gas giant. Previous works have determined a scaling of the pebble isolation mass with cube of the disc aspect ratio. Here, we expand on previous measurements and explore the dependency of the pebble isolation mass on all relevant parameters of the protoplanetary disc. We use 3D hydrodynamical simulations to measure the pebble isolation mass and derive a simple scaling law that captures the dependence on the local disc structure and the turbulent viscosity parameter α. We find that small pebbles, coupled to the gas, with Stokes number τf < 0.005 can drift through the partial gap at pebble isolation mass. However, as the planetary mass increases, particles must be decreasingly smaller to penetrate the pressure bump. Turbulent diffusion of particles, however, can lead to an increase of the pebble isolation mass by a factor of two, depending on the strength of the background viscosity and on the pebble size. We finally explore the implications of the new scaling law of the pebble isolation mass on the formation of planetary systems by numerically integrating the growth and migration pathways of planets in evolving protoplanetary discs. Compared to models neglecting the dependence of the pebble isolation mass on the α-viscosity, our models including this effect result in higher core masses for giant planets. These higher core masses are more similar to the core masses of the giant planets in the solar system.

  1. The comparative effect of FUV, EUV and X-ray disc photoevaporation on gas giant separations

    NASA Astrophysics Data System (ADS)

    Jennings, Jeff; Ercolano, Barbara; Rosotti, Giovanni P.

    2018-04-01

    Gas giants' early (≲ 5 Myr) orbital evolution occurs in a disc losing mass in part to photoevaporation driven by high energy irradiance from the host star. This process may ultimately overcome viscous accretion to disperse the disc and halt migrating giants by starving their orbits of gas, imprinting on giant planet separations in evolved systems. Inversion of this distribution could then give insight into whether stellar FUV, EUV or X-ray flux dominates photoevaporation, constraining planet formation and disc evolution models. We use a 1D hydrodynamic code in population syntheses for gas giants undergoing Type II migration in a viscously evolving disc subject to either a primarily FUV, EUV or X-ray flux from a pre-solar T Tauri star. The photoevaporative mass loss profile's unique peak location and width in each energetic regime produces characteristic features in the distribution of giant separations: a severe dearth of ≲ 2 MJ planets interior to 5 AU in the FUV scenario, a sharp concentration of ≲ 3 MJ planets between ≈1.5 - 2 AU in the EUV case, and a relative abundance of ≈2 - 3.5 MJ giants interior to 0.5 AU in the X-ray model. These features do not resemble the observational sample of gas giants with mass constraints, though our results do show some weaker qualitative similarities. We thus assess how the differing photoevaporative profiles interact with migrating giants and address the effects of large model uncertainties as a step to better connect disc models with trends in the exoplanet population.

  2. The comparative effect of FUV, EUV and X-ray disc photoevaporation on gas giant separations

    NASA Astrophysics Data System (ADS)

    Jennings, Jeff; Ercolano, Barbara; Rosotti, Giovanni P.

    2018-07-01

    Gas giants' early (≲5 Myr) orbital evolution occurs in a disc losing mass in part to photoevaporation driven by high energy irradiance from the host star. This process may ultimately overcome viscous accretion to disperse the disc and halt migrating giants by starving their orbits of gas, imprinting on giant planet separations in evolved systems. Inversion of this distribution could then give insight into whether the stellar FUV, EUV or X-ray flux dominates photoevaporation, constraining planet formation and disc evolution models. We use a 1D hydrodynamic code in population syntheses for gas giants undergoing Type II migration in a viscously evolving disc subject to either a primarily FUV, EUV or X-ray flux from a pre-solar T Tauri star. The photoevaporative mass loss profile's unique peak location and width in each energetic regime produces characteristic features in the distribution of giant separations: a severe dearth of ≲2 MJ planets interior to 5 au in the FUV scenario, a sharp concentration of ≲3 MJ planets between ≈1.5-2 au in the EUV case and a relative abundance of ≈2-3.5 MJ giants interior to 0.5 au in the X-ray model. These features do not resemble the observational sample of gas giants with mass constraints, although our results do show some weaker qualitative similarities. We thus assess how the differing photoevaporative profiles interact with migrating giants and address the effects of large model uncertainties as a step to better connect disc models with trends in the exoplanet population.

  3. An empirical mass-loss law for Population II giants from the Spitzer-IRAC survey of Galactic globular clusters

    NASA Astrophysics Data System (ADS)

    Origlia, L.; Ferraro, F. R.; Fabbri, S.; Fusi Pecci, F.; Dalessandro, E.; Rich, R. M.; Valenti, E.

    2014-04-01

    Aims: The main aim of the present work is to derive an empirical mass-loss (ML) law for Population II stars in first and second ascent red giant branches. Methods: We used the Spitzer InfraRed Array Camera (IRAC) photometry obtained in the 3.6-8 μm range of a carefully chosen sample of 15 Galactic globular clusters spanning the entire metallicity range and sampling the vast zoology of horizontal branch (HB) morphologies. We complemented the IRAC photometry with near-infrared data to build suitable color-magnitude and color-color diagrams and identify mass-losing giant stars. Results: We find that while the majority of stars show colors typical of cool giants, some stars show an excess of mid-infrared light that is larger than expected from their photospheric emission and that is plausibly due to dust formation in mass flowing from them. For these stars, we estimate dust and total (gas + dust) ML rates and timescales. We finally calibrate an empirical ML law for Population II red and asymptotic giant branch stars with varying metallicity. We find that at a given red giant branch luminosity only a fraction of the stars are losing mass. From this, we conclude that ML is episodic and is active only a fraction of the time, which we define as the duty cycle. The fraction of mass-losing stars increases by increasing the stellar luminosity and metallicity. The ML rate, as estimated from reasonable assumptions for the gas-to-dust ratio and expansion velocity, depends on metallicity and slowly increases with decreasing metallicity. In contrast, the duty cycle increases with increasing metallicity, with the net result that total ML increases moderately with increasing metallicity, about 0.1 M⊙ every dex in [Fe/H]. For Population II asymptotic giant branch stars, we estimate a total ML of ≤0.1 M⊙, nearly constant with varying metallicity. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory

  4. Regulation of star formation in giant galaxies by precipitation, feedback and conduction.

    PubMed

    Voit, G M; Donahue, M; Bryan, G L; McDonald, M

    2015-03-12

    The Universe's largest galaxies reside at the centres of galaxy clusters and are embedded in hot gas that, if left undisturbed, would cool quickly and create many more new stars than are actually observed. Cooling can be regulated by feedback from accretion of cooling gas onto the central black hole, but requires an accretion rate finely tuned to the thermodynamic state of the hot gas. Theoretical models in which cold clouds precipitate out of the hot gas via thermal instability and accrete onto the black hole exhibit the necessary tuning. Recent observational evidence shows that the abundance of cold gas in the centres of clusters increases rapidly near the predicted threshold for instability. Here we report observations showing that this precipitation threshold extends over a large range in cluster radius, cluster mass and cosmic time. We incorporate the precipitation threshold into a framework of theoretical models for the thermodynamic state of hot gas in galaxy clusters. According to that framework, precipitation regulates star formation in some giant galaxies, while thermal conduction prevents star formation in others if it can compensate for radiative cooling and shut off precipitation.

  5. Determination of Magma Ascent Rates From D/H Fractionation in Olivine-Hosted Melt Inclusions

    NASA Astrophysics Data System (ADS)

    Gaetani, G. A.; Bucholz, C. E.; Le Roux, V.; Klein, F.; Ghiorso, M. S.; Wallace, P. J.; Sims, K. W. W.

    2016-12-01

    The depths at which magmas are stored and the rates at which they ascend to Earth's surface are important controls on the dynamics of volcanic eruptions. Eruptive style is influenced by the rate at which magma ascends from the reservoir to the surface through its effect on vapor bubble nucleation, growth, and coalescence. However, ascent rates are difficult to quantify because few accurate geospeedometers are appropriate for a process occurring on such short timescales. We developed a new approach to determining ascent rates on the basis of D/H fraction associated with diffusive H2O loss from olivine-hosted melt inclusions. The utility of this approach was demonstrated on olivine-hosted melt inclusions in a hyaloclastite recovered from within Dry Valley Drilling Project core 3 from Hut Point Peninsula, Antarctica. All of the melt inclusions are glassy and contain vapor bubbles. The volumes of melt inclusions and vapor bubbles were determined by X-ray microtomography, and the density of CO2 within each bubble was determined using Raman spectroscopy. Olivines were then polished to expose individual inclusions and analyzed for volatiles and dDVSMOW by secondary ion mass spectrometry. Total CO2 was reconstructed by summing CO2 in the included glass and vapor bubble. Entrapment pressures calculated on the basis of reconstructed CO2 and maximum H2O concentrations using the MagmaSat solubility model [1] indicate a depth of origin of 24 km - in good agreement with the seismically determined depth to the Moho beneath Ross Island [2]. Magma ascent rates were determined using a finite difference model for melt inclusion dehydration during magma ascent. The positive correlation between H2O and CO2 is consistent with diffusive loss during ascent, but does not provide direct information on magma ascent rate. In contrast, the slope of the negative correlation between H2O and dDVSMOW is a reflection of transport time and, therefore, ascent rate. If it is assumed that magmas did

  6. On the wind production from hot accretion flows with different accretion rates

    NASA Astrophysics Data System (ADS)

    Bu, De-Fu; Gan, Zhao-Ming

    2018-02-01

    We perform two-dimensional simulations to study how the wind strength changes with accretion rate. We take into account bremsstrahlung, synchrotron radiation and the Comptonization. We find that when the accretion rate is low, radiative cooling is not important, and the accretion flow is hot. For the hot accretion flow, wind is very strong. The mass flux of wind can be ˜ 50 per cent of the mass inflow rate. When the accretion rate increases to a value at which radiative cooling rate is roughly equal to or slightly larger than viscous heating rate, cold clumps can form around the equatorial plane. In this case, the gas pressure gradient force is small and wind is very weak. Our results may be useful for the sub-grid model of active galactic nuclear feedback study.

  7. FUV Emission from AGB Stars: Modeling Accretion Activity Associated with a Binary Companion

    NASA Technical Reports Server (NTRS)

    Stevens, Alyx Catherine; Sahai, Raghvendra

    2012-01-01

    It is widely believed that the late stages of evolution for Asymptotic Giant Branch (AGB) stars are influenced by the presence of binary companions. Unfortunately, there is a lack of direct observational evidence of binarity. However, more recently, strong indirect evidence comes from the discovery of UV emission in a subsample of these objects (fuvAGB stars). AGB stars are comparatively cool objects (< or =3000 K), thus their fluxes falls off drastically for wavelengths 3000 Angstroms and shorter. Therefore, ultraviolet observations offer an important, new technique for detecting the binary companions and/or associated accretion activity. We develop new models of UV emission from fuvAGB stars constrained by GALEX photometry and spectroscopy of these objects. We compare the GALEX UV grism spectra of the AGB M7 star EY Hya to predictions using the spectral synthesis code Cloudy, specifically investigating the ultraviolet wavelength range (1344-2831 Angstroms). We investigate models composed of contributions from a photoionized "hot spot" due to accretion activity around the companion, and "chromospheric" emission from collisionally ionized plasma, to fit the UV observations.

  8. Evolution of Space Shuttle Range Safety (RS) Ascent Flight Envelope Design

    NASA Technical Reports Server (NTRS)

    Brewer, Joan D.

    2011-01-01

    Ascent flight envelopes are trajectories that define the normal operating region of a space vehicle s position from liftoff until the end of powered flight. They fulfill part of the RS data requirements imposed by the Air Force s 45th Space Wing (45SW) on space vehicles launching from the Eastern Range (ER) in Florida. The 45SW is chartered to protect the public by minimizing risks associated with the inherent hazards of launching a vehicle into space. NASA s Space Shuttle program has launched 130+ manned missions over a 30 year period from the ER. Ascent envelopes were delivered for each of those missions. The 45SW envelope requirements have remained largely unchanged during this time. However, the methodology and design processes used to generate the envelopes have evolved over the years to support mission changes, maintain high data quality, and reduce costs. The evolution of the Shuttle envelope design has yielded lessons learned that can be applied to future endevours. There have been numerous Shuttle ascent design enhancements over the years that have caused the envelope methodology to evolve. One of these Shuttle improvements was the introduction of onboard flight software changes implemented to improve launch probability. This change impacted the preflight nominal ascent trajectory, which is a key element in the RS envelope design. While the early Shuttle nominal trajectories were designed preflight using a representative monthly mean wind, the new software changes involved designing a nominal ascent trajectory on launch day using real-time winds. Because the actual nominal trajectory position was not known until launch day, the envelope analysis had to be customized to account for this nominal trajectory variation in addition to the other envelope components.

  9. Observational diagnostics of accretion on young stars and brown dwarfs

    NASA Astrophysics Data System (ADS)

    Stelzer, Beate; Argiroffi, Costanza

    I present a summary of recent observational constraints on the accretion properties of young stars and brown dwarfs with focus on the high-energy emission. In their T Tauri phase young stars assemble a few percent of their mass by accretion from a disk. Various observational signatures of disks around pre-main sequence stars and the ensuing accretion process are found in the IR and optical regime: e.g. excess emission above the stellar photosphere, strong and broad emission lines, optical veiling. At high energies evidence for accretion is less obvious, and the X-ray emission from stars has historically been ascribed to magnetically confined coronal plasmas. While being true for the bulk of the emission, new insight obtained from XMM-Newton and Chandra observations has unveiled contributions from accretion and outflow processes to the X-ray emission from young stars. Their smaller siblings, the brown dwarfs, have been shown to undergo a T Tauri phase on the basis of optical/IR observations of disks and measurements of accretion rates. Most re-cently, first evidence was found for X-rays produced by accretion in a young brown dwarf, complementing the suspected analogy between stars and substellar objects.

  10. A study to evaluate STS heads-up ascent trajectory performance employing a minimum-Hamiltonian optimization strategy

    NASA Technical Reports Server (NTRS)

    Sinha, Sujit

    1988-01-01

    A study was conducted to evaluate the performance implications of a heads-up ascent flight design for the Space Transportation System, as compared to the current heads-down flight mode. The procedure involved the use of the Minimum Hamiltonian Ascent Shuttle Trajectory Evaluation Program, which is a three-degree-of-freedom moment balance simulation of shuttle ascent. A minimum-Hamiltonian optimization strategy was employed to maximize injection weight as a function of maximum dynamic pressure constraint and Solid Rocket Motor burnrate. Performance Reference Mission Four trajectory groundrules were used for consistency. The major conclusions are that for heads-up ascent and a mission nominal design maximum dynamic pressure value of 680 psf, the optimum solid motor burnrate is 0.394 ips, which produces a performance enhancement of 4293 lbm relative to the baseline heads-down ascent, with 0.368 ips burnrate solid motors and a 680 psf dynamic pressure constraint. However, no performance advantage exists for heads-up flight if the current Solid Rocket Motor target burnrate of 0.368 ips is used. The advantage of heads-up ascent flight employing the current burnrate is that Space Shuttle Main Engine throttling for dynamic pressure control is not necessary.

  11. A Gas-poor Planetesimal Feeding Model for the Formation of Giant Planet Satellite Systems: Disk Size and Formation Timescale

    NASA Astrophysics Data System (ADS)

    Estrada, P. R.; Mosqueira, I.

    2003-05-01

    Mosqueira and Estrada (2003a) argue that following giant planet accretion a largely quiescent circumplanetary disk may form with most of the mass inside a radius located outside, but perhaps close to, the centrifugal radius rc = RH/48, where the specific angular momentum of the collapsing giant planet gaseous envelope achieves centrifugal balance, and extending as far as the irregular satellites at RH/5 due to the high specific angular momentum of parcels of gas accreted from distances several times RH during the final stages of planetary growth (Lubow et al. 1999). Provided that allowances are made for the capture of Triton from heliocentric orbit, this picture fits well with the primordial satellite systems of all four giant planets. Because strong gas turbulence would smooth out the gas surface density of the disk, this description can only apply if the turbulence subsides as planetary accretion ceases. Although the viability of a hydrodynamic shear instability in Keplerian disks that can sustain significant post-accretion turbulence and drive evolution of the gas disk is in serious doubt (see Mosqueira et al. this conference), the possibility has not yet been totally ruled out. This leads us to consider gas-poor scenarios that might produce a close-in regular satellite system. To this end, we re-examine the ideas of Safronov et al. (1986) to see whether a gas-free (or nearly gas-free) model can be made consistent with the extent of the regular satellites of the giant planets. In this model, planetesimals containing most of the mass of solids (Mizuno et al. 1978; Weidenschilling 1997) that are de-coupled from the gas and whose dynamics must be followed independently are collisionally captured and form a swarm of circumplanetary objects lasting for perhaps ˜ 106 years. While such a swarm might occupy a significant fraction of the Hill radius of the planet, the small net angular momentum of the swarm might lead to the formation of close-in prograde satellites as

  12. A magnetic accretion switch in pre-cataclysmic binaries

    NASA Astrophysics Data System (ADS)

    Drake, Jeremy J.; Garraffo, Cecilia; Takei, Dai; Gaensicke, Boris

    2014-02-01

    We have investigated the mass accretion rate implied by published surface abundances of Si and C in the white dwarf component of the 3.62 h period pre-cataclysmic binary and planet host candidate QS Vir (DA+M2-4). Diffusion time-scales for gravitational settling imply dot{M} ˜ 10^{-16} M_{odot } yr-1 for the 1999 epoch of the observations, which is three orders of magnitude lower than measured from a 2006 XMM-Newton observation. This is the first time that large accretion rate variations have been seen in a detached pre-cataclysmic variable (pre-CV). A third body in a 14 yr eccentric orbit suggested in a recent eclipse timing study is too distant to perturb the central binary sufficiently to influence accretion. A hypothetical coronal mass ejection just prior to the XMM-Newton observation might explain the higher accretion rate, but the implied size and frequency of such events appear too great. We suggest accretion is most likely modulated by a magnetic cycle on the secondary acting as a wind `accretion switch', a mechanism that can be tested by X-ray and ultraviolet monitoring. If so, QS Vir and similar pre-CVs could provide powerful insights into hitherto inscrutable CV and M dwarf magnetospheres, and mass- and angular-momentum-loss rates.

  13. Rocket ascent G-limited moment-balanced optimization program (RAGMOP)

    NASA Technical Reports Server (NTRS)

    Lyons, J. T.; Woltosz, W. S.; Abercrombie, G. E.; Gottlieb, R. G.

    1972-01-01

    This document describes the RAGMOP (Rocket Ascent G-limited Momentbalanced Optimization Program) computer program for parametric ascent trajectory optimization. RAGMOP computes optimum polynomial-form attitude control histories, launch azimuth, engine burn-time, and gross liftoff weight for space shuttle type vehicles using a search-accelerated, gradient projection parameter optimization technique. The trajectory model available in RAGMOP includes a rotating oblate earth model, the option of input wind tables, discrete and/or continuous throttling for the purposes of limiting the thrust acceleration and/or the maximum dynamic pressure, limitation of the structural load indicators (the product of dynamic pressure with angle-of-attack and sideslip angle), and a wide selection of intermediate and terminal equality constraints.

  14. Imaging accretion sources and circumbinary disks in young brown dwarfs

    NASA Astrophysics Data System (ADS)

    Reiners, Ansgar

    2010-09-01

    We propose to obtain deep WFC3/UVIS imaging observations of two accreting, nearby, young brown dwarf binaries. The first, 2M1207, is a brown dwarf with a planetary mass companion that became a benchmark in low-mass star formation and low-mass evolutionary models. The second, 2M0041, is a nearby young brown dwarf with clear evidence for accretion, but its space motion suggests a slightly higher age than the canonical accretion lifetime of 5-10 Myr. It has recently been discovered to be a binary and is likely to become a second benchmark object in this field. With narrow band images centered on the Halpha line that is indicative of accretion, we aim to determine the accretion ratio between the two components in each system. Halpha was observed in both systems but so far not spatially resolved. In particular, we want to search for accretion in the planetary mass companion of 2M1207. The evidence for accretion in 2M0041 and the possibility that it is in fact older than 10Myr suggests that the accretion lifetime is longer in brown dwarfs than in stars, and in particular that it is longer in brown dwarf binaries. Accretion could be sustained for a longer time if the accreting material is replenished by a circumbinary disk that might exist in both systems. We propose deep WFC/UVIS observations in the optical to search for circumbinary disks, similar to the famous disk around the binary TTauri system GG Tau.

  15. The Ascent of the Concrete: Grammatical Reification in Science Teaching Exchanges and Episodes

    ERIC Educational Resources Information Center

    Lim, Eunsook; Kellogg, David

    2008-01-01

    Foreign language learning and science teaching can both be seen as examples of Davydov's "ascent to the concrete", because they begin from abstract definitions and proceed in the direction of concrete use. The microgenetic lessons that enable these ontogenetic processes can also be seen as examples of "ascent of the concrete" because they involve,…

  16. Analysis of foot clearance in firefighters during ascent and descent of stairs.

    PubMed

    Kesler, Richard M; Horn, Gavin P; Rosengren, Karl S; Hsiao-Wecksler, Elizabeth T

    2016-01-01

    Slips, trips, and falls are a leading cause of injury to firefighters with many injuries occurring while traversing stairs, possibly exaggerated by acute fatigue from firefighting activities and/or asymmetric load carriage. This study examined the effects that fatigue, induced by simulated firefighting activities, and hose load carriage have on foot clearance while traversing stairs. Landing and passing foot clearances for each stair during ascent and descent of a short staircase were investigated. Clearances decreased significantly (p < 0.05) post-exercise for nine of 12 ascent parameters and increased for two of eight descent parameters. Load carriage resulted in significantly decreased (p < 0.05) clearance over three ascent parameters, and one increase during descent. Decreased clearances during ascent caused by fatigue or load carriage may result in an increased trip risk. Increased clearances during descent may suggest use of a compensation strategy to ensure stair clearance or an increased risk of over-stepping during descent. Copyright © 2015 Elsevier Ltd and The Ergonomics Society. All rights reserved.

  17. Dark-Spot Activity on the Secondary as the Origin of Variable Mass Accretion in Cataclysmic Variables

    NASA Astrophysics Data System (ADS)

    Qian, S.-B.; Zhu, L.-Y.; Fernández-Lajús, E.; He, J.-J.; Liao, W.-P.; Zhao, E.-G.; Liu, L.; Yang, Y.-G.

    2014-08-01

    In magnetic CVs (polars), the magnetic fields of the white dwarfs are strong enough to prevent materials from the main-sequence companions for forming an accretion disc. Therefore, polars especially eclipsing polars provide a good chance to study mass accretion directly. In the past 4 years, we have monitored several eclipsing polars (e.g., DP Leo and HU Aqr) by using the 2.4-m and 1.0-m telescopes in China and the 2.15-m telescope in Argentina. Nearly 100 eclipse profiles were obtained. In this talk, apart from the detection of a few giant planets orbiting polars, I will summarize some other progresses of our research group at Yunnan Observatories. Our results are as following: (1) the correlation between the out-of-eclipse brightness variation and the change of the eclipse profile suggests that both the accretion hot spot and the accretion stream brighten and become faint instantaneously. This is the direct evidence of variable mass transfer in a CV that is also supported by the relation between the out-of-eclipse brightness and the depth of eclipse. (2) We find the brightness state change is correlated with the dark-spot activity near the L1 point. The low state usually corresponds to the presence of a large spot at L1 point, while the dark spot disappear at a high state indicating that it is the dark-spot activity caused the mass transfer in CVs. (3) Magnetic activity cycles of the cool secondary did not correlate with the brightness state change revealing the variable mass accretion was not caused by magnetic activity cycles.

  18. Planetary Accretion in the Inner Solar System: Dependence on Nebula Surface Density Profile and Giant Planet Eccentricities

    NASA Technical Reports Server (NTRS)

    Chambers, J. E.; Cassen, P.

    2002-01-01

    We present 32 N-body simulations of planetary accretion in the inner Solar System, examining the effect of nebula surface density profile and initial eccentricities of Jupiter and Saturn on the compositions and orbits of the inner planets. Additional information is contained in the original extended abstract.

  19. CHEMICAL ABUNDANCES IN A SAMPLE OF RED GIANTS IN THE OPEN CLUSTER NGC 2420 FROM APOGEE

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

    Souto, Diogo; Cunha, K.; Smith, V.

    NGC 2420 is a ∼2 Gyr old well-populated open cluster that lies about 2 kpc beyond the solar circle, in the general direction of the Galactic anti-center. Most previous abundance studies have found this cluster to be mildly metal-poor, but with a large scatter in the obtained metallicities. Detailed chemical abundance distributions are derived for 12 red-giant members of NGC 2420 via a manual abundance analysis of high-resolution ( R = 22,500) near-infrared ( λ 1.5–1.7 μ m) spectra obtained from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. The sample analyzed contains six stars that are identified asmore » members of the first-ascent red giant branch (RGB), as well as six members of the red clump (RC). We find small scatter in the star-to-star abundances in NGC 2420, with a mean cluster abundance of [Fe/H] = −0.16 ± 0.04 for the 12 red giants. The internal abundance dispersion for all elements (C, N, O, Na, Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, Co and Ni) is also very small (∼0.03–0.06 dex), indicating a uniform cluster abundance distribution within the uncertainties. NGC 2420 is one of the clusters used to calibrate the APOGEE Stellar Parameter and Chemical Abundance Pipeline (ASPCAP). The results from this manual analysis compare well with ASPCAP abundances for most of the elements studied, although for Na, Al, and V there are more significant offsets. No evidence of extra-mixing at the RGB luminosity bump is found in the {sup 12}C and {sup 14}N abundances from the pre-luminosity-bump RGB stars in comparison to the post-He core-flash RC stars.« less

  20. Influence of accretion on lead in the Earth

    NASA Astrophysics Data System (ADS)

    Galer, Stephen J. G.; Goldstein, Steven L.

    The Pb abundance and isotope composition of the Earth is fundamentally altered from bulk solar system values by the processes occurring during accretion. The most important of the possible processes are volatile element loss and core formation, or some form of inhomogeneous accretion/condensation. The final result is an Earth highly impoverished in 204Pb and other Pb isotopes in primordial abundance. Depending on the exact timing, some radiogenic Pb is also lost either to space or to the core; the degree of loss occurs in the same order as the parent decay constants, namely 207Pb > 206Pb > 208Pb. In this contribution, we explore the likely effects accretion had on the Pb isotope composition of the present day bulk silicate Earth and its secular isotope evolution. This is used to address a number of questions: (1) What can be learned about accretion from the Pb isotope composition of the bulk silicate Earth? (2) Can effects of accretion reconcile the classical "Pb paradox" of a 206Pb-rich bulk silicate Earth? (3) What exactly is the meaning of the "age of the Earth" within the context of Pb isotopes? By consideration of a number of accretion scenarios it is demonstrated that Pb isotopes yield information only on the following two coupled quantities: Firstly, the accretion interval Δ T, the time between initial condensation of the solar nebula (at 4.566Ga) and when accretion-produced U/Pb fractionation (whether loss of Pb to the core or to space) in the silicate Earth ceased. Secondly, the mean 238U/204 Pb ratio μ during accretion—no details of changes in μ during the accretion interval can be resolved. The effects of accretion are thus adequately considered in terms of a simple two-stage model described by μ over ΔT followed by a postaccretion μ. The systematics of μ and ΔT are then examined for the cases of present day terrestrial reservoirs and Archean leads. These estimates of μ and ΔT for the present and past silicate Earth are not compatible with

  1. Remembering the Giants: Apollo Rocket Propulsion Development

    NASA Technical Reports Server (NTRS)

    Fisher, Steven C. (Editor); Rahman, Shamim A. (Editor)

    2009-01-01

    Topics discussed include: Rocketdyne - F-1 Saturn V First Stage Engine; Rocketdyne - J-2 Saturn V 2nd & 3rd Stage Engine; Rocketdyne - SE-7 & SE-8 Engines; Aerojet - AJ10-137 Apollo Service Module Engine; Aerojet - Attitude Control Engines; TRW - Lunar Descent Engine; and Rocketdyne - Lunar Ascent Engine.

  2. First-Principles Computer Simulations of Dense Plasmas and Application to the Interiors of Giant Planets

    NASA Astrophysics Data System (ADS)

    Militzer, Burkhard

    2013-06-01

    This presentation will review three recent applications of first-principles computer simulation techniques to study matter at extreme temperature-pressure conditions that are of relevance to astrophysics. First we report a recent methodological advance in all-electron path integral Monte Carlo (PIMC) that allowed us to extend this method beyond hydrogen and helium to elements with core electrons [1]. We combine results from PIMC and with density functional molecular dynamics (DFT-MD) simulations and derive a coherent equation of state (EOS) for water and carbon plasmas in the regime from 1-50 Mbar and 104-109 K that can be compared to laboratory shock wave experiments. Second we apply DFT-MD simulations to characterize superionic water in the interiors of Uranus and Neptune. By adopting a thermodynamic integration technique, we derive the Gibbs free energy in order to demonstrate the existence of a phase transformation from body-centered cubic to face-centered cubic superionic water [2]. Finally we again use DFT-MD to study the interiors of gas giant planets. We determine the EOS for hydrogen-helium mixtures spanning density-temperature conditions in the deep interiors of giant planets, 0.2-9.0 g/cc and 1000-80000 K [3]. We compare the simulation results with the semi-analytical EOS model by Saumon and Chabrier. We present a revision to the mass-radius relationship which makes the hottest exoplanets increase in radius by ~0.2 Jupiter radii at fixed entropy and for masses greater than 0.5 Jupiter masses. This change is large enough to have possible implications for some discrepant inflated giant exoplanets. We conclude by demonstrating that all materials in the cores of giant planets, ices, MgO, SiO2, and iron, will all dissolve into metallic hydrogen. This implies the cores of Jupiter and Saturn have been at least partially eroded. [1] K. P. Driver, B. Militzer, Phys. Rev. Lett. 108 (2012) 115502. [2] H. F. Wilson, M. L. Wong, B. Militzer, http://arxiv.org/abs/1211

  3. Accretion, winds and jets: High-energy emission from young stellar objects

    NASA Astrophysics Data System (ADS)

    Günther, Hans Moritz

    2009-03-01

    Stars form by gravitational collapse from giant molecular clouds. Due to the conservation of angular momentum this collapse does not happen radially, but the matter forms circumstellar disk first and is consequently accreted from the disk onto the star. This thesis deals with the high-energy emission from young stellar objects, which are on the one hand still actively accreting from their disk, and on the other hand are no longer deeply obscured by their natal cloud. Stars of spectral type B and A are called Herbig Ae/Be (HAeBe) stars in this stage, all stars of later spectral type are termed classical T Tauri stars (CTTS); strictly speaking both types are defined by spectroscopic signatures, which are equivalent to the evolutionary stage described above. In this thesis CTTS and HAeBes are studied through high-resolution X-ray and UV spectroscopy and through detailed physical simulations. Spectroscopic X-ray data is reduced and presented for two targets: The CTTS V4046 Sgr was observed with Chandra for 100 ks, using a high-resolution grating spectrometer. The lightcurve contains one flare and the He-like triplets of SiXIII, NeIX and OVII indicate high densities in the X-ray emitting regions. The second target is the HAeBe HD 163296, which was observed with XMM-Newton for 130 ks. The lightcurve shows only moderate variability, the elemental abundance follows a pattern, that is usual for active stars. The He-like triplet of OVII exhibits line ratios similar to coronal sources, indicating that neither a high density nor a strong UV-field is present in the region of the X-ray emission. Using these and similar observations, it can be concluded that at least three mechanisms contribute to the observed high-energy emission from CTTS: First, those stars have active coronae similar to main-sequence stars, second, the accreted material passes through a strong accretion shock at the stellar surface, which heats it to a few MK, and, third, some CTTS drive powerful outflows

  4. Incompressible Wind Accretion

    NASA Astrophysics Data System (ADS)

    Tejeda, E.

    2018-04-01

    We present a simple, analytic model of an incompressible fluid accreting onto a moving gravitating object. This solution allows us to probe the highly subsonic regime of wind accretion. Moreover, it corresponds to the Newtonian limit of a previously known relativistic model of a stiff fluid accreting onto a black hole. Besides filling this blank in the literature, the new solution should be useful as a benchmark test for numerical hydrodynamics codes. Given its simplicity, it can also be used as an illustrative example in a gas dynamics course.

  5. Radio Observations as a Tool to Investigate Shocks and Asymmetries in Accreting White Dwarf Binaries

    NASA Astrophysics Data System (ADS)

    Weston, Jennifer H. S.

    2016-07-01

    be used as an indicator of w hether a symbiotic is powered predominantly by shell burning on the surface of the WD or by accretion. We additionally make the first ever radio detections of seven of the targets in our survey. Our survey of seventeen radio bright symbiotics, comparing observations before and after the upgrades to the VLA, shows the technological feasibility to resolve the nebulae of nearby symbiotic binaries, opening the door for new lines of research. We spatially resolve extended structure in several symbiotic systems in radio for the first time. Additionally, our observations reveal extreme radio variability in symbiotic BF Cyg before and after the production of a jet from the system. Our results from our surveys of symbiotics provide some support for the model of radio emission where the red giant wind is photoionized by the WD, and suggests that there may be a greater population of radio faint, accretion driven symbiotic systems. This work emphasizes the powerful nature of radio observations as a tool for understanding eruptive WD binaries and their outflows.

  6. Ascent performance issues of a vertical-takeoff rocket launch vehicle

    NASA Astrophysics Data System (ADS)

    Powell, Richard W.; Naftel, J. C.; Cruz, Christopher I.

    1991-04-01

    Advanced manned launch systems studies under way at the NASA Langley Research Center are part of a broader effort that is examining options for the next manned space transportation system to be developed by the United States. One promising concept that uses near-term technologies is a fully reusable, two-stage vertical-takeoff rocket vehicle. This vehicle features parallel thrusting of the booster and orbiter with the booster cross-feeding the propellant to the orbiter until staging. In addition, after staging, the booster glides back unpowered to the launch site. This study concentrated on two issues that could affect the ascent performance of this vehicle. The first is the large gimbal angle range required for pitch trim until staging because of the propellant cross-feed. Results from this analysis show that if control is provided by gimballing of the rocket engines, they must gimbal greater than 20 deg, which is excessive when compared with current vehicles. However, this analysis also showed that this limit could be reduced to 10 deg if gimballing were augmented by throttling the booster engines. The second issue is the potential influence of off-nominal atmospheric conditions (density and winds) on the ascent performance. This study showed that a robust guidance algorithm could be developed that would insure accurate insertion, without prelaunch atmospheric knowledge.

  7. Scenarios of giant planet formation and evolution and their impact on the formation of habitable terrestrial planets.

    PubMed

    Morbidelli, Alessandro

    2014-04-28

    In our Solar System, there is a clear divide between the terrestrial and giant planets. These two categories of planets formed and evolved separately, almost in isolation from each other. This was possible because Jupiter avoided migrating into the inner Solar System, most probably due to the presence of Saturn, and never acquired a large-eccentricity orbit, even during the phase of orbital instability that the giant planets most likely experienced. Thus, the Earth formed on a time scale of several tens of millions of years, by collision of Moon- to Mars-mass planetary embryos, in a gas-free and volatile-depleted environment. We do not expect, however, that this clear cleavage between the giant and terrestrial planets is generic. In many extrasolar planetary systems discovered to date, the giant planets migrated into the vicinity of the parent star and/or acquired eccentric orbits. In this way, the evolution and destiny of the giant and terrestrial planets become intimately linked. This paper discusses several evolutionary patterns for the giant planets, with an emphasis on the consequences for the formation and survival of habitable terrestrial planets. The conclusion is that we should not expect Earth-like planets to be typical in terms of physical and orbital properties and accretion history. Most habitable worlds are probably different, exotic worlds.

  8. Observations of accreting pulsars

    NASA Technical Reports Server (NTRS)

    Prince, Thomas A.; Bildsten, Lars; Chakrabarty, Deepto; Wilson, Robert B.; Finger, Mark H.

    1994-01-01

    We discuss recent observations of accreting binary pulsars with the all-sky BATSE instrument on the Compton Gamma Ray Observatory. BATSE has detected and studied nearly half of the known accreting pulsar systems. Continuous timing studies over a two-year period have yielded accurate orbital parameters for 9 of these systems, as well as new insights into long-term accretion torque histories.

  9. First photographic records of the giant manta ray Manta birostris off eastern Australia.

    PubMed

    Couturier, Lydie I E; Jaine, Fabrice R A; Kashiwagi, Tom

    2015-01-01

    We present the first photographic evidence of the presence of the giant manta ray Manta birostris in east Australian waters. Two individuals were photographed off Montague Island in New South Wales and off the north east coast of Tasmania, during summer 2012 and 2014, respectively. These sightings confirm previous unverified reports on the species occurrence and extend the known distribution range of M. birostris to 40°S. We discuss these findings in the context of the species' migratory behaviour, the regional oceanography along the south east Australian coastline and local productivity events.

  10. First photographic records of the giant manta ray Manta birostris off eastern Australia

    PubMed Central

    Jaine, Fabrice R.A.; Kashiwagi, Tom

    2015-01-01

    We present the first photographic evidence of the presence of the giant manta ray Manta birostris in east Australian waters. Two individuals were photographed off Montague Island in New South Wales and off the north east coast of Tasmania, during summer 2012 and 2014, respectively. These sightings confirm previous unverified reports on the species occurrence and extend the known distribution range of M. birostris to 40°S. We discuss these findings in the context of the species’ migratory behaviour, the regional oceanography along the south east Australian coastline and local productivity events. PMID:25649395

  11. Accretion Processes in Cosmic Sources

    NASA Astrophysics Data System (ADS)

    2016-10-01

    Accretion is a universal phenomenon that takes place in the vast majority of astrophysical objects. The progress of ground-based and space-borne observational facilities has resulted in the great amount of information on various accreting astrophysical objects, collected within the last decades. The accretion is accompanied by the process of extensive energy release that takes place on the surface of an accreting object and in various gaseous envelopes, accretion disk, jets and other elements of the flow pattern. The results of observations inspired the intensive development of accretion theory, which, in turn, enabled us to study unique properties of accreting objects and physical conditions in the surrounding environment. One of the most interesting outcomes of this intensive study is the fact that accretion processes are, in a sense, self-similar on various spatial scales from planetary systems to galaxies. This fact gives us new opportunities to investigate objects that, by various reasons, are not available for direct study. Cataclysmic variable stars are unique natural laboratories where one can conduct the detailed observational study of accretion processes and accretion disks. This is the main reason why several participants and a few members of the Organizing Committee of the conference "The Golden Age of Cataclysmic Variables and Related Objects - III" (September 7-12, 2015, Palermo, Italy) have decided to hold a special conference, focused on accretion processes, as a branch of that series. Main topics: Young Stellar Objects, protoplanetary discs, exoplanets in binary stars Accretion on white dwarfs (Cataclysmic variables and related objects) Accretion on neutron stars (X-ray Binary Systems and related objects) Accretion on black holes (stellar BH and AGN) The workshop will include a few 35-minute general review talks to introduce the current problems, and 20-minute talks to discuss new experimental and theoretical results. A series of 15-minute talks

  12. The Large-scale Magnetic Fields of Thin Accretion Disks

    NASA Astrophysics Data System (ADS)

    Cao, Xinwu; Spruit, Hendrik C.

    2013-03-01

    Large-scale magnetic field threading an accretion disk is a key ingredient in the jet formation model. The most attractive scenario for the origin of such a large-scale field is the advection of the field by the gas in the accretion disk from the interstellar medium or a companion star. However, it is realized that outward diffusion of the accreted field is fast compared with the inward accretion velocity in a geometrically thin accretion disk if the value of the Prandtl number P m is around unity. In this work, we revisit this problem considering the angular momentum of the disk to be removed predominantly by the magnetically driven outflows. The radial velocity of the disk is significantly increased due to the presence of the outflows. Using a simplified model for the vertical disk structure, we find that even moderately weak fields can cause sufficient angular momentum loss via a magnetic wind to balance outward diffusion. There are two equilibrium points, one at low field strengths corresponding to a plasma-beta at the midplane of order several hundred, and one for strong accreted fields, β ~ 1. We surmise that the first is relevant for the accretion of weak, possibly external, fields through the outer parts of the disk, while the latter one could explain the tendency, observed in full three-dimensional numerical simulations, of strong flux bundles at the centers of disk to stay confined in spite of strong magnetororational instability turbulence surrounding them.

  13. The connection between the giant optical outbursts of the flat spectrum radio quasars and the black hole precession

    NASA Astrophysics Data System (ADS)

    Bachev, Rumen

    2018-02-01

    Flat Spectrum Radio Quasars (FSRQ) are a part of the blazar family, which in addition to the dominated nonthermal jet emission shows signatures, normally associated with the presence of a standard thin accretion disk, such like thermal continuum and broad emission lines. Furthermore, there is emerging evidence that the FSRQ are more likely to exhibit giant outbursts in the optical, with amplitudes reaching sometimes up to five magnitudes, compared to their quiescent state. We give examples, compiled from the literature and public archives in support of this statement. The most promising mechanism to account for such outbursts appears to be the changing Doppler factor (orientation with respect to the line of sights) of the jet. We attribute such orientation changes of the jet to the presence of misaligned thin accretion disk, leading to a black hole/accretion disk precession. Such a scheme can explain why FSRQ tend to produce large outbursts while other blazar types do not.

  14. GIANT IMPACT: AN EFFICIENT MECHANISM FOR THE DEVOLATILIZATION OF SUPER-EARTHS

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

    Liu, Shang-Fei; Hori, Yasunori; Lin, D. N. C.

    Mini-Neptunes and volatile-poor super-Earths coexist on adjacent orbits in proximity to host stars such as Kepler-36 and Kepler-11. Several post-formation processes have been proposed for explaining the origin of the compositional diversity between neighboring planets: mass loss via stellar XUV irradiation, degassing of accreted material, and in situ accumulation of the disk gas. Close-in planets are also likely to experience giant impacts during the advanced stage of planet formation. This study examines the possibility of transforming volatile-rich super-Earths/mini-Neptunes into volatile-depleted super-Earths through giant impacts. We present the results of three-dimensional hydrodynamic simulations of giant impacts in the accretionary and disruptivemore » regimes. Target planets are modeled with a three-layered structure composed of an iron core, silicate mantle, and hydrogen/helium envelope. In the disruptive case, the giant impact can remove most of the H/He atmosphere immediately and homogenize the refractory material in the planetary interior. In the accretionary case, the planet is able to retain more than half of the original gaseous envelope, while a compositional gradient suppresses efficient heat transfer as the planetary interior undergoes double-diffusive convection. After the giant impact, a hot and inflated planet cools and contracts slowly. The extended atmosphere enhances the mass loss via both a Parker wind induced by thermal pressure and hydrodynamic escape driven by the stellar XUV irradiation. As a result, the entire gaseous envelope is expected to be lost due to the combination of those processes in both cases. Based on our results, we propose that Kepler-36b may have been significantly devolatilized by giant impacts, while a substantial fraction of Kepler-36c’s atmosphere may remain intact. Furthermore, the stochastic nature of giant impacts may account for the observed large dispersion in the mass–radius relationship of close

  15. HYPERCRITICAL ACCRETION, INDUCED GRAVITATIONAL COLLAPSE, AND BINARY-DRIVEN HYPERNOVAE

    DOE PAGES

    Fryer, Chris L.; Rueda, Jorge A.; Ruffini, Remo

    2014-09-16

    We successfully, applied the induced gravitational collapse (IGC) paradigm to the explanation of GRB-SNe. The progenitor is a tight binary system composed of a CO core and a NS companion. Furthermore, the explosion of the SN leads to hypercritical accretion onto the NS companion, which reaches the critical mass, gravitationally collapsing to a BH with consequent emission of the GRB. The first estimates of this process were based on a simplified model of the binary parameters and the Bondi-Hoyle-Lyttleton accretion rate. We present the first full numerical simulations of the IGC process. We simulate the core-collapse, the SN explosion, andmore » the hydrodynamic evolution of the accreting material falling into the Bondi-Hoyle surface of the NS. For appropriate binary parameters, the IGC occurs in short timescale 102–103 s due to the combined action of photon trapping and neutrino cooling near the NS surface. We also address the observational features of this process.« less

  16. Gravitational Instabilities in Gaseous Protoplanetary Disks and Implications for Giant Planet Formation

    NASA Astrophysics Data System (ADS)

    Durisen, R. H.; Boss, A. P.; Mayer, L.; Nelson, A. F.; Quinn, T.; Rice, W. K. M.

    Protoplanetary gas disks are likely to experience gravitational instabilities (GIs) during some phase of their evolution. Density perturbations in an unstable disk grow on a dynamic timescale into spiral arms that produce efficient outward transfer of angular momentum and inward transfer of mass through gravitational torques. In a cool disk with sufficiently rapid cooling, the spiral arms in an unstable disk form self-gravitating clumps. Whether gas giant protoplanets can form by such a disk instability process is the primary question addressed by this review. We discuss the wide range of calculations undertaken by ourselves and others using various numerical techniques, and we report preliminary results from a large multicode collaboration. Additional topics include triggering mechanisms for GIs, disk heating and cooling, orbital survival of dense clumps, interactions of solids with GI-driven waves and shocks, and hybrid scenarios where GIs facilitate core accretion. The review ends with a discussion of how well disk instability and core accretion fare in meeting observational constraints.

  17. Making the Moon from a fast-spinning Earth: a giant impact followed by resonant despinning.

    PubMed

    Ćuk, Matija; Stewart, Sarah T

    2012-11-23

    A common origin for the Moon and Earth is required by their identical isotopic composition. However, simulations of the current giant impact hypothesis for Moon formation find that most lunar material originated from the impactor, which should have had a different isotopic signature. Previous Moon-formation studies assumed that the angular momentum after the impact was similar to that of the present day; however, Earth-mass planets are expected to have higher spin rates at the end of accretion. Here, we show that typical last giant impacts onto a fast-spinning proto-Earth can produce a Moon-forming disk derived primarily from Earth's mantle. Furthermore, we find that a faster-spinning early Earth-Moon system can lose angular momentum and reach the present state through an orbital resonance between the Sun and Moon.

  18. A giant protogalactic disk linked to the cosmic web

    NASA Astrophysics Data System (ADS)

    Martin, D. Christopher; Matuszewski, Mateusz; Morrissey, Patrick; Neill, James D.; Moore, Anna; Cantalupo, Sebastiano; Prochaska, J. Xavier; Chang, Daphne

    2015-08-01

    The specifics of how galaxies form from, and are fuelled by, gas from the intergalactic medium remain uncertain. Hydrodynamic simulations suggest that `cold accretion flows'--relatively cool (temperatures of the order of 104 kelvin), unshocked gas streaming along filaments of the cosmic web into dark-matter halos--are important. These flows are thought to deposit gas and angular momentum into the circumgalactic medium, creating disk- or ring-like structures that eventually coalesce into galaxies that form at filamentary intersections. Recently, a large and luminous filament, consistent with such a cold accretion flow, was discovered near the quasi-stellar object QSO UM287 at redshift 2.279 using narrow-band imaging. Unfortunately, imaging is not sufficient to constrain the physical characteristics of the filament, to determine its kinematics, to explain how it is linked to nearby sources, or to account for its unusual brightness, more than a factor of ten above what is expected for a filament. Here we report a two-dimensional spectroscopic investigation of the emitting structure. We find that the brightest emission region is an extended rotating hydrogen disk with a velocity profile that is characteristic of gas in a dark-matter halo with a mass of 1013 solar masses. This giant protogalactic disk appears to be connected to a quiescent filament that may extend beyond the virial radius of the halo. The geometry is strongly suggestive of a cold accretion flow.

  19. A giant protogalactic disk linked to the cosmic web.

    PubMed

    Martin, D Christopher; Matuszewski, Mateusz; Morrissey, Patrick; Neill, James D; Moore, Anna; Cantalupo, Sebastiano; Prochaska, J Xavier; Chang, Daphne

    2015-08-13

    The specifics of how galaxies form from, and are fuelled by, gas from the intergalactic medium remain uncertain. Hydrodynamic simulations suggest that 'cold accretion flows'--relatively cool (temperatures of the order of 10(4) kelvin), unshocked gas streaming along filaments of the cosmic web into dark-matter halos--are important. These flows are thought to deposit gas and angular momentum into the circumgalactic medium, creating disk- or ring-like structures that eventually coalesce into galaxies that form at filamentary intersections. Recently, a large and luminous filament, consistent with such a cold accretion flow, was discovered near the quasi-stellar object QSO UM287 at redshift 2.279 using narrow-band imaging. Unfortunately, imaging is not sufficient to constrain the physical characteristics of the filament, to determine its kinematics, to explain how it is linked to nearby sources, or to account for its unusual brightness, more than a factor of ten above what is expected for a filament. Here we report a two-dimensional spectroscopic investigation of the emitting structure. We find that the brightest emission region is an extended rotating hydrogen disk with a velocity profile that is characteristic of gas in a dark-matter halo with a mass of 10(13) solar masses. This giant protogalactic disk appears to be connected to a quiescent filament that may extend beyond the virial radius of the halo. The geometry is strongly suggestive of a cold accretion flow.

  20. Advancements in the LEWICE Ice Accretion Model

    NASA Technical Reports Server (NTRS)

    Wright, William B.

    1993-01-01

    Recent evidence has shown that the NASA/Lewis Ice Accretion Model, LEWICE, does not predict accurate ice shapes for certain glaze ice conditions. This paper will present the methodology used to make a first attempt at improving the ice accretion prediction in these regimes. Importance is given to the correlations for heat transfer coefficient and ice density, as well as runback flow, selection of the transition point, flow field resolution, and droplet trajectory models. Further improvements and refinement of these modules will be performed once tests in NASA's Icing Research Tunnel, scheduled for 1993, are completed.

  1. Human Mars Ascent Vehicle Configuration and Performance Sensitivities

    NASA Technical Reports Server (NTRS)

    Polsgrove, Tara P.; Thomas, Herbert D.; Stephens, Walter; Collins, Tim; Rucker, Michelle; Gernhardt, Mike; Zwack, Matthew R.; Dees, Patrick D.

    2017-01-01

    The total ascent vehicle mass drives performance requirements for the Mars descent systems and the Earth to Mars transportation elements. Minimizing Mars Ascent Vehicle (MAV) mass is a priority and minimizing the crew cabin size and mass is one way to do that. Human missions to Mars may utilize several small cabins where crew members could live for days up to a couple of weeks. A common crew cabin design that can perform in each of these applications is desired and could reduce the overall mission cost. However, for the MAV, the crew cabin size and mass can have a large impact on vehicle design and performance. This paper explores the sensitivities to trajectory, propulsion, crew cabin size and the benefits and impacts of using a common crew cabin design for the MAV. Results of these trades will be presented along with mass and performance estimates for the selected design.

  2. Laboratory unraveling of matter accretion in young stars

    PubMed Central

    Revet, Guilhem; Chen, Sophia N.; Bonito, Rosaria; Khiar, Benjamin; Filippov, Evgeny; Argiroffi, Costanza; Higginson, Drew P.; Orlando, Salvatore; Béard, Jérôme; Blecher, Marius; Borghesi, Marco; Burdonov, Konstantin; Khaghani, Dimitri; Naughton, Kealan; Pépin, Henri; Portugall, Oliver; Riquier, Raphael; Rodriguez, Rafael; Ryazantsev, Sergei N.; Yu. Skobelev, Igor; Soloviev, Alexander; Willi, Oswald; Pikuz, Sergey; Ciardi, Andrea; Fuchs, Julien

    2017-01-01

    Accretion dynamics in the formation of young stars is still a matter of debate because of limitations in observations and modeling. Through scaled laboratory experiments of collimated plasma accretion onto a solid in the presence of a magnetic field, we open a first window on this phenomenon by tracking, with spatial and temporal resolution, the dynamics of the system and simultaneously measuring multiband emissions. We observe in these experiments that matter, upon impact, is ejected laterally from the solid surface and then refocused by the magnetic field toward the incoming stream. This ejected matter forms a plasma shell that envelops the shocked core, reducing escaped x-ray emission. This finding demonstrates one possible structure reconciling current discrepancies between mass accretion rates derived from x-ray and optical observations, respectively. PMID:29109974

  3. Laboratory unraveling of matter accretion in young stars

    DOE PAGES

    Revet, Guilhem; Chen, Sophia N.; Bonito, Rosaria; ...

    2017-11-01

    Accretion dynamics in the formation of young stars is still a matter of debate because of limitations in observations and modeling. Through scaled laboratory experiments of collimated plasma accretion onto a solid in the presence of a magnetic field, we open a first window on this phenomenon by tracking, with spatial and temporal resolution, the dynamics of the system and simultaneously measuring multiband emissions. Here, we observe in these experiments that matter, upon impact, is ejected laterally from the solid surface and then refocused by the magnetic field toward the incoming stream. This ejected matter forms a plasma shell thatmore » envelops the shocked core, reducing escaped x-ray emission. Our finding demonstrates one possible structure reconciling current discrepancies between mass accretion rates derived from x-ray and optical observations, respectively.« less

  4. Laboratory unraveling of matter accretion in young stars.

    PubMed

    Revet, Guilhem; Chen, Sophia N; Bonito, Rosaria; Khiar, Benjamin; Filippov, Evgeny; Argiroffi, Costanza; Higginson, Drew P; Orlando, Salvatore; Béard, Jérôme; Blecher, Marius; Borghesi, Marco; Burdonov, Konstantin; Khaghani, Dimitri; Naughton, Kealan; Pépin, Henri; Portugall, Oliver; Riquier, Raphael; Rodriguez, Rafael; Ryazantsev, Sergei N; Yu Skobelev, Igor; Soloviev, Alexander; Willi, Oswald; Pikuz, Sergey; Ciardi, Andrea; Fuchs, Julien

    2017-11-01

    Accretion dynamics in the formation of young stars is still a matter of debate because of limitations in observations and modeling. Through scaled laboratory experiments of collimated plasma accretion onto a solid in the presence of a magnetic field, we open a first window on this phenomenon by tracking, with spatial and temporal resolution, the dynamics of the system and simultaneously measuring multiband emissions. We observe in these experiments that matter, upon impact, is ejected laterally from the solid surface and then refocused by the magnetic field toward the incoming stream. This ejected matter forms a plasma shell that envelops the shocked core, reducing escaped x-ray emission. This finding demonstrates one possible structure reconciling current discrepancies between mass accretion rates derived from x-ray and optical observations, respectively.

  5. Laboratory unraveling of matter accretion in young stars

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

    Revet, Guilhem; Chen, Sophia N.; Bonito, Rosaria

    Accretion dynamics in the formation of young stars is still a matter of debate because of limitations in observations and modeling. Through scaled laboratory experiments of collimated plasma accretion onto a solid in the presence of a magnetic field, we open a first window on this phenomenon by tracking, with spatial and temporal resolution, the dynamics of the system and simultaneously measuring multiband emissions. Here, we observe in these experiments that matter, upon impact, is ejected laterally from the solid surface and then refocused by the magnetic field toward the incoming stream. This ejected matter forms a plasma shell thatmore » envelops the shocked core, reducing escaped x-ray emission. Our finding demonstrates one possible structure reconciling current discrepancies between mass accretion rates derived from x-ray and optical observations, respectively.« less

  6. Ascent abort capability for the HL-20

    NASA Technical Reports Server (NTRS)

    Naftel, J. C.; Talay, T. A.

    1993-01-01

    The HL-20 has been designed with the capability for rescue of the crew during all phases of powered ascent from on the launch pad until orbital injection. A launch-escape system, consisting of solid rocket motors located on the adapter between the HL-20 and the launch vehicle, provides the thrust that propels the HL-20 to a safe distance from a malfunctioning launch vehicle. After these launch-escape motors have burned out, the adapter is jettisoned and the HL-20 executes one of four abort modes. In three abort modes - return-to-launch-site, transatlantic-abort-landing, and abort-to-orbit - not only is the crew rescued, but the HL-20 is recovered intact. In the ocean-landing-by-parachute abort mode, which occurs in between the return-to-launch-site and the transatlantic-abort-landing modes, the crew is rescued, but the HL-20 would likely sustain damage from the ocean landing. This paper describes the launch-escape system and the four abort modes for an ascent on a Titan III launch vehicle.

  7. Accreting Neutron Star and Black Hole Binaries with NICER

    NASA Astrophysics Data System (ADS)

    Chakrabarty, Deepto

    2018-01-01

    The NICER mission on the International Space Station has significant new capabilities for the study of accreting neutron stars and blackholes, including large effective area, low background, and excellent low-energy X-ray response. Both the NICER Burst and Accretion Working Group and the Observatory Science Working Group have designed observing programs that probe various aspects of accretion physics. I will present some early results from the first six months of the NICER mission, including observations of the black hole transients MAXI J1535-571 and GX 339-4, the high-mass X-ray binary pulsars GRO J1008-57 and Swift J02436+6124, and the X-ray burster 4U 1820-30.

  8. Deep-level magma dehydration and ascent rates at Mt. Etna (Sicily, Italy)

    NASA Astrophysics Data System (ADS)

    Armienti, P.; Perinelli, C.; Putirka, K.

    2012-04-01

    Magma ascent velocity, v (dH/dt; H = depth, t = time),can be determined from ascent rate (dP/dt), and rate of cooling (dT/dt): v= 1/(rgpg) (dP/dT)(dT/dt) where r is magma density, P is pressure, T is temperature and g is the acceleration of gravity. This equation for v provides a key to investigating the relationships between initial ascent rate of magma and the depths of magma dehydration, and v can be calculated using pressure and temperature (P - PH2O - T) estimates from mineral-liquid thermobarometry, and cooling rates inferred from Crystal Size Distribution (CSD) theory. For recent Mt. Etna lava flows, both dP/dT and dT/dt have been well characterized based, respectively, on clinopyroxene thermobarometry, and clinopyroxene CSDs (the latter yields dT/dt = 2x10-6 °C/s). Deep-level (>20 km) magma ascent rates range from practically 0 (where clinopyroxene P - T estimates form a cluster, and so dP/dT ≈ 0), to about 10 m/hr for flows that yield very steep P - T trajectories. Many lava flows at Mt. Etna yield P - T paths that follow a hydrous (about 3% water) clinopyroxene saturation surface, which closely approximates water contents obtained from melt inclusions. Independent assessments of deep level water content yield ascent rates of ~1 m/hr, in agreement with the slowest rates derived for magma effusion or vapor-driven ascent (~0.001 to >0.2 m/s, or 3.6 to 720 m/hr). Changes in P - T slopes, as obtained by pyroxene thermobarometry, indicate an upward acceleration of magma, which may be due to the onset of deep-level magma dehydration linked to the non-ideal behavior of water and CO2 mixtures that induce a deep-level maximum of water loss at P ≈ 0.4 MPa at T ≈ 1200 ° C for a CO2 content >1000ppm. Melt inclusion data on CO2 and H2O contents are successfully reproduced and interpreted in a context of magma dehydration induced by a CO2 flux possibly deriving by decarbonation reaction of the carbonate fraction of the Capo D'Orlando flysch.

  9. Dynamics of subduction, accretion, exhumation and slab roll-back: Mediterranean scenarios

    NASA Astrophysics Data System (ADS)

    Tirel, C.; Brun, J.; Burov, E. B.; Wortel, M. J.; Lebedev, S.

    2010-12-01

    A dynamic orogen reveals various tectonic processes brought about by subduction: accretion of oceanic and continental crust, exhumation of UHP-HP rocks, and often, back-arc extension. In the Mediterranean, orogeny is strongly affected by slab retreat, as in the Aegean and Tyrrhenian Seas. In order to examine the different dynamic processes in a self-consistent manner, we perform a parametric study using the fully coupled thermo-mechanical numerical code PARAFLAM. The experiments reproduce a subduction zone in a slab pull mode, with accretion of one (the Tyrrhenian case) and two continental blocks (the Aegean case) that undergo, in sequence, thrusting, burial and exhumation. The modeling shows that despite differences in structure between the two cases, the deformation mechanisms are fundamentally similar and can be described as follows. The accretion of a continental block at the trench beneath the suture zone begins with its burial to UHP-HP conditions and thrusting. Then the continental block is delaminated from its subducting lithosphere. During the subduction-accretion process, the angle of the subducting slab increases due to the buoyancy of the continental block. When the oceanic subduction resumes, the angle of the slab decreases to reach a steady-state position. The Aegean and Tyrrhenian scenarios diverge at this stage, due naturally to the differences of their accretion history. When continental accretion is followed by oceanic subduction only, the continental block that has been accreted and detached stays at close to the trench and does not undergo further deformation, despite the continuing rollback. The extensional deformation is located further within the overriding plate, resulting in continental breakup and the development of an oceanic basin, as in the Tyrrhenian domain. When the continental accretion is followed first by oceanic subduction and then by accretion of another continental block, however, the evolution of the subduction zone is

  10. Redshifted X-rays from the material accreting onto TW Hydrae: Evidence of a low-latitude accretion spot

    NASA Astrophysics Data System (ADS)

    Argiroffi, C.; Drake, J. J.; Bonito, R.; Orlando, S.; Peres, G.; Miceli, M.

    2017-10-01

    Context. High resolution spectroscopy, providing constraints on plasma motions and temperatures, is a powerful means to investigate the structure of accretion streams in classical T Tauri stars (CTTS). In particular, the accretion shock region, where the accreting material is heated to temperatures of a few million degrees as it continues its inward bulk motion, can be probed by X-ray spectroscopy. Aims: In an attempt to detect for the first time the motion of this X-ray-emitting post-shock material, we searched for a Doppler shift in the deep Chandra High Energy Transmission Grating observation of the CTTS TW Hya. This test should unveil the nature of this X-ray emitting plasma component in CTTS and constrain the accretion stream geometry. Methods: We searched for a Doppler shift in the X-ray emission from TW Hya with two different methods: by measuring the position of a selected sample of emission lines and by fitting the whole TW Hya X-ray spectrum, allowing the line-of-sight velocity to vary. Results: We found that the plasma at T 2 - 4 MK has a line-of-sight velocity of 38.3 ± 5.1 km s-1 with respect to the stellar photosphere. This result definitively confirms that this X-ray-emitting material originates in the post-shock region, at the base of the accretion stream, and not in coronal structures. The comparison of the observed velocity along the line of sight, 38.3 ± 5.1 km s-1, with the inferred intrinsic velocity of the post shock of TW Hya, vpost ≈ 110 - 120 km s-1, indicates that the footpoints of the accretion streams on TW Hya are located at low latitudes on the stellar surface. Conclusions: Our results indicate that complex magnetic field geometries, such as those of TW Hya, permit low-latitude accretion spots. Moreover, since on TW Hya the redshift of the soft X-ray emission is very similar to that of the narrow component of the C iv resonance doublet at 1550 Å, then the plasma at 2 - 4 MK and that at 0.1 MK likely originate in the same post

  11. The Emerging Paradigm of Pebble Accretion

    NASA Astrophysics Data System (ADS)

    Ormel, Chris W.

    Pebble accretion is the mechanism in which small particles ("pebbles") accrete onto big bodies big (planetesimals or planetary embryos) in gas-rich environments. In pebble accretion accretion , accretion occurs by settling and depends only on the mass of the gravitating body gravitating , not its radius. I give the conditions under which pebble accretion operates and show that the collisional cross section can become much larger than in the gas-free, ballistic, limit. In particular, pebble accretion requires the pre-existence of a massive planetesimal seed. When pebbles experience strong orbital decay by drift motions or are stirred by turbulence, the accretion efficiency is low and a great number of pebbles are needed to form Earth-mass cores. Pebble accretion is in many ways a more natural and versatile process than the classical, planetesimal-driven paradigm, opening up avenues to understand planet formation in solar and exoplanetary systems.

  12. Observations of Accreting Pulsars

    NASA Technical Reports Server (NTRS)

    Bildsten, Lars; Chakrabarty, Deepto; Chiu, John; Finger, Mark H.; Koh, Danny T.; Nelson, Robert W.; Prince, Thomas A.; Rubin, Bradley C.; Scott, D. Matthew; Stollberg, Mark; hide

    1997-01-01

    We summarize 5 years of continuous monitoring of accretion-powered pulsars with the Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory. Our 20-70 keV observations have determined or refined the orbital parameters of 13 binaries, discovered five new transient accreting pulsars, measured the pulsed flux history during outbursts of 12 transients (GRO J1744-28, 4U 0115+634, GRO J1750-27, GS 0834-430, 2S 1417-624, GRO J1948+32, EXO 2030+375, GRO J1008-57, A0535+26, GRO J2058+42, 4U 1145-619, and A1118-616), and also measured the accretion torque history during outbursts of six of those transients whose orbital param- eters were also known. We have also continuously measured the pulsed flux and spin frequency for eiaht persistently accreting pulsars (Her X-1, Cen X-3, Vela X-1, OAO 1657-415, GX 301-2, 4U 1626-67, 4U 1538-52, and GX 1+4). Because of their continuity and uniformity over a long baseline, BATSE observations have provided new insights into the long-term behavior of accreting magnetic neutron stars. We have found that all accreting pulsars show stochastic variations in their spin frequencies and luminosities, including those displaying secular spin-up or spin-down on long timescales, which blurs the con- ventional distinction between disk-fed and wind-fed binaries. Pulsed flux and accretion torque are strongly correlated in outbursts of transient accreting pulsars but are uncorrelated, or even anti- correlated, in persistent sources. We describe daily folded pulse profiles, frequency, and flux measurements that are available through the Compton Observatory Science Support Center at NASA/Goddard Space Flight Center.

  13. Exploring the Relationship Between Planet Mass and Atmospheric Metallicity for Cool Giant Planets

    NASA Astrophysics Data System (ADS)

    Thomas, Nancy H.; Wong, Ian; Knutson, Heather; Deming, Drake; Desert, Jean-Michel; Fortney, Jonathan J.; Morley, Caroline; Kammer, Joshua A.; Line, Michael R.

    2016-10-01

    Measurements of the average densities of exoplanets have begun to help constrain their bulk compositions and to provide insight into their formation locations and accretionary histories. Current mass and radius measurements suggest an inverse relationship between a planet's bulk metallicity and its mass, a relationship also seen in the gas and ice giant planets of our own solar system. We expect atmospheric metallicity to similarly increase with decreasing planet mass, but there are currently few constraints on the atmospheric metallicities of extrasolar giant planets. For hydrogen-dominated atmospheres, equilibrium chemistry models predict a transition from CO to CH4 below ~1200 K. However, with increased atmospheric metallicity the relative abundance of CH4 is depleted and CO is enhanced. In this study we present new secondary eclipse observations of a set of cool (<1200 K) giant exoplanets at 3.6 and 4.5 microns using the Spitzer Space Telescope, which allow us to constrain their relative abundances of CH4 and CO and corresponding atmospheric metallicities. We discuss the implications of our results for the proposed correlation between planet mass and atmospheric metallicity as predicted by the core accretion models and observed in our solar system.

  14. Panel 1: A pulsating red giant star and a compact, hot white dwarf star orbit each other.

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Panel 1: A pulsating red giant star and a compact, hot white dwarf star orbit each other. Panel 2: The red giant sheds much of its outer layers in a stellar wind. The white dwarf helps concentrate the wind along a thin equatorial plane. The white dwarf accretes some of this escaping gas forming a disk around the itself. Panel 3: When enough gas accumulates on the white dwarf's surface it explodes as a nova outburst. Most of the hot gas forms a pair of expanding bubbles above and below the equatorial disk. Panel 4: A few thousand years after the bubbles expand into space, the white dwarf goes through another nova outburst and makes another pair of bubbles, which form a distinctive hourglass shape.

  15. TESTING THE PROPAGATING FLUCTUATIONS MODEL WITH A LONG, GLOBAL ACCRETION DISK SIMULATION

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

    Hogg, J Drew; Reynolds, Christopher S.

    2016-07-20

    The broadband variability of many accreting systems displays characteristic structures; log-normal flux distributions, root-mean square (rms)-flux relations, and long inter-band lags. These characteristics are usually interpreted as inward propagating fluctuations of the mass accretion rate in an accretion disk driven by stochasticity of the angular momentum transport mechanism. We present the first analysis of propagating fluctuations in a long-duration, high-resolution, global three-dimensional magnetohydrodynamic (MHD) simulation of a geometrically thin ( h / r ≈ 0.1) accretion disk around a black hole. While the dynamical-timescale turbulent fluctuations in the Maxwell stresses are too rapid to drive radially coherent fluctuations in themore » accretion rate, we find that the low-frequency quasi-periodic dynamo action introduces low-frequency fluctuations in the Maxwell stresses, which then drive the propagating fluctuations. Examining both the mass accretion rate and emission proxies, we recover log-normality, linear rms-flux relations, and radial coherence that would produce inter-band lags. Hence, we successfully relate and connect the phenomenology of propagating fluctuations to modern MHD accretion disk theory.« less

  16. Variability at the edge: highly accreting objects in Taurus

    NASA Astrophysics Data System (ADS)

    Abraham, Peter; Kospal, Agnes; Szabo, Robert

    2017-04-01

    In Kepler K2, Campaign 13, we will obtain 80-days-long optical light curves of seven highly accreting T Tauri stars in the benchmark Taurus star forming region. Here we propose to monitor our sample simultaneously with Kepler and Spitzer, to be able to separate variability patterns related to different physical processes. Monitoring our targets with Spitzer during the final 11 days of the K2 campaign, we will clean the light curves from non-accretion effects (rotating stellar spots, dips due to passing dust structures), and construct, for the first time, a variability curve which reflects the time-dependent accretion only. We will then study and understand how time-dependent mass accretion affects the density and temperature structure of the protoplanetary disk, which sets the initial conditions for planet formation. The proposed work cannot be done without the unparalleled precision of Kepler and Spitzer. This unique and one-time opportunity motivated our DDT proposal.

  17. Giant cell arteritis mimicking a testicular tumour.

    PubMed

    Sundaram, S; Smith, D H

    2001-07-01

    Giant cell arteritis involving the testis was identified incidentally upon orchidectomy of a right testicular mass. The mass looked like a malignant process on ultrasound. The patient also had generalised disease and was treated appropriately. Giant cell arteritis involving the bladder, prostate, uterus, and adnexa have been described before. To our knowledge, this is the first described case of giant cell arteritis affecting the testis.

  18. Retired A Stars Revisited: An Updated Giant Planet Occurrence Rate as a Function of Stellar Metallicity and Mass

    NASA Astrophysics Data System (ADS)

    Ghezzi, Luan; Montet, Benjamin T.; Johnson, John Asher

    2018-06-01

    Exoplanet surveys of evolved stars have provided increasing evidence that the formation of giant planets depends not only on stellar metallicity ([Fe/H]) but also on the mass ({M}\\star ). However, measuring accurate masses for subgiants and giants is far more challenging than it is for their main-sequence counterparts, which has led to recent concerns regarding the veracity of the correlation between stellar mass and planet occurrence. In order to address these concerns, we use HIRES spectra to perform a spectroscopic analysis on a sample of 245 subgiants and derive new atmospheric and physical parameters. We also calculate the space velocities of this sample in a homogeneous manner for the first time. When reddening corrections are considered in the calculations of stellar masses and a ‑0.12 {M}ȯ offset is applied to the results, the masses of the subgiants are consistent with their space velocity distributions, contrary to claims in the literature. Similarly, our measurements of their rotational velocities provide additional confirmation that the masses of subgiants with {M}\\star ≥slant 1.6 M ⊙ (the “retired A stars”) have not been overestimated in previous analyses. Using these new results for our sample of evolved stars, together with an updated sample of FGKM dwarfs, we confirm that giant planet occurrence increases with both stellar mass and metallicity up to 2.0 M ⊙. We show that the probability of formation of a giant planet is approximately a one-to-one function of the total amount of metals in the protoplanetary disk {M}\\star {10}[{Fe/{{H}}]}. This correlation provides additional support for the core accretion mechanism of planet formation.

  19. Accretion of Moon and Earth and the emergence of life.

    PubMed

    Arrhenius, G; Lepland, A

    2000-08-15

    The discrepancy between the impact records on the Earth and Moon in the time period, 4.0-3.5 Ga calls for a re-evaluation of the cause and localization of the late lunar bombardment. As one possible explanation, we propose that the time coverage in the ancient rock record is sufficiently fragmentary, so that the effects of giant, sterilizing impacts throughout the inner solar system, caused by marauding asteroids, could have escaped detection in terrestrial and Martian records. Alternatively, the lunar impact record may reflect collisions of the receding Moon with a series of small, original satellites of the Earth and their debris in the time period about 4.0-3.5 Ga. The effects on Earth of such encounters could have been comparatively small. The location of these tellurian moonlets has been estimated to have been in the region around 40 Earth radii. Calculations presented here, indicate that this is the region that the Moon would traverse at 4.0-3.5 Ga, when the heavy and declining lunar bombardment took place. The ultimate time limit for the emergence of life on Earth is determined by the effects of planetary accretion--existing models offer a variety of scenarios, ranging from low average surface temperature at slow accretion of the mantle, to complete melting of the planet followed by protracted cooling. The choice of accretion model affects the habitability of the planet by dictating the early evolution of the atmosphere and hydrosphere. Further exploration of the sedimentary record on Earth and Mars, and of the chemical composition of impact-generated ejecta on the Moon, may determine the choice between the different interpretations of the late lunar bombardment and cast additional light on the time and conditions for the emergence of life.

  20. Accretion of Moon and Earth and the emergence of life

    NASA Technical Reports Server (NTRS)

    Arrhenius, G.; Lepland, A.

    2000-01-01

    The discrepancy between the impact records on the Earth and Moon in the time period, 4.0-3.5 Ga calls for a re-evaluation of the cause and localization of the late lunar bombardment. As one possible explanation, we propose that the time coverage in the ancient rock record is sufficiently fragmentary, so that the effects of giant, sterilizing impacts throughout the inner solar system, caused by marauding asteroids, could have escaped detection in terrestrial and Martian records. Alternatively, the lunar impact record may reflect collisions of the receding Moon with a series of small, original satellites of the Earth and their debris in the time period about 4.0-3.5 Ga. The effects on Earth of such encounters could have been comparatively small. The location of these tellurian moonlets has been estimated to have been in the region around 40 Earth radii. Calculations presented here, indicate that this is the region that the Moon would traverse at 4.0-3.5 Ga, when the heavy and declining lunar bombardment took place. The ultimate time limit for the emergence of life on Earth is determined by the effects of planetary accretion--existing models offer a variety of scenarios, ranging from low average surface temperature at slow accretion of the mantle, to complete melting of the planet followed by protracted cooling. The choice of accretion model affects the habitability of the planet by dictating the early evolution of the atmosphere and hydrosphere. Further exploration of the sedimentary record on Earth and Mars, and of the chemical composition of impact-generated ejecta on the Moon, may determine the choice between the different interpretations of the late lunar bombardment and cast additional light on the time and conditions for the emergence of life.

  1. Predicting changes in volcanic activity through modelling magma ascent rate.

    NASA Astrophysics Data System (ADS)

    Thomas, Mark; Neuberg, Jurgen

    2013-04-01

    It is a simple fact that changes in volcanic activity happen and in retrospect they are easy to spot, the dissimilar eruption dynamics between an effusive and explosive event are not hard to miss. However to be able to predict such changes is a much more complicated process. To cause altering styles of activity we know that some part or combination of parts within the system must vary with time, as if there is no physical change within the system, why would the change in eruptive activity occur? What is unknown is which parts or how big a change is needed. We present the results of a suite of conduit flow models that aim to answer these questions by assessing the influence of individual model parameters such as the dissolved water content or magma temperature. By altering these variables in a systematic manner we measure the effect of the changes by observing the modelled ascent rate. We use the ascent rate as we believe it is a very important indicator that can control the style of eruptive activity. In particular, we found that the sensitivity of the ascent rate to small changes in model parameters surprising. Linking these changes to observable monitoring data in a way that these data could be used as a predictive tool is the ultimate goal of this work. We will show that changes in ascent rate can be estimated by a particular type of seismicity. Low frequency seismicity, thought to be caused by the brittle failure of melt is often linked with the movement of magma within a conduit. We show that acceleration in the rate of low frequency seismicity can correspond to an increase in the rate of magma movement and be used as an indicator for potential changes in eruptive activity.

  2. Disk Evolution, Element Abundances and Cloud Properties of Young Gas Giant Planets

    PubMed Central

    Helling, Christiane; Woitke, Peter; Rimmer, Paul B.; Kamp, Inga; Thi, Wing-Fai; Meijerink, Rowin

    2014-01-01

    We discuss the chemical pre-conditions for planet formation, in terms of gas and ice abundances in a protoplanetary disk, as function of time and position, and the resulting chemical composition and cloud properties in the atmosphere when young gas giant planets form, in particular discussing the effects of unusual, non-solar carbon and oxygen abundances. Large deviations between the abundances of the host star and its gas giants seem likely to occur if the planet formation follows the core-accretion scenario. These deviations stem from the separate evolution of gas and dust in the disk, where the dust forms the planet cores, followed by the final run-away accretion of the left-over gas. This gas will contain only traces of elements like C, N and O, because those elements have frozen out as ices. ProDiMo protoplanetary disk models are used to predict the chemical evolution of gas and ice in the midplane. We find that cosmic rays play a crucial role in slowly un-blocking the CO, where the liberated oxygen forms water, which then freezes out quickly. Therefore, the C/O ratio in the gas phase is found to gradually increase with time, in a region bracketed by the water and CO ice-lines. In this regions, C/O is found to approach unity after about 5 Myrs, scaling with the cosmic ray ionization rate assumed. We then explore how the atmospheric chemistry and cloud properties in young gas giants are affected when the non-solar C/O ratios predicted by the disk models are assumed. The Drift cloud formation model is applied to study the formation of atmospheric clouds under the influence of varying premordial element abundances and its feedback onto the local gas. We demonstrate that element depletion by cloud formation plays a crucial role in converting an oxygen-rich atmosphere gas into carbon-rich gas when non-solar, premordial element abundances are considered as suggested by disk models. PMID:25370190

  3. Disk evolution, element abundances and cloud properties of young gas giant planets.

    PubMed

    Helling, Christiane; Woitke, Peter; Rimmer, Paul B; Kamp, Inga; Thi, Wing-Fai; Meijerink, Rowin

    2014-04-14

    We discuss the chemical pre-conditions for planet formation, in terms of gas and ice abundances in a protoplanetary disk, as function of time and position, and the resulting chemical composition and cloud properties in the atmosphere when young gas giant planets form, in particular discussing the effects of unusual, non-solar carbon and oxygen abundances. Large deviations between the abundances of the host star and its gas giants seem likely to occur if the planet formation follows the core-accretion scenario. These deviations stem from the separate evolution of gas and dust in the disk, where the dust forms the planet cores, followed by the final run-away accretion of the left-over gas. This gas will contain only traces of elements like C, N and O, because those elements have frozen out as ices. PRODIMO protoplanetary disk models are used to predict the chemical evolution of gas and ice in the midplane. We find that cosmic rays play a crucial role in slowly un-blocking the CO, where the liberated oxygen forms water, which then freezes out quickly. Therefore, the C/O ratio in the gas phase is found to gradually increase with time, in a region bracketed by the water and CO ice-lines. In this regions, C/O is found to approach unity after about 5 Myrs, scaling with the cosmic ray ionization rate assumed. We then explore how the atmospheric chemistry and cloud properties in young gas giants are affected when the non-solar C/O ratios predicted by the disk models are assumed. The DRIFT cloud formation model is applied to study the formation of atmospheric clouds under the influence of varying premordial element abundances and its feedback onto the local gas. We demonstrate that element depletion by cloud formation plays a crucial role in converting an oxygen-rich atmosphere gas into carbon-rich gas when non-solar, premordial element abundances are considered as suggested by disk models.

  4. Andromeda's SMBH Projected Accretion Rate

    NASA Astrophysics Data System (ADS)

    Wilson, John

    2014-03-01

    A formula for calculating the half-life of galaxy clusters is proposed. A galactic half-life is the estimated amount of time that the most massive supermassive black hole (SMBH) in the galaxy cluster will have accreted one half of the mass in the cluster. The calculation is based on a projection of the SMBH continuing its exponentially decreasing rate of accretion that it had in its first 13 billion years. The calculated half-life for the Andromeda SMBH is approximately 1.4327e14 years from the Big Bang. Several proposals have suggested that black holes could be significant factors in the formation of new universes. Part of the verification or falsification of this hypothesis could be done by an N-body simulation. These simulations require an enormous amount of computer power and time. Some plausible projection of the growth of the supermassive black hole is needed to prepare an N-body simulation budget proposal. For now, this method provides an estimate for the growth rate of the Andromeda SMBH and deposition of the outcome of most of the galaxy cluster's mass which is either accreted by the SMBH, lost by ejection from the cluster, or lost in the form of energy.

  5. Space shuttle: Aerodynamic characteristics of various MDAC space shuttle ascent configurations with parallel burn pressure-fed and SRM boosters. Volume 1: Tanks T1 and T2 ascent configurations

    NASA Technical Reports Server (NTRS)

    Jarrett, T. W.

    1972-01-01

    Various space shuttle ascent configurations were tested in a trisonic wind tunnel to determine the aerodynamic characteristics. The ascent configuration consisted of a NASA/MSC 040 orbiter in combination with various HO centerline tank and booster geometries. The aerodynamic interference between components of the space shuttle and the effect on the orbiter aerodynamics was determined. The various aerodynamic configurations tested were: (1) centerline HO tanks T1 and T2, (2) centerline HO tank T3, and (3) centerline HO tank H4.

  6. Chemical and dynamical perspectives on accretion and differentiation

    NASA Astrophysics Data System (ADS)

    Nimmo, F.

    2012-12-01

    The initial thermal and chemical state of a planet is largely determined by how it accreted. Although large bodies rapidly lose their memory of those initial conditions, smaller bodies do not: the Martian mantle has different isotopic reservoirs that were established early in its history and not subsequently homogenized [1], while the Martian dynamo may have been driven by an initially superheated core [2]. Accretion is also inefficient; impacts can modify planetary bulk compositions in subtle [3] or dramatic [4] ways. There are two main pathways for melting and differentiation of silicate bodies. Small rapidly-accreted bodies melt from the inside out due to 26Al decay, potentially leaving an unmelted carapace [5]. Large bodies melt due to release of gravitational energy via giant impacts. Both situations likely result in magma oceans, which may crystallize to yield unstable density structures [6]. The lifetime of magma oceans is highly uncertain and depends on whether a flotation crust develops, and whether a thick primordial atmosphere is present [7]. The Hf-W [8] and Pd-Ag [9] isotopic systems provide constraints on the timing and style of core formation. For instance, the rapid growth of planets in the ``Grand Tack'' model [10] may not be consistent with these constraints. The key uncertainty is the extent to which impactor cores equilibrate with the surrounding mantle during impacts. For example, the inferred rapid accretion of Mars [11] depends on an assumption of perfect re-equilibration. The physics of re-equilibration is imperfectly understood [12], and hard to model numerically [13]; laboratory experiments may provide a better approach [14]. Dynamical models suggest that the Earth's feeding zone moved outwards with time [15]. Isotopic [9] and element partitioning [16] models are consistent with this picture, suggesting that accreted material changed from volatile-poor and reduced to volatile-rich and oxidized as time progressed. [1] Halliday et al., SSR

  7. First-principles study of giant thermoelectric power in incommensurate TlInSe2

    NASA Astrophysics Data System (ADS)

    Ishikawa, M.; Nakayama, T.; Wakita, K.; Shim, Y. G.; Mamedov, N.

    2018-04-01

    Ternary thallium compound TlInSe2 exhibits a giant Seebeck effect below around 410 K, where Tl atoms form one dimensional incommensurate (IC) arrays. To clarify the origin of large thermoelectric power in the IC phase, the electronic properties of Tl-atom super-structured TlInSe2 were studied using the first-principles calculations. It was shown that the super-structures induce strong binding states between Se-p orbitals in the nearest neighboring layers and produce large density of states near lower conduction bands, which might be one of the origins to produce large thermoelectric power.

  8. Tiny crystals give away the where and when of magma ascent

    NASA Astrophysics Data System (ADS)

    Ruth, D. C. S.; Costa Rodriguez, F.; Bouvet de Maisonneuve, C.; Franco, L.; Cortes, J. A.; Calder, E.

    2016-12-01

    Open vent volcanoes exhibit passive degassing and can transition to explosive behavior, with limited or no warning. Melt inclusion chemistry and volatile contents have been used to infer the inner dynamics of magma storage, recharge, degassing, and eruption triggering mechanisms. However, the interpretation of melt inclusion chemistry is ambiguous because it cannot constrain the residence times of the host crystals, which could have various sources and growth histories. To resolve this issue we combine diffusion chronometry and melt inclusion entrapment pressures from olivine crystals sourced from the 2008 eruption of Llaima volcano (Chile). Olivine crystals (core Fo70-84, rim Fo77-84) are dominantly reverse zoned, although normal zoned and complex zoned crystals are observed. These data reflect mixing between the mafic injecting magma and the crystal-rich resident magma. Fe/Mg diffusion timescales range between 16 and 1375 days. The diffusion data show a non-uniform distribution with no discernible peaks, indicating that magma injection is likely progressive, rather than punctuated. Entrapment pressures range between 8 and 151 MPa, overlapping with an inferred crystal-rich region. Longer timescales correspond to higher pressures, strongly suggesting a link between magma residence time and ascent from depth. To our knowledge, this relationship has not been previously demonstrated. We infer that mafic magma intruded at depths of 5 km below the edifice and mingled with a pre-existing crystal-mush 3 yr before the eruption. Magma migration and mingling continued and stalled at 2.5 km depth about a year prior to the eruption. Precursory activity such as volcano-tectonic and long period seismicity, and a series of minor explosions overlap with the diffusion times 6 months before the eruption. Similar diffusion timescales have been reported for eruptions at other open vent volcanoes. Our study provides the first temporal and spatial constraints on magma storage and ascent

  9. Kuiper Prize: Giant Planet Atmospheres

    NASA Astrophysics Data System (ADS)

    Ingersoll, Andrew P.

    2007-10-01

    The study of giant planet atmospheres is near and dear to me, for several reasons. First, the giant planets are photogenic; the colored clouds are great tracers, and one can make fantastic movies of the atmosphere in motion. Second, the giant planets challenge us with storms that last for hundreds of years and winds that blow faster the farther you go from the sun. Third, they remind us of Earth with their hurricanes, auroras, and lightning, but they also are the link to the 200 giant planets that have been discovered around other stars. This talk will cover the past, present, and future (one hopes) of giant planet research. I will review the surprises of the Voyager and Galileo eras, and will discuss what we are learning now from the Cassini orbiter. I will review the prospects for answering the outstanding questions like: Where's the water? What is providing the colors of the clouds? How deep do the features extend? Where do the winds get their energy? What is the role of the magnetic field? Finally, I will briefly discuss how extrasolar giant planets compare with objects in our own solar system.

  10. A Terminal Area Analysis of Continuous Ascent Departure Fuel Use at Dallas/Fort Worth International Airport

    NASA Technical Reports Server (NTRS)

    Roach, Keenan; Robinson, John E., III

    2010-01-01

    Aircraft departing from the Dallas/Fort Worth International Airport (DFW) encounter vertical restrictions that prevent continuous ascent operations. The result of these restrictions are temporary level-offs at 10,000 feet. A combination of flow direction, specific Area Navigation (RNAV) route geometry, and arrival streams have been found to be the biggest factors in the duration and frequency of a temporary level-offs. In total, 20% of DFW departures are affected by these level-offs, which have an average duration of just over 100 seconds. The use of continuous descent approaches at DFW are shown to lessen the impact arrivals have on the departures and allow more continuous ascents. The fuel used in a continuous ascent and an ascent with a temporary level-off have been calculated using a fuel burn rate model created from a combination of actual aircraft track data, aircraft manufacturer flight operations manuals, and Eurocontrol's Base of Aircraft Data (BADA) simulation tool. This model represents the average aggregate burn rates for the current fleet mix at DFW. Continuous ascents would save approximately seven gallons of fuel out of 450 gallons used to climb to a cruise altitude of 31,000ft per departure.

  11. Black Hole Disk Accretion in Supernovae

    NASA Astrophysics Data System (ADS)

    Mineshige, Shin; Nomura, Hideko; Hirose, Masahito; Nomoto, Ken'ichi; Suzuki, Tomoharu

    1997-11-01

    Massive stars in a certain mass range may form low-mass black holes after supernova explosions. In such massive stars, fallback of ~0.1 M⊙ materials onto a black hole is expected because of a deep gravitational potential or a reverse shock propagating back from the outer composition interface. We study hydrodynamical disk accretion onto a newborn low-mass black hole in a supernova using the smoothed particle hydrodynamics method. If the progenitor was rotating before the explosion, the fallback material should have a certain amount of angular momentum with respect to the black hole, thus forming an accretion disk. The disk material will eventually accrete toward the central object because of viscosity at a supercritical accretion rate, Ṁ/Ṁcrit>106, for the first several tens of days. (Here, Ṁcrit is the Eddington luminosity divided by c2.) We then expect that such an accretion disk is optically thick and advection dominated; that is, the disk is so hot that the produced energy and photons are advected inward rather than being radiated away. Thus, the disk luminosity is much less than the Eddington luminosity. The disk becomes hot and dense; for Ṁ/Ṁcrit~106, for example, T ~ 109(αvis/0.01)-1/4 K and ρ ~ 103(αvis/0.01)-1 g cm-3 (with αvis being the viscosity parameter) in the vicinity of the black hole. Depending on the material mixing, some interesting nucleosynthesis processes via rapid proton and alpha-particle captures are expected even for reasonable viscosity magnitudes (αvis ~ 0.01), and some of them could be ejected in a disk wind or a jet without being swallowed by the black hole.

  12. Volatile accretion history of the Earth.

    PubMed

    Wood, B J; Halliday, A N; Rehkämper, M

    2010-10-28

    It has long been thought that the Earth had a protracted and complex history of volatile accretion and loss. Albarède paints a different picture, proposing that the Earth first formed as a dry planet which, like the Moon, was devoid of volatile constituents. He suggests that the Earth's complement of volatile elements was only established later, by the addition of a small veneer of volatile-rich material at ∼100 Myr (here and elsewhere, ages are relative to the origin of the Solar System). Here we argue that the Earth's mass balance of moderately volatile elements is inconsistent with Albarède's hypothesis but is well explained by the standard model of accretion from partially volatile-depleted material, accompanied by core formation.

  13. Airfoil Ice-Accretion Aerodynamics Simulation

    NASA Technical Reports Server (NTRS)

    Bragg, Michael B.; Broeren, Andy P.; Addy, Harold E.; Potapczuk, Mark G.; Guffond, Didier; Montreuil, E.

    2007-01-01

    NASA Glenn Research Center, ONERA, and the University of Illinois are conducting a major research program whose goal is to improve our understanding of the aerodynamic scaling of ice accretions on airfoils. The program when it is completed will result in validated scaled simulation methods that produce the essential aerodynamic features of the full-scale iced-airfoil. This research will provide some of the first, high-fidelity, full-scale, iced-airfoil aerodynamic data. An initial study classified ice accretions based on their aerodynamics into four types: roughness, streamwise ice, horn ice, and spanwise-ridge ice. Subscale testing using a NACA 23012 airfoil was performed in the NASA IRT and University of Illinois wind tunnel to better understand the aerodynamics of these ice types and to test various levels of ice simulation fidelity. These studies are briefly reviewed here and have been presented in more detail in other papers. Based on these results, full-scale testing at the ONERA F1 tunnel using cast ice shapes obtained from molds taken in the IRT will provide full-scale iced airfoil data from full-scale ice accretions. Using these data as a baseline, the final step is to validate the simulation methods in scale in the Illinois wind tunnel. Computational ice accretion methods including LEWICE and ONICE have been used to guide the experiments and are briefly described and results shown. When full-scale and simulation aerodynamic results are available, these data will be used to further develop computational tools. Thus the purpose of the paper is to present an overview of the program and key results to date.

  14. Accretion-driven turbulence in filaments - I. Non-gravitational accretion

    NASA Astrophysics Data System (ADS)

    Heigl, S.; Burkert, A.; Gritschneder, M.

    2018-03-01

    We study accretion-driven turbulence for different inflow velocities in star-forming filaments using the code RAMSES. Filaments are rarely isolated objects and their gravitational potential will lead to radially dominated accretion. In the non-gravitational case, accretion by itself can already provoke non-isotropic, radially dominated turbulent motions responsible for the complex structure and non-thermal line widths observed in filaments. We find that there is a direct linear relation between the absolute value of the total density-weighted velocity dispersion and the infall velocity. The turbulent velocity dispersion in the filaments is independent of sound speed or any net flow along the filament. We show that the density-weighted velocity dispersion acts as an additional pressure term, supporting the filament in hydrostatic equilibrium. Comparing to observations, we find that the projected non-thermal line width variation is generally subsonic independent of inflow velocity.

  15. Forming supermassive black holes by accreting dark and baryon matter

    NASA Astrophysics Data System (ADS)

    Hu, Jian; Shen, Yue; Lou, Yu-Qing; Zhang, Shuangnan

    2006-01-01

    Given a large-scale mixture of self-interacting dark matter (SIDM) particles and baryon matter distributed in the early Universe, we advance here a two-phase accretion scenario for forming supermassive black holes (SMBHs) with masses around ~109Msolar at high redshifts z(>~6). The first phase is conceived to involve a rapid quasi-spherical and quasi-steady Bondi accretion of mainly SIDM particles embedded with baryon matter on to seed black holes (BHs) created at redshifts z<~ 30 by the first generation of massive Population III stars; this earlier phase rapidly gives birth to significantly enlarged seed BH masses of during z~ 20-15, where σ0 is the cross-section per unit mass of SIDM particles and Cs is the velocity dispersion in the SIDM halo referred to as an effective `sound speed'. The second phase of BH mass growth is envisaged to proceed primarily via baryon accretion, eventually leading to SMBH masses of MBH~ 109Msolar such SMBHs may form either by z~ 6 for a sustained accretion at the Eddington limit or later at lower z for sub-Eddington mean accretion rates. In between these two phases, there is a transitional yet sustained diffusively limited accretion of SIDM particles which in an eventual steady state would be much lower than the accretion rates of the two main phases. We intend to account for the reported detections of a few SMBHs at early epochs, e.g. Sloan Digital Sky Survey (SDSS) 1148+5251 and so forth, without necessarily resorting to either super-Eddington baryon accretion or very frequent BH merging processes. Only extremely massive dark SIDM haloes associated with rare peaks of density fluctuations in the early Universe may harbour such early SMBHs or quasars. Observational consequences are discussed. During the final stage of accumulating a SMBH mass, violent feedback in circumnuclear environs of a galactic nucleus leads to the central bulge formation and gives rise to the familiar empirical MBH-σb correlation inferred for nearby normal

  16. Rethinking Black Hole Accretion Discs

    NASA Astrophysics Data System (ADS)

    Salvesen, Greg

    Accretion discs are staples of astrophysics. Tapping into the gravitational potential energy of the accreting material, these discs are highly efficient machines that produce copious radiation and extreme outflows. While interesting in their own right, accretion discs also act as tools to study black holes and directly influence the properties of the Universe. Black hole X-ray binaries are fantastic natural laboratories for studying accretion disc physics and black hole phenomena. Among many of the curious behaviors exhibited by these systems are black hole state transitions -- complicated cycles of dramatic brightening and dimming. Using X-ray observations with high temporal cadence, we show that the evolution of the accretion disc spectrum during black hole state transitions can be described by a variable disc atmospheric structure without invoking a radially truncated disc geometry. The accretion disc spectrum can be a powerful diagnostic for measuring black hole spin if the effects of the disc atmosphere on the emergent spectrum are well-understood; however, properties of the disc atmosphere are largely unconstrained. Using statistical methods, we decompose this black hole spin measurement technique and show that modest uncertainties regarding the disc atmosphere can lead to erroneous spin measurements. The vertical structure of the disc is difficult to constrain due to our ignorance of the contribution to hydrostatic balance by magnetic fields, which are fundamental to the accretion process. Observations of black hole X-ray binaries and the accretion environments near supermassive black holes provide mounting evidence for strong magnetization. Performing numerical simulations of accretion discs in the shearing box approximation, we impose a net vertical magnetic flux that allows us to effectively control the level of disc magnetization. We study how dynamo activity and the properties of turbulence driven by the magnetorotational instability depend on the

  17. The mass and age of the first SONG target: the red giant 46 LMi

    NASA Astrophysics Data System (ADS)

    Frandsen, S.; Fredslund Andersen, M.; Brogaard, K.; Jiang, C.; Arentoft, T.; Grundahl, F.; Kjeldsen, H.; Christensen-Dalsgaard, J.; Weiss, E.; Pallé, P.; Antoci, V.; Kjærgaard, P.; Sørensen, A. N.; Skottfelt, J.; Jørgensen, U. G.

    2018-05-01

    Context. The Stellar Observation Network Group (SONG) is an initiative to build a worldwide network of 1m telescopes with high-precision radial-velocity spectrographs. Here we analyse the first radial-velocity time series of a red-giant star measured by the SONG telescope at Tenerife. The asteroseismic results demonstrate a major increase in the achievable precision of the parameters for red-giant stars obtainable from ground-based observations. Reliable tests of the validity of these results are needed, however, before the accuracy of the parameters can be trusted. Aims: We analyse the first SONG time series for the star 46 LMi, which has a precise parallax and an angular diameter measured from interferometry, and therefore a good determination of the stellar radius. We use asteroseismic scaling relations to obtain an accurate mass, and modelling to determine the age. Methods: A 55-day time series of high-resolution, high S/N spectra were obtained with the first SONG telescope. We derive the asteroseismic parameters by analysing the power spectrum. To give a best guess on the large separation of modes in the power spectrum, we have applied a new method which uses the scaling of Kepler red-giant stars to 46 LMi. Results: Several methods have been applied: classical estimates, seismic methods using the observed time series, and model calculations to derive the fundamental parameters of 46 LMi. Parameters determined using the different methods are consistent within the uncertainties. We find the following values for the mass M (scaling), radius R (classical), age (modelling), and surface gravity (combining mass and radius): M = 1.09 ± 0.04M⊙, R = 7.95 ± 0.11R⊙ age t = 8.2 ± 1.9 Gy, and logg = 2.674 ± 0.013. Conclusions: The exciting possibilities for ground-based asteroseismology of solar-like oscillations with a fully robotic network have been illustrated with the results obtained from just a single site of the SONG network. The window function is still a

  18. jsc2018m000130_Orion Crew Module for Ascent Abort-2 Arrives in Houston

    NASA Image and Video Library

    2018-03-08

    Ascent Abort-2 Module Arrives in Houston---------------------------------------------------------- NASA’s Johnson Space Center is the center of activity leading the design and build up for a critical safety test of America’s new exploration spacecraft. An Orion crew module was delivered to Houston last week for assembly and outfitting for the April 2019 Ascent Abort-2 test, to demonstrate the ability of the spacecraft’s Launch Abort System to pull the crew module to safety if an emergency ever arises during ascent to space. Doing this work at JSC is part of a lean approach to development, to minimize cost and schedule risks associated with the test. _______________________________________ FOLLOW ORION! Twitter: https://twitter.com/NASA_Orion/ Facebook: https://www.facebook.com/NASAOrion/ Instagram: https://www.instagram.com/explorenasa/

  19. Accretion dynamics of EX Lupi in quiescence. The star, the spot, and the accretion column

    NASA Astrophysics Data System (ADS)

    Sicilia-Aguilar, Aurora; Fang, Min; Roccatagliata, Veronica; Collier Cameron, Andrew; Kóspál, Ágnes; Henning, Thomas; Ábrahám, Peter; Sipos, Nikoletta

    2015-08-01

    Context. EX Lupi is a young, accreting M0 star and the prototype of EXor variable stars. Its spectrum is very rich in emission lines, including many metallic lines with narrow and broad components. The presence of a close companion has also been proposed, based on radial velocity signatures. Aims: We use the metallic emission lines to study the accretion structures and to test the companion hypothesis. Methods: We analyse 54 spectra obtained during five years of quiescence time. We study the line profile variability and the radial velocity of the narrow and broad metallic emission lines. We use the velocity signatures of different species with various excitation conditions and their time dependency to track the dynamics associated with accretion. Results: We observe periodic velocity variations in the broad and the narrow line components, consistent with rotational modulation. The modulation is stronger for lines with higher excitation potentials (e.g. He II), which are likely produced in a confined area very close to the accretion shock. Conclusions: We propose that the narrow line components are produced in the post-shock region, while the broad components originate in the more extended, pre-shock material in the accretion column. All the emission lines suffer velocity modulation due to the rotation of the star. The broad components are responsible for the line-dependent veiling observed in EX Lupi. We demonstrate that a rotationally modulated line-dependent veiling can explain the radial velocity signature of the photospheric absorption lines, making the close-in companion hypothesis unnecessary. The accretion structure is locked to the star and very stable during the five years of observations. Not all stars with similar spectral types and accretion rates show the same metallic emission lines, which could be related to differences in temperature and density in their accretion structure(s). The contamination of photospheric signatures by accretion

  20. An optical study of X-ray sources in the old open clusters NGC 752 and NGC 6940

    NASA Astrophysics Data System (ADS)

    van den Berg, M.; Verbunt, F.

    2001-08-01

    We observed the optical counterparts of X-ray sources in the old open clusters NGC 752 and NGC 6940 to search for the origin of the X-rays. The photometric variability reported earlier for the blue straggler H 209 is not confirmed by our light curves, nor is an indication for variability seen in the spectra; thus its X-rays remain unexplained. The X-rays of VR 111 and VR 114 are likely not a result of magnetic activity as these stars lack strong Ca II H&K emission, while in VR 108 the level of activity could be enhanced. The short-period binary H 313 is a photometric variable; this supports the interpretation that it is a magnetically active binary. From the detection of the Li I 6707.8 Å line, we classify the giant in VR 84 as a first-ascent giant; this leaves its circular orbit unexplained. As a side-result we report the detection of Li I 6707.8 Å in the spectrum of the giant H 3 and the absence of this line in the spectrum of the giant H 11; this classifies H 3 as a first-ascent giant and H 11 as a core-helium-burning clump star, and confirms the faint extension of the red-giant clump in NGC 752. Based on observations made with the Jacobus Kapteyn Telescope and the William Herschel Telescope operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias.

  1. Three-dimensional hydrodynamical CO5BOLD model atmospheres of red giant stars. VI. First chromosphere model of a late-type giant

    NASA Astrophysics Data System (ADS)

    Wedemeyer, Sven; Kučinskas, Arūnas; Klevas, Jonas; Ludwig, Hans-Günter

    2017-10-01

    Aims: Although observational data unequivocally point to the presence of chromospheres in red giant stars, no attempts have been made so far to model them using 3D hydrodynamical model atmospheres. We therefore compute an exploratory 3D hydrodynamical model atmosphere for a cool red giant in order to study the dynamical and thermodynamic properties of its chromosphere, as well as the influence of the chromosphere on its observable properties. Methods: Three-dimensional radiation hydrodynamics simulations are carried out with the CO5BOLD model atmosphere code for a star with the atmospheric parameters (Teff ≈ 4010 K, log g = 1.5, [ M / H ] = 0.0), which are similar to those of the K-type giant star Aldebaran (α Tau). The computational domain extends from the upper convection zone into the chromosphere (7.4 ≥ log τRoss ≥ - 12.8) and covers several granules in each horizontal direction. Using this model atmosphere, we compute the emergent continuum intensity maps at different wavelengths, spectral line profiles of Ca II K, the Ca II infrared triplet line at 854.2 nm, and Hα, as well as the spectral energy distribution (SED) of the emergent radiative flux. Results: The initial model quickly develops a dynamical chromosphere that is characterised by propagating and interacting shock waves. The peak temperatures in the chromospheric shock fronts reach values of up to 5000 K, although the shock fronts remain quite narrow. Similar to the Sun, the gas temperature distribution in the upper layers of red giant stars is composed of a cool component due to adiabatic cooling in the expanding post-shock regions and a hot component due to shock waves. For this red giant model, the hot component is a rather flat high-temperature tail, which nevertheless affects the resulting average temperatures significantly. Conclusions: The simulations show that the atmospheres of red giant stars are dynamic and intermittent. Consequently, many observable properties cannot be reproduced

  2. Accretion onto CO White Dwarfs using MESA

    NASA Astrophysics Data System (ADS)

    Feng, Wanda; Starrfield, Sumner

    2018-06-01

    The nature of type Ia Supernovae (SNe Ia) progenitor systems and their underlying mechanism are not well understood. There are two competing progenitor scenarios: the single-degenerate scenario wherein a white dwarf (WD) star accretes material from a companion star, reaching the Chandrasekhar mass limit; and, the double-degenerate scenario wherein two WDs merge. In this study, we investigate the single-degenerate scenario by accretion onto carbon-oxygen (CO) WDs using the Modules for Experiments in Stellar Astrophysics (MESA). We vary the WD mass, composition of the accreting material, and accretion rate in our models. Mixing between the accreted material and the WD core is informed by multidimensional studies that suggest occurance after thermonuclear runaway (TNR) ensues. We compare the accretion of solar composition material onto CO WDs with the accretion of mixed solar and core material after TNR. As many of our models eject less material than accreted, our study supports that accretion onto CO WDs is a feasible channel for SNe I progenitors.

  3. A young Moon-forming giant impact at 70-110 million years accompanied by late-stage mixing, core formation and degassing of the Earth.

    PubMed

    Halliday, Alex N

    2008-11-28

    New W isotope data for lunar metals demonstrate that the Moon formed late in isotopic equilibrium with the bulk silicate Earth (BSE). On this basis, lunar Sr isotope data are used to define the former composition of the Earth and hence the Rb-Sr age of the Moon, which is 4.48+/-0.02Ga, or 70-110Ma (million years) after the start of the Solar System. This age is significantly later than had been deduced from W isotopes based on model assumptions or isotopic effects now known to be cosmogenic. The Sr age is in excellent agreement with earlier estimates based on the time of lunar Pb loss and the age of the early lunar crust (4.46+/-0.04Ga). Similar ages for the BSE are recorded by xenon and lead-lead, providing evidence of catastrophic terrestrial degassing, atmospheric blow-off and significant late core formation accompanying the ca 100Ma giant impact. Agreement between the age of the Moon based on the Earth's Rb/Sr and the lead-lead age of the Moon is consistent with no major losses of moderately volatile elements from the Earth during the giant impact. The W isotopic composition of the BSE can be explained by end member models of (i) gradual accretion with a mean life of roughly 35Ma or (ii) rapid growth with a mean life of roughly 10Ma, followed by a significant hiatus prior to the giant impact. The former assumes that approximately 60 per cent of the incoming metal from impactors is added directly to the core during accretion. The latter includes complete mixing of all the impactor material into the BSE during accretion. The identical W isotopic composition of the Moon and the BSE limits the amount of material that can be added as a late veneer to the Earth after the giant impact to less than 0.3+/-0.3 per cent of ordinary chondrite or less than 0.5+/-0.6 per cent CI carbonaceous chondrite based on their known W isotopic compositions. Neither of these on their own is sufficient to explain the inventories of both refractory siderophiles such as platinum group

  4. 24. NICHE IN GREAT WALL AT TOP OF WEST ASCENT, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    24. NICHE IN GREAT WALL AT TOP OF WEST ASCENT, NOTE SHELL SPILL, October 1987 - Meridian Hill Park, Bounded by Fifteenth, Sixteenth, Euclid & W Streets, Northwest, Washington, District of Columbia, DC

  5. Crew Exploration Vehicle Ascent Abort Trajectory Analysis and Optimization

    NASA Technical Reports Server (NTRS)

    Falck, Robert D.; Gefert, Leon P.

    2007-01-01

    The Orion Crew Exploration Vehicle is the first crewed capsule design to be developed by NASA since Project Apollo. Unlike Apollo, however, the CEV is being designed for service in both Lunar and International Space Station missions. Ascent aborts pose some issues that were not present for Apollo, due to its launch azimuth, nor Space Shuttle, due to its cross range capability. The requirement that a North Atlantic splashdown following an abort be avoidable, in conjunction with the requirement for overlapping abort modes to maximize crew survivability, drives the thrust level of the service module main engine. This paper summarizes 3DOF analysis conducted by NASA to aid in the determination of the appropriate propulsion system for the service module, and the appropriate propellant loading for ISS missions such that crew survivability is maximized.

  6. Flares, Magnetic Reconnections and Accretion Disk Viscosity

    NASA Astrophysics Data System (ADS)

    Welsh, William

    2001-07-01

    Accretion disks are invoked to explain a host of astrophysical phenomena, from protostellar objects to AGN. And yet the mechanism allowing accretion disks to operate are completely unknown. This proposal seeks to observe the ``smoking gun'' signature of magnetically-driven viscosity in accretion disks. Magnetically-induced viscosity is a plausible and generally accepted hypothesis {for esthetic reasons}, but it is completely untested. Determining the cause of accretion disk viscosity is of major significance to all accretion-disk powered systems {e.g. CVs, X-ray binaries, AGN and protostellar disks}. These data will also firmly establish the importance of magnetic fields in accretion disks. Because of its known flaring properites, we will observe the accretion disk in EM Cyg simulataneously with STIS/FUV and CHANDRA. The simultaneous X-rays are absolutely necessary for the unambiguous detection of accretion disk magnetic reconnection flares.

  7. Disk Accretion in the 10 Myr Old T Tauri Stars TW Hydrae and Hen 3-600A.

    PubMed

    Muzerolle; Calvet; Briceño; Hartmann; Hillenbrand

    2000-05-20

    We have found that two members of the TW Hydrae association, TW Hydrae and Hen 3-600A, are still actively accreting, based on the ballistic infall signature of their broad Halpha emission profiles. We present the first quantitative analysis of accretion in these objects and conclude that the same accretion mechanisms which operate in the well-studied 1 Myr old T Tauri stars can and do occur in older (10 Myr) stars. We derive the first estimates of the disk mass accretion rate in TW Hya and Hen 3-600A, which are 1-2 orders of magnitude lower than the average rates in 1 Myr old objects. The decrease in accretion rates over 10 Myr, as well as the low fraction of TW Hya association objects still accreting, points to significant disk evolution, possibly linked to planet formation. Given the multiplicity of the Hen 3-600 system and the large UV excess of TW Hya, our results show that accretion disks can be surprisingly long lived in spite of the presence of companions and significant UV ionizing flux.

  8. Accretion onto a charged Kiselev black hole

    NASA Astrophysics Data System (ADS)

    Abbas, G.; Ditta, A.

    2018-04-01

    Accretion of matter onto a compact is one of the interesting astrophysical processes. Here, we study the accretion of matter onto a charged Kiselev black hole. The problem of static and spherically symmetric accretion of a polytropic fluid is explored for the analytic solution of equations of motion. We have investigated the necessary conditions for existence of the critical flow points and the mass accretion rate. Finally, we discuss the polytropic gas accretion in detail. It has been found that in the accretion process the quintessence and charge parameters play a dominant role.

  9. TOWARD A DETERMINISTIC MODEL OF PLANETARY FORMATION. VII. ECCENTRICITY DISTRIBUTION OF GAS GIANTS

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

    Ida, S.; Lin, D. N. C.; Nagasawa, M., E-mail: ida@geo.titech.ac.jp, E-mail: lin@ucolick.org, E-mail: nagasawa.m.ad@m.titech.ac.jp

    2013-09-20

    The ubiquity of planets and diversity of planetary systems reveal that planet formation encompasses many complex and competing processes. In this series of papers, we develop and upgrade a population synthesis model as a tool to identify the dominant physical effects and to calibrate the range of physical conditions. Recent planet searches have led to the discovery of many multiple-planet systems. Any theoretical models of their origins must take into account dynamical interactions between emerging protoplanets. Here, we introduce a prescription to approximate the close encounters between multiple planets. We apply this method to simulate the growth, migration, and dynamicalmore » interaction of planetary systems. Our models show that in relatively massive disks, several gas giants and rocky/icy planets emerge, migrate, and undergo dynamical instability. Secular perturbation between planets leads to orbital crossings, eccentricity excitation, and planetary ejection. In disks with modest masses, two or less gas giants form with multiple super-Earths. Orbital stability in these systems is generally maintained and they retain the kinematic structure after gas in their natal disks is depleted. These results reproduce the observed planetary mass-eccentricity and semimajor axis-eccentricity correlations. They also suggest that emerging gas giants can scatter residual cores to the outer disk regions. Subsequent in situ gas accretion onto these cores can lead to the formation of distant (∼> 30 AU) gas giants with nearly circular orbits.« less

  10. The early history of giant cell arteritis and polymyalgia rheumatica: first descriptions to 1970.

    PubMed

    Hunder, Gene G

    2006-08-01

    Giant cell arteritis and polymyalgia rheumatica were described separately more than 100 years ago. However, the original reports of both conditions were neglected for many years. After the article by Horton et al on giant cell arteritis in the 1930s and studies published by others in the 1940s, giant cell arteritis began to be recognized as a specific disease. In the 1950s and 1960s, many of the numerous presentations and complications of giant cell arteritis were recorded. In a somewhat similar fashion, physicians became cognizant of polymyalgia rheumatica only after several independent descriptions in the 1940s and 1950s. The rapid response of both syndromes to glucocorticoid therapy was discovered shortly after cortisone's effect on rheumatoid arthritis was described. The origin of the proximal aching and stiffness in polymyalgia rheumatica was more difficult to understand. The relatively minor findings in the joints on physical examination seemed insufficient to account for the severe discomfort. As the link between polymyalgia rheumatica and giant cell arteritis became apparent, some thought the aching in polymyalgia rheumatica was related to vasculitis. The debate about whether proximal synovitis or vasculitis was the cause of the symptoms continued after 1970. Although the reason these 2 conditions were associated was not considered by 1970, the establishment of the syndromes as clinically linked entities provided the groundwork for further progress in the next decades.

  11. Six Degrees-of-Freedom Ascent Control for Small-Body Touch and Go

    NASA Technical Reports Server (NTRS)

    Blackmore, Lars James C.

    2011-01-01

    A document discusses a method of controlling touch and go (TAG) of a spacecraft to correct attitude, while ensuring a safe ascent. TAG is a concept whereby a spacecraft is in contact with the surface of a small body, such as a comet or asteroid, for a few seconds or less before ascending to a safe location away from the small body. The report describes a controller that corrects attitude and ensures that the spacecraft ascends to a safe state as quickly as possible. The approach allocates a certain amount of control authority to attitude control, and uses the rest to accelerate the spacecraft as quickly as possible in the ascent direction. The relative allocation to attitude and position is a parameter whose optimal value is determined using a ground software tool. This new approach makes use of the full control authority of the spacecraft to correct the errors imparted by the contact, and ascend as quickly as possible. This is in contrast to prior approaches, which do not optimize the ascent acceleration.

  12. Toward a Deterministic Model of Planetary Formation. II. The Formation and Retention of Gas Giant Planets around Stars with a Range of Metallicities

    NASA Astrophysics Data System (ADS)

    Ida, Shigeru; Lin, D. N. C.

    2004-11-01

    The apparent dependence of detection frequency of extrasolar planets on the metallicity of their host stars is investigated with Monte Carlo simulations using a deterministic core-accretion planet formation model. According to this model, gas giants formed and acquired their mass Mp through planetesimal coagulation followed by the emergence of cores onto which gas is accreted. These protoplanets migrate and attain their asymptotic semimajor axis a through tidal interaction with their nascent disk. Based on the observed properties of protostellar disks, we generate an Mp-a distribution. Our results reproduce the observed lack of planets with intermediate mass Mp=10-100 M⊕ and a<~3 AU and with large mass Mp>~103 M⊕ and a<~0.2 AU. Based on the simulated Mp-a distributions, we also evaluate the metallicity dependence of the fraction of stars harboring planets that are detectable with current radial velocity surveys. If protostellar disks attain the same fraction of heavy elements as contained in their host stars, the detection probability around metal-rich stars would be greatly enhanced because protoplanetary cores formed in them can grow to several Earth masses prior to their depletion. These large masses are required for the cores to initiate rapid gas accretion and to transform into giant planets. The theoretically extrapolated metallicity dependence is consistent with the observations. This correlation does not arise naturally in the gravitational-instability scenario. We also suggest other metallicity dependences of the planet distributions that can be tested by ongoing observations.

  13. Effects of Ascent to High Altitude on Human Antimycobacterial Immunity

    PubMed Central

    Aldridge, Robert W.; Siedner, Mark J.; Necochea, Alejandro; Leybell, Inna; Valencia, Teresa; Herrera, Beatriz; Wiles, Siouxsie; Friedland, Jon S.; Gilman, Robert H.; Evans, Carlton A.

    2013-01-01

    Background Tuberculosis infection, disease and mortality are all less common at high than low altitude and ascent to high altitude was historically recommended for treatment. The immunological and mycobacterial mechanisms underlying the association between altitude and tuberculosis are unclear. We studied the effects of altitude on mycobacteria and antimycobacterial immunity. Methods Antimycobacterial immunity was assayed in 15 healthy adults residing at low altitude before and after they ascended to 3400 meters; and in 47 long-term high-altitude residents. Antimycobacterial immunity was assessed as the extent to which participants’ whole blood supported or restricted growth of genetically modified luminescent Bacille Calmette-Guérin (BCG) mycobacteria during 96 hours incubation. We developed a simplified whole blood assay that could be used by a technician in a low-technology setting. We used this to compare mycobacterial growth in participants’ whole blood versus positive-control culture broth and versus negative-control plasma. Results Measurements of mycobacterial luminescence predicted the number of mycobacterial colonies cultured six weeks later. At low altitude, mycobacteria grew in blood at similar rates to positive-control culture broth whereas ascent to high altitude was associated with restriction (p≤0.002) of mycobacterial growth to be 4-times less than in culture broth. At low altitude, mycobacteria grew in blood 25-times more than negative-control plasma whereas ascent to high altitude was associated with restriction (p≤0.01) of mycobacterial growth to be only 6-times more than in plasma. There was no evidence of differences in antimycobacterial immunity at high altitude between people who had recently ascended to high altitude versus long-term high-altitude residents. Conclusions An assay of luminescent mycobacterial growth in whole blood was adapted and found to be feasible in low-resource settings. This demonstrated that ascent to or

  14. Mars Ascent Vehicle Design for Human Exploration

    NASA Technical Reports Server (NTRS)

    Polsgrove, Tara; Thomas, Dan; Sutherlin, Steven; Stephens, Walter; Rucker, Michelle

    2015-01-01

    In NASA's evolvable Mars campaign, transportation architectures for human missions to Mars rely on a combination of solar electric propulsion and chemical propulsion systems. Minimizing the Mars ascent vehicle (MAV) mass is critical in reducing the overall lander mass and also eases the requirements placed on the transportation stages. This paper presents the results of a conceptual design study to obtain a minimal MAV configuration, including subsystem designs and mass summaries.

  15. First report of Enterocytozoon bieneusi from giant pandas (Ailuropoda melanoleuca) and red pandas (Ailurus fulgens) in China.

    PubMed

    Tian, Ge-Ru; Zhao, Guang-Hui; Du, Shuai-Zhi; Hu, Xiong-Feng; Wang, Hui-Bao; Zhang, Long-Xian; Yu, San-Ke

    2015-08-01

    Enterocytozoon bieneusi is an emerging and opportunistic enteric pathogen triggering diarrhea and enteric disease in humans and animals. Despite extensive research on this pathogen, the prevalence and genotypes of E. bieneusi infection in precious wild animals of giant and red pandas have not been reported. In the present study, 82 faecal specimens were collected from 46 giant pandas (Ailuropoda melanoleuca) and 36 red pandas (Ailurus fulgens) in the northwest of China. By PCR and sequencing of the internal transcribed spacer (ITS) region of the ribosomal RNA (rRNA) gene of E. bieneusi, an overall infection rate of 10.98% (9/82) was observed in pandas, with 8.70% (4/46) for giant pandas, and 13.89% (5/36) for red pandas. Two ITS genotypes were identified: the novel genotype I-like (n=4) and genotype EbpC (n=5). Multilocus sequence typing (MLST) employing three microsatellites (MS1, MS3 and MS7) and one minisatellite (MS4) showed that nine, six, six and nine positive products were amplified and sequenced successfully at four respective loci. A phylogenetic analysis based on a neighbor-joining tree of the ITS gene sequences of E. bieneusi indicated that the genotype EbpC fell into 1d of group 1 of zoonotic potential, and the novel genotype I-like was clustered into group 2. The present study firstly indicated the presence of E. bieneusi in giant and red pandas, and these results suggested that integrated strategies should be implemented to effectively protect pandas and humans from infecting E. bieneusi in China. Copyright © 2015 Elsevier B.V. All rights reserved.

  16. SRB ascent aerodynamic heating design criteria reduction study, volume 2

    NASA Technical Reports Server (NTRS)

    Crain, W. K.; Frost, C. L.; Engel, C. D.

    1989-01-01

    Data are presented for the wind tunnel interference heating factor data base, the timewise tabulated ascent design environments, and the timewise plotted environments comparing the REMTECH results to the Rockwell RI-IVBC-3 results.

  17. Gravity signatures of terrane accretion

    NASA Astrophysics Data System (ADS)

    Franco, Heather; Abbott, Dallas

    1999-01-01

    In modern collisional environments, accreted terranes are bracketed by forearc gravity lows, a gravitational feature which results from the abandonment of the original trench and the initiation of a new trench seaward of the accreted terrane. The size and shape of the gravity low depends on the type of accreted feature and the strength of the formerly subducting plate. Along the Central American trench, the accretion of Gorgona Island caused a seaward trench jump of 48 to 66 km. The relict trench axes show up as gravity lows behind the trench with minimum values of -78 mgal (N of Gorgona) and -49 mgal (S of Gorgona) respectively. These forearc gravity lows have little or no topographic expression. The active trench immediately seaward of these forearc gravity lows has minimum gravity values of -59 mgal (N of Gorgona) and -58 mgal (S of Gorgona), respectively. In the north, the active trench has a less pronounced gravity low than the sediment covered forearc. In the Mariana arc, two Cretaceous seamounts have been accreted to the Eocene arc. The northern seamount is most likely a large block, the southern seamount may be a thrust slice. These more recent accretion events have produced modest forearc topographic and gravity lows in comparison with the topographic and gravity lows within the active trench. However, the minimum values of the Mariana forearc gravity lows are modest only by comparison to the Mariana Trench (-216 mgal); their absolute values are more negative than at Gorgona Island (-145 to -146 mgal). We speculate that the forearc gravity lows and seaward trench jumps near Gorgona Island were produced by the accretion of a hotspot island from a strong plate. The Mariana gravity lows and seaward trench jumps (or thrust slices) were the result of breaking a relatively weak plate close to the seamount edifice. These gravity lows resulting from accretion events should be preserved in older accreted terranes.

  18. ASTEROSEISMOLOGY OF RED GIANTS FROM THE FIRST FOUR MONTHS OF KEPLER DATA: GLOBAL OSCILLATION PARAMETERS FOR 800 STARS

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

    Huber, D.; Bedding, T. R.; Stello, D.

    2010-11-10

    We have studied solar-like oscillations in {approx}800 red giant stars using Kepler long-cadence photometry. The sample includes stars ranging in evolution from the lower part of the red giant branch to the helium main sequence. We investigate the relation between the large frequency separation ({Delta}{nu}) and the frequency of maximum power ({nu}{sub max}) and show that it is different for red giants than for main-sequence stars, which is consistent with evolutionary models and scaling relations. The distributions of {nu}{sub max} and {Delta}{nu} are in qualitative agreement with a simple stellar population model of the Kepler field, including the first evidencemore » for a secondary clump population characterized by M {approx}> 2 M{sub sun} and {nu}{sub max} {approx_equal} 40-110 {mu}Hz. We measured the small frequency separations {delta}{nu}{sub 02} and {delta}{nu}{sub 01} in over 400 stars and {delta}{nu}{sub 03} in over 40. We present C-D diagrams for l = 1, 2, and 3 and show that the frequency separation ratios {delta}{nu}{sub 02}/{Delta}{nu} and {delta}{nu}{sub 01}/{Delta}{nu} have opposite trends as a function of {Delta}{nu}. The data show a narrowing of the l = 1 ridge toward lower {nu}{sub max}, in agreement with models predicting more efficient mode trapping in stars with higher luminosity. We investigate the offset {epsilon} in the asymptotic relation and find a clear correlation with {Delta}{nu}, demonstrating that it is related to fundamental stellar parameters. Finally, we present the first amplitude-{nu}{sub max} relation for Kepler red giants. We observe a lack of low-amplitude stars for {nu}{sub max} {approx}> 110 {mu}Hz and find that, for a given {nu}{sub max} between 40 and 110 {mu}Hz, stars with lower {Delta}{nu} (and consequently higher mass) tend to show lower amplitudes than stars with higher {Delta}{nu}.« less

  19. Accretion Rates for T Tauri Stars Using Nearly Simultaneous Ultraviolet and Optical Spectra

    NASA Astrophysics Data System (ADS)

    Ingleby, Laura; Calvet, Nuria; Herczeg, Gregory; Blaty, Alex; Walter, Frederick; Ardila, David; Alexander, Richard; Edwards, Suzan; Espaillat, Catherine; Gregory, Scott G.; Hillenbrand, Lynne; Brown, Alexander

    2013-04-01

    We analyze the accretion properties of 21 low-mass T Tauri stars using a data set of contemporaneous near-UV (NUV) through optical observations obtained with the Hubble Space Telescope Imaging Spectrograph and the ground-based Small and Medium Aperture Research Telescope System, a unique data set because of the nearly simultaneous broad wavelength coverage. Our data set includes accreting T Tauri stars in Taurus, Chamaeleon I, η Chamaeleon, and the TW Hydra Association. For each source we calculate the accretion rate (\\dot{M}) by fitting the NUV and optical excesses above the photosphere, produced in the accretion shock, introducing multiple accretion components characterized by a range in energy flux (or density) for the first time. This treatment is motivated by models of the magnetospheric geometry and accretion footprints, which predict that high-density, low filling factor accretion spots coexist with low-density, high filling factor spots. By fitting the UV and optical spectra with multiple accretion components, we can explain excesses which have been observed in the near-IR. Comparing our estimates of \\dot{M} to previous estimates, we find some discrepancies; however, they may be accounted for when considering assumptions for the amount of extinction and variability in optical spectra. Therefore, we confirm many previous estimates of the accretion rate. Finally, we measure emission line luminosities from the same spectra used for the \\dot{M} estimates, to produce correlations between accretion indicators (Hβ, Ca II K, C II], and Mg II) and accretion properties obtained simultaneously.

  20. The Importance of Rotational Time-scales in Accretion Variability

    NASA Astrophysics Data System (ADS)

    Costigan, Gráinne; Vink, Joirck; Scholz, Aleks; Testi, Leonardo; Ray, Tom

    2013-07-01

    For the first few million years, one of the dominant sources of emission from a low mass young stellar object is from accretion. This process regulates the flow of material and angular moments from the surroundings to the central object, and is thought to play an important role in the definition of the long term stellar properties. Variability is a well documented attribute of accretion, and has been observed on time-scales of from days to years. However, where these variations come from is not clear. Th current model for accretion is magnetospheric accretion, where the stellar magnetic field truncates the disc, allowing the matter to flow from the disc onto the surface of the star. This model allows for variations in the accretion rate to come from many different sources, such as the magnetic field, the circumstellar disc and the interaction of the different parts of the system. We have been studying unbiased samples of accretors in order to identify the dominant time-scales and typical magnitudes of variations. In this way different sources of variations can be excluded and any missing physics in these systems identified. Through our previous work with the Long-term Accretion Monitoring Program (LAMP), we found 10 accretors in the ChaI region, whose variability is dominated by short term variations of 2 weeks. This was the shortest time period between spectroscopic observations which spanned 15 months, and rules out large scale processes in the disk as origins of this variability. On the basis of this study we have gone further to study the accretion signature H-alpha, over the time-scales of minutes and days in a set of Herbig Ae and T Tauri stars. Using the same methods as we used in LAMP we found the dominant time-scales of variations to be days. These samples both point towards rotation period of these objects as being an important time-scale for accretion variations. This allows us to indicate which are the most likely sources of these variations.

  1. Seismometer reading from impact made by Lunar Module ascent stage

    NASA Image and Video Library

    1969-11-20

    S69-59547 (20 Nov. 1969) --- The seismometer reading from the impact made by the Lunar Module ascent stage when it struck the lunar surface. The impact was registered by the Passive Seismic Experiment Package which was deployed on the moon by the Apollo 12 astronauts. PSEP, which is a component of the Apollo Lunar Surface Experiments Package, will detect surface tilt produced by tidal deformations, moonquakes, and meteorite impacts. The LM's ascent stage was jettisoned and sent journeying toward impact on the moon after astronauts Charles Conrad Jr. and Alan L. Bean returned to lunar orbit and rejoined astronaut Richard F. Gordon Jr. in the Command and Service Modules. Information from the PSEP is transmitted to Earth through the ALSEP's central station and monitored by equipment at the Manned Spacecraft Center.

  2. Episodic accretion in binary protostars emerging from self-gravitating solar mass cores

    NASA Astrophysics Data System (ADS)

    Riaz, R.; Vanaverbeke, S.; Schleicher, D. R. G.

    2018-06-01

    Observations show a large spread in the luminosities of young protostars, which are frequently explained in the context of episodic accretion. We tested this scenario with numerical simulations that follow the collapse of a solar mass molecular cloud using the GRADSPH code, thereby varying the strength of the initial perturbations and temperature of the cores. A specific emphasis of this paper is to investigate the role of binaries and multiple systems in the context of episodic accretion and to compare their evolution to the evolution in isolated fragments. Our models form a variety of low-mass protostellar objects including single, binary, and triple systems in which binaries are more active in exhibiting episodic accretion than isolated protostars. We also find a general decreasing trend in the average mass accretion rate over time, suggesting that the majority of the protostellar mass is accreted within the first 105 years. This result can potentially help to explain the surprisingly low average luminosities in the majority of the protostellar population.

  3. A Three-dimensional Simulation of a Magnetized Accretion Disk: Fast Funnel Accretion onto a Weakly Magnetized Star

    NASA Astrophysics Data System (ADS)

    Takasao, Shinsuke; Tomida, Kengo; Iwasaki, Kazunari; Suzuki, Takeru K.

    2018-04-01

    We present the results of a global, three-dimensional magnetohydrodynamics simulation of an accretion disk with a rotating, weakly magnetized central star. The disk is threaded by a weak, large-scale poloidal magnetic field, and the central star has no strong stellar magnetosphere initially. Our simulation investigates the structure of the accretion flows from a turbulent accretion disk onto the star. The simulation reveals that fast accretion onto the star at high latitudes occurs even without a stellar magnetosphere. We find that the failed disk wind becomes the fast, high-latitude accretion as a result of angular momentum exchange mediated by magnetic fields well above the disk, where the Lorentz force that decelerates the rotational motion of gas can be comparable to the centrifugal force. Unlike the classical magnetospheric accretion scenario, fast accretion streams are not guided by magnetic fields of the stellar magnetosphere. Nevertheless, the accretion velocity reaches the free-fall velocity at the stellar surface due to the efficient angular momentum loss at a distant place from the star. This study provides a possible explanation why Herbig Ae/Be stars whose magnetic fields are generally not strong enough to form magnetospheres also show indications of fast accretion. A magnetically driven jet is not formed from the disk in our model. The differential rotation cannot generate sufficiently strong magnetic fields for the jet acceleration because the Parker instability interrupts the field amplification.

  4. A Simple Analytic Model for Estimating Mars Ascent Vehicle Mass and Performance

    NASA Technical Reports Server (NTRS)

    Woolley, Ryan C.

    2014-01-01

    The Mars Ascent Vehicle (MAV) is a crucial component in any sample return campaign. In this paper we present a universal model for a two-stage MAV along with the analytic equations and simple parametric relationships necessary to quickly estimate MAV mass and performance. Ascent trajectories can be modeled as two-burn transfers from the surface with appropriate loss estimations for finite burns, steering, and drag. Minimizing lift-off mass is achieved by balancing optimized staging and an optimized path-to-orbit. This model allows designers to quickly find optimized solutions and to see the effects of design choices.

  5. Kinematics of metal-poor giants in an inner-halo field, with implications for disk formation

    NASA Technical Reports Server (NTRS)

    Morrison, Heather L.

    1993-01-01

    A sample of approximately 100 predominantly metal-weak giants, identified in a high-latitude field towards the galactic center using an automated objective-prism survey technique, is presented. Abundances and radial velocities have been measured for these giants, whose distances from the Sun range from 1 to 18 kpc. While the extremely metal-weak stars in the field have halo kinematics, the majority of the stars with intermediate abundance have thick disk kinematics, despite the fact that their average distance from the galactic plane is 3 kpc. The most satisfactory explanation for this effect is that the inner halo is moderately flattened, and the metal-weak stars of the thick disk have a scale height of about 2 kpc. It is suggested that the thick disk may have formed in a dissipational collapse, rather than in a separate event such as the accretion of a small satellite galaxy.

  6. Mixed ice accretion on aircraft wings

    NASA Astrophysics Data System (ADS)

    Janjua, Zaid A.; Turnbull, Barbara; Hibberd, Stephen; Choi, Kwing-So

    2018-02-01

    Ice accretion is a problematic natural phenomenon that affects a wide range of engineering applications including power cables, radio masts, and wind turbines. Accretion on aircraft wings occurs when supercooled water droplets freeze instantaneously on impact to form rime ice or runback as water along the wing to form glaze ice. Most models to date have ignored the accretion of mixed ice, which is a combination of rime and glaze. A parameter we term the "freezing fraction" is defined as the fraction of a supercooled droplet that freezes on impact with the top surface of the accretion ice to explore the concept of mixed ice accretion. Additionally we consider different "packing densities" of rime ice, mimicking the different bulk rime densities observed in nature. Ice accretion is considered in four stages: rime, primary mixed, secondary mixed, and glaze ice. Predictions match with existing models and experimental data in the limiting rime and glaze cases. The mixed ice formulation however provides additional insight into the composition of the overall ice structure, which ultimately influences adhesion and ice thickness, and shows that for similar atmospheric parameter ranges, this simple mixed ice description leads to very different accretion rates. A simple one-dimensional energy balance was solved to show how this freezing fraction parameter increases with decrease in atmospheric temperature, with lower freezing fraction promoting glaze ice accretion.

  7. Ultrafast syn-eruptive degassing and ascent trigger high-energy basic eruptions.

    PubMed

    Giuffrida, Marisa; Viccaro, Marco; Ottolini, Luisa

    2018-01-09

    Lithium gradients in plagioclase are capable of recording extremely short-lived processes associated with gas loss from magmas prior to extrusion at the surface. We present SIMS profiles of the 7 Li/ 30 Si ion ratio in plagioclase crystals from products of the paroxysmal sequence that occurred in the period 2011-2013 at Mt. Etna (Italy) in an attempt to constrain the final ascent and degassing processes leading to these powerful eruptions involving basic magma. The observed Li concentrations reflect cycles of Li addition to the melt through gas flushing, and a syn-eruptive stage of magma degassing driven by decompression that finally produce significant Li depletion from the melt. Modeling the decreases in Li concentration in plagioclase by diffusion allowed determination of magma ascent timescales that are on the order of minutes or less. Knowledge of the storage depth beneath the volcano has led to the quantification of a mean magma ascent velocity of ~43 m/s for paroxysmal eruptions at Etna. The importance of these results relies on the application of methods, recently used exclusively for closed-system volcanoes producing violent eruptions, to open-conduit systems that have generally quiet eruptive periods of activity sometimes interrupted by sudden re-awakening and the production of anomalously energetic eruptions.

  8. Mars’ Growth Stunted by an Early Giant Planet Instability

    NASA Astrophysics Data System (ADS)

    Clement, Matthew; Kaib, Nathan A.; Raymond, Sean N.; Walsh, Kevin J.

    2017-10-01

    Many dynamical aspects of the solar system can be explained by the outer planets experiencing a period of orbital instability. Though often correlated with a perceived delayed spike in the lunar cratering record known as the Late Heavy Bombardment (LHB), recent work suggests that this event may have occurred during the epoch of terrestrial planet formation. Though current simulations of terrestrial accretion can reproduce many observed qualities of the solar system, replicating the small mass of Mars requires modification to standard planet formation models. Here we use direct numerical simulations to show that an early instability in the outer solar system regularly yields properly sized Mars analogues. In 80% of simulations, we produce a Mars of the appropriate mass. Our most successful outcomes occur when the terrestrial planets evolve 10 million years (Myr), and accrete several Mars sized embryos in the Mars forming region before the instability takes place. Mars is left behind as a stranded embryo, while the remainder of these bodies are either ejected from the system or scattered towards the inner solar system where they deliver water to Earth. An early giant planet instability can thus replicate both the inner and outer solar system in a single model.

  9. Orion Guidance and Control Ascent Abort Algorithm Design and Performance Results

    NASA Technical Reports Server (NTRS)

    Proud, Ryan W.; Bendle, John R.; Tedesco, Mark B.; Hart, Jeremy J.

    2009-01-01

    During the ascent flight phase of NASA s Constellation Program, the Ares launch vehicle propels the Orion crew vehicle to an agreed to insertion target. If a failure occurs at any point in time during ascent then a system must be in place to abort the mission and return the crew to a safe landing with a high probability of success. To achieve continuous abort coverage one of two sets of effectors is used. Either the Launch Abort System (LAS), consisting of the Attitude Control Motor (ACM) and the Abort Motor (AM), or the Service Module (SM), consisting of SM Orion Main Engine (OME), Auxiliary (Aux) Jets, and Reaction Control System (RCS) jets, is used. The LAS effectors are used for aborts from liftoff through the first 30 seconds of second stage flight. The SM effectors are used from that point through Main Engine Cutoff (MECO). There are two distinct sets of Guidance and Control (G&C) algorithms that are designed to maximize the performance of these abort effectors. This paper will outline the necessary inputs to the G&C subsystem, the preliminary design of the G&C algorithms, the ability of the algorithms to predict what abort modes are achievable, and the resulting success of the abort system. Abort success will be measured against the Preliminary Design Review (PDR) abort performance metrics and overall performance will be reported. Finally, potential improvements to the G&C design will be discussed.

  10. EFFECTS OF DYNAMICAL EVOLUTION OF GIANT PLANETS ON THE DELIVERY OF ATMOPHILE ELEMENTS DURING TERRESTRIAL PLANET FORMATION

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

    Matsumura, Soko; Brasser, Ramon; Ida, Shigeru, E-mail: s.matsumura@dundee.ac.uk

    2016-02-10

    Recent observations started revealing the compositions of protostellar disks and planets beyond the solar system. In this paper, we explore how the compositions of terrestrial planets are affected by the dynamical evolution of giant planets. We estimate the initial compositions of the building blocks of these rocky planets by using a simple condensation model, and numerically study the compositions of planets formed in a few different formation models of the solar system. We find that the abundances of refractory and moderately volatile elements are nearly independent of formation models, and that all the models could reproduce the abundances of thesemore » elements of the Earth. The abundances of atmophile elements, on the other hand, depend on the scattering rate of icy planetesimals into the inner disk, as well as the mixing rate of the inner planetesimal disk. For the classical formation model, neither of these mechanisms are efficient and the accretion of atmophile elements during the final assembly of terrestrial planets appears to be difficult. For the Grand Tack model, both of these mechanisms are efficient, which leads to a relatively uniform accretion of atmophile elements in the inner disk. It is also possible to have a “hybrid” scenario where the mixing is not very efficient but the scattering is efficient. The abundances of atmophile elements in this case increase with orbital radii. Such a scenario may occur in some of the extrasolar planetary systems, which are not accompanied by giant planets or those without strong perturbations from giants. We also confirm that the Grand Tack scenario leads to the distribution of asteroid analogues where rocky planetesimals tend to exist interior to icy ones, and show that their overall compositions are consistent with S-type and C-type chondrites, respectively.« less

  11. You’re Cut Off: HD and MHD Simulations of Truncated Accretion Disks

    NASA Astrophysics Data System (ADS)

    Hogg, J. Drew; Reynolds, Christopher S.

    2017-01-01

    Truncated accretion disks are commonly invoked to explain the spectro-temporal variability from accreting black holes in both small systems, i.e. state transitions in galactic black hole binaries (GBHBs), and large systems, i.e. low-luminosity active galactic nuclei (LLAGNs). In the canonical truncated disk model of moderately low accretion rate systems, gas in the inner region of the accretion disk occupies a hot, radiatively inefficient phase, which leads to a geometrically thick disk, while the gas in the outer region occupies a cooler, radiatively efficient phase that resides in the standard geometrically thin disk. Observationally, there is strong empirical evidence to support this phenomenological model, but a detailed understanding of the disk behavior is lacking. We present well-resolved hydrodynamic (HD) and magnetohydrodynamic (MHD) numerical models that use a toy cooling prescription to produce the first sustained truncated accretion disks. Using these simulations, we study the dynamics, angular momentum transport, and energetics of a truncated disk in the two different regimes. We compare the behaviors of the HD and MHD disks and emphasize the need to incorporate a full MHD treatment in any discussion of truncated accretion disk evolution.

  12. X-ray observations of the accreting Be/X-ray binary pulsar A 0535+26 in outburst

    NASA Astrophysics Data System (ADS)

    Caballero, I.

    2009-04-01

    Neutron stars are compact objects, characterized by R~10-14 km radius, M~1.4Msun and extremely high central densities ~10e15 g/cm^3. If they are part of a binary system, a flow of matter can take place from the companion star onto the neutron star. The accretion of matter onto neutron stars is one of the most powerful sources of energy in the universe. The accretion of matter takes place under extreme physical conditions, with magnetic fields in the range B~10^(8-15)G, which are impossible to reproduce on terrestrial laboratories. Therefore, accreting neutron stars are unique laboratories to study the matter under extreme conditions. In this thesis, X-ray observations of the accreting Be/X-ray binary A 0535+26 during a normal (type I) outburst are presented. In this system, the neutron star orbits around the optical companion HDE 245770 in an eccentric orbit, and sometimes presents X-ray outbursts (giant or normal) associated with the passage of the neutron star through the periastron. After more than eleven years of quiescence, A 0535+26 showed outbursting activity in 2005. The normal outburst analyzed in this work took place in August/September 2005, and reached a maximum X-ray flux of ~400 mCrab in the 5-100 kev range. The outburst, which lasted for ~30 days, was observed with the RXTE and INTEGRAL observatories. We have measured the spectrum of the source. In particular, two absorption-like features, interpreted as fundamental and first harmonic cyclotron resonant scattering features, have been detected at E~46 kev and E~102 kev with INTEGRAL and RXTE. Cyclotron lines are the only direct way to measure the magnetic field of a neutron star. Our observations have allowed to confirm the magnetic field of A 0535+26 at the site of the X-ray emission to be B~5x10^12 G. We studied the luminosity dependence of the cyclotron line in A 0535+26, and contrary to other sources, we found no significant variation of the cyclotron line energy with the luminosity. Changes of

  13. Giant aneurysms: A gender-specific complication of Kawasaki disease?

    PubMed

    Dietz, Sanne M; Kuipers, Irene M; Tacke, Carline E A; Koole, Jeffrey C D; Hutten, Barbara A; Kuijpers, Taco W

    2017-10-01

    Kawasaki disease (KD) is a pediatric vasculitis of unknown origin. Its main complication is the development of coronary artery aneurysms (CAA) with giant CAA at the end of the spectrum. In this cohort study, we evaluated the association between patient characteristics and the development of giant CAA based on z-scores. Multivariable, multinomial logistic regression analysis was used to identify variables associated with giant CAA. A total of 301 KD patients, comprising 216 patients without enlargement, 45 with small-sized, 19 with medium-sized, and 21 with giant CAA with all echocardiographies at our center were retrospectively included. Remarkably, 95% of patients with giant CAA were boys. In addition to 'no/late intravenous immunoglobulin (IVIG) treatment', 'male gender' (OR 16.23, 95% CI 1.88-140.13), 'age<1 year' (OR 7.49, 95% CI 2.29-24.46), and 'IVIG re-treatment (9.79, 95% CI 2.79-34.37)' were significantly associated with an increased risk of giant CAA, with patients without enlargement as reference. Compared to patients with medium-sized CAA, 'IVIG re-treatment' was significantly associated with giant CAA. The majority of giant CAA continued to increase in size during the first 40 days. We identified risk factors associated with an increased risk of giant CAA. The difference in variables between the giant CAA group and the other CAA subgroups suggests a separation between patients with the treatment-resistant giant CAA and the other IVIG-responsive patients, in which gender may be factored as a most relevant genetic trait. The increase in size during the first 2 months indicates the need for repeated echocardiography. Copyright © 2017 Japanese College of Cardiology. Published by Elsevier Ltd. All rights reserved.

  14. Gravitomagnetic acceleration of accretion disk matter to polar jets

    NASA Astrophysics Data System (ADS)

    Poirier, John; Mathews, Grant

    2016-03-01

    The motion of the masses of an accretion disk around a black hole creates a general relativistic, gravitomagnetic field (GEM) from the moving matter (be it charged or uncharged) of the accretion disk. This GEM field accelerates moving masses (neutral or charged) near the accretion disk vertically upward and away from the disk, and then inward toward the axis of the disk. As the accelerated material nears the axis with approximately vertical angles, a frame dragging effect contributes to the formation of narrow jets emanating from the poles. This GEM effect is numerically evaluated in the first post Newtonian (1PN) approximation from observable quantities like the mass and velocity of the disk. This GEM force is linear in the total mass of the accretion disk matter and quadratic in the velocity of matter near to the disk with approximately the same velocity. Since these masses and velocities can be quite high in astrophysical contexts, the GEM force, which in other contexts is weak, is quite significant. This GEM effect is compared to the ordinary electromagnetic effects applied to this problem in the past.

  15. Mars Ascent Vehicle Test Requirements and Terrestrial Validation

    NASA Technical Reports Server (NTRS)

    Dankanich, John W.; Cathey, Henry M.; Smith, David A.

    2011-01-01

    The Mars robotic sample return mission has been a potential flagship mission for NASA s science mission directorate for decades. The Mars Exploration Program and the planetary science decadal survey have highlighted both the science return of the Mars Sample Return mission, but also the need for risk reduction through technology development. One of the critical elements of the MSR mission is the Mars Ascent Vehicle, which must launch the sample from the surface of Mars and place it into low Mars orbit. The MAV has significant challenges to overcome due to the Martian environments and the Entry Descent and Landing system constraints. Launch vehicles typically have a relatively low success probability for early flights, and a thorough system level validation is warranted. The MAV flight environments are challenging and in some cases impossible to replicate terrestrially. The expected MAV environments have been evaluated and a first look of potential system test options has been explored. The terrestrial flight requirements and potential validation options are presented herein.

  16. Accretion flows onto supermassive black holes

    NASA Technical Reports Server (NTRS)

    Begelman, Mitchell C.

    1988-01-01

    The radiative and hydrodynamic properties of an angular momentum-dominated accretion flow onto a supermassive black hole depend largely on the ratio of the accretion rate to the Eddington accretion rate. High values of this ratio favor optically thick flows which produce largely thermal radiation, while optically thin 'two-temperature' flows may be present in systems with small values of this ratio. Observations of some AGN suggest that thermal and nonthermal sources of radiation may be of comparable importance in the 'central engine'. Consideration is given to the possibilities for coexistence of different modes of accretion in a single flow. One intriguing possibility is that runaway pair production may cause an optically thick 'accretion annulus' to form at the center of a two-temperature inflow.

  17. The effects of Venus' thermal structure on buoyant magma ascent

    NASA Technical Reports Server (NTRS)

    Sakimoto, S. E. H.; Zuber, M. T.

    1992-01-01

    The recent Magellan images have revealed a broad spatial distribution of surface volcanism on Venus. Previous work in modeling the ascent of magma on both Venus and Earth has indicated that the planetary thermal structure significantly influences the magmatic cooling rates and thus the amount of magma that can be transported to the surface before solidification. In order to understand which aspects of the thermal structure have the greatest influence on the cooling of ascending magma, we have constructed magma cooling curves for both plutonic and crack buoyant ascent mechanisms, and evaluated the curves for variations in the planetary mantle temperature, thermal gradient curvature with depth, surface temperature gradient, and surface temperature. The planetary thermal structure is modeled as T/T(sub 0) = 1-tau(1-Z/Z(sub 0)(exp n), where T is the temperature, T(sub 0) is the source depth temperature, tau = 1-(T(sub s)/T(sub 0)) where T(sub s) is the planetary surface temperature, Z is the depth, Z(sub 0) is the source depth, and n is a constant that controls thermal gradient curvature with depth. The equation is used both for mathematical convenience and flexibility, as well as its fit to the thermal gradients predicted by the cooling half-space models. We assume a constant velocity buoyant ascent, body-averaged magma temperatures and properties, an initially crystal-free magma, and the same liquidus and solidus for both Venus and Earth.

  18. Optimal lifting ascent trajectories for the space shuttle

    NASA Technical Reports Server (NTRS)

    Rau, T. R.; Elliott, J. R.

    1972-01-01

    The performance gains which are possible through the use of optimal trajectories for a particular space shuttle configuration are discussed. The spacecraft configurations and aerodynamic characteristics are described. Shuttle mission payload capability is examined with respect to the optimal orbit inclination for unconstrained, constrained, and nonlifting conditions. The effects of velocity loss and heating rate on the optimal ascent trajectory are investigated.

  19. Swimming behaviour and ascent paths of brook trout in a corrugated culvert

    USGS Publications Warehouse

    Goerig, Elsa; Bergeron, Normand E.; Castro-Santos, Theodore R.

    2017-01-01

    Culverts may restrict fish movements under some hydraulic conditions such as shallow flow depths or high velocities. Although swimming capacity imposes limits to passage performance, behaviour also plays an important role in the ability of fish to overcome velocity barriers. Corrugated metal culverts are characterized by unsteady flow and existence of low‐velocity zones, which can improve passage success. Here, we describe swimming behaviour and ascent paths of 148 wild brook trout in a 1.5‐m section of a corrugated metal culvert located in Raquette Stream, Québec, Canada. Five passage trials were conducted in mid‐August, corresponding to specific mean cross‐sectional flow velocities ranging from 0.30 to 0.63 m/s. Fish were individually introduced to the culvert and their movements recorded with a camera located above the water. Lateral and longitudinal positions were recorded at a rate of 3 Hz in order to identify ascent paths. These positions were related to the distribution of flow depths and velocities in the culvert. Brook trout selected flow velocities from 0.2 to 0.5 m/s during their ascents, which corresponded to the available flow velocities in the culvert at the low‐flow conditions. This however resulted in the use of low‐velocity zones at higher flows, mainly located along the walls of the culvert. Some fish also used the corrugations for sheltering, although the behaviour was marginal and did not occur at the highest flow condition. This study improves knowledge on fish behaviour during culvert ascents, which is an important aspect for developing reliable and accurate estimates of fish passage ability.

  20. Algorithm for Determination of Orion Ascent Abort Mode Achievability

    NASA Technical Reports Server (NTRS)

    Tedesco, Mark B.

    2011-01-01

    For human spaceflight missions, a launch vehicle failure poses the challenge of returning the crew safely to earth through environments that are often much more stressful than the nominal mission. Manned spaceflight vehicles require continuous abort capability throughout the ascent trajectory to protect the crew in the event of a failure of the launch vehicle. To provide continuous abort coverage during the ascent trajectory, different types of Orion abort modes have been developed. If a launch vehicle failure occurs, the crew must be able to quickly and accurately determine the appropriate abort mode to execute. Early in the ascent, while the Launch Abort System (LAS) is attached, abort mode selection is trivial, and any failures will result in a LAS abort. For failures after LAS jettison, the Service Module (SM) effectors are employed to perform abort maneuvers. Several different SM abort mode options are available depending on the current vehicle location and energy state. During this region of flight the selection of the abort mode that maximizes the survivability of the crew becomes non-trivial. To provide the most accurate and timely information to the crew and the onboard abort decision logic, on-board algorithms have been developed to propagate the abort trajectories based on the current launch vehicle performance and to predict the current abort capability of the Orion vehicle. This paper will provide an overview of the algorithm architecture for determining abort achievability as well as the scalar integration scheme that makes the onboard computation possible. Extension of the algorithm to assessing abort coverage impacts from Orion design modifications and launch vehicle trajectory modifications is also presented.

  1. Young Brown Dwarfs and Giant Planets as Companions to Weak-Line T Tauri Stars

    NASA Astrophysics Data System (ADS)

    Brandner, Wolfgang; Frink, Sabine; Kohler, Rainer; Kunkel, Michael

    Weak-line T Tauri stars, contrary to classical T Tauri stars, no longer possess massive circumstellar disks. In weak-line T Tauri stars, the circumstellar matter was either accreted onto the T Tauri star or has been redistributed. Disk instabilities in the outer disk might result in the formation of brown dwarfs and giant planets. Based on photometric and spectroscopic studies of ROSAT sources, we have selected an initial sample of 200 weak-line T Tauri stars in the Chamaeleon T association and the Scorpius-Centaurus OB association. In the course of follow-up observations, we identified visual and spectroscopic binary stars and excluded them from our final list, as the complex dynamics and gravitational interaction in binary systems might aggravate or even completely inhibit the formation of planets (depending on physical separation of the binary components and their mass ratio). The membership of individual stars to the associations was established from proper motion studies and radial velocity surveys. Our final sample consists of 70 single weak-line T Tauri stars. We have initiated a program to spatially resolve young brown dwarfs and young giant planets as companions to single weak-line T Tauri stars using adaptive optics at the ESO 3.6 m telescope and HST/NICMOS. In this poster we describe the observing strategy and present first results of our adaptive optics observations. An update on the program status can be found at http://www.astro.uiuc.edu/~brandner/text/bd/bd.html

  2. On the Maximum Mass of Accreting Primordial Supermassive Stars

    NASA Astrophysics Data System (ADS)

    Woods, T. E.; Heger, Alexander; Whalen, Daniel J.; Haemmerlé, Lionel; Klessen, Ralf S.

    2017-06-01

    Supermassive primordial stars are suspected to be the progenitors of the most massive quasars at z ˜ 6. Previous studies of such stars were either unable to resolve hydrodynamical timescales or considered stars in isolation, not in the extreme accretion flows in which they actually form. Therefore, they could not self-consistently predict their final masses at collapse, or those of the resulting supermassive black hole seeds, but rather invoked comparison to simple polytropic models. Here, we systematically examine the birth, evolution, and collapse of accreting, non-rotating supermassive stars under accretion rates of 0.01-10 M ⊙ yr-1 using the stellar evolution code Kepler. Our approach includes post-Newtonian corrections to the stellar structure and an adaptive nuclear network and can transition to following the hydrodynamic evolution of supermassive stars after they encounter the general relativistic instability. We find that this instability triggers the collapse of the star at masses of 150,000-330,000 M ⊙ for accretion rates of 0.1-10 M ⊙ yr-1, and that the final mass of the star scales roughly logarithmically with the rate. The structure of the star, and thus its stability against collapse, is sensitive to the treatment of convection and the heat content of the outer accreted envelope. Comparison with other codes suggests differences here may lead to small deviations in the evolutionary state of the star as a function of time, that worsen with accretion rate. Since the general relativistic instability leads to the immediate death of these stars, our models place an upper limit on the masses of the first quasars at birth.

  3. When Push Comes to Shove: Gap-opening, Disk Clearing and the In Situ Formation of Giant Planets

    NASA Technical Reports Server (NTRS)

    Mosqueira, I.; Estrada, P. R.

    2004-01-01

    Here we investigate a scenario in which cores as small as a few Earth masses stall in the terrestrial planet region, but continue to grow as a result of the Type I migration of other Earth sized objects, taking place in a timescale approx. 10(exp 6) years similar to the disk clearing timescale (such migration may thus significantly reduce the accretion efficiency, particularly in the terrestrial planet region). Since the core may intercept such inwardly migrating objects (possibly by altering the surface density to the point that the object stalls within the core's feeding zone) or coalesce with neighboring cores, its growth may continue until it reaches a CCM. The question then arises whether such a core can accrete enough gas to become a Jovian-sized giant planet. In the limit of low opacity (such that the protoplanet s tidal torque fails to clear gas from its feeding zone in time to prevent its accretion), the final mass of the planet is given by the gaseous isolation mass (provided alpha is < or approx. = 10(exp -4) and that the gas component dominates the planet's mass).

  4. Does a microprocessor-controlled prosthetic knee affect stair ascent strategies in persons with transfemoral amputation?

    PubMed

    Aldridge Whitehead, Jennifer M; Wolf, Erik J; Scoville, Charles R; Wilken, Jason M

    2014-10-01

    Stair ascent can be difficult for individuals with transfemoral amputation because of the loss of knee function. Most individuals with transfemoral amputation use either a step-to-step (nonreciprocal, advancing one stair at a time) or skip-step strategy (nonreciprocal, advancing two stairs at a time), rather than a step-over-step (reciprocal) strategy, because step-to-step and skip-step allow the leading intact limb to do the majority of work. A new microprocessor-controlled knee (Ottobock X2(®)) uses flexion/extension resistance to allow step-over-step stair ascent. We compared self-selected stair ascent strategies between conventional and X2(®) prosthetic knees, examined between-limb differences, and differentiated stair ascent mechanics between X2(®) users and individuals without amputation. We also determined which factors are associated with differences in knee position during initial contact and swing within X2(®) users. Fourteen individuals with transfemoral amputation participated in stair ascent sessions while using conventional and X2(®) knees. Ten individuals without amputation also completed a stair ascent session. Lower-extremity stair ascent joint angles, moment, and powers and ground reaction forces were calculated using inverse dynamics during self-selected strategy and cadence and controlled cadence using a step-over-step strategy. One individual with amputation self-selected a step-over-step strategy while using a conventional knee, while 10 individuals self-selected a step-over-step strategy while using X2(®) knees. Individuals with amputation used greater prosthetic knee flexion during initial contact (32.5°, p = 0.003) and swing (68.2°, p = 0.001) with higher intersubject variability while using X2(®) knees compared to conventional knees (initial contact: 1.6°, swing: 6.2°). The increased prosthetic knee flexion while using X2(®) knees normalized knee kinematics to individuals without amputation during swing (88.4°, p = 0.179) but

  5. Some topics in the magnetohydrodynamics of accreting magnetic compact objects

    NASA Technical Reports Server (NTRS)

    Aly, J. J.

    1986-01-01

    Magnetic compact objects (neutron stars or white dwarfs) are currently thought to be present in many accreting systems that are releasing large amounts of energy. The magnetic field of the compact star may interact strongly with the accretion flow and play an essential role in the physics of these systems. Some magnetohydrodynamic (MHD) problems that are likely to be relevant in building up self-consistent models of the interaction between the accreting plasma and the star's magnetosphere are addressed in this series of lectures. The basic principles of MHD are first introduced and some important MHD mechanisms (Rayleigh-Taylor and Kelvin-Helmholtz instabilities; reconnection) are discussed, with particular reference to their role in allowing the infalling matter to penetrate the magnetosphere and mix with the field. The structure of a force-free magnetosphere and the possibility of quasistatic momentum and energy transfer between regions linked by field-aligned currents are then studied in some detail. Finally, the structure of axisymmetric accretion flows onto magnetic compact objects is considered.

  6. Supermassive black hole formation by cold accretion shocks in the first galaxies

    NASA Astrophysics Data System (ADS)

    Inayoshi, Kohei; Omukai, Kazuyuki

    2012-05-01

    We propose a new scenario for supermassive star (SMS: >rsim 105 M⊙) formation in shocked regions of colliding cold accretion flows near the centres of the first galaxies. Recent numerical simulations indicate that assembly of a typical first galaxy with virial temperature Tvir≳104 K proceeds via cold and dense flows penetrating deep to the centre, where supersonic streams collide with each other to develop a hot (˜104 K) and dense (˜103 cm-3) shocked gas. The post-shock layer first cools by efficient Lyα emission and contracts isobarically until ≃8000 K. Whether the layer continues its isobaric contraction depends on the density at this moment: if the density is high enough to excite H2 rovibrational levels collisionally (>rsim 104 cm-3), enhanced H2 collisional dissociation suppresses the gas from cooling further. In this case, the layer fragments into massive (>rsim 105 M⊙) clouds, which collapse isothermally (˜8000 K) by Lyα cooling without subsequent fragmentation. As an outcome, SMSs are expected to form and eventually evolve into the seeds of supermassive black holes (SMBHs). By calculating the thermal evolution of the post-shock gas, we delimit the range of post-shock conditions for SMS formation, which can be expressed as T≳6000 K (nH/104 cm-3)-1 for ? and T>rsim 5000 -6000 K for nH≳104 cm-3, depending somewhat on the initial ionization degree. We found that metal enrichment does not affect the above condition for metallicity below ≃10-3 Z⊙ if metals are in the gas phase, while condensation of several per cent of metals into dust decreases this critical value of metallicity by an order of magnitude. Unlike the previously proposed scenario for SMS formation, which postulates extremely strong ultraviolet radiation to quench H2 cooling, our scenario here naturally explains SMBH seed formation in the assembly process of the first galaxies, even without such strong radiation.

  7. Interpreting MAD within multiple accretion regimes

    NASA Astrophysics Data System (ADS)

    Mocz, Philip; Guo, Xinyi

    2015-02-01

    General relativistic magnetohydrodynamic (GRMHD) simulations of accreting black holes in the radiatively inefficient regime show that systems with sufficient magnetic poloidal flux become magnetically arrested disc (MAD) systems, with a well-defined relationship between the magnetic flux and the mass accretion rate. Recently, Zamaninasab et al. report that the jet magnetic flux and accretion disc luminosity are tightly correlated over 7 orders of magnitude for a sample of 76 radio-loud active galaxies, concluding that the data are explained by the MAD mode of accretion. Their analysis assumes radiatively efficient accretion, and their sample consists primarily of radiatively efficient sources, while GRMHD simulations of MAD thus far have been carried out in the radiatively inefficient regime. We propose a model to interpret MAD systems in the context of multiple accretion regimes, and apply it to the sample in Zamaninasab et al., along with additional radiatively inefficient sources from archival data. We show that most of the radiatively inefficient radio-loud galaxies are consistent with being MAD systems. Assuming the MAD relationship found in radiatively inefficient simulations holds at other accretion regimes, a significant fraction of our sample can be candidates for MAD systems. Future GRMHD simulations have yet to verify the validity of this assumption.

  8. Spin Evolution of Accreting Young Stars. II. Effect of Accretion-powered Stellar Winds

    NASA Astrophysics Data System (ADS)

    Matt, Sean P.; Pinzón, Giovanni; Greene, Thomas P.; Pudritz, Ralph E.

    2012-01-01

    We present a model for the rotational evolution of a young, solar-mass star interacting magnetically with an accretion disk. As in a previous paper (Paper I), the model includes changes in the star's mass and radius as it descends the Hayashi track, a decreasing accretion rate, and a prescription for the angular momentum transfer between the star and disk. Paper I concluded that, for the relatively strong magnetic coupling expected in real systems, additional processes are necessary to explain the existence of slowly rotating pre-main-sequence stars. In the present paper, we extend the stellar spin model to include the effect of a spin-down torque that arises from an accretion-powered stellar wind (APSW). For a range of magnetic field strengths, accretion rates, initial spin rates, and mass outflow rates, the modeled stars exhibit rotation periods within the range of 1-10 days in the age range of 1-3 Myr. This range coincides with the bulk of the observed rotation periods, with the slow rotators corresponding to stars with the lowest accretion rates, strongest magnetic fields, and/or highest stellar wind mass outflow rates. We also make a direct, quantitative comparison between the APSW scenario and the two types of disk-locking models (namely, the X-wind and Ghosh & Lamb type models) and identify some remaining theoretical issues for understanding young star spins.

  9. In Situ Quantification of Experimental Ice Accretion on Tree Crowns Using Terrestrial Laser Scanning

    PubMed Central

    Nock, Charles A.; Greene, David; Delagrange, Sylvain; Follett, Matt; Fournier, Richard; Messier, Christian

    2013-01-01

    In the eastern hardwood forests of North America ice storms are an important disturbance event. Ice storms strongly influence community dynamics as well as urban infrastructure via catastrophic branch failure; further, the severity and frequency of ice storms are likely to increase with climate change. However, despite a long-standing interest into the effects of freezing rain on forests, the process of ice accretion and thus ice loading on branches remains poorly understood. This is because a number of challenges have prevented in situ measurements of ice on branches, including: 1) accessing and measuring branches in tall canopies, 2) limitations to travel during and immediately after events, and 3) the unpredictability of ice storms. Here, utilizing a novel combination of outdoor experimental icing, manual measurements and terrestrial laser scanning (TLS), we perform the first in situ measurements of ice accretion on branches at differing heights in a tree crown and with increasing duration of exposure. We found that TLS can reproduce both branch and iced branch diameters with high fidelity, but some TLS instruments do not detect ice. Contrary to the expectations of ice accretion models, radial accretion varied sharply within tree crowns. Initially, radial ice accretion was similar throughout the crown, but after 6.5 hours of irrigation (second scanning) radial ice accretion was much greater on upper branches than on lower (∼factor of 3). The slope of the change in radial ice accretion along branches increased with duration of exposure and was significantly greater at the second scanning compared to the first. We conclude that outdoor icing experiments coupled with the use of TLS provide a robust basis for evaluation of models of ice accretion and breakage in tree crowns, facilitating estimation of the limiting breaking stress of branches by accurate measurements of ice loads. PMID:23741409

  10. Modeling and Detection of Ice Particle Accretion in Aircraft Engine Compression Systems

    NASA Technical Reports Server (NTRS)

    May, Ryan D.; Simon, Donald L.; Guo, Ten-Huei

    2012-01-01

    The accretion of ice particles in the core of commercial aircraft engines has been an ongoing aviation safety challenge. While no accidents have resulted from this phenomenon to date, numerous engine power loss events ranging from uneventful recoveries to forced landings have been recorded. As a first step to enabling mitigation strategies during ice accretion, a detection scheme must be developed that is capable of being implemented on board modern engines. In this paper, a simple detection scheme is developed and tested using a realistic engine simulation with approximate ice accretion models based on data from a compressor design tool. These accretion models are implemented as modified Low Pressure Compressor maps and have the capability to shift engine performance based on a specified level of ice blockage. Based on results from this model, it is possible to detect the accretion of ice in the engine core by observing shifts in the typical sensed engine outputs. Results are presented in which, for a 0.1 percent false positive rate, a true positive detection rate of 98 percent is achieved.

  11. Star-disc interaction in galactic nuclei: orbits and rates of accreted stars

    NASA Astrophysics Data System (ADS)

    Kennedy, Gareth F.; Meiron, Yohai; Shukirgaliyev, Bekdaulet; Panamarev, Taras; Berczik, Peter; Just, Andreas; Spurzem, Rainer

    2016-07-01

    We examine the effect of an accretion disc on the orbits of stars in the central star cluster surrounding a central massive black hole by performing a suite of 39 high-accuracy direct N-body simulations using state-of-the art software and accelerator hardware, with particle numbers up to 128k. The primary focus is on the accretion rate of stars by the black hole (equivalent to their tidal disruption rate for black holes in the small to medium mass range) and the eccentricity distribution of these stars. Our simulations vary not only the particle number, but disc model (two models examined), spatial resolution at the centre (characterized by the numerical accretion radius) and softening length. The large parameter range and physically realistic modelling allow us for the first time to confidently extrapolate these results to real galactic centres. While in a real galactic centre both particle number and accretion radius differ by a few orders of magnitude from our models, which are constrained by numerical capability, we find that the stellar accretion rate converges for models with N ≥ 32k. The eccentricity distribution of accreted stars, however, does not converge. We find that there are two competing effects at work when improving the resolution: larger particle number leads to a smaller fraction of stars accreted on nearly circular orbits, while higher spatial resolution increases this fraction. We scale our simulations to some nearby galaxies and find that the expected boost in stellar accretion (or tidal disruption, which could be observed as X-ray flares) in the presence of a gas disc is about a factor of 10. Even with this boost, the accretion of mass from stars is still a factor of ˜100 slower than the accretion of gas from the disc. Thus, it seems accretion of stars is not a major contributor to black hole mass growth.

  12. Association of activities of daily living with the load during step ascent motion in nursing home-residing elderly individuals.

    PubMed

    Masaki, Mitsuhiro; Ikezoe, Tome; Kamiya, Midori; Araki, Kojiro; Isono, Ryo; Kato, Takehiro; Kusano, Ken; Tanaka, Masayo; Sato, Syunsuke; Hirono, Tetsuya; Kita, Kiyoshi; Tsuboyama, Tadao; Ichihashi, Noriaki

    2018-04-19

    This study aimed to examine the association of independence in ADL with the loads during step ascent motion and other motor functions in 32 nursing home-residing elderly individuals. Independence in ADL was assessed by using the functional independence measure (FIM). The loads at the upper (i.e., pulling up) and lower (i.e., pushing up) levels during step ascent task was measured on a step ascent platform. Hip extensor, knee extensor, plantar flexor muscle, and quadriceps setting strengths; lower extremity agility using the stepping test; and hip and knee joint pain severities were measured. One-legged stance and functional reach distance for balance, and maximal walking speed, timed up-and-go (TUG) time, five-chair-stand time, and step ascent time were also measured to assess mobility. Stepwise regression analysis revealed that the load at pushing up during step ascent motion and TUG time were significant and independent determinants of FIM score. FIM score decreased with decreased the load at pushing up and increased TUG time. The study results suggest that depending on task specificity, both one step up task's push up peak load during step ascent motion and TUG, can partially explain ADL's FIM score in the nursing home-residing elderly individuals. Lower extremity muscle strength, agility, pain or balance measures did not add to the prediction.

  13. A model for accretion of the terrestrial planets

    NASA Technical Reports Server (NTRS)

    Weidenschilling, S. J.

    1974-01-01

    One possible origin of the terrestrial planets involves their formation by gravitational accretion of particles originally in Keplerian orbits about the sun. Some implications of this theory are considered. A formal expression for the rate of mass accretion by a planet is developed. The formal singularity of the gravitational collision cross section for low relative velocities is shown to be without physical significance when the accreting bodies are in heliocentric orbits. The distribution of particle velocities relative to an accreting planet is considered; the mean velocity increases with time. The internal temperature of an accreting planet is shown to depend simply on the accretion rate. A simple and physically reasonable approximate expression for a planetary accretion rate is proposed.

  14. Multi-wavelength Observations of Accreting Compact Objects

    NASA Astrophysics Data System (ADS)

    Hernandez Santisteban, Juan Venancio

    2016-11-01

    The study of compact binaries invokes core astrophysical concepts ranging from stellar and sub-stellar atmospheres and interiors, stellar and binary evolution to physics of accretion. All of these systems are hosts to a compact object a white dwarf, neutron star or black hole ???? which produces a wide variety of exotic and energetic phenomena across the full electromagnetic spectrum. In this thesis, I will make use of multi-wavelength observations ranging from far-ultraviolet to nearinfrared in order to investigate two main topics: a) the late evolution of cataclysmic variables, and b) the accreting state of transitional millisecond pulsars. Firstly, I analyse the Very Large Telescope X-Shooter time-resolved spectroscopy of the short orbital period cataclysmic variable, SDSS J1433+1011, in Chapter 2. The wide wavelength coverage allowed me to perform a detailed characterisation of the system, as well as a direct mass measurement of the brown dwarf companion. I show that the donor in SDSS J1433+1011 successfully transitioned from the stellar to sub-stellar regime, as predicted by evolutionary models. Further light-curve modelling allowed me to show that a low albedo as well as a low heat circulation efficiency is present in the atmosphere of the sub-stellar donor. In Chapter 3, I analyse data from large synoptic surveys, such as SDSS and PTF, to search for the predicted population of dead cataclysmic variables. Following the non-detection of dead CVs, I was able to estimate the space density (?0 < 2?10????5 pc????3) of this hidden population via a Monte Carlo simulation of the Galactic CV population. In Chapter 4, I present Hubble Space Telescope ultraviolet observations of the transitional millisecond pulsar PSR J1023+0038, during its latest accretion state. In combination with optical and near-infrared data, I show that a standard accretion disc does not reach the magnetosphere of the neutron star. Instead, the overall spectrum is consistent with a truncated disc

  15. Shuttle/Agena study. Annex A: Ascent agena configuration

    NASA Technical Reports Server (NTRS)

    1972-01-01

    Details are presented on the Agena rocket vehicle description, vehicle interfaces, environmental constraints and test requirements, software programs, and ground support equipment. The basic design concept for the Ascent Agena is identified as optimization of reliability, flexibility, performance capabilities, and economy through the use of tested and flight-proven hardware. The development history of the Agenas A, B, and D is outlined and space applications are described.

  16. Probing thermonuclear burning on accreting neutron stars

    NASA Astrophysics Data System (ADS)

    Keek, L.

    2008-12-01

    Neutron stars are the most compact stars that can be directly observed, which makes them ideal laboratories to study physics at extreme densities. Neutron stars in low-mass X-ray binaries accrete hydrogen and helium from a lower-mass companion star through Roche lobe overflow. This matter undergoes thermonuclear burning in the neutron star envelope, creating carbon and heavier elements. The fusion process may proceed in an unstable manner, resulting in a thermonuclear runaway. Within one second the entire surface is burned, which is observable as a sharp rise in the emitted X-ray flux: a type I X-ray burst. Afterwards the neutron star surface cools down on a timescale of ten to one hundred seconds. During these bursts the surface of an accreting neutron star can be observed directly, which makes them instrumental for studying this type of stars. We have studied rare kinds of X-ray bursts. One such rare burst is the superburst, which lasts a thousand times longer than an ordinary burst. Superbursts are thought to result from the explosive burning of a thick carbon layer, which lies deeper inside the neutron star, close to a layer known as the crust. A prerequisite for the occurrence of a superburst is a high enough temperature, which is set by the temperature of the crust and the heat conductivity of the envelope. The latter is lowered by the presence of heavy elements that are produced during normal X-ray bursts. Using a large set of observations from the Wide Field Camera's onboard the BeppoSAX satellite, we find that, at high accretion rate, sources which do not exhibit normal bursts likely have a longer superburst recurrence time, than the observed superburst recurrence time of one burster. We analyze in detail the first superburst from a transient source, which went into outburst only 55 days before the superburst. Recent models of the neutron star crust predict that this is too small a time to heat the crust sufficiently for superburst ignition, indicating

  17. Body composition and hematological changes following ascents of Mt. Aconcagua and Mt. Everest.

    PubMed

    Wagner, Dale R

    2010-11-01

    Both Mt. Aconcagua (22,841.2 ft/6962 m) and Mt. Everest (29,035.4 ft/ 8850 m) are highly prized summits by mountaineers, yet there are no published studies comparing the physiological adaptations that occur from climbing both peaks. This case study compares the changes in body composition and hematology of a mountaineer who ascended both peaks. The male subject was 41 yr of age during the Aconcagua ascent and 43 yr of age during the Everest ascent, and had a history of ascents above 19,685 ft (6000 m). Baseline body composition measurements and blood draws were done within a few days of departure for both expeditions. Body composition was assessed by air displacement plethysmography and the blood draw consisted of a complete blood count (CBC). Post-expedition measurements were taken 10-14 d after reaching the summits. The ascent of Aconcagua resulted in a 2.0-kg drop in body mass and a reduction in body fat (15.5% to 12.1%), but blood chemistry remained within +/- 2% of baseline values. Body mass was reduced from 65.0 kg to 60.5 kg during the Everest expedition with a drop in body fat from 17.3% to 10.2%. Despite no change in RBCs there were increases in hemoglobin and mean corpuscular hemoglobin of 12.7% and 13.7%, respectively. It took the subject 12 d to reach the summit of Aconcagua, whereas it took 50 d to reach the summit of Everest. The longer duration at higher altitude for the Everest expedition resulted in more dramatic physiological changes.

  18. A Jupiter-mass planet around the K0 giant HD 208897

    NASA Astrophysics Data System (ADS)

    Yılmaz, M.; Sato, B.; Bikmaev, I.; Selam, S. O.; Izumiura, H.; Keskin, V.; Kambe, E.; Melnikov, S. S.; Galeev, A.; Özavcı, İ.; Irtuganov, E. N.; Zhuchkov, R. Ya.

    2017-11-01

    For over 10 years, we have carried out a precise radial velocity (RV) survey to find substellar companions around evolved G, K-type stars to extend our knowledge of planet formation and evolution. We performed high precision RV measurements for the giant star HD 208897 using an iodine (I2) absorption cell. The measurements were made at TÜBİTAK National Observatory (TUG; RTT150) and Okayama Astrophysical Observatory (OAO). For the origin of the periodic variation seen in the RV data of the star, we adopted a Keplerian motion caused by an unseen companion. We found that the star hosts a planet with a minimum mass of m2sini = 1.40 MJ, which is relatively low compared to those of known planets orbiting evolved intermediate-mass stars. The planet is in a nearly circular orbit with a period of P = 353 days at about 1 AU distance from the host star. The star is metal rich and located at the early phase of ascent along the red giant branch. The photometric observations of the star at Ankara University Kreiken Observatory (AUKR) and the Hipparcos photometry show no sign of variation with periods associated with the RV variation. Neither bisector velocity analysis nor analysis of the Ca II and Hα lines shows any correlation with the RV measurements. This work was supported by The Scientific and Technological Research Council of Turkey (TÜBİTAK), the project number of 114F099.

  19. Human Mars Ascent Configuration and Design Sensitivities

    NASA Technical Reports Server (NTRS)

    Polsgrove, Tara P.; Gernhardt, Mike; Collins, Tim; Martin, John

    2017-01-01

    Human missions to Mars may utilize several small cabins where crew members could live for days up to a couple of weeks. At the end of a Mars surface mission the Mars Ascent Vehicle (MAV) crew cabin would carry the crew to their destination in orbit in a matter of hours or days. Other small cabins in support of a Mars mission would include pressurized rovers that allow crew members to travel great distances from their primary habitat on Mars while unconstrained by time limits of typical EVAs. An orbital crew taxi could allow for exploration of the moons of Mars with minimum impact to the primary Earth-Mars transportation systems. A common crew cabin design that can perform in each of these applications is desired and could reduce the overall mission cost. However, for the MAV, the crew cabin size and mass can have a large impact on vehicle design and performance. The total ascent vehicle mass drives performance requirements for the Mars descent systems and the Earth to Mars transportation elements. Minimizing MAV mass is a priority and minimizing the crew cabin size and mass is one way to do that. This paper explores the benefits and impacts of using a common crew cabin design for the MAV. Results of a MAV configuration trade study will be presented along with mass and performance estimates for the selected design.

  20. ULXs from Accreting Neutron Stars: the Light Cylinder, the Stellar Surface, and Everything in Between

    NASA Astrophysics Data System (ADS)

    Parfrey, K.; Tchekhovskoy, A.

    2017-10-01

    I will present results from the first relativistic MHD simulations of accretion onto magnetized neutron stars, performed in general relativity in the Kerr spacetime. The accretion flow is geometrically thick with a relativistic-gas equation of state, appropriate for super-Eddington systems. Four regimes are recovered, in order of increasing stellar magnetic field strength (equivalently, decreasing mass accretion rate): (a) crushing of the stellar magnetosphere and direct accretion; (b) magnetically channeled accretion onto the stellar poles; (c) the propeller state, where material enters through the light cylinder but is prevented from accreting by the centrifugal barrier; (d) almost perfect exclusion of the accretion flow from the light cylinder by the pulsar's electromagnetic wind. A Poynting-flux-dominated relativistic jet, powered by stellar rotation, is produced when the intruding plasma succeeds in opening the pulsar's previously closed magnetic field lines. I will demonstrate the effect of changing the relative orientation of the stellar dipole and the large-scale magnetic field in the accreting plasma, and discuss our results in the context of the neutron-star-powered ULXs, as well as the transitional millisecond X-ray/radio pulsars and jet-launching neutron-star X-ray binaries.

  1. Two K Giants with Supermeteoritic Lithium Abundances: HDE 233517 and HD 9746

    NASA Astrophysics Data System (ADS)

    Balachandran, Suchitra C.; Fekel, Francis C.; Henry, Gregory W.; Uitenbroek, Han

    2000-10-01

    Two unusual Li-rich K giants, HDE 233517 and HD 9746, have been studied. Optical spectroscopy and photometry have been obtained to determine the fundamental parameters of HDE 233517, a single K2 III with an extremely large infrared excess. The spectra yield Teff=4475 K, logg=2.25, [Fe/H]=-0.37, vsini=17.6 km s-1, and a non-LTE logɛ(7Li)=4.22. Photometric observations reveal low-amplitude light variability with a period of 47.9 days. Combined with other parameters, this results in a minimum radius of 16.7 Rsolar and minimum distance of 617 pc. Comparison of spectra obtained in 1994 and 1996 show profile variations in Hα and the Na D lines indicative of changing mass loss. Optical spectra of HD 9746, a chromospherically active giant, were analyzed. The Teff=4400 K and revised Hipparcos-based gravity of logg=2.30 lead to a non-LTE logɛ(7Li)=3.75. The Li abundances in both stars are supermeteoritic. By the inclusion and exclusion of 6Li in the syntheses, we show that consistent 7Li abundances are obtained only when 6Li is absent in the synthetic fit. This provides evidence for fresh 7Li production and excludes both preservation of primordial Li and planetary accretion as viable scenarios for the formation of Li-rich giants. Both stars lie in close proximity to the red giant luminosity bump supporting the hypothesis that 7Li production is caused by the same mixing mechanism that later results in CN processing and lowers the 12C/13C ratio to nonstandard values.

  2. Magnetospheric Accretion in Close Pre-main-sequence Binaries

    NASA Astrophysics Data System (ADS)

    Ardila, David R.; Jonhs-Krull, Christopher; Herczeg, Gregory J.; Mathieu, Robert D.; Quijano-Vodniza, Alberto

    2015-10-01

    The transfer of matter between a circumbinary disk and a young binary system remains poorly understood, obscuring the interpretation of accretion indicators. To explore the behavior of these indicators in multiple systems, we have performed the first systematic time-domain study of young binaries in the ultraviolet. We obtained far- and near-ultraviolet HST/COS spectra of the young spectroscopic binaries DQ Tau and UZ Tau E. Here we focus on the continuum from 2800 to 3200 Å and on the C iv doublet (λλ1548.19, 1550.77 Å) as accretion diagnostics. Each system was observed over three or four consecutive binary orbits, at phases ∼0, 0.2, 0.5, and 0.7. Those observations are complemented by ground-based U-band measurements. Contrary to model predictions, we do not detect any clear correlation between accretion luminosity and phase. Further, we do not detect any correlation between C iv flux and phase. For both stars the appearance of the C iv line is similar to that of single Classical T Tauri Stars (CTTSs), despite the lack of stable long-lived circumstellar disks. However, unlike the case in single CTTSs, the narrow and broad components of the C iv lines are uncorrelated, and we argue that the narrow component is powered by processes other than accretion, such as flares in the stellar magnetospheres and/or enhanced activity in the upper atmosphere. We find that both stars contribute equally to the narrow component C iv flux in DQ Tau, but the primary dominates the narrow component C iv emission in UZ Tau E. The C iv broad component flux is correlated with other accretion indicators, suggesting an accretion origin. However, the line is blueshifted, which is inconsistent with its origin in an infall flow close to the star. It is possible that the complicated geometry of the region, as well as turbulence in the shock region, are responsible for the blueshifted line profiles.

  3. Spirit Ascent Movie, Rover's-Eye View

    NASA Technical Reports Server (NTRS)

    2005-01-01

    A movie assembled from frames taken by the rear hazard-identification camera on NASA's Mars Exploration Rover Spirit shows the last few days of the rover's ascent to the crest of 'Husband Hill' inside Mars' Gusev Crater. The rover was going in reverse. Rover planners often drive Spirit backwards to keep wheel lubrication well distributed. The images in this clip span a timeframe from Spirit's 573rd martian day, or sol (Aug, 13, 2005) to sol 582 (Aug. 22, 2005), the day after the rover reached the crest. During that period, Spirit drove 136 meters (446 feet),

  4. Space Shuttle Ascent Flight Design Process: Evolution and Lessons Learned

    NASA Technical Reports Server (NTRS)

    Picka, Bret A.; Glenn, Christopher B.

    2011-01-01

    The Space Shuttle Ascent Flight Design team is responsible for defining a launch to orbit trajectory profile that satisfies all programmatic mission objectives and defines the ground and onboard reconfiguration requirements for this high-speed and demanding flight phase. This design, verification and reconfiguration process ensures that all applicable mission scenarios are enveloped within integrated vehicle and spacecraft certification constraints and criteria, and includes the design of the nominal ascent profile and trajectory profiles for both uphill and ground-to-ground aborts. The team also develops a wide array of associated training, avionics flight software verification, onboard crew and operations facility products. These key ground and onboard products provide the ultimate users and operators the necessary insight and situational awareness for trajectory dynamics, performance and event sequences, abort mode boundaries and moding, flight performance and impact predictions for launch vehicle stages for use in range safety, and flight software performance. These products also provide the necessary insight to or reconfiguration of communications and tracking systems, launch collision avoidance requirements, and day of launch crew targeting and onboard guidance, navigation and flight control updates that incorporate the final vehicle configuration and environment conditions for the mission. Over the course of the Space Shuttle Program, ascent trajectory design and mission planning has evolved in order to improve program flexibility and reduce cost, while maintaining outstanding data quality. Along the way, the team has implemented innovative solutions and technologies in order to overcome significant challenges. A number of these solutions may have applicability to future human spaceflight programs.

  5. On the Maximum Mass of Accreting Primordial Supermassive Stars

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

    Woods, T. E.; Heger, Alexander; Whalen, Daniel J.

    Supermassive primordial stars are suspected to be the progenitors of the most massive quasars at z ∼ 6. Previous studies of such stars were either unable to resolve hydrodynamical timescales or considered stars in isolation, not in the extreme accretion flows in which they actually form. Therefore, they could not self-consistently predict their final masses at collapse, or those of the resulting supermassive black hole seeds, but rather invoked comparison to simple polytropic models. Here, we systematically examine the birth, evolution, and collapse of accreting, non-rotating supermassive stars under accretion rates of 0.01–10 M {sub ⊙} yr{sup −1} using themore » stellar evolution code Kepler . Our approach includes post-Newtonian corrections to the stellar structure and an adaptive nuclear network and can transition to following the hydrodynamic evolution of supermassive stars after they encounter the general relativistic instability. We find that this instability triggers the collapse of the star at masses of 150,000–330,000 M {sub ⊙} for accretion rates of 0.1–10 M {sub ⊙} yr{sup −1}, and that the final mass of the star scales roughly logarithmically with the rate. The structure of the star, and thus its stability against collapse, is sensitive to the treatment of convection and the heat content of the outer accreted envelope. Comparison with other codes suggests differences here may lead to small deviations in the evolutionary state of the star as a function of time, that worsen with accretion rate. Since the general relativistic instability leads to the immediate death of these stars, our models place an upper limit on the masses of the first quasars at birth.« less

  6. Steepest entropy ascent quantum thermodynamic model of electron and phonon transport

    NASA Astrophysics Data System (ADS)

    Li, Guanchen; von Spakovsky, Michael R.; Hin, Celine

    2018-01-01

    An advanced nonequilibrium thermodynamic model for electron and phonon transport is formulated based on the steepest-entropy-ascent quantum thermodynamics framework. This framework, based on the principle of steepest entropy ascent (or the equivalent maximum entropy production principle), inherently satisfies the laws of thermodynamics and mechanics and is applicable at all temporal and spatial scales even in the far-from-equilibrium realm. Specifically, the model is proven to recover the Boltzmann transport equations in the near-equilibrium limit and the two-temperature model of electron-phonon coupling when no dispersion is assumed. The heat and mass transport at a temperature discontinuity across a homogeneous interface where the dispersion and coupling of electron and phonon transport are both considered are then modeled. Local nonequilibrium system evolution and nonquasiequilibrium interactions are predicted and the results discussed.

  7. Liquid Oxygen/Liquid Methane Ascent Main Engine Technology Development

    NASA Technical Reports Server (NTRS)

    Robinson, Joel W.; Stephenson, David D.

    2008-01-01

    The National Aeronautics & Space Administration (NASA) has identified Liquid Oxygen (LO2)/Liquid Methane (LCH4) as a potential propellant combination for future space vehicles based upon the Exploration Systems Architecture Study (ESAS). The technology is estimated to have higher performance and lower overall systems mass compared to existing hypergolic propulsion systems. The current application considering this technology is the lunar ascent main engine (AME). AME is anticipated to be an expendable, pressure-fed engine to provide ascent from the moon at the completion of a 210 day lunar stay. The engine is expected to produce 5,500 lbf (24,465 N) thrust with variable inlet temperatures due to the cryogenic nature of the fuel and oxidizer. The primary technology risks include establishing reliable and robust ignition in vacuum conditions, maximizing specific impulse, developing rapid start capability for the descent abort, providing the capability for two starts and producing a total engine bum time over 500 seconds. This paper will highlight the efforts of the Marshall Space Flight Center (MSFC) in addressing risk reduction activities for this technology.

  8. SPIN EVOLUTION OF ACCRETING YOUNG STARS. II. EFFECT OF ACCRETION-POWERED STELLAR WINDS

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

    Matt, Sean P.; Pinzon, Giovanni; Greene, Thomas P.

    2012-01-20

    We present a model for the rotational evolution of a young, solar-mass star interacting magnetically with an accretion disk. As in a previous paper (Paper I), the model includes changes in the star's mass and radius as it descends the Hayashi track, a decreasing accretion rate, and a prescription for the angular momentum transfer between the star and disk. Paper I concluded that, for the relatively strong magnetic coupling expected in real systems, additional processes are necessary to explain the existence of slowly rotating pre-main-sequence stars. In the present paper, we extend the stellar spin model to include the effectmore » of a spin-down torque that arises from an accretion-powered stellar wind (APSW). For a range of magnetic field strengths, accretion rates, initial spin rates, and mass outflow rates, the modeled stars exhibit rotation periods within the range of 1-10 days in the age range of 1-3 Myr. This range coincides with the bulk of the observed rotation periods, with the slow rotators corresponding to stars with the lowest accretion rates, strongest magnetic fields, and/or highest stellar wind mass outflow rates. We also make a direct, quantitative comparison between the APSW scenario and the two types of disk-locking models (namely, the X-wind and Ghosh and Lamb type models) and identify some remaining theoretical issues for understanding young star spins.« less

  9. AGN jet-driven stochastic cold accretion in cluster cores

    NASA Astrophysics Data System (ADS)

    Prasad, Deovrat; Sharma, Prateek; Babul, Arif

    2017-10-01

    Several arguments suggest that stochastic condensation of cold gas and its accretion on to the central supermassive black hole (SMBH) is essential for active galactic nuclei (AGNs) feedback to work in the most massive galaxies that lie at the centres of galaxy clusters. Our 3-D hydrodynamic AGN jet-ICM (intracluster medium) simulations, looking at the detailed angular momentum distribution of cold gas and its time variability for the first time, show that the angular momentum of the cold gas crossing ≲1 kpc is essentially isotropic. With almost equal mass in clockwise and counterclockwise orientations, we expect a cancellation of the angular momentum on roughly the dynamical time. This means that a compact accretion flow with a short viscous time ought to form, through which enough accretion power can be channeled into jet mechanical energy sufficiently quickly to prevent a cooling flow. The inherent stochasticity, expected in feedback cycles driven by cold gas condensation, gives rise to a large variation in the cold gas mass at the centres of galaxy clusters, for similar cluster and SMBH masses, in agreement with the observations. Such correlations are expected to be much tighter for the smoother hot/Bondi accretion. The weak correlation between cavity power and Bondi power obtained from our simulations also matches observations.

  10. Autonomous Mars ascent and orbit rendezvous for earth return missions

    NASA Technical Reports Server (NTRS)

    Edwards, H. C.; Balmanno, W. F.; Cruz, Manuel I.; Ilgen, Marc R.

    1991-01-01

    The details of tha assessment of autonomous Mars ascent and orbit rendezvous for earth return missions are presented. Analyses addressing navigation system assessments, trajectory planning, targeting approaches, flight control guidance strategies, and performance sensitivities are included. Tradeoffs in the analysis and design process are discussed.

  11. 41. VIEW LOOKING IN TANK, SHOWING TRAINING DURING ASCENT (WEARING ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    41. VIEW LOOKING IN TANK, SHOWING TRAINING DURING ASCENT (WEARING STEINKE HOOD) AT RIGHT, DIVING INSTRUCTOR AT LEFT MAINTAINING HIS POSITION ON THE WIRE No date - U.S. Naval Submarine Base, New London Submarine Escape Training Tank, Albacore & Darter Roads, Groton, New London County, CT

  12. Giant Cell Arteritis Presenting as Scalp Necrosis

    PubMed Central

    Maidana, Daniel E.; Muñoz, Silvia; Acebes, Xènia; Llatjós, Roger; Jucglà, Anna; Álvarez, Alba

    2011-01-01

    The differential of scalp ulceration in older patients should include several causes, such as herpes zoster, irritant contact dermatitis, ulcerated skin tumors, postirradiation ulcers, microbial infections, pyoderma gangrenosum, and giant cell arteritis. Scalp necrosis associated with giant cell arteritis was first described in the 1940s. The presence of this dermatological sign within giant cell arteritis represents a severity marker of this disease, with a higher mean age at diagnosis, an elevated risk of vision loss and tongue gangrene, as well as overall higher mortality rates, in comparison to patients not presenting this manifestation. Even though scalp necrosis due to giant cell arteritis is exceptional, a high level of suspicion must be held for this clinical finding, in order to initiate prompt and proper treatment and avoid blindness. PMID:21789466

  13. Giant cell phlebitis: a potentially lethal clinical entity.

    PubMed

    Kunieda, Takeshige; Murayama, Masanori; Ikeda, Tsuneko; Yamakita, Noriyoshi

    2012-08-01

    An 83-year-old woman presented to us with a 4-week history of general malaise, subjective fever and lower abdominal pain. Despite the intravenous infusion of antibiotics, her blood results and physical condition worsened, resulting in her sudden death. Autopsy study revealed that the medium-sized veins of the mesentery were infiltrated by eosinophil granulocytes, lymphocytes, macrophages and multinucleated giant cells; however, the arteries were not involved. Microscopically, venous giant cell infiltration was observed in the gastrointestinal tract, bladder, retroperitoneal tissues and myocardium. The final diagnosis was giant cell phlebitis, a rare disease of unknown aetiology. This case demonstrates for the first time that giant cell phlebitis involving extra-abdominal organs, including hearts, can cause serious morbidity.

  14. A scaling law for accretion zone sizes

    NASA Technical Reports Server (NTRS)

    Greenzweig, Yuval; Lissauer, Jack J.

    1987-01-01

    Current theories of runaway planetary accretion require small random velocities of the accreted particles. Two body gravitational accretion cross sections which ignore tidal perturbations of the Sun are not valid for the slow encounters which occur at low relative velocities. Wetherill and Cox have studied accretion cross sections for rocky protoplanets orbiting at 1 AU. Using analytic methods based on Hill's lunar theory, one can scale these results for protoplanets that occupy the same fraction of their Hill sphere as does a rocky body at 1 AU. Generalization to bodies of different sizes is achieved here by numerical integrations of the three-body problem. Starting at initial positions far from the accreting body, test particles are allowed to encounter the body once, and the cross section is computed. A power law is found relating the cross section to the radius of the accreting body (of fixed mass).

  15. Hydrodynamic Simulations of the Consequences of Accretion onto ONe White Dwarfs

    NASA Astrophysics Data System (ADS)

    Starrfield, Sumner; Bose, Maitrayee; Iliadis, Christian; Hix, William Raphael; Woodward, Charles E.; Wagner, Robert M.; José, Jordi; Hernanz, Margarita; Feng, Wanda

    2018-06-01

    Mass and luminosity variations of the white dwarf, combined with changes in the mass accretion rate and composition of the accreted material affect the evolution of the thermonuclear runaway (TNR) in classical and recurrent novae. Here we highlight continued investigations of these effects on accreting Oxygen-Neon (ONe) white dwarfs. We now use the results of the multi-dimensional studies of TNRs in white dwarfs, accreting only solar matter, which show that sufficient core material is dredged-up during the TNR to agree with the measurements of ejecta abundances in classical nova explosions. Therefore, we first accrete solar material and follow the evolution until a TNR is ongoing. We then switch the composition to a mixture with either 25% core material or 50% core material (plus accreted material) and follow the resulting evolution of the TNR through peak nuclear burning and decline. We use our 1D, Lagrangian, hydrodynamic code: NOVA. We will report on the results of these new simulations and compare the ejecta abundances to those measured in pre-solar grains that are thought to arise from classical nova explosions. We will also compare these results to our companion studies, done in a similar fashion, where we have followed the consequences of accretion onto Carbon-Oxygen white dwarfs. This work was supported in part by NASA under the Astrophysics Theory Program grant 14-ATP14-0007 and the U.S. DOE under Contract No. DE-FG02- 97ER41041. SS acknowledges partial support from NASA, NSF, and HST grants to ASU and WRH is supported by the U.S. Department of Energy, Office of Nuclear Physics.

  16. Accretion Rate: An Axis Of Agn Unification

    NASA Astrophysics Data System (ADS)

    Trump, Jonathan R.; Impey, C. D.; Kelly, B. C.

    2011-01-01

    We show how accretion rate governs the physical properties of broad-line, narrow-line, and lineless active galactic nuclei (AGNs). We avoid the systematic errors plaguing previous studies of AGN accretion rate by using accurate accretion luminosities from well-sampled multiwavelength SEDs from the Cosmic Evolution Survey (COSMOS), and accurate black hole masses derived from virial scaling relations (for broad-line AGNs) or host-AGN relations (for narrow-line and lineless AGNs). In general, broad emission lines are present only at the highest accretion rates (L/L_Edd>0.01), and these rapidly accreting AGNs are observed as broad-line AGNs or possibly as obscured narrow-line AGNs. Narrow-line and lineless AGNs at lower specific accretion rates (L/L_Edd<0.01) are unobscured and yet lack a broad line region. The disappearance of the broad emission lines is caused by an expanding radiatively inefficient accretion flow (RIAF) at the inner radius of the accretion disk. The presence of the RIAF also drives L/L_Edd<0.01 narrow-line and lineless AGNs to be 10-100 times more radio-luminous than broad-line AGNs, since the unbound nature of the RIAF means it is easier to form a radio outflow. The IR torus signature also tends to become weaker or disappear from L/L_Edd<0.01 AGNs, although there may be additional mid-IR synchrotron emission associated with the RIAF. Together these results suggest that specific accretion rate is an important physical "axis" of AGN unification, described by a simple model.

  17. The Ascent of Science

    NASA Astrophysics Data System (ADS)

    Silver, Brian L.

    2000-04-01

    From the revolutionary discoveries of Galileo and Newton to the mind-bending theories of Einstein and Heisenberg, from plate tectonics to particle physics, from the origin of life to universal entropy, and from biology to cosmology, here is a sweeping, readable, and dynamic account of the whole of Western science.In the approachable manner and method of Stephen Jay Gould and Carl Sagan, the late Brian L. Silver translates our most important, and often most obscure, scientific developments into a vernacular that is not only accessible and illuminating but also enjoyable. Silver makes his comprehensive case with much clarity and insight; his book aptly locates science as the apex of human reason, and reason as our best path to the truth. For all readers curious about--or else perhaps intimidated by--what Silver calls "the scientific campaign up to now", The Ascent of Science will be fresh, vivid, and fascinating reading.

  18. Giant Black Hole Rips Apart Star

    NASA Astrophysics Data System (ADS)

    2004-02-01

    was equivalent to a supernova. "Now, with all the data in hand, we have the smoking gun proof that this spectacular event has occurred," said coauthor Günther Hasinger, also of MPE. The black hole in the center of RX J1242-11 is estimated to have a mass of about 100 million times Earth's Sun. By contrast, the destroyed star probably had a mass about equal to the Sun, making it a lopsided battle of gravity. "This is the ultimate David versus Goliath battle, but here David loses," said Hasinger. The astronomers estimated about one percent of the star's mass was ultimately consumed, or accreted, by the black hole. This small amount is consistent with predictions that the momentum and energy of the accretion process will cause most of the destroyed star's gas to be flung away from the black hole. XMM-Newton Spectrum &Illustration of RX J1242-11 XMM-Newton Spectrum & Illustration of RX J1242-11 The force that disrupted the star in RX J1242-11 is an extreme example of the tidal force caused by differences in gravity acting on the front and back of an object. The tidal force from the Moon causes tides in Earth's oceans. A tidal force from Jupiter pulled Comet Shoemaker-Levy apart, before it plunged into the giant planet. The odds stellar tidal disruption will happen in a typical galaxy are low, about one in 10,000 annually. If it happened at the center of the Milky Way Galaxy, 26,000 light-years from Earth, the resulting X-ray outburst would be about 50,000 times brighter than the brightest X-ray source in our galaxy, beside the Sun, but it would not pose a threat to Earth. Other dramatic flares have been seen from galaxies, but this is the first studied with the high-spatial resolution of Chandra and the high-spectral resolution of XMM-Newton. Both instruments made a critical advance. Chandra showed the RX J1242-11 event occurred in the center of a galaxy, where the black hole lurks. The XMM-Newton spectrum revealed the fingerprints expected for the surroundings of a black

  19. The Ascent Study - Understanding the Market Environment for the Follow-on to the Space Shuttle

    NASA Astrophysics Data System (ADS)

    Webber, Derek

    2002-01-01

    The ASCENT Study - Understanding the Market Environment for the Follow-on to NASA's Marshall Space Flight Center in Huntsville, Alabama, awarded a contract (base plus option amounting to twenty months of analysis) to Futron Corporation in June 2001 to investigate the market environment, and explore the price elasticity attributes, relevant for the introduction of the Second Generation Reusable Launch Vehicle (the follow-on to the Space Shuttle) in the second decade of this century. This work is known as the ASCENT Study (Analysis of Space Concepts Enabled by New Transportation) and data collection covering a total of 42 different sectors took place during 2001. Modeling and forecasting activities for 26 of these markets (all of them international in nature) have been taking place throughout 2002, and the final results of the ASCENT Study, which include 20 year forecasts, are due by the end of January, 2003. This paper describes the markets being analyzed for the ASCENT Study, and includes some preliminary findings in terms of launch vehicle demand during the next 20 years, broken down by mass class and mission type. Amongst these markets are the potential public space travel opportunities. When completed, the final report of the ASCENT Study is expected to represent a significant reference document for all business development, financing and planning activities in the space industry for some time to come. One immediate use will be as a key factor in determining the cargo capability and launch rates to be used for designing the follow-on to the Space Shuttle. The Study will also provide NASA with a quantified indication of the extent to which the lower cost to orbit, made possible by a new class of launch vehicle, will bring into being new markets.

  20. Accretion Discs Around Black Holes: Developement of Theory

    NASA Astrophysics Data System (ADS)

    Bisnovatyi-Kogan, G. S.

    Standard accretion disk theory is formulated which is based on the local heat balance. The energy produced by a turbulent viscous heating is supposed to be emitted to the sides of the disc. Sources of turbulence in the accretion disc are connected with nonlinear hydrodynamic instability, convection, and magnetic field. In standard theory there are two branches of solution, optically thick, and optically thin. Advection in accretion disks is described by the differential equations what makes the theory nonlocal. Low-luminous optically thin accretion disc model with advection at some suggestions may become advectively dominated, carrying almost all the energy inside the black hole. The proper account of magnetic filed in the process of accretion limits the energy advected into a black hole, efficiency of accretion should exceed ˜ 1/4 of the standard accretion disk model efficiency.

  1. Workshop on the Early Earth: The Interval from Accretion to the Older Archean

    NASA Technical Reports Server (NTRS)

    Burke, K. (Editor); Ashwal, L. D. (Editor)

    1985-01-01

    Presentation abstracts are compiled which address various issues in Earth developmental processes in the first one hundred million years. The session topics included: accretion of the Earth (processes accompanying immediately following the accretion, including core formation); impact records and other information from planets and the Moon relevant to early Earth history; isotopic patterns of the oldest rocks; and igneous, sedimentary, and metamorphic petrology of the oldest rocks.

  2. Accretion shock geometries in the magnetic variables

    NASA Technical Reports Server (NTRS)

    Stockman, H. S.

    1988-01-01

    The first self consistent shock models for the AM Herculis-type systems successfully identified the dominant physical processes and their signatures. These homogenous shock models predict unpolarized, Rayleigh-Jeans optical spectra with sharp cutoffs and rising polarizations as the shocks become optically thin in the ultraviolet. However, the observed energy distributions are generally flat with intermediate polarizations over a broad optical band. These and other observational evidence support a non-homogenous accretion profile which may extend over a considerable fraction of the stellar surface. Both the fundamental assumptions underlying the canonical 1-D shock model and the extension of this model to inhomogenous accretion shocks were identified, for both radial and linear structures. The observational evidence was also examined for tall shocks and little evidence was found for relative shock heights in excess of h/R(1) greater than or equal to 0.1. For several systems, upper limits to the shock height can be obtained from either x ray or optical data. These lie in the region h/R(1) is approximately 0.01 and are in general agreement with the current physical picture for these systems. The quasi-periodic optical variations observed in several magnetic variables may eventually prove to be a major aid in further understanding their accretion shock geometries.

  3. IMPETUS: Consistent SPH calculations of 3D spherical Bondi accretion onto a black hole

    NASA Astrophysics Data System (ADS)

    Ramírez-Velasquez, J. M.; Sigalotti, L. Di G.; Gabbasov, R.; Cruz, F.; Klapp, J.

    2018-04-01

    We present three-dimensional calculations of spherically symmetric Bondi accretion onto a stationary supermassive black hole (SMBH) of mass 108M⊙ within a radial range of 0.02 - 10 pc, using a modified version of the smoothed particle hydrodynamics (SPH) GADGET-2 code, which ensures approximate first-order consistency (i.e., second-order accuracy) for the particle approximation. First-order consistency is restored by allowing the number of neighbours, nneigh, and the smoothing length, h, to vary with the total number of particles, N, such that the asymptotic limits nneigh → ∞ and h → 0 hold as N → ∞. The ability of the method to reproduce the isothermal (γ = 1) and adiabatic (γ = 5/3) Bondi accretion is investigated with increased spatial resolution. In particular, for the isothermal models the numerical radial profiles closely match the Bondi solution, except near the accretor, where the density and radial velocity are slightly underestimated. However, as nneigh is increased and h is decreased, the calculations approach first-order consistency and the deviations from the Bondi solution decrease. The density and radial velocity profiles for the adiabatic models are qualitatively similar to those for the isothermal Bondi accretion. Steady-state Bondi accretion is reproduced by the highly resolved consistent models with a percent relative error of ≲ 1% for γ = 1 and ˜9% for γ = 5/3, with the adiabatic accretion taking longer than the isothermal case to reach steady flow. The performance of the method is assessed by comparing the results with those obtained using the standard GADGET-2 and the GIZMO codes.

  4. Properties of two-temperature dissipative accretion flow around black holes

    NASA Astrophysics Data System (ADS)

    Dihingia, Indu K.; Das, Santabrata; Mandal, Samir

    2018-04-01

    We study the properties of two-temperature accretion flow around a non-rotating black hole in presence of various dissipative processes where pseudo-Newtonian potential is adopted to mimic the effect of general relativity. The flow encounters energy loss by means of radiative processes acted on the electrons and at the same time, flow heats up as a consequence of viscous heating effective on ions. We assumed that the flow is exposed with the stochastic magnetic fields that leads to Synchrotron emission of electrons and these emissions are further strengthen by Compton scattering. We obtain the two-temperature global accretion solutions in terms of dissipation parameters, namely, viscosity (α) and accretion rate ({\\dot{m}}), and find for the first time in the literature that such solutions may contain standing shock waves. Solutions of this kind are multitransonic in nature, as they simultaneously pass through both inner critical point (xin) and outer critical point (xout) before crossing the black hole horizon. We calculate the properties of shock-induced global accretion solutions in terms of the flow parameters. We further show that two-temperature shocked accretion flow is not a discrete solution, instead such solution exists for wide range of flow parameters. We identify the effective domain of the parameter space for standing shock and observe that parameter space shrinks as the dissipation is increased. Since the post-shock region is hotter due to the effect of shock compression, it naturally emits hard X-rays, and therefore, the two-temperature shocked accretion solution has the potential to explain the spectral properties of the black hole sources.

  5. Atmospheric Ascent Guidance for Rocket-Powered Launch Vehicles

    NASA Technical Reports Server (NTRS)

    Dukeman, Greg A.

    2002-01-01

    An advanced ascent guidance algorithm for rocket- powered launch vehicles is developed. This algorithm cyclically solves the calculus-of-variations two-point boundary-value problem starting at vertical rise completion through main engine cutoff. This is different from traditional ascent guidance algorithms which operate in a simple open-loop mode until high dynamic pressure (including the critical max-Q) portion of the trajectory is over, at which time guidance operates under the assumption of negligible aerodynamic acceleration (i.e., vacuum dynamics). The initial costate guess is corrected based on errors in the terminal state constraints and the transversality conditions. Judicious approximations are made to reduce the order and complexity of the state/costate system. Results comparing guided launch vehicle trajectories with POST open-loop trajectories are given verifying the basic formulation of the algorithm. Multiple shooting is shown to be a very effective numerical technique for this application. In particular, just one intermediate shooting point, in addition to the initial shooting point, is sufficient to significantly reduce sensitivity to the guessed initial costates. Simulation results from a high-fidelity trajectory simulation are given for the case of launch to sub-orbital cutoff conditions as well as launch to orbit conditions. An abort to downrange landing site formulation of the algorithm is presented.

  6. Accretion onto a higher dimensional black hole

    NASA Astrophysics Data System (ADS)

    John, Anslyn J.; Ghosh, Sushant G.; Maharaj, Sunil D.

    2013-11-01

    We examine the steady-state spherically symmetric accretion of relativistic fluids, with a polytropic equation of state, onto a higher-dimensional Schwarzschild black hole. The mass accretion rate, critical radius, and flow parameters are determined and compared with results obtained in standard four dimensions. The accretion rate, M˙, is an explicit function of the black hole mass, M, as well as the gas boundary conditions and the dimensionality, D, of the spacetime. We also find the asymptotic compression ratios and temperature profiles below the accretion radius and at the event horizon. This analysis is a generalization of Michel’s solution to higher dimensions and of the Newtonian expressions of Giddings and Mangano, which consider the accretion of TeV black holes.

  7. The first H-band spectrum of the giant planet β Pictoris b

    DOE PAGES

    Chilcote, Jeffrey; Barman, Travis; Fitzgerald, Michael P.; ...

    2014-12-12

    Using the recently installed Gemini Planet Imager (GPI), we have obtained the first H-band spectrum of the planetary companion to the nearby young star β Pictoris. GPI is designed to image and provide low-resolution spectra of Jupiter-sized, self-luminous planetary companions around young nearby stars. These observations were taken covering the H band (1.65 μm). The spectrum has a resolving power of ~45 and demonstrates the distinctive triangular shape of a cool substellar object with low surface gravity. Using atmospheric models, we find an effective temperature of 1600-1700 K and a surface gravity of log (g) = 3.5-4.5 (cgs units). Thesemore » values agree well with "hot-start" predictions from planetary evolution models for a gas giant with mass between 10 and 12 M Jup and age between 10 and 20 Myr.« less

  8. An actively accreting massive black hole in the dwarf starburst galaxy Henize 2-10.

    PubMed

    Reines, Amy E; Sivakoff, Gregory R; Johnson, Kelsey E; Brogan, Crystal L

    2011-02-03

    Supermassive black holes are now thought to lie at the heart of every giant galaxy with a spheroidal component, including our own Milky Way. The birth and growth of the first 'seed' black holes in the earlier Universe, however, is observationally unconstrained and we are only beginning to piece together a scenario for their subsequent evolution. Here we report that the nearby dwarf starburst galaxy Henize 2-10 (refs 5 and 6) contains a compact radio source at the dynamical centre of the galaxy that is spatially coincident with a hard X-ray source. From these observations, we conclude that Henize 2-10 harbours an actively accreting central black hole with a mass of approximately one million solar masses. This nearby dwarf galaxy, simultaneously hosting a massive black hole and an extreme burst of star formation, is analogous in many ways to galaxies in the infant Universe during the early stages of black-hole growth and galaxy mass assembly. Our results confirm that nearby star-forming dwarf galaxies can indeed form massive black holes, and that by implication so can their primordial counterparts. Moreover, the lack of a substantial spheroidal component in Henize 2-10 indicates that supermassive black-hole growth may precede the build-up of galaxy spheroids.

  9. Giant cell phlebitis: a potentially lethal clinical entity

    PubMed Central

    Kunieda, Takeshige; Murayama, Masanori; Ikeda, Tsuneko; Yamakita, Noriyoshi

    2012-01-01

    An 83-year-old woman presented to us with a 4-week history of general malaise, subjective fever and lower abdominal pain. Despite the intravenous infusion of antibiotics, her blood results and physical condition worsened, resulting in her sudden death. Autopsy study revealed that the medium-sized veins of the mesentery were infiltrated by eosinophil granulocytes, lymphocytes, macrophages and multinucleated giant cells; however, the arteries were not involved. Microscopically, venous giant cell infiltration was observed in the gastrointestinal tract, bladder, retroperitoneal tissues and myocardium. The final diagnosis was giant cell phlebitis, a rare disease of unknown aetiology. This case demonstrates for the first time that giant cell phlebitis involving extra-abdominal organs, including hearts, can cause serious morbidity. PMID:22859384

  10. Gas Accretion onto a Supermassive Black Hole: A Step to Model AGN Feedback

    NASA Astrophysics Data System (ADS)

    Nagamine, K.; Barai, P.; Proga, D.

    2012-08-01

    We study gas accretion onto a supermassive black hole (SMBH) using the 3D SPH code GADGET-3 on scales of 0.1-200 pc. First we test our code with the spherically symmetric, adiabatic Bondi accretion problem. We find that our simulation can reproduce the expected Bondi accretion flow very well for a limited amount of time until the effect of the outer boundary starts to be visible. We also find artificial heating of gas near the inner accretion boundary due to the artificial viscosity of SPH. Second, we implement radiative cooling and heating due to X-rays, and examine the impact of thermal feedback by the central X-ray source. The accretion flow roughly follows the Bondi solution for low central X-ray luminosities; however, the flow starts to exhibit non-spherical fragmentation due to the thermal instability for a certain range of central LX, and a strong overall outflow develops for greater LX. The cold gas develops filamentary structures that fall into the central SMBH, whereas the hot gas tries to escape through the channels in between the cold filaments. Such fragmentation of accreting gas can assist in the formation of clouds around AGN, induce star-formation, and contribute to the observed variability of narrow-line regions.

  11. Disk Accretion and the Stellar Birthline

    NASA Astrophysics Data System (ADS)

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

    1997-02-01

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

  12. Missile Aerodynamics for Ascent and Re-entry

    NASA Technical Reports Server (NTRS)

    Watts, Gaines L.; McCarter, James W.

    2012-01-01

    Aerodynamic force and moment equations are developed for 6-DOF missile simulations of both the ascent phase of flight and a tumbling re-entry. The missile coordinate frame (M frame) and a frame parallel to the M frame were used for formulating the aerodynamic equations. The missile configuration chosen as an example is a cylinder with fixed fins and a nose cone. The equations include both the static aerodynamic coefficients and the aerodynamic damping derivatives. The inclusion of aerodynamic damping is essential for simulating a tumbling re-entry. Appended information provides insight into aerodynamic damping.

  13. Increases to Inferred Rates of Planetesimal Accretion due to Thermohaline Mixing in Metal-accreting White Dwarfs

    NASA Astrophysics Data System (ADS)

    Bauer, Evan B.; Bildsten, Lars

    2018-06-01

    Many isolated, old white dwarfs (WDs) show surprising evidence of metals in their photospheres. Given that the timescale for gravitational sedimentation is astronomically short, this is taken as evidence for ongoing accretion, likely of tidally disrupted planetesimals. The rate of such accretion, {\\dot{M}}acc}, is important to constrain, and most modeling of this process relies on assuming an equilibrium between diffusive sedimentation and metal accretion supplied to the WD’s surface convective envelope. Building on the earlier work of Deal and collaborators, we show that high {\\dot{M}}acc} models with only diffusive sedimentation are unstable to thermohaline mixing and that models that account for the enhanced mixing from the active thermohaline instability require larger accretion rates, sometimes reaching {\\dot{M}}acc}≈ {10}13 {{g}} {{{s}}}-1 to explain observed calcium abundances. We present results from a grid of MESA models that include both diffusion and thermohaline mixing. These results demonstrate that both mechanisms are essential for understanding metal pollution across the range of polluted WDs with hydrogen atmospheres. Another consequence of active thermohaline mixing is that the observed metal abundance ratios are identical to accreted material.

  14. Simultaneous Spectral and Timing Observations of Accreting Neuron Stars

    NASA Technical Reports Server (NTRS)

    Kaaret, P.; Oliversen, Ronald J. (Technical Monitor)

    2002-01-01

    The goal of this proposal is to perform simultaneous x-ray spectral and millisecond timing observations of accreting neutron stars to further our understanding of their accretion dynamics and in the hope of using these systems as probes of the physics of strong gravitational fields. NAG5-9104 is the successor grant to NAG5-8408. Observations using the Rossi X-Ray Timing Explorer (RXTE) and BeppoSAX were performed of 4U1702-429, 4U1735-44, and Cyg X-2. Unfortunately, only a small fraction of the approved observing time was obtained for the first two targets and the data are of limited scientific value. Data analysis has been completed on the observations of Cyg X-2. We discovered a correlation between the frequency of the horizontal branch oscillations (HBO) and a soft, thermal component of the x-ray spectrum likely associated with emission from the accretion disk. This correlation may place constraints on models of the oscillations. A paper based on these results appeared in the Astrophysical Journal.

  15. Radius of the neutron star magnetosphere during disk accretion

    NASA Astrophysics Data System (ADS)

    Filippova, E. V.; Mereminskiy, I. A.; Lutovinov, A. A.; Molkov, S. V.; Tsygankov, S. S.

    2017-11-01

    The dependence of the spin frequency derivative \\dot ν of accreting neutron stars with a strongmagnetic field (X-ray pulsars) on the mass accretion rate (bolometric luminosity, L bol) has been investigated for eight transient pulsars in binary systems with Be stars. Using data from the Fermi/GBM and Swift/BAT telescopes, we have shown that for seven of the eight systems the dependence \\dot ν ( L bol) can be fitted by the model of angular momentum transfer through an accretion disk, which predicts the relation \\dot ν ˜ L 6/7 bol. Hysteresis in the dependence \\dot ν ( L bol) has been confirmed in the system V 0332+53 and has been detected for the first time in the systems KS 1947+300, GRO J1008-57, and 1A 0535+26. Estimates for the radius of the neutron star magnetosphere in all of the investigated systems have been obtained. We show that this quantity varies from pulsar to pulsar and depends strongly on the analytical model and the estimates for the neutron star and binary system parameters.

  16. Bondi-Hoyle accretion in an isothermal magnetized plasma

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

    Lee, Aaron T.; McKee, Christopher F.; Klein, Richard I.

    2014-03-01

    In regions of star formation, protostars and newborn stars will accrete mass from their natal clouds. These clouds are threaded by magnetic fields with a strength characterized by the plasma β—the ratio of thermal and magnetic pressures. Observations show that molecular clouds have β ≲ 1, so magnetic fields have the potential to play a significant role in the accretion process. We have carried out a numerical study of the effect of large-scale magnetic fields on the rate of accretion onto a uniformly moving point particle from a uniform, non-self-gravitating, isothermal gas. We consider gas moving with sonic Mach numbersmore » of up to M≈45; magnetic fields that are either parallel, perpendicular, or oriented 45° to the flow; and β as low as 0.01. Our simulations utilize adaptive mesh refinement in order to obtain high spatial resolution where it is needed; this also allows the boundaries to be far from the accreting object to avoid unphysical effects arising from boundary conditions. Additionally, we show that our results are independent of our exact prescription for accreting mass in the sink particle. We give simple expressions for the steady-state accretion rate as a function of β and M for the parallel and perpendicular orientations. Using typical molecular cloud values of M∼5 and β ∼ 0.04 from the literature, our fits suggest that a 0.4 M {sub ☉} star accretes ∼4 × 10{sup –9} M {sub ☉} yr{sup –1}, almost a factor of two less than accretion rates predicted by hydrodynamic models. This disparity can grow to orders of magnitude for stronger fields and lower Mach numbers. We also discuss the applicability of these accretion rates versus accretion rates expected from gravitational collapse, and under what conditions a steady state is possible. The reduction in the accretion rate in a magnetized medium leads to an increase in the time required to form stars in competitive accretion models, making such models less efficient than

  17. On the Red Giant Branch: Ambiguity in the Surface Boundary Condition Leads to ≈100 K Uncertainty in Model Effective Temperatures

    NASA Astrophysics Data System (ADS)

    Choi, Jieun; Dotter, Aaron; Conroy, Charlie; Ting, Yuan-Sen

    2018-06-01

    The effective temperature (T eff) distribution of stellar evolution models along the red giant branch (RGB) is sensitive to a number of parameters including the overall metallicity, elemental abundance patterns, the efficiency of convection, and the treatment of the surface boundary condition (BC). Recently there has been interest in using observational estimates of the RGB T eff to place constraints on the mixing length parameter, α MLT, and possible variation with metallicity. Here we use 1D Modules for Experiments in Stellar Astrophysics (MESA) stellar evolution models to explore the sensitivity of the RGB T eff to the treatment of the surface BC. We find that different surface BCs can lead to ±100 K metallicity-dependent offsets on the RGB relative to one another in spite of the fact that all models can reproduce the properties of the Sun. Moreover, for a given atmosphere T–τ relation, we find that the RGB T eff is also sensitive to the optical depth at which the surface BC is applied in the stellar model. Nearly all models adopt the photosphere as the location of the surface BC, but this choice is somewhat arbitrary. We compare our models to stellar parameters derived from the APOGEE-Kepler sample of first ascent red giants and find that systematic uncertainties in the models due to treatment of the surface BC place a limit of ≈100 K below which it is not possible to make firm conclusions regarding the fidelity of the current generation of stellar models.

  18. A Tale of Two Olivines: Magma Ascent in the Auckland Volcanic Field, New Zealand

    NASA Astrophysics Data System (ADS)

    Smid, E. R.; McGee, L. E.; Smith, I. E.; Lindsay, J. M.

    2013-12-01

    The Auckland Volcanic Field (AVF) is a nephelinitic to subalkali basaltic monogenetic field centered on the city of Auckland, New Zealand. Lavas are olivine-phyric, and the deposits of several volcanoes in the field contain olivine crystals with chrome spinel (Cr-spinel) inclusions. Microprobe analyses show at least two populations of olivine, categorised by their Mg# and their spinel inclusion compositions: the first has olivines that are euhedral, have compositions slightly less forsteritic than expected for whole rock Mg#, and have Cr-spinel inclusions with relatively low Cr2O3 contents of ~20%. These are interpreted as antecrysts inherited from the mantle source that yielded their host magma. The second population is characterised by olivines that are sub- to euhedral, are significantly more forsteritic than expected from their host whole rock Mg#, and have Cr-spinel inclusons with relatively high Cr2O3 contents of ~50%. These are interpreted as xenocrysts. The composition of these high Cr2O3 spinels very closely resembles the composition of spinels within olivines in dunite sampled from the Dun Mountain Ophiolite on the South Island of New Zealand. The northward extension of the Dun Mountain complex beneath the North Island is defined by the Junction Magnetic Anomaly, marking a crustal terrane boundary that underlies the Auckland Volcanic Field. These data indicate that the magmas that have risen to produce the volcanoes of the Auckland Volcanic Field have carried crystals from an underlying ultramafic crust as well as from their asthenospheric source. Euhedral olivine crystals which do not contain Cr-spinel are also present in AVF lavas and these are interpreted as true phenocrysts that crystallised directly from their host magmas. The lack of reaction textures at crystal margins suggests rapid ascent rates. A crustal origin for the xenocrysts not only has large implications for ascent rate modelling of olivines, but also for the crustal structure of the

  19. Probing Stellar Accretion with Mid-infrared Hydrogen Lines

    NASA Astrophysics Data System (ADS)

    Rigliaco, Elisabetta; Pascucci, I.; Duchene, G.; Edwards, S.; Ardila, D. R.; Grady, C.; Mendigutía, I.; Montesinos, B.; Mulders, G. D.; Najita, J. R.; Carpenter, J.; Furlan, E.; Gorti, U.; Meijerink, R.; Meyer, M. R.

    2015-03-01

    In this paper we investigate the origin of the mid-infrared (IR) hydrogen recombination lines for a sample of 114 disks in different evolutionary stages (full, transitional, and debris disks) collected from the Spitzer archive. We focus on the two brighter H I lines observed in the Spitzer spectra, the H I (7-6) at 12.37 μm and the H I (9-7) at 11.32 μm. We detect the H I (7-6) line in 46 objects, and the H I (9-7) in 11. We compare these lines with the other most common gas line detected in Spitzer spectra, the [Ne II] at 12.81 μm. We argue that it is unlikely that the H I emission originates from the photoevaporating upper surface layers of the disk, as has been found for the [Ne II] lines toward low-accreting stars. Using the H I (9-7)/H I (7-6) line ratios we find these gas lines are likely probing gas with hydrogen column densities of 1010-1011 cm-3. The subsample of objects surrounded by full and transitional disks show a positive correlation between the accretion luminosity and the H I line luminosity. These two results suggest that the observed mid-IR H I lines trace gas accreting onto the star in the same way as other hydrogen recombination lines at shorter wavelengths. A pure chromospheric origin of these lines can be excluded for the vast majority of full and transitional disks. We report for the first time the detection of the H I (7-6) line in eight young (<20 Myr) debris disks. A pure chromospheric origin cannot be ruled out in these objects. If the H I (7-6) line traces accretion in these older systems, as in the case of full and transitional disks, the strength of the emission implies accretion rates lower than 10-10 M ⊙ yr-1. We discuss some advantages of extending accretion indicators to longer wavelengths, and the next steps required pinning down the origin of mid-IR hydrogen lines.

  20. Towards combined modeling of planetary accretion and differentiation

    NASA Astrophysics Data System (ADS)

    Golabek, G. J.; Gerya, T. V.; Morishima, R.; Tackley, P. J.; Labrosse, S.

    2012-09-01

    accretion yield an onion-like thermal structure with very high internal temperatures due to powerful short-lived radiogenic heating in the planetesimals. These lead to extensive silicate melting in the parent bodies. Yet, magma ocean and impact processes are not considered in these models and core formation is, if taken into account, assumed to be instantaneous with no feedback on the mantle evolution. It was pointed out that impacts can not only deposit heat deep into the target body, which is later buried by ejecta of further impacts [1], but also that impacts expose in the crater region originally deep-seated layers, thus cooling the interior [2]. This combination of impact effects becomes even more important when we consider that planetesimals of all masses contribute to planetary accretion. This leads occasionally to collisions between bodies with large ratios between impactor and target mass. Thus, all these processes can be expected to have a profound effect on the thermal evolution during the epoch of planetary accretion and may have implications for the onset of mantle convection and cannot be described properly in 1D geometry. Here we present a new methodology, which can be used to simulate the internal evolution of a planetary body during accretion and differentiation: Using the N-body code PKDGRAV[3] we simulate the accretion of planetary embryos from an initial annulus of several thousand planetesimals. The growth history of the largest resulting planetary embryo is used as an input for the thermomechanical 2D code I2ELVIS [4]. The thermomechanical model takes recent parametrizations of impact processes like impact heating and crater excavation [5] into account. The model also includes both long- and short-lived radiogenic isotopes and a more realistic treatment of largely molten silicates [6]. Results show that late-formed planetesimals do not experience silicate melting and avoid thermal alteration, whereas in early-formed bodies accretion and iron

  1. Giant cells around bone biomaterials: Osteoclasts or multi-nucleated giant cells?

    PubMed

    Miron, Richard J; Zohdi, Hamoon; Fujioka-Kobayashi, Masako; Bosshardt, Dieter D

    2016-12-01

    Recently accumulating evidence has put into question the role of large multinucleated giant cells (MNGCs) around bone biomaterials. While cells derived from the monocyte/macrophage lineage are one of the first cell types in contact with implanted biomaterials, it was originally thought that specifically in bone tissues, all giant cells were bone-resorbing osteoclasts whereas foreign body giant cells (FBGCs) were found associated with a connective tissue foreign body reaction resulting in fibrous encapsulation and/or material rejection. Despite the great majority of bone grafting materials routinely found with large osteoclasts, a special subclass of bone biomaterials has more recently been found surrounded by large giant cells virtually incapable of resorbing bone grafts even years after their implantation. While original hypotheses believed that a 'foreign body reaction' may be taking place, histological data retrieved from human samples years after their implantation have put these original hypotheses into question by demonstrating better and more stable long-term bone volume around certain bone grafts. Exactly how or why this 'special' subclass of giant cells is capable of maintaining long-term bone volume, or methods to scientifically distinguish them from osteoclasts remains extremely poorly studied. The aim of this review article was to gather the current available literature on giant cell markers and differences in expression patterns between osteoclasts and MNGCs utilizing 19 specific markers including an array of CD-cell surface markers. Furthermore, the concept of now distinguishing between pro-inflammatory M1-MNGCs (previously referred to as FBGCs) as well as wound-healing M2-MNGCs is introduced and discussed. This review article presents 19 specific cell-surface markers to distinguish between osteoclasts and MNGCs including an array of CD-cell surface markers. Furthermore, the concept of now distinguishing between pro-inflammatory M1-MNGCs (often

  2. Modeling the ascent of sounding balloons: derivation of the vertical air motion

    NASA Astrophysics Data System (ADS)

    Gallice, A.; Wienhold, F. G.; Hoyle, C. R.; Immler, F.; Peter, T.

    2011-10-01

    A new model to describe the ascent of sounding balloons in the troposphere and lower stratosphere (up to ∼30-35 km altitude) is presented. Contrary to previous models, detailed account is taken of both the variation of the drag coefficient with altitude and the heat imbalance between the balloon and the atmosphere. To compensate for the lack of data on the drag coefficient of sounding balloons, a reference curve for the relationship between drag coefficient and Reynolds number is derived from a dataset of flights launched during the Lindenberg Upper Air Methods Intercomparisons (LUAMI) campaign. The transfer of heat from the surrounding air into the balloon is accounted for by solving the radial heat diffusion equation inside the balloon. In its present state, the model does not account for solar radiation, i.e. it is only able to describe the ascent of balloons during the night. It could however be adapted to also represent daytime soundings, with solar radiation modeled as a diffusive process. The potential applications of the model include the forecast of the trajectory of sounding balloons, which can be used to increase the accuracy of the match technique, and the derivation of the air vertical velocity. The latter is obtained by subtracting the ascent rate of the balloon in still air calculated by the model from the actual ascent rate. This technique is shown to provide an approximation for the vertical air motion with an uncertainty error of 0.5 m s-1 in the troposphere and 0.2 m s-1 in the stratosphere. An example of extraction of the air vertical velocity is provided in this paper. We show that the air vertical velocities derived from the balloon soundings in this paper are in general agreement with small-scale atmospheric velocity fluctuations related to gravity waves, mechanical turbulence, or other small-scale air motions measured during the SUCCESS campaign (Subsonic Aircraft: Contrail and Cloud Effects Special Study) in the orographically

  3. Ascent velocity and dynamics of the Fiumicino mud eruption, Rome, Italy

    NASA Astrophysics Data System (ADS)

    Vona, A.; Giordano, G.; De Benedetti, A. A.; D'Ambrosio, R.; Romano, C.; Manga, M.

    2015-08-01

    In August 2013 drilling triggered the eruption of mud near the international airport of Fiumicino (Rome, Italy). We monitored the evolution of the eruption and collected samples for laboratory characterization of physicochemical and rheological properties. Over time, muds show a progressive dilution with water; the rheology is typical of pseudoplastic fluids, with a small yield stress that decreases as mud density decreases. The eruption, while not naturally triggered, shares several similarities with natural mud volcanoes, including mud componentry, grain-size distribution, gas discharge, and mud rheology. We use the size of large ballistic fragments ejected from the vent along with mud rheology to compute a minimum ascent velocity of the mud. Computed values are consistent with in situ measurements of gas phase velocities, confirming that the stratigraphic record of mud eruptions can be quantitatively used to infer eruption history and ascent rates and hence to assess (or reassess) mud eruption hazards.

  4. Impact processes and the atmospheric composition of giant planets: lessons learned from the Solar System

    NASA Astrophysics Data System (ADS)

    Turrini, Diego; Grassi, Davide; Adriani, Alberto; Piccioni, Giuseppe; Altieri, Francesca; Barbieri, Mauro

    Over the last twenty years, the search for extrasolar planets revealed us the rich diversity of the outcomes of the processes shaping the formation and evolution of planetary systems. More recently, ground-based and space-based observations started to complement this information with the first data on the atmospheric composition of extrasolar planets. The full exploitation of the data that space-based and ground-based facilities will provide in growing number in the near future, however, requires that we improve our understanding of what are the sources and sinks of the chemical species and molecules that will be observed. Luckily, the study of the past history of the Solar System provides several indications on the effects of processes like migration, late accretion and secular impacts, and on the time they occur in the life of planetary systems. Here we will discuss what is already known about the factors influencing the composition of planetary atmospheres, focusing on the case of gaseous giant planets, and what instead still need to be investigated.

  5. The atmospheres of earthlike planets after giant impact events

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

    Lupu, R. E.; Freedman, Richard; Zahnle, Kevin

    2014-03-20

    It is now understood that the accretion of terrestrial planets naturally involves giant collisions, the moon-forming impact being a well-known example. In the aftermath of such collisions, the surface of the surviving planet is very hot and potentially detectable. Here we explore the atmospheric chemistry, photochemistry, and spectral signatures of post-giant-impact terrestrial planets enveloped by thick atmospheres consisting predominantly of CO{sub 2} and H{sub 2}O. The atmospheric chemistry and structure are computed self-consistently for atmospheres in equilibrium with hot surfaces with composition reflecting either the bulk silicate Earth (which includes the crust, mantle, atmosphere, and oceans) or Earth's continental crust.more » We account for all major molecular and atomic opacity sources including collision-induced absorption. We find that these atmospheres are dominated by H{sub 2}O and CO{sub 2}, while the formation of CH{sub 4} and NH{sub 3} is quenched because of short dynamical timescales. Other important constituents are HF, HCl, NaCl, and SO{sub 2}. These are apparent in the emerging spectra and can be indicative that an impact has occurred. The use of comprehensive opacities results in spectra that are a factor of two lower brightness temperature in the spectral windows than predicted by previous models. The estimated luminosities show that the hottest post-giant-impact planets will be detectable with near-infrared coronagraphs on the planned 30 m class telescopes. The 1-4 μm will be most favorable for such detections, offering bright features and better contrast between the planet and a potential debris disk. We derive cooling timescales on the order of 10{sup 5-6} yr on the basis of the modeled effective temperatures. This leads to the possibility of discovering tens of such planets in future surveys.« less

  6. Collimated Outflow Formation via Binary Stars: Three-Dimensional Simulations of Asymptotic Giant Branch Wind and Disk Wind Interactions

    NASA Astrophysics Data System (ADS)

    García-Arredondo, F.; Frank, Adam

    2004-01-01

    We present three-dimensional hydrodynamic simulations of the interaction of a slow wind from an asymptotic giant branch (AGB) star and a jet blown by an orbiting companion. The jet or ``collimated fast wind'' is assumed to originate from an accretion disk that forms via Bondi accretion of the AGB wind or Roche lobe overflow. We present two distinct regimes in the wind-jet interaction determined by the ratio of the AGB wind to jet momentum flux. Our results show that when the wind momentum flux overwhelms the flux in the jet, a more disordered outflow results with the jet assuming a corkscrew pattern and multiple shock structures driven into the AGB wind. In the opposite regime, the jet dominates and will drive a highly collimated, narrow-waisted outflow. We compare our results with scenarios described by Soker & Rappaport and extrapolate to the structures observed in planetary nebulae (PNs) and symbiotic stars.

  7. Vacuum birefringence and the x-ray polarization from black-hole accretion disks

    NASA Astrophysics Data System (ADS)

    Caiazzo, Ilaria; Heyl, Jeremy

    2018-04-01

    In the next decade, x-ray polarimetry will open a new window on the high-energy Universe, as several missions that include an x-ray polarimeter are currently under development. Observations of the polarization of x rays coming from the accretion disks of stellar-mass and supermassive black holes are among the new polarimeters' major objectives. In this paper, we show that these observations can be affected by the quantum electrodynamic (QED) effect of vacuum birefringence: after an x-ray photon is emitted from the accretion disk, its polarization changes as the photon travels through the accretion disk's magnetosphere, as a result of the vacuum becoming birefringent in the presence of a magnetic field. We show that this effect can be important for black holes in the energy band of the upcoming polarimeters and has to be taken into account in a complete model of the x-ray polarization that we expect to detect from black-hole accretion disks, both for stellar mass and for supermassive black holes. We find that, for a chaotic magnetic field in the disk, QED can significantly decrease the linear polarization fraction of edge-on photons, depending on the spin of the hole and on the strength of the magnetic field. This effect can provide, for the first time, a direct way to probe the magnetic field strength close to the innermost stable orbit of black-hole accretion disks and to study the role of magnetic fields in astrophysical accretion in general.

  8. First detection of winds in red giants by microwave continuum techniques

    NASA Technical Reports Server (NTRS)

    Drake, S. A.; Linsky, J. L.

    1983-01-01

    Eight red giants and supergiants have been observed at 4885 MHz (6 cm) with the Very Large Array in an attempt to detect continuum emission. The bright giant Alpha-1 Her (M5 II) was detected at an average flux density of 0.9 + or - 0.13 mJy. Since the likely source of this emission is an ionized, optically thick component of a stellar wind, this detection implies a mass loss rate of 2 x 10 to the -9th solar masses per yr for the ionized gas. The fraction of the outflow in Alpha-1 Her that is ionized (0.002-0.02) seems to be similar to that previously found for Alpha Ori and Alpha Sco A. Alpha Boo (K2 IIIp) and Beta Gem (K0 III) are probable and definite detections, respectively. The derived ionized mass loss rates for these two stars are about 1 x 10 to the -10th solar masses per yr, implying in the case of Alpha Boo that the wind is largely ionized.

  9. Accretion of magnetized matter into a black hole.

    NASA Astrophysics Data System (ADS)

    Bisnovatyj-Kogan, G. S.

    1999-12-01

    Accretion is the main source of energy in binary X-ray sources inside the Galaxy, and most probably in active galactic nuclei, where numerous observational data for the existence of supermassive black holes have been obtained. Standard accretion disk theory is formulated which is based on local heat balance. The whole energy produced by turbulent viscous heating is supposed to be emitted to the sides of the disk. Sources of turbulence in the accretion disk are discussed, including nonlinear hydrodynamic turbulence, convection and magnetic field. In standard theory there are two branches of solution, optically thick, anti-optically thin, which are individually self-consistent. The choice between these solutions should be done on the basis of a stability analysis. Advection in the accretion disks is described by differential equations, which makes the theory nonlocal. The low-luminosity optically thin accretion disk model with advection under some conditions may become advectively dominated, carrying almost all the energy inside the black hole. A proper account for magnetic field in the process of accretion limits the energy advected into a black hole, and does not allow the radiative efficiency of accretion to become lower than about 1/4 of the standard accretion disk model efficiency.

  10. Characterization of the Space Shuttle Ascent Debris using CFD Methods

    NASA Technical Reports Server (NTRS)

    Murman, Scott M.; Aftosmis, Michael J.; Rogers, Stuart E.

    2005-01-01

    After video analysis of space shuttle flight STS-107's ascent showed that an object shed from the bipod-ramp region impacted the left wing, a transport analysis was initiated to determine a credible flight path and impact velocity for the piece of debris. This debris transport analysis was performed both during orbit, and after the subsequent re-entry accident. The analysis provided an accurate prediction of the velocity a large piece of foam bipod ramp would have as it impacted the wing leading edge. This prediction was corroborated by video analysis and fully-coupled CFD/six degree of freedom (DOF) simulations. While the prediction of impact velocity was accurate enough to predict critical damage in this case, one of the recommendations of the Columbia Accident Investigation Board (CAIB) for return-to-flight (RTF) was to analyze the complete debris environment experienced by the shuttle stack on ascent. This includes categorizing all possible debris sources, their probable geometric and aerodynamic characteristics, and their potential for damage. This paper is chiefly concerned with predicting the aerodynamic characteristics of a variety of potential debris sources (insulating foam and cork, nose-cone ablator, ice, ...) for the shuttle ascent configuration using CFD methods. These aerodynamic characteristics are used in the debris transport analysis to predict flight path, impact velocity and angle, and provide statistical variation to perform risk analyses where appropriate. The debris aerodynamic characteristics are difficult to determine using traditional methods, such as static or dynamic test data, due to the scaling requirements of simulating a typical debris event. The use of CFD methods has been a critical element for building confidence in the accuracy of the debris transport code by bridging the gap between existing aerodynamic data and the dynamics of full-scale, in-flight events.

  11. Experimental Investigation of Magnesium Powder Combustion With C02 for Mars Ascent Applications

    NASA Technical Reports Server (NTRS)

    Foote, John P.; Litchford, Ronald J.

    2005-01-01

    Combustion of metals with CO2 has been identified as a possible propellant for Mars ascent applications. CO2 could be condensed from the Martian atmosphere, reducing the amount of propellant that must be transported from Earth. An attractive feature of this approach compared to other in situ propellant concepts is that no chemical processing on Mars is required. Magnesium has been identified as the most promising metal for this application because it ignites and burns easily in CO2. Preliminary systems studies indicate a 2 to 1 delivered mass advantage for Mg ascent propulsion using in situ C02, as compared to a conventional storable propellant system. The Propulsion Research Center at MSFC is undertaking an experimental investigation of magnesium powder combustion with CO2 in order to provide fundamental data on the combustion performance of Mg powder + CO2 mixtures needed to assess the feasibility of developing a practical Mg powder + CO2 rocket engine. Initial combustion experiments will be carried out in a small scale atmospheric pressure dump combustor. Effects of varying the Mg particle size, firing rate and O/F ratio on combustion stability and efficiency will be investigated. The combustion process will be characterized by optical flame measurements and extraction of combustion product samples. The experimental facility is currently being prepared and combustion experiments will begin during the first quarter of 2005. The final paper will describe the test facility and initial experimental results.

  12. Magnetic Coupling in the Disks around Young Gas Giant Planets

    NASA Astrophysics Data System (ADS)

    Turner, N. J.; Lee, Man Hoi; Sano, T.

    2014-03-01

    We examine the conditions under which the disks of gas and dust orbiting young gas giant planets are sufficiently conducting to experience turbulence driven by the magneto-rotational instability. By modeling the ionization and conductivity in the disk around proto-Jupiter, we find that turbulence is possible if the X-rays emitted near the Sun reach the planet's vicinity and either (1) the gas surface densities are in the range of the minimum-mass models constructed by augmenting Jupiter's satellites to solar composition, while dust is depleted from the disk atmosphere, or (2) the surface densities are much less, and in the range of gas-starved models fed with material from the solar nebula, but not so low that ambipolar diffusion decouples the neutral gas from the plasma. The results lend support to both minimum-mass and gas-starved models of the protojovian disk. (1) The dusty minimum-mass models have internal conductivities low enough to prevent angular momentum transfer by magnetic forces, as required for the material to remain in place while the satellites form. (2) The gas-starved models have magnetically active surface layers and a decoupled interior "dead zone." Similar active layers in the solar nebula yield accretion stresses in the range assumed in constructing the circumjovian gas-starved models. Our results also point to aspects of both classes of models that can be further developed. Non-turbulent minimum-mass models will lose dust from their atmospheres by settling, enabling gas to accrete through a thin surface layer. For the gas-starved models it is crucial to learn whether enough stellar X-ray and ultraviolet photons reach the circumjovian disk. Additionally, the stress-to-pressure ratio ought to increase with distance from the planet, likely leading to episodic accretion outbursts.

  13. Accretion of the terrestrial planets. II

    NASA Technical Reports Server (NTRS)

    Weidenschilling, S. J.

    1976-01-01

    The theory of gravitational accretion of the terrestrial planets is examined. The concept of a 'closed feeding zone' is somewhat unrealistic, but provides a lower bound on the accretion time. A velocity relation for planetesimals which includes an initial velocity component is suggested. The orbital parameters of the planetesimals and the dimensions of the feeding zone are related to their relative velocities. The assumption of an initial velocity does not seriously change the accretion time. Mercury, Venus, and the earth have accretion times on the order of 100 million years. Mars requires well over one billion years to accrete by the same assumptions. The lunar cratering history makes a late formation of Mars unlikely. If Mars is as old as the earth, nongravitational forces or a violation of the feeding zone concept is required. One such possibility is the removal of matter from the zone of Mars by Jupiter's influence. The final sweeping up by Mars would result in the scattering of a considerable mass among the other terrestrial planets. The late postaccretional bombardments inferred for the moon and Mercury may have had this source.

  14. Classical Accreting Pulsars with NICER

    NASA Technical Reports Server (NTRS)

    Wilson-Hodge, Colleen A.

    2014-01-01

    Soft excesses are very common center dot Lx > 1038 erg/s - reprocessing by optically thick material at the inner edge of the accretion disk center dot Lx < 1036 erg/s - photoionized or collisionally heated diffuse gas or thermal emission from the NS surface center dot Lx 1037 erg/s - either or both types of emission center dot NICER observations of soft excesses in bright X-ray pulsars combined with reflection modeling will constrain the ionization state, metalicity and dynamics of the inner edge of the magnetically truncated accretion disk Reflection models of an accretion disk for a hard power law - Strong soft excess below 3 keV from hot X-ray heated disk - For weakly ionized case: strong recombination lines - Are we seeing changes in the disk ionization in 4U1626-26? 13 years of weekly monitoring with RXTE PCA center dot Revealed an unexpectedly large population of Be/X-ray binaries compared to the Milky Way center dot Plotted luminosities are typical of "normal" outbursts (once per orbit) center dot The SMC provides an excellent opportunity to study a homogenous population of HMXBs with low interstellar absorption for accretion disk studies. Monitoring with NICER will enable studies of accretion disk physics in X-ray pulsars center dot The SMC provides a potential homogeneous low-absorption population for this study center dot NICER monitoring and TOO observations will also provide measurements of spinfrequencies, QPOs, pulsed fluxes, and energy spectra.

  15. Gamma-burst emission from neutron-star accretion

    NASA Technical Reports Server (NTRS)

    Colgate, S. A.; Petschek, A. G.; Sarracino, R.

    1983-01-01

    A model for emission of the hard photons of gamma bursts is presented. The model assumes accretion at nearly the Eddington limited rate onto a neutron star without a magnetic field. Initially soft photons are heated as they are compressed between the accreting matter and the star. A large electric field due to relatively small charge separation is required to drag electrons into the star with the nuclei against the flux of photons leaking out through the accreting matter. The photon number is not increased substantially by Bremsstrahlung or any other process. It is suggested that instability in an accretion disc might provide the infalling matter required.

  16. 20 Years of sea-levels, accretion, and vegetation on two Long ...

    EPA Pesticide Factsheets

    The long-term 1939-2013 rate of RSLR (Relative Sea-Level Rise) at the New London, CT tide gauge is ~2.6 mm/yr, near the maximum rate of salt marsh accretion reported in eastern Long Island Sound salt marshes. Consistent with recent literature RSLR at New London has accelerated since the 1980s; inter-annual variability can be high, but over the last three decades rates have averaged ~4.5 mm/yr, more than double the first 40 years of the New London record. Marsh surface elevation has been followed for 10 years with a SET array at the Barn Island system on Little Narragansett Bay and 20 years using an accretion pin array at Mamacoke Marsh on the Thames River. From 2003 – 2013 accretion averaged 2.3 mm/yr on the Barn Island marshes while RSLR increased 5.4 mm/yr. The increased hydroperiod is driving vegetation change at Barn Island, particularly in areas that started with lower “elevation capital”. Over two decades Mamacoke accretion closely matched RSLR: 4.7 vs 4.9 mm/yr, with no significant shifts in vegetation. For the 1st 12 years at Mamacoke, accretion was slower than RSLR: 3.2 vs 8.1 mm/yr. From 2006 to 2014, however elevation increase averaged 7.0 mm/yr while sea level rose just 7 mm. By 2014 accretion rates across the marsh ranged from 1.3 to 16.1 mm /yr. Preliminary core analysis confirms highly organic peat, but reveals sand concentrations at 2–4 cm in some areas, suggesting that Hurricanes Irene (2011) and Sandy (2012) may have contributed to Mama

  17. Quasispherical subsonic accretion in X-ray pulsars

    NASA Astrophysics Data System (ADS)

    Shakura, Nikolai I.; Postnov, Konstantin A.; Kochetkova, A. Yu; Hjalmarsdotter, L.

    2013-04-01

    A theoretical model is considered for quasispherical subsonic accretion onto slowly rotating magnetized neutron stars. In this regime, the accreting matter settles down subsonically onto the rotating magnetosphere, forming an extended quasistatic shell. Angular momentum transfer in the shell occurs via large-scale convective motions resulting, for observed pulsars, in an almost iso-angular-momentum \\omega \\sim 1/R^2 rotation law inside the shell. The accretion rate through the shell is determined by the ability of the plasma to enter the magnetosphere due to Rayleigh-Taylor instabilities, with allowance for cooling. A settling accretion regime is possible for moderate accretion rates \\dot M \\lesssim \\dot M_* \\simeq 4\\times 10^{16} g s ^{-1}. At higher accretion rates, a free-fall gap above the neutron star magnetosphere appears due to rapid Compton cooling, and the accretion becomes highly nonstationary. Observations of spin-up/spin-down rates of quasispherically wind accreting equilibrium X-ray pulsars with known orbital periods (e.g., GX 301-2 and Vela X-1) enable us to determine the main dimensionless parameters of the model, as well as to estimate surface magnetic field of the neutron star. For equilibrium pulsars, the independent measurements of the neutron star magnetic field allow for an estimate of the stellar wind velocity of the optical companion without using complicated spectroscopic measurements. For nonequilibrium pulsars, a maximum value is shown to exist for the spin-down rate of the accreting neutron star. From observations of the spin-down rate and the X-ray luminosity in such pulsars (e.g., GX 1+4, SXP 1062, and 4U 2206+54), a lower limit can be put on the neutron star magnetic field, which in all cases turns out to be close to the standard value and which agrees with cyclotron line measurements. Furthermore, both explains the spin-up/spin-down of the pulsar frequency on large time-scales and also accounts for the irregular short

  18. Advanced control concepts. [for shuttle ascent vehicles

    NASA Technical Reports Server (NTRS)

    Sharp, J. B.; Coppey, J. M.

    1973-01-01

    The problems of excess control devices and insufficient trim control capability on shuttle ascent vehicles were investigated. The trim problem is solved at all time points of interest using Lagrangian multipliers and a Simplex based iterative algorithm developed as a result of the study. This algorithm has the capability to solve any bounded linear problem with physically realizable constraints, and to minimize any piecewise differentiable cost function. Both solution methods also automatically distribute the command torques to the control devices. It is shown that trim requirements are unrealizable if only the orbiter engines and the aerodynamic surfaces are used.

  19. Theory of Bipolar Outflows from Accreting Hot Stars

    NASA Astrophysics Data System (ADS)

    Konigl, A.

    1996-05-01

    There is a growing number of observational indicators for the presence of bipolar outflows in massive, young stellar objects that are still accreting mass as part of their formation process. In particular, there is evidence that the outflows from these objects can attain higher velocities and kinetic luminosities than their lower-mass counterparts. Furthermore, the higher-mass objects appear to smoothly continue the correlation found in T Tauri stars between outflow and accretion signatures, and in several cases there are direct clues to the existence of a disk from optical and infrared spectroscopy. These results suggest that the disk--outflow connection found in low-mass pre--main-sequence stars extends to more massive objects, and that a similar physical mechanism may drive the outflows in both cases. In this presentation, I first critically examine the observational basis for this hypothesis, considering, among other things, the possibility that several low-luminosity outflows might occasionally masquerade as a single flow from a luminous object, and the effects that the radiation field of a hot star could have on the spectroscopic diagnostics of an accretion-driven outflow. I then go on to consider how the commonly invoked centrifugally driven wind models of bipolar outflows in low-mass stars would be affected by the various physical processes (such as photoionization, photoevaporation, radiation pressure, and stellar wind ram pressure) that operate in higher-mass stars. I conclude by mentioning some of the tantalizing questions that one could hope to address as this young field of research continues to develop (for example: is there a high-mass analog of the FU Orionis outburst phenomenon? Could one use observations of progressively more massive, and hence less convective, stars to elucidate the role of stellar magnetic fields in the accretion and outflow processes? Would it be possible to observationally identify massive stars that have reached the main

  20. Stochastic events lead to accretion in Saturn's rings

    NASA Astrophysics Data System (ADS)

    Esposito, Larry W.

    2010-05-01

    UVIS occultations indicate accretion is triggered at the B ring edge, in strong density waves in ring A and in the F ring. Moons may trigger accretion by streamline crowding (Lewis & Stewart); which enhances collisions, leading to accretion; increasing random velocities; leading to more collisions and more accretion. Cassini occultations of these strongly perturbed locations show not only accretion but also disaggregation, with time scales of hours to weeks. The collisions may lead to temporary aggregations via stochastic events: collisions can compress unconsolidated objects, trigger adhesion or bring small pieces into contact with larger or higher-density seeds. Disaggregation then can follow from disruptive collisions or tidal shedding. In the accretion/disruption balance, increased random motions could eventually give the upper hand to disruption… just as ‘irrational exuberance' can lead to financial panic in the economy; or the overpopulation of hares can lead to boom-and-bust in the population of foxes. This unstable equilibrium can similarly give rise to episodic cycles in accretion: explaining why the observable ring features that indicate embedded objects have been increasing since the beginning of Cassini's observations of Saturn in 2004.

  1. Identifying Li-rich giants from low-resolution spectroscopic survey

    NASA Astrophysics Data System (ADS)

    Kumar, Yerra Bharat; Reddy, Bacham Eswar; Zhao, Gang

    2018-04-01

    In this paper we discuss our choice of a large unbiased sample used for the survey of red giant branch stars for finding Li-rich K giants, and the method used for identifying Li-rich candidates using low-resolution spectra. The sample has 2000 giants within a mass range of 0.8 to 3.0it{M}_{⊙}. Sample stars were selected from the Hipparcos catalogue with colour (B-V) and luminosity (it{L}/it{L}_{⊙}) in such way that the sample covers RGB evolution from its base towards RGB tip passing through first dredge-up and luminosity bump. Low-resolution (R ≈ 2000, 3500, 5000) spectra were obtained for all sample stars. Using core strength ratios of lines at Li I 6707 Å and its adjacent line Ca I 6717 Å we successfully identified 15 K giants with A(Li) > 1.5 dex, which are defined as Li-rich K giants. The results demonstrate the usefulness of low-resolution spectra to measure Li abundance and identify Li-rich giants from a large sample of stars in relatively shorter time periods.

  2. Giant aerosol observations with cloud radar: methodology and effects

    NASA Astrophysics Data System (ADS)

    Guma Claramunt, Pilar; Madonna, Fabio; Amodeo, Aldo; Bauer-Pfundstein, Matthias; Papagiannopoulos, Nikolaos; Pappalardo, Gelsomina

    2017-04-01

    together with the increases of AOD. Finally, the effects of giant aerosols on precipitation at a regional scale have been studied. The observation of giant aerosols can be correlated to an enhancement of the accumulated precipitation, which is quite relevant in the first 12 hours after their observation, as well as of the maximum rain rate in presence of the unstable atmospheric conditions. The increase in the maximum rain rate is instead more remarkable in correlation with stable atmospheric conditions and mainly during the first 6 hours after their observations.

  3. Evolution of a steam atmosphere during earth's accretion

    NASA Astrophysics Data System (ADS)

    Zahnle, K. J.; Kasting, J. F.; Pollack, J. B.

    1988-04-01

    The evolution of an impact-generated steam atmosphere around an accreting earth is presently modeled under the assumption of Safronov (1978) accretion, in a scheme that encompasses the degassing of planetesimals on impact, thermal blanketing by the steam atmosphere, surface-to-interior water exchange, the shock heating and convective cooling of the earth's interior, and hydrogen escape due both to solar EUV-powered planetary wind and impact erosion. The model yields four distinct classes of impact-generated atmospheres: the first, on which emphasis is placed, has as its salient feature a molten surface that is maintained by the opacity of a massive water vapor atmosphere; the second occurs when the EUV-limited escape exceeds the impact degassing rate, while the third is dominated by impact erosion and the fourth is characterized by an atmosphere more massive than any thus far encountered.

  4. Evolution of a steam atmosphere during earth's accretion

    NASA Technical Reports Server (NTRS)

    Zahnle, Kevin J.; Kasting, James F.; Pollack, James B.

    1988-01-01

    The evolution of an impact-generated steam atmosphere around an accreting earth is presently modeled under the assumption of Safronov (1978) accretion, in a scheme that encompasses the degassing of planetesimals on impact, thermal blanketing by the steam atmosphere, surface-to-interior water exchange, the shock heating and convective cooling of the earth's interior, and hydrogen escape due both to solar EUV-powered planetary wind and impact erosion. The model yields four distinct classes of impact-generated atmospheres: the first, on which emphasis is placed, has as its salient feature a molten surface that is maintained by the opacity of a massive water vapor atmosphere; the second occurs when the EUV-limited escape exceeds the impact degassing rate, while the third is dominated by impact erosion and the fourth is characterized by an atmosphere more massive than any thus far encountered.

  5. Reconstructing the Accretion History of the Galactic Stellar Halo from Chemical Abundance Ratio Distributions

    NASA Astrophysics Data System (ADS)

    Lee, Duane M.; Johnston, Kathryn V.; Sen, Bodhisattva; Jessop, Will

    2015-03-01

    Observational studies of halo stars during the past two decades have placed some limits on the quantity and nature of accreted dwarf galaxy contributions to the Milky Way (MW) stellar halo by typically utilizing stellar phase-space information to identify the most recent halo accretion events. In this study we tested the prospects of using 2D chemical abundance ratio distributions (CARDs) found in stars of the stellar halo to determine its formation history. First, we used simulated data from 11 “MW-like” halos to generate satellite template sets (STSs) of 2D CARDs of accreted dwarf satellites, which are composed of accreted dwarfs from various mass regimes and epochs of accretion. Next, we randomly drew samples of ˜103-4 mock observations of stellar chemical abundance ratios ([α/Fe], [Fe/H]) from those 11 halos to generate samples of the underlying densities for our CARDs to be compared to our templates in our analysis. Finally, we used the expectation-maximization algorithm to derive accretion histories in relation to the STS used and the sample size. For certain STSs used we typically can identify the relative mass contributions of all accreted satellites to within a factor of two. We also find that this method is particularly sensitive to older accretion events involving low-luminosity dwarfs, e.g., ultra-faint dwarfs—precisely those events that are too ancient to be seen by phase-space studies of stars and too faint to be seen by high-z studies of the early universe. Since our results only exploit two chemical dimensions and near-future surveys promise to provide ˜6-9 dimensions, we conclude that these new high-resolution spectroscopic surveys of the stellar halo will allow us to recover its accretion history—and the luminosity function of infalling dwarf galaxies—across cosmic time.

  6. RECONSTRUCTING THE ACCRETION HISTORY OF THE GALACTIC STELLAR HALO FROM CHEMICAL ABUNDANCE RATIO DISTRIBUTIONS

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

    Lee, Duane M.; Johnston, Kathryn V.; Sen, Bodhisattva

    Observational studies of halo stars during the past two decades have placed some limits on the quantity and nature of accreted dwarf galaxy contributions to the Milky Way (MW) stellar halo by typically utilizing stellar phase-space information to identify the most recent halo accretion events. In this study we tested the prospects of using 2D chemical abundance ratio distributions (CARDs) found in stars of the stellar halo to determine its formation history. First, we used simulated data from 11 “MW-like” halos to generate satellite template sets (STSs) of 2D CARDs of accreted dwarf satellites, which are composed of accreted dwarfsmore » from various mass regimes and epochs of accretion. Next, we randomly drew samples of ∼10{sup 3–4} mock observations of stellar chemical abundance ratios ([α/Fe], [Fe/H]) from those 11 halos to generate samples of the underlying densities for our CARDs to be compared to our templates in our analysis. Finally, we used the expectation-maximization algorithm to derive accretion histories in relation to the STS used and the sample size. For certain STSs used we typically can identify the relative mass contributions of all accreted satellites to within a factor of two. We also find that this method is particularly sensitive to older accretion events involving low-luminosity dwarfs, e.g., ultra-faint dwarfs—precisely those events that are too ancient to be seen by phase-space studies of stars and too faint to be seen by high-z studies of the early universe. Since our results only exploit two chemical dimensions and near-future surveys promise to provide ∼6–9 dimensions, we conclude that these new high-resolution spectroscopic surveys of the stellar halo will allow us to recover its accretion history—and the luminosity function of infalling dwarf galaxies—across cosmic time.« less

  7. Habitable Mars Ascent Vehicle (MAV) Concept. [Mars Ascent Vehicle (MAV) Layout and Configuration: 6-Crew, Habitable, Nested Tank Concept

    NASA Technical Reports Server (NTRS)

    Dang, Victor; Rucker, Michelle

    2013-01-01

    NASA's ultimate goal is the human exploration of Mars. Among the many difficult aspects of a trip to Mars is the return mission that would transport the astronauts from the Martian surface back into Mars orbit. One possible conceptual design to accomplish this task is a two-stage Mars Ascent Vehicle (MAV). In order to assess this design, a general layout and configuration for the spacecraft must be developed. The objective of my internship was to model a conceptual MAV design to support NASA's latest human Mars mission architecture trade studies, technology prioritization decisions, and mass, cost, and schedule estimates.

  8. Gravitomagnetic acceleration from black hole accretion disks

    NASA Astrophysics Data System (ADS)

    Poirier, J.; Mathews, G. J.

    2016-05-01

    We demonstrate how the motion of the neutral masses in an accretion disk orbiting a black hole creates a general-relativistic magnetic-like (gravitomagnetic) field that vertically accelerates neutral particles near an accretion disk upward and then inward toward the axis of the accretion disk. Even though this gravitomagnetic field is not the only mechanism contributing to the production of jets, it presents a novel means to identify one general relativistic effect from a much more complicated problem. In addition, as the accelerated material above or below the accretion disk nears the axis with a nearly vertical direction, a frame-dragging effect twists the trajectories around the axis thus contributing to the collimation of the jet.

  9. Bimodal gas accretion in the Horizon-MareNostrum galaxy formation simulation

    NASA Astrophysics Data System (ADS)

    Ocvirk, P.; Pichon, C.; Teyssier, R.

    2008-11-01

    The physics of diffuse gas accretion and the properties of the cold and hot modes of accretion on to proto-galaxies between z = 2 and 5.4 is investigated using the large cosmological simulation performed with the RAMSES code on the MareNostrum supercomputing facility. Galactic winds, chemical enrichment, ultraviolet background heating and radiative cooling are taken into account in this very high resolution simulation. Using accretion-weighted temperature histograms, we have performed two different measurements of the thermal state of the gas accreted towards the central galaxy. The first measurement, performed using accretion-weighted histograms on a spherical surface of radius 0.2Rvir centred on the densest gas structure near the halo centre of mass, is a good indicator of the presence of an accretion shock in the vicinity of the galactic disc. We define the hot shock mass, Mshock, as the typical halo mass separating cold dominated from hot dominated accretion in the vicinity of the galaxy. The second measurement is performed by radially averaging histograms between 0.2Rvir and Rvir, in order to detect radially extended structures such as gas filaments: this is a good proxy for detecting cold streams feeding the central galaxy. We define Mstream as the transition mass separating cold dominated from hot dominated accretion in the outer halo, marking the disappearance of these cold streams. We find a hot shock transition mass of Mshock = 1011.6Msolar (dark matter), with no significant evolution with redshift. Conversely, we find that Mstream increases sharply with z. Our measurements are in agreement with the analytical predictions of Birnboim & Dekel and Dekel & Birnboim, if we correct their model by assuming low metallicity (<=10-3Zsolar) for the filaments, correspondingly to our measurements. Metal enrichment of the intergalactic medium is therefore a key ingredient in determining the transition mass from cold to hot dominated diffuse gas accretion. We find that

  10. On the Dependence of the X-Ray Burst Rate on Accretion and Spin Rate

    NASA Astrophysics Data System (ADS)

    Cavecchi, Yuri; Watts, Anna L.; Galloway, Duncan K.

    2017-12-01

    Nuclear burning and its dependence on the mass accretion rate are fundamental ingredients for describing the complicated observational phenomenology of neutron stars (NSs) in binary systems. Motivated by high-quality burst rate data emerging from large statistical studies, we report general calculations relating the bursting rate to the mass accretion rate and NS rotation frequency. In this first work, we ignore general relativistic effects and accretion topology, although we discuss where their inclusion should play a role. The relations we derive are suitable for different burning regimes and provide a direct link between parameters predicted by theory and what is to be expected in observations. We illustrate this for analytical relations of different unstable burning regimes that operate on the surface of an accreting NS. We also use the observed behavior of the burst rate to suggest new constraints on burning parameters. We are able to provide an explanation for the long-standing problem of the observed decrease of the burst rate with increasing mass accretion that follows naturally from these calculations: when the accretion rate crosses a certain threshold, ignition moves away from its initially preferred site, and this can cause a net reduction of the burst rate due to the effects of local conditions that set local differences in both the burst rate and stabilization criteria. We show under which conditions this can happen even if locally the burst rate keeps increasing with accretion.

  11. First Giant Mirror for the ESO VLT Ready at REOSC

    NASA Astrophysics Data System (ADS)

    1995-11-01

    The REOSC Contract In 1989, the European Southern Observatory (ESO), the European Organisation for Astronomy, awarded to REOSC, a subsidiary of the SFIM Group and located in Saint Pierre du Perray (France), a comprehensive contract for the polishing of four 8.2-metre diameter mirrors for the unit telescopes of the ESO Very Large Telescope (VLT) project. These mirrors are the largest ever manufactured and polished. This contract comprises not only the polishing and high-precision optical testing of each giant mirror, but also the safe condition of transportation of the blanks which were manufactured by Schott Glaswerke in Mainz (Germany). In order to fulfill the contract, REOSC conceived, built and equipped a novel, high-tech workshop which would allow to polish and test the mirrors, each of which has a surface area of more than 50 square metres. First 8.2-Metre Mirror is Ready and within Specifications The REOSC polishing facility for giant mirrors was built in Saint Pierre du Perray, just south of Paris. It is equipped with two machines: one for grinding and the other for polishing the mirrors, and both with 150-actuator systems that support the thin and flexible mirrors. All equipment is computer controlled. State-of-the-art interferometers probe the accuracy of the mirror surface as the polishing proceeds; they are installed at the top level of the facility in a 30-metre high tower, at the centre of the mirror's radius of curvature. The success of the work at REOSC is now evident by the fact that careful measurements of the first mirror earlier this month have shown that the final optical surface is correct to within 0.00005 millimetres. For illustration, this corresponds to an accuracy of only 1 millimetre deviation over a surface with a diameter of 165 kilometres (equivalent to the entire Paris area)! ESO Receives the First VLT Mirror After having been carefully placed in a special transport box designed by REOSC, the first mirror blank, weighing 23.5 tons and

  12. Balloon Ascent: 3-D Simulation Tool for the Ascent and Float of High-Altitude Balloons

    NASA Technical Reports Server (NTRS)

    Farley, Rodger E.

    2005-01-01

    The BalloonAscent balloon flight simulation code represents a from-scratch development using Visual Basic 5 as the software platform. The simulation code is a transient analysis of balloon flight, predicting the skin and gas temperatures along with the 3-D position and velocity in a time and spatially varying environment. There are manual and automated controls for gas valving and the dropping of ballast. Also, there are many handy calculators, such as appropriate free lift, and steady-state thermal solutions with temperature gradients. The strength of this simulation model over others in the past is that the infrared environment is deterministic rather than guessed at. The ground temperature is specified along with the emissivity, which creates a ground level IR environment that is then partially absorbed as it travels upward through the atmosphere to the altitude of the balloon.

  13. Progress in manufacturing the first 8.4 m off-axis segment for the Giant Magellan Telescope

    NASA Astrophysics Data System (ADS)

    Martin, H. M.; Burge, J. H.; Cuerden, B.; Davison, W. B.; Kingsley, J. S.; Kittrell, W. C.; Lutz, R. D.; Miller, S. M.; Zhao, C.; Zobrist, T.

    2008-07-01

    The first of the 8.4 m off-axis segments for the primary mirror of the Giant Magellan Telescope is being manufactured at the Steward Observatory Mirror Lab. In addition to the manufacture of the segment, this project includes the development of a complete facility to make and measure all seven segments. We have installed a new 28 m test tower and designed a set of measurements to guide the fabrication and qualify the finished segments. The first test, a laser-tracker measurement of the ground surface, is operational. The principal optical test is a full-aperture interferometric test with a null corrector that includes a 3.75 m spherical mirror, a smaller sphere, and a computer-generated hologram. We have also designed a scanning pentaprism test to validate the measurement of low-order aberrations. The first segment has been cast and generated, and is in the process of loose-abrasive grinding.

  14. X-Ray Spectra from MHD Simulations of Accreting Black Holes

    NASA Technical Reports Server (NTRS)

    Schnittman, Jeremy D.; Krolik, Julian H.; Noble, Scott C.

    2012-01-01

    We present the results of a new global radiation transport code coupled to a general relativistic magneto-hydrodynamic simulation of an accreting, nonrotating black hole. For the first time, we are able to explain from first principles in a self-consistent way the X-ray spectra observed from stellar-mass black holes, including a thermal peak, Compton reflection hump, power-law tail, and broad iron line. Varying only the mass accretion rate, we are able to reproduce the low/hard, steep power-law, and thermal-dominant states seen in most galactic black hole sources. The temperature in the corona is T(sub e) 10 keV in a boundary layer near the disk and rises smoothly to T(sub e) greater than or approximately 100 keV in low-density regions far above the disk. Even as the disk's reflection edge varies from the horizon out to approximately equal to 6M as the accretion rate decreases, we find that the shape of the Fe Ka line is remarkably constant. This is because photons emitted from the plunging region are strongly beamed into the horizon and never reach the observer. We have also carried out a basic timing analysis of the spectra and find that the fractional variability increases with photon energy and viewer inclination angle, consistent with the coronal hot spot model for X-ray fluctuations.

  15. X-Ray Emissions from Accreting White Dwarfs: A Review

    NASA Technical Reports Server (NTRS)

    Mukai, K.

    2017-01-01

    Interacting binaries in which a white dwarf accretes material from a companion-cataclysmic variables (CVs) in which the mass donor is a Roche-lobe filling star on or near the main sequence, and symbiotic stars in which the mass donor is a late type giant-are relatively commonplace. They display a wide range of behaviors in the optical, X-rays, and other wavelengths, which still often baffle observers and theorists alike. Here I review the existing body of research on X-ray emissions from these objects for the benefits of both experts and newcomers to the field. I provide introductions to the past and current X-ray observatories, the types of known X-ray emissions from these objects, and the data analysis techniques relevant to this field. I then summarize of our knowledge regarding the X-ray emissions from magnetic CVs, non-magnetic CVs and symbiotic stars, and novae in eruption. I also discuss space density and the X-ray luminosity functions of these binaries and their contribution to the integrated X-ray emission from the Galaxy. I then discuss open questions and future prospects.

  16. Counter-rotating accretion discs

    NASA Astrophysics Data System (ADS)

    Dyda, S.; Lovelace, R. V. E.; Ustyugova, G. V.; Romanova, M. M.; Koldoba, A. V.

    2015-01-01

    Counter-rotating discs can arise from the accretion of a counter-rotating gas cloud on to the surface of an existing corotating disc or from the counter-rotating gas moving radially inwards to the outer edge of an existing disc. At the interface, the two components mix to produce gas or plasma with zero net angular momentum which tends to free-fall towards the disc centre. We discuss high-resolution axisymmetric hydrodynamic simulations of viscous counter-rotating discs for the cases where the two components are vertically separated and radially separated. The viscosity is described by an isotropic α-viscosity including all terms in the viscous stress tensor. For the vertically separated components, a shear layer forms between them and the middle part of this layer free-falls to the disc centre. The accretion rates are increased by factors of ˜102-104 over that for a conventional disc rotating in one direction with the same viscosity. The vertical width of the shear layer and the accretion rate are strongly dependent on the viscosity and the mass fraction of the counter-rotating gas. In the case of radially separated components where the inner disc corotates and the outer disc rotates in the opposite direction, a gap between the two components opens and closes quasi-periodically. The accretion rates are ≳25 times larger than those for a disc rotating in one direction with the same viscosity.

  17. Allometry indicates giant eyes of giant squid are not exceptional.

    PubMed

    Schmitz, Lars; Motani, Ryosuke; Oufiero, Christopher E; Martin, Christopher H; McGee, Matthew D; Gamarra, Ashlee R; Lee, Johanna J; Wainwright, Peter C

    2013-02-18

    The eyes of giant and colossal squid are among the largest eyes in the history of life. It was recently proposed that sperm whale predation is the main driver of eye size evolution in giant squid, on the basis of an optical model that suggested optimal performance in detecting large luminous visual targets such as whales in the deep sea. However, it is poorly understood how the eye size of giant and colossal squid compares to that of other aquatic organisms when scaling effects are considered. We performed a large-scale comparative study that included 87 squid species and 237 species of acanthomorph fish. While squid have larger eyes than most acanthomorphs, a comparison of relative eye size among squid suggests that giant and colossal squid do not have unusually large eyes. After revising constants used in a previous model we found that large eyes perform equally well in detecting point targets and large luminous targets in the deep sea. The eyes of giant and colossal squid do not appear exceptionally large when allometric effects are considered. It is probable that the giant eyes of giant squid result from a phylogenetically conserved developmental pattern manifested in very large animals. Whatever the cause of large eyes, they appear to have several advantages for vision in the reduced light of the deep mesopelagic zone.

  18. IMPETUS: consistent SPH calculations of 3D spherical Bondi accretion on to a black hole

    NASA Astrophysics Data System (ADS)

    Ramírez-Velasquez, J. M.; Sigalotti, L. Di G.; Gabbasov, R.; Cruz, F.; Klapp, J.

    2018-07-01

    We present three-dimensional calculations of spherically symmetric Bondi accretion on to a stationary supermassive black hole of mass 108 M⊙ within a radial range of 0.02-10 pc, using a modified version of the smoothed particle hydrodynamics GADGET-2 code, which ensures approximate first-order consistency (i.e. second-order accuracy) for the particle approximation. First-order consistency is restored by allowing the number of neighbours, nneigh, and the smoothing length, h, to vary with the total number of particles, N, such that the asymptotic limits nneigh → ∞ and h → 0 hold as N → ∞. The ability of the method to reproduce the isothermal (γ = 1) and adiabatic (γ = 5/3) Bondi accretion is investigated with increased spatial resolution. In particular, for the isothermal models, the numerical radial profiles closely match the Bondi solution, except near the accretor, where the density and radial velocity are slightly underestimated. However, as nneigh is increased and h is decreased, the calculations approach first-order consistency and the deviations from the Bondi solution decrease. The density and radial velocity profiles for the adiabatic models are qualitatively similar to those for the isothermal Bondi accretion. Steady-state Bondi accretion is reproduced by the highly resolved consistent models with a percent relative error of ≲ 1 per cent for γ = 1 and ˜9 per cent for γ = 5/3, with the adiabatic accretion taking longer than the isothermal case to reach steady flow. The performance of the method is assessed by comparing the results with those obtained using the standard GADGET-2 and GIZMO codes.

  19. Radio outburst from a massive (proto)star. When accretion turns into ejection

    NASA Astrophysics Data System (ADS)

    Cesaroni, R.; Moscadelli, L.; Neri, R.; Sanna, A.; Caratti o Garatti, A.; Eisloffel, J.; Stecklum, B.; Ray, T.; Walmsley, C. M.

    2018-05-01

    Context. Recent observations of the massive young stellar object S255 NIRS 3 have revealed a large increase in both methanol maser flux density and IR emission, which have been interpreted as the result of an accretion outburst, possibly due to instabilities in a circumstellar disk. This indicates that this type of accretion event could be common in young/forming early-type stars and in their lower mass siblings, and supports the idea that accretion onto the star may occur in a non-continuous way. Aims: As accretion and ejection are believed to be tightly associated phenomena, we wanted to confirm the accretion interpretation of the outburst in S255 NIRS 3 by detecting the corresponding burst of the associated thermal jet. Methods: We monitored the radio continuum emission from S255 NIRS 3 at four bands using the Karl G. Jansky Very Large Array. The millimetre continuum emission was also observed with both the Northern Extended Millimeter Array of IRAM and the Atacama Large Millimeter/Submillimeter Array. Results: We have detected an exponential increase in the radio flux density from 6 to 45 GHz starting right after July 10, 2016, namely 13 months after the estimated onset of the IR outburst. This is the first ever detection of a radio burst associated with an IR accretion outburst from a young stellar object. The flux density at all observed centimetre bands can be reproduced with a simple expanding jet model. At millimetre wavelengths we infer a marginal flux increase with respect to the literature values and we show this is due to free-free emission from the radio jet. Conclusions: Our model fits indicate a significant increase in the jet opening angle and ionized mass loss rate with time. For the first time, we can estimate the ionization fraction in the jet and conclude that this must be low (<14%), lending strong support to the idea that the neutral component is dominant in thermal jets. Our findings strongly suggest that recurrent accretion + ejection

  20. Optimization of the medium for Lactobacillus acidophilus by Plackett-Burman and steepest ascent experiment.

    PubMed

    Chen, He; Niu, Jinfeng; Qin, Tao; Ma, Qi; Wang, Lei; Shu, Guowei

    2015-01-01

    Lactobacillus acidophilus not only improves the intestinal flora balance but also inhabits the growth of undesirable microorganisms in intestine, which is benefit to the health of humans and animals. Plackett-Burman and steepest ascent experiment are the rapid and concise ways of screening the main effective factors. This study is aimed to select the main influence factors and optimize the medium for Lactobacillus acidophilus by Plackett-Burman experiment and steepest ascent experiment. The ideal carbon source was screened among glucose, maltose, lactose and whey powder, and the ideal nitrogen source was screened among casein hydrolysate, peptone, yeast extract powder, fish meal, carbamide, ammonium sulfate and sodium nitrate by single factor experiment. Plackett-Burman and steepest ascent experiment were applied to screen the main effective factors of Lactobacillus acidophilus among peptone, beef extract, yeast extract powder, glucose, K2HPO4, C6H14O7N2, CH3COONa, MgSO4 and Tween-80. Result. The results indicated that glucose (p = 0.01510) as negative factor and K2HPO4 (p = 0.02017) as positive effect were the significant growth factors of Lactobacillus acidophilus, CH3COONa (p = 0.09273) as positive effect was an important factor, and the optimized medium was as follows: glucose - 21 g/L, K2HPO4 - 3.5 g/L, CH3COONa - 6.5 g/L, peptone - 10 g/L, beef extract - 8 g/L, yeast extract pow. nd. Lactobacillus acidophilus not only improves the intestinal flora balance but also inhabits the growth of undesirable microorganisms in intestine, which is benefit to the health of humans and animals. Plackett-Burman and steepest ascent experiment are the rapid and concise ways of screening the main effective factors. This study is aimed to select the main influence factors and optimize the medium for Lactobacillus acidophilus by Plackett-Burman experiment and steepest ascent experiment. Material and methods. The ideal carbon source was screened among glucose, maltose, lactose and

  1. Anticipatory kinematics and muscle activity preceding transitions from level-ground walking to stair ascent and descent.

    PubMed

    Peng, Joshua; Fey, Nicholas P; Kuiken, Todd A; Hargrove, Levi J

    2016-02-29

    The majority of fall-related accidents are during stair ambulation-occurring commonly at the top and bottom stairs of each flight, locations in which individuals are transitioning to stairs. Little is known about how individuals adjust their biomechanics in anticipation of walking-stair transitions. We identified the anticipatory stride mechanics of nine able-bodied individuals as they approached transitions from level ground walking to stair ascent and descent. Unlike prior investigations of stair ambulation, we analyzed two consecutive "anticipation" strides preceding the transitions strides to stairs, and tested a comprehensive set of kinematic and electromyographic (EMG) data from both the leading and trailing legs. Subjects completed ten trials of baseline overground walking and ten trials of walking to stair ascent and descent. Deviations relative to baseline were assessed. Significant changes in mechanics and EMG occurred in the earliest anticipation strides analyzed for both ascent and descent transitions. For stair descent, these changes were consistent with observed reductions in walking speed, which occurred in all anticipation strides tested. For stair ascent, subjects maintained their speed until the swing phase of the latest anticipation stride, and changes were found that would normally be observed for decreasing speed. Given the timing and nature of the observed changes, this study has implications for enhancing intent recognition systems and evaluating fall-prone or disabled individuals, by testing their abilities to sense upcoming transitions and decelerate during locomotion. Copyright © 2016 Elsevier Ltd. All rights reserved.

  2. Additional Improvements to the NASA Lewis Ice Accretion Code LEWICE

    NASA Technical Reports Server (NTRS)

    Wright, William B.; Bidwell, Colin S.

    1995-01-01

    Due to the feedback of the user community, three major features have been added to the NASA Lewis ice accretion code LEWICE. These features include: first, further improvements to the numerics of the code so that more time steps can be run and so that the code is more stable; second, inclusion and refinement of the roughness prediction model described in an earlier paper; third, inclusion of multi-element trajectory and ice accretion capabilities to LEWICE. This paper will describe each of these advancements in full and make comparisons with the experimental data available. Further refinement of these features and inclusion of additional features will be performed as more feedback is received.

  3. A pebbles accretion model with chemistry and implications for the solar system in the lights of Juno

    NASA Astrophysics Data System (ADS)

    Ali-Dib, Mohamad

    2016-10-01

    The chemical compositions of the solar system giant planets are a major source of informations on their origins. Since the measurements by the Galileo probe, multiple models have been put forward to try and explain the noble gases enrichment in Jupiter. The most discussed among these are its formation in the outer cold nebula and its formation in a partially photoevaporated disk. In this work I couple a pebbles accretion model to the disk's chemistry and photoevaporation in order to make predictions from both scenarios and compare them to the upcoming Juno measurements. The model include pebbles and gas accretion, type I and II migration, photoevaporation and chemical measurements from meteorites, comets and disks. Population synthesis simulations are used to explore the models free parameters (planets initial conditions), where then the results are narrowed down using the planets chemical, dynamical and core mass costraints. We end up with a population that fits all of the constrains. These are then used to predict the oxygen abundance and core mass in Jupiter, to be compared to results of Juno. Same calculations are also done for Saturn and Neptune for comparison. I will present the results from these simulations as well as the predictions from all of the different models.Ali-Dib, M. (2016ab, submitted to MNRAS)

  4. Influence of working memory and executive function on stair ascent and descent in young and older adults.

    PubMed

    Gaillardin, Florence; Baudry, Stéphane

    2018-06-01

    This study assessed the influence of attention division, working memory and executive function on stair ascent and descent in young and older adults. Twenty young (25.5 ± 2.1 yrs) and 20 older adults (68.4 ± 5.4 yrs) ascended and descended a 3-step staircase with no simultaneous cognitive task (single-motor task) or while performing a cognitive task (dual-task condition). The cognitive task involved either 1) recalling a word list of the subject's word-span minus 2 words (SPAN-2) to assess the attention division effect, 2) a word list of subject's word-span (SPAN-O) to assess the working memory effect, or 3) recalling in alphabetical order, a word list of the subject's word-span (SPAN-A) to assess the executive function effect. Word-span corresponds to the longest string of words that can be recalled correctly. The duration of ascent and descent of stairs was used to assess the cognitive-motor interaction. Stair ascent and descent duration did not differ between age groups for the single-motor task, and was similar between single-motor task and SPAN-2 in both groups (p > 0.05). In contrast, stair ascent and descent duration increased with SPAN-O compared with SPAN-2 for both groups (p < 0.01). Stair ascent (p = 0.017) and descent (p = 0.008) were longer in SPAN-A than SPAN-O only in older adults. Healthy aging was not associated with a decrease in the capacity to perform motor-cognitive dual tasks that involved ascending and descending of stairs when the cognitive task only required working memory. However, the decrease in dual-task performance involving executive functioning may reflect a subclinical cognitive decline in healthy older adults. Copyright © 2018 Elsevier Inc. All rights reserved.

  5. Review of gravitomagnetic acceleration from accretion disks

    NASA Astrophysics Data System (ADS)

    Poirier, J.; Mathews, G. J.

    2015-11-01

    We review the development of the equations of gravitoelectromagnetism and summarize how the motion of the neutral masses in an accretion disk orbiting a black hole creates a general-relativistic magnetic-like (gravitomagnetic) field that vertically accelerates neutral particles near the accretion disk upward and then inward toward the axis of the accretion disk. Even though this gravitomagnetic field is not the only mechanism to produce collimated jets, it is a novel means to identify one general relativistic effect from a much more complicated problem. In addition, as the accelerated material above or below the accretion disk nears the axis with a nearly vertical direction, a frame-dragging effect twists the trajectories around the axis thus contributing to the collimation of the jet.

  6. Accretion onto a noncommutative geometry inspired black hole

    NASA Astrophysics Data System (ADS)

    Kumar, Rahul; Ghosh, Sushant G.

    2017-09-01

    The spherically symmetric accretion onto a noncommutative (NC) inspired Schwarzschild black hole is treated for a polytropic fluid. The critical accretion rate \\dot{M}, sonic speed a_s and other flow parameters are generalized for the NC inspired static black hole and compared with the results obtained for the standard Schwarzschild black holes. Also explicit expressions for gas compression ratios and temperature profiles below the accretion radius and at the event horizon are derived. This analysis is a generalization of Michel's solution to the NC geometry. Owing to the NC corrected black hole, the accretion flow parameters also have been modified. It turns out that \\dot{M} ≈ {M^2} is still achievable but r_s seems to be substantially decreased due to the NC effects. They in turn do affect the accretion process.

  7. Helium shell flashes and evolution of accreting white dwarfs

    NASA Astrophysics Data System (ADS)

    Fujimoto, M. Y.; Sugimoto, D.

    1982-06-01

    The evolution of accreting white dwarfs is investigated from the onset of accretion through the helium shell flash. Properties of the helium shell flashes are studied by means of a generalized theory of shell flash and by numerical computations, and it is found that the shell flash grows up to the strength of a supernova explosion when the mass of the helium zone is large enough on a massive white dwarf. Although accretion onto a hot white dwarf causes a weaker shell flash than those onto cool ones, a strong tendency exists for the strength to be determined mainly by the accretion rate. For fast accretion, the shell flashes are weak and triggered recurrently, while for slow accretion the helium shell flash, once triggered, develops into a detonation supernova.

  8. Pulsed Accretion in the T Tauri Binary TWA 3A

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

    Tofflemire, Benjamin M.; Mathieu, Robert D.; Herczeg, Gregory J.

    TWA 3A is the most recent addition to a small group of young binary systems that both actively accrete from a circumbinary disk and have spectroscopic orbital solutions. As such, it provides a unique opportunity to test binary accretion theory in a well-constrained setting. To examine TWA 3A’s time-variable accretion behavior, we have conducted a two-year, optical photometric monitoring campaign, obtaining dense orbital phase coverage (∼20 observations per orbit) for ∼15 orbital periods. From U -band measurements we derive the time-dependent binary mass accretion rate, finding bursts of accretion near each periastron passage. On average, these enhanced accretion events evolvemore » over orbital phases 0.85 to 1.05, reaching their peak at periastron. The specific accretion rate increases above the quiescent value by a factor of ∼4 on average but the peak can be as high as an order of magnitude in a given orbit. The phase dependence and amplitude of TWA 3A accretion is in good agreement with numerical simulations of binary accretion with similar orbital parameters. In these simulations, periastron accretion bursts are fueled by periodic streams of material from the circumbinary disk that are driven by the binary orbit. We find that TWA 3A’s average accretion behavior is remarkably similar to DQ Tau, another T Tauri binary with similar orbital parameters, but with significantly less variability from orbit to orbit. This is only the second clear case of orbital-phase-dependent accretion in a T Tauri binary.« less

  9. Spatially resolving the outer atmosphere of the M giant BK Virginis in the CO first overtone lines with VLTI/AMBER

    NASA Astrophysics Data System (ADS)

    Ohnaka, K.; Hofmann, K.-H.; Schertl, D.; Weigelt, G.; Malbet, F.; Massi, F.; Meilland, A.; Stee, Ph.

    2012-01-01

    Context. The mass-loss mechanism in normal K-M giant stars with small variability amplitudes is not yet understood, although the majority among red giant stars are precisely of this type. Aims: We present high-spatial and high-spectral resolution observations of the M7 giant BK Vir with AMBER at the Very Large Telescope Interferometer (VLTI). Our aim is to probe the physical properties of the outer atmosphere by spatially resolving the star in the individual CO first overtone lines. Methods: BK Vir was observed between 2.26 and 2.31 μm using the 16-32-48 m telescope configuration with an angular resolution of 9.8 mas and a spectral resolution of 12 000. Results: The uniform-disk diameters observed in the CO first overtone lines are 12 - 31% larger than those measured in the continuum. We also detected asymmetry in the CO line-forming region, which manifests itself as non-zero/non-π differential and closure phases. The data taken 1.5 months apart show possible time variation on a spatial scale of 30 mas (corresponding to 3 × stellar diameter) at the CO band head. Comparison of the observed data with the MARCS photospheric model shows that whereas the observed CO line spectrum can be satisfactorily reproduced by the model, the angular sizes observed in the CO lines are much larger than predicted by the model. Our model with two additional CO layers above the MARCS photosphere reproduces the observed spectrum and interferometric data in the CO lines simultaneously. This model suggests that the inner CO layer at ~1.2 R⋆ is very dense and warm with a CO column density of ~1022 cm-2 and temperatures of 1900 - 2100 K, while the outer CO layer at 2.5-3.0 R⋆ is characterized by column densities of 1019-1020 cm-2 and temperatures of 1500 - 2100 K. Conclusions: Our AMBER observations of BK Vir have spatially resolved the extended molecular outer atmosphere of a normal M giant in the individual CO lines for the first time. The temperatures derived for the CO layers are

  10. Spectral Analysis and Experimental Modeling of Ice Accretion Roughness

    NASA Technical Reports Server (NTRS)

    Orr, D. J.; Breuer, K. S.; Torres, B. E.; Hansman, R. J., Jr.

    1996-01-01

    A self-consistent scheme for relating wind tunnel ice accretion roughness to the resulting enhancement of heat transfer is described. First, a spectral technique of quantitative analysis of early ice roughness images is reviewed. The image processing scheme uses a spectral estimation technique (SET) which extracts physically descriptive parameters by comparing scan lines from the experimentally-obtained accretion images to a prescribed test function. Analysis using this technique for both streamwise and spanwise directions of data from the NASA Lewis Icing Research Tunnel (IRT) are presented. An experimental technique is then presented for constructing physical roughness models suitable for wind tunnel testing that match the SET parameters extracted from the IRT images. The icing castings and modeled roughness are tested for enhancement of boundary layer heat transfer using infrared techniques in a "dry" wind tunnel.

  11. Development of 3D Ice Accretion Measurement Method

    NASA Technical Reports Server (NTRS)

    Lee, Sam; Broeren, Andy P.; Addy, Harold E., Jr.; Sills, Robert; Pifer, Ellen M.

    2012-01-01

    Icing wind tunnels are designed to simulate in-flight icing environments. The chief product of such facilities is the ice accretion that forms on various test articles. Documentation of the resulting ice accretion key piece of data in icing-wind-tunnel tests. Number of currently used options for documenting ice accretion in icing-wind-tunnel testing.

  12. The multiplicity and anisotropy of galactic satellite accretion

    NASA Astrophysics Data System (ADS)

    Shao, Shi; Cautun, Marius; Frenk, Carlos S.; Grand, Robert J. J.; Gómez, Facundo A.; Marinacci, Federico; Simpson, Christine M.

    2018-05-01

    We study the incidence of group and filamentary dwarf galaxy accretion into Milky Way (MW) mass haloes using two types of hydrodynamical simulations: EAGLE, which resolves a large cosmological volume, and the AURIGA suite, which are very high resolution zoom-in simulations of individual MW-sized haloes. The present-day 11 most massive satellites are predominantly (75 per cent) accreted in single events, 14 per cent in pairs, and 6 per cent in triplets, with higher group multiplicities being unlikely. Group accretion becomes more common for fainter satellites, with 60 per cent of the top 50 satellites accreted singly, 12 per cent in pairs, and 28 per cent in richer groups. A group similar in stellar mass to the Large Magellanic Cloud would bring on average 15 members with stellar mass larger than 104 M⊙. Half of the top 11 satellites are accreted along the two richest filaments. The accretion of dwarf galaxies is highly anisotropic, taking place preferentially perpendicular to the halo minor axis, and, within this plane, preferentially along the halo major axis. The satellite entry points tend to be aligned with the present-day central galaxy disc and satellite plane, but to a lesser extent than with the halo shape. Dwarfs accreted in groups or along the richest filament have entry points that show an even larger degree of alignment with the host halo than the full satellite population. We also find that having most satellites accreted as a single group or along a single filament is unlikely to explain the MW disc of satellites.

  13. Accretion physics: It's not U, it's B

    NASA Astrophysics Data System (ADS)

    Miller, Jon

    2017-03-01

    Black holes grow by accreting mass, but the process is messy and redistributes gas and energy into their environments. New evidence shows that magnetic processes mediate both the accretion and ejection of matter.

  14. Misaligned Accretion and Jet Production

    NASA Astrophysics Data System (ADS)

    King, Andrew; Nixon, Chris

    2018-04-01

    Disk accretion onto a black hole is often misaligned from its spin axis. If the disk maintains a significant magnetic field normal to its local plane, we show that dipole radiation from Lense–Thirring precessing disk annuli can extract a significant fraction of the accretion energy, sharply peaked toward small disk radii R (as R ‑17/2 for fields with constant equipartition ratio). This low-frequency emission is immediately absorbed by surrounding matter or refracted toward the regions of lowest density. The resultant mechanical pressure, dipole angular pattern, and much lower matter density toward the rotational poles create a strong tendency to drive jets along the black hole spin axis, similar to the spin-axis jets of radio pulsars, also strong dipole emitters. The coherent primary emission may explain the high brightness temperatures seen in jets. The intrinsic disk emission is modulated at Lense–Thirring frequencies near the inner edge, providing a physical mechanism for low-frequency quasi-periodic oscillations (QPOs). Dipole emission requires nonzero hole spin, but uses only disk accretion energy. No spin energy is extracted, unlike the Blandford–Znajek process. Magnetohydrodynamic/general-relativistic magnetohydrodynamic (MHD/GRMHD) formulations do not directly give radiation fields, but can be checked post-process for dipole emission and therefore self-consistency, given sufficient resolution. Jets driven by dipole radiation should be more common in active galactic nuclei (AGN) than in X-ray binaries, and in low accretion-rate states than high, agreeing with observation. In non-black hole accretion, misaligned disk annuli precess because of the accretor’s mass quadrupole moment, similarly producing jets and QPOs.

  15. MAKE SUPER-EARTHS, NOT JUPITERS: ACCRETING NEBULAR GAS ONTO SOLID CORES AT 0.1 AU AND BEYOND

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

    Lee, Eve J.; Chiang, Eugene; Ormel, Chris W., E-mail: evelee@berkeley.edu, E-mail: echiang@astro.berkeley.edu, E-mail: ormel@berkeley.edu

    Close-in super-Earths having radii 1-4 R {sub ⊕} may possess hydrogen atmospheres comprising a few percent by mass of their rocky cores. We determine the conditions under which such atmospheres can be accreted by cores from their parent circumstellar disks. Accretion from the nebula is problematic because it is too efficient: we find that 10 M {sub ⊕} cores embedded in solar metallicity disks tend to undergo runaway gas accretion and explode into Jupiters, irrespective of orbital location. The threat of runaway is especially dire at ∼0.1 AU, where solids may coagulate on timescales orders of magnitude shorter than gas clearingmore » times; thus nascent atmospheres on close-in orbits are unlikely to be supported against collapse by planetesimal accretion. The time to runaway accretion is well approximated by the cooling time of the atmosphere's innermost convective zone, whose extent is controlled by where H{sub 2} dissociates. Insofar as the temperatures characterizing H{sub 2} dissociation are universal, timescales for core instability tend not to vary with orbital distance—and to be alarmingly short for 10 M {sub ⊕} cores. Nevertheless, in the thicket of parameter space, we identify two scenarios, not mutually exclusive, that can reproduce the preponderance of percent-by-mass atmospheres for super-Earths at ∼0.1 AU, while still ensuring the formation of Jupiters at ≳ 1 AU. Scenario (a): planets form in disks with dust-to-gas ratios that range from ∼20× solar at 0.1 AU to ∼2× solar at 5 AU. Scenario (b): the final assembly of super-Earth cores from mergers of proto-cores—a process that completes quickly at ∼0.1 AU once begun—is delayed by gas dynamical friction until just before disk gas dissipates completely. Both scenarios predict that the occurrence rate for super-Earths versus orbital distance, and the corresponding rate for Jupiters, should trend in opposite directions, as the former population is transformed into the latter

  16. Minimum Hamiltonian Ascent Trajectory Evaluation (MASTRE) program (update to automatic flight trajectory design, performance prediction, and vehicle sizing for support of Shuttle and Shuttle derived vehicles) engineering manual

    NASA Technical Reports Server (NTRS)

    Lyons, J. T.

    1993-01-01

    The Minimum Hamiltonian Ascent Trajectory Evaluation (MASTRE) program and its predecessors, the ROBOT and the RAGMOP programs, have had a long history of supporting MSFC in the simulation of space boosters for the purpose of performance evaluation. The ROBOT program was used in the simulation of the Saturn 1B and Saturn 5 vehicles in the 1960's and provided the first utilization of the minimum Hamiltonian (or min-H) methodology and the steepest ascent technique to solve the optimum trajectory problem. The advent of the Space Shuttle in the 1970's and its complex airplane design required a redesign of the trajectory simulation code since aerodynamic flight and controllability were required for proper simulation. The RAGMOP program was the first attempt to incorporate the complex equations of the Space Shuttle into an optimization tool by using an optimization method based on steepest ascent techniques (but without the min-H methodology). Development of the complex partial derivatives associated with the Space Shuttle configuration and using techniques from the RAGMOP program, the ROBOT program was redesigned to incorporate these additional complexities. This redesign created the MASTRE program, which was referred to as the Minimum Hamiltonian Ascent Shuttle TRajectory Evaluation program at that time. Unique to this program were first-stage (or booster) nonlinear aerodynamics, upper-stage linear aerodynamics, engine control via moment balance, liquid and solid thrust forces, variable liquid throttling to maintain constant acceleration limits, and a total upgrade of the equations used in the forward and backward integration segments of the program. This modification of the MASTRE code has been used to simulate the new space vehicles associated with the National Launch Systems (NLS). Although not as complicated as the Space Shuttle, the simulation and analysis of the NLS vehicles required additional modifications to the MASTRE program in the areas of providing

  17. Bondi-Hoyle-Lyttleton Accretion onto Binaries

    NASA Astrophysics Data System (ADS)

    Antoni, Andrea; MacLeod, Morgan; Ramírez-Ruiz, Enrico

    2018-01-01

    Binary stars are not rare. While only close binary stars will eventually interact with one another, even the widest binary systems interact with their gaseous surroundings. The rates of accretion and the gaseous drag forces arising in these interactions are the key to understanding how these systems evolve. This poster examines accretion flows around a binary system moving supersonically through a background gas. We perform three-dimensional hydrodynamic simulations of Bondi-Hoyle-Lyttleton accretion using the adaptive mesh refinement code FLASH. We simulate a range of values of semi-major axis of the orbit relative to the gravitational focusing impact parameter of the pair. On large scales, gas is gravitationally focused by the center-of-mass of the binary, leading to dynamical friction drag and to the accretion of mass and momentum. On smaller scales, the orbital motion imprints itself on the gas. Notably, the magnitude and direction of the forces acting on the binary inherit this orbital dependence. The long-term evolution of the binary is determined by the timescales for accretion, slow down of the center-of-mass, and decay of the orbit. We use our simulations to measure these timescales and to establish a hierarchy between them. In general, our simulations indicate that binaries moving through gaseous media will slow down before the orbit decays.

  18. Gas Accretion and Star Formation Rates

    NASA Astrophysics Data System (ADS)

    Sánchez Almeida, Jorge

    Cosmological numerical simulations of galaxy evolution show that accretion of metal-poor gas from the cosmic web drives the star formation in galaxy disks. Unfortunately, the observational support for this theoretical prediction is still indirect, and modeling and analysis are required to identify hints as actual signs of star formation feeding from metal-poor gas accretion. Thus, a meticulous interpretation of the observations is crucial, and this observational review begins with a simple theoretical description of the physical process and the key ingredients it involves, including the properties of the accreted gas and of the star formation that it induces. A number of observations pointing out the connection between metal-poor gas accretion and star formation are analyzed, specifically, the short gas-consumption time-scale compared to the age of the stellar populations, the fundamental metallicity relationship, the relationship between disk morphology and gas metallicity, the existence of metallicity drops in starbursts of star-forming galaxies, the so-called G dwarf problem, the existence of a minimum metallicity for the star-forming gas in the local universe, the origin of the α-enhanced gas forming stars in the local universe, the metallicity of the quiescent BCDs, and the direct measurements of gas accretion onto galaxies. A final section discusses intrinsic difficulties to obtain direct observational evidence, and points out alternative observational pathways to further consolidate the current ideas.

  19. Upper Atmospheric Monitoring for Ares I-X Ascent Loads and Trajectory Evaluation on the Day-of-Launch

    NASA Technical Reports Server (NTRS)

    Roberts, Barry C.; McGrath, Kevin; Starr, Brett; Brandon, Jay

    2009-01-01

    During the launch countdown of the Ares I-X test vehicle, engineers from Langley Research Center will use profiles of atmospheric density and winds in evaluating vehicle ascent loads and controllability. A schedule for the release of balloons to measure atmospheric density and winds has been developed by the Natural Environments Branch at Marshall Space Flight Center to help ensure timely evaluation of the vehicle ascent loads and controllability parameters and support a successful launch of the Ares I-X vehicle.

  20. Instability, Turbulence, and Enhanced Transport in Collisionless Black-Hole Accretion Flows

    NASA Astrophysics Data System (ADS)

    Kunz, Matthew

    Many astrophysical plasmas are so hot and diffuse that the collisional mean free path is larger than the system size. Perhaps the best examples of such systems are lowluminosity accretion flows onto black holes such as Sgr A* at the center of our own Galaxy, or M87 in the Virgo cluster. To date, theoretical models of these accretion flows are based on magnetohydrodynamics (MHD), a collisional fluid theory, sometimes (but rarely) extended with non-MHD features such as anisotropic (i.e. magnetic-field-aligned) viscosity and thermal conduction. While these extensions have been recognized as crucial, they require ad hoc assumptions about the role of microscopic kinetic instabilities (namely, firehose and mirror) in regulating the transport properties. These assumptions strongly affect the outcome of the calculations, and yet they have never been tested using more fundamental (i.e. kinetic) models. This proposal outlines a comprehensive first-principles study of the plasma physics of collisionless accretion flows using both analytic and state-of-the-art numerical models. The latter will utilize a new hybrid-kinetic particle-in-cell code, Pegasus, developed by the PI and Co-I specifically to study this problem. A comprehensive kinetic study of the 3D saturation of the magnetorotational instability in a collisionless plasma will be performed, in order to understand the interplay between turbulence, transport, and Larmor-scale kinetic instabilities such as firehose and mirror. Whether such instabilities alter the macroscopic saturated state, for example by limiting the transport of angular momentum by anisotropic pressure, will be addressed. Using these results, an appropriate "fluid" closure will be developed that can capture the multi-scale effects of plasma kinetics on magnetorotational turbulence, for use by the astrophysics community in building evolutionary models of accretion disks. The PI has already successfully performed the first three-dimensional kinetic

  1. Investigation of surface water behavior during glaze ice accretion

    NASA Technical Reports Server (NTRS)

    Hansman, R. John, Jr.; Turnock, Stephen R.

    1988-01-01

    Microvideo observations of glaze ice accretions on 1-in-diameter cylinders in a closed-loop refrigerated wind tunnel were obtained to study factors controlling the behavior of unfrozen surface water during glaze ice accretion. Three zones of surface water behavior were noted, each with a characteristic roughness. The effect of substrate thermal and roughness properties on ice accretions was also studied. The contact angle and hysteresis were found to increase sharply at temperatures just below 0 C, explaining the high resistance to motion of water beads observed on accreting glaze ice surfaces. Based on the results, a simple multizone modification to the current glaze ice accretion model is proposed.

  2. The Dynamics of Truncated Black Hole Accretion Disks. I. Viscous Hydrodynamic Case

    NASA Astrophysics Data System (ADS)

    Hogg, J. Drew; Reynolds, Christopher S.

    2017-07-01

    Truncated accretion disks are commonly invoked to explain the spectro-temporal variability in accreting black holes in both small systems, I.e., state transitions in galactic black hole binaries (GBHBs), and large systems, I.e., low-luminosity active galactic nuclei (LLAGNs). In the canonical truncated disk model of moderately low accretion rate systems, gas in the inner region of the accretion disk occupies a hot, radiatively inefficient phase, which leads to a geometrically thick disk, while the gas in the outer region occupies a cooler, radiatively efficient phase that resides in the standard geometrically thin disk. Observationally, there is strong empirical evidence to support this phenomenological model, but a detailed understanding of the dynamics of truncated disks is lacking. We present a well-resolved viscous, hydrodynamic simulation that uses an ad hoc cooling prescription to drive a thermal instability and, hence, produce the first sustained truncated accretion disk. With this simulation, we perform a study of the dynamics, angular momentum transport, and energetics of a truncated disk. We find that the time variability introduced by the quasi-periodic transition of gas from efficient cooling to inefficient cooling impacts the evolution of the simulated disk. A consequence of the thermal instability is that an outflow is launched from the hot/cold gas interface, which drives large, sub-Keplerian convective cells into the disk atmosphere. The convective cells introduce a viscous θ - ϕ stress that is less than the generic r - ϕ viscous stress component, but greatly influences the evolution of the disk. In the truncated disk, we find that the bulk of the accreted gas is in the hot phase.

  3. The Dynamics of Truncated Black Hole Accretion Disks. I. Viscous Hydrodynamic Case

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

    Hogg, J. Drew; Reynolds, Christopher S.

    Truncated accretion disks are commonly invoked to explain the spectro-temporal variability in accreting black holes in both small systems, i.e., state transitions in galactic black hole binaries (GBHBs), and large systems, i.e., low-luminosity active galactic nuclei (LLAGNs). In the canonical truncated disk model of moderately low accretion rate systems, gas in the inner region of the accretion disk occupies a hot, radiatively inefficient phase, which leads to a geometrically thick disk, while the gas in the outer region occupies a cooler, radiatively efficient phase that resides in the standard geometrically thin disk. Observationally, there is strong empirical evidence to supportmore » this phenomenological model, but a detailed understanding of the dynamics of truncated disks is lacking. We present a well-resolved viscous, hydrodynamic simulation that uses an ad hoc cooling prescription to drive a thermal instability and, hence, produce the first sustained truncated accretion disk. With this simulation, we perform a study of the dynamics, angular momentum transport, and energetics of a truncated disk. We find that the time variability introduced by the quasi-periodic transition of gas from efficient cooling to inefficient cooling impacts the evolution of the simulated disk. A consequence of the thermal instability is that an outflow is launched from the hot/cold gas interface, which drives large, sub-Keplerian convective cells into the disk atmosphere. The convective cells introduce a viscous θ − ϕ stress that is less than the generic r − ϕ viscous stress component, but greatly influences the evolution of the disk. In the truncated disk, we find that the bulk of the accreted gas is in the hot phase.« less

  4. MINIMUM CORE MASSES FOR GIANT PLANET FORMATION WITH REALISTIC EQUATIONS OF STATE AND OPACITIES

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

    Piso, Ana-Maria A.; Murray-Clay, Ruth A.; Youdin, Andrew N., E-mail: apiso@cfa.harvard.edu

    2015-02-20

    Giant planet formation by core accretion requires a core that is sufficiently massive to trigger runaway gas accretion in less than the typical lifetime of protoplanetary disks. We explore how the minimum required core mass, M {sub crit}, depends on a non-ideal equation of state (EOS) and on opacity changes due to grain growth across a range of stellocentric distances from 5-100 AU. This minimum M {sub crit} applies when planetesimal accretion does not substantially heat the atmosphere. Compared to an ideal gas polytrope, the inclusion of molecular hydrogen (H{sub 2}) dissociation and variable occupation of H{sub 2} rotational statesmore » increases M {sub crit}. Specifically, M {sub crit} increases by a factor of ∼2 if the H{sub 2} spin isomers, ortho- and parahydrogen, are in thermal equilibrium, and by a factor of ∼2-4 if the ortho-to-para ratio is fixed at 3:1. Lower opacities due to grain growth reduce M {sub crit}. For a standard disk model around a Solar mass star, we calculate M {sub crit} ∼ 8 M {sub ⊕} at 5 AU, decreasing to ∼5 M {sub ⊕} at 100 AU, for a realistic EOS with an equilibrium ortho-to-para ratio and for grain growth to centimeter-sizes. If grain coagulation is taken into account, M {sub crit} may further reduce by up to one order of magnitude. These results for the minimum critical core mass are useful for the interpretation of surveys that find exoplanets at a range of orbital distances.« less

  5. Upper stellar mass limit by radiative feedback at low-metallicities: metallicity and accretion rate dependence

    NASA Astrophysics Data System (ADS)

    Fukushima, Hajime; Omukai, Kazuyuki; Hosokawa, Takashi

    2018-02-01

    We investigate the upper stellar mass limit set by radiative feedback for a forming star with various accretion rates and metallicities. Thus, we numerically solve the structures of both a protostar and its surrounding accretion envelope assuming a spherical symmetric and steady flow. The optical depth of the dust cocoon, a dusty part of the accretion envelope, differs for direct light from the stellar photosphere and diffuse light re-emitted as dust thermal emission. As a result, varying the metallicity qualitatively changes the way that the radiative feedback suppresses the accretion flow. With a fixed accretion rate of 10-3 M⊙ yr-1, both direct and diffuse light jointly operate to prevent mass accretion at Z ≳ 10-1 Z⊙. At Z ≲ 10-1 Z⊙, the diffuse light is no longer effective and the direct light solely limits the mass accretion. At Z ≲ 10-3 Z⊙, formation of the H II region plays an important role in terminating the accretion. The resultant upper mass limit increases with decreasing metallicity, from a few × 10 M⊙ to ∼103 M⊙ over Z = 1 Z⊙-10-4 Z⊙. We also illustrate how the radiation spectrum of massive star-forming cores changes with decreasing metallicity. First, the peak wavelength of the spectrum, which is located around 30 μm at 1 Z⊙, shifts to < 3 μm at Z ≲ 0.1 Z⊙. Secondly, a characteristic feature at 10 μm due to the amorphous silicate band appears as a dip at 1 Z⊙, but changes to a bump at Z ≲ 0.1 Z⊙. Using these spectral signatures, we can search massive accreting protostars in nearby low-metallicity environments with upcoming observations.

  6. Implosive accretion and outbursts of active galactic nuclei

    NASA Technical Reports Server (NTRS)

    Lovelace, R. V. E.; Romanova, M. M.; Newman, W. I.

    1994-01-01

    A model and simulation code have been developed for time-dependent axisymmetric disk accretion onto a compact object including for the first time the influence of an ordered magnetic field. The accretion rate and radiative luminosity of the disk are naturally coupled to the rate of outflow of energy and angular momentum in magnetically driven (+/- z) winds. The magnetic field of the wind is treated in a phenomenological way suggested by self-consistent wind solutions. The radial accretion speed u(r, t) of the disk matter is shown to be the sum of the usual viscous contribution and a magnetic contribution proportional to r(exp 3/2)(B(sub p exp 2))/sigma, where B(sub p)(r,t) is the poloidal field threading the disk and sigma(r,t) is the disk's surface mass density. An enhancement or variation in B(sub p) at a large radial distance leads to the formation of a soliton-like structure in the disk density, temperature, and B-field which propagates implosively inward. The implosion gives a burst in the power output in winds or jets and a simultaneous burst in the disk radiation. The model is pertinent to the formation of discrete fast-moving components in jets observed by very long baseline interferometry. These components appear to originate at times of optical outbursts of the active galactic nucleus.

  7. Giant pandas can discriminate the emotions of human facial pictures.

    PubMed

    Li, Youxu; Dai, Qiang; Hou, Rong; Zhang, Zhihe; Chen, Peng; Xue, Rui; Feng, Feifei; Chen, Chao; Liu, Jiabin; Gu, Xiaodong; Zhang, Zejun; Qi, Dunwu

    2017-08-16

    Previous studies have shown that giant pandas (Ailuropoda melanoleuca) can discriminate face-like shapes, but little is known about their cognitive ability with respect to the emotional expressions of humans. We tested whether adult giant pandas can discriminate expressions from pictures of half of a face and found that pandas can learn to discriminate between angry and happy expressions based on global information from the whole face. Young adult pandas (5-7 years old) learned to discriminate expressions more quickly than older individuals (8-16 years old), but no significant differences were found between females and males. These results suggest that young adult giant pandas are better at discriminating emotional expressions of humans. We showed for the first time that the giant panda, can discriminate the facial expressions of humans. Our results can also be valuable for the daily care and management of captive giant pandas.

  8. Bitz, Ginoux, Jacobson, Nizkorodov, and Yang Receive 2013 Atmospheric Sciences Ascent Awards: Response

    NASA Astrophysics Data System (ADS)

    Yang, Ping

    2014-07-01

    I am honored and humbled that the AGU Atmospheric Sciences section decided to select me as one of the five recipients of the 2013 Ascent Award and would like to thank the selection committee for this recognition.

  9. Pulmonary giant cell carcinoma associated with pseudomyxoma peritonei.

    PubMed

    Goldin, Mark; Li, Jinghong; Amirrezvani, Ali; Riker, David

    2012-01-01

    Pulmonary giant cell carcinoma is a rare subtype of sarcomatoid carcinoma. Pseudomyxoma peritonei (PMP) is a rare condition in which gelatinous material accumulates within the peritoneal cavity. It is believed PMP arises from a primary appendiceal mucinous neoplasm that perforates the gut, causing mucinous ascites. There are sporadic reports of PMP associated with neoplasms of other organs, rarely the lung. Here, we report on a 60-year-old woman with pulmonary giant cell carcinoma associated with PMP. She presented with progressive dyspnea and abdominal distention. Abdominal computed tomography revealed moderately dense ascites without an obvious mass. Chest computed tomography revealed a large, solitary right lower-lobe lung mass. She underwent transbronchial fine-needle aspiration of the mass, and was diagnosed with pulmonary giant cell carcinoma. The ascites showed scattered malignant cells in a background of mucin, confirming PMP. To our knowledge, this is the first report of pulmonary giant cell carcinoma associated with PMP.

  10. A Systems-Level Perspective on Engine Ice Accretion

    NASA Technical Reports Server (NTRS)

    May, Ryan D.; Guo, Ten-Huei; Simon, Donald L.

    2013-01-01

    The accretion of ice in the compression system of commercial gas turbine engines operating in high ice water content conditions is a safety issue being studied by the aviation sector. While most of the research focuses on the underlying physics of ice accretion and the meteorological conditions in which accretion can occur, a systems-level perspective on the topic lends itself to potential near-term operational improvements. This work focuses on developing an accurate and reliable algorithm for detecting the accretion of ice in the low pressure compressor of a generic 40,000 lbf thrust class engine. The algorithm uses only the two shaft speed sensors and works regardless of engine age, operating condition, and power level. In a 10,000-case Monte Carlo simulation, the detection approach was found to have excellent capability at determining ice accretion from sensor noise with detection occurring when ice blocks an average of 6.8% of the low pressure compressor area. Finally, an initial study highlights a potential mitigation strategy that uses the existing engine actuators to raise the temperature in the low pressure compressor in an effort to reduce the rate at which ice accretes.

  11. Quantification of Ice Accretions for Icing Scaling Evaluations

    NASA Technical Reports Server (NTRS)

    Ruff, Gary A.; Anderson, David N.

    2003-01-01

    The comparison of ice accretion characteristics is an integral part of aircraft icing research. It is often necessary to compare an ice accretion obtained from a flight test or numerical simulation to one produced in an icing wind tunnel or for validation of an icing scaling method. Traditionally, this has been accomplished by overlaying two-dimensional tracings of ice accretion shapes. This paper addresses the basic question of how to compare ice accretions using more quantitative methods. For simplicity, geometric characteristics of the ice accretions are used for the comparison. One method evaluated is a direct comparison of the percent differences of the geometric measurements. The second method inputs these measurements into a fuzzy inference system to obtain a single measure of the goodness of the comparison. The procedures are demonstrated by comparing ice shapes obtained in the Icing Research Tunnel at NASA Glenn Research Center during recent icing scaling tests. The results demonstrate that this type of analysis is useful in quantifying the similarity of ice accretion shapes and that the procedures should be further developed by expanding the analysis to additional icing data sets.

  12. Performance Evaluation of a Lower Limb Exoskeleton for Stair Ascent and Descent with Paraplegia*

    PubMed Central

    Farris, Ryan J.; Quintero, Hugo A.; Goldfarb, Michael

    2013-01-01

    This paper describes the application of a powered lower limb exoskeleton to aid paraplegic individuals in stair ascent and descent. A brief description of the exoskeleton hardware is provided along with an explanation of the control methodology implemented to allow stair ascent and descent. Tests were performed with a paraplegic individual (T10 complete injury level) and data is presented from multiple trials, including the hip and knee joint torque and power required to perform this functionality. Joint torque and power requirements are summarized, including peak hip and knee joint torque requirements of 0.75 Nm/kg and 0.87 Nm/kg, respectively, and peak hip and knee joint power requirements of approximately 0.65 W/kg and 0.85 W/kg, respectively. PMID:23366287

  13. Accretion in Radiative Equipartition (AiRE) Disks

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

    Yazdi, Yasaman K.; Afshordi, Niayesh, E-mail: yyazdi@pitp.ca, E-mail: nafshordi@pitp.ca

    2017-07-01

    Standard accretion disk theory predicts that the total pressure in disks at typical (sub-)Eddington accretion rates becomes radiation pressure dominated. However, radiation pressure dominated disks are thermally unstable. Since these disks are observed in approximate steady state over the instability timescale, our accretion models in the radiation-pressure-dominated regime (i.e., inner disk) need to be modified. Here, we present a modification to the Shakura and Sunyaev model, where the radiation pressure is in equipartition with the gas pressure in the inner region. We call these flows accretion in radiative equipartition (AiRE) disks. We introduce the basic features of AiRE disks andmore » show how they modify disk properties such as the Toomre parameter and the central temperature. We then show that the accretion rate of AiRE disks is limited from above and below, by Toomre and nodal sonic point instabilities, respectively. The former leads to a strict upper limit on the mass of supermassive black holes as a function of cosmic time (and spin), while the latter could explain the transition between hard and soft states of X-ray binaries.« less

  14. Accretion in Radiative Equipartition (AiRE) Disks

    NASA Astrophysics Data System (ADS)

    Yazdi, Yasaman K.; Afshordi, Niayesh

    2017-07-01

    Standard accretion disk theory predicts that the total pressure in disks at typical (sub-)Eddington accretion rates becomes radiation pressure dominated. However, radiation pressure dominated disks are thermally unstable. Since these disks are observed in approximate steady state over the instability timescale, our accretion models in the radiation-pressure-dominated regime (I.e., inner disk) need to be modified. Here, we present a modification to the Shakura & Sunyaev model, where the radiation pressure is in equipartition with the gas pressure in the inner region. We call these flows accretion in radiative equipartition (AiRE) disks. We introduce the basic features of AiRE disks and show how they modify disk properties such as the Toomre parameter and the central temperature. We then show that the accretion rate of AiRE disks is limited from above and below, by Toomre and nodal sonic point instabilities, respectively. The former leads to a strict upper limit on the mass of supermassive black holes as a function of cosmic time (and spin), while the latter could explain the transition between hard and soft states of X-ray binaries.

  15. LANDER program manual: A lunar ascent and descent simulation

    NASA Technical Reports Server (NTRS)

    1988-01-01

    LANDER is a computer program used to predict the trajectory and flight performance of a spacecraft ascending or descending between a low lunar orbit of 15 to 500 nautical miles (nm) and the lunar surface. It is a three degree-of-freedom simulation which is used to analyze the translational motion of the vehicle during descent. Attitude dynamics and rotational motion are not considered. The program can be used to simulate either an ascent from the Moon or a descent to the Moon. For an ascent, the spacecraft is initialized at the lunar surface and accelerates vertically away from the ground at full thrust. When the local velocity becomes 30 ft/s, the vehicle turns downrange with a pitch-over maneuver and proceeds to fly a gravity turn until Main Engine Cutoff (MECO). The spacecraft then coasts until it reaches the requested holding orbit where it performs an orbital insertion burn. During a descent simulation, the lander begins in the holding orbit and performs a deorbit burn. It then coasts to pericynthion, where it reignites its engines and begins a gravity turn descent. When the local horizontal velocity becomes zero, the lander pitches up to a vertical orientation and begins to hover in search of a landing site. The lander hovers for a period of time specified by the user, and then lands.

  16. Time-dependent Models of Magnetospheric Accretion onto Young Stars

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

    Robinson, C. E.; Espaillat, C. C.; Owen, J. E.

    Accretion onto Classical T Tauri stars is thought to take place through the action of magnetospheric processes, with gas in the inner disk being channeled onto the star’s surface by the stellar magnetic field lines. Young stars are known to accrete material in a time-variable manner, and the source of this variability remains an open problem, particularly on the shortest (∼day) timescales. Using one-dimensional time-dependent numerical simulations that follow the field line geometry, we find that for plausibly realistic young stars, steady-state transonic accretion occurs naturally in the absence of any other source of variability. However, we show that ifmore » the density in the inner disk varies smoothly in time with ∼day-long timescales (e.g., due to turbulence), this complication can lead to the development of shocks in the accretion column. These shocks propagate along the accretion column and ultimately hit the star, leading to rapid, large amplitude changes in the accretion rate. We argue that when these shocks hit the star, the observed time dependence will be a rapid increase in accretion luminosity, followed by a slower decline, and could be an explanation for some of the short-period variability observed in accreting young stars. Our one-dimensional approach bridges previous analytic work to more complicated multi-dimensional simulations and observations.« less

  17. Characterizing Uranus with an Ice giant Planetary Origins Probe (Ice-POP)

    NASA Technical Reports Server (NTRS)

    Marley, Mark S.; Fortney, Jonathan; Nettelmann, Nadine; Zahnle, Kevin J.

    2013-01-01

    We now know from studies of planetary transits and microlensing that Neptune-mass planets are ubitquitous and may be the most common class of planets in the Galaxy. As such it is crucial that we understand the formation and evolution of the ice giant planets in our own solar system so that we can better understand planet formation throughout the galaxy. An entry probe mission to Uranus would help accomplish this goal. In fact the Planetary Decadal Survey recommended a Uranus orbiter with entry probe but did not explore in detail the specifications for the entry probe. NASA Ames is currently studying thermal protection system requirements for such a mission and this has led to questions regarding the minimum interesting science payload of such an entry probe. The single most important in-situ measurement for an ice giant entry probe is a measurement of atmospheric composition. For Uranus this would specifically include the methane and noble gas abundances. An in situ measurement of the methane abundance, from below the methane cloud, would constrain the atmospheric carbon abundance, which is believed to be roughly 30 to 50 times solar. There are hints from the transiting planets that extrasolar ice giants show comparable or even greater enhancements of heavy elements compared to their primary stars. However the origin of this carbon enhancement is controversial. Is Uranus a "failed core" of a larger gas giant or was the atmosphere enhanced by accretion of icy planetesimals' Constraining atmospheric abundances of C and perhaps S or even N from below 5 bars would provide badly needed data to address such issues. A measurement of the N abundance would provide clues on the origin of the planetesimals that formed Uranus. Low N-abundance indicates planetesimals from 'warmer' regions where N was mainly in form of NH3, whereas a strong enrichment could indicate planetesimals / cometary material from the colder outer regions of the nebula. Furthermore CO and HCN have been

  18. Stochastic events lead to accretion in Saturn’s rings

    NASA Astrophysics Data System (ADS)

    Esposito, L. W.

    2009-12-01

    UVIS occultations indicate accretion is triggered at the B ring edge, in strong density waves in ring A and in the F ring. Moons may trigger accretion by streamline crowding (Lewis & Stewart); which enhances collisions, leading to accretion; increasing random velocities; leading to more collisions and more accretion. Cassini occultations of these strongly perturbed locations show not only accretion but also disaggregation, with time scales of hours to weeks. The collisions may lead to temporary aggregations via stochastic events: they can compress unconsolidated objects, trigger adhesion or bring small pieces into contact with larger or higher-density seeds. Disaggregation then can follow from disruptive collisions or tidal shedding. In the accretion/disruption balance, increased random motions could eventually give the upper hand to disruption… just as ‘irrational exuberance’ can lead to financial panic in the economy; or the overpopulation of hares can lead to boom-and-bust in the population of foxes. This unstable equilibrium can similarly give rise to episodic cycles in accretion: explaining why the observable ring features that indicate embedded objects have been increasing since the beginning of Cassini’s observations of Saturn in 2004.

  19. Kinetic and radiative power from optically thin accretion flows

    NASA Astrophysics Data System (ADS)

    Sądowski, Aleksander; Gaspari, Massimo

    2017-06-01

    We perform a set of general relativistic, radiative, magneto-hydrodynamical simulations (GR-RMHD) to study the transition from radiatively inefficient to efficient state of accretion on a non-rotating black hole. We study ion to electron temperature ratios ranging from TI/Te = 10 to 100, and simulate flows corresponding to accretion rates as low as 10^{-6}\\dot{M}_Edd, and as high as 10^{-2}\\dot{M}_Edd. We have found that the radiative output of accretion flows increases with accretion rate, and that the transition occurs earlier for hotter electrons (lower TI/Te ratio). At the same time, the mechanical efficiency hardly changes and accounts to ≈3 per cent of the accreted rest mass energy flux, even at the highest simulated accretion rates. This is particularly important for the mechanical active galactic nuclei (AGN) feedback regulating massive galaxies, groups and clusters. Comparison with recent observations of radiative and mechanical AGN luminosities suggests that the ion to electron temperature ratio in the inner, collisionless accretion flow should fall within 10 < TI/Te < 30, I.e. the electron temperature should be several percent of the ion temperature.

  20. Exclusion of a luminous red giant as a companion star to the progenitor of supernova SN 2011fe.

    PubMed

    Li, Weidong; Bloom, Joshua S; Podsiadlowski, Philipp; Miller, Adam A; Cenko, S Bradley; Jha, Saurabh W; Sullivan, Mark; Howell, D Andrew; Nugent, Peter E; Butler, Nathaniel R; Ofek, Eran O; Kasliwal, Mansi M; Richards, Joseph W; Stockton, Alan; Shih, Hsin-Yi; Bildsten, Lars; Shara, Michael M; Bibby, Joanne; Filippenko, Alexei V; Ganeshalingam, Mohan; Silverman, Jeffrey M; Kulkarni, S R; Law, Nicholas M; Poznanski, Dovi; Quimby, Robert M; McCully, Curtis; Patel, Brandon; Maguire, Kate; Shen, Ken J

    2011-12-14

    Type Ia supernovae are thought to result from a thermonuclear explosion of an accreting white dwarf in a binary system, but little is known of the precise nature of the companion star and the physical properties of the progenitor system. There are two classes of models: double-degenerate (involving two white dwarfs in a close binary system) and single-degenerate models. In the latter, the primary white dwarf accretes material from a secondary companion until conditions are such that carbon ignites, at a mass of 1.38 times the mass of the Sun. The type Ia supernova SN 2011fe was recently detected in a nearby galaxy. Here we report an analysis of archival images of the location of SN 2011fe. The luminosity of the progenitor system (especially the companion star) is 10-100 times fainter than previous limits on other type Ia supernova progenitor systems, allowing us to rule out luminous red giants and almost all helium stars as the mass-donating companion to the exploding white dwarf.